21,441 research outputs found
Efficient computation of updated lower expectations for imprecise continuous-time hidden Markov chains
We consider the problem of performing inference with imprecise
continuous-time hidden Markov chains, that is, imprecise continuous-time Markov
chains that are augmented with random output variables whose distribution
depends on the hidden state of the chain. The prefix `imprecise' refers to the
fact that we do not consider a classical continuous-time Markov chain, but
replace it with a robust extension that allows us to represent various types of
model uncertainty, using the theory of imprecise probabilities. The inference
problem amounts to computing lower expectations of functions on the state-space
of the chain, given observations of the output variables. We develop and
investigate this problem with very few assumptions on the output variables; in
particular, they can be chosen to be either discrete or continuous random
variables. Our main result is a polynomial runtime algorithm to compute the
lower expectation of functions on the state-space at any given time-point,
given a collection of observations of the output variables
Herschel-ATLAS: Dust temperature and redshift distribution of SPIRE and PACS detected sources using submillimetre colours
We present colourâcolour diagrams of detected sources in the Herschel-ATLAS science demonstration field from 100 to 500 ÎŒm using both PACS and SPIRE. We fit isothermal modified black bodies to the spectral energy distribution (SED) to extract the dust temperature of sources with counterparts in Galaxy And Mass Assembly (GAMA) or SDSS surveys with either a spectroscopic or a photometric redshift. For a subsample of 330 sources detected in at least three FIR bands with a significance greater than 3Ï, we find an average dust temperature of (28±8) K. For sources with no known redshift, we populate the colourâcolour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters, and compare to colours of observed sources to establish the redshift distribution of this sample. For another subsample of 1686 sources with fluxes above 35 mJy at 350 ÎŒm and detected at 250 and 500 ÎŒm with a significance greater than 3Ï, we find an average redshift of 2.2 ± 0.6
Herschel and SCUBA-2 imaging and spectroscopy of a bright, lensed submillimetre galaxy at z = 2.3
We present a detailed analysis of the far-infrared (-IR) properties of the bright, lensed, z = 2.3, submillimetre-selected galaxy (SMG), SMMâJ2135-0102 (hereafter SMMâJ2135), using new observations with Herschel, SCUBA-2 and the Very Large Array (VLA). These data allow us to constrain the galaxy's spectral energy distribution (SED) and show that it has an intrinsic rest-frame 8-1000-ÎŒm luminosity, L_(bol), of (2.3±0.2) Ă 10^(12) L_â and a likely star-formation rate (SFR) of ~400 yr-1. The galaxy sits on the far-IR/radio correlation for far-IR-selected galaxies. At âł70 ÎŒm, the SED can be described adequately by dust components with dust temperatures, T_d ~ 30 and 60 k. Using SPIRE's Fourier- transform spectrometer (FTS) we report a detection of the [C ii]â158 ÎŒm cooling line. If the [C ii], CO and far-IR continuum arise in photo-dissociation regions (PDRs), we derive a characteristic gas density, n ~ 10^3 cm^(-3), and a far-ultraviolet (-UV) radiation field, G_0, 10^(3)Ă stronger than the Milky Way. L_[CII]/L_(bol) is significantly higher than in local ultra-luminous IR galaxies (ULIRGs) but similar to the values found in local star-forming galaxies and starburst nuclei. This is consistent with SMMâJ2135 being powered by starburst clumps distributed across ~2 kpc, evidence that SMGs are not simply scaled-up ULIRGs. Our results show that SPIRE's FTS has the ability to measure the redshifts of distant, obscured galaxies via the blind detection of atomic cooling lines, but it will not be competitive with ground-based CO-line searches. It will, however, allow detailed study of the integrated properties of high-redshift galaxies, as well as the chemistry of their interstellar medium (ISM), once more suitably bright candidates have been found
Femtoscopy and energy-momentum conservation effects in proton-proton collisions at 900 GeV in ALICE
Two particle correlations are used to extract information about the
characteristic size of the system for proton-proton collisions at 900 GeV
measured by the ALICE (A Large Ion Collider experiment) detector at CERN. The
correlation functions obtained show the expected Bose-Einstein effect for
identical particles, but there are also long range correlations present that
shift the baseline from the expected flat behavior. A possible source of these
correlations is the conservation of energy and momentum, especially for small
systems, where the energy available for particle production is limited. A new
technique, first introduced by the STAR collaboration, of quantifying these
long range correlations using energy-momentum conservation considerations is
presented here. It is shown that the baseline of the two particle correlation
function can be described using this technique.Comment: Hot Quarks 2010 conference proceedings, to appear in Journal of
Physics: Conference Series (JPCS
Studies on the bit rate requirements for a HDTV format with 1920 1080 pixel resolution, progressive scanning at 50 Hz frame rate targeting large flat panel displays
This paper considers the potential for an HDTV delivery format with 1920 times 1080 pixels progressive scanning and 50 frames per second in broadcast applications. The paper discusses the difficulties in characterizing the display to be assumed for reception. It elaborates on the required bit rate of the 1080p/50 format when critical content is coded in MPEG-4 H.264 AVC Part 10 and subjectively viewed on a large, flat panel display with 1920 times 1080 pixel resolution. The paper describes the initial subjective quality evaluations that have been made in these conditions. The results of these initial tests suggest that the required bit-rate for a 1080p/50 HDTV signal in emission could be kept equal or lower than that of 2nd generation HDTV formats, to achieve equal or better image qualit
Chiral Gauge Theory on Lattice with Domain Wall Fermions
We investigate a U(1) lattice chiral gauge theory with domain wall fermions
and compact gauge fixing. In the reduced model limit, our perturbative and
numerical investigations show that there exist no extra mirror chiral modes.
The longitudinal gauge degrees of freedom have no effect on the free domain
wall fermion spectrum consisting of opposite chiral modes at the domain wall
and at the anti-domain wall which have an exponentially damped overlap.Comment: 16 pages revtex, 5 postscript figures, PRD versio
Remark on lattice BRST invariance
A recently claimed resolution to the lattice Gribov problem in the context of
chiral lattice gauge theories is examined. Unfortunately, I find that the old
problem remains.Comment: 4 pages, plain TeX, presentation improved (see acknowledgments
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