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Acharya R.,Space Applications Center | Roy B.,Space Applications Center | Sivaraman M.R.,Space Applications Center | Dasgupta A.,Institute of Radio Physics and Electronics
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2011

The total electron content (TEC) of the equatorial ionosphere is controlled by photochemical processes as well as the transport of the ionospheric plasma near the magnetic equator. The transport phenomenon is initiated by the vertical drift driven by the eastward electric field, which also drives the Equatorial Electrojet. The empirical relation between the Equatorial Electrojet and the anomaly component of the equatorial TEC has already been established. Taking this relation as a reference, a simplified physical model of the anomaly component of equatorial TEC is obtained as a function of Equatorial Electrojet. Influence of other factors like the solar incidence angle and the solar flux are also considered here and the extent of their influence are also investigated. This has been done using TEC data obtained from dual frequency GPS receivers during the low solar activity period of 2005. The derived model is based on the physics of the underlying fountain effect and matches with the observed empirical relation to a fair extent. Obtained results are found to corroborate with previous findings and these physical model values are found to have improved correlation with the observed data than the reference empirical relation. This establishes the conformity between the EEJ based ionospheric model and the physical phenomenon of the fountain effect. © 2011 Elsevier Ltd.


Acharya R.,Space Applications Center | Roy B.,Space Applications Center | Sivaraman M.R.,Space Applications Center | Dasgupta A.,Institute of Radio Physics and Electronics
Advances in Space Research | Year: 2011

The temporal variation of the equatorial electrojet is estimated utilising a suitably designed Kalman filter and using the established empirical relations between the anomaly component of equatorial TEC and the modified electrojet. TEC data obtained from dual frequency GPS receivers are used for the purpose. Estimation requires the a-priori knowledge of the peak electrojet value of the day and hence can be made in post temporal scenario only. Initial results obtained during a low solar activity time in an equinoctial month shows acceptable accuracy of the proposed algorithm. Limited analysis is done by segregating the results into temporal sessions of pre-attainment and post-attainment of the electrojet peak. © 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.


Acharya R.,Space Applications Center | Roy B.,Space Applications Center | Sivaraman M.R.,Space Applications Center | Dasgupta A.,Institute of Radio Physics and Electronics
Advances in Space Research | Year: 2011

The Ionospheric Total Electron Content is responsible for the group delay of the signals from the Navigation satellites. This delay causes ranging error, which in turn degrades the accuracy of position estimated by the receivers. For critical applications, single frequency receivers resort to Satellite Based Augmentation Systems in order to have improved accuracy and integrity. The performance of these systems in terms of accuracy can be improved if predictions of the delays are available simultaneously with real measurements. This paper attempts to predict the Total Electron Content using adaptive recurrent Neural Network at three different locations of India. These locations are selected at the magnetic equator, at the equatorial anomaly crest and outside the anomaly range, respectively. In-situ Learning Algorithm has been used for tracking the non-stationary nature of the variation. Prediction is done for different prediction intervals. It is observed that, for each case, the mean and root mean square values of prediction errors remain small enough for all practical applications. Analysis of Variance is also done on the results. © 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.


Pandit S.,Institute of Radio Physics and Electronics | Mandal C.,Indian Institute of Technology Kharagpur | Patra A.,Indian Institute of Technology Kharagpur
Integration, the VLSI Journal | Year: 2010

This paper presents an automated procedure for generation of high-level topologies for continuous-time ΣΔ modulator system. A functional topology of the system is generated from the given transfer function model of the modulator. Mathematical transformation technique is applied iteratively over the initial topology to generate a functional topology which is optimized for modulator sensitivity, hardware complexity and relative power consumption. This is then implemented using behavioral models of operational transconductance amplifiers and capacitors. The generated high-level topology is ensured to work with reasonable accuracy under non-ideal conditions. The entire procedure has been implemented in Matlab/Simulink environment. Numerical results have been provided to demonstrate the procedure. © 2010 Elsevier B.V. All rights reserved.


Mazumdar K.,Indian School of Mines | Singh V.P.,Indian School of Mines | Sharan A.,Indian School of Mines | Ghosal A.,Institute of Radio Physics and Electronics
Superlattices and Microstructures | Year: 2015

The fetching of a single-flux scattering theory of the InAs nanowire based MOSFET has been presented here. The backscattering coefficient has been studied for 1nm, 5nm and 10nm nanowire radius. The calculations are made for <100>, <110> and <111> nanowire orientations. It has been found that the value of the backscattering coefficient increased as the radius of the nanowire is increased from 1nm to 10nm but the spacing between <100>, <110> and <111> nanowire orientations decreased. The drain current IDsat-(VGS-VT) characteristics of InAs ballistic nanowire (5nm radius) has been discussed in detail. Also, the significant drain current IDsat versus electric field (V/m) characteristics of nonballistic InAs nanowire (5nmradius) MOSFET transistor for different orientations are obtained. © 2015 Elsevier Ltd.

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