Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The Earth magnetic field undergoes polarity reversals with a mean reversal rate that varies from zero during the supercrons to 4-5 per Myr in the present. Typically, these reversals have an asymmetric, saw-toothed shape. Recently, a bimodal distribution of the dipole moment has been observed with two peaks at about 4 x 10^22 (Am)^2 and at about twice that value. In an attempt to identify the basic mechanism of such reversals, we study a mean-field dynamo model with a spherically symmetric helical turbulence parameter alpha which is quenched by the magnetic energy and disturbed by additional noise. The basic features of geomagnetic polarity reversals are shown to be generic consequences of the dynamo action in the vicinity of branching points of the spectrum of the dynamo operator where two real eigenvalues coalesce and continue as complex conjugated pair of eigenvalues. The model yields long periods of constant polarity which are interrupted by asymmtric polarity reversals. In certain parameter regions, it exhibits a bimodal field distribution, and it gives a natural explanation of the correlation between polarity persistence time and field strength. Typical features of coherence resonance are identified in the dependence of the polarity persistence time on the noise.

Eine in ruhendem Wasser aufsteigende Luftblase wird parallel zur Wasseroberfläche in zwei zueinander senkrechte horizontale Richtungen parallel projiziert. Diese beiden Projektionen werden zunächst als Ellipsen approximiert. Anhand der Ellipsen wird die Blase dann als Rotationsellipsoid modelliert. Das Rotationsellipsoid eignet sich zur Analyse des Verhaltens von Blasen auf ihrem Weg durch das Wasser. Dies wird an einem Ensemble schraubenartig aufsteigender Blasen verdeutlicht.

An air bubble rising in resting water is imaged by a parallel projection in two perpendicular horizontal directions. Initially, these two projections are approximated by ellipses. In the next step, the bubble is modelled as a spheroid matching the ellipses. The resulting spheroid is suitable to analyse the orientation of the symmetry axis of the bubble during its propagation through the liquid phase. The capabilities of the method is illustrated on an ensemble of bubbles rising on a helical trajectory.

A SiC/SiC composite is characterized by X-ray diffraction, atomic force microscopy, and various positron spectroscopies (slow positron implantation, positron lifetime, re-emission). It is found that beside its main constituent 3C-SiC the composite still must contain some graphite. In order to better interpret the experimental findings of the composite, a pyrolytic graphite sample was also investigated by slow positron implantation and positron lifetime spectroscopies. In addition, theoretical calculations of positron properties of graphite are presented.

Results from coincidence Doppler broadening measurements on various Si samples and Brazilian quartz having low quartz structure are presented with the aim to give further strong evidence for the existence of a low quartz structure, but not Si divacancies, at the SiO2/Si interface.

We developed a new method for the three-dimensional modeling of Extended X-ray Absorption Fine Structure (EXAFS) spectra, which is suited to extract the local structure of aqueous metal complexes from spectral mixtures of several components. The new method combines two techniques: Monte Carlo simulation and Target Transformation Factor Analysis (TFA). Monte Carlo simulation is used to create random arrangements between the X-ray absorbing metal ion and the ligand atoms, and to calculate the theoretical EXAFS spectrum of each arrangement. The theoretical EXAFS spectrum is then introduced as test spectrum in the TFA procedure, in order to test whether the test spectrum is likely a component of the spectral mixtures or not. This coupled procedure is repeated, until the error in the test spectrum is minimized. The new method is thus able to isolate and refine the structure of complexes from spectral mixtures and to determine their relative concentrations, based solely on an estimate of the ligand structure. The performance of the proposed method was validated using uranium LIII-edge EXAFS spectra of binary mixtures of two uranium(VI) 3,4-dihydoxy benzoic acid complexes.

In this article we will describe experiments at microkelvin temperatures which were performed to give - at least partly - answers to the following questions:

a. will all nonmagnetic metals become superconducting if refrigerated to low enough temperatures,
b. what is the impact of the weakest version of magnetism, nuclear magnetism, on superconductivity.

a. The first question has intrigued low temperature physicists since the discovery of superconductivity by H. Kamerlingh-Onnes in 1911. He wrote already in 1913 “There is left little doubt that if Au and Pt could be obtained absolutely pure, they could also pass into the superconducting state at helium temperatures”. And in 1929 W. Meissner wrote “At present it does not seem unlikely that, opposite to former expectations, all metals will become superconducting at low enough temperature”. One can pose the question in more general terms: “Is the electron-phonon interaction or another possible pairing mechanism in all metals strong enough so that they will eventually become superconducting, if this transition is not hindered by other phenomena, like magnetic properties?” After all, somehow the conduction electrons have to get rid of their entropy when approaching absolute zero, and one way is a transition to a superconducting state.

Looking at the periodic system of the elements, one realizes that superconductivity is rather the rule than the exception. Most metallic elements become superconducting if they show no magnetic order like some 3d- and 4f-elements. Even most insulators, like S or O, if forced into a metallic state by high pressure, eventually enter the superconducting state. When we started our research, there were only two small “islands” in the periodic system of the elements where metals had shown neither a superconducting nor a magnetic transition: some alkali and alkaline-earth metals and the noble and platinum metals (Cu, Ag, Au, Rh, Pd, Pt).

b. Superconductivity in its simplest version - s-wave, singlet pairing of conduction electrons mediated by electron-phonon interaction - is counteracted by magnetic interactions. This has been well demonstrated by the depression of the superconducting transition temperature when magnetic impurities are introduced. The large variety of “magnetic interactions” has varying impacts on superconductivity. The clearest demonstration of its detrimental impact is the vanishing of the superconducting state when a superconducting metal enters a ferromagnetic state. This was demonstrated in 1977 by Matthias et al. for ErRh₄B₄ and by Ishikawa and Fischer for HoMo₈S₈.

The weakest known version of magnetism is caused by the interaction of nuclear magnetic moments. Hence, it was a natural question to investigate the impact of nuclear ferromagnetism on superconductivity. This investigation became possible when we had observed a nuclear ferromagnetic transition of the superconductor AuIn₂ at 35 µK in 1994. The results of the investigation of the interplay between nuclear ferromagnetism and superconductivity in AuIn₂ - some of it are not yet understood - will be described in Sect. 5. Further investigations of the impact of nuclear paramagnetism in AuAl₂, Al, Sn, AuIn₂, In, Rh, as well as TiH_2+x on superconductivity are discussed in Sect. 6. In Sect. 7, a first study of the interplay of hyperfine enhanced nuclear magnetism and superconductivity is presented. Eventually, in Sect. 8, we will summarize our results.

The experiments described in this article have been performed at the Forschungszentrum (formerly: Kernforschungsanlage) Jülich and at the University of Bayreuth

We present a planar large-area photoconducting emitter for impulsive generation of terahertz (THz) radiation. The device consists of an interdigitated electrode metal-semiconductor-metal (MSM) structure which is masked by a second metallization layer isolated from the MSM electrodes. The second layer blocks optical excitation in every second period of the MSM finger structure. Hence charge carriers are excited only in those periods of the MSM structure which exhibit a unidirectional electric field. Constructive interference of the THz emission from accelerated carriers leads to THz electric field amplitudes up to 85 V/cm when excited with fs optical pulses from a Ti:sapphire oscillator with an average power of 100 mW at a bias voltage of 65 V applied to the MSM structure. The proposed device structure has a large potential for large-area high-power THz emitters.

BaB₆ is a weakly ferromagnetic material with a Curie temperature TC well above room temperature. From the results of d.c. magnetization measurements on single crystalline BaB₆, the saturation magnetization at low temperatures is 8\times 10-4(\mu B/f.u.), in line with other weak ferromagnets of the hexaboride series. The ¹¹B-NMR spectra measured on a collection of single crystals of BaB₆ yield a quadrupolar frequency of 472 KHz, in good agreement with calculated field gradients for this type of materials. The central ¹¹B-NMR transition consists of two partially resolved signals, where the frequency displacement between them is of the order of 10 KHz. One of the signals exhibits a positive, the other a negative frequency shift, both of the order of 50 ppm. Between 7 K and room temperature these shifts do not vary with temperature. The temperature dependence of the spin-lattice relaxation rate T₁ ^-1(T) at the B sites is similar to that of other alkaline-earth hexaborides.

We report results of DC-magnetization and ¹¹B-NMR measurements on single crystalline YbB₆. The magnetization data at temperatures between 4 and 300 K reveal weak ferromagnetic order with a T _C>300 K. It involves very small ordered moments, of the order of 0.002 µ_B/f.u., representing only a small fraction of the effective paramagnetic moment per formula unit that is indicated by the magnetic susceptibility. The latter can be accounted for by assuming that 2% of all the Yb atoms adopt the Yb⁺³ configuration. Since almost all the Yb ions adopt the divalent configuration one expects YbB₆ to be a poor metal.

The state-of-the-art interpretation of physical processes during post-implantation annealing, such as defect evolution, transient-enhanced dopant diffusion and dopant activation, assumes that ion implantation produces only single vacancies and self-interstitials, and that these are the only mobile intrinsic defects. Theoretical investigations show that both assumptions may be not correct. The talk presents results of comprehensive atomistic simulations on the properties of di- and tri-interstitials. It is focused on the migration of these defects and on the atomic mechanisms of the defect diffusion. The results of the atomistic simulations are compared with experimental data. The fact that the simulations predict a high di-interstitial mobility may lead to a re-interpretation of some experimental results.

The thermal conductivities of stoichiometric CaB6, vacancy-doped Ca_1-B₆, and EuB₆have been measured between 6 and 300 K. All our data may be rather well described across the entire temperature regime covered on the basis of a Debye-type relaxation-time approximation and by assuming the concurring influence of various scattering channels on the mean free path of the phonons. An unusual and strong resonance in the scattering rate of the phonons of all investigated materials is attributed to a strong interaction between acoustic itinerant and localized modes, the latter arising from oscillations of the metal cations around their equilibrium position.

