共查询到20条相似文献，搜索用时 890 毫秒
1.
Alton P. Mayo 《Celestial Mechanics and Dynamical Astronomy》1979,19(4):317-333
Analytic expressions are derived for the perturbation of planetary orbits due to a thick constant density asteroid belt. The derivations include extensions and adaptations of Plakhov's analytic expressions for the perturbations in five of the orbital elements for closed orbits around Saturn's rings. The equations of Plakhov are modified to include the effect of ring thickness and additional equations are derived for the perturbations in the sixth orbital element, the mean anomaly. The gravitational potential and orbital perturbations are derived for the asteroid belt with and without thickness, and for a hoop approximation to the belt. The procedures are also applicable to Saturn's rings and the newly discovered rings of Uranus.The effects of the asteroid belt thickness on the gravitational potential coefficients and the orbital motions are demonstrated. Comparisons between the Mars orbital perturbations obtained using the analytic expressions and those obtained using numerical integration are discussed. The effects of the asteroid belt on the Earth based ranging to Mars are also demonstrated. 相似文献
2.
Machine-learning algorithms are applied to explore the relation between significant flares and their associated CMEs. The
NGDC flares catalogue and the SOHO/LASCO CME catalogue are processed to associate X and M-class flares with CMEs based on
timing information. Automated systems are created to process and associate years of flare and CME data, which are later arranged
in numerical-training vectors and fed to machine-learning algorithms to extract the embedded knowledge and provide learning
rules that can be used for the automated prediction of CMEs. Properties representing the intensity, flare duration, and duration
of decline and duration of growth are extracted from all the associated (A) and not-associated (NA) flares and converted to
a numerical format that is suitable for machine-learning use. The machine-learning algorithms Cascade Correlation Neural Networks
(CCNN) and Support Vector Machines (SVM) are used and compared in our work. The machine-learning systems predict, from the
input of a flare’s properties, if the flare is likely to initiate a CME. Intensive experiments using Jack-knife techniques
are carried out and the relationships between flare properties and CMEs are investigated using the results. The predictive
performance of SVM and CCNN is analysed and recommendations for enhancing the performance are provided. 相似文献
3.
Yin Jia Yao Yong-qiang Wang Hong-shuai Li Lin You Xian-long Zhou Yun-he Ma Jiang-long Liu Li-yong Li Jun-rong Qian Xuan 《Chinese Astronomy and Astrophysics》2012
The cloudiness is one of the most important factors which affect the quality of an astronomical site, the monitoring and processing of the night- time cloudiness are especially important. The ground-based cloudiness camera is adopted to carry out the monitoring of the all-sky cloudiness, the images taken need to be processed by means of an effective method so as to quantize the cloudiness. The night-time cloudiness images are seriously affected by the moon- light, and therefore, the night-time cloudiness images are processed by dividing them into the moonlight and moonless two sorts. In the light of the condition of moonless night, the processing method of night-time cloudiness is given. The positioning and photometry of the bright stars in the image are conducted to determine their magnitude differences. By referring to the magnitude differences of the bright stars in the clear-night image, the probability of the bright stars of which the magnitude differences are lower than the threshold value are regarded as the probability standard of clear nights. Three sorts of images are selected to test the method. The cloudiness is determined, and the effect of the threshold condition on the result is analyzed. Finally, the applicable range and uncertainty of the method are discussed. 相似文献
4.
M. V. Samokhin 《Astrophysics and Space Science》1993,203(1):109-120
The flow of the current along the magnetic field lines in the thin plasma directed opposite to the electric field is considered. The particles moving to the equatorial plane are supposed to have mirror points above the region of absorption (the ionosphere) and the particles moving to the ionosphere are supposed to have mirror points below the region of absorption. The current, therefore, flows. The functions of the distribution of the electrons and ions are considered to be mono-energetic. The energies of the electrons and the ions and their densities on the boundary of absorption are estimated for the potential difference and for the current density which are typical for the auroral field lines. 相似文献
5.
New ground-based BV RI CCD observations of the eclipsing binary systems NN Vir and YY CrB are analyzed and illustrated. New
times of minima are given and new ephemerides are proposed. The light curves are analyzed with the Wilson-Devinney light curve
synthesis code and new geometric and photometric elements are derived. These elements are used together with the available
spectroscopic data to compute absolute elements. The evolutionary status of each system is studied by means of mass-radius
diagrams. The systems NN Vir and YY CrB are found to be A-type and W-type W UMa systems, respectively. 相似文献
6.
Gregory Mendell 《Monthly notices of the Royal Astronomical Society》1998,296(4):903-912
Magnetohydrodynamic (MHD) equations are presented for the mixture of superfluid neutrons, superconducting protons and normal electrons believed to exist in the outer cores of neutron stars. The dissipative effects of electron viscosity and mutual friction resulting from electron-vortex scattering are also included. It is shown that Alfvén waves are replaced by cyclotron-vortex waves that have not been previously derived from MHD theory. The cyclotron-vortex waves are analogous to Alfvén waves with the tension arising from the magnetic energy density replaced by the vortex energy density. The equations are then put into a simplified form useful for studying the effect of the interior magnetic field on the dynamics. Of particular interest is the crust–core coupling time, which can be inferred from pulsar glitch observations. The hypothesis that cyclotron-vortex waves play a significant role in the core spin-up during a glitch is used to place limits on the interior magnetic field. The results are compared with those of other studies. 相似文献
7.
