Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Highly symmetric arranged ZnO nanowire arrays are produced by laser interference lithography and chemical vapor transport process. The resulting ZnO nanowires show a narrow diameter distribution as well as a uniform spacing. Liquid-phase assistant vapor-solid mechanism is proposed for one-to-one synthesized ZnO nanowires growth. Scanning cathodoluminescence microscopy is used to characterize the optical properties.

Since the discovery of uranium, the impact of actinides has dramatically increased in our every-day life, firstly through the naturally occurring elements Th, Pa and U, (that were first used mainly as color pigments or cancer-treatment) and secondly through the artificial ones, produced along all steps of the nuclear power process (mostly Pu, Np, Am and Cm). Considering the huge problem of providing safe and sustainable energy in order to supply the fast increasing world demand in the near future, nuclear power will be one of the major concerns of this century. It is therefore of tremendous importance to tackle associated problems, that are related either to the remediation of old mining and milling sites, to the control of fissile products throughout the nuclear power production cycle and finally to the long term disposal of generated wastes. In this field and according to the public concern, quantification and quality assurance are of outmost importance. However, owing to the radioactive properties of actinides, these objectives are liable to even more difficulties than for other, stable elements. Other problems that need to be overcome are mainly related to the complexity of the chemical behaviour of actinides, that display numerous oxidation states, a large tendency to hydrolysis, and, for the short-lived ones (mostly, elements above Cm), handling problems. Furthermore, the range of concentration of these elements which can be found in the environment (as a consequence of mining, milling, nuclear bomb testing and accidents, mainly) limit the use of speciation techniques, that need to be safe, fast, reliable and very sensitive. Fortunately enough, some major actinides display luminescence properties, which can be used for the determination of complex stabilities as well as for the direct detection of the formed species in different environments in a wide concentration range, from ultra traces to chemical usable concentrations up to reprocessing conditions.
In this chapter, we will present an overview of the field of actinide luminescence analysis (Time-Resolved Laser Induced Fluorescence Spectroscopy, TRLIFS), focussing on applications related to the nuclear fuel cycle, from reprocessing to validation of nuclear waste repositories. However, it is not possible to include all publications in this contribution and a personally influenced selection has been made, that highlights applications in solution. Also it should be mentioned that the contribution of laser-induced spectroscopy to actinide speciation has been reviewed recently in several publications [1-6]. Owing to the limited place allocated, the reader is also referred to books on basic actinide chemistry [7] and reviews [8].

The title compound, C₂₁H₃₆BrO₅ReS₂, was synthesized and characterized as non-radioactive surrogate of a novel Tc-containing fatty acid derivative prepared according to the tricarbonyl/dithioether design with the objective to develop new Tc-based radio-pharmaceuticals für the non-invasive diagnosis of myocardial metabolism. The Re chelate contains the metal core in the oxidation state +1 and is attached to the terminal position of a fatty acid. The complex formation was accomplished by ligand exchange reaction using [NBu₄]₂[Re(CO)₃Br₃] as starting material

The experiment is aimed to characterize the nature of the material damage in a mechanically loaded specimen of a ductile aluminium alloy in order to get the input needed for damage mechanics based evaluation of structural components. In the first step the as-received and the homo¬geneously deformed conditions of the aluminium alloy shall be investigated by SANS. The objective is to identify and separate the main features responsible for the measured scattering effects and especially to find out the nature of the additional defects introduced by the mechanical loading procedure.

In order to investigate the possibility to create and stabilize a DMS behavior in the (Ga,Fe)N-system, p-doped GaN was implanted with 200 keV 57Fe+ ions at 350°C, RT and -30°C with fluences Φ = 1*10^16 cm^-2 - 1.6*10^17 cm^-2. Magnetic electronic and structural properties of as implanted as well as subcequently annealed samples were investigated by AES, CEMS, TEM, SQUID and XRD techniques.

Flooding abandoned uranium mines normally involves mixing of shallow groundwater with acidic, iron-rich pore water. A simulation experiment in mesocosm scale showed that nanoparticles of 2-line ferrihydrite formed and took up about 97% of total uranium between pH 5-7. The molecular topology of ferrihydrite and the U(VI) surface complex structure were investigated by EXAFS and ATR-FTIR spectroscopy. The contribution of carbonate to surface sorption was studied by preparing reference samples at varied CO2 partial pressure and pH conditions, and by applying iterative target transformation factor analysis on EXAFS spectra. Surface sorbed UO22+ delayed the thermally induced aqueous phase transformation of ferrihydrite to hematite, shown by Mössbauer spec-troscopy. Desorption of U(VI) from the solid phase was less effective for original colloid and sediment samples from a uranium mine and for aged reference samples than for fresh U(VI)-ferrihydrite precipitates, suggesting that part of the uranium was fixed within the mineral lattice.

Fragment energy spectra of neutron-deficient isotopes are significantly more energetic than those of neutron-rich isotopes of the same element. This trend is well beyond what can be expected for the bulk multi-fragmentation of an equilibrated system. It can be explained, however, if some of these fragments are emitted earlier through the surface of the system while it is expanding and cooling.

Ziel/Aim:

The extradomain B of fibronectin (ED-B-FN) is an angiogenesis-associated marker of the tumoral extracellular matrix, which can be targeted by the human recombinant, high-affinity antibody fragment L19-SIP. By I-131-labeling L19-SIP becomes a radiotherapeutic agent, which is effective in several tumor models. In this study indirect and direct radioiodination methods were compared with regard to tumor uptake and in vivo stability of the obtained L19-SIP derivatives.

Methodik/Methods:

L-19-SIP was directly radioiodinate using the Iodogen methods, as well as indirectly by conjugation of I-125-Boltron Hunter reagent (I-125-BH) or I-125-succinimidylbenzoate (I-125-SIB). Pharmacokinetics and tumor accumulation of the iodinated L19-SIP derivatives were investigated in tumor bearing mice up to 72 h (F9, murine teratocarcinoma and U251, human glioblastoma) with subsequent dosimetry for the therapeutic isotope I-131.

Ergebnisse/Results:

In biodistribution studies the directly iodinated L-19-SIP showed increasing thyroid uptake over time due to dehalogenation of I-125 in vivo, whereas the indirectly iodinated L19-SIP showed improved stability of the iodine label. I-125-BH-L19-SIP and I-125-SIB-L19-SIP exhibited longer retenation in the tumor compared to I-125-L19-SIP. Tumor-to-blood ratios were significantly higher for the indirectly labelled compounds at later time points. It was calculated that activities of 48 MBq I-131-L19-SIP (Iodogen), 47 MBq I-131-BH-L19-SIP and 64 MBq I-131-SIB-L19-SIP could be injected per mouse before reaching the maximum tolerated dose of 2.5 Gy in the bone marrow, and would lead to doses of 42 Gy, 40 Gy and 144 Gy in 100 mg F9-tumors, respectively. The calculated tumor doses were comparable in both tumor models.

Schlussfolgerungen/Conclusions:

I-125-SIB-L19-SIP shows considerably higher in vivo stability and longer tumor retention compared to directly labelled L19-SIP leading to a substantially higher tumor dose.

In ruhendem Wasser emporsteigende Luftblasen werden oft durch zweiachsige Ellipsoide beschrieben, ohne dass dies näher begründet wird. Eine Rechtfertigung dafür soll dadurch gefunden werden, dass eine reale Blase erst als dreiachsiges Ellipsoid modelliert und dann geprüft wird, ob sie zu einem zweiachsigen Ellipsoid vereinfacht werden kann. Für diesen Zweck erfolgen zunächst drei orthogonale optische Projektionen der Blase. Diese ebenen Abbildungen werden durch drei Ellipsen beschrieben, aus denen anschließend das gesuchte dreiachsige Ellipsoid berechnet wird.

Bubbles ascending in resting water are often described without further explanation using biaxial ellipsoids. Justification of this practice can be found via primarily modelling a real bubble as triaxial ellipsoid and subsequently checking if it can be reduced to a biaxial ellipsoid. For this purpose three orthogonal optical projections are produced at first. These plane maps are expressed by three ellipses from which in a second step the required triaxial ellipsoid is calculated.

A recent Letter [R. Hollerbach and G. Rüdiger, Phys. Rev. Lett. 95, 124501 (2005)] has shown that the threshold for the onset of the magnetorotational instability in a Taylor-Couette flow is dramatically reduced if both axial and azimuthal magnetic fields are imposed. In agreement with this prediction, we present results of a Taylor-Couette experiment with the liquid metal alloy GaInSn, showing evidence for the existence of the magnetorotational instability at Reynolds numbers of order 1000 and Hartmann numbers of order 10.

Worldwide, semiconductor spin transfer electronics (spintronics) is of strongly increasing interest. One intention is the use of the spin for data storage to increase the possible storage density, another one is to overcome the fundamental limits of the computing speed. To realize such devices polarized carriers can be injected from a ferromagnetic metal into a diluted magnetic semiconductor (DMS). DMS are “conventional” semiconductors doped with transition metal or rare-earth ions which are diluted within the host matrix and ferromagnetically aligned via an indirect magnetic coupling. For applications, it is important that such DMS could be used at practical temperatures, i.e. above room temperature, and that they can base upon an already existing materials technology.

From theory, wide band gap semiconductors like GaN, ZnO, InN, AlP or SiC are the most promising candidates. Doping could be performed by Mn, V, Fe, Co or Ni with concentrations in the range of some %. The magnetism may originate either from a more or less random alloy in which the doping ion substitutes a host atom as interstitial or from small clusters. In the case of 57Fe as doping ion, Mössbauer spectroscopy can be used to investigate how it is built in the host matrix. The 57Fe ion acts both as doping and probe.

In the present study ion implantation is used as doping technique. 57Fe ions were implanted into GaN, ZnO and SiC. The produced layers were investigated by Mössbauer spectroscopy however this method is insufficient for a full characterization. Therefore, samples were studied by transmission electron microscopy, Auger electron spectroscopy, Zero-field-cooled/field-cooled SQUID measurements and by X-ray diffraction too. Depending on the implantation temperature and the annealing conditions diluted magnetic semiconductors could be obtained.

The broad application of low energy X-rays below about 50 keV in radiation therapy and diagnostics and especially in mammography substantiates the precise determination of their relative biological effectiveness (RBE). A quality factor of 1 is stated for photons of all energies in the ICRP Recommendations. However, the RBE of low-energy X-rays compared to high-energy photons was found to be dependent on photon energy, cell line and endpoints studied, hence varying from less than 1 up to about 4. In the present study, the human mammary epithelial cell line MCF-12A has been chosen due to the implementation of the results in the estimation of risk from mammography procedures. The RBE of 25 kV X-rays (W anode, 0.3 mm Al filter) relative to 200 kV X-rays (W anode, 0.5 mm Cu filter) was determined for clonogenic survival and micronuclei induction. The RBE for clonogenic survival was found to be significantly higher than 1 for surviving fractions in the range between 0.005 and 0.2. The RBE decreased with increasing survival, with an RBE0.1 at 10 % survival of 1.13 ± 0.03. The effectiveness of soft X-rays for micronuclei induction was found to be 1.40 ± 0.07 for the fraction of binuclear cells (BNC) with micronuclei (MN) and 1.44 ± 0.17 for the number of MN per BNC. In contrast, the RBE determined from the number of MN per MN-bearing BNC was found to be 1.08 ± 0.32. This indicates that the effectiveness of 25 kV X-rays results from an increase in the number of damaged cells, which, however, do not have higher number of micronuclei per cell.

X-ray absorption, resonant x-ray emission, and x-ray photoelectron spectra of the valence band
and core levels have been measured for LixCoO2 (0.6 < x < 1.0). Resonant O K x-ray emission
spectra of LiCoO2 showed localized excitonic states due to a dd transition between unoccupied and
occupied Co 3d states. On the base of measurements of Co 3s x-ray photoelectron and Co 2p and
O 1s x-ray absorption spectra it was established that in defective cobaltites the electronic holes are
localized mainly in O 2p states. Metallic character of conductivity of defective cobaltites LixCoO2 is
confirmed by a combination of x-ray photoelectron and O 1s x-ray absorption spectra. An evidence
of phase separation in LixCoO2 has been found.

