Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Spin dependent tunnel junctions (Si/Al2O3/Ta/CoFe/AlNx/CoFe/Ta) were studied with grazing angle of incidence Rutherford backscattering spectrometry experiments using a 1.6 MeV He+ beam. While the sensitivity to light elements is too small to detect the N directly, the thickness and composition of the AlNx insulating barrier can be obtained by carefully simulating the signal of the Al and of two CoFe layers, which can be separated. From the observed Al signal the corresponding energy loss can be calculated, and the extra energy loss required to obtain the observed CoFe layer separation is assigned to the N. Eventual oxidation in the AlNx layer during film deposition can be further identified and quantified by analysing a similar tunnel junction, but deposited on a DLC substrate. A depth resolution of 25 Å at the CoFe layers ensures a highly precise measurement of this complex magnetic system.

GaN epitaxial films were grown on silicon substrates by molecular beam epitaxy under different conditions. Some of the films were doped with the rare earths (RE) Er, Eu or Tm during the growth, and were studied regarding its composition and crystalline quality. The Rutherford backscattering/channelling and heavy ion elastic recoil detection techniques were combined in order to get information on the depth distribution of all the elements present in the films. The results show that the single crystalline quality of the films improves with increasing substrate temperature and Ga flux. For these conditions the Ga concentration is the one expected for a stoichiometric film. A decrease of the Ga flux or increase in the RE cell temperature allows an increase of the concentration of the RE incorporated during the growth. The light impurity present in all the films studied, within our detection limits, was hydrogen. The angular scans along the <0 0 0 1> reveal that a fraction of the RE is incorporated into regular lattice sites of the wurtzite structure of GaN. Moreover, the optical properties of the films correlate well with the crystalline quality and the Eu doped samples show an intense red luminescence at room temperature.

Experiments were performed to investigate heating up processes of fluids in storage tanks under the influence of an external heat source. Several tests were carried out both with heating from the bottom and with heating from the side walls. The test tank was equipped with thermocouples for measuring the temperature distribution and with needle probes for measuring of the local void fraction.
Calculations were performed using the CFD-code CFX-4. The simulation comprises two phase flow, subcooled boiling at the heated wall and steam release at the tank surface. The paper presents comparisons of measured and calculated temperatures and void fractions. CFX-4 simulations using the implemented boiling model reproduce and explain the observed physical phenomena. Convergence problems occurred with higher vapour volume fractions. As an application measures were investigated, to reduce the temperature stratification. It could be shown, that the insertion of buffle plates reduces and postpones the steam release.

We report on thin films in the ternary system B–C–N deposited by reactive magnetron sputtering of targets with different B/C ratio in an Ar/N2 gas mixture. First, the proportion of nitrogen in the gas was varied from 0 to 100% with the substrate being at floating potential in order to change the incorporated amount of nitrogen in the films. Secondly, at 50% nitrogen in the gas a negative substrate potential was applied for ion bombardment of the growing film. The film composition was measured by elastic recoil detection analysis. The mechanical properties, Young's modulus and hardness, were determined from nanoindentation measurements. All films were also investigated by Fourier-transformed infrared spectroscopy (FTIR). The mechanical properties show a great variation range in dependence on the film composition (up to a factor of three) and ion bombardment (up to a factor of two), which can be related to the bonding characteristics derived from the FTIR spectra.

Surface coating on austenitic stainless steel 304 (ASS) was generated by plasma immersion ionimmplantation (PIII) of nitrogen. The corrosion resistance was shown to increase by ca. four orders of magnitude. A barrier layer produced by PIII was observed to restrict the underlaying alloy surface exposed to the corrosion environment.

Relativistic heavy-ion collisions lead to a final state which has a higher degree of strangeness saturation than those of elementary collisions. A systematic analysis of this phenomenon, based on the strangeness saturation factor, is made for C+C, Si+Si and Pb+Pb collisions at the CERN SPS collider and for Au+Au collisions at RHIC energies. Strangeness saturation is shown to increase with the number of participants within a colliding system, at both CERN SPS and RHIC energies. The saturation observed in central collisions of lighter nuclei deviates from that seen in peripheral collisions of heavier nuclei with an equivalent participant number, which could be due to the difference in nuclear density.

Structural parameters for the near-neighbor surrounding of Pu(III), Th(IV), Np(IV) and Np(V) in complexes with various natural and synthetic humic and fulvic acids were determined by means of X-ray absorption fine structure (XAFS) spectroscopy. Furthermore, the interaction of the actinides with Bio-Rex70, a cation exchange resin having solely carboxylic groups as metal binding functional groups, was studied to determine structural parameters for the interaction of the respective actinide ions with carboxylic groups. Applying chemically modified humic acids with blocked phenolic/acidic OH groups, the influence of phenolic/acidic OH groups on the complexation of Np(V) by humic acids was studied in the neutral pH range. The structural parameters determined for actinide humate complexes were further compared with structural parameters of aqueous ions of the actinides and of solid actinide carboxylates given in the literature. The results indicate that the interaction between the actinide ions and humic acid is dominated by humic acid carboxylate groups. These carboxylate groups act predominantly as monodentate ligands. A contribution of phenolic/acidic OH groups to the complexation of Np(V) by humic acids at pH 7 cannot completely be excluded by EXAFS analysis.

Boron suboxide thin films have been deposited on Si(100) substrates by reactive RF magnetron sputtering of a sintered B target in an Ar/O2 atmosphere. Elastic recoil detection analysis was applied to determine the film composition and density. Film structure was studied by X-ray diffraction and transmission electron microscopy. The elastic modulus, measured by nanoindentation, was found to decrease as the film density decreased. The relationship was affected by tuning the negative substrate bias potential and the substrate temperature during film growth. A decrease in film density, by a factor of 1.55, caused an elastic modulus reduction by a factor of 4.5, most likely due to formation of nano-pores containing Ar. It appears evident that the large scattering in the published data on elastic properties of films with identical chemical composition can readily be understood by density variations. These results are important for understanding the elastic properties of boron suboxide, but may also be qualitatively relevant for other B-based material systems.

The deposition of homogeneous thin films on porous substrates has been investigated. The thin film deposition of Ta(N) by physical vapor deposition on porous films with different average pore sizes and material compositions has been studied. The continuity of Ta(N) films on top of porous low-k dielectrics is evaluated by means of ellipsometric porosimetry combined with sheet resistance and atomic force microscopy measurements. Interface reactions are analyzed by x-ray photoelectron spectroscopy profiling. It has been observed that the minimal Ta(N) thickness required to obtain a continuous metal layer on top of the porous film depends, on the one hand, on the porosity and pore size and, on the other hand, on the chemical interaction of the thin film with the porous substrate. The sealing of pores is favored by the presence of carbon in the dielectric matrix. This is explained through a mechanism of local enhancement of the degree of crosslinking in the dielectric matrix, catalyzed by Ta.

Der Erfindung liegt die Aufgabe zugrunde, die Lebensdauer einer Sputterionenquelle zu erhöhen, den Wartungsaufwand zu senken und die Zerstäubung der Teile der Ionenquelle, welche sich in der Nähe des für die Erzeugung der negativen Ionen erforderlichen Kathodeneinsatzes befinden, weitgehend zu verhindern.
Die Erfindung geht aus von den Bauteilen Ionisierer (2), Kathode (3), Sputtereinsatz (4), Formierungselektrode (5), Abschirmkappe (6) und Kathodenisolator (7) in einem vakuumdichten Gehäuse.

Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren zu entwickeln, dass Uran(VI) aus stark belasteten bergbaulichen Abwässern, Haldensicker-, und kontaminierten Grundwässern kostengünstig und umweltfreundlich in großen Mengen entfernt, wobei zur Uranfixierung ein Barrierematerial eingesetzt werden soll, das eine Beschaffenheit aufweist, die eine langzeitstabile, sichere Endlagerung oder Wiedergewinnung des angereicherten Urans ermöglicht.
Die technische Lösung geht davon aus, dass das Uran(VI) überwiegend als Karbonat, Sulfat oder Hydroxy-Komplex vorliegt und elementspezifische Filtermaterialien in einer geochemischen Barriere eingesetzt werden.

Die Erfindung betrifft ein Verfahren zur tomographischen Bildrekonstruktion für ein aus zwei asynchron rotierenden Komponenten bestehendes Objekt, wobei an einzelnen Drehwinkelpositionen der Objektkomponenten tomographische Projektionen vorgenommen werden.
Der Erfindung liegt die Aufgabe zugrunde, die beiden mit unterschiedlichen Winkelgeschwindigkeiten gegenüber ihrer Umgebung rotierenden Teilobjekte mit Hilfe eines Tomographen richtig abzubilden.

Die Erfindung betrifft ein bioaktives Material sowie ein Verfahren zu dessen Herstellung. Potentielle Anwendungen sind medizinische Implantologie, Gewebezüchtung und Biotechnologie. Der Erfindung liegt ein von einer Schicht zellausgeschiedener Produkte umgebenes Festkörpermaterial zugrunde.
Der Erfindung liegt die Aufgabe zugrunde, ein Material für Anwendungen in medizinischer Implantologie, Gewebezüchtung und Biotechnologie zu schaffen, bei welchem die Oberfläche für eine breite Klasse von Festkörpermaterialien bei Kontakt mit zellulären Medien zellbiologisch spezifische Wechselwirkungen aktiv vermittelt. Der Erfindung obliegt auch die Aufgabe, ein anwendungswirksames Verfahren zur Herstellung des genannten bioaktiven Materials vorzuschlagen.

