Horizontal plane

Abstract: An experimental study has been made of some aspects of the phenomena accompanying the collapse of liquid columns on to a rigid horizontal plane with air as the outer medium. The cases covered include the two-dimensional collapse of rectangular and semicircular sections, and the three-dimensional axial collapse of right circular cylinders. As the columns collapsed, the fluid spread across the horizontal plane, attaining a maximum velocity, which, in the two-dimensional cases, was proportional to the square root of the original height. It was not clear whether this proportionality would hold for the axial collapse of cylinders. If it did, then the factor of proportionality would be some 25 % lower. In the two-dimensional cases the top of the residual column accelerated downwards to a maximum velocity proportional to the square root of the product of the original height and the original height to base ratio. The nature of the subsequent retardation indicated that the downward velocity probably approached zero asymptotically with time.

Abstract: This study examines the source of direction-dependent errors in movement extent made by human subjects in a reaching task As in the preceding study, subjects were to move a cursor on a digitizing tablet to targets displayed on a computer monitor Movements were made without concurrent visual feedback of cursor position, but movement paths were displayed on the monitor after the completion of each movement We first examined horizontal hand movements made at waist level with the upper arm in a vertical orientation Targets were located at five distances and two directions (30 degrees and 150 degrees) from one of two initial positions Trajectory shapes were stereotyped, and movements to more distant targets had larger accelerations and velocities Comparison of movements in the two directions showed that in the 30 degrees direction responses were hypermetric, accelerations and velocities were larger, and movement times were shorter Since movements in the 30 degrees direction required less motion of the upper arm than movements in the 150 degrees direction, we hypothesized that the differences in accuracy and acceleration reflected a failure to take into account the difference in total limb inertia in the two directions To test this hypothesis we simulated the initial accelerations of a two-segment limb moving in the horizontal plane with the hand at shoulder level when a constant force was applied at the hand in each of 24 directions We compared these simulated accelerations to ones produced by our subjects with their arms in the same position when they aimed movements to targets in the 24 directions and at equal distances from an initial position The magnitudes of both simulated and actual accelerations were greatest in the two directions perpendicular to the forearm, where inertial resistance is least, and lowest for movements directed along the axis of the forearm In all subjects, the directional variation in peak acceleration was similar to that predicted by the model and shifted in the same way when the initial position of the hand was displaced The pattern of direction-dependent variations in initial acceleration did not depend on the speed of movement It was also unchanged when subjects aimed their movements toward targets presented within the workspace on the tablet instead of on the computer monitor These findings indicate that, in programming the magnitude of the initial force that will accelerate the hand, subjects do not fully compensate for direction dependent differences in inertial resistance(ABSTRACT TRUNCATED AT 400 WORDS)

Abstract: When a smooth jet of water falls vertically on to a horizontal plane, it spreads out radially in a thin layer bounded by a circular hydraulic jump, outside which the depth is much greater. The motion in the layer is studied here by means of boundary-layer theory, both for laminar and for turbulent flow, and relations are obtained for the radius of the hydraulic jump. These relations are compared with experimental results. The analogous problems of two-dimensional flow are also treated.

Abstract: A system (10) for externally locating a sensor in tissue, comprising an external probe including at least first and second electromagnetic output coils (12) with non-parallel longitudinal axes; and output coil (2) driver for alternately energizing the first and second output coils, for generating a time-varying magnetic field which penetrates the patient's skin (7); a sensor coil (30), having a longitudinal axis, for developing an induced electrical voltage in response to the time-varying magnetic field; a distance determinator, responsive to the induced voltage from the sensor coil (30), for determining from the induced voltage, the distance between the output coils (12) and the sensor coil (30), independently of the relative angle, in a horizontal plane, between the sensor coil (30) longitudinal axis, and the longitudinal axes of the output coils (12); and a direction determinator for determining and displaying the direction, in the horizontal plane, in which the sensor coil (30) longitudinal axis is pointing.

Abstract: A Galerkin-type finite element method is employed to solve the quasilinear partial differential equations of transient seepage in saturated-unsaturated porous media. The resulting computer program is capable of handling nonuniform flow regions having complex boundaries and arbitrary degrees of local anisotropy. Flow can take place in a vertical plane, in a horizontal plane, or in a three-dimensional system with radial symmetry. An arbitrary number of seepage faces can be considered simultaneously, and the positions of the exit points on these boundaries are adjusted automatically during each time step. Two examples, one of seepage through an earth dam with a sloping core and horizontal drainage blanket, and the other of seepage through a layered medium cut by a complex topography, are included. These examples indicate that the classical concept of a free surface is not always applicable when dealing with transient seepage through soils.