In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable. Since the magnetic properties of magnetic multilayers depend sensitively on the mutual interfaces a modification of these interfaces by light ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1]. As an example it will be demonstrated that ion irradiation in an applied magnetic field allows to set the uniaxial anisotropy direction on a micrometer scale in the case of soft magnetic alloys [2]. However, in order to modify the structural and magnetic properties not only light ion irradiation but also ion implantation doping can be used. If, for example, Cr is implanted in thin Permalloy films the Curie temperature and the saturation magnetization can be reduced, which consecutively leads to a decrease of the magnetic anisotropy and an increase of the magnetic damping behavior [3]. The formation of magnetically dead layers at the interfaces to buffer and cap layers can be investigated using Ni implantation [4].
In an alternative route to design magnetic properties periodically modulated substrates are employed. These modulated substrates are created by means of low energy ion erosion. A ripple structure with a typical periodicity of 30 – 50 nm and a ripple height of about 2 nm is created on a Si substrate. Subsequently deposited Permalloy films exhibit a uniaxial anisotropy which is about a factor of 20 larger than conventionally prepared films. If exchange bias bilayers are deposited the interplay between the unidirectional and the ripple-induced uniaxial anisotropy contributions can be investigated.

1. J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
2. J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
3. J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord, L. Schultz, R. Mattheis, Phys. Rev. B 73, 184410 (2006).
4. J. Fassbender, J. McCord, Appl. Phys. Lett. in press (2006).

Die Veranstaltung widmete sich mit der Borverdünnung in Druckwasserreaktoren bzw. mit der Verstopfung der Sumpfansaugsiebe durch freigesetztes Isolationsmaterial schwerpunktmäßig zwei Themen der Reaktorsicherheit, die auch in aktuellen Aufsichtsverfahren eine Rolle spielen. Eingebettet in den internationalen Kontext wollten die Veranstalter die sicherheitstechnische Bedeutung dieser Themen für die deutschen Anlagen beleuchten und die Auswirkungen auf die zu erbringenden Sicherheitsnachweise und den Anlagenbetrieb darstellen. Dabei kamen Gutachter, Vertreter der Forschung, Hersteller und Betreiber gleichermaßen zu Wort.
Der Fachtag sollte den Teilnehmern aber insbesondere vermitteln, welche Beiträge die privat und öffentlich finanzierte Reaktorsicherheitsforschung zur Aufklärung der jeweiligen Ereignisabläufe und ihrer sicherheitstechnischen Bedeutung geleistet hat.
In diesem Forschungskontext spielen, auch international, die Methoden der so genannten Computational Fluid Dynamics (CFD) eine zunehmende Rolle. Deshalb widmete sich eine Sitzung den Grundlagen, Möglichkeiten und Grenzen von CFD-Methoden.
Dabei wurden u. a. Anwendungen zur Borvermischung und zum Verhalten von Mineralwolle im Sumpf präsentiert.

Magnetic fields of planets, stars, and galaxies result from self-excitation in moving electro-conducting fluids, also known as dynamo effect. This phenomenon was recently experimentally confirmed in the Riga dynamo experiment, consisting of a helical motion of sodium in a long pipe followed by a straight back-flow in a surrounding annular passage, which provided adequate conditions for magnetic field self-excitation. We report here on the first attempt to simulate computationally the Riga experiment. The velocity and turbulence fields are modelled by a finite-volume Navier-Stokes solver using a Reynolds-Averaged-Navier-Stokes (RANS) turbulence model. The magnetic field is computed by an Adams-Bashforth finite-difference solver. The coupling of the two computational codes, although performed sequentially, provides an improved understanding of the interaction between the fluid velocity and magnetic fields in the saturation regime of the Riga dynamo experiment under realistic working conditions.

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Preface
The Forschungszentrum Rossendorf (FZR) at Dresden is a multidisciplinary research center within the Wissenschafts-Gemeinschaft G. W. Leibniz (WGL), one of the German agencies for extra-university research. The center is active in investigations on the structure of matter as well as in the life sciences and in environmental research. The Institute of Nuclear and Hadron Physics (IKH) within the FZR avails for its research the coupling of radiation to matter in subatomic dimensions as well as to tissue, to cells, and to their components. Its research in the field of Subatomic Physics is part of the FZR-program Structure of Matter and its investigations concerning the interaction of Biostructures and Radiation contribute to the bf Life Science program of the FZR. In this field the IKH exploits possibilities for transfer and introduction of experimental and theoretical techniques from particle and nuclear physics to projects in radiobiology and biophysics. Much of this kind of interdisciplinary transfer is connected to the Radiation Source ELBE at the FZR. With its superconducting accelerator for relativistic electrons this large installation provides photons in the wide wavelength range from fm to mm - i.e. bremsstrahlung for the investigation of photonuclear processes, hard X-rays for radiobiological and other studies and infrared light for research on the structural dynamics of biomolecules. The investigation of radiation-induced processes not only dominates the projects in nuclear astrophysics as pursued at ELBE, it also is a central theme of the experimental and theoretical research performed by the IKH in close connection to the heavy ion synchrotron SIS and the upcoming FAIR facility at Darmstadt. ELBE also will deliver compact bunches of secondary neutrons and fission fragments; both offer new possibilities in laboratory studies related to the cosmic breeding of the chemical elements thus complementing the astrophysics-motivated studies with bremsstrahlung photons...

The experimental and the numerically studies were applied to a non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated. The X-Ray cone beam tomography measurements were taken at five different stirrer speeds with thresholds of 50 rpm starting from 1000 rpm at which the gas inducement occurs for the given operating conditions.
The cone-beam type X-Ray tomography is a potential method to measure the phase-distributions in stirred vessels. Three-dimensional information can be gathered within only one tomographic scan. The reconstruction of a rotationally symmetric distribution-field is even possible from a single radiographic image. Such an experimental approach was carefully examined and applied to obtain the quantitative measurements of gas-fraction profiles in a stirred tank reactor. Additionally, a moving slit technique was adapted to estimate the inherent scattered radiation offset, which emerges while un-collimated x-rays penetrate the fluid-filled tank. An additional reference measurement was introduced and used to remove beam hardening artefacts. An absolute quantification was possible due to the knowledge of the ratio of the fluids and the reference-materials x-ray absorption coefficients. Phantom-measurements inside the vessel were conducted for performance evaluation. A systematic measurement error of less then 1.5% absolute gas fraction for local gas fractions up to 30% was achieved while maintaining a spatial resolution of better then 1 mm.
The computational fluid dynamics analyses of the stirred tank reactor were performed in 3D with CFX 10.0 numerical software. Five steady state simulations, at stirrer speeds corresponding to the ones at which the measurements were performed, were conducted to be compared with the experimental observations. The tetrahedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer described by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid and the liquid phase as continuous fluid. Different turbulence models and their suitability were considered in the simulations.

Over the last century two-phase flow mixing, engineered to take place in mechani-cally agitated tank reactors, has become one of the most common operations in the industry. Traditionally the gas-phase is supplied via a single pipe or a ring sparger mounted beneath the rotating impeller. The gas-inducing impellers provide an alter-native gas injection, in which case the gas is fed directly in the stirrer region.
A non-baffled laboratory-scale tank reactor mechanically agitated by a gas inducing turbine was experimentally and numerically studied. Above a certain impeller speed, at the investigated experimental conditions, the stirrer becomes able to induce gas and consequently disperse it into the bulk liquid phase. The two-phase system under examination comprises air as gas phase into isopropanol as liquid phase at room temperature. The gas-phase distribution was assessed at five different impeller speeds starting from 1000 rpm, at which gas inducement occurs.
The cone-beam type X-Ray tomography, which can provide three-dimensional infor-mation on the gas-phase distribution, was employed to experimentally study the two-phase system. The reconstruction of a rotationally symmetric distribution-field is pos-sible from a single radiographic image. Such an experimental approach was applied to obtain the quantitative measurements of gas-fraction profiles. Additionally, a mov-ing slit technique was adapted to estimate the inherent scattered radiation offset, which emerges while un-collimated X-rays penetrate the fluid-filled tank. An addi-tional reference measurement was introduced and used to remove beam hardening artefacts. An absolute quantification was possible due to the knowledge of the ratio of the fluids and the reference-materials X-ray absorption coefficients. Phantom-measurements inside the vessel were conducted for performance evaluation.
The computational fluid dynamics analyses of the stirred tank reactor were performed with CFX 10.0 numerical software. The numerical predictions at 1000 rpm used pre-vious simulation results at lower impeller speed as an initial guess. Starting from 1000rpm, five simulations were performed at stirrer speed thresholds of 50 rpm to be compared with X-Ray cone beam tomography experimental observations. The tetra-hedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer de-scribed by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid with a mean diame-ter of 1 mm and the liquid phase as continuous fluid.
The results demonstrate the X-Ray cone beam tomography and the CFD capabilities to capture the two-phase flow in detail, which can provide valuable information for the industry. In particular the special gas phase distribution can have a crucial impact on the reactor performance. This can be in detail predicted by the computational fluid dynamic software, which can prove to be an essential tool for the reactor optimisation and scale-up.

This study is concerned with a conceptual design of a new contactless AC induction flowmeter for liquid metal flows. The basic idea is to make use of the fact that the fluid flow disturbs not only the amplitude but also the phase distribution of an applied AC magnetic field. The goal is to consider the possibility of using the fluid flow induced phase shift of an AC magnetic field to measure the flow rate. In order to figure out the basic characteristics of such a flowmeter we consider several simple theoretical models where the liquid flow is approximated by a solid body motion. Based on these ideas a laboratory model of such a flowmeter has been built and tested at a liquid metal flow.

Hyperon production in the threshold region was studied in the reaction pp→K+Λp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at three different beam momenta pbeam=2.59, 2.68 and 2.85 GeV/c (corresponding to excess energies of var epsilon=85, 115 and 171 MeV). Total cross-sections were deduced to be 7.4±0.5 μb, 8.6±0.6 μb and 16.5±0.4 μb, respectively. Differential observables including Dalitz plots were obtained. From the investigation of the Dalitz plot at pbeam=2.85 GeV/c a dominant contribution of the Nasterisk operator(1650)-resonance to the reaction mechanism was found. In addition the pΛ-final-state interaction turned out to have a significant influence on the Dalitz plot distribution even 171 MeV above threshold.

The complexation of uranium(VI) with the amino acid L-glycine and L-cysteine has been investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and UV-vis spectroscopy at low pH range. The identified 1:1 and 1:2 uranyl-L-glycine complexes fluoresce and have similar absorbance properties. In contrast to the glycine system, uranyl forms with L-cysteine two different non-fluorescent 1:1 complexes showing individual absorbance properties under the given experimental conditions.The corresponding complex formation constants were calculated using the spectroscopic data.

Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids, especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications. In the range of small or moderate void fractions the UDV technique delivers both the bubble and the liquid velocity.
In our experiments we investigated the consequences of an application of both DC and AC magnetic fields on the velocity field of bubble plumes. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. The application of a transverse field leads not only to a general damping of the flow, but also favours the occurrence of vortices aligned parallel to the magnetic field direction. AC magnetic fields can be applied to generate flow structures being different from the recirculating flow known from classical bubble plumes. A tailoring of the flow using magnetic fields obviously allows a control of the heat and mass transfer in bubble plumes.

