733 research outputs found
Effect of Gravitational Lensing on Measurements of the Sunyaev-Zel'dovich Effect
The Sunyaev-Zel'dovich (SZ) effect of a cluster of galaxies is usually
measured after background radio sources are removed from the cluster field.
Gravitational lensing by the cluster potential leads to a systematic deficit in
the residual intensity of unresolved sources behind the cluster core relative
to a control field far from the cluster center. As a result, the measured
decrement in the Rayleigh-Jeans temperature of the cosmic microwave background
is overestimated. We calculate the associated systematic bias which is
inevitably introduced into measurements of the Hubble constant using the SZ
effect. For the cluster A2218, we find that observations at 15 GHz with a beam
radius of 0'.4 and a source removal threshold of 100 microJy underestimate the
Hubble constant by 6-10%. If the profile of the gas pressure declines more
steeply with radius than that of the dark matter density, then the ratio of
lensing to SZ decrements increases towards the outer part of the cluster.Comment: 11 pages, 3 figures, submitted to ApJ
Best-Bet Astrophysical Neutrino Sources
Likely astrophysical sources of detectable high-energy (>> TeV) neutrinos are
considered. Based on gamma-ray emission properties, the most probable sources
of neutrinos are argued to be GRBs, blazars, microquasars, and supernova
remnants. Diffuse neutrino sources are also briefly considered.Comment: 6 pages, 2 figures, in Proc. of TeV-Particle Astrophysics II,
Madison, WI, 28-31 Aug, 200
Effects of Dust on Gravitational Lensing by Spiral Galaxies
Gravitational lensing of an optical QSO by a spiral galaxy is often
counteracted by dust obscuration, since the line-of-sight to the QSO passes
close to the center of the galactic disk. The dust in the lens is likely to be
correlated with neutral hydrogen, which in turn should leave a Lyman-alpha
absorption signature on the QSO spectrum. We use the estimated dust-to-gas
ratio of the Milky-Way galaxy as a mean and allow a spread in its values to
calculate the effects of dust on lensing by low redshift spiral galaxies. Using
a no-evolution model for spirals at z<1 we find (in Lambda=0 cosmologies) that
the magnification bias due to lensing is stronger than dust obscuration for QSO
samples with a magnitude limit B<16. The density parameter of neutral hydrogen,
Omega_HI, is overestimated in such samples and is underestimated for fainter
QSOs.Comment: 18 pages, 4 figures, ApJ, in pres
Stellar black holes at the dawn of the universe
It is well established that between 380000 and 1 billion years after the Big
Bang the Inter Galactic Medium (IGM) underwent a "phase transformation" from
cold and fully neutral to warm (~10^4 K) and ionized. Whether this phase
transformation was fully driven and completed by photoionization by young hot
stars is a question of topical interest in cosmology. AIMS. We propose here
that besides the ultraviolet radiation from massive stars, feedback from
accreting black holes in high-mass X-ray binaries (BH-HMXBs) was an additional,
important source of heating and reionization of the IGM in regions of low gas
density at large distances from star-forming galaxies. METHODS. We use current
theoretical models on the formation and evolution of primitive massive stars of
low metallicity, and the observations of compact stellar remnants in the near
and distant universe, to infer that a significant fraction of the first
generations of massive stars end up as BH-HMXBs. The total number of energetic
ionizing photons from an accreting stellar black hole in an HMXB is comparable
to the total number of ionizing photons of its progenitor star. However, the
X-ray photons emitted by the accreting black hole are capable of producing
several secondary ionizations and the ionizing power of the resulting black
hole could be greater than that of its progenitor. Feedback by the large
populations of BH-HMXBs heats the IGM to temperatures of ~10^4 K and maintains
it ionized on large distance scales. BH-HMXBs determine the early thermal
history of the universe and mantain it as ionized over large volumes of space
in regions of low density. This has a direct impact on the properties of the
faintest galaxies at high redshifts, the smallest dwarf galaxies in the local
universe, and on the existing and future surveys at radio wavelengths of atomic
hydrogen in the early universe.Comment: 7 pages, 2 figures, accepted to be published in Astronomy and
Astrophysic
Variability in remission in family therapy for anorexia nervosa.