Das Biokompositmaterial enthält ein anorganisches Gel und darin homogen verteilte, trocknungsstabile Zellprodukte wie Sporen, Zellwand-Proteine oder abgetötete Zellen. Das Biokompositmaterial ist als Biofilter in der Umwelttechnik zur Entfernung von Schwermetallionen aus wässrigen Lösungen geeignet.

The influence of melt rotation on the microstructure formation of Nd-Fe-B alloys, mainly the volume fraction and grain size of the a-Fe phase, has been investigated using the electromagnetic levitation technique which allows the in-situ measurement of the solidification kinetics containerlessly. Samples were subjected to a strong rotation during levitation and compared to fixed samples without additional sample rotation in the levitation facility. Additionally, experiments have been carried out where specially sealed samples were subjected to a well-defined forced rotation. A distinct reduction of the a-Fe volume fraction in samples with strong rotation was observed by measuring the magnetic moment in a vibrating sample magnetometer (VSM). The influence of cooling rate and undercooling level on microstructure formation and phase distribution has been investigated as well. The melt flow in a levitated droplet is studied numerically under the additional effect of a global sample rotation which may give a strong suppression of internal motions.

The solidification process and the resulting microstructure of Nd-Fe-B alloys in consideration of melt convection has been investigated experimentally with a specially designed floating-zone arrangement. A controlled influence on the melt flow is possible via tailored magnetic fields which enable enhancement or suppression of the melt convection. A specially designed magnetic two-phase stirrer offers a strong influence on the melt flow in the floating-zone facility. As a result, the microstructure pattern, mainly the volume fraction and grain size of the a-Fe phase, vary strongly with the strength of the internal flow motion. The melt flow is studied numerically under the additional effect of the two-phase stirrer taking into account the coupled heat and fluid flow fields. The electromagnetically driven flow during the inductive heating turned out to be of strong influence on the resulting microstructure.

This study was carried out in the frame of the ADS European project aimed to the development of Accelerator Driven System technology for nuclear waste transmutation.
The scope is to verify the possibility to simulate a two phase HLM (Heavy Liquid Metal) bubbly flow using the commercial CFD code CFX4.4.
The first stage consisted of an experimental campaign for the measurement of the phase velocities by means of the ultrasound Doppler velocimetry (UDV) and local volume fractions using resistive probes. The eutectic alloy PbBi is located inside a cylindrical container made of stainless steel which is provided with an electrical heater. The measurements reported here were carried out at a fluid temperature of 180°C. Nitrogen (N2) gas was injected into the stagnant liquid metal by means of a single orifice with an inner diameter of 0.5 mm. The orifice is located in the centre of the cross-sectional area of the fluid container. The gas flow rate chosen for these experiments was restricted to values below 1.2 cm3/s in order to guarantee a single bubble flow regime.
The simulation of the experiment was performed using the two fluid Euler/Euler model of CFX-4.4. The implemented drag laws were tested and compared with other drag laws taken from literature. The influence of the "non-drag forces" like the turbulent dispersion force and the lift force was also tested. Finally an advanced interpolation method based on optimization techniques was adopted in order to get the best fitting of the simulated velocity curves with the experimental ones. The results shows in general a good qualitative agreement of the experiment and the calculations, but a much better agreement can be found using the drag law coefficients derived by the above mentioned optimization technique, especially in the cases where the mass flow rates and the bubble mean diameters are relatively small.

In Argentinien wird das Integralreaktorkonzept CAREM als alternativer Einstieg in die Kerntechnik - speziell für Länder der dritten Welt - entwickelt. Diese sammelten bislang in der Regel ihre ersten Erfahrungen in der Nukleartechnik mit Forschungsreaktoren. Das beim Betrieb der Forschungsreaktoren gesammelte Wissen ist jedoch zu speziell und nicht umfassend genug, um hiermit allein Leistungsreaktoren betreiben zu können. Da das CAREM Konzept sämtliche in großen Leistungsreaktoren vorkommende Systeme beinhaltet, können mit dem CAREM Reaktor bei vergleichsweise ähnlichen - wenn nicht sogar niedrigeren - Kosten wie bei Forschungsreaktoren sämtliche zum Betrieb mittlerer und großer Reaktoren notwendigen Systemkenntnisse erworben werden.

The radiation source ELBE at Dresden-Rossendorf is centered around a superconducting ELectron accelerator of high Brillance and low Emittance (ELBE) which produces electron beams up tu 40 MeV. This new facility delivers secondary radiation of diffrent kinds. Special emphasis will be given to the production of intense THz radiation from its Free-Electron-Lasers (FEL). This radiation will be used for various research activities including the life sciences. Two additional femtosecond Ti:sapphire lase system allow to exploid different methods of THz generation for such investigatin.

In the present work, composite AgSiO2 thin coatings, containing metal nanoparticles, were prepared on glass substrates by the sol–gel route. The coatings were thermally treated in oxidative and reductive conditions up to 500 °C for metal nanoparticle formation. The coating structure and the nanoparticle formation were studied by atomic force microscopy and Rutherford backscattering spectroscopy (RBS) techniques. In the case of RBS, 1.4 MeV 4He+ ions were used for all samples, and low energy 16O and 12C ions in selected ones (heavy ion RBS, HIRBS), in order to improve the depth resolution for the profiling of the metal component. The antibacterial activity against Escherichia coli is examined by antibacterial drop test. The coatings exhibited a high antibacterial activity, which was enhanced with the increase of the metal concentration and was reduced with the increase of the particle size of the metal nanoparticles. The possible correlation between the layer interdiffusion after the thermal treatment and the antibacterial activity is examined and analyzed. Although further studies are required, RBS and HIRBS seem to be excellent tools for the quality control in the production of sol–gel thin coatings.

For the calculation of experiments simulating the behavior of the lower head in a core melt down scenario like FOREVER (performed at the Royal Institute of Technology, Stockholm) it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model is developed based on the code ANSYS®. The CFD module is used to calculate the thermodynamics. The resulting temperature field of the vessel wall is applied to the mechanical model. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied.
After post-test calculations for the FOREVER-C2 experiment, pre-test calculations for the forthcoming experiments are performed. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios. After analyzing the results of the calculations, it seems to be advantageous to provide a vessel support, which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at least prolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it may be advantageous to install a passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a core melt down.

CNx thin films have been prepared by IBAD varying the C-atom to N-ion ratio during deposition. The layers were studied by means of TEM and EELS investigation, ERDA and AES depth profiling. The obtained films were amorphous. The incorporation probality of N into the films was found to depend on the C/N arrival ratio. Large amount of N incorporation was found above and small amount below a N/C arrival rate of 0.3. Due to intentional change in the N/C arrival rate, modulated structures have been produced. The N concentration in the individual layers of modulated samples was found to exhibit distinct values of approximately 5 and 20 at.%. The erosion rate of the various CNx layers upon Ar ion bombardment depends on their N content. The relative erosion rate of the samples containing nitrogen of 20 and 5at.% was found to be r(rel)=1.6. It was determined by XTEM and EELS that the origin of the TEM image contrast marking out the individual sublayers is mainly due to density variations in the modulated structure and partly due to thickness differences of the cross sectional TEM samples as a result of Ar ion milling of layers of various compositions

Recent data on the reaction pD -> (pp) n with a fast forward pp pair with very small excitation energy is analyzed within a covariant approach based on the Bethe-Salpeter formalism. It is demonstrated that the minimum non-relativistic amplitude is completely masked by relativistic effects, such as Lorentz boost and the negative-energy P components in the ¹S₀ Bethe-Salpeter amplitude of the pp pair.

Das „Master-Curve“ (MC)-Konzept nach Wallin empfiehlt sich als ein geeignetes Werkzeug zur bruchmechanischen Sprödbruchsicherheitsbewertung von Komponenten und Anlagen. Es hat mit dem ASTM Standard E 1921 bereits Eingang in die Regelwerke gefunden und steht unmittelbar vor einer breiteren internationalen Anwendung. MC-Referenztemperaturen T0 werden an russischern WWER-Druckbehälterstählen im un- und bestrahlten Zustand ermittelt und mit am gleichen Material gemessenen Charpy-V-Übergangstemperaturen TT verglichen. Die unterschiedliche Zähigkeit der verschiedenen Stähle lässt sich ebenso wie der Einfluss der Bestrahlung mit dem MC-Konzept nachweisen. T0 und TT zeigen eine gute Korrelation, wobei die T0 ca. 80 K niedriger liegen. Damit erniedrigen sich auch die Referenztemperaturen für die Reaktordruckbehälter Integritätsbewertung.

The spherical MHD mean-field dynamo is considered from a mathematical viewpoint. It is shown that its 2x2 operator matrix is formally pseudo-Hermitian (J-symmetric), lives in a Krein space and has paired complex eigenvalues. Based on the J-symmetry, an operator intertwining Ansatz with first-order differential intertwining operators is tested for its compatibility with the structure of the alpha²-dynamo operator matrix. An intrinsic structural inconsistency is obtained in the set of associated matrix Riccati equations. This inconsistency is interpreted as a no-go theorem which forbids the construction of isospectral alpha²-dynamo operator classes with the help of first-order differential intertwining operators.

Ziel/Aim: Prospektive Erfassung von Daten zur Charakterisierung des intratumoralen Mikromilieus mittels FDG-PET, interstitieller Messung des Sauerstoffpartialdruckes und MRT-Untersuchung der Tumorperfusion vor radikaler Radio- bzw. Radiochemotherapie und Evaluierung der prognostischen Wertigkeit der Parameter.

