17,898 research outputs found
Smear fitting: a new deconvolution method for interferometric data
A new technique is presented for producing images from interferometric data.
The method, ``smear fitting'', makes the constraints necessary for
interferometric imaging double as a model, with uncertainties, of the sky
brightness distribution. It does this by modelling the sky with a set of
functions and then convolving each component with its own elliptical gaussian
to account for the uncertainty in its shape and location that arises from
noise. This yields much sharper resolution than CLEAN for significantly
detected features, without sacrificing any sensitivity. Using appropriate
functional forms for the components provides both a scientifically interesting
model and imaging constraints that tend to be better than those used by
traditional deconvolution methods. This allows it to avoid the most serious
problems that limit the imaging quality of those methods. Comparisons of smear
fitting to CLEAN and maximum entropy are given, using both real and simulated
observations. It is also shown that the famous Rayleigh criterion (resolution =
wavelength / baseline) is inappropriate for interferometers as it does not
consider the reliability of the measurements.Comment: 16 pages, 38 figures (some have been lossily compressed for
astro-ph). Uses the hyperref LaTeX package. Accepted for publication by the
Monthly Notices of the Royal Astronomical Societ
Housing professionalism in the United Kingdom: the final curtain or a new age?
The unusually large, predominantly municipal, housing sector in the UK has provided the context for a large occupational grouping of "housing managers" that has claimed professional status. However, within the post-1945 British welfare state this professional project enjoyed limited success and social housing remained a fragile professional domain. This article explores the consequences for housing professionalism of the recent displacement of the bureau-professional "organisational settlement" by that characterising an emerging "managerial state". Managerialism constitutes a clear challenge to established forms of "professionalism", especially a weak profession such as housing management. However, professionalism is temporally and culturally plastic. Hence, the demands of managerialism, within the specific context of New Labour's quest for "community" cohesion, may be providing opportunities for a new urban network professionalism founded on claims to both generic and specific skills and also a knowledge base combining abstraction with local concreteness. The prominence in these networks of erstwhile "housing" practitioners may become the basis for a new, quite different, professional project. This argument is developed through both conceptual exploration and reference to empirical research. The latter involves reference to recent work by the authors on, first, the perception of housing employers of the changing nature and demands of "housing" work and its consequences for professionalism and, secondly, the professional project implications of the increasing prominence of neighbourhood management.</p
High-resolution Spectra of Very Low-Mass Stars
We present the results of high-resolution (1-0.4A) optical spectroscopy of a
sample of very low-mass stars. These data are used to examine the kinematics of
the stars at the bottom of the hydrogen-burning main sequence. No evidence is
found for a significant difference between the kinematics of the stars in our
sample with I-K > 3.5 (MBol > 12.8) and those of more massive M-dwarfs (MBol =
7-10). A spectral atlas at high (0.4A) resolution for M8-M9+ stars is provided,
and the equivalent widths of CsI, RbI and Halpha lines present in our spectra
are examined. We analyse our data to search for the presence of rapid rotation,
and find that the brown dwarf LP 944-20 is a member of the class of ``inactive,
rapid rotators''. Such objects seem to be common at and below the hydrogen
burning main sequence. It seems that in low-mass/low-temperature dwarf objects
either the mechanism which heats the chromosphere, or the mechanism which
generates magnetic fields, is greatly suppressed.Comment: 19 pages, 12 figure files. MNRAS style file. Accepted for publication
in MNRAS, August 199
- …