Coupling between membrane tilt-difference and dilation: a new ``ripple'' instability and multiple crystalline inclusions phases

A continuum Landau theory for the micro-elasticity of membranes is discussed, which incorporates a coupling between the bilayer thickness variation and the difference in the two monolayers' tilts. This coupling stabilizes a new phase with a rippled micro-structure. Interactions among membrane inclusions combine a dilation-induced attraction and a tilt-difference-induced repulsion that yield 2D crystal phases, with possible coexistence of different lattice spacings for large couplings. Inclusions favoring crystals are those with either a long-convex or a short-concave hydrophobic core.Comment: EURO LaTeX, 6 pages, 4 figures, to be published in Europhys. Let

Wormlike chain or tense string? A question of resolution

It is shown that a wormlike chain, i.e., a filament with a fixed contour-length S and a bending elasticity kappa, attached to a frame of length L, can be described--at low resolutions--by the same type of elastic free-energy as a tense string. The corresponding tension is calculated as a function of temperature, L, kappa and S.Comment: 13 pages, 3 figures. To appear in Continuum Mechanics and Thermodynamic

Anisotropic Capillary Interactions and Jamming of Colloidal Particles Trapped at a Liquid-Fluid Interface

We determine the capillary attraction and equilibrium configurations of particles trapped at a liquid-fluid interface due to the pinning of their contact-line. We calculate analytically the asymptotic interaction energy between two particles and, numerically, the multi-body energy landscape for up to four contacting particles. Our results are consistent with recent experiments. We show that a system composed of a large number of such particles behaves as a jammed system.Comment: 4 pages, 5 figures. To appear in Phys. Rev.

Microscopic membrane elasticity and interactions among membrane inclusions: Interplay between the shape, dilation, tilt and tilt-difference modes

A phenomenological Landau elasticity for the shape, dilation, and lipid-tilt of bilayer membranes is developed. The shape mode couples with the sum of the monolayers' tilt, while the dilation mode couples with the difference of the monolayers' tilts. Interactions among membrane inclusions within regular arrays are discussed. Inclusions modifying the membrane thickness and/or inducing a tilt-difference due to their convex or concave shape yield a dilation-induced attraction and a tilt-difference-induced repulsion. The resulting interaction can stabilize 2D crystal phases, with the possible coexistence of different lattice spacings when the dilation-tilt-difference coupling is large. Inclusions favoring crystals are those with either a long-convex or a short-concave hydrophobic core. Inclusions inducing a local membrane curvature due to their conical shape repel one another. At short inclusions separations, a tilt comparable with the inclusion's cone angle develops: it relaxes the membrane curvature and reduces the repulsion. At large separations the tilt vanishes, whatever the value of the shape-tilt coupling.Comment: 13 pages, 19 figure

The missing proof of Paley's theorem about lacunary coefficients

We modify the standard proof of Paley's theorem about lacunary coefficients of functions in $H^1$ to work without analytic factorization. This leads to the first direct proof of the extension of Paley's theorem that we applied to the former Littlewood conjecture about $L^1$ norms of exponential sums

Dynamin recruitment by clathrin coats: a physical step?

Recent structural findings have shown that dynamin, a cytosol protein playing a key-role in clathrin-mediated endocytosis, inserts partly within the lipid bilayer and tends to self-assemble around lipid tubules. Taking into account these observations, we make the hypothesis that individual membrane inserted dynamins imprint a local cylindrical curvature to the membrane. This imprint may give rise to long-range mechanical forces mediated by the elasticity of the membrane. Calculating the resulting many-body interaction between a collection of inserted dynamins and a membrane bud, we find a regime in which the dynamins are elastically recruited by the bud to form a collar around its neck, which is reminiscent of the actual process preempting vesicle scission. This physical mechanism might therefore be implied in the recruitment of dynamins by clathrin coats.Comment: 11 pages, 6 figures, to appear in C.R.A.S. ser II

La fibrothèque de la division de technologie de l'IRCT de Montpellier

Collection de plus de 2 000 échantillons de cotons provenant d'environ 50 pays producteurs. Les caractéristiques de chaque coton sont répertoriées dans des fichiers informatisés. Les objectifs de cette bibliothèque sont : une meilleure connaissance des différents types de coton du marché international, et la disposition d'une grande diversité de caractéristiques physico-chimiques. Cette diversité permet : l'étude des relations entre caractéristiques, l'étude du comportement des mélanges en filature, ainsi que des études particulière