共查询到20条相似文献,搜索用时 46 毫秒
1.
William B. Heard 《Astrophysics and Space Science》1976,43(1):63-82
The dynamics of an ensemble of particles emanating from a common point with a distribution of velocities is modeled as a continuum of particles described by a phase space distribution function. A general solution for the distribution function and the associated spatial density function is obtained for a general dynamical system. The special cases of linear dynamical systems and slow dispersion from a circular orbit are treated in detail. A transcendental equation is derived, the roots of which determine the time since initial dispersion from knowledge of the spatial density function at later times. 相似文献
2.
The behaviour of a subsystem of a many-body problem may be studied using the hierarchical relative coordinates defined by Nugeyre and Bouvier (1981), The present article employs a notation allowing the position vectors of the particles to be expressed explicity as functions of the hierarchical relative coordinates, This machinery is used to generalize a result of Patnaik's (1975) concerning escape from a many-body system. 相似文献
3.
M. N. Kremliovsky 《Solar physics》1995,159(2):371-380
The study of a nonlinear chaotic map of 11-year cycle maxima evolution recently derived from observations is presented with the purpose of predicting the features of the long-term variability of solar activity. It is stressed that dynamical forecast is limited by the Lyapunov time and a statistical approach can be justified due to the ergodic properties of the chaotic evolution. The Gleissberg variation is described as a chaotic walk and its distribution over length is shown to be broad. The global minima are identified as laminar slots of temporal intermittency and their typical distribution over length is also given. We note that a long sunspot cycle can be used as a precursor of the global minimum and a close sequence of global minima (once in approximately 1500–2000 years) may be responsible for the climatic changes (Little Ice Ages). 相似文献
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A. Kyrala 《Earth, Moon, and Planets》1982,26(1):105-107
An argument is given basing the persistence of the Great Red Spot of Jupiter on compensation of the natural decay of vorticity by collision with a portion of the vortices shed by the South boundary of the South Tropical Zone. The latter are deviated northward by Coriolis acceleration. The GRS itself is regarded as a Rankine vortex with a central depression revealing the coloration of a layer below. 相似文献
7.
Bibhas R. De 《Solar physics》1973,31(2):437-447
A mechanism is suggested for the formation of loop-type prominences in solar-active regions following flare events. The mechanism is based on the already existing idea of compression of a coronal plasma element resulting in enhanced radiation and consequent cooling of the element. A model is suggested for such a compression based on the concept of a contracting, force-free filamentary structure. If the current in a filament increases with time, then there is a radial contraction of the filament. Since the coronal plasma is frozen into the magnetic field lines of the filament, a contraction of the filament causes a compression of the filamentary plasma. This model of compression is shown to be in approximate qualitative and quantitative agreement with observations. 相似文献
8.
J. C. Sherman 《Astrophysics and Space Science》1973,24(2):459-485
A review is given of the experimental investigations concerning the critical velocity of the interaction between a neutral
gas and a plasma in relative motion. In most of the experiments this critical velocity is equivalent to a voltage limitation
of a discharge through a partially ionized magnetized plasma. The critical velocity phenomenon can have been of importance
in a large number of experiments but it has been observed in rather few cases and studied in detail in less than half a dozen
plasma machines. The major investigations were made in rotating plasma devices like the Homopolar, plasma guns and a plasma-neutral
gas impact experiment. The emphasis of this paper is concentrated, though not limited, to collision-free plasmas. Thus the
(MPD-)arc experiments are not extensively treated. It is concluded that the existence, under certain conditions, of a critical
velocity, critical voltage or criticalE/B (depending on the particular observation) is proved by sufficient experimental evidence.
In a following article in this issue by J. Sherman the theoretical work in the same field is discussed. 相似文献
9.
