Geometric mutual information at classical critical points

A practical use of the entanglement entropy in a 1d quantum system is to identify the conformal field theory describing its critical behavior. It is exactly $(c/3)\ln \ell$ for an interval of length $\ell$ in an infinite system, where $c$ is the central charge of the conformal field theory. Here we define the geometric mutual information, an analogous quantity for classical critical points. We compute this for 2d conformal field theories in an arbitrary geometry, and show in particular that for a rectangle cut into two rectangles, it is proportional to $c$. This makes it possible to extract $c$ in classical simulations, which we demonstrate for the critical Ising and 3-state Potts models.Comment: 5 pages. v3: published versio

Advanced Coordinated Beamforming for the Downlink of Future LTE Cellular Networks

Modern cellular networks in traditional frequency bands are notoriously interference-limited especially in urban areas, where base stations are deployed in close proximity to one another. The latest releases of Long Term Evolution (LTE) incorporate features for coordinating downlink transmissions as an efficient means of managing interference. Recent field trial results and theoretical studies of the performance of joint transmission (JT) coordinated multi-point (CoMP) schemes revealed, however, that their gains are not as high as initially expected, despite the large coordination overhead. These schemes are known to be very sensitive to defects in synchronization or information exchange between coordinating bases stations as well as uncoordinated interference. In this article, we review recent advanced coordinated beamforming (CB) schemes as alternatives, requiring less overhead than JT CoMP while achieving good performance in realistic conditions. By stipulating that, in certain LTE scenarios of increasing interest, uncoordinated interference constitutes a major factor in the performance of CoMP techniques at large, we hereby assess the resilience of the state-of-the-art CB to uncoordinated interference. We also describe how these techniques can leverage the latest specifications of current cellular networks, and how they may perform when we consider standardized feedback and coordination. This allows us to identify some key roadblocks and research directions to address as LTE evolves towards the future of mobile communications.Comment: 16 pages, 6 figures, accepted to IEEE Communications Magazin

Domestic competition and export performance of manufacturing firms in Côte d’Ivoire

Because of transportation costs, African manufacturing firms benefit from some market power on their domestic market, where they can charge a higher price than the export price, net of transportation cost. We present a simple theoretical model of an exporting firm that discriminates between the export and the domestic markets, where firms engage in Cournot competition. It is then shown that the impact of increased competition on export performance by the firms is ambiguous, and may be negative for a non trivial range of parameter values. Using survey data on Ivoirian firms, our empirical analysis gives some support to this prediction, showing that the probability of a firm exporting decreases with increased competition.

Approche par les principes, approche par les cas : les limites philosophiques d'une opposition

International audienceAnalyse de l'articulation entre cas et principe en éthique clinique, à partir du modèle élaboré par le Centre d'éthique clinique de l'hôpital Cochi

Guayaquil (1900-1940): agro-exportation et structuration de l'espace urbain

L'analyse des dynamiques urbaines de Guayaquil de 1900 à 1940 permet de mettre en valeur quatre structures élémentaires pour composer un modèle spécifique des structures spatiales du port principal de l'Équateur