3,595 research outputs found
Computing Matveev's complexity via crystallization theory: the boundary case
The notion of Gem-Matveev complexity has been introduced within
crystallization theory, as a combinatorial method to estimate Matveev's
complexity of closed 3-manifolds; it yielded upper bounds for interesting
classes of such manifolds. In this paper we extend the definition to the case
of non-empty boundary and prove that for each compact irreducible and
boundary-irreducible 3-manifold it coincides with the modified Heegaard
complexity introduced by Cattabriga, Mulazzani and Vesnin. Moreover, via
Gem-Matveev complexity, we obtain an estimation of Matveev's complexity for all
Seifert 3-manifolds with base and two exceptional fibers and,
therefore, for all torus knot complements.Comment: 27 pages, 14 figure
VIRIS: A Visual-Infrared Imaging System for the Lick Observatory 1-M Telescope
We describe a system in use at the Lick Observatory 1-m Nickel telescope for
near-simultaneous imaging at optical and near-infrared wavelengths. The
combined availability of a CCD and a NICMOS-3 camera makes the system
well-suited for photometric monitoring from 0.5-2.2 microns of a variety of
astrophysical objects. Our science program thus far has concentrated on
studying variability trends in young stellar objects.Comment: 11 pages LaTex, 3 Postscript figure, Pub. Astr. Soc. Pac. 1998, in
pres
New Ambitwistor String Theories
We describe new ambitwistor string theories that give rise to the recent
amplitude formulae for Einstein-Yang-Mills, (Dirac)-Born-Infeld, Galileons and
others introduced by Cachazo, He and Yuan. In the case of the
Einstein-Yang-Mills amplitudes, an important role is played by a novel
worldsheet conformal field theory that provides the appropriate colour factors
precisely without the spurious multitrace terms of earlier models that had to
be ignored by hand. This is needed to obtain the correct multitrace terms that
arise when Yang-Mills is coupled to gravity.Comment: 34 pages, 2 figures, 5 tables. v2: minor changes, published versio
The Infrared Surface Brightness Fluctuation Distances to the Hydra and Coma Clusters
We present IR surface brightness fluctuation (SBF) distance measurements to
NGC 4889 in the Coma cluster and to NGC 3309 and NGC 3311 in the Hydra cluster.
We explicitly corrected for the contributions to the fluctuations from globular
clusters, background galaxies, and residual background variance. We measured a
distance of 85 +/- 10 Mpc to NGC 4889 and a distance of 46 +/- 5 Mpc to the
Hydra cluster. Adopting recession velocities of 7186 +/- 428 km/s for Coma and
4054 +/- 296 km/s for Hydra gives a mean Hubble constant of H_0 = 87 +/- 11
km/s/Mpc. Corrections for residual variances were a significant fraction of the
SBF signal measured, and, if underestimated, would bias our measurement towards
smaller distances and larger values of H_0. Both NICMOS on the Hubble Space
Telescope and large-aperture ground-based telescopes with new IR detectors will
make accurate SBF distance measurements possible to 100 Mpc and beyond.Comment: 24 pages, 4 PostScript figures, 2 JPEG images; accepted for
publication in Ap
PG 1700+518 Revisited: Adaptive Optics Imaging and a Revised Starburst Age for the Companion
We present the results of adaptive-optics imaging of the z=0.2923 QSO PG
1700+518 in the J and H bands. The extension to the north of the QSO is clearly
seen to be a discrete companion with a well-defined tidal tail, rather than a
feature associated with the host galaxy of PG 1700+518 itself. On the other
hand, an extension to the southwest of the QSO (seen best in deeper, but
lower-resolution, optical images) does likely comprise tidal material from the
host galaxy. The SED derived from images in J, H, and two non-standard optical
bands indicates the presence of dust intermixed with the stellar component. We
use our previously reported Keck spectrum of the companion, the SED found from
the imaging data, and updated spectral-synthesis models to constrain the
stellar populations in the companion and to redetermine the age of the
starburst. While our best-fit age of 0.085 Gyr is nearly the same as our
earlier determination, the fit of the new models is considerably better. This
age is found to be remarkably robust with respect to different assumptions
about the nature of the older stellar component and the effects of dust.Comment: 11 pages; includes two eps figures. Latex (AASTEX). Two additional
figures in gif format. Postscript version including all figs. (424 kb) can be
obtained from http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
ApJ. Letter
Near-Infrared Adaptive Optics Imaging of the Central Regions of Nearby Sc Galaxies: I. M33
Near-infrared images obtained with the Canada-France-Hawaii Telescope (CFHT)
Adaptive Optics Bonnette (AOB) are used to investigate the stellar content
within 18 arcsec of the center of the Local Group spiral galaxy M33. AGB stars
with near-infrared spectral-energy distributions similar to those of giants in
the solar neighborhood and Baade's Window are detected over most of the field.