Methodik/Methods: 14 Patienten mit inoperablen Kopf-Hals-Tumoren (UICC Stadium IV) wurden untersucht. Der intratumorale p0₂-Gehalt wurde mit einer Eppendorf-Sonde polarographisch gemessen. Die Tumorperfusionsmessung wurde im MRT (1.5 T Siemens Vision mit Kopf-Hals-Spule) durch den gemessenen Signalverlust bei Kontrastmittel-Bolus-Passage ermittelt. Ferner wurden die Tumorvolumina im MRT bestimmt. Als Maß des Glukosestoffwechsels wurde der mittlere Standard uptake value (SUVmean) der Tumorregion im FDG-PET bestimmt (300 MBq ¹⁸F-FDG i.v., ECAT EXACT HR⁺, Siemens/CTI).

Ergebnisse/Results: Die Tumorvolumina reichten von 14 bis 220 cm³ (median 74 cm³). Die SUVmean betrugen im Median 9,7 und waren bis auf in einem Turnor deutlich erhöht (range 2,9 -12,0). Die medianen pO₂-Werte der individuellen Tumoren zeigten eine weite Variabilität (range 0,1 - 33,1 mm Hg), der Median der Gruppe betrug 7,5 mm Hg. Korrelationsanalysen ergaben R²-Werten von 0,25 für Tumorvolumen versus pO₂, 0,15 für SUVmean versus pO₂, 0,13 für Perfusion versus pO₂, 0,06 für SUVmean versus Tumorvolumen und 0,03 für Perfusion versus Tumorvolumen.

Schlussfolgerungen/Consequences: Die nicht vorhandenen bzw. sehr schwachen Korrelationen zwischen den gemessenen Parametern deuten an, dass mit den unterschiedlichen Messmethoden verschiedene Charakteristika des Tumormikromilieus erfasst werden und dass diese sich daher evtl. prognostisch ergänzen könnten. Die nur sehr schwache Korrelation zwischen Glukoseaufnahme und interstitiell gemessenem pO₂ des Tumors weist darauf hin, dass neben anaerober Glykolyse weitere Faktoren die Zuckeraufnahme des Tumors beeinflussen. Derzeit werden weitere Patienten in diese Untersuchung aufgenommen und das Follow-up ergänzt, um die prognostische Relevanz der verschiedenen Messergebnisse, ggf. auch in Kombination, auf die Tumorkontrolle nach Strahlentherapie zu prüfen.

The radiation source ELBE at Dresden Rossendorf is centered around a superconducting ELectron accelerator of high Brilliance and low Emittance (ELBE) which produces electron beams up to 40 MeV. This new facility delivers secondary radiation of different kinds. Special emphasis will be given to the production of intense THz radiation form its Free-Electron Lasers (FEL). This radiation will be used for various research activities including the life sciences. Two additional femtosecond Ti:sapphire laser systems allow to exploit different methods of THz generation for such investigations

Within QCD sum rules at finite baryon density we show the crucial role of four-quark condensates, such as ‹(overline{q} γμλ^aq)²›_n, for the in-medium modification of the ωmeson spectral function. In particular, such a global property as the sign of the in-medium omega meson mass shift is found to be governed by a parameter which describes the strength of the density dependence of the four-quark condensate beyond mean-field approximation.
To study self-consistently the broadening of the omega meson resonance we employ a hadron spectral function based on the omega meson propagator delivered by a effective chiral Lagrangian. Measurements of the ωmeson spectral change in heavy-ion collisions with the HADES detector can reveal the yet unknown density dependence of the four-quark condensate.

Free electron lasers (FELs) allow the generation of electromagnetic radiation (EM) in a wide field of frequencies (respectively wavelengths) throug the proper adjustment of energy of an electron beam and the field configuration of a magnetic undulator passed by this beam. Terahertz (THz) radiation covers the region of the electromagnetic spectrum between approximately 0.3 and 30 THz and thus can be considered a continuation of the optical spectrum beyond the far infrared (IR). The very interesting results obtained from various studies ot the interaction between IR radiation and biomolecules or tissue have stimulated increasing interest in the study of biological systems using THz radiation. This paper points out what role modern FELs can play in this research.

The atomic mechanisms of relaxation processes in carbon films during ion beam deposition and post-deposition annealing are studied using the method of molecular-dynamics with a modified hydrocarbon potential of Brenner. Deposition of films was simulated for ion energies E_ion =10-80 eV and for substrate temperatures T_s =100-900 K. Using a time-resolved analysis of atomic trajectories from the film deposition simulations, a short-term temperature-dependent relaxation stage (t~70-1000 fs), where the film formation is influenced by T_s , was identified. During this stage, depending on T_s , the carbon atoms at metastable four- or fivefold coordinated sites can relax into either three- or fourfold positions, giving rise to graphitic or tetrahedral (ta-C) amorphous carbon films, respectively. In agreement with experiment the simulations predict a sharp transition from ta-C to graphitic carbon as T_s exceeds a critical temperature T_c . Simulating post-deposition annealing, low-temperature structural relaxation of as-deposited ta-C was observed as evidenced by a reduction of potential energy and grown-in stress. The corresponding amorphous network rearrangements consist both in the sp³ -to-sp² conversion and in the
sp² -to-sp³ one. A nearly complete stress relief in ta-C with the sp³ content of ~80% and grown-in compressive stress of 11 GPa was simulated at an annealing temperature of ~1000 K.

Negative and positive charge trapping under constant current regime of high-field electron injection both from Al electrode and Si substrate in high-dose Ge+ ion implanted and then rapid thermal annealed thin-film dioxide has been studied. The negatively charged traps with >10-14 cm2, 1.8x10-15 cm2, 2x10-16 cm2 and 3x10-18 cm2 and generated positive charge with effective capture cross-section (5-7)x10-15 cm2 and 3.3x10-16 cm2 have been shown to be introduced into the oxide layer. A good correlation of the electron trap concentration with with a cross section of >10-14 cm2 and the concentration of the implanted Ge atoms, determined by RBS technique inside the oxide, have been observed. The decrease of Ge concentration within the oxide layer with increasing RTA duration have been associated with Ge atom outdiffision from the oxide at high-temperature annealing. The generated positive charge have been shown to be collected near the SiO2/Si interface during the high field electron injection, both from the Al and Si side. Correlation of the generated positive charge with the Ge atoms embedded in the SiO2/Si interface have been observed. The anode hole injection mechanism is suggested to be responsible for the observed generation of the positive charge.

For realizing futuristic optical communications networks with greater than 100Gb/s transmission capability, highly efficient, ultra-fast all-optical devices are crucial at communication wavelengths (<2 mm). Such devices can be realized by making use of the large and fast intersubband transition (ISBT) non-linearity. However, for achieving ISBTs in the communication wavelength region, one requires a large conduction-band offset material. We reported the possibility of one of the crucial all-optical device, all-optical switch, based on ISBT absorption saturation, operating in the < 2 mm wavelength range using InGaAs-AlAsSb quantum well structures. The efficiency of such a device is defined in terms of the switching response time and the switching energy. While the relaxation time related to the switching response time can be estimated from a direct pump-probe measurement, estimation of the saturation intensity related to the switching energy is not that straightforward. In this work, we carry out a detailed study to estimate the saturation current in Sb-based quantum wells

Nach dem heutigen Stand der Technik wird zur Produktion in Batch-Chemieanlagen der Anlagenstatus im Betrieb vom Anlagenbediener beurteilt. Dies setzt ein hohes Maß an Erfahrungen voraus. Dennoch kommt es zu Fehlproduktionen, die umweltrelevante Entsorgungs- und Nachbearbeitungsaufwände verursachen. Durch eine Zusammenführung aller verfügbaren Informationen und durch deren Verdichtung soll dem Bediener eine Unterstützung bei der Beurteilung des Prozessablaufes gegeben werden, so dass Fehlproduktionen frühzeitig erkannt und vermieden werden können.
Im Teilvorhaben 1 wurden verschiedene Methoden zur Zustandsüberwachung durch neuronale Netze hinsichtlich ihrer Anwendbarkeit anhand von Technikumsversuchen für eine homogene exotherme Veresterungsreaktion geprüft. Hier zeigte sich, dass sowohl die Zustandsbeurteilung als auch die Prognose mit neuronalen Netzen vielversprechende Ansätze liefern. Hierzu ist allerdings ein hohes Maß an Systemwissen in Vorverarbeitungsstufen zu integrieren.
Im Teilvorhaben 2 wurde ein Online-Monitoring-System (MoSys) entwickelt, das auf dimensionslosen Stoff- und Wärmebilanzen mit adaptiven Komponenten basiert. MoSys muss zuerst mit den Prozessdaten von normalen und unerwünschten Batch-Verläufen angelernt werden, die im Miniplant unter den Bedingungen des Industrieprozesses durchgeführt wurden. Die Adaption der Bilanzmodelle an die Zielanlage erfolgt durch zweischichtige Perceptron-Netze. Um eine vollständige Maßstabsübertragung zu gewährleisten, sollte MoSys mit Prozessdaten von mindestens einem normalen Batch-Verlauf in der Chemieanlage angepasst und validiert werden. MoSys wurde sowohl für eine homogene exotherme Veresterungsreaktion als auch für einen komplexen heterogenen exothermen Hydrierprozess konzipiert. Experimentelle Tests wurden für die Veresterung in einer Pilotanlage und für die Hydrierung in einer industriellen Chemieanlage durchgeführt.
Zur Industrieerprobung wurde MoSys in ein Batch-Informations-Management-System (BIMS) integriert, das auch entwickelt und in das Prozessleitsystem (PLS) einer Mehrzweckanlage im Feinchemie-Werk Radebeul (Degussa AG) implementiert wurde. Dadurch konnten die MoSys-Ausgaben simultan mit wichtigen Prozesssignalen auf den Terminals des PLS visualisiert werden. Zum Beispiel werden der Hydrierungsfortschritt, das vorhergesagte Reaktionsende und die Konzentrationsverläufe des Edukts, Zwischenprodukts und Produkts auf den Terminals der Operatorstationen angezeigt. Wenn unerwünschte Betriebszustände auftreten, wird das Bedienungspersonal frühzeitig alarmiert und Empfehlungen für Gegenmaßnahmen, die nur vom Operator ausgeführt werden dürfen, werden auf den Terminals angezeigt. Die Leistungsfähigkeit von MoSys/BIMS konnte während zweier Hydrierungs-Produktionskampagnen nachgewiesen werden.

