Cosmological Origin of the Stellar Velocity Dispersions in Massive Early-Type Galaxies

We show that the observed upper bound on the line-of-sight velocity dispersion of the stars in an early-type galaxy, sigma<400km/s, may have a simple dynamical origin within the LCDM cosmological model, under two main hypotheses. The first is that most of the stars now in the luminous parts of a giant elliptical formed at redshift z>6. Subsequently, the stars behaved dynamically just as an additional component of the dark matter. The second hypothesis is that the mass distribution characteristic of a newly formed dark matter halo forgets such details of the initial conditions as the stellar "collisionless matter" that was added to the dense parts of earlier generations of halos. We also assume that the stellar velocity dispersion does not evolve much at z<6, because a massive host halo grows mainly by the addition of material at large radii well away from the stellar core of the galaxy. These assumptions lead to a predicted number density of ellipticals as a function of stellar velocity dispersion that is in promising agreement with the Sloan Digital Sky Survey data.Comment: ApJ, in press (2003); matches published versio

Rings and Jets around PSR J2021+3651: the `Dragonfly Nebula'

We describe recent Chandra ACIS observations of the Vela-like pulsar PSR J2021+3651 and its pulsar wind nebula (PWN). This `Dragonfly Nebula' displays an axisymmetric morphology, with bright inner jets, a double-ridged inner nebula, and a ~30" polar jet. The PWN is embedded in faint diffuse emission: a bow shock-like structure with standoff ~1' brackets the pulsar to the east and emission trails off westward for 3-4'. Thermal (kT=0.16 +/-0.02 keV) and power law emission are detected from the pulsar. The nebular X-rays show spectral steepening from Gamma=1.5 in the equatorial torus to Gamma=1.9 in the outer nebula, suggesting synchrotron burn-off. A fit to the `Dragonfly' structure suggests a large (86 +/-1 degree) inclination with a double equatorial torus. Vela is currently the only other PWN showing such double structure. The >12 kpc distance implied by the pulsar dispersion measure is not supported by the X-ray data; spectral, scale and efficiency arguments suggest a more modest 3-4 kpc.Comment: 22 pages, 5 figures, 3 tables, Accepted to Ap

Topological regluing of rational functions

Regluing is a topological operation that helps to construct topological models for rational functions on the boundaries of certain hyperbolic components. It also has a holomorphic interpretation, with the flavor of infinite dimensional Thurston--Teichm\"uller theory. We will discuss a topological theory of regluing, and trace a direction in which a holomorphic theory can develop.Comment: 38 page

Meningococcal pericarditis in the absence of meningitis

Contains fulltext : 4464.pdf (publisher's version ) (Open Access

Factors that influence shelterbelt retention and removal in prairie agriculture as identified by Saskatchewan producers

Non-Peer ReviewedThe role of shelterbelts in prairie agriculture is changing. Traditionally, shelterbelts were promoted and adopted for soil stabilization and protection of farm infrastructure, equipment, and livestock from harsh weather elements; however, advances in production technology, larger scale operations, and the removal of a subsidy (distribution of free seedlings) have changed the context in which shelterbelts are currently being maintained, planted, or removed. This research identified the factors that are influencing producer’s management decisions related to retention and adoption of shelterbelts in the early 21st century in Saskatchewan, Canada. In the summer of 2013, surveys were conducted with producers from throughout the province of Saskatchewan (and several from Alberta). From the surveys, costs, benefits, and factors influencing producer’s management decisions, related to shelterbelts in the farm operations, were identified. Survey results show that 40% of the produces removed shelterbelts from their operations. Reasons for such decisions included: high labor requirements, difficulty in the operation of large equipment, and loss of land for production. Those who did not remove shelterbelts recognized their non-economic values more than those who removed them. Shelterbelts have the potential to play a major role in climate change mitigation by sequestering significant amounts of atmospheric CO2 into the soil and as biomass carbon in aboveground and belowground biomass of planted shelterbelt trees or shrubs within the agricultural landscape, both presently and in the future. As a result, understanding the context in which producers are making decisions related to this agroforestry practice will be important from a policy perspective

Quiescent times in gamma-ray bursts: II. Dormant periods in the central engine?

Within the framework of the internal-external shocks model for gamma-ray bursts, we study the various mechanisms that can give rise to quiescent times in the observed gamma-ray light-curves. In particular, we look for the signatures that can provide us with evidence as to whether or not the central engine goes dormant for a period of time comparable to the duration of the gaps. We show that the properties of the prompt gamma-ray and X-ray emission can in principle determine whether the quiescent episodes are due to a modulated relativistic wind or a switching off of the central engine. We suggest that detailed observations of the prompt afterglow emission from the reverse shock will strongly constrain the possible mechanisms for the production of quiescent times in gamma-ray bursts.Comment: 12 pages, 8 figures, with final revisions, MNRAS in pres

Predicting the large-scale consequences of offshore wind turbine array development on a North Sea ecosystem

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Three models were applied to obtaina first assessment of some of the potential impacts of large-scale operational wind turbine arrays on the marine ecosystem in a well-mixed area in a shelf sea: a biogeochemical model,a wave propagation model and an a coustic energy flux model.The results of the models are discussed separately and together to elucidate the combined effects. Overall,all three models suggested relatively weak environmental changes for the mechanisms included in this study, however these are only a subset of all the potential impacts,and a number of assumptions had to be made. Further work is required to address these assumptions and additional mechanisms. All three models suggested most of the changes with in the wind turbine array,and small changes up to several tens of km outside the array. Within the array, the acoustic model indicated the most concentrated, spatially repetitive changes to the environment,followed by the SWAN wave model,and the biogeochemical model being the most diffuse. Because of the different spatial scales of the response of the three models,the combined results suggested a spectrum of combinations of environmental changes with in the wind turbine array that marine organism smight respond to. The SWAN wave model and the acoustic model suggested a reduction in changes with increasing distance between turbines. The SWAN wave model suggested that the biogeochemical model, because of the in ability of its simple wave model to simulate wave propagation,over-estimated the biogeochemical changes by a factor of 2 or more. The biogeochemical model suggested that the benthic system was more sensitive to the environmental changes than the pelagic system. © 2014 Published by Elsevier Ltd.The work was carried out as part of the EBAO project (Optimising Array Form for Energy Extraction and Environmental Benefit, No. NE/J004227/1), and was jointly funded by NERC and Defra (Cefas contract C5325). Sonja van Leeuwen constructed the daily riverine loads database from which the runoff data were used in the GETM-ERSEM model. French water quality data were supplied by the Agence de l’eau Loire-Bretagne, Agence de l’eau Seine-Normandie and IFREMER. UK water quality data were processed from raw data provided by the Environment Agency, the Scottish Environment Protection Agency and the National River Flow Archive. The German river loads are based on data from the ARGE Elbe, the Niedersächsisches Landesamt für Ökologie and the Bundesanstalt für Gewässerkunde. The river load data for the Netherlands were supplied by the DONAR database. The authors gratefully acknowledge the ECMWF (European Centre for Medium Range Weather Forecasting) for allowing the use of the ERA-40 and Operational Hindcast data used as atmospheric forcing for the GETM-ERSEM model