Biopolymer Adsorption, with Special Reference to the Serum Albumin-Polystyrene Latex System

A study has been made of the adsorption of human serum albumin (HSA) on emursifier-free, negatively charged polystyrene (PS) latices. The adsorption has been followed directly and microcalorimetrically. Important variables are: pH, temperature, csalt and the surface charge a0 of the latex. Although all adsorption isotherms have a platform, the Langmuir theory is inadequate to account for them. Distinction must be made between the initial stages of adsorption, solely determined by the HSA-PS interaction and the later stages, where lateral interaction between adsorbed HSA molecules plays also an important role. The adsorption platform as a function of pH is maximal in the isoelectric point. Here the adsorbed amount is roughly compatible with side-on native HSA molecules. Both below and above the i. e. p. adsorption proceeds in a more unfolded conformation but a spread monolayer is never reached. The adsorption is largely driven by a net entropy gain, both in the initial and later states of the process. Besides this, there is a recognizable influence of the electrostatic attraction between the latex surface and local positive excesses inside the molecule

Biopolymer Adsorption, with Special Reference to the Serum Albumin-Polystyrene Latex System

A study has been made of the adsorption of human serum albumin (HSA) on emursifier-free, negatively charged polystyrene (PS) latices. The adsorption has been followed directly and microcalorimetrically. Important variables are: pH, temperature, csalt and the surface charge a0 of the latex. Although all adsorption isotherms have a platform, the Langmuir theory is inadequate to account for them. Distinction must be made between the initial stages of adsorption, solely determined by the HSA-PS interaction and the later stages, where lateral interaction between adsorbed HSA molecules plays also an important role. The adsorption platform as a function of pH is maximal in the isoelectric point. Here the adsorbed amount is roughly compatible with side-on native HSA molecules. Both below and above the i. e. p. adsorption proceeds in a more unfolded conformation but a spread monolayer is never reached. The adsorption is largely driven by a net entropy gain, both in the initial and later states of the process. Besides this, there is a recognizable influence of the electrostatic attraction between the latex surface and local positive excesses inside the molecule

Universality of collapsing two-dimensional self-avoiding trails

Results of a numerically exact transfer matrix calculation for the model of Interacting Self-Avoiding Trails are presented. The results lead to the conclusion that, at the collapse transition, Self-Avoiding Trails are in the same universality class as the O(n=0) model of Blote and Nienhuis (or vertex-interacting self-avoiding walk), which has thermal exponent $\nu=12/23$, contrary to previous conjectures.Comment: Final version, accepted for publication in Journal of Physics A; 9 pages; 3 figure

Monte Carlo study of the hull distribution for the q=1 Brauer model

We study a special case of the Brauer model in which every path of the model has weight q=1. The model has been studied before as a solvable lattice model and can be viewed as a Lorentz lattice gas. The paths of the model are also called self-avoiding trails. We consider the model in a triangle with boundary conditions such that one of the trails must cross the triangle from a corner to the opposite side. Motivated by similarities between this model, SLE(6) and critical percolation, we investigate the distribution of the hull generated by this trail (the set of points on or surrounded by the trail) up to the hitting time of the side of the triangle opposite the starting point. Our Monte Carlo results are consistent with the hypothesis that for system size tending to infinity, the hull distribution is the same as that of a Brownian motion with perpendicular reflection on the boundary.Comment: 21 pages, 9 figure

Nonlinear electrochemical relaxation around conductors

We analyze the simplest problem of electrochemical relaxation in more than one dimension - the response of an uncharged, ideally polarizable metallic sphere (or cylinder) in a symmetric, binary electrolyte to a uniform electric field. In order to go beyond the circuit approximation for thin double layers, our analysis is based on the Poisson-Nernst-Planck (PNP) equations of dilute solution theory. Unlike most previous studies, however, we focus on the nonlinear regime, where the applied voltage across the conductor is larger than the thermal voltage. In such strong electric fields, the classical model predicts that the double layer adsorbs enough ions to produce bulk concentration gradients and surface conduction. Our analysis begins with a general derivation of surface conservation laws in the thin double-layer limit, which provide effective boundary conditions on the quasi-neutral bulk. We solve the resulting nonlinear partial differential equations numerically for strong fields and also perform a time-dependent asymptotic analysis for weaker fields, where bulk diffusion and surface conduction arise as first-order corrections. We also derive various dimensionless parameters comparing surface to bulk transport processes, which generalize the Bikerman-Dukhin number. Our results have basic relevance for double-layer charging dynamics and nonlinear electrokinetics in the ubiquitous PNP approximation.Comment: 25 pages, 17 figures, 4 table

Surface critical behaviour of the Interacting Self-Avoiding Trail on the square lattice

The surface critical behaviour of the interacting self-avoiding trail is examined using transfer matrix methods coupled with finite-size scaling. Particular attention is paid to the critical exponents at the ordinary and special points along the collapse transition line. The phase diagram is also presented.Comment: Journal of Physics A (accepted

Stochastic series expansion method with operator-loop update

A cluster update (the ``operator-loop'') is developed within the framework of a numerically exact quantum Monte Carlo method based on the power series expansion of exp(-BH) (stochastic series expansion). The method is generally applicable to a wide class of lattice Hamiltonians for which the expansion is positive definite. For some important models the operator-loop algorithm is more efficient than loop updates previously developed for ``worldline'' simulations. The method is here tested on a two-dimensional anisotropic Heisenberg antiferromagnet in a magnetic field.Comment: 5 pages, 4 figure

Kinetic growth walks on complex networks

Kinetically grown self-avoiding walks on various types of generalized random networks have been studied. Networks with short- and long-tailed degree distributions $P(k)$ were considered ($k$, degree or connectivity), including scale-free networks with $P(k) \sim k^{-\gamma}$. The long-range behaviour of self-avoiding walks on random networks is found to be determined by finite-size effects. The mean self-intersection length of non-reversal random walks, , scales as a power of the system size $N$: $ \sim N^{\beta}$, with an exponent $\beta = 0.5$ for short-tailed degree distributions and $\beta < 0.5$ for scale-free networks with $\gamma < 3$. The mean attrition length of kinetic growth walks, , scales as $\sim N^{\alpha}$, with an exponent $\alpha$ which depends on the lowest degree in the network. Results of approximate probabilistic calculations are supported by those derived from simulations of various kinds of networks. The efficiency of kinetic growth walks to explore networks is largely reduced by inhomogeneity in the degree distribution, as happens for scale-free networks.Comment: 10 pages, 8 figure

Exact Multifractal Spectra for Arbitrary Laplacian Random Walks

Iterated conformal mappings are used to obtain exact multifractal spectra of the harmonic measure for arbitrary Laplacian random walks in two dimensions. Separate spectra are found to describe scaling of the growth measure in time, of the measure near the growth tip, and of the measure away from the growth tip. The spectra away from the tip coincide with those of conformally invariant equilibrium systems with arbitrary central charge $c\leq 1$, with $c$ related to the particular walk chosen, while the scaling in time and near the tip cannot be obtained from the equilibrium properties.Comment: 4 pages, 3 figures; references added, minor correction