Experimental investigation of water distribution in two-phase zone during gravity-dominated evaporation

We characterize the water repartition within the partially saturated (two-phase) zone (PSZ) during evaporation out of mixed wettable porous media by controlling the wettability of glass beads, their sizes, and as well the surrounding relative humidity. Here, Capillary numbers are low and under these conditions, the percolating front is stabilized by gravity. Using experimental and numerical analyses, we find that the PSZ saturation decreases with the Bond number, where packing of smaller particles have higher saturation values than packing made of larger particles. Results also reveal that the extent (height) of the PSZ, as well as water saturation in the PSZ, both increase with wettability. We also numerically calculate the saturation exclusively contained in connected liquid films and results show that values are less than the expected PSZ saturation. These results strongly reflect that the two-phase zone is not solely made up of connected capillary networks, but also made of disconnected water clusters or pockets. Moreover, we also find that global saturation (PSZ + full wet zone) decreases with wettability, confirming that greater quantity of water is lost via evaporation with increasing hydrophilicity. These results show that connected liquid films are favored in more hydrophilic systems while disconnected water pockets are favored in less hydrophilic systems

Lagrangian temperature, velocity and local heat flux measurement in Rayleigh-Benard convection

We have developed a small, neutrally buoyant, wireless temperature sensor. Using a camera for optical tracking, we obtain simultaneous measurements of position and temperature of the sensor as it is carried along by the flow in Rayleigh-B\'enard convection, at $Ra \sim 10^{10}$. We report on statistics of temperature, velocity, and heat transport in turbulent thermal convection. The motion of the sensor particle exhibits dynamics close to that of Lagrangian tracers in hydrodynamic turbulence. We also quantify heat transport in plumes, revealing self-similarity and extreme variations from plume to plume.Comment: 4 page

Universal scattering behavior of co-assembled nanoparticle-polymer clusters

Water-soluble clusters made from 7 nm inorganic nanoparticles have been investigated by small-angle neutron scattering. The internal structure factor of the clusters was derived and exhibited a universal behavior as evidenced by a correlation hole at intermediate wave-vectors. Reverse Monte-Carlo calculations were performed to adjust the data and provided an accurate description of the clusters in terms of interparticle distance and volume fraction. Additional parameters influencing the microstructure were also investigated, including the nature and thickness of the nanoparticle adlayer.Comment: 5 pages, 4 figures, paper published in Physical Review

Plastic deformation down to 4.2 K of CoO single crystals and T.E.M. observation of dislocations

Plastic deformation of CoO has been performed at 4.2 K by compression of single crystals along . The influence of thermodynamic conditions of specimen preparation has been shown. The dislocation structure observed by transmission electron microscopy (TEM) is not directly related to the one existing during deformation at very low temperature.On a déformé plastiquement CoO à 4,2 K par compression de monocristaux le long de . L'influence des conditions thermodynamiques de préparation des échantillons a été montrée. La structure des dislocations observée en microscopie électronique en transmission (TEM) n'est pas directement reliée à celle existant pendant la déformation à très basse température

Effects of electromagnetic waves on the electrical properties of contacts between grains

A DC electrical current is injected through a chain of metallic beads. The electrical resistances of each bead-bead contacts are measured. At low current, the distribution of these resistances is large and log-normal. At high enough current, the resistance distribution becomes sharp and Gaussian due to the creation of microweldings between some beads. The action of nearby electromagnetic waves (sparks) on the electrical conductivity of the chain is also studied. The spark effect is to lower the resistance values of the more resistive contacts, the best conductive ones remaining unaffected by the spark production. The spark is able to induce through the chain a current enough to create microweldings between some beads. This explains why the electrical resistance of a granular medium is so sensitive to the electromagnetic waves produced in its vicinity.Comment: 4 pages, 5 figure

Fluage de monocristaux de NiO

NiO single crystals have been subjected to constant-load compressive creep along (100). Stresses between 50 MPa and 120 MPa and temperatures between 950 °C and 1 200 °C were studied. The activation energy observed suggests that oxygen diffusion is the rate-controlling process.Des expériences de compression à charge constante, selon , ont été réalisées sur des monocristaux de NiO. Les contraintes utilisées vont de 50 MPa à 120 MPa et les températures de 950 °C à 1200 °C. L'énergie d'activation du fluage suggère que la diffusion de l'oxygène joue un rôle prédominant sur la cinétique de déformation plastique

Lognormal scale invariant random measures

In this article, we consider the continuous analog of the celebrated Mandelbrot star equation with lognormal weights. Mandelbrot introduced this equation to characterize the law of multiplicative cascades. We show existence and uniqueness of measures satisfying the aforementioned continuous equation; these measures fall under the scope of the Gaussian multiplicative chaos theory developed by J.P. Kahane in 1985 (or possibly extensions of this theory). As a by product, we also obtain an explicit characterization of the covariance structure of these measures. We also prove that qualitative properties such as long-range independence or isotropy can be read off the equation.Comment: 31 pages; Probability Theory and Related Fields (2012) electronic versio

Pure diffusional creep of NiO polycrystals

Compressive creep testing of polycrystalline NiO has been performed in air and argon, at temperatures between 1 100 and 1 500 °C (0.61 to 0.79 TM) under loads corresponding to initial applied stresses from 6 to 90 MPa. Nabarro creep was observed in the lower stress range; creep rate and oxygen diffusivity show a good correlation.Des essais de fluage en compression ont été faits sur des polycristaux de NiO, dans l'air et l'argon, à des températures entre 1 100 et 1 500 °C (0,61 à 0,79 TF) sous des charges correspondant à des contraintes initiales entre 6 et 90 MPa. Le fluage Nabarro a été observé à faible contrainte; la vitesse de déformation et la diffusivité de l'oxygène montrent une bonne corrélation

A nonextensive entropy approach to solar wind intermittency

The probability distributions (PDFs) of the differences of any physical variable in the intermittent, turbulent interplanetary medium are scale dependent. Strong non-Gaussianity of solar wind fluctuations applies for short time-lag spacecraft observations, corresponding to small-scale spatial separations, whereas for large scales the differences turn into a Gaussian normal distribution. These characteristics were hitherto described in the context of the log-normal, the Castaing distribution or the shell model. On the other hand, a possible explanation for nonlocality in turbulence is offered within the context of nonextensive entropy generalization by a recently introduced bi-kappa distribution, generating through a convolution of a negative-kappa core and positive-kappa halo pronounced non-Gaussian structures. The PDFs of solar wind scalar field differences are computed from WIND and ACE data for different time lags and compared with the characteristics of the theoretical bi-kappa functional, well representing the overall scale dependence of the spatial solar wind intermittency. The observed PDF characteristics for increased spatial scales are manifest in the theoretical distribution functional by enhancing the only tuning parameter $\kappa$, measuring the degree of nonextensivity where the large-scale Gaussian is approached for $\kappa \to \infty$. The nonextensive approach assures for experimental studies of solar wind intermittency independence from influence of a priori model assumptions. It is argued that the intermittency of the turbulent fluctuations should be related physically to the nonextensive character of the interplanetary medium counting for nonlocal interactions via the entropy generalization.Comment: 17 pages, 7 figures, accepted for publication in Astrophys.