Recently published excitation functions in proton-proton (pp) elastic scattering observables in the laboratory energy range 0.5-2.5GeV provide an excellent data base to establish firm upper limits on the elasticities ηel = Γel/Γtot of possible isovector resonant contributions to the nucleon-nucleon (NN) system. Such contributions have been predicted to arise from dibaryonic states, with c.m. masses between 2.1-2.9GeV/c2, but have not been confirmed experimentally. A method to determine quantitatively the maximum value of ηel compatible with experimental data is presented. We use energy-dependent phase shift fits to the pp data base to model the non-resonant interaction. Based upon the differential cross-section data measured by the EDDA Collaboration an unbiased statistical test is constructed to obtain upper limits on ηel, that exclude larger values with a 99% confidence level. Results in the c.m. mass range 2.05-2.85GeV/c2 and total widths of 10-100MeV/c2 in the partial waves 1S0, 1D2, 3P0, 3P1, and 3F3 are presented and discussed.

The EDDA-detector at the cooler-synchrotron COSY/Jülich has been operated with an internal CH2 fiber target to measure proton–proton elastic scattering differential cross-sections. For data analysis knowledge of beam parameters, like position, width and angle, are indispensable. We have developed a method to obtain these values with high precision from the azimuthal and polar angles of the ejectiles only, by exploiting the coplanarity of the two final-state protons with the beam and the kinematic correlation. The formalism is described and results for beam parameters obtained during beam acceleration are given.

Thin polypropylene fibers have been used for internal experiments in storage rings as an option for hydrogen targets. The change of the hydrogen content due to the radiation dose applied by the circulating proton beam has been investigated in the range 1 × 106–2 × 108 Gy at beam momenta of 1.5–3 GeV/c by comparing the elastic pp-scattering yield to that from inelastic p-carbon reactions. It is found that the loss of hydrogen as a function of applied dose receives contributions from a fast and a slow component.

The ultrasound Doppler velocimetry (UDV) was validated for its capability to measure both gas and liquid velocities in transparent as well as opaque two-phase flows. A special threshold method has been tested successfully for processing of UDV data acquired from bubble-driven flows. Our experimental work presented here is focused on the influence of a transverse static magnetic field on a bubble plume in a cylindrical vessel. The liquid flow field has been measured by means of the ultrasound Doppler velocimetry. Despite the well-known damping effect of a DC magnetic field, it was observed, that the application of a moderate magnetic field may also cause an intensification of the liquid recirculation. The global flow field was found to be dominated by quasi-two-dimensional large scale vortex structures, whose axes are parallel aligned with the magnetic field direction. Therefore, the time-averaged flow field shows a distinct anisotropy. Local recirculating zones are found in the meridional plane perpendicular to the magnetic field lines, while velocity distributions become more uniform in the other plane parallel to the magnetic field.

A secondary emission monitor and an auxiliary Faraday cup necessary for calibration purposes have been constructed and installed at the radiation physics beam line of the electron accelerator ELBE. These devices are to be applied for the precise beam-current monitoring in measurements of channeling radiation. Miscellaneous simulations of underlying interactions of the beam electrons with the target material as well as with the materials of the monitor equipment have been performed to optimize the design and to evaluate possible correction factors inherent to transmission monitoring.

The Riga dynamo experiment demonstrates that a strong enough and appropriately directed flow of a fluid electroconductor generates a magnetic field very similar as the Earth and other celestial bodies do. Two 100 kW motors are driving a propeller which forces molten sodium to circulate inside an annular vessel, a part of which is located in the basement of the sodium lab. The sodium flow is directed by two thin coaxial electroconducting cylindrical partition walls. In the central channel sodium is swirling down from the propeller. In the coaxial counter-flow channel the flow is raising straight up to the propeller. In an outer part of the vessel the sodium is at rest, it serves only for better electric boundary conditions. Depending on sodium temperature at a propeller speed of 1800-2000 rpm (flow-rate about 0.6 qm/s) the zero state for the magnetic field is becoming unstable and a field appears seemingly from nothing. The magnetic field values are recovered from coil voltage records by means of Fast Fourier processing. For finer spectral resolution two small coils were inserted alternately in a narrow channel tip penetrating deep inside the central flow. Examples for recorded signals and FFT processed fields are presented.

The spectrum of the spherically symmetric α²-dynamo is studied in the case of idealized boundary conditions. Starting from the exact analytical solutions of models with constant α-profiles a perturbation theory and a Galerkin technique are developed in a Krein-space approach. With the help of these tools a very pronounced α-resonance pattern is found in the deformations of the spectral mesh as well as in the unfolding of the diabolical points located at the nodes of this mesh. Non-oscillatory as well as oscillatory dynamo regimes are obtained. A Fourier component based estimation technique is developed for obtaining the critical α-profiles at which the eigenvalues enter the right spectral half-plane with non-vanishing imaginary components (at which overcritical oscillatory dynamo regimes form). Finally, Fréchet derivative (gradient) based methods are developed, suitable for further numerical investigations of Krein-space related setups like MHD α²-dynamos or models of PT-symmetric quantum mechanics.

The talk consists of two parts.

The results reported in the first part concern some unexpected properties of the spectrum of the α²-dynamo operator. In a work from February 2006 we investigated the unfolding of diabolical points in the spectrum of a dynamo operator with idealized boundary conditions (BCs). Similar to the Hamiltonians of PT-symmetric Quantum Mechanics this operator is selfadjoint in a Krein space. For constant α-profiles α₀ its spectrum λ[α₀] forms a mesh-like structure in the (α₀,Re λ)-plane with diabolical points (degeneration points of geometric and algebraic multiplicity two) at the nodes of the mesh. Under inhomogeneous perturbations of the α-profile the spectral mesh undergoes deformations which are accompanied by a resonant unfolding of the diabolical points. It was shown that each Fourier component of an α-profile α(x) induces a selective unfolding of diabolical points located on a specific parabola in the (α₀,Re λ)-plane. In recent research we extended this analysis to dynamo operators with realistic boundary conditions. Unexpectedly, it was found that the parabolas related to the resonant unfolding of diabolical points in models with idealized BCs coincide exactly with the spectral branches of dynamo operators with realistic BCs. We discuss some first aspects of the underlying mechanism responsible for this coincidence and indicate some of its possible implications.

In the second part of the talk, canonical representations of Jordan normal forms of PT-symmetric matrices are presented. These canonical representations are derived with the help of Jordan-algebra based conjugations which map Jordan blocks and Jordan chains into corresponding explicitly PT-symmetric matrices and their eigenvectors and associated vectors.

The early stage of the turbulent flow driven by a rotating magnetic field is studied via direct numerical simulations and electric potential measurements for the case of a cyindrical geometry. The numerical results show that the undisturbed flow remains stable up to the linear stability limit, wheras small perturbations may initiate nonlinear transition at subcritical Taylor numbers. The observed instabilities occur randomly as isolated pairs of Taylor-Görtler vortices, which grow from spots to long tubes until they are dissipated in the lid boundary layers. At 7.5 times the critical Taylor number, the flow is governed by large-scale 3D fluctuations and may be characterized as weakly turbulent. Taylor-Görtler vortices provide the major turbulence mechanism, apart from oscillations of the rotation axis. As the vortices tend to align with the azimuthal direction, they result in a locally two-dimensional turbulence pattern.

A method for the production of metallic fibres is proposed that uses melt extraction from a pending molten edge at the lower end of a metal sheet. Melting the sheet at its edge rather than between the two opposing branches of the inductor is achieved by a tailoring of the induction heating magnetic field. The basic feature of the configuration is the same direction of the electric current in both branches of the inductor. A proper choice of geometry, electrical conductivities of both extraction and substrate material, and the frequency of the alternating magnetic field have proven to be essential for the extraction process. Melting a platinum sheet at the edge and extraction of fibres only 20 micron in effective cross-section from a tin sheet were successfully demonstrated in model experiments.

Analysis of positron lifetime data for ZnO single crystals suggests that four well-separated lifetime levels exist between those for the bulk and the Zn vacancy. Due to the hydrothermal growth conditions of most ZnO single crystals studied so far, it is postulated that a hydrogen-defect interaction could be responsible for this finding.

Analysis of positron lifetime data for ZnO single crystals suggests that four well-separated lifetime levels exist between those for the bulk and the Zn vacancy. Due to the hydrothermal growth conditions of most ZnO single crystals studied so far, it is postulated that a hydrogen-defect interaction could be responsible for this finding.

Fabrication, handling and processing of wafers of intrinsically brittle and anisotropic single-crystalline GaAs require a high level of control of the material’s response to different loading conditions. The present work is focused on the response to hardness indentation. A short overview on the behaviour of (100) GaAs wafers in several doping conditions over a wide range of indentation loads from nano-indentation up to macro-indentation including sharp and blunt indenters is given. Special attention is paid to the pop-in effect in depth-sensing nano-indentation, to the anisotropy of indentation-induced radial crack formation and to the material’s crack resistance obtained from the indentation fracture mechanics approach. We have observed that, under certain conditions, the frequency of formation of radial cracks is essentially different for the two in-plane <110> directions. This observation is attributed to the occurrence of two different kinds of dislocations and to the lack of inversion symmetry. The effect turns out to be closely related to a left-right asymmetry in the material removal caused by wire sawing. This insight has paved the way to the optimization of the process of wire sawing of GaAs single crystals.

The state-of-the-art interpretation of physical processes during post-implantation annealing, such as defect evolution and transient-enhanced boron diffusion assumes that ion implantation produces a supersaturation of single vacancies and self-interstitials. They are supposed to be mobile and may recombine or may form immobile clusters. On the other hand, atomistic simulations demonstrated that implantation may generate not only single vacancies and self-interstitials but also more complex defects. Furthermore, recent theoretical studies showed that small interstitial clusters may be mobile as well. The present work gives an overview on the latter investigations. Due to the complex structure of the interstitial clusters, methods based on the estimation of migration barriers by considering the potential energy surface at 0 K are hardly applicable. Molecular dynamics (MD) simulations must be used to get a thorough understanding of the migration mechanisms. Ab-initio MD simulations are presently not practicable since they require a tremendous computational effort. Therefore atomic-level MD simulations are applied. The diffusivity of the small interstitial clusters, the self-diffusion coefficient per defect, and the corresponding effective migration barriers are determined. The implications of the present results for the explanation of experiments on post-implantation annealing and on room-temperature migration of implantation-induced self-interstitial defects are discussed.

An improved Stillinger-Weber-type potential for Ge is developed by adjusting the three-body parameters in such a manner that lattice parameter and cohesive energy are preserved, and the elastic constants and the melting point are reproduced satisfactorily. The dependence of the equilibrium concentration and the diffusivity of vacancies on the temperature as well as the contribution of vacancies to self-diffusion are determined by atomistic simulations and by thermodynamic considerations. The calculations are performed in the temperature range between 600 and 1100 K. The enthalpies and entropies for formation and migration are estimated. Similar investigations are performed for self-interstitials in order to check whether their contribution to self-diffusion in Ge can be neglected, as shown experimentally. Finally, the self-diffusion coefficient and the equilibrium concentration of vacancies are compared with experimental data from the literature.

To investigate the effect of dose rate and irradiation temperature on defect evolution in germanium during the ion implantation process a focused ion beam system is used. Channeling implantation of Ga is performed at two very different dose rates (3.5x1011 and 1.6x1019 cm-2s-1), at two temperatures (RT and 250 0C), and at five different doses, ranging from 5x1012 to 5x1014 cm-2. The depth distributions of Ga and of the implantation damage are determined by SIMS and micro-RBS/C, respectively. The shape of the measured range and damage profiles is strongly influenced by the dose rate and the implantation temperature. These results are explained by the competition between damage buildup and dynamic annealing during the ion bombardment. For the two implantation temperatures considered, the time scale for intracascade defect relaxation can be estimated. The measured Ga depth profiles can be reproduced by atomistic computer simulations using a phenomenological model to describe the probability that an implanted ion collides with a target atom of a damaged region in dependence on the total nuclear energy deposition per target atom.

