Raft Instability of Biopolymer Gels

Following recent X-ray diffraction experiments by Wong, Li, and Safinya on biopolymer gels, we apply Onsager excluded volume theory to a nematic mixture of rigid rods and strong ``$\pi/2$'' cross-linkers obtaining a long-ranged, highly anisotropic depletion attraction between the linkers. This attraction leads to breakdown of the percolation theory for this class of gels, to breakdown of Onsager's second-order virial method, and to formation of heterogeneities in the form of raft-like ribbons.Comment: 5 pages, 4 figure

Frustrated Polyelectrolyte Bundles and T=0 Josephson-Junction Arrays

We establish a one-to-one mapping between a model for hexagonal polyelectrolyte bundles and a model for two-dimensional, frustrated Josephson-junction arrays. We find that the T=0 insulator-to-superconductor transition of the {\it quantum} system corresponds to a continuous liquid-to-solid transition of the condensed charge in the finite temperature {\it classical} system. We find that the role of the vector potential in the quantum system is played by elastic strain in the classical system. Exploiting this correspondence we show that the transition is accompanied by a spontaneous breaking of chiral symmetry and that at the transition the polyelectrolyte bundle adopts a universal response to shear.Comment: 4 pages, 2 figures, 1 table minor changes to text, reference adde

The impact of new infrastructure on the spatial patterns of economic activities

This article attempts to present a systematic overview of the impact of transport infrastructure on spatial patterns of economic activities.The central element is that an improvement in the transport infrastructure leads to lower interaction costs. This has three major effects. First, anincrease in the access of actors and the accessibility of locations. Second an increase in the productivity of firms and households. Third, a change inthe volume and location of activities of firms and households. There also exist feed backs and intermediate factors which have an important impact onthe strength and time period in which transport infrastructure affects economicdevelopment. The overview of approaches show that major steps forward can be made bylinking modelling and non-modelling approaches

Viral self-assembly as a thermodynamic process

The protein shells, or capsids, of all sphere-like viruses adopt icosahedral symmetry. In the present paper we propose a statistical thermodynamic model for viral self-assembly. We find that icosahedral symmetry is not expected for viral capsids constructed from structurally identical protein subunits and that this symmetry requires (at least) two internal "switching" configurations of the protein. Our results indicate that icosahedral symmetry is not a generic consequence of free energy minimization but requires optimization of internal structural parameters of the capsid proteins.Comment: pdf file, 13 pages, three figure