Heteropolymers in a Solvent at an Interface

Exact bounds are obtained for the quenched free energy of a polymer with random hydrophobicities in the presence of an interface separating a polar from a non polar solvent. The polymer may be ideal or have steric self-interactions. The bounds allow to prove that a ``neutral'' random polymer is localized near the interface at any temperature, whereas a ``non-neutral'' chain is shown to undergo a delocalization transition at a finite temperature. These results are valid for a quite general a priori probability distribution for both independent and correlated hydrophobic charges. As a particular case we consider random AB-copolymers and confirm recent numerical studies.Comment: 4 pages, no figure

Higgs Couplings in Composite Models

We study Higgs couplings in the composite Higgs model based on the coset SO(5)/SO(4). We show that the couplings to gluons and photons are insensitive to the elementary-composite mixings and thus not affected by light fermionic resonances. Moreover, at leading order in the mixings the Higgs couplings to tops and gluons, when normalized to the Standard Model (SM), are equal. These properties are shown to be direct consequences of the Goldstone symmetry and of the assumption of partial compositeness. In particular, they are independent of the details of the elementary-composite couplings and, under the further assumption of CP invariance, they are also insensitive to derivative interactions of the Higgs with the composite resonances. We support our conclusions with an explicit construction where the SM fermions are embedded in the 14 dimensional representation of SO(5).Comment: 13 pages, 3 figures, 2 tables; v2: small improvements in the discussion, results unchanged; typos corrected; one reference added. Matches version submitted to PR

Holomorphic Parafermions in the Potts model and SLE

We analyse parafermionic operators in the Q-state Potts model from three different perspectives. First, we explicitly construct lattice holomorphic observables in the Fortuin-Kasteleyn representation, and point out some special simplifying features of the particular case Q=2 (Ising model). In particular, away from criticality, we find a lattice generalisation of the massive Majorana fermion equation. We also compare the parafermionic scaling dimensions with known results from CFT and Coulomb gas methods in the continuum. Finally, we show that expectation values of these parafermions correspond to local observables of the SLE process which is conjectured to describe the scaling limit of the Q-state Potts model.Comment: 18 pages. v2: references to related work clarified. v3: minor corrections, version accepted for publication in JSTA

Le mouvement associatif islamique en Ile-de-France

Associative islamic movement in Ile-de-France - The growth of religious organisations has become a new issue as far as migrants' groupings are concerned in France. The former defined themselves as the bulk identity makers of the muslim migrant populations, and thus try and set the line, by using various types of policy, either in the cultural field or in the political, say, symbolic ones, when negociating with the authorities at every rung of the ladder. By acting in such a way, are they building barriers between the muslim migrant populations and the native population, or rather, are they are trying to find ways and means in order to make the muslims cope with the guest society ? The paper deals with different aspects of muslim organisations: history and reasons of creation of the organisations; structuring of belongings; ways of communicating culture, language, religion; discourse on islam and its perception: relationships at local and national level.L'émergence de regroupements investissant dans le champ du sacré constitue une nouvelle donne dans l'espace associatif immigré. Ceux-ci se définissent comme sites des ressources identitaires, et, dans leur transaction avec les instances de la société d'accueil, élaborent et mettent en chantier de nouveaux schèmes d'expression culturelle, politique, symbolique. Les dirigeants de ces associations, en s'arrogeant le rôle d'« entrepreneurs identitaires », amorcent-ils une politique de marginalisation voire de repli des populations musulmanes, ou favorisent-ils un modèle d'intégration sociale ? L'article, après avoir retracé la genèse et les raisons de création de ces associations, analyse la structuration des appartenances, s'interroge sur les stratégies amorcées en vue de la transmission de la culture, langue et religion, et, d'autre part, rend compte des différents types de discours et des rapports entretenus au niveau local et national

Magnetic field dependence of the energy of negatively charged excitons in semiconductor quantum wells

A variational calculation of the spin-singlet and spin-triplet state of a negatively charged exciton (trion) confined to a single quantum well and in the presence of a perpendicular magnetic field is presented. We calculated the probability density and the pair correlation function of the singlet and triplet trion states. The dependence of the energy levels and of the binding energy on the well width and on the magnetic field strength was investigated. We compared our results with the available experimental data on GaAs/AlGaAs quantum wells and find that in the low magnetic field region (B<18 T) the observed transition are those of the singlet and the dark triplet trion (with angular momentum $L_z=-1$), while for high magnetic fields (B>25 T) the dark trion becomes optically inactive and possibly a transition to a bright triplet trion (angular momentum $L_z=0$) state is observed.Comment: 9 pages, 10 figures submitted to Phys. Rev.

MHC class II protein turnover in vivo and its relevance for autoimmunity in non-obese diabetic mice

Major histocompatibility complex class II (MHCII) proteins are loaded with endosomal peptides and reside at the surface of antigen-presenting cells (APCs) for a time before being degraded. In vitro, MHCII protein levels and turnover are affected by peptide loading and by rates of ubiquitin-dependent internalization from the cell surface, which is in turn affected by APC type and activation state. Prior work suggested that fast turnover of disease-associated MHCII alleles may contribute to autoimmunity. We recently developed novel stable isotope tracer techniques to test this hypothesis in vivo. In non-obese diabetic (NOD) mice, a model of type 1 diabetes (T1D), MHCII turnover was affected by APC type, but unaffected by disease-associated structural polymorphism. Differences in MHCII turnover were observed between NOD colonies with high and low T1D incidence, but fast turnover was dispensable for autoimmunity. Moreover, NOD mice with gene knockouts of peptide loading cofactors do not develop T1D. Thus, fast turnover does not appear pathogenic, and conventional antigen presentation is critical for autoimmunity in NOD mice. However, shared environmental factors may underpin colony differences in MHCII protein turnover, immune regulation, and pathogenesis