445 research outputs found
Self-Assessment and Planned Change of Placement and Career Services Center
In the 1990s, college and university career services and placement units face many challenges which may influence their success including (a) increased budgetary constraints, (b) changing student demographics, (c) increased availability of computer technologies, (d) new service delivery models, and (e) changing employer recruitment practices. In an effort to address these issues and examine its role within the university (Roth, 1994), the Placement and Career Information Center (PCIC) at Central Michigan University undertook a program of applied research, self-assessment and planned change. The purpose of this article is to briefly report our experiences in conducting this program of applied research. The assessment strategy is presented in the first part of this report. Next, the methods used to collect data and assessment, sampling procedures and response rates are described. Following this, highlights of the assessment results are presented including a summary of some changes already made and those planned for the future. The results of this study are presented in detail in Adams, et at. (1994)
A Complete Catalog of Swift GRB Spectra and Durations: Demise of a Physical Origin for Pre-Swift High-Energy Correlations
We calculate durations and spectral paramaters for 218 Swift bursts detected
by the BAT instrument between and including GRBs 041220 and 070509, including
77 events with measured redshifts. Incorporating prior knowledge into the
spectral fits, we are able to measure the characteristic spectral
peak energy and the isotropic equivalent energy
(1-- keV) for all events. This complete and rather extensive catalog,
analyzed with a unified methodology, allows us to address the persistence and
origin of high-energy correlations suggested in pre-Swift observations. We find
that the - correlation is present in the Swift
sample; however, the best-fit powerlaw relation is inconsistent with the
best-fit pre-Swift relation at >5 sigma significance. Moreover, it has a factor
>~ 2 larger intrinsic scatter, after accounting for large errors on . A large fraction of the Swift events are hard and subluminous
relative to (and inconsistent with) the pre-Swift relation, in agreement with
indications from BATSE GRBs without redshift. Moreover, we determine an
experimental threshold for the BAT detector and show how the -- correlation arises artificially due to partial
correlation with the threshold. We show that pre-Swift correlations found by
Amati et al.(2002), Yonetoku et al. (2004), Firmani et al.(2006) (and
independently by others) are likely unrelated to the physical properties of
GRBs and are likely useless for tests of cosmology. Also, an explanation of
these correlations in terms of a detector threshold provides a natural and
quantitative explanation for why short-duration GRBs and events at low redshift
tend to be outliers to the correlations.Comment: 25 pages, 9 figures, 2 tables, Accepted to Ap
Biases in Virial Black Hole Masses: An SDSS Perspective
We compile black hole (BH) masses for quasars in the redshift
range included in the Fifth Data Release of the
Sloan Digital Sky Survey (SDSS), using virial BH mass estimators based on the
\hbeta, \MgII, and \CIV emission lines. We find that: (1) within our sample,
the widths of the three lines follow log-normal distributions, with means and
dispersions that do not depend strongly on luminosity or redshift;(2) the
\MgII- and \hbeta-estimated BH masses are consistent with one another; and (3)
the \CIV BH mass estimator may be more severely affected by a disk wind
component than the \MgII and \hbeta estimators, giving a positive bias in mass
correlated with the \CIV-\MgII blueshift. Most SDSS quasars have virial BH
masses in the range . There is a clear upper mass limit of
for active BHs at , decreasing at lower
redshifts. Making the reasonable assumptions that the underlying BH mass
distribution decreases with mass and that the Eddington ratio distribution at
fixed BH mass has non-zero width, we show that the measured virial BH mass
distribution and Eddington ratio distribution are subject to Malmquist bias. A
radio quasar subsample (with ) has mean virial BH
mass larger by dex than the whole sample. A broad absorption line
(BAL) quasar subsample (with ) has identical virial
mass distribution as the nonBAL sample, with no mean offset. (Abridged)Comment: Updated virial mass measurements; improved presentation of the MC
simulation; added new discussion sections; conclusions unchanged. The full
table1 is available at
http://www.astro.princeton.edu/~yshen/BH_mass/datafile1.txt.tar.g
Avoiding selection bias in gravitational wave astronomy
When searching for gravitational waves in the data from ground-based
gravitational wave detectors it is common to use a detection threshold to
reduce the number of background events which are unlikely to be the signals of
interest. However, imposing such a threshold will also discard some real
signals with low amplitude, which can potentially bias any inferences drawn
from the population of detected signals. We show how this selection bias is
naturally avoided by using the full information from the search, considering
both the selected data and our ignorance of the data that are thrown away, and
considering all relevant signal and noise models. This approach produces
unbiased estimates of parameters even in the presence of false alarms and
incomplete data. This can be seen as an extension of previous methods into the
high false rate regime where we are able to show that the quality of parameter
inference can be optimised by lowering thresholds and increasing the false
alarm rate.Comment: 13 pages, 2 figure
Real-time Analysis and Selection Biases in the Supernova Legacy Survey
The Supernova Legacy Survey (SNLS) has produced a high-quality, homogeneous
sample of Type Ia supernovae (SNe Ia) out to redshifts greater than z=1. In its
first four years of full operation (to June 2007), the SNLS discovered more
than 3000 transient candidates, 373 of which have been confirmed
spectroscopically as SNe Ia. Use of these SNe Ia in precision cosmology
critically depends on an analysis of the observational biases incurred in the
SNLS survey due to the incomplete sampling of the underlying SN Ia population.
