Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

In the search for a deeper understanding of the factors governing the stability of liquid metal field-ion emitters, the behaviour of a liquid anode with an anomalous surface tension coefficient is studied.The main parameter in this experimental study is the emitter temperature. At the conclusion of the work an important result emerged: apart from the surface tension coefficient, space-charge effects constitute a major factor in influencing emitter stability.

A new biomolecule labeling method that utilizes the [^99mTc(N)(PNP)]^2+m metal fragment is presented. Thus, a series of nitrido mixed-ligand M(V) complexes (M = ^99mTc, ^99gTc, Re), [M(N)(Ln)(PNP)], where Ln is the dianionic form of a dithiolate or substituted-dithiolate ligand and PNP is an aminodiphosphine, is described. ^99mTc complexes can be prepared using either a two-step or a three-step procedure starting from generator-eluted pertechnetate through a pre-reduced mixture of [^99mTc(N)] containing species, followed by contemporary or sequential addition of the relevant dithiolate and aminodiphosphine. The reaction of 2,3-dimercapto propionic acid (H₂L1) with [Tc(N)(PNP)]²⁺ was investigated in detail. It was found that this bidentate ligand coordinated the metal fragment through the [S^-,S^-] donor atom pair, to yield neutral mixed-ligand complexes [^99mTc(N)(L1)(PNP)] in high specific activity. The additional carboxylic functional group was not involved in metal coordination, thus remaining available for conjugation to target-specific molecules. Dithiolates incorporating pendant functional group(s) gave rise to a 1:1 diastereoisomeric mixture of syn-[M(N)(Ln)(PNP)] and anti-[M(N)(Ln)(PNP)] derivatives, depending on the relative orientation of the dithiolate substituent(s) with respect to the terminal nitrido group, and no isomeric conversion was detected. ^99mTc species had been proven to be identical with the ^99gTc complexes prepared at the macroscopic level by comparison of the corresponding radiometric and UV/vis HPLC profiles. Challenge experiments with cysteine or glutathione indicated that these physiological agents had no effect on the stability of this class of mixed-ligand ^99mTc-complexes. Biodistribution studies in rats of selected ^99mTc-complexes showed a rapid clearance from the blood and tissues after 60 min. p.i..

We present a combined analysis of the behavior of rho and omega mesons within the Borel QCD sum rule taking into account finite widths.

Ab initio calculations are used to design a crystalline boron–oxygen–yttrium (BOY) phase. The essential constituent is yttrium substituting for oxygen in the boron suboxide structure (BO0.17) with Y/B and O/B ratios of 0.07. The calculations predict that the BOY phase is 0.36 eV/atom more stable than crystalline BO0.17 and experiments confirm the formation of crystalline thin films. The BOY phase was synthesized with reactive rf magnetron sputtering and identified with x-ray and selected area electron diffraction. Films with Y/B ratios ranging from 0.10 to 0.32, as determined via elastic recoil detection analysis, were grown over a wide range of temperatures (300–600 °C) and found to withstand 1000 °C.

The structures, formation energies and stable configurations of elementary defects (vacancies, antisite defects and self interstitials) in 3C- and 4H-SiC are studied using classical molecular dynamics simulation with a recently developed interatomic potential. The defect structures in 3C-SiC are relative simple, but those in 4H-SiC are more complicated. The interstitials between hexagonal and trigonal rings are characteristic for 4H-SiC and other hexagonal polytypes, but not for 3C-SiC. The number of non-equivalent defects in 4H-SiC is much higher than in 3C-SiC, and a considerable difference is found for some complex and anisotropic defects, in particular for the dumbbells D1Si-Si, D1Si-C and D2Si-C. The lattice deformation beyond the first nearest neighbor shell, which depends strongly on the polytype structure, plays an important role on these effects. However, the polytypism does not have a significant influence on the structure and energetics of the more compact and isotropic defects, such as vacancies and antisite defects. Despite the complexity of defect configurations, the tetrahedral interstitials have very similar properties in 3C- and 4H-SiC because their first, second and third nearest neighbor shells are equal.

The High Acceptance Di-Electron Spectrometer (HADES) at the heavy ion synchrotron SIS of GSI, Darmstadt, is a high-resolution second generation detector system for lepton pair spectroscopy. Its low-mass tracking system consists of two pairs of planes of trapezoidally shaped Multiwire Drift Chambers (MDC), installed on either side of a superconducting toroidal magnet. This paper summarizes some experiences with the construction and the in-beam operation of the six large-area chambers produced by Forschungszentrum Rossendorf. Studies on creeping of aluminum wires over a period of three years are presented. In addition, the observation of growth of filaments with various shapes and sizes in one of the chambers used in-beam will be discussed in detail.

This contribution presents experimental results of the investigation of water hammer and cavitation hammer at the pipeline test facility at Fraunhofer UMSICHT in the context of the EURATOM project WAHALoads. The main objective of this running project is the prediction of the strain on equipment and support structures caused by water and condensation hammer. Thus, some typical scenarios of power plants are conducted. For this purpose the test facility at Fraunhofer UMSICHT (PPP) was modified in order to simulate a piping system and associated supports that are typical of a power plant.

For a better understanding of thermohydraulic processes, new wire mesh sensors with thermocouples for the measurement of condensation heat transfer, and other innovative transient measurement techniques were implemented into PPP additionally.

Radiation hardening, displayed by the yield stress increase, and radiation embrittlement, described by the Charpy transition temperature shift, were experimentally determined for a broad variety of irradiation probes machined from different reactor pressure vessel base and weld materials and irradiated in several VVER-type reactors. Additionally, the same probes were investigated by small angle neutron scattering. The analysis of the neutron scattering data suggests the presence of nanoscaled radiation defects. The volume fraction of these defects depends from the neutron fluence and the material. Both radiation hardening and radiation embrittlement correlate with the square root of the defect volume fraction linearly. However, a generally valid proportionality is only a rough approximation; in detail chemical composition and technological pretreatment clearly affect the correlation.

This paper reports on the modeling and simulation of flashing-induced instabilities in natural circulation systems, with special emphasis on natural circulation Boiling Water Reactors (BWRs). For the modeling the 4-equation two-phase code FLOCAL (Rohde, 1986), developed at the Forschungzentrum Rossendorf (FZR, Germany), has been used. The model allows for the liquid and vapor to be in thermal non-equilibrium and, via drift-flux models, to have different velocities. The phenomenology of the instability has been studied and the dominating physical effects have been revealed. The results of the simulations have been compared qualitatively and quantitatively with experiments (Manera et al., 2002) that have been carried out within the framework of a European project (NACUSP) on the CIRCUS facility. The facility, built at the Delft University of Technology in The Netherlands, is a water/steam 1:1 height-scaled loop of the Dutch natural-circulation-cooled BWR Dodewaard.

An assessment of void fraction correlations and drift-flux models applied to stationary and transient flashing flows in a vertical pipe has been performed. Experiments have been carried out on a steam/water loop that can be operated both in forced and natural-circulation conditions. Advanced instrumentation, namely wire-mesh sensors, has been used to obtain a detailed picture of the void-fraction development in the system. On the basis of experimental data collected, three-dimensional flow-pattern visualization was achieved.

Saxony and Thuringia are mountainous German states featuring quaint villages, carved nutcrackers and centuries-old castles. But there is another side to this region. Decades of uranium mining to fuel former Soviet Union nuclear weapons and European nuclear power plants have devastated the region, which spills into the Czech Republic and Poland. Since the fall of the Berlin Wall, most mines have fallen into disuse, leaving an ominous legacy to threaten the long-term safety of the soil, subsoil and groundwater in nearby residential areas. Preliminary investigations in Thuringia and Saxony mining towns show elevated incidences of lung cancer in the men who worked the mines as well as in women who reside there.
These findings have raised fears about leaching and seepage of radionuclides from acid mine drainage waters and about contaminants from abandoned uranium waste rock piles dumped on valley slopes. Unfortunately, these environmental hazards are not limited to this region. Similar problems threaten the health of people in uranium mining areas in Hungary, Bulgaria, Estonia, Romania and Slovenia.
Closure, remediation and recultivation of former mining sites in Saxony and Thuringia have been underway since 1991. Conventional chemical and physical removal methods are useful for high concentrations of radionuclides and heavy metals, but not for low concentrations. After the initial remediation treatment, the remaining concentrations of these compounds are still above allowed limit values. So, scientists at Forschungszentrum Rossendorf Institute of Radiochemistry in Dresden, Germany are searching for alternative decontamination methods. They hope to develop a selective, yet effective process for completely removing metals and radionuclides from polluted effluents, wastewater, sediments and soils based on microorganisms.
Bacteria are the most frequent organisms on earth. They are able to live in extreme environments where higher organisms such as plants and animals are not able to survive, e.g. hot springs, antarctic ice, deep sea and deserts. For this reason it is not surprising, that researchers have found bacteria also in highly contaminated environments such as uranium mining waste piles. Above that the latter are big reservoirs for bacteria that are resistant to heavy metals. Many of the microorganisms living under these difficult conditions have developed different strategies to resist mobility and toxicity of metals and radionuclides. Bacteria interact not only with organic but also with inorganic compounds such as heavy metals. Some of them are able to solubilize metals or metalsulfides by oxidation. Others makes the opposite, they precipitate metals by reduction. Beside that many bacteria accumulate cobalt, molybdenum, lead, mercury, copper, manganese, aluminium, cadmium, gallium, barium and other toxic metals and transport them out of contaminated areas. All these properties offer interesting options for solving the above mentioned problems.

