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The influence of rheological behavior on the natural convection in a dielectric nanofluid with vertical AC electric field is investigated. The rheology of the nanofluid is described by Maxwell model for calculating the shear stresses from the velocity gradients. The employed model introduces the combined effects of movement of the molecules of the fluid striking the nanoparticles, thermophoresis and electrophoresis due to embedded nanoparticles. The exact solutions of the eigen model value problem for stress-free bounding surfaces are obtained analytically using one term Galerkin method to find the thermal Rayleigh number for onset of both non-oscillatory (stationary) and oscillatory motions. It is found that the oscillatory modes are possible for both bottom and top-heavy distributions of nanoparticles. It is observed that the value of critical Rayleigh number is decreased by a substantial amount with the increase in electric field intensity, whereas role of viscoelasticity (time relaxation parameter) is to hasten the occurence of oscillatory modes appreciably. The thermal Prandtl number is found to delay the occurence of oscillatory modes. These results are also shown graphically. [ABSTRACT FROM AUTHOR]

This paper considers a single-server queueing model in which the customers are served in batches of varying size depending on predetermined thresholds as well as available inventory. There is a finite buffer for the inventory and the service of every customer requires an inventory item. An ( s, S) -type inventory system is used for the models considered in this paper. Initially, the model is studied in detail using the matrix-analytic method by assuming all the underlying random variables to be exponentially distributed. Thereafter, an outline of the model in a more general set up is also presented. Due to complexity of the model when more general assumptions are made on the underlying random variables, simulation is opted after a satisfactory validation with the analytic counterpart of the exponential model. Finally, some illustrative numerical examples are also presented to accomplish our analysis. [ABSTRACT FROM AUTHOR]

A modified model considering effects of density as well as conductivity of nanoparticles is used to investigate the instability of a binary nanofluid layer. It is assumed that volume fraction of nanoparticles is small and remains constant at the initial state which leads to very interesting and useful results. The perturbed equations so found are analyzed using normal modes and weighted residual method. It is found that oscillatory motions are not possible and instability is invariably through stationary mode. After solving the problem analytically, numerical solutions are found for metallic (aluminium, copper, silver, iron) and non-metallic (alumina, silica, titanium oxide, copper oxide) nanoparticles using the software Mathematica. The effects of size of nanoparticles, difference in solute concentration, volume fraction of nanoparticles, difference in temperature, conductivity and density of nanoparticles are studied on the onset of convection. The increase in density of nanoparticles destabilizes the fluid layer system where as increase in conductivity stabilizes the same. Lower density of aluminium makes it more stable than other nanoparticles in spite of having its lower conductivity. Metals are largely more stable than non-metals. [ABSTRACT FROM AUTHOR]

Ginkgo biloba is one of the important traditional medicines mentioned in the Chinese pharmacopoeia as an antiasthmatic against polyuria and for the treatment of cardiovascular diseases. The present study was undertaken to investigate antioxidant efficacy of extract of Ginkgo biloba leaves. In cholesterol fed wistar rats. Result of the study showed a significant (P < 0. 01) increase in lipid peroxidation (TBARS level) with a concomitant decrease in glutathione (GSH) content (P < 0.01) and catalase (P < 0.05) activity in liver of cholesterol fed rats. Simultaneous treatment of Ginkgo bilobaleaves extract at 10, 25 and 50 mg/kg b.wt./day doses, orally for 90 days along with cholesterol feeding significantly prevented the rise of liver, TBARS level and improved the levels of glutathione and catalase in liver. The results of the present study suggest that extract of Ginkgo bilobasignificant antioxidant activities in Wistar rats. [ABSTRACT FROM AUTHOR]