共查询到20条相似文献，搜索用时 562 毫秒
1.
500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical Radio Telescope,FAST)是一个超大口径的可动望远镜,有三项技术创新,一是选址,二是轻型馈源索支撑,三是主动反射面。在主动反射面上,单元面板的面型和面板的出厂加工精度对电磁波在反射面的汇聚有很大影响。FAST主反射面由4 600块三角形反射面板拼接而成,每块面板为边长11 m三角形,这对FAST反射面面板的测量技术提出了更高的要求。摄影测量直接在影像上进行量测,无需接触物体本身;所摄影像信息丰富,可以从中获得所研究物体的大量几何信息和物理信息;适用于大范围、多目标测量,效率高。目前世界上最大的射电望远镜,如GBT和ARECIBO都是采用摄影测量技术进行反射面面形检测。在对现有的面型检测技术调研并试验后,提出基于数字近景摄影测量的方法,对FAST反射面11 m单元面板的面型进行检测,数分钟完成反射面板面型的一次检测,测量精度达到2.5 mm,经过调整后的单元面板的面型精度达到了3.0 mm,结果表明摄影测量应用于FAST反射面单元面板面型检测是可行的。 相似文献
2.
In experiments that are aimed at detecting astrophysical sources such as neutrino telescopes, one usually performs a search over a continuous parameter space (e.g. the angular coordinates of the sky, and possibly time), looking for the most significant deviation from the background hypothesis. Such a procedure inherently involves a “look elsewhere effect”, namely, the possibility for a signal-like fluctuation to appear anywhere within the search range. Correctly estimating the p-value of a given observation thus requires repeated simulations of the entire search, a procedure that may be prohibitively expansive in terms of CPU resources. Recent results from the theory of random fields provide powerful tools which may be used to alleviate this difficulty, in a wide range of applications. We review those results and discuss their implementation, with a detailed example applied for neutrino point source analysis in the IceCube experiment. 相似文献
3.
H. Asada 《Monthly notices of the Royal Astronomical Society》2005,356(4):1249-1255
We study analytically a gravitational lens due to a deformed star, which is modelled by using a monopole and a quadrupole moment. Positions of the images are discussed for a source on the principal axis. We present explicit expressions for the lens equation for this gravitational lens as a single real 10th-order algebraic equation. Furthermore, we compute an expression for the caustics as a discriminant for the polynomial. Another simple parametric representation of the caustics is also presented in a more tractable form. A simple expression for the critical curves is obtained to clarify a topological feature of the critical curves; the curves are simply connected if and only if the distortion is sufficiently large. 相似文献
4.
On the surface of a degerate star, a slow nuclear combustion process with a wake of escaping matter can exist. The evolution of this process has been studied by solving the nonadiabatic, time-dependent hydrodynamic equations. It has been found that this flow is almost stationary and is stable against small spherical symmetric perturbations. 相似文献
5.
P. Lantos 《Solar physics》2006,236(1):199-205
As a precursor for predicting the maximum amplitude of the coming solar cycle, the skewness of the previous cycle proposed
by Ramaswamy (1977) is revisited. The reliability of the prediction method is improved by separating odd and even cycles.
A first method is proposed on the basis of calculated skewness. In that case, the prediction is available at the end of the
previous cycle. A possibility to anticipate the availability of the skewness by about one year is pointed out. A second method,
adding prediction of the skewness itself is studied. The statistical reliability is lower than in the first case, but the
prediction of a cycle maximum is available at the maximum of the previous cycle. 相似文献
6.
Harold Willis Milnes 《Celestial Mechanics and Dynamical Astronomy》1973,7(3):295-300
An exact, closed-form solution of the problem of the motion of a satellite in the equatorial plane of an oblate body is obtained. It is shown that the classic formula for the motion of the perihelion is a first order approximation to the exact formula. 相似文献
7.
E. H. Nikogossian 《Astrophysics》2000,43(1):32-39
The hierarchical structure of the clusters of galaxies A 999, A 1016, and A 1142, which are part of one supercluster, is investigated.
The HTree method is used to determine that A 999 and A 1016 are a single, dynamically bound system consisting of two “cores”
and a common field of galaxies. The composition of the “cores” includes almost all the E and S0 galaxies, the luminosity function
of which is very nearly Gaussian. It is also established that the cluster A 1142 has a nonuniform structure, both in density
distribution and in radial velocity distribution. The location of the maxima in density and in the radial velocity distribution
correlates with the galaxies that are sources of radio and x-ray emission.
