Local computation of angular velocity in rotational visual motion

Retinal images evolve continuously over time owing to self-motions and to movements in the world. Such an evolving image, also known as optic flow, if arising from natural scenes can be locally decomposed in a Bayesian manner into several elementary components, including translation, expansion, and rotation. To take advantage of this decomposition, the brain has neurons tuned to these types of motions. However, these neurons typically have large receptive fields, often spanning tens of degrees of visual angle. Can neurons such as these compute elementary optic-flow components sufficiently locally to achieve a reasonable decomposition? We show that human discrimination of angular velocity is local. Local discrimination of angular velocity requires an accurate estimation of the center of rotation within the optic-flow field. Inaccuracies in estimating the center of rotation result in a predictable systematic error when one is estimating local angular velocity. Our results show that humans make the predicted errors. We discuss how the brain might estimate the elementary components of the optic flow locally by using large receptive fields.     

Diffusion of a fluid through a spherical elastic solid undergoing large deformations

The diffusion of a fluid through a spherical elastic solid undergoing large deformation is described in this paper. The constitutive model used is the single-constituent model for diffusion of fluids in nonlinear elastic solids, originally presented by Baek and Srinivasa [S. Baek, A.R. Srinivasa, Int. J. Nonlinear Mech. 39 (2004) 201-218] and based on a variational method and on the assumption of continuity of chemical potential across the solid-fluid interface. The balance laws for a single continuum with mass diffusion are cast in spherical coordinates, and suitable boundary conditions are posed to describe the radial diffusion of fluid through an elastic spherical shell with finite thickness. Its inner surface is adjacent to a rigid wall, either impermeable or permeable, while the outside surface is in contact with the fluid that swells the solid, diffuses through it, and exerts a hydrostatic pressure on its surface.     

Influence of Saffman's lift force on the motion of a particle in a Couette layer

The article is concerned with the study of the effect of E. S. Asmolov's corrections to Saffman's lift force for the wall vicinity and a nonzero ratio of Reynolds numbers. It is shown in what way these corrections change the particle paths in a Couette layer and the conditions of deposition.Notation x=X/D, y=Y/D dimensionless longitudinal and transverse coordinates - u=U _p /U , =V _p /U dimensionless projections of particle velocity on the longitudinal and transverse axes - =tU /D dimensionless time - U ²/(18D) Stokes number - = _g / _p , coefficient of the gas kinematic viscosity - particle diameter - /D - _g , _p densities of the gas and particle material - du/d - dv/d - P _s Saffman's force - C coefficient in the formula for Saffman's force - yRe _d ^1/2 - A v _r Re _d ^1/2 - 3.08 - Re V _r / - Re _k ²/)U _g /Y - A Re/Re _k ^1/2 - Re _d U D/ - V _r ((U _g –U _p )²+V _p ² )^1/2 Indices g refers to gas parameters - p refers to the parameters of particles - 0 at the time momentt=0 - S Saffman's force - k Reynolds number based on the velocity gradient - based on velocity - r relative velocity - x projection on thex axis     

Influence of variations in the angular rotational velocity of a spacecraft on thermal convection under conditions of weightlessness

Unlike the conventional approach where it is assumed that liquid motion under conditions of weightlessness is caused by vibrations or residual quasisteady-state microaccelerations, the present paper examines convection caused by variations in the angular rotational velocity of a spacecraft. It is shown that although the level of microaccelerations caused by variations in the angular rotational velocity is extremely low for the Shuttle spacecraft, Mir space station, and unmanned spacecraft, of the order of 0.1–1 μg, the ensuing convection and nonuniformity in the impurity distribution during crystal growth may be very appreciable. Pis’ma Zh. Tekh. Fiz. 23, 6–13 (December 26, 1997)     

Melting of an infinite solid with a spherical cavity

The embedding technique is employed to obtain the short time exact analytical solution for the melting or solidification of an infinite body with a spherical cavity, with melting or solidification starting from the interior surface of the cavity. General cases of zero and infinite rates of ablation are considered, with particular emphasis on the Neumann problem and the case corresponding to a sudden rise of temperature. Numerical results are presented, and the validity and accuracy of the solutions are briefly discussed.     

Impact of a solid body on a hinged spherical dome

A method of calculating a spherical dome with impact of a solid body is presented. The shell model is used for calculations. Equations are solved using Laplace's transform. Values of loads at which plastic deformations occur are obtained and areas of applicability of simpler impact loading schemes determined.Translated from Problemy Prochnosti, No. 9, pp. 57–59, September, 1991.     

Influence of fundamental force factors on the transverse velocity of fine particles moving in a turbulent gas stream

On the basis of a numerical solution of the equations of fine particle motion in a turbulent vertical stream forces of a different nature, acting in the radial direction and governing the average transverse particle velocity, are analyzed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 4, pp. 657–664, April, 1976.     

A novel and developed approximation for motion of a spherical solid particle in plane coquette fluid flow

The present article solves the couple equations of a spherical solid particle’s motion in plane coquette fluid flow by using the HPM-Padé technique which is a combination of the Homotopy Perturbation Method (HPM) and Padé approximation. The series solutions of the couple equations are developed. Generally, the truncated series solution is adequately in a small region and to overcome this limitation, the Padé techniques which have the advantage of turning the polynomial approximation into a rational function, are applied to the series solution to improve the accuracy and enlarge the convergence domain. The current results compared with those derived from HPM and the established fourth order Runge–Kutta method in order to ascertain the accuracy of the proposed method. It is found that this method can achieve more suitable results in comparison to HPM.     

