Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

G protein-coupled receptors (GPCRs) are heptahelical transmembrane proteins. They transduce a large variety of extracellular signals, allowing perception of taste, odor, hormones, and light. Binding of an extracellular ligand induces structural changes in the cytosolic domain of a GPCR which, thereby, catalyzes nucleotide exchange in a G protein. Rhodopsins, the visual pigments, are prototypical GPCRs that are activated by photoisomerization of covalently bound 11-cis retinal. Unlike other GPCRs, bovine rhodopsin and transducin, its cognate G protein, can be prepared from cow eyes in large quantities for spectroscopic and biochemical investigations. Rhodopsin is the best studied GPCR and the only one for which an X-ray structure has been solved. Structural information together with the wealth of biophysical data on native and recombinant rhodopsins allows to determine structure function relationships that are relevant to GPCR-dependent signaling in general. Here, results from Fourier-transform-infrared (FTIR) spectrocopic studies of rhodopsin and measurements of nucleotide-dependent transducin fluorescence are reviewed. Intra- and intermolecular processes during signaling by the photoreceptor have thus been identified and analyzed kinetically. Recent applications of these techniques concern rhodopsin transducin coupling in synthetic lipidic matrices and analysis of drug action at the receptor G protein interface.The data are discussed in the context of the crystal structure of rhodopsin and additional biochemical information if required for the understanding of the spectroscopic results.

Si (100) and (111) crystals were irradiated in the random as well as in the channeling direction, using 5 MeV 19F+ ions, to a maximum dose of approximately 1×1017 particles/cm2. The occurring deep implanted profiles were subsequently investigated using the Resonant Nuclear Reaction Analysis technique in the energy range Ep=950-1200 keV. The reaction 19F(p, αγ)16O reaction exhibits a strong resonant behavior in the above mentioned energy range, thus providing an excellent tool for the depth profiling of fluorine, yielding minimum detection limits of the order of a few ppm. The occurring profiles are analyzed with SRIM and c-TRIM and an attempt is made to explain the peculiarities of the experimental spectra, as well as to compare with results already existing in literature

We have measured the nuclear transparency of the fundamental process gamma n to pi- p in 4He. These measurements were performed at Jefferson Lab in the photon energy range of 1.6 to 4.5 GeV and at theta_cmSUP>pi = 70 and 90 . These measurements are the first of their kind in the study of nuclear transparency in photoreactions. They also provide a benchmark test of Glauber calculations based on traditional models of nuclear physics. the transparency results suggest deviations from the traditional nuclear physics picture. The momentum transfer dependence of the measured nuclear transparency is consistent with Glauber calculations which include the quantum chromodynamics phenomenon of color transparency.

Double differential cross sections d2?/dpd? have been measured for ?+ and K+ emitted around midrapidity in d+A and ?+A collisions at a beam kinetic energy of 1.15 GeV/nucleon. The total ?+ yield increases by a factor of about 2 when using an alpha projectile instead of of a deuteron whereas the K+ yield increases by a factor of about 4. According to transport calculations, the K+ enhancement depends both on the number of hadron-hadron collisions: their center-of-mass energy increases with increasing number of projectile nucleons.

During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in the microelectronics industry, as well as in the field of research and development. For special purposes like writing ion implantation or ion mixing in the µm- or sub-µm range ion species other than gallium are needed. Therefore alloy liquid metal ion sources (LMIS) were developed. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of an FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current I, ion mass m and emitter temperature T. For singly charged ions a predicted dependence of the energy spread, DE µ I2/3 m1/3 T1/2 found for Ga could be reasonable confirmed. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-100 especially for writing implantation to fabricate sub-µm pattern without any lithographic steps. A Co-FIB obtained from a Co36Nd64 alloy LMIS was applied for the ion beam synthesis of CoSi2 micro-structures down to 60 nm. Additionally, the possibility of varying the current density of the FIB by changing the pixel dwell-time was used for investigations of radiation induced damage and its dynamic annealing in Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume loss method. Especially this direct patterning 3D technique was used for the fabrication of various kinds of micro-tools.
All these examples underline the importance of FIBs in modern research and the new possibilities opened up by a mass separated system applying a broad spectrum of ion species.

Sophisticated microstructural analysis methods like small angle neutron scattering and atom probe field ion microscopy have proven the presence of so-called multicomponent clusters due to neutron irradiation in ferritic reactor pressure vessel steels. The formation of such clusters is surprising from the thermodynamic point of view. The cluster formation from the solid solution was modelled as phase transformation of the first kind that corresponds to the negative minimum of the so-called thermodynamic force under consideration of six components. The essential parameter is the sum of interaction energy between all pairs of atoms in the system. The approach result in stable multicomponent cluster if the clusters exhibit a high content of vacancies and a core-shell structure with very high vacancy content within the shell. The kinetics background of the suggested model was investigated using the cluster dynamic approach generalized for multiple components. The computed results are consistent with the experimental findings.

Aim. To investigate the mechanisms and dynamics of cholesteryl ester (neutral lipid) transfer protein activity in subjects with impaired glucose tolerance. Methods. Eighty six Caucasian subjects were recruited by advertisement from the local population between January 1998 and December 1999. The activity of cholesteryl ester transfer protein in 44 non-obese subjects with impaired glucose tolerance (plasma triglycerides 1.56-/+0.64 mmol/L; high density lipoprotein (HDL) cholesterol 0.96-/+0.25 mmol/L; and plasma insulin 78-/+8 pmol/L) and in 42 normoglycemic controls (plasma triglycerides 0.88-/+0.41 mmol/L; HDL cholesterol 1.48-/+0.29 mmol/L; and plasma insulin 38-/+14 pmol/L) was measured with a new fluorometric assay. Results. Cholesteryl ester transfer protein activity was increased in subjects with impaired glucose tolerance by 47% (39.5-/+7.8 vs 26.8-/+6.8 nmol/mL x h-1; t-test, p<0.05). Linear regression analysis showed that cholesteryl ester transfer protein activity in subjects with impaired glucose tolerance significantly correlated with the following parameters: plasma triglycerides (r=0.614, p<0.05), HDL-triglycerides (r=0.595, p<0.05), percentage of HDL-triglyceride (r=0.667, p<0.05), percentage of HDL cholesterol ester (r=-0.751, p<0.01), percentage of HDL phospholipid (r=0.648, p<0.05), 2-h-insulin (r=0.668, p<0.05), and 2-h-proinsulin (r=0.658, p<0.01). In a subgroup of 13 subjects with impaired glucose tolerance, cholesteryl ester transfer protein activity correlated with HDL apoA-I fractional catabolic rate (r=0.701, p<0.01). In normoglycemic subjects, significant correlations were found only between cholesteryl ester transfer protein activity and percentage of HDL-triglycerides (r=0.541, p<0.05), percentage of HDL cholesteryl ester (r=-0.639, p<0.01), 2-h-proinsulin (r=0.642, p<0.05), and HDL apoA-I fractional catabolic rate (n=10, r=0.587, p<0.05). Conclusion. Cholesteryl ester transfer is important for HDL composition and HDL catabolism both in normoglycemic subjects and subjects with impaired glucose tolerance. Under insulin resistant conditions, increased cholesteryl ester transfer protein activity modulates HDL metabolism more drastically than in normoglycemic conditions. This modulation may be explained by increased availability of triglyceride-rich lipoproteins for neutral lipid exchange in subjects with impaired glucose tolerance.

Several in vitro investigations showed that serum paraoxonase 1 (PON1) that is located on high-density lipoprotein reduces or prevents low-density lipoprotein (LDL) oxidation and therefore retards atherosclerosis. Accordingly, the well documented loss of PON1 activity in patients with overt diabetes mellitus was causally related to the development of micro- and macroangiopathy in the disease course. Because vascular complications start already in prediabetic states, e.g. impaired glucose tolerance (IGT), we investigated serum PON1 activities and circulating levels of oxidized LDL (oxLDL) in 125 IGT subjects, 75 patients with newly diagnosed diabetes mellitus type 2, and 403 individuals with normal glucose tolerance. Using three different substrates (paraoxon, phenylacetate, p-nitrophenylacetate) we found that PON1 activity is not significantly altered in IGT and diabetes mellitus subjects, respectively, when compared with normoglycemic controls. Both IGT subjects and diabetes mellitus patients had significantly increased levels of oxLDL in the circulation. However, serum PON1 activity variations and glutamine/arginine phenotype were not related to the levels of oxLDL. The data suggest that 1) PON1 activity loss is an event occurring later in the course of diabetes mellitus; and 2) PON1 does not affect oxidation of circulating LDL, at least in early diabetes mellitus.

