共查询到20条相似文献，搜索用时 31 毫秒
1.
In an earlier paper the evolution of a magnetic field was considered which permeates an electrically conducting fluid and its non-conducting surroundings. It was shown how the tensorial Green's function of the initial value problem posed by the governing equations can be constructed. The present paper gives a more detailed analysis of the case where the fluid occupies the interior of a sphere. The construction is carried out for arbitrary motions of the fluid. More special results are derived for differential rotation with angular velocity depending only on the radius, and explicit expressions of Green's functions are given for rigid body rotation. 相似文献
2.
H. Greiner-Mai 《Astronomische Nachrichten》1986,307(3):201-208
The theoreticl treatment of several geophysical problems presupposes the solution of field equations of the magnetic field in the Earth's mantle. The field equations are given in a scalar form for a spherical model of the Earth. It will be shown that analytical solutions are possible in all cases. The boundary conditions are discussed with regard to the dynamo process in the Earth's core and the existence of a field representation, which is investigated on the Earth's surface. The question is discussed, to what extend the mantle's field is given by this field representation, when some special assumptions about the Earth's model are made. 相似文献
3.
S. Selak 《Astrophysics and Space Science》1978,56(2):275-284
In this paper we shall consider the following question: ‘If the whole galactical system expands and if galaxies are separating away from one another just as much as they are separating from our galaxy, can we assume that such a reality will have repercussions on the formulation of basic physical laws in our surroundings?’ Considering a confirmative answer, we performed an attempt to find a physical interpretation of the perturbations of the metric tensor components. It was shown that they can be expressed in terms of the dilatation function which also appears to be one reason which prohibits the precise measurement of real time and distance. Considering that an observer in our wold knows nothing of the aperiodicity of atomic oscillations which ‘determine’ the unit of time, we discerned the meaning of time in two ways: (i) the time as it is accepted in special relativity and (ii) the ‘time’ based on the reading of clocks which suffer dilatation. The usual procedure for establishing equations of the gravitational field was then carried out. These equations reduce to those of the classical theory, if the dilatation function is proportional to Newtonian gravitational potential. On this basis, considering the Earth's expansion as a process which exists as a cosmological manifestation, we discussed the observed fact of the agreement between the rate of the Earth's radius and that of the universe, according to Hubble's law. 相似文献
4.
Pavel Voráček 《Astrophysics and Space Science》1982,81(1-2):85-94
Four situations are shown where the Schwarzschild metric cannot be used or is subject to unsurmountable problems. The first is the question of a metric useful for PPN-formalism checking different gravitational theories. The second problem occurs in connection with Mach's principle, when the flatness of the spacetime inside a massive hollow sphere is a generally accepted solution. The metrical discontinuity on the same spherical shell is a third problem. The fourth one is the anisotropy of the mass-energy of a test particle in the gravitational field. Three principles for solution are proposed:
- The space is not dilated, but rather contracted, in the gravitational field; then the measurement-rods are shorter and measured distances have greater magnitudes.
- The potential energy is to be related to a potential level where a stationary observer is placed and the general relativistic potential must be used.
- A new metric must be introduced which is distinct from the Schwarzschild metric, so that the space in the gravitational field is warped isotropically.
5.
The Einstein field equations for a perfect fluid with two commuting Killing vectors, which span the fluid's four-velocity, are considered. A third space time symmetry, which is a homothetic or a Killing vector, can be used to reduce these equations to a system of ordinary differential equations. This symmetry restricts the form of the differential rotation Ω of the fluid. A Bianchi classification of the resulting Lie algebras is performed and related to the kinematical properties of the fluid. 相似文献
6.
The fourth order field equations proposed by TREDER with a linear combination of BACH 's tensor and EINSTEIN 's tensor on the left-hand side admit static centrally symmetric solutions which are analytical and non-flat in some neighborhood of the centre of symmetry. 相似文献
7.
Uwe Kasper 《Astronomische Nachrichten》1972,294(5):201-206
In the framework of TREDER 's gravitational theory we elaborate the consequences of a class of field equations for some solar-system effects and their connection to the problem of cosmological singularity. These equations read on special conditions with components of the energy momentum tensor, KRONECKER 's symbol, tetrad components). ω is a real parameter. If we choose the integration constants of the static spherically symmetric vacuum case in such a way that red shift is the same like that of EINSTEIN 's theory and the source of gravitational field is that of a point mass we obtain for the perihelion rotation the expression is EINSTEINS value of the perihelion rotation.) For we obtain But only if ω > 2/5 cosmological models exist which have no cosmological singularity. On the other hand for ω > 2/5 the value is greater than. 相似文献
8.
Cosmic tests of Maxwell's equations 总被引：1，自引：0，他引：1
J. C. Byrne 《Astrophysics and Space Science》1977,46(1):115-132
9.
Joseph W. Gangestad George E. Pollock James M. Longuski 《Celestial Mechanics and Dynamical Astronomy》2010,108(2):125-145
A spacecraft that generates an electrostatic charge on its surface in a planetary magnetic field will be subject to a perturbative
Lorentz force. Active modulation of the surface charge can take advantage of this electromagnetic perturbation to modify or
to do work on the spacecraft’s orbit. Lagrange’s planetary equations are derived using the Lorentz force as the perturbation
on a Keplerian orbit, incorporating orbital inclination and true anomaly for the first time for an electrostatically charged
vehicle. The planetary equations reveal that orbital inclination is a second-order effect on the perturbation, explaining
results found in earlier studies through numerical integration. All of the orbital elements are coupled, but the coupling
notably does not depend on the magnitude of the electrostatic charge or on the strength of the magnetic field. Analytical
expressions that characterize this coupling are tested with a propellantless escape example at Jupiter. A closed-form solution
exists that constrains the set of equatorial orbits for which planetary escape is possible, and a sufficient condition is
identified for escape from inclined orbits. The analytical solutions agree with results from the numerically integrated equations
of motion to within a fraction of a percent. 相似文献
10.
