A radiative transfer scheme for cosmological reionization based on a local Eddington tensor

A radiative transfer scheme is presented, based on a moment description of the equation of radiative transfer and the so-called ``M1 closure model'' for the Eddington tensor. This model features a strictly hyperbolic transport step for radiation: it has been implemented using standard Godunov--like techniques in a new code called ATON. Coupled to simple models of ionization chemistry and photo-heating, ATON is able to reproduce the results of other schemes on a various set of standard tests such as the expansion of a HII region, the shielding of the radiation by dense clumps and cosmological ionization by multiple sources. Being simple yet robust, such a scheme is intended to be naturally and easily included in grid--based cosmological fluid solvers.Comment: 14 pages, 13 figures, submitted to MNRA

Free-floating molecular clumps and gas mixing: hydrodynamic aftermaths of the intracluster−-interstellar medium interaction

The interaction of gas-rich galaxies with the intra-cluster medium (ICM) of galaxy clusters has a remarkable impact on their evolution, mainly due to the gas loss associated with this process. In this work, we use an idealised, high-resolution simulation of a Virgo-like cluster, run with RAMSES and with dynamics reproducing that of a zoom cosmological simulation, to investigate the interaction of infalling galaxies with the ICM. We find that the tails of ram pressure stripped galaxies give rise to a population of up to more than a hundred clumps of molecular gas lurking in the cluster. The number count of those clumps varies a lot over time -- they are preferably generated when a large galaxy crosses the cluster (M$_{200c} > 10^{12}$ M$_\odot$), and their lifetime ($\lesssim 300$ Myr) is small compared to the age of the cluster. We compute the intracluster luminosity associated with the star formation which takes place within those clumps, finding that the stars formed in all of the galaxy tails combined amount to an irrelevant contribution to the intracluster light. Surprisingly, we also find in our simulation that the ICM gas significantly changes the composition of the gaseous disks of the galaxies: after crossing the cluster once, typically 20% of the cold gas still in those disks comes from the ICM.Comment: 9 pages, 6 figures. Accepted for publication in MNRA

Solvable Hydrodynamics of Quantum Integrable Systems

The conventional theory of hydrodynamics describes the evolution in time of chaotic many-particle systems from local to global equilibrium. In a quantum integrable system, local equilibrium is characterized by a local generalized Gibbs ensemble or equivalently a local distribution of pseudo-momenta. We study time evolution from local equilibria in such models by solving a certain kinetic equation, the "Bethe-Boltzmann" equation satisfied by the local pseudo-momentum density. Explicit comparison with density matrix renormalization group time evolution of a thermal expansion in the XXZ model shows that hydrodynamical predictions from smooth initial conditions can be remarkably accurate, even for small system sizes. Solutions are also obtained in the Lieb-Liniger model for free expansion into vacuum and collisions between clouds of particles, which model experiments on ultracold one-dimensional Bose gases.Comment: 6+5 pages, published versio

Inhomogeneous Gain Saturation in EDF: Experiment and Modeling

Erbium-Doped Fiber Amplifiers can present holes in spectral gain in Wavelength Division Multiplexing operation. The origin of this inhomogeneous saturation behavior is still a subject of controversy. In this paper we present both an experimental methods and a gain's model. Our experimental method allow us to measure the first homogeneous linewidth of the 1.5 $\mu$m erbium emission with gain spectral hole burning consistently with the other measurement in the literature and the model explains the differences observed in literature between GSHB and other measurement methods

Secrecy Sum-Rates with Regularized Channel Inversion Precoding under Imperfect CSI at the Transmitter

In this paper, we study the performance of regularized channel inversion precoding in MISO broadcast channels with confidential messages under imperfect channel state information at the transmitter (CSIT). We obtain an approximation for the achievable secrecy sum-rate which is almost surely exact as the number of transmit antennas and the number of users grow to infinity in a fixed ratio. Simulations prove this anaylsis accurate even for finite-size systems. For FDD systems, we determine how the CSIT error must scale with the SNR, and we derive the number of feedback bits required to ensure a constant high-SNR rate gap to the case with perfect CSIT. For TDD systems, we study the optimum amount of channel training that maximizes the high-SNR secrecy sum-rate.Comment: IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), May 2013. arXiv admin note: text overlap with arXiv:1304.585