N(O,S)-Ethoxycarbonyltrifluoroethyl amino acid esters are formed by the reaction of amino acids with ethylchloroformate plus trifluoroethanol plus pyridine. The use of these derivatives for a rapid and sensitive determination of 3-chlorotyrosine, a highly specific marker of myeloperoxidase-catalyzed protein oxidation, by using standard gas chromatography/electron impact mass spectrometry, is discussed.

Low density lipoprotein (LDL) apheresis is an effective treatment option for patients with severe hypercholesterolemia not adequately responding to diet and drug therapy. Membrane differential filtration (MDF), synonymous with double filtration plasmapheresis (DFPP), here named Lipidfiltration, and heparin-induced extracorporeal LDL-precipitation (HELP) are two of the five methods available for extracorporeal LDL apheresis. In this prospective investigation 6 patients with severe LDL-hypercholesterolemia and CAD were treated in a cross-over design with Lipidfiltration at two stages of technical development and HELP to compare the efficacy of these two LDL apheresis methods with respect to lowering and modifying plasma lipids and rheologically relevant plasma proteins, especially fibrinogen. In total, 44 LDL apheresis sessions were investigated. In weekly intervals, patients were treated with consecutive LDL apheresis sessions with either Lipidfiltration and HELP, treating identical plasma volumes. In one part of the investigation Lipidfiltration was performed with the novel Lipidfilter EC-50, combined with a newly developed blood and plasma therapy machine allowing optimized plasma heating. The results showed that the reduction rates of LDL-cholesterol, lipoprotein(a) and triglycerides were essentially identical for both methods. Also pretreatment levels of total cholesterol, triglycerides, LDL-cholesterol and HDL-cholesterol were not significantly different in both treatment groups. Both methods lead to a significant reduction of serum lipoproteins, especially for LDL-cholesterol, which was decreased by 61.4% with Lipidfiltration (treated plasma volume: 2998 ml) and 61.3% with HELP (treated plasma volume: 3013 ml). With respect to Lipidfiltration LDL-cholesterol reduction was more efficient with the novel Lipidfilter EC-50. Mean pretreatment HDL cholesterol concentrations remained unchanged. Comparing Cascadeflo AC-1770 with the novel Lipidfilter EC-50 reduction rates of HDL-cholesterol (17.4% versus 6.4%) and total protein (17.9% versus 7.8%) were significantly reduced. Lipidfiltration and HELP both resulted in a reduction of plasma viscosity and hemorheologically relevant plasma proteins, like fibrinogen.

Over the last 3 years in-beam PET has proven its capability of quality assurance in carbon ion tumour therapy at the pilot project of cancer therapy at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany. In this paper we investigate the possibility of using LSO as the scintillation material for the next generation of in-beam PET cameras. We address the issue of background coincidences arising from the natural radioactivity of LSO. Because the true count rate measured with a BGO-based dual-head positron camera (total sensitive area of each head 21 x 42 cm²) during the cancer treatment averages at only 100 coincidences/s we studied the influence of the LSO backround on realistic in-beam PET-images.

no abstract

The new TOPFLOW facility of the Forschungszentrum Rossendorf allows investigations of two-phase flow phenomena in vertical pipes with an inner diameter up to 194 mm (DN200) and a length up to 8.5 m. The maximum water mass flow of 50 kg/s equals to a superficial velocity of 1.7 m/s in such a pipe, while the maximum air flow rate of 900 m3/h corresponds to a superficial velocity of 8 m/s. For the measurements presented here, a wire-mesh sensor with 64*64 measuring points was installed. It corresponds to a lateral resolution of 3 mm. The senor delivers instantaneous void fraction distributions over the entire cross section with a time resolution of 2500 frames per second, which can be used for fast flow visualisation as well as to obtain averaged void fraction profiles and bubble size distributions. Earlier, similar experiments were carried out at a 51.2 mm pipe. In this case, sensors with 16x16 and 24x24 points were applied. A comparison of the data obtained for the two diameters allows to identify the effects of scaling on void fraction profiles, bubbles size distributions and the flow patterns. In the small pipe, the increase of the air flow rate leads to a transition from bubbly to slug flow. In the bubble size distributions a second peak corresponding to the class of large Taylor bubbles respectively gas plugs was found in the slug flow region. In the large pipe at identical superficial velocities a similar behaviour was found, though the large bubble fraction has a significantly bigger mean diameter, the peak is less high but wider. This reflects the fact that large bubbles move more freely than in the small pipe. The transition from a mono-modal to a bimodal bubble size distribution starts in both pipes, if bubbles with an equivalent diameter larger 1/3 of the pipe diameter occur. Due to the less pronounced confining action of the pipe walls, the bubbles show much more deformations. Their shape can be complicated and far from an ideal Taylor bubble. The small bubble fraction can also develop more freely in the large pipe. This is reflected by a wider bubble size distribution in the small bubble region. Small bubbles that surround the large bubbles obstruct the view and lead to the empirical impression of a direct transition from bubbly to churn turbulent flow.

Heavy-ion radiotherapy gives a good localized dose distribution just on a cancer tumor. In order to emphasize this advantage, the verification system of a particle range and an irradiated area in a human body has been developed for the Heavy Ion Medical Accelerator in Chiba (HIMAC) at National Institute of Radiological Sciences (NIRS). The idea comes from the fact that the stopping position of a short-lived positron emitting nuclei, such as ¹¹C, ¹⁵O or ¹⁹Ne, can be precisely detected by measuring annihilation gamma-rays.

In this seminar the production of nanopatterning by ion beam sputtering (IBS) is presented, namely ripple and dot morphologies. The work is focused on the irradiation of Si surfaces but a general view of this research field is also discussed. Finally, the search of potential applications for these nanostructures is addresed.

Middle frequency dual reactive magnetron sputter deposition was used in order to prepare the Indium tin oxide (ITO) films with an optimum of resistance and transmittance. The films were deposited on Si covered with 500 nm SiO2 and soda lime glass substrates. The plasma ions and neutrals flow parameters have been studied during the deposition process by the Langmuir probe, HIDEN analyzer, and optical emission spectroscopy. Complex characterization of the ITO films have been carried out in order to relate their properties with pulsed magnetron operation parameters. The optical constants and the thickness of these films were determined by means of spectroscopic ellipsometry (SE) operating within the wavelength range l=300-1700 nm. The optical transmittance was measured for l=350-2000 nm. Four probe technique was used to determine the film specific resistance. The dependence of the ITO film properties on the O2/Ar partial pressure relation was obtained similarly to known researches. The influence of the pulse duration and base pressure level on the film characteristics was detected. The decrease of the magnetron pulse on-time to the values of about 50 micro seconds, leads to strong increase of the films resistance at their high transmittance. The AFM data for these samples demonstrated five-times increase of the film grain sizes compared to those obtained at the on-time values 100 micro seconds. The observed decrease of optical transmittance in the near IR spectral range corresponds to the decrease of the film resistance. High optical transmittance at low resistance is found only at certain relation between the free electron plasma and relaxation frequency. The grading of optical constants was revealed by SE while the other techniques did not show depth grading of the film properties. Annealing of the ITO films in air atmosphere reduces the film resistance.

Die Positronen-Emissions-Tomographie (PET) bei der Schwerionentherapie ist eine wichtige Methode zur Qualitätskontrolle in der Tumortherapie mit Kohlenstoffionen. Die vorliegende Arbeit beschreibt die Verbesserungen des PET-Verfahrens, wodurch sich in der Folge präzisere Aussagen zur Dosisapplikation treffen lassen. Aufbauend auf den Grundlagen (Kap. 2) werden die Neuentwicklungen in den drei darauf folgenden Abschnitten (Modellierung des Abbildungsprozesses bei der PET, Streukorrektur für PET bei der Schwerionentherapie, Verarbeitung der rekonstruierten PET-Daten) beschrieben. Die PET-Methode bei der Schwerionentherapie basiert auf dem Vergleich zwischen den gemessenen und vorausberechneten Aktivitätsverteilungen. Die verwendeten Modelle in der Simulation (Erzeugung der Positronenemitter, deren Ausbreitung, der Transport und der Nachweis der Annihilationsquanten) sollten so präzise wie möglich sein, damit ein aussagekräftiger Vergleich möglich wird. Die Genauigkeit der Beschreibung der physikalischen Prozesse wurde verbessert und zeiteffiziente Algorithmen angewendet, die zu einer erheblichen Verkürzung der Rechenzeit führen. Die erwarteten bzw. die gemessenen räumlichen Radioaktivitätsverteilungen werden mit einem iterativen Verfahren rekonstruiert [Lau99]. Die gemessenen Daten müssen hinsichtlich der im Messobjekt auftretenden Comptonstreuung der Annihilationsphotonen korrigiert werden. Es wird ein geeignetes Verfahren zur Streukorrektur für die Therapieüberwachung vorgeschlagen und dessen Realisierung beschrieben. Zur Einschätzung der Güte der Behandlung wird die gemessene und die simulierte Aktivitätsverteilung verglichen. Dazu wurde im Rahmen der vorliegenden Arbeit eine Software entwickelt, das die rekonstruierten PET-Daten visualisiert und die anatomischen Informationen des Röntgentomogramms mit einbezieht. Nur durch dieses Auswerteverfahren war es möglich, Fehler im physikalischen Strahlmodell aufzudecken und somit die Bestrahlungsplanung zu verbessern.

