Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Carbon nanotubes embedded in single-stranded DNA (CNT@DNA) were investigated by self-consistent density-functional-based tight-binding calculations (DFTB). A phenomenological model for the stability was derived, which gives the CNT-DNA interaction energy as a function of the nanotube radii and the number of DNA chains. Single CNTs are readily complexed by the DNA, but for CNT bundles an essential energy gain is only obtained, if multiple chains wrap around the tubes. Hence, the destruction of the CNT bundles, e.g. by sonication, can promote the CNT@DNA complex formation. Pyrimidine-based homopolymeric DNA more effectively wraps the DNA, whereas purine-based DNA exhibits the larger radius selectivity. The CNT-DNA interaction is not a genuine Van-der-Waals’ interaction. In general, the electronic structure is close to the superposition of the DOS curves of the “free” DNA and CNT fragments, but the most strongly bonding systems are characterized by a number of the mixed electronic states below Fermi level. Hence, magic matching occurs in conjunction with remarkable charge transfer.

This paper deals with the speciation of U(VI) associated with the cells of bacterial strains isolated from extreme habitats. For this propose, a combination of synchrotron-based X-ray absorption spectroscopy (XAS), time-resolved laser-induced fluorescence spectroscopy (TRLFS), transmission electron microscope (TEM) coupled with energy dispersive-X ray (EDX) analysis and electron diffraction were used. XAS analysis indicated that the effect of pH on the local coordination of U in the U-complexes formed by the different bacterial strains is species specific. No structural differences were found between the U complexes formed by three different eco-types of Acidothiobacillus ferrooxidans at pH 2, 3 and 4.5. In contrast, the cells of Bacillus sphaericus JG-B7, Microbacterium oxydans M2, and Sphingomonas sp. S15-S1 precipitate U(VI) as a meta-autunite-like phase at pH 4.5, probably due to the release of the inorganic phosphate from the cells. At pH 2, the U is coordinated to the organic phosphate groups of the cells of the listed bacteria. Both organic and inorganic uranyl/bacterial complexes were formed at pH 3. TEM/EDX analysis confirms these results and showed strain-specific extracellular and/or intracellular uranium accumulation to varying degrees. We applied Iterative Target Test Factor Analysis to determine the uranium speciation at different pH values quantitatively from the EXAFS spectra. Different hypothesis explaining the different coordination chemistry of uranium to bacteria as a function of pH of uranium solution in terms of solubility of m-autunite and/or microbial activity will be discussed.

This communication presents the identification of a bacterial strain, MAH1, isolated from a seawater sample collected from the westernmost Mediterranean surface waters. This strain was characterized using polyphasic taxonomy. It is Gram-negative, growing between 2--43 ºC (optimum 28-37 ºC), heterotrophic, aerobic and required NaCl for growth (0.7-20.0%, optimum being 2%). This strain is rod-shaped slightly curved with a single polar flagellum. Results of phylogenetic analyses evidenced that the strain belongs to Idiomarina loihiensis species (Donachie et al., 2003). The strain MAH1 displays a DNA base composition in G+C of the 48.2 mol%. The similarity of the 16S rDNA sequence and of the DNA-DNA hybridization to I. loihiensis (AF288370) is 100% and 96.1% respectively. Polar lipids were predominantly odd-numbered and iso-branched (15 and 17). According to these data we propose that the isolated MAH1 is a strain of the I. loihiensis species.
A preliminary study of the MAH1 strain mineralization capability and heavy metal resistance has also been performed. When the MAH1 strain is cultivated in a sea water solid medium (yeast extract 0.5%, triptone 1%, purified agar-agar 2% in seawater, pH 7.6) produces carbonates and phosphates. On the other hand, the minimal inhibitory concentrations of Ag, Cd, Pb, U, Ni, Cu, Cr, Mn and Zn for the growth of this bacterial strain are (concentration expressed as mM) 0.125, 0.125, 8.00, 8.00, 4.00, 4.00, 1.00, 8.00 and 2.00, respectively.
The obtained results are especially interesting in relation to the Idiomarina genus (Ivanova et al 2000), a member of the family Alteromonadaceae (Ivanova and Mikhailov, 2001) belonging to the subclases of the Proteobacteria.

Donachie, S. P., S. Hou, T. S. Gregory, A. Malahoff, and M. Alam. 2003. Int. J. Syst. Evol. Microbiol. 53:1873-1879
Ivanova, E. P., and V. V. Mikhailov. 2001. Mikrobiologia 70:15-23
Ivanova, E. P., L. A. Romanenko, J. Chun, M. H. Matte, G. R. Matte, V. V. Mikhailov, V. I. Svetashev, A. Huq, T. Maugel, and R. R. Colwell. 2000. Int. J. Syst. Evol. Microbiol. 50:901–907

Experimental investigation of multiphase flows plays an important role in many research and industrial application areas. We introduce a novel surface sensor based on electrical capacitance (permittivity) measurements to imaging near-wall fluid distributions of multiphase flows. The sensor is formed by 32 x 32 interdigitated sensing structures and can be mounted on the edges of a pipe or vessel and thus has a minimal influence on the flow. An associated electronics measures the capacitance of the fluid overlaying each sensing structure in a multiplexed manner. This way, images of the fluid distribution can be achieved directly without the need for any reconstruction procedure. Images at up to 10,000 frames per second can be obtained. The system was evaluated showing good reproducibility and adequate accuracy. The system is able to well distinguish permittivity differences of up to one, which corresponds, for instance, to a two-phase flow of air and oil (rel. permittivity about 2).

We have developed and tested a new wire-mesh tomograph based on capacitance measurements, which may now be used for the investigation of non-conducting fluids. It can at the moment acquire up to 625 frames per second. For the experimental measurements we have employed a 16 x 16 laboratory wire-mesh sensor. The evaluation of the wire-mesh tomograph prototype has shown good reproducibility and accuracy in capacitance measurements, thus allowing the system to be employed in the investigation of a wide range of substances even with close relative permittivity values, such as for air and oil. Furthermore, time resolved measurements of different flow patterns for oil-air mixtures have been performed.

A new approach for fitting statistical models to time-resolved laser-induced fluorescence spectroscopy (TRLFS) spectra is presented. Such spectra result from counting emitted photons in defined intervals. Any photon can be described by emission time and wavelength as observable attributes and by component and peak affiliation as hidden ones. Understanding the attribute values of the emitted photons as drawn from a probability density distribution, the model estimation problem can be described as a statistical problem with incomplete data. To solve the maximum likelihood task, an expectation maximization (EM) algorithm is derived and tested. In contrast to the well known least squares method, the advantage of the new approach is the ability to decompose the spectrum into its components and peaks using the revealed hidden attributes of the photons. The simultaneous detection of temporal and spectral model parameters provides a mutually consistent description of TRLFS spectra. Theoretical aspects were investigated using simulated spectra and the applicability in practice is illustrated by spectra originating from uranyl species.

Three neutron-deuteron scattering experiments at 95 MeV have been performed recently at The Svedberg Laboratory in Uppsala. Subsets of the results of these experiments have been reported in two short articles, showing clear evidence for three-nucleon force effects. In this paper, we present a more detailed description of the experimental methods as well as further discussion of the results. In addition to neutron-deuteron scattering data, neutron-proton and C-12(n,n) elastic scattering data have been measured for normalization purposes, and O-16(n,n) data have been obtained for the first time at this energy.
It was possible to extract C-12(n,n(')) and O-16(n,n(')) inelastic scattering cross sections to excited states below 12 MeV excitation energy. The inelastic scattering data (for both carbon and oxygen) are shown to have a significant impact on the determination of nuclear recoil kerma coefficients.

Dynamics of the Molten Salt Reactor, one of the 'Generation IV International Forum' concepts, was studied in this paper. The graphite-moderated channel type MSR was selected for the numerical simulation. The MSR represents a liquid fueled reactor with very specific dynamics because of two physical peculiarities: the delayed neutrons precursors are drifted by the fuel flow and the fission energy is immediately released directly into the coolant. Presently, there are not many accessible numerical codes appropriate for the MSR simulation, therefore the DYN1D-MSR and DYN3D-MSR codes were developed based on the Light Water Reactor dynamics code DYN3D. It allows calculating of full 3D transient neutronics in combination with parallel channel type thermal-hydraulics. The codes were validated on experimental results of Molten Salt Reactor Experiment from Oak Ridge National Laboratory and applied to several transients typical for the liquid fuel system. Those transients were initiated by reactivity insertion, by overcooled or overfueled fuel slug, by the fuel pump start-up or coast-down, or by the blockage of single fuel channels. In these considered transients, the response of the MSR is characterized by the immediate change of the fuel temperature according to the power level. This causes fast feedback reactivity insertion, which is negative in the case of power increase. On the other hand, the graphite response is slower and its feedback coefficient is in some cases positive. The addition of erbium to the graphite can ensure the negative feedback and inherent safety features. The DYN1D-MSR and DYN3D-MSR codes have been shown as an effective tools for MSR dynamics studies.

A Si metal-oxide-semiconductor (MOS) electroluminescent device structure is reported which emits two colors, while being doped with a single rare-earth element. Thermally grown SiO2 oxide layers were implanted with Eu and subseqently annealed. Depending on the electrical excitation current, the luminescence is red or blue, which can be ascribed to electronic transitions in tri- and di-valent europium (Eu3+ and Eu2+), respectively.

Periodic addition of momentum by wall–parallel electromagnetic forces has a strong influence on the separated region of a stalled airfoil. As in the case of periodic blowing and suction, actuation frequency and momentum input are the main factors of influence. However, the control authority depends as well on the actuation wave form. This latter aspect is investigated in the present paper by means of time resolved particle image velocimetry data from the suction side of an inclined flat plate. The control effect is rated by the size of the remaining recirculation region in the time averaged flow fields. The controlled flow possesses typically a small number of relatively large vortices, which are believed to be related to the control mechanism. Consequently, the time resolved flow fields have been analyzed by proper orthogonal decomposition and continuous wavelet transform to extract dominant features of the flow.

wird nachgereicht

Some facts about the spectrum of a PT-symmetric quantum mechanical (PTSQM) toy model with potential V(x)=Gx²(ix)^ν in a box x∈[-L,L] are presented for the parameter region ν∈[-2,0]. The corresponding Hamiltonian is selfadjoint in an appropriately chosen Krein space and for ν=-1 the spectral problem maps into that of the hydrodynamic Squire equation. It is shown that in the limit L→∞ a spectral singularity occurs and that the PTSQM ⇄ Squire mapping can be interpreted as a special type of strong-coupling ⇄ weak-coupling (UV-IR) duality. Finally, the system behavior in the vicinity of a spectral triple point is sketched.
partially based on:
J. Math. Phys. 46, (2005), 063504, math-ph/0501069.
Czech. J. Phys. 55, (2005), 1099-1106, math-ph/0506021.

We suggest an experiment to observe vacuum birefringence induced by intense laser fields. A high-intensity laser pulse is focused to ultra-relativistic intensity and polarizes the vacuum which then acts like a birefringent medium. The latter is probed by a linearly polarized X-ray pulse. We calculate the resulting ellipticity signal within strong-field QED assuming Gaussian beams. The laser technology required for detecting the signal will be available within the next three years.

We show the possibility of transparency and soliton effects for an intense pulse propagating in a V-type medium in which two upper resonant sublevels experience fast field-induced decay due to incoherent coupling to an upper lying state or continuum. The transparency arises as a result of the combined action of population trapping on the sublevels leading to interference suppression of the relaxation channel, and coherent Rabi cycling induced by the laser field.