Traditional dechanneling dopant profiles in the silicon crystal wafers have been achieved by tilting the wafer away the incident beam. As feature sizes of device shrink, the advantages for channeled doping profiles for implants with small
or near zero degree incident angles are being recognized. For example, high-energy CMOS well spacing limitations caused by shadowing and encroachment of the ion beam by photoresist mask can be avoided for near zero degree incident implants. Accurate models of channeled profiles are essential to predict the device performance more important. This paper will discuss the factors important for channeled dopant profiles, such as the acceptance angle, dopant species, energy, incident angle, dose and damage accumulation in the crystal based on SIMS and Crystal-TRIM simulation results. In addition, the control requirements on ion implantation parameters from a channeling perspective will also be discussed.

Im internen Schlussbericht zum BMBF-Projekt 01RV9802/4 wird die Entwicklung des Online-Monitoring-System (MoSys) für homogene und heterogene exotherme chemische Reaktionen beschrieben. Zur Industrieerprobung wurde MoSys in ein neues Batch-Informations-Management-System (BIMS) integriert und in das Prozessleitsystem (PLS) einer Mehrzweckanlage im Feinchemie-Werk Radebeul (Degussa AG) implementiert. Die Betriebserfahrungen von zwei Hydrierungs-Produktionskampagnen werden vorgestellt.
Im Anhang ist eine Beschreibung der BIMS/MoSys-Bedienungsanleitung enthalten. Ferner sind die von BIMS/MoSys genutzten Daten und Informationen sowie ihre Tabellenstruktur in der BIMS-Datenbank zusammengestellt.

Aufgrund ihrer hervorragenden Eigenschaften, wie große Bandlücke, hohe thermische Leitfähigkeit und gesättigte Elektronendriftgeschwindigkeit, sind sowohl Siliziumkarbid als auch Diamant vielversprechende Halbleitermaterialien für elektronische Bauelemente, die unter extremen Bedingungen noch einwandfrei funktionieren sollen. Allerdings ist es bislang noch nicht gelungen, Diamant in zufrieden stellender Weise mit flachen Donatoren zu versehen. Im Gegensatz hierzu ist die p-Dotierung von Siliziumkarbid noch nicht befriedigend gelöst. Da aber sowohl p-leitender Diamant, als auch n-leitendes SiC sehr einfach zu realisieren sind, könnten Heterostrukturen aus diesen so dotierten Materialien erfolgversprechend sein.
Frühere Experimente haben gezeigt, dass eine Hochdosisimplantation von Si in Diamant zur Bildung von ß-SiC führen kann. In dieser Arbeit wurden die Leitfähigkeit und strukturellen Eigenschaften von Diamantproben untersucht, die mit Si-Dosen im Bereich von 3×1017 cm-2 bis 1×1018 cm-2 implantiert worden sind. Die Implantation erfolgte bei 900 °C, um die Schädigung der Diamantmatrix zu reduzieren. Der Einfluß des Implantationsschadens wurde anhand von Vergleichsproben studiert, die mit Argon implantiert wurden. Röntgenbeugung (XRD), IR Absorptionsspectrometrie, hochauflösende cross-sectional Transmissionselektronenmicroscopie (HRTEM) sowie Vierpunktmessungen in van der Pauw Geometrie dienten zur Charakterisierung der implantierten Diamanten.

This communication addresses the production of carbon nitride thin films with fullerene-like structure (f-CNx), i.e. bent and cross-linked graphitic basal planes [1]. Normally, f-CNx thin films are produced by Magnetron Sputtering and a key parameter appears to be the use of low-energy ion bombardment (<100 eV) during the growth process [2]. The aim of the investigations is to obtain f-CNx by means of Ion Beam Assisted Deposition (IBAD), which will provide a better understanding of the growth process since the role of neutrals and ions can be studied separately. In order to reproduce the growth conditions of f-CNx, an IBAD device has been re-constructed, incorporating an End-Hall ion source to operate in the low-energy range (50-150 eV). Preliminary results on the deposition of our films will be shown.
1. H. Sjöstrom, et al. Phys. Rev. Lett. 75 (1995) 1336.
2. L.Hultman, et al. Phys. Lett. 87 (2001) 225503.

Our six years experience in routine operation and maintenance of the Rossendorf CYCLONE 18/9 facility is given here along with improvements for a stable and reliable cyclotron operation.

[no abstract available]

Our quasi-particle model for deconfined matter near T_c is reviewed. The extrapolation of lattice QCD data to finite baryo-chemical is discussed. Determined by the chiral transition temperature T_c, the resulting equation of state of neutral and $\beta$ stable deconfined matter is soft and limits size and mass of pure quark stars.

Microorganisms have a potential to affect mobility and overall environmental behaviour of heavy metals and radionuclides through solubility and speciation changes, biosorption, bioaccumulation or other bio-transformations. In this study we used a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Infrared (IR) spectroscopy and Time Resolved Laser Induced Fluorescence Spectroscopy (TRLFS) to characterize the uranium complexes formed by different bacterial strains such as Acidithiobacillus ferrooxidans D2, Stenotrophomonas maltophilia JG-2, Bacillus sphaericus JG-A12 which were isolated from uranium mining wastes. In addition several reference strains namely Pseudomonas stutzeri ATCC 17588; 55595 and Pseudomonas migulae CIP 105470 which were demonstrated to be relevant to the bacterial populations in the uranium wastes were studied as well. The EXAFS analysis demonstrated that in the case of B. sphaericus JG-A12, the U(VI) is coordinated to carboxyl groups in a bidentate fashion with an average distance between the U atom and the C atom of 2.91 ± 0.02 Å and to phosphate groups in a monodentate fashion with an average distance between the U atom and the P atom of 3.59 ± 0.02 Å. In the case of the other bacteria, only phosphate groups are implicated in the complexation of uranium in a monodentate mode, with an average distance between the U atom and the P atom of 3.63 ± 0.02 Å. These results are consistent with those found by Infrared measurements. The latter demonstrates the complementary role which EXAFS spectroscopy can play in determining of metal distribution behaviour in the environment. In addition, we applied TRLFS in order to determine the energy and the shape of the emission bands and the fluorescence lifetime of the uranium complexes formed by the different bacterial biomass studied in this work.

Mohamed Merroun1, Johannes Raff1, Christoph Hennig1, Andre Rossberg1, Tobias Reich2 and Sonja Selenska-Pobell1
1Institute of Radiochemistry, Forschungszentrum Rossendorf,D-01314 Dresden, Germany, 2Johannes Gutenberg Universität Mainz, Institut für Kernchemie, Mainz, Germany
Microorganisms have a potential to affect mobility and overall environmental behaviour of heavy metals and radionuclides via bio-transformations such as oxidation and reduction which can change metal's speciation and solubility and also via different biosorption, bioaccumulation, and biomineralisation processes. In this study Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy was used to determine the structural parameters of the uranium complexes formed by vegetative cells of B. sphaericus JG-A12 which was recovered from a uranium mining waste pile and it's genomic analogue, B. sphaericus NTCC 9602. The complexation of uranium (VI) by the purified and recrystalized S-layers of these two strains was studied as well. The EXAFS analysis demonstrated that in all cases studied the U(VI) was coordinated to carboxyl groups in a bidentate fashion with an average distance between the U atom and the C atom of 2.91 ± 0.02 Å and to phosphate groups in a monodentate fashion with an average distance between the U atom and the P atom of 3.59 ± 0.02 Å. By using ICP-MS, "Stain-all" analysis and colourimetric methods it was demonstrated that the S-layers of B. sphaericus NCTC 9602 and B. sphaericus JG-A12 are phosphorylated. The latter explains the atomic structures of the U-complexes formed at the surfaces of the strains.
Interestingly, the uranium complexes formed by both the bacterial cells and the purified S-layer proteins possess the same structural parameters. These results indicate that the S-layers play the main role in the binding of this radionuclide and that they are acting as a protective barrier against it in the polluted environments.

The reaction p d -> d phi p_{sp} is studied within the Bethe-Salpeter formalism. Under special kinematical conditions (slow backward spectator proton p_{sp} and fast forward deuteron) relevant for forthcoming experiments at COSY, the cross section and a set of polarization observables factorize in the contribution of the pure subprocess p n -> d phi and a contribution stemming from deuteron quantities and kinematical factors. This provides a theoretical basis for studying threshold-near processes at quasi-free neutrons.

Design and optimisation of the thermal hydraulics of liquid metal reactor systems is strongly based on numerical simulations of the related fluid flow and heat & mass transfer processes. Whereas these numerical simulations are essentially based on local flow phenomena (small-scale vortices, turbulence or sub-grid scale modeling), experimental results are often limited to integral flow rates or local related data like temperature or pressure. Local velocity measurements would be highly desirable but are mostly lacking due to the very limited possibilities for velocity measurements in liquid metals.

During the last decades the Ultrasound Doppler Velocimetry (UDV) became a very 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 becomes 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 a number of specific problems: First of all, the application of the ultrasonic transducers is usually restricted to maximum temperatures of 150°C. The transmission of a sufficient amount of ultrasonic energy from the transducer to the fluid has to be guaranteed. Here, the acoustic coupling and the wetting conditions have to be considered as important issues. Moreover, the flow has to be seeded with reflecting particles to obtain Doppler signals from the fluid.

