Silica aerogels are known to be materials with exceptional characteristics, such as ultra-low density, high surface area, high porosity, high adsorption, and low-thermal conductivity. In addition, these unique properties are mainly related to their specific processing. Depending on the aerogel synthesis procedure, the aerogels texture can be tailored with meso and/or macroporosity. Fractal geometry has been observed and used to describe silica aerogels at nanoscales in certain conditions. In this review paper, we describe the fractal structure of silica aerogels that can develop depending on the synthesis conditions. X-ray and neutron scattering measurements allow to show that silica aerogels can exhibit a fractal structure over one or even more than two orders of magnitude in length. The fractal dimension does not depend directly on the material density but can vary with the synthesis conditions. It ranges typically between 1.6 and 2.4. The effect of the introduction of silica particles or of further thermal treatment or compression of the silica aerogels on their microstructure and their fractal characteristics is also resumed.

La microfluidique est l’ensemble de technologies permettant la manipulation et la caractérisation de fluides à des échelles micrométriques ou nanométriques. Elle peut être considérée à la fois comme une science visant à l’étude du comportement des fluides à l’intérieur de ces micro-canaux, et une technologie permettant la fabrication et l’utilisation de dispositifs microfluidiques. Ces dispositifs sont constitués d’une surface plane sur laquelle des capillaires et des chambres de réactions sont formés par photolithographie, moulage ou emboutissage. Des liquides en volumes micrométriques ou nanométriques sont ensuite insérés dans ces capillaires où ils sont déplacés, fractionnés, séparés ou mélangés pour obtenir des réactions chimiques. L’intérêt de travailler avec des volumes micrométriques, outre l’économie de moyens utilisés, réside dans l’accélération et l’automatisation du processus.Les puces et réacteurs microfluidiques peuvent être simples ou instrumentés (électrodes, capteurs, optiques, pompes…), la tendance étant à la complexification des outils, intégrant de plus en plus d’instruments sans pour autant être accompagnée d’une augmentation du prix. Lorsqu'une intégration optique est effectuée, on parle d'opto-microfluidique.Le travail proposé sera de construire un prototype de dispositif avec un double objectif :-Amélioration de la résolution des circuits de microfluidique par utilisation des nouvelles technologies de photoinscription Laser 2D et 3D haute résolution-Pousser l'intégration en implantant sur la même puce, à la fois le circuit microfluidique et un composant optique intégré.

The integration of optical circuits with microfluidic lab-on-chip (LoC) devices has resulted in a new era of potential in terms of both sample manipulation and detection at the micro-scale. On-chip optical components increase both control and analytical capabilities while reducing reliance on expensive laboratory photonic equipment that has limited microfluidic development. Notably, in-situ LoC devices for bio-chemical applications such as diagnostics and environmental monitoring could provide great value as low-cost, portable and highly sensitive systems. Multiple challenges remain however due to the complexity involved with combining photonics with micro-fabricated systems. Here, we aim to highlight the progress that optical on-chip systems have made in recent years regarding the main LoC applications: (1) sample manipulation and (2) detection. At the same time, we aim to address the constraints that limit industrial scaling of this technology. Through evaluating various fabrication methods, material choices and novel approaches of optic and fluidic integration, we aim to illustrate how optic-enabled LoC approaches are providing new possibilities for both sample analysis and manipulation.

Rationale: Prolonged mechanical ventilation is often associated with either a decrease (known atrophy) or an increase (supposed injury) in diaphragmatic thickness. Shear wave elastography is a noninvasive technique that measures shear modulus, a surrogate of tissue stiffness and mechanical properties.Objectives: To describe changes in shear modulus (SM) during the ICU stay and the relationship with alterations in muscle thickness. To perform a comprehensive ultrasound-based characterization of histological and force production changes occurring in the diaphragm.Methods: Translational study using critically ill patients and mechanically ventilated piglets. Serial ultrasound examination of the diaphragm collecting thickness and SM was performed in both patients and piglets. Transdiaphragmatic pressure and diaphragmatic biopsies were collected in piglets.Measurements and Main Results: We enrolled 102 patients, 88 of whom were invasively mechanically ventilated. At baseline, SM was 14.3 ± 4.3 kPa and diaphragm end-expiratory thickness was 2.0 ± 0.5 mm. Decrease or increase by more than 10% from baseline was reported in 86% of the patients for thickness and in 92% of the patients for SM. An increase in diaphragmatic thickness during the stay was associated with a decrease in SM (β = −9.34 ± 4.41; P = 0.03) after multivariable analysis. In the piglet sample, a decrease in SM over 3 days of mechanical ventilation was associated with loss of force production, slow and fast fiber atrophy, and increased lipid droplets accumulation.Conclusions: Increases in diaphragm thickness during critical illness is associated with decreased tissue stiffness as demonstrated by shear wave ultrasound elastography, consistent with the development of muscle injury and weakness.

We make the hypothesis that our universe is threedimensional and curved, hence our universe may be embedded in a fourdimensional Euclidean space where the four dimensions are (x, y, z, t). The fourth dimension is time t which is treated like a spatial dimension. Straightforwardly, this Euclidean space has an underlying hypersquare array for which the edges have a width of one Planck length. The eigenfunctions of each edge of this array are √ 2exp(ix i) where x_i = x, y, z or t. As previously published, the quarks are threedimensional in real space. The quark up has a mass of 2^ 21 eV/c 2 and the quark down 2^22 eV/c 2 (the quark down is an excited state of the quark up). Because the quark up is threedimensional (like the apex of a tetrahedron), each edge of the quark has an eigenvalue of 2 ^7 eV/c 2. Let us consider that the color charge of the gluons are in fact the coordinates in real space (x: red; y:blue; z: green). The gluons have no mass so they have no temporal dimension. Each pair of quarks, share one gluon (the gluons interfere with the quarks edges).Gluons are bosons and quarks are fermions so for each edge of the underlying array (except the temporal edges) we calculate the ground states. In one proton or in one neutron, there are 3 gluons and 3 quarks; as only the temporal edges of the 3 quarks are not in the ground states and because the protons and neutrons obey the Schrödinger equation, the masses of the proton or neutron are equal to 2^ 30 / ln(π)eV/c 2 = 937MeV/c 2. The difference between the masses of the proton and neutron comes from the difference between the experimental masses and the theoretical masses of quarks up and down. Straightforwardly, we found theoretical values of the masses of protons and neutrons within 2% of the experimental values of the masses of protons and neutrons.

We studied a colloidal suspension of polystyrene beads deposited on a glass substrate. The glass substrate contained either straight rough areas on the borders of an open channel or only straight rough areas. The drying of the suspension was observed with an optical microscope which light bulb acted as an energy source to evaporate the suspension. Moreover, the light bulb of the microscope provided optical pressure due to light. We observed that the colloidal particles where trapped on the rough areas of the substrate and not in the open channel, at the end of the drying process. In order to understand the experimental results, we modelled numerically the drying of the suspension by a Molecular Dynamics program. The forces acting on the substrate by the particles are their weight, the optical pressure due to the light bulb of the optical microscope, the attractive Van der Waals force and the repulsive diffuse layer force. The forces acting between two particles are the attractive Van der Waals forces, the repulsive diffuse layer force, the capillary force. The Gaussian random force (linked to the Brownian motion), the particle liquid viscous drag force (also linked to the Brownian motion) are horizontal and applied on one particle. The relation between the normal forces N (forces acting by the particles on the substrate) and the horizontal forces F is Amontons' third law for friction F ≤ µ k N ; in rough areas of the substrate µ k is larger than in smooth areas. This explains that particles are trapped in the large roughness areas.