Microbial diversity was studied in water samples collected at depths of 290 to 324 m from the monitoring site S15 near the city of Tomsk, Siberia, Russia. The 16S rDNA retrieval was applied, in order to overcome the problems of culturability of the bacteria and archaea indigenous for that extreme habitat. The biomass from the samples was concentrated via consequent filtration on a glass-fibre filter and on filters with pore sizes of 0.45 and 0.22 µm. In this work two bacterial clone libraries were analysed: one constructed for the DNA isolated from the biomass collected on the filter with a size of 0.45µm and another one for those of the 0.22µm filter. In addition, an archaeal clone library was generated for the total DNA extracted simultaneously from all the tree filters (unfractioned DNA). Comparative analyses of the two bacterial libraries revealed significant differences in the predominant groups and in the species composition. In the 0.45µm clone library a dominance of Dechlorosoma spp. populations was found. This result is in agreement with our previous study on bacterial diversity in water at the site S15 which was performed by using total unfractioned DNA (1). However, in contrast of that previous analysis, now the predominance of the Dechlorosoma spp. was not too strong and we were able to find a larger variety of species from: d-subclass of Proteobacteria, Gramm positive bacteria, and in addition members of Candidate divisions OP8, TM7 and the Termite group. In the 0.22µm clone library Dechlorosoma sp. was not identified any more. In this case populations of Chrysobacterium spp. from the Cytophaga/Flavobacterium/Bacteroides group were predominant. There were some common Proteobacterial and Actinobacterial species, which were identified in both the 0.45µm and the 0.22µm libraries. Interestingly, relatively dense and diverse populations of deeply branched not yet cultured Cyanobacteria were found in both bacterial clone libraries. The phylogenetic analysis of Archaeal populations in the S15 sample revealed the presence of sequences which belong to Crenarchaeota and Euryarchaeota. The members of the latter were methanogens and some of them were related to clones identified in metal-rich freshwaters by others (2). Most of the Crenarchaeota 16S rDNA sequences were also similar to those found in other metal-rich environments (3).
Our analysis indicates that microbial communities at the monitoring site S15 are rather complex and diverse. The 0.45µm clone library exhibits greater overall diversity than the 0.22µm clone library. The archaeal populations are represented mainly by clones affiliated with organisms found in other metal pollutd environments.

References:

1. Nedelkova, M., et al. (2003) Environmental Geology (in press).
2. Stein, L. et al. (2001) Env. Microb. 3(1) : 10-18.
3. Stein, L. et al. (2002) FEMS Microb. Ecol. 42 : 431-440.

Microbial communities were studied in several uranium mining wastes in Germany and in the USA by using the rDNA retrieval applying several sets of amplification primers flanking different regions of the rrn operons (1, 2). The bacterial populations in the studied soil samples were rather dense and extremely diverse. In the water samples a lower grade of bacterial diversity was found. Despite the fact that the composition of the bacterial communities was site-specific, several bacterial groups including also novel lineages seem to be characteristic for the studied heavy-metal-polluted environments. The archaeal populations, in contrast, were not very dense and were limited to several not yet cultured Crenarchaeotae lineages which were identified in other metal contaminated environments as well.
In parallel to the above mentioned direct molecular approach, the method of enrichment culturing was applied in order to recover and study particular bacterial strains indigenous for the U wastes. Bacterial isolates belonging to different species representing diverse bacterial groups were recovered and characterized (1). The resistance and the interactions of these isolates with U and with other heavy metals were demonstrated to be species- and even strain-specific. The atomic structures and the cellular location of the complexes formed with U(VI) by the isolates were studied using EXAFS spectroscopy, TEM, and EDX analyses. In all cases phosphate groups were predominantly implicated in the complexation of uranium but the structural parameters and the cellular location of the complexes differed between the studied bacterial groups (3).
Many of the studied strains possess unusual characteristics as the isolate JG-A12, for instance, which accumulates selectively U, Cu, Pb, Al, and Cd (4). This strain as well as its intrinsic S-layer are forming U(VI)-complexes with identical structural parameters in which phosphorous residues in addition to the carboxyl groups are involved. ICP-MS demonstrated that the S-layer of JG-A12 is phosphorylated. This can explain its high ability to complex uranium and other metals. The latter seems to give an advantage to the strain to survive in environments heavily polluted with uranium and other toxic metals from which it was recovered.
Sol-gel ceramics with high and reversible metal binding capacity were prepared via homogeneous dispersion and embedding of B. sphaericus JG-A12 vegetative cells (5, 6). This biological ceramics are very perspective for bioremediation of heavy metal contaminated water wastes.
In addition, Pd nanoclusters were also successfully grown on the surface of these bacteria. The latter is of interest for the nanotechnology. Interestingly, the above mentioned S-layer of JG-A12 possesses an unusual primary structure which indicates that lateral transfer was involved in the evolution of its gene.
References
1. Selenska-Pobell, S. (2002) Interactions of Microorganisms with Radionuclides p. 225-253; Elsevier, Oxford
2. Selenska-Pobell, S., et al. (2001) Antonie van Leeuwenhoek 79, 149-161.
3. Merroun M. et al. (2003) FZR-Report No. 364, p. 26-30
4. Selenska-Pobell, S. et al. (1999) FEMS Microbiol. Ecol. 29, 59-67
5. Raff, J. et al. (2003) Chem. Mater. 15 (1): 240-244.
6. Soltmann et al. (2003) J Sol-Gel Science and Technology 26, 1209-1212.

The strain Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile near the town of Johanngeorgenstadt. The drain water and the soil of this environment are highly contaminated with heavy metals and radionuclides. The cells of B. sphaericus JG-A12 are capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from the U waste waters (1). It was demonstrated that the strain JG-A12 is enveloped by a surface layer protein (S-layer) which differs significantly in its primary structure from the other B. sphaericus S-layers studied up to date (2). The highly ordered crystalline S-layers are one of the most common cell envelope structures of bacteria and archaea (3). They are composed of identical protein monomers which possess an ability to self-assemble into two-dimensional crystalline arrays. The highly regular structure of the S-layers with many pores of identical size offers good binding sites for many different metals and nucleation sites for the formation of metal nanoclusters or minerals. EXAFS-analyses of the uranium complexes formed by the S-layer of JG-A12 showed that this metal is coordinated to carboxyl and phosphate groups of the latter (4). Analyses of the amino acid composition of the C-terminus showed a high content of serine and treonine residues which are potential phosphorylation sites. These characteristic features of the S-layer of B. sphaericus JG-A12 make the strain perspective for bioremediation and nanotechnological applications.
In this work we are presenting the formation of Pd nanoclusters on the cells of B. sphaericus JG-A12 in the presence of H2 as a reducing agent. These nanoclusters are interesting for the development of bionanocatalysts and biosensors. Further, by embedding cells, spores or S-layers using sol-gel techniques bioceramics particles were produced (5, 6). These bioceramics can be used for bioremediation of heavy metal contaminated waters.

References
1. Selenska-Pobell, S. et al. (1999) FEMS Microbiol. Ecol. 29, 59-67
2. Raff, J. (2002) "Wechselwirkungen der Hüllproteine von Bakterien aus Uranabfallhalden mit Schwermetallen" PhD thesis, FZR-Report No. 358.

3. Sleytr, U. et al. (1997) FEMS Microbiol. Rev. 20, 47-97.
4. Merroun M. et al. (2003) FZR-Report No. 364, p. 26-30
5. Raff, J. et al. (2003) Chem. Mater. 15 (1): 240-244.
6. Soltmann et al. (2003) J Sol-Gel Science and Technology 26, 1209-1212.

Bacterial and archaeal populations in soil and water samples of the uranium mill tailings Gittersee/Coschütz were studied by using the rDNA retrieval applying different sets of PCR amplification primers. Bacterial communities found in both soil and water samples had similar composition as estimated via analyses of the constructed 16S rDNA43F-1404R and 16S rDNA7F-1513R clone libraries. They consisted of proteobacteria (mainly from the gamma-subclass) and of representatives of the Cytophaga/Flavobacterium/Bacteroides (CFB) group. In the soil samples Gram-positive bacteria were found as well. These results are in contrast to those obtained by the analysis of the samples collected from the uranium mining waste pile near the town of Johanngeorgenstadt where members of the alpha proteobacteria and of the Holophaga/Acidobacterium phylum were found to be predominant by using the same 16S rDNA PCR amplification primers (1, 2, 3).
The analysis of the water samples applying the ribosomal intergenic spacer amplification rDNA retrieval using the 16S rDNA968F and 23S rDNA130R PCR primers revealed much higher diversity. In addition to the members of the Proteobacteria and of the CFB, populations of Nitrospira, Verrucomicrobia, Planctomycetales, Actinobacteria and also of several novel bacterial divisions were found (4). This result is due to the primer structures (5).
The identified archaeal populations, in contrast to those of the bacteria, were not very diverse in the studied environment. In the archaea-specific 16S rDNA21F-958R clone libraries constructed for the above mentioned soil and water samples only a few populations of not yet cultured Crenarchaeota were found (6).
Most of the 16S rDNA sequences obtained in this work showed no close phylogenetic affiliation to cultured bacteria or archaea. For this reason, it is difficult to predict the phenotypic properties and the ecological role of the corresponding organisms. However, it is interesting that the most related 16S rDNA sequences found in the Gene Bank were retrieved in environments with geologic and ecological properties similar to those of the uranium wastes, such as gold mine and other acid mine drainage systems (7, 8).
Efforts to culture representatives from some of the most predominant microbial populations are in progress.