Kinematographically complete measurement of the pp to ppc0;⁰ reaction were performed for beam energies in the range 292 - 298 MeV. By detecting both protons in coincidence with the large acceptance COSY-TOF spectrometer set up at an external beam line of the proton synchrotron COSY-Jülich, total and differential cross sections and energy distributions were obtained. A strong enhancement is observed in the Dalitz plots resulting from the final state interaction between the outgoing proton pair; the data are well reproduced by Monte Carlo simulations with standard parameters for scattering lengths a0 = 7.83 fm and effective range r0 = 2.8 fm. The total cross section exceed the ones measured recently in internal target experiments at IUCF and CELSIUS by roughly 50%. Arguments are presented which link this discrepancy with the effect of the final state interaction pushing yield into the very small-angle region and the near-impossibility of an internal target experiment to cover just this range.

The reaction pp to pp η was measured at excess energies of 15 and 41 MeV at an external target of the Jülich Cooler Synchrotron COSY with the time-of-flight spectrometer. About 25000 events were measured for the excess energy of 15 MeV and about 8000 for 41 MeV. Both protons of the process pp η were detected with an acceptance of nearly 100 % and the η was reconstructed by the missing-mass technique. For both excess energies the angular distributions are found to be nearly isotropic. In the invariant-mass distributions strong derivations from the pure phase space distributions are seen.

The CIRCUS test facility (Circulation during startup) has been built to study the start-up phase of a natural-circulation BWR. During the start-up so called flashing-induced instabilities can arise. These instabilities are induced by flashing, due to steam production in the long adiabatic riser section, which is placed above the core to enhance the flow rate. Flashing occurring in the riser causes an unbalance between driving force and pressure losses in the natural-circulation loop, giving rise to flow oscillations.

Within the European-Union 5th Framework Programme, a project, NACUSP, has been started in December 2000, having as one of its main aims the understanding of the physics of the phenomena involved during the start-up phase of natural-circulation-cooled BWRs, providing a large experimental database and validating state-of-the-art thermalhydraulic codes in the low-pressure, low-power operational region of these reactors.

One part of this project deals with the modeling of selected CIRCUS tests using the thermo-hydraulic code ATHLET. This paper gives an overview about experimental results and the physics of the instabilities. ATHLET is used to investigate the dynamic behavior of the CIRCUS test facility and the results of the calculations are compared with the experimental data.

Mössbauer-effect study of metastable c-FeSi synthesized by molecular beam epitaxy (MBE) and by ion implantation

no abstract

In the last years, there were several reports about the enhanced risk from irradiation with soft X-rays (below 50 keV). This energy range is relevant for diagnostic radiology, such as mammography, radiotherapy, and for the application of novel radiotherapy approaches such as use of miniature X-ray devices. In order to study this phenomenon, the relative biological effectiveness (RBE) of the X-rays in this energy range has to be determined more precisely. Experiments for determination of biological response after conventional X-ray tube irradiation were performed at TU Dresden. Cell survival for NIH/3T3 mouse fibroblasts was measured for soft X-rays (25 kV) and reference X-rays (200 kV). RBE value of 1.28 ± 0.5 was determined from the linear-quadratic model fit at 10% survival level. Further endpoint to be studied is the formation of micronuclei. At present, experiments are performed on human keratinocytes and chinese hamster fibroblasts. However, the precise determination of the energy dependence of RBE has to be performed by means of irradiation with a monochromatic source. One of the applications of the superconducting electron linear accelerator ELBE, at present under construction at Forschungscentrum Rossendorf, will be to provide such X-rays. The first cell irradiation will be performed with X-rays in the range 10 - 50 keV generated by channeling radiation from relativistic electrons in a diamond crystal. The properties of the electron beam (picosecond structure) as well as the intrinsic energy and intensity distribution of the channeling radiation require consideration of precise dose delivery and monitoring, the results of which will be also presented.

no abstract

no abstract

no abstract

no abstract

no abstract

no abstract

no abstract

Heat transfer and boiling are key phenomena for power generation facilities. Whereas for 1D thermalhydraulic system codes modeling of boiling was state aof the art from the beginning of their development, the 3D modelling of boiling has not yet reached this maturity. In the paper the boiling model implemented in the CFD-code CFX-4 was applied, to analyse lots of experiments, their results were published in the literature. The validity of the implemented correlations is examined. In many cases the model yields a good agreement to experiments. Especially in the low pressure region, the steam volume fraction is calculated too low. The used models are critical reviewed and compared to alternative solutions. The sensitivity of the calculated results on different influences are compared. Needs for improvements of the model and for further experiments are derived. Main attention should be focused on measuring and modelling of the correct size of the generated steam bubbles.

Gallium nitride is a novel material for short wavelength (blue) optoelectronics. Our previous investigation showed that Mn doped GaN has paramagnetic or antiferromagnetic properties opening new possible applications. The high concentration of magnetic ions possibly allows for the use of such a material in magnetooptic and spintronic devices. GaMnN and GaMnMgN powders were prepared by heating mixtures of gallium and manganese powder or powders of gallium nitride and manganese in a stream of ammonia at the temperature up to 1250°C. The powders have a grain size about 1-10 µm and they contain more than 2% of manganese by weight. Powders of doped GaN were prepared in a series of technological processes at various temperatures, ammonia flow rates and concentration of dopants in initial mixtures. Since hydrogen largely attributes to the passivation of p-dopants it plays an essential role in determination of electrical properties of these materials. Hydrogen content analysis was performed by the NRA method using the 1H(15Na,alpha gamma)12C reaction. This reaction has a sharp resonance of the cross-section at 6.385 MeV. Therefore it is possible by changing the incident 15N beam energy to measure depth distribution of hydrogen. It was found out that hydrogen concentration in our materials was below 1.5at%.

To qualify CFD codes for two-phase flows, they have to be equipped with constitutive models standing for the interaction between the gaseous and the liquid phases. In case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. Information on the local structure of the flow is also required by 1D thermal-hydraulic codes. Gas-liquid flow in vertical pipes is a very good object for studying the corresponding phenomena. Here, the bubbles move under clear boundary conditions, resulting in a shear field of nearly constant structure where the bubbles rise for a comparatively long time. The evolution of the flow within the pipe depends on a very complex interaction between bubble forces and bubble coalescence and break-up. E.g. the Lift-force, which strongly influences the radial distribution of the bubbles, changes its sign depending on the bubble diameter. Basing on extensive experimental data with a high resolution in space and time the applicability and the limits for the simulation of bubble flow with current CFX-codes are demonstrated, using the simulation of vertical pipe flow with CFX-4 as an example. Using a simplified model, parametric studies can be conducted. They give an indication for necessary improvements of the codes. Finally a possible way for the improvement of the CFD-codes is shown.

It is known that transformation of martensite into austenite (alpha'--> gamma) can take place in the surface layers of steels treated with sufficiently intense pulses of laser, ion or plasma beams. Our present work focuses on the phase transformations in the near-surface layer of various types of steel irradiated with short(µs range) intense (5-6 xE-4 J/m2) argon and nitrogen plasma pulses. The results of CEMS measurements, the pin-on-disc wear tests and SEM observations are presented.

2,6-di(3-alkyl-1,2,4-oxadiazol-5-yl)pyridines, 2,6-di(5-alkyl-1,3,4-oxadiazol-2-yl)pyridines, and 2,6-di(5-alkyl-1,2,4-oxadiazol-3-yl)pyridines were synthesized and tested for their americium(III)-europium(III) selectivity by liquid-liquid extraction. 0.02 M solutions of the compounds extract americium(III) 2-bromohexanoates as monosolvates, AmA3B, from solutions of pH = 2, with an americium(III)-europium(III) separation factor of up to 23. Decreasing the alkyl chain length (butyl < ethyl < methyl) or the polarity of the diluent (chlorobenzene < toluene < tert.-butyl benzene) increased both americium(III) distribution ratio and americium(III)-europium(III) separation factor.

Reactive extraction processes represent efficient and smart technologies for separation and concentration of metal ions in solution, which are frequently used in industry. Despite the importance of anions in biology, medicine, environment and industry, practical examples of anion extraction are relatively limited compared to metal ion separation. Anion extraction processes are mainly based on the non-specific ion pair formation with hydrophobic ammonium cations. In this case the phase transfer of anions is dominated by their lipophilicity. The reasons for this situation are closely connected with the specific features of anions in contrast to cations. Novel approaches for specific binding and selective transport of anionic components are based both on the better understanding of the biological role of anions and on the possibilities of supramolecular chemistry to build up receptor architectures with complementary binding modes for anions. In the given review the authors discuss present research tendencies and application possibilities of new extractant types for separation and concentration of anionic species in solution.

