Search

Granular multiparticle ensembles are of interest from fundamental statistical viewpoints as well as for the understanding of collective processes in industry and in nature. Extraction of physical data from optical observations of three-dimensional (3D) granular ensembles poses considerable problems. Particle-based tracking is possible only at low volume fractions, not in clusters. We apply shadow-based and feature-tracking methods to analyze the dynamics of granular gases in a container with vibrating side walls under microgravity. In order to validate the reliability of these optical analysis methods, we perform numerical simulations of ensembles similar to the experiment. The simulation output is graphically rendered to mimic the experimentally obtained images. We validate the output of the optical analysis methods on the basis of this ground truth information. This approach provides insight in two interconnected problems: the confirmation of the accuracy of the simulations and the test of the applicability of the visual analysis. The proposed approach can be used for further investigations of dynamical properties of such media, including the granular Leidenfrost effect, granular cooling, and gas-clustering transitions.

International audience; In this review, we present a general overview of the current progress in pore scale experimentations related to CO2 geological storage. In such processes occurring in porous media, most of the phenomena start from (bio)geochemical reactions and transport mechanisms at the pore scale. Therefore, in order to predict the overall consequences of CO2 injection inside a deep reservoir and to ensure a safe installation, it is essential to access pore-scale information for geochemical numerical methods and to improve the understanding of the critical operating parameters. In this view, high pressure micromodels that mimic geological media (Geological Labs on Chip) have recently attracted interest to study multiphase flows and chemical reactivity in porous media. Emphasis is placed on experiments that can be performed in realistic pressure conditions representative of deep geological formations, for accessing information on reactive flows in porous media, mineralization/dissolution, but also (bio)chemical processes. The use of such micromodels continues to broaden the investigation space thanks to the design of in situ characterization techniques. Together high-fidelity data not easily accessed in conventional batch or core-scale procedures is made readily available.

International audience; Phase transition in fluids is ubiquitous in nature and has important applications in areas such as the food industry for volatile oils’ extraction or in nuclear plants for heat transfer. Fundamentals are hampered by gravity effects on Earth. We used direct imaging to record snapshots of phase separation that takes place in sulfur hexafluoride, SF6, under weightlessness conditions on the International Space Station (ISS). The system was already at liquid-vapor equilibrium slightly below the critical temperature and further cooled down by a 0.2-mK temperature quench that produced a new phase separation. Both full view and microscopic views of the direct observation cell were analyzed to determine the evolution of the radii distributions. We found that radii distributions could be well approximated by a lognormal function. The fraction of small radii droplets declined while the fraction of large radii droplets increased over time. Phase separation at the center of the sample cell was visualized using a 12× microscope objective, which corresponds to a depth of focus of about 5 μ m. We found that the mean radii of liquid droplets exhibit a t1/3 evolution, in agreement with growth driven by Brownian coalescence. It was also found that the mean radii of the vapor bubbles inside the liquid majority phase exhibit a t1/2 evolution, which suggest a possible directional motion of vapor bubbles due to the influence of weak remaining gravitational field and/or a composition Marangoni force.

International audience; This paper reports the carbon dioxide detection in silicon-Pyrex high pressure microfluidic devices mimicking geological conditions encountered in deep saline aquifers using an in situ infrared optical sensor. The middle infrared source inserted inside the microchannel is based on infrared emission from Dy3+ sulfide glass fibers. The broad emission of the Dy3+ doping in infrared fibers is used to directly probe the CO2 thanks to the perfect overlap between the rare earth emission centered at 4.4 μm and the CO2 absorption band located at 4.3 μm. CO2 and water were clearly distinguished when using segmented flow on chip at pressures ranging from 4.5 to 6 MPa. These results demonstrate the feasibility of the infrared optical detection of other gases displaying absorption bands in the middle infrared domain for further developments of gas sensors, which can find applications in geological media monitoring and microfluidics.