Discs of depleted uranium (DU), obtained from a British pristine military tank shell were used in our experiments. One sample was placed in a solution containing 2.5 • 10−3 M Ca(NO3)2 and 1.05 • 10−3 M (NH4)3PO4. After a contact time of 360 days the sample was taken out of the solution. IR- and TRLFS measurements were made on the surface of the sample. The spectra obtained were compared with those of natural uranium minerals, formed under oxidising weathering conditions. Comparison of the IR-spectra from the DU surface with those of the reference minerals revealed that the newly formed secondary mineral on DU is a uranium (VI) phosphate. Further identification of the respective uranium phosphate mineral was not possible with IR. However, a comparison between the TRLFS spectra of the newly formed unknown uranium phase on the DU disc with well-known TRLFS spectra of uranium reference compounds clearly showed the presence of meta-autunite.

Clay minerals and organic substances are widespread components of many soils, sediments, and rocks. As humic acids (HA) possess a strong ability for metal complexation, they can influence the migration of radioactive and toxic metal ions in clayey environments. However, the migration behavior of humic colloids and its impact on the actinide migration in clay formations is poorly understood.
Former studies discuss the influence of HA on the radionuclide migration in clays controversially. Wold and Eriksen [1] reported the diffusion of humic colloids through compacted bentonite without strong physical hindrance mobilizing metal ions. In contrast, Wang et al. [2] found a significant immobilization of Eu(III) by humic substances. Maes et al. [3] stressed the reversibility of the interaction between radionuclide, organic matter, and clay. The competition of the adsorbents for radionuclides is kinetic and determines their distribution between mobile and immobile phase.
In the present study we investigated the diffusion behavior of humic colloids in compacted clay as a function of compaction and pH. The impact on the uranium transport was studied by comparing the uranium diffusion in absence and presence of HA.
...
The migration of HA in clay is governed by diffusion. It is influenced by the colloidal behavior of HA. At higher clay bulk densities, size fractionation affects the diffusion parameters. In presence of HA colloids U(VI) is immobilized in association with HA near the high concentration boundary.
The German Federal Ministry of Economics and Technology funded this study under contract 02E9673. The technical assistance of Ch. Müller is gratefully acknowledged.
REFERENCES
[1] Wold, S., Eriksen, T.E. (2005) Proceedings of the 2nd International Symposium Clays in natural and engineered barriers for radioactive waste confinement. Tours, France, 14-18 March 2005, 547.
[2] Wang, X. et al. (2005) Adsorption Science and Technology, 23, 801-811.
[3] Maes, N. et al. (2004) Report SCK•CEN-BLG-988. SCK•CEN, Mol, Belgium.
[4] Sachs, S. et al. (2004) Report FZR-399, FZ Rossendorf, Dresden, Germany.
[5] Lead, et al. (2000) Environ. Sci. Technol. 34, 1365-1369.

The last decade has seen an increasing use of three-dimensional CFD codes to predict steady state and transient flows in nuclear reactors. The reason for the increased use of multidimensional CFD methods is that a number of important phenomena such as pressurized thermal shocks, boron mixing, and thermal striping cannot be predicted by traditional one dimensional system codes with the required accuracy and spatial resolution.

CFD codes contain empirical models for simulating turbulence, heat transfer, multi-phase flows, and chemical reactions. Such models must be validated before they can be used with sufficient confidence in NRS applications. The necessary validation is performed by comparing model results against trustworthy data. However, in order to obtain a reliable model assessment, CFD simulations for validation purposes must satisfy strict quality criteria. For instance, numerical errors caused by too coarse numerical grids should be separated from shortcomings of the physical models to avoid wrong conclusions about model performance.

CFD simulations are shown with an emphasis on validation in areas such as: heat transfer, buoyancy, multi-phase flows, natural circulation, free-surface flows, turbulent mixing, and complex geometries. These topics are related to NRS-relevant issues such as: pressurized thermal shocks, boron dilution, hydrogen distribution, induced breaks, subcooled boiling, thermal striping, etc.

Vanadium and silicon form several binary compounds; the most well characterized structures have the compositions V:Si= 3:1, 6:5, 5:3, 1:2. Density-functional band-structure calculations with a plane-wave basis for the valence electrons and norm-conserving pseudopotentials for the core-valence interaction have been carried out to investigate the structural properties and the phase stability for the experimentally known binary crystals. As the early transition metal silicides belong to the class of refractory materials, also the elastic properties were determined. It is furthermore shown that the electronic properties of the compounds depend strongly on the composition.

Tripodal polyamines based on the tris(2-aminoethyl)amine (tren) platform are useful complexing agents for cations or anions depending on the pH of the solution.[1,2] The binding properties of such compounds can be tuned by the addition of aromatic binding groups to the molecule.
A series of different substituted tren (1-4) derivatives were synthesised and characterised.
Here we present some recent solvent extraction and liquid membrane transport results that show a gradation in anion binding behaviour along I-, Cl-, Br-, CrO4
2-, SO4
2- and PO4
3-.
Finally, structural aspects of the anion complexes formed will be discussed, with the X-ray structure of the bromide complex of ligand 3 being presented.
[1] A.G. Blackman, Polyhedron, 2005, 24, 1-39
[2] K. Wichmann, B. Antonioli, T. Söhnel, M. Wenzel, K. Gloe, K. Gloe, J.R. Price, L. F.
Lindoy, A.J. Blake, M. Schröder, Coord. Chem. Rev., 2006, 250, 2987-3003

Mixed N,O-donor macrocycles have been shown to result in interesting complexation properties towards both cations and anions (the latter on protonation of the macrocycle's nitrogen functions).[1-3]
In the present study the phase transfer properties of 1 toward selected transition metal ions and anions have been evaluated by liquid-liquid extraction studies under different pH conditions. The order of increasing extraction follows the Irving-Williams series Co(II) < Ni(II) < Cu(II) > Zn(II), while the anion extraction is contolled by the Hofmeister series. A synergistic enhancement of metal extraction was obtained on exploiting a dual host strategy [4] in which the tripodal thiourea host 2 was incorporated in the system. In this case atypical anti-Hofmeister behaviour was obtained in which significant metal extraction of chloride or sulfate was observed from solution.
[1] N.A. Bailey, D. E. Fenton, S.J. Kitchen, T.H. Lilley, M.G. Williams, P.A. Tasker, A.J.
Leong and L.F. Lindoy, J. Chem. Soc. Dalton Trans., 1991, 627-637.
[2] H. Adams, N.A. Bailey, D.E. Fenton, I.G. Ford, S.J. Kitchen, M.G. Williams, P.A.
Tasker, A.J. Leong and L.F. Lindoy, J. Chem. Soc. Dalton Trans., 1991,1665-1674.
[3] L. Tušek-Božić, A. Višnjevac, E. Marotta, B. Kojić-Prodic, Polyhedron 24, 2005, 97–
111.
[4] K. Kavallieratos, R.A. Sachleben, G.J. Van Berkel and B.A. Moyer, Chem. Commun.,
2000, 187-188.

The responses of the bacterial community of a uranium mining waste pile to increased concentrations of uranyl or sodium nitrate were studied in microcosm experiments under conditions corresponding to the natural. For this study, the 16S rRNA (Fig. 1) and the narG-gene retrievals were applied. Both retrievals demonstrated that at the early stages of the treatments with sodium nitrate a strong activation of nitrate reducing and denitrifying populations, mainly of Firmicutes and Betaproteobacteria, occurred; they had overgrown the Acidobacteria, Alpha-, and Deltaproteobacteria which originally predominated in the untreated samples. Due to the U(VI) toxicity only a few populations of the mentioned Firmicutes and betaproteobacterial nitrate reducers proliferated in the samples treated with uranyl nitrate. More significant for these samples was the stimulation of the gammaproteobacterial denitrifyers, able to effectively interact with the added uranium. After longer incubations both treatments resulted in an establishment of betaproteobacterial populations and also of populations characteristic for the original, non-treated sample. As measured by using Mössbauer spectroscopy, at these stages a strong reduction of Fe(III) to Fe(II) occurred in the samples. Time-resolved laser fluorescence spectroscopic analyses demonstrated that most of the added U(VI) was bound in uranyl-hydro-phosphate phases or was complexed by organic phosphate groups (Fig. 2). The phosphate groups were liberated by different kinds of bacteria due to the activity of their intrinsic acidic phosphatases or were supplied by the lysed cells of the dead parts of the numerically reduced populations. The latter was confirmed by X-ray structural analyses of the formed bacteria - uranium complexes in the studied samples. Our results demonstrate that bacteria in uranium mining waste piles possess a high potential to deal with increased, toxic concentrations of U(VI) and nitrate, which usually co-contaminate these environments.

Mit Hilfe eines Finite Elemente Modells werden Eigenfrequenzen und Schwingungsformen eines DWR- Brennelements berechnet. Der Einfluss von Kontakt mit benachbarten Brennelementen wird untersucht. Der Bericht ist nicht öffentlich verfügbar (Industrieauftrag).

Reactions of rhenium chalcobromides Cs₄[{Re₆(µ₃-S)₈}Br₆]^.2H₂O, Cs₃[{Re₆(µ₃-Se)₈}Br₆]^.2H₂O, Cs₃[{Re₆(µ₃-Q)₇(µ₃-Br)}Br₆]^.H₂O (Q) S, Se), and K₂[{Re₆(µ₃-S)₆(µ₃-Br)₂}Br₆] with molten triphenylphosphine (PPh₃) have resulted in a family of novel molecular hybrid inorganic-organic cluster compounds. Six octahedral rhenium cluster complexes containing PPh₃ ligands with general formula [{Re₆(µ₃-Q)_8-n(µ₃-Br)_n}(PPh₃)_4-nBr_n+2] (Q ) S, n ) 0, 1, 2; Q ) Se, n ) 0, 1) have been synthesized and characterized by X-ray single-crystal diffraction and elemental analyses, ³¹P{¹H} NMR, luminescent measurements, and quantum-chemical calculations. It was found that the number of terminal PPh₃ ligands in the complexes is controlled by the composition and consequently by the charge of the cluster core {Re₆Q_8-nBr_n}ⁿ⁺². In crystal structures of the complexes with mixed chalcogen/bromine ligands in the cluster core all positions of a cube [Q_8-nBr_n] are ordered and occupied exclusively by Q or Br atoms. Luminescence characteristics of the compounds trans-[{Re₆Q₈}(PPh₃)₄Br₂] and fac-[{Re₆Se₇Br}(PPh₃)₃Br₃] (Q ) S, Se) have been investigated in CH₂Cl₂ solution and the broad emission spectra in the range of 600-850 nm were observed.

The decay of the very neutron-deficient isotope 101 Sn was studied at the GSI on-line massseparator using silicon detectors for recording charged particles and germanium detectors for gamma-ray spectroscopy. Based on the beta-delayed proton data the production cross-section of 101 Sn in the 50 Cr+58 Ni fusion-evaporation reaction was determined to be about 60 nb. The half-life of 101 Sn was measured to be 1.9±0.3 s. For the first time beta-delayed gamma rays of 101 Sn were tentatively identified, yielding weak evidence for a cascade of 352 and 1065 keV transitions in 101 In. The results are discussed by comparing them to predictions obtained from shell-model calculations employing a new interaction in the 88Sr to 132Sn model space.

The distance between irradiated features (precipitates, clusters and atmospheres) exceeds significantly the size of them in neutron irradiated reactor pressure vessel (RPV) steels. Therefore, cluster dynamics (CD) that originally has been suggested for small clusters and that can be applied to any ideal gas of clusters is found to be very effective to investigate the long-term behavior of the neutron stimulated changes of the microstructure of RPV steels.
In the present paper CD simulation have been carried out for model iron alloys with small and high copper content as well as for VVER 1000 steels R16, R17 and D under neutron irradiation. For this case CD simulations are needed for two sets of input parameters. The first one relates to the description of the local material damage at the cascade stage when the local temperature increases to the melting point and then decreases to a temperature of about 300°C over a time of some ps and CD is not applicable. The cascade stage is investigated by molecular dynamics (MD) and kinetic lattice Monte-Carlo (KLMC) methods that provide the data on the neutron cascade efficiency, rate of the vacancies (interstitials) that form the clusters, the planar or spherical or another shape of clusters, content and distribution of them by size at the end of cascade stage. The second set of input parameters contains the energy of formation and energy of migration, pre-exponential factor of diffusivity for vacancy and interstitial, copper, manganese, silicon and other alloying elements in iron; recombination radius for pair vacancy-interstitial; dislocation density, capture efficiency of vacancies (interstitials) by dislocations, surface tension for boundary between cluster and iron matrix; binding energy dependence on cluster size; lattice parameters of iron and precipitates. Some of these characteristics are well-known with some accuracy from the experiment and can be considered as materials constants for RPV steels.
It was found that the coupling between copper rich precipitates (CRP) and point defects in neutron irradiated iron alloys and VVER steels can be investigated by CD simulations using LSODA code as a solver of the stiff ordinary differential equations system. The additional consideration of the strain energy effect on CRP kinetics as well as the application of the regular solution model for the case of different fixed copper contents of CRP improves quantitatively the simulation results for considered model alloys. The additional accounting of the Ni effect in CD simulation is needed to study the kinetics in the investigated VVER steels under irradiation.