The efficiency of a series of amino-azacryptands for encapsulation and etraction of the oxoanions pertechnetate and perrhenate from aqueous solution is investigated and compared with that of their open-chain counterparts. The aqueous formation constants for oxoanion association with the cryptands were determined by pH potentiometry and/or NMR, and X-ray analysis of single crystals provides evidence for encapsulation. The extractabilities could not be explained solely on the basis of ligand lipophilicity; the level of protonation also plays an important role.

The design and synthesis of anion receptors of technical and biochemical significance is receiving more and more attention.^1-8 Currently, effective binding and selective phase transfer of the oxoanions pertechnetate and perrhenate is of considerable interest from different point of view. Due to its long half-life and environmental mobility, the radioactive pertechnetate is one of the most hazardous contaminants. In this context, effective and selective separation processes are of utmost importance.^9-12 On the other hand, there are some emerging possibilities for the application of the radiochemically active oxoanions pertechnetate and perrhenate in nuclear medicine.^13,14 The most commonly used isotope in diagnostic nuclear medicine ^99mTc is readily available from a ⁹⁹Mo/^99mTc generator system.^15-19 Likewise, the b-emitting ¹⁸⁸Re – discussed as one of the most interesting radionuclides for specific therapeutic applications – is conveniently produced by a ¹⁸⁸W/¹⁸⁸Re generator.^20-22 In both cases the radionuclides are available as oxoanions in isotonic solution, and it appears highly desirable to directly complex ^99mTcO₄ ^- and ¹⁸⁸ReO₄ ^- as they exist in the generator eluate itself. But, the binding of such large, lowly charged anions is a difficult venture. The enthalpic contribution for complexation is rather small. Hence, host compounds being capable to encapsulate these oxoanions are of great interest.
For both directions discussed above, some different requirements have to be fulfilled for the design of ligands. The essential properties of ligands serving as extractants and imaging/therapeutic agents are summarized in Table 1.

no abstract

ITO layers with low resistivity and high visible transmittance were produced by means of middle frequency reactive dual magnetron sputtering. The influence of base pressure, Ar/O2 ratio and magnetron pulse duration on the film composition, structure, electrical and optical properties has been investigated. The deposition rate is proportional to the magnetron operation power at changing pulse duration and constant Ar and O2 flows. At enhanced O2 flows an onset of the magnetron target oxidation is discussed as a reason for the decrease of the deposition rate. The presence of water vapor in the residual gas is determined to be a reason for deterioration of resistivity and optical transmittance observed for ITO films produced at base pressures higher than 5×10-4 Pa. It is demonstrated that spectroscopic ellipsometry can be used as a non contact tool to monitor the resistivity of ITO films.

The dependence of the strangeness saturation factor on the system size, centrality and energy is studied in relativistic
heavy-ion collisions.

The production of kaons and antikaons in nucleus-nucleus collisions has been studied with the kaon spectrometer at SIS/GSI. The K^-/K⁺ ration was measured in C+C, Ni+Ni, Au+Au collisions at 1.5 AGeV and was found to be almost independent of the system size. In Ni+Ni collisions at 1.93 AGeV we measured the phase-space distributions of K^- and K⁺ mesons. Within the framework of transport models, the measured K⁺ and K^- yields can only be explained if in-medium modifications of the K meson masses are assumed.
In Au-Au collisions at 1 AGeV, we observe non-vanishing elliptic flow near mid-rapidity and in-plane flow at target rapidity for K⁺ mesons. This effect can be explained by transport models when a repulsive in-medium K⁺ N potential is taken into account. The ratio of the K⁺ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energies. This effect is expected for a soft nuclear equation of state.

For the realization of good quality 3C-SiC films, epitaxially grown on Si, the perfection of the film during the early stage of growth is substantial. In this work the beneficial role of Flash Lamp Process (FLP) for defect elimination and strain reduction in the 3C-SiC films is discussed. FLP is a highly transient process with a flash duration of a few milliseconds (ms), preferentially occurring at the SiC/Si interface where the irradiated flux has its maximum absorption. If the energy density is sufficiently high, the temperature at the interface increases above the melting point of silicon. As a result, Si at the interface melts and subsequently dissolves the 3C-SiC in the vicinity of the interface, while the non-melted part of the film is annealed. During the re-solidification phase separation occurs and that part of the SiC film which is already dissolved into silicon is epitaxially deposited on the annealed uppermost part, which acts as the seed layer. The process resembles liquid phase epitaxy (LPE) resulting in substantial improvement of the SiC film. This process also eliminates the cavities and the stress at the 3C-SiC/Si interface. The irradiated 3C-SiC films were characterized by Transmission Electron Microscopy.

Differential production cross sections of K^- and K⁺ mesons have been measured as function of the polar emission angle in Ni+Ni collisions at a beam energy of 1.93 AGeV. In near-central collisions, the spectral shapes and the widths of the rapidity distributions of K^- and K⁺ mesons are in agreement with the assumption of isotropic emission. In non-central collisions, the K^- and K⁺ rapidity distributions are broader than expected for a single thermal source. In this case, the polar angle distributions are strongly forward-backward peaked and the nonisotropic contribution to the total yield is about one third both for K⁺ and K^- mesons. The K^-K⁺ ratio is found to be about 0.03 independent of the centrality of the reaction. This value is significantly larger than predicted by microscopic transport calculations if in-medium modifications of K mesons are neglected.

Isotope ratios of fragments produced at midrapidity in peripheral and central collisions of 114Cd ions with 98Mo target nuclei at E/A = 50 MeV are compared. The influence of the size (A), density, N/Z, E*/A, and Eflow/A of the emitting source on the measured isotope ratios was explored by comparison with a statistical model (SMM). The midrapidity region associated with peripheral collisions does not appear to be neutron-enriched relative to central collisions.

The defining characteristics of fragment emission resulting from the noncentral collision of 114Cd ions with 92Mo target nuclei at E/A = 50 MeV are presented. Charge correlations and average relative velocities for midvelocity fragment emission exhibit significant differences when compared to standard statistical decay. These differences associated with similar velocity dissipation are indicative of the influence of the entrance channel dynamics on the fragment production process.

The cost-shared project ARVI (assessment of reactor vessel integrity) involves a total of nine organisations from Europe and
USA. The objective of the ARVI Project is to resolve the safety issues that remain unresolved for the melt vessel interaction
phase of the in-vessel progression of a severe accident. The work consists of experiments and analysis development. Four tests were performed in the EC-FOREVER Programme, in which failure was achieved in-vessels employing the French pressure
vessel steel. The tests were analysed with the commercial code ANSYS-Multiphysics, and the codes SYSTUS+ and PASULA, and quite good agreement was achieved for the failure location. Natural convection experiments in stratified pools have been performed in the SIMECO and theCOPOfacilities, which showed that much greater heat is transferred downwards for immiscible layers or before layers mix. A model for gap cooling and a set of simplified models for the system codes have been developed.
MVITA code calculations have been performed for the Czech and Hungarian VVERs, towards evaluation of the in-vessel melt retention accident management scheme.
Tests have been performed at the ULPU facility with organised flow for vessel external cooling. Considerable enhancement
of the critical heat flux (CHF) was obtained. The ARVI Project has reached the halfway stage. This paper presents the results obtained thus far from the project.

For a realistic description of the coolant mixing during stationary and transient processes inside the reactor pressure vessel, a fast running semi-analytical model has been developed. This model is based on the technique of linear superposition of response functions on Dirac impulse shaped perturbation functions. The model has been coupled to the 3D neutron kinetic core model DYN3D.

A parameter study for a hypothetical boron dilution event including stationary and transient core calculations has been carried out. For the analysis a generic core loading pattern of the PWR KONVOI has been used. By varying the initial slug volume was found, that slugs of less than 16 m3 do not lead to over-criticality in stationary calculations. Transient calculations with higher slug volumes revealed a further conservatism of the calculations. An initial slug volume of 20 m3 is necessary to reach over-criticality in transient calculations. This leads to a significant reactivity insertion into the core and results in a power peak of more than 6500 MW. The power excursion is stopped by the Doppler feedback very effectively. The limited integral energy release does not lead to a significant rise of the coolant temperature. In the calculation with the bounding slug volume, the magnitude of the power peak is with about 8500 MW higher than in the previous calculation. The Doppler feedback stops the further power increase, too. Contrary to the 20 m3 case, the power peak occurs even before the boron concentration has reached its minimum. Because the positive reactivity insertion is continued after the power peak, typical secondary power peaks are observed. At the location of the power maximum, coolant boiling with a maximum void fraction of up to 70 % occurs for a short time. However, no heat transfer crisis was obtained.

