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The mathematical approach to General Relativity insists that all coordinate systems are equal. However physicists and astrophysicists in fact almost always use preferred coordinate systems not merely to simplify the calculations but also to help define quantities of physical interest. This suggests we should reconsider and perhaps refine the dogma of General Covariance. 相似文献
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Virginia Re Marco Bruni David R. Matravers Frances T. White 《General Relativity and Gravitation》2003,35(8):1351-1363
We develop an algebraic procedure to rotate a general Newman-Penrose tetrad in a Petrov type I spacetime into a frame with Weyl scalars 1 and 3 equal to zero, assuming that initially all the Weyl scalars are non vanishing. The new frame highlights the physical properties of the spacetime. In particular, in a Petrov type I spacetime, setting 1 and 3 to zero makes apparent the superposition of a Coulomb-type effect 2 with transverse degrees of freedom 0 and 4. 相似文献
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Trent D Lund Timothy W West Lilyan Y Tian Lihong H Bu Daniel L Simmons Kenneth DR Setchell Herman Adlercreutz Edwin D Lephart 《BMC neuroscience》2001,2(1):20-13
Background
In learning and memory tasks, requiring visual spatial memory (VSM), males exhibit superior performance to females (a difference attributed to the hormonal influence of estrogen). This study examined the influence of phytoestrogens (estrogen-like plant compounds) on VSM, utilizing radial arm-maze methods to examine varying aspects of memory. Additionally, brain phytoestrogen, calbindin (CALB), and cyclooxygenase-2 (COX-2) levels were determined. 相似文献4.
David Matravers 《Contemporary Physics》2013,54(5):491-492
(1) Combined Effects of Radioactive, Chemical and Thermal Rebases to the Environment. Proceedings of a Symposium held in Stockholm, 2–5 June 1975. Vienna, 1975. International Atomic Energy Agency. London, H.M.S.O., pp. 358. £10·00. (2) Impacts of Nuclear Releases into the Aquatic Environment. Proceedings of an International Symposium held at Ontaniemi, Finland, 30 June—4 July 1975. Vienna, 1975. International Atomic Energy Agency. London, H.M.S.O., pp. 524. £14.60. 相似文献
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D. R. Matravers 《General Relativity and Gravitation》1988,20(3):279-288
Einstein's field equations are solved with a two-parameter family of classical strings as the source for the gravitational field. The solutions have Kantowski-Sachs symmetry. The singularities of the solutions and the kinematical properties of the string world sheets are discussed. 相似文献
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Neil P. Humphreys Roy Maartens David R. Matravers 《General Relativity and Gravitation》2012,44(12):3197-3215
Physical (and weak) regularity conditions are used to determine and classify all the possible types of spherically symmetric dust spacetimes in general relativity. This work unifies and completes various earlier results. The junction conditions are described for general non-comoving (and non-null) surfaces, and the limits of kinematical quantities are given on all comoving surfaces where there is Darmois matching. We show that an inhomogeneous generalisation of the Kantowski-Sachs metric may be joined to the Lema?tre-Tolman-Bondi metric. All the possible spacetimes are explicitly divided into four groups according to topology, including a group in which the spatial sections have the topology of a 3-torus. The recollapse conjecture (for these spacetimes) follows naturally in this approach. 相似文献
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Conditions for smooth cosmological models are set out and applied to inhomogeneous spherically symmetric models constructed by matching together different Lemaître–Tolman–Bondi solutions to the Einstein field equations. As an illustration the methods are applied to a collapsing dust sphere in a curved background. This describes a region which expands and then collapses to form a black hole in an Einstein de Sitter background. We show that in all such models if there is no vacuum region then the singularity must go on accreting matter for an infinite LTB time. 相似文献