Yeast cell inactivation related to local heating induced by low-intensity electric fields with long-duration pulses

The effects of electric field (EF) treatments on Saccharomyces cerevisiae viability were investigated using a PG200 electroporator (Hoefer Scientific Instrument, San Fransisco, CA, USA) with specific attention to induced thermal effects on cell death. Lethal electric fields (1.5 kV cm(-1) for 5 s) were shown to cause heat variations in the cell suspension medium (water+glycerol), while corresponding classical thermal treatments at equivalent temperatures had no effect on the cells viability. Variations of the electrical conductivity of the intra- and extracellular matrix caused by ions and solutes transfer across the membrane were shown to be involved in the observed heating. The results permitted to build a theoretical model for the temperature variations induced by electric fields. Using this model and the electrical conductivity of the different media, a plausible explanation of the cell death induced by low-intensity electric fields with long-duration pulses has been proposed. Indeed, cell mortality could in part be caused by direct and indirect effects of electric fields. Direct effects are related to well known electromechanical phenomena, whereas indirect effects are related to secondary thermal stress caused by plasma membrane thermoporation. This thermoporation was attributed to electrical conductivity variations and the corresponding intracellular heating.     

Chemical modifications and surface properties of carbon blacks

Five carbon blacks, differing in origin or specific surface area, were submitted to a series of chemical treatments: moderate oxidation with potassium persulfate, severe air oxidation, halogenation with chlorine or bromine, and grafting of short (ethyl, butyl, pentyl) or long (lauroic) alkyl chains in order to modify their surface properties and to compare their reactivity in relation to their atomic structure. Various techniques such as elemental analysis, active surface-area determination and inverse gas chromatography were used to assess the consequences of the modifications. In particular, inverse gas chromatography at infinite dilution is shown to detect essentially the most active sites, and allows monitoring of the variation of surface properties upon chemical modification of the blacks.     

Using the tabulated diffusion flamelet model ADF-PCM to simulate a lifted methane-air jet flame

Two formulations of a turbulent combustion model based on the approximated diffusion flame presumed conditional moment (ADF-PCM) approach [J.-B. Michel, O. Colin, D. Veynante, Combust. Flame 152 (2008) 80-99] are presented. The aim is to describe autoignition and combustion in nonpremixed and partially premixed turbulent flames, while accounting for complex chemistry effects at a low computational cost. The starting point is the computation of approximate diffusion flames by solving the flamelet equation for the progress variable only, reading all chemical terms such as reaction rates or mass fractions from an FPI-type look-up table built from autoigniting PSR calculations using complex chemistry. These flamelets are then used to generate a turbulent look-up table where mean values are estimated by integration over presumed probability density functions. Two different versions of ADF-PCM are presented, differing by the probability density functions used to describe the evolution of the stoichiometric scalar dissipation rate: a Dirac function centered on the mean value for the basic ADF-PCM formulation, and a lognormal function for the improved formulation referenced ADF-PCMχ. The turbulent look-up table is read in the CFD code in the same manner as for PCM models. The developed models have been implemented into the compressible RANS CFD code IFP-C3D and applied to the simulation of the Cabra et al. experiment of a lifted methane jet flame [R. Cabra, J. Chen, R. Dibble, A. Karpetis, R. Barlow, Combust. Flame 143 (2005) 491-506]. The ADF-PCMχ model accurately reproduces the experimental lift-off height, while it is underpredicted by the basic ADF-PCM model. The ADF-PCMχ model shows a very satisfactory reproduction of the experimental mean and fluctuating values of major species mass fractions and temperature, while ADF-PCM yields noticeable deviations. Finally, a comparison of the experimental conditional probability densities of the progress variable for a given mixture fraction with model predictions is performed, showing that ADF-PCMχ reproduces the experimentally observed bimodal shape and its dependency on the mixture fraction, whereas ADF-PCM cannot retrieve this shape.     

Crack propagation from a pre-existing flaw at a notch root – II: Detailed form of the stress intensity factors at the initial crack tip and conclusion.

