Dense granular flows: two-particle argument accounts for friction-like constitutive law with threshold

A scalar constitutive law is obtained for dense granular flows, both in the inertial regime where the grain inertia dominates, and in the viscous regime. Considering a pair of grains rather than a single grain, the classical arguments yield a constitutive law that exhibits a flow threshold expressed as a finite effective friction at flow onset. The value of the threshold is not predicted. The resulting law seems to be compatible with existing data, provided the saturation at high velocity (collisional regime) is added empirically. The law is not exactly the same in both regimes, which seems to indicate that there is no "universal" law.Comment: 4 page

Note and calculations concerning elastic dilatancy in 2D glass-glass liquid foams

When deformed, liquid foams tend to raise their liquid contents like immersed granular materials, a phenomenon called dilatancy. We have aready described a geometrical interpretation of elastic dilatancy in 3D foams and in very dry foams squeezed between two solid plates (2D GG foams). Here, we complement this work in the regime of less dry 2D GG foams. In particular, we highlight the relatively strong dilatancy effects expected in the regime where we have predicted rapid Plateau border variations.Comment: 12 pages, 3 tables, 5 figure

Upscaling multi-component two-phase flow in porous media with partitioning coefficient

This paper deals with the upscaling of multicomponents two-phase flow in porous media. In this paper, chemical potential equilibrium at the interface between both phases is assumed to be described by a linear partitioning relationship such as Raoult or Henry’s law. The resulting macro-scale dispersion model is a set of two equations related by a mass transfer coefficient and which involves several effective coefficients. These coefficients can be evaluated by solving closure problems over a representative unit-cell. The proposed model is successfully validated through direct analytical and numerical calculations

Cable-Driven Robots with Wireless Control Capability for Pedagogical Illustration in Science

Science teaching in secondary schools is often abstract for students. Even if some experiments can be conducted in classrooms, mainly for chemistry or some physics fields, mathematics is not an experimental science. Teachers have to convince students that theorems have practical implications. We present teachers an original and easy-to-use pedagogical tool: a cable-driven robot with a Web-based remote control interface. The robot implements several scientific concepts such as 3D-geometry and kinematics. The remote control enables the teacher to move freely in the classroom.Comment: CAR - 8th National Conference on "Control Architecure of Robots" (2013

Patterns and determinants of urban chicken consumption in Haiti and Cameroon: similar contexts, differentiated prospects

Since the beginning of 2000s, in order to let poor people accede to meat consumption, several African and Caribbean countries have opened their domestic chicken market to foreign imports, by reducing import tariffs. Thus imported frozen pieces of chicken from the European Union or America compete with local chicken meat, causing the collapse of many poultry husbandry and the loss of many jobs in the local chicken food chain. In order to highlight the determinants of urban consumer’s choice relative to chicken types, and assess the opportunity for local chicken to restore its market share, investigations have been done in 2005 in Yaoundé (Cameroon) and in 2006 in Port-au-Prince (Haiti) applied to 180 urban households in each country. While imported frozen pieces of chicken have almost entirely substituted for the local chicken which has already quite disappeared in Port-au-Prince, Yaoundé consumers still prefer the local flesh chicken to the imported ones, at least for particular uses.chicken, urban consumption, developing countries, globalization, Cameroon, Haiti