Local transient rheological behavior of concentrated suspensions

This paper reports experiments on the shear transient response of concentrated non-Brownian suspensions. The shear viscosity of the suspensions is measured using a wide-gap Couette rheometer equipped with a Particle Image Velocimetry (PIV) device that allows measuring the velocity field. The suspensions made of PMMA particles (31$\mu$m in diameter) suspended in a Newtonian index- and density-matched liquid are transparent enough to allow an accurate measurement of the local velocity for particle concentrations as high as 50%. In the wide-gap Couette cell, the shear induced particle migration is evidenced by the measurement of the time evolution of the flow profile. A peculiar radial zone in the gap is identified where the viscosity remains constant. At this special location, the local particle volume fraction is taken to be the mean particle concentration. The local shear transient response of the suspensions when the shear flow is reversed is measured at this point where the particle volume fraction is well defined. The local rheological measurements presented here confirm the macroscopic measurements of Gadala-Maria and Acrivos (1980). After shear reversal, the viscosity undergoes a step-like reduction, decreases slower and passes through a minimum before increasing again to reach a plateau. Upon varying the particle concentration, we have been able to show that the minimum and the plateau viscosities do not obey the same scaling law with respect to the particle volume fraction. These experimental results are consistent with the scaling predicted by Mills and Snabre (2009) and with the results of numerical simulation performed on random suspensions [Sierou and Brady (2001)]. The minimum seems to be associated with the viscosity of an isotropic suspension, or at least of a suspension whose particles do not interact through non-hydrodynamic forces, while the plateau value would correspond to the viscosity of a suspension structured by the shear where the non-hydrodynamic forces play a crucial role

BaBar simulation production - A millennium of work in under a year

The BaBar experiment requires simulated events beyond the ability of a single computing site to provide. This paper describes the evolution of simulation and job management methods to meet the physics community requirements and how production became distributed to use resources beyond any one computing center. The evolution of BaBar simulation along with the development of the distribution of the computing effort is described. As the computing effort is distributed to more sites there is a need to simplify production so the effort does not multiply with number of production centers. Tools are created to be flexible in handling errors and failures that happen in the system and respond accordingly, this reduces failure rates and production effort. This paper will focus on one cycle of simulation production within BaBar as a description of a large scale computing effort which was fully performed, and provided new simulation data to the users on time

De l'heuristique au thaumaturgique en traitement des données d'écologie marine

In an answer to FRONTIER (1975)à the authors try to define their philosophy about data processing by mathematical methods in marine ecology. They point out that the ecologist may not expect miracles from these methods, but that, correctly used, they provide an especially heuristic tool if not a thaumaturgic one. They first discuss the exact suggest the main features of what should be any correct strategg in data processing, and try to give FRONTIER an answer on certain precise topics. [NOT CONTROLLED OCR]Dans cet article les auteurs définissent leur philosophie quant au traitement mathématique des données en écologie marine. Le texte est articulé en deux grandes parties qui débattent successivement de l'apport potentiel des méthodes mathématiques en écologie marine et de la stratégie d'utilisation de ces techniques. Dans la premeière partie, ils insistent sur la nécessité de ne pas considérer ces méthodes comme miraculeuses (thaumaturgiques), créatrices d'une information absente des données récoltées, mais comme des outils forts utiles (heuristiques) permettant, par une utilisation correcte, une description et une structuration de l'information recueillie. Elles permettent ainsi à l'écologiste de formuler d'une manière explicite et rigoureuse d'une part ses choix fondamentaux comme ses hypothèses, d'autre part ses conclusions. Dans ce chapitre, ils insistent sur deux points essentiels : - les problèmes de reconnaissance de structures sur un ensemble de points qui peuvent être par exemple des prélèvements, n'ont de sens que pour une topologie donnée ; - la possibilité de progresser dans la compréhension d'un pénomène écologique passe par le choix d'un modèle (être mathématique que l'on substitue à la réalité parce que plus maniable), qui peut être simplement descriptif ou explicatif selon les ambitions de départ. [OCR NON CONTRÔLE

Testing comparative spatial planning studies in the Latin American context: theoretical implications and challenges for regional development

Until recently, comparative spatial planning research had mostly focused on the European continent. Since the end of the 1980s, a growing number of studies contributed to the proliferation of theoretical and methodological approaches, as well as to a further definition of the object of study. Comparisons focusing on other parts of the World are much less frequent, if one excludes the rather ‘dry’ reports produced by international organizations. Aiming at investigating the reasons behind this empirical gap, the paper inquires the theoretical implications and challenges that emerge when applying to the global South conceptual and analytical frameworks developed in the Northern hemisphere. In so doing, it first raises awareness on the role played by the colonial legacy to then argue for the need to ‘go beyond technical efficiency’ and to consider dominant power relations hidden by the apparent neutrality of spatial governance and planning systems, particularly in relation to contexts where spatial inequalities are more pronounced. In this light, it suggests to consider informal practices alongside formal ones, as a way forward to better understand the drivers structuring spatial governance and planning systems in the Global South. Overall, to test comparative spatial governance and planning studies to the Latin American context could provide an added value for the development of the region, by setting up a regional agenda for more integrated and cooperative spatial planning in Latin America