共查询到20条相似文献，搜索用时 15 毫秒
1.
J. A. Vera 《Astrophysics and Space Science》2009,323(4):375-382
The non-canonical Hamiltonian dynamics of a triaxial gyrostat in Newtonian interaction with two punctual masses is considered.
This serves as a model for the study of the attitude dynamics of a spacecraft located at a Lagrangian equilibrium point of
the system formed by a binary asteroid and a spacecraft. Using geometric-mechanics methods, the approximated dynamics that
arises when developing the potential in series of Legendre functions and truncating the series to the second harmonics is
studied. Working in the reduced problem, the existence of equilibria in Lagrangian form are studied, in analogy with classic
results on the topic. In this way, the classical results on equilibria of the three-body problem, as well as other results
by different authors that use more conventional techniques for the case of rigid bodies, are generalized. The rotational Poisson
dynamics of a spacecraft located at a Lagrangian equilibrium and the study of the nonlinear stability of some important equilibria
are considered. The analysis is done in vectorial form avoiding the use of canonical variables and the tedious expressions
associated with them. 相似文献
2.
In this paper, we have considered a model of our universe containing five components as its constituents. Then, we have done
here the statefinder diagnostics for this model. This model can successfully explain the accelerated expansion of the universe
given that it satisfies a certain condition. Here we have considered the modified Chaplygin gas as the dynamically changing
part of the dark energy component of our universe. Chaplygin gas provides early deceleration and late time acceleration of
the universe. The graphical representation of statefinder parameters shows that the total evolution of the universe starts
from radiation era to phantom model. 相似文献
3.
An improved correlation between maximum sunspot number (SSNM) and the preceding minimum (SSNm) is reported when the monthly mean sunspot numbers are smoothed with a 13-month running window. This relation allows prediction of the amplitude of a sunspot cycle by making use of the sunspot data alone. The estimated smoothed maximum sunspot number (126±26) and time of maximum epoch (second half of 2000) of cycle 23 are in good agreement with the predictions made by some of the precursor methods. 相似文献
4.
The proposed model explains the Moon formation as a result of a thermo-nuclear explosion due to which a big land mass was torn off from the Earth. Within the model framework, on the one hand, the data on the Moon’s physical and chemical parameters are in good agreement. On the other hand, this model corresponds to modern ideas about the dynamism of the Earth’s geological structure which presupposes the presence of a powerful energy source in the Earth’s core, which might have thermonuclear origin. 相似文献
5.
6.
It is assumed that the original impulse producing Pi-2 pulsations is generated in the ionosphere at the moment of a brightening of aurora. The electric field is known to decrease in the auroral arc almost by an order of magnitude. The electric impulse that appears will be transferred along magnetic field lines and reflected from the ionosphere of the opposite hemisphere, forming the standing Alfvén wave. The electric field impulse of 100 is capable of causing magnetic field oscillations of order of 100 γ. Reflection of the Alfvén impulse from the ionosphere with horizontal inhomogeneities corresponding to different forms of auroras is studied. The following is found: (a) the resonance is possible only for harmonics with the rotating vector of polarization; (b) the resonance periods appear to depend essentially on the ionospheric conductivity; this may bring a significant error into determination of the magnetospheric plasma density from the pulsation periods; (c) the auroral zone exerts a screening influence on the pulsations excited at latitudes higher than the zone itself. 相似文献
7.
Gregory Paciga Douglas Scott Edward L. Chapin 《Monthly notices of the Royal Astronomical Society》2009,395(2):1153-1162
The steep source counts and negative K -corrections of bright submillimetre galaxies (SMGs) suggest that a significant fraction of those observed at high flux densities may be gravitationally lensed, and that the lensing objects may often lie at redshifts above 1, where clusters of galaxies are difficult to detect through other means. In this case, follow-up of bright SMGs may be used to identify dense structures along the line-of-sight. Here, we investigate the probability for SMGs to experience strong lensing, using the latest N -body simulations and observed source flux and redshift distributions. We find that almost all high-redshift sources with a flux density above 100 mJy will be lensed if they are not relatively local galaxies. We also give estimates of the fraction of sources experiencing strong lensing as a function of observed flux density. This has implications for planning follow-up observations for bright SMGs discovered in future surveys with the Submillimetre Common-User Bolometer Array 2 and other instruments. The largest uncertainty in these calculations is the maximum allowed lensing amplification, which is dominated by the presently unknown spatial extent of SMGs. 相似文献
8.