References

1. Selenska-Pobell, S. et al. (2002) Bacterial communities in uranium mining waste piles and their interaction with heavy metals, p.455-464; In Uranium in the aquatic environment. Springer-Verlag.
2. Selenska-Pobell, S., et al. (2001) Antonie van Leeuwenhoek 79, 149-161.
3. Geißler, A. (2003) Molekulare Analyse der bakteriellen Diversität in Uranabraumhalden. Diploma Thesis, FZR-Report No. 377
4. Selenska-Pobell, S. (2002) Diversity and activity of bacteria in uranium waste piles, p. 225-253; In, Interactions of Microorganisms with Radionuclides. Elsevier Sciences, Oxford, UK.
5. Derakshani, M., et al. (2001) Appl. Environ. Microbiol. 67: 623-631.
6. Radeva, G. and Selenska-Pobell, S. (2003) FZR-Report No. 373, p. 29
7. Takai, K., et al. (2001) Appl. Env. Microbiol. 67, 5750-5760.
8. Stein, L., et al. (2002) FEMS Microb. Ecol. 42, 431-440.

Bacterial diversity was investigated by using the 16S rDNA retrieval in soil samples collected from a uranium mining waste pile called Haberland situated near the town of Johanngeorgenstadt, Germany, and from one uranium mill tailings in the USA, namely Shiprock, New Mexico. Significant differences were found in the composition of the bacterial communities at the studied sites. Alpha-Proteobacteria and representatives of the Holophaga/Acidobacterium phylum are predominant at the uranium mining waste pile Haberland, whereas the Shiprock uranium mill tailings is mainly occupied by Bacillales, g-Proteobacteria, and Green non-sulfur bacteria. The observed differences in the composition of the bacterial communities in the two studied environments are most probably connected to their different grade of contamination with heavy metals, and also to their different geographic and geologic origin (1).
Representatives of the Geobacter genus were found in both samples studied, but mainly by using Geobacter specific primers. This indicates that the Geobacter populations are probably not predominant in the studied environments. The exact quantification of these populations will be performed by using Real-Time PCR (work in progress). Geobacteracea are involved in reduction of heavy metals (e.g. iron) and radionuclides (e.g. uranium). Because these bacteria can significantly influence the mobility of the mentioned metals (2) their quantification in the uranium wastes is of great importance.

References:

1. Geißler, A. (2003) Molekulare Analyse der bakteriellen Diversität in Uranabraumhalden. Diploma Thesis,
Wissenschaftlich-Technische Berichte des Forschungszentrums Rossendorf FZR-377.

2. Lovley, D. R. et al. (1993) Archives of Microbiology 159: 336-344.

A Sn liquid metal ion source was prepared employing a Ni needle to anchor the liquid ion emitter. The main source properties, i.e., the I-V curve, the mass spectra, the energy spread for the main species, as well as the long term source stability were systematically studied. Moreover, a new etching technique for Ni tips has been developed. The mass spectra show a large amount of Sn clusters, apart from the dominant species, Sn+ and Sn++. The source was stable down to 1µA emission current, corresponding to an energy spread for the singly-charged ions of 7 eV. Theoretical arguments strongly suggest that both Sn+ and Sn++ are emitted by direct field-evaporation from the liquid surface.

Detailed studies of the azimuthal dependence of the mean fragment and flow energies in the Au+Au and Xe+CsI systems are reported as a function of incident energy and centrality. Comparisons between data and model calculations show that the flow energy values along different azimuthal directions could be viewed as snapshots of the fireball expansion with different exposure times. For the same number of participating nucleons more transversally elongated participant shapes from the heavier system produce less collective transverse energy. Good agreement with Boltzmann-Uehling-Uhlenbeck calculations is obtained for a soft nuclear equation of state.

The presentation provides a short introduction to MHD dynamos and to the pseudo-Hermiticity properties of the matrix differential operator of the spherically symmetric α²-dynamo.
In the first part of the lecture, the underlying physics is described starting from a discussion of the homopolar disk dynamo, of field reversals of the Earth's magnetic field and of the dynamo experiments in Riga and Karlsruhe. Furthermore, a sketchy outline of the helicity based meanfield technique for the MHD induction equation is presented and the closing of the dynamo cycle is discussed.
In the second part, attention is paid to the derivation of the matrix differential operator for the spherically symmetric α²-dynamo and its associated quadratic operator pencil. Boundary conditions, pseudo-Hermiticity and Krein-space features are used to heuristically explain the level-crossing properties of the spectrum. Along the lines of [1], the derivation of a constructive no-go theorem for isospectral dynamo configurations is described and interesting open problems are listed.

[1] Günther U. and Stefani F., Isospectrality of spherical MHD dynamo operators: pseudo-Hermiticity and a no-go theorem,
J. Math. Phys. 44, 2003, 3097, math-ph/0208012.

Pseudo-Hermiticity as a generalization of usual Hermiticity is a rather common feature of (differential) operators emerging in various physical setups. Examples are Hamiltonians of PT- and CPT-symmetric quantum mechanical systems [1] as well as the operator of the spherically symmetric α²-dynamo [2] in magnetohydrodynamics (MHD). In order to solve the inverse spectral problem for these operators, appropriate uniqueness theorems should be obtained and possibly existing isospectral configurations should be found and classified. As a step toward clarifying the isospectrality problem of dynamo operators, we discuss an intertwining technique for η-pseudo-Hermitian 2×2-block-operator matrices with second-order differential operators as matrix elements. The intertwiners are assumed as first-order matrix differential operators with coefficients which are highly constrained by a system of nonlinear matrix differential equations. We analyze the (hidden) symmetries of this equation system, transforming it into a set of constrained and interlinked matrix Riccati equations. Finally, we test the structure of the spherically symmetric MHD α²-dynamo operator on its compatibility with the considered intertwining ansatz and derive a no-go theorem.

[1] Bender C.M. and Boettcher S., Real spectra in non-Hermitian Hamiltonians having PT symmetry, Phys. Rev. Lett. 80, 1998, 5243, physics/9712001; Znojil M., PT-symmetric harmonic oscillators, Phys. Lett. A259, 1999, 220, quant-ph/9905020; Bender C.M., Brody D.C. and Jones H.F., Complex extension of quantum mechanics, Phys. Rev. Lett. 89, 2002, 270401, quant-ph/0208076.

[2] Günther U. and Stefani F., Isospectrality of spherical MHD dynamo operators: pseudo-Hermiticity and a no-go theorem,
J. Math. Phys. 44, 2003, 3097, math-ph/0208012.

It is widely believed that almost all magnetic fields in a natural environment are the result of the dynamo process - the field generation in moving nearly homogeneous electro-conducting fluids. This dynamo process occurs in the depths of celestial bodies such as the Earth, most of the planets, the Sun, other stars, and even galaxies.The Riga dynamo experiment is not intended as a model of any particular celestial body. It aims at demonstrating the basic dynamo mechanism - that the intense motion in a large volume of a good electro-conducting liquid creates a magnetic field. In the present paper, the set-up and the main results of this experiment are presented, with some focus on the theoretical interpretation of the data.

Two-phase flow tests in a 194.1 mm diameter vertical pipe (DN200) with an air-water mixture are reported. Close to the upper end of a 9 m tall test section a wire-mesh sensor is installed that delivers instantaneous void fraction distributions over the entire cross section with time resolution of 2500 frames per second. The sensor disposes of 64x64 measuring points, which corresponds to a spatial resolution of 3 mm. Beside an fast flow visualisations, void-fraction profiles and bubble size distributions were obtained. Earlier, similar experiments were carried out in a pipe of 51.2 mm inner diameter (DN50). A comparison of the data from the two different facilities allows to study the scaling effects on void fraction profiles, bubbles size distributions and the flow patterns. In the small pipe, the increase of the air flow rate leads to a transition from bubbly via slug to churn turbulent flow.
The transition to slug flow is accompanied by the appearance of a second peak in the bubble size distribution that corresponds to the class of large Taylor bubbles. A similar qualitative behaviour was found in the large pipe, though the large bubble fraction has a significantly bigger mean diameter at identical superficial velocities, the peak is less tall but wider. Bubbles move more freely than in the small pipe, since the confining action of the pipe walls to the flow is less pronounced, while the large Taylor bubbles occupy almost the entire cross section in case of the small pipe. Furthermore, the bubbles show much more deformations in the large pipe. Shapes of such large bubbles were characterised in three dimensions for the first time. They can rather be complicated and far from the shape of ideal Taylor bubbles. Also the small bubble fraction tends to bigger sizes in the large pipe.

The mass spectra of the beam emitted by a Au82Si18 eutectic molten metal ion source are investigated in detail, as a function of emitter temperature. At the conclusion of the work it emerges that while Au+, Si+ and Si++ are the result of direct field-evaporation from the liquid surface, Au++ forms by the post-ionisation of Au+. Cluster ions are most probably the product of droplet break-up.

This paper considers numerically the linear and non-linear instability of a liquid metal in a vertical cylinder with hot bottom, cold top and adiabatic side walls subject to superimposed rotating and steady axisymmetric magnetic fields. In the non-linear case, a threshold is determined for the global stability against finite size perturbations. It is shown that a proper magnetic field combination stabilizes the system much better than any of the fields separately.

