Yazar "Camci, U" seçeneğine göre listele

Listeleniyor 1 - 13 / 13
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    Classifications of Kantowski-Sachs, Bianchi types I and III spacetimes according to Ricci collineations
    (World Scientific Publ Co Pte Ltd, 2003) Camci, U; Yavuz, I
    The Ricci collineation classifications of Kantowski-Sachs, Bianchi types I and III space-times are studied according to their degenerate and non-degenerate Ricci tensor. When the Ricci tensor is degenerate, the special cases are classified and it is shown that there are many cases of Ricci collineations (RCs) with infinite number of degrees of freedom, and the group of RCs is ten-dimensional in some spacial cases. Furthermore, it is found that when the Ricci tensor is non-degenerate, the group of RCs is finite-dimensional, and we have only either four which coincides with the isometries or six proper RCs in addition to the four isometries.
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    Conformal collineations and Ricci inheritance symmetry in string cloud and string fluids
    (World Scientific Publ Co Pte Ltd, 2002) Camci, U
    Conformal collineations (a generalization of conformal motion) and Ricci inheritance collineations, defined by pound xi R-ab = 2alphaR(ab), for string cloud and string fluids in general relativity axe studied. By investigating the kinematical and dynamical properties of such fluids and using the field equations, some recent studies on the restrictions imposed by conformal collineations are extended, and new results axe found.
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    Conformal collineations in string cosmology
    (World Scientific Publ Co Pte Ltd, 2002) Baysal, H; Camci, U; Tarhan, I; Yilmaz, I; Yavuz, I
    In this paper, we study the consequences of the existence of conformal collineations (CC) for string cloud in the context of general relativity. Especially, we interest in special conformal collineation (SCC), generated by a special affine conformal collineation (SACC) in the string cloud. Some results on the restrictions imposed by a conformal collineation symmetry in the string cloud are obtained.
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    Curvature inheritance symmetry in Riemannian spaces with applications to string cloud and string fluids
    (World Scientific Publ Co Pte Ltd, 1999) Yilmaz, I; Tarhan, I; Yavuz, I; Baysal, H; Camci, U
    We study, in this paper, curvature inheritance symmetry (CI), pound xi R-bcd(a) = 2 alpha R-bcd(a), where a is a scalar function, for string cloud and string fluid in the context of general relativity. Also, we have obtained some result when a proper CI (i.e., alpha not equal 0) is also a conformal Killing vector.
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    Dirac analysis and integrability of geodesic equations for cylindrically symmetric spacetimes
    (World Scientific Publ Co Pte Ltd, 2003) Camci, U
    Dirac's constraint analysis and the symplectic structure of geodesic equations are obtained for the general cylindrically symmetric stationary spacetime. For this metric, using the obtained first order Lagrangian, the geodesic equations of motion are integrated, and found some solutions for Lewis, Levi-Civita, and Van Stockum spacetimes.
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    Generation of Bianchi type V universes filled with a perfect fluid
    (Springer, 2001) Camci, U; Yavuz, I; Baysal, H; Tarhan, I; Yilmaz, I
    Assuming a perfect fluid distribution of matter Bianchi type V space-time is considered and using a new generation technique it is shown that the field equations are solvable for any arbitrary cosmic scale function. Solutions for particular forms of cosmic scale functions are obtained, and the geometrical and physical properties of these solutions discussed.
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    Matter collineations in Kantowski-Sachs, Bianchi types I and III spacetimes
    (Springer/Plenum Publishers, 2003) Camci, U; Sharif, M
    The matter collineation classifications of Kantowski- Sachs, Bianchi types I and III space times are studied according to their degenerate and non-degenerate energy-momentum tensor. When the energy-momentum tensor is degenerate, it is shown that the matter collineations are similar to the Ricci collineations with different constraint equations. Solving the constraint equations we obtain some cosmological models in this case. Interestingly, we have also found the case where the energy-momentum tensor is degenerate but the group of matter collineations is finite dimensional. When the energy-momentum tensor is non-degenerate, the group of matter collineations is finite-dimensional and they admit either four which coincides with isometry group or ten matter collineations in which four ones are isometries and the remaining ones are proper.
