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Article Citation - WoS: 21Citation - Scopus: 21Special Standard Static Space-Times(Pergamon-elsevier Science Ltd, 2004) Dobarro, F; Ünal, BEssentially, some conditions for the Riemannian factor and the warping function of a standard static space-time are obtained in order to guarantee that no nontrivial warping function on the Riemannian factor can make the standard static space-time Einstein. (C) 2004 Elsevier Ltd. All rights reserved.Article Citation - WoS: 61Citation - Scopus: 64A curvature condition for a twisted product to be a warped product(Springer-verlag, 2001) Fernández-López, M; García-Río, E; Kupeli, DN; Ünal, BIt is shown that a mixed Ricci-flat twisted product semi-Riemannian manifold can be expressed as a warped product semi-Riemannian manifold. Asa consequence, any Einstein twisted product semi-Riemannian manifold is in fact, a warped product serni-Riemannian manifold.Article Citation - WoS: 77Citation - Scopus: 74Doubly Warped Products(Elsevier Science Bv, 2001) Ünal, BIn this paper we study geodesic completeness of Riemannian doubly warped products and Lorentzian doubly warped products. We give necessary conditions for generalized Robertson-Walker spacetimes with doubly warped product spacial parts to be globally hyperbolic. We also state some results about killing and conformal vector fields of doubly warped products.Article Citation - WoS: 31Citation - Scopus: 30Characterizing Specific Riemannian Manifolds by Differential Equations(Springer, 2003) Erkekoglu, F; García-Río, E; Kupeli, DN; Ünal, BSome characterizations of certain rank-one symmetric Riemannian manifolds by the existence of nontrivial solutions to certain partial differential equations on Riemannian manifolds are surveyed.Article Citation - WoS: 30Citation - Scopus: 32Geodesic Structure of Standard Static Space-Times(Elsevier Science Bv, 2003) Allison, DE; Ünal, BThe geodesic structure of standard static space-times is studied and conditions are found which imply nonreturning and pseudoconvex geodesic systems. As a consequence, it is shown that if the Riemannian factor manifold F satisfies the nonreturning property and has a pseudoconvex geodesic system and if the warping function f : F --> (0, infinity) is bounded above then the standard static space-time (f)(a, b) x F is geodesically connected. (C) 2002 Elsevier Science B.V. All rights reserved.
