Phase diagram for ensembles of random close packed Ising-like dipoles as a function of texturation

International audienceWe study random close packed systems of magnetic spheres by Monte Carlo simulations in order to estimate their phase diagram. The uniaxial anisotropy of the spheres makes each of them behave as a single Ising dipole along a fixed easy axis. We explore the phase diagram in terms of the temperature and the degree of alignment (or texturation) among the easy axes of all spheres. This degree of alignment ranges from the textured case (all easy axes pointing along a common direction) to the non-textured case (randomly distributed easy axes). In the former case we find long-range ferromagnetic order at low temperature but, as the degree of alignment is diminished below a certain threshold, the ferromagnetic phase gives way to a spin-glass phase. This spin-glass phase is similar to the one previously found in other dipolar systems with strong frozen disorder. The transition between ferromagnetism and spin-glass passes through a narrow intermediate phase with quasi-long-range ferromagnetic order

Topology at zero and finite T in SU(2) Yang-Mills theory

We determine the topological susceptibility \chi at T=0 and its behaviour at finite T across the deconfining transition in pure SU(2) gauge theory. We use an improved topological charge density operator. \chi goes to zero above T_c, but more slowly than in SU(3) gauge theory

Perturbative expansions from Monte Carlo simulations at weak coupling: Wilson loops and the static-quark self-energy

Perturbative coefficients for Wilson loops and the static-quark self-energy are extracted from Monte Carlo simulations at weak coupling. The lattice volumes and couplings are chosen to ensure that the lattice momenta are all perturbative. Twisted boundary conditions are used to eliminate the effects of lattice zero modes and to suppress nonperturbative finite-volume effects due to Z(3) phases. Simulations of the Wilson gluon action are done with both periodic and twisted boundary conditions, and over a wide range of lattice volumes (from $3^4$ to $16^4$) and couplings (from $\beta \approx 9$ to $\beta \approx 60$). A high precision comparison is made between the simulation data and results from finite-volume lattice perturbation theory. The Monte Carlo results are shown to be in excellent agreement with perturbation theory through second order. New results for third-order coefficients for a number of Wilson loops and the static-quark self-energy are reported.Comment: 36 pages, 15 figures, REVTEX documen

The 2-dimensional non-linear sigma-model on a random lattice

The O(n) non-linear \sigma-model is simulated on 2-dimensional regular and random lattices. We use two different levels of randomness in the construction of the random lattices and give a detailed explanation of the geometry of such lattices. In the simulations, we calculate the mass gap for n=3,\ 4 and 8, analysing the asymptotic scaling of the data and computing the ratio of Lambda parameters \Lambda_{\rm random}/\Lambda_{\rm regular}. These ratios are in agreement with previous semi-analytical calculations. We also numerically calculate the topological susceptibility by using the cooling method

Niveau de végétalisation de l’alimentation pendant la grossesse et poids de naissance de l’enfant

National audienc

Niveau de végétalisation de l’alimentation pendant la grossesse et poids de naissance de l’enfant

National audienc

Niveau de végétalisation de l’alimentation pendant la grossesse et poids de naissance de l’enfant

International audienc