The experimental and the numerically studies were applied to a non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated. The X-Ray cone beam tomography measurements were taken at five different stirrer speeds with thresholds of 50 rpm starting from 1000 rpm at which the gas inducement occurs for the given operating conditions.
Cone-beam type X-ray computed tomography is a potential method to measure three-dimensional phase distributions in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. However, there are considerable difficulties for accurate quantitative measurements, for instance of average gas fraction in a fluid, due to beam hardening and radiation scattering effects. We have developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate void fraction measurement.
The computational fluid dynamics analyses of the stirred tank reactor were performed in 3D with CFX 10.0 numerical software. Five steady state simulations, at stirrer speeds corresponding to the ones at which the measurements were performed, were conducted to be compared with the experimental observations. The tetrahedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer described by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid and the liquid phase as continuous fluid. Different turbulence models and their suitability were considered in the simulations.

Systematic nuclear resonance fluorescence (NRF) experiments on all nine stable (seven even-even and two odd-mass) Xe isotopes have been performed at the bremsstrahlung facility of the 4.3-MV Stuttgart Dynamitron accelerator. For the first time thin-walled, high-pressure gas targets (about 70 bar) with highly enriched target material were used in NRF experiments. Precise excitation energies, transition strengths, spins, and decay branching ratios were obtained for numerous states, most of them previously unknown.
The systematics of the observed E 1 two-phonon excitations (2+,3-) and M1 excitations to 1+ mixed-symmetry states in the even-even isotopes are discussed with respect to the new critical point symmetry E(5). The fragmentation of these fundamental dipole excitation modes in the odd-mass isotopes 129,131 Xe is shown and discussed. In the even-even nuclei several low-lying E2 excitations were observed.

Aim
Suicide gene therapy utilizing herpes simplex virus type 1 thymidine kinase gene (HSV1-tk) requires careful monitoring of the successful transfection. ¹⁸F-labelled nucleoside analoga, especially acyclic nucleosides such as 9-[(3-[¹⁸F]fluoro-1-hydroxy-2-propoxy)methyl]guanine ([¹⁸F]FHPG) and 9-[(4-[¹⁸F]fluoro)-3-hydroxymethylbutyl]guanine ([¹⁸F]FHBG) are currently used as PET tracers for monitoring and quantification of HSV1-tk expression. To improve the tracer properties, two new precursors have been synthesized by introduction of bromine in order to get the new substrates 8-bromo-9-[(3-[¹⁸F]fluoro-1-hydroxy-2-propoxy)methyl]guanine ([¹⁸F]FHBrPG) and 8-bromo-9-[(4-[¹⁸F]fluoro)-3-hydroxymethylbutyl]guanine ([¹⁸F]FHBrBG) for monitoring gene expression of HSV1-tk.

Materials and methods
The precursors as well as the nonradioactive reference compounds were prepared by introduction a p-toluenesulphonyl leaving group and trityl protecting groups into the brominated derivatives of ganciclovir and penciclovir. In a further step the precursors reacted with a K[¹⁸F]F kryptofix complex to trityl-protected intermediates. Then, the protecting groups were removed by heating in methanolic acetic acid solution. Both tracers were purified by RP HPLC separation. The identity of the tracers with the nonradioactive reference compounds was proved by HPLC. The in vitro uptake of all compounds was evaluated in a glioblastoma cell line stably transfected with the HSV1-tk gene and in the respective non-transfected cell line. The biodistribution and biokinetics of the radiotracers have been studied in mice and rats by small animal PET.

Results
The radiochemical yield of the ¹⁸F-tracers amounts to 10-15% (decay corrected) after a synthesis time of 85 95 min, the radiochemical purity was > 98%. The average specific activity was 19 GBq/µmol at the end of synthesis. Cell-uptake studies were carried out with both the brominated and the non-brominated derivatives of ganciclovir and penciclovir as standards. The relative cellular uptake (ratio HSV-tk-positive/controls) was 12.4±4.5 after 1 h of incubation with [¹⁸F]FHBrBG. In contrast, the uptake ratio of the other tracers [¹⁸F]FHBrPG (1.7±0.4), [¹⁸F]FHBG (4.0±2.3) and [¹⁸F]FHPG (1.6±0.3) was significantly lower than that of [¹⁸F]FHBrBG. Renal elimination was the main route of tracer clearance from the body, however with increasing lipophilicity of the tracers, increasing amounts were also eliminated through liver and bile into the intestine.

Conclusions
The novel tracer [¹⁸F]FHBrBG showed a superior uptake in HSV1-tk transfected cells compared to the clinically tested PET-tracer [¹⁸F]FHBG. Therefore [¹⁸F]FHBrBG appears to be a novel tracer for an improved monitoring of HSV1-tk based gene therapy approaches with PET.

Aim:

Vascular-endothelial growth factor (VEGF) is expressed in response to various stimuli like hypoxia and plays a key role in tumor angiogenesis. In this study we analyzed the influence of experimental hypoxia on the upregulation of VEGF and its receptors in primary endothelial cells and tumor cell lines. Furthermore we quantified the uptake of radiotracers in these cells in response to experimental hypoxia in vitro.
Material and Methods:
Three types of primary endothelial cells were used: human umbilical vein endothelial cells (HUVEC), human dermal microvascular endothelial cells (HDMEC) and human aortic endothelial cells (HAEC) as well as the two tumor cell lines FaDu (squamous cell carcinoma) and HT-29 (colorectal adenocarcinoma), respectively. Experimental hypoxia was induced by cultivating cells for 24 to 72 hours in presence of <1% oxygen in a special incubator (Gasboy C40, Labotect). Expression of VEGF, and of the VEGF receptors FLT-1, KDR, FLT-4 and neuropilin 1 and 2 were quantified with quantitative PCR (Realplex, Eppendorf). Cellular uptake of [^99mTc]sestamibi, [¹⁸F]FDG, and [¹⁸F]F-misonidazole was determined after one to four hours incubation and measured after cell lysis with a Cobra II gamma counter (Packard).
Results:
After 48 h of experimental hypoxia all cell lines showed a significant upregulation of VEGF expression. VEGF receptors FLT-1, KDR and FLT-4 were expressed in endothelial cells but absent in tumor cells. Cellular uptake of [^99mTc]sestamibi was reduced under hypoxic conditions in all cell lines. Furthermore, we found that primary endothelial cells incorporated significantly higher amounts of [¹⁸F]FDG under experimental hypoxic conditions in comparison to normoxic conditions.
When compared to normoxia [18F]FDG uptake after 48h hypoxia was increased 4.3-fold in HUVECs, 3.4-fold in HDMECs, and 3.5-fold in HAECs. These values were substantially higher than the values for the tumor cells FaDu (1.9-fold) and HT-29 (2.1-fold).
Conclusion:
Our data show VEGF to be a suitable indicator for enhanced oxygen demand in both tumor and endothelial cells in vitro. Moreover, the results emphasize the particular relevance of endothelial cells as one important part of the tumor micromilieu.

The influence of the central depression in the density distribution of spherical superheavy nuclei on the shell structure is studied within the relativistic mean-field theory. A large depression leads to the shell gaps at the proton Z = 120 and neutron N = 172 numbers, whereas a flatter density distribution favors N = 184 and leads to the appearance of a Z = 126 shell gap and to the decrease of the size of the Z = 120 shell gap. The correlations between the magic shell gaps and the magnitude of the central depression are discussed for relativistic and nonrelativistic mean field theories.

A systematic investigation of the rotating N=Z even-even nuclei in the mass A=68-80 region has been performed within the frameworks of the cranked relativistic mean field, cranked relativistic Hartree-Bogoliubov theories, and cranked Nilsson-Strutinsky approach. Most of the experimental data are well accounted for in the calculations. The present study suggests the presence of strong isovector np pair field at low spin, whose strength is defined by the isospin symmetry. At high spin, the isovector pair field is destroyed and the data are well described by the calculations assuming zero pairing. No clear evidence for the existence of the isoscalar t=0 np pairing has been obtained in the present investigation performed at the mean field level.

Rotational and deformation dependence of isovector and isoscalar pairing correlations at finite temperature are studied in an exactly solvable cranked deformed shell model Hamiltonian. It is shown that isovector pairing correlations, as expected, decrease with increasing deformation and the isoscalar pairing correlations remain constant at temperature, T=0. However, it is observed that at finite temperature both isovector and isoscalar pairing correlations are enhanced with increasing deformation. It is also demonstrated that the pair correlations, which are quenched at T=0 and high rotational frequency reappear at finite temperature. The changes in the individual multipole pairing fields as a function of rotation and deformation are analyzed in detail.

Superdeformation and hyperdeformation in 108Cd have been studied for the first time within the framework of the fully self-consistent cranked mean-field theory, namely, cranked relativistic mean-field theory. The structure of observed superdeformed bands 1 and 2 have been analyzed in detail. The bumps seen in their dynamic moments of inertia are explained as arising from unpaired band crossings. This is contrary to an explanation given earlier within the framework of the projected shell model. It was also concluded that this nucleus is not a doubly magic superdeformed nucleus.

The lifetimes of excited states belonging to the lowest lying positive-parity bands in 106,108Cd have been measured using the Doppler-shift attenuation method. The resulting B(E2) transition rates show a significant decrease with increasing spin in 106Cd, whereas in 108Cd there is tentative evidence for a similar effect. The results are compared with cranking and semiclassical model calculations, which indicate that the structures have the properties expected from an "antimagnetic" rotational band resulting from the coupling of g9/2 proton holes to aligned pairs of h11/2 and g7/2 neutron particles.

An exclusive measurement of the Coulomb breakup of 8B into 7Be+p at 254A MeV was used to infer the low-energy 7Be(p,gamma)8B cross section. The radioactive 8B beam was produced by projectile fragmentation of 350A MeV 12C and separated with the FRagment Separator (FRS) at Gesellschaft für Schwerionenforschung in Darmstadt, Germany. The Coulomb-breakup products were momentum-analyzed in the KaoS magnetic spectrometer; particular emphasis was placed on the angular correlations of the breakup particles. These correlations demonstrate clearly that E1 multipolarity dominates within the angular cuts selected for the analysis. The deduced astrophysical S17 factors exhibit good agreement with the most recent direct 7Be(p,gamma)8B measurements. By using the energy dependence of S17 according to the recently refined cluster model for 8B of P. Descouvemont [Phys. Rev. C 70, 065802 (2004)], we extract a zero-energy S factor of S17(0)=20.6±0.8(stat)±1.2(syst) eV b. These errors do not include the uncertainty of the theoretical model to extrapolate to zero relative energy, estimated by Descouvemont to be about 5%.

PT-symmetric Quantum Mechanics, the Squire equation of hydrodynamics and the spherically symmetric α²-dynamo of magnetohydrodynamics (MHD) can be structurally linked and treated in a unified way as spectral problems in Krein spaces. We demonstrate their interrelation explicitly and provide examples for specific parameter dependencies of their spectra. Special emphasis is laid on the physical relevance of transitions between real and complex spectral branches in connection with phase transitions between sectors of exact PT-symmetry and spontaneously broken PT-symmetry in Quantum Mechanics as well as with possible polarity reversals of dynamo maintained magnetic fields of planets. We briefly comment on third order spectral branch points with geometric multiplicity one and algebraic multiplicity three as well as on a dynamo related resonant unfolding of diabolical points (spectral intersection points of geometric and algebraic multiplicity two).

Based on:

[1] U. Günther and F. Stefani, J. Math. Phys. 44, (2003), 3097-3111, math-ph/0208012.
[2] U. Günther, F. Stefani and G. Gerbeth, Czech. J. Phys. 54, (2004), 1075-1090, math-ph/0407015.
[3] U. Günther, F. Stefani and M. Znojil, J. Math. Phys. 46, (2005), 063504, math-ph/0501069.
[4] U. Günther and F. Stefani, Czech. J. Phys. 55, (2005), 1099-1106, math-ph/0506021.
[5] U. Günther and O. Kirillov, J. Phys. A: Math. General (2006), in press, math-ph/0602013.

The flow of an electrically conducting fluid exposed to an externally applied magnetic field leads to induced currents and hence to induced magnetic fields. These induced fields can be measured in the exterior of the fluid. The application of different external magnetic fields and the measurement of the corresponding induced magnetic fields allows to reconstruct the basic features of the velocity field of the melt. The principle of such a “Contactless Inductive Flow Tomography” (CIFT) is delineated, and a prototype experiment with a propeller driven flow of the eutectic alloy GaInSn is presented. The areas of application of CIFT, its limitations, and possible further developments are discussed.

