共查询到20条相似文献，搜索用时 234 毫秒
1.
Literal characterizations are developed for the eigenvalues and eigenvectors of a system of linear time-invariant equations which describes the attitude motion of flexible spacecraft in terms of hybrid coordinates. The eigenproblem is shown to reduce to that of a symmetric and positive definite matrix of lower dimension. For the zero damping case, both analytical and minimax characterization methods prove to be useful in localizing the eigenvalues, and eigenvectors for systems of large dimension are obtained explicitly in terms of a 3×1 matrix whose elements are available from a system of three algebraic equations provided. 相似文献
2.
J. F. C. Van Velsen 《Celestial Mechanics and Dynamical Astronomy》1981,23(4):383-395
The tensor
appearing in the equation of geodesic deviation is computed for the equilateral solution of the general three-body problem. The eigenvalues and eigenvectors ofC
k
i
are determined. It is found that at least one of the eigenvalues is negative, irrespective of the masses of the bodies. This implies that the equilateral solution is not stable. The eigenvectors with positive eigenvalues generate isoenergetic 1-parameter families of quasi-periodic solutions in the neighborhood of the equilateral solution. The relation between the 1-parameter families constructed here and those known from the literature is discussed. 相似文献
3.
Joel C. Carvalho 《Astrophysics and Space Science》2006,306(1-2):5-9
It is shown that the expressions of five fundamental masses appearing in physics and cosmology can be written in terms of the constants of nature. We study the time variation of them in the context of a generalized Dirac’s cosmology based on the large number hypothesis (LNH). This generalization allows one to have the gravitational constant not depending upon time contrary to Dirac’s original theory. It also allows the rest mass of the particle to vary with cosmological time. Further, we show that there exist simple algebraic relations between them and that their ratios can be expressed as powers of the large dimensionless number 1040. 相似文献
4.
Emmanuelle Julliard-Tosel 《Celestial Mechanics and Dynamical Astronomy》2000,76(4):241-281
We give here a proof of Bruns’ Theorem which is both complete and as general as possible:
Generalized Bruns’ Theorem.In the Newtonian (n+1)-body problem in
ℝ
p
with n≥2 and 1≤p≤n+1, every first integral which is algebraic with respect to positions, linear momenta and time, is an algebraic function of the
classical first integrals: the energy, the p(p−1)/2 components of angular momentum and the 2p integrals that come from the uniform linear motion of the center of mass.
Bruns’ Theorem only dealt with the Newtonian three-body problem in ℝ3; we have generalized the proof to n+1 bodies in ℝp with p≤n+1. The whole proof is much more rigorous than the previous versions (Bruns, Painlevé, Forsyth, Whittaker and Hagiara). Poincaré
had picked out a mistake in the proof; we have understood and developed Poincaré’s instructions in order to correct this point
(see Subsection 3.1). We have added a new paragraph on time dependence which fills in an up to now unnoticed mistake (see
Section 6). We also wrote a complete proof of a relation which was wrongly considered as obvious (see Section 3.3). Lastly,
the generalization, obvious in some parts, sometimes needed significant modifications, especially for the case p=1 (see Section 4).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
The yields of stable isotopes of Bi, Pb, Tl and Hg as well as yields of 205Pb are calculated with a parameterized model for “mini r-processing” in the Ne, O, C-rich zones of explosive burning in massive stars. The Pb isotopic compositions stand out by their comparatively low 207Pb yields and by the fact that this r-process variant yields 204Pb quite abundantly. The average 205Pb/204Pb yield ratio of 6.1 is the same order of magnitude as yield ratios deduced for s-processing. The Hg from this mini r-process looks like normal solar-system mercury, but with 196Hg missing and the light s-isotopes A = 198, 199, 200 and 201 depleted (especially the odd-A species). 相似文献
6.
The statistical behaviour of intermittent trajectories at the 3/1resonance is investigated. The elliptic planar restricted three-body problemis used as a model. Distribution functions for time intervals D betweeneccentricity bursts are obtained and theoretically interpreted. For smallervalues of D the distribution is found to be of Poisson type, while in itstail it is described by a power law D. This change in thedistribution occurs for values of D in the range105106Jupiter periods. The power-lawindexfor the integral distributions lies in the range (-2,-1) and istrajectory dependent. The algebraic decay in the tails of the distributionsis explained by the phenomenon of sticking of orbits to the chaos borderduring long intervals between bursts. 相似文献
7.