Translated from Astrofizika, Vol. 43, No. 1, pp. 45-54, January–March, 2000. 相似文献
8.
In this paper, a model is developed for the dynamics of a system of two bodies whose material points are under the influence of a central gravitational force. One of the bodies is assumed to be rigid and spherically symmetric, while the other is assumed to be deformable. To develop a tractable model for the system, the deformable body is modeled using Cohen and Muncaster's theory of a pseudo-rigid body. The resulting model of the system has several of the features, such as angular momentum conservation, exhibited by more restrictive models. We also show how the self-gravitation of the deformable body can be accommodated using appropriate constitutive equations for a force tensor. This enables our model to subsume many existing models of ellipsoidal figures of equilibrium. After the model and its conservations have been discussed, attention is restricted to steady motions of the system. Several results, which generalize recent works on rigid satellites, are established for these motions. For a specific choice of constitutive equations for the pseudo-rigid body, we determine the steady motions with the aid of a numerical continuation method. These results can also be considered as generalizations of earlier works on Roche's ellipsoids of equilibrium. 相似文献
9.
V. V. Mikhal’chuk 《Solar System Research》2007,41(2):150-161
Formulas for refining the phase of a spherical planet located a small distance from the Sun are derived. Finite heliocentric distance of the planet results in the formation on its visible disk of the geometric terminator, which is not coincident with the orthographic terminator. The visible disk is assumed to be observed from Earth in orthographic projection. We suggest introducing linear and surface phases for the geometric terminator in accordance with two existing definitions of the phase of a planet. Linear and surface phases of a planet are shown to be given by different sets of formulas. An example of the computation of the phase of Mercury is given. 相似文献
10.
P. F. Korotkov 《Solar System Research》2009,43(4):364-369
At large distances, due to atmospheric absorption and the dispersion of high-frequency components, the airwaves from the fall of large meteorites or heavy-yield explosions are transformed into an infrasonic wave train propagating over large distances via atmospheric sound channels. In approaching the antipode, the amplitude of infrasonic oscillations increases significantly and the nonlinear effects may trigger the formation of a blast wave, that is, another explosion. The condition which allows such a phenomenon to happen was obtained in this study. Infrasonic waves from the Tunguska fall event and waves generated by the largest nuclear explosions were considered in this study. 相似文献
11.
Roland Sergysels 《Celestial Mechanics and Dynamical Astronomy》1988,44(1-2):155-166
As is well known, the orbital and rotational motions of a solid are coupled, and the integrals of energy and angular momentum (in a gravitational field with spherical symmetry) impose restrictions on them. We study the regions allowed to the motion in configurational space. It turns out that even in the crudest model (planar motion of a triple rod) the restrictions on the libration angle and the orbital radius of the center of mass are coupled, so that excessive ellipticity of the orbit excludes stabilization in the neighbourhood of the spoke equilibrium position by gravitational forces only.Chargé de Cours. 相似文献
12.
Method of variation of arbitrary constants is applied to determining the first order perturbations of the orbital elements of a massive close binary caused by the hyperbolic distant flyby of a small mass. The perturbations are expressed by a sequence of analytical formulas involving definite integrals of the simple type and admitting the straightforward evaluation by computer. 相似文献
13.
The effects on a close binary system of one component becoming a neutron star as a result of a supernova explosion are discussed in this paper. In the case of a Type I supernova, the system can remain bound in many cases of interest. For a Type II supernova, the system will probably be disrupted although in some cases a remnant of the companion to the supernova may remain in a bound orbit.Consequently, neutron stars formed in Type I supernova explosions may exist in close binary systems. Such systems may be strong X-ray emitters due to mass flow as suggested by Shklovsky. Photons with energies in the 1–50 MeV region should also be emitted. 相似文献
14.
V. V. Emel’yanenko 《Solar System Research》2010,44(4):281-289
One of the main particular features of the structure of the Kuiper Belt is that it contains clusters of objects of small orbital
eccentricity and inclination (“cold population”). In order to solve the problem of the origin of the objects, we considered
the process of the gravitational interaction of a comparatively small-mass planet with a planetesimal disk. We found that
one particular property of the process is that the planet changes its direction of migration. The interaction with the planet
results in the transportation of a considerable portion of planetesimals from the inner zone out to the Kuiper Belt. After
such a transition of the objects, the planet returns to the inner regions of the planetesimal disk. Numerical simulations
show that the reversible migration of a planet of a mass similar to that of the Earth can explain the main properties of the
Kuiper Belt’s cold population orbit distribution. 相似文献
15.
