Some aspects of electrical conduction in granular systems of various dimensions

We report on measurements of the electrical conductivity in both a 2D triangular lattice of metallic beads and in a chain of beads. The voltage/current characteristics are qualitatively similar in both experiments. At low applied current, the voltage is found to increase logarithmically in good agreement with a model of widely distributed resistances in series. At high enough current, the voltage saturates due to the local welding of microcontacts between beads. The frequency dependence of the saturation voltage gives an estimate of the size of these welded microcontacts. The DC value of the saturation voltage ( ≃ 0.4 V per contact) gives an indirect measure of the number of welded contact carrying the current within the 2D lattice. Also, a new measurement technique provides a map of the current paths within the 2D lattice of beads. For an isotropic compression of the 2D granular medium, the current paths are localized in few discrete linear paths. This quasi-onedimensional nature of the electrical conductivity thus explains the similarity between the characteristics in the 1D and 2D systems.     

Observation of intermittency in wave turbulence

We report the observation of intermittency in gravity-capillary wave turbulence on the surface of mercury. We measure the temporal fluctuations of surface wave amplitude at a given location. We show that the shape of the probability density function of the local slope increments of the surface waves strongly changes across the time scales. The related structure functions and the flatness are found to be power laws of the time scale on more than one decade. The exponents of these power laws increase nonlinearly with the order of the structure function. All these observations show the intermittent nature of the increments of the local slope in wave turbulence. We discuss the possible origin of this intermittency.     

Covalent grafting of fibronectin onto plasma-treated PTFE: influence of the conjugation strategy on fibronectin biological activity

Surface coating of synthetic materials is often considered to improve biomedical devices biocompatibility. In this study, we covalently bound fibronectin (FN) onto ammonia plasma-treated PTFE via two crosslinkers, namely glutaric anhydride (GA) and sulfosuccinimidyl-4-(p-maleimidophenyl)butyrate (sulfo-SMPB). With respect to clean PTFE, cell adhesion increased markedly on both FN grafted surfaces, although it was twice higher on PTFE-GA-FN than on PTFE-SMPB-FN. ELISA experiments performed with a polyclonal antibody revealed that the amount of FN is identical on both surfaces while monoclonal antibody specific to the RGD binding site clearly demonstrated a greater availability when FN is surface grafted through GA. These results provide evidence of a variation in protein conformation correlated with the surface conjugation strategy.     

Anti-Fog Layer Deposition onto Polymer Materials: A Multi-Step Approach

A coating with anti-fog properties was developed for a polycarbonate (PC) substrate using a multi-step process. A silicon-containing multilayer was first deposited by atmospheric pressure Townsend discharge (APTD) using hexamethyldisiloxane (HMDSO) precursor to ensure cohesion between the coating and the PC and to protect the polymer against dissolution in solvents during subsequent spin-coating processes. The multilayer was also developed in a nitrogen environment in order to provide amino groups on the surface, which allowed for the subsequent covalent bonding of the anti-fog layer. This anti-fog layer was made of a spin-coated (poly(ethylene-maleic anhydride) (PEMA) layer, used as a linking arm, followed by a spin-coated poly(vinyl alcohol) (PVA) layer, for its anti-fog properties. Surface analyses (XPS, FTIR, and AFM) confirmed that the silicon-containing multilayer was successfully deposited with a good control obtained for each step. The anti-fog coating, also tested with promising results, displayed a negligible loss of optical transmission across the visible spectrum.     

Input/output reduced model of a damped nonlinear beam based on Volterra series and modal decomposition with convergence results

Nonlinear Dynamics - This paper addresses the model reduction and the simulation of a damped Euler–Bernoulli–von Kármán pinned beam excited by a distributed force. This...