Una nueva especulación alimentaria : «Posición ante las manifestaciones populares de los días 1 y 2 de septiembre de 2010», UNAC, Maputo, 8 Septiembre 2010

Incluye la nota "Trigo, agronegocio, exportación y especulación internacional", de GRAIN.Durante la edición de este número han llegado las primeras informaciones de una preocupante subida en el precio del trigo y otros cereales. Para ofrecer una explicación más certera reproducimos, por un lado, un extracto del análisis que la organización campesina UNAC de Mozambique hace de la situación, y por otro una explicación sobre el papel que el capital financiero y las grandes corporaciones han jugado en Rusia

Resuspension due to vertical oscillations: experiments and numerical modeling

International audienc

Development of Monte Carlo simulations to predict particle resuspension kinetics during airflow acceleration in a wind tunnel

International audienc

Evidence of inter-particles collision effect in airflow resuspension of poly-dispersed tungsten particles in monolayer deposits

International audiencePoly-dispersed particle resuspension by turbulent airflow was experimentally studied in a wind tunnel called BISE. The set-up was carefully validated to produce reference airflows with three absolute pressures and friction velocities values. Monolayer deposits of poly-dispersed tungsten particles on tungsten surfaces were used for the experiments. The fraction of detached particles by size bin from 1 µm to 50 µm was quantified to analyze the effects of friction velocity, absolute pressure and particles concentration on surface. Comparison of the results with Rock’n Roll and Monte-Carlo resuspension modelling revealed discrepancies for particles behavior with diameter below 4.5 µm. These discrepancies could not be understood by assessment of particle-surface adhesion force distribution carried out with Atomic Force Microscopy analysis. For particle surface concentrations ranging from 35 to 100 mm-2, a collision effect was identified due to the concentration and poly-dispersion of particles deposited on the surface. Indeed, a good linear correlation is obtained between the fraction of the small particles detached and a collision parameter, demonstrating that collisions could be responsible for the unexpectedly high resuspended fraction observed for particle size below 4.5 µm in diameter. The experimental data and the analysis presented in the paper show that particle surface concentration and collision effects are clearly relevant and should be considered in the above-mentioned resuspension models, especially for poly-dispersed particles assessment