共查询到20条相似文献，搜索用时 578 毫秒
1.
P. W. Terry 《Celestial Mechanics and Dynamical Astronomy》1981,23(2):119-130
The nature of the collision operator for a classical mechanical system whose dynamics is represented by a probability density satisfying the Liouville equation is illustrated with a soluble example. This example is that of a two-body problem with a particular perturbation. The collision operator
is found and the time reversibility of the system is examined utilizing the analysis of Stey. For negative energies, the collision operator is zero in the limitzi0+, while for zero energy, the collision operator is different from zero in that limit. This indicates that the system is reversible for negative energy and irreversible for zero energy. 相似文献
2.
D. L. Khokhlov 《Astrophysics and Space Science》2011,335(2):577-580
The Einstein static model of the universe as a whole is considered. The Hubble law is explained by the Doppler effect due
to the downward inertial acceleration along a certain radius experienced by an observer in the center of the universe, with
the total acceleration over all radii being equal zero. Evolution of the universe is introduced through the wave function
of the universe dependent on time. This yields the energy density of the universe hence the temperature of the universe dependent
on time. On the contrary, the energy, forth and intensity of radiation are fixed with time that allows to develop the Newtonian
physics in the whole universe. The time-temperature relation of the universe in the model considered is the same as in the
radiation dominated universe in the Friedmann model that allows to explain primordial nucleosynthesis as it is in the standard
scenario. The modern parameters of the universe in the model considered are consistent with the observations. 相似文献
3.
Using the teleparallel gravity versions of the Einstein and Landau–Lifshitz’s energy and/or momentum complexes, I obtain the
energy and momentum of the universe in viscous Kasner-type cosmological models. The energy and momentum components (due to
matter plus field) are found to be zero and this agree with a previous work of Rosen and Johri et al., who investigated the
problem of the energy in Friedmann–Robertson–Walker (FRW) universe. The result that the total energy and momentum components
of the universe in these models is zero same as Bergmann–Thomson’s energy–momentum and props the viewpoint of Tryon. Rosen
found that the energy of the FRW space–time is zero, which agrees with the studies of Tryon.
PACs Numbers: 04.20.-q; 04.50.+h
An erratum to this article is available at . 相似文献
4.
B. Barbanis 《Celestial Mechanics and Dynamical Astronomy》1984,33(4):385-395
We study the stochastic behaviour of a time-independent dynamical system that has closed zero velocity curves for arbitrarily large energies. Thus no escapes appear in such a system and we can study the stochasticity of the system for any value of the energy. The numerical results show that the degree of stochasticity grows as the energy increases from zero, but then it reaches a maximum and for still larger energies it decreases slowly. 相似文献
5.
We consider an elliptic restricted four-body system including three primaries and a massless particle. The orbits of the primaries are elliptic, and the massless particle moves under the mutual gravitational attraction. From the dynamic equations, a quasi-integral is obtained, which is similar to the Jacobi integral in the circular restricted three-body problem (CRTBP). The energy constant \(C\) determines the topology of zero velocity surfaces, which bifurcate at the equilibrium point. We define the concept of Hill stability in this problem, and a criterion for stability is deduced. If the actual energy constant \(C_{\mathrm{ac}}\ ( {>} 0 ) \) is bigger than or equal to the critical energy constant \(C_{\mathrm{cr}}\), the particle will be Hill stable. The critical energy constant is determined by the mass and orbits of the primaries. The criterion provides a way to capture an asteroid into the Earth–Moon system. 相似文献
6.
In this paper, using the energy definition in MØller’s tetrad theory of gravity we calculate the total energy of the universe in Bianchi-type I cosmological models which includes both the matter and gravitational fields. The total energy is found to be zero and this result agrees with a previous works of Banerjee and Sen who investigated this problem using the general relativity version of the Einstein energy-momentum complex and Xulu who investigated same problem using the general relativity versions of the Landau and lifshitz, Papapetrou and Weinberg’s energy-momentum complexes. The result that total energy of the universe in Bianchi-type I universes is zero supports the viewpoint of Tryon. 相似文献
7.
本文讨论了脉冲星的磁层运动和能量状态。对于满足一定条件的脉冲星系统,证明了在极轴处的等离子体的角速度和电荷密度趋于零。提出了一个磁层与星体非共转的简单模型以及边界条件。利用变分原理,求得参数值,从而,得出了与参数相关的各个物理量,例如:等离子体的漂移速度v_D,等离子体与星体的相对滑动速度v_s,脉冲星的输出功率等。结果表明:功率值比较接近观测值,非共转的模型相对通常采用的共转模型而言是比较合理的。 相似文献
8.
Pierre Lesaffre Steven A. Balbus † 《Monthly notices of the Royal Astronomical Society》2007,381(1):319-333
Axisymmetric incompressible modes of the magnetorotational instability (MRI) with a vertical wavenumber are exact solutions of the non-linear local equations of motion for a disc (shearing box). They are referred to as 'channel solutions'. Here, we generalize a class of these solutions to include energy losses, viscous, and resistive effects. In the limit of zero shear, we recover the result that torsional Alfvén waves are exact solutions of the non-linear equations. Our method allows the extension of these solutions into the dissipative regime.