International audience; In order to investigate at the pore scale the mechanisms involved during CO2 injection in a water saturated pore network, a series of displacement experiments is reported using high pressure micromodels (geological labs on chip - GLoCs) working under real geological conditions (25 < T (°C) < 75 and 4.5 < p (MPa) < 8). The experiments were focused on the influence of three experimental parameters: (i) the p, T conditions, (ii) the injection flow rates and (iii) the pore network characteristics. By using on-chip optical characterization and imaging approaches, the CO2 saturation curves as a function of either time or the number of pore volume injected were determined. Three main mechanisms were observed during CO2 injection, namely, invasion, percolation and drying, which are discussed in this paper. Interestingly, besides conventional mechanisms, two counterintuitive situations were observed during the invasion and drying processes.

Resume Les mediations therapeutiques sont une partie integrante du traitement par l'institution que nous proposons dans le cadre de la clinique Dupre. Elles contribuent a adapter ce cadre aux caracteristiques psychopathologiques des adolescents et jeunes adultes qui y sont traites. Elles representent une technique pour se lier, alors meme que le lien, qui est notre principal instrument therapeutique, est aussi ce qui menace le plus nos patients. Elles permettent d'elaborer les repetitions en utilisant les capacites empathiques des soignants inclus dans l'espace psychique elargi du patient. Ce faisant, elle contribue a une bonne intrication des mouvements de liaison et de deliaison si fortement mobilises chez les patients adolescents et jeunes adultes. Au travers d'un trajet de soins, nous tenterons de montrer la place et les enjeux therapeutiques des mediations dans notre dispositif institutionnel. Cette demarche nous conduit a definir un point de vue plus general sur la « psychotherapie par l'institution » et la place qu'y occupent les mediations therapeutiques.

We used a direct imaging technique to investigate concentration fluctuations enhanced by thermal fluctuations in a ternary mixture of methanol (Me), cyclohexane (C), and partially deuterated cyclohexane (C*) within 1mK above its consolute critical point. The experimental setup used a low-coherence white-light source and a red filter to visualize fluctuation images. The red-filtered images were analyzed off-line using a differential dynamic microscopy algorithm that allowed us to determine the correlation time, τ, of concentration fluctuations. From τ, we determined the mutual mass diffusion coefficient, D, very near and above the critical point of Me-CC* mixtures. We also numerically estimated both the background and critical contributions to D and compared the results against our experimental values determined from τ. We found that the experimental value of D is close to the prediction based on Stokes-Einstein diffusion law with Kawasaki’s correction.

International audience; Near the critical point of fluids, critical opalescence results in light attenuation, or turbidity increase, that can be used to probe the universality of critical behavior. Turbidity measurements in SF6 under weightlessness conditions on board the International Space Station are performed to appraise such behavior in terms of both temperature and density distances from the critical point. Data are obtained in a temperature range, far (1 K) from and extremely close (a few μK) to the phase transition, unattainable from previous experiments on Earth. Data are analyzed with renormalization-group matching classical-to-critical crossover models of the universal equation of state. It results that the data in the unexplored region, which is a minute deviant from the critical density value, still show adverse effects for testing the true asymptotic nature of the critical point phenomena.

The turbidity ( $$\tau $$ ) measurements of Guttinger and Cannell (Phys Rev A 24:3188–3201, 1981) in the temperature range $$28\,\text {mK}\le T-T_{c}\le 29\,\text {K}$$ along the critical isochore of homogeneous xenon are reanalyzed. The singular behaviors of the isothermal compressibility ( $$\kappa _{T}$$ ) and the correlation length ( $$\xi $$ ) predicted from the master crossover functions are introduced in the turbidity functional form derived by Puglielli and Ford (Phys Rev Lett 25:143–146, 1970). We show that the turbidity data are thus well represented by the Ornstein–Zernike approximant, within 1 % precision. We also introduce a new crossover master model (CMM) of the parametric equation of state for a simple fluid system with no adjustable parameter. The CMM model and the phenomenological crossover parametric model are compared with the turbidity data and the coexisting liquid–gas density difference ( $$\Delta \rho _{LV}$$ ). The excellent agreement observed for $$\tau $$ , $$\kappa _{T}$$ , $$\xi $$ , and $$\Delta \rho _{LV}$$ in a finite temperature range well beyond the Ising-like preasymptotic domain confirms that the Ising-like critical crossover behavior of xenon can be described in conformity with the universal features estimated by the renormalization-group methods. Only 4 critical coordinates of the vapor–liquid critical point are needed in the (pressure, temperature, molecular volume) phase surface of xenon.

