324 research outputs found
A national recursive simulation and linear programming model of some major crops in U.S. agriculture
IMPLICATIONS OF FEEDER PIG PRICE VARIABILITY IN VIRGINIA TELE-AUCTION MARKETS
Demand and Price Analysis,
ANALYZING THE ECONOMIC IMPACT OF NATIONAL BEEF IMPORT LEVEL CHANGES ON THE VIRGINIA BEEF AND PORK SECTORS
International Relations/Trade,
The Properties and Gaseous Environments of Powerful Classical Double Radio Galaxies
The properties of a sample of 31 very powerful classical double radio
galaxies with redshifts between zero and 1.8 are studied. The source
velocities, beam powers, ambient gas densities, total lifetimes, and total
outflow energies are presented and discussed. The rate of growth of each side
of each source were obtained using a spectral aging analysis. The beam power
and ambient gas density were obtained by applying the strong shock jump
conditions to the ends of each side of the source. The total outflow lifetime
was obtained by applying the power-law relationship between the beam power and
the total source lifetime derived elsewhere for sources of this type, and the
total outflow energy was obtained by combining the beam power and the total
source lifetime. Composite profiles were constructed by combining results
obtained from each side of each source. The composite profiles indicate that
the ambient gas density falls with distance from the central engine. The source
velocities, beam powers, total lifetimes, and total energies seem to be
independent of radio source size. This is consistent with the standard model in
which each source grows at a roughly constant rate during which time the
central engine puts out a roughly constant beam power. The fact that the total
source lifetimes and energies are independent of radio source size indicates
that the sources are being sampled at random times during their lifetimes.Comment: 7 pages, 5 figures, to appear in "Extragalactic Jets: Theory and
Observation from Radio to Gamma Ray", eds. T. A. Rector and D. S. De Young,
ASP conference series, Replaced version has minor textual correction
Improved Constraints on the Acceleration History of the Universe and the Properties of the Dark Energy
We extend and apply a model-independent analysis method developed earlier by
Daly & Djorgovski to new samples of supernova standard candles, radio galaxy
and cluster standard rulers, and use it to constrain physical properties of the
dark energy as functions of redshift. Similar results are obtained for the
radio galaxy and supernova data sets. The first and second derivatives of the
distance are compared directly with predictions in a standard model based on
General Relativity. The good agreement indicates that General Relativity
provides an accurate description of the data on look-back time scales of about
ten billion years. The first and second derivatives are combined to obtain the
acceleration parameter, assuming only the validity of the Robertson-Walker
metric, independent of a theory of gravity and of the physical nature of the
dark energy. The acceleration of the universe at the current epoch is indicated
by the analysis. The effect of non-zero space curvature on q(z) is explored. We
solve for the pressure, energy density, equation of state, and potential and
kinetic energy of the dark energy as functions of redshift assuming that
General Relativity is the correct theory of gravity, and the results indicate
that a cosmological constant in a spatially flat universe provides a good
description of each of these quantities over the redshift range from zero to
about one. We define a new function, the dark energy indicator, in terms of the
first and second derivatives of the coordinate distance and show how this can
be used to measure deviations of w from -1 and to obtain a new and independent
measure of Omega.Comment: 46 pages, submitted for publicatio
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