Exactly solvable models of adaptive networks

A satisfiability (SAT-UNSAT) transition takes place for many optimization problems when the number of constraints, graphically represented by links between variables nodes, is brought above some threshold. If the network of constraints is allowed to adapt by redistributing its links, the SAT-UNSAT transition may be delayed and preceded by an intermediate phase where the structure self-organizes to satisfy the constraints. We present an analytic approach, based on the recently introduced cavity method for large deviations, which exactly describes the two phase transitions delimiting this adaptive intermediate phase. We give explicit results for random bond models subject to the connectivity or rigidity percolation transitions, and compare them with numerical simulations.Comment: 4 pages, 4 figure

Політична освіта як складова політичної соціалізації молоді

Політична освіта та виховання молоді є основою підвищення її політичної активності. Для досягнення відповідного рівня цієї активності необхідне світосприйняття, сформоване згідно з принципами демократії, національної ідеї, а також особиста зацікавленість молодої людини в прогресивному розвитку суспільства, її участь в суспільно політичній діяльності

De la frise magdalénienne in situ … au centre d’interprétation du Roc-aux-Sorciers : l’usage de la 3D

La base de données 3D réalisée dans le cadre de la recherche archéologique sur les sculptures pariétales magdaléniennes (il y a 15 000 ans) a pu être exploitée également pour une reproduction grandeur nature des œuvres à destination du grand public dans le Centre d’interprétation du Roc-aux-Sorciers à Angles-sur-l’Anglin (Vienne, France). Cette réalisation originale est présentée par les différents acteurs du projet (maître d’ouvrage, maître d’œuvre, scientifiques, prestataire 3D) offrant ainsi le déroulé de la mise en œuvre de la restitution à partir de la base de données 3D et faisant part des éléments du cahier des charges pour l’enregistrement laser tridimensionnel dont l’exploitation s’est avérée répondre à des utilités variées. Quand les problématiques de la recherche conduisent à utiliser la 3D, il paraît logique que ce même outil puisse aider à la restitution au grand public et puisse être partagé avec la communauté scientifique ou avec les restaurateurs chargés de la conservation de ce patrimoine, comme le montre cette réalisation. Les implications du choix d'un mode de restitution à partir d’une base de données 3D sont également évoquées avec l'exemple de la frise sculptée magdalénienne de la Chaire-à-Calvin (Charente, France) dans le cadre d’un projet de valorisation.The creation of a 3D database within the framework of archaeological research on Magdalenian parietal sculptures (15,000 years old) has also been usable for a full-size reproduction of the figures for the benefit of the general public in the Interpretation Centre of Le Roc-aux-Sorciers at Angles-sur-l'Anglin (Vienne, France). This unique production is presented by the various participants in the project (contracting authority, prime contractor, scientists, 3D provider), thus providing the whole story of the reconstruction's implementation from the 3D database, and providing information on the specifications for 3-dimensional laser recording, the use of which proved to be useful in a variety of ways. When research problems lead one to find solutions through utilisation of 3D. it appears logical that this same tool might help in reconstructions for the general public, and may be shared with the scientific community or with restorers in charge of the conservation of this heritage; that is what this production demonstrates. The implications of the choice of a reconstruction method from a 3D database are also evoked through the example of the Magdalenian sculpted frieze of La Chaire-à-Calvin (Charente, France) within the framework of a valorisation project

The cavity method for large deviations

A method is introduced for studying large deviations in the context of statistical physics of disordered systems. The approach, based on an extension of the cavity method to atypical realizations of the quenched disorder, allows us to compute exponentially small probabilities (rate functions) over different classes of random graphs. It is illustrated with two combinatorial optimization problems, the vertex-cover and coloring problems, for which the presence of replica symmetry breaking phases is taken into account. Applications include the analysis of models on adaptive graph structures.Comment: 18 pages, 7 figure

Plasmacytoid Dendritic Cell Infection and Sensing Capacity during Pathogenic and Nonpathogenic Simian Immunodeficiency Virus Infection.

