RESUMEN
We present a measurement of the longitudinal spin asymmetry A(||) in photoproduction of pairs of hadrons with high transverse momentum p(T). Data were accumulated by the HERMES experiment using a 27.5 GeV polarized positron beam and a polarized hydrogen target internal to the HERA storage ring. For h(+)h(-) pairs with p(h(1))(T)>1.5 GeV/c and p(h(2))(T)>1.0 GeV/c, the measured asymmetry is A(||) = -0. 28+/-0.12(stat)+/-0.02(syst). This negative value is in contrast to the positive asymmetries typically measured in deep inelastic scattering from protons, and is interpreted to arise from a positive gluon polarization.
RESUMEN
Phase behavior and videomicroscopy experiments were used to investigate spontaneous emulsification of n-hexadecane/oleyl alcohol/C12E6 mixtures in water at 30 degreesC. It was found that complete emulsification of a drop of the oil phase to form small oil droplets having diameters of about 1 µm occurred only when diffusion of water into the initial oil drop first converted it completely into the lamellar liquid crystalline phase and/or a microemulsion and then caused this phase (or these phases) to become supersaturated in oil so that many oil droplets nucleated. This behavior occurred when the hydrocarbon/alcohol ratio of the initial oil drop was near that of the excess oil phase for a balanced system at this temperature, i.e., at the phase inversion temperature (PIT), and when surfactant content was sufficiently high. The stability of these emulsions was investigated by means of turbidity measurements. The most stable emulsion appeared to occur under conditions where the drops were coated by a layer of the lamellar phase. Copyright 1999 Academic Press.
RESUMEN
Drainage of a mobile, symmetric, plane parallel thin liquid film between two gas bubbles is studied. An analytical solution for the rate of thinning of such a liquid film with an insoluble surfactant and having both film elasticity and surface viscosity is presented for the first time. Analysis is extended to the more general case of a soluble surfactant and compared with previous analyses. Surfactant material parameters affecting the rate of thinning are identified and grouped into a single dimensionless parameter which describes the transition from a mobile to an immobile film. Significant deviation from the Reynolds velocity is found when this dimensionless parameter is small.
RESUMEN
Dimple formation has been studied numerically in foam films formed in the conventional Scheludko-Exerowa cell and in a miniature cell recently developed by O. D. Velev et al. (J. Colloid Interface Sci. 175, 68 (1995)). Results of the simulations provide a criterion for dimple formation in the conventional cell in the absence of disjoining pressure. Because the films in the miniature cell are very thin, disjoining pressure effects are important even during the liquid withdrawal step when the film is initially formed. If the disjoining pressure is repulsive, film thickness remains nearly uniform and constant as observed experimentally by the above authors. In other cases the simulations predict that dimple formation will occur in the miniature cell but that it will not be detectable by the usual interference techniques because film thickness is less than one-fourth the wavelength of visible light.