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     

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.     

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.     

Ultramicrocoulometric determination of ammonia in serum, plasma, and blood

A method has been developed for the ultramicrodetermination of ammonia in as little as 0.01 ml of serum, plasma, or blood by coulometric titration with electrogenerated hypobromite using a sensitive amperometric endpoint. The only accurate volumetric measurement required is the pipetting of the sample. The sample is added to a 33-mm microdiffusion cell for 10 min to separate the ammonia; the ammonia is collected in 0.1 ml of 0.0025 M sulfuric acid in the center compartment. The separated ammonia is added to a coulometric generation cell where an excess amount of hypobromite has been generated. The decrease in amperometric current due to the utilization of the hypobromite by the ammonia is taken as a measure of the ammonia content; comparison is made with diffused standards. An optimum pH of 8.6 for the titration has been found to give reproducible results at all levels encountered. One-tenth-milliliter blood samples are routinely analyzed. When elevated ammonia levels are encountered, 0.01-ml samples can be used with accurate results. The time for the analysis is 10–15 min after initiating the diffusion.     

Determination of lactate and lactic dehydrogenase by biamperometric monitoring of hexacyanoferrate(II) in a flowing stream

Summary Open tubular carbon electrodes were used to monitor the biamperometric current of hexacyanoferrate(II) ion produced by the LDH catalyzed reaction between hexacyanoferrate(III) ion and lactate, and that produced from the diaphorase catalyzed reaction between hexacyanoferrate(III) ion and NADH, product from the LDH catalyzed reaction between lactate and NAD. Reagents and samples were mixed in a flow stream. Reaction takes place between the mixing point and the electrodes, and measurements are taken after a constant time interval. Lactate and LDH standards in serum control solutions were measured using the NAD dependent reaction.

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Bestimmung von Lactat und Lactatdehydrogenase durch biamperometrische Messung von Hexacyanoferrat(II) im Durchfluß

Zusammenfassung Kohlenstoff-Röhrenelektroden wurden zur Messung des biamperometrischen Stromes des Hexacyanoferrat(II)-ions eingesetzt, das aus der LDH-katalysierten Reaktion zwischen Hexacyanoferrat(III) und Lactat bzw. der Diaphorase-katalysierten Reaktion zwischen Hexacyanoferrat(III) und NADH (Produkt der LDH-katalysierten Reaktion zwischen Lactat und NAD) stammte. Die Reagentien wurden mit den Proben im Durchfluß vermischt. Die Reaktion fand zwischen der Mischungsstelle und den Elektroden statt und die Messungen wurden nach einem Bestimmten Zeitintervall durchgeführt. Mit Hilfe der NAD-abhängigen Reaktion wurden Lactat- und LDH-Standards in Serumkontrollösungen bestimmt.

     

A comparative study of the effect of o-nitrophenyl octyl ether and o-nitrophenyl pentyl ether as plasticizers on the response and selectivity of carrier-based liquid membrane ion-selective electrodes

Lithium, potassium and caesium-selective microelectrodes were prepared by coating the tips of preconditioned silver wires, incorporated in a flow-cell, with PVC membranes containing four different ionophores. A dicarboxamide, a 14-crown-4 carboxylic acid, benzo-18-crown-6 and di-(tert-butylbenzo)-21-crown-7 ionophores were used in the electrode matrix. The first two ionophores were used in lithium ion-selective electrodes, the third in a potassium ion electrode and the fourth in a caesium ion electrode. Two different plasticizers, o-nitrophenyl octyl ether (NPOE) and o-nitrophenyl pentyl ether (NPP'E) were used. Enhancement of the signal and the slope of the calibration curve and improvement of the curve linearity were observed in all cases when NPP'E was used as plasticizer. A general trend of enhanced selectivity of the electrodes incorporating crown ether ionophores was also observed when NPP'E was the plasticizer.     

On the beam propagation through active media

An analytical iterative procedure has been established to determine the amplitude of a laser beam propagating through an active medium. The treatment is valid for both homogeneous and inhomogeneous broadening, and for arbitrary inhomogeneities of the parameters characterizing the active medium, namely, the refractive index, the small-signal gain and the saturation intensity. After a supplementary approximation, a thin-sheet gain approach is derived from the first iteration. The formalism enables us to provide analytical criteria for evaluating both the accuracy of each iteration and the propagation distances for which the thin-sheet solution can be used. This revised version was published online in November 2006 with corrections to the Cover Date.     

Spatial characterization of the transversal structure of rotationally symmetric pulsed beams

A simple analytical model is proposed to describe the transversal spatial structure of a tridimensional rotationally symmetric pulsed beam. The spatial behaviour of the pulse amplitude is shown to be linked to its (measurable) second- and higher-order intensity moments, namely, beam width, quality parameter and kurtosis. As an illustrative experimental example, this model has been applied to high-quality TEA CO2 laser pulses. This revised version was published online in November 2006 with corrections to the Cover Date.