Recently, a tachyonic field was presented as a dark energy model to represent the present acceleration of the Universe. In this paper, we consider a mixture of tachyonic fluid with a perfect fluid. For this purpose we consider barotropic fluid and Generalized Chaplygin gas (GCG). We present a particular form of the scale factor. We solve the equations of motion to get exact solutions of the density, tachyonic potential and the tachyonic field. We introduce a coupling term to show that the interaction decays with time. We also show that the nature of the potentials vary, so the interaction term reduces the potential in both cases. 相似文献
9.
The results of a photometric campaign in theB, V, R andI bands of the BL Lac object OJ 287 are presented. The source is found at the same level and spectral slope as in 1991, without any sign forecasting the predicted maximum in August 1994. 相似文献
10.
R. A. Burenin 《Astronomy Letters》2007,33(12):804-806
Variability on time scales δt < t is observed on numerous occasions in the afterglows of cosmic gamma-ray bursts (GRBs). It is well known that the radiation originating in an external shock produced by the interaction of an ultrarelativistic jet with the ambient interstellar medium should not contain such variability within the framework of simple models. The corresponding constraints were established by Ioka et al. (2005) and, in some instances, are inconsistent with observations. On the other hand, if the motion is not relativistic, then the rapid afterglow variability can be explained much more easily. Various estimates of the transition time to a nonrelativistic motion in a GRB source are discussed in this connection. It has been shown that this transition should occur on an observed time scale of ～10 days. In the case of a higher density of the surrounding material, ～102?104 cm?3, or a stellar wind with ? ～ 10?5?10?4 M ⊙ yr?1, the transition to a nonrelativistic motion can occur on a time scale of ～1 day. Such densities may well be expected in star-forming regions and around massive Wolf-Rayet stars. 相似文献
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12.
The study of a dynamical system comprises a variety of processes, each one of which requires careful analysis. A fundamental preliminary step is to detect and limit the regions where solutions may exist. In the case of the ring problem of (N+1)-bodies or, otherwise, the regular polygon problem of (N+1) bodies, the existence of a Jacobian-type integral of motion constitutes the key for the investigation of the areas where the motions of the small particle are realized. Based on the aforementioned integral, we present an extended study of the parametric evolution of the regions where 3-D particle motions may exist. 相似文献
13.
WeiWang Yong-HengZhao 《中国天文和天体物理学报》2001,1(6):487-493
There is strong evidence for the existence of black holes (BHs) in some X-ray binaries and in most galactic nuclei based on different types of measurement,but black holes have not been definitely identified for the lack of very firm observational evidence up to now. Because direct evidence for BHs should come from determination of strong gravitational redshift, we expect an object can fall into the region near the BH horizon where radiation can be detected. Therefore the object must be a compact star such as a neutron star (NS), and intense astrophysical processes will release highly energetic radiation that is transient and fast-varying.These characteristics may point to the observed gamma-ray bursts (GRBs). Recent observations of iron lines suggest that afterglows of GRBs show properties similar to those observed in active galactic nuclei (AGNs), implying that the GRBs may originate from intense events related to black holes. A model for GRBs and afterglows is proposed here to obtain the range of gravitational redshifts (Zg) of GRBs with known cosmological redshifts. Here, we provide a new method that, with a search for high-energy emission lines (X- or γ-rays) in GRBs, one can determine the gravitational redshift. We expect Zg to be 0.5 or even larger, so we can rule out the possibility of other compact objects such as NSs, and identify the central progenitors of GRBs as black holes. 相似文献
14.
