247 research outputs found
Large-Scale Distributed Bayesian Matrix Factorization using Stochastic Gradient MCMC
Despite having various attractive qualities such as high prediction accuracy
and the ability to quantify uncertainty and avoid over-fitting, Bayesian Matrix
Factorization has not been widely adopted because of the prohibitive cost of
inference. In this paper, we propose a scalable distributed Bayesian matrix
factorization algorithm using stochastic gradient MCMC. Our algorithm, based on
Distributed Stochastic Gradient Langevin Dynamics, can not only match the
prediction accuracy of standard MCMC methods like Gibbs sampling, but at the
same time is as fast and simple as stochastic gradient descent. In our
experiments, we show that our algorithm can achieve the same level of
prediction accuracy as Gibbs sampling an order of magnitude faster. We also
show that our method reduces the prediction error as fast as distributed
stochastic gradient descent, achieving a 4.1% improvement in RMSE for the
Netflix dataset and an 1.8% for the Yahoo music dataset
Family Medicine needs assessment: Studying the clinical work of general practitioners in Ethiopia
Background and Objective: Some universities in sub-Saharan Africa have initiated Family Medicine (FM) residency programs. This study was conducted by FM colleagues at Addis Ababa University (AAU) in Ethiopia and the University of Toronto, Canada to inform the FM residency curriculum at AAU. It was designed to determine the clinical problems that family physicians in Ethiopia may encounter.Methods: We used a mixed methods approach: Modified time-motion study and brief interviews. We observed 46 general practitioners (GPs) across ten sites in Ethiopia. Trained observers recorded time-motion data while GPs conducted their daily work. This data was supplemented by brief interviews with the GPs.Findings: Clinical encounters occupied 82% of GP work. The common symptoms were digestive-abdominal pain (21% visits), respiratory-cough (16%), and general-fever and chills (16%). The common diagnoses were infectious (22% visits), genitourinary (12%), circulatory (10%), and endocrine (10%). Challenges identified were lack of clinical resources (57% of GPs), difficulties in communication (48%) and excessive workload (33%). Most common requests were for information technology (78%) and HIV (46%) training.Conclusion: The profile of common symptoms and diagnoses indicated the competencies family physicians in the regions should have. This information will be used to develop an appropriate FM curriculum at AAU
On the evolution of environmental and mass properties of strong lens galaxies in COSMOS
Among the 100 strong lens candidates found in the COSMOS field, 20 with
redshifts in the range [0.34,1.13], feature multiple images of background
sources. Using the multi-wavelength coverage of the field and its spectroscopic
follow-up, we characterize the evolution with redshift of the environment and
of the dark-matter (DM) fraction of the lens galaxies. We present new redshift
of the strong lens candidates. The lens environment is characterized by the
projected 10 closest galaxies around each lens and by the number of galaxies
with a projected distance less than 1Mpc at the lens galaxy redshift. In both
cases, we perform similar measurements on a control sample of twin non-lens
early type galaxies (ETGs). In addition, we identify group members and field
galaxies in the X-ray and optical catalogs of galaxy groups. From those
catalogs, we measure the external shear contribution at the lens galaxy
positions. The systems are then modeled using a SIE plus the external shear due
to the groups. We observe that the average stellar mass of lens galaxies
increases with z and that the environment of lens galaxies is compatible with
that of the twins. During the lens modeling, we notice that, when let free, the
external shear points in a direction which is the mean direction of the
external shear due to groups and of the closest galaxy to the lens. We notice
that the DM fraction of the lens galaxies within the Einstein radius decreases
as the redshift increases. Given these, we conclude that, while the environment
of lens galaxies is compatible with that of non-lens ETGS, their mass
properties evolves significantly with redshift: it is still not clear whether
this advocates in favor of a stronger lensing bias toward massive objects at
high redshift or is simply representative of the high proportion of massive and
high stellar density galaxies at high redshift.Comment: Accepted for publication in A&A. Significant modifications in the
paper but similar conclusion
Clues from nearby galaxies to a better theory of cosmic evolution
The great advances in the network of cosmological tests show that the
relativistic Big Bang theory is a good description of our expanding universe.
