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

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.

L'utilisation de variables explicatives estimées dans les régressions économétriques

Cette note a pour objet de rappeler certains résultats de la littérature sur les problèmes posés par l'introduction dans une régression économétrique de variables explicatives qui ont été précédemment estimées à partir d'une équation auxiliaire en première étape. Les indicateurs de politique économique « révélée » par les résultats, telles qu'elles ont été initiées au CERDI il y a déjà un certain nombre d'années font en effet partie de cette classe de variables et ont éventuellement pour finalité d'être utilisés comme variables explicatives dans des régressions économétriques. Cette note présente les principaux résultats de l'article de Pagan (1984) qui est l'article de référence en la matière et des illustrations à partir d'articles utilisant ces résultats

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

The end of secularization in Europe? A socio-demographic perspective

Much of the current debate over secularization in Europe focuses only on the direction of religious change, and pays exclusive attention to social causes. Scholars have been less attentive to shifts in the rate of religious decline, and to the role of demography – notably fertility and immigration. This article addresses both phenomena. It uses data from the European Values Surveys and European Social Survey for the period 1981-2008 to establish basic trends in religious attendance and belief across the ten countries that have been consistently surveyed. These show that religious decline is mainly occurring in Catholic European countries and has effectively ceased among post-1945 birth cohorts in six northwestern European societies where secularization began early. It also provides a cohort component projection of religious affiliation for two European countries using fertility, migration, switching and age and sex-structure parameters derived from census and immigration data. These suggest that western Europe may be more religious at the end of our century than at its beginning