Investigation of acceptor centers in semiconductors with the diamond crystal structure by the μ − SR method

The residual polarization of negative muons in crystal silicon samples with phosphorus (P: 1.6×10¹³ cm⁻³) and antimony (Sb: 2×10¹⁸ cm⁻³) impurities is investigated. The measurements are made in a 1000 G magnetic field oriented in a direction transverse to the muon spin in the temperature range 4–300 K. The relaxation rate and shift of the precession frequency in the silicon sample with the phosphorus impurity are measured more accurately than previously. It is found that in antimony-doped silicon the acceptor center _μ A1 at temperatures below 30 K can be in both ionized and neutral states. The experimental data are interpreted on the basis of spin-lattice relaxation of the magnetic moment of an acceptor center, formation of acceptor-donor pairs, and recombination of charge carriers at the acceptor. Preliminary measurements showed a nonzero residual polarization of negative muons in germanium. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 61–66 (10 July 1998)     

Strategies for the development of a voltammetric sensor for the determination of hydrogen peroxide at high concentrations

Different strategies are presented for the development of a voltammetric sensor for in-line measurement and monitoring of H₂O₂ in high concentrations (up to 30 g/l) as used in textile bleaching systems. When using macroelectrodes, signal saturation is observed even at medium concentrations. Some improvement can be achieved by hydrodynamic electrodes like ring-disk electrodes. Satisfactory results up to the desired level in practical solutions (possessing only limited conductivity) are obtained with Pt-microelectrodes.     

Thermal conductivity and specific heat of amorphous Zr0.67Ni0.33 after structural relaxation

Low-temperature measurements of the thermal conductivity (0.3KT5K) and of the specific heatC (0.07KT3.5K) of splat-cooled amorphous superconducting Zr_0.67Ni_0.33(T _c 2.7K) after different annealing stages are reported. increases progressively (up to 55%) after annealing. An analysis of with the help of normal-state measurements belowT _c in an overcritical field shows that the phonon-electron scattering remains unaltered after annealing. Hence the increase in must be entirely attributed to structure-induced (intrinsic) scattering, i.e. by two-level tunneling states (TLS) at low temperatures (T1K). The specific heat shows a small decrease aboveT _c (by 8%) which is attributed to a small diminution of the electronic density of states at the Fermi level and to a small increase in the Debye temperature. ForTT _c where TLS dominate, the specific heatC decreases less upon annealing than expected from the increase of in the standard tunneling model. This points to a change in the TLS relaxation time spectrum upon annealing, as observed previously for Zr _x Cu_1–x glasses.     

Synthese von ungesättigten und gesättigten Aminosäurederivaten durch kathodische Reduktion von Azidozimtsäureester

Cathodic reduction of -azidocinnamic ester under aprotic conditions on Hg, Pt, or graphite electrodes can be directed to high yields of N,N-diacylated dehydroaminoacid derivates (f.i. addition of acetic anhydride) or to almost quantitative yields of -aminocinnamic ester in very pure form by careful addition of H⁺-donors. The dehydroamino compounds in turn can be further reduced to the corresponding saturated compounds by following H⁺-addition and changed electrolysis potential. Almost no dimerization occurs.

     

Investigation of the pharmacokinetics of celecoxib by liquid chromatography-mass spectrometry

A new method for the quantification of celecoxib in human plasma based on reversed-phase high-performance liquid chromatography (HPLC) coupled to atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) after liquid-liquid extraction is presented. The method is rapid, sensitive and highly selective. The retention time of celecoxib was 2.3 min. The limit of quantification was 5 microg/L. Rofecoxib was used as internal standard. After validation, the method was used to study the pharmacokinetic profile of celecoxib following administration of a single oral dose (200 mg) in 12 healthy volunteers. Since celecoxib should be metabolized primarily by cytochrome 2C9 (CYP2C9), a poor metabolizer (PM) for this cytochrome P450 enzyme was included in the study. Pharmacokinetic characteristics (mean +/- SD) of extensive metabolizers (EM) were t(max) 2.9+/-1.2h, c(max) 842+/-280 microg/L, AUC(infinity) 6246+/-2147 microg h/L and t(1/2) 7.8+/-2.7h. The area under the curve (AUC(infinity)) for the PM was 12561 microg h/L. However, we found no noticeable increase in half life in the PM (11.5 h) after a single dose of celecoxib.     

