Sharma K.,Ccs University |
Dabas R.S.,National Physical Laboratory India |
Ravindran S.,Vikram Sarabhai Space Center
Astrophysics and Space Science | Year: 2012
In recent years with the advancement in satellite based navigational applications, study of Total Electron Content (TEC) has gained significant importance. It is well known that due to dynamical behaviour of equatorial and low latitude ionosphere, the levels of ionization is relatively high herein. The sustained decrease in solar extreme ultraviolet radiations during the current minimum is greater than any in recent history. This gives us the opportunity to study the observations of global positioning system total electron content (GPS-TEC) dual frequency signals from the GPS satellites continuously recorded at Trivandrum (an equatorial station) and Delhi (a low latitude station) during the extremely low solar activity period from January 2007 to June 2009. This study illustrates the diurnal, seasonal and annual variations of TEC during the extended solar minimum period. This study also investigates the behaviour of daytime ionosphere around spring and autumn equinoxes at low solar activity period. The results clearly reveal the presence of equinoctial asymmetry which is more pronounced at equatorial station Trivandrum. The diurnal variation of TEC shows a short-lived day minimum which occurs between 0500 to 0600 LT at both the stations. Delhi TEC values show its steep increase and reach at its peak value between 1200 and 1400 LT, while at the equator the peak is broad and occurs around 1600 LT. Further, the daily maximum TEC ranges from about 5 to 40 TEC units at Trivandrum and about 10 to 40 TEC units at Delhi, which correspond to range delay variations of about 1 to 8 m at the GPS L1 frequency of 1. 575 GHz. The Maximum values of TEC were observed during spring equinox rather than autumn equinox, showing presence of semi annual variation at both the locations. The minimum values of TEC were observed during the summer solstice at Trivandrum indicating the presence of winter anomaly at equatorial region while Delhi TEC values were minimum during winter solstice showing absence of winter anomaly. Also the TEC values at both the locations have been decreasing since 2007 onwards exhibit good positive correlation with solar activity. © 2012 Springer Science+Business Media B.V.
Coondoo I.,University of Aveiro |
Panwar N.,University of Aveiro |
Tomar A.,Ccs University |
Bdikin I.,University of Aveiro |
And 3 more authors.
Thin Solid Films | Year: 2012
Piezoresponse force microscopy (PFM) technique has been utilized to characterize the nanoscale electromechanical properties of chemical solution deposited pristine (BiFeO 3, BFO) and 5% Cobalt-substituted bismuth ferrite (BiFe 0.95Co 0.05O 3, BFCO) thin films. Distinct PFM contrast was observed on the films' surface both in out-of-plane and in-plane modes. Piezoresponse signal was larger in BFCO film than BFO and the former film also exhibited negative self polarization. The calculated self polarization factor was - 0.94. Lateral signal (in-plane) changed its sign upon 180°sample rotation which ruled out spurious electrostatic contribution and confirmed piezoelectric nature of the effect. Square patterns were written by local poling and reversible nature of the piezoresponse behavior was established. Well saturated piezoelectric hysteresis loops were acquired with improved piezoelectric coefficient value in case of Co-substituted BFO film. The effect has been described on the basis of polarization rotation with doping. Magnetization of BFO film also increases with Co-substitution. The enhancement in magnetic and ferro/piezoelectric properties should be useful for multiferroic applications. © 2012 Elsevier B.V. All rights reserved.
Kumar U.,Ccs University |
Chandra S.,University of Delhi
Journal of Saudi Chemical Society | Year: 2011
The stereochemistry and coordination behavior of Co(II) and Cu(II) complexes of a novel 18-membered quadridentate macrocyclic ligand (3,4,12,13-tetraphenyl-1,2,5,6,10,11,14,15-octaazacyclooctadecane-7,9,16,18-tetraone-2,4,11,13-tetraene) have been investigated after their template synthesis. The synthesized macrocycles have been characterized by means of various physicochemical techniques viz. elemental analyses, magnetic, conductivity measurements,and spectral (IR, electronic, mass and EPR) techniques. The structure of complexes has been determined with the help of spectroscopic as well as conductivity values and found to be six coordinated octahedral and tetragonal for Co(II) and Cu(II), respectively. The ligand was coordinated to the metal ion via the malonylhydrazide moiety's imine nitrogen in a tetradentate fashion. Molar conductance measurements revealed that reported macrocyclic complexes were non-ionic in nature. All the complexes have been screened for their in vitro antifungal activity against a number of fungi isolated from plants. The compounds exhibit significant antifungal activity. © 2010.
Joarder A.,Reserve Bank of India RBI |
Krishna H.,Ccs University |
Kundu D.,Indian Institute of Technology Kanpur
Computational Statistics and Data Analysis | Year: 2011
In this article we consider the statistical inferences of the unknown parameters of a Weibull distribution when the data are Type-I censored. It is well known that the maximum likelihood estimators do not always exist, and even when they exist, they do not have explicit expressions. We propose a simple fixed point type algorithm to compute the maximum likelihood estimators, when they exist. We also propose approximate maximum likelihood estimators of the unknown parameters, which have explicit forms. We construct the confidence intervals of the unknown parameters using asymptotic distribution and also by using the bootstrapping technique. Bayes estimates and the corresponding highest posterior density credible intervals of the unknown parameters are also obtained under fairly general priors on the unknown parameters. The Bayes estimates cannot be obtained explicitly. We propose to use the Gibbs sampling technique to compute the Bayes estimates and also to construct the highest posterior density credible intervals. Different methods have been compared by Monte Carlo simulations. One real data set has been analyzed for illustrative purposes. © 2010 Elsevier B.V. All rights reserved.
Malik A.K.,Ccs University |
Singh K.P.,Singh Simutech Pvt. Ltd. |
Sajal V.,Jaypee Institute of Information Technology
Physics of Plasmas | Year: 2014
A mechanism of efficient and highly focused terahertz (THz) radiation generation by photo-mixing of top-hat like lasers with frequencies ω 1, ω 2 and wave numbers k 1, k 2 in pre-formed rippled density (corrugated) plasma is proposed. In this mechanism, intensity variation of lasers offers nonlinear ponderomotive force at frequency ω ′ = ω 1 - ω 2 and wave number k ′ = k 1 - k 2 which couples with density ripples in the plasma and leads to a strong nonlinear oscillatory current that resonantly excites highly focused and intense THz radiation at frequency ω U H = √(ωp2 + ωc2) (where ω c is electron cyclotron frequency). The efficiency of emitted THz radiation of the order of 15% is obtained under optimum conditions. It is observed that focus and intensity of emitted radiation can be controlled by selecting a proper profile index of the lasers, ripple parameters, and tuning of external magnetic field. © 2014 AIP Publishing LLC.