This paper pursues the study of crack kinking from a pre-existing crack emanating from some notch root. It was shown in Part I that the stress intensity factors at the tip of the small initial crack are given by universal (that is, applicable in all situations, whatever the geometry of the body and the loading) formulae; they depend only on the `stress intensity factor of the notch' (the multiplicative coefficient of the singular stress field near the apex of the notch in the absence of the crack), the length of the crack, the aperture angle of the notch and the angle between its bisecting line and the direction of the crack. Here we identify the universal functions of the two angles just mentioned which appear in these formulae, by considering the model problem of an infinite body endowed with a notch with straight boundaries and a straight crack of unit length. The treatment uses Muskhelishvili's complex potentials formalism combined with some conformal mapping. The solution is expressed in the form of an infinite series involving an integral operator, which is evaluated numerically. Application of Goldstein and Salganik's principle of local symmetry then leads to prediction of the kink angle of the crack extension. It is found that although the direction of the crack is closer to that of the bisecting line of the notch after kinking than before it, the kink angle is not large enough for the crack tip to get closer to this line after kinking, except perhaps in some special situations.     

Introduction of sulfur groups onto the surface of carbon blacks

Three methods were employed to introduce sulfur groups (thiol and thio ester groups) onto the surface of a carbon black. Positive results were obtained and controled by functional group analysis and radiochemistry.     

Carbon fibre in polymer reinforcement

The processing and the properties of carbon fibres are reviewed. Next the physical and mechanical properties of carbon and glass fibres are compared. Their use in polymeric composites is discussed.     

Dynamic mechanical properties of carbon fibers

We have determined the dynamic mechanical properties in a low frequency range (0.01–10 Hz) of carbon and graphite fibers at different temperatures and evaluated the influence of fiber stretching. The results, showing frequency and extension dependent losses and changes in Young's moduli, indicate the presence of relatively large, independently mobile fiber constituents, which appear to correspond to the slowly undulating ribbons recognized earlier as the basic carbon fiber components.     

Method for improving ladder bulk acoustic wave filters rejection

This paper address design guidelines for improving the rejection of ladder bulk acoustic wave filters. An overview of the bulk acoustic wave filters technology enables to outcome the principal features of ladder filters. The lack of out-of-band rejection is currently an important weakness of this topology. The design technique presented enables to improve bulk acoustic wave ladder filters rejection by using their input/output bonding wires. Finally, the technique is used for design and fabrication of a bulk acoustic wave ladder filter for application in W-CDMA reception (2.11–2.17 GHz) front-ends. The filter measurement results show a significant improvement on the filter rejection at the transmission band (from ?19 to 34 dB) and on the return loss (from ?10 to ?16 dB) without considerable modification of filter insertion loss and selectivity.     

Optical and physical properties of stratospheric aerosols from balloon measurements in the visible and near-infrared domains. III. Presence of aerosols in the middle stratosphere

The aerosol extinction measurements in the ultraviolet and visible wavelengths by the balloonborne spectrometer Spectroscopie d'Absorption Lunaire pour l'Observation des Minoritaires Ozone et NOx (SALOMON) show that aerosols are present in the middle stratosphere, above 25-km altitude. These observations are confirmed by the extinction measurements performed by a solar occultation radiometer. The balloonborne Laboratoire de Météorologie Dynamique (LMD) counter instrument also confirms the presence of aerosol around 30-km altitude, with an unrealistic excess of micronic particles assuming that only liquid sulfate aerosols are present. An unexpected spectral structure around 640-nm observed by SALOMON is also detectable in extinction measurements by the satellite instrument Stratospheric Aerosols and Gas Experiment III. This set of measurements could indicate that solid aerosols were detected at these altitude ranges. The amount of soot detected up to now in the lower stratosphere is too low to explain these measurements. Thus, the presence of interplanetary dust grains and micrometeorites may need to be invoked. Moreover, it seems that these grains fill the stratosphere in stratified layers.     

Etude de l'oxydation des carbones en oxyde graphitique

The oxidation of several types of carbons leading to the formation of lamellar oxides was studied. The progression of formation of graphitic oxides was followed by use of X-ray diffraction, i.r. spectroscopy, electron microscopy and by a study of carbon dioxide evolution. Kinetic studies of the formation of carbon dioxide indicate the existence of two reaction stages during the oxidation. The fraction of carbon transformable into graphitic oxides is independent of the reaction temperature and carbon characteristic. The oxidation rate of graphitic oxide into carbon dioxide depends on the structural organization of the initial carbon.