1,456 research outputs found
CHARACTERISTICS OF HIGHLY EFFICIENT FARMS
A sample of Kansas farms was used to examine the relationship between overall efficiency and farm characteristics. Overall efficiency was significantly related to operator age, farm size, and farm type. Approximately 26.7% of the farms were in the top one-third overall efficiency category for more than half of the sample period.Farm Management,
Impact of the U.S. House of Representatives BTU Tax Proposal on Whole Farm and Enterprise Production Costs in Kansas
Agricultural and Food Policy, Agricultural Finance,
Coherent network analysis for continuous gravitational wave signals in a pulsar timing array: Pulsar phases as extrinsic parameters
Supermassive black hole binaries are one of the primary targets for
gravitational wave searches using pulsar timing arrays. Gravitational wave
signals from such systems are well represented by parametrized models, allowing
the standard Generalized Likelihood Ratio Test (GLRT) to be used for their
detection and estimation. However, there is a dichotomy in how the GLRT can be
implemented for pulsar timing arrays: there are two possible ways in which one
can split the set of signal parameters for semi-analytical and numerical
extremization. The straightforward extension of the method used for continuous
signals in ground-based gravitational wave searches, where the so-called pulsar
phase parameters are maximized numerically, was addressed in an earlier paper
(Wang et al. 2014). In this paper, we report the first study of the performance
of the second approach where the pulsar phases are maximized semi-analytically.
This approach is scalable since the number of parameters left over for
numerical optimization does not depend on the size of the pulsar timing array.
Our results show that, for the same array size (9 pulsars), the new method
performs somewhat worse in parameter estimation, but not in detection, than the
previous method where the pulsar phases were maximized numerically. The origin
of the performance discrepancy is likely to be in the ill-posedness that is
intrinsic to any network analysis method. However, scalability of the new
method allows the ill-posedness to be mitigated by simply adding more pulsars
to the array. This is shown explicitly by taking a larger array of pulsars.Comment: 30 pages, 11 figures, revised version, published in Ap
A coherent method for the detection and estimation of continuous gravitational wave signals using a pulsar timing array
The use of a high precision pulsar timing array is a promising approach to
detecting gravitational waves in the very low frequency regime ( Hz) that is complementary to the ground-based efforts (e.g., LIGO,
Virgo) at high frequencies ( Hz) and space-based ones (e.g.,
LISA) at low frequencies ( Hz). One of the target sources for
pulsar timing arrays are individual supermassive black hole binaries that are
expected to form in galactic mergers. In this paper, a likelihood based method
for detection and estimation is presented for a monochromatic continuous
gravitational wave signal emitted by such a source. The so-called pulsar terms
in the signal that arise due to the breakdown of the long-wavelength
approximation are explicitly taken into account in this method. In addition,
the method accounts for equality and inequality constraints involved in the
semi-analytical maximization of the likelihood over a subset of the parameters.
The remaining parameters are maximized over numerically using Particle Swarm
Optimization. Thus, the method presented here solves the monochromatic
continuous wave detection and estimation problem without invoking some of the
approximations that have been used in earlier studies.Comment: 33 pages, 10 figures, submitted to Ap
The stochastic background: scaling laws and time to detection for pulsar timing arrays
We derive scaling laws for the signal-to-noise ratio of the optimal
cross-correlation statistic, and show that the large power-law increase of the
signal-to-noise ratio as a function of the the observation time that is
usually assumed holds only at early times. After enough time has elapsed,
pulsar timing arrays enter a new regime where the signal to noise only scales
as . In addition, in this regime the quality of the pulsar timing
data and the cadence become relatively un-important. This occurs because the
lowest frequencies of the pulsar timing residuals become gravitational-wave
dominated. Pulsar timing arrays enter this regime more quickly than one might
naively suspect. For T=10 yr observations and typical stochastic background
amplitudes, pulsars with residual RMSs of less than about s are already
in that regime. The best strategy to increase the detectability of the
background in this regime is to increase the number of pulsars in the array. We
also perform realistic simulations of the NANOGrav pulsar timing array, which
through an aggressive pulsar survey campaign adds new millisecond pulsars
regularly to its array, and show that a detection is possible within a decade,
and could occur as early as 2016.Comment: Submitted to Classical and Quantum Gravity for Focus Issue on Pulsar
Timing Arrays. 15 pages, 5 figure
Alpha clustering studied with the (6Li,d) and (d,6Li) reactions
The systematics, throughout the periodic table, of the (6Li,d) and (d,6Li) reactions are reviewed. The α‐spectroscopic factors extracted exhibit correlations with shell effects, nuclear pairing and nuclear deformation. The data are compared with calculations using SU3, pseudo‐SU3, the jj‐shell model, the pairing‐vibration and boson‐expansion models. Many, but not all of the experimental features are reproduced by existing models.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87458/2/308_1.pd
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