A Spectroscopic Study of Rhodopsin Alpha-Helix Orientation

Polarized Fourier transform infrared spectroscopy and far ultraviolet circular dichroism of oriented multilamellar films of photoreceptor membranes indicate rhodopsin alpha-helices are predominantly oriented perpendicular to the bilayer plane

The role of fundamental solution in Potential and Regularity Theory for subelliptic PDE

In this survey we consider a general Hormander type operator, represented as a sum of squares of vector fields plus a drift and we outline the central role of the fundamental solution in developing Potential and Regularity Theory for solutions of related PDEs. After recalling the Gaussian behavior at infinity of the kernel, we show some mean value formulas on the level sets of the fundamental solution, which are the starting point to obtain a comprehensive parallel of the classical Potential Theory. Then we show that a precise knowledge of the fundamental solution leads to global regularity results, namely estimates at the boundary or on the whole space. Finally in the problem of regularity of non linear differential equations we need an ad hoc modification of the parametrix method, based on the properties of the fundamental solution of an approximating problem

Co-existing lyotropic liquid crystals : commensurate, faceted and co-planar single hexagonal (HII) domains in lamellar photoreceptor membranes

The interactions of inverse hexagonal (HII) domains with a host lamellar (Lα) matrix have been investigated in two lyotropic liquid crystals via X-ray diffraction and electron microscopy. The domains exhibit internal structure which is geometrically coupled to the lamellar host : the crystallographic repeats are often commensurate and one hexagonal layer is co-planar with the host lamellae. Electron microscope thin-sections reveal the cross-section of single HII domains to be limited by facets which arise from the hexagonal structure. The domains are in equilibrium with the host and can be made to grow or shrink by variations in temperature or water content. The local hexagonal packing is two-dimensional; the third dimension often exhibits spiral and toroidal textures accompanied by branching defects. Consideration of the hydrophobic-hydrophilic constraints leads to a model for the domain wall. Coupled with a hypothesized surface-induced curvature, this suggests a model for the epitaxial growth of the domains.Les interactions de domaines hexagonaux inverses (HII) avec une matrice lamellaire (Lα) ont été étudiées dans deux cristaux liquides lyotropes par diffraction X et microscopie électronique. Les domaines présentent une structure interne qui est géométriquement couplée à l'hôte lamellaire : les périodes cristallographiques sont souvent commensurables et une couche hexagonale est coplanaire avec les lamelles. L'examen de couches minces au microscope électronique révèle une section de domaines HII limités par des facettes provenant de la structure hexagonale. Les domaines sont en équilibre avec leur hôte et peuvent être élargis ou comprimés en faisant varier la température ou la quantité d'eau. L'empaquetage hexagonal local est bidimensionnel; la troisième dimension présente souvent des textures spirales et toroïdales accompagnées de défauts et bifurcations. En prenant en compte les contraintes hydrophobes et hydrophiles on obtient un modèle pour la paroi limitant les domaines. L'hypothèse supplémentaire d'une courbure induite par la surface, suggère un modèle pour la croissance épitaxiale des domaines