Showing papers by "Paul Scherrer Institute published in 1993"
TL;DR: The electronic structure of nanocrystalline Si which shows visible photoluminescence is calculated using the density-functional approach for finite structures, and results for clusters suggest that the band gap scales linearly with L, where L is the cluster diameter.
Abstract: The electronic structure of nanocrystalline Si which shows visible photoluminescence is calculated using the density-functional approach for finite structures. Except for geometry this is the same theory as for first-principles band structures of semiconductors and other solids. Our results for clusters ranging up to 706 Si atoms suggest that the band gap scales linearly with ${\mathit{L}}^{\mathrm{\ensuremath{-}}1}$, where L is the cluster diameter. For such clusters it is found that dipole transitions across the gap are symmetry allowed. The finite structures thus show a direct band gap which is considerably larger than the one of bulk silicon. For larger clusters we find a strong decrease of oscillator strength, consistent with the occurrence of the indirect gap in the bulk limit.
421 citations
TL;DR: A homologous series of cuprates, Srn -1 Cun + 1 O2n, formed by introducing a parallel array of planar defects into the infinite-layer cuprate, SrCuO2, have been reported by Takano et al. as discussed by the authors.
Abstract: A homologous series of cuprates, Srn -1 Cun + 1 O2n, formed by introducing a parallel array of planar defects into the infinite-layer cuprate, SrCuO2, have been reported by Takano et al. In each CuO2 plane line defects consisting of CuO double chains result. An analysis of the electronic properties of such planes demonstrates that the stoichiometric compounds with n = 3, 7, 11,... will be frustrated quantum antiferromagnets and spin liquids. When lightly doped with holes the spin gap will remain and singlet superconductivity should occur on a separate but high temperature scale. This prediction may shed new light on the origin of the separate energy scales for the spin gap and superconductivity in other lightly doped cuprates.
316 citations
TL;DR: In this paper, the SINDRUM II spectrometer has been used to perform a search for μ → e conversion in muonic atoms with the assumption of a giant resonance excitation of the Ca nucleaus.
288 citations
TL;DR: In this paper, the authors proposed a semi-empirical method to determine the optimum aperture size and operating temperature of a solar cavity-receiver for which its energy conversion efficiency is maximized.
242 citations
TL;DR: In this paper, the coulombic capacity and reversibility of rechargeable magnesium batteries were investigated in acetonitrile solutions containing,,, and, and they reached up to 170 Ah/kg.
Abstract: The electrochemistry of , , , , and has been studied in several organic solvents containing in view of their application as positive electrodes in rechargeable magnesium batteries. Only showed promising coulombic capacity and reversibility. Mg2+ insertion into this oxide depends on the ratio between the amounts of and Mg2+ as well as on the absolute amount of in the electrolyte. Water molecules preferentially solvating Mg2+ions appear to facilitate the insertion process. The highest coulombic capacities of up to 170 Ah/kg were reached in acetonitrile solutions containing .
213 citations
TL;DR: In this article, an ultrasonic velocity profile measuring method has been developed at PSI for application in fluid mechanics and fluid flow measurement, which uses pulsed ultrasonic echography together with the detection of the instantaneous Doppler shift frequency.
210 citations
TL;DR: The results suggest that D2 dopamine receptor binding sites (mainly postsynaptically located) decrease as a consequence of normal aging in parallel with the decline of the presynaptic nigrostriatal dopaminergic neuronal system.
Abstract: • Human postmortem and animal experimental results suggest a decline of the cerebral dopaminergic neuronal system with age. In this study, the radiotracer carbon 11-labeled-raclopride and positron emission tomography were applied to determine the effect of age on striatal D 2 dopamine receptors in 32 healthy volunteer subjects (age range, 21 to 68 years; median, 31 years). An index of specific 11 C-raclopride binding was calculated for putamen, caudate nucleus, and other brain regions in each subject. A significant decrease with age of the index for specific tracer uptake was found in putamen and caudate nucleus. The decrease was steep until 30 years, but slower afterward. After approximately 30 years of age, the decline of specific 11 C-raclopride binding in putamen was found to be 0.6% per year. Our results suggest that D 2 dopamine receptor binding sites (mainly postsynaptically located) decrease as a consequence of normal aging in parallel with the decline of the presynaptic nigrostriatal dopaminergic neuronal system.
186 citations
TL;DR: The finding that T2 values in PD patients were reduced in the following brain regions: substantia nigra, caudate nucleus, and putamen supports the notion of increased iron deposition in the substantia Nigra of patients with PD.
