The consequences of yield stress on deployment of a non-Newtonian anti-HIV microbicide gel

A recent study in South Africa has confirmed, for the first time, that a vaginal gel formulation of the antiretroviral drug Tenofovir, when applied topically, significantly inhibits sexual HIV transmission to women [10]. However the gel for this drug, and anti-HIV microbicide gels in general, have not been designed using full understanding of how gel spreading and retention in the vagina govern successful drug delivery. Elastohydrodynamic lubrication theory can be applied to model such spreading of microbicide gels, which are inherently non-Newtonian [13], [15]. A yield stress is emerging as one of the important properties of microbicide gel vehicle deployment, as this may improve retention within the vaginal canal. On the other hand, a yield stress may decrease the initial extent of the coating flow. Here, we first explain a certain yield stress paradox observed generally in many lubrication flows. Four conditions are determined, via scaling analysis, which mitigate the inconsistency in the use of lubrication theory to analyze the specific problem of elastic wall squeezing flow of yield stress fluid. Parameters characterizing these conditions are obtained experimentally for a test gel. Using them, it is shown that the lubrication approximation may be applied to the elastic wall-squeezing problem for this gel.     

Biosensors based on immobilized insects fragments

The application of insect-sensing organs as parts of advanced biosensor devices with an electronic reading of the signals produced by the biological component is briefly reviewed, and some future applications are discussed. Dedicated to Professor Dr. Yakov I. Tur'yan on the occasion of his 85th birthday.     

Surface Complexation Modeling: II. Strategy for Modeling Polymer and Precipitation Reactions at High Surface Coverage

Three triple-layer model (TLM) surface complexation models that allow for the formation of multinuclear surface complexes or precipitates are compared, based on their ability to simulate cobalt sorption on α-Al₂O₃. These models include: (1) a surface solid solution model, (2) a surface polymer model, and (3) a surface continuum model. The solid solution model accounts for high coverage data by invoking a coprecipitation surface reaction, while the polymer model accomplishes the same task with multinuclear surface complexation reactions. In the continuum model, two polymer reactions and one precipitation reaction are proposed. Modeling results indicate that all of the models work reasonably well at predicting sorption data from moderate to high surface coverage (0.1 to 100%). Because the continuum model is the only one presented which is consistent with spectroscopic data throughout the range of surface coverages examined, this model is suggested as the preferred one for modeling metal ion sorption data. Model predictions of pH-edge and isotherm data are discussed and used in the assessment of the merits of the three TLM models.     

Coherent production ofρ − mesons in charged current antineutrino-neon interactions in BEBC

Coherent production ofρ ^? mesons in charged current antineutrino interactions on neon nuclei is studied in the BEBC bubble chamber exposed to the CERN SPS wide band beam. The cross section is measured to be (95±25)·10^?40 cm² per neon nucleus, averaged over the beam energy spectrum. The distributions of kinematical variables and the absolute value of the cross section are in agreement with theoretical predictions based on the CVC hypothesis and the vector meson dominance model.     

Transformation de Fourier et majoration de sommes exponentielles

Sans résumé The online version of the original article can be found at