The theory of Anstee & O'Mara for the broadening of spectral lines owing to collisions by neutral hydrogen atoms is extended to d–f and f–d transitions of neutral atoms. Width cross-sections are tabulated against effective principal quantum numbers for the upper and lower states of the transition, for a relative collision velocity of 104 m s−1 . The cross-sections are fitted to a variation with velocity of v −α , and results for the velocity parameter α are similarly tabulated. The data are tested by application to d–f spectral lines in the solar spectrum. The derived abundances are consistent with those for meteorites. 相似文献
8.
The radio luminosities of pulsars are given as functions of their period and the time variation of the period. The parameters
of that dependence are calculated and independent distances are determined for pulsars. The average electron densities toward
the pulsars are determined from the known dispersion measures. The results obtained are used to study the large-scale electron
density distribution in the Galaxy. The distribution maximum lies in the vicinity of the Sagittarius spiral arm. The electron
density falls off exponentially in the regions between spiral arms.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
从球对称引力场中光子在赤道面上的运动微分方程出发,采用后牛顿近似方法,讨论了Reissner-Nordstr(o|¨)m度规场中雷达回波延迟实验的后后牛顿修正.通过计算给出了后牛顿以及后后牛顿的修正结果,当荷电量Q为零时,该结果适用于电中性天体,其后牛顿部分的修正与经典文献一致.文中采用的近似展开方法同样适用于讨论更高阶的修正.雷达回波的高阶修正对目前展开的高精度空间引力试验有着重要的参考价值. 相似文献
10.
It is shown that it is possible to make a change of variables in a Lagrangian in such a way that the number of variables is increased. The Euler-Lagrange equations in the redundant variables are obtained in the standard way (without the use of Lagrange Multipliers!). These equations are not independent but they are all valid and consistent. In some cases they are simpler than if the minimum number of variables are used. The redundant variables are supposed to be related to each other by several constraints (not necessarily holonomic), but these constraints are not used in the derivation of the equations of motion. The method is illustrated with the well known Kustaanheimo-Stiefel Regularization. Some interesting applications to perturbation theory are also described.The present research was carried out partially at the University of California and partially at the Jet Propulsion Laboratory under contract NAS7-100 with NASA.Presently Visiting Associate Professor at the University of Texas. 相似文献
11.
Paul A. Keiter George A. Kyrala Robert G. Watt George C. Idzorek Robert R. Peterson Blake Wood Peter Adams Robert E. Chrien Darrell Peterson Merri Wood-Schultz 《Astrophysics and Space Science》2005,298(1-2):163-170
The results of a diffusive radiation transport experiment in a simple geometry are presented. The experiment depends primarily
on two variables, the target density and the temperature drive, which are characterized well. The experiment is designed to
verify and validate radiation transport in codes. The codes can then be used to model astrophysical systems. The results of
the experiments are found to be in good agreement with simulation results. 相似文献
12.
用周期图谱分析方法计算Blazar天体的光变周期 总被引：1，自引：0，他引：1
对适用于等间隔时间序列的周期图谱分析方法进行了研究,用模拟信号进行了检验,证实了它适用于有噪声的时间序列.并把这种方法应用到类星体3C 279、3C 345,BL Lac天体OJ 287、ON 231的光变周期分析中,得到它们的光变周期分别为7.14年、10.00年、11.76年、6.80年.结果表明用周期图谱分析方法得到的结论和其他文献用Jurkevich方法得到的结论一致.获得的周期对进一步研究Blazar天体的物理机制很有帮助.还分析了窗函数的影响,指出它们的优缺点,便于在实际工作中做出正确选择. 相似文献
13.
14.
S. I. Kuznetsov 《Astronomy Letters》2002,28(12):811-820
The RXTE observations of Scorpius X-1 in 1996–1999 are presented. The properties of its quasi-periodic X-ray oscillations are studied in detail. The results obtained are used for analysis in terms of the transition-layer model (TLM) and the relativistic-precession model (RPM) for a slowly rotating neutron star. Theoretical predictions of the two models are compared and their self-consistency is verified. The tilt of the magnetosphere to the accretion-disk plane, the neutron-star mass, and its angular momentum are determined in terms of the models. 相似文献
15.
最近的多普勒观测表明恒星HD 12661周围存在两颗中等偏心率轨道上运行的行星,内行星的最小质量为2．3木星质量,轨道周期为263．6天;外行星的最小质量为1．57木星质量,轨道周期为1444．5天．该系统的稳定性要求两颗行星处在平运动轨道共振．用数值方法研究了该系统形成初期在恒星气体盘作用下的轨道迁移与稳定性,计算了行星在迁移中被平运动共振俘获的概率．发现这两颗行星目前很可能正处在11:2平运动共振边缘,且运动是混沌的,从而澄清了关于系统目前构形的不同说法,并且很可能在系统形成后行星迁移到目前构形时,气体盘几乎消失了． 相似文献
16.
