Optimal Coarse-Grained Site Selection in Elastic Network Models of Biomolecules.

Elastic network models, simple structure-based representations of biomolecules where atoms interact via short-range harmonic potentials, provide great insight into a molecule's internal dynamics and mechanical properties at extremely low computational cost. Their efficiency and effectiveness have made them a pivotal instrument in the computer-aided study of proteins and, since a few years, also of nucleic acids. In general, the coarse-grained sites, i.

Curvature Softening and Negative Compressibility of Gel-Phase Lipid Membranes.

We show that gel-phase lipid membranes soften upon bending, leading to curvature localization and a negative compressibility. Using simulations of two very different lipid models to quantify shape and stress-strain relation of buckled membranes, we demonstrate that gel phase bilayers do not behave like Euler elastica and hence are not well described by a quadratic Helfrich Hamiltonian, much unlike their fluid-phase counterparts. We propose a theoretical framework which accounts for the observed softening through an energy density that smoothly crosses over from a quadratic to a linear curvature dependence beyond a critical new scale [Formula: see text](-1).

Determining the bending modulus of a lipid membrane by simulating buckling.

The force needed to buckle a thin elastic surface is proportional to its bending rigidity. This fact suggests using a buckling setup to measure the bending modulus of lipid membranes. Extending the work of Noguchi [Phys.

Improved adhesion of ultra-hard carbon films on cobalt-chromium orthopaedic implant alloy.

While interfacial graphite formation and subsequent poor film adhesion is commonly reported for chemical vapor deposited hard carbon films on cobalt-based materials, we find the presence of O(2) in the feedgas mixture to be useful in achieving adhesion on a CoCrMo alloy. Nucleation studies of surface structure before formation of fully coalesced hard carbon films reveal that O(2) feedgas helps mask the catalytic effect of cobalt with carbon through early formation of chromium oxides and carbides. The chromium oxides, in particular, act as a diffusion barrier to cobalt, minimizing its migration to the surface where it would otherwise interact deleteriously with carbon to form graphite.