International audience; Boiling phenomena in the two-phase region of SF6 close to its critical point have been observed using the high-quality thermal and optical environment of the CNES dedicated facility ALI-DECLIC on board the International Space Station (ISS). The weightlessness environment of the fluid, which cancels buoyancy forces and favorites the three-dimensional spherical shape of the gas bubble, is proven to be an irreplaceable powerful tool for boiling studies. To identify each key mechanism of the boiling phenomena, the ALI-DECLIC experiments have benefited from (i) the well-adapted design of the test cells, (ii) the high-fidelity of the ALI insert teleoperation when long-duration experiment in stable thermal and microgravity environment are required and (iii) the high repeatability of the controlled thermal disturbances. These key mechanisms were observed by light transmission and interferometry technique independently with two sample cells filled with pure SF6 at a near-critical density. The fluid samples are driven away from thermal equilibrium by using a heater directly implemented in the fluid, or a surface heater on a sapphire optical window. In the interferometry cell, the bulk massive heater distinguishes two symmetrical two-phase domains. The modification of the gas bubble shape is observed during heating. In the direct observation cell, the gas bubble is separated by a liquid film from the thin layered transparent heater deposited on the sapphire window. The liquid film drying and the triple contact line motion during heating are observed using light transmission. The experiments have been performed in a temperature range of 10 K below the critical temperature T c, with special attention to the range View the MathML source0.1mK≤Tc−T≤3mK very close to the critical temperature. The unique advantage of this investigation is to provide opportunities to observe the boiling phenomena at very low heat fluxes, thanks to the fine adjustment of the liquid-vapor properties, (e.g. surface tension), by precise control of the distance to the critical point. We present the new observations of the gas bubble spreading over the heating surface which characterizes the regime where vapor bubbles nucleate separately and grow, as well as liquid drying, vapor film formation, triple contact line motion, which are the key mechanisms at the origin of the boiling crisis when the formed vapor film reduces the heat transfer drastically at the heater wall.

International audience; This Letter reports a fast and accurate method to quantify dissolved carbon dioxide in water and salted water (NaCl) using microfluidic systems probed by confocal Raman spectroscopy. The relationship of CO2 solubility and Raman band intensity ratios (the νu of the CO2 Fermi dyad over the water stretching band) can be fit from third order polynomial forms, depending on NaCl concentration. This approach allows for a much faster determination of CO2 solubility measurements in pressurized aqueous media. More generally, by easily managing lithospheric fluids in microdevices, this strategy opens avenues towards true 'Geological Lab on chip'.

Super-Critical Water Oxidation (SCWO) is an attractive candidate technology for processing solid and liquid wastes for long duration space and extraterrestrial planetary missions. However, an experimental database for critical transition of water as well as SCWO under the microgravity conditions relevant to space and extra-terrestrial environments is currently lacking. The first building block for this database is the behavior of the critical transition of water from a two phase liquid-vapor system to a supercritical fluid. To this end, a collaborative experiment between NASA and the French space agency, CNES, was recently conducted on the International Space Station. This experiment studied the effects of microgravity on phase distribution, heat addition, evolution of bubbles, and hysteresis effects in a small constant volume system during the critical transition process. This paper describes the results from key test sequences from the experiment which focused on the behavior of water under the influence of a temperature gradient near the critical point. Experimental data consisted of images of the fluid, temperature measurements in the cell body, and images from a grid-displacement technique in the supercritical regime at near-critical conditions. Nomenclature Cp = specific heat at constant pressure k = thermal conductivity K = constant in Eq. (6) n = refractive index P = pressure r = fluid cell radius t = time T = temperature x, y = coordinates  = thermal diffusivity  = coefficient of thermal expansion  = shift in grid point location  = specific heat ratio  = density  = constant in Eq. (5) = spatial average

