Showing papers by "Paul Scherrer Institute published in 1994"

Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists

Abstract: A laser writing system for the fabrication of continuous-relief micro-optical elements in photoresist is described. The technology enables a wide range of planar micro-optical elements to be fabricated and replicated into polymer film using Ni shims electroformed from the photo-resist originals. The advantages and limitations of laser writing technology for micro-optics fabrication are discussed. Examples of fabricated micro-optical elements include Fresnel microlenses and microlens arrays, kinoforms, and other continuous-relief phase elements.

[11C]raclopride and positron emission tomography in previously untreated patients with Parkinson's disease Influence of L‐dopa and lisuride therapy on striatal dopamine D2‐receptors

Abstract: We studied cerebral dopamine D2-receptor binding using [11C]raclopride and PET in 18 previously untreated patients with Parkinson's disease (PD) and 14 healthy volunteer subjects. Sixteen patients were scanned before and after 3 to 4 months of stable oral therapy with either L-dopa (300 mg/d) (n = 7) or lisuride (0.8 to 1.2 mg/d) (n = 9). Two additional patients were investigated before and after a continuous IV infusion of L-dopa. In addition, we studied the effect of acute IV L-dopa and lisuride administration on [11C]raclopride binding in a healthy rhesus monkey. At baseline, PD patients showed higher uptake values in the putamen than did healthy subjects (p < 0.0001). Oral lisuride treatment lowered [11C]raclopride uptake in the putamen (-19%) and in the caudate nucleus (-15%) compared with baseline, but the difference did not reach significance upon Bonferroni correction for multiple comparisons. However, putamen tracer uptake returned to baseline in two patients when we repeated [11C]raclopride scans 4 days after lisuride withdrawal. Oral L-dopa treatment did not induce changes in the putamen or caudate nucleus indices. Acute lisuride (25 micrograms) administration in a healthy monkey reduced striatal uptake values, but acute injection of L-dopa (300 mg) did not. The results suggest that lisuride blocks [11C]raclopride binding at dopamine D2-receptor sites and demonstrate that 3 to 4 months' oral therapy with L-dopa or lisuride does not change striatal dopamine D2-receptor density in PD patients.

Superconductivity in a quasi-one-dimensional spin liquid.

Abstract: The single-rung [ital t]-[ital J] ladder is analyzed in a mean-field theory using Gutzwiller renormalization of the matrix elements to account for strong correlation. The spin-liquid (resonance valence bond) state at half-filling evolves into a superconducting state upon doping. The order parameter has a modified [ital d]-wave character. A lattice of weakly coupled ladders should show a superconducting phase transition.

Cation exchange membranes by pre-irradiation grafting of styrene into FEP films. I: Influence of synthesis conditions

Abstract: Gamma radiation-induced grafting of styrene into FEP films was investigated by the pre-irradiation method. The degree of grafting was found to be strongly dependent on the synthesis conditions, such as radiation dose, monomer concentration, crosslinker, temperature, and film thickness. The order of dependence of the rate of grafting on pre-irradiation dose and monomer concentration was found to be 0.64 and 1.90, respectively. The activation energy for the grafting in the temperature range of 50–80°C was determined to be 27.9 kJ/mol. A negative first order dependence of grafting on film thickness was observed. The results suggest that the initial grafting takes place at the film surface and proceeds to the middle by progressive diffusion of monomer through the polystyrene grafted layers. © 1994 John Wiley & Sons, Inc.

Multiple Coulomb scattering and spatial resolution in proton radiography.

Abstract: A simple formula for the spatial resolution of transmission proton radiography is derived for two different methods of measuring the proton coordinates. The effect of multiple Coulomb scattering and energy loss are taken into account. Experimental measurements of the spatial resolution have been done and are compared with the calculations. The technique of measuring entrance and exit coordinates in coincidence for each single proton improves the spatial resolution by a factor of 8 compared to a single coordinate measurement.

AC losses of superconducting high-Tc multifilament Bi-2223/Ag sheathd tapes in perpendicular magnetic fields

Abstract: We have measured at 4.2 K and partly also at 77 K the hysteresis and coupling losses of three different superconducting c -axis oriented Bi-2223/Ag multifilament tapes. The inter- and intragranular contributions to the hysteresis losses were analyzed and their dependence on d B /d t was investigated. The penetration field of a very flat filament was calculated. We could separate the measured coupling losses from the also d B /d t dependent hysteresis losses. Further we calculated the geometry dependence of the coupling losses of a very flat multifilament tape. The measured coupling losses can be described by a general scaling law with a generalized frequency ωτ. A skin-effect-like behavior has been found for ωτ>1 and AC loss saturation occurs for large AC field amplitudes.

Evolution of the electronic and geometric structure of size-selected Pt and Pd clusters on Ag(110) observed by photoemission.

