Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Ziel:

Intraluminale Betabestrahlung nach Ballonangioplastie führt zu einer Erniedrigung der neointimalen Proliferation. Eine erfolgversprechende Variante stellt der Einsatz radioaktiv markierter Stents dar (1,2). In der Studie wird die technische Durchführbarkeit der ^186/188Re-Markierung vaskulärer Stents und deren biologischer Effekt zur Inhibition der neointimalen Proliferation im Tiermodell getestet.

Methodik:

Palmaz Stents werden in einem "kitlike"-Verfahren mit ^186/188Re markiert und die Markierungsbedingungen, die Stentoberfläche, die Aktivitätsverteilung, die Thrombogenität sowie die in-vitro Stabilität untersucht. Die markierten Stents und Kontroll Stents werden nach Fütterung einer 0.5%igen Cholesterindiät und Ballonangioplastie in die infrarenalen Aorta von Neuseeland-Kaninchen implantiert. Es erfolgten szintigraphi-sche Messungen zu unterschiedlichen Zeiten und nach 6 Wochen wurden die Gefäße immunhistologisch untersucht.

Ergebnisse:

In Abhängigkeit von der Markierungszeit und der vorgelegten Aktivität gelingt es, definierte Aktivitätsmengen stabil und reproduzierbar auf die Stentoberfläche zu fixieren. In-vitro Untersuchungen in isotonischer Kochsalzlösung und Humanblut beweisen, dass nach 72 Std. Inkubation bei 37°C >95 % der abgeschiedenen ^186/188Re Aktivität am Stent gebunden bleiben. Thrombogenitätsuntersuchungen an markierten Stents ergaben keine Veränderungen im Vergleich zu den unbehandelten Vergleichs-stents. Die Implantation der Stents war bei allen Tieren erfolgreich, nach 14 Tagen verblieben mehr als 90 % des aufgebrachten Rheniums auf der Stentoberläche. Die Neointimafläche ließ sich von 2,2±0,2 mm bei den Kontrollstents auf 0 mm bei den markierten Stents reduzieren.

Schlußfolgerungen:

Es ist gelungen, Palmaz Stents reproduzierbar mit ¹⁸⁶Re und ¹⁸⁸Re zu markieren, wobei die aufgebrachte Aktivität in einem weiten Bereich variiert werden kann. Es wird eine hohe in-vitro und auch in-vivo-Stabilität erreicht, die Stents sind nicht trombogen. Innerhalb von 6 Wochen ließ sich die neointimale Proliferation komplett unterbinden.

1) Fishell et al., Circulation 1994; 90: 2956-2963
(2) Waksman et al., Circulation 1998; 98: I-651:3721

Ein zweiphasiges, aus einer gashaltigen Flüssigkeit bestehendes Medium wird in einer Axialpumpe von einem propellerartigen Laufrad senkrecht zur Drehachse die ses Laufrades transportiert. Die Wechselwirkung zwischen der Gasphase und dem Laufrad soll unter Verwendung von Gamma-Strahlung mittels Tomographie unter sucht werden. Dabei ist für die Rekonstruktion des Objektbildes das Prinzip der so genannten gefilterten Rückprojektion vorgesehen. Die methodischen Grundlagen für die Nutzung dieses Prinzips unter den vorgesehenen geometrischen und meßtech nischen Bedingungen sind Gegenstand dieser Arbeit.

Ion beam synthesis has been applied to fabricate semiconductor (Si, Ge) nanoclusters in thin gate SiO2 films for non-volatile memory applications. The cluster size (2-3 nm), the cluster density (>5x10E11 cm-2) and the short distance to the Si/SiO2 fulfill main requirements for a cluster related memory cell. The charge storage have been clearly established at MOS and transistor structures by the shift of the flatband or threshold voltage, respectively. Typical programming windows are in the order of 1-2 V and the endurance is > 10E6 w/e-cycles. Differences of Si- and Ge-cluster containing SiO2 films with respect to the retention behaviour are finally discussed.

Cosmic magnetic fields, including the magnetic field of the Earth, are produced by the homogeneous dynamo effect in moving electrically conducting fluids. We sketch the history of the underlying theory and comment on previous attempts to realize homogeneous dynamos in laboratory. For the main part, we report on two series of experiments carried out at the Riga dynamo facility. In November 1999 a slowly growing magnetic field eigenmode was observed for the first time in a liquid metal experiment. In July 2000, the magnetic field saturation regime was studied and a number of interesting back-reaction effects were observed. A preliminary interpretation of the measured data is also presented.

^99mTc is the most widely used radionuclide for nuclear medicine diagnostics. Efforts are made to design this unphysiological element for targeting specifically organs and cells. In this respect, lipophilic properties are of importance. We studied lipophilicity on a series of "3+1" mixed ligand oxoTc and -Re complexes with an [S-(CH₂)₂-E-(CH₂)₂-S] chelate unit [E = O, S, N-Me, N-Et] and a thiol ligand with various residues [alkyl, aryl; (CH₂)₂-NMe₂, -NEt₂,-NBu₂, -piperidinyl, -morpholinyl].
The lipophilicity/pH profiles were determined by RP-HPLC. A Perkin-Elmer HPLC Model 1022 equipped with a UV/VIS detector (254 nm) and a PRP-1 column (Hamilton, 250 x 4.1 mm, 10mm) was employed [mobile phase: isocratic eluent acetonitrile / buffer (volume ratio 3:1; pH range: 1.5 - 11); flow rate: 1.5 ml/min].
The lipophilicity determination is based on the linear relationship between the chromato-graphic retention (log k') and log D/P and results in D_HPLC/P_HPLC values. Aniline, benzene, and brombenzene were used as internal standards. The pK_a values were estimated from the turning point of sigmoidal curves and were corrected by using a calibration curve of amine standards since the measurements are performed in organic/aqueous solutions.
For amine group containing complexes (R²), that are used as models of neuroreceptor affine tracers, the influence of lipophilicity and/or pK_a on brain uptake was studied. High brain uptake relates with low pK_a, so that the highest uptake was found for morpholino-bearing complexes (0.9-2.0 % injected dose per rat brain, <5 min p.i.; pK_a 7.1-7.6). The log PHPLC values for Tc complexes are higher than for the corresponding Re complexes.

The Budker Institute of Nuclear Physics Novosibirsk proposed a highly intense 14 MeV neutron source on the base of a gas dynamic trap (GDT). The GDT is an axisymmetric mirror plasma device. In case of the complete effectiveness at the necessary parameters this type of neutron source promises several advantages in comparison to other proposals. Its actual disadvantage is the incomplete data basis which does not yet allow a reliable interpolation of its feasibility. To close this gap is the goal of the experimental and computational research presently being under way. Here the Monte Carlo codes TUBE for the hydrogen gas and MCFIT for the fast ions which have been developed by Forschungszentrum Rossendorf in collaboration with the Budker Institute take an important part. The paper shortly describes the MCFIT code, compares some numerical with measured results and draws certain conclusions.

Technetium(I) thioether carbonyl complexes and their reaction products with histidine were prepared and characterized by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy , various chromatographic and electrophoretic methods and electrospray mass spectrometry. Their behaviour in aqueous solutions was studied on the carrier-added (99Tc) and the no-carrier-added (99mTc) levels. HPLC and electrophoretic studies show the identity of reaction products at both concentration levels. Technetium(I) carbonyl complexes containing a bidentate dithioether ligand, [Tc(CO)3Cl(S-S)], as well as a tridentate carboxylato thioether ligand, [Tc(CO)3(S-S-O)], undergo a ligand exchange reaction with histidine and form the complex [Tc(CO)3His]. EXAFS measurements were performed to estimate structural parameters of the dissolved technetium(I) carbonyl complexes and their reaction products after the challenge experiments. The calculated bond lengths and coordination numbers are in accordance with the expected values and confirm the ligand exchange reactions.

The Budker Institute Novosibirsk made a proposal for a highly intense neutron source on the base of a gas dynamic trap. It is mainly intended for fusion material irradiation. The gas dynamic trap is an axisymmetric open system with a high mirror ratio for the confinement of a collision dominated plasma and a high-energetic ion component which is fed by an oblique neutral beam injection. In addition to research at the experimental facility of the Budker Institute an Integrated Transport Code System is under development in collaboration with the Forschungszentrum Rossendorf. It is to calculate the relevant physical effects connected with the target plasma, fast ions, neutral gas and the neutrons appearing inside the central cell of the device. The paper briefly describes the functions of the main modules and reports on the first exercise devoted to the planned upgrade of the facility.

Am Institut für Sicherheitsforschung (FWS) des Forschungszentrums Rossendorf (FZR) e.V. wird die Mehrzweckthermohydraulikversuchsanlage TOPFLOW (Transient Two Phase Flow Test Facility) zur Untersuchung stationärer und transienter Phänomene in Zweiphasenströmungen sowie zur Entwicklung und Validierung der in Computational Fluiddynamic (CFD) Codes enthaltenen Modelle aufgebaut. Die Versuchsanlage soll im Rahmen des Kompetenzerhaltungsprogramms Kerntechnik von dem Kompetenzzentrum Sachsen bestehend aus der Technischen Universität Dresden, der Hochschule für Technik, Wirtschaft und Soziales Zittau/Görlitz (FH) sowie dem Forschungszentrum Rossendorf e.V. betrieben werden.

We investigate the reaction pp to da₀ ⁺ at COSY and SIS energies together with accompanying background reactions and inclusive particle yields. The a₀ ⁺ is considered as a usual quark model state with two decay channels a₀ ⁺ to K⁺K⁰ and a₀ ⁺ to pi⁺ eta. Cross sections for a₀ ⁺ production as well as for the corresponding nonresonant channels pp to dK⁺K⁰ and pp to dpi⁺eta are compared. Especially in case of the final channel dpi⁺eta high statistics measurements are necessary to extract the a₀ ⁺ signal from the nonresonant background.

Structural properties of sputtered multilayers with different Co-, Cu- and NeFe- sequences of about 2nm individual layer thickness were investigated by means of synchrotron radiation techniques. Correlations between the layer combination and structural parameters such as layer thickness and rms interface roughness derived from specular scans were obtained, whereas the lateral characteristics of the interface morphology investigated by diffuse scattering were found to be similar for all multilayers. Wide angle diffraction measurements yielded lattice plane information, e.g. size-strain effects due to profile broadening and predominating <111> fibre textures.

In nuclei in the mass region of $A \approx 70 - 90$ a variety of phenomena
is observed which are based on single-particle and collective motion of the
nucleons. We discuss the properties of Br and Rb isotopes with neutron numbers
of 38 - 48. In light Br isotopes ($N$ = 37, 38) rotational bands have been
observed up to spins of 65/2 and rotational frequencies of 1.8 MeV. Both
features can be described in terms of the cranked Nilsson-Strutinsky formalism.
In Rb nuclei with $N$ = 45, 47 we found regular magnetic dipole bands
evolving at high spin whereas the low-spin structure of those less deformed
nuclei is irregular. These magnetic dipole bands represent magnetic rotation,
a new rotational mode predicted by the tilted-axis cranking model.
In nuclei at $N$ = 48 we found small collectivity in low-spin states and
multiplets based on multi-particle excitations at high spin. These properties
are interpreted in terms of the shell-model.

