Fundamental understanding of ionic transport at the nanoscale is essential for developing biosensors based on nanopore technology and new generation high-performance nanofiltration membranes for separation and purification applications. We study here ionic transport through single putatively neutral hydrophobic nanopores with high aspect ratio (of length L = 6 μm with diameters ranging from 1 to 10 nm) and with a well controlled cylindrical geometry. We develop a detailed hybrid mesoscopic theoretical approach for the electrolyte conductivity inside nanopores, which considers explicitly ion advection by electro-osmotic flow and possible flow slip at the pore surface. By fitting the experimental conductance data we show that for nanopore diameters greater than 4 nm a constant weak surface charge density of about 10−2 C m−2 needs to be incorporated in the model to account for conductance plateaus of a few pico-siemens at low salt concentrations. For tighter nanopores, our analysis leads to a higher surface charge density, which can be attributed to a modification of ion solvation structure close to the pore surface, as observed in the molecular dynamics simulations we performed.

Monte Carlo simulations are methods for simulating statistical systems. The aim is to generate a representative ensemble of configurations to access thermodynamical quantities without the need to solve the system analytically or to perform an exact enumeration. The main principles of Monte Carlo simulations are ergodicity and detailed balance. The Ising model is a lattice spin system with nearest neighbor interactions that is appropriate to illustrate different examples of Monte Carlo simulations. It displays a second order phase transition between a disordered (high temperature) and ordered (low temperature) phases, leading to different strategies of simulations. The Metropolis algorithm and the Glauber dynamics are efficient at high temperature. Close to the critical temperature, where the spins display long range correlations, cluster algorithms are more efficient. We introduce the rejection free (or continuous time) algorithm and describe in details an interesting alternative representation of the Ising model using graphs instead of spins with the Worm algorithm. We conclude with an important discussion of the dynamical effects such as thermalization and correlation time.

I'll present the construction of an index in 4d N=2 supersymmetric gauge theories which is smooth across walls of marginal stability and appears as a natural generalization of the CFIV index in two-dimensional theories. I'll explain its physical and geometric interpretation originating in the hyperkahler structure of the 3d theory obtained by compactification on a circle. In the end, I'll also briefly discuss the behavior under wall-crossing of certain generalized theta series which appear, in particular, in the description of NS5-brane instantons in Calabi-Yau compactifications of type II strings.

Polymers typically have intrinsic thermal conductivity much lower than other materials. Enhancement of this property may be obtained by the addition of conductive fillers. In this research, epoxy nanocomposites with exfoliated graphite nanoplatelets are prepared and characterized. The chosen approach requires no surface treatment and no sophisticated equipments allowing one to produce composites on a pilot scale. A significant increase of the thermal conductivity with the increasing of the graphite fillers content is nevertheless observed on 4 mm thick specimens. Our results viewed in the latest scientific findings suggest that the choice of resin is an important parameter to move towards composite materials with high thermal conductivity.

Phonon dispersion ω(q) and phonon density of states g(ω) of the high-pressure rocksalt phase of InN are calculated ab initio, at different pressures, using the density functional perturbation theory. Born effective charge e ∗ T , LDA values of dielectric con- stant ∞ and of the electronic gap E g are obtained as well. Building on the theoretical knowledge of phonon frequencies and their evolution with pressure, we attempt to interpret the set of six bands found previously in Raman spectra of epitaxial layers and of InN-nanowires.