This paper describes our real-time supernova detection and analysis procedures,
and uses detailed Monte Carlo simulations to examine the effects of Malmquist
bias and spectroscopic sampling. Such sampling effects are found to become
apparent at z~0.6, with a significant shift in the average magnitude of the
spectroscopically confirmed SN Ia sample towards brighter values for z>0.75. We
describe our approach to correct for these selection biases in our three-year
SNLS cosmological analysis (SNLS3), and present a breakdown of the systematic
uncertainties involved.Comment: Accepted for publication in A
Queers in quarantine: young LGBTQ+ people’s experiences during the COVID-19 pandemic in Sweden
The COVID-19 pandemic led to major restrictions of everyday life activities. This worsened the social situation of many people, and marginalised groups have been especially affected. This article explores how LGBTQ+ young adults in Sweden have been affected by the COVID-19 pandemic and the subsequent recommendations and restrictions. Fifteen participants between 20-29 years, who self-identified as LGBTQ+, were interviewed about their experiences. A thematic analysis of the data showed that the participants perceived their psychological wellbeing to have been greatly affected by the pandemic. Several reported symptoms of clinical depression, as well as anxiety, worry, rumination, and a heightened sensitivity to stress. Stressors included fear of the disease itself, and fear of spreading the virus, as well as the negative consequences of adhering to the recommendations of social distancing, which constantly interplayed with the marginalised position of being a young LGBTQ+ person. Most participants experienced a decrease in minority stress in face-to-face interaction with social distancing measures in place, but an increase in minority stress online. Those who faced minority stress at home experienced the isolation as particularly stressful. Limited access to the LGBTQ+ community was a common stressor. For transgender participants, the effects on transgender healthcare, such as prolonged waiting times for gender dysphoria assessment and hormone treatment, were a major challenge. Our results have added valuable knowledge to research indicating how vulnerable young adults were highly affected by the COVID-19 pandemic restrictions
An Unbiased Estimate of the Global Hubble Constant in the Region of Pisces-Perseus
We obtain an unbiased estimate of the global Hubble constant H0 in the volume
of cz<12000km/s in the region of Pisces-Perseus. The Tully-Fisher (TF) relation
is applied to a magnitude limited sample of 441 spirals selected from the
Arecibo 21cm catalog. The photometry data were calibrated with CCD observations
and we achieve 0.13mag for the photometric internal error. We use a maximum
likelihood method for the TF analysis. Monte-Carlo simulations demonstrate that
our method reproduces a given H0 at the 95% confidence level. By applying the
method to our sample galaxies, we obtain the unbiased global Hubble constant
H0=65+-2(+20,-14) km/s/Mpc; the first and the second terms represent the
internal random error and the external errors, respectively. We also find a
good agreement for our H0 with those recently obtained via Cepheid observation,
the TF relation and supernovae. Hubble velocities of the spirals inferred from
our H0 show no significant systematic difference from those given in the Mark
III catalog. The same analysis for H0 is carried out using r-band photometry
data of the Pisces-Perseus region given by Willick et al.(1997). We obtain a
global H0 which is consistent with that obtained from our B-band analysis. A
bulk motion in the Pisces-Perseus region is briefly discussed, based on our
calibration of H0. Our r-band TF analysis supports the notion of a coherent
streaming motion of the Pisces-Perseus ridge with -200km/s with respect to the
CMB, in agreement with most modern studies.Comment: 40 pages, 27 postscript figures, to appear in Ap.J. Figures are
included in the tex
Treading Water: Tools to Help US Coastal Communities Plan for Sea Level Rise Impacts
