No abstract

Systematic study of conventional and femtosecond optical tweezers demonstrates an interplay of thermal and optical nonlinearity due to tight focusing. Specifically, Brownian motion of the 250nm radius trapped bead is measured using a quadrant photodiode.

To highlight the advantage of femtosecond optical tweezers over conventional tweezers, we trapped 1µm diameter polystyrene beads suspended in water using a Ti:Sapphire laser.

A numerical analysis is carried out to comprehend the fluid flow and heat transfer phenomena of non-Newtonian power-law fluid flow around a rotating elliptic cylinder. The investigations are accomplished for the parameters namely aspect ratio of the cylinder, e=0.1; rotational speed of the cylinder, 0.5{less than or equal to}α{less than or equal to}2.0; Reynolds number, Re = 100; power-law index, 0.4{less than or equal to}n{less than or equal to}1.6; and Prandtl number, 1{less than or equal to}Pr{less than or equal to}100. A detailed vorticity and isotherm patterns are presented to demonstrate the vortex shedding and heat transfer phenomenon around the cylinder. The results show the strong dependency of fluid behavior and rotational speed on flow and heat transfer phenomena. At low rotational speed (α{less than or equal to}1.0), the standard vortex-shedding patterns appear. The behavior of the fluid mainly affect the size and strength of the vortices. At higher rotational speed, (α>1.0) a hovering vortex (HV) appears for Newtonian and shear-thinning fluids. The shear-thinning tendency of the fluid encourage the formation of HV, however for shear-thickening fluids HV is not observed. Due to rotational motion of the cylinder the surface Nusselt number vary in periodic manner with time. As expected the Prandtl number and shear-thinning behavior of the fluid encourage the heat transfer from cylinder. The rotational motion of cylinder also favors the heat transfer phenomena. At the end a correlation is presented for time average surface Nusselt number as the function of Prandtl number, fluid behavior, and rotational speed.

Aim of the paper is to investigate the effects of thermal radiation and velocity slip on steady MHD slip flow of viscous incompressible electrically conducting fluid over a permeable stretching cylinder saturated in porous medium in the presence of external magnetic field. The governing nonlinear partial differential equations are transformed into ordinary differential equations by suitable similarity transformation and solved numerically using Runge-Kutta fourth order method with shooting technique. Effect of various physical parameters on fluid velocity, temperature, skin –friction coefficient and Nusselt number are presented through graphs and discussed numerically.