Low-Rank Network Decomposition Reveals Structural Characteristics Of Small-World Networks

Small-world networks occur naturally throughout biological, technological, and social systems. With their prevalence, it is particularly important to prudently identify small-world networks and further characterize their unique connection structure with respect to network function. In this work we develop a formalism for classifying networks and identifying small-world structure using a decomposition of network connectivity matrices into low-rank and sparse components, corresponding to connections within clusters of highly connected nodes and sparse interconnections between clusters, respectively. We show that the network decomposition is independent of node indexing and define associated bounded measures of connectivity structure, which provide insight into the clustering and regularity of network connections. While many existing network characterizations rely on constructing benchmark networks for comparison or fail to describe the structural properties of relatively densely connected networks, our classification relies only on the intrinsic network structure and is quite robust with respect to changes in connection density, producing stable results across network realizations. Using this framework, we analyze several real-world networks and reveal new structural properties, which are often indiscernible by previously established characterizations of network connectivity

Discovery of a weak magnetic field in the photosphere of the single giant Pollux

Aims: We observe the nearby, weakly-active single giant, Pollux, in order to directly study and infer the nature of its magnetic field. Methods: We used the new generation spectropolarimeters ESPaDOnS and NARVAL to observe and detect circular polarization within the photospheric absorption lines of Pollux. Our observations span 18 months from 2007-2009. We treated the spectropolarimetric data using the Least-Squares Deconvolution method to create high signal-to-noise ratio mean Stokes V profiles. We also measured the classical activity indicator S-index for the Ca H&K lines, and the stellar radial velocity (RV). Results: We have unambiguously detected a weak Stokes V signal in the spectral lines of Pollux, and measured the related surface-averaged longitudinal magnetic field Bl. The longitudinal field averaged over the span of the observations is below one gauss. Our data suggest variations of the longitudinal magnetic field, but no significant variation of the S-index. We observe variations of RV which are qualitatively consistent with the published ephemeris for a proposed exoplanet orbiting Pollux. The observed variations of Bl appear to mimic those of RV, but additional data for this relationship to be established. Using evolutionary models including the effects of rotation, we derive the mass of Pollux and we discuss its evolutionary status and the origin of its magnetic field. Conclusions: This work presents the first direct detection of the magnetic field of Pollux, and demonstrates that ESPaDOnS and NARVAL are capable of obtaining sub-G measurements of the surface-averaged longitudinal magnetic field of giant stars, and of directly studying the relationships between magnetic activity, stellar evolution and planet hosting of these stars.Comment: 8 pages, 6 figures, accepted for publication in Astronomy and Astrophysic

SPIRAL II Project (electron option) - Preliminary Design Study

This document presents a Preliminary Design Study (PDS) of the electron option of the SPIRAL II project

Detection of Correlations with Adaptive Sensing

The problem of detecting correlations from samples of a high-dimensional Gaussian vector has recently received a lot of attention. In most existing work, detection procedures are provided with a full sample. However, following common wisdom in experimental design, the experimenter may have the capacity to make targeted measurements in an on-line and adaptive manner. In this work, we investigate such adaptive sensing procedures for detecting positive correlations. It it shown that, using the same number of measurements, adaptive procedures are able to detect significantly weaker correlations than their non-adaptive counterparts. We also establish minimax lower bounds that show the limitations of any procedure. Index Terms sequential testing, adaptive sensing, sparse covariance matrices, sparse principal component analysis, high-dimensional detection I

Safety Control of the Spiral2 Radioactive Gas Storage System

THPHA107, poster sessionInternational audienceThe phase 1 of the SPIRAL2 facility, extension project of the GANIL laboratory, isunder construction and the commissioning had started. During the run phases,radioactive gas, mainly composed of hydrogen, will be extracted from the vacuumchambers. The radioactive gas storage system function is to prevent any uncontrolledrelease of activated gas by storing it in gas tank during the radioactive decay,while monitoring the hydrogen rate in the tanks under a threshold. This confinementof radioactive materials is a safety function. The filling and the dischargeof the tanks are processed with monostable valves, making the storage a passivesafety system. Two separate redundant control subsystems, based on electricalhardware technologies, allow the opening of the redundant safety valves, accordingto redundant pressure captors, redundant di-hydrogen rate analyzers and limitswitches of the valves. The redundancy of the design of the control system meetsthe single failure criterion. The monitoring of the consistency of the two redundantsafety subsystems, and the non-safety control functions of the storage process, arethenmanaged by a Programmable Logic Controller

Technical report on operating accelerators 2001-2002

This issue of the Technical Report about the Accelerators describes the operation for physics experiments and beam tests, various technical improvements and projects for the years 2001-2002 during which the most eventful result was the start of the SPIRAL facility operation

EXODAT: A VO-Compliant Database for Exoplanetary Systems

International audienceThe EXODAT project aims to provide the information needed for the selection of the best targets and preparation of the statistical analysis for exoplanet searches. The COROT exoplanet mission will continuously observe a set of selected stars for 150 days to discover planetary transits. At the end of the mission in 2010, EXODAT will be the first exoplanet database with physical characteristics of parent stars and of their planets. EXODAT currently contains 10 million stars over 100 square degrees centered on two main regions (RA=6h50m Dec=0\deg, RA=18h50 Dec=0\deg). COROT team members can access: astrometry; broad-band photometry from UBVRi, 2MASS, USNO-A2 and DENIS; stellar parameters such as spectral type, luminosity class and reddening; and a subset of moderate resolution spectra with the derived stellar parameters T_\eff\, log g, [M/H], rotation velocity and binarity. Light curves and planet properties will be available after the mission's launch

Measuring presence in a virtual environment using electroencephalography: A study of breaks in presence using an oddball paradigm

International audiencePresence is one of the main factor conditioning the user-experience in virtual reality (VR). It corresponds to the illusion of being physically located in a virtual environment. Presence is usually measured subjectively through questionnaires.However, questionnaires cannot be filled in when the user is experiencing presence, as it would disrupt the feeling. The use of electroencephalography (EEG) to monitor users while they are immersed in VR presents an opportunity to bridge this gap and assess presence continuously. This study aims at investigating whether different levels of presence can be distinguished from EEG signals