4,683 research outputs found
Commuting charges and symmetric spaces
Every classical sigma-model with target space a compact symmetric space
(with classical) is shown to possess infinitely many local, commuting,
conserved charges which can be written in closed form. The spins of these
charges run over a characteristic set of values, playing the role of exponents
of , and repeating modulo an integer which plays the role of a Coxeter
number.Comment: LaTeX, 16 pages; v2: footnote adde
Conserved Charges and Supersymmetry in Principal Chiral Models
We report on investigations of local (and non-local) charges in bosonic and
supersymmetric principal chiral models in 1+1 dimensions. In the bosonic PCM
there is a classically conserved local charge for each symmetric invariant
tensor of the underlying group. These all commute with the non-local Yangian
charges. The algebra of the local charges amongst themselves is rather more
subtle. We give a universal formula for infinite sets of mutually commuting
local charges with spins equal to the exponents of the underlying classical
algebra modulo its Coxeter number. Many of these results extend to the
supersymmetric PCM, but with local conserved charges associated with
antisymmetric invariants in the Lie algebra. We comment briefly on the quantum
conservation of local charges in both the bosonic and super PCMs.Comment: 18 pages, LaTeX. Revised and up-dated version based on conference
talks by JME and NJ
High resolution sub-millimetre mapping of starburst galaxies: Comparison with CO emission
Researchers present first results from a program of submillimeter continuum mapping of starburst galaxies, and comparison of their dust and CO emission. This project was prompted by surprising results from the first target, the nearby starburst M82, which shows in the dust continuum a morphology quite unlike that of its CO emission, in contrast to what might be expected if both CO and dust are accurately tracing the molecular hydrogen. Possible explanations for this striking difference are discussed. In the light of these results, the program has been extended to include sub-mm mapping of the nearby, vigorously star forming spirals, M83 and Maffei 2. The latter were also observed extensively in CO, in order to study excitation conditions in its central regions. The James Clerk Maxwell Telescope was used in these studies
The Cleo III Ring Imaging Cherenkov Detector
The CLEO detector has been upgraded to include a state of the art particle
identification system, based on the Ring Imaging Cherenkov Detector (RICH)
technology, in order to take data at the upgraded CESR electron positron
collider. The expected performance is reviewed, as well as the preliminary
results from an engineering run during the first few months of operation of the
CLEO III detector.Comment: 5 pages, 2 Figures Talk given by M. Artuso at 8th Pisa Meeting on
Advanced Detectors, May 200
Recommended from our members
Methodology for fitting and updating predictive accident models with trend [forthcoming]
Reliable predictive accident models (PAMs) have a variety of important uses in traffic safety research and practice. They are used to help identify sites in need of remedial treatment, in the design of transport schemes to assess safety implications, and to estimate the effectiveness of remedial treatments. The PAMs currently in use in the UK are now quite old; the data used in their development was gathered up to 30 years ago. Many changes have occurred over that period in road and vehicle design, in road safety campaigns and legislation, and the national accident rate has fallen substantially. It seems unlikely that these aging models can be relied upon to provide accurate and reliable predictions of accident frequencies on the roads today. This paper addresses a number of methodological issues that arise in seeking practical and efficient ways to update PAMs. Models for accidents on rural single carriageway roads have been chosen to illustrate these issues, including the choice of distributional assumption for overdispersion, the choice of goodness of fit measures, questions of independence between observations in different years, and between links on the same scheme, the estimation of trends in the models, the uncertainty of predictions, as well as considerations about the most efficient and convenient ways to fit the required models, given the considerable advances that have been seen in statistical computing software in recent years
Monte Carlo Studies of a Novel LiF Radiator for RICH Detectors
We show that a multifaceted LiF radiator produces more Cherenkov light and
has better resolution per photon than a flat radiator slab when used in a ring
imaging Cherenkov counter. Such a system is being considered for the CLEO III
upgrade.Comment: 9 page
JHK Magnitudes for L and T Dwarfs and Infrared Photometric Systems
L and T dwarfs emit most of their radiation in the near infrared and their
spectral energy distributions are dominated by strong molecular absorption
bands. These highly structured energy distributions lead to JHK magnitudes that
are extremely sensitive to the exact filter bandpass used. In the case of the T
dwarfs, the differences between commonly used photometric systems can be as
large as 0.4 mag at J and 0.5 mag at J-K. To address this problem, we have
synthesized J,H and K magnitudes for some of the common photometric systems and
present transformation equations. If the spectral type of the dwarf is known,
our transformations allow data to be converted between systems to 0.01 mag,
which is better than the typical measurement uncertainty. Transforming on the
basis of color alone is more difficult because of the degeneracy and intrinsic
scatter in near-infrared colors of L and T dwarfs; in this case J magnitudes
can only be transformed to < 0.05 mag and H and K to < 0.02 mag.Comment: 26 pages including 9 figures, uses aastex, to be published in PASP
Jan 200
The Magnetic Distortion Calibration System of the LHCb RICH1 Detector
The LHCb RICH1 detector uses hybrid photon detectors (HPDs) as its optical
sensors. A calibration system has been constructed to provide corrections for
distortions that are primarily due to external magnetic fields. We describe
here the system design, construction, operation and performance.Comment: 9 pages, 14 figure
Infrared Colors at the Stellar/Substellar Boundary
We present new infrared photometry for 61 halo and disk stars around the
stellar/substellar boundary. These data are combined with available optical
photometry and astrometric data to produce color--color and absolute
magnitude--color diagrams. The disk and halo sequences are compared to the
predictions of the latest model atmospheres and structural models.
We find good agreement between observation and theory except for known
problems in the V and H passbands probably due to incomplete molecular data for
TiO, metal hydrides and HO. The metal--poor M subdwarfs are well matched by
the models as oxide opacity sources are less important in this case. The known
extreme M subdwarfs have metallicities about one--hundredth solar, and the
coolest subdwarfs have T K with masses 0.09M/M. The grainless models are not able to reproduce the flux
distributions of disk objects with T 2500 K, however a preliminary
version of the NextGen--Dusty models which includes homogeneous formation and
extinction by dust grains {\it is} able to match the colors of these very cool
objects. The least luminous objects in this sample are GD165B, three DENIS
objects --- DBD0205, DBD1058 and DBD1228 --- and Kelu-1. These have
T 2000 K and are at or below the stellar limit with masses
0.075M/M. Photometry alone cannot constrain these parameters
further as the age is unknown, but published lithium detections for two of
these objects (Kelu-1 and DBD1228) imply that they are young (aged about 1 Gyr)
and substellar (mass 0.06M/M).Comment: ApJ, in press. 18 pages. Also available at
ftp://ftp.jach.hawaii.edu/pub/ukirt/skl/dM_preprint
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