Lifetimes of states in the lowest lying positive parity band in ¹⁰⁶Cd have been measured using the Doppler shift attenuation method. The deduced D(E2) transition rates show a marked decrease with increasing spin. Cranking and semiclassical model calculation suggest that the structure has the character of a shears-type band resulting from the coupling of g_9/2 proton holes to aligned pairs of h_11/2and g_7/2 neutron particles. This is the first clear evidence for the phenomenon of "antimagnetic" rotation in nuclei.

High-spin states in ¹³⁵Nd were populated with the ¹¹⁰Pd(³⁰Si,5n)¹³⁵Nd reaction at a ³⁰Si bombarding energy of 133 MeV. Two dI=1 bands with close excitation energies and the same parity were observed. These bands are directly linked by dI=1 and dI=2 transitions. The chiral nature of these two bands is confirmed by comparison with three-dimensional tilted axis cranking calculations. This is the first observation of a three-quasiparticle chiral structure and establishes the primary geometric nature of this phenomenon.

The interaction of magnetic fields with moving electrically conducting fluids is the subject of magnetohydrodynamics. There is a vast area of applications, e.g. in metal casting and crystal growth, where magnetic fields are used to act on the melt flow in order to improve the quality of the products. On the other hand, the moving fluid can also influence externally applied magnetic fields, and for large magnetic Reynolds numbers it can even yield self-excitation of a magnetic field. This effect, called homogeneous dynamo effect, is at the root of magnetic field generation in planets, stars, and galaxies.
We focus on several inverse problems connected with the determination of velocities or velocity related quantities from magnetic field information that is measurable outside the fluid region. The underlying theory is presented in the framework of the integral equation approach to dynamos in finite domains, which can be cast into a linear inverse problem in case that the magnetic Reynolds number of the flow is not too large.
In this case it is necessary to apply external magnetic fields and to measure the flow induced electromagnetic fields. Two possibilities are considered: one can apply one magnetic field and measure the external induced magnetic field and the electric potential at the fluid boundary, or one can apply two different magnetic fields and measure the corresponding two sets of external induced magnetic fields.This latter contactless method is especially interesting for applications with hot and aggressive fluids or for facilities where the fluid boundary is not accessible for technological reasons. We consider the uniqueness problems of both methods finding that the rough topology of the flow can be determined from the measured data but that the depth dependence of the velocity must be inferred by regularization methods. We present first results of an experiment with a flow of InGaSn exposed to an externally magnetic field pointing subsequently in two different directions.
The linear character of the inverse MHD problem is lost when it comes to dynamos which work exclusively at large magnetic Reynolds numbers. Inverse dynamo problems are well known in geophysics and solar physics where information on the velocity structure is to be drawn from magnetic field data. They have acquired new relevance recently with the liquid sodium experiments in Riga and Karlsruhe. In connections with those experiment there are quite new inverse, design, and optimization problems. We show that even the simplest inverse spectral dynamo problems for very symmetric dynamos are far from trivial, compared to similar problems in quantum mechanics. We present examples where evolution strategies can successfully be employed to solve particular inverse
dynamo problems.

We have studied the performance of finger like LSO:Ce (LSO) crystals coupled one by one to pixels of avalanche photodiode detector (APD) arrays during their operation in coincidence at ¹²C ion beams of parameters being typical for tumor irradiations. In a first step of these experiments the parameters of the detectors and the signal processing setup has been characterized off-beam, i.e. by means of beta⁺ radioactive sources (²²Na, ⁶⁸Ge). Afterwards, the apparatus was installed at the medical beam line of the heavy ion synchrotron (SIS) of the Gesellschaft für Schwerionenforschung (GSI) at Darmstadt, Germany. Here, the beta⁺ activity produced by nuclear fragmentation reactions of ¹²C 200.3 AMeV heavy ion beams with polymerized methyl methacrylate (PMMA) phantoms were measured. Furthermore, a ⁶⁸Ge source was included into the in-beam experiment, in order to check the stability of the setup and to compare energy and time resolution before, during and after phantom irradiations. Additionally, it could be demonstrated by means of high resolution gamma-ray spectroscopy that LSO is not activated by the light projectile fragments escaping the patients downbeam during therapeutic irradiations. The experimental results indicate, that LSO scintillator is a suitable material for in-beam PET and, furthermore, the LSO/APD array is a feasible detector concept for in-beam monitoring of the dose application by means of PET.

Release and migration of ¹⁴C cannot be treated independently from the bulk of inorganic and organic carbon waste components in a repository. ¹⁴C is mainly produced by (n,p) reaction from ¹⁴N. Important sources of ¹⁴C is zircalloy (according ASTM standard Nmax: 65 ppm), the fuel (N contamination and ternary fission) as well as some other reactor components. In Germany, spent fuel elements from High Temperature Reactors (HTR) will contribute also to the total ¹⁴C load of a radioactive waste disposal. Additionally, organic materials containing ¹⁴C markers, metals containing ¹⁴C as carbides and other low level waste forms containing ¹⁴C in carbonates or in ashes have to be taken into account.
¹⁴C in graphite from spent HTR fuel elements is nearly immobile. Other waste forms may release ¹⁴C in a large variety of inorganic and organic species. Reactions of carbides with water/brine produce methane or acetylene gas. By microbial reactions, organic ¹⁴C can be transformed into gases ¹⁴CO₂ and ¹⁴CH₄.
Interactions of HTR fuel with brines were investigated at FZJ. At FZK-INE and FZR, various experimental and theoretical investigations have been performed in order to quantify the release of this isotope.
Limiting the concentrations of (bi-)carbonates in solution results in a low actinide solubility, especially at high pH. For this reason, at WIPP, a Mg bearing backfill material (periclase, MgO) is added to the wastes in order to keep the concentration of HCO₃-/CO₃ ^2- at a minimum. For the Asse salt mine, a backfill material was proposed by FZK-INE. This material consists mainly of brucite (Mg(OH)₂(s)) and sorel phases (Mg_2x(OH)_(2x-1)Cl·₄H₂O(s)). Various experimental and modelling studies were carried out to determine the stability of the Mg(OH)_2(s)-based material in the relevant brines, formation of the reaction products, and the effect of the material on actinide solubility in the case of carbonate-input to the brines. Experimental findings are in agreement with the modeling predictions. By precipitating carbonates from solution, an isotopic exchange effect will occur, which will control the ¹⁴C concentration in solution.
For the ERAM system, sorption of ¹⁴CO₃ ^2- onto salt concrete, sorel concrete and other backfill materials was investigated. For all materials under investigation, sorption showed distinct time dependences. The weakest sorption was observed in case of salt concrete. Sorel phases reduced the ¹⁴C concentration by more than 2 orders of magnitude during a 0.5 yr. period. Since the studied backfill materials contained to some extent solid carbonates, the retention process can be explained by isotopic exchange.
Sorption of methane (CH₄) onto the backfill materials was investigated by contacting a brine/backfill slurry with the gas. The tests were performed by monitoring the concentration of gaseous CH₄ in a mixture with a noble gas (Ar) which does not react with slurry components. The analysis of experimental results shows that the ratio of CH₄/Ar remains constant within a deviation of 5%. Consequently, the total methane sorption onto the studied backfill materials remains below 0.2 mmol CH₄/kg solid material.

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This study investigates the migration behavior of U(IV) and U(VI) in the system humic acid / uranium / quartz sand by means of column experiments. Humic acid exhibits a significant influence on the transport of U(IV) and U(VI). In case of U(VI) a clear mobilizing effect was observed. There are strong indications for a similar influence of humic acid on U(IV) transport. Both redox species of uranium differ slightly in their migration behavior in presence of humic acid. This is mainly reflected in a disagreement of their total recoveries. The observed difference amounts to approximately 25 %.

Knowledge of the migration of intrinsic point defects is crucial to understand defect recovery, various annealing stages and microstructural evolution after irradiation or ion implantation. Molecular dynamics (MD) and the nudged-elastic band method have been applied to investigate long-range migration of point defects in SiC over the temperature range from 0.36 to 0.95 Tm , and the defect diffusion coefficient, activation energy and defect correlation factor have been determined. The results show that the activation energies for C and Si interstitials in 3C-SiC are about 0.74 and 1.53 eV, respectively, while it is about 0.77 eV for a C interstitial in 4H-SiC. The minima energy paths reveal that the activation energies for C and Si vacancies are about 4.1 and 2.35 eV, respectively. Finally, the results are discussed and compared with experimental observations and available ab initio data.

Symmetry considerations and classical-potential computer simulations are employed to perform a comparative study of properties of intrinsic defects in 3C- and 4H-SiC. Investigations of the polytype structure reveal that the number of non-equivalent point defects in 4H-SiC should be significantly higher than in 3C-SiC. Most of the potential defects are found to be stable. A considerable difference between 3C- and 4H-SiC exists for some dumbbells with a complex and anisotropic structure. This is due to the important role of lattice deformations beyond the first neighbor shell and the fact that the spatial distribution of these deformations is strongly dependent on the polytype. The interstitials between hexagonal and trigonal rings are characteristic for 4H and other hexagonal polytypes. They do not exist in 3C-SiC. In the case of more compact and isotropic defects, such as vacancies, anitisites, hexagonal interstitials and many dumbbells, the influence of polytypism is small. The properties of tetrahedral interstitials in 3C- and 4H-SiC are very similar since in both polytypes their first, second and third neighbor shells are equal. Besides the elementary defects, the structure and energetics of defect clusters is investigated.