The influence of the cross section library on the results of the boron dilution transient has been investigated by using an alternative library. Differences in global core parameters lead to quantitative differences in the time and the height of the power excursion.

A special model, based on a particle-in-cell method for the description of the boron transport through the reactor core has been used. It is shown, that a proper description of the boron transport in case of transients with low fluid velocity is absolutely necessary to calculate the neutron kinetic behaviour of the core in a right manner.

According to all calculations, even a reactivity insertion of about 2 $ connected with a 36 m3 slug did not lead to safety relevant consequences. The power excursion is mitigated and stopped by the Doppler feedback.

Ion implantation is one of the major techniques to introduce dopants into Si and SiC in a controlled manner. However, ion irradiation produces defects which prevent their electrical activation. Therefore, subsequent annealing is necessary in order to restore the crystallinity and to obtain dopant activation. The precise knowledge of the spatial distribution of the implanted ions and the radiation damage as well as the understanding of the nature of ion-beam-induced defects are important prerequisites for further improvements in the technology of ion implantation doping. Besides experimental investigations, atomistic computer simulations play an important role to achieve progress in this field. Simulations based on the binary collision approximation (BCA) are employed to determine the depth profile of implanted ions and atomic displacements. The influence of various implantation parameters like energy, direction of ion incidence, dose, dose rate and temperature is considered. A phenomenological model is used to treat the dependence of channeling effects on damage buildup and dynamic annealing during ion bombardment. The implantation profiles determined by the simulations show a good agreement with available experimental data. On the other hand, BCA simulations are limited to the treatment of ballistic processes. They do not yield details of the (meta)stable defect structure formed in subsequent fast relaxation processes. In order to obtain such information, a combined simulation method is employed. Processes in the collision cascade with energy transfers above 100 eV are treated by BCA simulations. Classical molecular dynamics (MD) calculations are applied to consider processes in certain parts of the cascade which start with energy transfers less than 100 eV. Detailed investigations are performed to study the temporal evolution of the defect structure, and to determine the damage morphology obtained after the fast relaxation is finished. The influence of nuclear energy deposition and target temperature is discussed. The combination of BCA and MD methods allows the effective calculation of the total number and the depth distribution of different defect species (e.g. isolated vacancies and self-interstitials as well as more complex defects) formed on average per incident ion. The results obtained allow a microscopic interpretation of the phenomenological model employed in conventional BCA simulations to describe the enhanced dechanneling of implanted ions due to damage buildup during implantation. In particular the explicit dependence on the ion mass can be explained. Furthermore, the procedure yields more realistic initial conditions for the simulation of post-implantation annealing than hitherto used.

The project ECOSTAR (acronym for ex-vessel core melt stabilization research) involves in total 17 orgnizations from five European countries. The objective of the project is to demonstrate the technical feasibility of core melt mitigation measures outside the reactor pressure vessel (RPV) as well as the validation of a selected set of codes in order to provide the necessary input for the definition of a convincing safety concept to control corium melts for both existing and future reactors.
The ECOSTAR projects is focused on three key phenomena for ex-vessel mitigation measures, namely melt release from RPV, ex-vessel corium transport and long-term corium stabilization. The extensive work program covers different scenarios and consists of a large number of experiments with both simulant and real materials, code development and validation as well as analytical activities.
This paper presents the progress of work per end of the year 2001 and the results obtained since the launch of the project.

kein Abstract

We show that the 3D simulation code GPT (General Particle Tracer) can give very detailed results on both the produced radiation and the evolution of the elctron bunch when special subsets of electrons are tracked instead of individual macro- particles. The model and two apllications are presented.

We outline the diagnostic and transport system of the infrared beam produced by the two free-electron lasers of the ELBE facility.

Es werden Entwurf und Rechnungen zu einem partiellen Wellenleiter f"ur den U50 Undulator des Rossendorfer ELBE Projektes vorgestellt.

Die FEL Projekte am FZR werden vorgestellt.

Production cross sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating nucleon M(pi+)/A_part is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the Au target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating nucleon M(K+)/A_part are independent of the target size at 1 AGeV and at 1.8 AGeV. The K- multiplicity per participating nucleon M(K-)/A_part is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K mesons are neglected.

The RESQUE project aims at optimising and normalising reconstitution techniques and is now in its final phase. The project belongs to the AGE-cluster, that also involves the REFEREE project being used as an input to RESQUE. At FISA 97 the reference data on non-reconstituted specimens were presented together with a set of recommendations on temperature measurements (WP1, WP2). Now, the results on the quality and limiting conditions of the reconstituted weld seam are discussed.

Übersichtsvortrag zu Methoden der Nuklearmedizin

no abstract

no abstract

no abstract

no abstract

no abstract

no abstract

Only the investigation of reactor pressure vessel steel from operated NPPs offers the opportunity to evaluate the real toughness response of the material to neutron/ gamma radiation. By investigation of material from the formerly Greifswald NPP the evaluation of a standard VVER-440-RPV design and the assessment of the quality of the used as well prediction rules as assessment tools will be possible. The rather different states (irradiated, irradated/annealed, and irradated/annealed/reirradiated) of the RPVs are a special advantage of the four units operated in Greifswald between 1973 and 1990. The paper describes the first results of these investigations and the next steps.

The potential non-equivalent defects in both 3C- and 4H-SiC are classified by a new method that is based on symmetry considerations. In 4H-SiC their number is considerably higher than in 3C-SiC, since the hexagonal symmetry leads to diversification. The different theoretical methods hitherto used to investigate defects in 3C-SiC are critically reviewed. Classical MD simulations with a recently developed interatomic potential are employed to investigate the stability, structure and energetics of the large number of non-equivalent defects that may exist in 4H-SiC. Most of the potential defect configurations in 4H-SiC are found to be stable. The interstitials between hexagonal and trigonal rings, which do not exist in 3C-SiC, are characteristic for 4H-SiC and other hexagonal polytypes. The structure and energetics of some complex and anisotropic dumbbells depend strongly on the polytype. On the other hand, polytypism does not have a significant influence on the properties of the more compact and isotropic defects, such as vacancies, antisites, hexagonal interstitials, and many dumbbells. The results allow conclusions about the energy hierarchy of the defects.

The work was aimed at the experimental investigation and numerical simulation of coolant mixing in the downcomer and the lower plenum of pressurized water reactors (PWR). For the investigation of the relevant mixing phenomena, the Rossendorf test facility ROCOM has been designed. ROCOM is a 1:5 scaled Plexiglas model of a German PWR allowing conductivity measurements by wire mesh sensors and velocity measurements by LDA technique. The CFD calculations were carried out with the CFD-code CFX-4. For the design of the facility, calculations were performed to analyze the scaling of the model. It was found, that the scaling of 1:5 to the prototype meets both: physical and economical demands. Flow measurements and the corresponding CFD calculations in the ROCOM downcomer under steady state conditions showed a Re number independency at nominal flow rates. The flow field is dominated by recirculation areas below the inlet nozzles. Transient flow measurements with high performance LDA-technique showed in agreement with CFX-4 results, that in the case of the start up of a pump after a laminar stage large vortices dominate the flow. In the case of stationary mixing, the maximum value of the averaged mixing scalar at the core inlet was found in the sector below the inlet nozzle, where the tracer was injected. At the start-up case of one pump due to a strong impulse driven flow at the inlet nozzle the horizontal part of the flow dominates in the downcomer. The injection is distributed into two main jets, the maximum of the tracer concentration at the core inlet appears at the opposite part of the loop where the tracer was injected. For turbulent flows the CFD-Code CFX-4 was validated and can be used in reactor safety analysis. Due to the good agreement between measured results and the corresponding CFD-calculation efficient modules for the coupling of thermal hydraulic computer codes with three-dimensional neutron-kinetic models using the results of this work can be developed. A better description of the mixing processes inside the RPV is the basis of a more realistic safety assessment.

