Monodisperse Dry Granular Flows on Inclined Planes : Role of Roughness

Recent studies have pointed out the importance of the basal friction on the dynamics of granular flows. We present experimental results on the influence of the roughness of the inclined plane on the dynamics of a monodisperse dry granular flow. We found experimentally that it exists a maximum of the friction for a given relative roughness. This maximum is shown to be independent of the angle of the slope. This behavior is observed for four planes with different bump sizes (given by the size of the beads glued on the plane) from 200 microns to 2 mm. The relative roughness corresponding to the maximum of the friction can be predicted with a geometrical model of stability of one single bead on the plane. The main parameters are the size of the bumps and the size of the flowing beads. In order to obtain a higher precision, the model also takes into account of the spacing between the bumps of the rough plane. Experimental results and model are in good agreement for all the planes we studied. Other parameters, like the sphericity of the beads, or irregularities in the thickness of the layer of glued particles, are shown to be of influence on the friction.Comment: 17 pages, 15 figures, submitted to EPJ

Jeux d'enseignement/apprentissage sur un lieu de médiation scientifique. Une étude de cas sur les sables mouvants

International audienceOur work concerns the intervention of professional scientists for general public. We study the case of a physician researcher in granular maters meeting a family group, visiting a popular scientific event (called « Fête de la science »). The scientific theme which is tackled is quick sands, with an analogue model and an explanatory poster. The study aims, in a didactic perspective, to describe the action of the scientist involved and the knowledge in question. We refer to the frames of the Joint Action Theory in Didac-tics, and of resources systems of teachers. The central data we analyze are videos shot during the scientific event. We describe firstly the situation in everyday language. Then in a second step we introduce theoretical language to enrich the analysis. Results show that beyond material artifacts, resources like the researcher’s body and non scientific references (movies) exist. The body is also a semiotic tool for orchestrating the resources system. Free-choice learning of family members is illustrated by different behaviors, because of personal interests or understanding of the situation.Le travail présenté ici concerne l'intervention de scientifiques auprès du grand public. Nous étudions le cas de la rencontre d'une physicienne spécialiste des mi-lieux granulaires avec un groupe familial lors d'un atelier à la Fête de la science. Le thème abordé est celui des sables mouvants, à l'aide d'un modèle analogique de sable mouvant et d'un poster explicatif. Nous interrogeons, dans une perspective didactique, l'action de la scientifique engagée dans l'animation du stand et les savoirs en jeu, en nous appuyant sur la théorie de l'action conjointe en didactique ainsi que sur les systèmes de ressources. Notre analyse se base sur des films d'étude réalisés sur les lieux de l'action pendant la rencontre. Elle est développée en deux temps : une première description « en langage commun », une seconde dans le langage de nos cadres théoriques. Nos résultats font apparaître, au-delà des artefacts matériels du stand, des ressources telles que le corps de la physicienne et des réfé-rences non scientifiques (cinéma). Le corps est aussi un des instruments sémiotiques au service de l'orchestration du système de ressources. Le libre choix du public est illustré par des comportements différents des membres de la famille, liés à leur intérêt et à leur com-préhension de la situation. Mots-clés : théorie de l'action conjointe en didactique (TACD), ressource, événe-ment scientifique, sables mouvants, sciences, libre choix, sémiose, proxémique

The Transactions Demand For Money In The Presence Of Currency Substitution: Evidence From Vietnam

Currency substitution – the use of foreign money to finance transactions between domestic residents – is widespread in low income and transition economies. Traditionally, however, empirical models of the demand for money tend to concentrate on the portfolio, motive for holding foreign currency, while maintaining the assumption that the income elasticity of demand for domestic money is invariant to the degree of currency substitution.. We offer a simple re-specification of the demand for money which more accurately reflects the process of currency substitution by allowing for a variable income elasticity of demand for domestic money. This specification is estimated for Vietnam in the 1990s. Using a standard cointegration framework we find evidence for currency substitution only in the long-run but well-defined wealth effects operating in the short-run.

The Arab Spring: The Role of Quality Education and the Consequences of its Lack

The lack of quality education plays a major role in explaining the Arab Spring: As a result of past shortfalls in education, large shares of the working-age population in the Arab-Spring countries do not have the right qualifications for entering the labour market. This not only leads to high levels of unemployment but also entails poverty and social distress. At the macro level, it triggers a vicious cycle of underdevelopment by hampering an upgrade to economies driven by knowledge and innovation despite the substantial numbers of higher educated citizens of working age in these countries. This holds particularly true for Egypt. Remedying the current lack of quality education should be a top priority in the countries of North Africa, because it is the source of many deficiencies plaguing this region. In the Arab-Spring countries, the European Union's sectoral aid given for education has focused on quantity (e.g. raising enrolment by supporting the implementation of the Millennium Development Goals for Education) rather than on quality, where interventions usually target higher education (mostly through individual sponsorship programmes), although there are challenges at all levels, starting with basic education. The European Union's main priority should be to guide and assist these countries in developing training programmes for teachers as the driving force behind the entire system reform

Currency substitution and the transactions demand for money in Vietnam

We estimate the demand for money in Vietnam during the 1990s within a framework which distinguishes between currency substitution and portfolio dimensions of dollarization. This leads to a representation for the demand function in which the long-run income elasticity of demand is no longer constant but is a function of the expected rate of depreciation. We find evidence for currency substitution only in the long-run, and for portfolio effects only in the short-run. We interpret this as being consistent with the existence of costs associated with changing the transactions technology.Vietnam., Demand for Money, Currency Substitution, Dollarization

Is progress in education sustainable?

Projections of educational attainment are complementary to projections of enrolment. They give somehow the translation of projections of enrolment rates into educational levels of attainment. Population projections by level of education allow us to have a precise knowledge not only about the combined momentum of population growth and education spread but also on the actual number of in-school or potentially in-school population by levels of education and this according to some interesting scenarios. This paper shows an application of educational attainment projections at the level of thirteen world regions. It shows the challenges that will face governments and international organizations because of increasing school-age population and increases in enrollment rates. On the contrary, for those regions that are already very advanced in the demographic transition and education levels, the task of maintaining enrolment rates ore even increasing them will not be so daunting