3,547 research outputs found
Association of corotating magnetic sector structure with Jupiters decameter-wave radio emissions
Chree (superposed epoch) analyses of Jupiter's decameter-wave radio emission taken from the new Thieman (1979) catalog show highly significant correlation with solar activity indicated by the geomagnetic Ap index. The correlation effects can be explained in terms of corotating interplanetary magnetic sector features. At times when the solar wind velocity is relatively low, about 300 to 350 km/s, a sector boundary can encounter the Earth and Jupiter almost simultaneously during the period immediately before opposition. After opposition this will not normally occur as the solar wind velocities necessary are too low. The correlation effects are much enhanced for the three apparitions of 1962-1964 during which a relatively stable and long-lived sector pattern was present. Chree analyses for this period indicate periodicities, approximately equal to half the solar rotation period, in the Jupiter data
Direct evidence for solar wind control of Jupiter's hectometer-wavelength radio emission
Observations of the solar wind close to Jupiter, by the Voyager 1 and Voyager 2 spacecraft in 1978 and 1979, are compared with the hectometer wavelength radio emission from the planet. A significant positive correlation is found between variations in the solar wind plasma density at Jupiter and the level of Jovian radio emission output. During the 173-day interval studied for the Voyager 2 data, the radio emission displayed a long term periodicity of about 13 days, identical to that shown by the solar wind density at Jupiter and consistent with the magnetic sector structure association already proposed for groundbased observations of the decameter wavelength emission
A catalog of radio observations of Jupiter 1961-1964
Catalog of radio observations of Jupiter 1961 to 196
Observable Effects of Scalar Fields and Varying Constants
We show by using the method of matched asymptotic expansions that a
sufficient condition can be derived which determines when a local experiment
will detect the cosmological variation of a scalar field which is driving the
spacetime variation of a supposed constant of Nature. We extend our earlier
analyses of this problem by including the possibility that the local region is
undergoing collapse inside a virialised structure, like a galaxy or galaxy
cluster. We show by direct calculation that the sufficient condition is met to
high precision in our own local region and we can therefore legitimately use
local observations to place constraints upon the variation of "constants" of
Nature on cosmological scales.Comment: Invited Festscrift Articl
Radio astronomy program - Summarizing report of the activities of the Florida State University Radio Observatory, 1960 - 1969 Final summary report, 1 Feb. 1962 - 30 Jun. 1969
Summary of radio observatory activities concentrating on polarization and short time resolution burst structure of radiatio
The future asymptotics of Bianchi VIII vacuum solutions
Bianchi VIII vacuum solutions to Einstein's equations are causally
geodesically complete to the future, given an appropriate time orientation, and
the objective of this article is to analyze the asymptotic behaviour of
solutions in this time direction. For the Bianchi class A spacetimes, there is
a formulation of the field equations that was presented in an article by
Wainwright and Hsu, and we analyze the asymptotic behaviour of solutions in
these variables. We also try to give the analytic results a geometric
interpretation by analyzing how a normalized version of the Riemannian metric
on the spatial hypersurfaces of homogeneity evolves.Comment: 34 pages, no figure
<Radio Astronomy Programm> Status Report No. 6 /Final/, Aug. 1, 1964 - Jan. 31, 1965
Radio and polarization observations of Jupiter, correlation between Jupiter events and solar M-region storms, and observation comparisons with Doppler shifted cyclotron prediction
The Power of General Relativity
We study the cosmological and weak-field properties of theories of gravity
derived by extending general relativity by means of a Lagrangian proportional
to . This scale-free extension reduces to general relativity when
. In order to constrain generalisations of general relativity of
this power class we analyse the behaviour of the perfect-fluid Friedmann
universes and isolate the physically relevant models of zero curvature. A
stable matter-dominated period of evolution requires or . The stable attractors of the evolution are found. By considering the
synthesis of light elements (helium-4, deuterium and lithium-7) we obtain the
bound We evaluate the effect on the power spectrum of
clustering via the shift in the epoch of matter-radiation equality. The horizon
size at matter--radiation equality will be shifted by for a value of
We study the stable extensions of the Schwarzschild
solution in these theories and calculate the timelike and null geodesics. No
significant bounds arise from null geodesic effects but the perihelion
precession observations lead to the strong bound assuming that Mercury follows a timelike geodesic. The combination of
these observational constraints leads to the overall bound on theories of this type.Comment: 26 pages and 5 figures. Published versio
Structure and stability of the Lukash plane-wave spacetime
We study the vacuum, plane-wave Bianchi spacetimes described by
the Lukash metric. Combining covariant with orthonormal frame techniques, we
describe these models in terms of their irreducible kinematical and geometrical
quantities. This covariant description is used to study analytically the
response of the Lukash spacetime to linear perturbations. We find that the
stability of the vacuum solution depends crucially on the background shear
anisotropy. The stronger the deviation from the Hubble expansion, the more
likely the overall linear instability of the model. Our analysis addresses
rotational, shear and Weyl curvature perturbations and identifies conditions
sufficient for the linear growth of these distortions.Comment: Revised version, references added. To appear in Class. Quantum Gra
Von Bezold assimilation effect reverses in stereoscopic conditions
Lightness contrast and lightness assimilation are opposite phenomena: in contrast,
grey targets appear darker when bordering bright surfaces (inducers) rather than dark ones; in
assimilation, the opposite occurs. The question is: which visual process favours the occurrence
of one phenomenon over the other? Researchers provided three answers to this question. The
first asserts that both phenomena are caused by peripheral processes; the second attributes their
occurrence to central processes; and the third claims that contrast involves central processes,
whilst assimilation involves peripheral ones. To test these hypotheses, an experiment on an IT
system equipped with goggles for stereo vision was run. Observers were asked to evaluate the
lightness of a grey target, and two variables were systematically manipulated: (i) the apparent
distance of the inducers; and (ii) brightness of the inducers. The retinal stimulation was kept
constant throughout, so that the peripheral processes remained the same. The results show that
the lightness of the target depends on both variables. As the retinal stimulation was kept constant, we
conclude that central mechanisms are involved in both lightness contrast and lightness assimilation
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