The mixing phenomenon is relevant for the normal and off normal operation of the Nuclear Power Plant (NPP), because it influences the safety, mitigating the reactivity and structural consequences. The study of these issues was investigated performing experimental campaigns in large-scale test facilities and in real NPPs. In this framework ROCOM (Rossendorf Coolant Mixing Model) test facility was built with the purpose of investigating the coolant mixing phenomena occurring in the Reactor Pressure Vessel (RPV) of a Pressurizer Water Reactor (PWR). The experiments executed in this facility provide experimental data for code validation (CFD and TH-SYS codes). The purpose of this work is to address the capability of the RELAP5-3D© to reproduce ROCOM facility dynamic in simulating the mixing for a large range of operational and accident conditions. In particular, the attention is focused on the effects in the vessel downcomer, lower plenum and core inlet. Three experiments were selected for the analyses: two steady states and one transient. The ROCOM steady states are slug mixing experiments that analyze the mixing scalar trend inside the facility at different mass flow rates. The ROCOM transient represents the injection of a mixing scalar slug from one cold leg with an increasing mass flow rate in the same loop. A systematic comparison between ROCOM experimental data and the results of the simulations with the RELAP5-3D© is presented including a complete set of sensitivity analyses to find out the most relevant parameters which influence the results from nodalization and user effects points of view.

Das vom VKTA entwickelte elektrochemische Verfahren zur Aufbereitung schwefelsaurer Wässer aus Tagebau-Restseen befindet sich zurzeit in der Phase der Pilotierung. Hierzu wurde vom VKTA im Gebiet des Lausitzer Braunkohlen-Tagebaureviers eine Grubenwasserreinigungs-Pilotanlage errichtet. Durch das FZD wurden prozessbegleitende Untersuchungen sowohl zur Optimierung des Elektolyseprozesses als auch zur Aufbereitung der Koppelprodukte durchgeführt.

It is known that under-borated coolant can accumulate in the loops and that it can be transported towards the reactor core during a loss of coolant accident. Therefore, the mixing of weakly borated water inside the reactor pressure vessel was investigated using the ROCOM test facility. Wire mesh sensors based on electrical conductivity measurement are used to measure in detail the spreading of a tracer solution in the facility. The mixing in the downcomer was observed with a measuring grid of 64 azimuthal and 32 vertical positions. The resulting distribution of the boron concentration at the core inlet was measured with a sensor integrated into the lower core support plate providing one measurement position at the entry into each fuel assembly.
The boundary conditions for this mixing experiment are taken from an experiment at the thermal hydraulic test facility PKL operated by AREVA Germany. The slugs, which have a lower density, accumulate in the upper part of the downcomer after entering the vessel. The ECC water injected into the reactor pressure vessel falls almost straight down through this weakly borated water layer and accelerates as it drops over the height of the downcomer. On the outer sides of the ECC streak, lower borated coolant admixes and flows together with the ECC water downwards. This has been found to be the only mechanism of transporting the lower borated water into the lower plenum. In the core inlet plane, a reduced boron concentration is detected only in the outer reaches of the core inlet. The minimum instantaneous boron concentration that was measured at a single fuel element inlet was found to be 66.3 % of the initial 2500 ppm.

alpha,beta-dicyano substituted beta, beta*-dibutylquarterthiophene (DCNDButQT) was synthesized and fully characterized by 1H-NMR and 13C-NMR, elemental analysis, UV-visible spectroscopy, DSC, TGA and cyclic voltammetry. The band gap energy (deltaEg) calculated from cyclic voltammetry data was found to be 1.97 eV, which is in the range of semiconductor materials (deltaEg < 3.0 eV). DCNDButQT was deposited on different substrates (Al2O3, SiO2, TiO2) by vacuum deposition and solution-cast methods. The structure of the thin films analysed by AFM and XRD showed different morphology depending on cast method. The spin-coating and drop-casting films showed amorphous structure, whereas the vacuum-deposition films exhibit a fine crystalline structure. AFM of vacuum-deposition film revealed the formation of well-ordered terrace structures, the step between adjacent terraces is about 1.5 nm.

The morphological evolution of surfaces during ion-beam irradiation has attracted a significant interest due to possibility of the development and the controlling of selforganization in nanostructures. Pattering and texture on nanometer length scale at metal and semiconductor surfaces has become a topic of intense research. In particular the surface and subsurface ripple formation under 40Ar+ ion-beam irradiation of Si (100) crystal has been studied recently. Strong ripple formation has been found for an irradiation energy of 60keV and incident angles around 60degree. During implantation a corrugated surface layer is formed, consisting of a strongly damaged, amorphous near-surface layer followed by a nearly sinusoidal shaped interface towards the crystalline material. In the present work, we investigate the onset and evolution of ripple-formation as function of implantation energy and incidence angle of the ion beam.

Aims/hypothesis: Glycoxidized low density lipoprotein (LDL) has been implicated in the pathogenesis of atherosclerosis, one of the major diabetic complications. Since atherogenesis may occur early at the onset of diabetes, we investigated whether circulating LDL isolated from subjects with impaired glucose tolerance (n=20, IGT-LDL) showed an increased glycoxidation status and explored their proatherogenic effects on macrophages.
Methods/Results: Using gas chromatography/mass spectrometry we could demonstrate a 3- to 5-fold higher oxidative apolipoprotein B-100 proline, arginine, lysine, and tyrosine modification as compared to LDL obtained from subjects with normal glucose tolerance (n=20, NGT-LDL). Moreover, LDL glycoxidation estimated by both N Epsilon-(carboxymethyl)lysine (CML) and N Epsilon-(carboxyethyl)lysine (CEL) residues was increased more than 9-fold in IGT-LDL when compared to NGT-LDL. After one hour incubation of murine macrophages with LDL mRNA expression rates of the scavenger receptors CD36 and SR-BI and transcription factor PPAR Gamma were quantified by reverse-transcription real-time PCR. In comparison to NGT-LDL, IGT-LDL elicited a significantly higher CD36 (p<0.05) and PPAR Gamma (p<0.05) gene expression, whereas SR-BI mRNA expression was not affected.
Conclusion: These data suggest that impaired glucose tolerance is associated with increased glycoxidation of circulating LDL that might contribute to conversion of macrophages into a proatherogenic phenotype.

When a conducting fluid comes under the influence of a magnetic field, electrical currents are induced that give rise to a modification of this magnetic field. The ratio of induced magnetic field to applied magnetic field is characterized by the magnetic Reynolds number Rm of the flow. For large Rm, even self-excitation of a magnetic field can occur. This hydromagnetic dynamo effect is responsible for the maintenance of the magnetic fields of planets, stars and galaxies. In the present paper, we delineate some recent developments in the numerical treatment of induction effects in arbitrary geometry, and their application for dynamo experiments as well as for a Contactless Inductive Flow Tomography (CIFT).

Mechanical and tribological properties of successive C and N ion implantation into Al were studied in the present work. Ion sequence, substrate temperature and subsequent thermal treatment were performed in order to understand the involved mechanisms on the surface hardening. The results showed that independent of the ion sequence, a higher surface hardness is obtained for room temperature ion implantation (≈ 10 GPa). At high substrate temperature the hardness decreases to 7 GPa. The hardening mechanisms are discussed in terms of: solid solution, hard embedded precipitates in the soft Al matrix and the damage produced by the ion implantation process. Adhesive and abrasive regimes are identified from the friction coefficient profiles and are function of the ion implantation parameters. Wear resistance is improved if subsequent thermal treatment at high temperature is performed. Wear improvement is correlated to the presence of a high concentration of carbon clusters in the Al matrix.

Radiation damage in an (initially crystalline) silicon wafer was generated by microbeam implantation with 600 keV Si⁺ ions (fluence 5 x 10¹⁴ ions/cm²). To produce micro-areas with different degrees of damage, 14 implantations at different temperatures (between 23 and 225 °C) were done. The structural state of irradiated areas was characterized using Raman spectroscopy and electron back-scatter diffraction. All irradiated areas showed strong structural damage in surficial regions (estimated depth <1 μm), and at implant substrate temperatures of below 130 °C, the treatment has caused complete amorphization. Back-scattered electron (BSE) images exhibited that observed BSE intensities correlate with the degree of irradiation damage; all irradiated areas were higher in BSE than the surrounding host. Because there were no variations in the chemical composition and, with that, no Z contrast in our sample, this observation again supports the hypothesis that structural radiation damage may strongly affect BSE images of solids.

Dieser Bericht beinhaltet insbesondere diejenigen durchgeführten Arbeiten und Untersuchungen, welche für die Planung zukünftiger Experimente am KATHY - Versuchsstand relevant sind. Der Bericht unterteilt sich in zwei voneinander weitgehend unabhängige Teile, zum einen die technische Weiterentwicklung des Tomographen (Abschnitt 2) und zum anderen methodisch orientierte Studien und Experimente (Abschnitt 3) betreffend. Konzeptionell basiert der Bericht auf Auswertungen der an KATHY im Oktober 2005 und Januar 2006 durchgeführten Experimente, wobei diese Auswertungen hier nicht noch einmal in ihrer Gesamtheit dargelegt werden, sondern nur auf ihre zukünftig relevanten Aspekte Bezug genommen wird.

The work was aimed at the numerical simulation of coolant mixing in the downcomer and the lower plenum of the Rossendorf test facility ROCOM. ROCOM is a 1:5 scaled Plexiglas model of a German pressurized water reactor allowing conductivity measurements by wire mesh sensors and velocity measurements by LDA technique. The CFD calculations were carried out with the CFD-codes CFX-4 and CFX-5. In the case of stationary mixing, the maximum value of the averaged mixing scalar at the core inlet was found in the sector below the inlet nozzle, where the tracer was injected. The comparison of a very detailed mesh (CFX-5) and a mesh with simplifications and additional physical models (CFX-4) showed, that in the referred case the use of these models are allowed. For turbulent flows CFX-4 and CFX-5 were validated in accordance with the Best Practice Guidelines and can be used in the reactor safety analysis. A better description of the mixing processes inside the RPV is the basis of a more realistic safety assessment.

The complex formation of uranium(VI) with salicylhydroxamic, benzohydroxamic, and benzoic acid was investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS). We observed in all three systems a decrease in the fluorescence intensity with increasing ligand concentration. All identified complexed uranyl species are of the type MpLqHr. In the uranium(VI)-salicylhydroxamate system a 1:1 complex with a stability constant of log β111 = 17.34 ± 0.06 and a 1:2 complex with a stability constant of log β122 = 35.0 ± 0.11 was identified. Also in the uranium(VI)-benzohydroxamate system the stability constants are determined to be log β110 = 7.92 ± 0.11 and log β120 = 16.88 ± 0.49. In the uranium(VI)-benzoate system only a 1:1 complex is existent with a stability constant of log β110 = 3.56 ± 0.05.

