Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The effects of strong melt convection on microstructure evolution and resulting mechanical properties of Ti45Al55 peritectic alloys has been investigated. The samples are subjected to both conventional induction melting as well as enhanced melt stirring by applying an external magnetic field using a specially designed floating zone arrangement. The stirred samples show a significant improvement of the plastic deformability compared to the conventionally melted samples. Additionally, the fracture surface of the stirred samples exhibits more deformation. A strong change in the morphology of properitectic phase from dendritic to spherical together with an increase in the properitectic phase fraction was observed in the stirred samples. The possible reason of the change in morphology is explained as a result of spherical growth under forced convection. Compositional line-scan shows that the Al-depletion layer near the interface of (a2+g) colonies and g matrix reduces in the stirred samples due to the enhanced mass transfer under the effect of strong stirring.

We analyze numerically 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). The Chebyshev collocation method is used to calculate the eigenvalue spectrum for small amplitude perturbations.

The temperature dependence of electrical conductivity, thermoelectric power and viscosity of Pb-based eutectic and near eutectic systems were studied. An anomalous behavior of the physical properties in the liquid binary Pb-Sn, Pb-Bi, Pb-Mg and ternary Pb-Bi-Sn melts has been revealed well above the liquidus. The temperature range of the anomalies reaches hundreds degrees and depends on the sample composition. The results obtained are interpreted in the context of the assumption that microsegregation areas formed by micro and nanoclusters exist in the eutectic and near eutectic systems.

Electrical conductivity, s(T), and thermoelectric power, S(T), of liquid Pb-Bi alloys of eutectic and near eutectic compositions were investigated in the “melting-solidification” temperature region. The revealed discrepancies between the heating and cooling s(T) and S(T) curves as well as a hysteresis observed in course of heating-cooling cycles suggest a metastable microheterogeneous structure of the Pb-Bi melts. A solidification mechanism is proposed.

Iridium oxide thin films were grown with atomic layer deposition (ALD) from Ir(acac)3 and ozone between 165 and 200 °C. The films were successfully deposited on soda lime glass, silicon substrate with native oxide and Al2O3 adhesion layer. Saturation of the growth rate with respect to both precursors was verified and the film thickness depended linearly on the number of deposition cycles applied. The iridium oxide films had low impurity contents and good adhesion to all tested surfaces. IrO2 film deposited at 185 °C had homogeneous depth profile and contained 3.5 at. % hydrogen and less than 0.5 at. % carbon impurities. Resistivities of about 40 nm thick IrO2 films varied between 170 and 200 μΩcm. The films deposited above 200 °C were metallic iridium. All the films deposited were crystalline according to X-ray diffraction patterns.

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H interaction with defects in thin Nb films was investigated in this work. Thin Nb films were prepared by the cold cathode beam sputtering. First, microstructure of the as deposited films was characterized. The films sputtered at room temperature exhibit nanocrystalline grains, while those sputtered at high temperature (T = 850 ◦C) are epitaxial. Subsequently, the films were step-by-step electrochemically charged with H. Development of microstructure and evolution of defect structure with increasing H concentration was investigated by slow positron implantation spectroscopy combined with X-ray diffraction. It was found that H is trapped at open-volume defects in the thin films of both kinds. The nanocrystalline films exhibit significantly extended H solubility in the alpha-phase. Formation of the hydride-phase (Nb-H) at higher H concentrations leads to introduction of new defects. These are most probably dislocation loops that are emitted by growing hydride-phase particles.

The introduction of new defects due to H-loading of Nb, their population as a function of the H concentration, and the mechanism of their formation are investigated by positron annihilation spectroscopy (PAS). In addition, X-ray diffraction (XRD), and transmission electron microscopy (TEM) are applied. Furthermore, the results obtained by the experimental techniques are compared with theoretical calculations of energetic stability and positron characteristics of various defect-H configurations. It is found that vacancies surrounded by H atoms are introduced into the specimens by H-loading. The density of these vacancy-H complexes increases with increasing concentration of H in the specimens. The H-induced vacancies are formed even in the alpha-phase field, when the metal–H system is a single phase solid solution. The stability of the H-induced defects and the
mechanism of their formation are discussed.

We report on pressure-dependent superconducting and transport properties of the quasi-two-dimensional organic superconductor b"-(ET)₂SF₅CH₂CF₂SO₃. With increasing pressure both the superconducting transition temperature, T_c, as well as the effective mass, m_c, decrease monotonously. By assuming a direct relationship between m_c and the superconducting coupling parameter λ, the pressure dependence of T_c can be well described by the modified McMillan equation. For all pressures in the metallic state the resistance follows q = q0 + AT² at low temperatures. The coefficient A, however, is found to be not proportional to m² _c as expected for a purely electronic origin of the T² behavior.

In this study we report the synthesis and characterization of four samples prepared with a nominal RuSr₂GdCu₂O₈ starting composition following a two-step procedure, involving the Sr₂GdRuO₆ compound as precursor, in a controlled atmosphere. A chemicalvapour-transport process in an open system is used to control the Ru content in these samples during the annealing cycle. We observe that high Ru-oxides mass transport results in a change of the phases in equilibrium at the RuSr₂GdCu₂O₈ composition and a multiphase product is obtained. Rietveld refinement analysis and SEM-EDX studies are carried out in order to estimate the Ru content in the asprepared RuGd1212.

Engineers could soon have a much better idea of what is going on inside pipelines and industrial reactors thanks to a new flow sensor developed by scientists in Germany. The device is able to distinguish between different substances in a flowing mixture and it could help solve tricky flow problems such as how to move unruly mixtures of oil, gas and water from deep undersea wells to the surface.

Physikalische Modellierung von Strömungen für Kristallzüchtungen

Trickle bed reactor performance and safety may suffer from radial and axial liquid maldistribution and thus from non-uniform utilization of the catalyst packing. Therefore, experimental analysis and fluid dynamic simulation of liquid-gas flow in trickle bed reactors is an important topic in chemical engineering. In the presented study for the first time a truly high-resolution gamma ray tomography technique was applied to the quantitative analysis of the liquid flow texture in a laboratory cold flow trickle bed reactor of 90 mm diameter. The objective of this study was the comparative analysis of the liquid flow dynamics for two different initial liquid distributions and two different types of reactor configurations. Thus, the hydrodynamic behavior of a glass bead packing was compared to a porous Al2O3 catalyst particle packing using inlet flow from a commercial spray nozzle (uniform initial liquid distribution) and inlet flow from a central point source (strongly non-uniform initial liquid distribution), respectively. The column was operated in downflow mode at a gas flow rate of 180 L/h and at liquid flow rates of 15 L/h and 25 L/h.

In the first part we present results of direct numerical simulations on turbulent channel flow drag reduction using electromagnetic forces. The Lorentz force is created by the interaction of a permanent magnetic field and an electric current from electrodes placed on the bottom wall surface. We consider the two cases of a spanwise oscillating force and a streamwise steady force. In the second part the flow behind an electromagnetically self-moved sphere is considered for which a drag reduction is found. Results on the linear and nonlinear flow stability will be provided.

Trickle bed reactor performance and safety may suffer from radial and axial liquid maldistribution and thus from non-uniform utilization of the catalyst packing. Therefore, experimental analysis and fluid dynamic simulation of liquid-gas flow in trickle bed reactors is an important topic in chemical engineering. In the presented study for the first time a truly high-resolution gamma ray tomography technique was applied to the quantitative analysis of the liquid flow texture in a laboratory cold flow trickle bed reactor of 90 mm diameter. The objective of this study was the comparative analysis of the liquid flow dynamics for two different initial liquid distributions and two different types of reactor configurations. Thus, the hydrodynamic behavior of a glass bead packing was compared to a porous Al2O3 catalyst particle packing using inlet flow from a commercial spray nozzle (uniform initial liquid distribution) and inlet flow from a central point source (strongly non-uniform initial liquid distribution), respectively. The column was operated in downflow mode at a gas flow rate of 180 L/h and at liquid flow rates of 15 L/h and 25 L/h.

In order to investigate the effect of ion flux and irradiation temperature on defect evolution in germanium during the process of ion implantation, a focused ion beam system is used. Channeling implantation of Ga ions is performed at two very different ion fluxes (1012 and 1019 cm-2 s-1), at two temperatures (room temperature and 250 0C), and at five different fluences, ranging from 5x1012 to 5x1014 cm-2. The depth distributions of Ga and the implantation damage are determined by SIMS and micro-RBS/C, respectively. The fluence dependence of the measured range profiles and of the implantation damage is strongly influenced by the ion flux 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. At 250 °C, the maximum lifetime of the defects is less than 10 s. On the other hand, at room temperature no significant annealing is found within the first 10 s after ion impact. 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. This probability depends on the total nuclear energy deposition per target atom and on two empirical parameters [1].
[1] M. Posselt, L. Bischoff, D. Grambole, F. Herrmann, Appl. Phys. Lett. 89 (2006) 151918