In this paper we have considered a rotating, perfectly conducting sphere and have calculated the electric and magnetic field distributions measured by the rotating observer using the anholonomic approach. The calculations have been done for the following two cases: (1) rotating charged spherical shell and (2) a uniformely magnetized sphere. We have shown that in the limiting situation (a/c)2 1 and 1, the magnetic field distribution is the same for both observers, inertial and noninertial. The expressions obtained for the electric field components in the rotating frame have been compared with the corresponding expressions in the inertial frame, where the observer is at rest. Some of the results are in agreement with Post's approach to noninertial electrodynamics. 相似文献
11.
U. Dyllong 《Astronomische Nachrichten》1979,300(3):147-149
An exact solution of EINSTEIN 's field equations with cosmological constant coupled with the field equations of a massive vector field is given. The model has zero expansion and shear, but nonvanishing constant rotation. 相似文献
12.
In two earlier papers (BRÄUER and RÄDLER 1986, 1987) the evolution of a magnetic field was considered which pervades an electrically conducting fluid and its non-conducting surroundings. A construction principle for Green's functions of the corresponding initial value problem was proposed, and worked out for the case in which the fluid fills a spherical region. Now the principle is applied to the case of a fluid body occupying a half-space. Green's functions are constructed for arbitrary motions of the fluid. More concrete results are derived for shear flow, and explicit expressions of Green's functions are given for rigid body motion. 相似文献
13.
Peter W. Likins 《Celestial Mechanics and Dynamical Astronomy》1975,11(3):301-317
Identical equations of motion are shown to emerge for a system ofn+1 rigid bodies all interconnected byn points, each of which is common to two bodies, by means of each of the following derivation procedures, all of which employ a kinematical identity developed by Hooker and Margulies: The Hooker-Margulies/Hooker equations; Kane's quasicoordinate formulation of D'Alembert's principle; the combination of Lagrange's generalized coordinate equations and Lagrange's quasicoordinate equations; and the combination of Lagrange's generalized coordinate equations and the vector rotational equationM=H applied to the total system and resolved into a vector basis fixed in a reference body of the system. Thus the previously published Hooker-Margulies/Hooker equations are shown to be the natural result of several derivation procedures other than the Newton-Euler method originally used, provided that the central kinematical identity of the original derivation of Hooker and Margulies is employed. 相似文献
14.
15.
We present an exact solution of the vacuum Brans-Dicke field equations for cosmological models of Bianchi type-VI0. The solution represents anisotropic universe which has no analogy in Einstein's theory. 相似文献
16.
Z. Pazameta 《Astrophysics and Space Science》2012,339(2):317-322
Emergent concepts from astroparticle physics are incorporated into a classical solution of the Einstein-Maxwell equations for a binary magnetohydrodynamic fluid, in order to describe the final equilibrium state of compact objects infused with magnetic monopoles produced by proton-proton collisions within the intense dipolar magnetic fields generated by these objects during their collapse. It is found that the effective mass of such an object’s acquired monopolar magnetic field is three times greater than the mass of its native fluid and monopoles combined, necessitating that the interior matter undergo a transition to a state of negative pressure in order to attain equilibrium. Assuming full symmetry between the electric and magnetic Maxwell equations yields expressions for the monopole charge density and magnetic field by direct analogy with their electrostatic equivalents; inserting these into the Einstein equations then leads to an interior metric which is well-behaved from the origin to the surface, where it matches smoothly to an exterior magnetic Reissner-Nordström metric free of any coordinate pathologies. The source fields comprising the model are all described by simple, well-behaved polynomial functions of the radial coordinate, and are combined with straightforward regularity conditions to yield expressions delimiting several fundamental physical parameters pertaining to this hypothetical astrophysical object. 相似文献
17.
Celestial coordinate reference systems in curved space-time 总被引：1，自引：1，他引：0
S. M. Kopejkin 《Celestial Mechanics and Dynamical Astronomy》1988,44(1-2):87-115
18.
FIEDLER and SCHIMMING (1983) proved that the fourth order gravitational field equations with a linear combination of Bach's and Einstein's tensors on the left-hand side, which were proposed by TREDER , admit static centrally symmetric solutions which are analytical and non-flat in some neighbourhood of the centre of symmetry. The existence of these solutions, known at first only in a small neighbourhood of r = o (r radius), can now be extended to intervals o ≦ r ≦ α with arbitrarily large α , using the abstract theorem on inverse functions. Further it is proved that the Schwarzschild metrics are in a certain sense the only solutions of the above equations that are analytic, asymptotically flat, static and centrally symmetric around r = +∞. 相似文献
19.
V. Müller 《Astronomische Nachrichten》1982,303(6):321-327
As proposed by TREDER , possible consequences of a unitary field theory may be described phenomenologically by additional cross terms in EINSTEIN 's equations. The violation of the weak principle of equivalence and potential observable effects are discussed in deriving hydrodynamic EIH equations. Conclusions on gravitational instabilities follow in the quasistatic approximation. 相似文献
20.
H. F. M. Goenner 《Astronomische Nachrichten》1988,309(4):243-247
In the framework of Riemannian geometry alternative theories of gravitation with field equations differing from Einstein's are discussed. Examples of physically acceptable alternative theories with second, third or fourth-order field equations and without or with an additional coupling constant are given. 相似文献