3,000 research outputs found
Evidence for Circumburst Extinction of Gamma-Ray Bursts with Dark Optical Afterglows and Evidence for a Molecular Cloud Origin of Gamma-Ray Bursts
First, we show that the gamma-ray bursts with dark optical afterglows (DOAs)
cannot be explained by a failure to image deeply enough quickly enough, and
argue that circumburst extinction is the most likely solution. If so, many DOAs
will be ``revived'' with rapid follow up and NIR searches in the HETE-2 and
Swift eras. Next, we consider the effects of dust sublimation and
fragmentation, and show that DOAs occur in clouds of size R > 10L_{49}^{1/2} pc
and mass M > 3x10^5L_{49} M_{sun}, where L is the luminosity of the optical
flash. Stability considerations show that such clouds cannot be diffuse, but
must be molecular. Consequently, we compute the expected column density
distribution of bursts that occur in Galactic-like molecular clouds, and show
that the column density measurements from X-ray spectra of afterglows, DOAs and
otherwise, satisfy this expectation in the source frame.Comment: Invited Review. To appear in Procs. of Gamma-Ray Burst and Afterglow
Astronomy 2001: A Workshop Celebrating the First Year of the HETE Mission, 8
pages, 8 figures, LaTe
Testing for Employee Discrimination in Britain using Matched Employer-Employee Data.
We use recent matched employer-employee data to directly test if white workers have a taste for racial discrimination in Britain. We formally introduce individual and firm heterogeneity into the discrimination model used by Becker (1957, 1971) which we extend to generate predictions consistent with an employee taste for discrimination. We argue firstly that white employees with a taste for discrimination should report lower levels of job satisfaction the larger the proportion of ethnic minorities at their workplace. Secondly, white employees would have to be compensated by higher wages if required to work alongside ethnic minority co-workers. Both hypotheses are clearly supported for white males in our data, after comprehensively controlling for individual, job, and workplace characteristics. The white male wage premium for working amongst only ethnic minority co-workers, as compared to working only with whites, is about 12%. Importantly, it appears that neither of these effects operates via realised racial prejudice at the workplace or white employees' feelings concerning their job security.Matched employer-employee data, discrimination, job satisfaction, compensating wage differentials
d1005+68: A New Faint Dwarf Galaxy in the M81 Group
We present the discovery of d1005+68, a new faint dwarf galaxy in the M81
Group, using observations taken with the Subaru Hyper Suprime-Cam. d1005+68's
color-magnitude diagram is consistent with a distance of
Mpc, establishing group membership. We derive an absolute -band magnitude,
from stellar isochrone fitting, of , with a
half-light radius of pc. These place d1005+68 within
the radius-luminosity locus of Local Group and M81 satellites and among the
faintest confirmed satellites outside the Local Group. Assuming an age of 12
Gyr, d1005+68's red giant branch is best fit by an isochrone of [Fe/H] . It has a projected separation from nearby M81 satellite BK5N of only
5 kpc. As this is well within BK5N's virial radius, we speculate that d1005+68
may be a satellite of BK5N. If confirmed, this would make d1005+68 one of the
first detected satellites-of-a-satellite.Comment: 7 pages, 4 figures, 1 table, additional affiliations include
Evidence for a Molecular Cloud Origin for Gamma-Ray Bursts: Implications for the Nature of Star Formation in the Universe
It appears that the majority of rapidly-, well-localized gamma-ray bursts
with undetected, or dark, optical afterglows, or `dark bursts' for short, occur
in clouds of size R > 10L_{49}^{1/2} pc and mass M > 3x10^5L_{49} M_{sun},
where L is the isotropic-equivalent peak luminosity of the optical flash. We
show that clouds of this size and mass cannot be modeled as a gas that is bound
by pressure equilibrium with a warm or hot phase of the interstellar medium
(i.e., a diffuse cloud): Such a cloud would be unstable to gravitational
collapse, resulting in the collapse and fragmentation of the cloud until a
burst of star formation re-establishes pressure equilibrium within the
fragments, and the fragments are bound by self-gravity (i.e., a molecular
cloud). Consequently, dark bursts probably occur in molecular clouds, in which
case dark bursts are probably a byproduct of this burst of star formation if
the molecular cloud formed recently, and/or the result of lingering or latter
generation star formation if the molecular cloud formed some time ago. We then
show that if bursts occur in Galactic-like molecular clouds, the column
densities of which might be universal, the number of dark bursts can be
comparable to the number of bursts with detected optical afterglows: This is
what is observed, which suggests that the bursts with detected optical
afterglows might also occur in molecular clouds. We confirm this by modeling
and constraining the distribution of column densities, measured from absorption
of the X-ray afterglow, of the bursts with detected optical afterglows: We find
that this distribution is consistent with the expectation for bursts that occur
in molecular clouds, and is not consistent with the expectation for bursts that
occur in diffuse clouds. More...Comment: Accepted to The Astrophysical Journal, 22 pages, 6 figures, LaTe
The Ursinus Weekly, December 3, 1909
Football number • Credit due coach • The scrubs • Football rules discussed • A review of the football season • Comment • Choral concert • Seminary notes • Personals • Latin-Maths and Math-Phys meet • Slonaker hurt • Football managers electedhttps://digitalcommons.ursinus.edu/weekly/2817/thumbnail.jp
Metabolite profiling of yam (Dioscorea spp.) accessions for use in crop improvement programmes
Article purchased; Published online: 14 Oct. 2017Introduction Ninety-seven percent of yam (Dioscorea spp.) production takes place in low income food deficit countries (LIFDCs) and the crop provides 200 calories a day to approximately 300 million people. Therefore, yams are vital for food security. Yams have high-yield potential and high market value potential yet current breeding of yam is hindered by a lack of genomic information and genetic resources. New tools are needed to modernise breeding strategies and unlock the potential of yam to improve livelihood
in LIFDCs.
Objectives Metabolomic screening has been undertaken on a diverse panel of Dioscorea accessions to assess the utility of the approach for advancing breeding strategies in this understudied crop. Methods Polar and lipophilic extracts from tubers of accessions from the global yam breeding program have been
comprehensively profiled via gas chromatography-mass spectrometry.
Results A visual pathway representation of the measured yam tuber metabolome has been delivered as a resource for biochemical evaluation of yam germplasm. Over 200 compounds were routinely measured in tubers, providing a major advance for the chemo-typing of this crop. Core biochemical redundancy concealed trends that were only elucidated following detailed mining of global metabolomics data. Combined analysis on leaf and tuber material identified a subset of metabolites which allow accurate species classification and highlighted the potential of predicting tuber composition from leaf profiles. Metabolic variation was accessionspecific
and often localised to compound classes, which will aid trait-targeting for metabolite markers.
Conclusions Metabolomics provides a standalone platform with potential to deliver near-future crop gains for yam. The approach compliments the genetic advancements currently underway and integration with other ‘–omics’ studies will deliver a significant advancement to yam breeding strategies
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