Ising nematic fluid phase of hard-core dimers on the square lattice

We present a model of classical hard-core dimers on the square lattice that contains an Ising nematic phase in its phase diagram. We consider a model with an attractive interaction for parallel dimers on a given plaquette of the square lattice and an attractive interaction for neighboring parallel dimers on the same row ({\it viz} column) of the lattice. By extensive Monte carlo simulations we find that with a finite density of holes the phase diagram has, with rising temperatures, a columnar crystalline phase, an Ising nematic liquid phase and a disordered fluid phase, separated by Ising continuous phase transitions. We present strong evidence for the Ising universality class of both transitions. The Ising nematic phase can be interpreted as either an intermediate classical thermodynamic phase (possibly of a strongly correlated antiferromagnet) or as a phase of a 2D quantum dimer model using the Rokhsar-Kivelson construction of exactly solvable quantum Hamiltonians.Comment: 13 pages, 24 figure

Dynamical and Steady State Properties of a Bose-Hubbard Chain with Bond-Dissipation: A Study based on Matrix Product Operators

We study a dissipative Bose-Hubbard chain subject to an engineered bath using a superoperator approach based on matrix product operators. The dissipation is engineered to stabilize a BEC condensate wave function in its steady state. We then characterize the steady state emerging from the interplay between incompatible Hamiltonian and dissipative dynamics. While it is expected that interactions lead to this competition, even the kinetic energy in an open boundary condition setup competes with the dissipation, leading to a non-trivial steady state. We also present results for the transient dynamics and probe the relaxation time revealing the closing of the dissipative gap in the thermodynamic limit.Comment: 9 pages, 13 figure

Quit Smoking and Run For Your Life!

To The Editor: The World Health Organization promotes the World No Tobacco Day on May 31

Les caféiers en Afrique : diversité génétique et amélioration des plantes

Des collectes de caféiers sauvages, dans la zone tropicale humide africaine, ont permis de constituer une collection vivante des différentes espèces de #Coffea. L'étude de leur diversité génétique a été entreprise en utilisant des descripteurs botaniques et enzymatiques, ainsi que des tests d'hybridation interspécifique. On constate que les espèces de caféiers sont inégalement réparties sur l'ensemble de l'aire de la forêt tropicale humide. A l'intérieur des espèces, une structure génétique peut être mise en évidence, différente d'une espèce à l'autre. En combinant ces résultats aux observations des hybridations interspécifiques, il est proposé une organisation du genre #Coffea en trois sections. D'une façon générale, une réflexion est menée sur la notion d'espèce et l'évolution de ces espèces, en liaison avec les modifications du paléoenvironnement. Les conséquences pratiques de ces études pour l'amélioration des caféiers sont les suivantes : 1. L'introgression des formes cultivées est tentée avec les espèces sauvages possédant des caractères particuliers d'intérêt agronomique ; 2. L'espèce #C. canephora$ est constituée de deux groupes et les hybrides F1 entre les deux groupes sont très productifs ; un schéma de Sélection Récurrente Réciproque avec création d'hybrides F1 est donc appliqué. (Résumé d'auteur

Questionnaire-based assessment of wild boar/domestic pig interactions and implications for disease risk management in Corsica

Wild boars and domestic pigs belong to the same species (Sus scrofa). When sympatric populations of wild boars, feral pigs, and domestic pigs share the same environment, interactions between domestic and wild suids (IDWS) are suspected to facilitate the spread and maintenance of several pig pathogens which can impact on public health and pig production. However, information on the nature and factors facilitating those IDWS are rarely described in the literature. In order to understand the occurrence, nature, and the factors facilitating IDWS, a total of 85 semi-structured interviews were implemented face to face among 25 strict farmers, 20 strict hunters, and 40 hunting farmers in the main traditional pig-farming regions of Corsica, where IDWS are suspected to be common and widespread. Different forms of IDWS were described: those linked with sexual attraction of wild boars by domestic sows (including sexual interactions and fights between wild and domestic boars) were most frequently reported (by 61 and 44% of the respondents, respectively) in the autumn months and early winter. Foraging around common food or water was equally frequent (reported by 60% of the respondents) but spread all along the year except in winter. Spatially, IDWS were more frequent in higher altitude pastures were pig herds remain unattended during summer and autumn months with limited human presence. Abandonment of carcasses and carcass offal in the forest were equally frequent and efficient form of IDWS reported by 70% of the respondents. Certain traditional practices already implemented by hunters and farmers had the potential to mitigate IDWS in the local context. This study provided quantitative evidence of the nature of different IDWS in the context of extensive commercial outdoor pig farming in Corsica and identified their spatial and temporal trends. The identification of those trends is useful to target suitable times and locations to develop further ecological investigations of IDWS at a finer scale in order to better understand diseases transmission patterns between populations and promote adapted management strategies

Development of a radio-detection method array for the observation of ultra-high energy neutrino induced showers

The recent demonstration by the CODALEMA Collaboration of the ability of the radio-detection technique for the characterization of UHE cosmic-rays calls for the use of this powerful method for the observation of UHE neutrinos. For this purpose, an adaptation of the existing 21CM Array (China) is presently under achievment. In an exceptionally low electromagnetic noise level, 10160 log-periodic 50-200 MHz antennas sit along two high valleys, surrounded by mountain chains. This lay-out results in 30-60 km effective rock thicnesses for neutrino interactions with low incidence trajectories along the direction of two 4-6 km baselines. We will present first in-situ radio measurements demonstrating that this environment shows particularly favourable conditions for the observation of electromagnetic decay signals of taus originating from the interaction of 10^17-20 eV tau neutrinos.Comment: 4pages, 3 figures, Contribution to appear in the proceedings of ARENA 2008 conferenc