Construire l’espace public : du diagnostic au projet. La mission d'étude de diagnostic de la loi MOP adaptée aux projets de paysage

Ce document, réalisé à partir de contributions provenant de l\u27INHP, du STAP 37 et de l\u27ADAC1, a pour principale fonction d’expliciter les étapes préalables aux projets d’aménagement d’espaces publics dans le cadre de la loi MOP2. Il est principalement destiné aux maîtres d\u27ouvrage et aux maîtres d’oeuvre. La loi MOP fixe les différentes étapes d’élaboration d\u27un projet de maîtrise d\u27oeuvre. Dans le cadre des projets d\u27aménagement d\u27espaces publics, il semble de plus en plus évident que la mission de base définie par la loi n\u27est pas toujours suffisante pour intégrer en amont de la phase de conception l\u27ensemble des enjeux et des contraintes qui soustendent l\u27émergence d\u27un projet d\u27aménagement. Il existe un complément à la mission de base intitulé "études de diagnostic", qui permet d\u27intégrer une étude en amont mais qui est principalement destinée aux projets de réhabilitation. Concernant les projets d’aménagement d’espaces publics, nous sommes convaincus qu\u27une mission similaire pourrait être intégrée à la procédure d\u27élaboration du projet et qu\u27elle doit conduire à l\u27élaboration de schémas d\u27articulation posant les enjeux et les bases des futurs projets. A ce titre, il nous semble important, puisqu\u27elle ne fait pas partie intégrante de la mission de base, qu\u27elle soit réalisée dans le cadre du marché, sous la forme d\u27une mission complémentaire préalable demandée par le maître d\u27ouvrage. Dans ce contexte, elle diffère quelque peu de la version utilisée pour la réhabilitation, même si les étapes imposées peuvent être transposées dans un environnement urbain. L\u27objet de ce document est d\u27expliciter ce que recouvre la notion d\u27analyse préalable, sur le base du contenu de la mission complémentaire d\u27étude de diagnostic, et de proposer une méthodologie permettant de la mener à bien

Velocity measurement during evaporation of seeded, sessile drops on heated surfaces

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Evaporation of sessile drops has been studied extensively in an attempt to understand the effect of wetting on the evaporation process. Recently interest has also increased in the deposition of particles from such drops, with evaporative mass flux being deemed to be responsible for ring-like deposits and Marangoni convection counteracting this mass flux explaining more uniform deposition patterns. Understanding of such deposition processes is important in ink-jet printing and other micro-scale deposition technologies, where the nature of deposition can have a dramatic effect on the quality or effectiveness of the finished product. In most cases where deposition from evaporating drops has been studied, velocity information is inferred from the final deposition pattern or from mathematical modeling based on simplified models of the physics of the evaporation process. In this study we have directly measured the flow velocities in the base of sessile drops, using micro-PIV, viewing the drop from below, through the cover slide. The images obtained have also enabled us to observe the formation of holes in the liquid film during the latter stages of evaporation

Computer-Assisted Segmentation of Videocapsule Images Using Alpha-Divergence-Based Active Contour in the Framework of Intestinal Pathologies Detection

Visualization of the entire length of the gastrointestinal tract through natural orifices is a challenge for endoscopists. Videoendoscopy is currently the “gold standard” technique for diagnosis of different pathologies of the intestinal tract. Wireless Capsule Endoscopy (WCE) has been developed in the 1990's as an alternative to videoendoscopy to allow direct examination of the gastrointestinal tract without any need for sedation. Nevertheless, the systematic post-examination by the specialist of the 50,000 (for the small bowel) to 150,000 images (for the colon) of a complete acquisition using WCE remains time-consuming and challenging due to the poor quality of WCE images. In this article, a semiautomatic segmentation for analysis of WCE images is proposed. Based on active contour segmentation, the proposed method introduces alpha-divergences, a flexible statistical similarity measure that gives a real flexibility to different types of gastrointestinal pathologies. Results of segmentation using the proposed approach are shown on different types of real-case examinations, from (multi-) polyp(s) segmentation, to radiation enteritis delineation