Morgan-Morgan-NUT disk space via the Ehlers transformation

Using the Ehlers transformation along with the gravitoelectromagnetic approach to stationary spacetimes we start from the Morgan-Morgan disk spacetime (without radial pressure) as the seed metric and find its corresponding stationary spacetime. As expected from the Ehlers transformation the stationary spacetime obtained suffers from a NUT-type singularity and the new parameter introduced in the stationary case could be interpreted as the gravitomagnetic monopole charge (or the NUT factor). As a consequence of this singularity there are closed timelike curves (CTCs) in the singular region of the spacetime. Some of the properties of this spacetime including its particle velocity distribution, gravitational redshift, stability and energy conditions are discussed.Comment: 18 pages, 5 figures, RevTex 4, replaced with the published versio

Vibration Damping of a New Ionic Liquid under Electric Field Effect

Ionic liquids are recently-developed smart materials that are not well known by mechanical engineers. They are of great interest due to their non-volatility, viscosity and extremely high electrical conductivity. Up to now, no reports have appeared on their rheological properties under magnetic or electrical fields. In this work, we study the electro-rheological behaviour of a newly presented ionic liquid (2-hydroxyethylammonium formate). Our experiments show that the ionic liquid is not sensitive to magnetic fields. Nevertheless, resonably high damping ratios (42.8%) have been attained under relatively low electric fields (0.6 kVcm-1)

Abelian Gauge Theory in de Sitter Space

Quantization of spinor and vector free fields in 4-dimensional de Sitter space-time, in the ambient space notation, has been studied in the previous works. Various two-points functions for the above fields are presented in this paper. The interaction between the spinor field and the vector field is then studied by the abelian gauge theory. The U(1) gauge invariant spinor field equation is obtained in a coordinate independent way notation and their corresponding conserved currents are computed. The solution of the field equation is obtained by use of the perturbation method in terms of the Green's function. The null curvature limit is discussed in the final stage.Comment: 10 pages, typos corrected, reference adde

Multiple Photonic Shells Around a Line Singularity

Line singularities including cosmic strings may be screened by photonic shells until they appear as a planar wall.Comment: 6 page

Static cylindrically symmetric spacetimes

We prove existence of static solutions to the cylindrically symmetric Einstein-Vlasov system, and we show that the matter cylinder has finite extension. The same results are also proved for a quite general class of equations of state for perfect fluids coupled to the Einstein equations, extending the class of equations of state considered in \cite{BL}. We also obtain this result for the Vlasov-Poisson system.Comment: Added acknowledgemen

Biomedical Simulation Models of Human Auditory Processes

Detailed acoustic engineering models that explore noise propagation mechanisms associated with noise attenuation and transmission paths created when using hearing protectors such as earplugs and headsets in high noise environments. Biomedical finite element (FE) models are developed based on volume Computed Tomography scan data which provides explicit external ear, ear canal, middle ear ossicular bones and cochlea geometry. Results from these studies have enabled a greater understanding of hearing protector to flesh dynamics as well as prioritizing noise propagation mechanisms. Prioritization of noise mechanisms can form an essential framework for exploration of new design principles and methods in both earplug and earcup applications. These models are currently being used in development of a novel hearing protection evaluation system that can provide experimentally correlated psychoacoustic noise attenuation. Moreover, these FE models can be used to simulate the effects of blast related impulse noise on human auditory mechanisms and brain tissue

Gravitational Wave Propagation in Isotropic Cosmologies

We study the propagation of gravitational waves carrying arbitrary information through isotropic cosmologies. The waves are modelled as small perturbations of the background Robertson-Walker geometry. The perfect fluid matter distribution of the isotropic background is, in general, modified by small anisotropic stresses. For pure gravity waves, in which the perturbed Weyl tensor is radiative (i.e. type N in the Petrov classification), we construct explicit examples for which the presence of the anisotropic stress is shown to be essential and the histories of the wave-fronts in the background Robertson-Walker geometry are shear-free null hypersurfaces. The examples derived in this case are analogous to the Bateman waves of electromagnetic theory.Comment: 27 pages, accepted for publication in Phys.Rev.

Issues in the Blandford-Znajek Process for GRB Inner Engine

Several issues regarding the Blandford-Znajek process are discussed to demonstrate that it can be an effective mechanism for powering the gamma ray bursts. Using a simple circuit analysis it is argued that the disk power increases the effective power of the black hole-accretion disk system, although a part of disk power can be dissipated into black hole entropy. Within the framework of the force-free magnetosphere with the strong magnetic field, the magnetically dominated MHD flow is found to support the Blandford-Znajek process and it is demonstrated that the possible magnetic repulsion by the rotating black hole will not affect the efficiency substantially.Comment: 10 pages, 1 figure, 3 references added, more discussions on the magnetic field on the black hole, accepted for publication in Ap

Static Cylindrical Matter Shells

Static cylindrical shells composed of massive particles arising from matching of two different Levi-Civita space-times are studied for the shell satisfying either isotropic or anisotropic equation of state. We find that these solutions satisfy the energy conditions for certain ranges of the parameters.Comment: 9 pages, 3 figures, Latex; Final version, To appear in General Relativity and Gravitatio