Fast rotation of compact stars (at sub-millisecond period) and, in particular, their stability, are sensitive to the equation of state (EOS) of dense matter. Recent observations of XTE J1739-285 suggest that it contains a neutron star rotating at 1122 Hz. At such rotational frequency the effects of rotation on star’s structure are significant. We study the interplay of fast rotation, EOS, and gravitational mass of a sub-millisecond pulsar. We discuss the EOS dependence of spin-up to a sub-millisecond period, via mass accretion from a disk in a low-mass X-ray binary. 相似文献
10.
V. Belokurov M. G. Walker N. W. Evans G. Gilmore M. J. Irwin M. Mateo L. Mayer E. Olszewski J. Bechtold T. Pickering 《Monthly notices of the Royal Astronomical Society》2009,397(4):1748-1755
We announce the discovery of a new Milky Way satellite Segue 2 found in the data of the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We followed this up with deeper imaging and spectroscopy on the Multiple Mirror Telescope (MMT). From this, we derive a luminosity of M v =−2.5 , a half-light radius of 34 pc and a systemic velocity of ∼−40 km s−1 . Our data also provide evidence for a stream around Segue 2 at a similar heliocentric velocity, and the SEGUE data show that it is also present in neighbouring fields. We resolve the velocity dispersion of Segue 2 as 3.4 km s−1 and the possible stream as ∼7 km s−1 . This object shows points of comparison with other recent discoveries, Segue 1, Boo II and Coma. We speculate that all four objects may be representatives of a population of satellites of satellites – survivors of accretion events that destroyed their larger but less dense parents. They are likely to have formed at redshifts z > 10 and are good candidates for fossils of the reionization epoch. 相似文献
11.
The atmospheric circulation of Titan is investigated with a general circulation model. The representation of the large-scale dynamics is based on a grid point model developed and used at Laboratoire de Météorologie Dynamique for climate studies. The code also includes an accurate representation of radiative heating and cooling by molecular gases and haze as well as a parametrization of the vertical turbulent mixing of momentum and potential temperature. Long-term simulations of the atmospheric circulation are presented. Starting from a state of rest, the model spontaneously produces a strong superrotation with prograde equatorial winds (i.e., in the same sense as the assumed rotation of the solid body) increasing from the surface to reach 100 m sec-1 near the 1-mbar pressure level. Those equatorial winds are in very good agreement with some indirect observations, especially those of the 1989 occultation of Star 28-Sgr by Titan. On the other hand, the model simulates latitudinal temperature contrasts in the stratosphere that are significantly weaker than those observed by Voyager 1 which, we suggest, may be partly due to the nonrepresentation of the spatial and temporal variations of the abundances of molecular species and haze. We present diagnostics of the simulated atmospheric circulation underlying the importance of the seasonal cycle and a tentative explanation for the creation and maintenance of the atmospheric superrotation based on a careful angular momentum budget. 相似文献
12.
The stability of a rotating gas-dust gravitating disk in the zone of a possible inflection in the angular velocity is examined
theoretically. The stability limits are found for a rather wide range of curves in a special model of a dusty, pressure-free
medium with the general gravitational field of the galaxy taken into account. Applications to real galaxies are discussed.
Translated from Astrofizika, Vol. 51, No. 4, pp. 523–533 (November 2008). 相似文献
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Andrzej J. Maciejewski Maria Przybylska 《Celestial Mechanics and Dynamical Astronomy》2016,126(4):297-311
This paper discusses the dynamics of systems of point masses joined by massless rigid rods in the field of a potential force. The general form of equations of motion for such systems is obtained. The dynamics of a linear chain of mass points moving around a central body in an orbit is analysed. The non-integrability of the chain of three masses moving in a circular Kepler orbit around a central body is proven. This was achieved thanks to an analysis of variational equations along two particular solutions and an investigation of their differential Galois groups. 相似文献
15.
L. Mollwo 《Solar physics》1983,83(2):305-320
The earlier interpretation of the Zebra patterns by the concept of double resonance is examined for a realistic magneto-hydrostatic model of a coronal condensation over a bipolar spot group. It appears that the frequency drift of the Zebra stripes over a longer time can scarcely be explained by a change of state of the plasma as done till now. The proposed modified mechanism is based on a helical beam of electrons forming fronts that excite radiation at places of double resonance. Considering the field and density configuration conditions are found which produce drifting Zebra stripes. Structures of longer duration and absorptions arise from more or less overlapping stripe segments, which are excited by the fronts following one another in a beam of sufficient great length. The second stripe system of other drift direction found by Slottje (1972a) arises from lateral splitting of the beam. 相似文献
16.