Abstract: Postmortem studies of patients with Parkinson's disease (PD) reveal an increase in iron concentration in the substantia nigra. Iron content in the brain is associated with decreased signal intensity on T2-weighted MRI. We measured in vivo the T2 relaxation time in 30 PD patients and 33 healthy volunteer subjects, using a 1.5-T whole-body MRI system. In comparison with healthy controls, T2 values in PD patients were reduced in the following brain regions: substantia nigra, caudate nucleus, and putamen. Due to the overlap between patients and control subjects, we could not differentiate, in a given patient, healthy from diseased state on the basis of T2 relaxation time. Our findings support the notion of increased iron deposition in the substantia nigra of patients with PD. However, the shortening of T2 values in the substantia nigra did not correlate with disease duration nor with clinical severity.
178 citations
TL;DR: The preparation and in vitro characterization of tumor-specific superparamagnetic particles (SMP) are described and the polypeptide coat chosen provides an ideal platform for the attachment of biological modifiers needed for the reduction of the antigenicity and blood clearance rate of anti-CEA SMP.
165 citations
TL;DR: The metabolic pattern differed between the patient groups and allowed a discrimination between patients of mesial temporal and lateral temporal seizure onset, but there was no clear-cut correlation between the degree of hypometabolism and the location of EEG-defined epileptogenic focus.
Abstract: Metabolic abnormalities in the temporal lobe (TL) of 25 patients suffering from temporal lobe epilepsy of mesiobasal or lateral TL origin have been investigated using interictal [18F]-fluorodeoxyglucose (FDG) positron emission tomography (PET). The epileptogenic area was determined by ictal EEG recordings using foramen ovale and scalp electrodes in 20 patients, and by the use of stereo-electroencephalography in one patient. Four patients with structural lesions on their MRIs had noninvasive ictal surface EEG recordings. Sixteen patients had a clear-cut mesiobasal seizure onset, and in five patients the seizures originated from the lateral temporal neocortex. Twenty-four patients underwent selective surgery. Patients with temporal limbic seizures associated with mesial gliosis (n = 15) had the lowest FDG uptake in the entire TL, followed by patients with lateral temporal seizure origin (n = 5). Patients with tumors located in the mesiobasal TL (n = 5) showed, in general, only a slight decrease of glucose metabolism in all TL structures. There was no clear-cut correlation between the degree of hypometabolism and the location of EEG-defined epileptogenic focus. The metabolic pattern, however, differed between the patient groups and allowed a discrimination between patients of mesial temporal and lateral temporal seizure onset.
159 citations
TL;DR: A new precision measurement of the branching ratio of the rare pion decay into a positron and a neutrino ([pi][r arrow][ital e][nu]) has been completed.
Abstract: A new precision measurement of the branching ratio of the rare pion decay into a positron and a neutrino ([pi][r arrow][ital e][nu]) has been completed. A beam of positive pions was stopped in an active target of plastic scintillator surrounded by a 4[pi] BGO calorimeter. 3[times]10[sup 5] rare decays and 1.2[times]10[sup 6] normal pion decays ([pi][r arrow][mu][nu]) were recorded. The branching ratio was finally calculated from 1.2[times]10[sup 5] rare decays after various cuts in the time window from 7.5 to 200 ns after pion stop. The errors of the result (1.235[plus minus]0.005)[times]10[sup [minus]4] are 0.28% statistical and 0.29% systematical.
TL;DR: In this article, the authors presented a thermochemical process that uses concentrated solar radiation as the energy source of high-temperature process heat, where the chemical equilibrium components consist of metallic iron in the solid phase and a mixture of 667% H 2 and 333% CO in the gaseous phase.
TL;DR: In this article, the authors present a compact analytic result for the two-loop leading heavy top contribution to the p-parameter which is valid for arbitrary Higgs mass and explicitly check the validity of the Ward identities.
TL;DR: In this article, the relevance of colloid-facilitated transport to repository safety analyses was investigated in the case of deep groundwater in the crystalline basement of northern Switzerland, where colloid size distributions, compositions and sorption properties have been measured.
TL;DR: In this paper, two unmodified industrial CMOS processes have been used for the integration of highly interdigitated pn structures, and under forward bias these pn junctions emit narrow-band infrared light at 1160 nm with an electrical-to-optical power conversion efficiency of typically 10 −4.
Abstract: Two different unmodified industrial CMOS processes have been used for the integration of highly interdigitated pn structures. Under forward bias these pn junctions emit narrow-band infrared light at 1160 nm with an electrical-to-optical power conversion efficiency of typically 10 −4 . The same junctions show broad-band visible-light emission between 450 and 800 nm in the avalanche breakdown region under reverse bias with efficiencies of the order of 10 −8 . This is already enough for a first few practical applications as light-emitting devices (LEDs). No satisfactory explanation for this emission efrect, fitting all the experimentally observed electro-optical and physical properties of our silicon LEDS, has been found yet.
