Slow flows of yield stress fluids: complex spatio-temporal behaviour within a simple elasto-plastic model

A minimal athermal model for the flow of dense disordered materials is proposed, based on two generic ingredients: local plastic events occuring above a microscopic yield stress, and the non-local elastic release of the stress these events induce in the material. A complex spatio-temporal rheological behaviour results, with features in line with recent experimental observations. At low shear rates, macroscopic flow actually originates from collective correlated bursts of plastic events, taking place in dynamically generated fragile zones. The related correlation length diverges algebraically at small shear rates. In confined geometries bursts occur preferentially close to the walls yielding an intermittent form of flow localization.Comment: 4 pages, 4 figure

Thermo-poro-mechanical coupled processes during thermal pressurization around nuclear waste repository

This paper investigates the thermo-hydro-mechanical behavior of Callovo- Oxfordian claystone, a potential host formation for prospective nuclear waste disposal in France. Thermal pore pressure appears in low permeability soils and rocks due to the difference between the thermal expansion coefficients of water and the argillaceous skeleton, as well as the low permeability of the media and the its relative rigidity, which prevent dissipation of the fluid pressure. Coupled thermo-hydro-mechanical numerical analyses have been carried out to enhance the understanding of the Callovo-Oxfordian claystone behavior subjected to heat emitted from radioactive waste that diffuses through the near-field rock to the far-field. In this view, the “thermal pressurization coefficient”, defined as the increase of pore pressure due to 1°C increase of temperature, was calculated. This coefficient depends on the nature of the rock, i.e the thermo-poro-mechanical parameters such permeability, Biot’s coefficient, rigidity, thermal conductivity as well as their anisotropies. Finally, the effect of parameters’ variability on the thermal pressurization coefficient is discussed through a sensibility analysis

Micro-evaporators for kinetic exploration of phase diagrams

We use pervaporation-based microfluidic devices to concentrate species in aqueous solutions with spatial and temporal control of the process. Using experiments and modelling, we quantitatively describe the advection-diffusion behavior of the concentration field of various solutions (electrolytes, colloids, etc) and demonstrate the potential of these devices as universal tools for the kinetic exploration of the phases and textures that form upon concentration

Suelos volcanicos endurecidos

Scanning electron microscope (SEM) studies of calcareous encrusting in volcanic ash soils containing active and petrified roots of pine trees revealed that the calcified material is related to the fine root mat of the pine rhizosphere and particulary to a dense network of very thin biologic filaments of about 0,1um in diameter to 0,5um. The diversity in morphology of the calcitic accretions from fibers to rods with epitaxial growth of an hedral crystals, results from different stages in the calcification. In the first stage, freshly calcified filaments are semi-rigid and coated with gel-like products composed mainly of Ca, Al and Si. In the most advanced stages, secondary anhedral calcite crystals a few microns in size develop on the biologic structures and form an open network with the accumulated debris of calcified filaments. Amorphous silica, as a cementing agent, contributes to the hardening of this porous calcitic fabric. The most advanced stages of calcification are observed in soils below 30 to 50 years old pine trees, whereas 15 years old pine plantations display only filamentous and needly-fiber calcifications. (Résumé d'auteur)

The Consequences of Child Market Work on the Growth of Human Capital

Child labor is a phenomenon that has attracted a great amount of attention and research. theoretical propositions suggest that child labor is inefficient if it adversely affects future potential earning ability. this paper contributes to the literature on the effects of child market work on human capital by focusing on the long-term growth in human capital, which is widely known to significantly affect earning ability. the paper also uses better measures of human capital by focusing on the output of the human capital production function: numeracy skills, cognitive skills, and pulmonary function. using a rich longitudinal dataset on Indonesia, we find strong negative effects of child labor on the growth of both numeracy and cognitive skills in the next seven years. in addition, we find a strong and negative effect on pulmonary function as measured through lung capacity. comparing the effects by gender and type of work, we find that female child workers suffer from more adverse effects on their mathematical skills growth, while male child workers experience a much smaller growth in their pulmonary function. we also find that child workers who work for a wage outside the family bear worse effects compared to child workers who work in the family business. keywords: child labor, human capital, skills, health, Indonesia jel classifications: i12, i21, j13, j22, o1

Classical Loop Actions of Gauge Theories

Since the first attempts to quantize Gauge Theories and Gravity in the loop representation, the problem of the determination of the corresponding classical actions has been raised. Here we propose a general procedure to determine these actions and we explicitly apply it in the case of electromagnetism. Going to the lattice we show that the electromagnetic action in terms of loops is equivalent to the Wilson action, allowing to do Montecarlo calculations in a gauge invariant way. In the continuum these actions need to be regularized and they are the natural candidates to describe the theory in a ``confining phase''.Comment: LaTeX 14 page