In this work we study the mechanical and tribological properties (hardness, elastic modulus, friction and wear) of BCN coatings with controlled composition and structure. The influence of the carbon content in films with BCxN stoichiometry is discussed in connection with the bonding structure, and compared with the mechanical and tribological properties of reference compounds. Since ternary BCN compounds can exhibit a variety of compositions and bonding structures, the knowledge of these parameters is a pre-requisite to study any physical property of BCN coatings. Boron carbonitride (BCN) films were deposited at different temperatures using simultaneous evaporation from separated boron and carbon sources, assisted by different mixtures of Nitrogen and Argon ions from a Kauffman ion gun. In this way, we obtained films with selected composition, as verified with Energy Dispersive X-ray (EDX) spectroscopy, X-ray Absorption Near Edge Spectroscopy (XANES) and Elastic Recoil Detection Analysis (ERDA). The bonding structure of the coatings was determined by combining XANES with vibrational spectroscopies (infrared and Raman). Finally, the mechanical and tribogical characterization was performed with nanoindentation and pin-on-disk techniques, respectively.

Porous silicon (PS) has a great potential in optical applications due to its tuneable refractive index. In particular, multilayer structures consisting on PS layers with different refractive indexes can be used as interference filters. Due to the characteristics of PS and its production process, many types of interence filters can be produced: Bragg reflectors, monochromatic filters for light emitting devices (which can also be based on PS), microcavities for biosensing applications, Fabry-Pérot resonators, photonic crystals, etc.

In the present work the optical properties of porous silicon single layers and multilayer structures have been studied. PS is formed by the electrochemical etch of monocrystalline silicon wafers. Since PS can be modelled as an homogeneous mixture of silicon and air (and, eventually, silicon dioxide), its refractive index varies depending on the air content of the porous structure, according to the effective medium theories (EMTs). The electrochemical process gives a perfect control over the porosity –and hence, over the index of refraction- and thickness of the porous silicon layer, since both parameters are highly sensitive to the formation conditions, mainly current density and etching time. In addition, when the current density applied is periodically varied, a multilayer structure is formed. By simply adjusting the refractive index and thickness of each individual layer we can obtain a stack of porous silicon layers with the desired optical properties, resulting in an interference filter of predetermined band width.

The optical characterization has been carried out by spectrophotometric and spectroscopic ellipsommetry measurements. In addition, compositional analysis has been performed by means of Ion Beam Analysis (IBA) techniques, with special interest devoted to oxygen and hydrogen, in order to correlate the optical parameters and the chemical composition. Finally, multilayers structures have been produced and their operation has been checked.

The modification of the surface morphology by means of low-energy (0.1-10 keV) ion irradiation is a fascinating process that has been devoted to intense study during the last decades. The first implications of this process were considered due to secondary effects derived from the ion-modified roughness, such as secondary ion emission (SIMS). However, the ability to produce regular and self-organized patternings in the nanoscale range, related to the typical size of the ion collision cascade, has recently attracted the interest on this process due to its potential applications in Nanotechnology. Depending on the ion incidence angle, different morphologies can be induced on the surface, namely ripples and dots [1]. The universality of the process has been demonstrated by the production of patterns either on metals (Ag, Cu), semimetals (graphite), semiconductors (GaSb, GaAs, InP, Si, Ge) and insulators (glass, SiO2). The mechanisms leading to the formation of these patternings have also attracted intense theoretical studies [3]. The successful approach considers continuum equations where an instability results from the interplay between roughening, due to the dependence of the ion sputtering yield on the local surface curvature, and smoothing processes (thermal and ion-induced). Finally, the applications of these nanostructures are still to be exploited. Several applications as optical filters, quantum wires, quantum dots, magnetic nanostructures, and templates have been addressed. In addition, the latter application has been already realized, transferring the pattern from Si surfaces to polymeric and metallic films [4]. Complementary, the possible functionalization of the surface for biological or catalytic processes can also open a wide range of potential applications.

[1] Navez et al. C.R. Acad. Sci, Paris 254 (1962) 240; Facsko et al. Science 285 (1999) 1551.
[2] Gago et al. Appl. Phys. Lett. 78 (2001) 3316; Gago et al. Nanothecnology 13 (2002) 304.
[3] Bradley et al. J. Vac. Sci. Technol. A 6 (1988) 2390; Cuerno et al. Phy. Rev. Lett. 74 (1995) 4746.
[4] Azzaroni et al. Appl. Phys. Lett. 82 (2003) 457; Azzaroni et al. Nanotechnology (submitted)

One of the most active research topics within the nanoscience and nanotechnology fields are those related to large-scale fabrication, in an accurate manner, of nanostructured metal thin films [1]. This interest is due to their potential applications for different technological purposes such as electrocatalysis [2] and optical devices [3]. In order to obtain these nanostructured films different techniques, such as ion sandblasting [4] or nanotransfer printing [5], have been developed. In this work we present results on the largescale preparation of nanostructured metal thin films from surface-modified silicon nanodots templates [6]. The nanopatterning process is based on the deposition of a copper thin film (approximately 300nm thick) by physical vapor deposition on nanostructured silicon substrates [7], which were previously surface-modified with an octadecyltrichlorosilane (OTS) self-assembled monolayer in order to promote an easy metal film detachment after deposition. Once the 300 nm thick film has been deposited, a thick (10 mm approximately) film of copper is electrodeposited onto it to improve the mechanical properties of the physically-deposited nanostructured thin film. Thanks to the very low adhesion of OTS layer to the metal film the latter is easily mechanically detached from the template, leading to a surface nanostructure corresponding to the negative replica of the original nanopatterned silicon template. This metal nanopatterning strategy shows potential applications for accurate large-scale fabrication of nanostructured metal thin films.

[1] G.L. Egan, J.-S. Yu, C.H. Kimm, S.J. Lee, R.E. Schaak, T.E. Mallouk, Adv.Mater. 12,1040 (2000)
[2] G.S. Attard, et al., Science, 278, 838 (1997)
[3] M.B. Sobnack, et al., Phys.Rev.Lett. 80, 5667 (1998)
[4] S. Rusponi, G. Constantini, F. Buatier de Mongeot, C. Borago, U. Valvusa, Appl. Phys. Lett. 75, 3318 (1999).
[5] Y.-L. Loo, et al., J.Am.Chem.Soc. 124, 7654 (2002).
[6] O. Azzaroni, P.L. Schilardi, R.C. Salvarezza, R. Gago, L. Vázquez, Appl. Phys. Lett. 82, 457 (2003).
[7] R. Gago, L. Vázquez, R. Cuerno, M. Varela, C. Ballesteros, J.M. Albella, Appl.Phys.Lett. 178, 3316 (2001).

The albumin adsorption on non-hydrogenated amorphous carbon films with different diamond-like character (i.e. sp3 content) is addressed. The films were produced by ion beam assisted deposition and by filtered cathodic vacuum arc deposition to obtain a wide range of sp3 contents. A combination of the spectroscopic ellipsometry, Raman spectroscopy and elastic recoil detection analysis was used for characterization of the films. It is shown that an increase of the deposition temperature leads to a decrease of the film band gap, density and a shift of the Raman G-band position. The wettability of the film is not influenced by its sp3 content. Albumin adsorption on the surface depends more on its wetting behavior than on the sp3 content. In addition, Ar ion treatment of the layers can be used to reduce the amount of adsorbed proteins.

Leitfähigkeits-Gittersensoren ermöglichen die Untersuchung von Strömungen mit und ohne Gasanteil (Ein- und Zweiphasenströmungen) mit hoher räumlicher und zeitlicher Auflösung. Sie können damit für viele strömungsdiagnostische Probleme eingesetzt werden. Der Beitrag gibt einen Überblick über das Funktionsprinzip, die Gewinnung physikalischer Strömungsparameter aus den elektrischen Messsignalen sowie über Anwendungsgebiete solcher Sensoren.

The complex formation of uranium(VI) with glycerol 1-phosphate was determined by potentiometric titration, UV-vis and TRLFS spectroscopy. Three complexes were found by potentiometry in the pH range 3 - 8, and the stability constants were calculated for I = 0.1 M: 1 : 1 complex UO₂(C₃H₇O₃PO₃) (log beta₁₁ = 6.23 ± 0.09); 1 : 2 complex UO₂(C₃H₇O₃PO₃)₂ ^2- (log beta₁₂ = 10.22 ± 0.13); 2 : 3 complex (UO₂)₂(C₃H₇O₃PO₃)₃ ^2- (log beta₂₃ = 20.28 ± 0.03). The UV-vis spectra at pH 2 to 4 show an increase of the absorption intensity with increasing ligand concentration, connected with a red shift of the main absorption bands. The three complexes could be isolated by deconvolution of the measured spectra and the stability constants were determined (at I = 0.5 M) to be: log beta₁₁ = 6.15 ± 0.20, log beta₁₂ = 10.38 ± 0.39, and log beta₂₃ = 19.34 ± 0.65. The TRLFS spectra at pH = 4 show also an increase of the fluorescence intensity connected with a red shift of the emission spectra. But contrary to the both above mentioned methods only the 1 : 1 complex UO₂(C₃H₇O₃PO₃) could be detected under the specific experimental conditions. The main fluorescence emission bands and the lifetime of this complex were determined. The complex stability constant at I = 0.1 M was calculated to be log beta₁₁ = 6.15 ± 0.05.