Self-diffusion in Si is determined by the concentration and the mobility of both vacancies and self-interstitials. The self-diffusion coefficient is usually given by Dsd = fV CV DV + fI CI DI, where CV and CI are the relative concentrations of vacancies and self-interstitials, respectively; DV and DI denote the diffusivities. The quantities fV and fI describe the correlation between the migration of Si atoms and the migration of vacancies and self-interstitials; fV and fI are therefore called correlation factors. The statistical theory of diffusion [1,2] allows the determination of these factors if certain atomic mechanisms for vacancy and self-interstitial migration are assumed. On the other hand, the self-diffusion coefficient per point defect as well as the point defect diffusivity can be calculated by molecular dynamics (MD) simulations. The ratio of both quantities yields the correlation factors fV and fI. In this manner, they can be determined without any assumption about the atomic migration mechanisms.
In the present work, point defect migration and the related atomic mobility are investigated by MD simulations using the interatomic potentials of Stillinger-Weber and Tersoff. It is shown that the value of fV = 0.5 obtained by MD simulations is identical with that determined by the statistical diffusion theory, since the simple atomic mechanism assumed in this theory is also found by the simulations. The mechanisms of self-interstitial migration are more complex. The detailed study, including a visual analysis and investigations with the nudged elastic band method, reveals a variety of transformations between different self-interstitial configurations. MD simulations with the Stillinger-Weber potential show, that the self-interstitial migration is dominated by the dumbbell mechanism, whereas in the case of the Tersoff potential the interstitialcy mechanism prevails. The corresponding values of the correlation factor fI are different, namely 0.56 and 0.73 for the dumbbell and the interstitialcy mechanism, respectively. The latter value corresponds to that obtained by the statistical theory [2] which assumes an interstitialcy mechanism. However, results of recent investigations on intrinsic point defects in silicon using a unified view from crystal growth, wafer processing and metal diffusion [3], and on dopant and defect diffusion [4] demonstrate, that in the framework of state-of-the-art modeling a reasonable interpretation of experimental data can be only given by assuming fI = 0.5…0.6. The comparison with results of the present atomistic study leads to the conclusion that self-interstitial migration in Si should mainly occur via the dumbbell mechanism.
References:
[1] K. Compaan, Y. Haven, Trans. Faraday Soc. 52 (1956) 786
[2] K. Compaan, Y. Haven, Trans. Faraday Soc. 54 (1958) 1498
[4] V.V. Voronkov, R. J. Falster, Solid State Phenomena 108-109 (2005) 1
[3] H.Bracht, Physica B 376-377 (2006) 11

Bubbles in shear flows experience a lift force, causing them to migrate sideward while they are rising. This lateral migration is also observed in numerical simulations, which are carried out with an extended version of the highly parallelized code FS3D, employing an advanced Volume-of-Fluid method. The movement of single bubbles in linear shear flows is simulated to obtain the magnitude of the lift force – expressed by the lift force coefficient CL – for various bubble diameters and material data. Simulation results are in good agreement with experiments for medium liquid phase viscosities. The pressure and the velocity fields near the interface are investigated and the contribution of dynamic pressure and the circulation of the lift force are discussed.

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Die in diesem Bericht dokumentierten Ergebnisse sind vertraulich.

The Vertical Gradient Freeze (VGF) method is an important technique for the growth of bulk semiconductors from the melt. The structural and electrical properties of the crystals depend on the melt flow which can be influenced by external magnetic fields. By applying an AC field, the flow can be tailored to improve the quality of the crystals and the yield of the growth process. The induced melt flow, however, tends to be time-dependent which might be avoided by combining the AC field with a DC field.

Melt extraction is a near-net-shape casting process in which a swiftly rotating disc draws filaments out of a melt. The melt solidifies at the V-shaped circumferential edge upon first contact, and the layer grows while the disc moves further through the liquid pool. A disc may be equipped with several edges to increase the performance. Further, the perimeter may be notched to produce fibres having a certain length. During rapid cooling, the filament shrinks and is finally flung away by centrifugal force. Two different methods were developed in the seventies and established on industrial scale. Nonetheless, both still show their specific inadequacy. The extraction out of a crucible is characterised by a relatively large surface allowing multi-edge and thus efficient operation. Usually, the melt contained in a refractory is lifted slowly toward the disc. Induction heating and shear stress supplied by the disc lead to turbulent melt motion, which limits the process with respect to extraction velocity and, in turn, to relatively thick fibres. It is possible to extract ultra-fine filaments from a pending drop. That needs melting of a rod at its tip, which is usually accomplished by an oxygen-acetylene torch. Though the confined volume and capillary forces due to a small radius of curvature permit high extraction velocity, the productivity suffers from the fact that only one edge can be used.
Damping of velocity fluctuations may be realised by a static magnetic field. Concerning the crucible extraction, extended series measurements showed that globally applying such a magnetic brake has two effects:
(i) it is possible to achieve higher extraction speed, but
(ii) the fibre diameter is barely affected. High speed video recordings revealed that extraction takes place only during duty cycles. Instead of producing thinner fibres, as has to be expected from higher circumferential speed in case of continuous extraction due to conservation of mass, the damping also reduces the mean velocity, and in turn the mass transport onto the disc; the globally applied magnetic brake influences the length of the duty cycle. Here, the tailored magnetic solution is a concentration of magnetic flux density to the small meniscus region of the extraction zone by means of ferromagnetic parts. This local stabilisation significantly reduces the fibre diameter. Poor efficiency of the pending drop technique can be overcome with extraction from a molten edge. The problem to be solved is melting the sheet directly at its edge. Owing to geometric restrictions, electromagnetic heating with a long inductor having two opposing branches would either release most of the heat at a certain distance from the edge, or in the disc. Passing the current in the same direction through the branches in combination with optimisation with respect to the skin effect allows moving the area of heat impingement almost entirely outside the inductor toward the edge of the jutting through sheet. In two experiments, a platinum sheet was molten directly at its edge and very thin tin fibres were produced.

Au nanocrystals (NCs) were synthesized in a thin SiO2 layer by ion implantation and annealing in a tight distribution close to the Si/SiO2 interface. Between the NCs and the Si substrate a thin tunneling oxide forms self-organized during annealing totally depleted from Au NCs. Memory behavior is demonstrated by electron charging and discharging on metal-oxide-semiconductor capacitors. Lenticular liquid Au:Si droplets nucleate at the Si/SiO2 interface from silicon regions supersaturated by Au close to the oxide. Au NCs embedded in SiO2 above these droplets are stabilized during annealing due to a modified detailed balance of Au atom detachment and attachment. Capacitance-voltage and spreading resistance measurements reveal the impact of the Au contamination in the Si substrate. Structure and distribution of Au droplets and NCs are characterized by x-ray diffraction and transmission electron microscopy .

This multicenter study examined F-18-FDG PET measures in the differential diagnosis of Alzheimer's disease (AD), frontotemporal dementia (FTD), and dementia with Lewy bodies (DLB) from normal aging and from each other and the relation of disease-specific patterns to mild cognitive impairment (MCI). Methods: We examined the F-18-FDG PET scans of 548 subjects, including 110 healthy elderly individuals ("normals" or NLs), 114 MCI, 199 AD, 98 FTD, and 27 DLB patients, collected at 7 participating centers. Individual PET scans were Z scored using automated voxel-based comparison with generation of disease-specific patterns of cortical and hippocampal F-18-FDG uptake that were then applied to characterize MCI. Results: Standardized disease-specific PET patterns were developed that correctly classified 95% AD, 92% DLB, 94% FTD, and 94% NIL. MCI patients showed primarily posterior cingulate cortex and hippocampal hypometabolism (81%), whereas neocortical abnormalities varied accordi!
ng to neuropsychological profiles. An AD PET pattern was observed in 79% MCI with deficits in multiple cognitive domains and 31% amnesic MCI. F-18-FDG PET heterogeneity in MCI with non-memory deficits ranged from absent hypometabolism to FTD and DLB PET patterns. Conclusion: Standardized automated analysis of F-18-FDG PET scans may provide an objective and sensitive support to the clinical diagnosis in early dementia. Key Words: F-18-FDG PET; Alzheimer's disease; frontotemporal dementia; Lewy body dementia; mild cognitive impairment; normal aging; hippocampus.

Low-lying dipole strength and nuclear deformation

Tidal Waves and Boson Condensation in Transitional Nuclei

For the present study time periodic wall parallel Lorentz forces have been used to excite the separated flow on the suction side of an inclined flat plate. Experiments for a Reynolds number of 10^4 and an angle of attack of a = 13° are reported. The controlled flow is characterised by a small number of relatively large scale vortices, which are related to the control mechanism. The influence of the main parameters, i.e. the excitation frequency, amplitude and wave form on the suction side flow structures was investigated by analysing time resolved particle image velocimetry (TR–PIV) measurements using continuous wavelet analysis for vortex detection and characterisation. Statistical analysis of the coherent structures of the flow was performed on a large amount of data samples.

We report experimental results on laser-driven electron acceleration with low divergence. The electron beam was generated by focussing 750-mJ, 42-fs laser pulses into a gas-filled capillary discharge waveguide at electron densities in the range between 1018 cm−3 and 1019 cm−3. Quasi-monoenergetic electron bunches with energies as high as 500 MeV have been detected, with features reaching up to 1 GeV, albeit with large shot-to-shot fluctuations. A more stable regime with higher bunch charge (20-45 pC) and less energy (200-300 MeV) could also be observed. The beam divergence and the pointing stability are around or below 1 mrad and 8 mrad, respectively. These findings are consistent with self-injection of electrons into a breaking plasma wave.