DNS of turbulent flows with intermittency formed in a spherical layer with modulated velocity of rotation of the outer spherical boundary

Turbulent flow regimes in a layer of a viscous incompressible fluid confined between counter-rotating spherical boundaries have been numerically simulated in the case of periodic variations in the velocity of outer sphere rotation at a constant velocity of the inner sphere. The obtained solutions reveal temporal alteration of the laminar and turbulent regimes occupying the entire spatial region of flow in the spherical layer. The numerical results agree with the available experimental data on the shape of the velocity profile and the relative duration of its laminar phase. Factors responsible for the transition to chaos and the appearance of intermittency during this transition are established.     

Molecular heat exchange of a solid spherical particle with a gaseous medium

The process of molecular heat exchange of a motionless rather large solid spherical aerosol particle with the surrounding medium has been mathematically simulated at significant variations of the temperature in its vicinity. The obtained formulas make it possible to find directly the temperature distribution in the vicinity of the particle and the value of the molecular heat flow conducted from the particle surface taking into account the temperature jump and the temperature dependence of the thermal conductivity coefficient. The analysis of the theoretical results has shown that the increase in the surface temperature of the particle leads to a monotonic increase in the jump temperature of the gas near its surface. In the case of a rather large particle, this can lead to a strong decrease in the value of the molecular heat flow conducted from its surface.     

Effect of convection on the motion of spherical bubbles

An expression is derived for the drag coefficient of a spherical bubble, taking account of free, forced, and thermocapillary convection.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 1, pp. 52–58, January, 1981.     

Second-order wave force on a large cylinder

Summary A new technique has been developed for estimating the wave loadings on large circular cylinders. The theory, mainly due to Lighthill, has been applied to the case of large cylinders. Comparison with the previously reported experimental results shows favourable agreement for the range of parameters indicated in the graphs.Notations The following symbols are used in this paper a Wave amplitude - b Radius of the cylinder - D Diameter of the cylinder - F _l Linear force - F _d Dynamic force - F _q Quadratic force - F _w Water line force - g Acceleration due to gravity - h Depth of water - H=2a Total wave height - k Wave number,k=2/L - L Wave length - n Outward normal to body surface - n _x Direction cosine between the normaln and the given force - S Body surface - t Time - T Wave period - x, y, z Cartesian coordinates - r, ,z Cylindrical coordinates - W Vertical velocity of fluid - Density of fluid - Wave frequency, =2/T - Total velocity potential - _r , _z Partial derivatives with respect tor andz, respectively - ⁽¹⁾, _l Linear theory velocity potential - ⁽²⁾, _q Second-order velocity potential - Water surface elevation or wave height - _i Linear theory wave height - _q Quadratic theory wave height With 3 Figures     

Tangential friction on the wall of a container with a spherical charge and fluid motion through the charge

Viscous tangential stress on the interior wall of a container with a spherical charge, that develops in filtration of an incompressible fluid through the charge is investigated. Based on an analysis of an experimental dependence of the dimensionless stress on the Reynolds number, two critical Reynolds numbers are determined: the first number corresponds to the beginning of an abrupt drop in the stress, and the second number, to its reaching a regime that is self-similar in velocity. Comparison with the theory permits interpretation of the effects of pseudoturbulence and turbulence, respectively. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 1, pp. 50–54, January–February, 1997.     

A regression study on the solid particle erosion of copper and copper alloys by angular and spherical particles at normal incidence

A regression analysis is presented on the solid particle erosion results of copper and copper alloys impacted by angular and spherical silica particles at normal incidence. Particle shape, particle size, and zinc content of materials were selected as factors. Also, three levels were assigned to each factor. Experiments were performed under 50 mTorr vacuum utilizing an electrostatic accelerator erosion tester. A total of 10 g particles were sent to each substrate material in 10 increments. At the end of the experiments, the extent of erosion was calculated by dividing weight loss to the amount of particles sent. A regression analysis was conducted on the erosion data to see the individual and interaction effects of factors chosen.

Results indicate that quadratic components of zinc content, particle shape, and particle size and linear interaction between particle size and zinc content were effective in defining erosion in this study.     

Turbulent flow formation in a spherical layer at a variable velocity of rotation of the outer spherical boundary

Transitions to turbulent flow regimes in a layer of a viscous incompressible fluid confined between counterrotating spherical boundaries have been experimentally studied in the case of periodic variations in the outer sphere rotation velocity at a constant velocity of the inner sphere. A periodic flow regime formed during the rotation of spherical boundaries at constant velocities in the opposite direction is under consideration. The effect of the amplitude and frequency of modulation of the velocity of outer sphere on the transition from this regime to chaos has been determined. Based on the results of flow visualization and flow velocity measurements by the laser Doppler anemometry technique, it is shown that turbulent flows with spatiotemporal intermittency can be formed in the spherical layer.     

新型大扫描范围原子力显微镜的研究

研制了一种大扫描范围原子力显微镜(AFM)。设计了新的扫描驱动电路,使单幅图像的扫描范围大幅度提高;用步进电机和扫描器配合扫描,得到序列图像,序列图像拼接后获得大范围样品图像。实验结果表明,采用这一方法,在±150V 的电压驱动下,AFM 的扫描范围可增大到10 ìm?1 mm 的量级,同时保持 1 nm 量级的测试分辨力。     

The effect of a solid wall on the closure of a spherical cavitation pocket

We examine the effect of a solid wall on the closure of a spherical cavitation cavity or pocket. It is demonstrated that asymmetric flow substantially reduces the induced pressure and rate of closure for the cavity containing the gas. while in the case of a vapor cavity asymmetry of flow leads to conclusions qualitatively different from those which follow from the classical Rayleigh solution for an infinite fluid.     

Determination of the force acting on a spherical obstacle in an underexpanded jet

A method is proposed for determining the force acting on a spherical obstacle in an underexpanded jet. The method is based on the application of the momentum law.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 4, pp. 668–671, October, 1978.