4,871 research outputs found
Summation and transformation formulas for elliptic hypergeometric series
Using matrix inversion and determinant evaluation techniques we prove several
summation and transformation formulas for terminating, balanced,
very-well-poised, elliptic hypergeometric series.Comment: 21 pages, AMS-LaTe
Geometric Laws of Vortex Quantum Tunneling
In the semiclassical domain the exponent of vortex quantum tunneling is
dominated by a volume which is associated with the path the vortex line traces
out during its escape from the metastable well. We explicitly show the
influence of geometrical quantities on this volume by describing point vortex
motion in the presence of an ellipse. It is argued that for the semiclassical
description to hold the introduction of an additional geometric constraint, the
distance of closest approach, is required. This constraint implies that the
semiclassical description of vortex nucleation by tunneling at a boundary is in
general not possible. Geometry dependence of the tunneling volume provides a
means to verify experimental observation of vortex quantum tunneling in the
superfluid Helium II.Comment: 4 pages, 2 figures, revised version to appear in Phys. Rev.
A high-resolution radio survey of the Vela supernova remnant
This paper presents a high-resolution radio continuum (843 MHz) survey of the
Vela supernova remnant. The contrast between the structures in the central
pulsar-powered nebula of the remnant and the synchrotron radiation shell allows
the remnant to be identified morphologically as a member of the composite
class. The data are the first of a composite remnant at spatial scales
comparable with those available for the Cygnus Loop and the Crab Nebula, and
make possible a comparison of radio, optical and soft X-ray emission from the
resolved shell filaments. The survey, made with the Molonglo Observatory
Synthesis Telescope, covers an area of 50 square degrees at a resolution of
43'' x 60'', while imaging structures on scales up to 30'.Comment: 18 pages, 7 jpg figures (version with ps figures at
http://astro.berkeley.edu/~dbock/papers/); AJ, in pres
Evidence of a Curved Synchrotron Spectrum in the Supernova Remnant SN 1006
A joint spectral analysis of some Chandra ACIS X-ray data and Molonglo
Observatory Synthesis Telescope radio data was performed for 13 small regions
along the bright northeastern rim of the supernova remnant SN 1006. These data
were fitted with a synchrotron radiation model. The nonthermal electron
spectrum used to compute the photon emission spectra is the traditional
exponentially cut off power law, with one notable difference: The power-law
index is not a constant. It is a linear function of the logarithm of the
momentum. This functional form enables us to show, for the first time, that the
synchrotron spectrum of SN 1006 seems to flatten with increasing energy. The
effective power-law index of the electron spectrum is 2.2 at 1 GeV (i.e., radio
synchrotron-emitting momenta) and 2.0 at about 10 TeV (i.e., X-ray
synchrotron-emitting momenta). This amount of change in the index is
qualitatively consistent with theoretical models of the amount of curvature in
the proton spectrum of the remnant. The evidence of spectral curvature implies
that cosmic rays are dynamically important instead of being "test" particles.
The spectral analysis also provides a means of determining the critical
frequency of the synchrotron spectrum associated with the highest-energy
electrons. The critical frequency seems to vary along the northeastern rim,
with a maximum value of 1.1e17 (0.6e17 - 2.1e17) Hz. This value implies that
the electron diffusion coefficient can be no larger than a factor of ~4.5-21
times the Bohm diffusion coefficient if the velocity of the forward shock is in
the range 2300-5000 km/s. Since the coefficient is close to the Bohm limit,
electrons are accelerated nearly as fast as possible in the regions where the
critical frequency is about 1.0e17 Hz.Comment: 41 pages, 8 figures, accepted by Ap
Radio Observations of the Supernova Remnant Candidate G312.5-3.0
The radio images from the Parkes-MIT-NRAO (PMN) Southern Sky Survey at 4850
MHz have revealed a number of previously unknown radio sources. One such
source, G312.5-3.0 (PMN J1421-6415), has been observed using the
multi-frequency capabilities of the Australia Telescope Compact Array (ATCA) at
frequencies of 1380 MHz and 2378 MHz. Further observations of the source were
made using the Molonglo Observatory Synthesis Telescope (MOST) at a frequency
of 843 MHz. The source has an angular size of 18 arcmin and has a distinct
shell structure. We present the reduced multi-frequency observations of this
source and provide a brief argument for its possible identification as a
supernova remnant.Comment: 5 pages, 5 figures, Accepted for publication in MNRA
PSR J1016-5857: a young radio pulsar with possible supernova remnant, X-ray, and gamma-ray associations
We report the discovery of a young and energetic pulsar in the Parkes
