Some Effects of Physiographic and Biotic Factors on the Distribution of Anadromous Arctic Char (Salvelinus Alpinus) in Ungava Bay, Canada

Interviews with Inuit hunters and measurements of topographic maps were used to characterize 70 rivers discharging into Ungava Bay in northern Quebec in terms of their ability to sustain runs of anadromous arctic char. Field crews visited 29 of these to verify conclusions and add detail. Anadromous arctic char streams tend to differ from non-char streams in size, gradient and distance to overwintering lakes, but there are no clear distinctions. Shallow boulder-strewn areas with maze-like braided channels were the most common cause of lack of char or problems with fish passage. Inuit hunters reported that low flows in autumn, and associated mortalities among migrating fish, have become increasingly common in recent years. We attribute this, at least in part, to changes in climate and the effect of abundant caribou on vegetation. Both destablize flow regimes and increase the prevalence and severity of problems for fish migrating upstream. There is considerable opportunity for stream management to ease fish passage and increase production of anadromous arctic char. This is fortunate because the rapidly growing Inuit population is increasing the demand for subsistence harvests, expansion of the sports fishery and initiation of commercial fishing.Key words: anadromous arctic char streams, Ungava Bay, hunters, stream management L'Omble-chevalier arctique anadrome constitue un composant important du régime alimentaire des Inuits. Des enquêtes effectués auprès des pêcheurs inuits et l'étude de cartes topographiques ont permis de caractériser 70 rivières dans la Baie d'Ungava et de les classer en termes de possibilités de migration de l'omble-chevalier arctique anadrome. Des équipes ont visité 29 de ces rivières afin de vérifier les conclusions émises et d'y ajouter quelques détails. Les rivières à omble-chevalier arctique anadrome se distinguent des autres rivières par leur taille, leur pente et leur distance des lacs hivernaux, mais il est difficile de les séparer nettement. Les zones peu profondes à galets et blocs disséminés et à nombreux méandres expliquent l'absence d'omble-chevalier arctique anadrome ou son incapacité à migrer dans de telles eaux. D'après les pêcheurs inuits, les basses eaux d'autome, et les mortalités des poissons migrateurs qu'elles causent, sont de plus en plus nombreuses depuis quelques années. Ces basses eaux peuvent être partiellement attribués à des changements de climat et à l'effet de nombreux caribous sur la végétation environnante. Ces deux facteurs déstabilisent le régime des eaux et accroissent la fréquence et la gravité des conditions d'étiage. Les circonstances actuelles favorisent à un aménagement rationnel des cours d'eaux serait destiné à faciliter la migration des poissons et augmenter la production des ombles arctiques anadromes. Cette situation est d'autant plus favorable qu'il y a une augmentation de la population des Inuits, donc un besoin accru de nourriture de subsistance. De plus, des pressions sont exercées dans la région pour initier une pêche commerciale et développer la pêche sportive. Mots clés : rivières à omble arctique anadrome, la Baie d'Ungava, chasseurs, aménagement des cours d'ea

Casimir force on a piston

We consider a massless scalar field obeying Dirichlet boundary conditions on the walls of a two-dimensional L x b rectangular box, divided by a movable partition (piston) into two compartments of dimensions a x b and (L-a) x b. We compute the Casimir force on the piston in the limit L -> infinity. Regardless of the value of a/b, the piston is attracted to the nearest end of the box. Asymptotic expressions for the Casimir force on the piston are derived for a << b and a >> b.Comment: 10 pages, 1 figure. Final version, accepted for publication in Phys. Rev.

CsI(Tl) for WIMP dark matter searches

We report a study of CsI(Tl) scintillator to assess its applicability in experiments to search for dark matter particles. Measurements of the mean scintillation pulse shapes due to nuclear and electron recoils have been performed. We find that, as with NaI(Tl), pulse shape analysis can be used to discriminate between electron and nuclear recoils down to 4 keV. However, the discrimination factor is typically (10-15)% better than in NaI(Tl) above 4 keV. The quenching factor for caesium and iodine recoils was measured and found to increase from 11% to ~17% with decreasing recoil energy from 60 to 12 keV. Based on these results, the potential sensitivity of CsI(Tl) to dark matter particles in the form of neutralinos was calculated. We find an improvement over NaI(Tl) for the spin independent WIMP-nucleon interactions up to a factor of 5 assuming comparable electron background levels in the two scintillators.Comment: 16 pages, 8 figures, to be published in Nucl. Instrum. and Meth. in Phys. Res.

Growth, competition and cooperation in spatial population genetics

We study an individual based model describing competition in space between two different alleles. Although the model is similar in spirit to classic models of spatial population genetics such as the stepping stone model, here however space is continuous and the total density of competing individuals fluctuates due to demographic stochasticity. By means of analytics and numerical simulations, we study the behavior of fixation probabilities, fixation times, and heterozygosity, in a neutral setting and in cases where the two species can compete or cooperate. By concluding with examples in which individuals are transported by fluid flows, we argue that this model is a natural choice to describe competition in marine environments.Comment: 29 pages, 14 figures; revised version including a section with results in the presence of fluid flow

On the alpha activity of natural tungsten isotopes

The indication for the alpha decay of 180-W with a half-life T1/2=1.1+0.8-0.4(stat)+-0.3(syst)x10^18 yr has been observed for the first time with the help of the super-low background 116-CdWO_4 crystal scintillators. In conservative approach the lower limit on half-life of 180-W has been established as T1/2>0.7x10^18 yr at 90% C.L. Besides, new T1/2 bounds were set for alpha decay of 182-W, 183-W, 184-W and 186-W at the level of 10^20 yr.Comment: 16 pages, 8 figures, accepted in Phys. Rev.

Mycobacterium ulcerans in Mosquitoes Captured during Outbreak of Buruli Ulcer, Southeastern Australia

Mosquitoes positive for M. ulcerans were linked to outbreaks of Buruli ulcer in humans

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02