As communities grapple with rising seas and more frequent flooding events, they need improved projections of future rising and flooding over multiple time horizons, to assist in a multitude of planning efforts. There are currently a few different tools available that communities can use to plan, including the Sea Level Report Card and products generated by a United States. Federal interagency task force on sea level rise. These tools are a start, but it is recognized that they are not necessarily enough at present to provide communities with the type of information needed to support decisions that range from seasonal to decadal in nature, generally over relatively small geographic regions. The largest need seems to come from integrated models and tools. Agencies need to work with communities to develop tools that integrate several aspects (rainfall, tides, etc.) that affect their coastal flooding problems. They also need a formalized relationship with end users that allows agency products to be responsive to the various needs of managers and decision makers. Existing boundary organizations can be leveraged to meet this need. Focusing on addressing these needs will allow agencies to create robust solutions to flood risks, leading to truly resilient communities
The Ensemble Photometric Variability of ~25000 Quasars in the Sloan Digital Sky Survey
Using a sample of over 25000 spectroscopically confirmed quasars from the
Sloan Digital Sky Survey, we show how quasar variability in the rest frame
optical/UV regime depends upon rest frame time lag, luminosity, rest
wavelength, redshift, the presence of radio and X-ray emission, and the
presence of broad absorption line systems. The time dependence of variability
(the structure function) is well-fit by a single power law on timescales from
days to years. There is an anti-correlation of variability amplitude with rest
wavelength, and quasars are systematically bluer when brighter at all
redshifts. There is a strong anti-correlation of variability with quasar
luminosity. There is also a significant positive correlation of variability
amplitude with redshift, indicating evolution of the quasar population or the
variability mechanism. We parameterize all of these relationships. Quasars with
RASS X-ray detections are significantly more variable (at optical/UV
wavelengths) than those without, and radio loud quasars are marginally more
variable than their radio weak counterparts. We find no significant difference
in the variability of quasars with and without broad absorption line troughs.
Models involving multiple discrete events or gravitational microlensing are
unlikely by themselves to account for the data. So-called accretion disk
instability models are promising, but more quantitative predictions are needed.Comment: 41 pages, 21 figures, AASTeX, Accepted for publication in Ap
Starcounts Redivivus. IV. Density Laws Through Photometric Parallaxes
In an effort to more precisely define the spatial distribution of Galactic
field stars, we present an analysis of the photometric parallaxes of 70,000
stars covering nearly 15 square degrees in seven Kapteyn Selected Areas. We
address the affects of Malmquist Bias, subgiant/giant contamination,
metallicity and binary stars upon the derived density laws. The affect of
binary stars is the most significant. We find that while the disk-like
populations of the Milky Way are easily constrained in a simultaneous analysis
of all seven fields, no good simultaneous solution for the halo is found. We
have applied halo density laws taken from other studies and find that the
Besancon flattened power law halo model (c/a=0.6, r^-2.75) produces the best
fit to our data. With this halo, the thick disk has a scale height of 750 pc
with an 8.5% normalization to the old disk. The old disk scale height is
280-300 pc. Corrected for a binary fraction of 50%, these scale heights are 940
pc and 350-375 pc, respectively. Even with this model, there are systematic
discrepancies between the observed and predicted density distributions. Our
model produces density overpredictions in the inner Galaxy and density
underpredictions in the outer Galaxy. A possible solution is modeling the
stellar halo as a two-component system in which the halo has a flattened inner
distribution and a roughly spherical, but substructured outer distribution.
Further reconciliation could be provided by a flared thick disk, a structure
consistent with a merger origin for that population. (Abridged)Comment: 66 pages, accepted to Astrophysical journal, some figures compresse
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