1,045 research outputs found
The Imprint of Gravitational Waves on the Cosmic Microwave Background
Long-wavelength gravitational waves can induce significant temperature
anisotropy in the cosmic microwave background. Distinguishing this from
anisotropy induced by energy density fluctuations is critical for testing
inflationary cosmology and theories of large-scale structure formation. We
describe full radiative transport calculations of the two contributions and
show that they differ dramatically at angular scales below a few degrees. We
show how anisotropy experiments probing large- and small-angular scales can
combine to distinguish the imprint due to gravitational waves.Comment: 11 pages, Penn Preprint-UPR-
The Doppler Peaks from Cosmic Texture
We compute the angular power spectrum of temperature anisotropies on the
microwave sky in the cosmic texture theory, with standard recombination
assumed. The spectrum shows `Doppler' peaks analogous to those in scenarios
based on primordial adiabatic fluctuations such as `standard CDM', but at quite
different angular scales. There appear to be excellent prospects for using this
as a discriminant between inflationary and cosmic defect theories.Comment: 14 pages, latex, 3 figures, compressed and uuencoded, replaced
version has minor typographical correction
FIRST J102347.6+003841: The First Radio-Selected Cataclysmic Variable
We have identified the 1.4 GHz radio source FIRST J102347.6+003841 (hereafter
FIRST J1023+0038) with a previously unknown 17th-mag Galactic cataclysmic
variable (CV). The optical spectrum resembles that of a magnetic (AM Herculis-
or DQ Herculis-type) CV. Five nights of optical CCD photometry showed
variations on timescales of minutes to hours, along with rapid flickering. A
re-examination of the FIRST radio survey data reveals that the radio detection
was based on a single 6.6 mJy flare; on two other occasions the source was
below the ~1 mJy survey limit. Several other magnetic CVs are known to be
variable radio sources, suggesting that FIRST J1023+0038 is a new member of
this class (and the first CV to be discovered on the basis of radio emission).
However, FIRST J1023+0038 is several optical magnitudes fainter than the other
radio-detected magnetic CVs. It remains unclear whether the source simply had a
very rare and extraordinarily intense radio flare at the time of the FIRST
observation, or is really an unusually radio-luminous CV; thus further
observations are urged.Comment: 4 pages, 3 figures; accepted for December 2002 issue of Publications
of the Astronomical Society of the Pacifi
SPIRITS 16tn in NGC 3556: A heavily obscured and low-luminosity supernova at 8.8 Mpc
We present the discovery by the SPitzer InfraRed Intensive Transients Survey
(SPIRITS) of a likely supernova (SN) in NGC 3556 at only 8.8 Mpc, which,
despite its proximity, was not detected by optical searches. A luminous
infrared (IR) transient at mag (Vega), SPIRITS 16tn is
coincident with a dust lane in the inclined, star-forming disk of the host.
Using IR, optical, and radio observations, we attempt to determine the nature
of this event. We estimate 8 - 9 mag of extinction, placing it
among the three most highly obscured IR-discovered SNe to date. The [4.5] light
curve declined at a rate of 0.013 mag day, and the color
grew redder from 0.7 to 1.0 mag by 184.7 days post discovery.
Optical/IR spectroscopy shows a red continuum, but no clearly discernible
features, preventing a definitive spectroscopic classification. Deep radio
observations constrain the radio luminosity of SPIRITS 16tn to erg s Hz between 3 - 15 GHz, excluding many
varieties of radio core-collapse SNe. A type Ia SN is ruled out by the observed
red IR color, and lack of features normally attributed to Fe-peak elements in
the optical and IR spectra. SPIRITS 16tn was fainter at [4.5] than typical
stripped-envelope SNe by 1 mag. Comparison of the spectral energy
distribution to SNe II suggests SPIRITS 16tn was both highly obscured, and
intrinsically dim, possibly akin to the low-luminosity SN 2005cs. We infer the
presence of an IR dust echo powered by a peak luminosity of the transient of erg s erg s,
consistent with the observed range for SNe II. This discovery illustrates the
power of IR surveys to overcome the compounding effects of visible extinction
and optically sub-luminous events in completing the inventory of nearby SNe.Comment: 25 pages, 10 figures, submitted to Ap
A Serendipitous Galaxy Cluster Survey with XMM: Expected Catalogue Properties and Scientific Applications
This paper describes a serendipitous galaxy cluster survey that we plan to
conduct with the XMM X-ray satellite. We have modeled the expected properties
of such a survey for three different cosmological models, using an extended
Press-Schechter (Press & Schechter 1974) formalism, combined with a detailed
characterization of the expected capabilities of the EPIC camera on board XMM.
