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Bangalore, India

Das P.,Indian Institute of Technology Guwahati | Karthik K.,Indian Institute of Technology Guwahati | Chandra Garai B.,Satellite Center
Pattern Recognition | Year: 2012

Abstraction of a fingerprint in the form of a hash can be used for secure authentication. The main challenge is in finding the right choice of features which remain relatively invariant to distortions such as rotation, translation and minutiae insertions and deletions, while at the same time capturing the diversity across users. In this paper, an alignment-free novel fingerprint hashing algorithm is proposed which uses a graph comprising of the inter-minutia minimum distance vectors originating from the core point as a feature set called the minimum distance graph. Matching of hashes has been implemented using a corresponding search algorithm. Based on the experiments conducted on the FVC2002-DB1a and FVC2002-DB2a databases, we obtained an equal error rate of 2.27%. The computational cost associated with our fingerprint hash generation and matching processes is relatively low, despite its success in capturing the minutia positional variations across users. © 2012 Elsevier Ltd. All rights reserved.

Guha D.,University of Calcutta | Gupta B.,Girijananda Chowdhury Institute of Management and Technology | Kumar C.,Satellite Center | Antar Y.M.M.,Royal Military College of Canada
IEEE Transactions on Antennas and Propagation | Year: 2012

Hemispherical dielectric resonator antenna (HDRA) is reinvestigated by splitting it into four uniform quarters, which indeed generates a new DRA shape, proposed to call as "quarter-Hemispherical DRA" (q-HDRA). An innovative idea, gathered by the authors through their previous investigations, has been employed to investigate four-element q-HDRA resonating with dominant and first higher modes over a large impedance bandwidth (S 11 < - 10 dB) and producing improved monopole-like radiation pattern. The improvement has been described in terms of uniformity and symmetry in the radiation patterns obtained consistently over the entire operating bandwidth. No degradation or compromise in impedance bandwidth is observed. For this purpose, the new DRA unit (q-HDRA) has been characterized using simulated and measured data. Prototypes of single and multi-element q-HDRA have been measured and compared with some earlier versions. Unlike earlier one, consistently symmetric monopole-like radiation from a four element q-HDRA has been demonstrated. © 2006 IEEE.

Peter P.K.,Satellite Center | Peter P.K.,Indian Institute of Technology Bombay | Agarwal V.,Indian Institute of Technology Bombay
IEEE Transactions on Power Electronics | Year: 2012

The use of a switched capacitor (SC) dc-dc converter for tracking the maximum power point (MPP) of a photovoltaic (PV) array with the possibility of partial shading is described. The SC converter topology can be reconfigured to maximize conversion efficiency depending on the solar radiation and load. A new control scheme for MPP tracking based on tuning the input resistance (R rm IN) of the SC converter MPP tracker with a battery tied load to match the output resistance of the array at MPP is proposed. R rm IN of the SC converter MPP tracker is studied extensively. The limits of R rm IN and its sensitivity to Pulse-width modulation (PWM), frequency modulation (FM), and circuit parameters of the SC converter are analyzed. Based on the sensitivity analysis, the proposed control scheme consists of an inner FM loop for fine control, an outer PWM loop for coarse control, and a provision to increase the dynamic range of R rm IN with adjustments of certain converter circuit parameters. A hardware prototype of a 10-W SC converter-based MPP tracker is built. Experimental measurements on the hardware model confirm the theoretical analysis. An algorithm to implement the MPP tracking control scheme is also tested. © 1986-2012 IEEE.

Srinivasan G.,Satellite Center
New Astronomy Reviews | Year: 2010

Pulsars that have undergone a binary history have come to be known as "recycled pulsars" The very first binary pulsar to be discovered-the Hulse-Taylor pulsar-provided evidence for such a recycling. It is now widely accepted that the first-born neutron star dies a natural death as a pulsar due to its period lengthening. But eventually, it is spun back into life, once again, when it accretes matter and angular momentum from its companion. Such a spin up continues till the neutron star attains an "equilibrium period", which is determined by the strength of its magnetic field and the accretion rate. This article will attempt to give a historical perspective of how the various steps in the evolution of such a recycled neutron star were understood. © 2010.

Kalogirou V.,University of Rome Tor Vergata | Kalogirou V.,Satellite Center | Ferrazzoli P.,Satellite Center | Vecchia A.D.,University of Rome Tor Vergata
IEEE Transactions on Geoscience and Remote Sensing | Year: 2014

A discrete scattering model, based on the radiative-transfer theory, is used to simulate the backscattering of burned pine canopies at C-band. The model is first parameterized either with direct field measurements on a selected burned area in Greece or with proper estimations of the required variables, for which direct measurements were not possible. The simulated backscatter at VV polarization was compared against European Remote Sensing 2 (ERS-2) observations. The comparison was based on the observed backscattering of nine burned plots, during four different postfire acquisitions (n=36). In general, the model provides satisfying estimations of the backscattering with a root-mean-square error of 1.01 dB. The copolar signal for both HH and VV showed a mild decrease with increasing fire impacts and was considerably affected by the incidence angle. From the experiments performed in the simulated environment, it is concluded that the SAR copolar (C-band) backscatter varies with respect to certain fire impact levels. Other important acquisition- or stand-dependent variables (such as incidence angle and snag age) were also found to impact the relationship between backscatter and fire impacts. Finally, the backscattering variability on increasing volumetric soil moisture (VSM) and snag moisture was examined. The increase of VSM from 20% to 30% amplified the signal in both copolarized bands by 1.2-1.5 dB. This amplification was more apparent on VV polarization than in HH polarization. Instead, the HH signal proved to be more sensitive on the increase of snag moisture, which was tested under a stable dry soil. © 2014 IEEE.

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