multibeam survey of the Galactic plane. PSR J1016-5857 has a rotation period of
107 ms and period derivative of 8e-14, implying a characteristic age of 21 kyr
and spin-down luminosity of 2.6e36 erg/s. The pulsar is located just outside,
and possibly interacting with, the shell supernova remnant G284.3-1.8. Archival
X-ray data show a source near the pulsar position which is consistent with
emission from a pulsar wind nebula. The pulsar is also located inside the error
box of the unidentified EGRET source 3EG J1013-5915, for which it represents a
plausible counterpart.Comment: 5 pages, 3 included figures, accepted for publication by ApJ Letter
Vector Theory of Gravity
We proposed a gravitation theory based on an analogy with electrodynamics on
the basis of a vector field. For the first time, to calculate the basic
gravitational effects in the framework of a vector theory of gravity, we use a
Lagrangian written with gravitational radiation neglected and generalized to
the case of ultra-relativistic speeds. This allows us to accurately calculate
the values of all three major gravity experiments: the values of the perihelion
shift of Mercury, the light deflection angle in the gravity field of the Sun
and the value of radar echo delay. The calculated values coincide with the
observed ones. It is shown that, in this theory, there exists a model of an
expanding Universe.Comment: 9 page
Dynamics of bacterial blight disease in resistant and susceptible rice varieties
Bacterial blight (X. oryzae pv. oryzae) is a serious disease in rice across the world. To better control the disease, it is important to understand its epidemiology and how key aspects of this (e.g. infection efficiency, and spatial spread) change according to environment (e.g. local site conditions and season), management, and in particular, variety resistance. To explore this, we analysed data on the disease progress on resistant and susceptible varieties of rice grown at four sites in the Philippines across five seasons using a combination of mechanistic modelling and statistical analysis. Disease incidence was generally lower in the resistant variety. However, we found no evidence that the primary infection efficiency was lower in resistant varieties, suggesting that differences were largely due to reduced secondary spread. Despite secondary spread being attributed to splash dispersal which is exacerbated by wind and rain, the wetter sites of Pila and Victoria in south Luzon tended to have lower infection rates than the drier sites in central Luzon. Likewise, we found spread in the dry season can be substantial and should therefore not be ignored. In fact, we found site to be a greater determinant of the number of infection attempts suggesting that other environmental and management factors had greater effect on the disease than climate. Primary infection was characterised by spatially-random observations of disease incidence. As the season progressed, we observed an emerging short-range (1.6 m–4 m) spatial structure suggesting secondary spread was predominantly short-range, particularly where the resistant variety was grown
Third order perturbations of a zero-pressure cosmological medium: Pure general relativistic nonlinear effects
We consider a general relativistic zero-pressure irrotational cosmological
medium perturbed to the third order. We assume a flat Friedmann background but
include the cosmological constant. We ignore the rotational perturbation which
decays in expanding phase. In our previous studies we discovered that, to the
second-order perturbation, except for the gravitational wave contributions, the
relativistic equations coincide exactly with the previously known Newtonian
ones. Since the Newtonian second-order equations are fully nonlinear, any
nonvanishing third and higher order terms in the relativistic analyses are
supposed to be pure relativistic corrections. In this work we derive such
correction terms appearing in the third order. Continuing our success in the
second-order perturbations we take the comoving gauge. We discover that the
third-order correction terms are of -order higher than the second-order
terms where is a gauge-invariant combination related to the
three-space curvature perturbation in the comoving gauge; compared with the
Newtonian potential we have to the linear
order. Therefore, the pure general relativistic effects are of -order
higher than the Newtonian ones. The corrections terms are independent of the
horizon scale and depend only on the linear order gravitational potential
perturbation strength. From the temperature anisotropy of cosmic microwave
background we have . Therefore, our present result reinforces our
previous important practical implication that near current era one can use the
large-scale Newtonian numerical simulation more reliably even as the simulation
scale approaches near the horizon.Comment: 9 pages, no figur
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