Recent progress in astronomy, in many cases by satellite-based observatories, has led to much more precise astronomical data. Nuclear data with matching precision are necessary for a proper understanding of astronomical scenarios such as the big bang, stable and explosive stellar burning. In the case of nuclear reaction cross sections, precision data require measurements directly at Gamow peak energies, where the absolute value of the cross section is very low. In the present lecture, underground facilities for nuclear astrophysics are reviewed with a focus on providing cross section data. For activation studies, shallow and deep underground laboratories have been employed. Exemplary results from the Felsenkeller Dresden/Germany shallow underground laboratory and the Gran Sasso/Italy deep underground facility are shown and discussed. For in-beam gamma-spectroscopy studies, so far only the LUNA facility at Gran Sasso is available. The salient features of LUNA and some recent results are shown. The lecture ends with an outlook on currently proposed new underground accelerators in Italy, the United States, the United Kingdom and Romania.

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We present de Haas-van Alphen (dHvA) investigations on the nonmagnetic borocarbide
superconductors LuNi2B₂C and YNi₂B₂C. The measurements were carried out by use of a cantilevertorque method on a rotator set up in high magnetic fields up to 32 T and at low temperatures down to 50 mK. From the normal-state oscillations we determine the electronic band structure of the material. From comparison with full-potential local-orbital calculations we assigned the measured dHvA frequencies to the different bands identified the expected spherical, cubic and ‘cushion’-like closed Fermi surfaces. Additionally, we found frequencies that probably belong to a complicated multipleconnected Fermi-surface sheet. Further, we performed temperature-dependent measurements that allowed the extraction of the effective band masses of the different Fermi-surface sheets. We find mass enhancements in comparison to the calculated values that are due to electron-phonon coupling.
Finally, we are able to determine the angular dependences of the electron-phonon coupling for the different Fermi-surface sheets.
Below the upper critical field, Bc2, an additional damping of the oscillation amplitude appears. This decrease might be related to the increase of the superconducting gap parameter which could be calculated from quantitative measurements of this effect. However, the analysis is hampered by additional influences originating form changes in the flux-line lattice that appear close to the superconducting phase transition. Therefore, we compare two differently grown crystals. The one grown by a zone-melting method shows a rather abrupt vanishing of the oscillation amplitude in the superconducting state. In contrast, for the flux-grown crystals we observe a smooth damping
combined with a broad phase transition.

We introduce a method for stopping highly charged ions (HCIs) in a laser-cooled one-component plasma (OCP) of 24Mg+ ions and present results on stopping times derived from realistic molecular dynamics simulations of the complete stopping process. This stopping scheme can provide ultra-cold highly charged ions for future in-trap precision mass measurements. The choice of an ultra-cold ion plasma as a stopping medium is governed by the almost negligible charge exchange of the HCI with the laser-cooled ions and the very low temperatures which can be reached. In our analysis we focus on the stability and fast recooling of the plasma – two features essential for the experimental realization of this stopping scheme.

Antiferromagnetic quantum spin-1 chains have been the subject of intensive theoretical and
experimental studies, fostered especially by the Haldane conjecture (F.D.M. Haldane, Phys. Lett. 93A
(1983) 464). In this work we report results of high-magnetic-field studies of the new spin-1 chain
material NiC₂H₈N₂. The magnetic susceptibility, low-temperature magnetization
and high-field electron spin resonance (ESR) studies unambiguously indicate that NENB is a Haldanechain
material. Two critical fields were revealed by high-field (up to 15 T) magnetization
measurements indicating a field-induced collapse of the spin-singlet ground state and a finite
anisotropy of the g-factor in fields applied parallel and perpendicular to the chain direction. The spin
gap has been measured directly by means of the high-field ESR, revealing Δ = 17.4 K.

An approach to synthesize the electrophilic fluorinating agent no-carrier-added (n.c.a.) [¹⁸F]perchloryl fluoride ([¹⁸F]FClO₃) in superacidic media in the presence of KClO₄ or anhydrous perchloric acid starting from [¹⁸F]fluoride was demonstrated in this study. However, the radiochemical yields were low (1–6%) and poorly reproducible. Fluorosulphonic acid proved to be an essential intermediate as revealed by non-radioactive experiments. A key problem in the preparation of [¹⁸F]FClO₃ is the assumed kinetic inhibition due to the unfavourable stoichiometric ratio of the ClO₄ moiety to [¹⁸F]HSO₃F.

We present a new cooling scheme for the preparation of highly charged ions for future in-trap precision experiments. A plasma of laser cooled 24Mg+ ions trapped in a 3D harmonic confinement potential is used as a stopping medium for the highly charged ions. We focus on the dynamic evolution of the plasma, determining suitable cooling conditions for fast recooling of the 24Mg+ ions. The results of a realistic parallel simulation of the complete stopping process presented here indicate that a small, constant detuning of the laser frequency is sufficient for subsequent recooling of the plasma, thus maintaining the stability of the plasma.

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BACKGROUND:

Hepatic encephalopathy (HE) is considered to be mainly due to increased ammonia metabolism of the brain. If this hypothesis is true, cerebral glucose utilisation, which is considered to represent brain function, should be closely related to cerebral ammonia metabolism. The aim of the present study was to analyse if cerebral ammonia and glucose metabolism in cirrhotic patients with early grades of HE are as closely related as could be expected from current hypotheses on HE.

METHODS:

¹³N-ammonia- and ¹⁸F-fluorodesoxyglucose (FDG) - PET, magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) were performed in 21 cirrhotic patients with grade 0 -1 HE. Quantitative values of cerebral ammonia uptake and retention rate and glucose utilisation were derived for several regions of interest and were correlated to the MRS data of the basal ganglia, the white matter and the frontal cortex.

RESULTS:

A significant correlation between plasma ammonia levels and cerebral ammonia metabolism, respectively, and MRS alterations could be shown only for the white matter. In contrast, the MRS alterations in all three regions studied were significantly correlated with the glucose utilisation of several brain regions. Cerebral ammonia and glucose metabolism were not correlated.

CONCLUSION:

Increase of cerebral ammonia metabolism is an important but not the exclusive causal factor for the development of hepatic encephalopathy.

We present de Haas–van Alphen (dHvA) measurements of the nonmagnetic borocarbide LuNi₂B₂C. In the superconducting state below the upper critical field, B_c2, the dHvA signal shows an additional damping. For some field orientations we observe a very strong damping close to B_c2 and only a very weak effect at lower fields in the superconducting state. We discuss the origin of the different dampings and their relation to the superconducting gap.

Raman scattering and optical birefringence are used in to investigate a low-temperature phase transition in a single crystal of the two-dimensional Na5RbCu4(AsO4)(4)Cl-2. Phonon anomalies point to a first-order nature of the transition. The observed transition is most probably related to an order-disorder transition of the Rb ion positions along the z axis within the ionic framework of mixed alkali metal chloride lattices.

A composite of poly p-phenylene-2,6-benzobisoxazole (PBO) fiber and epoxy resin has excellent electrical insulation properties. However, it is a challenging issue to improve its mechanical properties because of poor adhesion between PBO fiber and matrix. The relatively smooth and chemically inactive surface of PBO fiber prevent efficient chemical bonding in the composite interface. Here, we report the surface modification of PBO fibers by UV irradiation, O-2 and NH3 plasma, as well as acidic treatments. We found that the surface free energy and roughness are increased for both sized and extracted fibers after plasma treatments together with maleic anhydride grafting. The sized fiber shows marginal improvement in adhesion strength and no change in fiber tensile strength because of the barrier effect of the finish. For the extracted fiber, however, the tensile strength of the fiber is sensitive to surface treatment conditions and considerable strength reduction occurred, parti! cularly for cases of acidic treatments and UV irradiation. This is because that the treatments increase the surface roughness and introduce more surface flaws. The extracted fiber surface has no adequate wetting and functional groups, which in turn results in coarse interface structures and causes reduction or no apparent variation of the adhesion strength. The fracture surfaces after single fiber pull-out tests exhibit adhesive interfacial failure along the fiber surface, which is further confirmed by similar adhesion strength and interlaminar shear strength values when the fiber was embedded in various epoxy resins with different temperature behavior.

Endotoxial growth of InSb nanocrystals

RBS investigations on Ge+ implanted silicon films on insulators

Gaussian generation-recombination is known to be a dominant mechanism of current noise in quantum well systems biased by electric field normal to the layers. We have found pronouncedly non-Gaussian excess current noise in n-type and p-type multiple quantum wells. The non-Gaussian noise has been attributed to metastable spatial configurations of electric field. The metastability is likely originating from negative differential conductance caused by intervalley scattering in n-type wells and heavy and light holes tunneling in p-type wells. At a constant bias the quantum well system randomly switches between a high resistivity state with low current flow and low resistive state with high current flow. The non-Gaussianity of the noise is more pronounced in p-type wells where the time traces of current fluctuations resemble closely two-level random telegraph signal which has not been straightforwardly observed in n-type wells. The non-Gaussian character of the noise in n-type systems has been revealed by measurements of nonzero skewness of the amplitude distributions. The difference between noise properties of n- and p-type systems has been attributed to small capture probability of electrons in n-type wells, as opposed to very high capture probability of holes in p-type wells. As a consequence the noise of any p-type multi-well system is dominated by fluctuations of a single while in the n-type the noise appears as a superposition of many fluctuators associated with individual wells.

The influence of the implantation sequence on the defect and implant distribution during (SiC)1-x (AlN)x formation was studied by Rutherford backscattering spectrometry/ion channelling (RBS/C) and elastic recoil detection. It is shown that the implantation sequence aluminum followed by nitrogen lead to an improved crystallinity compared to the reverse implantation sequence for implantation temperatures above 400o C. The results obtained are discussed in relation to the defects distributions calculated by using a developed model which includes the effect of stress self-consistently.

