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31.
In this paper, we critically discuss the so-far performed attempts aimed at the detection of the general relativistic gravitomagnetic Lense–Thirring effect in the gravitational field of the Earth with the existing LAGEOS satellites. In the latest reported measurement of the gravitomagnetic shift with the nodes of the LAGEOS satellites and the second generation GRACE-only EIGEN-GRACE02S Earth gravity model over an observational time span of 11 years a 5–10% total accuracy is claimed at 1–3σ, respectively. We will show that, instead, it might be 15–45% (1–3σ) if the impact of the secular variations of the even zonal harmonics is considered. Possible strategies in order both to make more robust and reliable the tests with the node-only LAGEOS–LAGEOS II combination used and to overcome the problems affecting it with other alternative combinations are presented. 相似文献
32.
D. R. K. Reddy 《Astrophysics and Space Science》2006,305(2):139-141
Explicit field equations of a scalar tensor theory of gravitation proposed by Saez and Ballester are obtained with the aid of Einstein–Rosen cylindrically symmetric metric in the presence of cosmic string source. The field equations being highly non–linear static and non–static cases have been considered separately. It is observed that in the static case the geometric strings do not exist while in the non–static case cosmological model does not exist in this theory. 相似文献
33.
Space experiments to test the Equivalence Principle (EP) are affected by a systematic radiometer effect having the same signature as the target signal. In [PhRvD 63 (2001) 101101(R)] we have investigated this effect for the three proposed experiments currently under study by space agencies: μSCOPE, STEP and GG, setting the requirements to be met—on temperature gradients at the level of the test masses—for each experiment to reach its goal. We have now re-examined the radiometer effect in the case of μSCOPE and carried out a quantitative comparative analysis, on this issue, with the proposed heliocentric LISA mission for the detection of gravity waves. We find that, even assuming that the μSCOPE spacecraft and payload be built to meet all the challenging requirements of LISA, temperature gradients along its test masses would still make the radiometer effect larger than the target signal of an EP violation because of flying in the low geocentric orbit required for EP testing. We find no way to separate with certainty the radiometer systematic disturbance from the signal. μSCOPE is designed to fly a second accelerometer whose test masses have the same composition, in order to separate out systematic effects which—not being composition dependent like the signal—must be detected by both accelerometers. We point out that this accelerometer is in fact insensitive to the radiometer effect, just as it is to an EP violation signal, and therefore even having it onboard will not allow this disturbance to be separated out. μSCOPE is under construction and it is scheduled to fly in 2004. If it will detect a signal to the expected level, it will be impossible to establish with certainty whether it is due to the well known classical radiometer effect or else to a violation of the equivalence principle—which would invalidate General Relativity. The option to increase the rotation speed of the spacecraft (now set at about 10−3 Hz) so as to average out the temperature gradients which generate the radiometer effect, is allowed in the GG design, not in that of STEP and μSCOPE. 相似文献
34.
D.-E. Liebscher 《Astronomische Nachrichten》1988,309(4):277-279
If we require the effective field equations for a local system to be second order partial differential equations, an affinely invariant theory (not presuming the existence of a metric tensor beforehand) has to be non-local, the action being a multiple integral over the manifold considered. 相似文献
35.
Cynthia Kolb Whitney 《Astrophysics and Space Science》1995,227(1-2):175-186
The image of a spiral galaxy is one of the most tantalizing images in nature. It demands that we ask: why do so many galaxies present this morphology? We currently have two main schools of thought concerning galaxy morphology, one based on gravitational effects and the other based on electromagnetic effects. The older gravitational models can explain how spirals might form, but they also predict that the spirals would quickly disintegrate. And the observed pervasiveness of spirals seems to imply not only their formation, but also their persistence over time. The newer plasma cosmology model is an improvement in that it explains how spirals might form and persist so long as plasma persists. But the formation of charge-neutral stars seems to return the scenario to the gravitational domain, and to subsequent dissolution. Clearly we need an additional idea to account for pervasive and persistent spiral galaxy structure. The present paper attempts to uncover a previously unrecognized gravitational mechanism that can serve as a viable candidate for sustaining persistent spiral galaxy structure. 相似文献
36.
37.
Z. Martinec 《Journal of Geodesy》2003,77(1-2):41-49
Three independent gradiometric boundary-value problems (BVPs) with three types of gradiometric data, {Γ
rr
}, {Γ
r
θ,Γ
r
λ} and {Γθθ−Γλλ,Γθλ}, prescribed on a sphere are solved to determine the gravitational potential on and outside the sphere. The existence and
uniqueness conditions on the solutions are formulated showing that the zero- and the first-degree spherical harmonics are
to be removed from {Γ
r
θ,Γ
r
λ} and {Γθθ−Γλλ,Γθλ}, respectively. The solutions to the gradiometric BVPs are presented in terms of Green's functions, which are expressed in
both spectral and closed spatial forms. The logarithmic singularity of the Green's function at the point ψ=0 is investigated
for the component Γ
rr
. The other two Green's functions are finite at this point. Comparisons to the paper by van Gelderen and Rummel [Journal of
Geodesy (2001) 75: 1–11] show that the presented solution refines the former solution.
Received: 3 October 2001 / Accepted: 4 October 2002 相似文献
38.
Ignazio Ciufolini Erricos C. PavlisAntonio Paolozzi John RiesRolf Koenig Richard MatznerGiampiero Sindoni Karl Hans Neumayer 《New Astronomy》2012,17(3):341-346
In this paper we respond to the criticisms of “Phenomenology of the Lense-Thirring effect in the Solar System” by Iorio et al. about the general relativistic phenomena of gravitomagnetism and frame-dragging. The claims of the paper by Iorio et al. are not reproducible in any of our independent analyses. 相似文献
39.