The bolometric luminosity function (LF) of these stars has a discontinuity near
M_{bol} = -5.25, and comparisons with evolutionary tracks suggest that most of
the AGB stars formed in a burst of star formation 1 - 3 Gyr in the past. The
images are also used to investigate the integrated near-infrared photometric
properties of the nucleus and the central light concentration. The nucleus is
bluer than the central light concentration, in agreement with previous studies
at visible wavelengths. The CO index of the central light concentration 0.5
arcsec from the galaxy center is 0.05, which corresponds to [Fe/H] = -1.2 for
simple stellar systems. Hence, the central light concentration could not have
formed from the chemically-enriched material that dominates the present-day
inner disk of M33.Comment: 23 pages of text + 11 figures; to appear in A
A Tolman Surface Brightness Test for Universal Expansion, and the Evolution of Elliptical Galaxies in Distant Clusters
We use the intercept of the elliptical galaxy radius--surface brightness (SB)
relation at a fixed metric radius as the standard condition for the Tolman SB
test of the universal expansion. We use surface photometry in the optical and
near-IR of elliptical galaxies in Abell~2390 () and Abell~851
(), and compare them to the Coma cluster at . The
photometric data for each cluster are well-described by the Kormendy relation
, where in the optical and in the
near-IR. The scatter about this near-IR relation is only in
at the highest redshift, which is much smaller than at low redshifts,
suggesting a remarkable homogeneity of the cluster elliptical population at
. We use the intercept of these fixed-slope correlations at ~kpc (assuming ~km~s~Mpc, , and
, where the results are only weakly dependent on the cosmology) to
construct the Tolman SB test for these three clusters. The data are fully
consistent with universal expansion if we assume simple models of passive
evolution for elliptical galaxies, but are inconsistent with a non-expanding
geometry (the tired light cosmology) at the confidence level at
. These results suggest luminosity evolution in the restframe -band
of ~mag from to the present, and are consistent with
the ellipticals having formed at high redshift. The SB intercept in elliptical
galaxy correlations is thus a powerful tool for investigating models of their
evolution for significant lookback times.Comment: to appear in The Astrophysical Journal (Letters); 13 pages, including
3 Postscript figures and 1 table; uuencoded, compressed format; the paper is
also available in various formats from
http://astro.caltech.edu/~map/map.bibliography.refereed.htm
Uncovering Spiral Structure in Flocculent Galaxies
We present K'(2.1 micron) observations of four nearby flocculent spirals,
which clearly show low-level spiral structure and suggest that kiloparsec-scale
spiral structure is more prevalent in flocculent spirals than previously
supposed. In particular, the prototypical flocculent spiral NGC 5055 is shown
to have regular, two-arm spiral structure to a radius of 4 kpc in the near
infrared, with an arm-interarm contrast of 1.3. The spiral structure in all
four galaxies is weaker than that in grand design galaxies. Taken in unbarred
galaxies with no large, nearby companions, these data are consistent with the
modal theory of spiral density waves, which maintains that density waves are
intrinsic to the disk. As an alternative, mechanisms for driving spiral
structure with non-axisymmetric perturbers are also discussed. These
observations highlight the importance of near infrared imaging for exploring
the range of physical environments in which large-scale dynamical processes,
such as density waves, are important.Comment: 12 pages AASTeX; 3 compressed PS figures can be retrieved from
ftp://ftp.astro.umd.edu/pub/michele as file thornley.tar (1.6Mbytes).
Accepted to Ap.J. Letters.(Figures now also available here, and from
ftp://ftp.astro.umd.edu/pub/michele , in GIF format.
Reliability analysis and repair activity for the components of 350 kw inverters in a large scale grid-connected photovoltaic system
The reliability of photovoltaic (PV) generators is strongly affected by the performance of Direct Current/Alternating Current (DC/AC) converters, being the major source of PV under-performance. However, generally, their reliability is not investigated at component level: thus, the present work presents a reliability analysis and the repair activity for the components of full bridge DC/AC converters. In the first part of the paper, a reliability analysis using failure rates from literature is carried out for 132 inverters (AC rated power of 350 kW each) with global AC power of 46 MW in a large scale grid-connected PV plant. Then, in the second part of the work, results from literature are compared with data obtained by analyzing industrial maintenance reports in the years 2015–2017. In conclusion, the yearly energy losses involved in the downtime are quantified, as well as their availability
New application of superconductors: high sensitivity cryogenic light detectors
In this paper we describe the current status of the CALDER project, which is
developing ultra-sensitive light detectors based on superconductors for
cryogenic applications. When we apply an AC current to a superconductor, the
Cooper pairs oscillate and acquire kinetic inductance, that can be measured by
inserting the superconductor in a LC circuit with high merit factor.
Interactions in the superconductor can break the Cooper pairs, causing sizable
variations in the kinetic inductance and, thus, in the response of the LC
circuit. The continuous monitoring of the amplitude and frequency modulation
allows to reconstruct the incident energy with excellent sensitivity. This
concept is at the basis of Kinetic Inductance Detectors (KIDs), that are
characterized by natural aptitude to multiplexed read-out (several sensors can
be tuned to different resonant frequencies and coupled to the same line),
resolution of few eV, stable behavior over a wide temperature range, and ease
in fabrication. We present the results obtained by the CALDER collaboration
with 2x2 cm2 substrates sampled by 1 or 4 Aluminum KIDs. We show that the
performances of the first prototypes are already competitive with those of
other commonly used light detectors, and we discuss the strategies for a
further improvement
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