We report about magnetic and structural studies on p-type GaN implanted with 57Fe with fuences from 1*10^16cm^-2 to 1.6*10^17cm^-2 at different temperatures and subsequently subjected to thermal treatment. X-ray diffraction, transmission electron microscopy, conversion electron Mössbauer spectroscopy and superconducting quantum interference device magnetometry were used for the crystallographic, electronic and magnetic characterization of the samples. Room temperature ferromagnetism was observed in GaN after implantation at 623 K with different fluences and is mainly ascribed to alpha-Fe precipitations. An additional contribution to ferromagnetic signal is observed in a Mössbauer spectrum and as a magnetization loop in SQUID in sample implanted with lowest fluence at 623 K which cannot be related to alpha-Fe. In samples implanted with low fluences at RT no ferromagnetism was observed by means of SQUID. However, in CEMS a 6.8 T magnetic hyperfine field was used to fit the experimental spectrum and is discussed in terms of possible origin. Samples implanted at 240 K do not exhibit ferromagnetic properties. Precipitation of alpha-Fe was successfully reduced by decreasing the implantation temperature, however this was accompanied by an enhanced crystal damage. Annealing between 973 K and 1123 K resulted in most cases predominantly in the formation of alpha-Fe-clusters. Thermal treatment brought no significant recover of the crystallinity as it was verified by RBS channeling measurements.

Eine homogenisierte Probe Opalinus-Ton wurde charakterisiert. Die erhaltenen Ergebnisse (CEC, BET, TOC, XRD, IR) stimmen mit denen in der Literatur beschriebenen Ergebnissen überein. Erste Untersuchungen der U(VI)-Komplexierung mit HS-Modellliganden wurden durchgeführt.

The strengths of resonances located at center-of-mass energies of E-c.m.=189, 304, 374, and 418 keV for the Mg-25(p,gamma) reaction have been measured for the first time with an off-line method: Mg targets were firstly activated with protons at the resonance energies and the produced Al-26(g) nuclei were counted by means of highly sensitive accelerator mass spectrometry (AMS). Thus, the production of Al-26 in its ground state is determined independently from the gamma-decay branching ratio. While the 304, 374, and 418 keV resonances show fair agreement with previous measurements, the 189 keV resonance yield a significantly less strength. In addition, an experimental upper limit for the E-c.m.=92 keV resonance was determined.

The results of investigation of the polycrystalline boron implanted by magnesium and argon plasma pulse treatment are presented. The four-probe electric conductivity measurements and magnetically modulated microwave absorption showed the presence of superconducting islands below the temperature of 25 K. Below T = 23 K we detected the Kondo effect, a logarithmic increase in the resistivity as the temperature is lowered, due to iron impurity.

We used time-resolved laser-induced fluorescence spectroscopy (TRLFS) in order to characterize the species of U(VI) adsorbed onto kaolinite in the absence and presence of HA. Two adsorbed U(VI) surface species on kaolinite were identified in the pH range of pH 5.0 to pH 8.5. Obtained results help to improve the understanding of the geochemical interactions of hexavalent actinides in environment.
Laser fluorescence spectroscopy measurements were carried out in the systems Am(III)-kaolinite and Am(III)-HA-kaolinite to study the surface complexes of Am(III) on kaolinite at different pH values (pH 5 - 8). HA decreases the fluorescence intensity of the samples. The shape of the measured fluorescence spectra in both systems, binary and ternary, differs from the spectrum observed in the solution. Further measurements are required to satisfactorily explain the obtained results.

The influence of density differences on the mixing of the primary loop inventory and the Emergency Core Cooling (ECC) water in the downcomer of a Pressurised Water Reactor (PWR) was analyzed at the ROssendorf COolant Mixing (ROCOM) test facility. ROCOM is a 1:5 scaled model of a German PWR, and has been designed for coolant mixing studies. It is equipped with advanced instrumentation, which delivers high-resolution information for temperature or Boron concentration fields. This paper presents ROCOM experiments in which water with higher density was injected into a cold leg of the reactor model. Wire-mesh sensors measuring the concentration of a tracer in the injected water were installed in the upper and lower part of the downcomer. An experiment with 5 % of the design flow rate in one loop and 10 % density difference between the ECC and loop water was selected for validation of the CFD software ANSYS CFX. A mesh with two million control volumes was used for the calculations. The effects of turbulence on the mean flow were modelled with a Reynolds stress turbulence model. The results of the experiment and of the numerical calculations show that mixing is dominated by buoyancy effects: At higher mass flow rates (close to nominal conditions) the injected slug propagates in the circumferential direction around the core barrel. Buoyancy effects reduce this circumferential propagation. The ECC water falls in an almost vertical path and reaches the lower down¬comer sen¬sor directly below the inlet nozzle. Therefore, density effects play an important role during natural convection with ECC injection in PWRs. ANSYS CFX was able to predict the observed flow patterns and mixing phenomena quite well.

High fluence P implantation (30 keV, 3x1015 cm-2) into pre-amorphized Ge and subsequent rapid thermal or flash lamp annealing is investigated. In contrast to previous assumptions a significant P diffusion in amorphous Ge is not observed. However, during the fast solid phase epitaxial regrowth a rapid redistribution of P occurs. After completion of the regrowth and at temperatures above 500 0C, a concentration-dependent diffusion of P in crystalline Ge takes place. An appreciable influence of implantation defects on the diffusion coefficient of P cannot be found. For 60 s rapid thermal annealing at 600 0C and for 20 ms flash lamp annealing at 900 0C, the junction depth and the sheet resistance vary between 140 and 200 nm and between 50 and 100 Ohm , respectively, and the maximum electrical activation of P is about 3 – 7x1019 cm-3.

For the investigation of co-current two-phase flows, the Horizontal Air/Water Channel (HAWAC) was built at Forschungszentrum Dresden-Rossendorf. A special inlet device provides well-defined as well as variable boundary conditions for generic horizontal two-phase flow experiments. Optical measurements were performed with a high-speed video camera during slug flow. By an interface capture method, the water level can be measured in any observed cross-section. As a result, the water level history can be extracted from the image sequences. Furthermore, the profiles of the time-averaged water level bounded by the standard deviation were presented and show the evolution of the flow structure and of its dynamic component along the channel.

This report summarizes the results of the first 24 months period of the NURESIM project for the work package 2.1 “Pressurized Thermal Shock (PTS)”. It mainly bases on the deliverables supplied by the partners involved in this work package. In the Introduction chapter some more general information on the PTS issue is given, which should help to clarify the integration of the single activities. Since the PTS scenario involves different flow situations, for which also different modelling approaches are necessary, the contributions are sorted according to these flow situations. The relation of the work done to the general aim of the NURESIM project, which is to establish a new code platform, is indicated by assigning the activities to 6 different types. The present status PTS work package is in agreement with the planning of the NURESIM project, the expected results were met by the deliverables. The work done leads to an improvement of the simulation capabilities regarding a PTS flow situation, but caused by the complexity of the issue it will still be a long way to enable reliable predictions for the whole process from such simulations.

This paper reports some activity about the Pressurized Thermal Shock (PTS) performed within the European Integrated Project NURESIM. The PTS phenomenon is expected to take place in some water cooled nuclear reactors equipped with pressure vessels during selected accident scenarios. The PTS implies the formation of temperature gradients in the thick vessel walls with consequent localized stresses and the potential for propagation of possible flaws present in the material. Current generation Pressurized Water Reactors, PWR (including the Russian VVER types), are primarily affected by the phenomenon which is investigated within three broad areas: material damage originated by irradiation, thermal-hydraulics (including single and two-phase flow conditions in the region of the ‘shock’) and structural mechanics with main reference to fracture mechanics. The present paper, in the area of thermal-hydraulics, focuses on the study of two-phase conditions that are potentially at the origin of PTS. Within the above context, the paper summarizes recent advances in the understanding of the two-phase phenomena occurring within the geometric region of the nuclear reactor, i.e. the cold leg and the downcomer, where the ‘PTS fluid-dynamics’ is relevant. Available experimental data for validation of two-phase CFD simulation tools are reviewed and the capabilities of such tools to capture each basic phenomenon are discussed. Key conclusions show that several two phase mechanisms (or sub-phenomena) are involved and can individually be simulated at least at a qualitative level, but the capability to simulate their interaction and the overall system performance (case of two phase flow) is presently not available.

Die CFD Modellierung hat Einzug gehalten in die nukleare Sicherheit. CFD-Codes werden erfolgreich eingesetzt, um komplexe Strömungsfelder in ganzen Druckwasserreaktoren zu berechnen. Dabei geht es vornehmlich um die Vermischung von Borsäure bei mit unboriertem Wasser und von kalten Notkühlwasser mit heißem Reaktorkühlmittel. Die Validierung anhand von Versuchen an verhätnismässig grossskaligen Testständen, die mit hochauflösender Leitfähigkeitsmesstechnik ausgestattet sind, zeigt die bereits erreichte hohe Zuverlässigkeit der Vorhersagen im Einphasenbereich. Diese Erkenntnisse können auf chemisch-verfahrenstechnische Anlagen übertragen werden. Beim Übergang zur Zweiphasenströmung treten zusätzliche Schwierigkeiten auf, die mit der Beschreibung der Prozesse an der Phasengrenze und der Modellierung der Topologie und Ausdehnung derselben zusammenhängen. Hierzu werden neuere Entwicklungen auf dem Gebiet der Zweifluidmodelle für Gas-Flüssigkeitsströmungen vorgestellt. Speziell handelt es sich um das Inhomogeneous MUSIG Model, das Bestandteil des Codes ANSYS CFX ist. Dieser Ansatz erlaubt die Beschreibung der Wechselwirkung mehrerer Blasenklassen unter Berücksichtigung der auf die Blasen wirkenden Kräfte und von Koaleszenz und Zerfall. Das Modell wurde ausgehend von Experimenten an vertikalen Rohrleitungen vorgeschlagen und dann anhand von Messergebnissen validiert. Auch hier kommen Leitfähigkeitssensoren zum Einsatz, die die Struktur der Phasengrenzfläche im gesamten Strömungsquerschnitt hochaufgelöst erfassen. Dabei wurden u. a. Strömungen mit Phasenübergang infolge Kondensation von Dampf an einer unterkühlten Flüssigphase untersucht. Mit solchen Gittersensoren wurden auch komplexe dreidimensionale Gas-Flüssigkeitsströmungen, z.T. bei Drücken bis zu 70 bar und Temperaturen bis 286 °C (Wasser-Dampf) vermessen, die charakteristische Merkmale von Strömungen in technisch relevanten Anlagenteilen aufweisen, wie Strömungsabriss, Staupunkte, Strahlausbildung, Rezirkulationsgebiete u. ä.. Der Vergleich zwischen Rechnungen und Experiment dokumentiert den erreichten Stand bei der dreidimensionalen Modellierung. Durch die Diskretisierung der zu untersuchenden Geometrie ist der CFD-Code in der Lage, die Einzelmodelle auch Geometrien zu übertragen, die bei der Validierung nicht betrachtetet wurden. Dies wird anhand von Rechenergebnissen für Sicherheitsventile demonstriert.

The talk summarizes the latest tests and results w.r.t. MRPCs with silicate glass resistive plates. These
have been tested in a high flux environment with a continous electron beam at ELBE.

The HADES experiment at SIS18 at GSI/Darmstadt is a dedicated experiment for studying medium modifications of hadrons, i.e. the light vector mesons rho, omega and phi, in pA, piA and AA collisions. Specifically, dileptonic decays of these vector mesons provide an direct probe for the properties of hadronic matter at high nuclear densities. The future FAIR facility at GSI/Darmstadt with SIS100/300 will provide heavy-ion beams with energies of up to 45 AGeV. It is planned to operate the HADES detector at these higher energies. In this work the principle possibilities of detecting dielectrons with an unmodified HADES detector are studied. Simulations of dielectron production for several beam energies have been performed using the UrQMDv1.3p1 transport code together with the PLUTO++ phase space generator. Future measurements of dileptons with HADES at FAIR are shown to be within reach of the current setup.