Assuming the hypothetical scenario of a severe accident with subsequent core meltdown and formation of a melt pool in the reactor pressure vessel (RPV) lower plenum of a Light Water Reactor (LWR) leads to the question about the behaviour of the RPV. One accident management strategy could be to stabilize the in-vessel debris configuration in the RPV as one major barrier against uncontrolled release of heat and radio nuclides.
To get an improved understanding and knowledge of the melt pool convection and the vessel creep and possible failure processes and modes occurring during the late phase of a core melt down accident the FOREVER-experiments (Failure Of REactor VEssel Retention) are currently underway at the Division of Nuclear Power Safety of the Royal Institute of Technology Stockholm (Sehgal, 1999). These experiments are simulating the behaviour of the lower head of the RPV under the thermal loads of a convecting melt pool with decay heating, and under the pressure loads that the vessel experiences in a depressurization scenario. The geometrical scale of the experiments is 1:10 compared to a common LWR.
During the first series of experiments the creep behaviour (FOREVER-C) of the vessel under the thermal attack of the melt pool and varying internal pressure loads is investigated. It is intended to enforce the creep process until vessel failure.
Due to the multi axial creep deformation of the vessel with a non-uniform temperature field these experiments are on the one hand an excellent source of data to validate numerical creep models which are developed on the basis of uniaxial creep tests. On the other hand the results of pre-test calculations can be used to optimize the experimental procedure and can help to make on-site decisions during the experiment.
Therefore an axisymmetric Finite Element (FE) model is developed based on the multi-purpose code ANSYS/Multiphysics®. Using the Computational Fluid Dynamics (CFD) module the temperature field within the melt pool and within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a creep model which takes into account large temperature, stress and strain variations.

We recently discovered a neutral dicalcium uranyl tricarbonate complex, Ca2UO2(CO3)3(aq.), in uranium mining related waters /1/. We are now reporting a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a non-fluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with Na2EDTA.
Slope analysis of the log (fluorescence intensity) versus log [Ca2+] with both methods have shown that two calcium ions are bound to form the complex Ca2UO2(CO3)3(aq.). The formation constants determined from the two independent methods are: i) log ßo213 = 25.26 ± 0.71 and ii) log ßo213 = 25.57 ± 0.37.
A bathochrome shift of 0.35 nm between the UO2(CO3)34- complex and the Ca2UO2(CO3)3(aq.) complex was observed in the UV-vis absorption spectrum and in the laser-induced photoacoustic spectrum (LIPAS), giving additional proof for the formation of the calcium uranyl carbonate complex.
EXAFS spectra at the LII and LIII - edges of uranium in uranyl carbonate solutions with and without calcium did not differ significantly. A somewhat better fit to the EXAFS of the Ca2UO2(CO3)3(aq.) complex was obtained by including the U-Ca shell. From the similarities between the EXAFS of the Ca2UO2(CO3)3(aq.) species in solution and the natural mineral liebigite, we conclude that the calcium atoms are likely to be in the same positions both in the solution complex and in the solid.
This complex influences considerably the speciation of uranium in the pH region from 6 to 10 in calcium-rich uranium-mining-related waters.

We studied the complexation of neptunium(IV) with various natural and synthetic humic and fulvic acids at pH 1 using X-ray absorption fine structure (XAFS) spectroscopy to observe the local structure around the neptunium ion. The results were compared to the interaction of neptunium(IV) with Bio-Rex70, a cation exchange resin having solely carboxylic groups. For both neptunium humate complexes and neptunium Bio-Rex70 complexes, 11 oxygen atoms were found at a mean distance of 2.36 Å. This verified that the carboxylic groups of humic substances are responsible for binding neptunium(IV) in the acidic pH range. The humic acid carboxylate groups are predominantly monodentately coordinated to neptunium(IV) ions.

Starting from the tripodal ligand 2,2',2"-nitrilotris(ethanethiol) (NS₃) and isocyanides (CNR) as co-ligands neutral mixed-ligand technetium(III) complexes of the general formulation [Tc(NS₃)(CNR)] have been synthesized and characterized. The ⁹⁹Tc complexes can be obtained by a two-step reduction/substitution procedure starting from [TcO₄]^- via the phosphine-containing precursor complex [Tc(NS₃)(PMe₂Ph)]. As shown by X-ray structural analyses the complexes adopt a nearly ideal trigonal-bipyramidal geometry with the trigonal plane formed by the three thiolate sulfurs of the tripodal ligand. The central nitrogen atom of the chelate ligand and the monodendate isocyanides occupy the apical positions.
The no-carrier-added preparation of the corresponding ^99mTc complexes was performed by a one-step procedure starting from ^99m[TcO₄]^- with stannous chloride as reducing agent.
Biodistribution studies in the rat demonstrated for the nonpolar, lipophilic compounds a significant initial brain uptake. In vitro challenge experiments with glutathione clearly indicated that no transchelation reaction occurs. Furthermore, there were no indications for reoxidation of Tc(III) to Tc(V) species or pertechnetate. We propose this type of complexes as a useful tool in designing of lipophilic ^99mTc or ¹⁸⁶Re/¹⁸⁸Re radiopharmaceuticals.

A theoretical investigation is carried out of the temperature and hydrogen concentration as a function of space in an aluminum workpiece during laser beam welding. The driving force for hydrogen transport is thermal diffusion, where a diffusion current is brought about by a temperature gradient. The sign of the respective transport coefficient is negative for H in Al, which implies that hydrogen will accumulate in the heated regions. Analytical solutions are obtained for the temperature and concentration fields which comprise convective and conductive heat transfer, and hydrogen transport by convection, diffusion and thermal diffusion. The spatial characteristics are discussed in detail using various approximations for the upstream and the downstream region as well as the region close to the keyhole.

PURPOSE:

To check the influence of structural characteristics on their permeation through the blood-Brain barrier (BBB), a set of radioactive [^99mTc]chelates bearing amine groups was synthesized and tested in vitro as well as in vivo.

METHODS:

Compounds with different log P and pK_a values were obtained by complex forming reactions of [^99mTc]pertechnetate with varying substituents. Transport was studied in rats and mice, as well as in an ECV304 cell culture model.

RESULTS:

In vitro higher permeation was found for compounds with electron attracting substituents in beta-position to the amine group (pK_a values 7.4 to 8.3) than for those with more basic amine groups (pK_a values > 8.9) even for similar logD_{ph 7.4}. In vivo brain uptake between 0.8 and 4.8% of the injected dose (ID) per organ was found for the former, whereas < 0.4% ID were present for the latter.

CONCLUSIONS:

Three structurally diverse classes of [^99mTc]chelates showed distinct patterns with regard to brain uptake in vivo and BBB permeability in vitro which could not be predicted by their lipophilicity alone. The close correlation between the data from rats and mice and those obtained with cell cultures render the ECV304 cells an attractive model for the screening of new compounds.

The evolution of strongly interacting matter during the cosmological confimement transition is reviewed. Despite of many proposed relics non specific signal from the rearrangement of quarks and gluons into hadrons has been identified by observations. In contrast to this, several observables in heavy-ion collisions at CERN-SPS energies point to the creation of a matter state near or slightly above deconfinement. We focus here on the analysis of dileptons and direct photons. Similarities and differences of the Big Bang and the Little Bang confinement dynamics are elaborated.

Tc(I) thioether tricarbonyl complexes were prepared and characterised by chromatographic and spectrometric methods. The complexes undergo various ligand exchange reactions in aqueous solutions. In Tc(I) dithioether tricarbonyl complexes of the formula [Tc(CO)₃Cl(S-S)] (S-S = bidentate dithioether ligand) chlorine is substituted by water in aqueous solution. Moreover, we found that Tc(I) tricarbonyl complexes containing a bidentate dithioether ligand, [Tc(CO)₃Cl(S-S)], as well as a tridentate carboxylato dithioether ligand, [Tc(CO)₃Cl(S-S-O)], react with histidine and form the complex [Tc(CO)₃His]. EXAFS measurements were performed to estimate structural parameters of the dissolved Tc(I) tricarbonyl complexes and their substitution products with water and histidine.

Gesamtziel des Vorhabens ist es, den Einfluß der Strömungen in der Schmelze auf die Phasengrenze flüssig-fest im Erstarrungsprozeß zu untersuchen und darüber hinaus eine gezielte Beeinflussung der Konvektion durch geeignete, für den jeweiligen Zweck maßgeschneiderte Magnetfelder vorzunehmen. Die Vielfalt der alternierenden (Strömungsantrieb) und statischen (Strömungsunterdrückung) Magnetfelder erlaubt eine Beeinflussung metallischer Schmelzen in sehr weiten Bereichen.
Umfangreiche Erfahrungen liegen z. B. für die Wirkung rotierender Magnetfelder auf die Strömung vor. Der sich daraus ergebende Einfluß auf das resultierende Erstarrungsgefüge bei reinen Metallen oder binären Legierungen ist teilweise aus der Literatur bzw. eigenen Arbeiten bekannt. Langjährige Vorarbeiten für die Schmelzkontrolle bei Halbleiter-Kristallzüchtungsprozessen bis hin zur industriellen Nutzung derart optimierter Magnetsysteme liegen ebenfalls vor.
Im Projekt sollen systematische Untersuchungen zur Beeinflussung der Erstarrung von Nd-Fe-B-Schmelzen über die Kontrolle der Schmelzströmungen durchgeführt werden. Dazu werden die am IFW Dresden vorhandenen Techniken der Floating-Zone-Züchtung und der elektromagnetischen Levitation eingesetzt. Am Beispiel der Floating-Zone-Züchtung wird demonstriert, wie auf der Basis einer theoretisch-numerischen Analyse der prozeßbedingt im System vorhanden Strömungsarten (Marangoni, HF-Heizung, Auftrieb) eine optimierte und flexible Strömungskontrolle über ein zusätzliches Magnetsystem möglich ist.
Für die elektromagnetische Levitation werden Ergebnisse zur Strömung im Tropfen präsentiert, die sowohl für das Verständnis der Erstarrungsvorgänge als auch die Ermittlung thermophysikalischer Parameter aus derart prozessierten Proben wichtig sind.

We discuss the configurations in which singly and doubly quantized vortex lines coexist in a rotating superfluid. General principles of energy minimization lead to the conclusion that in equilibrium the two vortex species segregate within a cylindrical vortex cluster in two coaxial domains where the singly quantized lines are in the outer annular region. This is confirmed with simulation calculations on descrete vortex lines. Experimentally the coexistence can be studied in rotating superfluid 3He-A. With cw NMR techniques we find the radial distrubution of the two vortex species to depend on how the cluster is prepared: (i) By cooling through Tc in rotation, coexistence in the minimum energy configuration is confirmed. (ii) A disordered agglomerate is formed of one starts with an equilibrium cluster of single quantum vortex lines and adds to it sequentially double quantum lines, by increasing the rotation velocity in the superfluid state. This proves that the energy barriers, which seperate different cluster configurations, are too high for metastabilities to anneal.

