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Thermal convection in a ferromagnetic fluid layer with magnetic field dependent viscosity: a correction applied

Prakash J., Kumar R., Kumari K.

Studia Geotechnica et Mechanica

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2017

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Vol. 39, nr 3

39--46

EN

The effect of magnetic field dependent (MFD) viscosity on thermal convection in a horizontal ferromagnetic fluid layer has been investigated numerically. A correction is applied to Sunil et al. [24] which is very important in order to predict the correct behavior of MFD viscosity. Linear stability analysis has been carried out for stationary convection. The MFD viscosity parameter δ as well as the measure of nonlinearity of magnetization M3, both have a stabilizing effect on the system. Numerical results are also obtained for large values of magnetic parameter M1 and predicted graphically.

2

The onset of convection in a rotating multicomponent fluid layer

Prakash J., Singh V., Kumar R., Kumari K.

Journal of Theoretical and Applied Mechanics

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2016

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Vol. 54 nr 2

477--488

EN

The onset of convective instability is analysed in a rotating multicomponent fluid layer in which density depends on n stratifying agents (one of them is heat) having different diffusivities. Two problems have been analysed mathematically. In the first problem, a sufficient condition is derived for the validity of the principle of the exchange of stabilities. Further, when the complement of this condition holds good, oscillatory motions of neutral or growing amplitude can exist, and thus it is important to derive upper bounds for the complex growth rate of such motions when at least one of the bounding surfaces is rigid so that exact solutions of the problem in closed form are not obtainable. Thus, as the second problem, bounds for the complex growth rates are also obtained. Above results are uniformly valid for quite general nature of the bounding surfaces.

3

Dielectric relaxation and ac conductivity of WO3 added (Na1/2Bi1/2)TiO3 ceramic

Prasad K., Kumari K., Chandra K. P., Yadav K. L., Sen S.

Materials Science Poland

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2009

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Vol. 27, No. 2

373--384

EN

Ceramic samples of WO3 added (Na1/2Bi1/2)TiO3 were prepared using a high-temperature solid-state reaction method. X-ray diffraction analyses indicate the formation of a single-phase orthorhombic structure. The apparent particle size and lattice strain are estimated using the Williamson-Hall plot. Dielectric studies revealed the relaxor behaviour and addition of WO3 shifted phase transition temperature as well as depolarization temperature of (Na1/2Bi1/2)TiO3 to higher side. ac impedance plots were used to analyse the electrical behaviour of samples in function of frequency at various temperatures. The ac impedance studies revealed the presence of the grain boundary effect and evidence of a negative temperature coefficient of resistance. Cole-Cole analysis indicated a non-Debye type dielectric relaxation. The ac conductivity obeys the universal power law. The pair approximation type correlated barrier hopping model explains the universal behaviour of the s exponent. The apparent activation energy of the conduction process and density of states at the Fermi level have been discussed.