3,464 research outputs found
Spitzer Observations of Gamma-Ray Burst Host Galaxies: A Unique Window into High Redshift Chemical Evolution and Star-formation
We present deep Spitzer 3.6 micron observations of three z~5 GRB host
galaxies. Our observations reveal that z~5 GRB hosts are a factor of 3 less
luminous than the median rest-frame V-band luminosity of spectroscopically
confirmed z~5 galaxies in the GOODS fields and the UDF. The strong connection
between GRBs and massive star formation implies that not all star-forming
galaxies at these redshifts are currently being accounted for in deep surveys
and GRBs provide a unique way to measure the contribution to the star-formation
rate density from galaxies at the faint end of the galaxy luminosity function.
By correlating the co-moving star-formation rate density with co-moving GRB
rates at lower redshifts, we estimate a lower limit to the star-formation rate
density of 0.12+/-0.09 and 0.09+/-0.05 M_sun/yr/Mpc^3 at z~4.5 and z~6,
respectively. Finally, we provide evidence that the average metallicity of
star-forming galaxies evolves as (stellar mass density)^(0.69+/-0.17) between
and , probably indicative of the loss of a significant
fraction of metals to the intergalactic medium, particularly in low-mass
galaxies.Comment: ApJ, in pres
Fault slip-rate variations during crustal-scale strain localisation, central Italy
Rates of plate motion are generally uniform over 10–102 Myrs timescales. Faults between tectonic plates might, therefore, be expected to show temporally-uniform slip-rates if the same number of faults remain active. For an extending region of the Eurasia-Africa plate boundary, Italy, finite throw values (vertical component of the slip) for seismogenic normal faults are less than that predicted when recent throw-rates are extrapolated over the fault lifetimes. The effect correlates with distance from the fault system tips and demonstrates that the slip-rates on centrally-located faults have increased with time. Neighbouring normal faults were active in the Quaternary but show no signs of surface faulting during the latest Pleistocene to Holocene. Death of these faults has provided the extra strain per unit time to drive the increased slip-rates measured on other faults. Thus, fault interaction and death modify slip-rates and seismic hazards associated with plate tectonics
Use of hospital services by age and comorbidity after an index heart failure admission in England: an observational study
© Published by the BMJ Publishing Group Limited.Objectives To describe hospital inpatient, emergency department (ED) and outpatient department (OPD) activity for patients in the year following their first emergency admission for heart failure (HF). To assess the proportion receiving specialist assessment within 2â €...weeks of hospital discharge, as now recommended by guidelines. Design Observational study of national administrative data. Setting All acute NHS hospitals in England. Participants 82â €...241 patients with an index emergency admission between April 2009 and March 2011 with a primary diagnosis of HF. Main outcome measures Cardiology OPD appointment within 2â €...weeks and within a year of discharge from the index admission; emergency department (ED) and inpatient use within a year. Results 15.1% died during the admission. Of the 69â €...848 survivors, 19.7% were readmitted within 30â €...days and half within a year, the majority for non-HF diagnoses. 6.7% returned to the ED within a week of discharge, of whom the majority (77.6%) were admitted. The two most common OPD specialties during the year were cardiology (24.7% of the total appointments) and anticoagulant services (12.5%). Although half of all patients had a cardiology appointment within a year, the proportion within the recommended 2â €...weeks of discharge was just 6.8% overall and varied by age, from 2.4% in those aged 90+ to 19.6% in those aged 18-45 (p<0.0001); appointments in other specialties made up only some of the shortfall. More comorbidity at any age was associated with higher rates of cardiology OPD follow-up. Conclusions Patients with HF are high users of hospital services. Postdischarge cardiology OPD follow-up rates fell well below current National Institute for Health and Care Excellence guidelines, particularly for the elderly and those with less comorbidity
Leveling the playing field: Exploiting technology to enhance tertiary learning
This paper reports on an on-going case study project to explore ICT/ eLearning across several disciplines and with students from diverse backgrounds at tertiary level in New Zealand. The project has been designed to address issues of tertiary-level pedagogy, epedagogy, and research with the goal of building eLearning capacity, leveraging pedagogical change, and closing participatory gaps for students and lecturers. Initial design decisions, the pedagogy that has informed the case studies, and the challenges and benefits of working across subjects and levels in a multi-disciplinary team are described. We also discuss research knowledge mobilization within our own instructional context and more broadly elsewhere
