Shape optimization of flow split ducting elements using an improved Box complex method

Iterative search methods, such as the Box complex method, can be used for inverse shape design problems. In the present article, an improved version of the Box complex method is proposed specifically for computational fluid dynamics-based optimization of fluid flow ducting elements. The original Box complex method is improved by (1) assigning non-uniform weights for the estimation of the centroid, (2) using a reduced reflection factor for accelerated convergence, and (3) introducing measures to prevent premature breakdown of the iterative process. The success of the improved Box complex method over the original Box complex method is demonstrated on two benchmark functions and by applying it to two fluid flow problems of engineering. The improved method is shown to substantially accelerate the convergence with approximately 50% reduction in computational effort for the T-junction and manifold problems.     

Assessment of iodine deficiency disorders using the 30 cluster approach in the National Capital Territory of Delhi

OBJECTIVE: Iodine Deficiency Disorders (IDD) are a major public health problem in India. The National Capital Territory (NCT) of Delhi is a known iodine deficiency endemic area. The Delhi Government banned the sale of non-iodised salt since 1989. The present study was conducted to assess the status of IDD after 7 years of salt iodisation programme in the state. DESIGN: Cross sectional. METHODOLOGY: The recent indicators recommended by the World Health Organization-United Nations Childrens Fund-International Council for the Control of Iodine Deficiency Disorders (WHO-UNICEF-ICCIDD) were utilized for the assessment of IDD. A total of 30 clusters were selected using population proportionate to size cluster sampling procedure. In each identified cluster, one primary school was selected using random sampling. A total of 6911 school children in the age group of 8-10 years were included for the study. RESULTS: The total goiter prevalence rate was 8.6% while 2.1, 8.4, 17.6 and 71.9% of the children had urinary iodine excretion levels of < 2, 2-4.9, 5-9.9 and 10 and above mcg/dl, respectively. The median urinary iodine excretion was 17 mcg/dl. Of the 1854 salt samples analyzed, salt with a nil iodine content was consumed only by 1.4% of the beneficiaries. Forty one per cent of families consumed salt with an iodine content of less than 15 ppm. CONCLUSION: IDD continues to be a public-health problem in the NCT of Delhi. There is a need of strengthening the existing monitoring system for the quality of iodised salt.     

Amplitude and phase-shaping effects in beamwaveguides

Results are presented of an investigation on improvements in a geometrical optics design of a beam-waveguide antenna for operation at multiple frequency bands. Improvements might be possible by changing the design of the lower-frequency input pattern to the beam waveguide. The effects of amplitude and phase shaping the input pattern have been studied with an aperture diffraction model. Accurate vector near-field computations were made rapidly with a spherical wave expansion of the input and scattered fields. Numerical results indicate that for aperture sizes of less than 30 wavelengths, there is insufficient control on defocusing due to amplitude and phase shaping. Design tradeoffs on spillover loss and defocusing are possible by changing the amplitude and phase distribution of the input wavefront for larger size apertures     

Application of spherical wave expansions to reflector antennasusing truncated field data

The electromagnetic field radiated by paraboloidal and hyperboloidal reflector antennas excited by an azimuthally independent, linearly polarized source is considered. The electromagnetic field is sampled on a spherical surface in order to numerically generate a set of spherical wave mode coefficients which, in turn, are used to compute antenna patterns. Patterns are produced in the near- and far-field regions based on both full and partial, or truncated, near- and far-field data as a function of the antenna parameters and the truncation angle location. The similarity of the patterns obtained from truncated field data to the untruncated patterns is found to depend on the pattern level at the truncation point, the location of the truncation point, the antenna parameters, and the radial distance between the spherical surfaces on which the electromagnetic field is sampled and produced     

On internal higher order mode coupling in slot arrays

Internal higher-order mode coupling between adjacent longitudinal radiating slots cut in a broad wall of a rectangular waveguide is examined rigorously. Method-of-moments solutions to pertinent coupled integral equations are investigated. Higher-order mode coupling effects on the amplitude and phase of the aperture electric field are studied as a function of waveguide and slot parameters. It is shown that higher-order mode coupling effects are accounted for, to a substantial extent in standard-height waveguides and almost completely in reduced-height waveguides, by including the TE₂₀ mode coupling in the analysis     

Modeling and simulation of centroid and inversion charge density in cylindrical surrounding gate MOSFETs including quantum effects

An analytical model for surrounding gate metal–oxide–semiconductor field effect transistors(MOSFETs)considering quantum effects is presented.To achieve this goal,we have used a variational approach for solving the Poisson and Schrodinger equations.This model is developed to provide an analytical expression for the inversionchargedistributionfunctionforallregionsofthedeviceoperation.Thisexpressionisusedtocalculatethe other important parameters like the inversion charge centroid,threshold voltage and inversion charge density.The calculated expressions for the above parameters are simple and accurate.The validity of this model was checked for the devices with different device dimensions and bias voltages.The calculated results are compared with the simulation results and they show good agreement.     

Modelling the centroid and charge density in double-gate MOSFETs including quantum effects

An analytical model for double-gate metal–oxide–semiconductor field-effect transistors considering quantum effects is presented in this article. The variational method is used to solve the Schrodinger–Poisson's equation. The simple and accurate mathematical expressions for centroid and inversion charge density are obtained. It is seen that the minimum energy of the sub-bands and the inversion charge density decreases as the silicon thickness of the device increases. The analytical results obtained from the proposed model are compared and agreed well with a device simulation tool named SCHRED.     

Admittance of an isolated waveguide-fed slot radiating betweenbaffles using a spectrum of two-dimensional solutions

An efficient method of computing resonant length and admittance characteristics of an isolated broad-wall shunt slot radiating between baffles of finite height is presented. The outer three-dimensional (3D) field problem associated with this geometry is reduced to a two-dimensional (2D) one via a Fourier transformation with respect to the longitudinal z direction. For each value of the longitudinal wave number k_z an integral equation is solved for the E field in the mouth of the plates using the method of moments. This procedure is repeated for several discrete values of k_z, to obtain a spectrum of 2D solutions which are then inverse-transformed to construct the 3D solution in the spatial domain for the exterior baffle region and the half space. The slot aperture field is determined by the conventional moment method solution to the integral equation that enforces the continuity of the H field across the slot. Scattering properties of the slot are then deduced. Numerical results for the resonant length and resonant conductance are presented. Computer results are found to be in good agreement with experimentally measured data     

Compound coupling slots for arbitrary excitation of waveguide-fedplanar slot arrays

A resonant coupling slot cut in the common broad wall of two crossed rectangular waveguides is analyzed. The slot is offset from the center line and tilted with respect to the longitudinal axis of the main waveguide, whereas it is centered-tiled in the branch waveguide. It is shown that the slot offset and tilt control the branch waveguide excitation amplitude with a phase variability of 360°. Pertinent integral equations are developed, taking into account finite wall thickness. The integral equations are solved for the slot aperture electric field using the method of moments. Dominant mode scattering by the slot in both waveguides is obtained