Biomedical subjects

Benoit Palmieri

Publications and source records attributed to Benoit Palmieri.

3 recordsLinked to original sources

PubMed2006

Effective classical partition functions with an improved time-dependent reference potential.

The original Feynman-Kleinert [Phys. Rev. A 34, 5080 (1986)] variational approach to Euclidean path integrals is improved by introducing a reference harmonic potential whose center is allowed to change with time. The motion of the center of the potential is varied such that the "effective potential" of Feynman and Kleinert is minimized and leads to an equation of motion for the classical path in the reference system that closely reproduces the "exact" average path. The formalism is applied to the double-well potential V(x)=-x(2)/2 + gx(4)/4+1/4g. This modification improves the accuracy of the approximate quantum-mechanical distribution function and, to a larger extent, the density matrix.

Journal Article↗

PubMed2005

Diffusion in channeled structures. II. Systems with large energy barriers.

The methods developed in a previous paper (Phys. Rev. E.: Stat. Phys., Plasmas, Fluids, Relat. Interdiscip. Top. 2003, 68, 046127) are used to calculate the permeability of argon in alpha-quartz, a system containing large energy barriers. The permeability is reported at three different temperatures and follows Arrhenius behavior. The permeabilities obtained from a hopping model combined with transition state theory closely follow our predicted values but are systematically lower. Lattice flexibility cannot be neglected in this system, and the energy-transfer between alpha-quartz and the argon atom through lattice vibrations occurs on a fast enough time scale such that it plays a role in the guest diffusive motion.

Journal Article↗

PubMed2003

Diffusion in channeled structures: xenon in a crystalline sodalite.

The theory of Ronis and Vertenstein [J. Chem. Phys. 85, 1628 (1986)] is used to calculate the permeability of xenon in Theta-1, a crystalline sodalite containing one-dimensional channels. The required time-correlation functions are obtained from numerical simulations performed using a small number of target crystal atoms. The dynamics of the target atoms reproduce those of the full crystal by the means of a generalized Langevin equation of motion. An approximate expression for the potential of mean force inside the crystal is derived. The plane average space-dependent diffusion coefficient D(z) obeys the Smoluchowski prediction at infinite dilution. The permeability is reported and compared in detail with that obtained from transition state theory.

Journal Article↗