Results of experimental investigations of thin films and multilayers of binary systems deposited by PLD at room temperature are presented. Poles of sputtering, implantation, rapid quenching, and solid state diffusion in microstructure formation of thin metal an alloy films synthesized prom pulsed erosion jets are considered. Examples of non-conventional microstructure (amorphization, pseudomorphism, superstructures) formation are given.

Reflektometrieuntersuchung von Fe-Cr-Schichten, die durch Laserablation (PLD) auf einem oxidierten Si(100)-Wafer aufgebracht wurden, mittels Synchrotronstrahlung unter Ausnutzung der anomalen Streuung im Bereich der Fe- bzw.Cr-Absorptionskante. Bestimmung der Interfacebreiten (Sigma rms Rauigkeit) und der Rauigkeitsstruktur (laterale Korrelationslänge und Rauigkeitsexponent) der Fe/Cr-bzw.Cr/Fe-Doppelschichten durch Simulationsrechnungen mit dem Programmcode REFS ( Bede Scientific).

An Eisendisilizid-Einkristallen wurden winkelabhängige Mößbaueruntersuchungen durchgeführt.

Eisen und Magnesium sind über den gesamten Konzentrationsbereich nicht miteinander mischbar. Durch Ionenimplantation ist es jedoch möglich, dünne Legierungsschichten mit beiden Metallen herzustellen.
Bei der vorliegenden Untersuchung wurden Eisenionen in Magnesium implantiert (Energie 200 keV, Dosis bis 1018 /cm²). Die Charakterisierung der so hergestellten Schichten erfolgte mittels Augerelektronen-Spektroskopie, Konversionselektronen-Mössbauerspektroskopie sowie Röntgendiffraktion. Es zeigte sich, dass durch die Implantation Eisenkonzentrationen von über 90 Atom-% erreicht werden konnten. Bei solchen hohen Konzentrationen waren die Schichten magnetisch, es entstand eine Schicht aus a-Eisen, in das Magnesium eingelagert war. Bei niedrigen Eisenkonzentrationen wurde das Eisen auf zwei unterschiedlichen Positionen im Magnesium eingelagert. Temperte man die Schichten bei Temperaturen bis 400 °C, schied sich das Eisen erwartungsgemäss aus

Mittels DCEMS wurde eine tiefenselektive Phasenanalyse der Fe-Disilizid-Bildung in Fe-ionenimplantiertem Si durchgeführt.

Silicon was implanted with high doses of nitrogen and carbon Shallow by PIII.

Reciprocal Space Mapping was performed on Silicon Implanted with Nitrogen and Carbon by
PIII

Porous silicon was implanted with N by PIII.

In some PIII devices the sputtering of the surface under treatment is a problem to overcome.

200 keV Fe ions were implanted into Si(111) at 350 °C .

A DC glow discharge plasma source was used in a PIII experiment.

High-resolution X-ray diffraction methods have been used to characterize nitrogen doped silicon obtained by PIII.

A simple industrially feasible screen printing process for bifacial silicon (Si) solar cells has been developed. The process sequence is based on co-firing of front and rear contacts through surface-passivating remote plasma-enhanced chemical vapour deposited (RPECVD) silicon nitride (SiN) antireflection coatings. Due to the thermal stability of the RPECVD silicon nitride films the firing step results in an excellent front and rear surface passivation which is comparable to a high-efficiency process with vacuum-evaporated metal contacts. The proposed rear surface design is also well-suited for the improvement of the front efficiency of screen-printed monofacial Si solar cells presently produced by the photovoltaic industry. Special attention is paid to the optimisation of the rear efficiency as well as to the understanding of the mechanism of contact formation in the firing-through-SiN process.

A simple magnetic spectrometer for high resolution RBS and NRA has been designed and installed at a dual beam facility, where both beams from a 3 MV Tandetron and a 500 kV implanter are available. The spectrometer is attached to an UHV scattering chamber with a precision 5 axes goniometer for channeling experiments. The spectrometer is described and details of the design are discussed.

Uranium (VI) complexes formation at surfaces of Acidithiobacillus ferrooxidans types was studied using uranium LIII-edge Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. In all samples the uranium is coordinated by two axial oxygen atoms (Oax) at distance of 1.77-1.78 Å. The distance between uranium and the equatorial oxygen atoms (Oeq) is 2.35 Å. To within the experimental error, there are no differences in the U-O bond distances between samples from the 3 types of A. ferrooxidans. The coordination number for Oeq is 5-6. The fit to the EXAFS data of samples measured as wet pastes gave the same results as for dried samples. No significant structural differences were observed for the uranium complexes formed by the eco-types of A. ferrooxidans. However, the EXAFS spectra are indicating formation of uranium complexes which are different from those formed by Bacilli. In addition, Time-resolved laser fluorescence spectroscopy (TRLFS) and Infrared spectroscopy (IR) were performed to obtain complementary information about the exact chemical structure of the uranium complexes formed on the surfaces of A. ferrooxidans types.
Fig:1. k3-weighted ULIII-edge EXAFS spectra (left) and the corresponding Fourrier transform (right) of uranyl complexes with A. ferrooxidans type.

INTRODUCTION: The importance of the intrauterine environment for the fetal brain development has been revealed by studies showing persistent behavioral abnormalities in prenatally stressed animals. Inadequate nutritional supply, mainly due to uteroplacental insufficiency or restricted maternal protein intake in the late gestation period, is mostly responsible for asymmetrical intrauterine growth restriction (IUGR). The immature dopaminergic system appears to be sensitive for inadequate prenatal nutritional supply followed by IUGR in offsprings, because the dopamine content in brainstem of fetal IUGR guinea-pigs is increased despite an unchanged oxygen delivery and an altered dopamine release persisted in IUGR born rats after maternal protein malnutrition. This, is suggested to contribute to etiological factors of the attention deficit hyperactivity disorder, a highly prevalent neurodevelopmental disorder with prefrontal and nigrostriatal dysfunction. However, the effects of IUGR on regional in vivo brain dopamine metabolism have yet not been determined. Therefore, we estimated the AADC activity, the ultimate enzyme in dopamine synthesis, together with the regional cerebral blood flow (CBF), the brain tissue PO₂ and the cerebral metabolic rate of oxygen (CMRO₂) in newborn normal weight (NW) and IUGR piglets.
METHODS: PET studies using FDOPA as tracer were performed in two groups of ten anesthetized (0.5% isoflurane, 70% N₂O, 30% O₂), 2-5 days old NW and IUGR piglets [1]. Blood pressure, gases, glucose and lactate, EEG and ECG were monitored. PET scans (three planes, 35 frames between 30 and 600 s) began simultaneously with the FDOPA injection (30-50 Mbq). 49 arterial blood samples were taken and plasma activity was measured. Plasma metabolites of FDOPA were determined by HPLC in 9 samples (between 2 and 120 min p.i.). The blood-brain clearance K₁ ^FDOPA, the clearance rate constant from brain k₂F^DOPA, the decarboxylation rate constant (k₃ ^FDOPA) and a constant for the clearance pathway (k_cl ^FDA+acids) of F-dopamine metabolites were calculated using a compartment model which corrects for the blood-brain transfer of 3-O-methyl-FDOPA [2]. Additionally, the cerebral blood flow (CBF) was measured with colored microspheres in both groups of animals [3].
RESULTS: In IUGR piglets the body weight was pronouncedly reduced (42% of NW group). Naturally occurring growth restriction in swine is asymmetrical with an increase in the mean ratio of brain weight to liver weight from 0.61±0.16 to 1.42±0.24 (P < 0.01). The reduction in brain weight was quite small (83 % of NW group). In contrast, the decrease in liver weight (35 % of NW group) was similar compared to that in body weight (42 % of NW group). All differences in organ weight were significant (P < 0.01). Physiological values measured for newborn NW and IUGR piglets were consistent with other data obtained from mildly anesthetized and artificially ventilated newborn piglets. The arterial blood pressure, the heart rate, and the arterial glucose content were mildly but significantly lower in IUGR piglets (P < 0.05). Other obtained physiological values such as the CMRO₂, the brain tissue PO₂, and the regional CBF were similar in NW and IUGR piglets. PET time curves of ¹⁸F activity accumulated in the striatum showed a distinctly higher tracer amount in IUGR piglets (P < 0.05). The regional transport of FDOPA to the brain indicated by K₁ ^FDOPA and PS^FDOPA, and the clearance rate of labelled metabolites from brain tissue (k_cl ^FDA+acids) were similar in both groups. However, the regional rate constants for backflux from the brain (k₂ ^FDOPA) was markedly increased in IUGR piglets in the striatum (72%) and the frontal cortex (83%) (P < 0.05). Furthermore, the

Due to significant differences in material properties such as density or
surface tension the behavior of gas bubbles reveals some pecularities in
liquid metal applications as compared with ordinary water flows. Moreover,
questions about the wetting of solid surfaces or the role of impurities which
have a minor importance in water systems show a more dominant influence in
metallic melts.
In this lecture some examples with respect to the bubble generation process,
the dispersion of gas bubbles or the momentum and heat transfer properties
of liquid metal bubbly flows will be presented.
The variety of standard measuring techniques to characterize liquid metal
flows is limited due to the nature of metallic melts. A selection of measuring
techniques will be discussed with respect to their capabilities and
restrictions in various applications.
An interesting point is the possibility to control liquid metal two-phase flows
by the application of external magnetic fields. Some examples will be presented
showing the influence of a stationary magnetic field on the generation of gas
bubbles, on the interfacial momentum transfer or on the turbulent dispersion
of gas bubbles.

Die Erzeugung eines Magnetfeldes allein durch die Strömung einer leitfähigen Schmelze wird von Astro- und Geophysik allgemein als Quelle kosmischer Magnetfelder akzeptiert. Dieser grundlegende physikalische Mechanismus wurde jedoch bis vor kurzem noch nie in einem Laborexperiment nachgewiesen. Am Institut für Physik Riga (Lettland) wurde in enger Kooperation mit der Abteilung MHD des Forschungszentrums Rossendorf seit etwa 6 Jahren ein solches Experiment aufgebaut, das im wesentlichen aus einer helikalen Strömung flüssigen Natriums besteht. Bei den Messungen im November 99 wurde erstmals der Effekt der Magnetfeldselbsterregung beobachtet: Bei maximaler Strömungsgeschwindigkeit wurde ein allmählich wachsendes Magnetfeld gemessen. Die charakteristischen Werte der gemessenen Magnetfeldsignale (Frequenz und Wachstumsrate) stimmen sehr gut mit den vorausberechneten überein. Weitere Messungen vom Juli 2000 bestätigten diese Ergebnisse und lieferten ein konsistentes Bild des Rigaer Dynamos: exponentielles Anwachsen des Magnetfeldes oberhalb der kritischen Strömungsrate, stabiles Magnetfeld auf Sättigungsniveaus im Bereich einiger Hundert Gauss, und axial veränderliche Sättigungsniveaus auf Grund der Rückwirkung der Lorentzkraft auf die Strömung

Experimental results for the stability of electromagnetically levitated solid and liquid spheres are presented. It is shown that the stability is solely determined by the non-dimensional frequency as predicted by theory. Quantitative values are derived for the critical frequency threshold above which rotational or oscillatory motions of the levitated sample occur.

