Optimum power allocation for uniform illuminance in indoor visible light communication

In this paper an optimal power allocation scheme is proposed to acheive uniform illuminance. Regular arrays and random geometries are considered for an arrangement of the source LEDs. Uniform illuminance is accomplished by considering the variance of the received power on the receiver plane as metric and framing it as a convex optimization problem. Numerical results show that the quality factor of random geometries are superior to fixed geometries. While preserving uniformity, the cost of the system can be reduced when random geometries are used. © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Narasimham Committee Report - Some Further Ramifications and Suggestions

This paper while agreeing with the general thrust of the Narasimham Committee Report. Calls attention to some logical corollaries of the Report and analyses some possible fallout from implementing the Report. We agree with the view that control of banking system should be under an autonomous body supervised by the RBI. However at the level of individual banks, closer scrutiny of lending procedures may be called for than is envisaged in the Report. In a freely functioning capital market the potential of government bonds is enormous, but this necessitates restructuring of the government bond market. The government bonds may then also be used as suitable hedging mechanisms by introducing options and futures trading. We recommend freeing up the operation of pension and provident fund to enable at least partial investment of such funds in risky securities. In the corporate sector, we believe that the current 2:1 debt equity norm is too high and not sustainable in the long term. We envisage that high debt levels and higher interest rates, combined with higher business risk may result in greater incidence of corporate sickness. This may call for various schemes for retrenched workers and amendment to land laws for easy exit of companies. On account of interdependencies across different policies, any sequencing of their implementation may be highly problematic. We therefore suggest a near simultaneity in the implementation of various reforms in order to build up a momentum which would be irreversible if people are to have confidence that the reforms will endure, and if we are to retain our credibility with international financial institutions.

Maximum likelihood detection for decode and forward cooperation with interference

In this paper, we obtain the maximum likelihood (ML) decision for a decode and forward (DF) cooperative system in Nakagami-m fading in the presence of co-channel interference at the relay as well as the destination. Through simulation results, we first show that conventional ML designed for interference free systems fails to combat the deleterious effect of interference. An optimum ML decision for combating interference is then derived for integer m. This receiver is shown to be superior to conventional ML through bit error rate (BER) performance simulations. Further, our results also indicate that optimum ML preserves relay diversity in the presence of interference

Effects of Radiation Absorption and Mass Transfer on the Free Convective Flow Passed a Vertical Flat Plate through a Porous Medium in an Aligned Magnetic Field

This article analyses the effects of radiation absorption and mass transfer on the steady free convective flow of a viscous, incompressible and electrically conducting fluid past an infinite vertical flat plate through a porous medium with an aligned magnetic field. Analytical solutions for concentration, temperature, and velocity are obtained by solving the governing equations in two cases namely (i) when the plate is at uniform temperature and concentration and (ii) when the plate is at constant heat and mass flux. Further the rate of mass transfer in terms of the Sherwood number, rate of heat transfer in terms of Nusselt number and skin friction in terms of shear stress are also derived. The effects of various flow parameters on concentration, temperature, velocity, Sherwood number, Nusselt number and skin-friction affecting the flow field are discussed and analyzed

Chemical Reaction and Hall Effects on MHD Convective Flow along an Infinite Vertical Porous Plate with Variable Suction and Heat Absorption

In this paper an attempt is made to study the chemical reaction and combined buoyancy effects of thermal and mass diffusion on MHD convective flow along an infinite vertical porous plate in the presence of Hall current with variable suction and heat generation. A uniform magnetic field is applied in a direction normal to the porous plate. The equations governing the fluid flow are solved using the perturbation technique and the expressions for the velocity, the temperature and the concentration distributions have been obtained. Dimensionless velocity, temperature and concentration profiles are displayed graphically for different values of the parameters entering into the problem like Prandtl number Pr, Hartmann number M, Grashof number G, modified Grashof number Gc, Hall parameter m, Heat source parameter δ, Schmidt number Sc, and Chemical reaction parameter Kr. The Skin-friction coefficient, rate of heat transfer and mass transfer at the plate have been obtained and also discussed through tables. It has been observed that an increase in the Prandtl number leads to a decrease in the primary and secondary velocities, and also a decrease in the primary and secondary temperatures. The primary and secondary velocities decrease with increase in the Chemical reaction parameter or Magnetic field parameter

Power Allocation for Uniform Illumination with Stochastic LED Arrays

Light has traditionally been used for making objects visibl e to the naked eye. Lately, there has been tremendous interest in using it for free space communication [1]. This has simultaneously been accompanied by significant interest in light emitting diodes (LEDs) that have been replacing conventional light sources in almo st all applications [2–4]. Fair amount of existing literature has focused on achieving unif orm irradiance over a planar surface [5–8], beginning with the problem of finding the opti mal LED geometry at the light source to achieve uniform irradiance [9]. This was don e by using the irradiance distributions at the closest points on the incident surface . The case of LEDs using a freeform lens with a large view angle has been considered in [ 10]. More literature on similar themes is available in [11,12]

A Distributed Parameter Model for a Solid Oxide Fuel Cell: Simulating Realistic Operating Conditions

We present a detailed multiphysics model capable of simulating the dyn amic behavior of a solid oxide fuel cell (SOFC). This model includes a description of a ll the important physical and chemical processes in a fuel cell: fluid flow, mass and heat trans fer, electronic and ionic potential fields, as well as the chemical and electrochemical react ions. The resulting highly nonlinear, coupled system of differential equations is solved using a fi nite volume discretization. Our interest lies in simulating realistic operating conditions with the obj ective of high efficiency operation at high fuel utilization. While there are a number of studies in the literature that present multiphysics models for SOFCs, few have focused on simulat ing operating conditions that are necessary if SOFC systems are to realize their promise of h igh efficiency conversion of chemical energy to electrical energy. In this report we present s imulation results at operating conditions that approach the required ranges of power density an d overall efficiency. Our results include a) the temperature and composition profiles along a typical f uel cell in a SOFC stack, b) the dynamic response of the cell to step changes in the available inpu t variables. Since models such as the one presented here are fairly expensive computationa lly and cannot be directly used for online model predictive control, one generally looks to use simplifie d reduced order models for control. We briefly discuss the implications of our model results o n the validity of using reduced models for the control of SOFC stacks to show that avoid ing operating regions where well-known degradation modes are activated is non-trivial without u sing detailed multiphysics models

Hints of spin-orbit resonances in the binary black hole population

Binary black hole spin measurements from gravitational wave observations can reveal the binary's evolutionary history. In particular, the spin orientations of the component black holes within the orbital plane, $\phi_1$ and $\phi_2$, can be used to identify binaries caught in the so-called spin-orbit resonances. In a companion paper, we demonstrate that $\phi_1$ and $\phi_2$ are best measured near the merger of the two black holes. In this work, we use these spin measurements to provide the first constraints on the full six-dimensional spin distribution of merging binary black holes. In particular, we find that there is a preference for $\Delta \phi = \phi_1 - \phi_2 \sim \pm \pi$ in the population, which can be a signature of spin-orbit resonances. We also find a preference for $\phi_1 \sim -\pi/4$ with respect to the line of separation near merger, which has not been predicted for any astrophysical formation channel. However, the strength of these preferences depends on our prior choices, and we are unable to constrain the widths of the $\phi_1$ and $\Delta \phi$ distributions. Therefore, more observations are necessary to confirm the features we find. Finally, we derive constraints on the distribution of recoil kicks in the population, and use this to estimate the fraction of merger remnants retained by globular and nuclear star clusters. We make our spin and kick population constraints publicly available