The integral cohomology rings of some p-groups

We determine the integral cohomology rings of an infinite family of p-groups, for odd primes p, with cyclic derived subgroups. Our method involves embedding the groups in a compact Lie group of dimension one, and was suggested by P H Kropholler and J Huebschmann

An HI interstellar bubble surrounding WR85 and RCW118

We analyze the distribution of the interstellar matter in the environs of the Wolf-Rayet star LSS3982 (= WR85, WN6+OB?) linked to the optical ring nebula RCW118. Our study is based on neutral hydrogen 21cm-line data belonging to the Southern Galactic Plane Survey (SGPS). The analysis of the HI data allowed the identification of a neutral hydrogen interstellar bubble related to WR 85 and the 25' diameter ring nebula RCW118. The HI bubble was detected at a systemic velocity of -21.5 km/s, corresponding to a kinematical distance of 2.8+/-1.1 kpc, compatible with the stellar distance. The neutral stucture is about 25' in radius or 21+/-8 pc, and is expanding at 9+/-2 km/s. The associated ionized and neutral masses amount to 3000 Mo. The CO emission distribution depicts a region lacking CO coincident in position and velocity with the HI structure. The 9'.3 diameter inner optical nebula appears to be related to the approaching part of the neutral atomic shell. The HI void and shell are the neutral gas counterparts of the optical bubble and have very probably originated in the action of the strong stellar wind of the central star during the O-type and WR phases on the surrounding interstellar medium. The HI bubble appears to be in the momentun conserving stage.Comment: 9 pages, 7 figures, accepted in MNRA

Entropy-based parametric estimation of spike train statistics

We consider the evolution of a network of neurons, focusing on the asymptotic behavior of spikes dynamics instead of membrane potential dynamics. The spike response is not sought as a deterministic response in this context, but as a conditional probability : "Reading out the code" consists of inferring such a probability. This probability is computed from empirical raster plots, by using the framework of thermodynamic formalism in ergodic theory. This gives us a parametric statistical model where the probability has the form of a Gibbs distribution. In this respect, this approach generalizes the seminal and profound work of Schneidman and collaborators. A minimal presentation of the formalism is reviewed here, while a general algorithmic estimation method is proposed yielding fast convergent implementations. It is also made explicit how several spike observables (entropy, rate, synchronizations, correlations) are given in closed-form from the parametric estimation. This paradigm does not only allow us to estimate the spike statistics, given a design choice, but also to compare different models, thus answering comparative questions about the neural code such as : "are correlations (or time synchrony or a given set of spike patterns, ..) significant with respect to rate coding only ?" A numerical validation of the method is proposed and the perspectives regarding spike-train code analysis are also discussed.Comment: 37 pages, 8 figures, submitte

Multifractal analysis with the probability density function at the three-dimensional Anderson transition

The probability density function (PDF) for critical wavefunction amplitudes is studied in the three-dimensional Anderson model. We present a formal expression between the PDF and the multifractal spectrum f(alpha) in which the role of finite-size corrections is properly analyzed. We show the non-gaussian nature and the existence of a symmetry relation in the PDF. From the PDF, we extract information about f(alpha) at criticality such as the presence of negative fractal dimensions and we comment on the possible existence of termination points. A PDF-based multifractal analysis is hence shown to be a valid alternative to the standard approach based on the scaling of general inverse participation ratios.Comment: 4 pages, 7 figure