Evidence for a Gradual Decline in the Universal Rest-Frame UV Luminosity Density for z < 1
We have utilized various magnitude-limited samples drawn from an extremely
deep and highly complete spectroscopic redshift survey of galaxies observed in
seven colors in the Hawaii Survey Fields and the Hubble Deep Field to
investigate the evolution of the universal rest-frame ultraviolet luminosity
density from z = 1 to the present. The multi-color data (U', B, V, R, I, J,
HK') enable the sample selection to be made in the rest-frame ultraviolet for
the entire redshift range. Due to the large sample size and depth (U_{AB} =
24.75, B_{AB} = 24.75, I_{AB} = 23.5), we are able to accurately determine the
luminosity density to z = 1. We do not confirm the very steep evolution
reported by Lilly et al. (1996) but instead find a shallower slope,
approximately (1+z)^{1.5} for q0 = 0.5, which would imply that galaxy formation
is continuing smoothly to the present time rather than peaking at z = 1. Much
of the present formation is taking place in smaller galaxies. Detailed
comparisons with other recent determinations of the evolution are presented.Comment: 37 pages including 18 figures. Also available at
http://www.ifa.hawaii.edu/~acowie/uvlum.html To be published in the August,
1999 Astronomical Journal (accepted April 22, 1999
An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly
We present an integrated study of star formation and galactic stellar mass
assembly from z=0.05-1.5 and galactic metallicity evolution from z=0.05-0.9
using a very large and highly spectroscopically complete sample selected by
rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit
Bruzual & Charlot (2003) models to compute the galactic stellar masses and
extinctions. We determine the expected formed stellar mass density growth rates
produced by star formation and compare them with the growth rates measured from
the formed stellar mass functions by mass interval. We show that the growth
rates match if the IMF is slightly increased from the Salpeter IMF at
intermediate masses (~10 solar masses). We investigate the evolution of galaxy
color, spectral type, and morphology with mass and redshift and the evolution
of mass with environment. We find that applying extinction corrections is
critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the
green valley are 24um sources, but after correcting for extinction, the bulk of
the 24um sources lie in the blue cloud. We find an evolution of the
metallicity-mass relation corresponding to a decrease of 0.21+/-0.03 dex
between the local value and the value at z=0.77 in the 1e10-1e11 solar mass
range. We use the metallicity evolution to estimate the gas mass of the
galaxies, which we compare with the galactic stellar mass assembly and star
formation histories. Overall, our measurements are consistent with a galaxy
evolution process dominated by episodic bursts of star formation and where star
formation in the most massive galaxies (>1e11 solar masses) ceases at z<1.5
because of gas starvation. (Abstract abridged)Comment: 48 pages, Accepted by the Astrophysical Journa
Conceptual Frameworks for Multimodal Social Signal Processing
This special issue is about a research area which is developing rapidly. Pentland gave it a name which has become widely used, ‘Social Signal Processing’ (SSP for short), and his phrase provides the title of a European project, SSPnet, which has a brief to consolidate the area. The challenge that Pentland highlighted was understanding the nonlinguistic signals that serve as the basis for “subconscious discussions between humans about relationships, resources, risks, and rewards”. He identified it as an area where computational research had made interesting progress, and could usefully make more
Exponential Distributions in a Mechanical Model for Earthquakes
We study statistical distributions in a mechanical model for an earthquake
fault introduced by Burridge and Knopoff [R. Burridge and L. Knopoff, {\sl
Bull. Seismol. Soc. Am.} {\bf 57}, 341 (1967)]. Our investigations on the size
(moment), time duration and number of blocks involved in an event show that
exponential distributions are found in a given range of the paramenter space.
This occurs when the two kinds of springs present in the model have the same,
or approximately the same, value for the elastic constants. Exponential
distributions have also been seen recently in an experimental system to model
earthquake-like dynamics [M. A. Rubio and J. Galeano, {\sl Phys. Rev. E} {\bf
50}, 1000 (1994)].Comment: 11 pages, uuencoded (submitted to Phys. Rev. E
- …