The complex formation in the aqueous systems of uran(VI) with glucose 6-phosphate (G6P) and fructose 6-phosphate (F6P), respectively, were studied by means of potentiometric titration, TRLFS, and EXAFS. In each case two complexes with a metal-to-ligand ratio of 1 : 1 and 1 : 2 could be observed. Complex stability constants were determined by potentiometric titration for both complexes to be log beta₁₁(G6P) = 5.89 ± 0.40, log beta₁₂(G6P) = 9.45 ± 0.08, log beta₁₁(F6P) = 5.72 ± 0.21, and log beta₁₂(F6P) = 9.54 ± 0.09. By TRLFS stability constants could be calculated under the specific experimental conditions only for the 1 : 1 complexes (log beta₁₁(G6P) = 6.35 ± 0.28, and log beta₁₁(F6P) = 5.66 ± 0.17).
The TRLFS measurements resulted in that the UO₂G6P complex shows no fluorescence properties. For this system only a decrease of the fluorescence intensity with increasing ligand concentration could be observed. For the uranyl fructose 6-phosphate system a red shift of the fluorescence emission bands of about 8 to 9 nm compared to the free uranyl ion was observed. The fluorescence emission wavelengths of the UO₂F6P complex were determined to be 483, 496, 518, 542, and 567 nm, and the lifetime of this complex is 0.13 ± 0.05 µs.
Uranium L_III-edge EXAFS measurements at different pH values yielded a shortened U - O_eq bond distance (2.31 ± 0.02 to 2.37 ± 0.02 Angström) compared to the UO₂ ²⁺(H₂O)₅ ion (2.40 ± 0.02 Angström) due to a monodentate coordination via the oxygen atoms of the phosphate group.

S-(¹⁸F]fluoromethyl)-(+)-McN5652 ([¹⁸F](+)-FMe-McN5652) has recently been synthesized as a new potential radiotracer for positron emission tomography (PET) imaging of the 5-HT transporter. It is an analog of [¹¹C](+)-McN5652, which has been used in clinical PET studies for 5-HT transporter imaging. This article describes the comparison of these two radiotracers in pigs with respect to their in vivo binding characteristics. PET images revealed that the highest accumulation of both radiotracers was found in the ventral midbrain, thalamus, olfactory lobe, and pons which is consistent with the known density of 5-HT transporters. The specific binding was determined by subtracting the values of the inactive (-) enantiomers or of the occipital cortex from those obtained with [¹¹C](+)-McN5652 or [¹⁸F](+)-FMe-McN5652 in the time period between 75 and 115 min after radiotracer injection. The specific binding of the ¹⁸F-labeled derivative was about 40 % higher than that of the ¹¹C-labeled derivative. A strong inhibition of the specific binding was observed for both radiotracers after pre-treatment with the selective 5-HT uptake inhibitor citalopram. [¹⁸F](+)-FMe-McN5652 showed faster kinetics than [¹¹C](+)-McN5652. It reached the binding equilibrium during a study length of 120 min, which was not the case for [¹¹C](+)-McN5652. It is concluded that [¹⁸F-FMe-McN5652 is suitable for 5-HT transporter imaging with PET.

We present a complete systematics (excitation functions and system-size dependences) of global stopping and sideflow for heavy ion reactions in the energy range between 0.09A GeV and 1.93A GeV. For the heaviest system, Au+Au, we observe a plateau of maximal stopping extending from about 0.2A to 0.8A GeV with a fast drop on both sides. The degree of stopping, which is shown to remain significantly below the expectations of a full stopping scenario, is found to be highly correlated to the amount of sideflow.

Die hochauflösende Rutherford Rückstreu-Spektrometrie (HRBS) hat ein großes Potential bei der Charakterisierung von dünnen Schichten mit Dicken im Nanometer-Bereich bis hin zu Dicken im Monolagen-Bereich. Der Bedarf der Materialforschung an quantitativen, schnellen und zuverlässigen Tiefenprofilen solcher Proben wächst ständig. Der wesentliche Unterschied zur weit verbreiteten Standard-RBS besteht dabei im Einsatz von Spektrometern in Verbindung mit ortsauflösenden Detektoren. Diese Konfiguration bietet zum einen die Möglichkeit einer verbesserten Energieauflösung bei der Detektion der gestreuten Ionen. Zum anderen ist die Verwendung schwerer Primärionen, deren größeres Bremsvermögen eine bessere Tiefenauflösung erlaubt, damit erst ohne nennenswerte Einschränkungen der Energieauflösung möglich. Die Verwendung von Spektrometern bringt es allerdings mit sich, dass Ionen mit verschiedenen Ladungszuständen getrennt gemessen werden müssen.
Messungen an Mehrfachschichtsystemen mit Li und C als Primärionen illustrieren die Tiefenauflösung im Tiefenbereich bis 20 nm, die mit der HRBS am Rossendorfer Browne-Buechner-Spektrometer erreicht werden kann. An einem einfachen Schichtsystem mit sehr dünnen Einzelschichten werden die exzellenten Möglichkeiten der HRBS im Vergleich zur Standard-RBS und zur MEIS vorgeführt. Die Auswertung der HRBS-Spektren liefert auch Aussagen über das Straggling und den Energieverlust schwerer Ionen in den untersuchten Materialien. Für C-Ionen wurde der Einfluss der Schädigung während der Messung untersucht. Eine Verwendung von Ionen, welche schwerer als C sind, erweist sich bei den am Rossendorfer Tandetron zur Verfügung stehenden Energien auf Grund der erhöhten Schädigung ohne gleichzeitige Verbesserung der Tiefenauflösung als nicht sinnvoll.

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kein abstract

In recent years, several novel material systems (such as II-VI’s and nitrides) have been explored with the goal of achieving intersubband absorption in the 1.5 micron telecommunication wavelength region. This could lead to novel near-infrared modulators, detectors and (quantum cascade) lasers with high modulation frequencies.
We have investigated two different material systems grown on InP substrates:
(1) Heavily strained, but overall strain compensated InxGa1-xAs/AlAs/InyAl1-yAs structures grown by gas-source MBE. Here the conduction band offset between the In0.7Ga0.3As and the pure AlAs is approximately 1.23 eV.
(2) Lattice matched In0.53Ga0.47As/AlAs0.56Sb0.44 structures grown by solid-source MBE, with a conduction band offset of approximately 1.6 eV.
In both systems, absorption wavelengths shorter than 2 micron (0.62 eV photon energy) were observed. In the strained system, we investigated multiple quantum wells (MQW) as well as short-period superlattices. The absorption strength in the MQWs (Fig.1) diminishes dramatically for wells narrower than 20 Å, either due to problems in dopant activation (although the doping was put into the wells), or because the second subband has already moved into the continuum. The short-period superlattices show clear evidence of dispersive minibands as well as a small, but non-negligible s-polarized absorption. X-ray diffraction data show that the individual layers are elastically strained, with an overall strain compensation better than 0.2%.
The MQW structures of the antimonide system (modulation doped) exhibit very strong absorption, not degrading for wells down to 27 Å thickness (Fig. 2). Due to the high barriers, a wavelength shorter than 2 microns can be reached already with this thickness value.

The Cs sputter ion source HVEE 860-C has shown significant erosion of inner parts after an operation time of some thousand hours. This is caused by Cs ions generated at hot surfaces outside the spherical ioniser surface. The calculated trajectories of these ions and the erosion patterns show an excellent correspondence. The suppression of the disturbing ions has resulted in increased lifetimes of the ion source and an improved focus of the primary Cs ions on the sputter target. The modified sputter ion source is still in operation without any maintenance (about 3000 operating hours at October 2003).

Social isolation of rodents is used to model human psychopathological processes. In the present study, the effects of intermediate and long term isolation housing on postsynaptic 5-HT_1A and 5-HT_2A receptors were analyzed in male mice housed in groups or isolation for 4 and 12 weeks. [³H]8-OH-DPAT and [³H]ketanserin were used to label 5-HT_1A and 5-HT_2A receptors. Four representative sagittal sections (planes 1–4) were scored by in vitro autoradiography. Whereas after 4 weeks of housing both receptor densities were lowered significantly in isolated mice, after 12 weeks of housing only marginal isolation effects were seen. Intermediate isolation reduced 5-HT_1A receptors especially in the lateral frontal, parietal and entorhinal cortex (-63%), in the lateral CA1–3 and dentate gyrus region of the hippocampus (-68%), in the basolateral, basomedial, central and medial amygdaloid nuclei (between -38 and -66%), and in the hypothalamus (–28%). 5-HT_2A receptors were strongly reduced in the frontal cortex (between -47 and -74%), in the hippocampus (between -47 and -95%), in the striatum (between -66 and -76%), and in the accumbens nucleus (between -59 and -73%) in comparison to group housed control mice. After 12 weeks of isolation in the hippocampus continuously decreased 5-HT_1A receptor densities were demonstrated (between -24 and -61%). But increased 5-HT_2A receptor densities were seen in the lateral striatum (+86%) compared to control mice. Age-dependent effects were also found. After 12 weeks of group housing the 5-HT_1A and 5-HT_2A receptor densities were decreased (between -28 and -54%) in all analyzed brain regions in comparison to 4 weeks of group housing. Isolated animals showed diminished 5-HT_1A receptor densities in the cortex (-14%) and hippocampus (-15%), but increased 5-HT_1A receptor densities in the amygdala (+33%) after 12 weeks. The 5-HT_2A receptor densities were increased in all analyzed regions (between +31 and +96%) after 12 weeks of isolation compared to 4 weeks. To explain these dynamic, time-dependent pattern of isolation-induced changes different regulation processes are supposed regarding 5-HT_1A and 5-HT_2A receptors. Besides metabolism-related adaptation processes also neurotransmitter and hormonal (e.g., glucocorticoid) interactions especially in limbic regions have to be considered.

