Neutrino-Antineutrino Asymmetry around Rotating Black Holes

Propagation of fermion in curved space-time generates gravitational interaction due to the coupling between spin of the fermion and space-time curvature. This gravitational interaction, which is an axial-vector appears as CPT violating term in the Lagrangian. It is seen that this space-time interaction can generate neutrino asymmetry in Universe. If the back-ground metric is spherically asymmetric, say, of a rotating black hole, this interaction is non-zero, thus the net difference to the number density of the neutrino and anti-neutrino is nonzero.Comment: 3 pages, pramana style; to appear in a special issue of Pramana -- J. Phys., as proceedings of IXth Particle-String-Cosmology (PASCOS), January 3-8, 2003, TIFR, Mumbai, Indi

Colossal enhancement of magnetoresistance in La0.67_{0.67}Sr0.33_{0.33}MnO3_{3} / Pr0.67_{0.67}Ca0.33_{0.33}MnO3_{3} multilayers: reproducing the phase-separation scenario

Colossal enhancement of magnetoresistance has been achieved over a broad temperature range which extends upto the room temperature, in ferromagnetic metal-charge ordered insulator manganite multi-layers. The artificially created phase coexistence in the multilayers reproduce the characteristic signatures of metastability in the magnetotransport properties commonly observed in electronically phase-separated manganites

Giant enhancement of room temperature magnetoresistance in La_{0.67}Sr_{0.33}MnO_{3}/Nd_{0.67}Sr_{0.33}MnO_{3} multilayers

The metal-insulator transition temperature in CMR manganites has been altered and brought close to the room temperature by preparing La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO)/ Nd$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (NSMO) multilayers with ultra thin individual layers of LSMO and NSMO. The LSMO/NSMO multilayers with ultra thin individual layers of thickness of about $10\AA$ exhibits 150% magnetoresistance at 270 K whereas LSMO/NSMO multilayers with moderate individual layer thickness of about $40\AA$ each exhibits a mere 15% magnetoresistance at the same temperature. We have shown that the reduction in thickness of the individual layers leads to increased spin fluctuation which results in the enhancement of magnetoresistance.Comment: Replaced with revised version and new figure, 9 pages, 4 figure

A method for obtaining reduced-order control laws for high-order systems using optimization techniques

A method of synthesizing reduced-order optimal feedback control laws for a high-order system is developed. A nonlinear programming algorithm is employed to search for the control law design variables that minimize a performance index defined by a weighted sum of mean-square steady-state responses and control inputs. An analogy with the linear quadractic Gaussian solution is utilized to select a set of design variables and their initial values. To improve the stability margins of the system, an input-noise adjustment procedure is used in the design algorithm. The method is applied to the synthesis of an active flutter-suppression control law for a wind tunnel model of an aeroelastic wing. The reduced-order controller is compared with the corresponding full-order controller and found to provide nearly optimal performance. The performance of the present method appeared to be superior to that of two other control law order-reduction methods. It is concluded that by using the present algorithm, nearly optimal low-order control laws with good stability margins can be synthesized

Separation of Dirac equation in the 3+1 dimensional constant curvature black hole background and its solution

The behavior of spin-half particles is discussed in the 3 + 1-dimensional constant curvature black hole (CCBH) spacetime. We use Schwarzschild-like coordinates, valid outside the black hole event horizon. The constant time surfaces corresponding to the time-like Killing vector are degenerate at the black hole event horizon and also along an axis. We write down the Dirac equation in this spacetime using Newman-Penrose formalism which is not easily separable unlike that in the Kerr metric. However, with a particular choice of basis system the equation is separable and we obtain the solutions. We discuss the structural difference in the Dirac equation in the CCBH spacetime with that in the Kerr geometry, due to difference in the corresponding spacetime metric, resulting complexity arised in separation in the earlier case.Comment: 13 latex pages; accepted for publication in Classical and Quantum Gravit

Description of Pseudo-Newtonian Potential for the Relativistic Accretion Disk around Kerr Black Holes

We present a pseudo-Newtonian potential for accretion disk modeling around the rotating black holes. This potential can describe the general relativistic effects on accretion disk. As the inclusion of rotation in a proper way is very important at an inner edge of disk the potential is derived from the Kerr metric. This potential can reproduce all the essential properties of general relativity within 10% error even for rapidly rotating black holes.Comment: 5 Latex pages including 1 figure. Version to appear in Astrophysical Journal, V-581, N-1, December 10, 200