Godel-Type Metrics in Various Dimensions

Godel-type metrics are introduced and used in producing charged dust solutions in various dimensions. The key ingredient is a (D-1)-dimensional Riemannian geometry which is then employed in constructing solutions to the Einstein-Maxwell field equations with a dust distribution in D dimensions. The only essential field equation in the procedure turns out to be the source-free Maxwell's equation in the relevant background. Similarly the geodesics of this type of metric are described by the Lorentz force equation for a charged particle in the lower dimensional geometry. It is explicitly shown with several examples that Godel-type metrics can be used in obtaining exact solutions to various supergravity theories and in constructing spacetimes that contain both closed timelike and closed null curves and that contain neither of these. Among the solutions that can be established using non-flat backgrounds, such as the Tangherlini metrics in (D-1)-dimensions, there exists a class which can be interpreted as describing black-hole-type objects in a Godel-like universe.Comment: REVTeX4, 19 pp., no figures, improved and shortened version, note the slight change in the title [accepted for publication in Classical and Quantum Gravity

Lienard-Wiechert Potentials in Even Dimensions

The motion of point charged particles is considered in an even dimensional Minkowski space-time. The potential functions corresponding to the massless scalar and the Maxwell fields are derived algorithmically. It is shown that in all even dimensions particles lose energy due to acceleration

Investıgatıon of Removal of Dye from Aqueous Solutıon by Advanced Treatment

The textile dyeing and finishing industry use a significant amount of water and produce water pollution. Conventional biological treatment processes have some difficulties for degradation of nonbiodegradable compounds. Dye-bearing wastewaters have high COD and colour. In this study, a photo reactor process was used to remove color from aqueous solution.Effects of pH on Reactive Red 4 and cationic dye removal using 1g/L TiO2, as catalyst were studied at constant inital dye concentration (25 mg/l). Cationic dye removal efficiency is better than Reactive dye removal efficiency for photocatalytic oxidation in this stud

``Good Propagation'' Constraints on Dual Invariant Actions in Electrodynamics and on Massless Fields

We present some consequences of non-anomalous propagation requirements on various massless fields. Among the models of nonlinear electrodynamics we show that only Maxwell and Born-Infeld also obey duality invariance. Separately we show that, for actions depending only on the F_\mn^2 invariant, the permitted models have $L \sim \sqrt{1 + F^2}$. We also characterize acceptable vector-scalar systems. Finally we find that wide classes of gravity models share with Einstein the null nature of their characteristic surfaces.Comment: 11 pages, LaTeX, no figure

Accelerated Born-Infeld Metrics in Kerr-Schild Geometry

We consider Einstein Born-Infeld theory with a null fluid in Kerr-Schild Geometry. We find accelerated charge solutions of this theory. Our solutions reduce to the Plebanski solution when the acceleration vanishes and to the Bonnor-Vaidya solution as the Born-Infeld parameter b goes to infinity. We also give the explicit form of the energy flux formula due to the acceleration of the charged sources.Comment: Latex file (12 pp

U(1) Instantons on AdS_4 and the Uplift to Exact Supergravity Solutions

We consider self-duality equation of U(1) gauge fields on Euclidean AdS_4 space, and find a simple finite action solution. With a suitable ansatz, we are able to embed this solution into the 10d supergravity background of AdS_4\times CP^3. Further, we show that the solution can be uplifted to an exact solution in 11d supergravity background of AdS_4\times SE_7.Comment: 12 pages, a comment on boundary conditions and refs. adde

The General Supersymmetric Solution of Topologically Massive Supergravity

We find the general fully non-linear solution of topologically massive supergravity admitting a Killing spinor. It is of plane-wave type, with a null Killing vector field. Conversely, we show that all solutions with a null Killing vector are supersymmetric for one or the other choice of sign for the Chern-Simons coupling constant \mu. If \mu does not take the critical value \mu=\pm 1, these solutions are asymptotically regular on a Poincar\'e patch, but do not admit a smooth global compactification with boundary S^1\times\R. In the critical case, the solutions have a logarithmic singularity on the boundary of the Poincar\'e patch. We derive a Nester-Witten identity, which allows us to identify the associated charges, but we conclude that the presence of the Chern-Simons term prevents us from making a statement about their positivity. The Nester-Witten procedure is applied to the BTZ black hole.Comment: Minor correction

Spatially homogeneous Lifshitz black holes in five dimensional higher derivative gravity

We consider spatially homogeneous Lifshitz black hole solutions in five dimensional higher derivative gravity theories, which can be possible near horizon geometries of some systems that are interesting in the framework of gauge/gravity duality. We show the solutions belonging to the nine Bianchi classes in the pure R^2 gravity. We find that these black holes have zero entropy at non-zero temperatures and this property is the same as the case of BTZ black holes in new massive gravity at the critical point. In the most general quadratic curvature gravity theories, we find new solutions in Bianchi Type I and Type IX cases.Comment: 15 pages, no figure; v2, refs added, version to appear in JHE