The dynamic stability of the voltage of Van de Graaff belt generators depends to a great extend on the internal impedance of the charging current supply and on the dynamic precision of the current measurement. A charging stabilizer with increased dynamic precision based on guard technique was developed. The arrangement and results are explained, a disturbance compensation is discussed.

The use of flash lamp annealing for ultra-shallow junction formation in silicon has been described. Low energy boron and arsenic implants have been heat-treated in this way using peak temperatures in the range of 1100o to 1300oC and effective anneal times of 20 ms and 3 ms. Secondary ion mass spectrometry and four point probe measurements have been undertaken to determine the junction depth and the sheet resistance, respectively. Optimum processing conditions have been identified, under which one can obtain combinations of junction depth and sheet resistance values that meet the 90 nm technology node requirements and beyond.

The 6th dynamic AER Benchmark is used for the systematic validation of coupled 3D neutron kinetic/thermal hydraulic system codes. It was defined at the 10th AER-Symposium. In this benchmark, a hypothetical double ended break of one main steam line at full power in a VVER-440 plant is investigated. The main thermal hydraulic features are the consideration of incomplete coolant mixing in the lower and upper plenum of the reactor pressure vessel and an asymmetric operation of the feed water system. For the tuning of the different nuclear cross section data used by the participants, an isothermal re-criticality temperature was defined.
First solutions of the benchmark were compared during the 11th AER-Symposium. Due to the considerable spreading of these first results, the participants continued the work on the calculation of the benchmark. Updated solutions were received from VTT Processes Espoo (HEXTRAN/SMABRE), Kurchatov Institute Moscow (BIPR8/ATHLET), NRI Rez (RELAP5-3D) and Forschungszentrum Rossendorf (DYN3D/ATHLET). The solution of KFKI AEKI Budapest (KIKO3D/ATLET) remained unchanged.
The paper gives an overview on the behaviour of the main thermal hydraulic and neutron kinetic parameters in the provided solutions. The differences in the updated solution in comparison to the previous ones are described. Improvements in the modelling of the transient led to a better agreement of a part of the results while for another part the deviations rose up. The sensitivity of the core power behaviour on the secondary side modelling is discussed in detail.

The cross section for production of phi mesons inproton-nucleus reactions is calculatedas a function of the target mass. The decay width of the phi meson is affected by the change of the masses of the phi, K+ and K- mesons in the medium. A strong attractive K- potential leads to a measurable change of the behavior of the cross section as a function of the target mass. Comparison between the kaon and electron decay modes are made.

The A(e,e'K+)YX reaction has been investigated in Hall C at Jefferson Laboratory. Data were taken for Q^2= 0.35 and 0.5 GeV^2 at a beam energy of 3.245 GeV for 1H,2H,3He, 4He targets. The missing mass spectra are fitted with Monte Carlo simulations taking into account the production of Lambda and Sigma0 hyperon production off the proton, and Sigma- off the neutron. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for Lambda-hypernuclear bound states is seen for 3,4 He targets. This is the first time, the electroproduction of these hypernuclei has been measured.

APFIM investigation of irradiated VVER 440-type reactor pressure vessel steels suggests the appearance of multi-component clusters. The effect is surprising from the thermodynamic point of view. Numerical estimations of the negative minimum of the thermodynamic driving forces for a multi-component system are carried out considering a quasi-quaternary system consisting of Fe, Mn, Si and vacancies. A relative minimum was only found for a composite model of the multi-component clusters composed from a Fe containing core and a vacancies-rich shell. Such structures can agree with the small angle neutron scattering curves measured. On the other hand, the scattering curves do not provide features which prove the existence of core-shell-structures.

The depth dependence of elemental composition, phase distribution, and cross sectional morphology of rf plasma nitrocarburized 304 austenitic stainless steel were investigated using glow discharge optical spectroscopy (GDOS), grazing incidence X-ray
diffraction (GIXRD), and optical microscope (OM), respectively. A step-wise mechanically polishing method was used to remove successive sublayers of the treated surface. It is found that the properties of the nitrocarburized layer depend critically on the plasma gas composition, which controls the supersaturation of nitrogen and carbon through the compound layer depth. Iron nitride phases and/or nitrogen expanded austenite phase (gN) were detected in the nitrocarburized layer prepared at high plasma nitrogen (N2) content. In the compound layer processed at high plasma carbon (C2H2) content, besides the carbon expanded austenite phase (gC), carbide phases were found predominantly in the top-layer, in which the carbon concentration has a maximum value of ~2 wt. %. The lattice expansion of the expanded austenite phases depends on the depth with the variation of the local nitrogen and carbon content. The plasma processing power has enormous influence on the nitrogen and carbon distribution in treated sublayers.

Ni was surface-alloyed with Si by ion implantation. The material was examined for its redox and electrocatalytic behaviour in NaOH by cyclic voltammetry. The surface war characterized by X-ray photoelectron spectroscopy, X-ray and electron diffraction, and electron and atomic force microscopy. The activity toward the redox conversion of Ni(OH)2 " NiOOH and the anodic oxidation of glucose was enhanced by ca. 3.5 times and ca. 2.8 times, respectively. The material is an amorphous mixed oxide of Ni and Si. The effect was discussed considering the true surface area and the generation of active surface sites in relation to the oxygen evolution.

The core baffle of a PWR is loaded by the pressure difference between bypass and core and by temperature profiles developing from gamma and neutron heating and heat transfer into the coolant. Strain, deformation and gaps between the sheets resulting from this load are determined considering the effect of neutron irradiation induced creep of the core baf-fle bolts. The finite element code ANSYS is applied for the thermal and mechanical analyses. The FE-model comprises a complete 45° sector of the core baffle structure in-cluding the core barrel, the formers, the core baffle sheets and about 230 bolt connections with non-linear contact between the single components and the effect of friction. The com-plete analysis requires three major steps:

1. Evaluation of the three dimensional distribution of neutron flux and gamma in-duced internal heating with the Monte Carlo code MCNP®. These calculations are based on pin wise power distributions at the core edge for typical loading patterns.
2. Calculation of the temperature distribution in the core baffle for different opera-tional conditions and core loading patterns, considering heat conduction in the components with internal heat sources and convectional boundary conditions (heat transfer coefficients and bulk temperature of the coolant).
3. Calculation of time dependent deformation, stresses and strains taking into account weight, pressure loads, temperature fields for different load situations, prestressing, irradiation induced creep of the bolts as correlated to neutron flux.
The results show the equalizing effect of redistribution of bolt loads from high flux to lower flux exposure locations in a self controlled process, keeping the mechanical and geometrical stability of the core baffle structure and leaving the gaps between sheet edges unaffected.

In the paper the experiences of more than 30 years operation and development at the electrostatic accelerators at the Forschungszentrum Rossendorf, Dresden/Germany are summarized and focused on the necessary equipment for beam diagnostics at electrostatic accelerators, especially for measurement and monitoring of the current, position, stability and profile of the ion beam.

The paper provides an overview of the advantages and problems of superconducting RF guns. The results of the Rossendorf experiments are presented here. These results are integrated in the design of a new 3.4 cell superconducting RF gun. The beam parameters of this gun correspond to the demands of the new generation of high current, high brightness injectors.

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The pair correlations in mesoscopic systems such as nanometer-size superconducting clusters and nuclei are studied at a finite temperature for the canonical ensemble of fermions in model spaces with a fixed particle number: (i) a degenerate spherical shell (strong-coupling limit), (ii) an equidistantly spaced deformed shell (weak-coupling limit). It is shown that after the destruction of the pair correlations at T = 0 by a strong magnetic field or rapid rotation, heating can bring them back. This phenomenon is a consequence of the fixed number of fermions in the canonical ensemble.

The cranked relativistic Hartree-Bogoliubov theory has been applied for a systematic study of the nuclei around ²⁵⁴No, the heaviest element for which detailed spectroscopic data are available. The deformation, rotational response, pairing correlations, quasiparticle, and other properties of these nuclei have been studied with different parametrizations for the effective mean-field Lagrangian. Pairing correlations are taken into account by a finite range two-body force of Gogny type. While the deformation properties are well reproduced, the calculations reveal some deficiencies of the effective forces both in the particle-hole and particle-particle channels. For the first time, the quasiparticle spectra of odd deformed nuclei have been calculated in a fully self-consistent way within the framework of the relativistic mean field (RMF) theory. The energies of the spherical subshells, from which active deformed states of these nuclei emerge, are described with an accuracy better than 0.5 MeV for most of the subshells with the NL1 and NL3 parametrizations. However, for a few subshells the discrepancies reach 0.7¿1.0 MeV. In very heavy systems, where the level density is high, this level of accuracy is not sufficient for reliable predictions of the location of relatively small deformed shell gaps. The calculated moments of inertia reveal only small sensitivity to the RMF parametrization and, thus, to differences in the single-particle structure. However, in contrast to lighter systems, it is necessary to decrease the strength of the D1S Gogny force in the pairing channel in order to reproduce the moments of inertia.

