Proving More Observational Equivalences with ProVerif

This paper presents an extension of the automatic protocol verifier ProVerif in order to prove more observational equivalences. ProVerif can prove observational equivalence between processes that have the same structure but differ by the messages they contain. In order to extend the class of equivalences that ProVerif handles, we extend the language of terms by defining more functions (destructors) by rewrite rules. In particular, we allow rewrite rules with inequalities as side-conditions, so that we can express tests ''if then else'' inside terms. Finally, we provide an automatic procedure that translates a process into an equivalent process that performs as many actions as possible in- side terms, to allow ProVerif to prove the desired equivalence. These extensions have been implemented in ProVerif and allow us to au- tomatically prove anonymity in the private authentication protocol by Abadi and Fournet

Public expenditure and consumption volatility

Recent estimates of the welfare cost of consumption volatility find that it is significant in developing nations, where it may reach an equivalent of reducing consumption by 10 percent per year. Hence, examining the determinants of consumption volatility is of utmost relevance. Based on cross-country data for the period 1960-2005, the paper explains consumption volatility using three sets of variables: one refers to the volatility of income and the persistence of income shocks; the second set of variables refers to policy volatility, considering the volatility of public spending and the size of government; while the third set captures the ability of agents to smooth shocks, and includes the depth of the domestic financial markets as well as the degree of integration to international capital markets. To allow for potential endogenous regressors, in particular the volatility of fiscal policy and the size of government, the system is estimated using the instrumental variables method. The results indicate that, besides income volatility, the variables with the largest and most robust impact on consumption volatility are government size and the volatility of public spending. Results also show that deeper and more stable domestic financial markets reduce the volatility of consumption, and that more integrated financial markets to the international capital markets are associated with lower volatility of consumption.Economic Conditions and Volatility,Emerging Markets,Economic Stabilization,Economic Theory&Research,Currencies and Exchange Rates

On the second cohomology of K\"ahler groups

Carlson and Toledo conjectured that any infinite fundamental group $\Gamma$ of a compact K\"ahler manifold satisfies $H^2(\Gamma,\R)\not =0$. We assume that $\Gamma$ admits an unbounded reductive rigid linear representation. This representation necessarily comes from a complex variation of Hodge structure (\C-VHS) on the K\"ahler manifold. We prove the conjecture under some assumption on the \C-VHS. We also study some related geometric/topological properties of period domains associated to such \C-VHS.Comment: 21 pages. Exposition improved. Final versio

Optical gratings induced by field-free alignment of molecules

We analyze the alignment of molecules generated by a pair of crossed ultra-short pump pulses of different polarizations by a technique based on the induced time-dependent gratings. Parallel polarizations yield an intensity grating, while perpendicular polarizations induce a polarization grating. We show that both configurations can be interpreted at moderate intensity as an alignment induced by a single polarized pump pulse. The advantage of the perpendicular polarizations is to give a signal of alignment that is free from the plasma contribution. Experiments on femtosecond transient gratings with aligned molecules were performed in CO2 at room temperature in a static cell and at 30 K in a molecular expansion jet.Comment: 10 pages, 5 figures, submitted to PR

Les espaces périurbains non bâtis en France : entre publicisation "urbaine" et privatisation "rurale" ?

International audienceCet article propose d'appréhender les sociabilités en construction au sein des Espaces Périurbains Non Bâtis (EPNB) à partir d'une grille d'interprétation problématisée en termes de processus croisés de publicisation et de privatisation. Après avoir posé les enjeux actuels de ces EPNB, morphologiquement ruraux mais soumis à l'influence urbaine, les auteurs explicitent les rouages de ces deux mouvements antagonistes qui renforcent l'incertitude du jeu social et conduisent les acteurs ordinaires à inventer leurs propres règles de coexistence. Or, en accentuant le rôle des accommodements quotidiens, cette tension interroge également le caractère opératoire du clivage rural-urbain. Alors que, depuis quelques années, des approches théoriques prônent l'émergence de nouvelles catégories de connaissance pour penser le périurbain, cet article invite à considérer que les relations sociales à l'œuvre dans les EPNB demeurent encore de l'ordre d'une hybridation entre rural et urbain. Cette perspective ouvre des pistes pour envisager les modalités concrètes d'une régulation publique de ces espaces en France

Sida et développement : un enjeu mondial

L’article propose une revue des débats économiques que suscite la pandémie de SIDA en Afrique, notamment les débats portant sur l’accès restreint aux thérapeutiques brevetées et sur le droit international en matière de propriété intellectuelle (OMC, accords TRIPs). Après une rapide description de la maladie, de son épidémiologie, et des traitements existants, il énonce les différentes formes d’impact de la maladie sur l’économie et examine les études macroéconomiques disponibles pour les pays africains. La méconnaissance des aspects différés du choc, sur l’accumulation de capital et sur l’éducation, peut avoir conduit les études à sous-estimer l’effet de la maladie sur les mécanismes de développement de ces pays très pauvres. Ce constat, la gravité de la maladie, ainsi que l’observation des formes concrètes de l’échange international, plaident pour une intervention publique mondiale à deux niveaux : d’une part une réévaluation critique de la législation sur la protection des droits de propriété intellectuelle, mise en place sous l’égide de l’Organisation mondiale du commerce ; d’autre part la constitution d’un « fonds global » de connaissances et de moyens financiers, dans lequel les pays pauvres pourraient trouver les traductions concrètes des solidarités et d’une véritable gouvernance mondiales