The μSR facilities at PSI

TheSR Facility Instruments presently available at PSI and the envisaged medium- and long-term developments are presented. The plans focus on further upgrades of the existing instruments and the development of new techniques using the very high fluxes becoming available at PSI, in particular the setup of a beamline with a fast kicker for muons on request (MORE) and the development of very low energy muon beams.     

A liquid chromatography-mass spectrometry method for the quantification of both etoricoxib and valdecoxib in human plasma

A practicable and selective liquid chromatography-mass spectrometry assay for the determination of two cyclooxygenase-2 inhibitors, etoricoxib and valdecoxib, in human plasma is presented. The analytical technique is based on reversed-phase high-performance liquid chromatography (HPLC) coupled to atmospheric pressure chemical ionisation (APCI) mass spectrometry (Finnigan Mat LCQ ion trap). Mass analysis was performed in the positive ion mode. The ion trap was operated in the tandem MS mode (MS2) and the transitions of etoricoxib (m/z 359.2 --> 280.3) and valdecoxib (m/z 315.1 --> 235.1) were followed by selected reaction monitoring. Retention times of etoricoxib and valdecoxib were 1.05 and 1.08 min, respectively. The method was validated over a linear range 10-2500 and 5-1000 microg/L using the other substrate as internal standard. After validation, the method was used to study the pharmacokinetic pro fi le of etoricoxib or valdecoxib in a healthy volunteer after administration of a single oral dose (valdecoxib, 20 mg; etoricoxib, 90 mg). The presented method was suf fi cient to cover more than 90% of the area under the plasma concentration time curve.     

Incoherent tunnelling of positive muons and trapping by vacancies in electron-irradiated aluminium

We have measured the transverse spin relaxation of positive muons ⁺ in Al single crystals after irradiation at 150 K with 3 MeV electrons. The relaxation functions agree with those expected for diffusion-limited trapping of the ⁺ in monovacancies. Between 215 K and 60 K the ⁺ diffusivity is well described by the Flynn-Stoneham law (multi-phonon incoherent tunnelling between ground states) with an activation enthalpyH _a = (30±2) meV. At lower temperatures, few-phonon (in particular one-phonon) processes become important. The decrease of the vacancy concentration by a factor of 100 during annealing between 227 K and 267 K has been studied.     

TEXTURE AND CRYSTALLINITY EVOLUTION IN ISOTACTIC POLYPROPYLENE INDUCED BY ROLLING AND THEIR INFLUENCE ON MECHANICAL PROPERTIES

The orientation and crystallinity evolution of isotactic polypropylene （iPP） induced by rolling were studied using wide angle X-ray scattering with an area detector. The tensile mechanical properties of rolled isotactic polypropylene sheets were also measured in this work. The texture component method was used to analyze the rolling texture. The rolling texture consists mainly of （010）[001], （130）[001] and [001]//RD fiber components in the sample with a rolling true strain of 1.5. The results reveal that crystallinity drastically decreases during rolling. It is suggested that amorphization is a deformation mechanism which takes place as an alternative to crystallographic intralamellar slip depending on the orientation of the lamellae. Both the orientation and crystallinity affect the tensile mechanical properties of rolled polypropylene. Crystallinity influences the elastic modulus on both directions and yield strength on transverse direction at the first stage of deformation. Orientation is the main reason for the changes of mechanical properties, especially at the latter part of deformation. The changes of both tensile strength and elongation percentage on rolling direction are larger than those on transverse direction, which results from the orientation. At last, the anisotropic mechanical properties occur on the rolling and transverse direction： high tensile strength with low elongation percentage on rolling direction and low tensile strength with high elongation percentage on transverse direction.