Multigap Resistive Plate Chambers (MRPC) provide the possibility for assembling high-granularity, large-area TOF sytems designed for modern nuclear and particle physics experiments. Currently, experiments like ALICE, STAR, FOPI, HADES prepare MRCP based TOF systems with time resolutions of less than 100 ps. The planned CBM experiment at the future FAIR facility at GSI/Darmstadt considers using an MRPC system provided sufficient time resolution and rate stability can be achieved. These properties of MRCP have been successfully demonstrated in prototype tests performed at the FZD electron linac ELBE, using continuous e− beams of 20-40 MeV. Typical time resolutions of 70 ps were achieved. The rate capabilities of MRCP using special low-resistive silicate glas were tested and stable efficiencies up to rates of 20 kHz/cm2 were observed.

4H silicon carbide (Si1-xC1-y)Gex+y solid solutions with an average Ge incorporation on lattice sites ranging from 0.7 to 2.5 percent were formed by ion beam synthesis. RBS and RBS/C investigations revealed a decreasing Ge lattice incorporation with increasing implantation dose above 10%. The carried out rapid thermal annealing at 1300 °C reduces the residual damage, increases the lattice site occupation and led to negligible change in the concentration profiles.

Slugs of under-borated, or even boron-free, coolant can be formed in the primary circuit during different accident scenarios, e. g. due to a malfunction of the chemical and volume control system, or due to an SBLOCA with partial failure of the safety injection system. An unintentional, or even unavoidable, decrease of boron concentration in the reactor core leads to a reactivity increase and may result in a power excursion, a so-called boron dilution transient. Whether re-criticality of the scrammed reactor occurs, and how high the power peak is, depends among other factors, in a sensitive manner, on the mixing of the too weakly borated water with the ambient coolant in the downcomer and the lower plenum on its way to the core. For an adequate simulation of such boron dilution transients, 3D neutron kinetic core models coupled with advanced thermal hydraulic system codes are necessary. Such analyses should be completed by a simulation of the above mentioned coolant mixing processes inside the reactor pressure vessel.

An earlier developed fast running semi-analytical coolant mixing model has been recently extended to natural circulation conditions. A parameter study, incorporating stationary and transient core calculations, was carried out for a hypothetical boron dilution event in a pressurized water reactor during the operation of the residual heat removal system, using the coupled 3D neutron kinetics/thermal hydraulics code system DYN3D/ATHLET in combination with this coolant mixing model. According to the boundary conditions, this analysis is carried out at atmospheric pressure conditions and a coolant temperature of 25 °C. By varying the initial slug volume, it was found in stationary calculations that, for the given core configuration, slugs of less than 6 m³ do not lead to re-criticality. Transient core calculations from 8 to the maximum initial slug volume of 15 m3 show a significant reactivity insertion and over-criticality. The resulting power excursion is mitigated and stopped by Doppler and moderator density feedback. The power increase in all calculations is accompanied by significant coolant boiling in single channels. It should be pointed out, that the thermal hydraulics simulations at low pressure are quite challenging because of the high density difference between water and steam and therefore, high sensitivity of void fraction versus coolant enthalpy. Although in all calculations local coolant boiling occurs over several tenths of seconds, the integrity of the fuel is always ensured according to the calculation results.

e⁺e^- production was studied using the High Acceptance DiElectron Spectrometer (HADES). In pp collisions at 2.2 GeV kinetic energy, the exclusive η production and the Dalitz decay η -> γe⁺e^- have been reconstructed. The electromagnetic form factor of the latter decay was found to be in good agreement with the existing theoretical predictions. In addition, an inclusive e⁺e^- invariant-mass spectrum from the ¹²C +¹²C reaction at 2 AGeV is presented and compared with a simplified thermal model.

The catalytic effect of nickel nanoparticles on the formation and on the structure of fullerene-like carbon nanostructures prepared by ion beam sputtering at different temperatures was studied by wavelength dependent Raman spectroscopy. Compared to nickel-free reference films the formation of carbon nanostructures is enhanced in the whole range of deposition temperatures from 25°C =< T (°C) <= 500°C. Several phases characterized by different ratios of amorphous and graphite-like carbon, a different film transparency, and a different elastic Raman background intensity, were observed. Amorphous carbon structures are preferentially formed at lower deposition temperatures, whereas graphitic structures are dominant for higher growth temperatures. Based on data for different excitation wavelengths and using difference spectroscopy, a quantitative model for the composition of these nanostructured carbon materials is developed. The results are in full agreement with those obtained by TEM, XANES and XRD analysis.[1] The model might be used as well for the analysis of other pure carbon or carbon based composite materials like CN and BCN films.
[1] G. Abrasonis, A. Mücklich, K. Küpper, M. Krause, U. Kreissig, A. Kolitsch, W. Möller, K. Sedlackova, G. Radnoczi, R. Torres, and I. Jimenez, "Morphology and bonding structure of fullerene-like nanocomposite C:Ni (~30 at%.) thin films grown by ion beam sputtering", to be presented on XXI. IWEPNM, Kirchberg, 2007

The superposition of the quantum rotational motion (tunneling) of the encapsulated Sc₂C₂ complex with the classical rotational motion of the surrounding C₈₄ molecule in a powder crystal of Sc₂C₂@C₈₄ fullerite is investigated by theory. Since the quantum rotor is dragged along by the C₈₄ molecule, any detection method which couples to the quantum rotor (in casu the C₂ bond of the Sc₂C₂ complex) also probes the thermally excited classical motion (uniaxial rotational diffusion and stochastic meroaxial jumps) of the surrounding fullerene. The dynamic rotation-rotation response functions in frequency space are obtained as convolutions of quantum and classical dynamic correlation functions. The corresponding Raman scattering laws are derived, and the overall shape of the spectra and the width of the resonance lines are studied as functions of temperature. The results of the theory are confronted with experimental low-frequency Raman spectra on powder crystals of Sc₂C₂@C₈₄ [M. Krause et al., Phys. Rev. Lett. 93, 137403 (2004)]. The agreement of theory with experiment is very satisfactory in a broad temperature range.

Conversion of the Au/n-ZnO contact from Ohmic to rectifying with H2O2 pretreatment was studied systematically using I-V measurements, x-ray photoemission spectroscopy, positron annihilation spectroscopy, and deep level transient spectroscopy. H2O2 treatment did not affect the carbon surface contamination or the EC–0.31 eV deep level, but it resulted in a significant decrease of the surface OH contamination and the formation of vacancy-type defects (Zn vacancy or vacancy cluster) close to the surface. The formation of a rectifying contact can be attributed to the reduced conductivity of the surface region due to the removal of OH and the formation of vacancy-type defects.

We report on the status quo of the Dresden High Magnetic Field Laboratory (HLD) that is being set up at the Forschungszentrum Dresden-Rossendorf in Dresden, Germany. First pulsed-field coils reaching up to 71T with a pulse duration of about 100 ms have been designed, constructed, and tested. A two-coil 100 T magnet and a long-pulse (1000 ms) 60T magnet are under construction. Electrical transport and magnetization experiments are running routinely in the pilot laboratory at the IFW Dresden. The feasibility of NMR experiments in pulsed-field environments has been proven.

The single molecule magnet system (MnIIL2)3MnII.

There has been considerable interest in high-k-dielectrics rare earth oxides as replacement for SiO2 in advanced field-effect transistors (FETs). Promising candidates are the perovskites SmScO3, GdScO3 and DyScO3. A tendency towards antiferromagnetic ordering at low temperatures is observed for the high magnetic moments at rare earth atoms. We analyse the electronic structure of the single crystalline samlpes by means of X-ray photoelectron spectroscopy and firstprinciples theory. The electronic structure calculations are performed with the augmented plane waves method (WIEN2k code) of the density functional theory, taking into account the spin-orbit interaction and orbital-dependent potential (LDA+U). The calculated positions of the main features in the valence band agree with the XPS data, the underlying chemical bonding can be analysed in detail. Small differences in the electronic structure, resulting in different stability of ferroand antiferromagnetic configurations, are discussed.

We report the imaging of the magnetic excitation spectrum of a single cross-tie wall by means of x-ray magnetic circular dichroism - photoemission electron microscopy (XMCD-PEEM). The permalloy rectangle was excited by a short magnetic in plane pulse with a maximum field value of about 20 Oe. The high temporal and lateral resolution allows a detailed quantitative analysis of the magnetodynamic excitations. We find new eigenmodes in the frequency domain which are characteristic for the vortex-antivortex interaction in a single cross-tie wall. We discuss our experiment along micromagnetic simulations.

The activities of the nanomagnetism group at the Forschungszentrum Dresden-Rossendorf will be briefly presented.
Special emphasis will be given to lateral and time resolved x-ray microscopies in order to study the magnetization
dynamics of micromagnetic elements in detail.

Purpose
Stimulated by the German Feed-in-Law, a number of grid-connected Megawatt PV plants have been put into operation during the last 5 years. Because of the higher irradiance these plants were originally concentrated in the southern part of Germany (Bavaria and Baden-Wuerttemberg). Starting in 2004 some plants have been also installed in Central Germany. The paper describes design and operation results of seven plants operating in the region of Saxony and Thuringia.

Locations and design
The most plants are concentrated in a region earlier defined by the DWD as "solar island" around Leipzig and Chemnitz. One plant is located in north-west Thuringia.
All plants were built on heavily used or loaded areas (former industrial sites or waste sites). Different types of fundaments and rack support constructions (desks) were used for the module mounting. The connection with the grid was done in the 10 to 20 kV voltage level, the distance between the plants and the grid was several thousands meters in some cases. All plants started their operation before 2006. The operation of the plants is monitored by the owners or by professional service providers.

Results and conclusions
The operation results of the year 2006 are exemplarily presented. The solar irradiance in 2006 was higher than the long year average, similar to the years before. The final yield of the plants ranges between 950 and 1050 kWh/kW. These surprisingly high values are near the values which were only found in Germany south of 50° latitude so far. The final yield of the tracked plant in Borna surpasses the yield of the other plants by 25%.
The performance ratios were determined to be between 0.77 and 0.84. The sources of energy losses are analysed and discussed. Beside component failures in the plants also grid disconnections reduced the feed-in energy in some cases.
Finally a long term estimation of the yield for the different plants will be given. Based on the data of the year 2006 a mean yield between 900 and 1000 kWh/kW can be expected.

Im Beitrag werden die Optionen und die Herausforderung für die Nutzung der Kernenergie im 21. Jahrhundert aufgezeigt. Ausgangspunkt sind die vorhandenen Vorräte an Kernbrennstoff und die Darstellung seiner derzeitigen Nutzung. Die Entwicklung der Kernkraftwerkstechnik seit 1960 wird beispielhaft dargestellt. Die Optionen und Entwicklungsziele der Kernreaktoren der 4. Generation (EInsatz etwa ab 2040) werden exemplarisch vorgestellt. Dabei wird besonders auf die zentrale Rolle der schnellen Brutreaktoren eingegangen.Ein besonderer Abschnitt ist der Wiederaufarbeitung und Endlagerung von Kernbrennstoff gewidmet.

Die LIBD ist eine Methode, die Kolloidpartikel in sehr niedrigen Konzentrationen zu vermessen vermag. Sie wurde bisher vorwiegend zur Untersuchung von Kolloidproblemen in der Umweltforschung eingesetzt. Wegen ihrer hohen Empfindlichkeit könnte die LIBD potentiell aber auch für die Überwachung von Reinst- und Prozesswässern in der Halbleiterindustrie interessant sein. Hier ist die etablierte Methode zur Überwachung der Partikelfreiheit von Wässern das Single Particle Counting (SPC), vor allem mit den kommerziellen Geräten von PMS und Horiba. Es wird gezeigt, dass (i) für Kolloidpartikel > 50 nm das SPC der LIBD bezüglich der Konzentrationsempfindlichkeit deutlich überlegen ist, (ii) für Kolloidpartikel < 50 nm die Konzentrationsempfindlichkeit der LIBD heute unbefriedigend ist (sie liegt über den zu vermutenden typischen Konzentrationen der Partikel < 50 nm in den Reinstwässern der Halbleiterindustrie), (iii) die LIBD die einzige Methode ist, die überhaupt eine Information über Partikel < 50 nm liefern kann und (iv) durch technische Weiterentwicklung die LIBD wahrscheinlich in den erforderlichen Bereich der Partikelkonzentrationsempfindlichkeit gebracht werden könnte. Die Methode würde (nach Weiterentwicklung) für die Halbleiterindustrie interessant, wenn Partikel der Größe < 50 nm als Verunreinigungen interessant werden.

