Sparse square roots.

We show that it can be decided in polynomial time whether a graph of maximum degree 6 has a square root; if a square root exists, then our algorithm finds one with minimum number of edges. We also show that it is FPT to decide whether a connected n-vertex graph has a square root with at most n − 1 + k edges when this problem is parameterized by k. Finally, we give an exact exponential time algorithm for the problem of finding a square root with maximum number of edges

Dark Matter directional detection: comparison of the track direction determination

Several directional techniques have been proposed for a directional detection of Dark matter, among others anisotropic crystal detectors, nuclear emulsion plates, and low-pressure gaseous TPCs. The key point is to get access to the initial direction of the nucleus recoiling due to the elastic scattering by a WIMP. In this article, we aim at estimating, for each method, how the information of the recoil track initial direction is preserved in different detector materials. We use the SRIM simulation code to emulate the motion of the first recoiling nucleus in each material. We propose the use of a new observable, D, to quantify the preservation of the initial direction of the recoiling nucleus in the detector. We show that in an emulsion mix and an anisotropic crystal, the initial direction is lost very early, while in a typical TPC gas mix, the direction is well preserved.Comment: 9 pages, 5 figure

Probe of Lorentz Invariance Violation effects and determination of the distance of PG 1553+113

The high frequency peaked BL Lac object PG 1553+113 underwent a flaring event in 2012. The High Energy Stereoscopic System (H.E.S.S.) observed this source for two consecutive nights at very high energies (VHE, $E>$100~GeV). The data show an increase of a factor of three of the flux with respect to archival measurements with the same instrument and hints of intra-night variability. The data set has been used to put constraints on possible Lorentz invariance violation (LIV), manifesting itself as an energy dependence of the velocity of light in vacuum, and to set limits on the energy scale at which Quantum Gravity effects causing LIV may arise. With a new method to combine H.E.S.S. and Fermi large area telescope data, the previously poorly known redshift of PG 1555+113 has been determined to be close to the value derived from optical measurements.Comment: 2014 Fermi Symposium proceedings - eConf C14102.

Les cochenilles des Myrtaceae en Amazonie péruvienne : 1. Description de deux nouveaux ravageurs de Myrciaria dubia (Homoptera, Coccidae et Kerriidae)

#Ceroplastes flosculoides Matile-Ferrero n.sp. (Coccidae) et #Austrotachardiella sexcordata Matile-Ferrero n.sp. (Kerriidae), sont décrits et illustrés. Les deux espèces sont des ravageurs d'une Myrtacée cultivée, #Myrciaria dubia, en Amazonie péruvienne. #Austrotachardiella trilobata (Mendes) n.comb. est transférée de #Tachardiella$ Cockerell. (Résumé d'auteur