We report observation of the specific heat anomaly within the superconducting state of the heavy fermion CeCoIn₅. It appears in the vicinity of the superconducting critical field H _c2, where the superconducting transition changes from second to first order, above 10 T for H || [1 1 0] and H || [1 0 0], and above 4.7 T for H || [0 0 1], and at temperatures on the order of 0.1Tc. We interpret the anomaly within the superconducting state as a signature of a Fulde–Ferrell–Larkin–Ovchinnikov FFLO inhomogeneous superconducting state.

We present specific heat data for the heavy fermion superconductor CeCoIn₅ close to the upper critical field H _c2 for magnetic fields applied along the [1 0 0] crystallographic axis. For fields above 10 T, the superconducting phase transition becomes first-order. In the same field range, we observe a second specific heat anomaly within the superconducting state, which we attribute to a Fulde–Ferrell–Larkin–Ovchinnikov state.

Magnetic enhancement of superconductivity

The phase diagram of FeSi_1-xGe_x, obtained from magnetic, thermal, and transport measurements on single crystals, shows a discontinuous transition from Kondo insulator to ferromagnetic metal with x at a critical concentration, x _c ≈ 0.25. The gap of the insulating phase strongly decreases with x. The specific heat γ coefficient appears to track the density of states of a Kondo insulator. The phase diagram is consistent with an insulator-metal transition induced by a reduction of the hybridization with x in conjunction with disorder on the Si=Ge ligand site

We report specific heat measurements of the heavy fermion superconductor CeCoIn₅ in the vicinity of
the superconducting critical field H _c2, with magnetic fields in the [110], [100], and [001] directions, and at temperatures down to 50 mK. The superconducting phase transition changes from second to first
order for fields above 10 T for H ║ [110] and H ║ [100]. In the same range of magnetic fields, we observe
a second specific heat anomaly within the superconducting state. We interpret this anomaly as a
signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. We obtain similar results for H ║ [100], with the FFLO state occupying a smaller part of the phase
diagram.

We measured the specific heat and resistivity of heavy fermion CeCoIn₅ between the superconducting critical field _c2 = 5 T and 9 T, with the field in the [001] direction, and at temperatures down to 50 mK. At 5 T the data show a non-Fermi liquid (NFL) behavior down to the lowest temperatures. At the field above 8 T the data exhibit a crossover from the Fermi liquid to a non-Fermi liquid behavior. We analyzed the scaling properties of the specific heat and compared both the resistivity and the specific heat with the predictions of a spin-fluctuation theory. Our analysis leads us to suggest that the NFL behavior is due to incipient antiferromagnetism (AFM) in CeCoIn₅ with the quantum critical point in the vicinity of H_c2. Below H_c2 the AFM phase which competes with the paramagnetic ground state is superseded by the superconducting transition.

We have measured the magneto-optical Kerr rotation of ferromagnetic Eu_1-xCa_xB₆ with x=0.2 and 0.4, as well as of YbB₆ serving as the nonmagnetic reference material. As previously for EuB₆, we could identify a feature at 1 eV in the Kerr response which is related with electronic transitions involving the localized 4 f electron states. The absence of this feature in the data for YbB₆ confirms the relevance of the partially occupied 4 f states in shaping the magneto-optical features of Eu-based hexaborides. Disorder by Ca-doping broadens the itinerant charge carrier contribution to the magneto-optical spectra.

We have measured the optical reflectivity R(ω) of Eu_0.6Ca_0.4B₆ as a function of temperature (T) between 1.5 and 300 K and in external magnetic fields (H) up to 7 T. R(ω) increases with decreasing T and increasing H field, but the plasma edge feature does not exhibit the sharp onset and steep slope that is observed in EuB₆. The analysis of the H-field dependence of the low-T optical conductivity confirms the previously observed exponential decrease of the electrical resistivity upon increasing bulk magnetization at constant T. The individual exponential magnetization dependences of the plasma frequency and scattering rate are also extracted from the optical data.

We have combined the results of magnetization and Hall effect measurements to conclude that the ferromagnetic moments of lightly doped CaB₆ samples display no systematic variation with electron doping level.
Removal of the surface with acid etching substantially reduces the measured moment, although the Hall constant and resistivity are unaffected, indicating that the ferromagnetism largely resides on and near the sample surface. Electron microprobe experiments reveal that Fe and Ni are found at the edges of facets and growth steps, and on other surface features introduced during growth. Our results indicate that the weak ferromagnetism previously reported in undoped CaB₆ is most likely of extrinsic origin.

The specific heat and electrical resistivity of Sr₃Ru₂O₇ single crystals are measured in several magnetic
fields applied along the c axis for temperatures below 2 K and at fields up to 17 T. Near the critical metamagnetic
field at B ₁ ^*~7.8 T, the electronic specific heat divided by temperature increases logarithmically as the
temperature decreases, over a large range of T, before saturating below a certain T* (which is sample dependent),
indicating a crossover from a non-Fermi liquid (NFL) region dominated by quantum critical fluctuations
to a Fermi liquid (FL) region. This crossover from a NFL to a FL state is also observed in the resistivity data
near the critical metamagnetic field for I║c and B║c. The coefficient of electronic specific heat, γ, plotted as a
function of field shows two peaks, consistent with the two metamagnetic transitions observed in magnetization
and magnetic torque measurements. At the lowest temperatures, a Schottky-like upturn with decreasing temperature
is observed. The coefficient of the Schottky anomaly exhibits a field dependence similar to that of γ,
implying an influence by the electrons near the Fermi surface on the Schottky level splitting.

We have measured the thermal conductivity of the heavy-fermion superconductor CeCoIn₅ in the vicinity of the upper critical field, with the magnetic field perpendicular to the c axis. Thermal conductivity displays a discontinuous jump at the superconducting phase boundary below critical temperature T ₀≈1 K, indicating a change from a second- to first-order transition and confirming the recent results of specific heat measurements on CeCoIn₅. In addition, the thermal conductivity data as a function of field display a kink at a field H_k below the superconducting critical field, which closely coincides with the recently discovered anomaly in specific heat, tentatively identified with the appearance of the spatially inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state. Our results indicate that the thermal conductivity is enhanced within the FFLO state, and call for further theoretical investigations of the order parameter’s real-space structure (and, in particular, the structure of vortices) and of the thermal transport within the inhomogeneous FFLO state.

Upon substituting Ca for Eu in the local-moment ferromagnet EuB₆, the Curie temperature T_C
decreases substantially with increasing dilution of the magnetic sublattice and is completely suppressed
for x ≤0:3. The Ca substitution leads to significant changes of the electronic properties across the
Eu _x Ca_1-x B₆ series. Electron microscopy data for x ≈ 0.27 indicate a phase separation into Eu- and
Ca-rich clusters of 5 to 10 nm diameter, leading to percolation-type phenomena in the electrical
transport properties. The related critical concentration x _p is approximately 0.3. For x ≈ 0.27, we
observe colossal negative magnetoresistance effects at low temperatures, similar in magnitude as those
reported for manganese oxides.

We present a specific heat and resistivity study of CeIrIn₅ in magnetic fields up to 17 T and temperature down to 50 mK. Both quantities were measured with the magnetic field parallel to the c axis (H║[001]) and within the a-b plane (H┴[001]). Non-Fermi-liquid (NFL) behavior develops above 12 T for H║[001]. The Fermi-liquid state is much more robust for H║[001] and is suppressed only moderately at the highest applied field. Based on the observed trends and the proximity to a metamagnetic phase transition, which exists at fields above 25 T for H║[001], we suggest that the observed NFL behavior in CeIrIn₅ is a consequence of a metamagnetic quantum critical point.

At present, the GDT facility of the Budker Institute of Nuclear Physics Novosibirsk is being upgraded. The first stage of the upgrade is the Synthesized Hot Ion Plasmoid (SHIP) experiment. It aims, on the one hand, at the investigation of plasmas the parameters of which are expected to appear in the region of high neutron production in a GDT based fusion neutron source as proposed by the Budker Institute and, on the other hand, at the investigation of plasmas the parameters of which have never been achieved before in magnetic mirrors.
The experiment is performed in a small mirror section which is installed at the end of one side of GDT. The magnetic field on axis is in the range of 0.5-20 Tesla and the mirror ratio is 1.2-1.4. The mirror is filled with background plasma streaming in from the central cell. This plasma component is maxwellized and has an electron temperature of about 100 eV. Two neutral beam injectors perpendicularly inject a total current of about 50 Atom Amperes of deuterium neutrals with an energy of 20 keV
as a pulse with a duration of about 1 ms. Ionization of the beams generates the high-energy ion component. The device has been equipped with several diagnostic methods which are successfully used in GDT experiments.
The paper presents first results of plasma parameter measurements in the SHIP experiment.

Using magnetron sputter deposition a number of glass/Ta 7nm/PtMn 20nm/CoFe 4nm/Ta 4nm samples with large exchange bias field were prepared for magnetic pattering investigations. By means of optical lithography and physical etching several patterns with decreasing lateral sizes of either the elements or the spacing between the elements were prepared. The largest square is 50 x 50 µm2 and the smallest only 1 µm2. The separating lines range from 10 µm to 2 µm width. The magnetic characterization of the samples was done by VSM and MOKE. Kerr microscopy and MFM investigations in an applied magnetic field have been performed in order to get a deeper understanding of the domain pattern. All images show a monodomain magnetization state in zero magnetic field. The shape of the structure itself dose not influence the magnetization direction. The shape anisotropy contribution is thus smaller than the unidirectional anisotropy given by the exchange bias. In addition 5 keV He+ ion irradiation was used to decrease exchange bias field value and thereby modify the ratio between unidirectional and shape anisotropy. The magnetic domain structure is investigated as a function of this ratio.

The effect of magnetic fields on momentum and mass transfer in electrochemical processes has been studied by means of Digital Particle Image Velocimetry (DPIV), shadowgraphy and mean current
density measurements.

Chronoamperometric copper electrolysis was carried out in a small electrolytic cell (29x46x6 mm) made mainly from PMMA. The sidewalls forming the vertical electrodes consist of thin copper plates behind
which permanent magnets could be fixed. The Lorentz force generated from the faradaic currents and the permanent magnets field has been always parallel to the electrodes. Depending on the orientation of the magnets, downwards or upwards directed Lorentz forces could be generated.