TL;DR: In this paper, the authors show a homogeneous distribution of polystyrene across the grafted film and show that the specific resistivity decreases with increasing degree of grafting, reflected by an increasing hydration of the sulfonic acid groups.
TL;DR: In this paper, the temperature dependence of the luminescence quantum yield of powdered titanium dioxide in vacuum, nitrogen, and water vapor, respectively, was measured in the temperature range 300 K to 800 K.
Abstract: The temperature dependence of the luminescence quantum yield of powdered titaniumdioxide in vacuum, nitrogen, and water vapor, respectively, was measured in the temperature range 300 K to 800 K. The observed luminescence is attributed to luminescence from surface states. We find that the luminescence is thermally quenched, as predicted by a simple model. Furthermore, the luminescence is shifted towards shorter wavelengths with increasing temperature. We also observed that the luminescence in vacuum is weakly quenched in the presence of nitrogen or water vapor.
TL;DR: In this article, a continuous surface-relief diffractive optical element for two-dimensional array generation (fan-out) is designed and fabricated, and the phase-grating microstructures are generated by laser-beam writing lithography in a single exposure step and converted to nickel shims by electroplating.
Abstract: Continuous surface-relief diffractive optical elements for two-dimensional array generation (fan-out) are designed and fabricated. Separable and nonseparable solutions for the two-dimensional element design are compared. The phase-grating microstructures are generated by laser-beam writing lithography in a single exposure step and converted to nickel shims by electroplating, enabling low-cost replicas to be produced by using laboratory and commercial replication processes. Results are presented for a 9 x 9 fan-out diffractive optical element with a measured efficiency of 94% and an overall uniformity within +/-8%; replicas in epoxy have the same efficiency and a uniformity of +/-15%.
TL;DR: In this paper, a gauge invariant way to compute one loop corrections to processes involving the production and decay of unstable particles is presented, which is a generalization of the approach presented in this paper.
Abstract: We present a gauge invariant way to compute one loop corrections to processes involving the production and decay of unstable particles.
TL;DR: The results suggest that dopamine D2 receptor binding sites (mainly post‐synaptically located) decrease as a consequence of normal aging in parallel with the decline of the pre‐synaptic nigrostriatal dopa‐minergic system.
Abstract: Human post-mortem and animal experimental results suggest a decline of the cerebral dopaminergic neuronal system with age. In this study, the radiotracer [11C]raclopride (dopamine D2 antagonist) and positron emission tomography were applied to determine the effect of age on striatal dopamine D2 receptors in 32 healthy volunteer subjects (age range 21-68 years). Subjects were divided in two age groups on the basis of median age (31 years). An index for specific tracer uptake was calculated for caudate nucleus and putamen. Uptake indices in the older group of subjects were reduced on average 26% in putamen and 20% in caudate nucleus. The decline appeared to be steep until 30 years, but slower afterwards. After 30 years of age the decline of specific raclopride binding was found to be 0.6% per year. These results suggest that dopamine D2 receptor binding sites (mainly post-synaptically located) decrease as a consequence of normal aging in parallel with the decline of the pre-synaptic nigrostriatal dopaminergic system.
TL;DR: In this article, the top 12 m of a loess profile from Luochuan, Central China was measured in a new time scale which was in good agreement with that of Kukla et al.
Abstract: 10Be and magnetic susceptibility have been measured in the top 12 m of a loess profile from Luochuan, Central China. Comparison of the 10Be concentration record with the SPECMAP δ18O profile of the last 130 ka (Imbrie et al., 1984] results in a new time scale which is in good agreement with that of Kukla et al. [1990]. The calculated loess accumulation rates can be compared with existing records of dust falls in Pacific deep sea sediments and Antarctic ice cores. A simple model for the 10Be dust flux demonstrates that a significant part of the magnetic susceptibility signal in palaeosol horizons is due to in situ pedogenic production. During times of high loess accumulation (cold palaeoclimate) this contribution is negligible.
01 Mar 1993-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a self-reading chip for silicon strip detectors with analog event pipeline has been fabricated (SACMOS 2 μm technology) and tested at the HERA ep collider at a bunch crossing rate of 10.4 MHz.