These new solutions serve as benchmarks for simulations including dissipation and energy loss, and to calibrate numerical viscosity and resistivity in the zeus3d code. We quantify the anisotropy of numerical dissipation and compute its scaling with time and space resolution. We find a strong dependence of the dissipation on the mean magnetic field that may affect the saturation state of the MRI as computed with zeus3d . It is also shown that elongated grid cells generally preclude isotropic dissipation and that a Courant time-step smaller than that which is commonly used should be taken to avoid spurious anti-diffusion of magnetic field. 相似文献
These new solutions serve as benchmarks for simulations including dissipation and energy loss, and to calibrate numerical viscosity and resistivity in the zeus3d code. We quantify the anisotropy of numerical dissipation and compute its scaling with time and space resolution. We find a strong dependence of the dissipation on the mean magnetic field that may affect the saturation state of the MRI as computed with zeus3d . It is also shown that elongated grid cells generally preclude isotropic dissipation and that a Courant time-step smaller than that which is commonly used should be taken to avoid spurious anti-diffusion of magnetic field. 相似文献
9.
Connor Jackman 《Celestial Mechanics and Dynamical Astronomy》2017,128(2-3):183-195
Consider the spatial Newtonian three-body problem at fixed negative energy and fixed angular momentum. The moment of inertia I provides a measure of the overall size of a three-body system. We will prove that there is a positive number \(I_0\) depending on the energy and angular momentum levels as well as the masses such that every solution at these levels passes through \(I\le I_0\) at some instant of time. Motivation for this result comes from trying to prove the impossibility of realizing a certain syzygy sequence in the zero angular momentum problem. 相似文献
10.
We deal with the problem of a zero mass body oscillating perpendicular to a plane in which two heavy bodies of equal mass orbit each other on Keplerian ellipses. The zero mass body intersects the primaries plane at the systems barycenter. This problem is commonly known as theSitnikov Problem. In this work we are looking for a first integral related to the oscillatory motion of the zero mass body. This is done by first expressing the equation of motion by a second order polynomial differential equation using a Chebyshev approximation techniques. Next we search for an autonomous mapping of the canonical variables over one period of the primaries. For that we discretize the time dependent coefficient functions in a certain number of Dirac Delta Functions and we concatenate the elementary mappings related to the single Delta Function Pulses. Finally for the so obtained polynomial mapping we look for an integral also in polynomial form. The invariant curves in the two dimensional phase space of the canonical variables are investigated as function of the primaries eccentricity and their initial phase. In addition we present a detailed analysis of the linearized Sitnikov Problem which is valid for infinitesimally small oscillation amplitudes of the zero mass body. All computations are performed automatically by the FORTRAN program SALOME which has been designed for stability considerations in high energy particle accelerators. 相似文献
11.
Magnetic field annihilation in resistive viscous incompressible plasmas is analyzed. Anisotropic viscous transport is modeled
by the dominant terms in the Braginskii viscous stress tensor. An analytical solution for steady-state magnetic merging, driven
by vortical plasma flows in two dimensions, is derived. Resistive and viscous energy dissipation rates are calculated. It
is shown that, except in the limiting case of zero vorticity, viscous heating can significantly exceed Joule heating at the
merging site. The results strongly suggest that viscous dissipation can provide a significant fraction of the total energy
release in solar flares, which may have far-reaching implications for flare models. 相似文献
12.
Pavel Voráček 《Astrophysics and Space Science》1989,161(1):165-166
A possible solution is presented of the issue of the ascertained zero cosmological constant in connection to its high value expected from the existence of vacuum energy density. The answer should be that in the metric space the virtual particle pairs arise together with a correlated negative quantum energy defect, so that the total mass-energy of every pair precisely equals zero. The various observed phenomena can still be explained. 相似文献
13.
T. J. Mazurek 《Astrophysics and Space Science》1975,35(1):117-135
Typically collapsing supernova hydrodynamic computations assume LTE neutrino transport andimpose photon-like behavior, i.e., fix the neutrino chemical potentials at zero. The validity of the latter condition is investigated in the diffusion approximation to transport. A coupled system of diffusion equations for energy and lepton number is solved in a collapsing supernova ambience. The results indicate a substantial growth in the neutrino chemical potential for densities above 1012 gm cm?3. The rate of energy transport is affected significantly by the concomitant increases in Fermi integrals and gradients in chemical potential counter to those of temperature. It is found that the extent of neutrino particle/antiparticle interaction also affects energy diffusion rates. Thus the photon-like condition on neutrino transport may misrepresent supernova energetics substantially. An extension of the usual Sn transport to include lepton characteristics is deemed necessary for a definitive answer to the neutrino transport supernova question. 相似文献
14.
