97 research outputs found
Time, trade and identity : bone and antler combs in Northern Britain c.AD 700-1400
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
An Increasing Stellar Baryon Fraction in Bright Galaxies at High Redshift
Recent observations have shown that the characteristic luminosity of the
rest-frame ultraviolet (UV) luminosity function does not significantly evolve
at 4 < z < 7 and is approximately M*_UV ~ -21. We investigate this apparent
non-evolution by examining a sample of 178 bright, M_UV < -21 galaxies at z=4
to 7, analyzing their stellar populations and host halo masses. Including deep
Spitzer/IRAC imaging to constrain the rest-frame optical light, we find that
M*_UV galaxies at z=4-7 have similar stellar masses of log(M/Msol)=9.6-9.9 and
are thus relatively massive for these high redshifts. However, bright galaxies
at z=4-7 are less massive and have younger inferred ages than similarly bright
galaxies at z=2-3, even though the two populations have similar star formation
rates and levels of dust attenuation. We match the abundances of these bright
z=4-7 galaxies to halo mass functions from the Bolshoi Lambda-CDM simulation to
estimate the halo masses. We find that the typical halo masses in ~M*_UV
galaxies decrease from log(M_h/Msol)=11.9 at z=4 to log(M_h/Msol)=11.4 at z=7.
Thus, although we are studying galaxies at a similar mass across multiple
redshifts, these galaxies live in lower mass halos at higher redshift. The
stellar baryon fraction in units of the cosmic mean Omega_b/Omega_m rises from
5.1% at z=4 to 11.7% at z=7; this evolution is significant at the ~3-sigma
level. This rise does not agree with simple expectations of how galaxies grow,
and implies that some effect, perhaps a diminishing efficiency of feedback, is
allowing a higher fraction of available baryons to be converted into stars at
high redshifts.Comment: Accepted to ApJ. 15 pages, 5 figures, 6 table
The Evolution of the Galaxy Stellar Mass Function at z= 4-8: A Steepening Low-mass-end Slope with Increasing Redshift
We present galaxy stellar mass functions (GSMFs) at 4-8 from a
rest-frame ultraviolet (UV) selected sample of 4500 galaxies, found via
photometric redshifts over an area of 280 arcmin in the CANDELS/GOODS
fields and the Hubble Ultra Deep Field. The deepest Spitzer/IRAC data
yet-to-date and the relatively large volume allow us to place a better
constraint at both the low- and high-mass ends of the GSMFs compared to
previous space-based studies from pre-CANDELS observations. Supplemented by a
stacking analysis, we find a linear correlation between the rest-frame UV
absolute magnitude at 1500 \AA\ () and logarithmic stellar mass
() that holds for galaxies with . We
use simulations to validate our method of measuring the slope of the - relation, finding that the bias is minimized with a hybrid
technique combining photometry of individual bright galaxies with stacked
photometry for faint galaxies. The resultant measured slopes do not
significantly evolve over 4-8, while the normalization of the trend
exhibits a weak evolution toward lower masses at higher redshift. We combine
the - distribution with observed rest-frame UV luminosity
functions at each redshift to derive the GSMFs, finding that the low-mass-end
slope becomes steeper with increasing redshift from
at to at
. The inferred stellar mass density, when integrated over
-, increases by a factor of
between and and is in good agreement with the time integral of the
cosmic star formation rate density.Comment: 27 pages, 17 figures, ApJ, in pres
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Clustering of Red Galaxies around the Z = 1.53 Quasar 3C 270.1
In the paradigm of hierarchical galaxy formation, luminous radio galaxies mark mass assembly peaks that should contain clusters of galaxies. Observations of the z = 1.53 quasar 3C 270.1 with the Spitzer Space Telescope at 3.6–24 μm and with the 6.5 m MMT in the z and Y bands allow the detection of potential cluster members via photometric redshifts. Compared with nearby control fields, there is an excess of ∼11 extremely red objects (EROs) at 1.33 zphot 1.73, consistent with a protocluster around the quasar. The spectral energy distributions of 3/4 of the EROs are better fitted with passive elliptical galaxies than with dust-reddened starbursts, and of four sources well detected on an archival Hubble Space Telescope (HST) snapshot image, all have undisturbed morphologies. However, one ERO, not covered by the HST image, is a double source with 0.8 separation on the z image and a marginal (2σ) 24 μm detection indicating a dust-enshrouded starburst. The EROs are more luminous than L (H = −23.6 AB mag at z ≈ 1.5).Astronom
The Science Case for an Extended Spitzer Mission
Although the final observations of the Spitzer Warm Mission are currently
scheduled for March 2019, it can continue operations through the end of the
decade with no loss of photometric precision. As we will show, there is a
strong science case for extending the current Warm Mission to December 2020.
