29,286 research outputs found
Can Local Food Go Mainstream?
Local Food, Relocalization, Supermarket, Distribution Center, Economies of Size, Transportation Efficiency, Food Consumption/Nutrition/Food Safety, Marketing,
Two tails in NGC 3656, and the major merger origin of shell and minor axis dust lane ellipticals
I report on the discovery of two faint (~ 26.8 Rmag/arcsec^2) tidal tails
around the shell elliptical NGC 3656 (Arp 155). This galaxy had previously been
interpreted as a case of accretion, or minor merger. The two tidal tails are
inconsistent with a minor merger, and point instead to a disk-disk major merger
origin. NGC 3656 extends Toomre's merger sequence toward normal elliptical
galaxies, and hints at a major merger origin for shells and minor-axis dust
lanes. A dwarf galaxy lies at the tip of one of the tidal tails. A prominent
shell, which shows sharp azymuthal color discontinuities, belongs to a rotating
dynamical component of young stars which includes the inner dust lane.Comment: 9 pages, 2 plates, 1 figure, uses aaspp.sty, accepted for publication
in The Astrophysical Journal Letters. Files also available by anonymous ftp
at ftp.iac.es, directory ./pub/balcell
LRG-BEASTS III: Ground-based transmission spectrum of the gas giant orbiting the cool dwarf WASP-80
We have performed ground-based transmission spectroscopy of the hot Jupiter
orbiting the cool dwarf WASP-80 using the ACAM instrument on the William
Herschel Telescope (WHT) as part of the LRG-BEASTS programme. This is the third
paper of a ground-based transmission spectroscopy survey of hot Jupiters using
low-resolution grism spectrographs. We observed two transits of the planet and
have constructed transmission spectra spanning a wavelength range of
4640-8840A. Our transmission spectrum is inconsistent with a previously claimed
detection of potassium in WASP-80b's atmosphere, and is instead most consistent
with a haze. We also do not see evidence for sodium absorption at a resolution
of 100A.Comment: 11 pages, 9 figures. Accepted for publication in MNRA
Seasonal variations in Greenland Ice Sheet motion : Inland extent and behaviour at higher elevations
Peer reviewedPreprin
External Shear in Quadruply Imaged Lens Systems
We use publicly available N-body simulations and semi-analytic models of
galaxy formation to estimate the levels of external shear due to structure near
the lens in gravitational lens systems. We also describe two selection effects,
specific to four-image systems, that enhance the probability of observing
systems to have higher external shear. Ignoring additional contributions from
"cosmic shear" and assuming that lens galaxies are not significantly flattened,
we find that the mean shear at the position of a quadruple lens galaxy is 0.11,
the rms shear is roughly 0.15, and there is roughly a 45% likelihood of
external shear greater than 0.1. This is much larger than previous estimates
and in good agreement with typical measured external shear. The higher shear
primarily stems from the tendency of early-type galaxies, which are the
majority of lenses, to reside in overdense regions.Comment: 5 pages, 2 figures, ApJ in press, minor revision
Calibration of radii and masses of open clusters with a simulation
Context: A recent new approach to apply a simple dynamical mass estimate of
tidally limited star clusters is based on the identification of the tidal
radius in a King profile with the dynamical Jacobi radius. The application to
an unbiased open cluster catalogue yields significantly higher cluster masses
compared to the classical methods. Aims: We quantify the bias in the mass
determination as function of projection direction and cluster age by analysing
a simulated star cluster. Methods: We use direct -body simulations of a star
cluster including stellar evolution in an analytic Milky Way potential and
apply a best fit to the projected number density of cluster stars. Results: We
obtain significantly overestimated star cluster masses which depend strongly on
the viewing direction. The overestimation is typically in the range of 10-50
percent and reaches a factor of 3.5 for young clusters. Mass segregation
reduces the derived limiting radii systematically.Comment: 9 pages, 10+1 figures, accepted by Astronomy and Astrophysic
Hopf algebras and characters of classical groups
Schur functions provide an integral basis of the ring of symmetric functions.
It is shown that this ring has a natural Hopf algebra structure by identifying
the appropriate product, coproduct, unit, counit and antipode, and their
properties. Characters of covariant tensor irreducible representations of the
classical groups GL(n), O(n) and Sp(n) are then expressed in terms of Schur
functions, and the Hopf algebra is exploited in the determination of
group-subgroup branching rules and the decomposition of tensor products. The
analysis is carried out in terms of n-independent universal characters. The
corresponding rings, CharGL, CharO and CharSp, of universal characters each
have their own natural Hopf algebra structure. The appropriate product,
coproduct, unit, counit and antipode are identified in each case.Comment: 9 pages. Uses jpconf.cls and jpconf11.clo. Presented by RCK at
SSPCM'07, Myczkowce, Poland, Sept 200
Using a fuzzy inference system to control a pumped storage hydro plant
The paper discusses the development of a fuzzy inference system (FIS) based governor control for a pumped storage hydroelectric plant. The First Hydro Company's plant at Dinorwig in North Wales is the largest of its kind in Europe and is mainly used for frequency control of the UK electrical grid. In previous investigations, a detailed model of the plant was developed using MATLAB(R)/SIMULINK(R) and this is now being used to compare FIS governor operation with the proportional-integral-derivative (PID) controller currently used. The paper describes the development of an FIS governor, and shows that its response to a step increase in load is superior to the PID under certain conditions of load. The paper proceeds to discuss the implications of these results in view of the possible practical application of an FIS governor at the Dinorwig plant
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