The feasibility of velocity profile measurements by UDV has already been demonstrated for low temperature liquid metals like mercury [1] and gallium [2]. We report on first successful measurements in liquid sodium at 150°C [3]. We will present mean profiles of a flow in a rectangular duct exposed to an external, transverse magnetic field. To demonstrate the capability of UDV the transformation of the well-known turbulent, piston-like profile to an M-shaped velocity profile for growing magnetic field strength was observed. The significance of artefacts such as caused by the existence of reflecting interfaces in the measuring domain will be discussed. In the sodium case, the measurements were performed through the channel wall.

An integrated ultrasonic sensor with acoustic wave-guide has been developed to overcome the limitation of ultrasonic transducers to temperatures lower than 200°C. This sensor can presently be applied at maximum temperatures up to 800°C. Stable and robust measurements have been performed in various PbBi flows in our laboratory at FZR as well as at the THESYS loop of the KALLA laboratory of the Forschungszentrum Karlsruhe (FZK). We will present experimental results obtained in a PbBi bubbly flow at 250...300°C. Argon bubbles were injected through a single orifice in a cylindrical container filled with stagnant PbBi. Velocity profiles were measured in the bubble plume. Mean values of the liquid as well as the bubble velocity were extracted from the data and will be presented as function of the gas flow rate. At the THESYS loop of FZK stable velocity profils have been measured in a round tube of diameter 60mm during a period of about 72 hours at temperatures between 180°C and 350°C. Velocity profiles have been obtained at different temperatures for variations of the liquid flow rate. In the PbBi case, the acoustic wave-guide was always in direct contact to the melt. In addition, some results of UDV velocity measurements with a wave-guide in a CuSn alloy of about 620°C and in an Al melt of about 750°C will be presented.

The A(e,e'K⁺)YX reaction has been investigated in Hall C at Jefferson Lab. Data were taken for Q² approx 0.35 and 0.5 GeV² at a beam energy of 3.245 GeV for ³He,⁴He. The missing mass spectra are fitted with Monte Carlo simulations including Lambda, Sigma⁰, Sigma^- hyperon production. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for Lambda-hypernuclear bound states is seen for ^3,4He targets.

Electrical resistance of monotectic melts strongly depends on the state of phase separation. The gravity driven sedimentation leads to an arrangement of the lighter phase above the heavier one,. Because resistance of both phases are different, the state of demixing can be determined by the overall melt resistance using the four-probe-method. Resistance of hypermonotectic Zn-Pb liquid alloys has been measured in a wide temperature range between 820°C and a monotectic line and its dependence on different parameters has been discussed. The results are compared with theoretical predictions. It was shown that the electrical resistance of the demixed melt changed if transport processes (Marangoni convection) took place under microgravity conitions. The measuring arrangement used in the microgravity experiment on Zn-Pb melts during the flight of TEXUS 39 is presented.

The microstructure of Nd-Fe-B alloys changes if the convection in the melt varies. A controlled influence on the melt flow is possible via magnetic fields or sample rotations. The experimental techniques behind are the electromagnetic levitation, mechanical sample rotations and a specially designed float-zone arrangement. We present theoretical/numerical results for the melt convection in those configurations. The melt flow in a levitated droplet is studied under the additional effect of a global sample rotation which may lead to a strong suppression of internal motions. A specially designed two-phase stirrer offers a strong influence on the melt flow in the float-zone facility.

The solidification process and the resulting microstructure of Nd-Fe-B alloys in consideration of melt convection has been investigated using the electromagnetic levitation technique, forced rotation experiments and the application of alternating magnetic fields. The electromagnetic levitation technique, which allows the in-situ measurement of the solidification kinetics containerlessly, has been used in order to investigate the influence of the internal melt motion on the microstructure formation of Nd-Fe-B alloys, mainly with respect to the volume fraction and grain size of the a-Fe phase. Moreover, experiments where specially sealed samples were subjected to a well-defined forced rotation have been carried out. The determination of the a-Fe volume fraction by measuring the magnetic moment in a vibrating sample magnetometer (VSM) resulted in a distinct reduction of the a-Fe volume fraction in samples with strong rotation. The influence of the cooling rate and the undercooling level on the microstructure formation and phase distribution has been investigated as well. Furthermore, a new category of experiment has been started where a tailored magnetic field was applied in order to study the microstructure evolution due to an enhancement or suppression of the melt convection by additional alternating magnetic fields.

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. This paper gives an overview about experimental results and the physics of the instabilities. The thermo-hydraulic code ATHLET is used to investigate the dynamic bevavior of the test facility.

We describe the electric characteristics and mass spectra of two liquid metal alloy ion sources;namely Er70Fe22Cr3Ni5 and Er69Ni31.Erbium ions are of great interest for optoelectronic applications.For the first time in the literature the energy spread of triply charged ions (Er 3+ ) is reported.

Radiopharmaceuticals are drugs containing a radionuclide and are used routinely in nuclear medicine for the diagnosis or therapy of various diseases. They are mostly small organic or inorganic compounds, but can also be macromolecules such as monoclonal antibodies or their fragments labeled with a radionuclide. Those agents whose biodistribution is determined by biological interaction, e. g. receptor binding, are termed target-specific radiopharmaceuticals.

For diagnostic imaging agents, technetium-99m is frequently the radionuclide of choice because it has optimal nuclide properties (half-life of 6h and appropriate Gamma-energy of 140 keV). The inconvenience of purchasing a short-lived radionuclide was overcome by the development of the ⁹⁹Mo/^99mTc generator, which is based on transient equilibrium between the parent radionuclide ⁹⁹Mo (66h half-life) and the daughter radionuclide ^99mTc (6h half-life). The generator makes this radionuclide both routinely available and economical. Finally, the ^99mTc-radiopharmaceutical can easily be prepared in the clinic by means of prefabricated kits. So it is no surprise that more than 90% of routine in vivo imaging is performed with technetium-99m [1,2].

Table 1. Metal nuclides for diagnostic or therapeutic application

Beside technetium, many other radiometals have been or are being investigated for their uses in nuclear medicine [3]. This comprises not only radiometal-labeled agents used in gamma scintigraphy and positron emission tomography (PET), but also beta and alpha emitters for radionuclide therapy [4] (Table 1).
The development of effective metalloradiopharmaceuticals is a complex task which is not simply accomplished by attaching a radionuclide to a nonradiolabeled targeting vector (Fig.1).

Fig.1. Schematic representation of the bifunctional approach as a strategy of radiopharmaceutical design

Because of the unphysiological nature of the radiometal, the structure of the biomolecule where the chelate is appended, will be altered and the biodistribution will change drastically. The search for metalloradiopharmaceuticals involves therefore chelate systems that stable bind the radiometal, and, since it will be directly involved in optimizing the biochemical properties of the radiopharmaceutical, it has to be compatible in structure and physicochemical properties. In recent years, new chelate systems have been developed (Fig.2) for binding technetium (as well its congener rhenium) at oxidation states V, III, and I involving metallnitrido cores (1) [5], mixed-ligand complexes (2) [6] and metal-tricarbonyl derived complexes (3) [7,8].

The stability of the complexes of '3+1' type depends not only on the nature of the tridentate ligand but also on the nature of monodentate co-ligand.^[1,2] The recently introduced (tri)bidentate heterofunctionalized phosphines, (H₂PNX; X=O,S), which are quite versatile in terms of charge and denticity towards the [M=O]³⁺ core, form '3+1' mixed-ligand complexes with different thiolated monodentate co-ligands.^[3,4] These complexes show different in vitro stabilities, confirming the importance of the nature of the donor atoms on the stability. Using the H₂PNS ligand and a thiolated arylpiperazine derivative we succeeded on the preparation of the stable '3+1' oxocomplex [M(O)(eta³- PNS)(SCH₂CH₂NHCH₂CH₂CH₂(2-MeOPhpip))] (M = Re, ^99mTc). In spite of its high stability, the complex showed low affinity for the 5HT_1A receptor (120 nM ± ).^[5]
These results prompted us to introduce some chemical modifications in the monodentate co-ligand, in order to increase the affinity and selectivity to the receptor. So, herein we report on the synthesis and characterization of the new thiolated arylpiperazine derivatives and on the preparation of the corresponding '3+1' oxocomplexes at the macroscopic and at the n.c.a. level (80-95% yield). The ^99mTc-complexes obtained were identified by comparing their radioactive HPLC profiles with those of the analogous Re complexes. After purification by semi-preparative HPLC, the radiochemical purity of the complexes is higher than 95%.
The stability of the purified ^99mTc-complexes was studied in saline, 0.01M PBS (pH 7.4) at 37ºC, and all of the complexes revealed stable. No significant exchange with glutathione (1mM and 10mM solutions, 37ºC) was observed.
In order to determine the effect of the chemical modifications introduced in the monodentate ligand, binding affinities and specificities for the 5HT_1A receptor have still to be evaluated.

Acknowledgements: This work is being supported by the COST Action B12.

References
[1] Syhre, R.; Seifert, S.; Spies, H.; Gupta, A.; Johannsen, B.; Eur. J. Nucl. Med. 1998, 25:793.
[2] Seifert S. et al Radioch. Acta, in press.
[3] Correia, J. D. G.; Domingos, A.; Santos, I.; Eur. J. Inorg. Chem. 2000, 7:1523.
[4] Correia, J. D. G.; Domingos, A.; Paulo, A.; Santos, I.; J. Chem. Soc. , Dalton Trans. 2000, 14: 2477.
[5] Fernandes, C.; Correia, J. D. G.; Gano, L.; Santos, I.; Seifert, S.; Syhre, R.; Spies, H.; J. Labelled Cpd. Radiopharm. 2001, 44, Suppl. 1, S518.