Spitzer has already made major impacts in the fields of exoplanets (including
microlensing events), characterizing near Earth objects, enhancing our
knowledge of nearby stars and brown dwarfs, understanding the properties and
structure of our Milky Way galaxy, and deep wide-field extragalactic surveys to
study galaxy birth and evolution. By extending Spitzer through 2020, it can
continue to make ground-breaking discoveries in those fields, and provide
crucial support to the NASA flagship missions JWST and WFIRST, as well as the
upcoming TESS mission, and it will complement ground-based observations by LSST
and the new large telescopes of the next decade. This scientific program
addresses NASA's Science Mission Directive's objectives in astrophysics, which
include discovering how the universe works, exploring how it began and evolved,
and searching for life on planets around other stars.Comment: 75 pages. See page 3 for Table of Contents and page 4 for Executive
Summar
Building demand-led and gender-responsive breeding programs
Gender-responsive breeding is a new approach to making sure modern breeding takes advantage of opportunities to improve gender equality in agriculture. Conventional research on the acceptability of modern varieties has scarcely addressed gender differences during adoption studies. Gender-responsive breeding starts from a different premise that adoption and social impact will be enhanced if gender is addressed at early stages of variety design and priority setting in breeding. However, until recently, there was no concrete way to integrate gender considerations into the practice of breeding. This chapter draws lessons for the future from three RTB breeding programs innovating with gender-responsive breeding with a focus on piloting novel tools. The new G+ tools are designed to help gender researchers and breeders make joint, evidence-based decisions about the significance of gender differences for customer targeting and trait prioritization in variety development. Their piloting in the context of each program’s practice of gender-responsive breeding throws light on some valuable good practices that contributed to successful innovation
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The adaptive designs CONSORT extension (ACE) statement: a checklist with explanation and elaboration guideline for reporting randomised trials that use an adaptive design
Abstract: Adaptive designs (ADs) allow pre-planned changes to an ongoing trial without compromising the validity of conclusions and it is essential to distinguish pre-planned from unplanned changes that may also occur. The reporting of ADs in randomised trials is inconsistent and needs improving. Incompletely reported AD randomised trials are difficult to reproduce and are hard to interpret and synthesise. This consequently hampers their ability to inform practice as well as future research and contributes to research waste. Better transparency and adequate reporting will enable the potential benefits of ADs to be realised. This extension to the Consolidated Standards Of Reporting Trials (CONSORT) 2010 statement was developed to enhance the reporting of randomised AD clinical trials. We developed an Adaptive designs CONSORT Extension (ACE) guideline through a two-stage Delphi process with input from multidisciplinary key stakeholders in clinical trials research in the public and private sectors from 21 countries, followed by a consensus meeting. Members of the CONSORT Group were involved during the development process. The paper presents the ACE checklists for AD randomised trial reports and abstracts, as well as an explanation with examples to aid the application of the guideline. The ACE checklist comprises seven new items, nine modified items, six unchanged items for which additional explanatory text clarifies further considerations for ADs, and 20 unchanged items not requiring further explanatory text. The ACE abstract checklist has one new item, one modified item, one unchanged item with additional explanatory text for ADs, and 15 unchanged items not requiring further explanatory text. The intention is to enhance transparency and improve reporting of AD randomised trials to improve the interpretability of their results and reproducibility of their methods, results and inference. We also hope indirectly to facilitate the much-needed knowledge transfer of innovative trial designs to maximise their potential benefits. In order to encourage its wide dissemination this article is freely accessible on the BMJ and Trials journal websites.“To maximise the benefit to society, you need to not just do research but do it well” Douglas G Altma
The Evolution of the Galaxy Rest-Frame Ultraviolet Luminosity Function Over the First Two Billion Years
We present a robust measurement and analysis of the rest-frame ultraviolet
(UV) luminosity function at z=4-8. We use deep Hubble Space Telescope imaging
over the CANDELS/GOODS fields, the Hubble Ultra Deep Field and the Year 1
Hubble Frontier Field deep parallel observations. These surveys provides an
effective volume of 0.6-1.2 x 10^6 Mpc^3 over this epoch, allowing us to
perform a robust search for faint (M_UV=-18) and bright (M_UV < -21) galaxies.
