13,297 research outputs found
Lensed Arcs and Inner Structure of Abell 697
We present new optical observations of the z=0.282 cluster Abell 697 from the
Keck II telescope. Images show an unusual disturbed structure in the cD halo
and a previously unknown faint gravitational lens arc. A spectrum of the arc
did not yield a redshift, but its spectrum and colors suggest it lies at z>1.3.
We construct models to reproduce the arc that show the potential is likely to
be highly elliptical. We suggest that this cluster may have undergone a recent
merger and is in the process of forming its cD galaxy. Analysis of X-ray data
from ROSAT and ASCA suggests that the merging process is sufficiently advanced
that the gas in the cluster has relaxed, and A697 lies near the L_x-T_x
relation for normal clusters.Comment: LaTeX; 12 pages, 3 figures, submitted to ApJ Letter
Outflow and dense gas emission from massive Infrared Dark Clouds
Infrared Dark Clouds are expected to harbor sources in different, very young
evolutionary stages. To better characterize these differences, we observed a
sample of 43 massive Infrared Dark Clouds, originally selected as candidate
high-mass starless cores, with the IRAM 30m telescope covering spectral line
tracers of low-density gas, high-density gas, molecular outflows/jets and
temperature effects. The SiO(2-1) observations reveal detections toward 18
sources. Assuming that SiO is exclusively produced by sputtering from dust
grains, this implies that at least in 40% of this sample star formation is
on-going. A broad range of SiO line-widths is observed (between 2.2 and
65km/s), and we discuss potential origins for this velocity spread. While the
low-density tracers 12CO(2-1) and 13CO(1-0) are detected in several velocity
components, the high-density tracer H13CO+(1--0) generally shows only a single
velocity component and is hence well suited for kinematic distance estimates of
IRDCs. Furthermore, the H13CO+ line-width is on average 1.5 times larger than
that of previously observed NH3(1,1). This is indicative of more motion at the
denser core centers, either due to turbulence or beginning star formation
activity. In addition, we detect CH3CN toward only six sources whereas CH3OH is
observed toward approximately 40% of the sample. Estimates of the CH3CN and
CH3OH abundances are low with average values of 1.2x10^{-10} and 4.3x10^{-10},
respectively. These results are consistent with chemical models at the earliest
evolutionary stages of high-mass star formation. Furthermore, the CH3OH
abundances compare well to recently reported values for low-mass starless
cores.Comment: 22 pages (ApJ referee style), 7 figures, accepted for Ap
Quasi-particle continuum and resonances in the Hartree-Fock-Bogoliubov theory
The quasi-particle energy spectrum of the Hartree-Fock-Bogoliubov (HFB)
equations contains discrete bound states, resonances, and non-resonant
continuum states. We study the structure of the unbound quasi-particle spectrum
of weakly bound nuclei within several methods that do not rely on imposing
scattering or outgoing boundary conditions. Various approximations are examined
to estimate resonance widths. It is shown that the stabilization method works
well for all HFB resonances except for very narrow ones.
The Thomas-Fermi approximation to the non-resonant continuum has been shown
to be very effective, especially for coordinate-space HFB calculations in large
boxes that involve huge amounts of discretized quasi-particle continuum states.Comment: 12 pages,11 figures,submitted to PR
Candida and invasive candidiasis: Back to basics.
The ubiquitous Candida spp. is an opportunistic fungal pathogen which, despite treatment with antifungal drugs, can cause fatal bloodstream infections (BSIs) in immunocompromised and immunodeficient persons. Thus far, several major C. albicans virulence factors have been relatively well studied, including morphology switching and secreted degradative enzymes. However, the exact mechanism of Candida pathogenesis and the host response to invasion are still not well elucidated. The relatively recent discovery of the quorum-sensing molecule farnesol and the existence of quorum sensing as a basic regulatory phenomenon of the C. albicans population behavior has revolutionized Candida research. Through population density regulation, the quorum-sensing mechanism also controls the cellular morphology of a C. albicans population in response to environmental factors, thereby, effectively placing morphology switching downstream of quorum sensing. Thus, the quorum-sensing phenomenon has been hailed as the 'missing piece' of the pathogenicity puzzle. Here, we review what is known about Candida spp. as the etiological agents of invasive candidiasis and address our current understanding of the quorum-sensing phenomenon in relation to virulence in the host
The KX method for producing K-band flux-limited samples of quasars
The longstanding question of the extent to which the quasar population is
affected by dust extinction, within host galaxies or galaxies along the line of
sight, remains open. More generally, the spectral energy distributions of
quasars vary significantly and flux-limited samples defined at different
wavelengths include different quasars. Surveys employing flux measurements at
widely separated wavelengths are necessary to characterise fully the spectral
properties of the quasar population. The availability of panoramic
near-infrared detectors on large telescopes provides the opportunity to
undertake surveys capable of establishing the importance of extinction by dust
on the observed population of quasars. We introduce an efficient method for
selecting K-band, flux-limited samples of quasars, termed ``KX'' by analogy
with the UVX method. This method exploits the difference between the power-law
nature of quasar spectra and the convex spectra of stars: quasars are
relatively brighter than stars at both short wavelengths (the UVX method) and
long wavelengths (the KX method). We consider the feasibility of undertaking a
large-area KX survey for damped Ly-alpha galaxies and gravitational lenses
using the planned UKIRT wide-field near-infrared camera.Comment: 6 pages, 3 figures, to appear in MNRA
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