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S Fritzsche

Publications and source records attributed to S Fritzsche.

At least 19 recordsLinked to original sources
PubMed2006

First measurement of the linear polarization of radiative electron capture transitions.

For radiative electron capture into the K shell of bare uranium ions, a study of the polarization properties has been performed. For this purpose a position sensitive germanium detector has been used as an efficient Compton polarimeter. This enabled us to measure the degree of linear polarization by analyzing Compton scattering inside the detector and to determine the orientation of the polarization plane. Depending on the observation angle and the beam energy used, the radiation is found to be linearly polarized by up to 80%. In all cases studied, the plane of polarization coincides with the collision plane. The results will be discussed in the context of rigorous relativistic calculations, showing that relativistic effects tend to lead to a depolarization of the radiation emitted.

Journal Article↗
PubMed2006

Optimal binding site of a methane molecule on the silanol covered (010) surface of silicalite-1: ONIOM calculations.

The binding energies and the corresponding structures of a methane molecule on the silanol covered (010) surface of silicalite-1 have been investigated using ab initio methods. Different levels of calculations, HF/6-31G(d), MP2/6-31G(d) and ONIOM (MP2/6-31G(d):HF/6-31G(d)) including the correction of an error due to an unbalance of the basis set, known as basis set super position error (BSSE), as well as the size of the cluster representing the silicalite-1 surface, were systematically examined to validate the model used. The ONIOM method with the BSSE correction was found to be a compromise between accuracy and computer time required. The optimal binding site on the silicalite-1 surface was observed at the configuration where the methane molecule points one H atom toward the O atom of the silanol group. The corresponding binding energy is -1.71 kJ/mol. This value is significantly higher than that of -5.65 kJ/mol when the methane molecule approaches the center of the straight channel. At this configuration, the C atom of methane was observed to locate exactly at the center of the channel. This leads to the conclusion that the methane molecule will relatively seldom be adsorbed on the silanol covered (010) surface of silicalite-1. Instead, the adsorption process will take place directly at the center of the straight channel.

Journal Article↗
PubMed2006

Be I isoelectronic ions embedded in hot plasma.

The influence of plasma screening on the 2s(2 1)S0-->2s2p(3)p(0)1 intercombination and the 2s(2 1)S0-->2s2p(1)p(0)1 allowed transitions is investigated theoretically for several ions along the isoelectronic sequence (C III, N IV, O V, Si XI, Fe XXIII, and Mo XXXIX). For the case of a weakly coupled hot plasma, multiconfiguration Dirac-Fock computations have been carried out for these ions by considering a (time averaged) Debye-Hückel potential for both the "electron-nucleus" and "electron-electron" interaction. The plasma screening is found to enlarge the 2s(2 1)S0-->2s2p(3)p(0)1 excitation energy uniformly along the Be I isoelectronic sequence, leading to an increasing blueshift of this intercombination line as the nuclear charge is increased. For the 2s(2 1)S0-->2s2p(1)p(0)1 resonance line, in contrast, the transition energy is either blueshifted or redshifted in dependence of the screening parameter and owing to a cancellation of the plasma screening on the electron-nucleus and electron-electron interaction. This interplay of the (external) plasma screening with the internal interactions in the berylliumlike ions leads, for instance, to a shift of the resonance transition from red to blue in going from O V to Si XI ions. Apart from the screening effects on the transition energies, we also investigate their influence on the oscillator strengths and emission rates along the Be I isoelectronic sequence.

Journal Article↗
PubMed2006

Concomitant down-regulation of SPRY1 and SPRY2 in prostate carcinoma.