We select candidate galaxies using a well-tested photometric redshift technique
with careful screening of contaminants, finding a sample of 7446 galaxies at
3.51000 galaxies at z~6-8. We measure the luminosity function
using a Markov Chain Monte Carlo analysis to measure robust uncertainties. At
the faint end our results agree with previous studies, yet we find a higher
abundance of UV-bright galaxies at z>6, with M* ~ -21 at z>5, different than
that inferred based on previous trends at lower redshift. At z=8, a single
power-law provides an equally good fit to the UV luminosity function, while at
z=6 and 7, an exponential cutoff at the bright-end is moderately preferred. We
compare to semi-analytical models, and find that the lack of evolution in M* is
consistent with models where the impact of dust attenuation on the bright-end
of the luminosity function decreases at higher redshift. We measure the
evolution of the cosmic star-formation rate density, correcting for dust
attenuation, and find that it declines as (1+z)^(-4.3 +/- 0.5) at z>4,
consistent with observations at z>9. Our observations are consistent with a
reionization history that starts at z>10, completes at z>6, and reaches a
midpoint (x_HII = 0.5) at 6.7<z<9.4. Finally, our observations predict that the
abundance of bright z=9 galaxies is likely higher than previous constraints,
though consistent with recent estimates of bright z~10 galaxies. [abridged]Comment: Re-submitted to the Astrophysical Journal after first referee's
report. 34 pages, 21 figures, 7 tables. The source file includes a machine
readable table of our full galaxy sampl
Situational awareness within objective structured clinical examination stations in undergraduate medical training - a literature search
Background: Medical students may not be able to identify the essential elements of situational awareness (SA) necessary for clinical reasoning. Recent studies suggest that students have little insight into cognitive processing and SA in clinical scenarios. Objective Structured Clinical Examinations (OSCEs) could be used to assess certain elements of situational awareness. The purpose of this paper is to review the literature with a view to identifying whether levels of SA based on Endsley's model can be assessed utilising OSCEs during undergraduate medical training. Methods: A systematic search was performed pertaining to SA and OSCEs, to identify studies published between January 1975 (first paper describing an OSCE) and February 2017, in peer reviewed international journals published in English. PUBMED, EMBASE, PsycINFO Ovid and SCOPUS were searched for papers that described the assessment of SA using OSCEs among undergraduate medical students. Key search terms included "objective structured clinical examination", "objective structured clinical assessment" or "OSCE" and "non-technical skills", "sense-making", "clinical reasoning", "perception", "comprehension", "projection", "situation awareness", "situational awareness" and "situation assessment". Boolean operators (AND, OR) were used as conjunctions to narrow the search strategy, resulting in the limitation of papers relevant to the research interest. Areas of interest were elements of SA that can be assessed by these examinations. Results: The initial search of the literature retrieved 1127 publications. Upon removal of duplicates and papers relating to nursing, paramedical disciplines, pharmacy and veterinary education by title, abstract or full text, 11 articles were eligible for inclusion as related to the assessment of elements of SA in undergraduate medical students. Discussion: Review of the literature suggests that whole-task OSCEs enable the evaluation of SA associated with clinical reasoning skills. If they address the levels of SA, these OSCEs can provide supportive feedback and strengthen educational measures associated with higher diagnostic accuracy and reasoning abilities. Conclusion: Based on the findings, the early exposure of medical students to SA is recommended, utilising OSCEs to evaluate and facilitate SA in dynamic environment
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