We study the simple periodic orbits of a particle that is subject to the gravitational action of the much bigger primary bodies
which form a regular polygonal configuration of (ν+1) bodies when ν=8. We investigate the distribution of the characteristic curves of the families and their evolution in the phase space of
the initial conditions, we describe various types of simple periodic orbits and we study their linear stability. Plots and
tables illustrate the obtained material and reveal many interesting aspects regarding particle dynamics in such a multi-body
system. 相似文献
15.
Dagoberto Escobar Carlos R. Fadragas Genly Leon Yoelsy Leyva 《Astrophysics and Space Science》2014,349(1):575-602
In this work we present a phase space analysis of a quintessence field and a perfect fluid trapped in a Randall-Sundrum’s Braneworld of type 2. We consider a homogeneous but anisotropic Bianchi I brane geometry. Moreover, we consider the effect of the projection of the five-dimensional Weyl tensor onto the three-brane in the form of a negative Dark Radiation term. For the treatment of the potential we use the “Method of f-devisers” that allows investigating arbitrary potentials in a phase space. We present general conditions on the potential in order to obtain the stability of standard 4D and non-standard 5D de Sitter solutions, and we provide the stability conditions for both scalar field-matter scaling solutions, scalar field-dark radiation solutions and scalar field-dominated solutions. We find that the shear-dominated solutions are unstable (particularly, contracting shear-dominated solutions are of saddle type). As a main difference with our previous work, the traditionally ever-expanding models could potentially re-collapse due to the negativity of the dark radiation. Additionally, our system admits a large class of static solutions that are of saddle type. These kinds of solutions are important at intermediate stages in the evolution of the universe, since they allow the transition from contracting to expanding models and viceversa. New features of our scenario are the existence of a bounce and a turnaround, which lead to cyclic behavior, that are not allowed in Bianchi I branes with positive dark radiation term. Finally, as specific examples we consider the potentials V∝sinh?α (β?) and V∝[cosh(ξ?)?1] which have simple f-devisers. 相似文献
16.
A homogeneous cosmological model in Kaluza–Klein metric is obtained assuming a time-dependent equation of state. The solution is in fact generalization of an earlier work by Hajj and Boutros for a perfect fluid. It is also found that dimensional reduction of the extra space takes place such that the five-dimensional universe naturally evolves into an effective four-dimensional one. The dynamical behaviour of the model is examined and it is also found that with a decrease in extra space the observable three-dimensional space entropy increase thus accounting for the large value of entropy observable at present. 相似文献
17.
A replot of period derivative against period is done for about 300 pulsars, and the main features of the plot are discussed. The significance of a gap in this plot is reexamined and the existence of pulsars with nulling and subpulse drifting behaviour below this gap is pointed out. The implications of this for pulsar evolution are also discussed. 相似文献
18.
Using a volume-limited sample of Main Galaxies from SDSS Data Release 5,we investigate the dependence of galaxy properties on local environment.For each galaxy,a local three-dimensional density is calculated.We find that the galaxy morphological type depends strongly on the local environment:galaxies in dense environments have predominantly early type morphologies.Galaxy colors have only a weak dependence on the environment.This puts an important constraint on the process of galaxy formation. 相似文献
19.
A new class of solutions of Einstein field equations is investigated for a cylindrically symmetric space-time when the source of gravitation is a perfect fluid. To get the deterministic solution a relation between metric coefficients A=(BC) n is assumed. Certain physical and geometric properties of the model are also discussed. 相似文献
20.
Rabindra Nath Das 《Astrophysics and Space Science》2008,317(1-2):119-126
The linear singular integral equation derived from the nonlinear integral equation of Chandrasekhar’s H-function in radiative transfer is considered here to develop a new form of H-function as a solution of a Riemann–Hilbert problem using Plemelj and Cauchy integral formulae for complex domain. This new form of H-function is a simple integral of known functions. Forms of H-function both for conservative and nonconservative cases are obtained. Their numerical evaluations are made by Simpson’s one-third rule to arrive at an accuracy to ninth places of decimals. 相似文献