Aufgabe der Erfindung ist es, eine wirkliche Echtzeit-Beobachtung der laufenden Bestrahlung weitgehend verzerrungsfrei zu ermöglichen. Außerdem soll mit dem Verfahren eine Korrektur der physiologischen Prozesse möglich werden.
Die Erfindung beinhaltet, dass die Flugzeitdifferenz der Annihilationsquanten gemessen wird und deren Korrelation mit der Mikro- und/oder Makrostruktur des Strahls und den Ortskoordinaten kombiniert und in ein Echtzeitdatenerfassungssystem eingespeist wird und dass in Echtzeit eine bildliche Darstellung der ß+-Aktivität, die im Patienten erzeugt wird, sowie eine off-line-Korrektur der Abbildungsfehler auf Grund physiologischer Prozesse erfolgt.

Aufgabe der vorliegenden Erfindung ist es, eine Anordnung zur schnellen Messung der Phasen- oder der Komponentenverteilung in einem Strömungsquerschnitt für Stoffgemische auch nichtleitender Art auf Basis einer Messung der komplexen elektrischen Admittanz anzugeben.
Die Erfindung beinhaltet im Wesentlichen, dass

• den Sendeelektroden (3a) der Anregungsebene mindestens ein Sinusgenerator (5) vorgeschaltet ist, der die Sendeelektroden (3a) mit einer Wechselspannung beaufschlagt,
• den Empfängerelektroden (3b) Strom-Spannungswandler (7) nachgeschaltet sind, die den von mindestens einer Anregungselektrode (3a) durch das Medium zu den Empfängerelektroden (3b) fließenden Wechselstrom verstärken und in ein Spannungssignal umwandeln,
• den Strom-Spannungswandler (7) Filtergruppen (10, 11, 16) und Vektorvoltmeter (8) nachgeschaltet sind, mit denen das komplexe Signalverhältnis Ua/Ue messtechnisch erfasst wird.

Die Aufgabe der vorliegenden Erfindung besteht darin, eine Durchflussmessung zu ermöglichen, die ohne mechanischen oder elektrischen Kontakt zum fließenden Medium auskommt, keine Vielzahl von Magnetfeldmessstellen erfordert, eine Durchflussmessung hoher zeitlicher Auflösung liefert, gegenüber äußeren Einflüssen möglichst unempfindlich ist und nicht die lageempfindlichen Amplituden in Empfängerspulen bei Wechselstromerregung benutzt.
Die Erfindung geht aus von einem magnetischen Wechselfeld außerhalb des elektrisch leitfähigen Mediums und beinhaltet, dass der Einfluss des strömenden Mediums auf das angelegte Magnetfeld zu einer Phasenverschiebung in den Magnetfeldsignalen an zwei verschiedenen Messorten führt, die als direktes Maß für die mittlere Durchflussgeschwindigkeit des Mediums verwendet wird. Die Phasenverschiebung kann auch mittels zweier Empfängerspulen entlang des Strömungskanals gemessen werden.

Der Erfindung liegt die Aufgabe zugrunde, die Geschwindigkeit einer in eine Form einströmenden, flüssigen Metallschmelze beim steigenden Gießen unter Schwerkrafteinfluss durch externe Magnetfelder so zu beeinflussen, dass eine beruhigte Formfüllung unter ausreichender Vermeidung von starken Verwirbelungen der Schmelze und des Auftretens von Instabilitäten der Oberflächenschicht und der einströmenden Schmelzefront erreicht wird.
Die technische Lösung beinhaltet, dass die magnetische Induktion B0 des angelegten Magnetfeldes anfangs mindestens zwei Werte übersteigt.
Gemäß der Anordnung wird ein Magnet am unteren Ende des vertikalen Eingusskanals vor der Umlenkung in den horizontalen Gießlauf angeordnet und mit einer Einrichtung zur Regelung der magnetischen Induktion verbunden.

Die Erfindung betrifft eine Vorrichtung und ein Verfahren zur Herstellung metallischer Fasern durch Schmelzextraktion. Es können unterschiedliche Metalle oder deren Legierungen zu Fasern mit vorgebbaren Faserdurchmessern und Faserlängen hergestellt werden. Dabei ist es Aufgabe der Erfindung die Effektivität der Faserherstellung zu erhöhen und die Nachteile der Schmelzextraktion aus einer in einem Tiegel vorgehaltenen Schmelze zu vermeiden. Erfindungsgemäß wird mindestens eine radial äußere Kante einer rotierenden durch linienförmig ausgebildete Schmelze an einem Substrat geführt. Die lienienförmige Schmelze wird an einem stirnseitigen Rand eines metallischen Subtrates, das nachführbar ist, induktiv ausgebildet.

Growth regimes of C:Ni (~ 30 at.%) composite thin films grown by ion beam co-sputtering in the temperature range of RT-500◦C are investigated. the combination of elastic recoil detection analysis, X-ray diffraction, transmission electron microscopy and Raman spectroscopy employing two excitation wavelengths was used to characterize the coexisting carbon and nickel constituents of the composite structure. Three growth regimes are identified characterized by different Ni nanoparticle shape (granular, columnar) and crystal structure (Ni3C or fcc Ni). The comparison of the Raman spectroscopy results from a carbon reference and C:Ni (~30 at.%) thin films shows that the presence of Ni enhances significantly the 6-fold ring clustering process at temperatures as low as RT, while at higher temperatures it favors ordering within the 6-fold ring clusters. The enhancement occurs independently on Ni nanoparticle size, shape or phase and is related to processes taking place on the surface of the growing film growth rather than in the bulk.

Single crystalline AISI 316L austenitic stainless steel (ASS) samples of different orientations (001), (110), (310) were implanted at 400 °C with 1.2 keV nitrogen ions using a high current density of 0.5 mA˙cm− 2. Quantitative nitrogen distribution profiles were determined using nuclear reaction analysis (NRA), while the structure of the nitrided layer was analyzed using X-ray diffraction mapping of the reciprocal space. For identical nitriding conditions it is observed that surface N concentration does not depend on the orientation (not, vert, similar23-24 at%), on contrary to the N penetration depth which is larger for the (001) and (310) orientations than for the (110) one. In each single crystal, lattice expansion in the nitrided layer is similar for all the studied crystallographic planes but it increases with the thickness of the nitrided layer. In addition, it is shown that during nitriding a simultaneous lattice rotation of a few degrees (< 5°) of the nitrided layer accompanies the lattice expansion with an increased mosaïcity.

The mould filling process of aluminium investment casting consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment.
We present results on the design and application of a DC magnetic field to control the pouring velocity. Special attention is given on model experiments using the low melting point eutectic melt GaInSn. Ultrasonic Doppler velocimetry was applied to carry out detailed velocity measurements in the model. In addition, high-speed video camera observation of the incoming melt front was performed revealing the key importance of the initial flow structure for the final casting product quality.
Based on this modelling knowledge, a DC magnetic field has been developed in order to control the mould filling process. This DC field has been tested under industrial conditions. The primary action of the magnetic field, i.e. the reduction of the velocity peaks at the beginning of the process, was clearly demonstrated. The amplitude of the DC field was tuned during the process as the braking action is only needed during the first part of the process. In this way, a clear reduction of the peak velocities is obtained without a significant prolongation of the overall filling time. Eventually, a remarkable diminishment of defects in the casting products was achieved. A multitude of investment casting units have been produced showing a significant improvement of the casting properties due to the magnetic field control of the filling process.

We use ab-initio methods to optimizes the structure of a thin
Pd-film on the surface of different piezoelectric oxides and
calculate electronic and magnetic properties.
It is known from bulk Pd, that the valence electrons order
ferromagnetic at a critical expansion of the lattice constant.
With piezoelectric oxides it might be possible to control the
magnetization of the Pd-film by varying the structural parameters

Although, most of the work reported on two-phase flows are limited to small pipe diameters, two-phase flow in large risers are increasingly being encountered in the petroleum and nuclear industries. In the present work, a wire mesh sensor was employed to obtain void fraction and bubble size distribution data and visualizations of steam/water flow in a large vertical pipe (194mm in diameter) at 46bar. For comparison purposes, measurements were made at similar phase velocities and physical properties to the data of Omebere-Iyari et al. (2007), which is for nitrogen/naphtha flow in a similar-sized riser. There exist significant differences between both sets of data. Churn-turbulent flow is observed in the present work instead of slug flow, and this differs from the intermittent and semi-annular flow patterns reported by Omebere-Iyari et al. (2007). The mean void fraction of the nitrogen/naphtha data is higher than that of the present steam/water data due to the differences in composition in the liquid phases. Furthermore, core peak distributions are observed for the present work in contrast to the flatter profiles predicted for the data of Omebere-Iyari et al. (2007) using a power law relationship.

A brief description is given of the subject of EPM and, in particular, the Chinese-German cooperation program in this field.

Die Arbeiten und Methoden der in der Abteilung durchgeführten Forschungen zur MHD werden vorgestellt.

Electrical conductivity, s(T), and thermoelectric power, S(T), of liquid Pb-Bi alloys of eutectic and near eutectic compositions were investigated in the “melting-solidification” temperature region. The revealed discrepancies between the heating and cooling s(T) and S(T) curves as well as a hysteresis observed in course of heating-cooling cycles suggest a metastable microheterogeneous structure of the Pb-Bi melts. A solidification mechanism is proposed.

