The elastic behavior of mixed bilayers composed of two amphiphilic components with different chain length ~and identical head groups! is studied using two molecular level models. In both, the bilayer free energy is expressed as a sum of chain, head group and interfacial contributions as well as a mixing entropy term. The head group and interfacial terms are modeled using simple phenomenological...

We evaluate the effective Hamiltonian governing, at the optically resolved scale, the elastic properties of micromanipulated membranes. We identify floppy, entropic-tense and stretched-tense regimes, representing different behaviors of the effective-area elasticity of the membrane. The corresponding effective tension depends on the microscopic parameters (total area, bending rigidity) and on th...

Red-cell shape is encoded in the mechanical properties of the membrane. The plasma membrane contributes bending rigidity; the protein-based membrane skeleton contributes stretch and shear elasticity. When both effects are included, membrane mechanics can reproduce in detail the full stomatocyte-discocyte-echinocyte sequence by variation of a single parameter related to the bilayer couple origin...

The Kerr effect on vesicle-likedroplets (vesicles, cells or emulsion droplets) is described. Wegive a derivation of the Kerr constant for a dielectric fluiddroplet immersed in another fluid, assuming that the droplet in aweak electric field becomes a prolate ellipsoid. The Kerr constantis evaluated also for a droplet covered by a membrane of nonzerothickness. Comparing the theory with the exper...

We numerically investigate the rigidity percolation transition in two-dimensional flexible, random rod networks with freely rotating cross links. Near the transition, networks are dominated by bending modes and the elastic modulii vanish with an exponent f=3.0+/-0.2, in contrast with central force percolation which shares the same geometric exponents. This indicates that universality for geomet...

Destabilization of soft interfaces into thin cylindrical filaments under external stresses is ubiquitous and is generally the first step toward breakup. We show that such filaments, called tethers, emerge from a vesicle subjected to gravity. Contrary to the pendant drop experiment, we demonstrate that the bending rigidity, a specific membrane property of vesicles, ensures the tethers reach a st...

The conformational properties of a semiflexible polymer chain, anchored at one end in a uniform force field, are studied in a simple two-dimensional model. Recursion relations are derived for the partition function and then iterated numerically. We calculate the angular fluctuations of the polymer about the direction of the force field and the average polymer configuration as functions of the b...

Effects of sequence disorder on looping and cyclization of the double-stranded DNA are studied theoretically. Both random intrinsic curvature and inhomogeneous bending rigidity are found to result in a remarkably wide distribution of cyclization probabilities. For short DNA segments, the range of the distribution reaches several orders of magnitude for even completely random sequences. The ense...

Pseudoelastic NiTi structural components have been shown to exhibit tension/compression asymmetry. Under tension, phase transformation induces localized strains of nearly 7% that spread under constant stress, while compression the leads hardening at significantly higher strain is smaller and grows homogeneously. Bending tubes ovalizes their cross-section, a nonlinearity reduces bending rigidity...

Parkinson’s disease is one of the most common movement disorders characterized by bradykinesia, rigidity, resting tremor and postural instability (Fahn, 2003). It affects nearly five million elderly people worldwide (de Lau & Breteler, 2006). As the population ages, the incidence and prevalence of Parkinson’s disease are expected to increase dramatically (Dorsey et al., 2007; Tanner & Goldman, ...