A better understanding and optimisation of liquid metal processes requires experimental data of the velocity field. Numerical simulations alone are often of limited value. To measure local velocities in liquid metals or to measure channel flow rates in a contact-less way, almost nothing is available commercially.
We report on various measuring technique developments, their test in different liquid metals, and applications in hot melts. For local velocity measurements, a mechano-optical probe working up to temperatures of about 800°C has been developed [1]. It delivers the two mean velocity components perpendicular to the sensor axis. In the presence of an external steady magnetic field, the use of local potential probes allows to analyse the turbulent properties of the flow in addition to the mean velocity [2]. However, both sensor techniques rely on the introduction of probes into the melt and are thus mainly of interest for laboratory purposes.
The Ultrasound Doppler Velocimetry (UDV) became a powerful tool to measure the velocity structure of liquid flows. Because of the ability to work in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications. In addition, it can principally operate through the channel wall though a direct contact to the melt reduces ultrasonic losses. However, in case of hot metallic melts the user is confronted with several problems: the application of the ultrasonic transducers is usually restricted to maximum temperatures of 200°C, and a good acoustic coupling between the liquid metal and the related interfaces has to be provided. We report on successful measurements in liquid sodium at 150°C [3] which were performed through the channel wall. To overcome the limitation of ultrasonic transducers to temperatures lower than 200°C, an integrated ultrasonic sensor with acoustic wave-guide has been developed. This sensor can presently be applied at maximum temperatures up to 1000°C. Stable and robust velocity measurements have been performed in various PbBi flows at about 250-300°C. We report on first successful measurements in a CuSn melt of about 620°C and in an Al melt of about 750°C.
Evidently, a fully contact-less measuring technique would be most desirable. Such a method has been developed making use of external magnetic field measurements and inverse reconstruction techniques [4]. We will report on a first demonstration experiment showing the feasibility of this approach for the reconstruction of the three-dimensional mean velocity structure.
For the flow rate measurement in a pipe, a contact-less solution based on a pair of alternating magnetic field transmitter and receiver has been developed. Test results from a laboratory model and an industrial Al casting process will be presented.

We report on laboratory studies using cold liquid metals as a model of realistic light metal processes. The main feature of such cold (temperatures up to about 300°C) liquid metal models is the availability of measuring techniques allowing to analyse the local transport phenomena with a sufficient resolution. Note that water models of liquid metal processes are only meaningful if the melt flow Reynolds number represents the only determining parameter of the transport processes under consideration, which is seldom the case for real casting processes. As soon as temperature gradients, free-surface phenomena, two-phase flows or electromagnetic phenomena play a role, the water model is always of very limited value.
First we present results on the flow modelling of an investment casting process of aluminium alloys. The configuration basically consists in a U-bend, and the main request is to reduce the high flow velocities during the starting phase of the filling process. They are considered as the main source of problems like bubble or inclusion entrapment. The process was simulated using a plexiglas model and the eutectic melt InGaSn which is liquid at room-temperature. Local velocity measurements have been performed using the ultrasonic Doppler velocimetry, whereas flow rates have been determined independently using the contact-less transmitter technique. Measurements and video visualizations clearly show effects like flow rate oscillations or gas bubble entrapment. Depending on geometric and process parameters, the time-scale to get rid of these entrapments may become longer than the process itself. In order to decrease the maximum values of the velocity at the beginning of the process, an external steady magnetic field has been applied. The measurements show that it is capable of reducing these velocity peaks significantly. The experimental results are compared to numerical simulations.
As a second example we report on model experiments of the electromagnetic stirring of liquid metals in a cylindrical cavity. Different types of alternating magnetic fields, like rotating or travelling fields, are employed for such stirrers. The model experiments reveal that by application of just one type of those fields a strong flow results, but this flow is often of a rather rigid type without a noticeable three-dimensional mixing of the melt. An efficient mixing can be obtained by a combination of the field types. Velocity measurements in rotating, travelling, and combined rotating-travelling fields will be presented demonstrating this behaviour.
Third, we report on systematic studies about the influence of a rotating magnetic field (RMF) on the resulting microstructure of Pb-Sn alloys. The RMF strongly influences the flow in the liquid phase and, thus, the local heat transfer. It results in a significant influence on the nucleation and growth processes, leading to a variety of microstructures. Temperature as well as ultrasonic velocity profile measurements have been performed. Main goal is to find a strategy for refining the microstructure of castings by an optimal combination of magnetic field intensity, field frequency and cooling rate. For a Pb-85wt%Sn alloy, the application of the RMF is capable of changing the columnar dendritic microstructure to an equiaxed one.

Transition to turbulence of a rotating magnetic field driven liquid metal flow in a cylinder is studied experimentally by a probe-less method. A sudden, wide frequency band transition as well as intermittency are observed just at the theoretically predicted linear instability limit. A small geometrical imperfection triggers the transition in the linearly stable regime in a control parameter range where additional unstable steady solutions have been detected numerically. We discuss possibilities to predict theoretically the non-normal transition and its characteristics.

Dendrimere sind nanoskalige, dreidimensional verzweigte Moleküle mit sphärischer Architektur, die auf vielfältige Weise funktionalisiert und modifiziert werden können. Die speziellen Eigenschaften der Dendrimere eröffnen zahlreiche neue Anwendungsmöglichkeiten, insbesondere im Pharmabereich (drug delivery systems, tumor targeting etc.) und motivieren damit auch zu umfassenden Untersuchungen der zugrunde liegenden physiko-chemischen Prozesse. Es ist bekannt, dass die Struktur und die Komplexierungseigenschaften von Dendrimeren in wässrigen Lösungen wesentlich von den Säure-Base-Eigenschaften (Protonierungsgrad) der funktionellen Gruppen und damit vom pH-Wert bestimmt werden.
Im Rahmen dieses Beitrages werden Ergebnisse kalorimetrischer und potentiometrischer pH-Titrationsexperimente in wässriger Lösung an Polyamidoamin-Dendrimeren (PAMAM), die an der Peripherie unterschiedlich funktionalisiert sind (-NH2, -OH, -COOH Gruppen), vorgestellt und diskutiert. Die potentiometrischen pH-Titrationskurven können unter Verwendung von minimal drei simultanen Protonierungsgleichgewichten mit guter Genauigkeit beschrieben werden. Die Ergebnisse sind konsistent mit dem typischen Verhalten von Polyelektrolyten.
Die kalorimetrischen pH-Titrationskurven widerspiegeln die komplexe Natur der ablaufenden Prozesse wesentlich deutlicher. Neben unterschiedlichen Stufen in den kalorimetrischen Titrationskurven, die prinzipiell den Protonierungsgleichgewichten zugeordnet werden können, treten zum Teil endotherme Effekte auf, deren Ursachen noch nicht geklärt sind. Die quantitative Beschreibung der Titrationskurven auf der Basis reiner Protonierungsreaktionen gelingt dadurch nicht vollständig.
Weiterhin werden erste kalorimetrische Ergebnisse zur aus pharmakologischer Sicht wichtigen Wechselwirkung von Dendrimeren mit potentiellen Targetmaterialien am Beispiel von Human Serum Albumin (HSA) präsentiert und diskutiert.

Two asymmetric electroluminescence bands with tunable maxima at around 1.044-1.065 and 0.90-1.00 eV are observed at low temperature in silicon pn diodes prepared by boron ion implantation and subsequent high temperature annealing. The intensity of the two bands increases strongly with increasing the boron concentration above the solubility. A large blue shift of the two bands with increasing the injection carrier concentration was attributed to the three-dimensional confinement of holes in p-type doped spikes localized on a nanometer scale. They are produced by the boron clustering at the end of range defects close to the pn junction. The two bands with a smaller binding energy is attributed to the spatially indirect recombination of the excitons confined around the strain-free p-type doped spike. The band with a higher binding energy is associated with highly strained p-type doped spikes around dislocations. A significant enhancement of the room temperature electroluminescence efficiency of the silicon diode is observed which is attributed to the spatial modulation of the band structure around these p-type doped spikes.

Large improvement of the electroluminescence efficiency was observed from silicon pn diodes prepared by boron implantation. The temperature dependence of the EL and PL of the pn diode shows a different behavior compared to the PL from bulk silicon substrates. Two asymmetric EL bands from trap bands below the free exciton emission band are observed at around 1.065 and 0.92-0.96 eV at low temperature in the silicon pn diode. The intensity of the two bands increases strongly with increasing boron concentration. A blue shift of the two bands with increasing the injection current was observed which is similar to EL in deta-doped semiconductors. The temperature dependence of the EL intensity from the different bands shows that the thermal emission of carriers from these traps is responsible for a strong increase of the band edge radiative emission of silicon. These results are consistent with a rate equation model based on the emission, trapping and recombination processes for a system containing free excitons and bound excitons. Our results give an alternative explanation to the strong increase of the EL efficiency in boron implanted silicon pn diodes [1].
[1] W.L. Ng et al., Nature 410, 192 (2001).

A bound-exciton-induced current bistability is observed under forward bias in an efficient silicon light-emitting diode at low temperatures. Two stable states of the S-type differential conductivity correspond to empty and filled states of bound excitons, espectively. The relationship between the current-voltage characteristic and the bound-exciton population can be accounted for using a rate equation model for bound and free excitons. The consistency between the theoretical and experimental results indicates that bound excitons, despite their neutral-charged states, contribute to the current bistability in silicon p-n junction diodes.