The problem of secular stability of a homogeneous and cold differentially rotating gravitating stellar ring in an external gravitational field is considered. For the analysis of stability we use the method of variation of the system energy in the frames of the local hydrodynamical approximation. We show that the considered stellar system is always characterized by secular instability for all non–zero values of the density. This conclusion is valid also in the case of solid–body rotation of the ring. 相似文献
15.
New theoretical and experimental results have prompted a reinvestigation of the HCO+/HOC+ abundance ratio in dense interstellar clouds. These results pertain principally but not exclusively to the reaction between HOC+ and H2, which was previously calculated by DeFrees, McLean, and Herbst to possess a large activation energy barrier. New calculations, reported here, indicate that this activation energy barrier is quite small and may well be zero. In addition, experimental results at higher energy and temperature indicate strongly that the reaction proceeds efficiently at interstellar temperatures. If HOC+ does indeed react efficiently with H2 in interstellar clouds, the calculated HCO+/HOC+ abundance ratio rises to substantially greater value under standard dense cloud conditions than in deduced via the tentative observation of HOC+ in Sgr B2. 相似文献
16.
Du Jiulin 《Astrophysics and Space Science》1998,262(2):119-125
The nonequilibrium dynamical bifurcation analyses of the core 3He nuclear reaction diffusion system show that if the system is influenced by a flow velocity field that emerges in the Sun's core, the system becomes unstable to jump from the original state to a new state in which the total amount of 3He is enhanced and therefore may suppress the generation of both 7Be and 8B neutrinos. Furthermore, if the instability takes place in a local region, this allows a locally heightened energy generation more than its surroundings. 相似文献
17.
We discuss the contribution of cosmic-ray protons at all energies above 1 MeV to the absorbed doses of the surface layers of a comet. Since there exists no calculation which takes into account proton energy losses by means of losses to electrons and nuclear collisions (in a cascade process), and losses due to the low energy end-products of the cascade, we have made a rough estimate of all of these contributions. An analytical formula is proposed that allows a rapid estimate of ranges and the dose absorbed at any depth. We give dose-depth curves for two extreme values of the energy at which nuclear collisions begin to dominate the slowing-down process, and for an intermediate value we display the dose-depth curve down to 20 m from the surface. The relevance of these findings to dosimetry in comets and some alterations of cometary material are considered. The need for improving the analytical expression proposed is stressed. 相似文献
18.
G. Narasimhulu Naidu M. P. Ranga Rao Hira Lal Yadav 《Astrophysics and Space Science》1983,89(1):77-87
Self-similar unsteady flows with zero temperature gradient behind strong spherical shocks propagating in non-uniform perfect gas at rest are investigated. The total energy of the flow is assumed to be varying with the shock radius obeying a power law. Approximate solutions in a closed analytical form are obtained using the integral method. Also these solutions are shown to be useful to calculate easily and quickly the shock temperature, X-ray surface brightness and luminosity which are important in astrophysical problems. It is found that these approximate solutions are in close agreement with numerical solutions. 相似文献
19.
Garth A. Barber 《Astrophysics and Space Science》2002,282(4):683-730
A theory is described which produces continuous creation by adapting that of Brans-Dicke. The universe is seen to be created
out of the zero point energy field by self-contained gravitational, scalar, and matter fields. The theory is conformally equivalent
to General Relativity in vacuo.Both the Jordan and the Einstein frames are physical and they conserve energy and four-momentum respectively. The conformal
equivalence has the consequence that predictions of the theory in solar system experiments are identical with General Relativity,
but definitive experiments exist which distinguish between the two theories. The cosmological solution yields a linear expansion
with a dynamical density parameter Omega of
anda cold matter density parameter of
, but the universe is closed. The theory is free of the horizon, smoothness and density problems of GR and therefore does
not need Inflation. It does however require an exotic equation of state with negative pressure and it is suggested that this
is provided by a false vacuum or zero point energy determined, and there forelimited by, its field equations thereby overcoming
the ‘lambda problem’.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
A.P. Ingersoll 《Icarus》1976,29(2):245-253
Three new results of the Pioneer 10 and 11 mission are discussed. The first is that effective temperature is the same at the poles and equator in spite of the large differences in solar energy deposition. This is consistent with theories of convection which suggest that an extremely small equator-to-pole temperature difference at the level of infrared emission could suppress the internal heat flux at the equator relative to the pole by an amount sufficient to balance the difference in solar energy deposition.The second result is that the effective temperature of belts is 3 to 4K greater than that of zones, which is almost exactly accounted for by the lower albedo of belts. This result cannot be interpreted uniquely, but is consistent with a model in which the internal heat flux is the same under belts and zones, and the horizontal atmospheric heat flux is zero.The third observation provides evidence of instability along the south edges of zones in the northern hemisphere. These are the latitudes of minimum prograde velocity, where instability is most likely to occur in a barotropic fluid, as pointed out by Ingersoll and Cuzzi (1969). A more realistic baroclinic stability analysis suggests instability at these same latitudes. 相似文献