Introduction
To expand the scope of ¹¹C-labelled compounds, novel ¹¹C-C bond forming reactions gain more and more attention [1]. The versatile availability of [¹¹C]methyl iodide makes this labelling precursor favourable in several transition-metal mediated cross-coupling reactions. In this contex, technically simple, high-yielding and functional group tolerating reactions are of particular interest. The Sonogashira copper-palladium catalysed coupling of terminal alkynes with aromatic and vinylic halides [2] represents such a reaction. To the best of our knowledge, the Sonogashira-reaction has not yet been employed in ¹¹C-chemistry. Herein, we describe a modified Sonogashira-like reaction [3] for labelling the terminal alkyne group of the potent contraceptive steroid mestranol 1 with [¹¹C]methyl iodide.

Results and Discussion
The classical conditions of the Sonogashira reaction (Pd⁰, CuI and TEA or DIPA as thebase) can not be employed for ¹¹C-labelling with [¹¹C]methyl iodide due to the rapid quaternization the amine base. Therefore, we tested alternative catalyst/base combinations. By using tetrakis(triphenylphosphine)-palladium(0) (TTPP), copper(I) iodide, and 1,8-bis(dimethylamino)naphthalene as a non-nucleophilic base, about 5% of [¹¹C]methyl iodide was converted into [¹¹C]2. Similar results were obtained using the catalyst TTPP and silver oxide as the base. However, in the reaction of 1 with tris-(dibenzylidineacetone)-dipalladium(0), triphenylarsine, and tetrabutylammonium fluoride, 42-53% of [¹¹C]MeI was converted into [¹¹C]2

Scheme 1: ¹¹C-labelling of steroid 1

Conclusion
We developed a new method for a ¹¹C-C bond formation employing the cross-coupling of terminal alkynes with [¹¹C]methyl iodide via a Sonogashira-like reaction in sufficient radiochemical yields.

References
[1] B. Långström et al. Acta Chem. Scand. 53 (1999) 651-669.
[2] K. Sonogashira et al. Tetrahedron Lett. (1974) 4467-4470.

Introduction
Besides the herpes simplex virus type-1 thymidine kinase (HSV-1 TK), cytosine deaminase (CD) presents another system for gene therapy. CD catalyses the hydrolytic deamination of cytosine to form uracil. Its lack in mammalian cells and the ability to convert 5-fluorocytosine to the cell-toxic 5-fluorouracil makes it suitable for use in several gene therapy protocols [1,2]. An appropriate radiolabelled cytosine derivative would make it possible to monitor gene expression with positron emission tomography (PET), providing a sufficient amount of the tracer is trapped in the tumor cells. For this purpose, several cytosine derivatives were tested.

Results
CD was obtained by over-expression and following purification from transformed E. coli bacteria in good yields. The specific activity and K_M were determined using cytosine and 5-fluorocytosine. Some compounds (listed in table 1) were incubated in tris-buffer solution containing the isolated enzyme. Samples were taken and the rate of metabolites formation determined by HPLC.

For cytosine, the specific activity of 38 U/mg enzyme (one unit is the amount of enzyme catalysing the deamination of 1 µmol substrate per minute at 25°C) and a K_M of 0.63 mM falls in the range of further data published [3,4]. For 5-fluorocytosine, the decrease in specific activity (2.1 U/mg protein) and the increase of K_M (5.2 mM) of one dimension is also in good agreement with published data [1]. Additionally, it was shown that the CD tolerates some structural variations of its possible substrates. Beside substances which are varied at the 5-position (5-fluorocytosine, 5-methylcytosine), N-substituted derivatives like N-methylcytosine and N-hydroxycytosine are also accepted. This results offer a number of fluorine-18 labelled compounds as candidates for monitoring gene therapy.

Table 1
-----------------------------------------------------------------------
Turnover to the corresponding product in % after
Compound............10 min.....30 min.....60 min
-----------------------------------------------------------------------
Cytosine...............88.84......100..........100
5-Fluorocytosine......9.39.......22.42........28.61
5-Methylcytosine.....1.07.........5.94........10.25
N-Methylcytosine....1.47..........5.22.........8.53
N-Hydroxycytosine.20.11.......31.23........42.88

References
[1] Rowley, S. et al. J. Surgical Oncology 1996, 61, 42-48.
[2] Haberkorn, U. et. al. J. Nucl. Med. 1996, 37, 87-94.
[3] Ipata, P. L. Methods Enzymol. 1978, 51, 394-401.
[4] Balestreri, E. et al. Biochim Biophys Acta 1973, 315, 443-448.

Introduction
For monitoring gene expression of the herpes simplex virus type-1 thymidine kinase (HSV-1 tk), several reporter probes such as acycloguanosine analogues labelled with fluorine-18 have been described [1]. Studying several methods for radiolabelling eligible precursors with the isotope fluorine-18, we noticed highly varying yields, depending on the precursor used. This is due to the occurrence of competitive reactions that reduce the labelling yields of the tracers.

Results
Conversion of the precursors 5 and 6 into [¹⁸F]FHPG 1 and [¹⁸F]FHBG 2, but also into the non-radioactive fluorine compounds, resulted in a much lower yield compared to the methylated derivatives 7 and 8.

The nucleophilic fluorination with Kryptofix K2.2.2 to prepare the labelled compounds 1-4 was performed according to [2,3]. The unreacted ¹⁸F was removed by purification with a silica gel cartridge eluted with CH₂Cl₂/MeOH 85:15. In splitting off the methoxytrityl protection groups by of aqueous HCl, the precursors behave different. With the acycloguanosines derivatives 1 and 3 bearing an oxygen in their side-chain a by-product was delivered. The carba-analogues 2 and 4 are stable under these conditions.

Non-radioactive fluorination of compounds 5 and 6 delivers a N¹/O (from -OTs) bridged structure (characterized by ¹H NMR, IR, MS and elemental analysis) as by-product in a yield of 20%. This concurrent reaction was also observed in the ¹⁸F-labelling experiments. Since the methyl group in the N¹-position inhibits the cyclisation, 7 and 8 do not form such a by-product.
The splitting off the methoxytrityl protection groups by aqueous HCl is accompanied by decomposition. The two-phase system water-dichloromethane did not allow a satisfying control of the reaction temperature and in consequence, the acyclic side-chain of 1 and 3 was splitted off to result a by-product. These problems were overcome by using methanolic HCl as splitting agent. Its miscibility with CH₂Cl₂ allows a better reaction control, resulting in shorter reaction times and reducing the by-products.

References
[1] Wiebe, L. I. et al. Q. J. Nucl. Med. 1997, 41, 79-89.
[2] Alauddin, M. M. et al. Nucl. Med. Biol. 1998, 25, 175-180.
[3] Alauddin, M. M. et al. Nucl. Med. Biol. 1999, 26, 371-376.
[4] Shiue, G. G. et al. Nucl. Med. Biol. 2001, 28, 875-883.

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The development of DYN3D-MSR code is described in the paper. This code is based on a three-dimensional code DYN3D for calculation of steady states and transients in light water reactors LWR, which was developed in FZR. The MSR modification of DYN3D code is designed to calculate steady states and transients of Molten Salt Reactors. The fuel of this reactor should be liquid in a form of molten salt mixture and should act also as a coolant. The thermal-hydraulic and neutron kinetic characteristic will differ from classical LWR. For the code development a MSR design with fuel floating in channels inside hexagonal graphite structure is considered. The first step of development is a 1D version, which is based on a numerical method for hexagonal fuel element geometry from original code and which includes new models describing fuel flow. DYN1D-MSR as the first step of 3D version development is already an effective tool for transient analysis of MSR. The first results for fuel flow slowdown have shown the ability to provide space dynamics calculations.

Drug analysis and development with PET should fully exhaust the ability of this tomographic technique to quantify regional tracer concentrations in vivo. Data evaluation based on visual assessment of regional image contrast is not sufficient for this purpose since much of the information present in dynamically acquired data is not used by these approaches. Compartment modelling of dynamic PET data is generally the method of choice since it allows a quantitative assessment of the underlying pharmacokinetic parameters describing drug transport, metabolism and molecular interactions. We present here an overview of key issues of compartment modelling with specific attention to the assumptions underlying the various models and their limitations. We believe that a thorough understanding of the applicability of models is mandatory for the development, successful execution and analysis of quantitative PET studies. Otherwise, meaningful and interpretable results will often not be obtained.

Insulin resistance is a frequently observed side effect of highly active antiretroviral therapy (HAART). Currently, very little is known about the mechanisms or specific tissues involved. We aimed to identify possible defects in skeletal muscle glucose uptake andhietabolism in HIV patients receiving HAART. Whole-body glucose disposal and oxidation were determined by combination of the euglycemic-hyperinsulinemic clamp technique and indirect calorimetry. Muscle glucose uptake of the thighs was measured simultaneously by dynamic 2[¹⁸F]fluoro-2-deoxy-D-glucose positron emission tomography. Patients receiving HAART had signs of lipodystrophy as confirmed by dual energy x-ray absorptiometry. Whole-body glucose disposal was significantly reduced in these patients compared with untreated patients. Analysis of kinetic constants using a three-compartment model indicated reduced skeletal glucose uptake caused by significantly impaired glucose transport and phosphorylation. Skeletal muscle glucose uptake was reduced by 66% in treated patients and explained 46% and 43% of whole-body glucose disposal in patients on HAART and therapy-naive patients, respectively. Insulin-stimulated whole-body oxidative and nonoxidative glucose disposal was significantly lower in the treated group, as was suppressive insulin action on lipolysis. To our knowledge, this is the first report providing in vivo evidence that, in lipodystrophic HIV patients, impaired glu-
cose transport and phosphorylation cause redu ' ced insulin-mediated glucose uptake.