Bakterien in stark kontaminierten Umgebungen mussten effiziente Entgiftungsstrategien zum Überleben ausbilden. Diese können zur Entwicklung ebenso effizienter und innovativer Biosanierungsverfahren auf der Basis der immobilisierten Biokomponenten genutzt werden. Ausgewählt wurden Bakterien einer Uranabfallhalde in Form von intakten Zellen, Sporen und Teilen der Zellwand. Diese binden selektiv und reversibel Uran, Kupfer, Blei, Aluminium und Cadmium mit hoher Kapazität. Ausgangspunkt für die Einbettung der Biokomponenten sind Siliciumoxid-Sole, die durch Änderung des pH-Wertes oder durch Temperaturerhöhung schnell gelieren. Durch Trocknung der Biokompositsole entstehen poröse Xerogele, die als selektive und wiederverwendbare Filter in Sanierungsverfahren zum Einsatz kommen können.

Im Bestrahlungsprogramm Rheinsberg II wurden zur Temperaturbestimmung Temperaturmonitoren aus Diamantpulver verwendet. Das Verfahren nutzt den Einfluss der Temperatur auf die bestrahlungsbedingte Änderung der Gitterkonstanten des Diamantgitters und ist in einer russischen Prüfvorschrift standardisiert. Zur Ermittlung der Temperatur wurde die Gitterkonstante mit einem Röntgen-Diffraktometer nach Bestrahlung und anschließenden Ausheilglühungen in isochronenTemperaturstufen von 50 - 100 K bestimmt. Der Unstetigkeitspunkt auf dem linearisierten Temperaturverlauf der Gitterkonstanten liefert einen Wert für die Bestrahlungstemperatur, der gemäß der Prüfvorschrift neutronenflussabhängig zu korrigieren ist. Es werden starke Messwertstreuungen festgestellt, die die Genauigkeit der Bestimmung des Unstetigkeitspunktes erheblich beeinträchtigen. Darüber hinaus treten systematische Fehler auf. Insgesamt ist die Temperaturbestimmung mit Diamantpulver im Bestrah-lungsprogramm Rheinsberg II als nicht zufriedenstellend einzuschätzen. Der wahrscheinlichste Wert liegt im Bereich von 255 - 265 °C und somit nahe dem Wert, der aus den thermischen Randbedingungen der Experimente abgeschätzt werden kann.

Nitrogen ions were implanted into (100)GaAs at high temperature (400 and 600oC) and high dose (2x10^17 and 6x10^17 ions cm-2) in order to synthesize small GaN crystallites. The defective strip due to implantation is about 500 nm thick and stacking faults appeared as the characteristic defect. Selected area diffraction patterns show that cubic GaN was formed in samples implanted at 600oC. The precipitates formed are typically 5 nm large and are epitaxial to the host GaAs. Some larger precipitates are also observed from which the matching of the two lattices could be determined.

In the axially symmetric magnetic mirror device gas dynamic trap (GDT), on-axis transverse beta (ratio of the transverse plasma pressure to magnetic field pressure) exceeding 0.4 in the fast ion turning points has been first achieved. The plasma has been heated by injection of neutral beams, which at the same time produced anisotropic fast ions. Neither enhanced losses of the plasma nor anomalies in the fast ion scattering and slowing down were observed. This observation confirms predicted magnetohydrodynamic stability of plasma in the axially symmetric mirror devices with average min-B, like the GDT is. The
measured beta value is rather close to that expected in different versions of the GDT based 14 MeV neutron source for fusion materials testing.

GDT experiments of significance to a GDT based neutron source development are reported in the areas of generation of axially peaked neutron flux profile, stable confinement with on-axis plasma beta ~40%, and radial electric field control. Skew injection of 4 MW 15-17 keV deuterium neutral beams into central cell resulted in generation of strongly peaked axial profile of neutron flux density. This can be described by a model of fast ion relaxation, which involves classical mechanisms of electron drag and binary ion-ion collisions only. Experiments with the radial limiter biasing show that the plasma density profile and radial losses respond to the electric field profile. An increase of plasma energy was achieved with increased magnetic field in the central cell and optimised radial profile of electric field. In these regimes the on-axis plasma beta near the turning points of fast deuterons exceeded ~40%. The plans for future upgrade of the GDT device are discussed. It suggests considerable increase of NB injected power (up to 10 MW) and extension of the pulse duration from 1 ms up to 3-5 ms. After the upgrade, a significant increase of the electron temperature up to 250-300 eV could be obtained. Properties of the plasma with parameters approaching those in the full-scale neutron source are planned to study in experiments with NB injection into an additional mirror cell which will be installed near to one of the standard mirror coils.

Thin films (dB nm)of hydrogenated amorphous silicon carbide (a-SiC:H),deposited by RF reactive magnetron sputtering,have been ion implanted with high doses (D=1E16¿1E17cm^2) of Ga+ as the implant species.The increased disorder and additional structural modi .cation of a-SiC:H,induced by the implantation of Ga+ results in a considerable change of the optical properties, best manifested by a significant shift of the optical absorption edge to lower photon energies in the results obtained by optical transmission and re .ection measurements and as derived from photo-thermal-deflection spectroscopy results.This shift may be attributed both to additional defect introduction and to accompanying structural modi .cation effects,as confirmed by optical absorption measurements in the infra-red region and by Raman spectroscopy results.

Proceedings volume!

In order to enable a better description of ballistic and athermal processes occurring in the initial stage of ion-beam-induced defect formation, the repulsive part of the interatomic potentials of Gao and Tersoff is improved. The first modification concerns the two-body part of the potentials. At small interatomic distances it is replaced by the well-tested potential of Ziegler, Biersack, and Littmark (ZBL). For repulsive interactions between zero and some ten electron volt, an exponential spline function is employed to connect the ZBL potential with the two-body parts of the Tersoff and the Gao potential. The modified two-body potentials and their first derivatives are continuous and monotonic over the whole range of repulsive interaction. They are in good agreement with data obtained by density-functional-theory calculations. Furthermore, the three-body part of the Tersoff and the Gao potential is modified in order to avoid the strong dependence of repulsive interactions between two atoms on the bond-order parameter, i.e. on their coordinations. The modification is performed in such a manner that the total potential and its first derivative remain continuous and monotonic for all repulsive interactions.

The present paper deals with advanced conductivity probes for local void measurements, which were equipped with a micro-thermocouple, which is integrated into the probe at the place of the electrode wire. These probes were used for rapid transient condensation tests in a heat exchanger pipe immersed into a cooling water tank. The experiments serve as data sources for the validation of thermal-hydraulic system codes concerning the modelling of the condensation, particularly with respect to the behaviour and effect of non-condensable gases. The present tests were carried out at the pressurizer test facility DHVA of the University for Applied Sciences in Zittau/Görlitz serving as steam source. The slightly downwards inclined condensation tube was connected to the head of the pressure vessel and supplied with steam in this way. The application of a new type of two-phase instrumentation has revealed details about the transient condensation process. Since test were performed with and without the presence of a non-condensable gas (air), the effect of the gas could be studied. The merits of the probes lie in the ability to distinguish between steam and gas. Without the synchronous temperature and void measurement performed by the probes it would have not been possible to clarify the physical background of the temperature jumps found during the experiments with the non-condensable gas.

Most of the level monitoring systems for pressure vessels containing saturated steam-water mixture use the hydrostatic method. Differential pressure transducers are connected by pulse tubes with nozzles at different height of the pressure vessel. A disadvantage of this method is given by measuring errors cause by evaporation and/or degassing processes in vertical parts of these pulse lines. The error is caused by the decrease of the fluid density in the reference pipe, when a two-phase mixture appears. The present work aimed at the test of a novel differential pressure measuring system that eliminates the influence of density changes in the pulse lines. It is based on two differential pressure transducers, placed accurately at the elevation of the connecting nozzles. They are connected with the pressure vessel only by horizontal pipes. The vertical distance is bridged by a standpipe, the fluid of which is completely separated from the fluid in the vessel. Degassing respectively evaporation effects can therefore completely excluded in the reference column of the new system. The method was tested at the pressurizer test facility of the University of Applied Sciences Zittau/Görlitz on three types of transients including a rapid pressure decrease similar to a loss-of-coolant transient. Traditional differential pressure systems as well as local void probes were used for comparison. The method has proven its advantages compared to the traditional hydrostatic level measurement method.

Im Zuge von Modellbildungen ist es nicht immer möglich, das zu beschreibende Objekt sofort oder direkt durch ein einzelnes Modell vollständig zu erfassen. Vielmehr wird es zunächst mehrere untergeordnete Modelle geben, die jeweils nur verschiedene eingeschränkte Sichten auf das Objekt repräsentieren. Im Beitrag wird untersucht, wie solche Modelle zu einer Modellsymbiose verbunden werden können und wie mit deren Hilfe dann nach einem verbesserten Einzelmodell des zu beschreibenden Objektes gesucht werden kann.

