32,347 research outputs found
Formation of safety conditions for development of deposits by open mining
The researched parameters of the catching device, which
ensures the safe operation of equipment and working people in deep open
pits, where are formed the benches by steep dipping layers. For obtaining
the results, the following methods were used: analytical β in determining
existing devices for the capture of rocks; geometric β in determining the
direction of the flight of blocks, semigraphical β in plotting and analyzing
them. The modern technological catching devices, their structure,
construction are analyzed. These structures protective devices can be used
in deep pits in the development of deposits. Analytical dependence of the
height of the jump the block of rock after hitting about a horizontal surface
is improved, which takes into account the rate of falling and the angle of
rebound the block, the elasticity of the surface. Creating of catching
designs which capture the blocks of rock in the falling from the upper
horizons in open pits allows to operate safely the mining equipment and to
save the lives of workers. Especially this is important in the development
of deposits by steep dipping layers. Proposed solutions can improve the
safe using of dump trucks and moving workers in the work zone in the
mining ledges of height over 30 meters
How soccer players head the ball: a test of optic acceleration cancellation theory with virtual reality
We measured the movements of soccer players heading a football in a fully immersive virtual reality environment. In mid-flight the ballβs trajectory was altered from its normal quasi-parabolic path to a linear one, producing a jump in the rate of change of the angle of elevation of gaze (Ξ±) from player to ball. One reaction time later the players adjusted their speed so that the rate of change of Ξ± increased when it had been reduced and reduced it when it had been increased. Since the result of the playerβs movement was to regain a value of the rate of change close to that before the disturbance, the data suggest that the players have an expectation of, and memory for, the pattern that the rate of change of Ξ± will follow during the flight. The results support the general claim that players intercepting balls use servo control strategies and are consistent with the particular claim of Optic Acceleration Cancellation theory that the servo strategy is to allow Ξ± to increase at a steadily decreasing rate
Swift Launch Lithograph
This one-page lithograph describes the science conducted by NASA-s Swift satellite mission and provides an activity for students. Swift's primary goal is to unravel the mystery of gamma ray bursts. Educational levels: Middle school, Intermediate elementary
Decentralized collaborative transport of fabrics using micro-UAVs
Small unmanned aerial vehicles (UAVs) have generally little capacity to carry
payloads. Through collaboration, the UAVs can increase their joint payload
capacity and carry more significant loads. For maximum flexibility to dynamic
and unstructured environments and task demands, we propose a fully
decentralized control infrastructure based on a swarm-specific scripting
language, Buzz. In this paper, we describe the control infrastructure and use
it to compare two algorithms for collaborative transport: field potentials and
spring-damper. We test the performance of our approach with a fleet of
micro-UAVs, demonstrating the potential of decentralized control for
collaborative transport.Comment: Submitted to 2019 International Conference on Robotics and Automation
(ICRA). 6 page
Paradoxical popups: Why are they hard to catch?
Even professional baseball players occasionally find it difficult to
gracefully approach seemingly routine pop-ups. This paper describes a set of
towering pop-ups with trajectories that exhibit cusps and loops near the apex.
For a normal fly ball, the horizontal velocity is continuously decreasing due
to drag caused by air resistance. But for pop-ups, the Magnus force (the force
due to the ball spinning in a moving airflow) is larger than the drag force. In
these cases the horizontal velocity decreases in the beginning, like a normal
fly ball, but after the apex, the Magnus force accelerates the horizontal
motion. We refer to this class of pop-ups as paradoxical because they appear to
misinform the typically robust optical control strategies used by fielders and
lead to systematic vacillation in running paths, especially when a trajectory
terminates near the fielder. In short, some of the dancing around when
infielders pursue pop-ups can be well explained as a combination of bizarre
trajectories and misguidance by the normally reliable optical control strategy,
rather than apparent fielder error. Former major league infielders confirm that
our model agrees with their experiences.Comment: 28 pages, 10 figures, sumitted to American Journal of Physic
Foraging behavior and Doppler shift compensation in echolocating hipposiderid bats, I-Iipposideros bicolor and I-Iipposideros speoris
1. Two hipposiderid bats,H. bicolor andH. speoris, were observed in their natural foraging areas in Madurai (South India). Both species hunt close together near the foliage of trees and bushes but they differ in fine structure of preferred hunting space:H. bicolor hunts within the foliage, especially whenH. speoris is active at the same time, whereasH. speoris never flies in dense vegetation but rather in the more open area (Fig. 1, Table 1).
2. Both species emit CF/FM-sounds containing only one harmonic component in almost all echolocation situations. The CF-parts of CF/FM-sounds are species specific within a band of 127β138 kHz forH. speoris and 147β159 kHz forH. bicolor (Tables 2 and 3).
3. H. speoris additionally uses a complex harmonic sound during obstacle avoidance and during laboratory tests for Doppler shift compensation.H. bicolor consistently emits CF/FM-sounds in these same situations (Fig. 2).
4. Both hipposiderid bats respond to Doppler shifts in the returning echoes by lowering the frequency of the emitted sounds (Fig. 3). However, Doppler compensations are incomplete as the emitted frequencies are decreased by only 55% and 56% (mean values) of the full frequency shifts byH. speoris andH, bicolor, respectively.
5. The differences in Doppler shift compensation, echolocating and hunting behavior suggest thatH. speoris is less specialized on echolocation with CF/FM-sounds thanH. bicolor
How to catch a cricket ball
A cricket or baseball fielder can run so as to arrive at just the right place at just the right time to catch a ball. It is shown that if the fielder runs so that d2(tan alpha)/dt2 = 0, where alpha is the angle of elevation of gaze from fielder to ball, then the ball will generally be intercepted before it hits the ground. This is true whatever the aerodynamic drag experienced by the ball. The only exception is if the ball is not approaching the fielder before he starts to run
Anti-gravity device
An educational toy useful in demonstrating fundamental concepts regarding the laws of gravity is described. The device comprises a sphere 10 of radius r resting on top of sphere 12 of radius R. The center of gravity of sphere 10 is displaced from its geometrical center by distance D. The dimensions are so related that D((R+r)/r) is greater than r. With the center of gravity of sphere 10 lying on a vertical line, the device is in equilibrium. When sphere 10 is rolled on the surface of sphere 12 it will return to its equilibrium position upon release. This creates an illusion that sphere 10 is defying the laws of gravity. In reality, due to the above noted relationship of D, R, and r, the center of gravity of sphere 10 rises from its equilibrium position as it rolls a short distance up or down the surface of sphere 12
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