Enquêter dans les graphes

International audienceLes jeux combinatoires à deux joueurs impliquant des agents mobiles dans les graphes (e.g., jeu des gendarmes et du voleur, jeu du dominant éternel, etc.) ont été beaucoup étudiés car ils permettent, d'une part, de comprendre comment coordonner des individus afin de réaliser une tâche commune, et d'autre part d'étudier les propriétés structurelles des graphes. Outre la définition et l'étude d'un nouveau de ces jeux, une contribution importante de cet article est de montrer que la programmation linéaire permet de nouveaux progrès dans l'étude de ce type de jeux. Nous définissons le jeu dans lequel un premier agent, le Suspect, se déplace dans un graphe à vitesse s ≥ 2 à la recherche d'une position à distance au moins d + 1 de tous les autres agents, les Détectives, qui veulent le surveiller (i.e. s'assurer qu'il y ait toujours au moins un détective à distance au plus d du suspect). Etant donné un graphe G, le nombre minimum de détectives nécessaires pour satisfaire cet objectif est noté $gn_{s,d}(G)$. Le problème est de calculer $gn_{s,d}(G)$ ainsi qu'une stratégie correspondante pour les détectives. Ce jeu à deux joueurs (suspect et détectives) ressemble aux jeux de gendarmes et voleur et généralise celui du Dominan éternel. Nous étudions la complexité du calcul de $gn_{s,d}(G)$ et présentons des stratégies gagnantes pour les détectives dans diverses classes de graphes. Certaines de nos preuves sont combinatoires, tandis que d'autres sont basées sur l'utilisation de la Programmation Linéaire dont nous espérons démontrer ainsi l'intérêt dans l'analyse de ce type de jeux

Membranes by the Numbers

Many of the most important processes in cells take place on and across membranes. With the rise of an impressive array of powerful quantitative methods for characterizing these membranes, it is an opportune time to reflect on the structure and function of membranes from the point of view of biological numeracy. To that end, in this article, I review the quantitative parameters that characterize the mechanical, electrical and transport properties of membranes and carry out a number of corresponding order of magnitude estimates that help us understand the values of those parameters.Comment: 27 pages, 12 figure

Antrum Approach Planning for Removal of Impacted Tooth Using Cone-Beam Computed Tomography

Due to the great number of structures in the maxillofacial region, cone-beam computed tomography (CBCT) is an important procedure in presurgical planning for removal of impacted teeth. Most of the information provided by this imaging technique cannot be visualized in conventional radiographs. In addition, CBCT reduces patient exposure to radiation in comparison with helical computed tomography and provides dental practitioners with easy access. We report the clinical case of a patient who underwent a surgical procedure for removal of an impacted maxillary premolar. CBCT-assisted presurgical treatment was used, enabling a more conservative surgical access, a less traumatic and less time consuming procedure than conventional surgical intervention

A Deviation from the Bipolar-Tetrapolar Mating Paradigm in an Early Diverged Basidiomycete

In fungi, sexual identity is determined by specialized genomic regions called MAT loci which are the equivalent to sex chromosomes in some animals and plants. Usually, only two sexes or mating types exist, which are determined by two alternate sets of genes (or alleles) at the MAT locus (bipolar system). However, in the phylum Basidiomycota, a unique tetrapolar system emerged in which four different mating types are generated per meiosis. This occurs because two functionally distinct molecular recognition systems, each encoded by one MAT region, constrain the selection of sexual partners. Heterozygosity at both MAT regions is a pre-requisite for mating in both bipolar and tetrapolar basidiomycetes. Tetrapolar mating behaviour results from the absence of genetic linkage between the two regions bringing forth up to thousands of mating types. The subphylum Pucciniomycotina, an early diverged lineage of basidiomycetes encompassing important plant pathogens such as the rusts and saprobes like Rhodosporidium and Sporidiobolus, has been so far poorly explored concerning the content and organization of MAT loci. Here we show that the red yeast Sporidiobolus salmonicolor has a mating system unlike any previously described because occasional disruptions of the genetic cohesion of the bipolar MAT locus originate new mating types. We confirmed that mating is normally bipolar and that heterozygosity at both MAT regions is required for mating. However, a laboratory cross showed that meiotic recombination may occur within the bipolar MAT locus, explaining tetrapolar features like increased allele number and evolution rates of some MAT genes. This pseudo-bipolar system deviates from the classical bipolar–tetrapolar paradigm and, to our knowledge, has never been observed before. We propose a model for MAT evolution in the Basidiomycota in which the pseudo-bipolar system may represent a hitherto unforeseen gradual form of transition from an ancestral tetrapolar system to bipolarity

Impact of PGL-I Seropositivity on the Protective Effect of BCG Vaccination among Leprosy Contacts: A Cohort Study

Although leprosy has become a neglected disease, it is an important cause of disability, and 250,000 new cases are still diagnosed worldwide every year. The current study was carried out in Brazil, where almost 40,000 new cases of leprosy are diagnosed every year. The study targeted contacts of leprosy patients, who are at the highest risk of contracting the disease. We studied 2,135 contacts who were diagnosed at the Leprosy Outpatient Clinic at the Oswaldo Cruz Foundation in Rio de Janeiro, RJ, Brazil, between 1987 and 2007. The presence of antibodies against a specific Mycobacterium leprae antigen (PGL-I) at the first examination and BCG vaccination status were evaluated. PGL-I-positive contacts had a higher risk of developing leprosy than PGL-I-negative contacts. Among the former, vaccinated contacts were at higher risk than unvaccinated contacts. Our results indicate that contact examination combined with PGL-I testing and BCG vaccination appears to justify the targeting of PGL-I-positive individuals for enhanced surveillance. Furthermore, it is highly recommended that PGL-I-positive contacts and contacts with a high familial bacterial index (i.e., the sum of results from index and co-prevalent cases), regardless of serological response, should be monitored. This group could be considered as a target for chemoprophylaxis