In the supercritical phase, pure fluids have great potential for industrial applications and are increasingly used by industry as nonpolluting solvents of organic materials and media for high yield chemical reactions. The experimental data were recorded in microgravity for sulfur hexafluoride (SF6) and on Earth for density-matching binary mixture of methanol and partially deuterated cyclohexane (CC*-Me). We used small angle light scattering experiments to investigate fluctuations in SF6 near critical point and in density-matched binary mixture CC*-Me in the absence of convective flows. For binary mixture, we used three different filtering methods: bright filed (BF - no filter), phase contrast (PC - quarter wave plate at focal point) and dark field (DF - small opaque object at focal point). The power spectrum of scattered light contains information about local inhomogeneities encountered by light traveling through the sample cell unit (SCU). We found that the spatial correlations revealed by Fourier transforms follow power laws both for SF6 in microgravity and binary mixture on Earth. This is an indication of the universality of fluctuation mechanisms. Temporal correlations of fluctuations were investigated using the correlation time.

By introducing three well-defined dimensionless numbers, we establish the link between the scale dilatation method able to estimate master (i.e., unique) singular behaviors of the one-component fluid subclass and the universal crossover functions recently estimated [Garrabos and Bervillier, Phys. Rev. E 74, 021113 (2006)] from the bounded results of the massive renormalization scheme applied to the ${\ensuremath{\Phi}}_{d}^{4}(n)$ model of scalar order parameter $(n=1)$ and three dimensions $(d=3)$, representative of the Ising-like universality class. The master (i.e., rescaled) crossover functions are then able to fit the singular behaviors of any one-component fluid without adjustable parameter, using only one critical energy scale factor, one critical length scale factor, and two dimensionless asymptotic scale factors, which characterize the fluid critical interaction cell at its liquid-gas critical point. An additional adjustable parameter accounts for quantum effects in light fluids at the critical temperature. The effective extension of the thermal field range along the critical isochore where the master crossover functions seems to be valid corresponds to a correlation length greater than three times the effective range of the microscopic short-range molecular interaction.

The effect of a linear harmonic vibration on heat propagation is investigated in near-critical SF6 under weightlessness conditions in space. Heat was issued from a pointlike source (thermistor), a situation representative of an industrial use of pressurized supercritical fluid storage. Two kinds of vibrations were used, large amplitude (64 mm) at 0.2 Hz and low amplitude (0.8 mm) at 1.6 Hz, with temperatures from 5 K to 20 mK from the critical temperature. The vibrations are seen to strongly affect the evolution and shape of the hot boundary layer (HBL), the heat exchange between the heat source and the fluid, and the bulk thermalization process by the adiabatic piston-effect process. The HBL is initially convected as symmetrical plumes over a distance that only depends on the vibration velocity and which corresponds to a Rayleigh-Bénard-like instability where the vibration acceleration acts as the earth gravity. Then the extremities of the plumes are convected perpendicularly to the direction of oscillation as two "pancakes," a process encountered in the vibrational Rayleigh-Bénard instability. When the vibration velocity is small, only one pancake centered at the hot source is observed. Temperature evolutions of the hot source and the fluid are studied in different locations. Convection flows and adiabatic piston effect compete to determine the thermal dynamics, with the latter being the most efficient near the critical point. The experimental results are compared with a two-dimensional numerical simulation that highlights the similarities and differences between the very compressible van der Waals gas and an ideal gas.

International audience; A study is presented concerning an experiment under weightlessness. A pure fluid (SF6) is heated near and below its critical point, where liquid coexists with vapor. After the temperature rise, the vapor phase passes well beyond the temperature of the heating walls. This surprising finding is discussed in the light of an adiabatic heat transfer or "Piston effect" and the special geometry of the liquid and vapor. In addition, the shape of the gas-liquid interface is distorted near the solid wall by the thrust of vapor production ("recoil" force), a precursor to the well-known boiling crisis in heat exchanger.

