Arbres minimaux d'un graphe preordonne

AbstractWe study the minimal spanning trees of a connected graph G = (X,U) where U is partially preordered (or quasi-ordered). We characterize several kinds of optimal spanning trees and give conditions for existence of strongly optimal trees. Generalizations to bases of matroids (binary matroïds in part 2) are immediate. Sone of our results are given in terms of Krugdahl's dependence graphs. They imply previous results of Rosenstiehl and Gale in the case of linear orders or preorders.RésuméOn étudie les arbres minimaux d'un graphe connexe G = (X,U), où U est partiellement préordonné. On caractérise diverses sortes d'arbes optimaux et on donne des conditions d'existence des arbres fortement optimaux. Des généralisations aux bases de matroides (matroides binaires dans la partie 2) sont immédiates. Certains de nos résultats utilisent les graphes de déviance de Krogdahl. Its impliquent des résultats de Rosenstiehl et de Gale dans les cas dependances et de préorders totaux

Un effet Gutman en ACP

The recourse to multidimensional methods in the data treatment allows for extracting structures of unidimensional data, when they exist, and one speaks then about Guttman effect. If the disclosure of such an effect is well-known in Correspondences Analysis, it can be also carried out in Principal Component Analysis, as presented here, while studying special properties of this effect (component of size, diagonal component, etc). The study of such a structure offers a very particular intelligibility to the results of research undertaken in the field of the social sciences, as connection with the social representation of homosexuality on the one hand and intelligence in its relationship with gender on the other hand.Le recours à des méthodes multidimension-nelles dans le traitement des données permet d’extraire des structures de données unidimen-sionnelles, lorsqu’elles existent, et l’on parle alors d’effet Guttman. Si la mise au jour d’un tel effet est bien connu en Analyse des Correspondances, elle peut également se réa-liser en Analyse en Composantes Principales, ce que nous exposons ici, en étudiant les propriétés particulières de cet effet (composante de taille, composante diagonale, etc.). L’étude d’une telle structure offre une intelligibilité toute particulière aux résultats des recherches conduites dans le domaine des sciences humaines, comme il en va dans les deux exemples présentés ici à propos des représentations sociales de l’homosexualité d’une part et de l’intelligence au masculin et au féminin d’autre part

Mid- and Far-Infrared Marker Bands of the Metal Coordination Sites of the Histidine Side Chains in the Protein Cu,Zn-Superoxide Dismutase

International audienceVibrational spectroscopy gives important information on the properties of ligand and metal–ligand bonds in metalloenzymes. Infrared spectroscopy is appealing for the study of metal active sites that are not amenable to Raman spectroscopy. We present a combined experimental and theoretical approach to analyze the mid- and far-IR spectra of Cu,Zn-superoxide dismutase (Cu,Zn-SOD) as a probe of the histidine ligands. This metalloenzyme provides a unique model to identify specific IR signatures of metal–histidine coordination and to study their alterations as a function of the metal (copper/zinc), the copper valence state (+I/+II), the histidine coordination mode (Nτ and Nπ) and the histidine protonation state. DFT calculations combined with normal mode descriptions from potential energy distribution calculations were performed on two slightly different cluster models. Differences in the constraints at the side chain of one histidine Cu ligand sensibly modify the geometric parameters and vibrational properties. Electrochemically induced FTIR difference spectroscopy provided mid- and far-IR fingerprint spectra of the Cu protein in aqueous media that are sensitive to the redox state of the Cu centre at the active site. Comparisons of the DFT predictions with the experimental IR modes of the histidine ligands at the Cu,Zn-SOD active site showed that useful mid-IR markers of histidine Nτ and Nπ coordination were predicted with good accuracy. The DFT analysis further demonstrated a link between the ν(C4–C5) mode frequency of His46 and the specific properties of the His46–Cu bond in Cu,Zn-SOD. A combined theoretical and experimental approach on samples in H2O and 2H2O or 15N-labelled samples identified the contributions from the histidine side chain modes in the 669–629 cm–1 region

CD4+CD25+ regulatory T cells inhibit natural killer cell functions in a transforming growth factor–β–dependent manner

Tumor growth promotes the expansion of CD4+CD25+ regulatory T (T reg) cells that counteract T cell–mediated immune responses. An inverse correlation between natural killer (NK) cell activation and T reg cell expansion in tumor-bearing patients, shown here, prompted us to address the role of T reg cells in controlling innate antitumor immunity. Our experiments indicate that human T reg cells expressed membrane-bound transforming growth factor (TGF)–β, which directly inhibited NK cell effector functions and down-regulated NKG2D receptors on the NK cell surface. Adoptive transfer of wild-type T reg cells but not TGF-β−/− T reg cells into nude mice suppressed NK cell–mediated cytotoxicity, reduced NKG2D receptor expression, and accelerated the growth of tumors that are normally controlled by NK cells. Conversely, the depletion of mouse T reg cells exacerbated NK cell proliferation and cytotoxicity in vivo. Human NK cell–mediated tumor recognition could also be restored by depletion of T reg cells from tumor-infiltrating lymphocytes. These findings support a role for T reg cells in blunting the NK cell arm of the innate immune system

L'étude mathématique des structures psycho-sociales

Flament Claude. L'étude mathématique des structures psycho-sociales. In: L'année psychologique. 1958 vol. 58, n°1. pp. 119-131

La performance des groupes de travail. Rapports entre la structure de l'activité et celle du réseau de communication

Flament Claude. La performance des groupes de travail. Rapports entre la structure de l'activité et celle du réseau de communication. In: L'année psychologique. 1958 vol. 58, n°1. pp. 71-89

Où en est notre Allocation d'études?

Flament Claude. Où en est notre Allocation d'études?. In: Bulletin du Groupe d'études de psychologie de l'Université de Paris, 4e année n°13, 1951. p. 798

Influence sociale et perception

Flament Claude. Influence sociale et perception. In: L'année psychologique. 1958 vol. 58, n°2. pp. 377-400