International audienceHelium mass flow rates in a microchannel were measured, for a wide Knudsen-number range, in isothermal steady conditions. The flow Knudsen numbers, considered here, cover the range from continuum slip regime to the near free molecular regime. We used a single-channel system involved in an experimental platform more powerful than those previously used. The experimental errors and uncertainties were accurately investigated and estimated. In the continuum slip regime, it was found that the first-order approach is pertinent for Knudsen number between 0.03 and 0.3. Moreover, the slip coefficient was deduced by comparing the experiments with the theoretical first-order slip continuum approach. For Knudsen number between 0.03 and 0.7, a polynomial second-power form is proposed for the mass flow rate expression. Otherwise, the experimental results on the mass flow rate were compared with theoretical values calculated from kinetic approaches over the 0.03–50 Knudsen number range, and an overall agreement appears through the comparison. It was also found, when the Knudsen number increased, that the wall influence on measurement occurred first through the accommodation process in the transition regime followed by the wall influence through the aspect ratio in the free molecular regime

International audienceThe main objective of this experimental investigation on the gas flow slip regime is to measure the mass flow rate in isothermal steady flows through cylindrical micro tubes. Two technical procedures devoted to mass flow rate measurements are compared, and the measured values are also compared with the results yielded by different approximated analytical solutions of the gas dynamics continuum equations. Satisfactory results are obtained and the way is clearly opened to measuring mass flow rates for higher Knudsen numbers, over all the micro flow transitional regime

The density-matrix renormalization group method has become a standard computational approach to the low-energy physics as well as dynamics of low-dimensional quantum systems. In this paper, we present a new set of applications, available as part of the ALPS package, that provide an efficient and flexible implementation of these methods based on a matrix product state (MPS) representation. Our applications implement, within the same framework, algorithms to variationally find the ground state and low-lying excited states as well as simulate the time evolution of arbitrary one-dimensional and two-dimensional models. Implementing the conservation of quantum numbers for generic Abelian symmetries, we achieve performance competitive with the best codes in the community. Example results are provided for (i) a model of itinerant fermions in one dimension and (ii) a model of quantum magnetism

International audienceAn experimental investigation of the reflection/accommodation process at the wall in a single silica microtube and isothermal stationary flow conditions was carried out. Several gases and different diameters were studied through various regimes. Especially for helium, the Knudsen number range was investigated as far as the free molecular regime. This kind of investigation requires a powerful experimental platform to measure mass flow rates, which we have carried out. An analytic expression of the mass flow rate, based on the Navier–Stokes equations with second order boundary condition, was used to yield the tangential momentum accommodation coefficient TMAC in the 0.003–0.3 Knudsen number range. Otherwise, the experimental results of the mass flow rate were compared with theoretical values calculated from kinetic approaches using variable TMAC as parameter over the 0.3–30 Knudsen number range, and an overall agreement appears through the comparison. Finally, whatever the theoretical approach the TMAC obtained from gas nitrogen, xenon, argon, and helium-surface fused silica pairs is similar and lower than unity. A tendency of the TMAC values seems to appear according to the molecular mass of the gases. In addition for each gas, the second order slip coefficient magnitude seems to decrease when the tube diameter increases

International audienceExperimental investigations of isothermal steady flows for various gases have been carried out in a silica micro tube. This study is focused on the mass flow rate measurements of these flows in slip regime using a suitable powerful platform. First we analyse, for each gas, the pertinence of a first or second order continuum treatment ; then we deduce from experiments, using the appropriate treatment, the tangential momentum accommodation coefficient (TMAC) of each gas. The TMAC obtained for the various pairs of gas (nitrogen, argon, helium)/surface (fused silica) exclude a full diffuse reflection

An experimental investigation in a single silica microtube in isothermal stationary flow for various gases is made from the hydrodynamic to the near free molecular regime to study the reflection/accommodation process at the wall. This kind of investigation requires, more than other Micro-Electro-Mechanical-Systems (MEMS) experiments, a powerful experimental platform to measure very small mass flow rate. A global analytic expression, based on the Navier-Stokes (NS) equations with second order boundary conditions, is used to yield the Tangential Momentum Accommodation Coefficient (TMAC) in 0.003–0.3 Knudsen number range. Otherwise, the experimental results of the mass flow rate is compared with theoretical values calculated from kinetic approaches using variable TMAC as fitting parameter over the 0.3–30 Knudsen number range. Finally, whatever the theoretical approach the TMAC values obtained from the different gas-surface pairs are rather close one to other, but the TMAC values seem decreasing when the molecular mass increases.

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