906 research outputs found
The Importance of Boundary Conditions for Fluctuation Induced Forces between Colloids at Interfaces
We calculate the effective fluctuation induced force between spherical or
disk-like colloids trapped at a flat, fluid interface mediated by thermally
excited capillary waves. This Casimir type force is determined by the partition
function of the system which in turn is calculated in a functional integral
approach, where the restrictions on the capillary waves imposed by the colloids
are incorporated by auxiliary fields. In the long-range regime the fluctuation
induced force is shown to depend sensitively on the boundary conditions imposed
at the three-phase contact line between the colloids and the two fluid phases.
The splitting of the fluctuating capillary wave field into a mean-field and a
fluctuation part leads to competing repulsive and attractive contributions,
respectively, which give rise to cancellations of the leading terms. In a
second approach based on multipole expansion of the Casimir interaction, these
cancellations can be understood from the vanishing of certain multipole moments
enforced by the boundary conditions. We also discuss the connection of the
different types of boundary conditions to certain external fields acting on the
colloids which appear to be realizable by experimental techniques such as the
laser tweezer method.Comment: 24 pages, 4 figure
Effective forces between colloids at interfaces induced by capillary wave-like fluctuations
We calculate the effective force mediated by thermally excited capillary
waves between spherical or disklike colloids trapped at a fluid interface. This
Casimir type interaction is shown to depend sensitively on the boundary
conditions imposed at the three-phase contact line. For large distances between
the colloids an unexpected cancellation of attractive and repulsive
contributions is observed leading to a fluctuation force which decays
algebraically very rapidly. For small separations the resulting force is rather
strong and it may play an important role in two-dimensional colloid aggregation
if direct van der Waals forces are weak.Comment: 7 pages, 3 figures, minor revisions, one additional figur
Low temperature electron transfer in strongly condensed phase
Electron transfer coupled to a collective vibronic degree of freedom is
studied in strongly condensed phase and at lower temperatures where quantum
fluctuations are essential. Based on an exact representation of the reduced
density matrix of the electronic+reaction coordinate compound in terms of path
integrals, recent findings on the overdamped limit in quantum dissipative
systems are employed. This allows to give for the first time a consistent
generalization of the well-known Zusman equations to the quantum domain.
Detailed conditions for the range of validity are specified. Using the Wigner
transform these results are also extended to the quantum dynamics in full phase
space. As an important application electronic transfer rates are derived that
comprise adiabatic and nonadiabatic processes in the low temperature regime
including nuclear tunneling. Accurate agreement with precise quantum Monte
Carlo data is observed.Comment: 16 pages, 6 figures, revised version with minor change
Plant cells synthesize glucose-containing lipid-linked oligosaccharides similar to those found in animals and yeast
Solvent-mediated interactions between nanoparticles at fluid interfaces
We investigate the solvent mediated interactions between nanoparticles
adsorbed at a liquid-vapor interface in comparison to the solvent mediated
interactions in the bulk liquid and vapor phases of a Lennard-Jones solvent.
Molecular dynamics simulation data for the latter are in good agreement with
results from integral equations in the reference functional approximation and a
simple geometric approximation. Simulation results for the solvent mediated
interactions at the interface differ markedly from the interactions of the
particles in the corresponding bulk phases. We find that at short interparticle
distances the interactions are considerably more repulsive than those in either
bulk phase. At long interparticle distances we find evidence for a long-ranged
attraction. We discuss these observations in terms of interfacial interactions,
namely, the three-phase line tension that would operate at short distances, and
capillary wave interactions for longer interparticle distances.Comment: 22 pages, 6 figure
Analysis of stochastic time series in the presence of strong measurement noise
A new approach for the analysis of Langevin-type stochastic processes in the
presence of strong measurement noise is presented. For the case of Gaussian
distributed, exponentially correlated, measurement noise it is possible to
extract the strength and the correlation time of the noise as well as
polynomial approximations of the drift and diffusion functions from the
underlying Langevin equation.Comment: 12 pages, 10 figures; corrected typos and reference
Dysbalance of intestinal inflammation and immunity in patients with inherited caspase-8 deficiency
Physiological and ultrastructural investigations of caryopsis dormancy in Setaria lutescens (Gramineae)
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