Noncommutative BTZ Black Hole and Discrete Time

We search for all Poisson brackets for the BTZ black hole which are consistent with the geometry of the commutative solution and are of lowest order in the embedding coordinates. For arbitrary values for the angular momentum we obtain two two-parameter families of contact structures. We obtain the symplectic leaves, which characterize the irreducible representations of the noncommutative theory. The requirement that they be invariant under the action of the isometry group restricts to $R\times S^1$ symplectic leaves, where $R$ is associated with the Schwarzschild time. Quantization may then lead to a discrete spectrum for the time operator.Comment: 10 page

Crystal structure of [1-(3-chlorophenyl)- 5-hydroxy-3-methyl-1H-pyrazol-4-yl](p-tolyl) methanone

RK acknowledges the Department of Science & Technology for the single-crystal X-ray diffractometer sanctioned as a National Facility under Project No. SR/S2/CMP-47/2003.Peer reviewe

Porous ceramics for multistage Knudsen micropumps—modeling approach and experimental evaluation

This paper describes the evaluation of four types of porous ceramics for use as thermal transpiration materials in Knudsen pumps that operate at atmospheric pressure. Knudsen pumps are motionless gas pumps that utilize thermal transpiration along a channel or a set of channels; the channels must have a temperature gradient and must constrain the flow to remain within the free molecular or transitional flow regimes. Of the ceramics evaluated, a clay-based, 15 bar synthetic ceramic (15PC) presents the most favorable properties for Knudsen pumps. For an input power of 3.4 W, a 25 _ 25 mm 2 nine-stage Knudsen pump that uses this material provides a maximum pressure head of 12 kPa and a maximum gas flow rate of ≈3.7 µL min _1 . Reliability tests demonstrate more than 11 750 h of continuous operation without any deterioration in their gas pumping capabilities. A fitted model suggests that the temporal evolution of pressure at the sealed outlet of a Knudsen pump can be captured adequately using four parameters. These parameters correspond to various nonidealities that play dominant roles in the transient response of these pumps.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90805/1/0960-1317_21_9_095029.pd

Controlling hysteresis in superconducting constrictions with a resistive shunt

We demonstrate control of the thermal hysteresis in superconducting constrictions by adding a resistive shunt. In order to prevent thermal relaxation oscillations, the shunt resistor is placed in close vicinity of the constriction, making the inductive current-switching time smaller than the thermal equilibration time. We investigate the current-voltage characteristics of the same constriction with and without the shunt-resistor. The widening of the hysteresis-free temperature range is explained on the basis of a simple model.Comment: 6 pages, 7 figures, including Supplementary Informatio

Finite element analysis of melting effects on MHD stagnation-point non-Newtonian flow and heat transfer from a stretching/shrinking sheet

A numerical study is presented for boundary layer flow and heat transfer of micropolar (non-Newtonian) fluid from a stretching/shrinking sheet in the presence of melting and viscous heating. In this study the velocity of ambient fluid and stretching/shrinking velocity vary linearly with the distance from the stagnation-point. A uniform magnetic field is applied normal to the sheet and moves with the free stream as encountered in certain magnetic materials processing systems. Using similarity transformations, the governing partial differential equations are transformed into a system of coupled, nonlinear ordinary differential equations. A variational finite element code is implemented to solve the resulting dimensionless boundary value problem. The influence of magnetic body force (M), stretching/shrinking (ε) and melting (Me) parameters on velocity, microrotation, temperature, surface shear stress function (skin-friction) and local Nusselt number are elaborated in detail. Velocity is decreased with a rise in melting parameter, whereas far from the wall microrotation is reduced and furthermore temperatures are depressed. The flow is accelerated, micro-rotation (angular velocity of micro-elements) increased and temperature enhanced with increasing stretching rate (ε > 0) whereas the converse behaviour is observed with increasing shrinking rate (ε < 0). Increasing magnetic parameter is found to both increase temperatures and to accelerate the flow whereas it reduces microrotation near the wall and enhances it further from the wall. Special cases of the present model (with magnetic, dissipative and melting effects negated) are benchmarked with earlier results from the literature and found to be in excellent agreement. Excellent convergence and stability is achieved with the numerical method

Birefringence analysis of multilayer leaky cladding optical fibre

We analyse a multilayer leaky cladding (MLC) fibre using the finite element method and study the effect of the MLC on the bending loss and birefringence of two types of structures: (i) a circular core large-mode-area structure and (ii) an elliptical-small-core structure. In a large-mode-area structure, we verify that the multilayer leaky cladding strongly discriminates against higher order modes to achieve single-mode operation, the fibre shows negligible birefringence, and the bending loss of the fibre is low for bending radii larger than 10 cm. In the elliptical-small-core structure we show that the MLC reduces the birefringence of the fibre. This prevents the structure from becoming birefringent in case of any departures from circular geometry. The study should be useful in the designs of MLC fibres for various applications including high power amplifiers, gain flattening of fibre amplifiers and dispersion compensation.Comment: 18 page

Spin-phonon coupling in multiferroic RCrO3_3 (R-Y, Lu, Gd, Eu, Sm): A Raman study

Raman study on a select few orthochromites, RCrO$_3$ (R = Y, Lu, Gd, Eu and Sm) shows that the phonon behavior at TN in compounds with magnetic R-ion (Gd and Sm) is remarkably different from that of non-magnetic R-ion (Y, Lu and Eu). While anomalies in most of the observed phonon frequencies in all these compounds may result from the distortion of CrO$_6$ octahedra due to size effect and magnetostriction arising from Cr-ordering, the anomalous behavior of their linewidths observed at TN for the compounds with only magnetic R-ion suggests spin-phonon coupling. The presence of spin-phonon coupling and the anomalies in the low frequency modes related to R-ion motion in orthochromites (R = Gd and Sm) support the suggestion that the coupling between 4f-3d moments play important role in inducing switchable electric polarization.Comment: 6 pages (two column format), 7 figures; The updated version of the manuscript can be found at Euro. Phys. Lett. 101, 17008 (2013