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     

Multimode pumped continuous-wave solid-state Raman laser

We demonstrate the continuous-wave operation of a solid-state Raman laser containing a barium nitrate crystal as the Raman medium. The Raman laser, which has a singly resonant cavity, is pumped by multimode radiation. The Raman oscillation threshold is reached at approximately 2 W of pump power. As much as 500 kW/cm2 of Stokes power density at 60-kW/cm2 pump power density is obtained in the cavity.     

Observation of Raman conversion for 70-fs pulses in KGd(WO4)2 crystal in the regime of impulsive stimulated Raman scattering

Raman conversion of femtosecond pulses in a solid-state medium is reported. Stimulated Raman scattering (SRS) was observed in an impulsive SRS regime when the pump pulse's duration was comparable with the period of Raman-active vibration. The generation of super broadband radiation, which is a distinguishing feature of impulsive SRS, is shown.     

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.     

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.     

Passively Q-switched diode-pumped Raman laser with third-order Stokes eye-safe oscillation

We demonstrate a passively Q-switched all-solid-state laser system with intracavity Raman frequency conversion to the eye-safe spectral region. Laser oscillation at the 1.064 μm wavelength with a pulse repetition rate of several kilohertz was provided by a Nd:YAG crystal and a Cr:YAG passive absorber. Third Stokes oscillations at the 1.599 and 1.494 μm wavelengths were obtained in Ba(NO₃)₂ and PbWO₄ crystals with output pulse energies of 5 μJ and 6 μJ, respectively. The results of the numerical simulation of the pulse dynamics are in good agreement with the experimental data.     

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.     

Modeling and experimental investigation of short pulse Raman microchip laser

The results of experimental and theoretical investigations of passive Q-switch Raman microchip lasers based on Nd³⁺:LSB active medium and Ba(NO₃)₂ Raman crystal are presented. It has been demonstrated that intracavity Raman conversion in the microchip lasers is a simple and efficient method, capable of delivering high power pulses with sub-100 ps duration. Intracavity generation of the 1st Stokes pulses with duration from 180 down to 48 ps and a peak power of 48 kW has been performed and studied. High peak power and short duration of the 1st Stokes pulses in microchip laser with Ba(NO₃)₂ Raman crystal allows to easily perform extracavity harmonic generation and frequency sum mixing in LBO, BBO, and KTP crystals with discrete-tunable wavelength from ∼1200 down to ∼240 nm. We have developed a generalized model of Q-switched Raman microchip lasers, that takes into account spatial inhomogeneity of pump, laser, and Stokes beams, thermalization within the upper and lower multiplets of activator ions in laser medium, and saturable absorber bleaching and recovery. For the microchip lasers with different saturable absorbers, the model achieves very good agreement with the presented experimental results in a wide range of pump powers.