The moderate magnetic field of permanent magnets placed behind the electrodes, although its action is limited to the vicinity of the electrodes, is able to promote convection in the whole cell. Flow
structures measured by DPIV compare very well with the patterns of the concentration field given by shadography. Steady state limiting current densities as well as initially instationary current density
values can be explained by the corresponding velocity measurements. It will be shown that the interplay of Lorentz and buoyancy forces is substantial for the resulting flow structure.

In recent experiments, on-axis transverse beta exceeding 0.4 in the fast ion turning points near the end mirrors has been achieved in the GDT experiment with 4 MW injection of 15-17 keV deuterium neutral beams at the center of the device. Neither enhanced transverse losses of the plasma nor anomalies in the fast ion scattering and slowing down were observed. The measured beta value is close to that needed in the versions of the GDT based 14 MeV neutron source. At the same time, the electron
temperature for given injection power and pulse duration is limited to 100-130 eV. Its further increase is planned after upgrading the injection system and increasing the magnetic field at the center of the device up to 0.3 T. The upgrade of the injection system assumes that the neutral beam power incident on the plasma will be increased up to 9-10 MW and the pulse duration is extended from 1.2 to 5 ms. According to the results
of numerical simulations, for the extended pulse duration
a plasma steady state will be achieved with electron temperature of 250-320 eV depending upon the assumptions on the transverse energy loss rate. Future experiments at the GDT upgrade are discussed in the paper.

The remarkable phenomenon of weak magnetization hysteresis loops, observed recently deep in the vortex-liquid state of a nearly two-dimensional (:213) superconductor at low temperatures and high magnetic fields, is shown to reflect the existence of an unusual vortex-liquid state, consisting of collectively pinned crystallites of easily sliding vortex chains.

We report on a detailed investigation of the pressure-dependent structural and electronic properties close to the pres-sure-induced metal-insulator transition of the quasi-two-dimensional organic superconductor beta"-(BEDT-TTF)₂SF₅CH₂CF₂SO₃, where BEDT-TTF stand for bisethylenedithio-tetrathiafulvalene (or ET for short). Although the pressure-dependent hysteresis of the metal-insulator transition suggests a structural origin, no major crystallo-graphic modifications could be detected by neutron-scattering experiments. Shubnikov-de Haas (SdH) experiments, on the other hand, show that a reconstructed band structure precedes the phase transition to the insulating state. A new SdH frequency with a rather small effective mass appears.

Electrical-transport measurements of the semimetal CeBiPt in magnetic fields up to 60 T reveal a drastic change of the electronic band structure. The oscillating Shubnikov-de Haas signal vanishes above about 25 T although the quantum limit is not yet reached. Above this field the magneto resistance rises strongly independent of angle and temperature. These unique features are caused by the Cc 4f electrons as evidenced by the absence of any unconventional behavior in the sister compound LaBiPt.

Theoretical calculations of rotating N approximate to Z nuclei with A = 58 - 80 within the cranked Nilsson+Strutinsky approach, cranked relativistic mean field and cranked relativistic Hartree+Bogoliubov theories show good agreement with experiment. They point on the presence of the isovector t = 1 np-pairing, but do not show any indications of the isoscalar t = 0 np-pairing.

Knowledge of the influence of nuclear shell structure on the survival probability of heavy compound nuclei against fission is important for a quantitative understanding of the production rates of spherical super-heavy elements (SHE). Fission probabilities of N = 126 isotones beyond astatine can be used as test cases for the production of spherical super-heavy elements, as those isotones possess a strong shell correction energy and are highly fissile. Here, we report on two new experimental approaches which probe the effect of the closed neutron shell at N = 126 on the competition between fission and particle evaporation using projectile fragmentation and electromagnetic-induced fission of radioactive beams. We conclude that these nuclei lose at least a great part of their stability against fission at low excitation energies and angular momenta-mostly due to the influence of collective contributions in the level density. Implications on the production of spherical SHE will be!
discussed.

We present new measurements of the Be-7(p,gamma)B-8 cross section from (E) over bar (cm) = 116 to 2460 keV. Our new measurements lead to S-17(0) = 22.1 +/- 0.6(expt) +/- 0.6(theor) eV b based on data from (E) over bar (cm) = 116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. We compare our results to other S-17(0) values extracted from both direct (Be-7(p, gamma)B-8) and indirect (Coulomb dissociation and heavy-ion reaction) measurements, and show that the results of these 3 types of experiments are not mutually compatible. We recommend a "best" value, S-17(0) = 21.4 +/- 0.5(expt) +/- 0.6(theor) eV b, based on the mean of all modern direct measurements below the 1(+) resonance.

Thin beta-FeSi2 layers have been prepared by ion beam synthesis (IBS) on (111)Si substrates. The obtained samples have been characterized by means of infrared and Raman spectroscopies. The infrared (IR) transmittance spectra show the absorption at 310 cm(-1) as an indication of the initial nucleation of beta-FeSi2 precipitates during the implantation of iron into silicon substrate. The main feature of the photoluminescence (PL) measurements at 12 K in the beta-FeSi2/(111)Si samples annealed at 850 degreesC for 90 min is an intense peak localized at 0.811 eV. This peak is assigned to optical radiative transitions intrinsic to beta-FeSi2. (C) 2004 Elsevier Ltd. All rights reserved.

Electrons confined in a flat semiconductor quantum dot with a parabolic in-plane potential act like a collective many-particle oscillator under coherent intraband excitation. We investigate theoretically the properties of these oscillators under a simultaneous scale transformation of the lateral dimensions and the electron occupation number. As the lateral size increases from a few nm (typical for self-assembled dots) to the mesoscopic regime, the physics of the system is changing qualitatively: Quantization effects gradually lose importance against Coulomb interactions and eventually the electron lake in a mesoscopic dot resembles a classical Wigner liquid. This parabolically confined "Wigner lake" behaves to the outside like a form-elastic "superparticle" of high charge. It can be coherently controlled by THz dipole radiation just like a single electron, but with reduced Brownian diffusion in the phonon heat bath. We propose a flexible method to fabricate single mesoscopic!
dots of a controlled shape, Coulomb-coupled groups of dots, and almost arbitrary potential landscapes, using current semiconductor technology. As a first example, the collective modes of two Coulomb-coupled superparticles in neighboring dots are calculated. Also, we consider the possibility of steering a superparticle with shaped laser pulses to follow any complex two-dimensional orbit.

We investigate numerically the transition to turbulence in a flat-plate boundary layer controlled by electromagnetic forces. The fluid considered is incompressible, Newtonian and low conductive. Similar to boundary layer suction, when applying a steady, wall-parallel, and streamwise orientated Lorentz force, (as suggested by Gailitis and Lielausis [1] in the early 1960s) the Blasius velocity profile is transformed to an exponential one gaining a critical Reynolds number which is increased by two orders of magnitude.

Two and three dimensional direct numerical simulation (DNS) of both linear and nonlinear stages of the transition process were performed, as well as alinear stability analysis (LSA) of the calculated intermediate velocity profiles. DNS and preliminary LSA results confirm the expected increased stability of the controlled flow. Depending on Lorentz force strength transition to turbulence is delayed or even stopped. Suprisingly, both DNS and LSA results suggest interesting stability characteristics of the intermediate velocity profiles.

In DNS, to initiate transition, small amplitude disturbances are introduced by means of an oscillating body force within a small region near the inflow boundary, forming Tollmien-Schlichting waves (TSW) which grow and decay in uncontrolled case corresponging to linear stability theory. When applying Lorentz force, TSW of all investigated frequencies 0.4 <= F+ <= 3.75 are damped within the computational domain extending over 900 times the inflow displacement thickness d1i. Reynolds number, based on d1i, is 360. The decay rate based on the maximum rms value in wall-normal direction of the streamwise velocity component, is maximum in a region near the onset of control and decreases as the velocity profile approaches the exponential state. This observation could suggest that in the intermediate region there are profiles more stable than the exponential one, although we are aware that from these decay rates one cannot conclude directly the stability of a velocity profile, notably its critical reynolds number. However, our assumption is confirmed by preliminary LSA results where critical Reynolds numbers of intermediate profiles are found to be larger than for the exponential profile.

By three dimensional DNS we show that transition to turbulence can be stopped even in it's late stage. While the evolution of Lambda vorticies from former two dimensional TSW remains almost unchanged, the emerge of Omega vorticies is supressed with increasing Lorentz force strength, thus relaminarizing the flow.

[1] A. Gailitis, O. Lielausis: On a possibility to reduce the hydrodynamic resistance of a plate in an electrolyte. Applied Magnetohydrodynamics, Reports of the Physics Institute Riga, Vol. 12, pp. 143-146, 1961

During reactive sputter deposition, target "poisoning", i.e. the formation of a compound layer at the target surface, may reduce the sputter erosion rate substantially and thereby represent a major limitation to achieve high deposition rates. In order to investigate the formation of the poisoned layer, the TRIDYN program has been employed to simulate the processes that take place at the target surface during sputtering at ion energies which are typical for a magnetron discharge, in a typical gas mixture of Ar with a small (<10%) addition of a reactive gas (e.g. oxygen). The bulk of the sputtering results from Ar ion bombardment, while the reactive gas ions contribute to compound formation due to implantation into the subsurface layer. In addition, reactive gas molecules are adsorbed on the surface and react with target metal atoms to add to the formation of the compound layer. Thus, both chemisorption and ion implantation of energetic reactive ions are the two main mechanism! s for the formation of the poisoned layer.TRIDYN simulations have been performed at varying reactive ion to total ion flux ratio, and at varying ion to reactive neutral flux ratio, for fluences which are sufficiently large to achieve a stationary deposition/erosion balance. The results illustrate that the two mechanisms will generate almost identical shapes of the poisoned layer. They also demonstrate the significance of recoil implantation from the chemisorbed layer for the formation of the compound layer. In agreement with experimental findings, the calculated sputter erosion rate of the target is predicted to decrease monotonically as the partial pressure of the reactive gas increases. The shape of the sputter erosion curve hardly changes between conditions dominated by ion implantation or chemisorption. We therefore conclude that ion implantation basically acts as an additional source of reactive atoms to the target surface.