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    Matter collineations of Bianchi V spacetime
    (World Scientific Publ Co Pte Ltd, 2005) Camci, U
    Matter collineations of the Bianchi V spacetime are studied according to degenerate or non-degenerate energy-momentum tensor. We have found that in degenerate case there are infinitely many matter collineations, whereas two cases give finite number of matter collineations which are five and six. When the energy-momentum tensor is non-degenerate, we obtain either four, five, six or seven independent matter collineations, out of which three are minimal Killing vectors and the rest are proper matter collineations.
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    Matter collineations of spacetime homogeneous Godel-type metrics
    (Iop Publishing Ltd, 2003) Camci, U; Sharif, M
    The spacetime homogeneous Godel-type spacetimes which have four classes of metrics are studied according to their matter collineations. The results obtained are compared with Killing vectors and Ricci collineations. It is found that these spacetimes have an infinite number of matter collineations in the degenerate case, i.e. det(T-ab) = 0, and do not admit proper matter collineations in the non-degenerate case, i.e. det(T-ab) not equal 0. The degenerate case has the new constraints on the parameters m and w which characterize the causality features of the Godel-type spacetimes.
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    Ricci collineations in Friedmann-Robertson-Walker spacetimes
    (Iop Publishing Ltd, 2002) Camci, U; Barnes, A
    Ricci collineations and Ricci inheritance collineations of Friedmann-Robertson-Walker spacetimes are considered. When the Ricci tensor is nondegenerate, it is shown that the spacetime always admits a 15-parameter group of Ricci inheritance collineations; this is the maximal possible dimension for spacetime manifolds. The general form of the vector generating the symmetry is exhibited. It is also shown, in the generic case, that the group of Ricci collineations is six-dimensional and coincides with the isometry group. In special cases the spacetime may admit either one or four proper Ricci collineations in addition to the six isometries. These special cases are classified and the general form of the vector fields generating the Ricci collineations is exhibited. When the Ricci tensor is degenerate, the groups of Ricci inheritance collineations and Ricci collineations are infinite-dimensional. General forms for the generating vectors are obtained. Similar results are obtained for matter collineations and matter inheritance collineations.
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    Ricci collineations in perfect fluid Bianchi V spacetime
    (Springer/Plenum Publishers, 2004) Camci, U; Türkyilmaz, I
    The Bianchi V spacetimes with perfect-fluid matter are classified according to their Ricci collineations. We have found that in the degenerate case there are infinitely many Ricci collineations whereas a subcase gives a finite number of Ricci collineations which are five. In the non-degenerate case the group of Ricci collineations is finite, i.e. four or five or six or seven. Also, all results obtained satisfy the energy conditions.
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    Ricci collineations of the Bianchi type II, VIII, and IX space-times
    (Plenum Publ Corp, 1996) Yavuz, I; Camci, U
    Ricci and contracted Ricci collineations of the Bianchi type II, VIII, and IX space-times, associated with the vector fields of the form (i) one component of xi(alpha)(x(b)) is different from zero and (ii) two components of xi(alpha)(x(b)) are different from zero, for a, b = 1, 2, 3, 4, are presented. In subcase (i.b), which is xi(alpha) = (0, xi(1)(x(alpha)), 0, 0), some known solutions are found, and in subcase (i.d), which is xi(alpha) = (0, 0, 0, xi(4)(x(alpha))) choosing S(t) = const. x R(t), the Bianchi type II, VIII, and IX spacetime is reduced to the Robertson-Walker metric.
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    Ricci collineations of the Bianchi types I and III, and Kantowski-Sachs spacetimes
    (World Scientific Publ Co Pte Ltd, 2001) Camci, U; Baysal, H; Tarhan, I; Yilmaz, I; Yavuz, I
    Ricci collineations of the Bianchi types I and III, and Kantowski-Sachs spacetimes are classified according to their Ricci collineation vector (RCV) field of the form (I)-(iv) one component of xi (a)(x(b)) is nonzero, (v)-(x) two components of xi (a)(x(b)) are nonzero, and (xi)-(xiv) three components of xi (a)(x(b)) are nonzero. Their relation with isometries of the spacetimes is established. In case (v), when det(R-ab) = 0, some metrics are found under the time transformation, in which some of these metrics are known, and the other ones new. Finally, the family of contracted Ricci collineations (CRC) are presented.