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Changanācheri, India

Unnikrishnan K.,Nss Hindu College | Unnikrishnan K.,Mahatma Gandhi University
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2012

Nonlinear dynamical models of the magnetosphere derived from observational time series data using phase space reconstruction techniques have yielded new advances in the understanding of its dynamics. Considering the solar wind-magnetosphere interaction to be a natural input-output system its dynamical features can be reconstructed on the storm time scale by using the method of time delay embedding. Here, fourteen magnetic storm intervals belonging to low/moderate and high solar activity periods are considered and a suitable state space model has designed by performing training and validation tests, for which dawn to dusk electric field (VBz) is chosen as the input, and the AL time series as the output. The percentage of the output variations that is reproduced by the model is termed as fit_model and a higher number of fit_model means a better model. The number of components m used in the state space model is varied from 1-9 and the best prediction is obtained when m=4. The fit_model values of time series used for validation are 67.96, 67.2, 72.44, and 70.89, with m=4. In the present study most of the storms considered are having D stmax in between -100 and -300nT, and they can be predicted well with this procedure. To reveal the prediction capability of the proposed state space model the 30 steps ahead outputs for the storm events are generated, which reasonably reproduce the observed values. © 2011 Elsevier Ltd. Source

Unnikrishnan K.,Nss Hindu College | Unnikrishnan K.,Mahatma Gandhi University
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2014

Present work is the first attempt to predict horizontal component of earth's magnetic field (. H) and range in H (δ. H) over Indian sector by considering the stations, namely, Trivandrum, Pondicherry, Visakhapatnam, and Nagpur, using the concept of neural network (NN). Through training procedure, solar flux (. F10.7), latitude, longitude, day of the year, local time, Ap index, IMF Bz, and ion number density are identified as the optimum choice of input parameters, whereas the inclusion of solar wind pressure and velocity has not significantly improved the performance of the model. Thus an appropriate neural network model, NSSHC has been developed with 12 hidden neurons and 500 iterations to predict H component and range in H (δ. H) during the period 1996-2001, to capture diurnal, seasonal, latitudinal, magnetic and solar activity effects. © 2014 Elsevier Ltd. Source

Subhadra Devi P.K.,Mahatma Gandhi University | Subhadra Devi P.K.,P.A. College | Unnikrishnan K.,Mahatma Gandhi University | Unnikrishnan K.,Nss Hindu College
Advances in Space Research | Year: 2014

In this study, 30 storm sudden commencement (SSC) events during the period 2001-2007 for which daytime vertical E × B drift velocities from JULIA radar, Jicamarca (geographic latitude 11.91 S, geographic longitude 283.11 E, 0.81 N dip latitude), Peru and ΔH component of geomagnetic field measured as the difference between the magnitudes of the horizontal (H) components between two magnetometers deployed at two different locations Jicamarca (geographic latitude 11.91 S, geographic longitude 283.11 E, 0.81 N dip latitude) and Piura (geographic latitude 5.21 S, geographic longitude 279.41 E, 6.81 N dip latitude), in Peru, were considered. It is observed that a positive correlation exists between peak value of daytime vertical E × B drift velocity and peak value of ΔH for the three consecutive days of SSC. A qualitative analysis made after selecting the peak values of daytime vertical E × B drift velocity and ΔH showed that 57% of the events have daytime vertical E × B drift velocity peak in the magnitude range 20-30 m/s and 63% of the events have ΔH peak in the range 80-100 nT. The maximum probable (45%) range of time of occurrence of peak value for both vertical E × B drift velocity and ΔH during the daytime hours were found to be the same, i.e.; 10:00-12:00 LT. A strong positive correlation was also found to exist between the daytime vertical E × B drift velocity and ΔH for all the three consecutive days of SSC, for all the events considered. To establish a quantitative relationship between day time vertical E × B drift velocity and ΔH, linear and polynomial (order 2 and 3) regression analysis (Least Square Method (LSM)) were carried out, considering the fully disturbed day after the commencement of the storm as 'disturbed period' for the SSC events selected for analysis. The formulae indicating the relationship between daytime vertical E × B drift velocity and ΔH, for the 'disturbed periods', obtained through the regression analysis were verified using the JULIA radar observed E × B drift velocity for 3 selected events. Root Mean Square (RMS) error analysis carried out for each case suggest that polynomial regression (order 3) analysis provides a better agreement with the observations from among the linear, polynomial (order 2 and 3) analysis. © 2014 COSPAR. Published by Elsevier Ltd. All rights reserved. Source