Abstract: A readout chip for silicon strip detectors with analog event pipeline has been fabricated (SACMOS 2 μm technology) and tested. The chip has been designed to operate at the HERA ep collider at a bunch crossing rate of 10.4 MHz. Each channel has a layout width of 44 μm and consists of a fast, low noise, low power preamplifier followed by a switched capacitor analog event pipeline. The preamplifier consists of a single CMOS push-pull gain cell and offers minimal power consumption. A novel feature of our chip is a self-reading architecture that allows the preamplifier to re-read its own pipeline buffers and thus permits a extensive parallel analog signal processing that is digitally controlled. The results from radiation damage tests with 60 Co are given for doses up to 240 krad.
TL;DR: A new type of ideal nonimaging secondary concentrator is presented, the tailored edge-ray concentrator, that can closely approach the thermodynamic limit of concentration.
Abstract: For both linear and point-focus Fresnel reflectors, we present a new type of ideal nonimaging secondary concentrator, the tailored edge-ray concentrator, that can closely approach the thermodynamic limit of concentration. For large rim-angle heliostat fields, practical-sized secondaries with shapes that should be relatively easy to fabricate can achieve concentrations substantially above those of compound parabolic concentrators. This superiority stems from designing so as to accommodate the particular flux from the heliostat field. The edge-ray principle used for generating the new secondary dictates a heliostat tracking strategy that is different from the conventional one but is equally easy to implement.
TL;DR: MEMO is a fully vectorized nonhydrostatic mesoscale model using terrain-following coordinates as discussed by the authors, and the numerical solution is based on second-order discretization applied on a staggered grid which is allowed to be non-equidistant in all directions.
TL;DR: The goundstate phase diagram of the one dimensional Kondo lattice model is discussed based on exact analyses in several limiting cases and numerical results interpolating those limits.
Abstract: The goundstate phase diagram of the one dimensional Kondo lattice model is discussed based on exact analyses in several limiting cases and numerical results interpolating those limits. In one dimension there are three phases: a ferromagnetic metallic phase, a paramagnetic metallic phase and an insulating spin-liquid phase. Emphasis is placed upon the strong coupling limits which are important to understand the properties of these phases.
TL;DR: In this article, a three-step degradation pattern was observed from thermograms of all the membranes and was attributed to the dehydration, desulfonation, and degradation of the FEP backbone.
Abstract: Thermal behavior of radiation-grafted and sulfonated poly(tetrafluoroethylene-hexafluoropropylene)-g-polystyrene membranes was evaluated using thermogravimetric analysis. A three-step degradation pattern was observed from thermograms of all the membranes and was attributed to the dehydration, desulfonation, and degradation of the FEP backbone. The evidence for desulfonation was reflected in the loss in ion exchange capacity of the heat-treated samples. The membranes were found to undergo loss in ion exchange capacity beyond [approximately] 200 C. No trace of sulfonic acid groups as the ion exchange sites was found above [approximately] 350 C. The swelling of heat-treated membranes was also reduced considerably. However, the loss in swelling was much higher than that in the ion exchange capacity of the corresponding membrane. The results were explained in terms of cross-linking reaction occurring in the membrane matrix during the desulfonation process that imparts rigidity in the membrane matrix.
TL;DR: In this paper, a xenon time projection chamber (TPC) with an active volume of 180 liters has been built to study neutrinoless double-beta decay in Xe-136.
Abstract: A xenon time projection chamber (TPC) with an active volume of 180 liters has been built to study neutrinoless double-beta decay in Xe-136 The experiment was performed in the Gotthard Underground Laboratory, with 5 atm of xenon enriched to 625% in Xe-136 The experimental details, background considerations, detector performance, and data analysis are discussed From 6830 h of data, no evidence has been found for the 0nu 0+-->0+ transition Half-life limits of T1/2(0nu) > 34(64) X 10^(23) yr in the mass mechanism mode, and T1/2(0nu) > 26(49) X 10^23 yr in the right-handed currents mode, at the 90(68)% CL, were derived, corresponding to an upper limit on the Majorana neutrino mass parameter [m(nu)] of about 28 eV Limits on two-neutrino double-beta decay of T1/2(2nu) /2 > 2 1 X 10^(20) yr, and on neutrinoless double-beta decay with Majoron emission of T1/2(0nuchi) > 49 X 10^(21) yr, both at 90% CL, were also derived Accordingly, a limit on the effective Majoron-neutrino coupling parameter of [g(M)] < 24 X 10^(-4) was deduced
TL;DR: Several schemes to introduce finite width effects to reactions involving unstable elementary particles are given and the differences between them are investigated in this article, where the effects of different schemes are investigated numerically for W pair production.
TL;DR: In this paper, the ion exchange mechanism of polyaniline (PANI) and sulfonated polyaniliine (SPAN) was studied. But the results were limited to the case of PANI.