1,693 research outputs found
Interpreting the eH Stretching Region, Through Infrared Partial Deuteration Studies
Information derived from a study of \u27isolated\u27 CH stretching
frequencies, measured in partially deuterated organic and organemetallic compounds, is reviewed. This includes CH bond lengths and dissociation energies, and HCH angles in methyl groups, Excellent agreement is found between CH bond length differences predicted from VCH\u27s values and those calculated by ab initio methods. V\u27sCH data also agree with the results of high overtone, local mode studies in distinguishing differences in CH bond strengths. The former however are based on spectra which are easier to assign
to specific bonds. They also enable one to understand the spectra
of normal, undeuterated molecules in the CH stretching region,
through \u27energy factored force field\u27 calculations. Reference is made to situations involvlng free internal rotation of methyl groups, and to studies of other \u27isolated\u27 MH bonds (M = N, Si, Ge, Sn)
Mass along the Line of Sight to the Gravitational Lens B1608+656: Galaxy Groups and Implications for H_0
We report the discovery of four groups of galaxies along the line of sight to the B1608+656 gravitational lens system. One group is at the redshift of the primary lensing galaxy (z = 0.631) and appears to have a low mass, with eight spectroscopically confirmed members and an estimated velocity dispersion of 150 ± 60 km s^(-1). The three other groups are in the foreground of the lens. These groups contain ~10 confirmed members each and are located at redshifts of 0.265, 0.426, and 0.52. Two of the three additional groups are centered roughly on the lens system, while the third is centered ~1' south of the lens. We investigate the effect of each of the four groups on the gravitational lensing potential of the B1608+656 system, with a particular focus on the implications for the value of H_0 derived from this system. We find that each group provides an external convergence of ~0.005-0.060, depending on the assumptions made in the calculation. For the B1608+656 system, the stellar velocity dispersion of the lensing galaxy has been measured, thus breaking the mass sheet degeneracy due to the group that is physically associated with the lens. The effect of the other groups along the line of sight can be folded into the overall uncertainties due to large-scale structure (LSS) along the line of sight. Because B1608+656 appears to lie along an overdense line of sight, the LSS will cause the measurement of H_0 to be biased high for this system. This effect could be 5% or greater
The Cosmic Lens All-Sky Survey parent population - I. Sample selection and number counts
We present the selection of the Jodrell Bank Flat-spectrum (JBF) radio source
sample, which is designed to reduce the uncertainties in the Cosmic Lens
All-Sky Survey (CLASS) gravitational lensing statistics arising from the lack
of knowledge about the parent population luminosity function. From observations
at 4.86 GHz with the Very Large Array, we have selected a sample of 117
flat-spectrum radio sources with flux densities greater than 5 mJy. These
sources were selected in a similar manner to the CLASS complete sample and are
therefore representative of the parent population at low flux densities. The
vast majority (~90 per cent) of the JBF sample are found to be compact on the
arcsecond scales probed here and show little evidence of any extended radio jet
emission. Using the JBF and CLASS complete samples we find the differential
number counts slope of the parent population above and below the CLASS 30 mJy
flux density limit to be -2.07+/-0.02 and -1.96+/-0.12, respectively.Comment: 10 pages, 4 figures, accepted for publication in MNRA
2-D constrained Navier-Stokes equation and intermediate asymptotics
We introduce a modified version of the two-dimensional Navier-Stokes
equation, preserving energy and momentum of inertia, which is motivated by the
occurrence of different dissipation time scales and related to the gradient
flow structure of the 2-D Navier-Stokes equation. The hope is to understand
intermediate asymptotics. The analysis we present here is purely formal. A
rigorous study of this equation will be done in a forthcoming paper
Keck spectroscopy of CLASS gravitational lenses
We present the optical spectra of four newly discovered gravitational lenses
from the Cosmic Lens All-Sky Survey (CLASS). These observations were carried
out using the Low Resolution Imaging Spectrograph on the W. M. Keck-I Telescope
as part of a program to study galaxy-scale gravitational lenses. From our
spectra we found the redshift of the background source in CLASS B0128+437
(z_s=3.1240+-0.0042) and the lensing galaxy redshifts in CLASS B0445+123
(z_l=0.5583+-0.0003) and CLASS B0850+054 (z_l=0.5883+-0.0006). Intriguingly, we
also discovered that CLASS B0631+519 may have two lensing galaxies
(z_l,1=0.0896+-0.0001, z_l,2=0.6196+-0.0004). We also found a single
unidentified emission line from the lensing galaxy in CLASS B0128+437 and the
lensed source in CLASS B0850+054. We find the lensing galaxies in CLASS
B0445+123 and CLASS B0631+519 (l,2) to be early-type galaxies with Einstein
Radii of 2.8-3.0 h^{-1} kpc. The deflector in CLASS B0850+054 is a late-type
galaxy with an Einstein Radius of 1.6 h^{-1} kpc.Comment: 9 pages, 5 figures, accepted for publication in MNRA
Proper motion in lensed radio jets at redshift 3:A possible dual super-massive black hole system in the early Universe
In this paper, we exploit the gravitational lensing effect to detect proper
motion in the highly magnified gravitationally lensed source MG B2016+112. We
find positional shifts up to 6 mas in the lensed images by comparing two Very
Long Baseline Interferometric (VLBI) radio observations at 1.7 GHz that are
separated by 14.359 years, and provide an astrometric accuracy of the order of
tens of as. From lens modelling, we exclude a shift in the lensing galaxy
as the cause of the positional change of the lensed images, and we assign it to
the background source. The source consists of four sub-components separated by
pc, with proper motion of the order of tens as yr for
the two components at highest magnification () and of the order of
a few mas yr for the two components at lower magnification ().
We propose single AGN and dual AGN scenarios to explain the source plane.
Although, the latter interpretation is supported by the archival
multi-wavelength properties of the object. In this case, MG B2016+112 would
represent the highest redshift dual radio-loud AGN system discovered thus far,
and would support the merger interpretation for such systems. Also, given the
low probability () of detecting a dual AGN system that is also
gravitationally lensed, if confirmed, this would suggest that such dual AGN
systems must be more abundant in the early Universe than currently thought.Comment: 11 pages, 4 figures; accepted for publication by Astronomy and
Astrophysic
The effect of high temperature upon the transmittance and the emission spectrum of infrared window materials
The effect of high temperatures such as those expected to be encountered in the Pioneer Venus Probe mission upon the transmittance of zinc selenide and cadmium telluride infrared window materials was investigated and the radiation emitted by these materials at high temperatures was determined
Hard Discs on the Hyperbolic Plane
We examine a simple hard disc fluid with no long range interactions on the
two dimensional space of constant negative Gaussian curvature, the hyperbolic
plane. This geometry provides a natural mechanism by which global crystalline
order is frustrated, allowing us to construct a tractable model of disordered
monodisperse hard discs. We extend free area theory and the virial expansion to
this regime, deriving the equation of state for the system, and compare its
predictions with simulation near an isostatic packing in the curved space.Comment: 4 pages, 3 figures, included, final versio
A study of blow-ups in the Keller-Segel model of chemotaxis
We study the Keller-Segel model of chemotaxis and develop a composite
particle-grid numerical method with adaptive time stepping which allows us to
accurately resolve singular solutions. The numerical findings (in two
dimensions) are then compared with analytical predictions regarding formation
and interaction of singularities obtained via analysis of the stochastic
differential equations associated with the Keller-Segel model
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