Background
Bacteria play an important role in biogeochemical transformations and migration of uranium (U) in nature. In order to understand how U(VI) interacts with natural bacterial communities of U mining waste piles a series of microcosm experiments was performed.
Methods
Several portions of a solid sample collected from the U mining waste pile near the city of Johanngeorgenstadt in Germany were supplemented with different amounts of U(VI), starting from the original 40 mg U/kg up to 300 mg/kg.
The solubility of the U originally present and of the added U was assessed by selective sequential extraction (SSE). The composition of bacterial communities present in the original and in the supplemented with U samples was analyzed applying 16S rDNA retrieval by using 43F and 1404R degenerated primers.
Results
SSE analysis demonstrated that in the original sample the main part of uranium was strongly bound in mineral phases. The bacterial community of this sample was predominated by Alphaproteobacteria and by representatives of Holophaga /Acidobacterium phylum.
The bacterial community structure of the sample was noticeable changed by increasing its U content to 100 mg/kg . No Holophaga/Acidobacterium and only a few representatives of Alphaproteobacteria were retrieved in this sample. Instead, a large number of sequences of mainly Gamma-Pseudomonas, and of Arthrobacter sp. were found. The propagation of several populations of Deltaproteobacteria and especially of Geobacter sp. was induced in the sample as well. After 4 weeks of incubation, most of the U added to this sample was still only weakly complexed.
The bacterial community structure of the most contaminated sample, containing 300 mg U/kg, differed significantly from the two samples described above and depended on the aeration conditions during the incubation. In this sample the number of 16S rDNA sequences representing Cytophaga/Flavobacterium /Bacteroides group was extremely high. Arthrobacter sp. populations were also identified but not as strongly predominant.
Conclusions
The addition of U(VI) to a low contaminated U mining waste sample induces significant shifting in the indigenous bacterial populations. The effect of the added U(VI)seems to depend on its amount and on the redox conditions.

Background
Microorganisms strongly influence the migration of radionuclides in the environment. For this reason analysis of natural bacterial and archaeal communities near radioactive wastes deposition sites is of great importance for risk assessments. In this study diversity was studied of the microorganisms indigenous for a monitoring well near the radioactive waste injection site Tomst-7 in Siberia. In addition, interactions of several bacterial isolates from this site with uranium and other metals was investigated.
Methods
Microbial diversity was studied applying the 16S rDNA7F-1513F for bacteria and 16S rDNA21f-958R for archaea. The diversity of the autotrophic bacteria was estimated by direct analysis of different RubisCO gene forms. Oligotrophic bacteria were cultured in low nutrient R2A medium. Interactions of the cultured bacterial isolates with U, Ni, Pb, As, and other metals were studied by using ICP-MS, flow cytometry and X-ray spectroscopic analyses.
Results
Our analyses demonstrated presence of a large number of diverse bacterial and archaeal groups at a depth of about 300m at the Siberian depository site Tomsk-7 where the radioactive wastes were injected. The most predominant bacterial populations were those of Betaproteobacteria mainly from the Rhodocyclus group, of Citophaga/Flavo-bacterium/Bacteroides, and of several novel “Cyanobacteria-like” groups. The RubisCO approach confirmed the Betaproteobacterial predominance in the samples studied.
Bacterial isolates were cultured from the samples belonging to Sphingomonas sp., Brevundimonas sp., Methylobacter sp., and a large microdiverse group of Actinobacteria closely related to Microbacterium oxydans. They tolerated U and other heavy metals in a species- and even strain-specific way. EXAFS analyses demonstrated that the isolates of Microbacterium sp. and of Sphingomonas sp. are complexing U(VI) at pH 4.5 via phosphorus (P) in a form of meta-autunite. The latter was connected to the liberation of inorganic phosphate by these strains due to their exo-phosphatase activity. At lower pH values the U is bound to organic phosphate residues.
Conclusions
The environment around the radioactive waste injection site Tomsk-7 possesses a large variety of microorganisms with a potential to bind and possibly transport radionuclides.

Deep level defects E1/E2 were observed in He-implanted, 0.3 and 1.7 MeV electron-irradiated n-type 6H-SiC. Similar to others' results, the behaviors of E-1 and E-2 (like the peak intensity ratio, the annealing behaviors or the introduction rates) often varied from sample to sample. This anomalous result is not expected of E-1/E-2 being usually considered arising from the same defect located at the cubic and hexagonal sites respectively. The present study shows that this anomaly is due to another DLTS peak overlapping with the E-1/E-2. The activation energy and the capture cross section of this defect are E-C-0.31 eV and sigma similar to 8 x 10(-11) cm(2), respectively.

Lorentz forces on the suction side flow of NACA 0015 and PTL IV hydrofoils is investigated experimentally. Emphasis is placed on separation control. Steady as well as time periodic Lorentz forces will be discussed. Their effect is compared mainly in respect of the attainable increase of the maximum lift and in terms of power consumption.

I will discuss two recent advances related to semiconductor light sources in the infrared and THz regions. One example is a quantum cascade laser operating at a wavelength shorter than 4 microns above room temperature with high peak power. It is based on strained InGaAs/InAlAs on InP, with the addition of high barriers of pure AlAs for better confinement and strain compensation. In a novel few-cycle THz emitter we try to combine the advantages of the high electric bias field in photoconductive antennas with a large active area. This is achieved with an interdigitated electrode structure, partially covered in order to mask one field polarity. As a result no destructive interference of the emitted THz wave occurs, which allows upscaling of the device area.

Recent developments at the Dresden High Magnetic Field Laboratory

We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.

The radiosynthesis and the radiopharmacological evaluation of pyrazolo steroid 2´-(4-fluorophenyl)-21-[¹⁸F]fluoro-20-oxo-11β,17α-dihydroxy-pregn-4-eno[3,2-c]pyrazole [¹⁸F]-2 is described. The radiolabeling was accomplished in 3 - 4 % decay-corrected radiochemical yield within 80 min at an specific radioactivity of 0.8-1.2 Ci/μmol. Biodistribution studies in male Wistar rats showed an initial brain uptake of 0.25 ± 0.03 % ID/g after 5 min, which remained constant over 60 min. The radiopharmacological evaluation of compound [¹⁸F]-2 was completed with autoradiography using rat brain sections and micro-PET imaging.

Further developments for the Dresden High Field Laboratory

In order to design and optimize pulsed field coils, their current leads, and in particular their reinforcement, we currently test commercial Finite Element software of various suppliers. We concentrate on these programs which have implemented so called "multiphysics modules" which are able to solve combined problems as they typically occur in high field techniques: e.g. calculation of the magnetic field from a current distribution along with the resulting Lorentz forces, stresses, dislocations etc.. In detail, we focus on the programs ANSYS, ANSOFT, as well as FEMLAB. We like to give a brief survey of their usefulness, perspectives, and last but not least, of their cost.

In the frame of the high field project Dresden, a new building to be constructed at the research center Rossendorf is in its design phase. The HLD building will be located near the IR-free electron lasers of the superconducting linear accelerator ELBE in order to provide the possibility of IR spectroscopy in high pulsed magnetic fields. Following the present plans, five magnet cells for pulsed magnets, preparation rooms, a lab for superconducting magnets and four labs for accompanying experiments are located around a central room which houses the capacitor bank. In addition, a workshop, stores, and a technical section on one side, as well as the offices for stuff and guests and a control room on the other side are located in separate sections. We present the plans emphasising the ability and the safety items in order to get your feedback.

The novel 2-mercaptoimidazolde derivatives, 1-[4-((2-methoxyphenyl)-1-piperazinyl)-butyl]-2-mercaptoimidazolde (3) and methyl[4-((2-methoxyphenyl)-1-piperazinyl))butyl] (2-mercapto-1-methylimidazol-5-yl)methanamide (8), were efficiently labelled with ¹¹C through methylation of the thioketone function with [¹¹C]methyl iodide. The resulting radioligands 1-[4-((2-methoxyphenyl)-1-piperazinyl))butyl]-2-thio[¹¹C]-methylimidazole ([¹¹C]9) and methyl [4-((2-methoxyphenyl)-1-piperazinyl))butyl] (2-thio[¹¹C]methyl-1-methylimidazol-5-yl)-methanamide ([¹¹C]10) were synthesized in radiochemical yields of 20 - 30 % (decay-corrected, related to [¹¹C]CO₂) at a specific radioactivity of 0.2-0.4 Ci/μmol within 40-45 min including HPLC-purification. The radiochemical purity exceeded 99 %. The reference compounds 9 and 10 were tested in a competitive receptor binding assay to determine their affinity toward the 5-HT_1A recptor. Both compounds exhibit excellent sub-nanomolar affinities (IC₅₀ = 0.576 ± 0.008 nM (9); IC₅₀ = 0.86 ± 0.02 nM (10)) for the 5-HT_1A receptor while displaying a high selectivity towards the 5-HT_2A subtype of receptors (IC₅₀ > 480 nM). By contrast, compound 9 also shows substantial binding for the alpha-adrenergic receptor (IC₅₀ = 3.00 ± 0.02 nM) when compared with compound 10 (IC₅₀ = 54.5 ± 0.6 nM). Preliminary biodistribution studies in rats showed an initial brain uptake of 1.14 ± 0.11 and 0.37 ± 0.04 % ID/g after 5 min, which decreased to 0.18 ± 0.04 and 0.16 ± 0.01 % ID/g after 60 min for compounds [¹¹C]9 and [¹¹C]10, respectively. For both compounds, the cerebellum and rest of the brain uptake are very similar at the different time points. Unlike [¹¹C]9, the radioligand [¹¹C]10 has significant uptake and retention in the adrenal glands. Due to their washout from the brain compounds [¹¹C]9 and [¹¹C]10 seem not to be good condidates as radioligands for imaging 5-HT_1A receptors by PET.

