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771.
W. J. Chaplin G. Houdek Y. Elsworth D. O. Gough G. R. Isaak R. New 《Monthly notices of the Royal Astronomical Society》2005,360(3):859-868
We investigate the frequency dependence of the power spectral density of low-degree solar p modes by comparing measurements with the results of a stochastic-excitation model. In the past it was common practice to use the total power in such investigations. Using the maximum of the power spectral density instead provides a direct comparison with the measured mode heights in the observed power spectrum. This method permits a more careful calibration of the adjustable parameters in the excitation model, a model which we present here, for the first time, in a format that precisely and unambiguously relates the amplitudes of the modes of oscillation to the Reynolds stress in the equilibrium model. We find that errors in the theory of the linear mode damping rates, particularly at low frequency, have a dramatic impact on the predictions of the mode heights in the spectral density, whereas parameter changes in the stochastic excitation model, within a plausible domain of parameter space, have a comparatively small effect. 相似文献
772.
Steven J. Ostro Lance A. M. Benner Christopher Magri Jon D. Giorgini Randy Rose Raymond F. Jurgens Donald K. Yeomans Alice A. Hine Michael C. Nolan Daniel J. Scheeres Stephen B. Broschart Mikko Kaasalainen Jean‐Luc Margot 《Meteoritics & planetary science》2005,40(11):1563-1574
Abstract— We present June 2004 radar images of asteroid 25143 Itokawa (1998 SF36) that improve upon the longitude‐latitude coverage of images obtained in 2001 by Ostro et al. (2004) and use the 2001–2004 data to refine that paper's constraints on Itokawa's shape. The 2004 images, the first of the asteroid's southern side, look distinctly different from the 2001 images, revealing leading edges that are much more curved and rugged than the nearly convex leading edges seen at northern latitudes in 2001. Itokawa is shaped like a slightly asymmetrical, bent, lumpy ellipsoid with dimensions along the principal axes within 10% of 594 times 320 times 288 m. To illustrate the uncertainty space associated with shape reconstruction from images with suboptimal orientational coverage, we present two alternative three‐dimensional models of the object. 相似文献
773.
774.
C. D. Murray 《Celestial Mechanics and Dynamical Astronomy》1985,36(2):163-164
An examination of Le Verrier's seventh-order expansion of the disturbing function has revealed only one non-trivial error in Le Verrier's work. The error occurs in a sixth order term in the eccentricities. 相似文献
775.
R. G. Langebartel 《Astrophysics and Space Science》1985,115(1):39-41
The average radial and angular velocity components are obtained for a rotating two-dimensional self-gravitating system near an equilibrium state. First-order perturbation configurations of flaring straight bars emanating from the center provide examples of such systems. In these systems the average velocity field to first order is incompressible and irrotational. The second-order effects on the product of the average velocity components with the spatial density are essentially independent of the angular coordinate. 相似文献
776.
Profiles of spectral lines emitted from an accretion ring around an object with strong gravitational field should be affected by Doppler shift, gravitational redshift, and deflection of light. Taking these effects into account, precise line profile of a Keplerian ring around a Kerr black hole for a distant observer is obtained by solving the kinetic equation of photons. 相似文献
777.
E. I. Timoshkova 《Celestial Mechanics and Dynamical Astronomy》1985,36(2):105-121
The first integrals of motion of the restricted planar circular problem of three bodies are constructed as the formal power series in r1/2, r being the distance of a moving particle from the primary. It is shown that the coefficients of these series are trigonometric polynomials of an angular variable. Some particular solutions have been found in a closed form. The proposed method for constructing the formal integrals can be generalized to a spatial problem of three bodies. 相似文献
778.
In situ measurements at the lunar surface at millimeter resolution by the Apollo astronauts have been analyzed. Several statistical parameters have been determined for the landing site. The surface roughness has been found to be very nearly gaussian. The root-mean-square slopes have been obtained over scales between 0.5 mm and 5 cm. They steadily decrease with increasing scale length from 58° to 2° and are in reasonable agreement with radar-measured values. The autocorrelation coefficient of the height distribution has also been obtained. It has a scale-length of 0.7 mm.Adjunct Professor at the University of Massachusetts.Visiting Scholar at the University of Massachusetts. 相似文献
779.
F. M. F. El-Sabaa 《Celestial Mechanics and Dynamical Astronomy》1985,37(1):71-79
The equation of motion of a rigid body in Kovaleveskaya case is reduced to a plane motion. By using the method of small parameters introduced by Poincaré, the existence of a periodic solution is established. 相似文献
780.
Donald C. Gordon Peter J. Cranford Con Desplanque 《Estuarine, Coastal and Shelf Science》1985,20(2):205-227
The Cumberland Basin, a 118 km2 estuary at the head of the Bay of Fundy which has an average tidal range of about 11m, contains large tracts of salt marsh (15% of the area below highest high water). Low marsh (below about 0·9 m above mean high water) is composed almost exclusively of Spartina alterniflora while the vegetation on high marsh is more diverse but dominated by Spartina patens. Because of its higher elevation, high marsh is flooded infrequently for short periods by only extreme high tides. Low marsh is inundated much more frequently by water as much as 4m deep for periods as long as 4 h per tide. Temporal variability in the occurrence of extreme tides influences the flooding frequency of high marsh for any given month and year. Using a modification of Smalley's method, the mean annual net aerial primary production (NAPP) of low and high marsh is estimated to be 272 and 172 g C m?2, respectively. Vegetation turnover times average 1·0 and 2·0 y for low and high marsh, respectively. Because of abundant tidal energy, much of the low marsh production appears to be exported and distributed widely about the estuary. Since high levels of turbidity suppress phytoplankton production, salt marshes produce approximately half of the carbon fixed photosynthetically in the Cumberland Basin. It is concluded that salt marshes play a major ecological role in the Cumberland Basin. 相似文献