Towards a consistent picture for quasi-1D organic superconductors

The electrical resistivity of the quasi-1D organic superconductor (TMTSF)2PF6 was recently measured at low temperature from the critical pressure needed to suppress the spin-density-wave state up to a pressure where superconductivity has almost disappeared. This data revealed a direct correlation between the onset of superconductivity at Tc and the strength of a non-Fermi-liquid linear term in the normal-state resistivity, going as r(T) = r0 + AT + BT2 at low temperature, so that A goes to 0 as Tc goes to 0. Here we show that the contribution of low-frequency antiferromagnetic fluctuations to the spin-lattice relaxation rate is also correlated with this non-Fermi-liquid term AT in the resistivity. These correlations suggest that anomalous scattering and pairing have a common origin, both rooted in the low-frequency antiferromagnetic fluctuations measured by NMR. A similar situation may also prevail in the recently-discovered iron-pnictide superconductors.Comment: ISCOM'09 proceedings to be published in Physica

Rapid magnetic oscillations and magnetic breakdown in quasi-1D conductors

We review the physics of magnetic quantum oscillations in quasi-one dimensional conductors with an open Fermi surface, in the presence of modulated order. We emphasize the difference between situations where a modulation couples states on the same side of the Fermi surface and a modulation couples states on opposite sides of the Fermi surface. We also consider cases where several modulations coexist, which may lead to a complex reorganization of the Fermi surface. The interplay between nesting effects and magnetic breakdown is discussed. The experimental situation is reviewed.Comment: 10 pages, 8 figures, Contribution to the memorial issue in honor of J. Friedel, C. R. Acad. Sci. Pari

The Hilbert scheme of points and its link with border basis

In this paper, we give new explicit representations of the Hilbert scheme of $\mu$ points in \PP^{r} as a projective subvariety of a Grassmanniann variety. This new explicit description of the Hilbert scheme is simpler than the previous ones and global. It involves equations of degree $2$. We show how these equations are deduced from the commutation relations characterizing border bases. Next, we consider infinitesimal perturbations of an input system of equations on this Hilbert scheme and describe its tangent space. We propose an effective criterion to test if it is a flat deformation, that is if the perturbed system remains on the Hilbert scheme of the initial equations. This criterion involves in particular formal reduction with respect to border bases

The Subsidiarity Bias in Regulation

We study the choice of the regulatory structure when a regulated firm engages in different activities for different countries. Under decentralization each activity is regulated independently and the contracts offered to the firm suffer from two oppos- ite distortions with respect to centralization: the competition between regulatory authorities forces them to offer too high-powered incentive contracts; however, be- cause the ownership structure of the firm is dispersed across the countries, each regulator does not fully internalize the effect of his regulation on the firm's rent and contracts tend to be too low-powered. When the activities of the firm are suf- ficiently substitutable we show that decentralization always leads to an inefficient drift of the regulatory contracts towards fixed-price contracts. Nonetheless, when regulators have private agendas and possess the discretion to distort their policy to gain the support of some interest groups, then decentralization of the regulat- ory powers may be preferred to centralization as competition between regulatory authorities eradicates their discretionary power.incentives, decentralization, regulation.

Rheological and restoring force models regarding belt tensioner dymamic behavior: prediction and experiment

The objective of this paper is to compare the Masing and modified Dahl model efficiency regarding the prediction of the hysteretic behavior of a belt tensioner used for automotive engines. A first experimental study with deflection imposed on the tensioner is carried out to identify hysteresis loop parameters for the two models. The models are then implemented in the general motion equations modeling the behavior of a belt - tensioner - mass system. The comparison beteen numerical and experimental results show that these two models perform satisfactorily and that the modified Dahl model is a little more efficient

An analysis of the modified Dahl and Masing models: application to a belt tensioner

The objective of this paper is to describe the modified Dahl and Masing models used for predicting hysteretic behavior, and tested on a belt tensioner for automotive engines. An experimental study with deflection imposed on the tensioner is first carried out to identify hysteresis loop parameters for the two models. The models are implemented in the general motion equations which govern the behavior of a belt–tensioner–mass system. Particular attention is paid to the use of numerical schemes. The numerical and experimental investigations show the reliability of the modified Dahl model

Model Consistency for Learning with Mirror-Stratifiable Regularizers

Low-complexity non-smooth convex regularizers are routinely used to impose some structure (such as sparsity or low-rank) on the coefficients for linear predictors in supervised learning. Model consistency consists then in selecting the correct structure (for instance support or rank) by regularized empirical risk minimization. It is known that model consistency holds under appropriate non-degeneracy conditions. However such conditions typically fail for highly correlated designs and it is observed that regularization methods tend to select larger models. In this work, we provide the theoretical underpinning of this behavior using the notion of mirror-stratifiable regularizers. This class of regularizers encompasses the most well-known in the literature, including the $\ell_1$ or trace norms. It brings into play a pair of primal-dual models, which in turn allows one to locate the structure of the solution using a specific dual certificate. We also show how this analysis is applicable to optimal solutions of the learning problem, and also to the iterates computed by a certain class of stochastic proximal-gradient algorithms.Comment: 14 pages, 4 figure

Modèle par éléments discrets pour l’étude du comportement dynamique d’un matériau élastique.

Le comportement mécanique des matériaux est généralement simulé par des approches issues de la mécanique des milieux continus. Cependant, lorsqu’il s’agit de simuler des phénomènes de multi fissurations voir de multi fracturations, les modèles de la mécanique discrète s’avèrent mieux adaptés, car ils prennent en compte naturellement les discontinuités générées par les interfaces. La difficulté est alors de s’assurer qu’une approche par éléments discrets (DEM) permet bien de retrouver le comportement mécanique au sens de la mécanique des milieux continus. Cet article propose une méthodologie permettant, à partir des données connues du matériau à simuler (module de Young, coefficient de Poisson, célérité de propagation des ondes), de quantifier les paramètres « microscopiques » du modèle DEM

Optimisation of solvent replacement procedures according to economic and environmental criteria in pharmaceutical industry

During pharmaceutical syntheses, the reaction solvent has often to be switched off from one reaction step to the following one. Because of the standard industrial practices, solvent replacement generally constitutes a slow and high solvent-consuming operation. In this paper, a specific methodology, based on a batch processes optimisation framework, is proposed for the optimisation of solvent replacement procedures. Optimisation may be performed at different levels according to economic and environmental criteria and satisfying safety and waste treatment constraints. In fact, the proposed methodology allows both to design new procedures of solvent replacement and to improve existing industrial processes. Two industrial applications are detailed to emphasize the benefits related to this methodology. In each case, the proposed methodology leads to the suitable recipe from comparison of traditional and empirical replacement procedures generally used in the pharmaceutical industry