2,438 research outputs found
Facilitating Equitable Access and Retention for Underrepresented Students at the University of Mary Washington
Higher education institutions are facing increasing pressure to find new ways to attract, retain, and graduate the diverse populations of college students. As a result, colleges and universities need to adapt to the changing demographics of students who benefit from more sustained and engaged forms of support that are responsive to their specific social, cultural, and economic backgrounds. This sequential mixed methods study seeks to understand the ways in which the University of Mary Washington serves its underrepresented students in order to develop strategies to enhance the recruitment and retention of Black, Hispanic/Latinx, low-income, and first-generation college students. Building on the literature on retention and persistence, sense of belonging, and organizational change, researchers developed a student sense of belonging survey, an organizational readiness for change assessment, and conducted focus group discussions with UMW students. In particular, the project sought to understand the current institutional culture regarding inclusion and sense of belonging for underrepresented students. This study\u27s findings inform how the University of Mary Washington can better facilitate the recruitment, retention, and graduation of underrepresented students
Radiation from collision-dominated relativistic pair fireballs
It is generally accepted that gamma-ray bursts (GRBs) are initiated by a
relativistic pair fireball, converting its internal energy into kinetic energy
of a relativistically moving plasmoid and subsequently into radiation. Here, we
investigate the early stages of this evolution, after the pair fireball has
become optically thin to gamma-gamma pair production. We show that for a short
period of time, ~ 0.1 - a few seconds after the initial explosion, the pair
plasmoid evolution might be dominated by collisional processes prior to the
formation of a collisionless shock. We simulate these processes during the
early pair plasmoid evolution and calculate the expected radiative signatures.
We show that the radiation from the collision-dominated pair plasmoid phase
results in a short (~ a few ms) flash of thermal soft X-ray emission, followed
by a transition phase of < 1 s during which the fireball turns Thomson thin,
but its radiation remains dominated by thermal Comptonization, peaking at
around E_pk ~ 100 MeV - a few GeV. While the very early thermal emission could
be associated with the quasi-thermal radiation signatures found in the very
early phases of several bright BATSE GRBs, the predicted subsequent flash of
high-energy emission should be easily detectable with the GLAST satellite.Comment: AASTeX, 25 pages, including 7 figures. Accepted for publication in
Ap
Modelling the extremes of seasonal viruses and hospital congestion: The example of flu in a Swiss hospital
Viruses causing flu or milder coronavirus colds are often referred to as âseasonal virusesâ as they tend to subside in warmer months. In other words, meteorological conditions tend to impact the activity of viruses, and this information can be exploited for the operational management of hospitals. In this study, we use 3 years of daily data from one of the biggest hospitals in Switzerland and focus on modelling the extremes of hospital visits from patients showing flu-like symptoms and the number of positive flu cases. We propose employing a discrete generalized Pareto distribution for the number of positive and negative cases. Our modelling framework allows for the parameters of these distributions to be linked to covariate effects, and for outlying observations to be dealt with via a robust estimation approach. Because meteorological conditions may vary over time, we use meteorological and not calendar variations to explain hospital charge extremes, and our empirical findings highlight their significance. We propose a measure of hospital congestion and a related tool to estimate the resulting CaRe (Charge-at-Risk-estimation) under different meteorological conditions. The relevant numerical computations can be easily carried out using the freely available GJRM R package. The empirical effectiveness of the proposed method is assessed through a simulation study
Meridional variations of the springtime phytoplankton community in the Sargasso Sea
Meridional distributions of particle, pigment, optical, chemical and physical in situ oceanographic properties, as well as satellite-sensed sea-surface temperature and color imagery, are used to investigate phytoplankton community distributions and their relation to the near-surface water masses of the S bnargasso Sea. 0-H3059 Measurements were made during April of 1985 along a 1200 km transect on 70W (from 24N to 35N). The seasonal evolution of subtropical Mode water (18° water) is shown to be the primary factor controlling the spatial distribution and evolution of the phytoplankton community in the northern Sargasso Sea (31 to 35N). The springtime near-surface restratification of recently ventilated 18° water initiated a diatom-dominated phytoplankton bloom. As the bloom declined, the phytoplankton community evolved into a diverse assemblage. The consequences of these phytoplankton successions were observed both temporally and as spatial variations along the meridional section. South of the region of 18° water wintertime ventilation (south of 31N), phytoplankton concentrations were considerably less and appeared to be regulated by different processes than the northern region. In particular, influences of subtropical convergence fronts were observed. For the northern Sargasso Sea, the wintertime ventilation of 18° water is shown to be the primary new nutrient flux into the euphotic zone, comprising most of the expected annual new production for this region