A new diagnostic indicator of FDG PET scan abnormality, based on age-adjusted t statistics and an automated voxel-based procedure, is presented and validated in a large data set comprising 110 normal controls and 395 patients with probable Alzheimer's disease (AD) that were studied in eight participating centers. The effect of differences in spatial resolution of PET scanners was minimized effectively by filtering and masking. In controls FDG uptake declined significantly with age in anterior cingulate and frontolateral perisylvian cortex. In patients with probable AD decline of FDG uptake in posterior cingulate, temporoparietal, and prefrontal association cortex was related to dementia severity. These effects were clearly distinct from age effects in controls, suggesting that the disease process of AD is not related to normal aging. Women with probable AD had significantly more frontal metabolic impairment than men. The new indicator of metabolic abnormality in AD-related regions provided 93% sensitivity and specificity for distinction of mild to moderate probable AD from normals, and 84% sensitivity at 93% specificity for detection of very mild probable AD (defined by Mini Mental Score 24 or better). All regions related to AD severity were already affected in very mild AD, suggesting that all vulnerable areas are affected to a similar degree already at disease onset. Ventromedial frontal cortex was also abnormal. In conclusion, automated analysis of multicenter FDG PET is feasible, provides insights into AD pathophysiology, and can be used potentially as a sensitive biomarker for early AD diagnosis.

Potentially redox-active NAD⁺/NADH-analogous pyridinium- and quinolinium-salt bearing Re- and ^99mTc-mixed-ligand complexes were synthesized. The complexes vary in the chelate type, the oxidation state of the metal, the spacer length to the chelate and the substituent at the pyridine/quinoline nitrogen. The complexes were reduced to dihydropyridines and dihydroquinolines respectively and investigations concerning their stability against reoxidation were performed. In competition experiments with NADH the quinoliniuni-salt/dihydroquinoline bearing complexes display enzymatic inhibition of the lactate dehydrogenase.

Purpose:

The diagnostic role of positron emission tomography (PET) with 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) in squamous cell carcinoma of the oral cavity is evaluated.

Procedures:

In 38 patients, the results of FDG-PET, magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound were compared. The standard uptake values (SUV) of FDG-PET were correlated to histopathological grading and DNA-image cytometry.

Results:

In the case of lymph node metastases, the sensitivity of FDG-PET (93%) was higher than the sensitivity for the compared methods. The specificity was best for CT. SUVs of diploid tumor cell lines seemed to be lower than in non-diploid tumor cell lines.

Conclusions:

The high sensitivity and the high negative predictive value of PET may lead to more restrictive therapeutic regimens regarding lymph. node metastases. Studies are necessary regarding possible relationships between glucose metabolism and tumor grading.

Introduction:

The role of positron emission tomography (PET) with 2-[¹⁸F]fiuoro-2-deoxy-D-glucose ([¹⁸F]FDG) is currently under evaluation in urologic oncology. The aim of the present study was to investigate the use of [¹⁸F]FDG positron emission tomography ([¹⁸F]FDG-PET) in the detection and treatment control of malignant germ cell tumors compared to computed tomography (CT).
Materials and Methods:
Thirty-two PET studies and CT scans were carried out in 23 patients with histologically proven germ cell tumors (10 seminomas, 12 non-seminomatous germ cell tumors (NSGCT), 1 unclassified serologic recurrent disease) Lugano stage I-III. The scans were done either after initial diagnosis (n = 21) and/or within 3-45 days after chemotherapy was completed (n = 11). PET and CT were validated either by histology (n = 7) or clinical follow-up of 6-11 months after the last PET study has been performed (n = 16). Sensitivity, specificity, accuracy, positive and negative predictive values were determined for PET and CT. Differences between PET and CT for parameters of diagnostic value were evaluated by chi² test.
Results:
Although not statistically significant, the sensitivity, accuracy and negative predictive value were higher for PET than for CT with respect to the detection of metastatic infradiaphragmatic and supradiaphragmatic lesions after initial diagnosis. The specificity and positive predictive value of PET and CT were comparable. After chemotherapy, PET was found to be significantly superior in specificity and accuracy compared to CT with respect to infradiaphragmatic lesions (p < 0.05). False-positive PET findings in supradiaphragmatic lesions after chemotherapy occurred in the case of inflammatory processes and resulted in a loss of specificity and accuracy compared to CT (p < 0.05).
Conclusions:
These preliminary results demonstrate [¹⁸F]FDG-PET to be a useful diagnostic tool for the initial staging and treatment control in patients with germ cell tumors. Possible advantages compared to CT, however, are as yet not clearly defined. The possibility of false-positive PET findings due to reactive supradiaphragmatic inflammatory processes early after chemotherapy have to be considered.

The core baffle of a PWR is loaded by the pressure difference between bypass and core and by temperature profiles developing from gamma heating and heat transfer into the coolant. Strain, deformation and gaps between the sheets resulting from this load are determined considering the effect of neutron irradiation induced creep of the core baffle bolts. The finite element code ANSYS is applied for the thermal and mechanical analyses. The FE-model comprises a complete 45° sector of the core baffle structure including the core barrel, the formers, the core baffle sheets and about 230 bolt connections with non-linear contact between the single components and the effect of friction.
The analysis shows that some of the bolts loose a significant part of their pre-stress during operation, especially those bolts that are located in the neutron flux maximum. However, the load is taken over by other bolts located at lower flux positions. This global stress relocation is a self regulating process, which keeps the mechanical and geometrical stability of the core baffle structure till end of life.

The scaling-down of the gate oxide thickness in modern MOS memory devices below 20 nm requires low energy ion implantation for ion beam synthesis (IBS) of nanocrystals (NC) in SiO2. Lowering the ion energy, the implanted and damaged SiO2-layer will be located closer to the SiO2 surface and the interaction of this layer with the ambient becomes more and more dangerous. In the damaged near surface layer the high number of broken bonds due to displaced Si and O atoms forms in the glassy network pathes, which are open for diffusion and in which moisture from the ambient can be absorbed. Therefore chemical reactions of the implanted impurities with hydrogen and oxygen must be expected during subsequent annealing. Water 16, H2O18) absorption in Si-, Ge-, and Sn-implanted SiO2 layers has been studied by H-depth profiling using Nuclear Reaction Analysis (NRA) and by O18-depth profiling using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), respectively. H- and O-depth profiles were measured after storage under clean room conditions and after additional wet cleaning, as well as after annealing. The amounts of H and O incorporated into as-implanted SiO2 already during storage are comparable with the concentration of the implanted impurities and are sufficient to interfere significantly with the precipitation and Ostwald-ripening of NCs during IBS.

The report includes results of hydrogen depth profiling using Nuclear Reaction Analysis (NRA) as well as 18O depth profiling using Time-of-Fligt Secondary Ion Mass Spectroscopy (ToF-SIMS) in as implanted SiO2-layers. The measured depth profiles of H and 18O, respectively, clearly show, that as-implanted SiO2-layers soak in humidity from the ambient, which significanly influences the processes of nanocluster growth in thin SiO2-layers during thermal processing of these layers.

Es wird ein Überblich über die Möglichkeiten der Anwendung der Ionenstrahltechnik zur Erzeugung von Nanostrukturen durch Ionenimplantation und anschließender termischer Behandlung gegeben. Nanostrukturen, wie Nanocluster, Nanodrähte, Ketten von Nanoclustern usw. bilden sich dabei durch die Phasenseparation in übersättigten Festkörperlösungen und Selbstorganisation. Desweiteren werden die Selbstorganisation von 2D Anordnungen von Nanoclustern durch Ionenbestrahlung von Grenzflächen (z. B. SiO2/Si) sowie die Modifizierung von Nanostrukturen unter Ionenbestrahlung (Inverses Ostwald-Reifen) diskutiert.
Zum Schluß wird beispielhaft gezeigt, welche Möglichkeiten sich durch den Einsatz eines feinfokussierten Ga-Ionenstrahls zur Bestrahlung von Silizium ergeben, um 3D-Strukturelemente im nm-Bereich herzustellen.

The formation of structural defects in hydrogen plasma treated (100)- and (111)-oriented p-type Czochralski (Cz) Si and in [100]-oriented n-type Si was studied by Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The samples were treated either by a 110 MHz or 13.56 MHz hydrogen plasma at 250 gradC for 60 min. The distribution of hydrogen was studied by nuclear reaction analysis. It is found that, after the hydrogen plasma treatment, the surface of Cz Si is structured and the roughness of the surface depends on the orientation and doping level of the substrate. The defect density increases for (100)-oriented wafers for the higher plasma frequency but for (111)-oriented wafers it is lower, applying the same hydrogen plasma frequency. Different defect types were found: stacking faults on { 111 } planes,dislocations and circular shaped defects exhibiting a strong stress field. The formation of nearly free hydrogen molecules (Raman shift of about 4150 cm -1 ) was observed by Raman spectroscopy after the plasma hydrogenation. It was found that the H2 molecule concentration depends on the concentration of structural defects. The hydrogen molecules can be formed in both n- and p-type Si, unlike the case of remote plasma hydrogenation.

