623,349 research outputs found
Cross-sectional river shapes: A variational discharge-resistance formulation
Cross-sectional river shapes were obtained from a variational principle: minimizing the bed friction for a given discharge and a given maximum lateral bed slope (angle of repose). The optimal shape is found to be independent of both the exponent in the friction law adopted and the value of the discharge, but it does depend on the angle of repose. The optimal profile is a single stream; for braided rivers the solution is suboptimal
Approximate Optimal Atmospheric Entry Trajectories
Approximate optimal atmospheric entry trajectories maximizing terminal function of velocity, heading angle, flight path angle, and altitud
Drop on a Bent Fibre
Inspired by the huge droplets attached on cypress tree leaf tips after rain,
we find that a bent fibre can hold significantly more water in the corner than
a horizontally placed fibre (typically up to three times or more). The maximum
volume of the liquid that can be trapped is remarkably affected by the bending
angle of the fibre and surface tension of the liquid. We experimentally find
the optimal included angle () that holds the most water.
Analytical and semi-empirical models are developed to explain these
counter-intuitive experimental observations and predict the optimal angle. The
data and models could be useful for designing microfluidic and fog harvesting
devices
Kinematics of the swimming of Spiroplasma
\emph{Spiroplasma} swimming is studied with a simple model based on
resistive-force theory. Specifically, we consider a bacterium shaped in the
form of a helix that propagates traveling-wave distortions which flip the
handedness of the helical cell body. We treat cell length, pitch angle, kink
velocity, and distance between kinks as parameters and calculate the swimming
velocity that arises due to the distortions. We find that, for a fixed pitch
angle, scaling collapses the swimming velocity (and the swimming efficiency) to
a universal curve that depends only on the ratio of the distance between kinks
to the cell length. Simultaneously optimizing the swimming efficiency with
respect to inter-kink length and pitch angle, we find that the optimal pitch
angle is 35.5 and the optimal inter-kink length ratio is 0.338, values
in good agreement with experimental observations.Comment: 4 pages, 5 figure
Drop on a Bent Fibre
Inspired by the huge droplets attached on cypress tree leaf tips after rain,
we find that a bent fibre can hold significantly more water in the corner than
a horizontally placed fibre (typically up to three times or more). The maximum
volume of the liquid that can be trapped is remarkably affected by the bending
angle of the fibre and surface tension of the liquid. We experimentally find
the optimal included angle () that holds the most water.
Analytical and semi-empirical models are developed to explain these
counter-intuitive experimental observations and predict the optimal angle. The
data and models could be useful for designing microfluidic and fog harvesting
devices
Optimal View Angle in Collective Dynamics of Self-propelled Agents
We study a system of self-propelled agents in which each agent has a part of
omnidirectional or panoramic view of its sensor disc, the field of vision of
the agent in this case is only a sector of a disc bounded by two radii and the
included arc. The inclination of these two radii is characterized as the view
angle. Contrary to our intuition, we find that, the non-omnidirectional-view
for swarm agents with periodic boundary conditions in noiseless Vicsek model
can accelerate the transient process of the emergence of the ordered state. One
consequent implication is that, there are generally superfluous communications
in the Vicsek Model, which may even obstruct the possible fast swarm emergence.
This phenomenon may invoke further efforts and attentions to explore the
underlying mechanism of the emergence in self-propelled agents.Comment: 4 pages, 6 figure
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