The investigation of insulation debris generation, transport and sedimentation becomes more important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core coolant systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are for example the particle load on strainers and corresponding pressure drop, the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow. A joint research project on such questions is being performed in cooperation with the University of Applied Sciences Zittau/Görlitz. The project deals with the experimental investigation and the development of CFD models for the description of particle transport phenomena in coolant flow. While the experiments are performed at the University in Zittau, the theoretical work is concentrated at Forschungszentrum Dresden-Rossendorf.

The lesson 6 of the "Short Course on Multiphase Flow Modelling" describes the practical simulation of the flow in a bubble column. The necessiy of the correct simulation of the momentum exchange between the phases is shown comparing different results with experiments.

The lesson 4 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.

In recent years in close cooperation with ANSYS/CFX a population balance model was developed to simulate multiphase flow with higher gas volume fraction. Several dispersed gaseous phases are modeled having a distinct velocity field. Bubble fragmentation and coalescence is simulated by decades of gaseous sub-size mass fractions, which are assigned to the few dispersed gaseous phases. This approach was called “inhomogeneous MUSIG model” and enables the simulation of bubble size dependent bubble forces.
The presentation reports the basic principles and the application of the model approach to simulate a TOPFLOW experiment, in which a complex three dimensional flow field was measured. A half moon shaped obstacle was arranged in the DN200 test section and the two phase flow field was analysed by a wire mesh sensor.
Applying this approach a more deep understanding of the flow structure is possible. To improve the quantitative accuracy further developments particularly of the models describing bubble fragmentation and coalescence are necessary.

Mg ion implantation into boron substrates followed by pulsed Ar plasma treatment was used to form MgB2 compound. Rutherford Backscattering (RBS) analysis of the best samples revealed that the ratio of atomic concentration of Mg to B atoms could be close to the stoichiometry of MgB2 in the range of about 100 nm beneath the surface. Results of magnetically modulated microwave absorption (MMMA), magnetic moment and electrical conductivity measurements indicate the presence of superconductive grains with critical temperature T-c=25 K. A gradual onset of microscopic percolation is inferred starting from 15 K although no full percolation has been reached.

Superconducting regions of magnesium diboride (MgB2) on magnesium substrate were formed by the combined methods of ion implantation and transient annealing using three different ion fluences and three different energy density of Ar plasma pulses. The samples were characterized by Rutherford back scattering (RBS) and superconductivity detection techniques. The results of these characterizations are presented and discussed. The highest critical temperature observed T-C = 33.8 K.

This paper deals with an experimental study of the two-phase flow in the mixing chamber of an effervescent atomizer. Not only do operational conditions and media properties affect the process of effervescent atomization but also the pattern (quality) of the two-phase flow. Therefore, it is necessary to describe the phenomena associated with the mixing process. Two-phase flow structure was investigated in a mixing chamber with an inner diameter of 8 mm. During the experiment, the effervescent nozzle was operated in the air pressure range of 1 to 0.5 MPa and mass GLR (Gas-to-liquid- ratio) was between 1 and 25%. Mass flow rates of water ranged from 5 up to 50 g•s-1. Since optical measurement techniques fail to provide sufficient quantitative information on the flow structure at higher GLR we applied the conductivity wire-mesh sensor technology to this problem. Therefore, a new miniature wire-mesh sensor for small-diameter tubes was developed. The measuring principle of this sensor is based on the measurement of electrical conductivity in the crossing points of a wire mesh. Due this principle we used a conductive liquid (deionized water). The two-phase flow in the chamber is highly unstable and the wire-mesh sensor provides also data for an evaluation of two-phase flow pulsation.

Resonantly enhanced nonlinear absorption between conduction subbands in InGaAs/AlGaAs quantum wells induces a two-photon photocurrent under femtosecond excitation, which is exploited to determine electron intersubband relaxation and dephasing times. The approach allows us to study systematically the dependence of these time constants on structural parameters, including carrier density and modulation/well doping, and to discriminate between different scattering processes.

kein Abstract verfügbar

During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance with the development of the nano-technology. For special purposes like writing ion implantation for doping or ion beam synthesis (IBS) in the µm- as well as in the nm-range without any lithographic steps ion species other than gallium become more and more relevant. Therefore mass separated FIB systems equipped with alloy liquid metal ion sources (LMIS) play an increasing role.
A Co-FIB obtained from a Co36Nd64 alloy LMIS was applied for the IBS at elevated sample temperatures and subsequent annealing for the fabrication CoSi2 nano-structures down to 20 nm on Si(111) and Si(100) substrates. The combination of FIB implantation (top-down approach) and self organization processes during IBS (bottom-up approach) can provide a spatial reduction of the FIB implanted structures. A second investigated process is the defect induced formation of CoSi2 nanoparticles and nanowires using other ions than cobalt in the FIB, focused down to a spot diameter less than 30 nm at room temperature. The source for Co atoms for the NW growth was a 10 nm thin Co film evaporated onto the rear side of the wafer. The FIB irradiation of Nd, Ga, Si and Au ions and doses of 1015-1017 cm-2 creates a broad spectrum of defects in the substrate. Subsequent annealing leads amongst others to the formation of rod-like extended {311}-defects, which act as a prime source of transient enhanced diffusion of impurities in silicon. Also these defects can dissolve and form other rod-like defects always aligned to the (110) direction with a diameter of 10 – 20 nm and a length of some hundred nm. The heat treatment (1000°C, 30 min, N2) leads to a gettering of cobalt atoms in these defects followed by a CoSi2 formation through Ostwald ripening which stabilizes the origin of the defect rods. The obtained crystalline CoSi2 nanowires showed a diameter of 10 – 30 nm and a length up to some ten micrometer always aligned along the (110) orientations independent of the FIB writing direction with respect to the wafer orientation. These structures were studied by SEM/EDX and AFM analysis as well as by electrical characterization after contacting with W-pads, fabricated by FIB MO-CVD [1].
Furthermore, the high resolution mass separated Rossendorf FIB system, equipped with a CANION 31Mplus column (Orsay Physics) and a Ga liquid metal ion source (LMIS) as well as with different alloy LMIS (CoNd, AuSi, etc.) was used to fabricate other nanostructures.

[1] C. Akhmadaliev, B. Schmidt and L. Bischoff, Appl. Phys. Lett. 89 (2006) 223129

We applied X-ray microtomography (XMT) to determine the macroporosity distribution in polypropylene macroparticles extracted from a gas phase polymerisation process. Different specimens were scanned with a laboratory XMT setup comprising a microfocus X-ray source and an X-ray image intensifier. The XMT technique provides comprehensive three dimensional data volumes representing the local X-ray attenuation in voxels of 5.3 μm x 5.3 μm x 5.3 μm size. After 3D image reconstruction with the Feldkamp algorithm the resulting volume data were processed with histogram based binarisation, connectivity check and volume rendering algorithms. From the resulting 3D images void size distributions in different radial regions of the particles were computed. This enables characterisation of the particles regarding their morphology and elucidation of the effect of given process conditions on morphogenesis.

The method of two-step c cascades following the thermal neutron capture is described. An example of two-step cascade data from measurements with 162Dy target is given together with interpretation of these data in terms of scissors-mode resonances built on excited levels in 163Dy. With the aim of verifying the correctness of the method results of benchmark testing measurements with a 56Fe target are compared with the outcome of the GEANT3 simulations.

Ion beam implantation is one of the major technologies in the semiconductor industry. Although there have been a lot of technological applications there is relatively little known about the structural changes of semiconductors after ion beam implantation. Of particular interest is the creation of lateral nanostructures using different methods of ion beam implantation. One method is to exploit the phenomenon of self-organization during the Ar+ implantation using an oblique ion beam bombarding the sample surface. This results in the growth of the periodic wavelike or ripple like morphology which is produced as a result of the interplay between a roughening process caused by the ion beam erosion (sputtering) of surface and a smoothening process caused by thermal or ion-beam-induced surface diffusion. At least the developing surface structures can be well described in terms of the Bradley-Harper model and respective extensions. Lot of investigations is going on to understand the formation of such nano-structures but mostly looking on the top surface. However, the ion energy dissipation takes place below the surface. Thus the investigation of the interface between the almost amorphous top layer and the underlying crystalline material is important for the understanding of pattern formation.
Detailed studies on the ion induced ripple formation on Si have revealed that they appear only in a limited range of incident angles. The ripple wavelength appears to be linearly dependent on the ion energy and varies in between several nm and hundreds of nm when the ion energy changes from 0.5 to 100 keV. If the ion beam energy was increased up to the 100keV range one-dimensional ripple structures on Si (100) surfaces with wave lengths up to the micro meter range have been observed.Recent investigations using TEM and depth resolved X-ray diffraction methods discovered that the ripples at the surface are followed by a nearly sinusoidal shaped buried interface between the strongly damaged, not completely amorphous near-surface region and the crystalline material. Depending on the chosen energy and the irradiation dose the “amorphous” layer could be reach a thickness of 100nm and corresponds fairly well to the end of range distance of implanted ions.

Ziel/Aim:

Gegenstand der Arbeiten war die In-vitro- und In-vivo-Charakterisierung von radioaktiv beladenen Humanserumalbumin-Mikrosphären (HSAM). Ziel war dabei die Bewertung der Partikel hinsichtlich ihrer Eignung zur radiotherapeutischen Behandlung von Krebserkrankungen der Leber.