Jay H. Lieske 《Celestial Mechanics and Dynamical Astronomy》1975,12(1):5-17
In his effort to develop series expressions for the coordinates of the Galilean satellites accurate to one are second (Jovicentric), R. A. Sampson was forceda priori to adopt certain numerical values for several constants imbedded in his theory. His final numerical values for the series expressions are not amenable to adjustment of the constants of integration nor of physical constants which affect the motion of the satellites. A method which utilizes computer-based algebraic manipulation software has been developed to reconstruct Sampson's theory, to remove existing errors, to introduce neglected effects and to provide analytical expressions for the coordinates as well as for the partial derivatives with respect to orbital parameters, Jupiter and satellite masses, Jupiter's oblateness (J 2,J 4) and Jupiter's pole and period of rotation. The computer-based manipulations enable one to perform, for example, the approximately 108 multiplications required in calculating some perturbations (and their partial derivatives) of Satellite II by Satellite III with ease, and provide algebraic expressions which can readily be adjusted to generate theories corresponding to revised constants of integration and physical parameters. 相似文献
8.
Ian Halliday Arthur A. Griffin Alan T. Blackwell 《Meteoritics & planetary science》1981,16(2):153-170
The Innisfree meteorite was the third fall for which accurate orbital data were secured from a camera network. Nine fragments were found within three months of the fall with a total mass of 4.58 kg. The ellipse of fall is unusually small because of the steep path in the atmosphere. The photograph from the Vegreville station reveals six trails below 26 km and these are correlated with the six main fragments, all with masses in excess of 300 g. A photometric study indicates that Innisfree had a peak absolute magnitude Mpan = ?12.1 at a height of 36 km. The recovered meteorites provide known masses for the late stages of the photographic trails which, combined with dynamical data, allow luminous efficiencies to be derived with unusual confidence. Late in the flight where shock wave effects dominate ablation, luminous efficiencies vary from 3 × 10?5 to 5 × 10?2 for velocities between 3 and 10 km s?1 and masses from 0.3 to 2.0 kg. The mean luminous efficiency for the entire flight is estimated between 4 × 10?2 and 8 × 10?2. 相似文献
9.
In this paper we show that the explosive products from O-shells of massive stars which contain 124Xe with large overproduction factors do not contain any of the naturally occurring isotopes of Os and Pb. We show further that the explosive products from C-shells (explosive carbon burning) do contain Os and Pb along with Xe which is strongly enriched in r-Xe of anomalous isotopic composition. The composition of Os in this matter is probably s-like rather than r-like. Pb in this matter is enriched in 208Pb. The results and arguments of this paper have implications for studies of isotopic compositions of Xe, Os, and Pb in residues of the Allende and other carbonaceous chondrites. 相似文献
10.
Angelo James Skalafuris 《Astrophysics and Space Science》1974,29(1):L9-L17
Given an equation of State, the three equations of mass, momentum and energy conservation determine the vortex free flow fields in a star. The solar data processed by Athay (1966) is a measure of the dissipation of the fluid, while the use of an empirical temperature profile (BCA, 1968) permits values for the gradients in the equations of fluid flow rendering them algebraic, with solutions independent of boundary conditions. This approach serves as a consistency check on the methods with which data have been processed by inquiring to what degree the basic conservation laws have been satified, and by directly implying a velocity field which can be scrutinized for its observational consequences. We find that the most consistent interpretation to this data is that the temperature minimum should not be coincident with flux maximum as the BCD model photosphere is, and that the temperature profile must rise higher at the 1500 km. region above optical depth one. Furthermore, more emissions must occur in the U-V metals at this region to support such a temperature increase, but at least an order of magnitude decrease in H? emission should also be expected, as well as some suppression of the Balmer. As a theoretical consequence horizontal stratification of the velocity field occurs, suggesting either cellular motions or differential rotation with surface velocities as high as 60 km s?1, but on the average near 30 to 40 km s?1, across the solar surface. 相似文献
11.
This paper presents a non-iterative approach to solve Kepler’s Equation, M = E − e sin E, based on non-rational cubic and rational quadratic Bézier curves. Optimal control point coordinates are first shown to be
linear with respect to orbit eccentricity for any eccentric anomaly range. This property yields the development of a piecewise
(e.g., 3, 4) solving technique providing accuracies better than 10−13 degree for orbit eccentricity e ≤ 0.99. The proposed method does not require large pre-computed discretization data, but instead solves a cubic/quadratic
algebraic equation and uses a single final Halley iteration in only a few lines of code. The method still provides accuracies
better than 10−5 degree for the near parabolic worst case (e = 0.9999) with very small mean anomalies (M < 0.0517 deg). The complexity of the proposed algorithm is constant, independent of the parameters e and M. This makes the method suitable for extensive orbit propagations.
Presented at the 7th Dynamics and Control of Systems and Structures in Space Conference, July 18–22, 2006, Greenwich, England. 相似文献
12.
