9,831 research outputs found
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 for an interval of length in an infinite system,
where 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 . This makes it possible to extract 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
Guayaquil (1900-1940): agro-exportation et structuration de l'espace urbain
L'analyse des dynamiques urbaines de Guayaquil de 1900 Ă 1940 permet de mettre en valeur quatre structures Ă©lĂ©mentaires pour composer un modĂšle spĂ©cifique des structures spatiales du port principal de l'Ăquateur
Propositions méthodologiques pour l'étude des feux agro-sylvo-pastoraux en montagne pyrénéenne. Evaluation qualitative et quantitative des résidus d'incendies à partir des analyses pédo-anthracologiques
International audienceNous proposons dans cet article une rĂ©flexion mĂ©thodologique autour de la reprĂ©sentativitĂ© qualitative et quantitative des charbons dans les sols provenant de pratiques pastorales et agricoles du feu dans les PyrĂ©nĂ©es. Nous exposons ici une mĂ©thode dâĂ©tude des charbons provenant des feux actuels et rĂ©cents dans le but dâĂ©tablir un rĂ©fĂ©rentiel permettant de clarifier la lecture des diagrammes anthracologiques. Aucun rĂ©sultat nâest prĂ©sentĂ© ici car les analyses sont en cours, mais notre dĂ©marche vise Ă montrer lâimportance de la connaissance des pratiques de feux pour mieux comprendre la reprĂ©sentation de leurs vestiges carbonĂ©s. Il est essentiel de partir de ce que lâon peut vĂ©rifier aujourdâhui afin dâinterprĂ©ter les donnĂ©es palĂ©o-environnementales. Chaque site dâĂ©tude, la forĂȘt dâAntenac (Luchon, Haute-Garonne) et le Pays de Sault (Aude, AriĂšge), ont Ă©tĂ© sĂ©lectionnĂ©s en fonction des frĂ©quences de feux connues pour le premier, et des travaux Ă©co-historiques fournissant des cartes dĂ©taillĂ©es sur les formations forestiĂšres, les landes et les dĂ©frichements depuis la RĂ©formation de 1669 jusquâĂ lâactuel, pour le second. Chaque site a Ă©tĂ© traitĂ© selon un protocole expĂ©rimental spĂ©cifique prĂ©sentĂ© dans cet article
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