Methodik/Method:

An vorgefertigte HSAM (3 Chargen mit unterschiedlicher Oberflächenrauigkeit; mittlerer Durchmesser 25 µm) wurden oberflächlich DOTA-Chelatoren kovalent gebunden. Anschließend erfolgte die Markierung mit Y-86, indem die DOTA-HSAM in einer Lösung des Radionuklides suspendiert wurden. Die In-Vitro-Charakterisierung der markierten Partikel erfolgte durch Inkubation in Humanplasma und Challenge mit DTPA. Die In-vivo-Stabilität der Y-86-DOTA-HSAM wurde bestimmt durch Bioverteilungsstudien in gesunden Wistarratten. Nach intravenöser Applikation der Y-86 markierten Partikel kommt es zum vollständigen Trapping der Mikrosphären in der Lunge, die in useren Untersuchungen als Zielorgan diente. Aus dem Verschwinden der Radioaktivität aus der Lunge können Rückschlüsse auf die Stabilität der Markierung und damit verbunden auf die Stabilität der HSA-Partikel gezogen werden.

Ergebnisse/Results:

DOTA konnte in Form eines Isothiocyanat-Derviates an Oberflächenaminogruppen der HSAM gebunden werden. Unter optimierten Bedingungen enthielten 1 mg Mikrosphären 2 x 10^-7 mol DOTA. Die Markierung der Partikel mit Y-86 gelang in hohen reproduzierbaren Ausbeuten (96 ± 1 %, n = 7) nach 15minütigem Schütteln der suspendierten DOTA-HSAM in Acetatpuffer (pH = 6,5). Die markierten Mikrosphären zeigten hohe Stabilität in Humanplasma und in Anwesenheit von DTPA. Bei den Bioverteilungsstudien fanden wir große Unterschiede zwischen den einzelnen Mikrosphärenchargen mit unterschiedlicher Oberflächenrauigkeit. Partikel mit glatter Oberfläche zeigten die höchste Stabilität. Hier war das Aktivitätsniveau in der Lunge über 48 Stunden annähernd konstant.

Schlussfolgerungen/Consequences:

Die Kopplung von Chelatoren an die Oberfläche von HSAM stellt eine einfache Strategie zu deren Beladung mit Radionukliden dar. Aufgrund ihrer höheren In-Vivo-Stabilität sind Partikel mit glatter Oberfläche besser für radiotherapeutische Anwendungen geeignet als raue Mikrosphären.

Late myocardial damage induced by radiotherapy has become an important issue in radio-oncology since several studies have demonstrated increased incidence of cardiovascular disease following radiotherapy.

AC magnetic fields are used in industrial practice for melt stirring. The requirements are manifold for miscellaneous metallurgical operations or casting technologies, mainly the magnetic field application should provide an efficient mixing of the melt in order to achieve homogeneous distributions of solute and/or temperature. Applications of different magnetic fields (rotating, traveling, pulsating and combinations thereof) are connected with the occurrence of a more or less symptomatic flow pattern. Various forms of electromagnetic stirring have been studied in our laboratory. Here we consider exclusively the use of a rotating magnetic field (RMF), which has already become widespread in industrial practice. For instance, the rotary stirring during solidification has been proved to be a striking method in order to achieve a purposeful alteration of the microstructure of casting ingots, such as a distinct grain refining or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET). However, the imposition of an RMF on a metal column also causes problems like the occurrence of typical segregation pattern or a deflection of the upper free surface leading to surface defects or the entrainment of gas. The RMF application provides a permanent radial inward flow along the solidification front. Such flow is responsible for the transport of solute to the axis of the ingot resulting in typical freckle segregation pattern in form of vertical channels filled with alloy of eutectic composition. In this paper we present a new innovative method of electromagnetic stirring using a modulated RMF which offers a considerable potential for a well-aimed modification of casting properties
Solidification experiments as well as numerical simulations were carried out considering the directional solidification of Pb Sn alloys from a water-cooled copper chill. A modulated rotating magnetic field (RMF) was applied for melt agitation. Thermocouples were used to measure the temperature field during solidification. The velocity field in the liquid phase was determined by means of Ultrasound Doppler velocimetry (UDV). Our numerical model is based on the classical mixture formulation. To calculate the viscosity in the mushy region the model proposed by Roplekar and Dantzig (2001) was implemented into the code. The comparison between numerical simulations and solidification experiments delivered a good agreement. Our results demonstrate the modulation magnetic field enables an effective control of the flow field and the structure of the solidified samples. Modifications of the grain structure and macrosegregation effects are discussed with respect to the details of the flow field.

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 contact-less 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 our experiments we investigated the consequence of an application of a DC magnetic field on both the bubble and the liquid velocity. The motion of single argon bubbles rising in GaInSn were analyzed in terms of the terminal velocity, the drag coefficient, the oscillation frequency of the bubble velocity and the Strouhal number. Because the gas bubble is electrically non-conducting, it does not experience the effect of the electromagnetic force directly. However, the bubble behaviour is influenced by the magnetically induced modifications in the liquid flow structure around the bubble. The measurements reveal a distinct effect of the magnetic field on the bubble velocity as well as the bubble wake. The magnetic field application leads to a mitigation of the horizontal components of the bubble velocity resulting in a more rectilinear bubble path. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. As a result of the interaction between magnetic field and liquid flow electric currents were induced inside the liquid causing a damping of the flow by Joule dissipation. However, a characteristic feature of the electromagnetic dissipation is the anisotropy. Thus, 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.
Our investigations focus on the use of AC magnetic fields, too. Velocity measurements in a liquid metal bubble plume demonstrated that the application of a travelling magnetic field (TMF) can lead to completely new flow structures in the liquid phase. This fact offers new perspectives regarding the control of the heat and mass transfer in liquid metal bubble plumes. For instance, reversals of the mean flow direction can be organised. Moreover, the formation of dead flow regions at the bottom of the fluid vessel was prevented. Therefore, the use of AC magnetic fields could be an efficient tool to considerably reduce the mixing time of refining operations.

Die Erweiterung eines Fokussierten Ionenstrahles (FIB) mit einem Massenseparator (ExB Filter) wird vorgestellt, wodurch Legierungs-Flüssigmetallionenquellen eingesetzt werden können, die eine ganze Reihe von anderen Ionnarten als Gallium bereitstellen können. Die Herstellung solcher Quellen wird gezeigt und anhand ausgewählter Beispiele näher erläutert. Die Massenspektren sowie die Besonderheiten der Handhabung der Ionenoptik werden diskutiert. Anwendungsbeispiele, wie effektives Ionenzerstäuben (sputtern) durch schwere Ionen wie Gold, die Implantation von verschiedenen Spezies zur lokalen Änderung magnetischer oder elektrischer Eigenschaften sowie die Ionenstrahlsynthese von CoSi2 – Nanostrukturen unterstützen das wachsende Interesse an massenseparierten FIB Anlagen in Forschung und Industrie.

Der Begriff “Nanostrukturen” wird definiert und anhand von Beispielen erläutert. Speziell eingegangen wird auf Methoden der Herstellung von Nanostrukturen wie Nanodrähten und Nanocluster mit dem Fokussierten Ionenstrahl (FIB), die im Forschungszentrum Dresden-Rossendorf praktiziert werden. Die Ionenstrahlsynthese von CoSi2 Nanostrukturen wird präsentiert und erläutert. Weiterin wird die 3D Nanostrukturherstellung mittels FIB Implantation und anschließender anisotroper naßchemischer Ätzung gezeigt und an Beispielen demonstriert.

The metal (Ni) contamination on crystallized silicon obtained by metal induced crystallizaion (MIC) was estimated by Spectroscopic Ellipsometry (SE) using a new simulation approach. The method employs the addition of Ni as reference for a Bruggeman Effektive Medium Approximation (BEMA) to simulate the optical response of the crystallized silicon.
Samples with different initial metal/silicon ratios were annealed and crystallized. Besides determining thickness, surface roughness and crystalline fraction, this new approach using SE has shown to be sensible to changes on the initial metal thickness used on the crystallization process being able of determining in a quick and non destructive way the Ni concentration inside MIC poly-Si films.
The effectiveness of the obtained results was confirmed by RBS. An accurate determination of the initial Ni thickness that is deposited onto the amorphous silicon prior to crystallization is not possible using a quartz oscillator due to the very low quantity of evaporated materials. A better relation between defferent metal amounts present inside the crystallized films can be obtained by integratingthe Ni distribution in the RBS spectra. The obtained values are proportional to the Ni volume fraction determined by SE ellipsometry proves to be sensible to a metal volume fraction as low as 0.24%, corresponding to an initial Ni average thickness of 0.05 nm.

The TOPFLOW facility at Forschungszentrum Dresden-Rossendorf (FZD) is used to investigate two-phase upward flows in 50 mm diameter and 200 mm dia meter pipes. The facility enables conducting Experiments with air-water and steam-water flows for temperature range of 35-280 °C and pressure range of 1-70 bar. The test pipes are equipped with a wire -mesh sensor, which is a conductivity-based void fraction sensor developed by FZD. It provides void fraction measurements in a matrix of 64×64 points and a measuring frequency of 2.5 kHz. CFD models have to demonstrate their validity in geometries, where phenomena like flow separation, recirculation regions, stagnation points, free jet formation and similar are present. In the experiment described in this paper the flow around an asymmetric, half-moon shaped obstacle put into the large vertical test section of TOPFLOW is studied. In order to obtain information in three dimensions, the obstacle was traversed along the pipe axis. In this way, it was possible to record 2D void fraction distributions at different distances upstream and downstream of the obstacle using a stationary wire-mesh sensor. The fact that the high resolution data supplied by the sensor contains information on all individual bubbles that cross the measuring plane gives the opportunity to extract more detailed information on the flow structure. In particular, from the transit time of bubbles through the sensor plane approximate axial profiles of the liquid velocity were obtained. The lateral movement of the 2D image of bubbles in the measuring plane during their passage was evaluated to reconstruct 2D velocity fields in the environment of the obstacle. In this way, a full three-dimensional vector field of the velocity was provided for code validation. The paper presents the methods of data evaluation, an assessment of the obtained accuracy of the velocity estimation, experimental results and a comp arison to the results of CFD calculations.

