A comparative study of scintillation analysis over two line-of-sight paths at 6.7 GHz and 7.6 GHz

A comparison of the signal intensity fluctuations or scintillation of signal level, observed over two line-of-sight links is presented. These links are situated over Calcutta, DumDum-Andul (6.7 GHz) and Delhi, Delhi-Sonepat (7.6 GHz). The study reveals departures, in the occurrence and variation of the scintillation over the Calcutta path as compared with the path over Delhi. This deviation has been attributed to the large variation in humidity which exists in the coastal region, and also which plays a major role in microwave propagation in the troposphere.     

TES-based video source modeling for performance evaluation ofintegrated networks

The letter considers modeling methodologies of variable bit-rate (VBR) video sources for performance evaluation of integrated networks. The authors consider an example in which compressed H.261 standard VBR video is transmitted over a local area network carrying both video and data. A group-of-block (GOB) level source model has been constructed using TES (transform-expand-sample)-a new general methodology for generating stationary autocorrelated time series, which can simultaneously capture a prescribed marginal distribution and autocorrelation function. The TES model is used to drive CSMA/CD network simulations for a performance evaluation study. Numerical comparisons with a conventional autoregressive (AR) modeling approach are given     

Improved depth map through optimal axis stereo

Feature-based stereo correspondence techniques suffer from the major limitation that it is difficult to match along epipolar lines and this often results in a sparse set of depth points. Past researchers attempted to solve this problem through trinocular stereo. In this paper, a new method has been proposed for reducing the sparsity of depth points by orienting the epipolar line of the cameras in a direction that maximizes the number of feature points. The corresponding epipolar axis has been termed as the optimal axis. Our analytical as well as simulation results have established that for a limited edge scenario, the proposed approach can lead to considerable improvement in the number of feature points that can be matched. We have introduced a figure-of-merit for the optimal axis and discussed how it is qualitatively related to the variance of the probability density function (pdf). We have also presented the results of our simulation experiment, termed as the random stick experiment. Finally, we have also shown the results of improved reconstructed surface of a synthetic image using optimal axis alignment.     

The architecture of a knowledge-based process planning system for small scale industriee

The objective of this paper is to describe a knowledge-based system to assist engineers to generate optimum process plans. The knowledge base is defined using a PASCAL-like language and is maintained in the form of PROLOG sentences. The knowledge base may be readily modified by process planners to meet their specific requirements. An inferece engine systematically tries to apply the rules to generate basic process plans. These plans are then optimised by repeated applications of user difined rules. The system is being written in PROLOG.     

Redshifting and broadening of quantum-well infrared photodetector'sresponse via impurity-free vacancy disordering

The partial intermixing of the well and barrier materials offers unique opportunities to shift locally the bandgap of quantum-well (QW) structures. We have demonstrated redshifting and broadening of the wavelength responses of bound-to-continuum GaAs and InP based quantum-well infrared photodetectors (QWIP's) after growth via impurity-free vacancy disordering (IFVD). A comprehensive set of experiments is conducted on QWIP's fabricated from both as-grown and multiple-quantum-well (MQW) structures. Compared to the as-grown detector, the peak spectral responses of the disordered detectors were shifted to longer wavelengths. The peak absolute response of the disordered GaAs based QWIP is lower by almost a factor of four. However, the responsivity characteristics of the disordered InP based QWIP show no major degradation. In general, with the spectral broadening taken into account, the overall performance of the disordered QWIP's has not dropped significantly. Thus, the postgrowth control of the QW composition profiles by impurity-free vacancy disordering offers unique opportunities to fine tune various aspects of a photodetector's response. Theoretical calculations of the absorption coefficient spectrum are in excellent agreement with the experimental data