• wird nachgereicht

In 2007 the Dresden High Magnetic Field Laboratory (HLD) [1] will come into operation. This collective project of five institutes located in Dresden will used by the high field community in Europe. The IT tasks concerning the shared use of the experimental facilities should be solved using Grid technologies. The report describes the requirements on the HLD-Grid.

Mixing phenomena observed when the flow rate in a single loop of the primary circuit is changed can influence the operation of Pressurized Water Reactor (PWR) by inducing local gradients of boron concentration or coolant temperature. Analysis of one-dimensional Laser Doppler Anemometry measurements during the start-up and shutdown of pump on a single loop of the ROCOM test facility has been performed. The effect of a step change and a ramped change in the flow rate on the axial and azimuthal velocities was examined. Numerical simulations were also performed for the step change in the flow rate that gave quantitative agreement with the axial velocities. Phenomenological agreement was made on the turbulent kinetic energy; however, observed values were a factor of 10 less than the turbulent kinetic energy derived from the measurements.

The ultra-thin 2” diameter silicon (111)-H(1x1) wafer appeared to be a promising material for a mirror focusing He-atom beam in a scanning atom microscope. To increase achievable at present resolution from 1.5 µm to a sub-micron range the 50 µm thick (111) silicon wafer with shape thickness variation better than +-1 µm and 0.05° precision of miscut value is necessary. The purpose of this paper was to adapt X-ray measurements to control the miscut value with high precision for the 50 µm thick silicon wafers as well as to control the deviation of the wafer surface from ideal flat plane by measurements of low-angle reflection using X-ray high resolution diffractometer (HRXRD). The crucial point was the construction of a stress-free ultra-thin wafer holder. The precision of 0.01° miscut value was obtained. The deviation of the surface from the ideal flat surface obtained but X-ray measurements were compared with the one estimated from optical (confocal) method. A satisfactory good conformity between both methods has been observed.

The chemical composition and interplanar spacing profiles as well the lateral homogeneity of AIIIBV heterostructures containing a highly strained In(x)Ga(1-x)As layer were investigated. The heterostructures grown by metallorganic chemical vapor deposition were chracterized by means of high resolution x-ray diffractometry, x-ray reflectometry and Rutherford backscattering. In order to analyze the experimental results an algorithm for calculating the x-ray profiles based on the Darwin diffraction theory has been worked out. The developed method was applied to find out: the dependence of the growth rate and the interface profiles of the highly strained In(x)Ga(1-x)As layer on the deposition time to supervise the growth process of a resonant cavity enhanced photodiode heterostructure for which a highly strained In(x)Ga(1-x)As layer is an essential part.

Bispidines (bispidine = 3,7-diazabicyclo[3.3.1]-nonane) show unique complexation properties towards transition metals. The high thermodynamic stability of the complexes of these structurally reinforced ligands with Cu(II) offers the possibility to apply such complexes for diagnostic and therapeutic purposes (^64/67Cu). Furthermore, the bispidine structure opens suitable chemical approaches to introduce bio-molecules onto the skeleton, an important feature in view of the targeting of such complexes.
We want to present the synthesis and the coordinating properties of novel hexadentate bispidine derivatives having pyridine and/or imidazole units as donor groups. Cu(II) complexes of some bispidines have been isolated and the structures were solved by X-ray single crystal diffraction. As shown in the following figure, the copper(II) complex of the hexadentate bis(amine)tetrakis(pyridine) bispidine ligand L is six-coordinate having a distorted octahedral structure. It is evident from this structure that the copper(II) ion is almost completely shielded from the environment resulting in a very high stability against exogenous competing ligands.
Preliminary labelling experiments of bispidine ligands with ^64/67Cu indicate the rapid formation of stable complexes under mild conditions.

The particular structural features of transition metal oxygen anion clusters cause a rapidly expanding scientific as well as practical interest for these compounds, e.g. applications in areas including catalysis, materials chemistry and biochemistry. In the past decade, especially polyoxometalates (POMs) based on V(V), Mo(VI) and W(VI) were found as attractive candidates for medical applications. Such polynuclear metal compounds show unique transport properties into cells, and may act as antiviral and antitumoral agents.
We want to report the enzyme inhibition behaviour of the polyoxotungstates [W₁₂O₃₉]^6- (1), [W₁₂PO₄₀]^3- (2), [Ti₂W₁₀PO₄₀]^7- (3), [TiW₁₁CoO₄₀]^8- (4), [Co₄(H₂O)₂(W₉PO₃₄)₂]^10- (5), and [NaSb₉W₂₁O₈₆]^18- (6) towards the ecto-nucleotidases NTPDase 1, 2 and 3.
The polyoxotungstates (3) and (4) have been characterised by single X-ray diffraction showing the typical Keggin structure.
All of the polyoxotungstates investigated are potent inhibitors of the NTPDases 1-3 with Ki values between 0.14 and 29 µM.

Excess vacancies generated by high energy implantation with 1.2 MeV Si+ and 2 MeV Ge+ ions in SiGe were investigated after rapid thermal annealing at 900 °C. Excess vacancies were probed by decoration with Cu and measuring the Cu profile by secondary ion mass spectrometry. Cross section transmission electron microscopy of cleaved specimen enabled us to visualize nanocavities resulting from agglomeration of excess vacancies. The ion-induced damage in SiGe increases with increasing Ge fraction of the alloy. The amorphization threshold decreases and the extension of a buried amorphous layer increases for given implantation and annealing conditions.
In contrast to ballistic simulations of excess defect generation where perfect local self-annihilation is assumed the concentrations of excess vacancies and excess interstitials in SiGe increase with increasing Ge fraction. The main contribution to the high excess vacancy concentration in SiGe was found to result from the inefficient recombination of vacancies and interstitials. The widely used +1 model describing the ion-induced damage in Si is not valid for SiGe.

Technetium-labeled fatty acids intended for myocardial metabolism imaging and the respective rhenium model complexes were synthesized according to the “4+1” mixed-ligand approach and investigated in vitro and in vivo. The non-radioactive rhenium model complexes were characterized by NMR, IR, EA and the geometrical impact of the chelate unit on the integrity of the fatty acid head structure was determined by single crystal X-ray analyses. To estimate the diagnostic value of the ^99mTc-labeled fatty acids the compounds were investigated in experiments in vitro and in biodistribution studies using male Wistar rats. The new fatty acid tracers contain the metal core in the oxidation states +3, well-wrapped in a trigonal-bipyramidal coordination moiety which is attached at the ω-position of a fatty acid chain. This structural feature is considered to be a good imitate of the well-established iodinated phenyl fatty acids. High heart extraction in perfused heart studies (up to 26% ID) and noticeable heart uptake of the ^99mTc tracers in vivo being in the order of 2% ID/g at 5 min p.i., accompanied by a good heart to blood ratio of 8, confirms that the new Tc-compounds are suitable as fatty acid tracer.

Rhenium model complexes and the respective Technetium-labeled fatty acids for myocardial metabolism imaging, were synthesized according to the “4+1” mixed-ligand approach and investigated in vitro and in vivo. The non-radioactive rhenium model complexes were characterized by NMR, IR, EA and the geometrical impact of the chelate unit on the integrity of the fatty acid structure was determined by X-ray analyses. The new fatty acid tracers contain the metal core in the oxidation states +3, well-wrapped in a trigonal-bipyramidal coordination moiety which is attached at the ω-position of a fatty acid chain as isocyano ligand in the case A. The compounds of group B contain the fatty acid moitie coupled on the tetradentate ligand. High heart extraction in perfused heart studies (up to 26% ID) and noticeable heart uptake of the ^99mTc tracers in vivo (using male Wistar rats) being in the order of 2% ID/g at 5min p.i. accompanied by a good heart to blood ratio of 8, confirms the target comparability.

Die elektromagnetische Strömungsbeeinflussung spielt eine wichtige Rolle in der metallischen Werkstofftechnik. Wichtige potentielle Anwendungsgebiete sind Strömungsoptimierungen für die Herstellung einkristalliner Halbleiterkristalle (450 mm Siliziumwafer) und die Optimierung von Stahlgussprozessen.
Zur Validierung der numerischen Strömungssimulationen verwendet man häufig ein Wassermodell des zugehörigen Prozesses. Dieses ermöglicht prinzipiell den Einsatz von Laserverfahren zur Strömungsvermessung, spiegelt jedoch wegen der unterschiedlichen Eigenschaften von Metallen und Wasser die physikalische Realität nur unzureichend wider.
Zur Strömungsmessung in Metallschmelzen bedient man sich daher häufig der Ultraschall-Messtechnik unter Ausnutzung des Doppler-Effektes. Die Messaufbauten ermöglichen in der Regel die Messung einer Geschwindigkeitskomponente entlang einer Linie.
Zukünftige Messaufgaben wie beispielsweise die Vermessung inkohärenter Strömungsfelder können mit den vorhandenen Messgeräten nicht realisiert werden. Das liegt im wesentlichen an der fehlenden zeitlichen Auflösung der Messsysteme und der langsamen Traversierung.
Der Vortrag präsentiert aktuelle Ergebnisse bei Ultraschallmessungen in der Metallurgie. Dabei wird vorgestellt, wie die Erhöhung der zeitlichen Auflösung und damit die Messung instationärer Felder erreicht werden kann. Beschrieben werden dabei grundsätzliche Erwägungen hinsichtlich der Wandler-Geometrie und des Schallfeldes, Probleme bei der Schallanregung in der Flüssigkeit und Elemente der Signalverarbeitung. Die erreichbare maximale zeitliche und örtliche Auflösung wird theoretisch und experimentell dargelegt.

Es wird ein Überblick über die Möglichkeiten der elektromagnetischen Strömungskontrolle für Anwendungen in der Giessereitechnik und in der Metallurgie gegeben, namentlich zur Kontrolle der Formfüllung beim Feinguß, zur elektromagnetischen Beeinflussung der Strömungsstruktur in Flüssigmetall-Zweiphasenströmungen sowie bei der Erstarrung von Legierungen unter Magnetfeldeinfluß. Insbesondere wird auf die Bedeutung von Modellexperimenten mit metallischen Modellschmelzen hingewiesen, die einen wesentlichen Beitrag zum Verständnis der Strömungs-vorgänge in praxisrelevanten Anordnungen liefern können. Betrachtet man für die industriellen Anwendungen realistische Parameterbereiche liefern diese Wassermodelle liefern allerdings oft falsche Ergebnisse und sind völlig wertlos für Untersuchungen zur elektromagnetischen Strömungskontrolle.

SPECT- images performed with radiolabeled fatty acids (FA) allow detailed studies about the heart function, because flow and metabolism are represented. Up to now, only ¹²³iodinated FA are available for myocardial viability diagnostics in some parts of the world, but the application is limited due to serious disadvantages: first, the expensive production of pure ¹²³I requires a cyclotron and second, the radiolabeled FA compounds must be purchased by outside vendors which resulted in disproportional costs and logistical problems. ^99mTc, has ideal physical properties for SPECT-imaging (Eγ-= 140 keV), a short half- life of 6 h, and is available through a ⁹⁹Mo/^99mTc generator whenever needed. The development of ^99mTc- labeled FA has been a goal of various research groups in the past. Despite many different approaches, no appropriate ^99mTc compound with similar myocardial extraction properties as found with BMIPP and DMIPP is available to date. Most previous work in this field has focused on radiometal coordination by use of a polar tetradentate N₂S₂ chelate with a central oxometal(V) core. We concentrated on the development and experimental evaluation of alternative coordination moieties according to the ‘4+1’ mixed ligand approach to create newly technetium labeled FA with an improved myocardial profile. In the ‘4+1’ donor atom arrangement, 99mTc is coordinated by both a tetradentae ligand and by a monodentate bearing the FA moiety. This system is rather lipophilic and show high stability towards, e.g. challenging SH-agents. While the conventional ‘4+1’ ^99mTc FA are built on in the sequence Tc-chelate, alkyl chain (a), carboxyl group (c) ->(Tc-a-c) we also developed and investigated some compounds with a new design according to the sequence carboxyl group (c), alkyl chain, Tc chelate, lipophilic tail (lt) -> (c – a – Tc – lt), transferring the ^99mTc chelate from the end- to a more central position of the compound.