Ziel/Aim:

Cyclooxygenase-2 (COX-2) ist ein Enzym das hauptsächlich bei Entzündungen freigesetzt wird, jedoch ist eine Überexpression von COX-2 auch im Zusammenhang mit verschiedenen Tumorerkrankungen beobachtet worden [1]. Obwohl in der Literatur die Markierung von COX-2 Inhibitoren mit PET-Radioisotopen mehrfach beschrieben worden ist [2-5], existieren bis heute wenig Untersuchungen über das Potential dieser Substanzen zur Tumordarstellung mittels PET. Wir berichten über die Radiosynthese sowie erste Ergebnisse der radiopharmakologischen und biologischen Evaluierung von 1-(4-[¹¹C]Methoxyphenyl)-2-(4-methylsulfonyl)-1-cyclopenten als ¹¹C-markierter COX-2 Inhibitor.

Methodik/Method:

Die Radiomarkierung wurde als eine ¹¹C-Methylierungsreaktion des entsprechenden Desmethyl-Präkursors mit [¹¹C]CH₃I in DMF in einem TRACERLab FX_C Synthesizer® durchgeführt. Studien zur Bioverteilung wurden an der Wistar-Ratte und Kleintier-PET Untersuchungen an HT-29 tumortragenden Mäusen mittels eines micro-PET®P4 Scanners durchgeführt.

Ergebnisse/Results:

Die Radiomarkierung des Präkursors 1-(4-Hydroxyphenyl)-2-(4-methylsulfonyl)-1-cyclopenten mit [¹¹C]CH₃I erfolgte 3 Minuten bei 60°C in DMF/wässriger NaOH (siehe Abb.). Nach semi-preparativer HPLC Reinigung und Festphasenextraktion wurde der ¹¹C-markierte COX-2 Inhibitor in 12-14% zerfallskorrigierter radiochemischer Ausbeute mit einer spezifischen Aktivität von 30-40 GBq/µmol (EOS) in radiochem. Reinheit >97% isoliert. Bioverteilungsexperimente zeigten eine Anreicherung des [¹¹C]-COX-2 Inhibitors in der Leber, den Nebennieren und braunem Fettgewebe von 0.6 - 0.8+/-0.1 %ID/g. In Kleintier-PET Untersuchungen an HT-29 tumortragenden Mäusen wurde ein Tumor/Muskel Verhältnis von 1.7+/-0.2 1h p.i.. bestimmt.

Schlussfolgerungen/Consequences:

Erste radiopharmakologische Untersuchungen zeigen eine Anreicherung des ¹¹C-markierten COX-2 Inhibitors am HT-29 Tumor. Aufgrund der hohen Lipophilie der Verbindung (logP=4.2) erfolgt ebenfalls eine Akkumulation in fettreichem Gewebe mit dem Ergebnis einer hohen unspezifischer Bindung. Weitere Experimente an verstärkt COX-2 exprimierenden Zellen sowie blocking/non-blocking Studien sind geplant.

Referenzen/References:

[1] E. F.J. De Vries, Current Pharmaceutical Design 12 (2006) 3847-3856.
[2] E.F.J. De Vries et.al., J. Nucl. Med. 44 (2003) 1700-1706.
[3] T.J. Mc Carthy et.al., J. Nucl. Med. 43 (2002) 117-124.
[4] V.J. Majo et.al., Bioorg. Chem. Lett. 15 (2005) 4268-4271.
[5] T. Toyokuni et.al., Bioorg. Chem. Lett. 15 (2005) 4499-4702.

The first electron beam of an RF gun with a 3.5 cell superconducting cavity is expected in July 2007 in FZD. This cavity has been designed for small bunch charges. In this paper we present the design of a similar cavity and of 1.5 cell gun cavities for large bunch charges. For a charge of 2.5 nC, which is the design value of the BESSY-FEL, and a bunch length of 21 ps a projected transverse emittance less then 1 πμ has been obtained (without thermal emittance).

We show the design and the parameters of operation of the long-wavelength (U100) FEL at ELBE. First lasing has been shown in August, 2006. Since then, the laser has undergone thorough commissioning and is available for user experiments since fall, 2006. Besides in-house users the IR beam is available to external users in the FELBE (FEL@ELBE) program witch is a part of the integrated activity on synchrotron and free electron laser science in the EU. At the beginning of 2007 lasing in the full designed wavelength range from 20 µm to 200 µm was demonstrated. The laser power typically reaches several Watts in cw operation but drops for very long wavelengths depending on the size of the used out-coupling hole. However, there exists a serious problem with small gaps in the wavelength spectrum. We attribute this behaviour to the transmission characteristics of the overmoded partial waveguide used from the undulator entrance to the first mirror.

The radiation source ELBE (Electron Linac of high Brilliance and low Emittance) at Forschungszentrum Dresden-Rossendorf is based on a superconducting linac that produces a high power continuous wave (cw) electron beam up to 40 MeV and 1 mA. Electron beams with variable bunch charges up to 80 pC and variable repetition rates up to 260 MHz are produced using a pulsed thermionic DC gun followed by a two-stage RF bunching system. Two cryomodules each containing two 9-cell RF-cavities (1.3 GHz) accelerate the electrons to about 40 MeV. The linac is used to drive two free-electron lasers producing infrared radiation from 3 to 200 microns wavelength. Additionally, from several conversion targets, MeV-bremsstrahlung (< 20 MeV) and X-rays (10-100 keV) from electron channelling are generated. Presently facilities for neutron and positron beams are commissioned at ELBE. The superconducting RF accelerator technology used, details of the machine instrumentation and several kinds of electron beam diagnosis will be described. In particular the generation of Infrared radiation and Bremsstrahlung and some examples of their applications will be discussed.

In contrast to the TESLA cavities the shapes and the mechanical stiffness of the four SRF-Gun cells differ from each other. Furthermore the axis field to achieve a “flat” surface field over all cells has a profile of 60% in the first and 100% in the TESLA like cells, respectively. Due to the different mechanical properties one tuner for the half cell and one for the three TESLA cells are assembled. Both of them are equipped to manipulate the field of the cavity during the adjustment of the tuner bias and later during operation. Hence it is very important to determine the fields inside the cleaned and closed cavity.
The poster presents a method that provides the field profile by measuring the passband frequencies based on the well known equivalent circuit for cell coupled cavities. At least one complete field and frequency measurement prior the last cleaning is necessary. The comparison with real measured values demonstrates the accuracy of the predicted field distribution within a range of 2%.

Most of the proposed electron accelerator projects for future FELs, ERLs, or 4th generation light sources require electron beams with an unprecedented combination of high-brightness, low emittance and high average current. In all projects photo guns will be applied: DC-photoguns, normal conducting RF photoguns (NC-guns), and superconducting RF photoguns (SRF-guns). While the concepts of DC- and NC-guns are well proofed, the SRF gun development still possesses a high risk. Challenges are the design of the superconducting cavity, the choice of the right photocathode type, its life time and possible cavity contamination, the difficulty of coupling high-average power into the gun, and beam excitation of higher order cavity modes. But in combination with SRF linacs, the SRF guns will be the best solution for high average currents. Continuous wave operation is simple to achieve. Thus, several R&D projects of SRF-gun have been launched.
The talk will give an overview of the progress of the SRF photoinjector development. In detail, the technical concept, performance, and status of the Rossendorf superconducting rf gun project, a collaboration of BESSY, DESY, MBI and FZD, will be presented. Main design parameters of this SRF gun are a final electron energy of 9.5 MeV, an average current of 1 mA, transverse normalized emittances (rms) of 1 mm mrad at 77 pC and 2.5 mm mrad at 1 nC bunch charge. The 1.3 GHz cavity consists of three full cells with TESLA geometry, a specially designed half-cell in which the photo cathode is placed, and a choke filter in order to prevent rf losses at the cathode side of the cavity. The photocathode with a Cs2Te photoemission layer is normal-conducting and are cooled by liquid nitrogen. The SRF gun cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid nitrogen cooled thermal shield, a titanium He tank with two-phase supply tube. A heater pot in the He input port will be used for He level control. The 10-kW fundamental power coupler is adopted from the ELBE cryomodule. The gun will be installed at the ELBE superconducting linear accelerator. In a first commissioning and test period the gun will be operated in parallel to the accelerator. A diagnostic beamline will allow beam parameter measurement and further optimization of the SRF gun.

