We consider the symmetry and physical origin of collective displacement modes playing a crucial role in the morphological transformation during the maturation of the HK97 bacteriophage and similar viruses. It is shown that the experimentally observed hexamer deformation and pentamer twist in the HK97 procapsid correspond to the simplest irreducible shear strain mode of a spherical shell. We also show that the icosahedral faceting of the bacteriophage capsid shell is driven by the simplest irreducible radial displacement field. The shear field has the rotational icosahedral symmetry group I while the radial field has the full icosahedral symmetry I_{h}. This difference makes their actions independent. The radial field sign discriminates between the icosahedral and the dodecahedral shapes of the faceted capsid shell, thus making the approach relevant not only for the HK97-like viruses but also for the parvovirus family. In the frame of the Landau-Ginzburg formalism we propose a simple phenomenological model valid for the first reversible step of the HK97 maturation process. The calculated phase diagram illustrates the discontinuous character of the virus shape transformation. The characteristics of the virus shell faceting and expansion obtained in the in vitro and in vivo experiments are related to the decrease in the capsid shell thickness and to the increase of the internal capsid pressure.

I will present our studies of the Casimir-Lifshitz interaction in a system consisting of two different one-dimensional dielectric lamellar gratings at two different temperatures, immersed in an environment having a third temperature [1]. The calculations are based on the knowledge of the scattering operators, obtained through the Fourier modal method. It will be shown that the interplay between non-equilibrium effects and geometrical periodicity offers a rich scenario for the manipulation of the force. Finally I will present our latest results on a sphere-grating system at equilibrium [2]. 

Heat transfer or between bodies and Casimir-Lifshitz (CL) interactions between them share in common the fact that they can be characterized by the electromagnetic response of these bodies. It has been shown, in the framework of a general theory [1], that the knowledge of the so-called scattering matrix of an object is sufficient to perform its thermal of Casimir interaction with another body. Among the different configurations studied experimentally, those involving gratings and spheres are of special interest. From the theoretical point of view, when one is equipped with the scattering matrix based theory [1], it is “in principle” straightforward to compute the heat transfer or the CL force. In reality, it turns out that computing the S-matrices is not that easy, especially when it has to be determined for a huge number of modes. It is thus of fundamental importance to use extremely efficient methods. We will discuss the different families of existing approaches for diffraction gratings and examine in more details one of the most efficient ones: the Fourier Modal Method that we used recently to compute CL interactions between gratings out of thermal equilibrium [2] and between a sphere and a grating [3].

Alumina-coated silica nanoparticles (NPs) grafted with phosphonic acids of different hydrophobicitywere used as filler in poly(ethylacrylate) nanocomposites. Phosphonic acids bearing short alkyl chains ora diethylene glycol group have been grafted at densities up to 3.2 P/nm2 on NPs (20 nm) dispersed inwater. Nanocomposites at particle fractions up to 10 vol% have been formulated by casting from thecolloidal mixtures of modified NPs and nanolatex in water. The dispersion of the NPs in the polymermatrix has been studied by TEM combined with small-angle scattering, evidencing aggregation of NPs.TEM shows micrometer-scale inhomogeneities depending on the surface/polymer matrix compatibility.For the local interparticle correlations, a quantitative analysis of the intensity based on the mapping ontothe effective structure factor of polydisperse hard spheres is developed. This mapping allows the modelfreedetermination of the internal volume fraction of aggregates, termed compacity k, to between 10%and 30%, compatible with the TEM analysis. k is found to increase for the higher particle volume fractions,to decrease with grafting density, and to be mostly independent of the nature and mass of thegraft. Preliminary evidence for an improved compatibility of grafted with respect to bare NPs is found, asopposed to their aqueous precursor suspensions where some pre-aggregation is induced by grafting.

Spin noise spectroscopy is a quite attractive experimental tool for studying unperturbed spin dynamics and magnetic resonance in semiconductor nanostructures. However in some cases its practical interest maybe severely limited by the weakness of the spin noise signal to be detected. In this paper we examine by how much the detection of spin noise of magnetic atoms or of nuclei, in quantum wells or quantum dots, can be improved by making use of cavity-enhanced Faraday rotation. The conditions for optimized cavities are first determined. In reflection geometry it corresponds to tune the cavity to the critical point of impedance matching. It is shown that even for optimized cavities the enhancement in spin noise detection is intrinsically limited by absorption. It turns out that the cavity effect improves the spin noise detection only when the inhomogeneous broadening of the involved optical resonance is large compared to its radiative broadening.