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  • Author: R. Kumar x
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Diamagnetic susceptibilities for a number of 4H-1,4-benzothiazines and their sulfones are reported. A theoretical method to estimate diamagnetic susceptibilities of 4H-1,4-benzothiazines is also reported. Benzothiazine has been considered to be composed of two units, one consisting of a benzene ring containing amino and thio groups at ortho positions with other substituents and other consisting of β-diketones/β-ketoesters. Diamagnetic contributions of these two units have been calculated from diamagnetic susceptibilities of substituted o-aminobenzenethiols and β-diketones/β-ketoesters and have been used in estimating diamagnetic susceptibilities of 1,4- benzothiazines. It has provided excellent results of theoretical diamagnetic susceptibility. Such an excellent agreement between experimental and theoretical results has been attributed to the fact that the interactions between substituents, which do affect diamagnetism, have been duly accounted for in such calculations. Diamagnetic susceptibility contribution of oxygen atoms attached to sulphur forming sulfone group is also reported.

Abstract

Eleven seaweeds were collected from seven different sites—one from the backwaters of Muttukadu, Chennai and six regions along the coast, Tamil Nadu, India and tested for antibacterial activity against the plant pathogenic bacterium, Xanthomonas oryzae pv. oryzae. Unsaponified fractions of red and green seaweeds exhibited maximum antibacterial activity followed by petroleum ether extracts, lipophilic fractions, diethyl ether extracts, saponified fractions, chloroform extracts and methanol extracts. However, methanol extracts of brown seaweeds showed the highest antibacterial activity followed by lipophilic fractions, unsaponified fractions, ethanol extracts, saponified fractions, chloroform:methanol (2:1 v/v) extracts and chloroform extracts. The antibacterial potential of the seaweeds was in the following order: Enteromorpha flexuosa > Sargassum wightii > Turbinaria conoides > Padina boergesenii > Gracilaria edulis > G. blodgettii > Hypnea valentiaeH. musciformis > Spyridia insignis > Chnoospora minima > Ulva lactuca. Seaweeds collected from the backwaters of Muttukadu possessed higher antibacterial potential than the same species collected from coastal waters. Significant seasonal differences in antibacterial activity of seaweeds were found in specimens collected at seven different localities.

Abstract

The thermal instability of a layer of Rivlin-Ericksen elastico-viscous fluid acted on by a uniform rotation is considered. For stationary convection, a Rivlin-Ericksen elastico-viscous fluid behaves like a Newtonian fluid. It is found that rotation has a stabilizing effect and introduces oscillatory modes in the system. The visco-elasticity also introduces oscillatory modes in the system. A suffi-cient condition for the non-existence of overstability is also obtained.

Abstract

The thermal instability of a layer of Rivlin-Ericksen elastico-viscous fluid acted on by a uniform vertical magnetic field is considered. For stationary convection, a Rivlin-Ericksen elastico-viscous fluid behaves like a Newtonian fluid. The magnetic field has a stabilizing effect. It is found that the presence of a magnetic field introduces oscillatory modes which were non-existent in its absence. The sufficient condition for the non-existence of overstability is also obtained.

Abstract

The stability of the plane interface separating two Rivlin-Ericksen elastico-viscous superposed fluids of uniform densities when the whole system is immersed in a uniform horizontal magnetic field has been studied. The stability analysis has been carried out, for mathematical simplicity, for two highly viscous fluids of equal kinematic viscosities and equal kinematic viscoelasticities. It is found that the stability criterion is independent of the effects of viscosity and viscoelasticity and is dependent on the orientation and magnitude of the magnetic field. The magnetic field is found to stabilize a certain wave-number range of the unstable configuration. The behaviour of growth rates with respect to kinematic viscosity and kinematic viscoelasticity parameters are examined numerically.

This paper presents a convective dominated reliable diffusion process in an axi-symmetric tube with a local constriction simulating a stenos artery considering the porosity effects. The investigations demonstrate the effects of wall shear stress and recirculation flow on the concentration distribution in the vessels lumen and on wall mass transfer keeping the porosity in view. The flow is governed by the incompressible Navier-Stokes equations for Newtonian fluid in porous medium. The convection diffusion equation has been used for the mass transport. The effect of porosity is examined on the velocity field and wall stress. The numerical solutions of the flow equations and the coupled mass transport equations have been obtained using a finite difference method. This paper explains the reliable effects of flow porosity on the mass transport.