A new facility for experiments in pulsed high magnetic fields is under construction at the Forschungszentrum Rossendorf in Dresden, Germany. Its heart will be a modular 50 MJ / 24 kV capacitor bank in a new laboratory. In order to offer a wide spectrum of experimental possibilities, pulsed field coils are planned in the parameter range 60 T, 50 mm, 1s to 100 T, 20 mm, 0.01 s for maximum field, bore, and pulse duration. Experience in the construction of the pulsed capacitive power supply as well as in the experimental equipment has been gained from a pilot laboratory at the IFW since 1999. The pulsed magnets will be complemented by commercial superconducting magnets for dc fields up to 20 T. Besides many other experimental possibilities, as a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible in pulsed fields by connecting the pulsed field lab to the new free-electron-lasers of the neighbouring superconducting electron linear accelerator ELBE of the FZR.
The laboratory building will be completed in 2004. The 50 MJ power supply can be partly used in 2005 and will be fully operational by 2006. First pulsed test coils have already been built and will be tested in 2004 by the 1.44 MJ / 24 kV pilot power supply manufactured at FZR. The user coils as well as the experimental equipment will be installed in 2006, so that the facility can open its doors as a user laboratory in 2007.

* The HLD project has been jointly submitted for funding by the FZR, the Leibniz-Institut für Festkörper- und Werkstoffforschung IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the Technische Universität Dresden. It is jointly funded for installation by the Bundesministerium für Bildung und Forschung of Germany and the Sächsische Ministerium für Wissenschaft und Kunst in the years 2003 to 2006.

We present measurements of the dc magnetization M(B) of van Vleck paramagnets, e.g. PrNi₅, at high magnetic fields up to B = 60 T. At low fields up to 10 T, we observe magnetizations which increase linearly with the applied field. Beyond 10 T, the magnetizations start to become nonlinear as the result of the shifts of the energy levels of the crystalline electrical field (CEF) states of the 4f-Pr³⁺ electrons through the external field. A significant change of slope of the magnetization M(B) as well as of the corresponding susceptibility dM/dB occurs in PrNi5 at B = 20 T which can be explained by a level crossing of the two lowest singlet CEF states. We compare our data to calculations from a point charge model.

We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.

We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.

Since the first experimental finding of a competition between nuclear magnetism and superconductivity in the nuclear ferromagnet AuIn2, investigations have been extended to Al, Sn, Rh, In, AuAl₂, and very recently to Pr_1-xLa_xTe. The experiments have demonstrated that the contribution of nuclear magnetism to Cooper pair breaking is a common phenomenon. Even in a system with tiny nuclear magnetic moments (e.g. Sn), a reduction of the critical field B_c(T) has been detected at ultralow temperatures. In more detail, the observed influences of nuclear magnetism on superconductivity vary strongly with the size of hyperfine coupling, ranging between a tiny reduction of B_c(T) in the case of weak hyperfine coupling (AuAl₂) and the complete destruction of superconductivity in the opposite case of strongly coupled and hyperfine enhanced nuclear spin systems (e.g. Pr_0.50La_0.50Te). The hyperfine interaction appeares to be the dominant mechanism for the nuclear magnetic contribution to Cooper pair breaking.

In the course of our investigation of the heavy fermion compound CeCu₆,
we have recently performed measurements of the heat capacity as well as elastic neutron diffraction down to ultralow temperatures. In the last decade, various groups have investigated this compound by means of susceptibility, magnetization, nuclear quadrupole resonance, and thermal expansion as well. There is a strong evidence for a magnetic ordering transition at about 2.5 mK. Here we like to present our latest heat capacity data taken at 0.1 mK ≤ T ≤ 100 K as well as neutron diffraction data taken down to 15 mK. These results give further
hints for magnetic correlation effects in CeCu₆.

We have investigated the strongly correlated electronic and nuclear magnetic properties of the cubic Van Vleck paramagnets PrS, PrTe, and PrBi by means of SQUID magnetometry at 2 K≤T≤300 K as well as ac susceptometry at ultralow temperatures, 0.06 mK≤T ≤100 mK. We observe magnetic ordering transitions of the hyperfine enhanced magnetic moments of the ¹⁴¹Pr nuclei in all three compounds. Our ac susceptibility data taken at ultralow temperatures point to antiferromagnetic ground states. The observed Neel temperatures, T_N(PrS, PrTe, PrBi) = 0.09, 0.60, 1.20 mK, scale with the size of the Van Vleck susceptiblity and related hyperfine enhancement factor respectively. The nuclear fcc spin-5\2 antiferromagnets PrS, PrTe, and PrBi are promising candidates for interesting spin structures. Currently we use the metallurgical possibility to substitute Pr by La and Pb in these compounds in order to study the multiple interplay between electronic magnetism, nuclear magnetism, superconductivity (e.g. in Pr_1-xLa_xTe), and semiconductivity (e.g. in Pr_1-xPb_xTe).

Compared to magnetically doped superconductors described by the theory of Abrikosov and Gorkov, electronic singlet ground state systems can have a much larger critical concentration of magnetic impurities, following the model of Keller and Fulde. The recent study of the superconducting Van Vleck paramagnet La_{1-x}Pr_xTe revealed a critical Pr^{3+} concentration x close above 0.50. Surprisingly, in La_{0.50}Pr_{0.50}Te the superconducting state with T_c = 0.20 K appeares not to be stable down to zero temperature. Instead, a reentrant transition to the normal state likely caused by the hyperfine enhanced magnetic moments of the ^{141}Pr nuclei occurs at about 0.02 K. Although these moments are not in a magnetically ordered ground state at T = 0.02 K, their contribution to Cooper pair breaking seems to be even stronger than of ferromagnetically ordered but non enhanced nuclear moments in type-I superconducting AuIn₂.

We have measured the ac susceptibility and resistivity of highly pure samples of the intermetallic compound LaCu₆ down to ultralow temperatures. We have prepared the samples by arc melting of stoichiometric amounts of 99.99\% La and 99.9999\% Cu in a water-cooled copper crucible under Ar protective atmosphere and analysed them by x-ray diffraction and SQUID magnetometry. At T≤T_c = 0.16 K we observe a superconducting transition. Due to the manifold physical properties of isostructural ReCu₆ compounds (e.g. RE = Ce: heavy fermion system, RE = Pr: hyperfine enhanced nuclear spin system, RE = Nd: electronic antiferromagnet), numerous studies of interplay phenomena may become possible in the quasibinary compounds RE_1-xLa_xCu₆, respectively.

Die Internationale Länderkommission Kerntechnik (ILK) hat 2004 eine Stellungnahme zur Bewertung der Nachhaltigkeit der Kernenergie und anderer Technologien zur Stromerzeugung vorgelegt.
Die Bewertung beruht u. a. auf der Quantifizierung von Indikatoren, wie etwa die Produktionskosten oder die CO-2-Emission, die verschiedene Nachhaltigkeitsaspekte charakterisieren und der Aggregation dieser Indikatoren zu einem einzigen Nachhaltigkeitskennwert für jede der betrachteten Energieoptionen.
Die Aggregation kann beispielsweise über den Totalkostenansatz oder mit Hilfe der Multikriteriellen Entscheidungsanalyse (MCDA) erfolgen. Die beiden Verfahren führen in der Regel zu unterschiedlicher Nachhaltigkeitsbewertung. Dies liegt zum einen daran, dass einige der Indikatoren finanziell nicht fassbar sind und deshalb im Totalkostenansatz nicht berücksichtigt werden. Zum anderen sind bei der Aggregation mit Hilfe der MCDA Wichtungsfaktoren für Einzelindikatoren und die "Nachhaltigkeitssäulen" Wirtschaft, Umwelt, Gesellschaft festzulegen. Bislang stehen keine Leitlinien für die Fixierung dieser Gewichtungen zur Vefügung. Der Vortrag stellt die genannten Aggregationsverfahren vor und diskuiterit dann Vor- und Nachteile.

The present paper discuss the posibility to obtain information about the field flatness of a 1.5 cell normal conducting RF gun cavity during the running of the gun. By measurements of the microwave network parameters at room temperature and by measurement of the passband frequencies in the running regime of the gun it is possible to estimate the perturbation of field flatness, caused by an inhomogeneous temperature distribution.

N,N-Dimethyl-2-(2-amino-4-methylthiophenylthio)benzylamine (SMe-ADAM, 1) was found to be a highly potent and selective inhibitor of the serotonin transporter (SERT). This compound was labelled with carbon-11 by methylation of the S-desmethyl precursor 10 with [¹¹C]methyl iodide to obtain the potential positron emission tomography radiotracer [¹¹C]SMe-ADAM. Radiochemical yield was 27  5 % and the specific radioactivity was 26 – 40 GBq/µmol at the end of synthesis . Ex vivo and in vivo biodistribution experiments in rats demonstrated a rapid accumulation of the radiotracer in brain regions known to be rich in SERT, such as the thalamus/hypothalamus region (3.59 ± 0.41 %ID/g at 5 min after injection). This is the highest brain uptake ever reported for this type of radiotracer in rats. The specific uptake reached a thalamus to cerebellum ratio of 6.74 ± 0.95 at 60 min post injection. The [¹¹C]SMe-ADAM uptake in the thalamus was significantly decreased by pre-treatment with fluoxetine to 45 ± 9 % of the control values. Furthermore, no metabolites of [¹¹C]SMe-ADAM could be detected in the SERT rich regions of the rat brain. It is concluded that [¹¹C]SMe-ADAM may be a suitable PET ligand for SERT imaging in the living brain.

The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC magnetic field was examined. The magnetic field lines were aligned either in longitudinal or in transverse direction. The magnetic field strength was chosen up to 0.3 T corresponding to magnetic interaction parameters N of 1.5. The experiments were carried out in the following parameter range: 2500 < Re < 5500, 2 < Eo < 7, Mo = 2.4e-13. The liquid metal was in a cylindrical container at rest. The Ultrasound Doppler Velocimetry (UDV) was applied to determine bubble and liquid velocities simultaneously. The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. Within the present interaction number range (N < 2), the applied magnetic field can either increase or decrease the bubble drag coefficient depending on the bubble size and the magnetic interaction parameter. Moreover, significant modifications of the bubble wake structure were observed. Raising of the magnetic field strength causes an enlargement of the eddy structures in the wake. In case of the longitudinal magnetic field the Strouhal number St decreases with increasing magnetic interaction parameter.

