Kinetic Monte Carlo Modelling to Study Diffusion in Zeolite. Understanding the Impact of Dual Site Isotherm on the Loading Dependence of n-Hexane and n-Heptane Diffusivities in MFI Zeolite, as Revealed by QENS Experiments

ENERGIE:MATERIAUX+HJO:NLAInternational audienceThis study concerns the diffusion of single-component molecules in zeolites, characterised by an isotherm represented by a dual-site Langmuir model with a point of inflection. The systems investigated are n-hexane and n-heptane in MFI zeolite at 300 K. Experiments conducted using the Quasi-Elastic Neutron Scattering (QENS) technique have demonstrated that this inflection has an impact on the loading dependence of the transport Dt and corrected DC diffusion coefficients of these systems. The results of these experiments are described here. A Kinetic Monte Carlo study is then conducted, showing how the energy levels of the molecule adsorption sites in a zeolite affect the loading dependence of the diffusion coefficients of these molecules

Flexible-Link Robot Control Using a Linear Parameter Varying Systems Methodology

This paper addresses the issues of the Linear Parameter Varying (LPV) modelling and control of flexible-link robot manipulators. The LPV formalism allows the synthesis of nonlinear control laws and the assessment of their closed-loop stability and performances in a simple and effective manner, based on the use of Linear Matrix Inequalities (LMI). Following the quasi-LPV modelling approach, an LPV model of a flexible manipulator is obtained, starting from the nonlinear dynamic model stemming from Euler-Lagrange equations. Based on this LPV model, which has a rational dependence in terms of the varying parameters, two different methods for the synthesis of LPV controllers are explored. They guarantee the asymptotic stability and some level of closed-loop ℒ 2 -gain performance on a bounded parametric set. The first method exploits a descriptor representation that simplifies the rational dependence of the LPV model, whereas the second one manages the troublesome rational dependence by using dilated LMI conditions and taking the particular structure of the model into account. The resulting controllers involve the measured state variables only, namely the joint positions and velocities. Simulation results are presented that illustrate the validity of the proposed control methodology. Comparisons with an inversion-based nonlinear control method are performed in the presence of velocity measurement noise, model uncertainties and high-frequency inputs

Power law velocity fluctuations due to inelastic collisions in numerically simulated vibrated bed of powder}

Distribution functions of relative velocities among particles in a vibrated bed of powder are studied both numerically and theoretically. In the solid phase where granular particles remain near their local stable states, the probability distribution is Gaussian. On the other hand, in the fluidized phase, where the particles can exchange their positions, the distribution clearly deviates from Gaussian. This is interpreted with two analogies; aggregation processes and soft-to-hard turbulence transition in thermal convection. The non-Gaussian distribution is well-approximated by the t-distribution which is derived theoretically by considering the effect of clustering by inelastic collisions in the former analogy.Comment: 7 pages, using REVTEX (Figures are inculded in text body) %%%Replacement due to rivision (Europhys. Lett., in press)%%

Presa de Grandval

This important project is situated on the top section of the river Truyere, within the region of the French Central Massif. The dam has been constructed by the Electricité de France. The total hydroelectric development project in this zone involves six dams and six power stations, to exploit an overall hydrostatic head of 520 ms. The water accumulated by these dams has a maximum volume of 540.106 cubic metres, and will produce a yearly output of 1450 .106 kWh. The Grandval dam rests on strong microschistous rock folds. Its length is 330 ms, and its maximum height 88 ms, measured from the foundation base. Structurally it is formed by a series of vaults supported by abutments, which are spaced at 50 ms intervals. The mean thickness of the vaults at the base is 4.90 ms, and 1.50 at the crown. The vertical slope on the upstream side is 0.70. A feature of this design is that the vaults are not uniformly cylindrical up to the top, as is customary. The top part of the dam consists, in fact, of a small gravity dam, resting on the underlying vaulted structure. The dam is straight at the top, and a road runs along it, on an overhanging structure. The dam has a surface spillway, which is ski jump shaped, and runs over the two abutments on either side of the power station.Esta importante obra se halla situada en el tramo superior del río Truyère, en la región del Macizo Central francés. Las presas se han realizado por cuenta de Electricité de France. El conjunto del aprovechamiento hidroeléctrico tiene seis presas y otras tantas centrales que aprovechan un salto total de 530 m de altura, y las aguas almacenadas en un embalse cuya capacidad total se eleva a 540x106m3 que proporcionarán una producción anual de 1.450x106 kWh. La presa se apoya sobre un banco microesquistoso, que en algunas partes presenta grandes pliegues de gran potencia. El dique de cierre tiene una longitud total de 330 m y 88 m de altura máxima, a partir de la base de cimientos. Su estructura está constituida por una serie de bóvedas que se apoyan en contrafuertes. La luz entre éstos es de 50 metros

Campylobacter in the Pork Food Chain : a quantitative hazard analysis

Campylobacter are one of the most frequent causes of bacterial enteritis in industrialized countries and are widespread in food animals. Pigs are known to be largely contaminated in farms, but few data exist about the status of the pork food chain. The purpose of this study was to quantify the Campylobacter contamination of the French pork food chain: prevalence, contamination level, bactenal species in primary production (piglets and fattening pigs when slaughtered), and in first and second transformation process (from carcasses before chilling to deboned meat cuts)

Heap Formation in Granular Media

Using molecular dynamics (MD) simulations, we find the formation of heaps in a system of granular particles contained in a box with oscillating bottom and fixed sidewalls. The simulation includes the effect of static friction, which is found to be crucial in maintaining a stable heap. We also find another mechanism for heap formation in systems under constant vertical shear. In both systems, heaps are formed due to a net downward shear by the sidewalls. We discuss the origin of net downward shear for the vibration induced heap.Comment: 11 pages, 4 figures available upon request, Plain TeX, HLRZ-101/9

Oxide phosphors for light upconversion; Yb3+ and Tm3+ co-doped Y2BaZnO5

Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. This article appeared in Journal of Applied Physics 109, 063104 (2011) and may be found at

Effect of rising atmospheric carbon dioxide on the marine nitrogen fixer Trichodesmium

Diazotrophic (N2-fixing) cyanobacteria provide the biological source of new nitrogen for large parts of the ocean. However, little is known about their sensitivity to global change. Here we show that the single most important nitrogen fixer in today's ocean, Trichodesmium, is strongly affected by changes in CO2 concentrations. Cell division rate doubled with rising CO2 (glacial to projected year 2100 levels) prompting lower carbon, nitrogen and phosphorus cellular contents, and reduced cell dimensions. N2 fixation rates per unit of phosphorus utilization as well as C:P and N:P ratios more than doubled at high CO2, with no change in C:N ratios. This could enhance the productivity of N-limited oligotrophic oceans, drive some of these areas into P limitation, and increase biological carbon sequestration in the ocean. The observed CO2 sensitivity of Trichodesmium could thereby provide a strong negative feedback to atmospheric CO2 increase

Observation of Sommerfeld precursors on a fluid surface

We report the observation of two types of Sommerfeld precursors (or forerunners) on the surface of a layer of mercury. When the fluid depth increases, we observe a transition between these two precursor surface waves in good agreement with the predictions of asymptotic analysis. At depths thin enough compared to the capillary length, high frequency precursors propagate ahead of the ''main signal'' and their period and amplitude, measured at a fixed point, increase in time. For larger depths, low frequency ''precursors'' follow the main signal with decreasing period and amplitude. These behaviors are understood in the framework of the analysis first introduced for linear transient electromagnetic waves in a dielectric medium by Sommerfeld and Brillouin [1].Comment: to be published in Physical Review Letter