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Many biological microorganisms and artificial microswimmers react to external cues of environmental gradients by changing their swimming directions. We study here the behavior of eukarytic flagellated microswimmers in linear viscosity gradients. We employ a model of flagellum consisting of a semi-flexible filament with a travelling wave of spontaneous curvature to study viscotaxis of actively beating flagella in two spatial dimensions. The propulsion of the flagellum in a fluid due to a hydrodynamic friction anisotropy is described by resistive-force theory. Using numerical simulations and analytical theory, we show that beating flagella exhibit positive viscotaxis, reorienting themselves toward higher viscosity areas. We quantify this behavior by characterization of the dependence of the rotational velocity on beat amplitude, swimming speed, and wave length. We also examining the effects of asymmetric flagellar wave forms, which imply circular trajectories in the absence of viscosity gradients; here, large asymmetry leads to trochoid-like trajectories perpendicular to the gradient in the form drifting circles. The flagellar deformability strongly reduce the beat amplitude and the viscotatic response. The viscotatic response is shown to be captured by a universal function of the sperm number., Comment: 15 figures

In this paper we propose an easy algorithm for real time hand finger counting involving one or more than one hand. Hand finger counting is a simple medium for Human-Computer Interface which can prove to be a convenient input method for driving interactive menus, small applications and interactive games. Here, we also calculate the orientation of the hand which can be used to provide inputs for the direction and/or speed control of a robot, controlling mouse cursor or slide-show presentations. If being used by a single person, with his or her two hands, the person can trigger ten different commands with fingers in addition to the orientation of the hand. We tried to use very simple algorithm using very basic mathematics of 2D coordinate geometry and avoided the conventional use of calculus, contours and convex hull. Anyone seeking for an easy to implement hand finger counting algorithm can refer to it., Comment: 8 pages, 4 sets of figures