Bubbly flow is encountered in a wide variety of industrial applications ranging from flows in nuclear reactors to process flows in chemical reactors. The presence of a second phase, recirculating flow, instabilities of the gas plume and turbulence, complicate the hydrodynamics of bubble column reactors.
This paper describes experimental and numerical results obtained in a rectangular bubble column 0.1 m wide and 0.02 m in depth. The bubble column was operated in the dispersed bubbly flow regime with gas superficial velocities up to 0.02 m/s. Images obtained from a high speed camera were used to observe the general flow pattern and have been processed to calculate bubble velocities, bubble turbulence parameters and bubble size distributions. Gas disengagement technique was used to obtain the volume averaged gas fraction over a range of superficial gas velocities. A wire mesh sensor was applied, to measure the local volume fraction at two different height positions. Numerical calculations were performed with an Eulerian-Eulerian two-fluid model approach using the commercial code CFX.
The paper details the effect of various two-fluid model interfacial momentum transfer terms on the numerical results. The inclusion of a lift force was found to be necessary to obtain a global circulation pattern and local void distribution that was consistent with the experimental measurements. The nature of the drag force formulation was found to have significant effect on the quantitative volume averaged void fraction predictions.

The talk was given during the Siemens In-Beam PET workshop 9-10 May 2006 at OnkoRay, Dresden. The achievements and issues in reconstruction procedure of in-beam PET data were discussed

Challenges for in-beam PET at hard photon beams

Gegenstand des Vorhabens im Rahmen der WTZ mit Russland ist die Versprödung des Reaktordruckbehälters infolge der Strahlenbelastung mit schnellen Neutronen im kernnahen Bereich.
Um den Einfluss von bestrahlungsinduzierten Gitterdefekten auf die mechanischen Eigenschaften zu ermitteln, wurden analytische Berechnungen zum Einfluss von Hindernissen auf die Beweglichkeit von Versetzungen und damit auf die Ausbildung einer plastischen Zone an der Rissspitze durchgeführt. Es wird demonstriert, dass sich die an der Rissspitze entstehenden Versetzungen an dem Hindernis (bestrahlungsinduzierte Punktdefekte) aufstauen. In Abhängigkeit der Rissbelastung KI und der Entfernung des Hindernisses von der Rissspitze werden die Versetzungsdichte und das durch den Versetzungsstau verursachte Spannungsfeld berechnet.
Mit Hilfe von Experimenten zur Neutronenkleinwinkelstreuung (SANS – small angle neutron scattering) an verschiedenen WWER-Stählen und Modelllegierungen wurden Größenverteilungen und die Volumenanteile der strahleninduzierten Defekte für verschiedene Bestrahlungszustände (Fluenzen, Bestrahlungstemperaturen) ermittelt. Es wurde gezeigt, dass sich die strahleninduzierte Werkstoffschädigung durch Wärmebehandlung weitgehend wieder ausheilen lässt. Nach der thermischen Ausheilung ist der Werkstoff bei erneuter Bestrahlung weniger anfällig für strahleninduzierte Defekte. Die Ergebnisse der SANS-Untersuchungen wurden mit der Änderung der mechanischen Eigenschaften (Härte, Streckgrenze und Sprödbruchübergangstemperatur) korreliert.
Mit der kinetischen Gitter-Monte-Carlo-Methode wurden numerische Sensitivitätsstudien zum Einfluss des Cu-Gehalts auf die Stabilität von Defekt-Clustern durchgeführt. Die Berechnungen zeigen, dass die Anwesenheit von Cu-Atomen zur Bildung von langlebigen Defekten führt. Dabei werden Leerstellen in Cu/Leerstellen-Cluster eingefangen. Leerstellen in reinem Eisen sind bei Bestrahlungstemperaturen von 270 °C dagegen nicht stabil, die Lebensdauer liegt zwischen 0.01 s und 1 s. Die kritische Cu-Konzentration, ab welcher stabile Defekte entstehen, beträgt ca. 0.1 Masseprozent.

Low-temperature photoluminescence spectroscopy has revealed a series of features labeled S1, S2, S3 in n-type 6H-SiC after neutron and electron irradiation. Thermal annealing studies showed that the defects S1, S2, S3 disappeared at 500 °C. However, the well-known D1 center was only detected
for annealing temperatures over 700 °C. This experimental observation not only indicated that the defects S1, S2, S3 were a set of primary defects and the D1 center was a kind of secondary defect, but also showed that the D1 center and the E1, E2 observed using deep level transient spectroscopy
might not be the same type of defects arising from the same physical origin.

Colloid formation and solubility of U(IV) in acidic HClO4/NaClO4 solutions are investigated by coulometric titration. Quantification of traces of U(VI) by laser fluorescence spectroscopy proves that the tetravalent state of uranium had been maintained. Laser-induced breakdown detection (LIBD) is applied for the detection of traces of uranium colloids as the pH is increased. The pH values at the onset of colloid formation are used for thermodynamic calculations aimed at determining the solubility products Ksp0 of crystalline and amorphous uranium dioxides. The particle size of the colloids determined by means of LIBD is taken into account since it influences the solubility product. The results indicate the formation of crystalline UO2(cr) at low pH ~ 1 (log Ksp0 = 59.6 ± 1.0) whereas the amorphous hydrous oxide UO2·xH2O(am) is formed at pH ~ 3 (log Ksp0 = -54.4 ± 1.0). Measurements by EXAFS, XRD and REM confirm the occurrence of these different modifications. The obtained solubility products fit well in the known series of solubility products of the other tetravalent actinides.

Purpose
The development and the perspectives of photovoltaic plants (PVP) in Saxony will be described. The development reflects the effects of the different funding instruments as well as the technical progress which has been made during the past 15 years.

Funding as accelerator
The first large step in the PVP installation in Saxony was done with the German 1000-Roofs-Program between 1991 and 1995. In the frame of this program the first 150 PVP were installed with a total power of 450 kW (see Fig.1). A new high light was set when the 100.000-Roofs-Program came into force. More than 450 PVP with a total power of 1,5 MW were connected to the grid. With the EEG (Renewable Energy Act) this development was continued. Starting with 2004 also Megawatt PVP were put into operation, the PVP Espenhain (5 MW power) belongs also today to the world largest PVP.

Technical development
The first PVPs reflect the technical level of the early nineties. The power was limited to 5 kW, and the DC-voltage was restricted to 140 V. Beginning with the year 2000 the mean power of the PVP has been clearly increased. Sonny Boy is the dominating inverter type (with a share of more than 50 %), but the module types vary strongly. An increase in the mean module power has been certainly observed.

Some operation results
A mean annual yield of 750 kWh/kW was found for the first generation of PVP, which was influenced by the low quality of some module types. New systematic monitoring programs were started in 2000. These investigations allowed the evaluation of new built PVP (yields up to 1000 kWh/KW, Fig. 2), but also the long time behaviour of the older PVP could be observed (Figs. 3 and 4).

Conclusions
The development generally confirms the politically decisions for PV funding in Germany. It could be proofed, that new PVPs in Saxony with optimal design and components, respectively, can generate up to 950 kWh/kW in an "average" year.

For the estimation of the expected annual energy gain and the month by month check of the system performance, methods based on irradiance maps published by weather services, both general or dedicated to solar energy application, are in use. Examples for this type of information for Germany are annual and monthly irradiance maps published by the German weather service DWD or the data bank of hourly irradiance data with continuous spatial coverage prepared by the University of Oldenburg and offered as commercial service by the company Meteocontrol. The DWD maps are derived from both, satellite images and ground measurements and are given with a spatial resolution of 1km x 1km. The Oldenburg data bank is basically derived from satellite data only (resolution ~ 5km x 5km), although an option for amelioration by ground station data exists.
To assess the validity of these data sets for the aforementioned tasks, a case study for a region covering the German federal state of Saxony is performed, using data for the years 2004-2005.
Saxony is characterised by a wide variety of topographical features, ranging from flat relief to highly structured mountainous terrain. For this region an independent high quality ground data set given by a dense network operated for agro-meteorological purposes is available. An assessment of the end use accuracy of the irradiance data can by done via a set of monthly yield data of grid connected PVsystems.
The comparison of information on radiation sums is on one hand performed by the monthly analysis of the bias and the rms-error for the data bank versus the ground station data. On the other hand, the quality of the information on the spatial structure of the radiation field that is extractable from the data banks is analysed via the inspection of the a co- and cross-variograms.
For the assessment of the end use accuracy of the data, procedures to derive an estimation of the system yield from irradiance data as developed by the PVSAT2 project are applied for the Oldenburg data set.
A first impression of the reliability of the map data is given by the inter comparison of the annual maps for the year 2004. This shows deviations of up to 40 kWh/m², which presents an relative error of about 4%. Besides a systematic bias of about 20 kWh/m² in favour the Oldenburg data, remarkable differences in the spatial structure of the irradiance field concerning the homogeneity/inhomogeneity within some regions occur.
Thus, to pin down the reliability of the content of the maps it has to be compared to the ground data.
For the Oldenburg data it can be stated that even having a quite low bias for each station on an annual scale, monthly sums can deviate by up to 40%, especially for the winter months. This finding is coherent with the results of the PVSAT project, indicating the general increase of the uncertainties of satellite based estimates in months with low radiation sums.
Concerning the annual end use accuracy, a typical deviation of ? 5% for the estimated annual energy gain of a set PV-systems - chosen for their excellent yield figures - can be stated. Regarding the fact, that the system simulation is base on data sheet information rather than system specific parameters, this result is quite satisfactory. However, as expected remarkable relative deviation for the winter
months are hidden by these annual figures which are dominated by the PV gain in the summer months.
Using the respective results of for sets of both 2004 and 2005 general conclusions on the uncertainties connected to the use of state of the art irradiance information in view of PV application can be draw.

Heterophase interfaces are boundaries, which join two material types with different physical and chemical nature. Therefore, heterophase interfaces can exhibit a large variety of geometric morphologies ranging from atomically sharp boundaries to gradient materials, in which an interface-specific phase is formed, which provides a continuous change of the structural parameters and thus reduces elastic strains and deformations.

In addition, also the electronic properties of the two materials may be different, e.g. at boundaries between an electronically conducting metal and a semiconductor or an insulating material. Due to the deviations in the electronic structure, various bonding mechanisms are observed, which span the range from weakly interacting systems to boundaries with strong, directed bonding and further to reactively bonding systems which exhibit a new phase at the interface. Thus, both elastic and electronic factors may contribute to the formation of a new, often amorphous phase at the interface. Numerical simulations based on electronic structure theory are an efficient tool to distinguish and quantify these different influence factors, and massively parallel computers nowadays provide the required numerical power to tackle structurally more demanding systems. Here, this power has been exploited by the parallelisation over an optimised set of integration points, which split the solution of the Kohn-Sham equations into a set of matrix equations with equal matrix sizes. In this way, the analysis and prediction of material properties at the nanoscale has become feasible.

Isolated and crystalline Mo6S6 nanowires, doped with Li to form Li2Mo6S6, are investigated with the density-functional techniques. We find that Li atoms "decorate" individual wires at the S-coordinated sites and occupy the interstitial positions between 3 S atoms in crystalline nanowires.
Doping with Li changes the lattice constants by less than 0.1 Angstrom, but it decreases the modulus of elasticity along the wire axis in the crystalline form. Doping raises the Fermi energy but retains the strongly uniaxial metallic character of nanowires, attributed to the Mo(4d) electrons.

