ON THE VARYING BRACHISTOCHRONE SHAPE WITH ALLOWANCE FOR CHUTE LOADING LIMITATION

first time. Here, the dynamic equations for the motion of the material body rolling down the chute are formulated neglecting the friction forces. It is shown that if the stress limit for the chute material is taken into account, the shape of the chute varies greatly as a function of the parameter. Four possible cases are analyzed when the parameter is: equal to zero, more than unity, less than unity, and equal to unity. It is found that if the parameter is more than unity, the chute shape represents almost horizontal and vertical segments of a trajectory, which is clear from a physical point of view, since for this type of the trajectory the chute is least affected by the body moving along. If the parameter is equal to unity, the chute takes a specific loop-like shape. If the parameter is equal to zero, the system of equations describes a classical brachistochrone. The solution to the problem is applicable in practice for predicting the shape of the chute withstanding high loads when the stress limit for the material is known.

Motion and Muscle Activity of Synchronized Rolling-Type Double-Leg Circles on a Pommel Horse

Experimental analyses of motions of a double-leg circle were conducted for a smooth and dynamic movement. A motion capture system provided the data for two different gymnasts; one is well trained and the other has an average skill level. Lissajous analysis was done for a tip-toe circling motion and a rolling motion around a longitudinal axis of a body. The results show that synchronization between the tip-toe circling and the body-rolling around the body’s longitudinal axis is crucial. Muscle activity was also analyzed from electromyogram data when the gymnasts performed double-leg circles, and the muscle activity characteristics of synchronized rolling-type circles were uncovered.

Evasive mating behaviour by female nurse sharks, Ginglymostoma cirratum (Bonnaterre, 1788), in an equatorial insular breeding ground

ABSTRACT Mating events and aggregations of vulnerable nurse sharks Ginglymostoma cirratum were recorded in the insular protected area of Fernando de Noronha (FEN), Brazil, between April and August 2015. Female sharks were observed clustering in groups of up to 14 individuals in shallow water adjacent to the shore. Several evasive mating behaviours in the presence of males were noticed, including shoreward movement, positioning ventral side up at the sea surface with emerged pectoral and pelvic fins, body rolling and caudal fin thrashing. Fresh bite marks indicative of male courtship and coupling attempts were visible in female's pectoral and caudal fins. Altogether, the observed behaviours match previous reports of non-cooperative female nurse sharks during mating opportunities. An extended mating season coupled with a persistent use of inshore habitats result in nurse sharks being particularly vulnerable to human pressure during a most sensitive stage of their life cycle. The effective conservation of nurse shark populations from the western South Atlantic may thus depend on the protection of critical habitats where this species aggregates to reproduce. Explicitly addressing environmental requirements by vulnerable species in local management strategies is indispensable to ensure that human pressure, including ecotourism development, does not collide with stipulated conservation aims.

Rolling Prevention Mechanism for Underground Pipe Erosion Inspection Robot with a Real Time Vision System

Pipe inspection is one of the areas that have attracted high research interest for robot applications especially in oil and chemical industry and civil engineering. Robot body rolling while it travels within a pipe has been a problem for accurately collecting inspection data. Under certain circumstances where vision systems have to be employed, robot body rolling may cause vision inspection data to have little value as it is difficult to know where exactly the camera was looking at. This paper proposes an anti-rolling mechanism to hold consistent camera orientation. By changing the position angle of the robot legs, the mechanism is able to adjust the resistance to rolling within a pipe, therefore preventing robot rolling happening. The design makes use of the friction force caused by the gravity force of the robot to prevent the robot body rolling. The design analysis quantifies the effect of pipe radius, robot weight, payload, and payload offset distance in robot rolling. A test model was built based on the design concept. The experimental results obtained from the test model match the predication of the computational analysis. A real time vision system has been developed using FPGA and the algorithm of the structured laser light stripe configuration in the context of pipe inspection. The real-time hardware implementation of the algorithms on the robot itself removes the need to transmit raw video data back to an operator.