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  • 1
    Electronic Resource
    Electronic Resource
    Fluids with spin and twist (1995)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 778-795 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Fluids with persistent vortices that exhibit shear plus expansion (or contraction) in noninertial frames are common physical phenomena. The concept of intrinsic rotation is commonly referred to as spin; the equivalent concept for shear would be shear momenta, referred to as twist in this work. The motion of the Earth's atmosphere is a prime example of such motion in which the driving engine is the rotation of the Earth plus solar radiation. The general analytical features of persistent vortices that exhibit shear plus expansion and contraction are introduced using the methods of affine geometry. The same theoretical considerations can also be applied to astrophysical examples. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.531341
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  • 2
    Electronic Resource
    Electronic Resource
    Minimal coupling of electromagnetic fields in Riemann–Cartan space-times for perfect fluids with spin density (1992)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 1073-1081 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The electromagnetic field is minimally coupled to gravity in a Riemann–Cartan space-time containing a charged magnetized spinning fluid. It is required that the overall Lagrangian of the gravitational field, spinning matter, and the electromagnetic field be invariant under a gauge transformation of the vector potential. The theory preserves both charge conservation and particle number conservation. The electromagnetic field, via the vector potential, now interacts directly with the spin energy momentum. The spin transport equation, in addition to the usual Fermi–Walker transport term, contains a contribution due to the torque of the electromagnetic field acting on a magnetic dipole. In the absence of electromagnetism, the field equations reduce to those of the usual self-consistent Lagrangian formalism for a perfect fluid with spin density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529769
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  • 3
    Electronic Resource
    Electronic Resource
    Including spin in the Raychaudhuri equation (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 485-487 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The Raychaudhuri equation for a spin fluid matter content is developed. The equation is applied to the behavior of an irrotational, unaccelerated fluid. The development of singularities in the expansion is studied for constant spin densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529439
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  • 4
    Electronic Resource
    Electronic Resource
    Spinning Fluid Energy-Momentum Tensors in the Einstein-Cartan Theory (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 422 (1984), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1984.tb23401.x
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  • 5
    Electronic Resource
    Electronic Resource
    Gravitational radiation in asymptotic de Sitter space (1978)
    Springer
    International journal of theoretical physics 17 (1978), S. 5-20 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A solution of the gravitational field equations is found by using an axially symmetric metric which is asymptotically a de Sitter space metric. We use the general approach of Bondi, van der Burg, and Metzner as applied to the asymptotic flat-space case and search for the necessary conditions for gravitational radiation in asymptotic de Sitter space. We find that the character of the gravitational radiation, if it exists at all, is considerably different from that obtained in the case of asymptotic flat space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00669782
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  • 6
    Electronic Resource
    Electronic Resource
    Semiclassical expanding discrete space-times (1982)
    Springer
    International journal of theoretical physics 21 (1982), S. 757-763 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Given the close ties between general relativity and geometry one might reasonably expect that quantum effects associated with gravitation might also be tied to the geometry of space-time, namely, to some sort of discreteness in space-time itself. In particular we suppose space-time to consist of a discrete lattice of points rather than the usual continuum. Since astronomical evidence seems to suggest that the universe is expanding, we also demand that the lattice is expanding. Some of the implications of such a model are that the proton should presently be stable, and the universe should be closed although the mechanism for closure is quantum mechanical.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01856871
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  • 7
    Electronic Resource
    Electronic Resource
    Parametrization of the cosmological scale factor (1994)
    Springer
    International journal of theoretical physics 33 (1994), S. 2099-2117 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We show that the growth of the cosmological scale factorR(λ) can be conveniently parametrized as a function of a space-time-dependent cosmological functionλ(x). To show the parametrization, we introduce a simple heuristic model of the cosmological functionλ(x) during the inflationary period by assuming that it is spatially uniform but time dependent with an exponential growth phase followed by a rapid decay. Based upon this relatively simple empirical model we are able to calculate directly all the required features of an inflationary period such as exponential growth of the scale factor plus a natural relaxation (graceful exit) ofλ to apositive present-day cosmological constant. The model also predicts the presence of a very large, negative Planckian cosmological constant at the Planck time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00675175
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  • 8
    Electronic Resource
    Electronic Resource
    Minimal coupling of electromagnetic field in Riemann-Cartan spacetime for perfect fluids (1992)
    Springer
    International journal of theoretical physics 31 (1992), S. 1253-1265 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We minimally couple the electromagnetic field to gravity in Riemann-Cartan spacetime in the self-consistent formalism for perfect fluids by treating the internal energy of matter as a function of the electromagnetic field. The overall Lagrangian of the gravitational field, perfect fluid, and the electromagnetic field is constrained to be gauge invariant under gauge transformations of the vector potential. The theory preserves both charge conservation and particle number conservation, and gives the usual form of the free field equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00673926
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  • 9
    Electronic Resource
    Electronic Resource
    Parametrized post-Newtonian approximation and Rastall's gravitational field equations (1978)
    Springer
    Foundations of physics 8 (1978), S. 59-68 
    Details
    ISSN: 1572-9516
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The parametrized post-Newtonian (PPN) approximation is generalized to accommodate Rastall's modification of Einstein's theory of gravity, which allows nonzero divergence of the energy-momentum tensor. Rastall's theory is then shown to have consistent field equations, gauge conditions, and the correct Newtonian limit of the equations of motion. The PPN parameters are obtained and shown to agree experimentally with those for the Einstein theory. In light of the nonzero divergence condition, integral conservation laws are investigated and shown to yield conserved energy-momentum and angularmomentum. We conclude that the above generalization of metric theories, within the PPN framework, is a natural extension of the concept of metric theories.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00708486
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  • 10
    Electronic Resource
    Electronic Resource
    Metric-affine variational principles in general relativity II. Relaxation of the Riemannian constraint (1981)
    Springer
    General relativity and gravitation 13 (1981), S. 1037-1056 
    Details
    ISSN: 1572-9532
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We continue our investigation of a variational principle for general relativity in which the metric tensor and the (asymmetric) linear connection are varied independently. As in Part I, the matter Lagrangian is minimally coupled to the connection and the gravitational Lagrangian is taken to be the curvature scalar, but we now relax the Riemannian constraint as far as possible—that is, as far as the projective invariance of the assumed gravitational Lagrangian will allow. The outcome of this procedure is a gravitational theory formulated in a volume-preserving space-time (i.e., with torsion and tracefree nonmetricity). The vanishing of the trace of the nonmetricity is due to the remaining vector constraint. We also discuss the physical significance of the relaxation of the Riemannian constraint, the possible relaxation of the vector constraint, the notion of the hypermomentum current, and its possible relation to elementary particle physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00756364
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