Adding Virtualization Capabilities to Grid'5000

Ce rapport révisé a fait l'objet d'une publication, voir hal-00946971Almost ten years after its premises, the Grid'5000 testbed has become one of the most complete testbed for designing or evaluating large-scale distributed systems. Initially dedicated to the study of High Performance Computing, the infrastructure has evolved to address wider concerns related to Desktop Computing, the Internet of Services and more recently the Cloud Computing paradigm. This report present recent improvements of the Grid'5000 software and services stack to support large-scale experiments using virtualization technologies as building blocks. Such contributions include the deployment of customized software environments, the reservation of dedicated network domain and the possibility to isolate them from the others, and the automation of experiments with a REST API. We illustrate the interest of these contributions by describing three different use-cases of large-scale experiments on the Grid'5000 testbed. The first one leverages virtual machines to conduct larger experiments spread over 4000 peers. The second one describes the deployment of 10000 KVM instances over 4 Grid'5000 sites. Finally, the last use case introduces a one-click deployment tool to easily deploy major IaaS solutions. The conclusion highlights some important challenges of Grid'5000 related to the use of OpenFlow and to the management of applications dealing with tremendous amount of data.Dix ans environ après ses prémisses, la plate-forme Grid'5000 est devenue une des plates-formes les plus complètes utilisée pour la conception et l'évaluation de systèmes distribués à grande échelle. Dédiée initialement au calcul à haute performance, l'infrastructure a évolué pour supporter un ensemble de problèmes plus vaste liés au calcul de type Desktop, l'internet des objets et plus récemment l'informatique dans les nuages (aussi appelé Cloud Computing). Ce rapport présente les améliorations récentes apportées au logiciels et pile de services pour supporter les expérimentations à grande échelle utilisant les technologies de virtualisation comme blocs de base. Nos contributions incluent le déploiement d'environnements logiciels customisés, la réservation de domaines réseaux dédiés et la possibilité de les isoler entre eux, et l'automatisation des expérimentations grâce à une API REST. Nous illustrons l'intérêt de ces contributions en décrivant trois expériences à large échelle sur la plate-forme Grid'5000. La première expérience utilise des machines virtuelles pour conduire des expérimentations de grande taille sur 4000 pairs. La seconde expérience décrit le déploiement de 10000 instances KVM sur 4 sites Grid'5000. Enfin le dernier exemple présente un outil de déploiement simple pour déployer des solutions de Cloud de type IaaS. La conclusion discute de prochains défis importants de Grid'5000 liés à l'utilisation d'OpenFlow et à la gestion d'applications gérant des grandes masses de données

Adding Virtualization Capabilities to Grid'5000

Ce rapport révisé a fait l'objet d'une publication, voir hal-00946971Almost ten years after its premises, the Grid'5000 testbed has become one of the most complete testbed for designing or evaluating large-scale distributed systems. Initially dedicated to the study of High Performance Computing, the infrastructure has evolved to address wider concerns related to Desktop Computing, the Internet of Services and more recently the Cloud Computing paradigm. This report present recent improvements of the Grid'5000 software and services stack to support large-scale experiments using virtualization technologies as building blocks. Such contributions include the deployment of customized software environments, the reservation of dedicated network domain and the possibility to isolate them from the others, and the automation of experiments with a REST API. We illustrate the interest of these contributions by describing three different use-cases of large-scale experiments on the Grid'5000 testbed. The first one leverages virtual machines to conduct larger experiments spread over 4000 peers. The second one describes the deployment of 10000 KVM instances over 4 Grid'5000 sites. Finally, the last use case introduces a one-click deployment tool to easily deploy major IaaS solutions. The conclusion highlights some important challenges of Grid'5000 related to the use of OpenFlow and to the management of applications dealing with tremendous amount of data.Dix ans environ après ses prémisses, la plate-forme Grid'5000 est devenue une des plates-formes les plus complètes utilisée pour la conception et l'évaluation de systèmes distribués à grande échelle. Dédiée initialement au calcul à haute performance, l'infrastructure a évolué pour supporter un ensemble de problèmes plus vaste liés au calcul de type Desktop, l'internet des objets et plus récemment l'informatique dans les nuages (aussi appelé Cloud Computing). Ce rapport présente les améliorations récentes apportées au logiciels et pile de services pour supporter les expérimentations à grande échelle utilisant les technologies de virtualisation comme blocs de base. Nos contributions incluent le déploiement d'environnements logiciels customisés, la réservation de domaines réseaux dédiés et la possibilité de les isoler entre eux, et l'automatisation des expérimentations grâce à une API REST. Nous illustrons l'intérêt de ces contributions en décrivant trois expériences à large échelle sur la plate-forme Grid'5000. La première expérience utilise des machines virtuelles pour conduire des expérimentations de grande taille sur 4000 pairs. La seconde expérience décrit le déploiement de 10000 instances KVM sur 4 sites Grid'5000. Enfin le dernier exemple présente un outil de déploiement simple pour déployer des solutions de Cloud de type IaaS. La conclusion discute de prochains défis importants de Grid'5000 liés à l'utilisation d'OpenFlow et à la gestion d'applications gérant des grandes masses de données