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431.
432.
433.
Daniel Steichen 《Celestial Mechanics and Dynamical Astronomy》1998,68(3):205-224
We describe a semi-analytical averaging method aimed at the computation of the motion of an artificial satellite of the Moon.
In this paper, the first of the two part study, we expand the disturbing function with respect to the small parameters. In
particular, a semi-analytic theory of the motion of the Moon around the Earth and the libration of the lunar equatorial plane
using different reference frames are introduced. The second part of this article shows that the choice of the canonical Poincaré
variables lead to equations in closed form without singularities in e = 0 or I = 0. We introduce new expressions that are
sufficiently compact to be used for the study of any artificial satellite.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
434.
Richard B. Larson 《Monthly notices of the Royal Astronomical Society》1998,301(2):569-581
It has frequently been suggested in the literature that the stellar IMF in galaxies was top-heavy at early times. This would be plausible physically if the IMF depended on a mass-scale such as the Jeans mass that was higher at earlier times because of the generally higher temperatures that were present then. In this paper it is suggested, on the basis of current evidence and theory, that the IMF has a universal Salpeter-like form at the upper end, but flattens below a characteristic stellar mass that may vary with time. Much of the evidence that has been attributed to a top-heavy early IMF, including the ubiquitous G-dwarf problem, the high abundance of heavy elements in clusters of galaxies, and the high rate of formation of massive stars in high-redshift galaxies, can be accounted for with such an IMF if the characteristic stellar mass was several times higher during the early stages of galaxy evolution. However, significant variations in the mass-to-light ratios of galaxies and large amounts of dark matter in stellar remnants are not as easily explained in this way, because they require more extreme and less plausible assumptions about the form and variability of the IMF. Metal-free 'population III' stars are predicted to have an IMF that consists exclusively of massive stars, and they could help to account for some of the evidence that has been attributed to a top-heavy early IMF, as well as contributing importantly to the energetics and chemical enrichment of the early Universe. 相似文献
435.
Ian A. Bonnell & Melvyn B. Davies 《Monthly notices of the Royal Astronomical Society》1998,295(3):691-698
We investigate the evolutionary effect of dynamical mass segregation in young stellar clusters. Dynamical mass segregation acts on a time-scale of order the relaxation time of a cluster. Although some degree of mass segregation occurs earlier, the position of massive stars in rich young clusters generally reflects the cluster's initial conditions. In particular, the positions of the massive stars in the Trapezium cluster in Orion cannot be due to dynamical mass segregation, but indicate that they formed in, or near, the centre of the cluster. Implications of this for cluster formation and for the formation of high-mass stars are discussed. 相似文献
436.
437.
An integrated wavelet concept of physical geodesy 总被引:4,自引:1,他引:3
For the determination of the earth's gravity field many types of observations are nowadays available, including terrestrial
gravimetry, airborne gravimetry, satellite-to-satellite tracking, satellite gradio-metry, etc. The mathematical connection
between these observables on the one hand and gravity field and shape of the earth on the other is called the integrated concept
of physical geodesy. In this paper harmonic wavelets are introduced by which the gravitational part of the gravity field can
be approximated progressively better and better, reflecting an increasing flow of observations. An integrated concept of physical
geodesy in terms of harmonic wavelets is presented. Essential tools for approximation are integration formulas relating an
integral over an internal sphere to suitable linear combinations of observation functionals, i.e. linear functionals representing
the geodetic observables. A scale discrete version of multiresolution is described for approximating the gravitational potential
outside and on the earth's surface. Furthermore, an exact fully discrete wavelet approximation is developed for the case of
band-limited wavelets. A method for combined global outer harmonic and local harmonic wavelet modelling is proposed corresponding
to realistic earth's models. As examples, the role of wavelets is discussed for the classical Stokes problem, the oblique
derivative problem, satellite-to-satellite tracking, satellite gravity gradiometry and combined satellite-to-satellite tracking
and gradiometry.
Received: 28 February 1997 / Accepted: 17 November 1997 相似文献
438.
L1估计的分布及统计性质 总被引:3,自引:0,他引:3
推导了L1估计的密度函数,讨论了L1估计的统计性质,证明L1估计是无偏估计,同时还证明L1估计优于LS估计。 相似文献
439.
讨论了格上可测结构的封闭性以及此结构上落影函数的有关问题。指出并证明了逐次扩张与同时扩张的充要条件 ,以及落影函数与模糊集的关系 相似文献
440.
高温高压下水的剪切粘滞度的平衡分子动力学计算 总被引:3,自引:1,他引:2
本项工作用TIP4P模型对水分子进行了平衡分子动力学模拟。根据Green-Kubo理论,计算了温度从652K到814K,密度从0.5360g/cm3到0.8638g/cm3六个不同温度和密度水的剪切粘滞度,并和实验值进行了对比。在所计算的温度和密度范围,平衡分子动力学计算结果与实验值的平均绝对值差别为15%,好于使用非平衡分子动力学方法获得的粘滞度值。平衡分子动力学的方法将是获得地学中高温高压下流体输运性质的重要途径。 相似文献