Carbon-13 cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy (13C-CP/MAS-NMR) was applied to study the chemical modification process of humic acids (HA) with diazomethane and the subsequent alkaline hydrolysis of the methylated HA, which results in HA with blocked phenolic OH groups. We investigated different chemically modified and unmodified natural and synthetic HA with carbon-13 of natural abundance. In addition, we studied carbon-13 labeled modified synthetic HA, that were synthesized with [13C]diazomethane as methylation reagent, to confirm the assumed modification process and to determine the type of functional groups that have the highest affinity for methylation.
The results of the NMR studies with carbon-13 labeled HA show that carboxyl and acidic (phenolic) OH groups are methylated with diazomethane. Due to the alkaline saponification of the methylated HA, methyl esters of carboxyl groups are hydrolyzed, whereas phenolic OH groups remain methylated. Carboxyl groups show the highest affinity for methylation.
From the spectra of the modified and unmodified HA with carbon-13 of natural abundance it can be concluded that the applied modification procedure causes only the desired structural changes in HA.

Die bildgebende Darstellung funktioneller Vorgänge im lebenden Organismus bei gleichzeitiger Möglichkeit ihrer Quantifizierung ist nur mittels der Positronen-Emissions-Tomographie möglich. Dazu ist die Entwicklung und Anwendung von Radiotracern erforderlich, die mit Positronen emittierenden Radionukliden markiert sind. Das entsprechende Radionuklid mit den günstigsten kernphysikalischen Eigenschaften ist Fluor-18 (Halbwertszeit 110 min)[1]. Eine spezielle Aufgabenstellung ist die Darstellung von Rezeptorarealen, die nur in sehr niedrigen absoluten Stoffmengen vorliegen, weshalb auch der Radiotracer in sehr niedrigen Konzentrationen eingesetzt werden muss. Dementsprechend müssen Fluor-18 - markierte Verbindungen mit einer sehr hohen molaren Aktivität (spez. Aktivität) zum Einsatz kommen. Dies bedeutet ein sehr kleines Verhältnis zwischen den identischen fluorierten Molekülen, die mit nicht-radioaktivem Fluor und Fluor-18 versehen sind.
Anwendungsgebiete sind in der Nuklearmedizin und die Anwendung von deren Methoden in der Pharmakaentwicklung sowie biochemischen Grundlagenforschung.

Der Fluorierungsschritt, die Markierung mit Fluor-18, ist bei der Synthese solcher Radiotracer von besonderer Wichtigkeit.
Zunehmendes Interesse haben Verbindungen, bei denen das Fluoratom an elektrophile Gruppen gebunden ist. Die elektrophile Einführung von Fluor-18 in entsprechende Moleküle wurde bisher stets ausgehend von [¹⁸F]F₂ durchgeführt, wobei die Zugabe einer großen Menge an nicht-radioaktivem Fluor (10...100 µmol F₂) erforderlich ist.

Bei der Suche nach einer Alternative zur Verwendung elementaren Fluors bieten sich elektrophile Fluorierungsmittel an, die ausgehend von [¹⁸F]Fluorid ohne Zusatz von nicht-radioaktiven Fluoriden hergestellt werden müssen [2].

Perchlorylfluorid FclO₃ ist die einzige elektrophile Verbindung, die z.Zt. ausgehend von Fluorid, d.h. ohne die Verwendung elementaren Fluors, hergestellt werden kann. Ausgehend von Literaturdaten wurde eine Synthese erarbeitet die es gestattet, [¹⁸F]FclO₃ ohne Trägerzusatz in Stoffmengen von ca. 50 nmol bei einem hohem Radioaktivitätsniveau herzustellen. Ausgangsprodukt ist stets wässrige [¹⁸F]HF- Lösung.

Die Umsetzung erfolgt nach Entfernung des Wassers unter streng wasserfreien Bedingungen als Eintopf-Reaktion. Die wasserfreie HclO₄ wird durch Destillation durch P₄O₁₀ gewonnen, die HF-Lösung mittels Oleum entwässert.
Vorgehensweise: Wasserfreie HclO₄ wird in ein Gemisch von Oleum/[¹⁸F]HF aqu. eindestilliert. Nach kurzer Wartezeit wird das entstandene [¹⁸F]FclO₃ (Gl.1) in eine Vorlage abdestilliert, in der sich eine Lösung eines metalliertern Präkursors (Carbanionen in Form von Na-diethylmalonsäurediethylester oder Phenyllithium) befindet. Durch die Umsetzung mit diesen Substanzen (Gl.2, Gl.3) erfolgt gleichzeitig der Nachweis des gebildeten [¹⁸F]FclO₃ unter Nutzung der Radio-HPLC.

[¹⁸F]HF + HClO₄ _ _ [¹⁸F]FClO₃ (1)
[¹⁸F]FClO₃ + NaCH(COOEt)₂ _ [¹⁸F]FCH(COOEt)₂ (2)
[¹⁸F]FClO₃ + C₆H₅Li _ [¹⁸F]C₆H₅F (3)

Der mögliche Mechanismus wird diskutiert.

Die bisher erreichte radiochemische Ausbeute liegt bei 6 % (zerfallskorrigiert). Damit können erstmals elektrophile Radiofluorierungen mit Fluor-18 ohne Trägerzusatz vorgenommen werden.

Literatur:

[1] Yu-Shin Ding, J. Fluorine Chem.101(2000) 291-295
[2] J. Steinbach, Chr. Fischer, K. Neubert, B. Johannsen, XIIth International Symposium on Radiopharmaceutical Chemistry,
Uppsala, Sweden, June 15-19, 1997, Abstracts S. 14-16

It has been found that phase transformations in implanted iron may strongly depend on the sample thickness. The effect essentially relies on lower impurity concentration required for given phase formation in thin films when compared with thick layers or bulk samples and most likely should be attributed to the stress formed during layer deposition. The phase transformation in thin films is also more complete, for example full transformation of thin iron layers into iron nitrides was observed, whereas in thick and bulk samples about 20 % of Fe atoms in implanted layer remain in crystalline alpha-Fe phase.

Ultrafine-grained (UFG) high purity nickel samples produced by equichannel angular pressing were submitted to thermal treatment and cyclic plastic deformation at different temperatures in order to investigate the stability of the defect structure. After annealing recrystallization already occurs in a temperature range between 425K - 475K. Impurities increase the recrystallization temperature. At room temperature cyclic plastic deformation induces a coarsening of grains and subgrains and at 425K a dynamic recrystallization. Additionally , the mean volume expansion, long-range and short-range internal strains, investigated by synchrotron radiation diffraction for the UFG deformation stage are diminished in consequence of cyclic plastic deformation.

Für die Bewertung des Gefahrenpotentials bei der Herstellung von Grignard-Reagenzien sind neben der sehr hohen Exothermie der Grignard-Reaktionen vor allem deren spontanes Startverhalten von entscheidender Bedeutung. Um Störfälle in industriellen Chemieanlagen zu vermeiden, darf ein Reaktionsstart nicht mehr bei einer hohen Akkumulation des Arylhalogenids erfolgen. Zu diesem Zweck werden die reaktions-technischen Parameter des Startprozesses am Beispiel einer häufig industriell angewendeten Grignard-Reaktion in einem geschlossenen Reaktionskalorimeter untersucht. Die Ergebnisse zeigen, dass neben online-FTIR-Konzentrationsmessungen auch der Anstieg der Reaktortemperatur und des Druckes zur Überwachung des Startens der Grignard-Reaktion genutzt werden können.

The aim of the presentation is to give an overview of the equipment and the experimental activities of the Dep. of Experimental Fluid Dynamics relating to the investigations on exothermic chemical processes.
The experimental equipment consists of several reaction calorimeters, analytical instruments and a modular computer controlled miniplant.
With the help of this equipment a number of processes were investigated on the basis of industrial contracts and research projects.
The research results are presented with two examples:

• the calorimetric investigations of the formation of Grignard reagents
• the characterization of reaction pathways and process kinetics of the catalytic hydrogenation process of a special nitroaromatic compound.

Im Rahmen der externen Validierung des von der Gesellschaft für Anlagen- und Reaktorsicherheit entwickelten Störfallcodes ATHLET, der in der Version Mod 1.2 Cycle C vorlag, wurden zwei Experimente nachgerechnet und analysiert, die an der japanischen Versuchsanlage CCTF durchgeführt wurden.
Die Versuchsanlage CCTF ist ein 1:25 volumenskaliertes Modell eines 1000 MW Druckwasserreaktors. Bei den Experimenten handelt es sich um die Versuche C2-04/62 und C2-19/79, in denen jeweils ein 2F-Bruch im kalten Strang mit kaltseitiger bzw. kombinierter Notkühleinspeisung simuliert wurde. Die Versuchsanlage wurde so ausgelegt, daß die Wiederfüll- bzw. Wiederflutphase bei Druckwasserreaktor-Störfällen mit großem Leck simuliert werden kann.
Die Auswertung der Rechnungen zeigt, daß die wesentlichen Phänomene im Verlauf der Transiente gut wiedergegeben werden. Das betrifft vor allem das zeitliche Verhalten der Wiederbenetzungsfront und die damit verbundene Kühlung der Brennelemente. Wie eine Analyse der experimentellen Daten zeigt, spielen im Reaktorkern radiale Effekte eine wesentliche Rolle. In der CCTF Anlage wird sowohl eine axiale als auch eine radiale Leistungsverteilung im Kern simuliert. Radiale Effekte treten insbesondere bei der kombinierten Notkühleinspeisung auf. Hier wird die Einspeisung über das Obere Plenum durch den in Gegenrichtung strömenden Dampf teilweise behindert. Die Wiederbenetzungsfront schreitet in den Randbereichen schneller voran als im Zentrum. Dieses Verhalten wurde in den ATHLET-Rechnungen durch eine Zweikanal-Modellierung des Reaktorkerns nachgebildet. Die Ergebnisse der ATHLET Rechnungen zeigen sowohl für das Zentrum als auch für die Randbereiche des Kerns eine gute Übereinstimmung mit den experimentellen Daten.
Die Schwachstellen der Rechnungen liegen vor allem bei der Notkühleinspeisung in der Anfangsphase der Transiente. Hier wird kaltes Notkühlwasser in Volumina mit reinem Dampf eingespeist. Die Rechnungen liefern dabei zu hohe Kondensationsraten, welche mit einer unrealistischen Druckabsenkung verbunden sind. Desweiteren wird der Druckaufbau durch die Verdampfung beim Wiederbenetzen der Brennelemente offensichtlich unterschätzt.
Die Ergebnisse der Rechnungen zeigen darüberhinaus, daß die sicherheitsrelevanten Aussagen der Experimente durch den Code ATHLET reproduziert werden.