The Mangala Valles system is an ∼
∼900 km fluvially carved channel system located southwest of the Tharsis rise and is unique among the martian outflow channels
in that it heads at a linear fracture within the crust as opposed to a collapsed region of chaos as is the case with the circum-Chryse
channels. Mangala Valles is confined within a broad, north–south trending depression, and begins as a single valley measuring
up to 350 km wide that extends northward from a Memnonia Fossae graben, across the southern highlands toward the northern
lowlands. Approximately 600 km downstream, this single valley branches into multiple channels, which ultimately lose their
expression at the dichotomy boundary. Previous investigations of Mangala Vallis suggested that many of the units mapped interior
to the valley were depositional, related to flooding, and that a minimum of two distinct periods of flooding separated by
tens to hundreds of millions of years were required to explain the observed geology. We use infrared and visible images from
the THermal EMission Imaging System (THEMIS), and topographic data from the Mars Orbiting Laser Altimeter (MOLA), to investigate
the nature of the units mapped within Mangala Vallis. We find that the geomorphology of the units, as well as their topographic
and geographic distribution, are consistent with most of them originating from a single assemblage of volcanic flow deposits,
once continuous with volcanic flows to the south of the Memnonia Fossae source graben. These flows resurfaced the broad, north–south
trending depression into which Mangala Vallis formed prior to any fluvial activity. Later flooding scoured and eroded this
volcanic assemblage north of the Mangala source graben, resulting in the present distribution of the units within Mangala
Vallis. Additionally, our observations suggest that a single period of catastrophic flooding, rather than multiple periods
separated by tens to hundreds of millions of years, is consistent with and can plausibly explain the interior geology of Mangala
Vallis. Further, we present a new scenario for the source and delivery of water to the Mangala source graben that models flow
of groundwater through a sub-cryosphere aquifer and up a fracture that cracks the cryosphere and taps this aquifer. The results
of our model indicate that the source graben, locally enlarged to a trough near the head region of Mangala, would have required
less than several days to fill up prior to any spill-over of water to the north. Through estimates of the volume of material
missing from Mangala (13,000–20,000 km3), and calculation of mean discharge rates through the channel system (∼
∼5 × 106 m3 s−1), we estimate that the total duration of fluvial activity through the Mangala Valles was 1–3 months. 相似文献
13.
The energy density of Vaidya-Tikekar isentropic superdense star is found to be decreasing away from the center, only if the
parameter K is negative. The most general exact solution for the star is derived for all negative values of K in terms of circular and inverse circular functions. Which can further be expressed in terms of algebraic functions for K = 2-(n/δ)2 < 0 (n being integer andδ = 1,2,3 4). The energy conditions 0 ≤ p ≤ αρc
2, (α = 1 or 1/3) and adiabatic sound speed conditiondp dρ ≤ c
2, when applied at the center and at the boundary, restricted the parameters K and α such that .18 < −K −2287 and.004 ≤ α ≤ .86. The maximum mass of the star satisfying the strong energy condition (SEC),
(α = 1/3) is found to be3.82 Mq· at K=−2/3, while the same for the weak energy condition (WEC), (α =1) is 4.57 M_
⊙ atK=−>5/2. In each case the surface density is assumed to be 2 × 1014 gm cm-3. The solutions corresponding to K>0 (in fact K>1) are also made meaningful by considering the hypersurfaces t= constant as 3-hyperboloid by replacing the parameter R
2 by −R2 in Vaidya-Tikekar formalism. The solutions for the later case are also expressible in terms of algebraic functions for K=2-(n/δ2 > 1 (n being integer or zero and δ =1,2,3 4). The cases for which 0 < K < 1 do not possess negative energy density gradient and therefore are incapable of representing any physically plausible
star model. In totality the article provides all the physically plausible exact solutions for the Buchdahl static perfect
fluid spheres.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Penumbral line-core shifts at different heights are determined from the lines Fei 5434.5 Å, Fei 5435.2 Å, and Nii 5435.8 Å using two adjacent water vapor lines for an absolute wavelength scale. The large granular blue shift of 0.6 km s-1 for the faint Fe 5435 line from deep layers yields for the centre-side penumbra absolute velocities up to 3 km s-1. This value is much larger than velocities deduced from the bisectors of the line wings of Ni 5436 and Fe 5434, thus supporting the concern against an interpretation of the line asymmetries in term of a velocity gradient with depth. 相似文献
15.
李焱 《中国天文和天体物理学报》1989,(4)
本文发展了一种解恒星线性非绝热非径向脉动问题的退耦化方法。这个方法把非绝热非径向脉动问题的六阶线性微分方程,分解为由一个代数方程联系起来的一个四阶线性微分方程和另一个二阶线性微分方程进行数值求解。这样的一个退耦处理,有利于克服以前在数值解这类问题时常常遇到的收敛域小和收敛速度慢等困难,并且为数值解方程时所采用的Henyey方法提供了一个自然和方便的初始猜测解。 相似文献
16.
