4,047 research outputs found
Identifying Blue Horizontal Branch Stars Using the z Filter
In this paper we present a new method for selecting blue horizontal branch
(BHB) candidates based on color-color photometry. We make use of the Sloan
Digital Sky Survey z band as a surface gravity indicator and show its value for
selecting BHB stars from quasars, white dwarfs and main sequence A type stars.
Using the g, r, i, and z bands, we demonstrate that extraction accuracies on
par with more traditional u, g, and r photometric selection methods may be
achieved. We also show that the completeness necessary to probe major Galactic
structure may be maintained. Our new method allows us to efficiently select BHB
stars from photometric sky surveys that do not include a u band filter such as
the Panoramic Survey Telescope and Rapid Response System.Comment: Accepted for publication in The Astronomical Journa
Can a charged dust ball be sent through the Reissner--Nordstr\"{o}m wormhole?
In a previous paper we formulated a set of necessary conditions for the
spherically symmetric weakly charged dust to avoid Big Bang/Big Crunch, shell
crossing and permanent central singularities. However, we did not discuss the
properties of the energy density, some of which are surprising and seem not to
have been known up to now. A singularity of infinite energy density does exist
-- it is a point singularity situated on the world line of the center of
symmetry. The condition that no mass shell collapses to if it had initially thus turns out to be still insufficient for avoiding a
singularity. Moreover, at the singularity the energy density is
direction-dependent: when we approach the singular
point along a const hypersurface and when we
approach that point along the center of symmetry. The appearance of
negative-energy-density regions turns out to be inevitable. We discuss various
aspects of this property of our configuration. We also show that a permanently
pulsating configuration, with the period of pulsation independent of mass, is
possible only if there exists a permanent central singularity.Comment: 30 pages, 21 figures; several corrections after referee's comments, 4
figures modifie
On the Geroch-Traschen class of metrics
We compare two approaches to semi-Riemannian metrics of low regularity. The maximally 'reasonable' distributional setting of Geroch and Traschen is shown to be consistently contained in the more general setting of nonlinear distributional geometry in the sense of Colombea
Monodon baculovirus from Australia: Ultrastructural observations
The cytopathology, virogenesis and replication of monodon baculovirus (MBV) in Penaeus monodon from Australia are described. Electron-dense unenveloped nucleocapsids, not previously described for MBV, are shown in the cytoplasm and attached to the nuclear envelope of infected hepatopancreatocytes. These nucleocapsids comprise a missing link in the published literature on the replication cycle of MBV by providing evidence for the means by which the viral genome travels from the plasma membrane of the hepatopancreatocyte to the nucleus. Features similar to those of MBV from other areas, but not previously reported for MBV from Australia include empty capsids attached to the nuclear pore, central filaments in developing capsids, capsids partly filled with nucleic acid, and filaments in subapical envelope expansions. A model for virogenesis and replication is illustrated which takes into account the new observations as well as previously described ultrastructural characteristics of the developing viral particle
A Cross Country Comparison of Best Practices in Recruitment and Selection
This study examines best practices in hiring related to the recruitment and selection process in English-speaking countries with an Anglo-Saxon heritage. Since such countries share a similar cultural backgrounds and histories, best practices are likely to be somewhat similar. Studies of best practices were examined in the following countries: United States of America, Australia, United Kingdom, Canada, and New Zealand. After looking at commonalities across ābest practicesā studies, the current investigation presents a common set of such practices in terms of usage
A Cross Country Comparison of Best Practices in Recruitment and Selection
This study examines best practices in hiring related to the recruitment and selection process in English-speaking countries with an Anglo-Saxon heritage. Since such countries share a similar cultural backgrounds and histories, best practices are likely to be somewhat similar. Studies of best practices were examined in the following countries: United States of America, Australia, United Kingdom, Canada, and New Zealand. After looking at commonalities across ābest practicesā studies, the current investigation presents a common set of such practices in terms of usage
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