In order to explain the fact that the pressure in the Friedmann equations is negative, only the hypothetical presence of dark energy is used in present theories. But, the dimensions of the pressure $p$ are $f/r^2$ and thus $p$ can not account for the acceleration of the expansion of the universe. Indeed, the hypersurface of our universe is threedimensional and curved, so a force has an effect on the universe if it is applied on the universe's boundaries. As these boundaries (hypersurface) correspond to the threedimensional universe itself at time $t$, there must exist a positive force density $f/r^3$. The relation between the pressure $p$ (calculated within the Friedmann model) and the force density is a simple derivation with respect to $r$ the space variable. And the derivation of a negative pressure leads to a positive force density.

Silica gels were synthesized from TMOS and MTMS in different proportions changing the ionic liquid concentration. EMIMac have significant influence in the gelation processe. The textural characterizations showed an effect of these concentrations on the corresponding aerogels: pore size distributions and effectives surfaces. The structure of the aerogels was measured with a SAXS apparatus and was typical of acid catalyzed aerogels. Conductivity measurements, operated on the ionogels, were carried out using an original electrical 4 electrodes set up which allowed us to study the ionic conductivity at the pore scale. The results obtained showed that one can model the electrical temporal response of the EMIMAc silica ionogel with a RLC series circuit.

The nature of dark matter is linked to the fluctuations of curvature of the hyper-surface of our three dimensional universe. These fluctuations of curvature have gravitational effects and deviate radiations. While we question dark energy, as another theory by Olivi-Tran [4] accounts for the acceleration of the expansion of our universe by analyzing the nature of time.

We analyze the nature of the Schrödinger equation and of the Dirac equation. Due to the theoretical reversibility of time (see Olivi-Tran [1, 2, 3, 4]), a simple transformation of Scḧrödinger equation leads to that conclusion. In the case of Dirac equation the nature itself of the Dirac matrices leads to a quantization of time when solving this equation with the associated matrices.

The knowledge of the internal structure of porous materials is of main importance to compute their physical properties. This article focuses on base-catalyzed and colloidal silica aerogels, which are fractal materials and we use an original method for the reconstruction of these aerogels from TEM images. The method used is iterative and leads to the same fractal dimension as the real material, computed from the internal two-point correlation function. Unlike the reconstruction of porous materials found in literature, our method is based on the distribution of matter and not of the porous network, and has the additional advantage of being only half statistical, i.e. only the coordinates in the z direction are statistically obtained while the coordinates x and y of the elements of matter are accurately obtained from TEM images of our samples

I show here that due to the fact that time has a logarithmic increase as a function of the radius of curvature of our threedimensional universe, the rate of expansion of the universe is accelerating. The instantaneous pressure within this universe is negative (as predicted by the litera- ture) because black holes lead to a leak of matter and light from our universe. Though, the total energy of the universe is increasing. The transition from a still fourdimensional universe with no physical laws to our threedimensional curved universe is due to Heisenberg's uncertainty principle.