We present a straightforward comparison of model calculations for the α-effect, helicities, and magnetic field line twist
in the solar convection zone with magnetic field observations at atmospheric levels. The model calculations are carried out
in a mixing-length approximation for the turbulence with a profile of the solar internal rotation rate obtained from helioseismic
inversions. The magnetic field data consist of photospheric vector magnetograms of 422 active regions for which spatially-averaged
values of the force-free twist parameter and of the current helicity density are calculated, which are then used to determine
latitudinal profiles of these quantities. The comparison of the model calculations with the observations suggests that the
observed twist and helicity are generated in the bulk of the convection zone, rather than in a layer close to the bottom.
This supports two-layer dynamo models where the large-scale toroidal field is generated by differential rotation in a thin
layer at the bottom while the α-effect is operating in the bulk of the convection zone. Our previous observational finding
was that the moduli of the twist factor and of the current helicity density increase rather steeply from zero at the equator
towards higher latitudes and attain a certain saturation at about 12 – 15∘. In our dynamo model with algebraic nonlinearity, the increase continues, however, to higher latitudes and is more gradual.
This could be due to the neglect of the coupling between small-scale and large-scale current and magnetic helicities and of
the latitudinal drift of the activity belts in the model. 相似文献
17.
Neidig Donald F. Švestka ZdenĚk Cliver Edward W. Airapetian Vladimir Henry Timothy W. 《Solar physics》1997,170(2):321-339
Faintly visible, darkened regions in H lying outside but adjacentto bright flare emissionwere found to occur in 10 of 31 major flares investigated. Without exception, the darkenings occur over magnetically neutral areas, and these are usually bordered by ridges ofoppositely-poled field, where one border is shared in common with a flare ribbon. Thedarkenings probably result from the formation of faint, outlying loop systems, similar topost-flare loops seen in absorption, but which are connected to magnetic features outsidethe flare and are unresolved or only marginally resolved in patrol images. Simple modelsfor post-flare loops incorporating the results of statistical equilibrium calculations readilydemonstrate that darkenings of several percent (consistent with our photometric measurements) can be produced by loop structures of cross-sectional diameter 102 km (unresolved by patrol instruments) and containing gas at densities 5 × 1010–5 × 1011 cm-3 andtemperatures 8000–15000 K. Outlying loop systems might be formed by magnetic fieldreconnection, analogous to the mechanism ascribed to eruptive two-ribbon flares, butassociated with field structures adjacent to the flare. Alternatively, these outlying loopsystems may not erupt but become visible as a result of heating and chromospheric evaporation at the footpoints shared with the flare ribbon. In either case, the observations presented here have interesting implications for both the spatial scale and the topology of thecoronal magnetic fields in which eruptions occur. 相似文献
18.
Henri E. Mitler 《Astrophysics and Space Science》1972,17(1):186-218
The production of deuterium, He3, lithium, beryllium, and boron by galactic cosmic rays in the interstellar medium, over the life of the Galaxy, is calculated. It is found that high-energy - reactions contribute in an essential way to the observed lithium. When allowance is made for the interchange of material between stars and the interstellar gas and for the change of cosmic-ray intensity with time, the Li6, Be9, and boron produced turn out to be ample to explain the observed abundances, and with remarkable internal consistency. Deuterium and He3 arenot produced in significant amounts, nor Li7 in sufficient amount, however. To explain the Li7/Li6 ratio measured terrestrially and in chondritic meteorites, we invoke cosmological production of Li7. This implies the production of deuterium, He3, and He4 as well, in amounts consistent with observation. The theory in its present form cannot explain a solar-system Li7/Li6 ratio of 12and stellar ratios as low as 3, but additional processes can be adduced to reconcile them. The consistency of the numbers when cosmological production is included lends additional support to the big-bang hypothesis. An incidental result is that the mean luminosity of the Galaxy over its lifetime has been about 3 times its present luminosity. 相似文献
19.
The relationship between the depletions of 6Li and 7Li is studied for two models of lithium burning, below the convective zone. The parametersof the depletion models are submitted
to the constraint that the slope ofthe 7Li theoretical depletion curve agrees with the slope of theobserved depletion curve, for cool subdwarfs. Other less restrictive
modelsare also considered.In all cases, a 6Li depletion less than 0.5 dex implies a 7Lidepletion less than 0.1 dex. With the constraint on the slope of the7Li curve, the depletion of 7Li for the same depletion of 6Li is below 0.05 dex.
The still unsolved problem for the true 7Li abundance in subdwarfs is the possible influence of temperature inhomogeneities, raised by Kurucz,subsequently shown to
be small in the solar case, but not yet computed withthe inclusion of departure from LTE for metal-poor stars.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献