Global Analysis of the Flows of Fluids with Pressure-Dependent Viscosities

 To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments. While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small, special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place. Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are global in time, for a large class of physically meaningful viscosity-pressure relationships. (Accepted May 1, 2002) Published online November 15, 2002 Communicated by S. S. ANTMAN     

Submicrosecond Pulsed Electron Beam Formation in Electron Sources and Accelerators with Plasma Emitters

The most popular methods for submicrosecond electron beam generation and physical processes underlying electron extraction from plasma in plasma emitters are considered. Electron sources and accelerators developed on the basis of plasma emitters allow pulsed beams with currents from tens to 10³ A and current densities of several amperes per square centimeter, pulse durations of hundreds of nanoseconds, and high repetition rates to be generated.     

Guided modes of integrated optical guides. A mathematical study

A waveguide in integrated optics is defined by its refractiveindex. The guide is assumed to be invariant in the propagationdirection while in the transverse direction it is supposed tobe a compact perturbation of an unbounded stratified medium.We are interested in the modes guided by this device, whichare waves with a transverse energy confined in a neighbourhoodof the perturbation. Our goal is to analyse the existence of such guided modes. Underthe assumptions of weak guidance the problem reduces to a two-dimensionaleigenvalue problem for a scalar field. The associated operatoris unbounded, selfadjoint, and bounded from below. Its spectrumconsists of the discrete spectrum corresponding to the guidedmodes and of the essential spectrum corresponding to the radiationmodes. We present existence results of guided modes and an asymptoticstudy at high frequencies, which shows that contrarily to thecase of optical fibers, the number of guided modes can remainbounded. The major tools are the min-max principle and comparisonof results between different eigenvalue problems. The originalityof the present study lies in the stratified character of theunbounded reference medium.     

Interaction of the mu-opioid receptor with GPR177 (Wntless) inhibits Wnt secretion: potential implications for opioid dependence

Background  

Opioid agonist drugs produce analgesia. However, long-term exposure to opioid agonists may lead to opioid dependence. The analgesic and addictive properties of opioid agonist drugs are mediated primarily via the mu-opioid receptor (MOR). Opioid agonists appear to alter neuronal morphology in key brain regions implicated in the development of opioid dependence. However, the precise role of the MOR in the development of these neuronal alterations remains elusive. We hypothesize that identifying and characterizing novel MOR interacting proteins (MORIPs) may help to elucidate the underlying mechanisms involved in the development of opioid dependence.     

Emission properties of a plasma cathode based on a glow discharge for generating nanosecond electron beams

The emission properties of a plasma cathode based on a nanosecond pulsed glow discharge with currents of up to 200A at a pressure of 5×10⁻² Pa are studied experimentally. Stable ignition and burning of the discharge are ensured if the current in the auxiliary pulsed discharge is 25–30% of that in the main discharge and its pulse duration exceeds that of the main discharge by more than an order of magnitude. Emission current pulses from the cathode with amplitudes of up to 140A fully reproduce the discharge current and are determined by the transparency of the grid anode. Zh. Tekh. Fiz. 69, 62–65 (November 1999)     

High precision delta(17)O isotope measurements of oxygen from silicates and other oxides: method and applications

The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd.     

Influence of a current jump on vacuum arc parameters

Based on time of flight method, influence of short time vacuum arc current jump on arc plasma parameters were investigated. Superposition of the current pulse of a vacuum arc with a high operating voltage results in the appearance of ions of higher charge state in the discharge plasma and in an increase in the mean ion charge state for most of the cathode materials used in the experiment. The method of a “short-time current jump” can be also used to investigate the parameters of a vacuum arc, in particular to estimate the ion direct velocities in vacuum arc plasmas. Our estimates show that in the presence of a current step the ion velocities are almost identical for all differently charged ions and depend only on the peak current and the ion mass     

Test of bell’s inequality using the one-atom micromaser

We examine a local realist bound in the case of a one-atom micromaser. It is shown that such a bound is violated using a simplified treatment of the micromaser. We consider the effect of dissipation in a proposed experiment with the real micromaser. It is seen that the magnitude of violation of a Bell-type inequality depends significantly on the cavity parameters.     

Generation of Multiply Charged Ions in the Plasma of a Vacuum Arc Discharge

This paper presents the results of a study on the generation of multiply charged ions in the plasma of a vacuum arc discharge. The average charge of ions in the plasma is increased by using a strong magnetic field, a current burst, or an accelerated electron beam. The results of measurements of the ion charge distribution for each case are reported.     

Modification of the Material Surface by Boron Ions Based on Vacuum Arc Discharge Systems and a Planar Magnetron

Russian Physics Journal - The principle of operation and the characteristics of the experimental equipment intended for the generation of boron ion plasma and beams are presented. The equipment...