5,755 research outputs found
Computer Imaging to Determine Seed Quality and Performance
Author Institution (McDonald and Bennett): Department of Horticulture and Crop Science, The Ohio State University; Author Institution (Ling): Department of Food, Agricultural and Biological Engineering, The Ohio State University; Author Institution (Fujimura): Department of Computer Science and Engineering, The Ohio State Universit
Mucosal Tolerance to Aflatoxin B 1 a
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73623/1/j.1749-6632.1996.tb21162.x.pd
Superintegrable relativistic systems in spacetime-dependent background fields
14 pagesWe consider a relativistic charged particle in background electromagnetic fields depending on both space and time. We identify which symmetries of the fields automatically generate integrals (conserved quantities) of the charge motion, accounting fully for relativistic and gauge invariance. Using this we present new examples of superintegrable relativistic systems. This includes examples where the integrals of motion are quadratic or nonpolynomial in the canonical momenta
The Evolution of the Intracluster Medium Metallicity in Sunyaev-Zel'dovich-Selected Galaxy Clusters at 0 < z < 1.5
We present the results of an X-ray spectral analysis of 153 galaxy clusters
observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These
clusters, which span 0 < z < 1.5, were drawn from a larger, mass-selected
sample of galaxy clusters discovered in the 2500 square degree South Pole
Telescope Sunyaev Zel'dovich (SPT-SZ) survey. With a total combined exposure
time of 9.1 Ms, these data yield the strongest constraints to date on the
evolution of the metal content of the intracluster medium (ICM). We find no
evidence for strong evolution in the global (r<R500) ICM metallicity (dZ/dz =
-0.06 +/- 0.04 Zsun), with a mean value at z=0.6 of = 0.23 +/- 0.01 Zsun
and a scatter of 0.08 +/- 0.01 Zsun. These results imply that >60% of the
metals in the ICM were already in place at z=1 (at 95% confidence), consistent
with the picture of an early (z>1) enrichment. We find, in agreement with
previous works, a significantly higher mean value for the metallicity in the
centers of cool core clusters versus non-cool core clusters. We find weak
evidence for evolution in the central metallicity of cool core clusters (dZ/dz
= -0.21 +/- 0.11 Zsun), which is sufficient to account for this enhanced
central metallicity over the past ~10 Gyr. We find no evidence for metallicity
evolution outside of the core (dZ/dz = -0.03 +/- 0.06 Zsun), and no significant
difference in the core-excised metallicity between cool core and non-cool core
clusters. This suggests that strong radio-mode AGN feedback does not
significantly alter the distribution of metals at r>0.15R500. Given the
limitations of current-generation X-ray telescopes in constraining the ICM
metallicity at z>1, significant improvements on this work will likely require
next-generation X-ray missions.Comment: 11 pages, 8 figures, 2 tables. Submitted to ApJ. Comments welcome
From covariant to canonical formulations of discrete gravity
Starting from an action for discretized gravity we derive a canonical
formalism that exactly reproduces the dynamics and (broken) symmetries of the
covariant formalism. For linearized Regge calculus on a flat background --
which exhibits exact gauge symmetries -- we derive local and first class
constraints for arbitrary triangulated Cauchy surfaces. These constraints have
a clear geometric interpretation and are a first step towards obtaining
anomaly--free constraint algebras for canonical lattice gravity. Taking higher
order dynamics into account the symmetries of the action are broken. This
results in consistency conditions on the background gauge parameters arising
from the lowest non--linear equations of motion. In the canonical framework the
constraints to quadratic order turn out to depend on the background gauge
parameters and are therefore pseudo constraints. These considerations are
important for connecting path integral and canonical quantizations of gravity,
in particular if one attempts a perturbative expansion.Comment: 37 pages, 5 figures (minor modifications, matches published version +
updated references
(Broken) Gauge Symmetries and Constraints in Regge Calculus
We will examine the issue of diffeomorphism symmetry in simplicial models of
(quantum) gravity, in particular for Regge calculus. We find that for a
solution with curvature there do not exist exact gauge symmetries on the
discrete level. Furthermore we derive a canonical formulation that exactly
matches the dynamics and hence symmetries of the covariant picture. In this
canonical formulation broken symmetries lead to the replacements of constraints
by so--called pseudo constraints. These considerations should be taken into
account in attempts to connect spin foam models, based on the Regge action,
with canonical loop quantum gravity, which aims at implementing proper
constraints. We will argue that the long standing problem of finding a
consistent constraint algebra for discretized gravity theories is equivalent to
the problem of finding an action with exact diffeomorphism symmetries. Finally
we will analyze different limits in which the pseudo constraints might turn
into proper constraints. This could be helpful to infer alternative
discretization schemes in which the symmetries are not broken.Comment: 32 pages, 15 figure
Wide-field global VLBI and MERLIN combined monitoring of supernova remnants in M82
From a combination of MERLIN (Multi-Element Radio-Linked Interferometer
Network) and global VLBI (Very Long Baseline Interferometry) observations of
the starburst galaxy M82, images of 36 discrete sources at resolutions ranging
from ~3 to ~80 mas at 1.7 GHz are presented. Of these 36 sources, 32 are
identified as supernova remnants, 2 are HII regions, and 3 remain unclassified.