We estimate that, over the ten year design lifetime of XMM, the EPIC camera
will image a total of ~800 square degrees in fields suitable for the
serendipitous detection of clusters of galaxies. For the presently-favored
low-density model with a cosmological constant, our simulations predict that
this survey area would yield a catalogue of more than 8000 clusters, ranging
from poor to very rich systems, with around 750 detections above z=1. A
low-density open Universe yields similar numbers, though with a different
redshift distribution, while a critical-density Universe gives considerably
fewer clusters. This dependence of catalogue properties on cosmology means that
the proposed survey will place strong constraints on the values of Omega-Matter
and Omega-Lambda. The survey would also facilitate a variety of follow-up
projects, including the quantification of evolution in the cluster X-ray
luminosity-temperature relation, the study of high-redshift galaxies via
gravitational lensing, follow-up observations of the Sunyaev-Zel'dovich effect
and foreground analyses of cosmic microwave background maps.Comment: Accepted to ApJ. Minor changes, e.g. presentation of temperature
errors as a figure (rather than as a table). Latex (20 pages, 6 figures, uses
emulateapj.sty
Sea surface temperature changes in the southern California borderlands during the last glacial-interglacial cycle
A variety of evidence suggests that average sea surface temperatures (SSTs) during the last glacial maximum in the California Borderlands region were significantly colder than during the Holocene. Planktonic foraminiferal δ18O evidence and average SST estimates derived by the modern analog technique indicate that temperatures were 6°-10°C cooler during the last glacial relative to the present. The glacial plankton assemblage is dominated by the planktonic foraminifer Neogloboquadrina pachyderma (sinistral coiling) and the coccolith Coccolithus pelagicus, both of which are currently restricted to subpolar regions of the North Pacific. The glacial-interglacial average SST change determined in this study is considerably larger than the 2°C change estimated by Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) [1981]. We propose that a strengthened California Current flow was associated with the advance of subpolar surface waters into the Borderlands region during the last glacial
Evidence-based decision support for pediatric rheumatology reduces diagnostic errors.
BACKGROUND: The number of trained specialists world-wide is insufficient to serve all children with pediatric rheumatologic disorders, even in the countries with robust medical resources. We evaluated the potential of diagnostic decision support software (DDSS) to alleviate this shortage by assessing the ability of such software to improve the diagnostic accuracy of non-specialists.
METHODS: Using vignettes of actual clinical cases, clinician testers generated a differential diagnosis before and after using diagnostic decision support software. The evaluation used the SimulConsult® DDSS tool, based on Bayesian pattern matching with temporal onset of each finding in each disease. The tool covered 5405 diseases (averaging 22 findings per disease). Rheumatology content in the database was developed using both primary references and textbooks. The frequency, timing, age of onset and age of disappearance of findings, as well as their incidence, treatability, and heritability were taken into account in order to guide diagnostic decision making. These capabilities allowed key information such as pertinent negatives and evolution over time to be used in the computations. Efficacy was measured by comparing whether the correct condition was included in the differential diagnosis generated by clinicians before using the software ( unaided ), versus after use of the DDSS ( aided ).
RESULTS: The 26 clinicians demonstrated a significant reduction in diagnostic errors following introduction of the software, from 28% errors while unaided to 15% using decision support (p \u3c 0.0001). Improvement was greatest for emergency medicine physicians (p = 0.013) and clinicians in practice for less than 10 years (p = 0.012). This error reduction occurred despite the fact that testers employed an open book approach to generate their initial lists of potential diagnoses, spending an average of 8.6 min using printed and electronic sources of medical information before using the diagnostic software.