New results concerning the production of neutral strange particles, K⁰ and Λ in Ni+Ni collisions at 1.93 AGeV, measured with the FOPI detector at GSI Darmstadt, are presented. Rapidity density distributions and Boltzmann slope parameter distributions are measured in nearly the full phase space of the reaction. The observables are compared to existing K⁺ and proton data. While the K⁰ data agree with previously reported K⁺ measurements, the Λ distributions show a different behavior relative to that of protons. The strangeness balance and the production yield per participating nucleon as a function of the centrality of the reaction are discussed, for the first time at SIS energies.

The paper presents the results of recent study of anisotropic plasma with thermonuclear ions confined in the axially symmetric Gas Dynamic Trap (GDT) mirror. Anisotropic ions are produced by the perpendicular injection of two focused 18 keV neutral beams in the small mirror section attached to the GDT central cell. We observed build-up of density of anisotropic ions up to approximately 10^13cm^−3 with the localized spatial profile and the mean energy of 7 keV. The average fast ion density three times exceeded the background plasma density. Fast ion accumulation is accompanied by the decrease of the plasma flux from the central cell recorded outside the mirror, that was qualified as a potential barrier development causing confinement improvement. Analysis of measurement results compared with estimates of plasma parameters in the compact mirror allows to scale to the experiments with next generation neutral beams with increased power and pulse duration.

The results of [¹¹C]CH₃I synthesis through hydrogen gas reduction of [¹¹C]CO₂ on different nickel catalysts (HARSHAW-nickel, SHIMALITE-nickel, nickel on silica/alumina, nickel nanosize 99.99%) followed by gas phase iodination using a TRACERlab FX_C synthesis unit are reported. Further reaction parameters such as furnace temperatures, flow rate of hydrogen gas and reduction time were optimized. It was found that reduction of [¹¹C]CO₂ proceeded in 28-83% yield depending on the nickel catalyst and temperature. The gas phase iodination (methane conversion) gave 31-62% of [¹¹C]CH₃I depending on temperature and amount of iodine in the iodine furnace. [¹¹C]CH₃I was used for heteroatom methylation reactions exemplified by a piperazine and a phenol (1 and 3). The specific activity of the ¹¹C-labelled products 2 and 4 was determined after HPLC purification and solid-phase extraction. Compounds 2 and 4 were obtained in 8-14% radiochemical yield (decay-corrected, based upon trapped [¹¹C]CH₄) within 30 minutes. The specific activity was determined to be in the range of 20-30 GBq/µmol at the end-of-synthesis. Nickel catalyst nanosize was found to be superior compared with other Ni catalysts tested. The relatively low specific activity may be mainly due to carbon contaminations originating from the long copper tubing (500m) between the cyclotron and the radiochemistry facility.

The High Acceptance Di-Electron Spectrometer HADES has been constructed at the SIS accelerator (GSI Darmstadt) to investigate electron-positron pairs produced in proton, pion and heavy ion induced reactions. The main goal of these studies is to explore properties of hadrons in nuclear matter. The apparatus and the experimental results from C+C at 2.0 AGeV and 1.0 AGeV and p+p at 2.2 GeV compared with Monte-Carlo events from a generator based on known cross-sections and branching ratios are presented.

Velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating (RMF) and a traveling magnetic field (TMF). In a cylindrical container, an RMF as well as a TMF alone cause axisymmetric volume forces, which drive according axisymmetric base flows. The combination of both fields gives rise to an inherent three-dimensional part of the electromagnetic force distribution. In case of equal frequencies, this drives a three-dimensional flow consisting of a single large-scale helical motion, which implicates an intense mixing of the melt. The necessary admixture of a TMF to accomplish a qualitative change of the flow structure in a given RMF is shown to be two orders of magnitude smaller in case of equal field frequencies compared to the case of differing frequencies.

A brief overview is given over recent results on the spectral properties of spherically symmetric MHD α²-dynamos. In particular, the spectra of sphere-confined fluid or plasma configurations with physically realistic boundary conditions (BCs) (surrounding vacuum) and with idealized BCs (super-conducting surrounding) are discussed. The subjects comprise third-order branch points of the spectrum, self-adjointness of the dynamo operator in a Krein space as well as the resonant unfolding of diabolical points. It is sketched how certain classes of dynamos with a strongly localized α-profile embedded in a conducting surrounding can be mode decoupled by a diagonalization of the dynamo operator matrix. A mapping of the dynamo eigenvalue problem to that of a quantum mechanical Hamiltonian with energy dependent potential is used to obtain qualitative information about the spectral behavior. Links to supersymmetric Quantum Mechanics and to the Dirac equation are indicated.

Quantum well infrared photodetector (QWIP) technology has opened up new opportunities to realize focal plane arrays (FPA) for high-performance thermal imaging [1]. High thermal and spatial resolution, low 1/f noise, low fixed-pattern noise, and high pixel operability makes QWIP FPAs appropriate for many applications. Due to their narrow absorption bands with relative spectral widths of the order of 10%, QWIPs are particularly suitable for thermal imaging applications involving several atmospheric transmission bands or several colors within the same band. For dual-band/dual-color FPAs, QWIP technology has the unique property that the active region for the long-wavelength band is transparent for the short-wavelength band. In this talk, I will report on typical QWIP structures optimized for thermal imaging applications and on the performance of some state-of-the-art QWIP cameras which were jointly realized by the Fraunhofer-Institute for Applied Solid State Physics (Freiburg, Germany) and AIM Infrarot-Module GmbH (Heilbronn, Germany). Besides imagers for the 8 – 12 µm long-wavelength infrared (LWIR) and 3 – 5 µm mid-wavelength infrared (MWIR) regimes these include a LWIR/MWIR dual-band QWIP FPA with 384x288 pixels which, at 6.8 ms integration time, exhibits a noise-equivalent temperature difference as low as 20.6 mK in the LWIR and 26.7 mK in the MWIR spectral bands. A specially designed diffraction grating is used for optical coupling of both spectral regimes. The array, which is based on a photoconductive QWIP for the MWIR and a photovoltaic "low-noise" QWIP for the LWIR, allows for synchronous and pixel-registered image acquisition in both bands. This functionality yields several advantages, including better distinction between target and background clutter, operation in a much wider range of ambient conditions, and the ability of remote absolute temperature measurement.
[1] H. Schneider and H. C. Liu, Quantum Well Infrared Photodetectors: Physics and Applications, ISBN 3540363238, Springer Series in Optical Sciences Vol. 126, 2006.

The in-medium behaviour of the nucleon spectral density including self-energies is revisited within the framework of QCD sum rules. Special emphasis is given to the density dependence of four-quark condensates. A complete catalog of four-quark condensates is presented and relations among them are derived. Generic differences of such four-quark condensates occuring in QCD sum rules for light baryons and light vector mesons are discussed.

An analytical solution for the startup of an external source in a homogeneous subcritical reactor problem is developed. The problem is described through an approximation of the Boltzmann Transport equation, the Telegrapher's or time dependent P1 equation. The analytical solution to the problem is expressed in terms of a Green's function.

We report on the development of a high resolution gamma ray tomography scanner that is operated with a Cs-137 isotopic source at 662 keV gamma photon energy and achieves a spatial image resolution of 0.2 lp/mm at 10% MTF for non-collimated detectors. It is primarily intended for the scientific study of flow regimes and phase fraction distributions in fuel element assemblies, chemical reactors, pipelines and hydrodynamic machines. Furthermore, it is applicable to non-destructive testing of larger radiologically dense objects. The radiation detector is based on advanced avalanche photo diode technology in conjunction with LYSO scintillation crystals. The detector arc comprises 320 single detector elements which are operated in pulse counting mode. For measurements at fixed vessels or plant components we built a CT scanner gantry that comprises rotational and translational stages, power supply via slip rings and data communication to the measurement PC via wireless LAN.

We demonstrate experimentally in a low temperature model that a rotating magnetic field (RMF) has the potential to stabilize the inverse temperature gradient in a medium scale Czochralski facility with a high initial melt level. This stabilization occurs as a result of a flow transition from large scale buoyancy driven to small scale magnetically driven turbulence. The dependency of the required field strength is found vs.\ the imposed temperature drop for an at least 10 times higher Grashof number than in earlier experiments. The observed scaling agrees well with previous results. It is observed that the flow transition becomes even more pronounced, i.e. occurs in a more narrow range of the magnetic forcing, as the Grashof number is increased. The influence of the RMF frequency is investigated. It is found that an increasing frequency of the RMF gradually eliminates the stabilizing effect. The optimum dimensionless frequency is found minimizing the required strength of the RMF. The characteristic azimuthal velocity of the flow is measured by the temperature correlation technique.

Nd-Fe-B alloys are widely used in many technical applications due to their excellent permanent magnetic properties. YNi2B2C intermetallic compounds own much attention because of the coexistence of superconductivity and magnetic ordering phenomena. Er2PdSi3 alloys with hexagonal AlB2-type crystallographic structure are of special interest because of their complex magnetic ordering, Kondo and heavy fermion behaviour. The thermophysical properties (electrical conductivity, thermoelectric power, thermal conductivity and viscosity) of these liquid multicomponent intermetallic alloys have been measured in order to supply necessary information for crystal growth and casting processes. Good reproducibility of the results has been obtained.

The thermal expansion a has been measured for single-crystalline HoNi2B2C in the range between 2 and 200 K. At low temperatures, a is dominated by magnetic contributions leading to a strongly anisotropic behaviour with different signs for the expansion coefficients near the antiferromagnetic phase transition. Analysing the magnetic and lattice contributions of a well above this temperature, a nearly isotropic behaviour of the latter one can be deduced. Using the Ehrenfest relation, a relatively weak pressure dependence of the superconducting transition temperature of dTc=dp ¼ 0:1K=GPa was determined for pressure applied along the c direction which points to a rather small pressure-induced lattice stiffening. The ratio between expansion coefficient and specific-heat features large values at the onset of magnetic order.

The differences between two- and single-domain ZnO epitaxial films, grown by reactive pulsed magnetron sputtering, have been studied with respect to their texture development and x-ray coherence length behavior at various substrate temperatures and oxygen partial pressures. The film in-plane ordering depends on the surface pretreatment of the sapphire substrate. After pretreatment in an oxygen radio-frequency plasma, single-domain films form even at a substrate temperature of 100 degrees C in a wide range of oxygen pressures, and at a growth rate up to 1.2 nm/s. The single-domain films show a linear dependence of the x-ray coherence length on the substrate temperature, while a steplike dependence is characteristic of the two-domain films. The ZnO complex dielectric function was obtained using a parametrized semiconductor oscillator model for spectroscopic ellipsometry data analysis. For the films grown at 550 degrees C, the band gap of 3.29 +/- 0.01 eV is independent of the type of in-plane ordering and variation of the texture. The oscillator broadening correlates with the width of (0002) diffraction peak rocking curve. Both parameters increase at high oxygen pressure and low substrate temperature, which is attributed to a higher defect (dislocation) density.

