We report an experimental study of a dilute “gas” of inelastically colliding particles excited by vibrations in low gravity. We show that recording the collision frequency together with the impulses on a wall of the container gives access to several quantities of interest. We observe that the mean collision frequency does not scale linearly with the number N of particles in the container. This is due to the dissipative nature of the collisions and is also directly related to the non-extensive behaviour of the kinetic energy (the granular temperature is not intensive).
Strongly driven granular media are known to undergo a transition from a gas-like to a cluster regime when the density of particles is increased. However, the main mechanism triggering this transition is not fully understood so far. Here, we investigate experimentally this transition within a 3D cell filled with beads that are driven by two face-to-face vibrating pistons in low gravity during parabolic flight campaigns. By varying large ranges of parameters, we obtain the full phase diagram of the dynamical regimes reached by the out-of-equilibrium system: gas, cluster or bouncing aggregate. The images of the cell recorded by two perpendicular cameras are processed to obtain the profiles of particle density along the vibration axis of the cell. A statistical test is then performed on these distributions to determinate which regime is reached by the system. The experimental results are found in very good agreement with theoretical models for the gas-cluster transition and for the emergence of the bouncing state. The transition is shown to occur when the typical propagation time needed to transmit the kinetic energy from one piston to the other is of the order of the relaxation time due to dissipative collisions.
Light transmission measurements performed in SF 6 close to its liquidgas critical point are used to obtain turbidity data in the reduced temperature rangeAutomatic experiments (ALICE 2 facility) were made at a near critical density, i.e., ρ −ρ c ρ c = 0.8 %, in the one-phase homogeneous region, under the microgravity environment of the Mir Space Station ( ρ is the average density, ρ c is the critical density). The turbidity data analysis verifies the theoretical crossover formulations for the isothermal compressibility κ T and the correlation length ξ . These latter formulations are also used to analyze very near T c thermal diffusivity data obtained under microgravity conditions by Wilkinson et al. (Phys. Rev. E 57, 436, 1998).
A new experimental facility has been designed and constructed to study driven granular media in a low-gravity environment. This versatile instrument, fully automatized, with a modular design based on several interchangeable experimental cells, allows us to investigate research topics ranging from dilute to dense regimes of granular media such as granular gas, segregation, convection, sound propagation, jamming, and rheology-all without the disturbance by gravitational stresses active on Earth. Here, we present the main parameters, protocols, and performance characteristics of the instrument. The current scientific objectives are then briefly described and, as a proof of concept, some first selected results obtained in low gravity during parabolic flight campaigns are presented.
International audienceWe present the master (i.e., unique) behavior of the squared capillary length—the so-called Sugden factor—as a function of the temperaturelike field along the critical isochore, asymptotically close to the gas-liquid critical point of about twenty (one-component) fluids. This master behavior is obtained using the scale dilatation of the relevant physical fields of the one-component fluids. The scale dilatation method introduces the fluid-dependent scale factors in a manner analog to the linear relations between physical fields and scaling fields needed by the renormalization theory applied to any physical system belonging to the Ising-like universality class. The master behavior for the Sugden factor satisfies hyperscaling. It can be asymptotically fitted by the leading terms of the theoretical crossover functions for the correlation length and the susceptibility in the homogeneous domain, recently obtained from massive renormalization in field theory. In the absence of corresponding estimation of the theoretical crossover functions for the interfacial tension, we define the range of the temperaturelike field where the master leading power law can be practically used to predict the singular behavior of the Sugden factor, in conformity with the theoretical description provided by the massive renormalization scheme within the extended asymptotic domain of the one-component fluid “subclass.
The authors describe a setup to measure accurately the normal restitution coefficient between a quasiresonant ball and a plane. It uses the fact that the trajectory of a single ball in a cylindrical box with a vibrating wall reduces rapidly to a merely periodic one dimensional dynamics, with little rotation. The ball speed is measured accurately from the time series of impacts. It is also used to study and calibrate a sphere-plane impact sensor. This sensor allows to determine the collision time at a microsecond accuracy and the maximum force applied. The collision is found to obey the Hertz law.
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