The transmission of breakdown plasma generated in water during laser shock processing experiments was investigated theoretically. A numerical model based on a rate equation formalism has been developed to calculate the characteristics (peak irradiance and duration) of the laser pulses transmitted through the breakdown plasmas generated in water. Results are in good agreement with previous experimental data for 25 ns−1064 nm laser pulses. Above 10 GW/cm2, the transmitted peak irradiance saturates and the transmission starts to decrease. The results have been extended to shorter wavelengths (532 and 355 nm). At 1064 nm, the breakdown process is dominated by avalanche ionization, whereas for shorter wavelengths, multiphoton ionization plays the major role.

A systematic parameters study is performed in a DC pulsed glow discharge in oxygen in order to improve the wettability of thin polystyrene layers. The experimental parameters considered are the pressure P, the gas flow rate Q, the interelectrode voltage V, the frequency ν of the pulsed power supply and the treatment time tt. The wettability is characterized by the contact angle technic and evaluated by the determination of the $\Delta\Theta/\Theta_{\rm i}= (\Theta_{\rm i}-\Theta_{\rm f})/\Theta_{\rm i}$ ratio ($\Theta_{\rm i}$ and $\Theta_{\rm f}$ are respectively the initial and final contact angles). In the first part of the paper, the relative contact angle variations $\Delta\Theta/\Theta_{\rm i}$ as a function of the treatment duration time tt are investigated. In the second part, the specific energy ε and the economical criterion γ are introduced to deduce the best running conditions through a chemical engineering approach. Taking into account the weak duty factor of the power supply (1% ), it is shown that the polymer surface is treated with a minimum of energy. Finally, it is deduced that the duration time necessary to reach the same $\Delta\Theta/\Theta_{\rm i}$ value is shorter for an oxygen plasma than for a nitrogen plasma.

The goal of this study is a better understanding of the interaction between cells and a solidification front during a cryopreservation process. This technique of freezing is commonly used to conserve biological material for long periods at low temperatures. However the biophysical mechanisms of cell injuries during freezing are difficult to understand because a cell is a very sophisticated microstructure interacting with its environment. We have developed a finite element model to simulate the response of cells to an advancing solidification front. A special front-tracking technique is used to compute the motion of the cell membrane and the ice front during freezing. The model solves the conductive heat transfer equation and the diffusion equation of a solute on a domain containing three phases: one or more cells, the extra-cellular solution and the growing ice. This solid phase growing from a binary salt solution rejects the solute in the liquid phase and increases the solute gradient around the cell. This induces the shrinkage of the cell. The model is used to simulate the engulfment of one cell modelling a red blood cell by an advancing solidification front initially planar or not is computed. We compare the incorporation of a cell with that of a solid particle.

The aim of the present work is to provide data to understand better and quantify the dielectric strength of pure compressed N2 (1 < P < 8 bar). The lack of agreement of results found in the literature leads us to study the electrical and physical characteristics of this gas as a function of a wide set of parameters. Experiments are mainly performed in point to plane nitrogen gaps up to 40 mm length using three different rod radii. Gas conditioning phenomenon in positive polarity and corresponding change in characteristics of discharge mechanism are demonstrated here. In our experimental conditions, no leader is involved in the discharge development whatever the polarity is. The values of the breakdown reduced field $E_{\rm b}/P$ are determined as a function of the pressure. Two different experiments are performed in order to take into account the mechanisms of initiatory electron production: the influence of the γ-ray irradiated N2 and that of the surface roughness of the HV electrode. In negative polarity, the free electrons are provided from the cathode whereas they are provided from the gas under positive polarity. Voltage waveform influences on the U50 breakdown voltage are dealt with in a large pressure range (1 < P < 12 bar). The role of the non-uniformity of the applied electric field on the U50 value is pointed out in both polarities. Finally, the reduced guiding field of negative streamer is experimentally measured.

Experiments have shown that highly intense and collimated cluster beams can be produced by a simple aerodynamic lens coupled to the nozzle of a pulsed microplasma cluster source. The mechanism of the observed cluster focusing is here presented. We discuss, as a case example, a supersonic beam of helium seeded by carbon clusters. The laminar flow of the helium-clusters mixture through a focalizing nozzle assembly has been numerically simulated and compared to the experiments. A three-dimensional steady compressible flow model has been considered for the simulation. Carbon clusters have been modeled by rigid spheres with uniform density. The trajectories of the particles are calculated during their travel through the nozzle. The simulations show that the effect of the focalizing nozzle is to divert the particles from their streamlines towards the center of the beam, thus narrowing the spatial and velocity cluster distribution. The dependence of these effects on the nozzle geometry and on the beam parameters is reproduced by the simulations in good agreement with the experimental findings.

This paper presents the principle of an air wavelength standard for high accuracy length metrology. According to the definition of the Mètre, nanometric accuracy by interferometric measurement techniques can be reached only for measurements made under vacuum or by taking into account the fluctuations of the refractive index of air. We have developed a new type of laser source whose wavelength is insensitive to slow fluctuations of the refractive index of air. The sensitivity of our air wavelength standard to some characteristics (such as temperature, pressure, ageing behaviour...) has been measured. Results show that the relative uncertainty level of the wavelength of our source is below 10−8.

We investigate the effects of geometrical micro-irregularities on the conversion efficiency of reactive flows in narrow channels of millimetric size. Three-dimensional simulations, based upon a Lattice-Boltzmann-Lax-Wendroff code, indicate that periodic micro-barriers may have an appreciable effect on the effective reaction efficiency of the device. Once extrapolated to macroscopic scales, these effects can result in a sizeable increase of the overall reaction efficiency.

The formation of defects during the LCM processing of composite parts depends on various injection parameters. Industrial users need to realize pieces with good physical and mechanical properties and appearance. This requires to predict what is named a “processability window”. This term defines a range of parameters which will ensure a nearly absence of defects. Knowing that most of the defects created during an injection are voids, a bibliographical background about the formation and removal of these voids is presented. An original model of void fraction prediction is developed. This model is based on an empirical analysis of void formation and of the flow behaviour. An experimental qualitative validation of the model is presented.The proposed model can be used as an effective prediction tool at the design stage of a composite part.

The same typographical error crept in the last term on the right sides of equations (19), (21) and (23) referred of the paper above. Please replace −1 by −δ (t). All other equations as well as our results are not affected. We regret any inconvenience caused by this error.

A transcription error crept in the last term on the right sides of equations (10), (12) and (14) of the referred paper above. Please replace −1 by $-\delta (t)$. All other equations as well as our results are not affected. We regret any inconvenience caused by this error.