Sizes, flux densities and radio brightnesses are given for all of the detected
sources. Additionally, global VLBI only data from this project are used to
image four of the most compact radio sources. These data provide a fifth epoch
of VLBI observations of these sources, covering a 19-yr time-line. In
particular, the continued expansion of one of the youngest supernova remnants,
43.31+59.3 is discussed. The deceleration parameter is a power-law index used
to represent the time evolution of the size of a supernova remnant. For the
source 43.31+59.3, a lower limit to the deceleration parameter is calculated to
be 0.53+/-0.06, based on a lower limit of the age of this source.Comment: 31 pages, 12 figures, 7 table
Lettuce ( Lactuca sativa L.) seed quality evaluation using seed physical attributes, saturated salt accelerated aging and the seed vigour imaging system
High seed quality is essential for optimum stand establishment in
lettuce. As a result, it is necessary to have seed vigour tests that
permit rapid, objective and accurate evaluation of seed quality. This
study evaluated physical and physiological seed quality components of
four seed lots of six lettuce varieties obtained from a commercial
company. Seeds were evaluated for seedling emergence under greenhouse
conditions, standard germination, seed physical aspects, the Saturated
Salt Accelerated Aging (SSAA) test and the Seed Vigour Imaging System
(SVIS). Results indicated that large-seeded lettuce varieties had
higher percentage germination, higher SSAA values, higher SVIS index
and more rapid and uniform greenhouse emergence. Black-seeded lettuce
varieties possessed higher seed quality and less fungal invasion when
evaluated by the SSAA test. The SVIS index significantly correlated
with SSAA values and seedling emergence under greenhouse conditions
suggesting it can be used as a measure of seed vigour. It is concluded
that the SSAA and SVIS tests are practical and accurate determinants of
lettuce seed quality and distinguish between high and poor quality
lettuce seed lots
Closed-Form Bayesian Inferences for the Logit Model via Polynomial Expansions
Articles in Marketing and choice literatures have demonstrated the need for
incorporating person-level heterogeneity into behavioral models (e.g., logit
models for multiple binary outcomes as studied here). However, the logit
likelihood extended with a population distribution of heterogeneity doesn't
yield closed-form inferences, and therefore numerical integration techniques
are relied upon (e.g., MCMC methods).
We present here an alternative, closed-form Bayesian inferences for the logit
model, which we obtain by approximating the logit likelihood via a polynomial
expansion, and then positing a distribution of heterogeneity from a flexible
family that is now conjugate and integrable. For problems where the response
coefficients are independent, choosing the Gamma distribution leads to rapidly
convergent closed-form expansions; if there are correlations among the
coefficients one can still obtain rapidly convergent closed-form expansions by
positing a distribution of heterogeneity from a Multivariate Gamma
distribution. The solution then comes from the moment generating function of
the Multivariate Gamma distribution or in general from the multivariate
heterogeneity distribution assumed.
Closed-form Bayesian inferences, derivatives (useful for elasticity
calculations), population distribution parameter estimates (useful for
summarization) and starting values (useful for complicated algorithms) are
hence directly available. Two simulation studies demonstrate the efficacy of
our approach.Comment: 30 pages, 2 figures, corrected some typos. Appears in Quantitative
Marketing and Economics vol 4 (2006), no. 2, 173--20
Star-Forming Brightest Cluster Galaxies at 0.25 < z < 1.25: A Transitioning Fuel Supply
We present a multi-wavelength study of 90 brightest cluster galaxies (BCGs)
in a sample of galaxy clusters selected via the Sunyaev Zel'dovich effect by
the South Pole Telescope, utilizing data from various ground- and space-based
facilities. We infer the star formation rate (SFR) for the BCG in each cluster,
based on the UV and IR continuum luminosity, as well as the [O II] emission
line luminosity in cases where spectroscopy is available, finding 7 systems
with SFR > 100 Msun/yr. We find that the BCG SFR exceeds 10 Msun/yr in 31 of 90
(34%) cases at 0.25 < z < 1.25, compared to ~1-5% at z ~ 0 from the literature.
At z > 1, this fraction increases to 92(+6)(-31)%, implying a steady decrease
in the BCG SFR over the past ~9 Gyr. At low-z, we find that the specific star
formation rate in BCGs is declining more slowly with time than for field or
cluster galaxies, most likely due to the replenishing fuel from the cooling ICM
in relaxed, cool core clusters. At z > 0.6, the correlation between cluster
central entropy and BCG star formation - which is well established at z ~ 0 -
is not present. Instead, we find that the most star-forming BCGs at high-z are
found in the cores of dynamically unrelaxed clusters. We investigate the
rest-frame near-UV morphology of a subsample of the most star-forming BCGs
using data from the Hubble Space Telescope, finding complex, highly asymmetric
UV morphologies on scales as large as ~50-60 kpc. The high fraction of
star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times
suggests that the dominant mode of fueling star formation in BCGs may have
recently transitioned from galaxy-galaxy interactions to ICM cooling.Comment: 20 pages, 10 figures. Submitted for publication in ApJ. Comments
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