An overview of the research activities of the FIB group in the Research Centre
Rossendorf is given. More in detail the fabrication technology of alloy LMIS as well
as their characterization is discussed. The FIB system IMSA-100 is briefly
introduced and typical applications are presented: writing implantation of Co ions
into a heated Si target in order to create maskless sub-micron CoSi2 structures,
bombardment of semiconductor materials with different ions in a wide range of
current density, dose and temperature allows to study the damage creation and
dynamic annealing process.

Simplified theoretical models are presented for the highly coupled phenomena of heat transfer, convection and solidification during VGF crystal growth. The models are essential in order to inverse the general approach: optimal conditions at the solidification front can be translated into temperature conditions at the heaters and the corresponding heater regimes. The Stefan problem of the unknown geometry of the solidification front is solved in a simplified analytical way in good approximation with the full numerical solution.

The theory of magnetic field generation in cosmic bodies due to the homogeneous dynamo effect has been widely elaborated during the last decades. However, an experimental verification of this effect was still missing until recently. At the Riga dynamo facility, self-excitation of a magnetic field in a liquid metal flow has been observed for the first time in November 1999. For increasing rotation rate of the driving propeller, the amplification of an applied magnetic field has been measured. At the highest rotation rate of 2150 rpm, an exponentially increasing 1.3 Hz signal has been detected on the background of the amplified 1 Hz signal. Additionally, after switching off the excitation current at a slightly lower rotation rate, a slowly decreasing eigenmode was observed. The results are shown to correspond convincingly with numerical predictions.

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Ein wichtiges Thema der Sicherheitsforschung zum Störfallverhalten von Druckwasserreaktoren sind Reaktivitätsstörfälle. Beispiele für solche Transienten sind Lecks im Frischdampfsystem und Borverdünnungstransienten. Wenn zu kaltes Wasser oder Wasser mit einer zu geringen Borkonzentration in den Reaktorkern gelangt, kann es zu einem so hohen Reaktivitätseintrag kommen, dass der abgeschaltete unterkritische Reaktor wieder kritisch wird. Einerseits kann es bei einem Leck auf der Dampferzeuger-Sekundärseite zu einer Unterkühlung des Kühlwassers auf der Primärseite in dem entsprechenden Loop kommen. Die Unterkühlung kann bis zu 100 K gegenüber der normalen Kereintrittstemperatur betragen. Andererseits besteht die Möglichkeit, dass sich bei einem kleinen bis mittleren Leck im Primärkreis bei teilweisen Ausfall der HD-Notkühlung und Reflux-Condenser-Bedingungen Kondensat in den Dampferzeuger-Kollektoren und den Pumpenbögen ansammelt. Nach dem Wiederauffüllen des Kreislaufes und Anlauf der Kühlmittelzirkulation würde unterboriertes Wasser in den Kern gelangen. Ob der zuvor abgeschaltete Reaktor wieder kritisch wird und wie hoch die Leistungsspitze dabei ist, hängt davon ab, wie weit sich das kalte oder zu schwach borierte Wasser auf dem Wege von den Kühlschleifen durch den Ringraum und das untere Plenum zum Reaktorkern mit dem heißeren und hochborierten Kühlmittel im Reaktor vermischt. Aus diesem Grunde werden an der ROCOM-Versuchsanlage im Institut für Sicherheitsforschung des FZR generische Vermischungsuntersuchungen durchgeführt. Sie dienen vorrangig der Validierung von CFD-Berechungen zur Simulation der verschiedenen Vermischungsszenarien.

We investigate the temperature dependence of the mass spectrum of the ion beam emitted by an Au77Ge14Si9 liquid metal alloy ion source. Our results strongly point towards the co-existance of two mechanisms for the emission of doubly-charged monomer ions: direct field evaporation and post-ionization.

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

Informations can be requested. Email: M.Posselt@fz-rossendorf.de

After the dynamo experiment in November 1999 had shown magnetic field self-excitation in a spiraling liquid metal flow, in a second series of experiments emphasis was placed on the magnetic field saturation regime. The dependence of the strength of the magnetic field on the rotation rate is studied. Various features of the saturated magnetic field are outlined and possible saturation mechanisms are discussed.

We demonstrate the realization of a quantum cascade laser (QCL) based on strained InGaAs/AlGaAs/GaAs grown on GaAs substrate using molecular beam epitaxy. The material is compared to a GaAs/AlGaAs structure with nominally identical radiative transitions. Lasing at 10 microns was achieved in the strained and the unstrained material. The strained material shows an improved temperature performance with a T0=112K between 125 K and 200 K and a maximum working temperature of T=200 K.

This paper presents a digitized version of a thermodynamic sorption database, implemented as a relational database with MS Access. It is mineral-specific and can therefore also be used for additive models of more complex solid phases such as rocks or soils. An integrated user interface helps users to access selected mineral and sorption data, to extract internally consistent data sets for sorption modeling, and to export them into formats suitable for other modeling software. Data records comprise of mineral properties, specific surface area values, characteristics of surface binding sites and their protolysis, sorption ligand information, and surface complexation reactions. An extensive bibliography is also included, providing links not only to the above listed data items, but also to background information concerning surface complexation model theories, surface species evidence, and sorption experiment techniques.

The monoenergetic positron beamline ‚SPONSOR' at Rossendorf has been used to investigate the positron behaviour in a naturally grown Brasilian quartz, two synthetic quartz crystals of different origin, and synthetic silica glass. The measurements allow to obtain the positron diffusion length of free positrons and Bloch para-positronium (p-Ps), if formed, in these materials.
In addition, hydrothermal treatment of a synthetic quartz has been used to introduce hydrogen into the crystal up to a certain depth. The presence of hydrogen is found to influence the formation of p-Ps. The depth distribution of hydrogen has been measured independently by nuclear reaction analysis (NRA), and will be discussed in comparison with the depth results deduced from the positron studies.

Im vorliegenden Bericht werden Anwendung und Ergebnisse rauschdiagnostischer Untersuchungen von Schwingungen, die zu Beschädigungen der Einbauten des Reaktordruckgefäßes geführt haben, im Detail beschrieben. Sie waren in den Jahren 1975 bzw. 1985 an den WWER-440/230-Reaktoren der russischen Baureihe der Blöcke 1 und 2 des Kernkraftwerkes Greifswald aufgetreten. Der Bericht enthält die wesentlichen Angaben zum Betriebsverhalten während des gestörten Betriebes, die Inspektionsergebnisse, die charakteristischen experimentellen Befunde unter Verwendung rauschdiagnostischer Analysemethoden, die physikalische Aufklärung des Schwingungsprozesses und seiner Ursachen durch spezielle Untersuchungen sowie einige Empfehlungen zur Schwingungsüberwachung und -minimierung.

The intermetallic compound TiAl is very interesting for high temperature application due to its high temperature strength and low density. Above 700 °C, the use in e.g. aircraft engines is hindered because of a low oxidation resistance. Even though the compound contains 50at% Al, this is not sufficient to form a protective Al2O3 scale. Instead, a mixed oxide scale composed of TiO2 and Al2O3 is formed. Extended alloy development has shown, that additional elements which are beneficial for the oxidation often have a bad influence on the mechanical bulk properties. Cl doping has a strong effect even in very low concentrations of about 500 ppm ("Microalloy"). Ion Implantation of 1016 Cl/cm2 protects TiAl at 900 °C for up to 1000 h against oxidation in a wide range of implantation energies.

In order to apply this effect for complicated shaped parts, the high temperature oxidation behavior after plasma immersion ion implantation of chlorine into different TiAl alloys was investigated. A specialized chamber has been setup up for the strongly etching Cl plasma. Particularly with regard to contaminations, the chamber and the RF- antenna had to be made from aluminum. Since it is known that the Cl effect in TiAl requires a well defined Cl concentration, a variation of the implantation parameters has been performed. The resulting depth profiles of Cl are investigated using depth profiling with Auger electron spectroscopy (AES). After treatment (3*105 to 3*106 30 kV pulses of 5µs at a repetition rate from 150 Hz to 1500 Hz), the Cl is located close to the surface. The process is governed by the interplay between etching and implanting during the HV pulses. Therefore the retained dose depends mainly on the temperature during implantation, which is controlled by the repetition rate of the pulses. Oxidation tests at 900°C in air for 100 h showed a strong reduction of the oxidation, which are comparable to conventional beam line im-plantations of Cl.

In der Energie- und der Verfahrenstechnik spielen Zweiphasenströmungen eine wichtige Rolle. Sie treten in Rohrleitungen und Apparaten auf, und beeinflussen dort chemische Reaktionen, sowie Wärme- und Stoffübergänge. Um die komplexen Vorgänge in den Zweiphasenströmungen modellieren zu können, bedarf es der Ergebnisse umfangreicher Experimente. Zur Ermittlung der charakterisierenden Parameter einer Zweiphasenströmung, wie die Phasenverteilung und die Strömungsgeschwindigkeiten, ist eine Messtechnik notwendig, die eine räumlich und zeitlich hochaufgelöste Visualisierung der Strömung ermöglicht. Für diese Aufgabe eignen sich bspw. konduktive Messverfahren.

Im Institut für Sicherheitsforschung des FZ Rossendorf wurde in den vergangenen Jahren ein Gittersensor zur Untersuchung von Zweiphasenströmungen entwickelt. Dieser basiert auf der Messung der momentanen lokalen elektrischen Leitfähigkeit des Zweiphasengemischs. Er ermöglicht eine hochaufgelöste Visualisierung der Strömung. Bei einer Reihe unterschiedlicher Experimente wurde die Anwendbarkeit des Gittersensors zur Ermittlung der Phasenverteilung in einer Zweiphasenströmung nachgewiesen.

In dieser Arbeit soll die Genauigkeit des Gittersensors bei der Ermittlung von Blasengrößen untersucht werden. Dafür wurde ein Plexiglaskanal angefertigt, in den die Elektroden des Sensors direkt eingebaut wurden. Da es nicht möglich war, für einen Vergleich in der Kanalströmung einzelne Blasen mit einem definierten Volumen zu erzeugen, wurde die Bewegung der Blasen in diesem Kanal mit einer Hochgeschwindigkeits-Videoeinrichtung erfasst. Mit beiden Verfahren wurden synchron Messungen bei unterschiedlichen Strömungsgeschwindigkeiten und mit verschiedenen Blasenvolumen durchgeführt. Mit Hilfe von Rechnerprogrammen wurden aus den Kamerabildern die Durchmesser der Blasen bestimmt und daraus die Volumen berechnet. Damit konnten die ermittelten Blasenvolumen des Gittersensors mit denen der Kameraaufnahmen verglichen werden. Dieser Vergleich ließ qualitative und teilweise quantitative Aussagen über die Genauigkeit des Gittersensors zu.