Complete solutions to the metric of spherically collapsing dust in an expanding spacetime with a cosmological constant
We present semi-analytical solutions to the background equations describing
the Lema\^itre-Tolman-Bondi (LTB) metric as well as the homogeneous Friedmann
equations, in the presence of dust, curvature and a cosmological constant
Lambda. For none of the presented solutions any numerical integration has to be
performed. All presented solutions are given for expanding and collapsing
phases, preserving continuity in time and radius. Hence, these solutions
describe the complete space time of a collapsing spherical object in an
expanding universe. In the appendix we present for completeness a solution of
the Friedmann equations in the additional presence of radiation, only valid for
the Robertson-Walker metric.Comment: 23 pages, one figure. Numerical module for evaluation of the
solutions released at
http://web.physik.rwth-aachen.de/download/valkenburg/ColLambda/ Matches
published version, published under Open Access. Note change of titl
Cosmological background solutions and cosmological backreactions
The cosmological backreaction proposal, which attempts to account for
observations without a primary dark energy source in the stress-energy tensor,
has been developed and discussed by means of different approaches. Here, we
focus on the concept of cosmological background solutions in order to develop a
framework to study different backreaction proposals.Comment: 14 pages, 5 figures; major changes, replaced to match the version
published in General Relativity and Gravitatio
Observational constraints on inhomogeneous cosmological models without dark energy
It has been proposed that the observed dark energy can be explained away by
the effect of large-scale nonlinear inhomogeneities. In the present paper we
discuss how observations constrain cosmological models featuring large voids.
We start by considering Copernican models, in which the observer is not
occupying a special position and homogeneity is preserved on a very large
scale. We show how these models, at least in their current realizations, are
constrained to give small, but perhaps not negligible in certain contexts,
corrections to the cosmological observables. We then examine non-Copernican
models, in which the observer is close to the center of a very large void.
These models can give large corrections to the observables which mimic an
accelerated FLRW model. We carefully discuss the main observables and tests
able to exclude them.Comment: 27 pages, 7 figures; invited contribution to CQG special issue
"Inhomogeneous Cosmological Models and Averaging in Cosmology". Replaced to
match the improved version accepted for publication. Appendix B and
references adde
Conserved quantities in Lemaitre-Tolman-Bondi cosmology
We study linear perturbations to a Lema{\^\i}tre-Tolman-Bondi (LTB)
background spacetime. Studying the transformation behaviour of the
perturbations under gauge transformations, we construct gauge invariant
quantities. We show, using the perturbed energy conservation equation, that
there are conserved quantities in LTB, in particular a spatial metric trace
perturbation, \zeta_{SMTP}, which is conserved on all scales. We then briefly
extend our discussion to the Lema{\^\i}tre spacetime, and construct
gauge-invariant perturbations in this extension of LTB spacetime.Comment: 16 pages, 0 figures, revtex4; v5: minor changes, additional 2+2
formalism appendix added, references added, version accepted by CQ
A two-mass expanding exact space-time solution
In order to understand how locally static configurations around
gravitationally bound bodies can be embedded in an expanding universe, we
investigate the solutions of general relativity describing a space-time whose
spatial sections have the topology of a 3-sphere with two identical masses at
the poles. We show that Israel junction conditions imply that two spherically
symmetric static regions around the masses cannot be glued together. If one is
interested in an exterior solution, this prevents the geometry around the
masses to be of the Schwarzschild type and leads to the introduction of a
cosmological constant. The study of the extension of the Kottler space-time
shows that there exists a non-static solution consisting of two static regions
surrounding the masses that match a Kantowski-Sachs expanding region on the
cosmological horizon. The comparison with a Swiss-Cheese construction is also
discussed.Comment: 15 pages, 5 figures. Replaced to match the published versio
Averaging inhomogeneities in scalar-tensor cosmology
The backreaction of inhomogeneities on the cosmic dynamics is studied in the
context of scalar-tensor gravity. Due to terms of indefinite sign in the
non-canonical effective energy tensor of the Brans-Dicke-like scalar field,
extra contributions to the cosmic acceleration can arise. Brans-Dicke and
metric f(R) gravity are presented as specific examples. Certain representation
problems of the formalism peculiar to these theories are pointed out.Comment: Comments and references added. 14 page
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