3,119 research outputs found

### An outline of polar spaces: basics and advances

This paper is an extended version of a series of lectures on polar spaces
given during the workshop and conference 'Groups and Geometries', held at the
Indian Statistical Institute in Bangalore in December 2012. The aim of this
paper is to give an overview of the theory of polar spaces focusing on some
research topics related to polar spaces. We survey the fundamental results
about polar spaces starting from classical polar spaces. Then we introduce and
report on the state of the art on the following research topics: polar spaces
of infinite rank, embedding polar spaces in groups and projective embeddings of
dual polar spaces

### Measuring Cosmological Parameters with the JVAS and CLASS Gravitational Lens Surveys

The JVAS (Jodrell Bank-VLA Astrometric Survey) and CLASS (Cosmic Lens All-Sky
Survey) are well-defined surveys containing about ten thousand flat-spectrum
radio sources. For many reasons, flat-spectrum radio sources are particularly
well-suited as a population from which one can obtain unbiased samples of
gravitational lenses. These are by far the largest gravitational (macro)lens
surveys, and particular attention was paid to constructing a cleanly-defined
sample for the survey itself and for the underlying luminosity function. Here
we present the constraints on cosmological parameters, particularly the
cosmological constant, derived from JVAS and combine them with constraints from
optical gravitational lens surveys, `direct' measurements of $\Omega_{0}$,
$H_{0}$ and the age of the universe, and constraints derived from CMB
anisotropies, before putting this final result into the context of the latest
results from other, independent cosmological tests.Comment: LaTeX, 9 pages, 6 PostScript figures, uses texas.sty. To appear in
the Proceedings of the 19th Texas Symposium on Relativistic Astrophysics and
Cosmology (CD-ROM). Paper version available on request. Actual poster (A0 and
A4 versions) available from
http://multivac.jb.man.ac.uk:8000/helbig/research/publications/info/
texas98.htm

### Growth saturation of unstable thin films on transverse-striped hydrophilic-hydrophobic micropatterns

Using three-dimensional numerical simulations, we demonstrate the growth
saturation of an unstable thin liquid film on micropatterned
hydrophilic-hydrophobic substrates. We consider different transverse-striped
micropatterns, characterized by the total fraction of hydrophilic coverage and
the width of the hydrophilic stripes. We compare the growth of the film on the
micropatterns to the steady states observed on homogeneous substrates, which
correspond to a saturated sawtooth and growing finger configurations for
hydrophilic and hydrophobic substrates, respectively. The proposed
micropatterns trigger an alternating fingering-spreading dynamics of the film,
which leads to a complete suppression of the contact line growth above a
critical fraction of hydrophilic stripes. Furthermore, we find that increasing
the width of the hydrophilic stripes slows down the advancing front, giving
smaller critical fractions the wider the hydrophilic stripes are. Using
analytical approximations, we quantitatively predict the growth rate of the
contact line as a function of the covering fraction, and predict the threshold
fraction for saturation as a function of the stripe width.Comment: 11 pages, 5 figure

### CLASS B1152+199 and B1359+154: Two New Gravitational Lens Systems Discovered in the Cosmic Lens All-Sky Survey

The third phase of the Cosmic Lens All-Sky Survey (CLASS) has recently been
completed, bringing the total number of sources imaged to over 15000 in the
CLASS and JVAS combined survey. In the VLA observations carried out in March
and April of 1998, two new candidate lensed systems were discovered: CLASS
B1152+199 and B1359+154. B1152+199 is a 1.6 arcsecond double, with a background
quasar at z=1.019 lensed by a foreground galaxy at z=0.439. The relatively flat
radio spectra of the lensed images, combined with a previous ROSAT detection of
the source, make B1152+199 a strong candidate for time delay studies at both
radio and X-ray wavelengths. B1359+154 is a quadruply lensed quasar at z=3.235,
with a maximum image separation of 1.7 arcseconds. As yet, the redshift of the
lensing object in this system is undetermined. The steep spectral index of the
source suggests that B1359+154 will not exhibit strong variability, and is
therefore unlikely to be useful for determining the Hubble constant from
measured time delays.Comment: accepted for publication in The Astronomical Journa

### B0850+054: a new gravitational lens system from CLASS

We report the discovery of a new gravitational lens system from the CLASS
survey. Radio observations with the VLA, the WSRT and MERLIN show that the
radio source B0850+054 is comprised of two compact components with identical
spectra, a separation of 0.7 arcsec and a flux density ratio of 6:1. VLBA
observations at 5 GHz reveal structures that are consistent with the
gravitational lens hypothesis. The brighter of the two images is resolved into
a linear string of at least six sub-components whilst the weaker image is
radially stretched towards the lens galaxy. UKIRT K-band imaging detects an
18.7 mag extended object, but the resolution of the observations is not
sufficient to resolve the lensed images and the lens galaxy. Mass modelling has
not been possible with the present data and the acquisition of high-resolution
optical data is a priority for this system.Comment: 5 pages, 4 figures, accepted for publication in MNRA

### Extrinsic Radio Variability of JVAS/CLASS Gravitational Lenses

We present flux-ratio curves of the fold and cusp (i.e. close multiple) images of six JVAS/CLASS gravitational lens systems. The data were obtained over a period of 8.5 months in 2001 with the Multi-Element Radio-Linked Interferometer Network (MERLIN) at 5-GHz with 50 mas resolution, as part of a MERLIN Key-Project. Even though the time delays between the fold and cusp images are small (<~1 d) compared to the time-scale of intrinsic source variability, all six lens system show evidence, based on their flux-ratio curves, that might suggest the presence of extrinsic variability. In contrast, the cusp images of B2045+265 -- regarded as the strongest case of the violation of the cusp relation -- show extrinsic variations in their flux-ratios up to \~40% peak-to-peak on time scales of several months. Its low Galactic latitude of b=-10deg and a line-of-sight toward the Cygnus superbubble region suggest that Galactic scintillation is the most likely cause. The cusp images of B1422+231 at b=+69deg do not show strong extrinsic variability. Galactic scintillation can therefore cause significant scatter in the cusp and fold relations of some radio lens systems (up to 10% rms), even though these relations remain violated when averaged over a <~1 year time baseline

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