Mechanical and electronic properties of hypothetical carbon nanostructures, on the basis of C28 building blocks, hyperdiamond and hyperlonsdaleite, have been investigated by DFT-based methods. The low mass density and large internal surface suggest applications as catalyst, nanosieve and ga storage material. We estimate the active volume accessible by H2. Special emphasis is given to tune the properties by endo- and exohedral intercalation with Zn, Ti, and K. While endohedral intercalation with Zn does not affect the overall structure, endohedral Ti intercalation has different consequences on the structural stability of the two allotropes. Exohedral intercalation with K leads to an ionic fullerite phase with metallic conductivity.

The role of the lift force for the stability of the homogeneous flow regime in a bubble column is investigated. Instabilities caused by the lift force may be one important reason for the transition from homogeneous to heterogeneous bubble column. The lift force acts on rising bubbles in lateral direction, when gradients of the liquid velocity are present. Such gradients may result from circulation cells in the bubble column as well as from local disturbances. Depending on the sign of the lift force such local disturbances in a homogeneous flow may be damped or enhanced. The corresponding feedback mechanism was analysed by means of a linear stability analyses. In the result criteria for stability were obtained for mono-dispersed flow, for a with two bubble size groups and finally with some additional approximations also for the case of N bubble size groups or a given bubble size distribution. In a next step the effects were investigated by CFD calculations. The obtained criteria for stability fit well together with the observed effects in CFD simulations. Recently two different groups confirmed the stability criteria experimentally.

The electrical properties of heavily Al doped (5x1019 – 1.5x1021 cm-3) single and nanocrystalline 4H-SiC layers on semi-insulating 4H-SiC substrate, prepared by multi-energy, high-fluence Al implantation and subsequent furnace annealing, are investigated by sheet resistance and Hall effect measurements. The reliability of recent results on enhanced acceptor activation in heavily Al doped, nanocrystalline SiC on conductive substrate is evaluated by direct comparison with doped SiC layers on semi-insulating substrate.

The conventional magnetic induction equation that governs hydromagnetic dynamo action is transformed to an equivalent integral equation system. An advantage of this approach is that the computational domain is restricted to the region occupied by the electrically conducting fluid and to its boundary. This integral equation approach is applied to simulate kinematic dynamos within cylindrical geometry including the von Karman sodium (VKS) experiment and the Riga dynamo experiment. A modified version of this approach is utilized to investigate magnetic induction effects under the influence of externally applied magnetic fields. The computed induced magnetic fields for the VKS experiment show a satisfactory agreement with the experimental results.

The influence of ion energy on the hydrogen incorporation has been investigated for alumina thin films, deposited by reactive magnetron sputtering in an Ar/O2/H2O environment. Ar+ with an average kinetic energy of ~5 eV was determined to be the dominating species in the plasma. The films were analyzed with x-ray diffraction, x-ray photoelectron spectroscopy, and elastic recoil detection analysis, demonstrating evidence for amorphous films with stoichiometric O/Al ratio. As the substrate bias potential was increased from –15 V (floating potential) to –100 V, the hydrogen content decreased by ~70%, from 9.1 to 2.8 at.%. Based on ab initio calculations, these results may be understood by thermodynamic principles, where a supply of energy enables surface diffusion, H2 formation, and desorption [Rosén et al., J. Phys.: Condens. Matter 17, L137 (2005)]. These findings are of importance for the understanding of the correlation between ion energy and film composition and also show a pathway to reduce impurity incorporation during film growth in a high vacuum ambient.

We present an approach of photoconductive terahertz (THz) generation providing a broad bandwidth and exceptional electric field amplitude. A large-area interdigitated two-electrode structure is applied to a GaAs substrate to offer high electric fields. Photocarriers excited by a Ti:Sapphire oscillator laser with MHz repetition rate are accelerated there, yielding an intense THz output. An appropriate binary mask covers every second electrode interval and carriers are excited in uniform electric field areas only. Hence contrary carrier acceleration and destructive interference is avoided. Due to the periodic nature of the electrode structure, the size of the excitation spot on the photoconductive THz emitter can be varied. This results in a THz beam of variable divergence. By electro-optic sampling the THz radiation is detected and characteristic properties of the THz source are measured. For an excitation spot diameter of about 300 μm, which corresponds to the central wavelength of the THz pulses, the THz generation is most efficient. THz radiation with an average power of 145 µW is generated with an efficiency of 2 × 10^-4 for the conversion from NIR to THz power. Furthermore, the THz radiation has excellent focusing properties. A Gaussian beam profile with a diameter (FWHM) of less than 1.4 of the central wavelength of the THz pulses is found. The THz field amplitude in the center of the focused THz beam is 1.5 kV/cm, which is almost one order of magnitude more of what is achieved with conventional semi-large aperture photoconductive emitters and a similar excitation spot diameter. Exceptionally large signal-to-noise ratios are achieved by modulating the bias voltage in the kHz range and using lock-in technique. We suggest that the THz power can be further improved by a sufficient cooling system, e.g. water cooling. Furthermore the use of LT GaAs instead of semiinsulating GaAs can result in larger THz bandwidth.

Static magnetic fields are known to be suitable for damping mean flow and turbulent motion in an electrically conducting liquid. In this paper, an experimental study is presented considering the influence of a horizontal magnetic field on a bubble-driven flow of a liquid metal. The investigation is focused on the liquid circulation inside a liquid metal column driven by a central jet produced by gas injection. The fluid vessel has a circular cross section and electrically insulating walls. Low gas flow rates were applied resulting in a plume of separated bubbles rising inside a spot around the cylinder axis. This axisymmetric configuration is exposed to a horizontal magnetic field. We present detailed experimental data describing the spatial as well as the temporal structure of the velocity field. Measurements of the vertical and the radial velocity component, respectively, were performed using the ultrasound Doppler velocimetry (UDV) allowing for the first time a complete mapping of the liquid velocity distribution for a bubble-driven liquid metal flow. The magnetic field considerably modified the global and local properties of the flow field compared to an ordinary bubble plume. In the parameter range considered here we did not find a prior flow suppression, but, in fact, a restructuring of the convective motion. The original axisymmetric flow field became anisotropic with respect to the direction of the magnetic field lines. An upwards flow dominated in a plane parallel to the magnetic field, whereas the recirculating motion was enforced in the orthogonal plane. Contrary to usual expectations, the application of a moderate magnetic field (100 < Ha < 400, 1 < N < 10) destabilizes the global flow and gives rise to transient, oscillating flow pattern with predominant frequencies.

A Pt/C multilayer stack (15 layer-pairs) with Fe impurities was prepared on a glass substrate by the ion sputtering technique. Ion irradiation effects on this multilayer were studied following irradiation with 2 MeV Au ions at fluences from 1 · 1014 to 1 · 1015 ions/ cm2. Irradiation induced atomic displacements in such multilayers have been earlier analyzed by a combined X-ray standing wave (XSW) and X-ray reflectivity (XRR) technique with a depth resolution better than 0.2 nm [S.K. Ghose, B.N. Dev, Phys. Rev. B 63 (2001) 245409; S.K. Ghose, D.K. Goswami, B. Rout, B.N. Dev, G. Kuri, G. Materlik, Appl. Phys. Lett. 79 (2001) 467]. Using the combined XSW-XRR technique ion beam induced preferential movement of Fe from C- to Pt-layers has been detected. At the highest ion fluence Pt layers (containing Fe) break into nanoparticles apparently surrounded by C. Grazing incidence X-ray diffraction (GIXRD) measurements indicate the formation of FePt particles in the irradiated multilayer samples. Results of magnetic force microscopy (MFM) and magneto-optical Kerr effect (MOKE) measurements reveal that while the virgin sample hardly shows any magnetism, the irradiated samples show a soft ferromagnetism with an increasing coercive field with increasing ion fluence. Use of focused ion beam to fabricate ferromagnetic nanodots and their possible uses in spin electronics are discussed.

The S-layer of Bacillus sphaericus strain JG-A12, isolated from a uranium-mining site, exhibits a high metal-binding capacity, indicating that it may provide a protective function by preventing the cellular uptake of heavy metals and radionuclides. This property has allowed the use of this and other S-layers as self-assembling organic templates for the synthesis of nano-sized heavy metal cluster arrays. However, little is known about the molecular basis of the metal protein interactions and their impact on secondary structure. We have studied the secondary structure, protein stability, and Pd(II) coordination in S-layers from the B. sphaericus strains JG-A12 and NCTC 9602 to elucidate the molecular basis of their biological function and of the metal nanocluster growth. Fourier-transform IR-spectroscopy reveals similar secondary structures, containing ~35 % -sheets and little helical structure. pH-induced IR absorption changes of the side chain carboxylates evidence a remarkably low pK < 3 in both strains and a structural stabilisation when Pd(II) is bound. The COO--stretching absorptions reveal a predominant Pd(II)-coordination by chelation / bridging by Asp and Glu residues. This agrees with XANES and EXAFS data revealing oxygens as coordinating atoms to Pd(II). The additional participation of nitrogen is assigned to side chains rather than to the peptide backbone. The topology of nitrogen- and carboxyl-bearing side chains appears to mediate heavy metal-binding binding to the large number of Asp and Glu in both S-layers at particularly low pH as an adaptation to the environment from which the strain JG-A12 has been isolated. These side chains are thus prime targets for the design of engineered S-layer-based nanoclusters.

We have studied the oxidation states of Fe and Mo and the presence of grain boundaries in the magneto resistive (MR) compounds Sr2FeMoO6 by means of x-ray photoelectron spectroscopy (XPS), Mössbauer spectroscopy and electrical resistivity measurements. XPS of the Mo 3d and Fe 3s core levels is indicating a mixed valence state involving around 30% Fe3+- Mo5+ and 70% Fe2+- Mo6+ states. Mössbauer studies confirm the presence of a valence fluctuation state and an essential amount of grain boundaries in the present Sr2FeMoO6 crystals. Resistivities and magnetoresistance studies evidenced strong grain boundary effects.

For modeling multi-phase where the disperse phase play a major role for determining the flow structure and inter phase transfer quantities, the size distribution of the particles has to be considered. This can be done by extension of the mass balance equation to a population balance equation. In this work, a least squares spectral method is tested for predicting the evolution of the disperse phase in a vertical two phases bubbly flow. The least squares spectral method consists in minimizing the L2 norm of the residual over the simulation domain. The results are compared with experimental data obtain for two different initial bubble distribution.

In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable. Since the magnetic properties of magnetic multilayers depend sensitively on the mutual interfaces a modification of these interfaces by light ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1]. As an example it will be demonstrated that ion irradiation in an applied magnetic field allows to set the uniaxial anisotropy direction on a micrometer scale in the case of soft magnetic alloys [2]. However, in order to modify the structural and magnetic properties not only light ion irradiation but also ion implantation doping can be used. If, for example, Cr is implanted in thin Permalloy films the Curie temperature and the saturation magnetization can be reduced, which consecutively leads to a decrease of the magnetic anisotropy and an increase of the magnetic damping behavior [3]. The formation of magnetically dead layers at the interfaces to buffer and cap layers can be investigated using Ni implantation [4].
In an alternative route to design magnetic properties periodically modulated substrates are employed. These modulated substrates are created by means of low energy ion erosion. A ripple structure with a typical periodicity of 30 – 50 nm and a ripple height of about 2 nm is created on a Si substrate. Subsequently deposited Permalloy films exhibit a uniaxial anisotropy which is about a factor of 20 larger than conventionally prepared films. If exchange bias bilayers are deposited the interplay between the unidirectional and the ripple-induced uniaxial anisotropy contributions can be investigated.

[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
[2] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
[3] J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord, L. Schultz, R. Mattheis, Phys. Rev. B, in press.
[4] J. Fassbender, J. McCord, Appl. Phys. Lett., in press.

