6,983 research outputs found
Searching for high-redshift centimeter-wave continuum, line and maser emission using the Square Kilometer Array
We discuss the detection of redshifted line and continuum emission at radio
wavelengths using a Square Kilometer Array (SKA), specifically from
low-excitation rotational molecular line transitions of CO and HCN (molecular
lines), the recombination radiation from atomic transitions in almost-ionized
hydrogen (radio recombination lines; RRLs), OH and water maser lines, as well
as from synchrotron and free-free continuum radiation and HI 21-cm line
radiation. The detection of radio lines with the SKA offers the prospect to
determine the redshifts and thus exact luminosities for some of the most
distant and optically faint star-forming galaxies and active galactic nuclei
(AGN), even those galaxies that are either deeply enshrouded in interstellar
dust or shining prior to the end of reionization. Moreover, it provides an
opportunity to study the astrophysical conditions and resolved morphologies of
the most active regions in galaxies during the most active phase of star
formation at redshift z~2. A sufficiently powerful and adaptable SKA correlator
will enable wide-field three-dimensional redshift surveys at chosen specific
high redshifts, and will allow new probes of the evolution of large-scale
structure (LSS) in the distribution of galaxies. The detection of molecular
line radiation favours pushing the operating frequencies of SKA up to at least
26 GHz, and ideally to 40 GHz, while very high redshift maser emissions
requires access to about 100 MHz. To search for LSS the widest possible
instantaneous field of view would be advantageous.Comment: 12 pages, 2 figures. To appear in "Science with the Square Kilometer
Array," eds. C. Carilli and S. Rawlings, New Astronomy Reviews (Elsevier:
Amsterdam
On the X-ray Properties of OH Megamaser Sources: Chandra Snapshot Observations
We present Chandra snapshot observations for a sample of 7 sources selected
from the Arecibo OH megamaser (OHM) survey at z~0.13-0.22 and with far-infrared
luminosities in excess of 10^{11} L_sun. In contrast with the known H2O
megamasers, which are mostly associated with powerful Active Galactic Nuclei
(AGN), the situation is far less clear for OHMs, which have been poorly studied
in the X-ray band thus far. All of the observed sources are X-ray weak, with
only one OHM, IRAS FSC 03521+0028 (z=0.15), being detected by Chandra (with 5
counts). The results from this pilot program indicate that the X-ray emission,
with luminosities of less than ~10^{42} erg/s, is consistent with that from
star formation (as also suggested in some cases by the optical spectra) and
low-luminosity AGN emission. If an AGN is present, its contribution to the
broad-band emission of OHM galaxies is likely modest. Under reasonable
assumptions about the intrinsic X-ray spectral shape, the observed count
distribution from stacking analysis suggests absorption of ~10^{22} cm^{-2}.Comment: 8 pages, 3 figures, accepted for publication in MNRA
Military reliability: is the gain worth the cost?
Thesis (M.BA.)--Boston Universit
Undertaking a face to face Summative OSCE assessment during the COVID-19 Pandemic - a descriptive narrative
The 2020 Covid19 pandemic has caused significant disruption to medical education across the world. At the University of Sheffield final year medical students undertook a virtual OSCE via technology in order to graduate however for our Physician Associate course this was more problematic as following completion of the assessments at the university students are also required to pass a national examination with a formal Objective Structured Clinical Examination (OSCE). Due to this it was felt that it was crucial to run an OSCE examination for our students on a face to face basis but within the context of managing the potential safety and risks inherent in doing so.
This piece of work describes the process of running the examination including detail which we feel will be useful to others who may seek to undertake examinations for the same reason within the current health emergency or any future such events. It is important to note that some innovations we put in place with respect to technology enhancing safety will remain for future OSCE examinations in any circumstances
Draft Genome Sequence of Curtobacterium flaccumfaciens Strain UCD-AKU (Phylum Actinobacteria).
Here we present the draft genome of an actinobacterium, Curtobacterium flaccumfaciens strain UCD-AKU, isolated from a residential carpet. The genome assembly contains 3,692,614Â bp in 130 contigs. This is the first member of the Curtobacterium genus to be sequenced
Relaxation at late stages in an entropy barrier model for glassy systems
The ground state dynamics of an entropy barrier model proposed recently for
describing relaxation of glassy systems is considered. At stages of evolution
the dynamics can be described by a simple variant of the Ehrenfest urn model.
Analytical expression for the relaxation times from an arbitrary state to the
ground state is derived. Upper and lower bounds for the relaxation times as a
function of system size are obtained.Comment: 9 pages no figures. to appear in J.Phys. A: Math. and Ge
HI and OH absorption in the lensing galaxy of MG J0414+0534
We report the detection of \HI 21-cm absorption in the early-type
lensing galaxy towards MG J0414+0534 with the Green Bank Telescope. The
absorption, with total , is resolved into two strong components, probably due to the two
strongest lens components, which are separated by 0.4\arcsec. Unlike the other
three lenses which have been detected in \HI, J0414+0534 does not exhibit
strong OH absorption, giving a OH/\HI column density ratio of N_{\rm
OH}/N_{\rm HI}\lapp10^{-6} (for K, K and
). This underabundance of molecular gas may indicate
that the extreme optical--near-IR colour () along the line-of-sight
is not due to the lens. We therefore suggest that despite the strong upper
limits on molecular absorption at the quasar redshift, as traced by millimetre
lines, the extinction occurs primarily in the quasar host galaxy.Comment: Accepted by MNRAS Letters, 5 (and a bit) pages, 5 figure
High-dimensional quantum dynamics of adsorption and desorption of H at Cu(111)
We performed high-dimensional quantum dynamical calculations of the
dissociative adsorption and associative desorption of hydrogen on Cu(111). The
potential energy surface (PES) is obtained from density functional theory
calculations. Two regimes of dynamics are found, at low energies sticking is
determined by the minimum energy barrier, at high energies by the distribution
of barrier heights. Experimental results are well-reproduced qualitatively, but
some quantitative discrepancies are identified as well.Comment: 4 two column pages, revtex, 4 figures, to appear in Phys. Rev. Let
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