Gauge Invariant Wave Equations in Curved Space-Times and Primordial Magnetic Fields

The inflationary production of magnetic field seeds for galaxies is discussed. The analysis is carried out by writing the wave equation of the electromagnetic field in curved spacetimes. The conformal invariance is broken by taking into account of the interaction of the electromagnetic field with the curvature tensor of the form $\lambda R_{\alpha\beta\gamma\delta} F^{\alpha\beta} F^{\gamma\delta}$. Such a term induces an amplification of the magnetic field during the reheating phase of the universe, but no growth of the magnetic field occurs in the de Sitter epoch. The resulting primordial magnetic field turns out to have strengths of astrophysical interest.Comment: 5 pages, no figures, 1 tabl

Neutrino coupling to cosmological background: A review on gravitational Baryo/Leptogenesis

In this work we review the theories of origin of matter-antimatter asymmetry in the Universe. The general conditions for achieving baryogenesis and leptogenesis in a CPT conserving field theory have been laid down by Sakharov. In this review we discuss scenarios where a background scalar or gravitational field spontaneously breaks the CPT symmetry and splits the energy levels between particles and anti-particles. Baryon or Lepton number violating processes in proceeding at thermal equilibrium in such backgrounds gives rise to Baryon or Lepton number asymmetry.Comment: 62 pages, no figures. Invited review to appear in IJMP

Maximum life spiral bevel reduction design

Optimization is applied to the design of a spiral bevel gear reduction for maximum life at a given size. A modified feasible directions search algorithm permits a wide variety of inequality constraints and exact design requirements to be met with low sensitivity to initial values. Gear tooth bending strength and minimum contact ratio under load are included in the active constraints. The optimal design of the spiral bevel gear reduction includes the selection of bearing and shaft proportions in addition to gear mesh parameters. System life is maximized subject to a fixed back-cone distance of the spiral bevel gear set for a specified speed ratio, shaft angle, input torque, and power. Significant parameters in the design are: the spiral angle, the pressure angle, the numbers of teeth on the pinion and gear, and the location and size of the four support bearings. Interpolated polynomials expand the discrete bearing properties and proportions into continuous variables for gradient optimization. After finding the continuous optimum, a designer can analyze near optimal designs for comparison and selection. Design examples show the influence of the bearing lives on the gear parameters in the optimal configurations. For a fixed back-cone distance, optimal designs with larger shaft angles have larger service lives

Downlink Coverage Analysis in a Heterogeneous Cellular Network

In this paper, we consider the downlink signal-to-interference-plus-noise ratio (SINR) analysis in a heterogeneous cellular network with K tiers. Each tier is characterized by a base-station (BS) arrangement according to a homogeneous Poisson point process with certain BS density, transmission power, random shadow fading factors with arbitrary distribution, arbitrary path-loss exponent and a certain bias towards admitting the mobile-station (MS). The MS associates with the BS that has the maximum SINR under the open access cell association scheme. For such a general setting, we provide an analytical characterization of the coverage probability at the MS.Comment: 6 pages, 5 figures, submitted to IEEE Globecom 2012 - Wireless Communications Symposium on Apr 2, 201

Network Security in Biometrics

Biometric security is mostly executed in conditions with basic physical security prerequisites or that are profoundly inclined to data fraud. Biometric security-based frameworks or motors store human body qualities that don't change over a person's lifetime. These incorporate fingerprints, eye texture, voice, hand patterns and facial recognition. A person's body qualities are pre-stored in a biometric security framework or scanner, which might be accessed by approved staff. At the point when an individual strolls into an office or attempts to access a framework, the biometric scanner assesses his/her physical attributes, which are coordinated with put away records. On the off chance that a match is found, the individual is conceded get to