Universal dynamic exponent at the liquid-gas transition from molecular dynamics

The liquid-gas system is expected to exhibit distinct dynamic behavior in the fluid's critical region (model H). We present molecular dynamics simulations of a Lennard-Jones fluid model starting from specially designed, near-equilibrium, initial conditions. By following the fluid's relaxation towards equilibrium, we calculate the requisite transport coefficients in the critical region. The results yield the scaling behavior of the thermal diffusion coefficient D(T) approximately xi(-1.023+/-0.018) (xi is the correlation length) and a nonconventional divergent heat conductivity, all of which are in accord with mode-coupling and renormalization group predictions, as well as some experimental data.     

Diffusion trapping times and dynamic percolation in an Ising system

We address the problem of diffusion through dynamic Ising network structures using random walkers (RWs) whose net displacements are partitioned into two contributions, arising from (1) transport through neighboring "conducting" clusters and (2) self-diffusion of the site on which the RW finds itself, respectively. At finite temperatures, the conducting clusters in the network exhibit correlated dynamic behavior, making our model system different to most prior published work, which has largely been at the random percolation limit. We also present a novel heuristic scaling analysis for this system that utilizes a new scaling exponent theta(z) for representing RW trapping time as a function of "distance" from the dynamic percolation transition. Simulation results in two-dimensional networks show that when theta(z) = 2, a value found from independent physical arguments, our scaling equations appear to capture universal behavior in the system, at both the random percolation (infinite temperature) and finite temperature conditions studied. This study suggests that the model and the scaling approach given here should prove useful for studying transport in physical systems showing dynamic disorder.     

Substrate specificity analysis of protein kinase complex Dbf2-Mob1 by peptide library and proteome array screening

Background  

The mitotic exit network (MEN) is a group of proteins that form a signaling cascade that is essential for cells to exit mitosis in Saccharomyces cerevisiae. The MEN has also been implicated in playing a role in cytokinesis. Two components of this signaling pathway are the protein kinase Dbf2 and its binding partner essential for its kinase activity, Mob1. The components of MEN that act upstream of Dbf2-Mob1 have been characterized, but physiological substrates for Dbf2-Mob1 have yet to be identified.     

Classical, non-classical critical divergences and partial molar properties from adsorption measurements in near-critical mixtures

This paper presents results related to the development of methods for measuring and analyzing dilute solute thermodynamic properties in near-critical solvent mixtures. An analysis of limiting conditions at the system's critical point provides results that were used to analyze capacity factor data for a variety of organic solutes in near-critical mixtures of carbon dioxide and ethane. Both classical and non-classical perspectives were employed in the analysis, with particular focus on solvent mixtures with compositions close to that of the critical azeotrope in the carbon dioxide---ethane system. These solvent mixtures have unique critical divergence properties and the theoretical results obtained for this system are qualitatively borne out by the data taken. Partial molar volumes and enthalpies for several dilute solutes at a range of thermodynamic conditions have been presented in mixtures of 0.26, 0.30 and 0.70 mole fraction ethane in carbon dioxide. The isothermal data were taken at three temperatures (308, 328 and 343 K) and pressures ranged from 50 to 107 bar. The isobaric data were taken at 65.3 and 75.5 bar over a temperature range of 295.5–441 K. The solutes used were benzene, toluene, o-xylene, naphthalene and 2,6-dimethylnaphthalene. Because at the present time such data are not available in the published literature these data were often compared with values obtained by model calculations. Agreement between the two approaches has been fairly good and suggests that the approach taken here should contribute towards developing methods for reliable and rapid thermodynamic property estimation in mixtures.     

Steady streaming around a spherical drop displaced from the velocity antinode in an acoustic levitation field

The steady (acoustic) streaming associated with a sphericaldrop displaced from the velocity antinode of a standing waveis studied. The ratio of the particle size to the acoustic wavelengthis treated as small but non-zero, and the solution is developedin the form of a two-term expansion in terms of the correspondingsmallness parameter. The drop viscosity is assumed to be muchhigher than that of the surrounding fluid, which is the casefor a drop in a gas medium. There are essentially three distinctregions where the steady streaming flow is analysed: insidethe drop (internal circulation), in the Stokes shear-wave layerat the surface on the gas side, and the gas outside the Stokeslayer (the outer streaming region). Solutions for the internalcirculation and the outer streaming are obtained in the limitof small Reynolds number. Despite the gas-to-liquid viscosity ratio being small, the outerstreaming may be dramatically affected by the fact that thesphere is liquid as opposed to solid. The parameter that measuresthe effect of liquidity is essentially the viscosity ratio dividedby the relative (to the particle size) thickness of the Stokeslayer. The case of a solid sphere is recovered by letting thisparameter go to zero.     

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