Singh A.K.,Banaras Hindu University |
Singh S.B.,Banaras Hindu University |
Singh S.B.,VKS University |
Patel R.P.,MMHPG College
Physica Scripta | Year: 2010
Observation of whistler-mode chorus emissions recorded at the Indian Antarctic station, Maitri (lat=70°46′S, long=11°50′E, L=4.5), during a quiet period on 5 February 2001 has been reported. The detailed spectral analysis of recorded chorus emissions shows that each chorus element originates from the upper edge of the underlying hiss band. To explain the observed dynamic spectra of these chorus emissions, a possible generation mechanism is presented based on the recent nonlinear theory. It is observed that the seeds of chorus emissions with rising frequency are generated near the magnetic equator as a result of a nonlinear growth mechanism that depends on the wave amplitude. On the basis of this theory, the frequency sweep rate of chorus emission is computed and compared with that of our experimentally observed values, which in general shows good agreement. © 2010 The Royal Swedish Academy of Sciences.
Kumar P.,Vks University |
Singh B.P.,Tilka Manjhi Bhagalpur University |
Sinha T.P.,Bose Institute of India |
Singh N.K.,Vks University
Physica B: Condensed Matter | Year: 2011
The complex perovskite oxide a barium samarium niobate (BSN) synthesized by solid-state reaction technique has single phase with cubic structure. The scanning electron micrograph of the sample shows the average grain size of BSN∼1.22 μm. The field dependence of dielectric response and loss tangent were measured in the temperature range from 323 to 463 K and in the frequency range from 50 Hz to 1 MHz. The complex plane impedance plots show the grain boundary contribution for higher value of dielectric constant in the low frequency region. An analysis of the dielectric constant (ε′) and loss tangent (tan δ) with frequency was performed assuming a distribution of relaxation times as confirmed by the scaling behaviour of electric modulus spectra. The low frequency dielectric dispersion corresponds to DC conductivity. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with an activation energy of 0.71 eV. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behaviour of imaginary part of electric modulus M″ and dielectric loss spectra suggest that the relaxation describes the same mechanism at various temperatures in BSN. All the observations indicate the polydispersive relaxation in BSN. © 2010 Elsevier B.V. All rights reserved. All rights reserved.
Rai R.,Indian Institute of Technology Delhi |
Rai R.,University of Aveiro |
Mishra S.K.,Vks University |
Singh N.K.,Vks University |
And 2 more authors.
Current Applied Physics | Year: 2011
A simple and effective method of solid state reaction followed by quenching process is used to prepare multiferroic Er3+ and La3+ doped BiFeO3 ceramics. X-ray diffraction patterns indicated that these ceramics were of single-phase perovskite structure. Doping with La enhanced the dielectric, ferroelectric and ferromagnetic properties of BiFeO3. A-site substitution with the La and Er ions has been found to suppress the spiral spin structure of BiFeO3 giving rise to the appearance of room-temperature weak ferromagnetism. The enhanced multiferroic properties are attributed to the enhanced magnetoelectric interaction, which results from the La and Er substitution-induced destruction of the spin cycloid. © 2010 Elsevier B.V. All rights reserved.
Shekhar H.,Vks University |
Salim S.S.,Vks University
National Academy Science Letters | Year: 2011
The solid-liquid equilibrium data of 8-hydroxyquinoline (HQ)acetanilide (ACT) system determined by thaw melt method, exhibit the formation of a 1:2 addition compund (at 106°C) followed by two side by side eutectic alloys E1, (67°C) and E2(98°C) at 0.315 and 0.810 mole fraction of ACT respectively. The activity and activity coefficient values of the system obtained through heat of fusion data, compute the partial and integral excess and mixing thermodynamic quantities which highlight the ordering, stability and structure of the eutectic and noneutectic alloys. The Gibbs-Duhem equation also evaluates the value of activity and activity coefficient of a constituent in the binary mix. The stability functions also favour the stability of alloys and molecular complex.
Kumar S.,Vks University |
Singh A.K.,P.A. College |
Paul D.K.,Patna University
Nature Environment and Pollution Technology | Year: 2014
Considering the impacts of industrial effluents on the water quality of many ponds, reservoirs, lakes and rivers as reported in the literature, the present study of water quality of a polluted pond was undertaken. Several physico-chemical parameters of the polluted pond namely Suman Lal Ka Pokhara were analysed to evaluate its suitability for washing, pisciculture and irrigation purposes by determining parameters like water temperature, pH, conductivity, DO, alkalinity, total hardness, BOD, nutrients, etc. Water was found acidic. Contents of chloride and TDS were not within the limits accepted for irrigation. Other parameters also suggested that the pond is not fit for other purposes also.
Singh S.B.,Vks University |
Patel K.,Banaras Hindu University |
Patel R.P.,P.A. College |
Singh A.K.,Banaras Hindu University |
And 2 more authors.
Journal of Physics: Conference Series | Year: 2010
The VHF amplitude scintillations recorded during the period from January 1991 to December 1993 in the declining phase of a solar cycle and April 1998 to December 1999 in the ascending phase of the next solar cycle and from January 2008 to July, 2008 at low latitude station Varanasi (geomag. lat. 14° 55′ N, long. 154° E, Dip angle 37.3°, Sub-ionospheric dip 34°) have been analyzed to study the characteristics of ionospheric irregularities during the active solar and magnetic periods. In this paper, the expression for flux tube integrated linear growth rate of irregularities supposed to be produced through generalized Rayleigh-Taylor instability (GRTI) have been derived. Realistic atmospheric and ionospheric density model inputs are used to compute R-T growth rates for a range of geophysical conditions. The derived parameters of irregularities from scintillation data observed at low latitude are compared with computed values. An attempt is made to produce a model for ionospheric low latitude irregularities. © 2010 IOP Publishing Ltd.
Kant V.,VKS University |
Shekhar H.,VKS University
Chemistry | Year: 2014
The present communication aims at investigating the Nicotinamide (NA) - Thiourea (TU) binary system in the solid state emphasizing thermodynamic and interfacial studies. It was found from the solid-liquid phase diagram of the system that an A 1:5 additive co-crystal formed at 161°C and two side by side eutectic solid dispersions E2 (mole fraction 0.407 of TU) and E1 (mole fraction 0.968 of TU) at 142°C and 116°C respectively. The activity coefficient model based on enthalpy of fusion was employed to calculate the excess thermodynamic properties that of gE, hE and s E, which predict the nature of molecular interaction, ordering and stability between the components. The negative value of integral Gibbs free energy of mixing, ΔGM for all the eutectic and non-eutectic solid dispersions favours the spontaneous mixing in all solid dispersions. The driving force of nucleation during solidification (ΔGv) and the critical free energy of nucleation (ΔG*) at different undercoolings have also been highlighted. The value of radius of critical nucleus (r*) of solid dispersions has been found in nm scale which suggests new dimensions of solidification process for nano solid drug dispersions and it would be very surprising for the pharma world. The solid-liquid interface energy (σ), grain boundary energy (σgb) and the Gibbs-Thomson coefficient (τ) of all drug alloys have also been discussed. Interface morphology of the alloys follows the Jackson's surface roughness (α) theory and predicts the faceted growth (α > 2) proceeds in all the cases.