ObjectiveThe evolution toward more stringent conceptualizations of remission in family therapy for adolescent anorexia nervosa (AN) has, with time, introduced variability in outcomes across randomized controlled trials (RCTs). An examination of remission across the history of research on family therapy for AN shows that earlier studies adopted lenient definitions and generally yielded higher rates of remission than studies of the past decade that have used stricter definitions of remission. In this study, we investigate the reactivity of remission rates to the application of different definitions of remission used within the family therapy for AN literature, within a single RCT data set.MethodWe conducted a secondary analysis of data from a single-site RCT which compared the relative efficacy of two formats of family therapy in a sample of 106 Australian adolescents with AN. Using end-of-treatment data, we compared remission rates using 11 definitions of remission that have been used in studies of family therapy for AN spanning more than three decades.ResultsWe found wide variability in remission rates (21.7-87.7%; Cochran's Q Ï2 (10, N = 106) = 303.55, p = .000], depending on which definition of remission was applied. As expected, more lenient criteria produced higher remission rates than more stringent definitions.DiscussionApplying different criteria of remission to a single data set illustrates the impact of changing how remission is defined. Failure to consider the greater stringency of remission criteria in recent studies could result in false inferences concerning the efficacy of family therapy for AN over time
An Empirically-Calibrated Model For Interpreting the Evolution of Galaxies During the Reionization Era
[Abridged] We develop a simple star formation model whose goal is to
interpret the emerging body of observational data on star-forming galaxies at
z>~6. The efficiency and duty cycle of the star formation activity within dark
matter halos are determined by fitting the luminosity functions of Lya emitter
and Lyman-break galaxies at redshifts z~5-6. Using our model parameters we
predict the likely abundance of star forming galaxies at earlier epochs and
compare these to the emerging data in the redshift interval 7<z<10. We find
that the abundance of luminous Lyman-break galaxies in the 500 Myr between z~6
and 10 can be naturally explained by the hierarchical assembly of dark matter
haloes; there is only marginal evidence for strong physical evolution. In
contrast, the first estimates of the abundance of less luminous star forming
galaxies at z=9-10 are higher than predicted and, if verified by further data,
may suggest a top-heavy stellar mass function at these early epochs. Although
these abundances remain uncertain because of the difficulty of spectroscopic
confirmation and cosmic variance, even a modest improvement in survey
capability with present or upcoming facilities should yield great progress. In
this context, we use our model to consider those observational techniques that
hold the most promise and make predictions for specific surveys that are, or
will soon be, underway. We conclude that narrowband Lya emitter surveys should
be efficient on searches at z~7-8; however, such conventional surveys are
unlikely to detect sufficient galaxies at z~10 to provide useful constraints.
For this reason, gravitational lensing offers the best prospect for probing the
z~10 universe prior to JWST.Comment: 17 pages, 12 figures, submitted to Ap
Augmentative Approaches in FamilyâBased Treatment for Adolescents with Restrictive Eating Disorders: A Systematic Review
ObjectiveTo systematically review the literature reporting outcomes of augmentative familyâbased treatment (FBT) interventions for adolescents with restrictive eating disorders (EDs).MethodArticles were identified through a systematic search of five electronic databases (PsycINFO, MEDLINE, EMBASE, CINAHL, Cochrane Database).ResultsThirty articles were included, reporting on FBT augmentations featuring adjunctive treatment components, modified treatment structure and/or content with adherence to FBT principles, and adaptations allowing FBT delivery in different settings. All reported significant improvements in weight and/or ED symptoms at endâofâtreatment, although few compared augmentative and standard FBT interventions and good quality followâup data was generally lacking.ConclusionsThere is early evidence for the effectiveness of augmentative FBTâbased approaches in facilitating weight and/or ED symptom improvements for adolescents with restrictive EDs. There remains a lack of robust evidence demonstrating superior effects of such approaches over standard FBT, and further controlled studies are required to expand on the current evidence. Copyright © 2017 John Wiley & Sons, Ltd and Eating Disorders Association.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142429/1/erv2577.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142429/2/erv2577_am.pd