Sprouty proteins encoded by the SPRY genes act as modulators and feedback inhibitors of signalling by epidermal growth factor (EGF) and fibroblast growth factor (FGF). Overactivity of EGF and FGF signalling common in prostate cancer might therefore be exacerbated by Sprouty down-regulation. Indeed, down-regulation of SPRY1 and SPRY2 expression has been independently reported. We found both genes modestly down-regulated by microarray expression analysis of microdissected prostate cancers and by quantitative RT-PCR in macrodissected specimens compared with benign tissues. Importantly, the decreases paralleled each other and expression levels of both genes were significantly lower in cancers that recurred within the average follow-up period of 32 months. In contrast to a previous report, no hypermethylation was found to accompany down-regulation of SPRY2 in cancer tissues and cell lines. We additionally investigated the expression of an SPRY1 alternative transcript presumed to be specific for fetal tissues and found its expression moderately well correlated with expression of the standard transcript through diverse tissues and cell lines. The present study confirms and extends previous reports by demonstrating concomitant down-regulation and a significant association with recurrence of SPRY genes.

Cell Line, Tumor↗
PubMed2005

Concentration dependence of the methane structure in silicalite-1: a molecular dynamics study using the Møller-Plesset-based potential.

Møller-Plesset perturbation-based potentials have been used in molecular dynamics simulations to examine methane diffusion in silicalite-1. The simulation box contains 2 unit cells of silicalite-1 and varying loading numbers (n(ld)) from 1, 2, 3, to 4 methane molecules per intersection, corresponding to 8, 16, 24, and 32 molecules per simulation box, respectively. Consistent with the previous study, a preferential diffusing path for methane is close to the channel axes. The structure of the methane molecules in the silicalite-1 pore was exhibited in terms of the methane-methane radial distribution function (RDF) in which the first peak appears at 6.4 A for n(ld) < or = 2, becomes a broad maximum at n(ld) = 3, and splits into two sharp peaks centered at 6.4 and 8.6 A at n(ld) = 4. This fact can be clearly described by an intensification of the methane density in the straight and zigzag channels but a decrease in the intersection when the loading increases. These features of the observed RDFs are in contrast with the previous report using a molecular dynamics force-field potential in which the RDFs for all concentrations show first maxima at approximately 4 A. The analysis of the relative residence times of methane at different sites inside the silicalite suggests that the zigzag channel is the most favored location. The computed self-diffusion coefficients as well as the heat of adsorptions are in reasonable agreement with the available values.

Journal Article↗
PubMed2005

Structure and energetics of water-silanol binding on the surface of silicalite-1: quantum chemical calculations.

Quantum mechanical calculations have been carried out to investigate the structural properties and the interaction between water molecules and silanol groups on the surface of silicalite-1. The (010) surface, which is perpendicular to the straight channel, has been selected and represented by three fragments taken from different parts of the surface. Calculations have been performed using different levels of accuracy: HF/6-31G(d,p), B3LYP/6-31G(d,p), HF/6-31++G(d,p), and B3LYP/6-31++G(d,p). The basis set superposition error has been taken into account. The geometry of the silanol groups and that of the water molecules have been fully optimized. The results show that the most stable conformation takes place when a water molecule forms two hydrogen bonds with two silanols, with only one silanol lying on the opening of the pore of the straight channel. The corresponding binding energy is -48.82 kJ/mol. These areas are supposed to be the first binding sites which have to be covered when the water molecule approaches the surface. When the water loading increases, the next favorable silanols are those of the opening of the pore in which the four possible complex conformations yield a binding energy between -25.62 and -37.41 kJ/mol. It was also found that the calculated O-H bond length of the silanol in the free form was slightly shorter than that in the complex. In terms of the stretching frequency, the complexation leads to a red shift of the O-H stretching of the silanol group.

Journal Article↗
PubMed2003

High precision wavelength measurements of QED-sensitive forbidden transitions in highly charged argon ions.

We present the results of an experimental study of magnetic dipole (M1) transitions in highly charged argon ions (Ar X, Ar XI, Ar XIV, Ar XV) in the visible spectral range using an electron beam ion trap. Their wavelengths were determined with, for highly charged ions, unprecedented accuracy up to the sub-ppm level and compared with theoretical calculations. The QED contributions, calculated in this Letter, are found to be 4 orders of magnitude larger than the experimental error and are absolutely indispensable to bring theory and experiment to a good agreement. This method shows great potential for the study of QED effects in relativistic few-electron systems.