CONCLUSIONS: These findings suggest that decision support can reduce diagnostic errors and improve use of relevant information by generalists. Such assistance could potentially help relieve the shortage of experts in pediatric rheumatology and similarly underserved specialties by improving generalists\u27 ability to evaluate and diagnose patients presenting with musculoskeletal complaints.
TRIAL REGISTRATION: ClinicalTrials.gov ID: NCT02205086
Hubble Space Telescope Imaging of Lyman Alpha Emission at z=4.4
We present the highest redshift detections of resolved Lyman alpha emission,
using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in
parallel with the Wide Field Camera 3 Early Release Science program in the
GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically
confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the
sample of LAEs with resolved Lyman alpha emission. Comparing the light
distribution between the rest-frame ultraviolet continuum and narrowband
images, we investigate the escape of Lyman alpha photons at high redshift.
While our data do not support a positional offset between the Lyman alpha and
rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out
of the three galaxies are significantly larger in Lyman alpha than in the
rest-frame UV continuum. This result is confirmed when comparing object sizes
in a stack of all objects in both bands. Additionally, the narrowband flux
detected with HST is significantly less than observed in similar filters from
the ground. These results together imply that the Lyman alpha emission is not
strictly confined to its indigenous star-forming regions. Rather, the Lyman
alpha emission is more extended, with the missing HST flux likely existing in a
diffuse outer halo. This suggests that the radiative transfer of Lyman alpha
photons in high-redshift LAEs is complicated, with the interstellar-medium
geometry and/or outflows playing a significant role in galaxies at these
redshifts.Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figure
Open education and critical pedagogy
This paper argues for a revaluation of the potential of open education to support more critical forms of pedagogy. Section I examines contemporary discourses around open education, offering a commentary on the perception of openness as both a disruptive force in education, and a potential solution to contemporary challenges. Section II examines the implications of the lack of consensus around what it means to be open, focusing on the example of commercial and proprietary claims to openness commonly known as ‘openwashing’. Section III uses Raymond’s influential essay on open source software ‘The Cathedral and the Bazaar’ as a framework for thinking through these issues, and about alternative power structures in open education. In Section IV an explicit link is drawn between more equal or democratic power structures and the possibility for developing pedagogies which are critical and reflexive, providing examples which show how certain interpretations of openness can raise opportunities to support critical approaches to pedagogy
New Hubble Space Telescope Discoveries of Type Ia Supernovae at z > 1: Narrowing Constraints on the Early Behavior of Dark Energy
We have discovered 21 new Type Ia supernovae (SNe Ia) with the Hubble Space
Telescope (HST) and have used them to trace the history of cosmic expansion
over the last 10 billion years. These objects, which include 13
spectroscopically confirmed SNe Ia at z > 1, were discovered during 14 epochs
of reimaging of the GOODS fields North and South over two years with the
Advanced Camera for Surveys on HST. Together with a recalibration of our
previous HST-discovered SNe Ia, the full sample of 23 SNe Ia at z > 1 provides
the highest-redshift sample known. Combined with previous SN Ia datasets, we
measured H(z) at discrete, uncorrelated epochs, reducing the uncertainty of
H(z>1) from 50% to under 20%, strengthening the evidence for a cosmic jerk--the
transition from deceleration in the past to acceleration in the present. The
unique leverage of the HST high-redshift SNe Ia provides the first meaningful
constraint on the dark energy equation-of-state parameter at z >1.
The result remains consistent with a cosmological constant (w(z)=-1), and
rules out rapidly evolving dark energy (dw/dz >>1). The defining property of
dark energy, its negative pressure, appears to be present at z>1, in the epoch
preceding acceleration, with ~98% confidence in our primary fit. Moreover, the
z>1 sample-averaged spectral energy distribution is consistent with that of the
typical SN Ia over the last 10 Gyr, indicating that any spectral evolution of
the properties of SNe Ia with redshift is still below our detection threshold.Comment: typos, references corrected, minor additions to exposition 82 pages,
17 figures, 6 tables. Data also available at:
http://braeburn.pha.jhu.edu/~ariess/R06. Accepted, Astrophysical Journal vol.
656 for March 10, 200
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