For the analysis of the core behaviour during boron dilution transients and main steam line breaks, coupled neutron kinetic / thermal hydraulic codes are necessary. These codes (e.g. DYN3D-ATHLET) must contain models of the coolant mixing on its way from the inlet noz-zles to the core entrance, because the reactivity insertion strongly depends on the distribution of temperature and boron concentration at the core inlet. The coolant mixing mainly happens in the three-dimensional flow field inside the complex geometry of the downcomer and lower plenum. The modelling of coolant mixing was carried out by detailed computational fluid dynamics (CFD) calculations with the code CFX 4.3. For the validation of the computational results, the ROCOM test facility was built, a fluid dynamic 1:5 scaled model of the Konvoi reactor. The reactor vessel is made of Plexiglas for flow visualisation and LDA measure-ments. The use of a system of wire-mesh sensors allows to measure salt concentrations at over 1000 locations with a maximum time resolution of 200 Hz. In case of stationary coolant flow in all loops a disturbance of boron concentration or temperature is transferred to a sector of the core inlet plane, which corresponds to the location of the inlet nozzle. A short plug of boron diluted water experiences a better mixing: due to the vortices in the downcomer different por-tions of the disturbance are transported with different velocities. This causes a dispersion of the front and the end of the plug (axial mixing). Further, experiments and calculations are go-ing on to investigate mixing under transient conditions (start of circulation).

Model experiments with low-energy ions under controlled vacuum conditions have been performed in order to identify the surface processes and the diffusion mechanism associated with the nitrogen transport during ion nitriding of stainless steel 316 and pure aluminium. A necessary condition for an efficient nitriding is the transmission of the implanted ions through a surface oxide layer which results from a balance of ion sputtering and re-oxidation from the residual gas. For ion energies around 1 keV and ion current densities around 0.2 mA/cm2, oxygen partial pressures of less than about 3A10-6 mbar and 3A10-7 mbar are required for stainless steel and aluminium, respectively. Diffusion under the influence of traps controls the transport of nitrogen in stainless steel, with dynamic trapping at the Cr atoms of the alloy. In contrast, stoichiometric AlN grows on aluminium due to Al diffusion from the underlying bulk. From the surface and diffusion mechanisms, limitations of plasma nitriding and plasma immersion ion nitriding are derived, and the implications for industrial applications are discussed.

Five-coordinate oxotechnetium(V) mixed-ligand complexes [TcO(SES)(S-p-C₆H₄-OMe)], where SES is a tridentate dithiolato fragment of the type ^-S(CH₂)₂E(CH₂)₂S^- (E = O, 1; E = S, 2; E = NMe, 3) are converted via reduction-substitution reactions in the presence of PMe₂Ph into the corresponding five-coordinate Tc(III) complexes [Tc(SES)(S-p-C₆H₄-OMe)(PMe₂Ph)] (E = O, 4; E = S, 5; E = NMe, 6). Rearrangement of the original square pyramidal '3 + 1' oxo-species to the trigonal bipyramidal '3+1+1' Tc(III) complexes occurs by placing the three thiolate donors on the basal plane, the phosphine phosphorus and the heteroatom of the tridentate ligand at the apexes of the bipyramid. These Tc(III) complexes are diamagnetic species, thereby allowing multinuclear NMR characterization in solution, which confirm their structures to be identical to those observed in the solid state via X-ray determinations.

Introduction:

Choline is the metabolic precursor of neurotransmitter acetylcholine and of the membrane phospholipid phosphatidylcholine. This amine is not synthesized by the brain and is therefore taken up from the blood. It is transported by a specific transport system which is much less characterized than the transporter for glucose and amino acids. Carnitine which is important for the intracellular transport of fatty acids has been found to inhibit the choline transport. On the other hand specific transporters for carnitine are known (OCTN1, OCTN2) which have not been described at the blood-brain-barrier (BBB) up to know. Therefore we have studied the transport of the two amines at an in vitro model of the BBB. In this study, we have demonstrated that at least two different transport systems for choline and carnitine are functionally expressed.
Methods:
The RBE4 cell line was used as an in-vitro model of the BBB and it has been shown that these cells express typical BBB markers such as gamma-glutamyltransferase and alkaline phosphatase(1). Tracer uptake studies were performed in 24 multi-well plates using buffers containing either 25 mM Tris/Hepes (pH 8.5 for choline uptake) or 25 mM Hepes/Tris (pH 7.5 for carnitine uptake), supplemented with 0.5% albumin, 5 mM glucose, 5.4 mM KCl, 1,8 mM CaCl₂, 0.8 mM MgSO₄ and 140 mM NaCl. Whenever Na⁺-free buffers were used, NMDG chloride replaced NaCl isoosmotically. Cells were washed before starting the uptake and then incubated at room temperature (choline uptake) or 37°C (carnitine uptake) with radiolabeled substrates added to the incubation buffer. K_m values and V_max values were calculated from the uptake data. Specific inhibitors of the transporters were added to the incubation buffer to study the specificity of the process.
An RBE4 cell cDNA library was constructed using the Superscript plasmid system. This plasmid cDNA library, grown on NitroPure transfer membranes, was screened by the colony screening method as described by Vogeli and Kaytes (2). The cDNA probe used for screening was 2.1 kb pair long and consisted of most of the coding region of rOCTN2 cDNA. The probe was labeled with [alpha-₃₂P]dCTP using the ready-to-go oligolabeling kit, and used to screen the RBE4 cDNA library under low stringency conditions. The cDNA was functionally expressed in HeLa cells by vaccinia virus expression system (3). Transport measurements were made at room temperature using the same uptake buffer as described above without albumin.
Results:
The RBE4 cells express a Na⁺-independent choline transporter. Hemicholinium, an inhibitor for the Na⁺-dependent choline transporter, also inhibits the choline uptake found in these cells while tetraethylammonium (TEA) does not. The uptake of choline is saturable with a K_m value of 22 µM and a V_max of 515 pmol/(mg protein * 10 min).
We also isolated a full-length OCTN2 clone from the RBE4 cDNA library. HeLa cells transfected with this clone express Na⁺-independent TEA uptake and Na⁺-dependent carnitine uptake. These transfected cells also take up fatty acid esters of carnitine like propionylcarnitine and acetylcarnitine. The K_m value for the carnitine uptake at 37°C in RBE4 cells is about 50 µM. Specific inhibitors for the OCTN2 transporter (MPP⁺ and TEA) inhibit the carnitine uptake in RBE4 cells.
Comments:
In summary, we have found two separate transporters for choline and carnitine are expressed in the RBE4 cells. While the choline transporter is expected to supply the brain with choline for neurotransmitter synthesis OCTN2 is described as an carnitine carrier which also transports short fatty acids as carnitine esters through the cell membrane. The expression of OCTN2 at the BBB may help to understand the way of supplying the brain with acetyl groups for the synthesis of acetylcholine ...

The paper presents a method for the prediction of the radial gas fraction profile in vertical pipe flow for a given bubble size distribution. A large number of bubble classes is considered. An equilibrium of the forces acting on a bubble perpendicular to the flow direction is assumed. On basis of the radial profile of the liquid velocity, radial distributions of the volume fraction are calculated separately for all bubble classes according to a given bubble size distribution. The sum of these distributions is the radial profile of the gas fraction. It again influences the liquid velocity. The final solution is obtained by an iteration process, which consideres the feedback between the gas fraction profile and the profile of the liquid velocity. The model is the basis of a fast running one-dimensional steady state computer code. The results of the model are compared with experimental data for a number of gas and liquid volume flow rates.

The wire-mesh sensor developed by the Forschungszentrum Rossendorf produces sequences of instantaneous gas fraction distributions in a cross section with a time resolution of 1200 frames per second and a spatial resolution of about 2-3 mm. At moderate flow velocities (up to 1-2 m/s), bubble size distributions can be obtained, since each individual bubble is mapped in several successive distributions. The method was used to study the evolution of the bubble size distribution in a vertical two-phase flow. For this purpose, the sensor was placed downstream of an air injector, the distance between air injection and sensor was varied. The bubble identification algorithm allows to select bubbles of a given range of effective diameter and to calculate partial gas fraction profiles for this diameter range. In this way, the different behaviour of small and large bubbles in respect to the action of the lift force was observed in a realistic flow situation.

In this paper we report on the design of a decel lens system for low energy ion implantation. The novel lens system consisting of a converging and a diverging lens in a compact arrangement allows to compensate the spherical aberration. Therefore implantation into large areas at low energies can be performed with high dose uniformity. The implantation chamber with the decel lens system is fitted to the beamline 2 of the medium energy implanter DANFYSIK 1090 at the Forschungszentrum Rossendorf. Using a beam energy of 30 keV the ions can be decelerated up to 2 keV with a dose uniformity of < 5% for 100 mm diameter.

The ever increasing demands for high precision machining and increased cutting performance, in terms of cutting speed and lifetime, require wear resistant tools of large dimensional accu-racy that have very sharp cutting edges. All these requirements can not be fulfilled by the clas-sic PVD and CVD technologies because they result in rather thick overlay coatings.
In this report, first experiments are presented on a hybride plasma immersed ion implantation process (PIII) for depositing thin TiN coatings on hardened and annealed high speed steel or cemented carbides. The layers were produced using a dc-cathodic arc source with a titanium cathode and a nitrogen feed gas. As the cathodic arc generates additional to the metal plasma, a large amount of liquid metal droplets, the plasma was guided to the samples through a 900 magnetic bending field avoiding the deposition of droplets on the samples. The obtained layer thickness was below 1 µm for deposition times of 2 min.
To improve the adhesion of the deposited layers on the substrate materials, of energetic ions were used during the initial phase of the process. Hereto negative high voltage pulses in the range from zero to 5 kV have been applied to the samples during the deposition. The effect of the energy of these ions on the coating structure was also investigated by SEM, TEM and XRD. Mechanical and functional properties were investigated by hardness measurements and fretting wear tests respectively. Finally cutting performance tests of PIII-treated drills were performed, revealing that a 0.8µm thick TiN PIII-coating increased the lifetime of the drills by a factor of 2.5.

We have studied the interminiband absorption and the current-voltage characteristics on the same GaAs/AlGaAs superlattices. The Esaki-Tsu type negative differential resistance is observed as well as the thermal (de)population of the minibands. The possibility of mapping the nonequilibrium electron distribution function through infrared absorption measurements under bias is discussed.