Abstract: Mass-selected ${\mathrm{Pt}}_{\mathit{n}}$ and ${\mathrm{Pd}}_{\mathit{n}}$ (n=1\char21{}15) clusters, generated by ion bombardment, are deposited at room temperature in submonolayer quantities on an Ag(110) single-crystal surface and characterized by electron spectroscopy (x-ray-photoemission spectroscopy and ultraviolet photoemission spectroscopy). The monodispersed clusters indicate individual discrete electronic structure features of the Pt 5d and Pd 4d emission. For the monomers virtual bound-state formation as in dilute (3%) PtAg and PdAg alloys is observed. With increasing cluster size, first, the increasing splitting between the bondinglike and antibondinglike d states reflects the increase in cohesive energy due to molecular interaction and second, the shift of the center of gravity of the d emission towards the Fermi energy indicates the trend to metal formation. The Pt 4f and Pd 3d core levels show practically no shift with increasing cluster size indicating a two-dimensional cluster structure. Total-energy calculations, performed within this study using the embedded-atom method, suggest a chain structure for small ${\mathrm{Pt}}_{\mathit{n}}$ (n=1\char21{}7) and ${\mathrm{Pd}}_{\mathit{n}}$(n=1\char21{}17) clusters on the Ag(110) surface, lying along the [1\ifmmode\bar\else\textasciimacron\fi{}10] direction.

Preoperative and postoperative glucose consumption in mesiobasal and lateral temporal lobe epilepsy.

Abstract: We have studied 25 patients with interictal 18 F-fluorodeoxyglucose ( 18 F-FDG) positron emission tomography (PET) before and after selective surgery for temporal lobe epilepsy (TLE). Based on the findings of the presurgical evaluation, including ictal intracranial EEGs, histopathologic findings, and the postoperative outcome, we classified the patients in three subgroups: (1) patients with TLE of lateral temporal origin (n = 5), (2) patients with mesiobasal limbic TLE associated with mesial gliosis (n = 14), and (3) patients with mesiobasal limbic TLE and small mesial tumors (n = 6). Postoperatively, patients with mesiobasal limbic TLE and mesial gliosis and five of six patients with mesiobasal limbic TLE and mesial tumors were seizure-free; the remaining sixth patient had one generalized seizure. Patients with TLE of lateral temporal origin had more than 90% reduction of seizure frequency. The main postoperative metabolic findings were as follows: (1) marked increase of regional cerebral metabolic rate of glucose (rCMRglu), both in the ipsilateral and, significantly, in the contralateral hemisphere in patients with mesiobasal limbic TLE and mesial gliosis–the changes of brain metabolism were characteristic for patients with the syndrome of “mesial temporal lobe epilepsy” (MTLE); (2) decrease of rCMRglu values in the contralateral mesiobasal temporal lobe (TL) cortex in all patient groups–the reduction of rCMRglu in homologous brain structures contralateral to the operated side provides evidence for stronger interhemispheric connections between both mesial TL structures than were hitherto supposed; and (3) a trend toward a normalization of rCMRglu values in the ipsilateral temporal neocortex 12 months after surgery in patients with MTLE syndrome.

Trajectory Analysis of High-Alpine Air Pollution Data

Abstract: The EUROTRAC subproject ALPTRAC (High Alpine Aerosol and Snow Chemistry Study) is devoted to the investigation of air and snow pollution at high Alpine sites. The aerosol surface concentration is continuously recorded at Jungfraujoch (3450 m a.s.1., 7° 59’E, 46° 32’N) in the Swiss Alps and Sonnblick (3106 m a.s.1, 12° 57’E,47° 03’N) in the Austrian Alps with a time resolution of 30 min with an epiphaniometer (Gaggeler et al., 1989; Baltensperger, et al. 1991). The measurements showed a pronounced seasonal cycle with mean summer concentrations more than one order of magnitude higher than mean winter concentrations, and the occurrence of episodes with especially high or low concentrations (Seibert et al., 1993). While the seasonal cycle is mainly to be explained by the atmospheric stability, the short-term variations are caused by synoptic-scale transports. These have been investigated using isobaric back trajectories at 700 hPa with a length of 72 h, computed twice daily for a period of three years (July 1990 - June 1993). Due to technical problems at Sonnblick, only 925 trajectories were available for the analysis; most of the missing data fall on winter.

Deep-inelastic scattering from off-shell nucleons.

Abstract: We derive the general structure of the hadronic tensor required to describe deep-inelastic scattering from an off-shell nucleon within a covariant formalism. Of the large number of possible off-shell structure functions we find that only three contribute in the Bjorken limit. In our approach the usual ambiguities encountered when discussing problems related to off shellness in deep-inelastic scattering are not present. The formulation therefore provides a clear framework within which one can discuss the various approximations and assumptions which have been used in earlier work. As examples, we investigate scattering from the deuteron, nuclear matter, and dressed nucleons. The results of the full calculation are compared with those where various aspects of the off-shell structure are neglected, as well as with those of the convolution model.