Homogeneous and heterogeneous catalysis approaches to hydrogenation have different advantages and disadvantages and hybrid approaches are sought to maximise the advantages of both. Bacterial cells, of length 1-2 microns, present an economical alternative to conventional micro-scale supports such as graphite and alumina. Certain strains of bacteria can reduce soluble Pd(II), from stock solutions or acid extracts of spent catalysts, forming nanocrystals of Pd which are supported within the bacterial cell surface layers. The biologically-supported nano-Pd contains particles of size ~ 5nm and below, as determined using magnetic measurements (SQUID) and EXAFS. Bio-nano-Pd supported on exemplar Gram negative and Gram positive bacterial types catalysed the hydrogenation of itaconic acid (initial rates 1.1 and 1.2 × 10-4 mol gPd-1 s-1 ) comparing well with commercial 5% Pd-graphite (1.3 × 10-4 mol gPd-1 s-1).

A new mother wavelet function for extended X-ray absorption fine-structure (EXAFS) data analysis has been designed, combining a model EXAFS function derived from the ab initio EXAFS code FEFF8.20 and the complex Morlet wavelet. This new FEFF–Morlet mother wavelet routine allows the generation of wavelets well adapted to specific EXAFS problems. A substantial gain in resolution of the wavelet ridges in k and r space is achieved. The method is applied to a structural problem of Zn–Al double-layer hydroxides, demonstrating unequivocally the homogeneity of the metal cation distribution in the hydroxide layers.

Treatments of a soil sample from a uranium mining waste pile with uranyl nitrate led to a shifting in the crenarchaeal populations from subgroup 1.1a to 1.1b. Efforts to culture members of these Crenarchaeota resulted in an enrichment of a mixed microbial consortium consisting of representatives of 1.1b Crenarchaeota and Firmicutes.
In this study interactions of U(VI) with a pure culture of Paenibacillus sp. JG35+U4-B1 isolated from the mentioned consortium were studied by using a combination of wet chemistry and microscopic methods. Preliminary analyses on U sorption showed that the Paenibacillus strain studied accumulated up to 85 mg U/g dry biomass from a solution with an initial uranium concentration of 120 mg U/l. Live/Dead cell staining indicated that less than 10% of the U-treated cells were viable. Transmission electron microscope (TEM) analyses showed that the cells of the isolated strain accumulated uranium intracellularly as needle-like fibrils (Fig. 1A), and also at the cell surface (Fig. 2A). Energy dispersive X-ray (EDX) analysis of these U accumulates demonstrated the presence of U and P peaks (Figs. 1B and 2B) indicating that in both cases the phosphate groups are, probably, the main functional binding sites for U(VI).

Al_1−xIn_xN (0001) thin films of the pseudobinary AlN–InN system were grown epitaxially onto (111)-oriented MgO wafers with seed layers of Ti_1−yZr_yN by dual direct current magnetron
sputtering under ultrahigh vacuum conditions. The relaxed film c-axis lattice parameters determined
by x-ray diffraction were studied as a function of composition in the range of 0.07 < x < 0.82 measured by Rutherford backscattering spectrometry. We find a relative deviation by as much as
37% from the linear dependency described by Vegard’s rule for the lattice parameter versus film
composition. The highest relative deviations were found at low InN mole fractions, while the largest
absolute deviation was found at x=0.63. This shows that Vegard’s rule is not directly applicable to
determine the compositions in the wurtzite Al_1−xIn_xN system. © 2007 American Institute of Physics.
[DOI: 10.1063/1.2450675 ]

Metal plasma immersion ion implantation and deposition (MePIIID) provides a useful technique to control composition and structure of metal-based thin films. By this method Ti-based coatings such as Ti nitrides, oxides or oxynitrides are formed on the objects with an irregular shape from a plasma produced by cathodic arc evaporation of Ti under addition of nitrogen and/or oxygen to the ambient near the substrate. Coating with Ti oxide or Ti-nitride-oxide (TiNOX) is a promising method to improve the blood compatibility of materials for use as medical implants.

In this work layers of the ternary system Ti-N-O were produced in a wide range of composition by MePIIID and their structure, physicochemical properties and blood compatibility were investigated. In the dependence on the relation of the reactive gases partial pressure Ti nitride and oxide have been produced as crystalline phases. For pure N2 flow and for the relationship p(O2)/p(N2) = 1/3 XRD patterns are typical for the fcc structure of TiN. For p(N2) = p(O2) a two-phase system of fcc TiN and fcc TiO has been found. Further enhancing O2 flow leads to the beginning formation of rutile and anatase modifications of TiO2. For p(O2)/p(N2) = 1/3 up to p(N2) = p(O2) in addition to the phases detected by the XRD the amorphous TiO2 phase with nitrogen substitution has been found.
The polar component of the surface energy and the hydrophobicity of the surface show a dependence on the composition of the coating. The crystalline TiO2 surface was the most hydrophobic, but also the crystalline TiN phase showed a slightly higher hydrophobicity than the mainly amorphous mixed phases.
The clotting time of blood plasma, the thrombocyte adhesion and activation as well as the fibrinogen adsorption on the surface were investigated to study the correlation between structure of the coating and blood compatibility. The blood compatibility of Ti oxide can be improved by the addition of N into the layer. TiN and oxynitrides show the longest clotting time in comparison with TiO2 (rutile). The lowest platelet activation was found on TiN and oxynitrides in comparison with rutile. The thrombocyte adhesion and fibrinogen adsorption were lower for TiNxOy than for TiO2. This behavior is correlated with the decreasing of contact angle and is inversely correlated with the increasing of surface energy (especially with its polar component).
In this study the blood platelet adhesion on the surfaces in general was very low, usually below 3% of the whole amount of blood platelets present in the plasma sample. It renders this class of surfaces a promising candidate for good blood compatibility and low clotting activation.

The quasistable odd-odd-mass nucleus 176 Lu is of special interest in nuclear structure physics and, above all, in nuclear astrophysics. Systematic photon scattering experiments have been performed at the bremsstrahlung facility of the 4.3-MV Stuttgart Dynamitron accelerator with bremsstrahlung end-point energies of 2.3 and 3.1 MeV to determine the low-energy dipole strength distribution in the s-only isotope 176 Lu. The main goal was to pin down possible intermediate states (IS) for the photoactivation of the short-lived 123-keV isomer, which is the key process determining the effective lifetime of 176 Lu in a stellar photon bath and hence for the use of this isotope as a stellar chronometer. Using an enriched sample, 29 transitions ascribed to 176 Lu were detected below 2.9-MeV excitation energy. The corresponding excitation strengths were determined. For the previously proposed lowest IS at 839 keV, an upper limit for the excitation strength corresponding to a lifetime of 1.5 ps can be given. Astrophysical consequences, also in view of new Stuttgart photoactivation experiments, are discussed. The fragmentation of the dipole strength is compared to those in neighboring even-even and odd-even nuclei.

Plant-measured data provided within the specification of the OECD/NEA VVER-1000 coolant transient benchmark (V1000CT) were used to validate the DYN3D/ATHLET coupled code system. Phase 1 of the benchmark (V1000CT-1) refers to the main coolant pump (MCP) switching-on experiment conducted in the frame of the plant-commissioning activities at the NPP Kozloduy-6 in Bulgaria.
The transient is characterized by a rapid increase in the primary coolant flow through the core and, as a consequence, a decrease of the space-dependent core inlet temperature. A DYN3D/ATHLET model of the primary and secondary circuit of the plant including MCP characteristics, boundary conditions and benchmark-specified nuclear data library was created. For an adequate modeling of the redistribution of the coolant flow in the reactor pressure vessel (RPV) during the transient a simplified mixing model for the DYN3D/ATHLET code was developed and validated against a computational fluid dynamics (CFD) calculation with the code ANSYS CFX. The results of the coupled code calculation are in good agreement with the available experimental data. The discrepancies between experimental data and the results of the calculation do not exceed the accuracy of the measurement data. This concerns the initial steady state data as well as the time histories during the transient.
The above mentioned CFD model was used also in the second phase of the benchmark (V1000CT-2). In this part of the benchmark, post-test calculations of coolant mixing experiments at the same NPP are carried out. The comparison is made with assembly-wise mixing coefficients being the results of the experiments. The numerical grid model contains 4.7*106 tetrahedral elements. Different advanced turbulence models were used in the numerical simulations. The best agreement with the experimental data at the core inlet shows the Detached-Eddy-Simulation. Strong fluctuations occur in the downcomer of the RPV. The results show a clear sector formation of the affected loop in the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.3%.

Electrochemical, complexation, and electronic properties of uranyl(VI)- and uranyl(V) carbonato complexes in aqueous Na2CO3 solution have been investigated to define the appropriate conditions for preparing pure uranyl(V) samples and to understand the difference in coordination character between UO22+ and UO2+. Cyclic voltammetry (CV) using three different working electrodes of Pt, Au, and glassy carbon has suggested that the electrochemical reaction of uranyl(VI) carbonate species proceeds quasireversibly. Electrolysis of UO22+ has been performed in the Na2CO3 solutions more than 0.8 M with the limited pH range of 11.7 < pH < 12.0 using a Pt mesh electrode. It produces high purity of uranyl(V) carbonate solution that has been confirmed to be stable at least for two weeks in a sealed glass cuvette. EXAFS measurements revealed the structural arrangement of uranyl(VI)- and uranyl(V) tricarbonato complexes, [UO2(CO3)3]n- (n = 4 for uranyl(VI), 5 for uranyl(V)). The bond distances of U-Oax, U-Oeq, U-C, and U-Odist are determined to be 1.81, 2.44, 2.92, and 4.17 Å for the uranyl(VI) complex, and 1.91, 2.50, 2.93, and 4.23 Å for the uranyl(V) complex, respectively. The validity of the structural parameters obtained from EXAFS has been supported by quantum chemical calculations for the uranyl(VI) complex. The uranium LI- and LIII-edge XANES spectra have been interpreted in terms of electron transitions and multiple scattering features.

Die Kombination von Bio- und Nanotechnologie eröffnet ein großes Potential für die Entwicklung neuer Materialien. Da sich Nanopartikel in ihren chemischen und physikalischen Eigenschaften oft grundlegend von ihren Ausgangsmaterialien unterscheiden, sind sie von großem Interesse für die Entwicklung neuer Materialien und Werkstoffe wie Katalysatoren oder Biosensoren, in der Nanoelektronik, in der optischen Industrie, Halbleiterindustrie, aber auch für biomedizinische Anwendungen.
Eine aussichtsreiche, unkomplizierte Alternative zu konventionellen Methoden bei der Herstellung regelmäßig angeordneter Nanopartikel ist die Verwendung von selbstorganisierenden biologischen Trägermaterialien als Matrix. Besonders aussichtsreiche Biomoleküle sind hierbei die selbstorganisierenden Hüllproteine (S-Layer) von Bakterien.

In einem interdisziplinären Ansatz werden neuartige Materialien auf der Basis von Nanopartikeln aus metallischen, magnetischen und halbleitenden Materialien entwickelt. Für ihre Synthese werden verschiedene bakterielle Hüllproteine (S-Layer) als biologische Trägermaterialien (sogen. Template) verwendet. Diese bestehen meist aus Proteinmonomeren, welche nach ihrer Sekretion an der Zelloberfläche regelmäßige Gitterstrukturen unterschiedlicher Symmetrie ausbilden. Für ihre technische Nutzung ist es bemerkenswert, dass die isolierten Monomere ihre Eigenschaft der Selbstorganisation beibehalten und an Grenzflächen parakristalline Monolagen bilden. Die regelmäßig angeordneten Poren dieser Proteine bieten ideale Strukturen für die Bindung von Metallkomplexen und die Synthese von hochgeordneten Nanopartikeln definierter Größe. Die Synthese erfolgt dabei zweistufig: Nach der Anbindung der Metallkomplexe aus einer wässerigen Metallsalzlösung und anschließender Dialyse erfolgt eine Reduktion der Komplexe durch die Zugabe eines Reduktionsmittels. Auf diese Weise konnten bislang erfolgreich Pd-, Pt-, Au- und Pb-Nanopartikel einer einheitlichen Größe hergestellt werden, deren chemische und magnetische Eigenschaften sich z.T. erheblich von denen der jeweiligen makroskopischen Materialien unterscheiden. Durch die Beschichtung verschiedener technisch relevanter Materialien wie Keramiken, Zeolithe, Aluminiumoxid, Siliziumdioxid und Kohlenstoff mit den Proteinen sollen neuartige Materialien entwickelt werden, die in der Industrie Verwendung finden können.