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Das Antiphospholipidsyndrom (APS), mit den typischen klinischen Manifestationen von rezidivierenden Thrombosen und Aborten, wird laborchemisch durch das Vorkommen von Antiphospholipidantikörpern (aPL) definiert. Das Krankheitsbild gewinnt in letzter Zeit als mögliches Bindeglied zwischen Autoimmunität und Atherosklerose zunehmend an Bedeutung. Sowohl aPL, als auch oxidierten low-density Lipoproteinen (oxLDL) und deren Antikörpern (Anti-oxLDL) wird eine pathogenetische Bedeutung in der Atherogenese zugesprochen. In unserer Studie verglichen wir die Serumspiegel von oxLDL und AntioxLDL bei APS-Patienten (20 Patienten primäres/14 sekundäres APS) und nonAPS-Patienten (24 phänotypisch gesunde Kontrollpersonen und 12 Patienten mit Systemischem Lupus erythematodes/ SLE/) und untersuchten Assoziationen dieser Parameter zur Intima-Media-Dicke (IMT), einem klinischen Surrogatparameter der Atherosklerose.
SLE-Patienten mit und ohne APS wiesen signifikant erhöhte Anti-oxLDL-Spiegel im Vergleich zur Kontrollgruppe auf (p = 0,038 bzw. p = 0,007). Dahingegen unterschieden sich die oxLDL-Konzentrationen nicht signifikant bei Kontrollen und Patienten. DieAntioxLDL- Spiegel korrelierten signifikant mit Anticardiolipin- (p = 0,002) und 2-Glykoprotein-IAntikörpern (p < 0,048), jeweils vomIgG-Isotyp. Nur SLE-Patienten ohne APS wiesen eine signifikant erhöhte Produktion reaktiver Sauerstoffspezies (ROS) als Zeichen eines proatherogenen oxidativen Stresses in der Zirkulation auf (p < 0,002). Sowohl die zirkulierenden oxLDL- als auch die AntioxLDL- Spiegel wiesen keine Assoziation zur Atherosklerose, gemessen an der IMT, bei den Patientengruppen auf. Zusammenfassend ergibt sich aus unseren experimentellen Daten kein Hinweis darauf, dass bei APS-Patienten eine durch oxidativen Stress beschleunigte Atherosklerose auftritt.

Adhesion of phagocytes to endothelial cells constitutes a crucial step in atherogenesis. Oxidized low density lipoproteins (LDL) are supposed to facilitate the adhesion process. We investigated the molecular mechanisms by which mildly and extensively hypochlorite-oxidized LDL force adhesion of murine macrophages and human neutrophils to human umbilical venous endothelial cells. After 1 h of co-incubation of macrophages, endothelial cells, and lipoproteins adhesion significantly increased to 160 ± 13 % (S.E.M., n=5) in the presence of mildly oxidized lipoprotein, and 210 ± 11 % (S.E.M., n=5) in the presence of extensively oxidized lipoprotein. Similar results were obtained with neutrophils. CD36 antibody (FA6-152) significantly reduced adhesion to 102 ± 7 % (S.E.M., n=5) using mildly oxidized low density lipoprotein and to 179 ± 16 % (S.E.M., n=5) using extensively oxidized low density lipoprotein. Native high density lipoprotein and to a lesser extent methionine-oxidized high density lipoprotein significantly counteracted the effects of low density lipoprotein. Prior incubation of endothelial cells with modified lipoproteins followed by their removal and subsequent incubation with macrophages or neutrophils resulted in only minor changes of adhesion. This suggests that the direct contact of low density lipoprotein with phagocytes followed by activation of a respiratory burst with release of reactive oxygen species facilitates the adhesion process. Accordingly, the addition of antioxidants (superoxide dismutase and catalase) to the co-incubation medium was followed by a significant decrease in phagocyte adhesion. It is concluded that oxidized low density lipoprotein-induced respiratory burst activation of phagocytes with subsequent release of oxidants constitutes a crucial step in promoting the adhesion of phagocytes to endothelial cells.

Hypochlorite-oxidized low-density lipoprotein (oxLDL) possesses a substantial proinflammatory potential by modulating respiratory burst activities of polymorphonuclear neutrophils (PMN). As evaluated by luminol-amplified chemiluminescence (CL) incubation of 10⁶ PMN/ml with 70 nM oxLDL was followed by substantial induction of neutrophil oxidant (ROS) generation. We evaluated the inhibitory capacity of high-density lipoprotein (HDL) and its lipid and protein constituents against the activating effects of oxLDL. At a HDL or apolipoprotein AI/LDL protein ratio of 1.0, native HDL decreased the respiratory burst activation by 64 %, followed by trypsinized HDL (57 %) and native apoAI (43 %). The inhibitory effects of native HDL did not require prior incubation with PMN or with oxLDL suggesting an instantaneously acting protective mechanism in the minute range. OxLDL modulated ROS production not only of resting PMN but also that of activated PMN, as indicated by a 14-fold increase in FMLP-stimulated CL response and a 50 % decreased in zymosan-mediated CL answer. HDL itself did not protect PMN from activation by FMLP and zymosan. However, it clearly reduced effects of oxLDL on FMLP-activation and slightly counteracted the oxLDL-mediated decrease in zymosan-induced ROS generation. Taken together, these findings may offer new insight into atheroprotective mechanisms of HDL.

Oxidative modification of proteins can interfere with critical cellular functions, and is widely regarded as a crucial event in the pathogenesis of various diseases ranging from rheumatoid arthritis to atherosclerosis and cancer. In this line, a new GC-MS methodology using N(O)-ethoxycarbonyl trifluoroethyl amino acid esters (ECEE-F-3) for rapid and sensitive determination of 3-chlorotyrosine, 5-hydroxy-2-aminovaleric acid (HAVA), and 6-hydroxy-2-aminocaproic acid (HACA) in proteins has been developed. 3-Chlorotyrosine is a highly specific marker of myeloperoxidase catalyzed protein oxidation, whereas gamma-glutamyl semialdehyde (gammaGSA) and alpha-aminoadipyl semialdehyde (alphaASA), which by reduction form HAVA and HACA, respectively, are specifically formed by metal catalyzed oxidation processes. ECEE-F3 derivatives are formed by the unlabored reaction of amino acids with ethylchloroformate plus trifluoroethanol plus pyridine. The key steps of the methodology employed are (i) enzymatic hydrolysis of target proteins to prevent decomposition of oxidation products during hydrolysis and (ii) an uniquely rapid derivatization of amino acids completing sample preparation for GC within a few minutes in aqueous solution at room temperature. The use of these stable products of protein amino acid side chain oxidation as potential markers for assessing oxidative damage in LDL apoB-100 recovered from human aortic vascular lesions is demonstrated. These observations provide quantitative chemical evidence for metal catalyzed oxidative processes in the human artery wall.

Summary. An alteration of low density lipoprotein (LDL) apolipoprotein (apo) B-100 structure by direct oxidative modification is an important mechanism involved in atherogenesis. There is difficulty in quantifying this type of modification because a lack of specific assays. The use of N(O,S)-ethoxycarbonyl trifluoroethyl amino acid esters for a rapid and sensitive determination of 6-hydroxy-2-aminocaproic acid (HACA), a highly specific marker of metal catalyzed protein oxidation, by using standard gas chromatography/electron impact mass spectrometry, is discussed. The derivatives are formed by the unlabored reaction of amino acids with ethylchloroformate plus trifluoroethanol plus pyridine. Femtomole levels of HACA can be reproducible measured in different LDL preparations subjected to oxidative damage in the presence of iron or copper. HACA determination compares well with the measurement of carbonyl groups that are generally accepted as a nonspecific index of protein oxidation. Thus, the method could prove to be a sensitive assay for studying specific apoB-100 modification.

Oxidative modification of low density lipoprotein (LDL) is regarded as a crucial event in athergenesis. Data concerning the role of circulating oxidized LDL (oxLDL) in the development of atherosclerosis are scarce. One reason for this is the shortage of methaods for direct assessment of metabolism of oxLDL in vivo. We reprot an improved methodology for labelling of both native LDL (nLDL) and oxLDL with fluorine-18 (¹⁸F) by N-succinimidyl 4-[¹⁸F]fluorobenzoate ([¹⁸F]SFB) and the use of LDL-[¹⁸]FB-conjugates in dynamic PET studies in Wistar rats. For labelling experiments, pools of chemically well characterized human nLDL and oxLDL, respectively, were used. Preparation of [¹⁸F]SFB was achieved within 40 min with radiochemical yields of 50±5% and purity of >95% using O-(N-succinimidyl)-N-N,N´,N´-tetramethyluronium tetrafluoroborate (TSTU) as activating reagent. LDL labelling with [¹⁸F]SFB resulted in radiochemical yields of 30±10%. The method was evaluated with respect to uptake of FB-conjugated nLDL in HepG2 cells and of FB-conjugated oxLDL in primary human macrophages, respectively. Biodistribution studies revealed high in vivo stability for the LDL-[¹⁸F]FB conjugates. The metabolic fate of LDL-[¹⁸F]FB conjugates in vivo was delineated by PET using a dedicated small animal tomograph (microPET; spatial resolution of 2 mm). In conclusion, [¹⁸F]SFB-labelling of LDL and the use of PET provide a valuable tool for assessment of metabolism of nLDL and oxLDL in vivo.

We consider the flow of an electrically conducting fluid around a sphere with some internal source of alternating magnetic field. The resulting electromagnetic forces of this inductive scheme lead to a thrust of the sphere and a changed drag coefficient which balance each other in the self-moved regime. Allowing for a free choice of physically meaningful field distributions, the inverse problem is addressed of looking for such magnetic fields which result in a low drag. Without claiming to have found a global minimum, we present some examples of electromagnetic forces providing strong reductions of the sphere drag. Numerical results up to Re=1000 are given, the corresponding modifications of surface pressure and vorticity are discussed. The energetic balance is not yet analysed as it requires to consider the coupled hydrodynamic and electromagnetic problems.