In order to improve the microstructure of casting ingots a rotating magnetic field (RMF) is widely used to stir the liquid phase during solidification. Usually, the interaction between the solidification process and the RMF driven flow has been discussed only in terms of the flow pattern well-known from the laminar, isothermal case being a superposition of a primary swirling flow in azimuthal direction and a secondary flow occurring as a double vortex in the r-z plane. Effects arising from the propagation of the solidification front, the extension of the mush zone or the spin-up of the flow at higher cooling rates are almost not taken into account. We present experimental and numerical investigations concerning the influence of a RMF driven flow on the momentum, heat and mass transfer within a binary Sn-Pb alloys solidified directionally.
Solidification experiments were carried out using a Sn-15wt%Pb alloy in a cylindrical mold positioned on a water-cooled copper chill. The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow during solidification. The temperature field was monitored using thermocouples. The set-up was enclosed by an inductor providing the RMF. The Taylor numbers Ta were varied between 10e5 and 10e8.
The continuum formulation based model has been adopted for numerical simulations using the following assumptions: all transport properties, such as thermal and electrical conductivity or viscosity, are assumed to be constant; the density of solid phase equals the density of liquid phase; the phases are in local thermodynamic equilibrium; the velocity of solid phase in the upper part of the mushy zone is equal to the velocity of the liquid phase. The mushy region is modeled using a mixture viscosity formulation. The Lorentz force in the Navier-Stokes equation has been calculated by means of an analytical solution for the time-averaged Lorentz force for a finite cylinder. The resulting set of eqiuations is discretized by an implicit finite-volume, finite-difference based method, and solved by using the SIMPLE algorithm.
Our results show that the velocity field undergoes distinct modifications during solidification indicating the occurrence of more sophisticated flow patterns as known from the isothermal case.

Dendritic oxybathophenanthroline ligands (generation 0 to 3) have been synthesized by treatment of 4,7-bis(4´-hydroxyphenyl)-1,10-phenanthroline with the corresponding Fréchet-type dendrons carrying a benzylic bromide function at the focal point. The complexation of copper(II) has been studied by liquid-liquid extraction using the radioisotope ⁶⁴Cu and time-resolved laser-induced fluorescence (TRLFS) measurements in organic media proving the formation of 1:3 complexes (Cu : dendritic ligand). The stability of the copper complexes is mainly determined by the 1,10-phenanthroline core element. The stability constants of the 1:3 complexes were found to be in the order of log K ~ 16 in CHCl₃. On the other hand, increasing generation of the dendritic Fréchet-type branches leads to enhanced shielding of the copper ion from the environment. Additional information about this behaviour was obtained by the fluorescence lifetimes which are much less influenced upon addition of copper(II) salt to solutions of the higher generation ligands.

Mixing in stirred vessels of different density liquids is common operation in the process industry. The hydrodynamic behaviour of such a system could be crucial for the overall process performance. The aim of this work is to numerically predict the dynamics of the mixing process of initially stratified system of two different density liquids. Stratified conditions could occur in the stirred vessel, especially in the case of impeller malfunctioning, i.e. impeller breakdown. This effect might prove to be of significant importance, particularly in the case of reacting liquids for large-scale reactors operating in the industry.
The CFD analyses were performed for a non-baffled stirred vessel reactor, mechanically agitated by the Pfaudler impeller. The two main cases of passive and reactive tracer mixing behaviour were numerically predicted by the means of the CFD software CFX 5.7. In both cases the system of two miscible liquids with different densities was dynamically predicted in 3D from an initially stratified to a complete mixing condition. The full 3D simulation was applied in order to capture the flow instabilities associated with the impeller blade passage, especially pronounced in the first few seconds after the impeller start. In order to study the effect of the free surface deformation on the mixing process, the gas phase was also involved into the system via the free surface model. The different density liquids were comprised into the liquid phase by the means of the multicomponent model. In the case of the reactive tracer mixing, the alkali was diluted in the lighter liquid. The simulations were performed on different grids in order to obtain grid independent results.
The accuracy of the numerical simulations was evaluated experimentally using video visualisation technique. The lighter (alcoholic) coloured component and the heavier (water) transparent one which were initially stratified were brought into motion by the rotating impeller. In the case of the passive tracer mixing, the alcoholic phase was coloured by blue dye whereas in the case of the reactive mixing a phenolphthalein indicator was applied. The mixing process was captured by a digital camcorder and subsequently the images were digitally processed. The mixing of different initial lighter phase concentrations was visually investigated to obtain the colour calibration curve. The numerical predictions were evaluated against several locations, close to vessel central line and wall, for which the optical distortion was minimal.

Die Grignard-Chemie erlebt eine Renaissance bei der industriellen Herstellung neuer pharmazeutischer Wirkstoffe, Lebensmitteladditive und Feinchemikalien. Sicherheitsprobleme können aufgrund der sehr großen Exothermie und der hohen Reaktivität der Grignard-Reagenz beim Scale-up in den großtechnischen Maßstab auftreten. Die Hauptgefahrenquelle ist das spontane Starten der Grignard-Reaktion, wenn bereits eine kritische Menge an organischem Halogenid akkumuliert ist, und dann die durchgehende Startreaktion durch den starken Druckanstieg zur Stofffreisetzung führt. Die genaue Bestimmung der reaktionstechnischen Prozessparameter zur Auslegung des Kühlsystems für das Produktions-Betriebsregime wird an einem ge-schlossenen Reaktionskalorimeter mit integriertem in-situ FTIR-Spektrometer für eine industrielle Grignard-Reaktion beschrieben. Weiterhin werden Möglichkeiten zur Detektion des Reaktionsstarts und zur Verfolgung der Halogenid-Akkumulation vorgestellt. Durch den Einsatz der in-situ FTIR-Spektroskopie läßt sich einerseits der Re-aktionsstart eindeutig detektieren, andererseits können sowohl der Verbrauch des organischen Halogenids als auch der Aufbau der Grignard-Reagenz in Echtzeit überwacht werden. Neben den Online-Konzentrationsmessungen können an einem geschlossenen Rührkesselreaktor auch die steilen Anstiege der Reaktortemperatur und des Druckes sowie die Wärmebilanz zum Nachweis des Reaktionsstarts genutzt werden. Durch Online-Konzentrationsmessungen und/oder Wärmebilanzmessungen ist es außerdem möglich, das Einschlafen der Hauptreaktion durch Verunreinigungen zu erkennen und das spätere Wiederstarten zu verhindern. Darüber hinaus konnte nachgewiesen werden, daß im geschlossenen Reaktionskalorimeter die reaktionstechnischen Parameter, wie Induktionszeit, Dauer des Startprozesses und Reaktionsenthalpie, wesentlich genauer als im offenen Reaktor gemessenen werden können. Ferner werden Untersuchungen dieser Grignard-Reaktion im adiabatischen Reaktionskalorimeter (PhiTecII) diskutiert, das auch zur Dimensionierung von Notentlastungssystemen dienen kann.

A non-baffled stirred vessel reactor was investigated computationally with CFX-5 numerical package. The mixing of two miscible liquids with different densities was dynamically predicted from an initially stratified to a complete mixing condition. Although for a non-baffled vessel an axi-symmetric behaviour can be expected, the process was regarded as three dimensional in order to demonstrate the local instabilities associated with the blade passage. Additionally, the gas phase was involved into the simulations to investigate the effect of the free surface deformation on the mixing process. The two-phase gas-liquid interactions were modelled using the free surface model. The different density liquids were comprised into the liquid phase by the means of the multicomponent model. The grid elements size was kept relatively low because of the dynamic behaviour of the liquid surface central vortex. Furthermore, the available turbulence models were considered to obtain the closest possible match with the experimental observations. In such a way, the stirred vessel hydrodynamics was dynamically calculated in 3-D in order to study the effect of the density difference.
The numerical simulations were evaluated experimentally using video visualisation technique. The lighter (alcoholic) coloured component and the heavier (water) transparent one, which were initially stratified, were brought into motion by the means of the rotating impeller and the mixing process was captured by digital camcorder and subsequently the images were digitally processed. Several points, close to vessel central line and wall, for which the optical distortion was minimal were considered for evaluation of the numerical predictions.
The hydrodynamics of the above described system is of particular concern for many chemical and biochemical reactions engineered to take place in stirred vessel reactor. Although the initial conditions were to some extend idealised in order to avoid some complications raised by the presence on an injection, the studies showed strong influence on the density difference on the homogenisation. Such so called idealised conditions, however, also might occur in the stirred vessel, especially in the case of impeller malfunctioning. In case of impeller stoppage, i.e. breakdown, different density liquids present in the vessel might get stratified. This effect might prove to be of significant importance, especially in the case of reacting liquids for large-scale reactors operating in the industry.

Seit 10 Jahren wird in Deutschland das Programm "Sonne in der Schule" durchgeführt. An mehr als 1000 Schulen wurden dabei netzgekoppelte Photovoltaik-Anlagen errichtet. Im Beitrag werden die erreichten Betriebsergebnisse dieser Anlagen dargestellt. Darüber hinaus wird auf die Nutzung der Anlagen im Unterricht eingegangen.

The formation of a thin strained Si layer on top of a strain-relaxed SiGe buffer is a recent approach to improve the drive current of complementary metal-oxide-semiconductor devices by inducing strain within the transistor channel. At the same time, advanced process technologies require junction formation processes with minimal diffusion and very high dopant activation. Solid-phase epitaxial regrowth is a low temperature process based on preamorphization and subsequent regrowth leading to highly activated and shallow junctions. In this letter, we investigate the stability of the thin strained Si layer, during solid-phase epitaxial regrowth process by monitoring the Ge redistribution/strain after the preamorphization step (without any anneal) and after the thermal regrowth process.

