1,255 research outputs found
Efficiency of encounter-controlled reaction between diffusing reactants in a finite lattice: topology and boundary effects
The role of dimensionality (Euclidean versus fractal), spatial extent,
boundary effects and system topology on the efficiency of diffusion-reaction
processes involving two simultaneously-diffusing reactants is analyzed. We
present numerically-exact values for the mean time to reaction, as gauged by
the mean walklength before reactive encounter, obtained via application of the
theory of finite Markov processes, and via Monte Carlo simulation. As a general
rule, we conclude that for sufficiently large systems, the efficiency of
diffusion-reaction processes involving two synchronously diffusing reactants
(two-walker case) relative to processes in which one reactant of a pair is
anchored at some point in the reaction space (one walker plus trap case) is
higher, and is enhanced the lower the dimensionality of the system. This
differential efficiency becomes larger with increasing system size and, for
periodic systems, its asymptotic value may depend on the parity of the lattice.
Imposing confining boundaries on the system enhances the differential
efficiency relative to the periodic case, while decreasing the absolute
efficiencies of both two-walker and one walker plus trap processes. Analytic
arguments are presented to provide a rationale for the results obtained. The
insights afforded by the analysis to the design of heterogeneous catalyst
systems are also discussed.Comment: 15 pages, 8 figures, uses revtex4, accepted for publication in
Physica
Polyelectrolyte Bundles
Using extensive Molecular Dynamics simulations we study the behavior of
polyelectrolytes with hydrophobic side chains, which are known to form
cylindrical micelles in aqueous solution. We investigate the stability of such
bundles with respect to hydrophobicity, the strength of the electrostatic
interaction, and the bundle size. We show that for the parameter range relevant
for sulfonated poly-para-phenylenes (PPP) one finds a stable finite bundle
size. In a more generic model we also show the influence of the length of the
precursor oligomer on the stability of the bundles. We also point out that our
model has close similarities to DNA solutions with added condensing agents,
hinting to the possibility that the size of DNA aggregates is under certain
circumstances thermodynamically limited.Comment: 10 pages, 8 figure
Stress Induced Protein Changes in Tall Fescue
Tall fescue (Festuca arundinacea Schreb.), the most important pasture grass in Arkansas, exhibits different agricultural properties when it is infected by its mutualistic endophyte Acremonium coenophialum Morgan-Jones and Gams. We postulate that the presence of endophyte exerts a stress on the host that enhances or detracts from the host\u27s ability to express specific genes. We tested this hypothesis by heat stressing infected and non-infected, juvenile and mature tall fescue, and examining their protein profiles by SDS-PAGE analysis. The results indicate that mature, infected, stressed grass produced greater amounts of Rubisco (ribulose bisphosphate carboxylase-oxygenase) than all other treatments. Additionally, the mature, infected, stressed grass exhibited a 20 k Dalton protein band which was not apparent in other treatments. These observations support the possibility that the endophyte prestresses the grass, and they suggest a molecular mechanism for this response
Hydrodynamic coupling between two fluid membranes
The coupled in-plane diffusion dynamics between point-particles embedded in
stacked fluid membranes are investigated. We calculate the contributions to the
coupling longitudinal and transverse diffusion coefficients due to particle
motion within the different as well as the same membranes. The stacked geometry
leads to a hydrodynamic coupling between the two membranes.Comment: 9 Pages, 5 figures. Accepted for publication in J. Phys.: Condens.
Matte
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