The Master Curve (MC) concept allows to quantify the variation of fracture toughness with the temperature throughout the ductile-to-brittle transition region of ferritic steels. Limit curves of fracture toughness for defined failure probabilities and a refer-ence temperature, T0, can be determined using this method. MC Approach and the associated T0 as defined in the standard ASTM E1921, is rapidly moving to the appli-cation in the integrity assessment of nuclear reactor pressure vessels (RPV). T0 is a fracture mechanics defined ductile-to-brittle transition temperature which replaces reference temperatures based on a correlation of Charpy V-notch and NDT tests in the RPV integrity assessment.
The presentation gives an overview about the MC approach and the application to dif-ferent western and Russian WWER-type RPV steels. Further, the influence of the test conditions as test temperature and loading rate on the MC evaluation is assessed.

Four seminar talks without abstract

• Principles of biomaterials testing
• Biomaterials in bone
• Biomaterials in blood
• The complement system

no abstract

Irradiated heats representing WWER 440-type and 1000-type base and weld metal in their chemical composition, heats of the ASTM steels A533B Cl. 1 (JRQ), A508 Cl. 3 (JFL) and iron test alloys were investigated.
The radiation defects detected by SANS correlate with the radiation hardening and embrittlement. The ratio between nuclear and magnetic neutron scattering provides information on the type of radiation defects.

Gegenstand der Forschungstätigkeiten der Arbeitsgruppe Verfahrenschemie bilden Untersuchungen zur Erhöhung der Anlagen- und Umweltsicherheit sowie der Effektivität chemischer Prozesse. Die Arbeiten erstrecken sich über ein weites Feld, angefangen bei der Reaktionsaufklärung und der Ermittlung von Stoffeigenschaften mittels Reaktionskalorimetrie, einschließlich der Nutzung chemischer Analytik, über numerische und experimentelle Prozesssimulation, experimentelle Arbeiten zur Modellierung reagierender Strömungen bis hin zur Erarbeitung von Prozessführungsstrategien und Methoden zum Monitoring chemischer Prozesse.
Gegenstand des Vortrags ist ein Überblick über die experimentelle Ausstattung der Arbeitsgruppe Verfahrenschemie und die Forschungstätigkeiten anhand zweier Beispiele.

Die Arbeitsgruppe verfügt über mehrere Reaktionskalorimeter (RC1, DSC, PhiTecII), die in Verbindung mit entsprechender Analysentechnik (Insitu-Spektrometer, HPLC) zur Reaktionsaufklärung und zur Ermittlung thermokinetischer Parameter chemischer Prozesse Verwendung finden.
Ein modular aufgebauter automatischer Laborreaktor (Miniplant) dient der experimentellen Simulation chemischer Prozesse, einschließlich scale-up-/ scale-down-Untersuchungen.
Darüber hinaus verfügt die Abteilung über eine schnelle Impuls-Röntgenanlage, die zukünftig verstärkt zur Visualisierung und, in Verbindung mit entsprechender Bildverarbeitungs-, Modellierungs- und Simulationssoftware (CFD), zur Modellierung hydrodynamischer Prozesse in Chemieapparaten verwendet wird.

Reaktionen zur Herstellung von Grignard-Reagenzien haben aufgrund der Verwendung dieser Reagenzien für zahlreiche organische Synthesen eine besondere Bedeutung in der chemischen Industrie. Großtechnisch werden diese Reaktionen als Semibatch-Prozesse unter Rückfluss-Kühlung bei Siedetemperatur des Lösungsmittels betrieben.
Die Experimente wurden im Reaktionskalorimeter RC1 durchgeführt. Im Gegensatz zur industriellen Prozessführung und zu bisherigen Untersuchungen wurden die Reaktionen zur Minimierung der Fehlereinflüsse der Bilanzierung im geschlossenen Drucksystem realisiert. Weiterhin erfolgte die Erfassung der Konzentrationsverläufe während der Reaktion mittels Insitu-FTIR-Spektroskopie.

Das durch die Arbeitsgruppe Verfahrenschemie entwickelte Online-Monitoring-System MoSys ist ein Softwaresystem, das dem Operator zusätzliche Informationen über den Prozessfortschritt, das voraussichtliche Reaktionsende, die Akkumulationen von Edukten oder Zwischenprodukten, den Durchmischungszustand oder die Gefahr einer thermischen Explosion durch unzureichende Kühlung zur Verfügung stellt. Zusätzliche Prozessmesstechnik in Form von Online-Analytik wird nicht benötigt. Das Zustandserkennungssystem basiert auf adaptiven Stoff- und Wärmebilanzen.
MoSys wurde auf der Grundlage von Experimenten im automatischen Laborreaktor entwickelt. Als Modellprozess wurde die heterogen katalysierte Hydrierung eines Nitroaromaten ausgewählt.
Ein derartiges Online-Zustandserkennungssystem ist bei allen ausreichend exothermen Batch- und Semibatch-Prozessen einsetzbar, wenn die Nutzinformationen in der Wärme- und Stoffbilanz enthalten sind. Neben einer Erhöhung der Anlagen- und Umweltsicherheit wird durch den Einsatz des Zustandserkennungssystems weiterführendes Prozesswissen generiert, das als Grundlage für eine Prozessoptimierung genutzt werden kann.

Der Vortrag endet mit einem Ausblick auf geplante Forschungsarbeiten der Abteilung für Experimentelle Thermofluiddynamik auf dem Gebiet der Verfahrenschemie.

Die Reinigung schwermetallbelasteter Abwässer erlangt zunehmende Bedeutung, bedingt durch die negativen Auswirkungen der giftigen oder radioaktiven Substanzen auf Gesundheit und Umwelt. Herkömmliche Reinigungsverfahren sind oft kostenintensiv und weniger effizient. Der Einsatz innovativer Entfernung von toxischen Substanzen oder Radionukliden aus Abwässern. Ausgangspunkt sind Silicium- oder Metalloxid-Sole, die durch Hydrolyse der entsprechenden Alkoxide gebildet werden. So entstehen stabile nanokristalline Dispersionen, die durch Änderung des pH-Wertes oder durch Temperaturerhöhung schnell gelieren und damit die Biokomponenten effektiv immobilisieren.....

Column experiments were carried out to investigate the influence of humic colloids on subsurface uranium migration. The columns were packed with well-characterized aeolian quartz sand and equilibrated with groundwater rich in humic colloids (dissolved organic carbon (DOC): 30 mg dm-3). U migration was studied under an At/1% CO2 gas atmosphere as a function of the migration time, which was controlled by the flow velocity or the column length. In addition, the contact time of U with groundwater prior to introduction into a column was varied. U(VI) was found to be the dominant oxidation state in the spiked groundwater. The breakthrough curves indicate that U was transported as a humic colloid-borne species with a velocity up to 5% faster than the mean groundwater flow. The fraction of humic colloid-bome species increases with increasing prior contact time and also with decreasing migration time. The migration behavior was attributed to a kinetically controlled association/dissociation of U onto and from humic colloids and also a subsequent sorption of U onto the sediment surface. The column experiments provide an insight into humic colloid-mediated U migration in subsurface aquifers.

kein Abstract

At present, there are two possible approaches, which practically are used for the thermal-hydraulic analysis of the reactor core in simulations, where crossflow effects are relevant: the representation of the core by a system of separated parallel flow subchannels with provision of a forced crossflow mixing by implementation of additional formulations and the porous body approach, in which the core geometry is replaced by a structure of homogenized zones of porous media. When crossflow is comparable with flow along the bundles, the porous body approach is the only one suitable method to perform steady-state and transient flow calculations for safety analyses.
The CFD – code CFX-4 offers a porous region model for the modelling of the core geometry as a homogenized medium. This model is characterised by a set of properties (volume porosity, resistance to flow and so on).
The Core Crossflow Experimental Facility (CCEF) was built with the objective to obtain experimental data for the flow in a rod bundle under the conditions of forced crossflow with relatively low Reynolds numbers and variable flow angle.
The test section of CCEF (a plexi-glass model) contains the test rod bundle. The test rod bundle is based on the geometry of a typical PWR with a pitch/diameter ratio of 1.33 and was scaled with a factor 1.5. The crossflow was induced by an asymmetrical outlet condition for the bundle. The test bundle consists of the 100 plexiglass rods, arranged in 4 rows. Additional internals, which are typical for a reactor core geometry, were not installed in the test section. The working fluid in the experiments was water. For the velocity measurements the one-component laser-Doppler anemometer (LDA) was used.
Calculations for the comparison with experimental data were performed in two different approaches. The detailed geometry was created for the calculation of flow fields with k-e turbulence model and a relative simple geometry of the test section for the flow simulations in the porous region approach.
The results of the experimental investigations on the CCEF and the comparison with the calculations, performed with CFX-4 Code in the geometry of the test section are presented in this paper.

We give an overview about our recent activities to solve inverse problems appearing in various branches of MHD. The very general problem, the full reconstruction of velocity or turbulence parameters of fluid flows with arbitrary magnetic Reynolds numbers from externally measured magnetic fields varying in space and time, is tackled from two different corners. First, we explore the restricted inverse dynamo problem of determining, from a limited number of spectral data, the radial profile alpha(r) of an isotropic alpha^2 dynamo model. Among our results is the construction of oscillatory dynamos of this type, which might be of some interest for stellar dynamos. Second, we consider the topic of contactless velocity reconstruction in industrial applications with moderate magnetic Reynolds numbers from the measured deformation of two different external magnetic fields.

kein Abstract

The integral equation approach to steady dynamos in finite domains is employed to solve the eigenvalue problem for spherically symmetric, isotropic alpha^2 dynamo models. Three examples of the function alpha(r) with steady and oscillatory solutions are considered. A convergence rate proportional to the inverse square of the number of grid points is achieved. Based on this method, a convergence accelerating strategy is developed and the convergence rate is improved dramatically. The computed results show a good agreement with analytical results and results obtained by a differential equation solver. Typically, quite accurate results can be obtained with a few tens of grid points.

kein Abstract

kein Abstract