The map of 3D curvatures of a porous medium characterizes most of its capillary properties. A model for directly computing curvatures from athree-dimensional image of the solid matrix of a porous medium is presented. Aprecise distance map of the object is built using the “chamfer” distance of discretegeometry. The set of local maxima of the distance map is used for quick location ofthe normal to each point P of the object's surface. The normal being known,principal radii of curvature are computed in 2D and lead to 3D curvature. This modelwas validated on geometric shapes of known curvature, then applied on a natural snowsample. The snow image was obtained from a serial cut (performed in cold laboratory)observed under specularly reflected light. Views of both fresh and sublimated sectionswere taken for each of the 64 section planes: this allowed easier distinction betweensnow and filling medium and made possible automatic contouring of section planeimages. Curvature maps computed from pore and grain phases respectively were found tobe in excellent agreement for each tested object shape, including the snow sample.

The properties of porous silicon microcavities impregnated with a laser dye are investigated by photoluminescence and reflection measurements. The spontaneous emission spectrum of the optically excited rhodamine 800 is drastically modified by microcavity effects: the peak emission intensity is increased, the linewidth is narrowed. These results demonstrate that using all porous silicon or dye-filled microcavities provides new possibilities to improve the properties of photonic devices.

The unsteady forced convection involved in incompressible laminarboundary-layer over a semi-infinite plate is investigated. Initially, a steady stateconvective heat transfer with constant plate temperature or constant plate heat fluxis established between the plate and the flow. By differential method, we study thethermal effect on this first state of a positive or a negative sudden change in eitherthe plate temperature or plate heat flux. Numerical solution of differential equationsis obtained for the whole transient from the initial steady state to the final one.Detailed results of the effect of the wall conditions change on the transient processare given for the fluids encountered in the usual applications (0.6 ≤ Pr ≤ 100).An exponential law of the instantaneous heat coefficient is deduced as function ofPr in the said Prandtl number range.

A systematic parameter study from analytic calculations is presented to optimize ozone concentration in an oxygen-fed wire-to-cylinder ozonizer. Using experimental results,an analytic temperature law is deduced and included in a previously publishedanalytical model [1]. From this latter a systematic parameters study shows thatoptimum conditions for ozone generation depend on electric power, gas flow andozonizer geometry. A general relationship is given to calculate the best workingconditions. The Mayn physical functions for ozone production (formation anddestruction overall coefficients, ozone concentration, specific energy and economicalcriterion) are studied and commented. These results are finally compared withexperiments for a wide range of parameters and a good agreement is found.

In this paper, a mathematical model of the mechanical behaviour of prosthetic blood vascular structures is analysed when taking into account effects of finite deformations, residual stresses which can be induced by fabrication processes and the composite nature of the material constituting those structures. The case of particular applied strains, viewed as arising during surgical manipulation and implying axial and circular shear stresses, is also studied. The resulting distribution of stresses within the wall shows large gradients which can be reduced when the effects of adequate pre-existing initial stresses are present.

A stable positive corona discharge in coaxial electrode system withvarying humidity is analysed using a model which separates the corona in two distinctregions. A careful choice of boundary conditions in the drift region, particularly atthe cathode surface, is needed. A new method of current and electric fieldmeasurements with a linear biased probe, incorporated in the outer cylinder, is used.The corona current, at a given voltage, decreases with humidity but the electric field at the outer cylinder is independent of humidity. The fields at the surfaces of thecathode and the anode vary linearly with the applied voltage between electrodes. Theexact value of the average mobility of positive ions in the drift region is deducedfrom current and field measurements. This mobility increases when the potentialdifference across the drift region increases and it decreases slightly as the air ismade more humid. Other parameters of the positive corona are successively determinedby the current and field measurements, in particular, the total field distributionbetween electrodes.

Considering the increase of the fault current level in electrical network, the current limiters become very interesting. The superconducting limiters are based on the quasi-instantaneous intrinsic transition from superconducting state to normal resistive one. Without detection of default or given order, they reduce the constraints supported by electrical installations above the fault. To avoid the destruction of the superconducting coil, the temperature must not exceed a certain value. Therefore the design of a superconducting coil needs the simultaneous resolution of an electrical equation and a thermal one. This papers deals with a resolution of this coupled problem by the method of Monte-Carlo. This method allows us to calculate the evolution of the resistance of the coil as well as the current of limitation. Experimental results are compared with theoretical ones.

Due to technical errors, the figures have been badly printed. We publish entirely the article herein, sincerely apologizing to the authors for the unpleasant inconvenience.