The stability and electronic properties of the associates of the single-walled carbon nanotubes wrapped by homopolymeric single-stranded DNA molecules (CNT@DNA) are considered using a quantum mechanical density-functional tight-binding method (DFTB). A phenomenological model of the CNT@DNA formation energy depending on the nanotube radii is developed, which shows that the decoration of a CNT by a few DNA chains leads to a high water solubility of CNT@DNA. Pyrimidine-based DNAs are found to be more effective to wrap the CNTs than other DNAs. The densities-of-states of the CNT@DNA complexes are close to the superposition of those of the “free” components with some additional states below Fermi level. The band gap in a hybrid CNT@DNA system is determined by the competition between the Fermi levels of the “free” DNA and CNT. In a few specific cases a considerable charge transfer from the DNA to the CNT was observed, combined with an additional gain in the CNT@DNA formation energy.

The preferred adsorption sites and the propensity for a self-organised growth of the molybdenum sulfide cluster Mo6S8 on the Au(111) surface are investigated by density-functional band-structure calculations with pseudopotentials and a plane wave basis set. The quasi-cubic cluster preferentially adsorbs via a face and remains structurally intact. It experiences a strong, mostly non-ionic attraction to the surface at several quasi-isoenergetic adsorption positions. A scan of the potential energy surface exhibits only small barriers between adjacent strong adsorption sites. Hence, the cluster may move in a potential well with degenerate local energy minima at room temperature. The analysis of the electronic structure reveals a negligible electron transfer and S-Au hybridised states, which indicate that the luster-surface interaction is dominated by S-Au bonds, with minor contributions from the Mo atom in the surface vicinity. All results indicate that Mo6S8 clusters on the Au(111) surface can undergo a template-mediated self-assembly to an ordered inorganic monolayer, which is still redox active and may be employed as surface-active agent in the integration of noble metal and ionic or biological components within nano-devices. Therefore, a classical potential model was developed on the basis of the DFT data, which allows to study larger cluster assemblies on the Au(111).

We have performed high temperature nitrogen plasma immersion ion implantation (PIII) of Ti6Al4V by heating the samples for up to 800 °C, using tungsten filaments inside the sample holder. Ion implantation was done with the high voltage pulser at 5 kV, 40 μs duration and 400 Hz frequency, and a nitrogen glow discharge as the plasma source. Nanoindentation analysis of the treated surface indicated an improvement of 5 times in hardness for PIII treatment of 120 min. X-ray diffraction indicated the formation of Ti2N. Auger Electron Spectroscopy (AES) showed that the peak concentration is greater than 30% in the implanted nitrogen with the maximum penetration of 150 nm for the sample treated during 120 min.

The influence of low magnetic fields (B≤130 G) on the plasma parameters of a DC nitrogen glow discharge is investigated with a double Langmuir probe. The discharge was optimized for maximum plasma density for different values of a magnetic field, and a condition was found in which density was enhanced by an order of magnitude. In this condition partial suppression of secondary electron emission was obtained during ion implantation experiments. Silicon samples implanted in this optimum density condition showed larger retained dose and penetration depth compared with samples treated in non-magnetized plasmas as shown by Auger electron spectroscopy depth profile analysis. These results were compared with previous similar experiments in much denser magnetized vacuum arc plasmas, in which total suppression of secondary electrons (SE) was obtained, corroborating the theory that the maintenance of a virtual cathode for SE suppression is favored by higher plasma density. Silicon samples implanted in magnetized magnesium plasmas exhibited much larger doses (as expected) and penetration depths (not so obvious) than the ones treated in non-magnetized plasmas. The deeper ion penetration obtained in magnetized gaseous and vacuum arc plasmas indicates that an enhanced diffusion may be taking place induced by the large ion bombardment in dense plasmas.

The local structure of U(VI) sulfato complexes in aqueous solution has been investigated by U L3-edge EXAFS, high energy x-ray scattering (HEXS), x-ray diffraction (XRD) and UV-Vis spectroscopy using samples of 50 mM U(VI) and total sulfate concentrations, 0.05 ≤ [SO42-] ≤ 3 M at pH 1 and 2. At low [SO42-]/[UO22+] ratio (~1), where the UO2SO4(aq) species prevails, the sulfate coordinates in a monodentate fashion. At high [SO42-]/[UO22+] ratio, where UO2(SO4)22- species prevails, bidentate sulfate coordination becomes dominant. In all cases, the equatorial coordination number NOeq, remains 5. According to the bond-valence rule this is in line with the average bond distance between U(VI) and oxygen of ~2.42 Å observed by EXAFS and HEXS. The bidentate sulfate reaches a maximal coordination number NSbid of 2 for a [SO42-]/[UO22+] ratio of 60, hence, related with the structure of [UO2(SO4)2bidH2O]2-. The upper limit of NSbid allows to rule out the existence of a species with three monodentate coordinated sulfate groups, [UO2(SO4)3bid]4-. This observation has been confirmed by MCD measurements. Therefore, the species UO2(SO4)34- might be related with the structure [UO2(SO4)2bid(SO4)mon]4-. The existence of two bidentate coordinated sulfate groups has up to now never been observed in crystal structures. The evaporation of the above mentioned solutions with several [SO42-]/[UO22+] ratios resulted always in crystal structures where the sulfate group acts monodentate-bridging. The coordination of U(VI) by two bidentate coordinated sulfate groups might be restricted to solution species. This observation indicates a structural re-arrangement of SO42- during the crystallization. The potential structures in solution were modeled by DFT calculation and compared with the experimental data from EXAFS and HEXS.

Detailed information about aqueous species of uranium(VI) is an indispensable prerequisite for a reliable assessment of its migration in the environment. Up to now the identification of distinct U(VI) species in aqueous solution was mostly accomplished by thermodynamical calculations based on non-structural experiments such as potentiometric titration [1] and by spectroscopic investigations of UO22+ solutions in the upper millimolar range at low pH values [2,3].
Attenuated total reflectance (ATR)-FT-IR spectroscopy has shown to be a useful tool for investigations of molecule complexes formed during sorption processes in aqueous solutions [4]. In this study we focus on the hydrolysis reactions of U(VI) under atmospheric conditions throughout a wide pH range (pH 2 – 9).
First, we investigated diluted uranyl(VI) solutions. Due to the low concentration ([UO22+] = 20 µM) the acquisition of infrared spectra of UO22+ solutions have become feasible even at high pH values avoiding the precipitation of solid uranyl phases. Our results clearly demonstrate that already at pH values < 4 not yet identified hydroxo uranyl complexes considerably contribute to the infrared spectra which is in contrast to recent thermodynamical calculations. It is also quite conceivable that we identified new U(VI) species in aqueous solutions. At higher pH values (> 7) the spectra indicate the formation of another uranyl species possibly with contributions of atmospheric carbonate anions which can be derived from model spectra of the pure UO2(CO3)34− complex.
In a second series of experiments we studied the hydroxo species of uranium(VI) at different concentrations (5 mM – 5 µM UO22+) at a constant pH value (pH 4). Upon lowering the concentration below 500 µM the fraction of the uncomplexed uranyl species is significantly reduced and can not be detected at a concentration of 50 µM any longer. Simultaneously two other hydroxo complexes are obviously formed at these lower concentrations.
A critical evaluation of literature data and the obtained spectral data constitute a reference to a modified speciation of U(VI) in particular at lower pH values and at concentrations in the micromolar range.

[1] R. Guillaumont et al. (OECD-NEA TDB), Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium, Elsevier, 2003.
[2] H. Moll et al., Radiochim. Acta 88, 411 (2000).
[3] F. Quilès and A. Burneau, Vib. Spec. 23, 231 (2000).
[4] G. Lefèvre, Adv. Colloid Interface Sci. 107, 109 (2004).

Introduction:

Highly thermodynamically stable Cu(II) complexes are required for the development of new copper(II) target-specific radiopharmaceuticals. In this perspective, azamacrocycle derivatives [1], and in particular a 1,4,7-triazacyclononane derivative containing two pyridine pendant arms [2] is a potentially promising ligand candidate. The further addition of a carboxylic group to this chelating agent could provide an attractive lead for the labelling of biomolecules with copper radionuclides.

Experimental:

A new ligand, 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid (1), has been synthesised, and the X-ray structure of a corresponding copper(II)-complex determined. A bioconjugate (2) was obtained by coupling a modified bombesin derivative [3] to 1 (HBTU, DIPEA, DMF, r.t.). 2 was purified by semi-preparative HPLC. The free ligand 1 and the bioconjugate 2 were labelled with ⁶⁴Cu. To 100 µl of ligand solution (0.0001 M ligand dissolved in 0.05 M NH₄OAc), 200 kBq of ⁶⁴CuCl₂ was added. Labelling yields were studied by TLC.

Results and Discussion:

The structure of [1-Cu-complex]²⁺ was solved by X-ray single-crystal diffraction and indicates that the ligand is able to bind Cu²⁺ in a hexacoordinate manner. A high complex stability (logK₁ > 20) was determined. The bioconjugation of 1 to a bombesin derivative was successfully achieved via amide coupling to give 2. The free ligand 1 and the bioconjugate 2 were labelled with ⁶⁴Cu and the resulting complexes were found to be stable in the presence of a large excess of competing ligands such as cyclam and glutathione as well as in rat plasma. These ⁶⁴Cu complexes are highly hydrophilic (logD_o/w < -2.3).

Conclusion:

A bis(2-pyridylmethyl) derivative of 1,4,7-triazacyclononane 1 and its bombesin bioconjugate 2 can readily form ⁶⁴Cu complexes with high stability. The bifunctional chelating agent 1 may be an attractive candidate for developing new copper radiopharmaceuticals. Preliminary biodistribution studies of ⁶⁴Cu complexes of 2 are currently underway.

[1] K. P. Guerra et al., Dalton Trans., 2006, 4124-4133.
[2] G. A. McLachlan et al., Inorg. Chem. 1994, 33, 4663-4668.
[3] E. Garcia Garayoa et al., Quart. J. Nucl. Med. Molec. Imaging, 2006, 50, 15-16.

Molecular recognition and self-assembly, based on weak non-covalent interactions, are significant processes in chemical and biological systems [1], e.g. in enzyme-substrate binding or formation of protein complexes. So, the development of efficient synthetic receptors with the ability to bind substrates selectively is important. The water-soluble naphthalene clip with substituted phosphonate groups (Fig. 1) offers electron-rich side walls, which are suitable to bind electron-poor guests [2]. The complexation behavior of this clip toward nucleosides has been studied by time resolved laser fluorescence spectroscopy with ultrafast pulses (fs-TRLFS).

[1] Vögtle, F. (1997) Supramolekulare Chemie, Teubner Verlag, Stuttgart.
[2] Jasper, C. et al. (2002) Angew. Chem. 114, 1411-1415.

Noncovalent intermolecular forces play a fundamental, ubiquitous role in living systems particularly in view of molecular recognition and self-organization / self-assembly. In an increasing extent the principles found in organized biological systems are utilized for the development of artificial structures which are able to mimic certain properties of the naturally occurring systems. In this context, some novel supramolecular receptors such as dendritic hosts, molecular tweezers, helical systems, and synthetic flavylium salts gain more and more importance. Fine-tuning of photochemical, photophysical and electrochemical properties of host-guest systems provide the possibility of tailoring the supramolecular reactivity opening fascinating and important development in biomedical application such as the design of novel diagnostic and therapeutic agents. This field is in its infancy, and in particular a deep understanding about binding and transport behaviour in both aqueous and mixed organic-aqueous systems must be achieved. The study of molecular recognition and self-assembly processes in the most competitive environment - the aqueous media - is still a challenge and a stimulus for the creation of novel supramolecular ensembles which possess more simple structures but similar functions as the complex biological systems.