Sunil Paul M.M.,Mahatma Gandhi University | Aravind U.K.,Mahatma Gandhi University | Pramod G.,Nss Hindu College | Saha A.,UGC-DAE Consortium for Scientific Research | Aravindakumar C.T.,Mahatma Gandhi University
Organic and Biomolecular Chemistry | Year: 2014

Oxidative destruction and mineralization of emerging organic pollutants by hydroxyl radicals (OH) is a well established area of research. The possibility of generating hazardous by-products in the case of OH reaction demands extensive investigations on the degradation mechanism. A combination of pulse radiolysis and steady state photolysis (H2O2/UV photolysis) followed by high resolution mass spectrometric (HRMS) analysis have been employed to explicate the kinetic and mechanistic features of the destruction of theophylline, a model pharmaceutical compound and an identified pollutant, by OH in the present study. The oxidative destruction of this molecule, for intermediate product studies, was initially achieved by H2O 2/UV photolysis. The transient absorption spectrum corresponding to the reaction of OH with theophylline at pH 6, primarily caused by the generation of (T8-OH), was characterised by an absorption band at 330 nm (k2 = (8.22 ± 0.03) × 109 dm3 mol-1 s-1). A significantly different spectrum (λmax: 340 nm) was observed at highly alkaline pH (10.2) due to the deprotonation of this radical (pKa ∼ 10.0). Specific one electron oxidants such as sulphate radical anions (SO4 -) and azide radicals (N 3) produce the deprotonated form (T(-H)) of the radical cation (T+) of theophylline (pKa 3.1) with k2 values of (7.51 ± 0.04) × 109 dm3 mol-1 s-1 and (7.61 ± 0.02) × 109 dm3 mol-1 s-1 respectively. Conversely, oxide radicals (O -) react with theophylline via a hydrogen abstraction protocol with a rather slow k2 value of (1.95 ± 0.02) × 109 dm3 mol-1 s-1. The transient spectral studies were complemented by the end product profile acquired by HRMS analysis. Various transformation products of theophylline induced by OH were identified by this technique which include derivatives of uric acids (i, iv & v) and xanthines (ii, iii & vi). Further breakdown of the early formed product due to OH attack leads to ring opened compounds (ix-xiv). The kinetic and mechanistic data furnished in the present study serve as a basic frame work for the construction of OH induced water treatment systems as well as to understand the biological implications of compounds of this kind. © the Partner Organisations 2014. Source

Remanan R.,Mahatma Gandhi University | Unnikrishnan K.,Mahatma Gandhi University | Unnikrishnan K.,Nss Hindu College
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2013

The present study is an analysis of the effects of storm sudden commencements (SSC) on geomagnetic field components H, D and Z during 1995-2001 with the data of five low-latitude stations in India, namely Pondicherry (PND, 2.85°N, 79.92°E), Visakhapatnam (VSK, 8.34°N, 83.32°E), Alibag (ABG, 10.19°N, 72.87°E), Nagpur (NGP, 12.12°N, 79.08°E) and Ujjain (UJJ, 14.43°N, 75.78°E). The characteristics of geomagnetic H, D and Z field components are studied under various geophysical conditions. For both quiet and storm times, the maximum amplitude of H is obtained at PND and it decreases with increase in latitude for the period 1995-2001.The amplitude of D component is larger at VSK and smaller at UJJ for both quiet and storm periods during 1995-2001. It is clear that the storm time Hmin values show no variation with solar activity at 2.85°N (PND). However, all the other latitudes in the present study such as at 8.34°N, 10.19°N, 12.12°N and 14.43°N, storm time Hmin values decrease with increase of S10.7. The values of δHmin shows positive correlations with solar activity, for the stations PND, VSK, ABG, NGP and UJJ, considered in the present study. The value of correlation coefficient obtained between H and interplanetary magnetic field and H and interplanetary electric field increases with increase of solar activity. The values of δHmin (δHmin=Hstorm-Hquiet) increase with increase of solar activity and correlate well with Dstmax for the five low-latitudes studied here. © 2013 Elsevier Ltd. Source

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