Stress is a common property of thin films. After a brief summary of origins and effects of stresses in thin films the particular situation in amorphous and nano-crystalline films is discussed. The problems related to the extremely high compressive stresses in cubic boron nitride (cBN) have been tackled either by the deposition of buffer layers or by attempts to reduce the stress in the film. These approaches are compared and discussed. Intrinsic stress depth profiles in BN films, as well as the influence of post-deposition thermal treatment and ion irradiation on the global stress, as obtained from in-situ cantilever bending measurements, are reviewed. A technique for the growth of cBN films with significantly reduced compressive stress is demonstrated.

An intensity modulated focused ion beam (FIB) which is hitting the surface of a solid, heats up a small near subsurface region to a temperature which is sufficient for thermal elastic wave generation. The measurement of these waves can be used for analysis and imaging of surface as well as subsurface structures in the material. The modified FIB equipment IMSA-100 working with 35 keV Ga+ and Au+ ions, respectively, and a current of about 3 nA was employed to obtain acoustic images from structures on silicon and glass targets. The acoustic signals were detected using a PZT transducer delivering an output voltage of 50 - 100 nV. The modulation frequency was varied in the range of 60 - 170 kHz. The obtained lateral resolution of the ion acoustic images at these frequencies was about 15 µm on silicon and about 7µm on glass, respectively. Furthermore some estimations due to the reachable resolution and a short description of the set-up is given.

The surface hardness of the titanium alloy Ti-6Al-4V, widely used as construction material, can be improved by nitrogen implantation. The paper reports on a complex study of the structural mechanisms of hardening and its loss at higher temperatures with different methods (grazing incidence X-ray diffraction, in-situ high temperature diffraction with synchrotron radiation, ERDA, hardness and surface inspection by SEM). Plasma immersion ion implantation produces a nitrogen profile directly below the surface. The formation of small TiN crystallites is detected but the hardness increase is only about 40%. Annealing leads to the reduction of the TiN phase and the formation of Ti2N deeper in the material. The in-situ XRD study of the phase formation gives information about the temperature range of the changes. The hardness increases after annealing by a factor of 2.5 compared to the unimplanted state. It is explained by precipitation hardening due to the formation of titanium nitrides in different depths of the material.

Real-time ellipsometry (RTE) in combination with particle flux measurement is applied to ion beam assisted deposition (IBAD) of boron nitride (BN) films. RTE is used as a toll for process diagnostic to improve the deposition stability. A novel technique for the determination of absolute density depth profiles from dynamic growth rate data and film forming particle flux is employed. From real-time cantilever curvature measurement and simultaneously recorded film thickness data instantaneous stress depth profiles are derived with a depth resolution in the nm--range. The synergistic effects on the information obtained from RTE, particle flux, and cantilever bending data are demonstrated. The density of turbostratic BN (tBN) is found to increase slightly with film thickness while the compressive stress decreases, indicating an increasing quality and/or size of crystallites in the course of film growth. Refractive index and density depth profiles in cubic BN (cBN) films correspond perfectly to structural information obtained from dark field TEM graphs. The established tBN/cBN 2-layer model is found to be a crude approximation that has to be replaced by a 3-layer model including nucleation, grain growth, and coalescence of cBN. The instantaneous compressive stress in a homogeneous tBN film is found to decrease while the density increases during growth. The instantaneous compressive stress depth profiles in cBN films are more complex and not easy to understand but reliable information on the structural evolution during growth can be extracted.

Gegenstand der vorliegenden Arbeit ist die Weiterentwicklung von Verfahren zur Ermittlung der Rißeinleitungszähigkeit (Jid) unter schlagartigen Belastungsbedingungen. Als Indikationsmethode für die duktile Rißinitiierung wurde die Messung der unter Beanspruchung im Werkstoff freigesetzten elastischen Energie - der Schallemission (SE) - genutzt.

Die Eignung dieser Methode wurde im instrumentierten Kerbschlagbiegeversuch an modifizierten ISO-V-Proben geprüft. Als zuverlässige Basis für eine Beurteilung der damit bestimmten Kennwerte wird die physikalische Rißinitiierungszähigkeit angesehen. Dieser Referenzwert wird in Verbindung mit der Messung der Stretchzonenbreite aus der nach der Mehrpro-ben-Spaltbruchmethode ermittelten Rißwiderstandskurve gewonnen. Die Bestimmung des SE-definierten Initiierungswertes wurde mit zusätzlichen dynamischen Einprobenverfahren (Laser-COD, magnetische Emission) und ergänzenden Versuchsanordnungen (invertiertes Pendelschlagwerk, dynamischer Dreipunktbiegeversuch) verifiziert. Die Untersuchungen wurden an Stählen mit unterschiedlichen Festigkeits-Zähigkeitseigenschaften durchgeführt.

Die Ergebnisse lassen sich wie folgt zusammenfassen:

• Nach dem Aufprall des Hammers führen die rasch wechselnden Kontaktbedingungen zwischen Finne, Probe und Widerlager zu „schlagbedingter" SE, die frequenzselektiv nicht eliminiert werden kann. Geringfügige Änderungen der Kontaktgeometrie beeinflussen die schlagbedingte SE.
• Unabhängig von der verwendeten Versuchsanordnung (normal, invertiert) wurden grund-sätzlich vergleichbare SE-Signale erhalten.
• Neben der schlagbedingten SE lassen sich reproduzierbar SE-Ereignisse nachweisen, die mit Verformungs- und Bruchprozessen im Werkstoff in Verbindung stehen. Bei prellfreier Belastung konnten solche SE-Ereignisse im Streckgrenzenbereich nachgewiesen werden.
• Vor dem Kraftmaximum treten „rißbedingte" SE-Ereignisse auf, die im Zusammenhang mit der Schädigungsentwicklung vor der Rißspitze stehen. Die damit definierte Rißinitiierungszähigkeit stimmt gut mit dem nach der Mehrproben-Technik bestimmten Referenzwert überein.
• Rißbedingte SE tritt nicht bei jedem Stahltyp oder -zustand mit gleicher Evidenz auf. Tendenziell zeigte sich, daß mit zunehmender Zähigkeit der Nachweis duktiler Rißinitiierung durch SE schwieriger wird. Der kausale Zusammenhang zwischen SE und mikrostruktureller Schädigung ist nicht eindeutig zu belegen.
• Auf der Grundlage der Ergebnisse können Kriterien zur automatisierbaren SE-Auswertung definiert werden.

Der durch rißbedingte SE definierte Zähigkeitsparameter wurde mit der physikalischen Rißinitiierungszähigkeit verifiziert. Obgleich die riß- von der schlagbedingten SE nicht immer ohne Ermessensspielraum zu trennen ist, werden plausible und im Vergleich zu technischen Parametern konservative Jid-Werte bestimmt.

Damage has been observed in 40 keV He ion-implanted Si away from the projected ion range Rp, mainly around Rp/2. Cu gettering has been used for the detection of irradiation defects which are formed during rapid thermal annealing (RTA) of 800°C/10 min. The transmission electron microscopy (TEM) micrographs show no visible defects at Rp/2. The Cu gettering peak at Rp/2 is well known for MeV-ion-implanted and annealed Si (Rp/2 effect). In this study the corresponding effect is observed for low ebergy implantation of a light ion like He.

The formation of Ge nanowires in V-grooves on (001)Si wafers has been studied experimentally as well as theoretically. The V-grooves were formed by anisotropic etching and subsequent oxidation of their surface. The implantation of 1E17 Ge$^{+}$cm$^{-2}$ at 70 keV into the oxide layer leads to an enrichment of Ge in the V-groove bottom. In this Ge rich bottom region, subsequent annealing in N$_{2}$ atmosphere results in the formation of a nanowire by coalescence of Ge precipitates. STEM-EDX investigations of as-implanted samples have confirmed the Ge accumulation at the V-groove bottom, whereas cross-sectional TEM studies of annealed samples prove the formation of a Ge nanowire. The formation mechanisms were studied theoretically by means of a continuum description of sputtering and kinetic 3D lattice Monte-Carlo simulations of phase separation. The preliminary results indicate the possibility of achieving nanowires being several nanometers wide by further growth optimizations.

Due to their unique structural features and properties dendrimers are ideally suited for use in diagnostic imaging and therapy, transfection, and drug delivery systems.¹ We are especially interested in efficient binding and controlled release of medicinally and biologically relevant anions with dendrimers tailored. In this context poly(propyleneamine)-dendrimers (POPAM) having anion affecting groups at the periphery seems to be very promising. Thus, we could show that urea-functionalized dendrimers are efficient carriers for oxyanions.²

This paper reports the binding behaviour of POPAM-dendrimers having the pH-switchable unit methyl orange at the periphery I. Furthermore POPAM-dendrimers possessing 2,6-diamidopyridine moieties IIa and IIb are investigated. The extractability of the radioactive pertechnetate TcO₄ ^- and the nucleotides AMP, ADP, and ATP with dendrimers are evaluated quantitatively by tracer methods in CHCl₃/H₂O systems. The extraction efficiency is studied in dependence on time, pH, buffer system, dendrimer concentration and generation. A dendritic effect is clearly visible for all dendrimers investigated. Controlled release of anionic guest molecules from the dendrimer host is allowed by alteration the pH.

[1] D.A. Tomalia, A.M. Naylor, W.A Goddart III, Angew. Chem. Int. Ed. Engl. 1990, 29, 138; Y. Kim, S.C. Zimmermann, Curr. Opin. Chem. Biol. 1998, 2, 733; O.A. Matthews, A.N. Shipway, J.F. Stoddart, Prog. Polym. Sci 1998, 23, 1; M. Fischer, F. Vögtle, Angew. Chem. Int. Ed. Engl. 1999, 38, 884; A.W. Bosman, H.M. Janssen, E.W. Meijer, Chem. Rev. 1999, 99, 1665.
[2] H. Stephan, H. Spies, B. Johannsen, L. Klein, F. Vögtle, Chem. Commun. 1999, 1875-1876

A nuclear resonance fluorescence experiment on the spherical N=50 nucleus 88Sr has been performed with bremsstrahlung of 6.7 MeV endpoint energy using two EUROBALL CLUSTER detectors. Dipole excitations observed in the energy region 4.5 MeV $\leq Ex \leq$ 5.5 MeVare proposed to be scissors-like excitations on top of the dynamically deformed quadrupole vibrational state.

FOREVER (Failure Of Reactor Vessel Rentention) experiments has been carried out in order to simulate the behaviour the lower head of a reactor pressure vessel under the conditions of a depressurized core melt down scenario. In particular the creep behaviour and the vessel failure mode have been investigated. Metallographic post test investigations have complemented the experimental programme. Samples of different height positions of the vessel of the FOREVER-C1 and -C2 experiments were metallographically examined and characteristic microstructural appearances were identified. Additionally samples with uneffected microstructure were annealed at different temperatures and cooled by different rates and afterwards investigated. In this way the microstructural effects of the temperature regime, the thermo-mechanical loads and the environmental attack could be characterized. Remarkable effects were characteristic for the FOREVER-C2 experiment where the highest-loaded region below the welding joint reached temperatures of approx. 1100°C and a strong creep damage occured. In the FOREVER-C1 experiment creep damage could not be observed and the maximum temperature did not exceed 900°C. Environmental attack generated decarburization and oxidation but the effect was restricted to a narrow surface layer. There was almost no chemical interaction between the oxidic melt and the vessel material.