In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable. Since the magnetic properties of magnetic multilayers depend sensitively on the mutual interfaces a modification of these interfaces by light ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1]. As an example it will be demonstrated that ion irradiation in an applied magnetic field allows to set the uniaxial anisotropy direction on a micrometer scale in the case of soft magnetic alloys [2]. However, in order to modify the structural and magnetic properties not only light ion irradiation but also ion implantation doping can be used. If, for example, Cr is implanted in thin Permalloy films the Curie temperature and the saturation magnetization can be reduced, which consecutively leads to a decrease of the magnetic anisotropy and an increase of the magnetic damping behavior [3]. The formation of magnetically dead layers at the interfaces to buffer and cap layers can be investigated using Ni implantation [4].
In an alternative route to design magnetic properties periodically modulated substrates are employed. These modulated substrates are created by means of low energy ion erosion. A ripple structure with a typical periodicity of 30 – 50 nm and a ripple height of about 2 nm is created on a Si substrate. Subsequently deposited Permalloy films exhibit a uniaxial anisotropy which is about a factor of 20 larger than conventionally prepared films. If exchange bias bilayers are deposited the interplay between the unidirectional and the ripple-induced uniaxial anisotropy contributions can be investigated.

[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
[2] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
[3] J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord, L. Schultz, R. Mattheis, Phys. Rev. B, in press.
[4] J. Fassbender, J. McCord, Appl. Phys. Lett., in press.

High quality ZnO single crystals of dimensions 10 x 10 x 0.3 mm3, grown either using a pressurized melt or a hydrothermal growth approach, have been investigated in their as-received state and are compared regarding their properties revealed by positron annihilation and Hall effect measurements. By positron annihilation performed at room temperature it is found that the pressurized melt grown crystals contain a certain amount of Zn+O divacancies but no Zn vacancies are detected, whereas the hydrothermally grown crystals contain a dominating defect yet unknown in its structure but maybe connected to the Zn vacancy. Furthermore, the influence of an additional refined chemical-mechanical polishing of the crystal surface by a special procedure on the depth distribution of vacancy-type defects is demonstrated. Hall measurements, performed in the temperature range 20 – 325 K, showed that the crystal growth method has a strong influence on the carrier mobility, and the estimated acceptor densities also differ significantly in both types of crystal.

Bu₄N[ReO(abt)₂] was obtained via the precursor Bu₄N[ReOCl₄], its conversion into an ethylene glycol complex as an intermediate and subsequent ligand exchange by H₂abt to form the tetrabutylammonium salt of the abt complex in 62 % yield. Elemental analysis, mass, NMR and IR spectra confirm the composition Bu₄N[ReO(abt)₂]. The crystal structure contains well separated ReO(NHC₆H4S)₂ anions and Bu₄N⁺ counter cations. The coordinationgeometry of Re is distorted square pyramidal, with an apical Re O bond length of 1.676(5)A°.The dihedral angle between the two benzene rings is 33.75(1)°. These values do not differ
much from those of the corresponding Tc compound.

Capillarity-driven surface-free-energy minimization may lead to morphological changes of nanowires (NWs), e.g. their decay into chains of nanoclusters (NCs) by the Rayleigh instability. At the nano-scale, such capillary effects are more pronounced than in macroscopic systems due to the large surface-to-volume ratio. However, the capillary-driven NW decay is subject to increasing fluctuations with decreasing dimensions. This might prevent the formation of NC chains with long-range order which is needed for potential applications (e.g. in nanophotonics as light guides). We predict a novel method to fabricate long-range-ordered NC chains by decay of NWs under the control of an external temperature field. The prediction is based on the temperature dependence of surface tension causing thermocapillary effects. Surface tension gradients trigger atomic migration from hot to cold regions. Thus, long-range-order of NC chains may be achieved by a weak periodic temperature field along the NW. Such a temp. profile might be realized by a standing surface-plasmon-polariton wave. Here, a feasibility evaluation of the prediction will be presented which is based on computer experiments. The NW decay with and without external temperature fields was examined by kinetic Monte Carlo simulations. Just a small, symmetry-breaking periodic temperature field is needed to control long-range-order. In practice, the field must be stronger than thermally induced fluctuations along the NW, as is discussed.

Nanowires (NWs) play an important role as basic components of electronic and photonic devices, such as interconnects or surface-plasmon propagators. Here, theoretical studies are presented on reaction pathways of the CMOS-compatible fabrication of metal silicide or semiconductor nanowires (NWs) by focused ion beam (FIB) implantation and subsequent thermal annealing. On realistic time and length scales, the simulation of the whole process is divided into two steps: (i) The spatio-temporal evolution of FIB implantation profiles is calculated by a new computer code including dynamical target changes, local ion erosion etc. The FIB implantation along a straight trace leads to a local and surface-near supersaturation in the substrate. (ii) Post-implantation annealing causes NW formation by self-organization, which is described theoretically by kinetic Monte Carlo simulations. It is demonstrated that the evolution of the FIB implantation profile proceeds in three well-separated stages: (1) Phase separation by nucleation and growth, (2) NW formation by coalescence of nanoclusters, (3) NW surface smoothening. After this evolution, a NW diameter which is several times smaller than the width of the FIB implantation trace (some tens of nanometers) is found. Likewise, components for functional devices involving several NWs, like T- or X-junctions, can be obtained by crossing different FIB traces.

A combination of transmission electron microscopy (TEM) and local density-functional theory (LDFT) is employed to analyze the microscopic structure of the rhombohedral (-1012) and the prismatic Sigma-3 (10-10) twin interfaces in alpha-alumina. LDFT provides interface energies, atomic and electronic structures for competing structure models. With high-resolution TEM the atomic structure at the interface is imaged quantitatively along two orthogonal zone axes. Electron energy loss spectroscopy in TEM yields the interfacial electronic structure with nano-scale spatial resolution. All experiments confirm the theoretically preferred model for each of the two grain boundaries quantitatively.

We consider the magnetorotational instability (MRI) of a hydrodynamically stable Taylor-Couette flow with a helical external magnetic field in the inductionless approximation defined by a zero magnetic Prandtl number (Pm=0). This leads to a considerable simplification of the problem eventually containing only hydrodynamic variables. First, we point out that the energy of any perturbation growing in the presence of magnetic field has to grow faster without the field. This is a paradox because the base flow is stable without the magnetic while it is unstable in the presence of a helical magnetic field without being modified by the latter as it has been found recently by Hollerbach and Rüdiger (Phys. Rev. Lett. {95}, 124501, 2005). We revisit this problem by using a Chebyshev collocation method to calculate the eigenvalue spectrum of the linearized problem. In this way, we confirm that MRI with helical magnetic field indeed works in the inductionless limit where the destabilization effect appears as an effective shift of the Rayleigh line. Second, we integrate the linearized equations in time to study the transient behavior of small amplitude perturbations, thus showing that the energy arguments are correct as well. However, there is no real contradiction between both facts. The linear stability theory predicts the asymptotic development of an arbitrary small-amplitude perturbation, while the energy stability theory yields the instant growth rate of any particular perturbation, but it does not account for the evolution of this perturbation. Thus, although switching off the magnetic field instantly increases the energy growth rate, in the same time the critical perturbation ceases to be an eigenmode without the magnetic field. Consequently, this perturbation is transformed with time and so looses its ability to extract energy from the base flow necessary for the growth.

The SUZUKI reaction of organoboron compounds with 4-[¹⁸F]fluoroiodobenzene has been developed as a novel radiolabelling technique in ¹⁸F chemistry. The cross-coupling reaction of p-tolylboronic acid with 4-[¹⁸F]fluoroiodobenzene was used to screen different palladium complexes, bases and solvents. Optimised reaction conditions (Pd₂(dba)₃, Cs₂CO₃, acetonitrile, 60 °C for 5 minutes) were further applied to the synthesis of various ¹⁸F-labelled biphenyls bearing different functional groups. The reaction proceeded in excellent radiochemical yields of up to 94 % within 5 min while showing good compatibility to many functional groups.

Challenges for further development in in-beam PET

Chains of metallic nanoparticles may be applied as surface-plasmonpolariton (SPP) waveguides. Moreover, nanoparticle waveguide structures with small bend radii, e.g. L-turns or beam splitting T-junctions, are of technological interest. In this contribution, we present reaction pathways of the fabrication of 1D metallic nanostructures by focused metal ion implantation and subsequent thermal treatment. Nanowires (NWs) as well as structures consisting of metallic nanoparticle chains were found. The search for reaction pathways was performed by kinetic Monte Carlo simulations including realistic focused ion beam (FIB) implantation profiles which were determined by spatially dependent dynamic ion range calculations. During annealing, buried NWs and more complex structures (e.g. T- or X-junctions) form that are embedded in the matrix along the FIB implantation trace. The diameter of the synthesized NWs is about five times smaller than the width of the FIB implantation trace. The dominating driving force of NW formation is a free energy gain by phase separation and by reduction of high interface curvatures. During longterm thermal annealing, NWs disintegrate into regular chains of nanodots because of the built-up of long-wavelength interface undulations (Rayleigh instability). Crosses, corners or ends of NWs are subject to a preferential disintegration. Thus, by choosing appropriate geometries and implantation conditions, SPP waveguides based on multiple nanodot chains, e.g. L-turns, X- or T-junctions, might be fabricated by FIB implantation. The simulations were performed for focused Co ion implantation into Si since CoSi2 might be a metallic waveguide material with several advantages: monocrystalline embedding into c-Si with coherent (and defect-free) interfaces, CMOS-compatibility, and surface plasmon resonance in the infrared where Si is transparent.

We present reaction pathways of a novel method of semiconductor nanowire (NW) fabrication using a focused ion beam (FIB). This investigation is based on kinetic Monte Carlo simulations including realistic FIB implantation profiles which were determined by spatially dependent dynamic ion range calculations. A focused implantation of Si or Ge ions into SiO2 along a straight trace leads to local supersaturation of the implanted species in the dielectric substrate. During post-implantation annealing, semiconductor NWs embedded in the dielectric matrix form along the FIB implantation trace. Even complex structures involving several NWs, e.g. T- or X-junctions, may be obtained. The dominating driving force of NW formation is a free energy gain by phase separation and by reduction of high interface curvatures. The diameter of the synthesized NWs is about five times smaller than the width of the FIB implantation trace. During long-term thermal annealing, NWs disintegrate into regular chains of nanodots because of the built-up of long-wavelength interface undulations (Rayleigh instability). Crosses, corners or ends of NWs are subject to a preferential disintegration. Thus, structures suitable for single-electron-transistors may be realized where an isolated nanocluster is located in a tunnel distance from several NW contacts. Moreover, multi-gate NW field effect transistors may be fabricated by crossing FIB traces of different ion fluences.

Nanofluidic devices are going to play an important role in miniaturization, automation and parallelization of chemical, biological, or medical systems. At present, the fabrication of microfluidic channel networks requires a large number of sophisticated processing steps. For "lab on a chip" devices, CMOS compatibility is desired in the fabrication process, additionally. In this contribution, we present potential reaction pathways of a nonconventional, however, CMOS-compatible fabrication method of nanofluidic channels and channel networks. The reaction pathways are predicted by Monte Carlo simulations which atomistically describe the evolution of a sample configuration during a thermal treatment. Referring to the "empty space-in-silicon" formation technique (T. Sato et al., Jnp. J. Appl. Phys. 43 (2003) 12.), a Si-(100) substrate is assumed which contains isolated trenches that are arranged in a line. This approach is modified by using trenches of different depths and diameters. During thermal treatment in a low-pressure hydrogen atmosphere, migration of surface atoms leads to an overall surface minimization. Thin trenches decouple quickly from the wafer surface forming buried voids. In a self-organizing manner, neighboring voids may coalesce and, thus, they construct a buried channel. Due to their lower surface-to-volume ratio, thick trenches are more stable. They remain in contact with the wafer surface and, therefore, they may act as vertical supply and drain pipes for the buried channels. In addition, the simulations predict the formation of elementary nanochannel networks such as T-junctions, X-junctions, or Hfilters. The channel surface of the whole active layer can be transformed into SiO2 by postfabrication oxidation.