R. A. Lyttleton 《Astrophysics and Space Science》1974,26(2):497-511
Owing to its extremely slow rotation, Venus must be regarded as a triaxial body with differences of all three principal moments of inertia comparable in magnitude, thus rendering it a body essentially different from a rapidly rotating planet. The dynamical problem then arises of how such a body, with a rotation-period comparable with its orbital period, would be affected by couples exerted upon it by the gravitational action of the Sun. Equations for the rotatory motion are set up in a form suitable for numerical solution by machine-calculations, but the problem so presented can be adequately investigated only for a hypothetical planet with far larger differences of principal moments than could hold for Venus. Results obtained on this limited basis nevertheless suggest that for the actual planet the direction of the rotation axis may move almost randomly between the two hemispheres defined by the orbital plane and thus that the present direction near the south celestial pole of the orbit may be only a temporary situation. Order-of-magnitude considerations based on the equations of motion suggest that a time-scale of order 107 to 108 yr may on average be required for large changes in direction of the rotation axis to take place. 相似文献
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Time scales of the transition from contact binary systems of the W UMa type to single stars of the blue straggler type are estimated. A model of one-way mass transfer from the primary component to the companion inside a common envelope (Eggen et al.) and a model of a contact binary lying on the zero-age main sequence with a companion that is losing mass (F. van't Veer) are used to calculate these scales. The merging times of components were calculated for 304 contact systems of the W UMa type from the Catalog of Approximate Photometric and Absolute Elements of Eclipsing Variable Stars on a scale of loss of mass and orbital angular momentum due to magnetic braking, under the assumption of synchronization of the axial rotation and orbital revolution. On the basis of the resulting statistics, the characteristic merging scales are 0.4-0.6 and 0.5-0.7 Gyr, respectively, for the above two models. The results of a comparison with the work of other authors are discussed. 相似文献
19.
A. N. Kryshtal S. V. Gerasimenko A. D. Voitsekhovska O. K. Cheremnykh 《Kinematics and Physics of Celestial Bodies》2014,30(3):147-154
We study the process of occurrence of “quasi-mode” decay instability of kinetic Alfven waves (KAW) in the chromosphere of a solar active region before a flare, namely, in plasma of magnetic loops near their footpoints. The decay of a primary KAW into a kinetic ion-acoustic wave and a secondary KAW was considered as a specific type of three-wave interaction. Necessary conditions for the KAW decay instability occurrence were found for two semiempirical models of the solar atmosphere with the use of a modified expression for the growth rate of instability in the case of nonlinear interaction of low-frequency waves with an abnormally low excitation threshold. It was shown that the main criteria for the development of this instability significantly depend on the amplitude of external magnetic field in the region under study as well as on a model of the solar atmosphere. 相似文献
20.
A. P. Markeev 《Astronomy Letters》2005,31(9):627-633
We investigate the stability of the periodic motion of a satellite, a rigid body, relative to the center of mass in a central Newtonian gravitational field in an elliptical orbit. The orbital eccentricity is assumed to be low. In a circular orbit, this periodic motion transforms into the well-known motion called hyperboloidal precession (the symmetry axis of the satellite occupies a fixed position in the plane perpendicular to the radius vector of the center of mass relative to the attractive center and describes a hyperboloidal surface in absolute space, with the satellite rotating around the symmetry axis at a constant angular velocity). We consider the case where the parameters of the problem are close to their values at which a multiple parametric resonance takes place (the frequencies of the small oscillations of the satellite’s symmetry axis are related by several second-order resonance relations). We have found the instability and stability regions in the first (linear) approximation at low eccentricities. 相似文献