Positron emission tomography (PET) is a powerful imaging technique for the in vivo study of molecular interactions and molecular pathways in the human body. In combination with approprately labelled radiotracers, PET offers exceptional possibilities to study physiology, metabolism, pharmacokinetics and modes of action of novel and established drugs, and food ingredients.

The key element of PET is the PET-radiotracer, a compound labelled with a short-lived positron emitter. The most useful positron emitters for the labelling of organic moleculars are ¹¹C and ¹⁸F which have half-lives measured in minutes, bein 20.4 min and 109.6 min, respectively. Consequently, time dominates all aspects of PET. In this connection the extensive performance of organic radiochemistry using ¹¹C and ¹⁸F is fundamental but also a special challenge. This review will address the recent developemts of organic PET radiochemistry in the synthesis of PET radiotracers with special focus on ¹¹C and ¹⁸F

Examples of a new type of cryptophane molecule incorporating aromatic groups in the bridges (1 - 4) and for the first time, being also supplied with three endo-positional ionizable carboxylic acid function (1) have been synthesized and characterized. The cryptophane triester 2 yielded a solvate (channel inclusion compound) with trichloromethane and water, the X-ray crystal structure of which is reported. The complexation of 1 with low-molecular-weight alcohols in solution was studied, and the liquid-liquid extraction of different metal ions including alkali (Na⁺, Cs⁺), alkaline earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), and the lanthanide metal ions Eu³⁺ and Yb³⁺ in an extraction system containing metal nitrate buffer/H₂O/1/CHCl₃ was examined. Molecular modeling calculations of the cryptophanes 1 and 2, and of the Eu³⁺ complex of 1 were carried out contributing to the discussion.

Low concentration of toxic radioactive metals in environmental samples often limits the interpretation of results of infrared studies investigating the interaction processes between the metal ions and environmental compartments. For the first time, we show that photothermal infrared spectroscopy performed with a pulsed free electron laser can provide reliable infrared spectra throughout a distinct spectral range of interest. In this model investigation, we provide vibrational absorption spectra of a rare earth metal salt dissolved in a KBr matrix and a natural calcite sample obtained by thermal beam deflection technique and FT-IR spectroscopy, respectively. General agreement was found between all spectra of the different recording techniques. Spectral deviations were observed with samples containing low concentration of the rare earth metal salt indicating a lower detection limit of the photothermal method compared to conventional FT-IR spectroscopy.

A new method of preparing alumina ceramic surface for brazing it to kovar with conventional Ag-Cu eutectic brazes is presented. The key concept of this approach consists in formation of two inter-layers on the ceramic surface: (i) thin (in nm scale) layer of TiO_x using pulse plasma beams, and (ii) thicker (about 2 µm) layer of TiO_x or metallic Ti using arc PVD technique. Grazing incidence X-ray diffraction (GXRD) analysis shows that the first layer consists most likely of Ti₇O₁₃, whereas the second is either Ti₂O, or metallic Ti - depending on the deposition conditions. Commercial housings of semiconductor diodes have been used as the samples. Brazed housings were tested under routine industrial conditions. The ultimate tensile strength (UTS) of joints reaches the average value of 90 MPa. Vacuum tightness is better than 5x10^-6 mbar l/s. The values of parameters are sufficient to pass the production requirements.

Bezüglich eines hypothetischen Kernschmelzeszenarios in einem Leichtwasserreaktor ist es notwendig, mögliche Versagensformen des Reaktordruckbehälters sowie Versagenszeiträume zu untersuchen, um die Belastung für das Containment bestimmen zu können. Es wurden bereits eine Reihe von Experimenten durchgeführt, welche Erkenntnisse hierüber liefern sollen. Begleitend wurden in Einzelversuchen Materialeigenschaften ermittelt, sowie theoretische und numerische Arbeiten durchgeführt.
Für die Simulation von Experimenten zum Versagen der Bodenkalotte, wie OLHF oder FOREVER, ist es notwendig, Kriechen und Plastizität zu berücksichtigen. Gleichzeitig müssen geeignete Modelle das Temperaturfeld in der Behälterwand für die mechanischen Rechnungen bereitstellen. Vom Institut für Sicherheitsforschung des FZR wird ein Finite-Elemente-Modell erstellt, das sowohl die Temperaturfeldberechnung für die Wand als auch die elasto-plastische Mechanik der Behälterwand modelliert. Die bisher durchgeführten Arbeiten werden in diesem Bericht kurz erläutert und mit Beispielen belegt.
Am FZR wurde ein Finite-Elemente-Model entwickelt, das die Verwendung von einfachen Kriechgesetzen, die mit ihren angepassten Konstanten nur für begrenzte Spannungs- und Temperaturbereiche gültig sind, umgeht. Stattdessen wird eine numerische Kriechdatenbasis angelegt, in der die Kriechdehnrate in Abhängigkeit von der Gesamtdehnung, der Temperatur und der Vergleichsspannung abgelegt ist. Eine wesentliche Aufgabe für diese Vorgehensweise besteht in der Generierung und Validierung der Kriechdatenbasis. Zusätzlich wurden alle relevanten temperaturabhängigen Materialeigenschaften mit entsprechenden Modellen in den Code eingegeben. Für die Bestimmung der Versagenszeit wurde ein Schädigungsmodel nach einem Vorschlag von Lemaitre implementiert.
Die Validierung des numerischen Models erfolgt durch die Simulation von und den Vergleich mit Experimenten. Dies geschieht in 3 Stufen: zunächst werden einzelne einachsige Kriechversuche nachgerechnet, was als 1D-Problem bezeichnet wird. In der nächsten Stufe werden sogenannte ¿Rohrversagensexperimente¿ simuliert: das RUPTHER-14 und das ¿MPA-Meppen¿-Experiment. Diese Experimnete werden als 2D-Probleme betrachtet. Schließlich kann das Modell auf skalierte 3D-Versuche angewendet werden, in denen die Bodenkalotte eines Druckwasserreaktors mit ihrer halbkugelförmigen Geometrie wiedergegeben wird. Ein Beispiel hierfür sind die FOREVER-Experimente. In Zusammenarbeit mit den Experimentatoren an der KTH in Stockholm wurden Pre- und Posttest-Rechnungen für diese bisher einzigartigen Experimente durchgeführt, deren Ergebnisse qualitativ und quantitativ sehr zufriedenstellend sind.
Eine wichtige Frage im Rahmen dieser Arbeit ist die Vergleichbarkeit des französischen Reaktordruckbehälterstahls 16MND5 und des deutschen 20MnMoNi5-5, welche chemisch nahezu identisch sind. Da diese beiden Stähle ein ähnliches Verhalten zeigen, sollte es in gewissem Umfang zulässig sein, experimentelle und numerische Daten und Erkenntnisse zwischen beiden zu übertragen.

This paper reports on an extensive study of the characteristics of AuGeSi and CoNd liquid metal alloy ion sources (Focused Ion Beams From Liquid Metal Ion Sources,Research Studies Press,Taunton,Somerset,UK,1991).Such characteristics include current –voltage curves and ion beam mass spectra.A careful investigation has been undertaken where the emitter temperature is the main variable experimental parameter.Theoretical models,or theoretical attempts in certain cases,tend to support the experimental results.The experimental results,in conjunction with existing theories, suggest that simply for reasons of self-consistency two mechanisms must be operative for the production of doubly- charged ions from the AuGeSi source:direct .eld-evaporation and post-ionisation.

We report on the direct measurement of surface plasmon transmissivity of narrow grooves in thin silver films using near-field optical microscopy in an attenuated-total-reflection setup. For different groove widths, we observe characteristic changes in transmissivity that are attributed to resonant gap modes. The results are in good agreement with existing theoretical predictions.

Der Aufbau und die erste Nutzung eines kompakten Flugzeitsystems zur energiedispersiven Untersuchung der Wechselwirkung von schnellen Neutronen mit Materialien sind Inhalt eines Vernetzungsprojektes des Forschungszentrums Rossendorf, an dem auch die Technische Universität Dresden im Rahmen eines gemeinsamen DFG-Projektes mitarbeitet. Die geplanten Flugzeit-Experimente mit gepulsten Neutronen werden an der Strahlungsquelle ELBE durchgeführt werden. Erste Ergebnisse zur Entwicklung eines Neutronen-Produktionstargets werden vorgestellt. Mit Hilfe von Strahlungstransport- und Finite-Elemente-Programmen wurden die Verteilungen der Energiefreisetzung des von der Strahlungsquelle ELBE genutzten Elektronenstrahls und der Temperatur im Neutronen-Radiator sowie die zu erwartenden Teilchenspektren und -flüsse am Messplatz berechnet. Überlegungen zur Entwicklung des Strahlfängers werden diskutiert.