The principles of the numerical modeling of marine impacts of large cosmic bodies are described. Three underwater impact structures, MjØlnir, Lockne, and Eltanin, are considered with the aim of studying the characteristics of the crater formation at varying sea depths; the distinctions between the underwater and continental craters are discussed. The mechanisms for tsunami-wave generation are studied at different ratios of sea depth to impactor size. The calculation results are compared to the experimental data obtained during underwater nuclear explosions. 相似文献
17.
Walter E. Mitchell Jr. 《Solar physics》1982,80(1):3-14
The intensity residuals are analyzed from a series of solar limb-darkening measurements in the wavelength range 5656 to 2997 Å. The lengths of residual strings of the same sign exceed expectation by several orders of magnitude. The power spectrum of the residuals shows a weak excess around 6000 km. For further study the 34 000 limb-darkening residuals are subdivided into 5100 bright and faint cells. The frequency distribution of cell sizes peaks around 4500 km and increases from center to limb, the faint cells showing the greater center-limb effect. The cells are also studied as to contrast. A synoptic view indicates that only 12% of the cells are identifiable after a half hour. Phenomena that may combine to produce the observed wide spectrum of brightness inhomogeneities are briefly discussed. 相似文献
18.
T. A. Vinogradova O. M. Kochetova Yu. A. Chernetenko V. A. Shor E. I. Yagudina 《Solar System Research》2008,42(4):271-280
The results of improving the orbit accuracy for the asteroid Apophis and the circumstances of its approach to Earth in 2029 are described. Gravitational perturbations from all of the major planets and Pluto, Ceres, Pallas, and Vesta are taken into account in the equations of motion of the asteroid. Relativistic perturbations from the Sun and perturbations due to the oblateness of the Sun and Earth and due to the light pressure are also included in the model. Perturbations from the Earth and Moon are considered separately. The coordinates of the perturbing bodies are calculated using DE405. The phase correction and the gravitational deflection of light are taken into account. The numerical integration of the equations of motion and equations in variations is performed by the 15th-order Everhart method. The error of the numerical integration over the 2005–2029 interval, estimated using forward and backward computations, is not more than 3 × 10?11 AU. Improved coordinates and velocities at epoch JD2454200.5 (April 10, 2007) were obtained applying the weighted leastsquares fit. For the period from March 15, 2004, to August 16, 2006, 989 optical and 7 radar observations were used. The resulting system represents the optical observations with an error of 0.37 (66 conditional equations were rejected). The residuals of the radar observations are an order, or more, smaller than their errors. The system of Apophis’ elements and the estimates of their precision obtained in this study are in perfect agreement with the results published by other authors. The minimum Apophis-Earth distance is about 38 200 km on April 13, 2029. This estimate agrees to within 20 km with those calculated based on other published systems of elements. The effect of some model components on the minimum distance is estimated. 相似文献
19.
W. M. Napier 《Monthly notices of the Royal Astronomical Society》2001,321(3):463-470
A Markov chain model is constructed to investigate fluctuations in the mass of the zodiacal cloud. The cloud is specified by a three-dimensional grid, each element of which contains the numbers of dust particles as a function of semimajor axis, eccentricity and mass. The evolutionary pathways of dust particles owing to radiation pressure are described by fixed transition probabilities connecting the grid elements. Other elements are absorbing states representing infall to the Sun or ejection to infinity: particles entering these states are removed from the system. Particles are injected through the breakup of comets entering short-period, high-eccentricity orbits at random times, and are subject to the PoyntingRobertson effect and removal through collisional disintegration and radiation pressure. The main conclusions are that the cometary component of the zodiacal cloud is highly variable, and that in the wake of giant comet entry into a short-period, near-Earth orbit, the dust influx to the Earth's atmosphere may acquire a climatically significant optical depth. 相似文献
20.
The one-dimensional Newtonian three-body problem is known to have stable (quasi-)periodic orbits when the masses are equal. The existence and size of the stable region is discussed here in the case where the three masses are arbitrary. We consider only the stability of the periodic (generalized) Schubart's (1956) orbit. If this orbit is linearly stable it is almost always surrounded by a region of stable quasi-periodic orbits and the size and shape of this stable region depends on the masses. The three-dimensional linear stability of the periodic orbits is also determined. Final results show that the region of stability has a complicated shape and some of the stable regions in the mass-plane are quite narrow. The non-linear three-dimensional stability is studied independently by extensive numerical integrations and the results are found to be in agreement with the linear stability analysis. The boundaries of stable region in the mass-plane are given in terms of polynomial approximations. The results are compared with a similar work by Héenon (1977).We thank the referee for pointing out this reference to us. 相似文献