S. A. Gasanov 《Astronomy Letters》2008,34(3):179-188
We have found libration points and investigated their Lyapunov stability in the problem of the motion of a star inside a layered inhomogeneous rotating elliptical galaxy with a variable mass. We have constructed the surfaces of zero velocity and obtained stability conditions for unsteady motion in the first approximation. We analyze general case where the densities of the galactic nucleus and layers vary with time according to different laws. 相似文献
16.
Yu. V. Barkin H. Hanada K. Matsumoto S. Sasaki M. Yu. Barkin 《Solar System Research》2014,48(6):403-419
An analytical theory of lunar physical librations based on its two-layer model consisting of a non-spherical solid mantle and ellipsoidal liquid core is developed. The Moon moves on a high-precision orbit in the gravitational field of the Earth and other celestial bodies. The defined fourth mode of a free libration is caused by the influence of the liquid core, with a long period of 205.7 yr, with amplitude S = 0″0395 and with an initial phase Π0 = ?134° (for the initial epoch 2000.0). Estimates of dynamic (meridional) oblatenesses of a liquid core of the Moon have been estimated: ?D = 4.42 × 10?4, μD = 2.83 × 10?4 (?D + μD = 7.24 × 10?4). These results have been obtained as a result of comparison of the developed analytical theory of physical librations of the Moon with the empirical theory of librations of the Moon constructed on the basis of laser observations. 相似文献
17.
Pavel Voráček 《Astrophysics and Space Science》1987,133(2):393-395
A deeper analysis connected to general relativity is presented, considering dynamics of a solid body in a gravitational field. Two basic situations are described: namely, the case of weightlessness in free fall, and that when a solid body at rest relative to the source of the gravitational field has weight. Finally, the principle of equivalence is reformulated. 相似文献
18.
The model of a young star with a protoplanetary disk and a low-mass companion (q ≤ 0.1) moving in a circular orbit inclined to the disk plane is considered. Hydrodynamic models of such a system have been calculated by the SPH method. The perturbations in the disk caused by the orbital motion of the companion are shown to lead to a strong dependence of the disk illumination conditions on azimuth (because of extinction variations between the star and the disk surface) and, as a result, to the appearance of a large-scale asymmetry in the disk images. Calculations show that the dependence of the disk illumination on azimuth is stronger in the central part of the disk than on the periphery. The bright and dark (shadow) regions are located asymmetrically relative to the line of nodes. The sizes of these regions and their positions on the disk depend on model parameters and orbital phase. During the orbital motion, the bright and dark regions do not follow the companion but execute small-amplitude oscillations relative to some direction. The model properties described above open up new possibilities for detecting low-mass companions in the vicinity of young stars. Stars with protoplanetary disks seen face-on or at low inclinations i are best suited for this purpose. 相似文献
19.
S. P. Buslaev 《Solar System Research》2013,47(7):605-609
An estimate for the probability of a successful spacecraft landing în the complex relief of a celestial body given random initial landing conditions is considered. The estimation is performed according to values of these initial conditions, including landing orientation, the linear and angular velocity of the lander, as well as surface relief and behavior of the ground at the landing site. For a trial sample involving random landing situations, the equations of motion of the lander are solved, from which the discrimination rule is derived. Then a successful landing is predicted by means of the rule without the solution of the equations of motion during landing. 相似文献
20.
Ramesh Chander Kapoor 《Astrophysics and Space Science》1985,117(2):363-373
A numerical study has been made of the motion of a compact object consisting of a supermassive black hole with a dense cluster of stars around through a galaxy which has recoiled from the center of the latter as a result of anisotropic emission of gravitational radiation or asymmetrical plasma emission. We find that the effect of dynamical friction on its motion through the galaxy (mass1011
M
) estimated using the impulsive approximation technique, is minimal for an object mass 109
M
and for recoil taking place at a velocity larger than that of escape. A velocity 1.1 times the escape velocity is needed for the object to escape from the galaxy, whereas for velocities of recoil less than this critical velocity, damped oscillatory motion ensures. The energy exchange of the object with the galaxy is not large enough to cause appreciable change in the internal energy of the latter. 相似文献