We present a micro-gravity experimental study of the statistical properties of intermediate number density vibro-fluidized inelastic spheres in a rectangular container. It is found that although when taking all the particles into account, the probability distributions of velocities both along and perpendicular to the vibration direction are exponential and symmetric, when dividing particles along the vibration direction into different bins, the local velocity distributions are found to deviate measurably from a symmetric distribution for the velocity component in the vibrating direction. The skewness analysis of the local distribution profiles for vx and vy shows that the local distribution of vx remains symmetric, however, the skewness of the distribution profile in vy changes nearly linear from positive to negative with skew = 0 near the center bin. This indicates a long range boundary effect of the asymmetry in vy. We further studied the hydrodynamic profiles granular pressure px and py, and temperature Tx and Ty in positive and negative components such as p+x and p−x, and Tx+ and Tx−, in accordance with the sign of velocity components. The profiles for the two components are found different along the y direction. Along vibration direction granular medium is found inhomogeneous and anisotropic not only in the particle number densities, but also in vy, py and Ty. This suggests new hydrodynamical modeling is needed for such vibro-fluidized granular systems.

Surgical exeresis and radiation therapy are effective means of treatment for facial carcinomas. In some areas that are difficult to manage (nose, ears, periorbital region), the respective importance of both approaches is discussed. We report on the retrospective study of 309 patients seen after a skin carcinology consultation in which a dermatologist, a surgeon and a radiotherapist were associated. These 309 patients, with a mean age of 73 years, presented with 375 carcinomas, i.e. 246 basal-cell (BC) and 119 epidermoid (EC) carcinomas. The most frequent sites were the nose (33.8% of BC), the inner canthus (12.7% of BC), the lower lip (23.8% of EC) and the ear (15.6% of EC). Management mainly consisted of surgery (50.8%) then Curie therapy (37%). The rate of recurrence was the same (10.5%) after surgery and radiation therapy. The study of the results leads us to advocating surgery for carcinomas of the ear (due to the occurrence of radiation necrosis in every third case after radiation therapy) and Curie therapy for carcinomas of the lower lid (except the inner canthus) because of recurrence in every second case treated with surgery. We currently prefer surgery for carcinomas of the lower lip (radiodermatitis in 11.8% of cases) and Curie therapy for the nose (lower rate of recurrence than with surgery). However, in the last two cases, the proposals for treatment should be confirmed by randomized studies. Thus facial carcinomas of the skin surrounding the orifices of the face and/or those that affect patients who are difficult to treat must be seen during a skin carcinology consultation by a dermatologist, a surgeon and a radiotherapist working together.(ABSTRACT TRUNCATED AT 250 WORDS)

International audience; Analyses of ground-based experiments on near-critical fluids to precisely determine their density can be hampered by several effects, especially the density stratification of the sample, the liquid wetting behavior at the cell walls, and a possible singular curvature of the "rectilinear" diameter of the density coexisting curve. For the latter effect, theoretical efforts have been made to understand the amplitude and shape of the critical hook of the density diameter, which depart from predictions from the so-called ideal lattice-gas model of the uniaxial 3D-Ising universality class. In order to optimize the observation of these subtle effects on the position and shape of the liquid-vapor meniscus in the particular case of SF6, we have designed and filled a cell that is highly symmetrized with respect to any median plane of the total fluid volume. In such a viewed quasi-perfect symmetrical fluid volume, the precise detection of the meniscus position and shape for different orientations of the cell with respect to the Earth's gravity acceleration field becomes a sensitive probe to estimate the cell mean density filling and to test the singular diameter effects. After integration of this cell in the ALI-R insert, we take benefit of the high optical and thermal performances of the DECLIC Engineering Model. Here we present the sensitive imaging method providing the precise ground-based SF6 benchmark data. From these data analysis it is found that the temperature dependence of the meniscus position does not reflect the expected critical hook in the rectilinear density diameter. Therefore the off-density criticality of the cell is accurately estimated, before near future experiments using the same ALI-R insert in the DECLIC facility already on-board the International Space Station.

Conventional lab scale tools are adequate to access some experimental data related to CO2 geological storage in deep saline aquifers. However, they are lacking from in situ characterization techniques, thus limiting the monitoring and the understanding of the various involved processes. Therefore, new methods are needed to investigate deeply the fundamental mechanisms associated with these four trapping mechanisms. In this context, microfluidics approaches have bring several advantages over conventional experimental means, including fast screening of the parameters, fast heat and mass transfer and the ease of implementation of various characterization techniques. By adapting such approaches to porous media, our team has demonstrated the fabrication and use of the first high pressure / high temperature microreactors, able to withstand harsh conditions up to 20 MPa and 400°C, which were adapted to studies dealing with fluidic within porous media, so called “Geological Labs on Chip – GLoCs”. These tools are at the core of the collaborative project CGSµLab N° ANR-12-SEED-0001 funded by the French national research agency (ANR). We illustrate here after some key results obtained from the use of GLoCs coupled to optical and spectroscopy characterization methods.