The Institute of Safety Research of the Forschungszentrum Rossendorf, Germany, has developed electrode-mesh sensors, which allow the measurement of the electrical conductivity distribution in a flow duct. This can be used either for the detection of the gaseous phase in a gas-liquid flow or for mixing studies in single phase flow, when the components have different electric conductivities. Due to the high measuring rate each bubble is mapped in several successive instantaneous frames. This allows to obtain bubble size distributions as well as bubble-size resolved gas fraction profiles beside the visualisation and the calculation of profiles of the time-averaged void fraction. The sensor is widely used to study the evolution of the flow pattern in an upwards air-water flow. The experiments aim at closure equations describing forces acting on bubbles as well as coalescence and fragmentation frequencies for the implementation in CFD-codes. Some other prominent examples of the application of wire-mesh sensors were given, like (1) boiling water reactor stability studies, (2) the visualization of cavitation at fast-acting cut-off valves, (3) the visualization of the flow structure behind a closing globe valve, and finally (4) mixing studies in single-phase flow at the ROCOM test facility in Rossendorf, which are aimed at the mixing of deborated slugs during boron dilution transients.

Second subject of the paper is radiation tomography. A gamma-tomography setup for imaging a periodically changing density field is described. It is based on a time-resolved acquisition of the detector signals. It was used to visualize the gas fraction distribution within the impeller of an axial turbo-pump operating at about 1500 rpm, that delivered a gas-liquid mixture, as well as to a hydraulic clutch (coupling). In the field of X-ray tomography, the status of the development of an ultra-fast system based on a scanning electron beam is presented. An electron beam is linearly deflected over a tungsten target with a frequency of 1 kHz. X-rays generated by the traveling focus penetrate the object and arrive at a detector line placed behind the object. The detectors are read-out with a sufficiently high speed in order to obtain projections of the density distribution in different projecting directions, which change thanks to the scanning. First results showing tomographic image sequences of a phantom consisting of small spheres kept in arbitrary motion in a cylindrical test box will be presented. Moving spheres of 3 mm diameter with cylindrical holes of 1 mm diameter were resolved at a framing rate of 1 kHz.

Der Vortrag plädiert für einen Mix aus Atomenergie und erneuerbaren Energien, um die Versorgung für die Zukunft sicher zu stellen. Kernkraftwerke sind ebenso wirtschaftlich, wie heute die Energiegewinnung aus fossilen Brennstoffen, jedoch mit wesentlich geringeren Stoffströmen verbunden: Der Ertrag aus der Spaltung von einem Kilogramm Uran 235 oder Plutonium 239 entspricht dem aus der Verbrennung von rund 2800 Tonnen Steinkohle. Dies ist die Stärke der Kernenergie, denn dadurch ist sie die einzige Primärenergiequelle, bei der die Abfälle vollständig erfasst und geordnet entsorgt werden können. Unrealistisch ist die Vorstellung, Deutschland könne seinen Energiebedarf bis 2050 zur Hälfte aus regenerativen Quellen decken. Speichermöglichkeiten sind begrenzt, weshalb bei idealen Witterungsbedingungen Überkapazitäten auftreten würden, die nicht verwertet werden könnten. Bei einer Flaute oder bedecktem Himmel wiederum müsste Strom importiert oder beispielsweise aus fossilen Kraftwerken eingespeist werden. Beides würde den ohnehin schon hohen Strompreis aus diesen Quellen in unvertretbare Höhen treiben. Weiterhin betrachtet werden die Verfügbarkeit von Spaltmaterial, der erreichte Stand bei der Sicherheit der Kernkraftwerke sowie die Endlagerproblematik.

Gefährlich, riskant, umweltschädigend, gesundheitsschädlich, unverantwortbar, unwirtschaftlich, unsozial, nicht nachhaltig - das sind Adjektive, mit der die Nutzung der Kernenergie zur Stromversorgung häufig belegt wird. Tatsächlich tragen die Kernkraftwerke jedoch stabil zur kostengünstigen Stromversorgung bei. In Deutschland haben sie einen Anteil von 30 %, in einigen Ländern mehr. Unter dem Eindruck spürbar anwachsender Brennstoffpreise bei den fossilen Energieträgern und immer deutlicher werdender Folgen der Klimaveränderungen mehren sich die Stimmen, die eine Renaissance der Kernenergie für notwendig halten. In einer solchen Situation ist es wichtig, die Potenzen der Energiegewinnung durch Kernspaltung zu kennen und die wichtigsten Behauptungen der Kernenergiegegner kritisch zu hinterfragen. Speziell für Deutschland wird ein Blick auf die gängigen Konzeptionen zur Energiestrategie der nächsten 50 Jahre geworfen. Letztendlich wird der Schluss gezogen, dass langfristig ein Umsteuern auf einen Mix aus nuklearen und regenerativen Energiequellen erfolgen muss, um zu einer nachhaltigen und ökonomisch, sozial und ökologisch vertretbaren Energieversorgung zu gelangen.

The turbulence of the liquid phase has a signi cant dispersion e ect on the migration of bubbles in a vertical ow. Based on a double averaging approach and by adopting the Favre averaged velocity, a generalized model, called the Favre Averaged Drag (FAD) Model, was developed for the turbulent dispersion force for Eulerian simulations of multiphase ows [Burns et al., 2004]. The model formulation was originally derived from the instant Eulerian model equations as a result of the correlation between the inter phase drag and the volume fractions. In this work, a new model derivation from the two-way coupled Lagrangian formulation is provided. This derivation makes the sense of the double averaging approach straightforward. Moreover, the new derivation provides a theoretical foundation for applying the FAD model to the Lagrangian solver, which will signi cantly increase the computational e ciency. We also provide validation and evaluation for this model by numerical and experimental investigations of bubbly ows in a vertical pipe. The experimental data were obtained by using the wire-mesh sensor technique. The computations were carried out by applying poly-dispersed models. The emphasis is to examine the model applicability under various ow conditions including bubbly ows with a wall peak and a core peak of the gas volume fraction, ows in the transition region between them, and in the nely dispersed ow regime. The e ect of the drag force model on the turbulent dispersion force was also examined.

This paper reports about the DYN1D-MSR code development and dynamics studies of the molten salt reactors (MSR) – one of the ‘Generation IV International Forum’ concepts. In this forum the graphite-moderated channel type MSR based on the previous Oak Ridge National Laboratory research is considered.
The liquid molten salt serves as a fuel and coolant, simultaneously and causes two physical peculiarities: the fission energy is released predominantly directly into the coolant and the delayed neutrons precursors are drifted by the fuel flow. The drift causes the spread of delayed neutrons distribution to the non-core parts of primary circuit and it can lead to a reactivity loss or gain in the case of fuel flow acceleration or deceleration, respectively. Therefore, specific 3D tool based on in house code DYN3D was developed in FZR. The code DYN3D-MSR is based on the solution of two-group neutron diffusion equation by the help of a nodal expansion method and it includes models of delayed neutrons drift and specific MSR heat release distribution.
In this paper the development and verification of 1D version DYN1D-MSR of the code is described. The code has been validated with the experimental data gained from the molten salt reactor experiment performed in the Oak Ridge and after the validation it was applied to several typical transients (overcooling of fuel at the core inlet, reactivity insertion, and the fuel pump trip).

Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. At the Institute of Safety Research of the FZR a finite element model has been developed simulating the thermal processes and the viscoplastic behaviour of the vessel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal hydraulic and the mechanical calculations are sequentially and recursively coupled. The model is capable of evaluating fracture time and fracture position of a vessel with an internally heated melt pool. The model was applied to pre-and post test calculations for the FOREVER test series of the KTH Stockholm. First calculations for a PWR geometry were performed to work out differences and commonalities between prototypic scenarios and scaled experiments.

General information on the ISTC program are given. The working procedures of the CEG-SAM are explained and the currently running ISTC projects related to SAM are presented in brief.

Due to their abilities for complex and colloid formation as well as their redox properties, humic acids influence the migration of actinides in the environment. Therefore, risk assessments, related to the behavior of actinides in the environment, require basic knowledge on the interaction of humic acids with metal ions. Thus, the interaction of humic acids with actinides is studied, e.g., the Np(V)-humic acid-complexation and the redox stability of uranium(VI) humate complexes, applying synthetic and natural humic acids.

We report on the first analysis of directed and elliptic flow with the new method of Lee-Yang zeroes. Experimental data are presented for Ru+Ru reactions at 1.69A GeV measured with the FOPI detector at SIS/GSI. The results obtained with several methods, based on the event-plane reconstruction, on Lee-Yang zeroes, and on multi-particle cumulants (up th 5th order) applied for the first time at SIS energies, are compared. They show conclusive evidence that azimuthal correlations between nucleons and composite particles at this energy are largely dominated by anisotropic flow.

Turbulence dispersion has a significant dispersion effect on the migration of bubbles in a vertical flow. Based on a double averaging approach and by adopting the Favre averged velocity, we developed the Favre Averaged Drag (FAD) turbulent dispersion force model for Eulerian simulations of multiphase flows. The model formulation was originally derived from the instant Eulerian model equations as a result of the correlation between the interphase drag and the volume fractions. In this work, a new model derivation from the two-way coupled Lagrangian formulation is provided. This derivation explains the physical mechanism and makes the sense of the double averaging approach straightford. Moreover, the new derivation provides a theoretical foundation for applying the FAD model to the Lagrangian solver, which will significantly increase the computational efficiency.

We also provide a systematic model evaluation based on numerical simulations of bubbly flows in a vertical pipe using both mono- and poly-dispersed flow models. The numerical results for the radial distribution of the gas concentration were compared with the experimental data measured by using the wire-mesh sensor technique. The results confirm that the bubble size and the liquid flow Reynolds number have a strong effect on the turbulent dispersion as is shown in the model derivation.

The aim of this work is to characterize the complexation ability of F-, BF4 -, PF6 -, and Tf2N- toward uranyl ions in aqueous solution. These anions were chosen as they represent the anionic part of the most studied roomtemperature ionic liquids. Time-resolved emission spectroscopy and X-ray absorption spectroscopy were used to retrieve structural data on the complexes formed. The results obtained were compared with computational data.
Tf2N- does not complex uranyl, even at high concentration. Other fluorinated acids form inner-sphere complexes with U(VI), in a monodentate fashion in the case of BF4 and PF6.