Polarised foreground removal at low radio frequencies using rotation measure synthesis: uncovering the signature of hydrogen reionisation
Measurement of redshifted 21-cm emission from neutral hydrogen promises to be
the most effective method for studying the reionisation history of hydrogen
and, indirectly, the first galaxies. These studies will be limited not by raw
sensitivity to the signal, but rather, by bright foreground radiation from
Galactic and extragalactic radio sources and the Galactic continuum. In
addition, leakage due to gain errors and non-ideal feeds conspire to further
contaminate low-frequency radio obsevations. This leakage leads to a portion of
the complex linear polarisation signal finding its way into Stokes I, and
inhibits the detection of the non-polarised cosmological signal from the epoch
of reionisation. In this work, we show that rotation measure synthesis can be
used to recover the signature of cosmic hydrogen reionisation in the presence
of contamination by polarised foregrounds. To achieve this, we apply the
rotation measure synthesis technique to the Stokes I component of a synthetic
data cube containing Galactic foreground emission, the effect of instrumental
polarisation leakage, and redshifted 21-cm emission by neutral hydrogen from
the epoch of reionisation. This produces an effective Stokes I Faraday
dispersion function for each line of sight, from which instrumental
polarisation leakage can be fitted and subtracted. Our results show that it is
possible to recover the signature of reionisation in its late stages (z ~ 7) by
way of the 21-cm power spectrum, as well as through tomographic imaging of
ionised cavities in the intergalactic medium.Comment: 22 pages including 11 figures. Minor revisions following referee's
report. MNRAS, in pres
B2 0902+34: A Collapsing Protogiant Elliptical Galaxy at z=3.4
We have used the visible integral-field replicable unit spectrograph
prototype (VIRUS-P), a new integral field spectrograph, to study the spatially
and spectrally resolved Lyman-alpha emission line structure in the radio galaxy
B2 0902+34 at z=3.4. We observe a halo of Lyman-alpha emission with a velocity
dispersion of 250 km/s extending to a radius of 50 kpc. A second feature is
revealed in a spatially resolved region where the line profile shows
blueshifted structure. This may be viewed as either HI absorption at -450 km/s
or secondary emission at -900 km/s from the primary peak. Our new data, in
combination with the 21 cm absorption, suggest two important and unexplained
discrepancies. First, nowhere in the line profiles of the Lyman-alpha halo is
the 21 cm absorber population evident. Second, the 21 cm absorption redshift is
higher than the Lyman-alpha emission redshift. In an effort to explain these
two traits, we have undertaken the first three dimensional Monte Carlo
simulations of resonant scattering in radio galaxies. Though simple, the model
produces the features in the Lyman-alpha data and predicts the 21 cm
properties. To reach agreement between this model and the data, global infall
of the HI is strictly necessary. The amount of gas necessary to match the model
and data is surprisingly high, >= 10E12 solar masses, an order of magnitude
larger than the stellar mass. The collapsing structure and large gas mass lead
us to interpret B2 0902+34 as a protogiant elliptical galaxy.Comment: 30 pages, 8 figures, 4 tables, accepted in Ap
A meta-analysis of the relation between therapeutic alliance and treatment outcome in eating disorders.
The therapeutic alliance has demonstrated an association with favorable psychotherapeutic outcomes in the treatment of eating disorders (EDs). However, questions remain about the inter-relationships between early alliance, early symptom improvement, and treatment outcome. We conducted a meta-analysis on the relations among these constructs, and possible moderators of these relations, in psychosocial treatments for EDs. Twenty studies met inclusion criteria and supplied sufficient supplementary data. Results revealed small-to-moderate effect sizes, ÎČsâ=â0.13 to 0.22 (pâ<â.05), indicating that early symptom improvement was related to subsequent alliance quality and that alliance ratings also were related to subsequent symptom reduction. The relationship between early alliance and treatment outcome was partially accounted for by early symptom improvement. With regard to moderators, early alliance showed weaker associations with outcome in therapies with a strong behavioral component relative to nonbehavioral therapies. However, alliance showed stronger relations to outcome for younger (vs. older) patients, over and above the variance shared with early symptom improvement. In sum, early symptom reduction enhances therapeutic alliance and treatment outcome in EDs, but early alliance may require specific attention for younger patients and for those receiving nonbehaviorally oriented treatments
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