International audienceHuman immunodeficiency virus (HIV) in humans and simian immunodeficiency virus (SIV) in macaques (MAC) lead to chronic inflammation and AIDS. Natural hosts, such as African green monkeys (AGM) and sooty mangabeys (SM), are protected against SIV-induced chronic inflammation and AIDS. Here, we report that AGM plasmacytoid dendritic cells (pDC) express extremely low levels of CD4, unlike MAC and human pDC. Despite this, AGM pDC efficiently sensed SIVagm, but not heterologous HIV/SIV isolates, indicating a virus-host adaptation. Moreover, both AGM and SM pDC were found to be, in contrast to MAC pDC, predominantly negative for CCR5. Despite such limited CD4 and CCR5 expression, lymphoid tissue pDC were infected to a degree similar to that seen with CD4(+) T cells in both MAC and AGM. Altogether, our finding of efficient pDC infection by SIV in vivo identifies pDC as a potential viral reservoir in lymphoid tissues. We discovered low expression of CD4 on AGM pDC, which did not preclude efficient sensing of host-adapted viruses. Therefore, pDC infection and efficient sensing are not prerequisites for chronic inflammation. The high level of pDC infection by SIVagm suggests that if CCR5 paucity on immune cells is important for nonpathogenesis of natural hosts, it is possibly not due to its role as a coreceptor. The ability of certain key immune cell subsets to resist infection might contribute to the asymptomatic nature of simian immunodeficiency virus (SIV) infection in its natural hosts, such as African green monkeys (AGM) and sooty mangabeys (SM). This relative resistance to infection has been correlated with reduced expression of CD4 and/or CCR5. We show that plasmacytoid dendritic cells (pDC) of natural hosts display reduced CD4 and/or CCR5 expression, unlike macaque pDC. Surprisingly, this did not protect AGM pDC, as infection levels were similar to those found in MAC pDC. Furthermore, we show that AGM pDC did not consistently produce type I interferon (IFN-I) upon heterologous SIVmac/HIV type 1 (HIV-1) encounter, while they sensed autologous SIVagm isolates. Pseudotyping SIVmac/HIV-1 overcame this deficiency, suggesting that reduced uptake of heterologous viral strains underlays this lack of sensing. The distinct IFN-I responses depending on host species and HIV/SIV isolates reveal the host/virus species specificity of pDC sensing

Dendritic Cells from HIV Controllers Have Low Susceptibility to HIV-1 Infection In Vitro but High Capacity to Capture HIV-1 Particles

ANRS CO21 CODEX cohortInternational audienceHIV controllers (HICs), rare HIV-1 infected individuals able to control viral replication without antiretroviral therapy, are characterized by an efficient polyfunctional and cytolytic HIV-specific CD8+ T cell response. The mechanisms underlying the induction and maintenance of such response in many HICs despite controlled viremia are not clear. Dendritic cells play a crucial role in the generation and reactivation of T cell responses but scarce information is available on those cells in HICs. We found that monocyte derived dendritic cells (MDDCs) from HICs are less permissive to HIV-1 infection than cells from healthy donors. In contrast MDDCs from HICs are particularly efficient at capturing HIV-1 particles when compared to cells from healthy donors or HIV-1 patients with suppressed viral load on antiretroviral treatment. MDDCs from HICs expressed on their surface high levels of syndecan-3, DC-SIGN and MMR, which could cooperate to facilitate HIV-1 capture. The combination of low susceptibility to HIV-1 infection but enhanced capacity to capture particles might allow MDDCs from HICs to preserve their function from the deleterious effect of infection while facilitating induction of HIV-specific CD8+ T cells by cross-presentation in a context of low viremia

Genome-Scale Analysis of Mycoplasma agalactiae Loci Involved in Interaction with Host Cells

Mycoplasma agalactiae is an important pathogen of small ruminants, in which it causes contagious agalactia. It belongs to a large group of “minimal bacteria” with a small genome and reduced metabolic capacities that are dependent on their host for nutrients. Mycoplasma survival thus relies on intimate contact with host cells, but little is known about the factors involved in these interactions or in the more general infectious process. To address this issue, an assay based on goat epithelial and fibroblastic cells was used to screen a M. agalactiae knockout mutant library. Mutants with reduced growth capacities in cell culture were selected and 62 genomic loci were identified as contributing to this phenotype. As expected for minimal bacteria, “transport and metabolism” was the functional category most commonly implicated in this phenotype, but 50% of the selected mutants were disrupted in coding sequences (CDSs) with unknown functions, with surface lipoproteins being most commonly represented in this category. Since mycoplasmas lack a cell wall, lipoproteins are likely to be important in interactions with the host. A few intergenic regions were also identified that may act as regulatory sequences under co-culture conditions. Interestingly, some mutants mapped to gene clusters that are highly conserved across mycoplasma species but located in different positions. One of these clusters was found in a transcriptionally active region of the M. agalactiae chromosome, downstream of a cryptic promoter. A possible scenario for the evolution of these loci is discussed. Finally, several CDSs identified here are conserved in other important pathogenic mycoplasmas, and some were involved in horizontal gene transfer with phylogenetically distant species. These results provide a basis for further deciphering functions mediating mycoplasma-host interactions