Gravity on Noncommutative D-Branes

The effective action for the low energy scattering of two gravitons with a D-brane in the presence of a constant antisytmetric $B$ field in bosonic string theory is calculated and the modification to the standard D-brane action to first order in $\alpha'$ is obtained.Comment: 18 pages, Latex file, accepted in Int. J. Mod. Phys.

Community-based distribution and contraception usage in Iran

Objective: Despite the availability of free contraception from family planning clinics, the rate of unwanted pregnancy in Iran is still high. The effectiveness of other methods for contraceptive supply should, therefore, be evaluated. The aim of this study was to determine the effects of community-based distribution (CBD) on contraceptive usage in Iran. Methods: This controlled field trial study involved 297 individuals (100 subjects in the CBD group and 197 subjects in the control group) from four major remote areas of Hamedan, Iran. Stratified random sampling was used. Results: Data analysis suggested that using CBD has four major effects: (1) it increases the level of contraceptive knowledge (p<0.0001), (2) it enhances correct contraceptive choice by couples (p<0.0001), (3) it improves contraceptive usage (p<0.0001) and (4) it improves contraceptive continuation rates (p<0.0001). Conclusions: CBD facilitates better knowledge, proper choice, and correct and continuous usage of contraception. This method should, therefore, be adopted for family planning services in remote areas of Iran

Energy and exergy analysis of a novel turbo-compounding system for supercharging and mild hybridization of a gasoline engine

Number of hybrid vehicles has increased around the world significantly. Automotive industry is utilizing the hybridization of the powertrain system to achieve better fuel economic and emissions reduction. One of the options recently considered in research for hybridization and downsizing of vehicles is to employ waste heat recovery systems. In this paper, the addition of a turbo-compound system with an air Brayton cycle to a naturally-aspirated engine was studied in AVL BOOST software. In addition, a supercharger was modeled to charge extra air into the engine and Air Brayton cycle (ABC). The engine was first validated against the experimental data prior to turbo compounding. The energy and exergy analysis were performed to understand the effects of the proposed design at engine rated speed. Results showed that between 16 to 18% increase in engine mechanical power can be achieved by adding turbo-compressor. Furthermore, the recommended ABC system can recover up to 1.1 kW extra electrical power from the engine exhaust energy. The energy and exergy efficiencies were both improved slightly by turbo-compounding and BSFC reduced by nearly 1% with the proposed system. Furthermore, installing the proposed system resulted in increasing of backpressure up to approximately 23.8 kPa

Yet Another Realization of Kerr/CFT Correspondence

The correspondence between the Kerr black hole and a boundary CFT has been conjectured recently. The conjecture has been proposed first only for the half of the CFT, namely for left movers. For right movers, the correspondence has been also found out through the suitable asymptotic boundary condition. However, the boundary conditions for these two studies are exclusive to each other. The boundary condition for left movers does not allow the symmetry of right movers, and vice versa. We propose new boundary condition which allows both of left and right movers.Comment: 6 pages, references adde

Caustic avoidance in Horava-Lifshitz gravity

There are at least four versions of Horava-Lishitz gravity in the literature. We consider the version without the detailed balance condition with the projectability condition and address one aspect of the theory: avoidance of caustics for constant time hypersurfaces. We show that there is no caustic with plane symmetry in the absence of matter source if \lambda\ne 1. If \lambda=1 is a stable IR fixed point of the renormalization group flow then \lambda is expected to deviate from 1 near would-be caustics, where the extrinsic curvature increases and high-energy corrections become important. Therefore, the absence of caustics with \lambda\ne 1 implies that caustics cannot form with this symmetry in the absence of matter source. We argue that inclusion of matter source will not change the conclusion. We also argue that caustics with codimension higher than one will not form because of repulsive gravity generated by nonlinear higher curvature terms. These arguments support our conjecture that there is no caustic for constant time hypersurfaces. Finally, we discuss implications to the recently proposed scenario of ``dark matter as integration constant''.Comment: 19 pages; extended to general z \geq 3, typos corrected (v2); version accepted for publication in JCAP (v3

New Attractors, Entropy Function and Black Hole Partition Function

By making use of the entropy function formalism we study the generalized attractor equations in the four dimensional N=2 supergravity in presence of higher order corrections. This result might be used to understand a possible ensemble one could associate to an extremal black hole.Comment: 20 pages, latex file, V2: minor corrections, typos corrected, Refs added, V3: the version appeared in JHE

Entropy function and attractors for AdS black holes

We apply Sen's entropy formalism to the study of the near horizon geometry and the entropy of asymptotically AdS black holes in gauged supergravities. In particular, we consider non-supersymmetric electrically charged black holes with AdS_2 xS^{d-2} horizons in U(1)^4 and U(1)^3 gauged supergravities in d=4 and d=5 dimensions, respectively. We study several cases including static/rotating, BPS and non-BPS black holes in Einstein as well as in Gauss-Bonnet gravity. In all examples, the near horizon geometry and black hole entropy are derived by extremizing the entropy function and are given entirely in terms of the gauge coupling, the electric charges and the angular momentum of the black hole.Comment: 27 pages, no figures, references adde