In this contribution, results of predictive atomistic computer simulations are presented which describe the ion beam synthesis of single-crystalline CoSi2 nanowires (NWs) embedded in Si. In order to simulate the Co implantation, the binary collision codes TRIDYN and TRIM were adapted to the particular experimental situation of a finely focused Co ion beam of a few tens of nanometers in width. The resulting 3D implantation profile serves as input for a kinetic lattice Monte-Carlo code by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are described.
Due to the systems tendency towards a reduction of interfacial free energy (Rayleigh instability), it will be demonstrated that the orientation of the Co implantation profile to the Si matrix influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the CoSi2(111)/Si(111) interface, faceting forces occur if the Co implantation profile is not aligned with the Si-[011] direction. Thus, intentional misalignment is a possible way to a controlled decay of the NW into a chain of monodisperse and equidistant nanoclusters which is applicable as plasmon waveguide.

The presentation discusses the application of X-ray micro-tomography to the measurement of size, shape and porosity of polymer particles.

In nondestructive testing (NDT) of microelectronic components many applications using X-ray radiography are well established. This method is based on the attenuation of radiation intensities of x-rays transmitting an object. Computer tomography (CT), however, is a visualization method which is based on reconstructing three-dimensional models from several two-dimensional X-ray projections of the object. It is only recently used for NDT because it is more expensive and time consuming than conventional X-ray imaging. Nevertheless, there are applications where simple radiography provides only poor results because of superimposed object layers. This article discusses NDT specific problems of CT such as beam hardening and shows some microelectronic applications benefiting from CT as well as examples where modifications of the standard CT procedure are necessary to gain depth information about the object. This so called limited angle tomography reaches a higher image resolution than CT when flat modules are tested.

We introduce a new method to noninvasively and continuously measure the swelling process of the nasal mucosa. Thereby we use light of different wavelengths in the near infrared range which is transilluminated through the nasal tissue and whose extinction is recorded as a function of time. From the temporal and spectral extinction data we are able to extract characteristic parameters that describe the swelling process quantitatively by means of a regression type parameter estimation algorithm. Furthermore, we show the capability of the method to quantify hemoglobin saturation in the surplus blood volume and introduce a bilateral measurement approach that allows us to examine the swelling process in both nasal cavities simultaneously. The method has been applied to the nasal allergen provocation test and verified on a limited number of volunteers.

The presentation discusses the application of conventional X-ray CT, X-ray cone beam CT and ultrafast limited angle X-ray CT to the measurement of phase distributions in multiphase flow problems.

Hexapotassium dihydrogen monotitanoundecatungstocobaltate(II) tridecahydrate, K₆H₂[TiW₁₁CoO₄₀]×13H₂O, crystallizes from aqueous solution in the cubic space group P43m. The structure was refined as an inversion twin. The [TiW₁₁CoO₄₀]^8- anion has a Keggin structure with one W-atom site occupied by titanium and a central tetrahedral CoO₄ group.

I will discuss two recent advances related to semiconductor light sources in the infrared and THz regions. One example is a quantum cascade laser operating at a wavelength shorter than 4 microns above room temperature with high peak power. It is based on strained InGaAs/InAlAs on InP, with the addition of high barriers of pure AlAs for better confinement and strain compensation. In a novel few-cycle THz emitter we try to combine the advantages of the high electric bias field in photoconductive antennas with a large active area. This is achieved with an interdigitated electrode structure, partially covered in order to mask one field polarity. As a result no destructive interference of the emitted THz wave occurs, which allows upscaling of the device area.

Humic acids (HA) comprise an important part of natural organic materials. Due to their interactions with organic and inorganic pollutants produced by human activity, they play a significant role in biochemical cycles of ecosystems. By the formation of soluble anionic complexes with the range of more or less toxic metals, including radionuclides, HA can affect the transport of these contaminants. Therefore, the understanding of their impact on the actinide migration in geologic environments is essential for a reliable safety assessment of nuclear waste disposal sites. In the present study the influence of HA on the U(VI) sorption onto kaolinite was studied. Kaolinite represents a well-defined model substance for clay-rich host formations.
Batch experiments were combined with EXAFS spectroscopy to obtain molecular-level information on the interaction of U(VI) with HA (14C-labeled HA) and kaolinite (KGa-1b).
Three kinds of batch experiments were performed under different experimental conditions: HA sorption in the absence of U(VI), U(VI) sorption in the absence and U(VI) sorption in the presence of HA. The sorption curves have shown that the U(VI) sorption on kaolinite is influenced by experimental conditions such as pH, U(VI) concentration, CO2 and HA presence. U(VI) sorption increases with pH up to pH 8.5, then it decreases. In the absence of CO2, no decrease is observed. In the presence of CO2 HA effects U(VI) adsorption onto kaolinite over the entire pH range. At pH < 5 the presence of HA enhances the U(VI) uptake relative to the HA-free system because the adsorbed HA forms additional binding sites for U(VI). In the pH range between pH 5 and pH 8.5 the U(VI) sorption decreases in the presence of HA due to desorption of HA from the kaolinite surface resulting in the formation of dissolved U(VI)-HA complexes. At pH > 8.5 uranium sorption increases again relative to the HA-free system (Fig.1).
We performed EXAFS measurements with U(VI)-HA-kaolinite sorbates in order to characterize the surface complexes of U(VI) in the presence of HA. Results of the spectroscopic measurements are interpreted and compared with the EXAFS results in the binary system without HA [1] to obtain information on the influence of HA on the near-neighbor surrounding of U(VI) in the kaolinite surface complexes.

[1] Amayri et al.: EXAFS - Untersuchungen zur U(VI) - Sorption an Kaolinit, presentation on BMWA Project Meeting, Saarbrücken, May 2004.

The TRIDYN collisional computer simulation has been modified to account for emission of ionic species and molecules during sputter depth profiling, by introducing a power law dependence of the ion yield as a function of the oxygen surface concentration, and by modelling the sputtering of monoxide molecules. The results are compared to experimental data obtained with dual beam TOF-SIMS depth profiling of ZrO2/SiO2/Si high-k dielectric stacks with thicknesses of the SiO2 interlayer of 0.5, 1, and 1.5 nm. Reasonable agreement between experiment and computer simulation is obtained for most of the experimental features, demonstrating the effects of ion-induced atomic relocation, i.e. atomic mixing and recoil implantation, and preferential sputtering. The depth scale of the obtained profiles is significantly distorted by recoil implantation and the depth-dependent ionization factor. A pronounced double peak structure in the experimental profiles related to Zr is not explained by the computer simulation, and is attributed to ion-induced bond breaking and diffusion, followed by a decoration of the interfaces by either mobile Zr or O.

The GRS methodology to assess the uncertainty of the calculation results of computer simulation codes was applied to the coupled code system DYN3D/ATHLET, consisting of a 3D neutron kinetic core model and a thermal hydraulic system code. It was used to make a statistical analysis of the result parameters from the output data of the DYN3D/ATHLET-calculation. A number of variation calculations with randomly distributed input parameters within given boundaries was carried out. On that basis, time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations.

The polarization dependence of U L1 edge EXAFS spectra is relatively simple because the photoelectron is excited from ground state (l = 0) to one excited state (l = 1). By contrast, the polarization dependence is more complicated at the L2 and L3 edges were the photoelectron is excited from p ground state into final states s (l = 0) and d (l = 2). The EXAFS expression of L2 and L3 edges comprises here pure s, pure d and coupled s-d states. The polarization effect at the U L1 and L3 edges was investigated using a single crystal of Ca[UO2PO4]2•6H2O. The high symmetry in the equatorial shell allows to compare successful the measurements with the theory. In a second part two types of applications will be discussed. It will be shown, that powder samples have a texture which can lead to an erroneous determination of coordination numbers. A use of the magic angle allows to avoid this problem. A second example will be discussed where the polarization dependency can be used to determine the orientation of actinyl ions sorbed at mineral surfaces.

Lecture on the present status of ion irradiation in exchange bias systems.

Risk assessments of actinide-contaminated soils and sediments require detailed knowledge of actinide speciation and its long-term kinetics. Former Saxonian mine tailings, which have been covered but else left undisturbed, are ideally suited to study changes in uranium speciation over timescales of decades. We investigated the major uranium species in two samples from buried mine tailings using a combination of Synchrotron-based microfocus-techniques (μ-XRF, μ-XRD with micrometer resolution), bulk EXAFS spectroscopy, and chemical extractions.
In sample F1 (5 m depth, oxic, pH 8, U=440 mg/kg, high Ca, S, Pb, Cu, Zn concentrations), uranium is diffusely distributed among aggregates of layer silicates (muscovite, illite and kaolinite). The chemical extractions and EXAFS results confirm that uranium is sorbed to these minerals, but is not incorporated into their crystal structure. Sorption is also in line with the high pH and low carbonate concentrations in pore water. In sample F3 (12 m depth, oxic, pH 4, U=430 mg/kg), the combination of μ-XRF and μ-XRD enabled us to identify several U(IV) and U(VI) containing minerals like coffinite, uraninite, uranyl hydroxide, and vanuralite. Only a minor part of U is sorbed to layer silicates as confirmed by chemical extractions and EXAFS spectroscopy.
At smaller depth (F1, 5 m), sulfuric acid from the ore extraction procedure was completely neutralized by the construction waste used as cover material, resulting in precipitation of jarosite and gypsum. Even 30 years after the ore extraction, uranium remains highly soluble. At greater depth (F3, 12 m), the low pH from ore extraction was conserved. The presence of U(IV) minerals suggest either precipitation of secondary (IV) minerals due to microbial redox activity, or incomplete dissolution of primary (IV) minerals due to ore processing inefficiency of these older sediments. The U(IV) minerals were recalcitrant during chemical extractions, suggesting low uranium solubility even at oxic redox conditions. The results demonstrate a very high variability of uranium speciation and hence potential mobility, which seems to depend on geochemical parameters and site history, but shows little influence of time.

The light meson dilepton identification in the HADES detection system is based on an invariant mass reconstruction of their decay into e⁺e^- pairs. Methods of the dilepton signal reconstruction in the HADES spectrometer and preliminary dilepton spectra for C+C reactions at 2 AGeV are presented in this paper. In the signal reconstruction particularly important is the reduction of the huge combinatorial background arising from wrong combinations of electrons and positrons into un-like sign pairs. A purity of the dilepton signal is determined by using GEANT simulation with the full HADES geometry and a realistic detector response.