2,735 research outputs found
Radio and X-ray nebulae associated with PSR J1509-5850
We have discovered a long radio trail at 843 MHz which is apparently
associated with middle age pulsar PSR J1509-5850. The radio trail has a length
of ~7 arcmin. In X-rays, Chandra observations of PSR J1509-5850 reveal an
associated X-ray trail which extends in the same orientation as the radio
trail. Moreover, two clumpy structures are observed along the radio trail. The
larger one is proposed to be the supernova remnant (SNR) candidate MSC
319.9-0.7. Faint X-ray enhancement at the position of the SNR candidate is
found in the Chandra data.Comment: Accepted by A&A, 5 pages, 4 figures, 1 tabl
MILK PRICING IN THE UNITED STATES
This report provides a primer on the complex pricing system that has evolved in the United States to deal with milk production, its assembly (collection), and its distribution to alternative users. All the various government and private institutions making up the system are expected to work together to ensure that the public gets the milk it wants, while dairy farmers get the economic returns needed to provide the milk. The major institutions are the Federal milk price support program and milk marketing orders, the Northeast Interstate Dairy Compact, State regulations, dairy cooperatives, and milk and dairy product futures and options markets. Our goal is to provide a primer on milk pricing that can serve as a steppingstone to other, more detailed works for those so inclined.Dairy, milk pricing, Demand and Price Analysis, Livestock Production/Industries,
Structure of Dairy Markets: Past, Present, Future
The U.S. dairy industry, many segments of which supported dairy policy changes in the 1996 Federal Agriculture Improvement and Reform Act, is much different than it was 20 or even 10 years ago. This report provides a historical overview of the industry, more detailed examinations of the fluid milk market and selected manufactured dairy product markets, a discussion of future prospects and trends in the industry, and some thoughts on the implications of those prospects and trends for dairy farmers and their organizations, processors, dairy product manufacturers, and retailers.dairy, butter, cheese, nonfat dry milk, market structure, pricing, competition, Livestock Production/Industries, Marketing,
A Ray-Tracing Model of the Vela Pulsar
In the relativistic plasma surrounding a pulsar, a subluminal ordinary-mode
electromagnetic wave will propagate along a magnetic field line. After some
distance, it can break free of the field line and escape the magnetosphere to
reach an observer. We describe a simple model of pulsar radio emission based on
this scenario and find that applying this model to the case of the Vela pulsar
reproduces qualitative characteristics of the observed Vela pulse profile.Comment: 23 pages, 9 figures, accepted for publication in Ap
The Parkes Pulsar Timing Array
Detection and study of gravitational waves from astrophysical sources is a
major goal of current astrophysics. Ground-based laser-interferometer systems
such as LIGO and VIRGO are sensitive to gravitational waves with frequencies of
order 100 Hz, whereas space-based systems such as LISA are sensitive in the
millihertz regime. Precise timing observations of a sample of millisecond
pulsars widely distributed on the sky have the potential to detect
gravitational waves at nanohertz frequencies. Potential sources of such waves
include binary super-massive black holes in the cores of galaxies, relic
radiation from the inflationary era and oscillations of cosmic strings. The
Parkes Pulsar Timing Array (PPTA) is an implementation of such a system in
which 20 millisecond pulsars have been observed using the Parkes radio
telescope at three frequencies at intervals of two -- three weeks for more than
two years. Analysis of these data has been used to limit the gravitational wave
background in our Galaxy and to constrain some models for its generation. The
data have also been used to investigate fluctuations in the interstellar and
Solar-wind electron density and have the potential to investigate the stability
of terrestrial time standards and the accuracy of solar-system ephemerides.Comment: 9 pages, 6 figures, Proceedings of "40 Years of Pulsars: Millisecond
Pulsars, Magnetars and More", Montreal, August 2007. Corrected SKA detection
limi
Predictions for the First Parker Solar Probe Encounter
We examine Alfv\'en Wave Solar atmosphere Model (AWSoM) predictions of the
first Parker Solar Probe (PSP) encounter. We focus on the 12-day closest
approach centered on the 1st perihelion. AWSoM (van der Holst et al., 2014)
allows us to interpret the PSP data in the context of coronal heating via
Alfv\'en wave turbulence. The coronal heating and acceleration is addressed via
outward-propagating low-frequency Alfv\'en waves that are partially reflected
by Alfv\'en speed gradients. The nonlinear interaction of these
counter-propagating waves results in a turbulent energy cascade. To apportion
the wave dissipation to the electron and anisotropic proton temperatures, we
employ the results of the theories of linear wave damping and nonlinear
stochastic heating as described by Chandran et al. (2011). We find that during
the first encounter, PSP was in close proximity to the heliospheric current
sheet (HCS) and in the slow wind. PSP crossed the HCS two times, namely at
2018/11/03 UT 01:02 and 2018/11/08 UT 19:09 with perihelion occuring on the
south of side of the HCS. We predict the plasma state along the PSP trajectory,
which shows a dominant proton parallel temperature causing the plasma to be
firehose unstable.Comment: 16 pages, 5 figures; accepted for publication in the Astrophysical
Journal Letter
Pulsar science with the Five hundred metre Aperture Spherical Telescope
With a collecting area of 70 000 m^2, the Five hundred metre Aperture
Spherical Telescope (FAST) will allow for great advances in pulsar astronomy.
We have performed simulations to estimate the number of previously unknown
pulsars FAST will find with its 19-beam or possibly 100-beam receivers for
different survey strategies. With the 19-beam receiver, a total of 5200
previously unknown pulsars could be discovered in the Galactic plane, including
about 460 millisecond pulsars (MSPs). Such a survey would take just over 200
days with eight hours survey time per day. We also estimate that, with about 80
six-hour days, a survey of M31 and M33 could yield 50--100 extra-Galactic
pulsars. A 19-beam receiver would produce just under 500 MB of data per second
and requires about 9 tera-ops to perform the major part of a real time
analysis. We also simulate the logistics of high-precision timing of MSPs with
FAST. Timing of the 50 brightest MSPs to a signal-to-noise of 500 would take
about 24 hours per epoch.Comment: 9 pages, 10 figures; accepted for publication in A&
Accelerating incoherent dedispersion
Incoherent dedispersion is a computationally intensive problem that appears
frequently in pulsar and transient astronomy. For current and future transient
pipelines, dedispersion can dominate the total execution time, meaning its
computational speed acts as a constraint on the quality and quantity of science
results. It is thus critical that the algorithm be able to take advantage of
trends in commodity computing hardware. With this goal in mind, we present
analysis of the 'direct', 'tree' and 'sub-band' dedispersion algorithms with
respect to their potential for efficient execution on modern graphics
processing units (GPUs). We find all three to be excellent candidates, and
proceed to describe implementations in C for CUDA using insight gained from the
analysis. Using recent CPU and GPU hardware, the transition to the GPU provides
a speed-up of 9x for the direct algorithm when compared to an optimised
quad-core CPU code. For realistic recent survey parameters, these speeds are
high enough that further optimisation is unnecessary to achieve real-time
processing. Where further speed-ups are desirable, we find that the tree and
sub-band algorithms are able to provide 3-7x better performance at the cost of
certain smearing, memory consumption and development time trade-offs. We finish
with a discussion of the implications of these results for future transient
surveys. Our GPU dedispersion code is publicly available as a C library at:
http://dedisp.googlecode.com/Comment: 15 pages, 4 figures, 2 tables, accepted for publication in MNRA
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