Condensation and Metastability in the 2D Potts Model

For the first order transition of the Ising model below $T_c$, Isakov has proven that the free energy possesses an essential singularity in the applied field. Such a singularity in the control parameter, anticipated by condensation theory, is believed to be a generic feature of first order transitions, but too weak to be observable. We study these issues for the temperature driven transition of the $q$ states 2D Potts model at $q>q_c=4$. Adapting the droplet model to this case, we relate its parameters to the critical properties at $q_c$ and confront the free energy to the many informations brought by previous works. The essential singularity predicted at the transition temperature leads to observable effects in numerical data. On a finite lattice, a metastability domain of temperatures is identified, which shrinks to zero in the thermodynamical limit. ~Comment: 32 pages, 6 figures, Late

Self-Organized Criticality and Thermodynamic formalism

We introduce a dissipative version of the Zhang's model of Self-Organized Criticality, where a parameter allows to tune the local energy dissipation. We analyze the main dynamical features of the model and relate in particular the Lyapunov spectrum with the transport properties in the stationary regime. We develop a thermodynamic formalism where we define formal Gibbs measure, partition function and pressure characterizing the avalanche distributions. We discuss the infinite size limit in this setting. We show in particular that a Lee-Yang phenomenon occurs in this model, for the only conservative case. This suggests new connexions to classical critical phenomena.Comment: 35 pages, 15 Figures, submitte

Generalised Factorial Moments and QCD Jets

{ In this paper we present a natural and comprehensive generalisation of the standard factorial moments (\clFq) analysis of a multiplicity distribution. The Generalised Factorial Moments are defined for all $q$ in the complex plane and, as far as the negative part of its spectrum is concerned, could be useful for the study of infrared structure of the Strong Interactions Theory of high energy interactions (LEP multiplicity distribution under the ${\cal Z}_0$). The QCD calculation of the Generalised Factorial Moments for negative $q$ is performed in the double leading log accuracy and is compared to OPAL experimental data. The role played by the infrared cut-off of the model is discussed and illustrated with a Monte Carlo calculation. }Comment: 11pages 4 figures uuencode, LATEC, INLN 94/

Angular Intermittency in QCD Jets

URL: http://www-spht.cea.fr/articles/T93/011 http://fr.arxiv.org/abs/hep-ph/9302249International audienceUsing two methods, via fluctuations and correlations, an analytical formula is derived for the factorial multiplicity moments in a QCD jet at the Double Leading Logarithm accuracy. The resulting self-similar dependence on the solid-angle cell size is characteristic of an intermittency behaviour in angular variables. The intermittency indices depend on the diffusion angle through the running of $\alpha_ s.$ Physical features of jet fluctuations such as collimation at large angles and saturation at small angles are well described in the perturbative framework. A parameter-free prediction of angular intermittency is proposed for ${\cal Z}^0$ decays into hadrons, assuming hadron-parton duality.Dans cet article, les auteurs généralisent des résultats obtenus dans l'approximation planaire de QCD. A l'approximation du double logarithme dominant, ils montrent que les variables caractéristiques d'un comportement intermittent sont les variables angulaires des partons au lieu des rapidités dans le cas précédent. Cette analyse tient compte de la variation de la constante de couplage en QCD qui se manifeste par la saturation de l'effet pour les petits angles. Une prédiction est proposée pour les désintégrations de ${\cal Z}_0$ en hadrons en supposant la dualité hadron-partons

Stay or drift? Queen acceptance in the ant Formica paralugubris

Abstract.: The acceptance of new queens in ant colonies has profound effects on colony kin structure and inclusive fitness of workers. Therefore, it is important to study the recognition and discrimination behaviour of workers towards reproductive individuals entering established colonies. We examined the acceptance rate of queens in populations of the highly polygynous ant F. paralugubris, where the genetic differentiation among nests and discrimination ability among workers suggest that workers might reject foreign queens. We experimentally introduced young queens in their natal nest and in foreign nests. Surprisingly, the survival rate of mated queens did not differ significantly when introduced in a foreign male-producing nest, a foreign female-producing nest, or the natal nest. Moreover, the survival of virgin queens in their natal nest was twice the one of mated queens, suggesting that mating status plays an important role for acceptance. The results indicate that other factors than queen discrimination by workers are implicated in the limited longdistance gene flow between nests in these population

Cross-Over between universality classes in a magnetically disordered metallic wire

In this article we present numerical results of conduction in a disordered quasi-1D wire in the possible presence of magnetic impurities. Our analysis leads us to the study of universal properties in different conduction regimes such as the localized and metallic ones. In particular, we analyse the cross-over between universality classes occurring when the strength of magnetic disorder is increased. For this purpose, we use a numerical Landauer approach, and derive the scattering matrix of the wire from electron's Green's function.Comment: Final version, accepted for publication in New Journ. of Physics, 27 pages, 28 figures. Replaces the earlier shorter preprint arXiv:0910.427

Interpretation of Light-Quenching Factor Measurements

We observe that the pattern of the quenching factors for scintillation light from various ions, recently studied in $CaWO_4$ in connection with dark matter detectors, can be understood as a saturation phenomenon in which the light output is simply proportional to track length, independent of the ion and its energy. This observation is in accord with the high dE/dx limit of Birks' law. It suggests a simple model for the intrinsic resolution of light detectors for low energy ions, which we briefly discuss.Comment: Seven pages, seven figures, some with colo

The SPHERE data center: a reference for high contrast imaging processing

The objective of the SPHERE Data Center is to optimize the scientific return of SPHERE at the VLT, by providing optimized reduction procedures, services to users and publicly available reduced data. This paper describes our motivation, the implementation of the service (partners, infrastructure and developments), services, description of the on-line data, and future developments. The SPHERE Data Center is operational and has already provided reduced data with a good reactivity to many observers. The first public reduced data have been made available in 2017. The SPHERE Data Center is gathering a strong expertise on SPHERE data and is in a very good position to propose new reduced data in the future, as well as improved reduction procedures.Comment: SF2A proceeding