713 research outputs found
Virulence of Escherichia coli Isolates Obtained from Layer Chickens with Colibacillosis Associated with Pericarditis, Perihepatitis, and Salpingitis in Experimentally Infected Chicks and Embryonated Eggs
To evaluate the virulence of avian pathogenic Escherichia coli (APEC) isolates obtained from colibacillosis cases associated with pericarditis, perihepatitis, and salpingitis, the embryo lethality assay and experimental infection model in chicks were used in this study. According to the established criteria based on mortality in the embryo lethality assay for evaluating the virulence of E. coli isolates, 23 of the 26 APEC isolates associated with pericarditis and perihepatitis and 8 of the 20 isolates associated with salpingitis were found to be virulent. Isolate D137, which had been obtained from a case with pericarditis and perihepatitis and had an embryo mortality of 92%, and isolate D445, which had been obtained from a case with pericarditis and perihepatitis and had an embryo mortality of 17%, were used for the experimental infection. Four of the five 11-day-old chickens inoculated through the air sac with isolate D137 died 1 day postinoculation, and the challenge strain was recovered from the air sac, pericardial sac, or liver; however, colibacillosis lesions were found in only one of the five birds postmortem. All five chicks inoculated with isolate D445 survived for 7 days postinoculation and exhibited airsacculitis or pericarditis lesions at 7 days postinoculation; the challenge strain was not recovered from the lesions postmortem. The results obtained in this study suggest that the different APEC isolates tested cause illness in chickens through distinct pathogenesis
Imprint of Gravitational Lensing by Population III Stars in Gamma Ray Burst Light Curves
We propose a novel method to extract the imprint of gravitational lensing by
Pop III stars in the light curves of Gamma Ray Bursts (GRBs). Significant
portions of GRBs can originate in hypernovae of Pop III stars and be
gravitationally lensed by foreground Pop III stars or their remnants. If the
lens mass is on the order of and the lens redshift is
greater than 10, the time delay between two lensed images of a GRB is s and the image separation is as. Although it is difficult to
resolve the two lensed images spatially with current facilities, the light
curves of two images are superimposed with a delay of s. GRB light
curves usually exhibit noticeable variability, where each spike is less than
1s. If a GRB is lensed, all spikes are superimposed with the same time delay.
Hence, if the autocorrelation of light curve with changing time interval is
calculated, it should show the resonance at the time delay of lensed images.
Applying this autocorrelation method to GRB light curves which are archived as
the {\it BATSE} catalogue, we demonstrate that more than half light curves can
show the recognizable resonance, if they are lensed. Furthermore, in 1821 GRBs
we actually find one candidate of GRB lensed by a Pop III star, which may be
located at redshift 20-200. The present method is quite straightforward and
therefore provides an effective tool to search for Pop III stars at redshift
greater than 10. Using this method, we may find more candidates of GRBs lensed
by Pop III stars in the data by the {\it Swift} satellite.Comment: 13 pages, 13 figures, accepted for publication in Ap
Study of Electron Swarm in High Pressure Hydrogen Gas Filled RF Cavities
A high pressure hydrogen gas filled RF cavity has been proposed for use in the muon collection system for a muon collider. It allows for high electric field gradients in RF cavities located in strong magnetic fields, a condition frequently encountered in a muon cooling channel. In addition, an intense muon beam will generate an electron swarm via the ionization process in the cavity. A large amount of RF power will be consumed into the swarm. We show the results from our studies of the HV RF breakdown in a cavity without a beam and present some results on the resulting electron swarm dynamics. This is preliminary to actual beam tests which will take place late in 2010
Ordering of the Heisenberg spin glass in two dimensions
The spin and the chirality orderings of the Heisenberg spin glass in two
dimensions with the nearest-neighbor Gaussian coupling are investigated by
equilibrium Monte Carlo simulations. Particular attention is paid to the
behavior of the spin and the chirality correlation lengths. In order to observe
the true asymptotic behavior, fairly large system size L\gsim 20 (L the linear
dimension of the system) appears to be necessary. It is found that both the
spin and the chirality order only at zero temperature. At high temperatures,
the chiral correlation length stays shorter than spin correlation length,
whereas at lower temperatures below the crossover temperature T_\times, the
chiral correlation length exceeds the spin correlation length. The spin and the
chirality correlation-length exponents are estimated above T_\times to be
\nu_SG=0.9+-0.2 and \nu_CG=2.1+-0.3, respectively. These values are close to
the previous estimates on the basis of the domain-wall-energy calculation.
Discussion is given about the asymptotic critical behavior realized below
T_\times.Comment: to appear in a special issue of J. Phys.
Microlensing of Broad Absorption Line Quasars: Polarization Variability
Roughly 10% of all quasars exhibit Broad Absorption Line (BAL) features which
appear to arise in material outflowing at high velocity from the active
galactic nucleus (AGN). The details of this outflow are, however, very poorly
constrained and the particular nature of the BAL material is essentially
unknown. Recently, new clues have become available through polarimetric studies
which have found that BAL troughs are more polarized than the quasar continuum
radiation. To explain these observations, models where the BAL material
outflows equatorially across the surface of the dusty torus have been
developed. In these models, however, several sources of the BAL polarization
are possible. Here, we demonstrate how polarimetric monitoring of
gravitationally lensed quasars, such as H 1413+117, during microlensing events
can not only distinguish between two currently popular models, but can also
provide further insight into the structure at the cores of BAL quasars.Comment: 17 pages, 3 figures, accepted to PAS
Gravitational Microlensing as a probe of the Electron Scattering Region in Q2237+0305
Recent observations have provided strong evidence for the presence of an
Electron Scattering Region (ESR) within the central regions of AGNs. This is
responsible for reprocessing emission from the accretion disk into polarised
radiation. The geometry of this scattering region is, however, poorly
constrained. In this paper, we consider the influence of gravitational
microlensing on polarised emission from the ESR in the quadruply imaged quasar,
Q2237+0305, demonstrating how correlated features in the resultant light curve
variations can determine both the size and orientation of the scattering
region. This signal is due to differential magnification between
perpendicularly polarised views of the ESR, and is clearest for a small ESR
width and a large ESR radius. Cross- and auto-correlation measures appear to be
independent of lens image shear and convergence parameters, making it ideal to
investigate ESR features. As with many microlensing experiments, the time-scale
for variability, being of order decades to centuries, is impractically long.
However, with a polarization filter oriented appropriately with respect to the
path that the quasar takes across the caustic structure, the ESR diameter and
radius can be estimated from the auto- and cross-correlation of polarized light
curves on much shorter time-scales.Comment: 11 pages, 12 figures, 1 table, accepted for MNRA
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