We report on the analysis of the response of a near-critical fluid sample cell submitted to heating at different distances from the critical temperature T c , in the Mir station microgravity environment We recall the hydrodynamic and thermodynamic bases of the mechanisms of fast adiabatic heating, also called thermalization by Piston Effect (PE). We give a phenomenological approach of these mechanisms in a highly compressible critical fluid submitted to heating until a steady state is reached, and present the main results of numerical experiments in a Van der Waals fluid. We then use this phenomenological understanding to analyze an experimental case of heating in reduced gravity onboard Mir, using the Alice 2 facility between 1996 and 1999 (Cassiopea to Perseus missions) We have measured the characteristic time of the PE as a fonction of the critical temperature distance, and investigated the crossover behavior from the pure adiabatic regime for a surrounding wall of infinite conductivity, to the bottleneck conductivity regime induced by a real cell. Close to T c , we have evidenced the key influence of the geometry of the cell and of the thermal properties of the wall materials

International audience; The behavior of gases and liquids during a phase transition is severely affected by gravity effects which unavoidably drive the denser phase downwards and the lighter phase upwards. When such gravity effects are suppressed a number of new and surprising behavior are observed. The studies are performed mostly in the vicinity of a critical point where the behavior can be expressed in scaled units of a natural length scale (the correlation length of the order parameter fluctuations) and a natural timescale (the characteristic relaxation time of the order parameter fluctuations). We will review the main results obtained with binary liquids and simple fluids. Firstly, a phase change is initiated by quenching down the fluid from above the coexistence curve, where the fluid is homogeneous, to inside the coexistence curve, where its phase separates into two phases. The main result is the recognition that the hydrodynamics of coalescence eventually induces the pattern morphology and the phase transition kinetics. The volume fraction, is the key parameter which decides whether drops fuse because of random, Brownian collisions [pattern of drops, growth law in (time)1/3], or coalesce in a continuous process where the flow due to a coalescence event induces another coalescence (growth proportional to time, interconnected drop pattern). The presence of a wall modifies by its geometry and wetting properties the phase development. Coalescence is constrained and leads to new growth laws in the immediate vicinity of the wall. We emphasize that these phase ordering processes are quite general; they can be applied with success to quite different ordering situations, such as the sorting of embryonic tissues, an important process in morphogenesis. Secondly, when a gas–liquid, two-phase fluid, is heated from below the critical point to above, the process appears to be driven by the wetting and thermal properties of the boundary layer near the heating wall. Under terrestrial gravity, the dynamics is driven by a Rayleigh–Taylor instability. Under weightlessness, the liquid/vapor contact angle on the wall is modified in such a way that the gas seemingly “wets” the wall. We propose the vapor recoil force to be at the origin of this non-equilibrium “wetting” transition.

International audience; We report on the observation of the periodic pattern occuring in a two-dimensional (2D) assembly of heavy beads (of diameter D = 280-630 μm) immersed in water when the vessel containing the fluid and the beads is submitted to horizontal vibrations (of frequency f and oscillation amplitude A). Under vibrations, regularly spaced, one bead thick lines perpendicular to the direction of vibrations are formed at small surface fraction. In the ranges f = 10-20 Hz and A = 0.7-3.5 mm, the amplitude of the oscillatory motion of the beads relative to the fluid B is found to vary linearly with A. A simple phenomenological model based on dynamic solid friction and viscous drag gives qualitatively account for this linear dependence. The period of the pattern λ is found to vary with viscosity v, ω = 2πf, D, and B according to the law λ/D ∼ (B/D)0.5(BωD/v)−0.21. The dynamics of pattern formation exhibits several scenarii, depending on the initial bead distribution, as well as several characteristic time scales. We review and discuss possible mechanisms of pattern formation reported in literature and proposed for similar phenomena observed in the frame of rheology of suspensions and acoustic streaming flows.