830 research outputs found
Paradox lost : the cost of a virtual world
This paper touches on a number of seemingly disparate topics-Artificial Intelligence, Fuzzy Logic, String Theory, the search for extra-terrestrial intelligence, the Cantorian concept of infinite sets-in order to support the thesis that for a large part of the educated public in the Western world, the very concept of reality has been changing over the last few generations, and that the change is being accelerated by our increasing acceptance of the Virtual as a substitute for the traditional Real. This, as I hope to convince you, is a momentous shift in the our world view, and like so many profound but gradual shifts, has gone largely unnoticed. Whether the shift is ultimately a good thing or a bad, it ought not to go unscrutinized; this paper aims to bring it to public attention. (The paradox whose loss is referred to in the title is discussed at the end of the paper.
An upper limit to [C II] emission in a z ~= 5 galaxy
Low-ionization-state far-infrared (FIR) emission lines may be useful
diagnostics of star-formation activity in young galaxies, and at high redshift
may be detectable from the ground. In practice, however, very little is known
concerning how strong such line emission might be in the early Universe. We
attempted to detect the 158 micron [C II] line from a lensed galaxy at z =
4.926 using the Caltech Submillimeter Observatory. This source is an ordinary
galaxy, in the sense that it shows high but not extreme star formation, but
lensing makes it visible. Our analysis includes a careful consideration of the
calibrations and weighting of the individual scans. We find only modest
improvement over the simpler reduction methods, however, and the final spectrum
remains dominated by systematic baseline ripple effects. We obtain a 95 per
cent confidence upper limit of 33 mJy for a 200 km/s full width at half maximum
line, corresponding to an unlensed luminosity of 1x10^9 L_sun for a standard
cosmology. Combining this with a marginal detection of the continuum emission
using the James Clerk Maxwell Telescope, we derive an upper limit of 0.4 per
cent for the ratio of L_CII/L_FIR in this object.Comment: 5 pages, 2 figures, accepted for publication in MNRA
A Density Spike on Astrophysical Scales from an N-Field Waterfall Transition
Hybrid inflation models are especially interesting as they lead to a spike in
the density power spectrum on small scales, compared to the CMB, while also
satisfying current bounds on tensor modes. Here we study hybrid inflation with
waterfall fields sharing a global symmetry. The inclusion of many
waterfall fields has the obvious advantage of avoiding topologically stable
defects for . We find that it also has another advantage: it is easier to
engineer models that can simultaneously (i) be compatible with constraints on
the primordial spectral index, which tends to otherwise disfavor hybrid models,
and (ii) produce a spike on astrophysically large length scales. The latter may
have significant consequences, possibly seeding the formation of
astrophysically large black holes. We calculate correlation functions of the
time-delay, a measure of density perturbations, produced by the waterfall
fields, as a convergent power series in both and the field's correlation
function . We show that for large , the two-point function is
and the
three-point function is .
In accordance with the central limit theorem, the density perturbations on the
scale of the spike are Gaussian for large and non-Gaussian for small .Comment: 15 pages in double column format, 6 figures. V2: Further
clarifications, updated to coincide with version published in Physics Letters
Interpolation by polynomials with non-negative coefficients
We consider the problem of determining whether a polynomial of a given order and having only nonnegative coefficients can be found to interpolate a given set of positive data. This problem arises in the design of maximally robust integrating feedback controllers for linear discrete-time plants and is also relevant to the design of nonovershooting control systems. We present an algorithm for determining whether such a polynomial exists for given interpolation data
An upper limit to polarized submillimetre emission in Arp 220
We report the results of pointed observations of the prototypical ultraluminous infrared galaxy (ULIRG) Arp 220 at 850 μm using the polarimeter on the Submillimetre Common User Bolometer Array instrument on the James Clerk Maxwell Telescope. We find a Bayesian 99 per cent confidence upper limit on the polarized emission for Arp 220 of 1.54 per cent, averaged over the 15-arcsec beam-size. Arp 220 can serve as a proxy for other, more distant such galaxies. This upper limit constrains the magnetic field geometry in Arp 220 and also provides evidence that polarized ULIRGs will not be a major contaminant for next-generation cosmic microwave background polarization measurements
The brighter side of sub-mm source counts: a SCUBA scan-map of the Hubble Deep Field
We present an 11 X 11 arcminute map centred on the Hubble Deep Field taken at
850 microns with the SCUBA camera on the JCMT. The map has an average one-sigma
sensitivity to point sources of about 2.3 mJy and thus probes the brighter end
of the sub-mm source counts. We find 7 sources with a flux greater than 9 mJy
(roughly 4 sigma), and therefore estimate N(>9 mJy)= 208 (+90/-72) per degree.
This result is consistent with work from other groups, but improves the
statistics at the bright end, and is suggestive of a steepening of the counts.Comment: 4 pages, 2 figures. UMass/INAOE conference proceedings on Deep
Millimeter Survey
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