But the properties of nearby galaxies that can be observed in greatest detail
suggest a still better theory would more rapidly gather matter into galaxies
and groups of galaxies. This happens in theoretical ideas now under discussion.Comment: published in Natur
THE VLT LEGA-C spectroscopic survey:the physics of galaxies at a lookback time of 7 Gyr
The Large Early Galaxy Census (LEGA-C) is a Public Spectroscopic Survey of ~3200 K-band selected galaxies at redshifts z = 0.6 − 1.0 with stellar masses , conducted with VIMOS on ESO's Very Large Telescope. The survey is embedded in the COSMOS field (R.A. = 10h00; ). The 20 hr long integrations produce high-signal-to-noise ratio continuum spectra that reveal ages, metallicities and velocity dispersions of the stellar populations. LEGA-C's unique combination of sample size and depth will enable us for the first time to map the stellar content at large lookback time, across galaxies of different types and star formation activity. Observations started in 2014 December and are planned to be completed by mid 2018, with early data releases of the spectra and value-added products. In this paper we present the science case, the observing strategy, an overview of the data reduction process and data products, and a first look at the relationship between galaxy structure and spectral properties, as it existed 7 Gyr ago
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Unveiling the nature of infrared bright, optically dark galaxies with early JWST data
Over the last few years, both Atacama Large Millimeter/submillimeter Array (ALMA) and Spitzer observations have revealed a population of likely massive galaxies at z \u3e 3 that was too faint to be detected inHubble Space Telescope(HST) rest-frame ultraviolet imaging. However, due to the very limited photometry for individual galaxies, the true nature of these so-called HST-dark galaxies has remained elusive. Here, we present the first sample of such galaxies observed with very deep, high-resolution NIRCam imaging from the Early Release Science programme CEERS. 30 HST-dark sources are selected based on their red colours across 1.6–4.4 μ role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; font-optical-sizing: inherit; font-kerning: inherit; font-feature-settings: inherit; font-variation-settings: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; text-wrap: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3eμ�m. Their physical properties are derived from 12-band multiwavelength photometry, including ancillary HST imaging. We find that these galaxies are generally heavily dust-obscured (AV ∼ 2 mag), massive (log (M/M⊙) ∼ 10), star-forming sources at z ∼ 2−8 with an observed surface density of ∼0.8 arcmin−2. This suggests that an important fraction of massive galaxies may have been missing from our cosmic census at z \u3e 3 all the way into the Epoch of Reionization. The HST-dark sources lie on the main sequence of galaxies and add an obscured star formation rate density of 3.2−1.3+1.8×10−3M⊙yr−1Mpc−3 role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; font-optical-sizing: inherit; font-kerning: inherit; font-feature-settings: inherit; font-variation-settings: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; text-wrap: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3e3.2+1.8−1.3×10−3M⊙yr−1Mpc−33.2−1.3+1.8×10−3M⊙yr−1Mpc−3 at z ∼ 7, showing likely presence of dust in the Epoch of Reionization. Our analysis shows the unique power of JWST to reveal this previously missing galaxy population and to provide a more complete census of galaxies at z = 2−8 based on rest-frame optical imaging
Using social reproduction theory to understand unfree labour
Most scholarship within social reproduction theory focuses on women’s paid and unpaid care and domestic work, typically within the global North. Rarely has social reproduction theory grappled with unfree labour in commodity supply chains, particularly in the global South. However, these labour relations also involve gendered power relations that cut across the productive and reproductive realms of the economy, which can be illuminated by social reproduction theory analysis. In this article, we reflect on how social reproduction theory can be used to make sense of unfree labour’s role in global supply chains, expanding its geographical scope and the forms of labour exploitation encompassed within it. Conceptually, we harness the insights of social reproduction theory, and Jeffrey Harrod and Robert W Cox’s work on ‘unprotected work’ in the global economy to examine how gendered power relations shape patterns of unfree labour. Empirically, we analyse interview and survey data collected among cocoa workers in Ghana through LeBaron’s Global Business of Forced Labour project. We argue that social reproduction theory can move global supply chain scholarship beyond its presently economistic emphasis on the productive sphere and can shed light into the overlaps between social oppression, economic exploitation, and social reproduction
CANDELS Observations of the Structural Properties and Evolution of Galaxies in a Cluster at z=1.62
We discuss the structural and morphological properties of galaxies in a
z=1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope
Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic
Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology
relation: galaxies with colors of quiescent stellar populations generally have
morphologies consistent with spheroids, and galaxies with colors consistent
with ongoing star formation have disk-like and irregular morphologies. The size
distribution of the quiescent cluster galaxies shows a deficit of compact (<
1kpc), massive galaxies compared to CANDELS field galaxies at z=1.6. As a
result the cluster quiescent galaxies have larger average effective sizes
compared to field galaxies at fixed mass at greater than 90% significance.
Combined with data from the literature, the size evolution of quiescent cluster
galaxies is relatively slow from z~1.6 to the present, growing as
(1+z)^(-0.6+/-0.1). If this result is generalizable, then it implies that
physical processes associated with the denser cluster region seems to have
caused accelerated size growth in quiescent galaxies prior to z=1.6 and slower
subsequent growth at z<1.6 compared to galaxies in the lower density field. The
quiescent cluster galaxies at z=1.6 have higher ellipticities compared to lower
redshift samples at fixed mass, and their surface-brightness profiles suggest
that they contain extended stellar disks. We argue the cluster galaxies require
dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk
material and to match the relations for ellipticity, stellar mass, size, and
color of early-type galaxies in z<1 clusters.Comment: Accepted for publication in ApJ. 14 pages in emulateapj format.
Replacement includes improvements from referee report, and updates and
additions to reference
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