Biomedical subjects

A Drzewiński

Publications and source records attributed to A Drzewiński.

6 recordsLinked to original sources

PubMed2003

Pulling reptating polymers by one end: magnetophoresis in the Rubinstein-Duke model.

We consider the magnetophoresis problem within the Rubinstein-Duke model, i.e., a reptating polymer pulled by a constant field applied to a single end of a chain. Extensive density matrix renormalization calculations are presented of the drift velocity and the profile of the chain for various strengths of the driving field and chain lengths. We show that the velocities and the average densities of the stored length are well described by simple interpolating crossover formulas, derived under the assumption that the difference between the drift and curvilinear velocities vanishes for sufficiently long chains. The profiles, which describe the average shape of the reptating chain, also show such interesting features as some nonmonotonic behavior of the link densities for sufficiently strong pulling fields. We develop a description in which a distinction is made between links entering at the pulled head and at the unpulled tail. At weak fields the separation between the head zone and the tail zone meanders through the whole chain, while the probability of finding it close to the edges drops off. At strong fields the tail zone is confined to a small region close to the unpulled edge of the polymer.

Journal Article↗

PubMed2001

Near-critical confined fluids and Ising films: density-matrix renormalization-group study.

Two-dimensional Ising strips subject to identical surface fields h(1)=h(2) > or =0 are studied for temperatures above and below the bulk critical temperature T(c) and a range of bulk fields h by means of the density-matrix renormalization-group method. In the case of nonvanishing surface fields, the near-critical behavior of the solvation force f(solv), total adsorption Gamma, inverse longitudinal correlation length xi(parallel)( -1) and specific heat C(H) is strongly influenced by the (pseudo) capillary condensation that occurs below T(c). We obtain scaling functions of f(solv), Gamma, and xi(parallel)(-1). C(H) exhibits a weakly rounded singularity on crossing the pseudocoexistence line. We contrast these results with those for the case of free boundaries where, for temperatures slightly below T(c), f(solv) and C(H) exhibit a sharp extremum away from h=0. Our results have direct repercussions for the properties of near-critical Ising films in three dimensions and we argue that the long-ranged solvation (Casimir) force in confined fluids should be more attractive in the neighborhood of the capillary critical point than exactly at the bulk critical point.

Journal Article↗

PubMed2001

Universal phase boundary shifts for corner wetting and filling.

The phase boundaries for corner wetting (filling) in square and diagonal lattice Ising models are exactly determined and show a universal shift relative to wetting near the bulk criticality. More generally, scaling theory predicts that the filling phase boundary shift for wedges and cones is determined by a universal scaling function R(d)(psi) depending only on the opening angle 2psi. R(d)(psi) is determined exactly in d = 2 and approximately in higher dimensions using nonclassical local functional and mean-field theory. Detailed numerical transfer matrix studies of the magnetization profile in finite-size Ising squares support the conjectured connection between filling and the strong-fluctuation regime of wetting.

Journal Article↗

PubMed2001

Crossover behavior for long reptating polymers.

The Rubinstein-Duke model for polymer reptation is analyzed by means of density matrix renormalization techniques. It is found that the crossover in the scaling behavior of polymer renewal time (or viscosity) arises from the competing effect of the contribution due to tube length fluctuations and higher-order corrections, which are of opposite sign. Experiments which ought to emphasize both contributions are suggested. The exponent describing the subleading scaling behavior of the diffusion coefficient is also investigated.

Journal Article↗

PubMed2000

Influence of capillary condensation on the near-critical solvation force.

We argue that in a fluid, or magnet, confined by adsorbing walls which favor liquid, or the (+) phase, the solvation (Casimir) force in the vicinity of the critical point is strongly influenced by capillary condensation which occurs below the bulk critical temperature T(c). At T slightly below and above T(c), a small bulk field h<0, which favors gas, or the (-) phase, leads to residual condensation and a solvation force which is much more attractive (at the same large wall separation) than that found exactly at the critical point. Our predictions are supported by results obtained from density-matrix renormalization-group calculations in a two-dimensional Ising strip subject to identical surface fields.

Journal Article↗

PubMed1999

Crossover between ordinary and normal transitions in two dimensional critical Ising films.

We investigate two dimensional critical Ising films of width L with surface fields H(1)=H(L) in the crossover between ordinary (H(1)=0) and normal (H(1)=infinity) transitions. Using exact transfer-matrix diagonalization and density matrix renormalization-group (DMRG) methods, we calculate magnetization profiles m(z), the excess magnetization Gamma, and the analog of the solvation force f(solv) as functions of H1 for several L. Scaling functions of the above quantities deviate substantially from their asymptotic forms at fixed points for a broad region of the scaling variable LH21 approximately L/l(1), where l(1) is the length induced by the surface field H1. The scaling function for /f(solv)/ has a deep minimum near LH(2)(1)=1, which is about one order of magnitude smaller than its value at both fixed points (the "Casimir" amplitude). For weak H1 (l(1)>L) the magnetization profile has a maximum at the center of the film, and f(solv) decays much faster than L-2. For stronger H1 (1 >l(1) the solvation force decays according to the universal power law f(solv) approximately L(-2). The results of the approximate DMRG method show remarkable agreement with the exact ones.

Journal Article↗