High-spin states in 72Br and 73Br were studied with the EUROBALL III spectrometer.
The negative-parity band observed in 72Br displays a signature inversion around spin I = 16. Fully consistent cranked Nilsson-Strutinsky calculations show that this signature inversion can only be understood if the nuclear shape evolves from a triaxial shape with rotation around the intermediate axis at low spin through a collective prolate shape to a triaxial shape with rotation around the shortest principal axis at high spin. Rotational bands in 73Br
were observed up to spins of I = 65/2 at excitation energies of 26 MeV. Cranked Nilsson-Strutinsky calculations indicate that one of the negative-parity bands terminates at spin 63/2. Since this spin coincides with the maximum spin observed in the corresponding experimental band, we conclude that we observed this band up to its termination.

A quasi-particle model is presented which describes QCD lattice results for the 0, 2 and 4 quark-flavor equation of state.
The results are mapped to finite baryo-chemical potentials.
As an application of the model we make a prediction of deconfined matter with appropriate inclusion of strange quarks and consider pure quark stars.

Der Beitrag ist der Zwischenbericht des von der DFG geförderten gleichnamigen Forschungsvorhabens, Kennwort Prozessführung bei Pulverhandhabung.
Es wird auf folgende Bearbeitungsschwerpunkte näher eingegangen:

• Auswahl und Charakterisierung der für die Untersuchungen ausgewählten Pulver
• Untersuchungen zu Möglichkeiten der Insitu-Messung des Schüttgutverhaltens auf Basis von:

• Untersuchungen zum Strecken- und Regelverhalten eines entwickelten Schwingförderers sowie zur Schüttgutabhängigkeit der Reglerparameter, Erprobungsergebnisse eines fuzzy-adaptiven Dosierreglers (s. FWS 00-04)
• Entwurf eines fuzzy-adaptiven und eines Fuzzy-Reglers für die kontinuierliche Dosierung durch masse-Verlaufsregelung im Kleinstdosierbereich (<40mg/s), siehe FWS 00-01

Es werden die Eigenschaften des Schwingförderers als Förder- und Dosierorgan beschrieben. Aus dem Übertragungsverhalten des Schwingförderers werden die Aufgaben für den Einsatz in einer Dosierwaage formuliert. Anstelle der sonst üblichen Massestrom-Regelung wird die Masse-Verlaufs-Regelung als Folgeregelung eingesetzt, da sie für Dosierprozesse, die eine Zeitsynchronisation und eine Massebilanzierung erfordern, von Vorteil ist. Es wurde als Labormuster eine Dosierwaage, bestehend aus einer kommerziellen Präzisionswaage und einem Schwingförderer (Eigenentwicklung FZR) aufgebaut. Als Dosierregler wurde ein fuzzy-adaptiver PI-Regler entwickelt, der PC-implementiert im Echtzeit- Simulations- und Reglersystem DynStar der Hochschule Zittau realisiert wurde. Damit wurde der Prototyp eines universellen und flexiblen adaptiven Dosierreglers geschaffen, der für die kontinuierliche Dosierung von Pulvern im Kleinstbereich (< 40 mg/s) eingesetzt werden kann.
Der Beitrag entstand im Rahmen des von der DFG geförderten Forschungsvorhabens Prozessführung bei Pulverhandhabung.

Es wird ein Messverfahren zur Erfassung der Haufwerksrückwirkung und damit der Schüttguteigenschaften aus den Schwingungsgrößen eines Resonanzsystems beschrieben und Untersuchungsergebnisse an einem aufgebauten Labormuster vorgestellt. Das Verfahren ist zum Patent angemeldet. Es wird gezeigt, dass zwischen Fließverhalten und den am Resonanztopf gemessenen Merkmalen Frequenz und Tastverhältnis ein signifikanter Zusammenhang besteht. Damit kann es für die Klassifizierung und Parameteradaption bei Dosierreglern in Abhängigkeit vom Schüttgut verwendet werden. Das Messverfahren ist geeignet, als Insitu-Messung in eine Prozesslinie zur Schüttgutdosierung zu integrieren.
Der Beitrag entstand im Rahmen des von der DFG geförderten Forschungsvorhabens Prozessführung bei Pulverhandhabung.

Es werden die Eigenschaften des Schwingförderers als Feder-Masse-System beschrieben. Daraus wird das Förderverhalten von Schüttgütern bzw. Pulvern abgeleitet. Für die Förderung bzw. Dosierung von Pulvern kleiner Mengen wird ein speziell entwickelter Förderer, der als Patent angemeldet ist, vorgestellt. Für die Beschreibung des Förderverhaltens wird die empirische Größe Diskontinuität abgeleitet. Es wird anhand von Untersuchungen gezeigt, wie Förderbarkeit und Fließverhalten sowie Förder- und Regelverhalten zusammenhängen. Durch die qualitative Beschreibung des Förderverhaltens ist der Vergleich der Fördergüter mit unterschiedlichen Eigenschaften sowie der Vergleich verschiedener Förderorgane möglich. Es ist vorgesehen, die als Insitu-Messgröße gewonnene Diskontinuität für die Klassifizierung und damit Prozessoptimierung, d.h. für die schüttgutabhängige Parametereinstellung bei Dosierreglern zu verwenden.
Der Beitrag entstand im Rahmen des von der DFG geförderten Forschungsvorhabens Prozessführung bei Pulverhandhabung.

The phase formation and annealing behaviour are reported after nitrogen PIII in two austenitic stainless steels, DIN 1.4541
(X6CrNiTi18.10) and DIN 1.4571 (X6CrNiMoTi17.12.2), differing only in the Mo content. The treatment parameter were
pulses of 10 s and 40 kV for a nitrogen dose of 4×1018 cm-2 at a temperature of 380°C. In 1.4541, without Mo, the modified
layer is limited to 1.5 m while the 2 wt.% Mo-containing 1.4571 exhibits a layer thickness of 15 m. No difference in the
hardness (corrected for the layer thickness) and the wear behaviour was observed. Using X-ray diffraction (XRD) a lattice
expansion between 5 and 11%, was observed, not correlated with the nitrogen content (as determined by glow discharge
optical spectroscopy ¯¯ GDOS). After annealing at 400 and 425°C for different times, the lattice constant is slightly reduced,
albeit no phase transformation was observed in 1.4571. In 1.4541 at a temperature of 425°C a strong reduction of the lattice
expansion, coupled with an inward diffusion of the nitrogen was observed. No mechanism explaining this behaviour is available
at the moment.

Stainless steels show excellent corrosion resistance, which is lost during conventional hardening processes at temperatures
above 500°C, like gas or plasma nitriding, to improve the low hardness and to reduce the high wear rate. For aluminium alloys
it is impossible to improve the mechanical properties by traditional nitriding. Plasma immersion ion implantation (PIII) of
nitrogen is successfully used for hardening both austenitic stainless steels and aluminium alloys. Compared to the untreated
materials the hardness and the wear resistance can be improved significantly. For austenitic stainless steels an `expanded
austenite' layer of up to several tens of micrometer thickness and for aluminium alloys an AlN layer of more than 10-m
thickness were formed over a few hours. Corrosion tests showed no or only small changes in the corrosion behaviour for
stainless steel. The AlN layer can be used as a supporting layer for the deposition of hard materials like CrN on aluminium
alloys. It is shown that the partial pressure of oxygen in the residual gas in the vacuum chamber plays an important role for the
nitriding of both stainless steel and aluminium alloys

Das vorliegende Projekt wurde im Rahmen einer Kooperationsvereinbarung zwischen dem Forschungszentrum Rossendorf (FZR) und der wissenschaftlichen Gruppe von Prof. Melnikon von der Technischen Universität Nishny Novgorod (TUNN) der Russischen Föderation durchgeführt. Es ist Teil des Wissenschaftsunterstützungsprogramms / FSU der Bundesregierung im Rahmen der Beratungshilfe für den Aufbau von Demokratie und sozialer Marktwirtschaft (TRANSFORM). Neue Methoden der Instrumentierung für Zweiphasenströmungen wurden entwickelt: Ultraschall-Wellenleitersonden können zur lokalen Gas- bzw. Dampfgehaltsmessung eingesetzt werden. Der neue Ultraschall-Gittersensor erlaubt eine Visualisierung der Zweiphasenströmung mit ca. 250 Bildern/Sekunde. Sowohl die lokalen Sonden als auch der Ultraschall-Gittersensor können erfolgreich unter den Bedingungen von Wasser-Dampf-Gemisch bei hohem Druck und hoher Temperatur, sowie in anderen Fluiden, wie organischen Flüssigkeiten und Kältemitteln, eingesetzt werden. Darüber hinaus wurden berührungslos arbeitende Wellenleitersonden für die Durchschallung von Rohrleitungen und Dichtesensoren, die auf der Messung der Ausbreitungsgeschwindigkeit von Ultraschall in Wellenleitern beruhen, die sich im Messmedium befinden, entwickelt und getestet. Bei dem gegenwärtigen Stand der Entwicklung können die berührungslosen Sensoren lediglich als qualitativer Nachweis von Gas in einer Flüssigkeitsströmung dienen. Die Funktion der Dichtesensoren wurde anhand von Messungen in verschiedenen einphasigen Flüssigkeiten unterschiedlicher Dichte demonstriert. Für einen praktischen Einsatz ist die weitere Verbesserung der elektronischen Signalerfassung erforderlich. Die hauptsächliche Innovation wird durch den Ultraschall-Gittersensor verkörpert, dessen Auflösung mit der von schnellen elektrischen Gittersensoren und ultraschnellen Röntgentomographen vergleichbar ist, während das Gerät selbst sehr robust und preiswert ist.

The 6th dynamic benchmark concerns a double ended break of one main steam line (asymmetric MSLB) in a VVER-440 plant. The core is at the end of its first cycle in full power conditions. The control rods of group K6 are at position 175 cm from bottom of the core. All other groups of control rods are out of the core. The initial state conditions of the core in the beginning of the transient are given. The isothermal re-criticality temperature of the core is defined to be 210°C. It should be achieved by tuning the worth of all control rods. Otherwise, own best estimate nuclear data are to be used. The main geometrical parameters of the plant and the characteristics of control and safety systems to be considered are given. Otherwise, own input data decks developed for a VVER-440 plant and for the applied codes can be used. The objective is to calculate the behaviour of the core during this re-criticality event using coupled codes, which combine a three-dimensional neutron kinetics code for the core with a thermohydraulics system code. This benchmark is a logical continuation of the work in the 5th dynamic benchmark. Additional new features include asymmetric operation of the feed water system, effects of coolant mixing in the reactor vessel, and the definition of a fixed isothermal re-criticality temperature for normalising the nuclear data.