We present a set of complementary experimental and numerical tools for studying miscible fluid displacements in porous media with large scale heterogeneities.Experiments are realized in transparent 2D Hele-Shaw cells allowing opticalobservations and in 3D packings of glass beads with an acoustical technique forimaging fluid displacements. Permeability heterogeneities are modeled by spatialvariations of either the local aperture of the Hele-Shaw cell or the diameter of thegrains used in the packing. The Hele-Shaw cell model provides high resolution maps ofthe invasion front location at regular time intervals and of the flow lines: thevelocity field is determined by combining these informations. Acoustical images ofrelative concentration distributions in the 3D packing are in agreement with Hele-Shawcell data and can be obtained in a broader range of experimental situations. Suchexperiments realized with a stabilizing density contrast between invading and displacedfluids demonstrate a strong reduction of the front width at low flow velocities, asimilar reduction is obtained at high velocities with a stabilizing viscositycontrast. The technique is also applicable to study fluid displacements in naturalopaque media. Numerical simulations by a Boltzmann lattice technique using aStokes-like diffusive term to smooth out the effect of permeability discontinuitiesprovide complementary informations. They are shown to give similar results asexperiments for same flow parameter values and to allow for a fast exploration of abroad range of fluid properties and flow situations.

The experiments on the propagation of acoustic air waves in the low atmospheric layer show a large influence of aerological parameters. In particular, there were only few measurements carried out outdoors to approach thermal turbulent values [1]. There are many thermal sensors ranging from a simple platinum resistance to quartz crystal. Each technology has some advantages depending on the type of measurement one intends to perform. To explore the earth boundary layer, we chose a micro-thermocouple of type S. Its small size (1.27 µm) allows us to obtain a low calorific capacity and a high thermal conductance. On the other hand, its sensitivity is low and it was necessary to associate an amplifier with a gain of 100 000. The whole device was set outside on a bar 2 m above the ground. The different experiments carried out with one or several microthermocouples showed very small turbulences of different types depending on the role of the different layers in the low atmosphere. They also enabled to visualize convection due to the ground or due to the wind as a function of time.

Electron transport properties in tensile strained Si-based materials are theoretically analyzed using Monte-Carlo calculation. We focus our interest on in-plane transport inSi and Si1−y Cy (y ≤ 0.03), grown respectively on 〈001〉Si1−x Gex pseudo-substrate and Si substrate, with a view toField-Effect-Transistor application. In comparison with unstrained Si, the tensilestrain effect is shown to be very attractive in Si: drift mobilities greater than 3000 cm2/Vs are obtained at 300 K for a Ge fraction mole of 0.2 in thepseudo-substrate. In the Si1−y Cy /Si system, that does not need anypseudo-substrate, the beneficial strain effect on transport is counterbalanced by thealloy scattering whose influence on mobility is studied. If the alloy potential isgreater than about 1 eV, the advantage of strain-induced reduction of effective massis lost in terms of stationary transport performance at 300 K.

A magnetoelectrostatic trap consists of a spindle cusp magnetic field configuration and transverse electrostatic potentials applied to the electrodes at the ring and point cusp ends. Plasma confinement studies in this trap is made with a single positive charged particle. When the plasma is injected in such a system a potential well for the positive ions is formed where they could be trapped. Three-dimensional trajectory of the particle was developed by a single-gap mathematical model. The trajectory of a positive ion in the system was analyzed numerically by Runge-Kutta fourth order method. The equations of motion were constructed from the Hamiltonian function. The three-dimensional trajectory of an ion was traced for various possible input parameters. When the electrostatic potentialand angle of injection are kept zero almost all the injected ions (post-cusp region) escape through the aperture. But there exists a critical injection velocity and magnetic field intensity to reflect the particle at axial cusp region. In this forward and backward motion the particle moves in a helical path encircling about the same magnetic lines of force. While introducing some potential difference to the electrodes in the cusp ends, the particle exhibits a "double helix" trajectory about the axis of the spindle cusp configuration. This double helical path leads long duration confinement of the particle in such a system and obviously cusp losses are suppressed. The results are reported for a wide range of input parameters.

This paper describes an automatic lineshape recording device applied to thestudy of the rotational molecular transition J: 2 → 3 of OCS gasat 36.489 GHz. The device includes a microwave oversized cell associatedwith a DC voltage amplifier and a microcontroller stabilizer. Itparticularly permits the automatic recording of the lineshape with anaccuracy better than 1 kHz for the frequency and 1 mV for the voltage.By fitting with a Lorentz or Voigt profile, we directly determine theevolution of the shape, the center frequency, the broadening parameter andthe intensity of the line versus the pressure. At low pressure, the Dopplerbroadening effect has been measured.

Anode for a non-transferred DC plasma spray torch was designed to improve electrothermal efficiency. A theoretical calculation was made for the electrothermalefficiency in a DC plasma torch operating with argon at atmospheric pressure withpower level in the range of 5.2–20 kW using energy balance equations. ANOVA for thetwo level factorial design was done. Plasma gas flow rate, current intensity,nozzle diameter and length were found to influence the efficiency. The efficiencywas found to decrease with increase in current intensity and nozzle length and toincrease with increase in nozzle diameter and gas flow rate. The overall energy balance calculations showed that the heat transfer to the plasma-forming gas decreases with increase in arc current and the same was moresignificant at higher flow rates. Plasma jet velocity for different flow rates, input to the torch and nozzle dimensions was calculated from the gas enthalpy. Itwas found that the velocity increased with increase in the power input to the torchand gas flow rate and decreased with increase in nozzle length and diameter. The current–voltage characteristics of the torch operating with argon gas were studied for different gas flow rates. The Nottingham coefficients were calculated using least – square method.