Vapour—liquid equilibrium of the square-well fluid of variable range via a hybrid simulation approach

The equilibrium between vapour and liquid in a square-well system has been determined by a hybrid simulation approach combining chemical potentials calculated via the Gibbs ensemble Monte Carlo technique with pressures calculated by the standard NVT Monte Carlo method. The phase equilibrium was determined from the thermodynamic conditions of equality of pressure and chemical potential between the two phases. The results of this hybrid approach were tested by independent NPT and μPT calculations and are shown to be of much higher accuracy than those of conventional GEMC simulations. The coexistence curves, vapour pressures and critical points were determined for SW systems of interaction ranges λ = 1.25, 1.5, 1.75 and 2. The new results show a systematic dependence on the range λ, in agreement with results from perturbation theory where previous work had shown more erratic behaviour.     

PHOTO-ELECTRIC EFFECTS IN BILAYER MEMBRANES; ELECTROMETERS AND VOLTAGE CLAMPS COMPARED

Abstract— Laser flash induced voltage transients recorded with high speed electrometers are compared to signals generated by voltage clamps, using chromophores which generate photo-electric effects in membranes by different mechanisms and with time constants that varied from < 100 ns to > 1 s. The chromophores used were; (i) azo dye, 3,3-bis-(α-(trimethylammonium)methyl) azobenzene-bromide, (ii) cyanine dye, 3,3-dimethyl-2,2-oxacarbocyanine-chloride, (iii) xanthene dye, 2,4, 5, 7-tetraiodofluorescein or erythrosin, and (iv) chlorophyll a . A scheme for classifying photo-electric effects is presented. Voltage clamp signals are functions of both apparatus and photo-current time constants. They vary with aqueous solution salt concentration, and usually mask kinetic information that may be obtained with electrometers.     

Modelling of Non-coalescing Liquid Drops in the Presence of Thermocapillary Convection

A fluid-dynamic model of two non-coalescing liquid drops of the same liquid, pressed against one another in the presence of thermocapillary convection, is proposed to correlate experimental results on the deformation of the drop surfaces, on the pressure distribution and on the thickness of the air film between the drops. The two-point boundary value problem for the Gauss–Laplace hydrostaticequation, subjected to the constant volume constraint, is solved by a fourth order Runge Kutta method to evaluatethe shapes of the drops for different values of the applied pressure jump across the surface exposed to a constant ambient pressure. The flow fields in the liquid drops and in the air layer are obtained by numerical solutions of the dynamic problem. Thenumerical results qualitatively agree with the experimental ones, explain why an air film could be created between the two drops and show that film thicknesses of some microns exist with excess pressures of the same order of magnitude of the pressure needed to deform the drops.     

Asymptotic behaviour of the ratio of density gradient to electron density for atomic systems

The asymptotic behaviour of the negative ratio of the density gradient to the electron density, q(r), for neutral and singly charged atoms has been investigated. The results show that, for large r, q(r) can approach its limit √8?, where ? is the first ionization potential, from either above or below depending on the specific system considered.