In this study, the secondary uranium(VI) silicate minerals boltwoodite, sodium boltwoodite and uranophane were synthesized. Sodium boltwoodite was successfully obtained following a new reaction procedure. Their analytical characterization was carried out by means of inductively coupled plasma mass spectrometry and atomic absorption spectroscopy, scanning electron microscopy, X-ray powder diffraction, differential thermal analysis combined with thermogravimetry and infrared spectroscopy. Furthermore, the fluorescence behaviour was measured using time-resolved laser fluorescence spectroscopy. Herewith, the fluorescence properties of the three silicious uranyl phases were determined at room temperature.

Gamma ray tomography has been used to visualize fluid distributions in a rotating fluid test coupling at different operation points. The gamma ray CT system comprises a Cs-137 isotopic source and a high resolution gamma ray detector. By means of an angle synchronized tomographic data acquisition technique we were able to produce sharp two-dimensional slice images of the fluid distribution inside the coupling at full pump rotation of up to 780 rpm and lower turbine speeds. Three-dimensional images have been synthesized from different scans along the coupling axis. The data has been used to assess the hydraulic behavior of the fluid coupling and greatly improves our understanding of the flow structure development and its implications on torque transfer in such a device.

An intense channeling radiation X-ray source installed at ELBE is presented.

Heller wird's scheller
Richtet man intensives Laserlicht auf Materie, so werden geladene Teilchen freigesetzt und auf hohe Energien beschleunigt. Für eine kontrollierte Laser-Teilchenbeschleunigung sind zwar noch einige technologische Hürden zu meistern, erste Anwendungen in der Medizin sind aber absehbar.
Relativistische Optik
Wenn das intensive Licht moderner Hochleistungskurzpulslaser mit Materie in Wechselwirkung tritt, reichen die Gesetze der klassischen Optik zur Beschreibung nicht mehr aus. Vielmehr muss man sich der relativistischen Optik zuwenden, deren Effekte auch zur Beschleunigung von Teilchen genutzt werden können.

Outstanding wear resistance of austenitic stainless steel after nitrogen insertion and formation of expanded austenite in the temperature range below 420 degrees C is a well established phenomena. However, detailed information on the wear mechanism for the modified surfaces is still missing. This paper presents the results of wear experiments performed in a dry oscillating geometry against a WC ball (diameter 3 mm, load 3 N), together with metallographic investigations of the resulting cross-sections, both with and without nitriding. Comparisons with calculated stress distributions indicate that those nitrided samples showing a specific wear reduction by a factor of about 100 were subjected to a combination of stress maxima within the surface layer and below the layer in the bulk material.

no abstract for this publication

Bacteria have a great influence on the migration behaviour of heavy metals in the environment. Lipopolysaccharides form the main part of the outer membrane of Gram-negative bacteria. We investigated the interaction of the uranyl cation (UO22+) with lipopolysaccharide (LPS) from Pseudomonas aeruginosa by using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH and concentration range. Generally, LPS consists of a high density of different functionalities for metal binding such as carboxyl, phosphoryl, amino and hydroxyl groups. The dissociation constants and corresponding site densities of these functional groups were determined using potentiometric titration. The combination of both methods, potentiometry and TRLFS, show that at an excess of LPS uranyl phosphoryl coordination dominates, whereas at a slight deficit on LPS compared to uranyl, carboxyl groups also become important for uranyl coordination. The stability constants of one uranyl carboxyl complex and three different uranyl phosphoryl complexes and the luminescence properties of the phosphoryl complexes are reported.

It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures were found on a large variety of materials, such as semiconductors, metals, and insulating surfaces [1]. The formation and early evolution of the ripple patterns can be qualitatively reproduced by a linear continuum equation derived by Bradley and Harper [2]. However, at longer times nonlinear terms have to be taken into account, leading to nonlinear models based on the Kuramoto-Sivashinsky equation [3].
In this work, we studied the evolution of ion induced ripple patterns on Si(100) during sputtering at sub-keV energies by means of ex-situ AFM. At a certain stage of the evolution, larger corrugations appear and superpose the ripple pattern. With increasing time, these corrugations get more pronounced until they become the dominating feature of the surface. The morphology of the surface was characterized by determining the dynamic scaling exponents in direction normal and parallel to the ripples. Different scaling behavior is found for the ripples and the corrugations, respectively.
In order to gain better understanding of the evolution of the surface morphology, simulations of the damped Kuramoto-Sivshinsky equation [4] were performed, finding good qualitative agreement. Quantitatively, however, the simulations fail to reproduce the experimentally observed scaling behavior.

[1] U. Valbusa et al., J. Phys.: Condens. Matter 14 (2002), 8153
[2] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6 (1988), 2390
[3] M. A. Makeev et al., Nucl. Inst. Meth. Phys. Res. B 197 (2002), 185
[4] S. Facsko et al., Phys. Rev. B 69 (2004), 153412

The effect of irradiation-induced damage on the hardening of RPV steels is evaluated on the basis of SANS, TEM, PAS and TAP applied to Fe-based model alloys. Composition (especially Cu, Mn and Ni) and neutron dose of these alloys were systematically varied. The applied methods were utilized in order to separate the contributions to the irradiation-induced yield stress increase caused by different type of defects including dislocation loops, vacancy-type clusters, Cu-rich precipitates and Ni/Mn-rich precipitates.

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Scanning electron microscopy (SEM) and cathodoluminescence (CL) in combination with scanning transmission electron microscopy (STEM) have been used to investigate thermally grown amorphous silicon dioxide layers implanted isoelectronically with group IV ions (C+, Si+, Ge+, Sn+, Pb+) as well as with group VI ions (O+, S+, Se+).

L10 ordered c-axis oriented FePt thin films belong to the most promising ferromagnetic materials for future magnetic storage media. The layer coercivity can be significantly improved if changing from a homogeneous to granular film morphology, or even to arrays of FePt nanoislands.
This contribution describes the formation of self-assembled FePt nanoislands by conventional DC magnetron sputtering deposition on single-crystalline Si(001) or amorphous SiO2/Si substrates. The deposition was performed with substrate temperature of 320 °C and a working pressure of 0.4 Pa. In these conditions the deposition rate for FePt is about 0.4 Å/s, leading to an equivalent film thickness of 6 nm. An ultra thin Ag buffer layer, deposited in the same working conditions but with a deposition rate of about 1 Å/s, that, because of its nanoparticulate morphology, is supporting the islands formation.
The well-separated FePt islands exhibit a quite regular size of typical 20 – 30 nm, for both employed substrates. X-ray diffraction analysis reveals the existence of L10 ordered FePt phase. However, it is noteworthy that the islands formation is obtained both for crystalline and amorphous substrate which is of significant practical relevance. The enhanced coercivity of patterned FePt films with respect to homogeneous FePt layers has been confirmed by SQUID measurements. The formation of the nanoisland structure is discussed in terms of the adatom surface mobility, the influence of energetic ions and the ratio of surface to stress-energy during thin film deposition.

We report on scalable photoconductive antennas for both emission and detection of THz radiation. The concept yields THz emitters with high efficiencies for the conversion of near infrared into far infrared radiation and provides detectors which do not require tight focusing of both the THz beam and the near infrared gating beam. GaAs substrates implanted with dual energy implants of N+ and As+ ions of various doses are compared with semi-insulating and low-temperature-grown GaAs. We discuss which material properties are desirable for emitters and detectors and identify which material is optimal as either emitter or detector substrate. Best results for detectors are found for implanted samples with doses in the 1013 cm-2 range for GaAs:N and for LT-GaAs. Best emitters for typical excitation conditions with a Ti:sapphire oscillator system are based on SI-GaAs

Different scenarios of small break Loss of Coolant Accident (LOCA) for pressurised water reactors (PWR) lead to the reflux-condenser mode in which steam enters the hot leg from the reactor pressure vessel (RPV) and condenses in the steam generator. A part of the condensate flows back towards the RPV in counter current to the steam. During the reflux-condenser mode, a counter-current flow limitation (CCFL) must be prevented because this would limit the core cooling. The simulation of CCFL conditions, which is dominated by 3D effects, requires the use of a computational fluid dynamics (CFD) approach. These methods are not yet mature and have to be validated before they can be applied to nuclear reactor safety. Therefore, dedicated experimental data is needed with high resolution in space and time.

In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, the "hot leg model" was built at Forschungszentrum Dresden-Rossendorf (FZD). This setup is devoted to optical measurement techniques, therefore, a flat test-section design was chosen with a width of 50 mm. The test-section outlines represent the hot leg of a German Konvoi PWR at a scale of 1:3, which corresponds to a channel height of 250 mm in the straight part of the hot leg. The test-section is mounted between two separators, one simulating the reactor pressure vessel and the other is connected to the steam generator inlet chamber. This allows to perform co-current as well as counter-current flow experiments. Moreover, the hot leg model is built in the pressure vessel of the TOPFLOW facility of FZD, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the vessel. Therefore, the test section can be designed with thin materials and equipped with big size windows like in the hot leg model.

The presented air/water experiments focus on the flow structure observed in the region of the riser and of the steam generator inlet chamber at room temperature and pressures up to 5 bars. The performed high-speed observations show the evolution of the stratified interface and the distribution of the two-phase mixture (droplet and bubbles). Counter-current flow limitation, or the onset of flooding, was found by analysing the water levels measured in the separators. A confrontation with the images indicates that the initiation of flooding coincides with the formation of slug flow. Furthermore, the CCFL data was compared with similar experiments and empirical correlations available in the literature. The agreement of the CCFL curve is good and indicate that the data is relevant for CFD validation purposes. The zero penetration was found at lower values of the Wallis parameter than in most of the previous work, which can be attributed to the rectangular geometry of the hot leg model.