Journal Article↗
PubMed2003

First observation of atomic levels for the element fermium (Z=100).

The atomic level structure of the element fermium was investigated for the first time using a sample of 2.7x10(10) atoms of the isotope 255Fm with a half-life of 20.1 h. The atoms were evaporated from a filament and stored in the argon buffer gas of an optical cell. Atomic levels were sought by the method of resonance ionization spectroscopy using an excimer-dye-laser combination. Two atomic levels were found at wave numbers (25 099.8+/-0.2) and (25 111.8+/-0.2) cm(-1). Partial transition rates to the 5f(12)7s(2) (3)H(e)(6) ground state have been determined from their saturation characteristics. Multiconfiguration Dirac-Fock calculations suggest that the leading orders of these levels could be the 5f(12)7s7p (5)I(o)(6) and 5f(12)7s7p (5)G(o)(5) terms.

Journal Article↗
PubMed2003

Doppler-free resonant Raman auger spectroscopy of Ne+ 2s2p(5)3p excited states.

Using very high resolution achieved by the Doppler-free resonant Raman Auger technique, we have resolved the lowest terms of the series of inner-valence excitations 2s2p(5)((1,3)P)np 2S, 2P, and 2D in Ne+. The measured Auger anisotropic parameters and branching ratios help to establish the assignments of these levels. The measured lifetime widths are in reasonable agreements with ab initio calculations available in the literature.

Journal Article↗
PubMed2002

Lyman- alpha(1) decay in hydrogenlike ions: interference between the E1 and M2 transition amplitudes.

For the Lyman- alpha(1) transition (2p(3/2)-->1s(1/2)) in hydrogenlike ions an interference between the leading E1 decay channel and the much weaker M2 multipole transition gives rise to a remarkable modified angular distribution of the emitted photons from aligned ions. This effect is most pronounced for the heaviest elements but results in a still sizable correction for medium- Z ions. For the particular case of hydrogenlike uranium where the angular distribution of the Lyman- alpha(1) x rays following radiative electron capture has been measured, the former variance with theoretical findings is removed when this E1-M2 interference is taken into account.

Journal Article↗
PubMed1994

[Reduction of NMR image artefacts by using optimal materials as diagnostic aids and implants].

Differences in magnetic susceptibility, as occur for example at the boundary between implant materials and the surrounding body tissue, result in artefacts and a signal loss in magnetic resonance imaging. By using materials with a magnetic susceptibility matched to the respective environment, it is possible to minimize both artefacts and signal loss. Such materials can be made by combining two materials of different magnetic susceptibility (e.g. diamagnetic and paramagnetic materials) in such a way that the resulting material has the desired effective magnetic susceptibility.

Artifacts↗
PubMed1988

[Pathogenetic role of the dependence potential of drugs of the hypnotic and tranquilizer type with special reference to the iatrogenic factor].

The author considers dependency on hypnotics/sedatives and tranquilizers as a complex phenomenon in which the main emphasis is placed on the potential for becoming dependent on medicines (self-inducing drugs), that is, their contribution to causing the development of the illness. Personality structure and social factors can play a favourable role here. From this the danger of iatrogenia (the practice of over-subscribing) can arise. The phenomena of cross tolerance and rebound are considered. With respect to therapy the leading role of psychotherapeutic practices, above all, group therapy is emphasized.

Humans↗
PubMed1988

[Correlation of physical and psychological aspects in alcohol and drug dependence].

Dependence to alcohol and drug must be consistently viewed as the consequence of a combination of physical and psychological elements. This is substantiated both philosophically and by taking issue with dualist concepts as well as those which absolutize the psychological aspect. The medical definition of dependence as an illness should be adhered to, whilst at the same time recognizing that psychological and social factors play a determining role.

Alcoholism↗