Asymmetric diurnal temperature change in the Alpine Region

Abstract: By now there is general agreement that the annual mean temperature of earth's surface has increased during the last century. Recently, it has become obvious that this warming is quite inhomogeneous in various respects. Besides the spatial and seasonal variability of the temperature trend a diurnal asymmetry of increase has been observed. In large continental regions the annual mean of the daily minimum temperature has increased noticeably faster than the annual mean of the daily maximum. The same behaviour is found in the present study for low-lying stations in Central Europe. However, data from mountain top stations show a similar increase for both minimum and maximum of daily temperatures. No diurnal asymmetry was observed for these stations. The good agreement of the time series from different mountain stations leads us to believe that the observed trends of minimum and maximum temperature are not caused by particular local influences or observation errors. An analysis of monthly and seasonal means shows that most of the warming took place in fall.

Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresist

Abstract: Progress in the fabrication of continuous-relief micro-optical elements by direct laser writing in photoresist followed by replication into epoxy or polymer materials is described. The technology enables a wide range of micro-optical elements to be fabricated and replicated using Ni shims electroformed from the photoresist originals. Examples of fabricated micro- optical elements are described, including microlens arrays, Fresnel microlenses, kinoforms, and other continuous microrelief phase elements.

Development of radiation‐grafted FEP‐g‐polystyrene membranes: Some property–structure correlations

Abstract: Property–structure correlation in proton exchange membranes, prepared by simultaneous radiation grafting of styrene into FEP films and their subsequent sulfonation, was evaluated. The distribution of ionic sites across the membrane matrix was determined by microprobe measurements. The properties of these membranes, such as ion exchange capacity, swelling and ionic resistivity as a function of the degree of grafting, were studied. The thermal stability of membranes was studied using thermogravimetric analysis and ion exchange capacity measurements. Membranes undergo considerable structural changes in terms of the increase in the ionic content, enhanced hydrophilicity and decrease in crystallinity with the increasing degree of grafting. A correlation between some physical properties and stuctural changes occurring during the membrane preparation was established.

Influence of the A-site cation in AMnO3+x and AFeO3+x (A=La, Pr, Nd and Gd) perovskite-type oxides on the catalytic activity for methane combustion

Abstract: The effect of rare-earth ions (La, Pr, Nd and Gd) in AMnO3+x and AFeO3+x perovskites on the thermal behavior and on the catalytic activity for the deep oxidation of methane has been studied. AMnO3+x perovskites showed after preparation an oxidative non-stoichiometry. Oxygen desorption analysis revealed for the four manganites different desorption steps occurring between 930 and 1370 K. Stoichiometry was reached after the first desorption step. Heating the samples at temperatures above 1300 K resulted in phase segregation to the simple oxides. AFeO3+x perovskites were more stable towards thermal decomposition than the Mn-perovskites, showing no oxygen evolution up to 1400 K. The reducibility of these perovskites in hydrogen correlated inversely with the relative effective ionic radii of the trivalent rare-earth cations. Comparative catalytic studies were carried out in a fixed-bed microreactor at atmospheric pressure in the temperature range 600–1200 K. The activities at 770 K, expressed as reaction rates referred to the BET surface area, varied between 1.4 × 10−7 and 2.9 × 10−7 mol s−1 m−7 for the AMnO3+x, and between 1.1 × 10−7 and 1.6 × 10−7 mols−1m−2for the AFeO3+x perovskites.

Rates for the reactions $$\bar pp \to \pi \phi $$ and? ?

Abstract: We study ¯pp annihilation at rest intoπφ andγφ. Rescattering by ¯K*K+K*¯K and ρ+ρ− for ¯pp→πφ states is sizable, of order (0.90 to 2.6) × 10−4 in the branching ratio, but smaller than experiment. For ¯pp→γφ the rescattering contributions are negligible, but theγφ channel is well explained by aρφ intermediate state combined with vector meson dominance.

Control of the cell cycle

Abstract: Cell biology has made major progress in identifying the molecules that drive the cell cycle. The evidence accumulating from these studies indicates that derangements in the cell cycle machinery contribute to the uncontrolled cell growth of tumours. The cell cycle machinery has been found to be substantially altered in tumour cells and also may be crucial for carcinogenesis. In this context, various aspects of tumour cell growth have been studied in an effort to understand 1) why tumour cells display uncontrolled growth, 2) why radiation selectively affects growing cells, and 3) whether aspects of the cell cycle and tumour cell growth may be used in tumour diagnosis and prognosis.

Progress in the analysis of experimental chaos through periodic orbits

Abstract: The understanding of chaotic systems can be considerably improved with the knowledge of their periodic-orbit structure. The identification of the low-order unstable periodic orbits embedded in a strange attractor induces a hierarchical organization of the dynamics which is invariant under smooth coordinate changes. The applicability of this technique is by no means limited to analytical or numerical calculations, but has been recently extended to experimental time series. As a specific example, the authors review some of the major results obtained on a nuclear-magnetic-resonance laser which have led to an extension of the conventional (Bloch-Kirchhoff) equations of motion, to the construction of approximate generating partitions, and to an efficient control of the chaotic system around various unstable periodic orbits. The determination of the symbolic dynamics, with the precision achieved by recording all unstable cycles up to order 9, improves the topological and metric characterization of a heteroclinic crisis. The periodic-orbit approach permits detailed study of chaotic motion, thereby leading to an improved classification scheme which subsumes the older ones, based on estimates of scalar quantities such as fractal dimensions and metric entropies.