Irreversibble Bimolecular Reactions of Langevin Particles

The reaction A+B --> B is studied when the reactants diffuse in phase space, i.e. their dynamics is described by the Langevin equation. The steady-state rate constants are calculated for both the target (static A and mobile B's) and trapping (mobile A and static B's) problems when the reaction is assumed to occur at the first contact. For Brownian dynamics (i.e., ordinary diffusion), the rate constant for both problems is a monotonically decreasing function of the friction coefficient $\gamma$. For Langevin dynamics, however, we find that the steady-state rate constant exhibits a turnover behavior as a function of $\gamma$ for the trapping problem but not for the target problem. This turnover is different from the familiar Kramers' turnover of the rate constant for escape from a deep potential well because the reaction considered here is an activationless process.Comment: 29 pages including 7 figure

Size-independence of statistics for boundary collisions of random walks and its implications for spin-polarized gases

A bounded random walk exhibits strong correlations between collisions with a boundary. For an one-dimensional walk, we obtain the full statistical distribution of the number of such collisions in a time t. In the large t limit, the fluctuations in the number of collisions are found to be size-independent (independent of the distance between boundaries). This occurs for any inter-boundary distance, including less and greater than the mean-free-path, and means that this boundary effect does not decay with increasing system-size. As an application, we consider spin-polarized gases, such as 3-Helium, in the three-dimensional diffusive regime. The above results mean that the depolarizing effect of rare magnetic-impurities in the container walls is orders of magnitude larger than a Smoluchowski assumption (to neglect correlations) would imply. This could explain why depolarization is so sensitive to the container's treatment with magnetic fields prior to its use.Comment: 5 page manuscript with extra details in appendices (additional 3 pages

Occupational Health Problem Network : the Exposome

We present a thinking on the concept of relational networks applied to the french national occupational disease surveillance and prevention network (R\'eseau National de Vigilance et de Pr\'evention des Pathologies Professionnelles, RNV3P). This approach consists in searching common exposures to occupational health problems

Influence of the Environment Fluctuations on Incoherent Neutron Scattering Functions

In extending the conventional dynamic models, we consider a simple model to account for the environment fluctuations of particle atoms in a protein system and derive the elastic incoherent structure factor (EISF) and the incoherent scattering correlation function C(Q,t) for both the jump dynamics between sites with fluctuating site interspacing and for the diffusion inside a fluctuating sphere. We find that the EISF of the system (or the normalized elastic intensity) is equal to that in the absence of fluctuations averaged over the distribution of site interspacing or sphere radius a. The scattering correlation function is $C(Q,t)=\sum_{n} \psi(t)$, where the average is taken over the Q-dependent effective distribution of relaxation rates \lambda_n(a) and \psi(t) is the correlation function of the length a. When \psi(t)=1, the relaxation of C(Q,t) is exponential for the jump dynamics between sites (since \lambda_n(a) is independent of a) while it is nonexponential for diffusion inside a sphere.Comment: 7 pages, 7 eps figure

Theoretical formulation for mosquito host-feeding patterns : Application to a west nile virus focus of Southern France

Host-feeding patterns play a key role in the transmission of vector-borne diseases such as West Nile fever, which involves two kinds of vertebrates, birds and mammals. In this study, we propose a theoretical formulation for mosquito host-feeding patterns using three quantities, as follows: the apparent attractiveness/contact probabilities, the conditional host(-feeding) preferences, and the enzootic versus bridge probabilities. Using results from host-baited trap collections, the quantities deÞned above were assessed for the most abundant mosquito species in the main West Nile virus focus of southern France.Wefound that host availability is important in determining the efÞciency of bridge vectors, and that even ornithophilic mosquitoes like Culex species, classically classiÞed as enzootic vectors, may turn out to be efÞcient bridge vectors in certain contexts of host abundance. Our developed theoretical framework can easily be adapted and applied to other experimental data and other vector-borne diseases. (Résumé d'auteur

Long range correlations in DNA : scaling properties and charge transfer efficiency

We address the relation between long range correlations and charge transfer efficiency in aperiodic artificial or genomic DNA sequences. Coherent charge transfer through the HOMO states of the guanine nucleotide is studied using the transmission approach, and focus is made on how the sequence-dependent backscattering profile can be inferred from correlations between base pairs.Comment: Submitted to Phys. Rev. Let

Simulation of a semiflexible polymer in a narrow cylindrical pore

The probability that a randomly accelerated particle in two dimensions has not yet left a simply connected domain ${\cal A}$ after a time $t$ decays as $e^{-E_0t}$ for long times. The same quantity $E_0$ also determines the confinement free energy per unit length $\Delta f=k_BT\thinspace E_0$ of a semiflexible polymer in a narrow cylindrical pore with cross section ${\cal A}$. From simulations of a randomly accelerated particle we estimate the universal amplitude of $\Delta f$ for both circular and rectangular cross sections.Comment: 10 pages, 2 eps figure