786 research outputs found
Coefficient of restitution for viscoelastic disks
The dissipative collision of two identical viscoelastic disks is studied. By
using a known law for the elastic part of the interaction force and the
viscoelastic damping model an analytical solution for the coefficient of
restitution shall be given. The coefficient of restitution depends
significantly on the impact velocity. It approaches one for small velocities
and decreases for increasing velocities.Comment: 11 pages, 3 figure
Non-Abelian Duality for Open Strings
We examine non-abelian duality transformations in the open string case. After
gauging the isometries of the target space and developing the general
formalism, we study in details the duals oftarget spaces with SO(N) isometries
which, for the SO(2) case, reduces to the known abelian T-duals. We apply the
formalism to electrically and magnetically charged 4D black hole solutions and,
as in the abelian case, dual coordinates satisfy Dirichlet conditions.Comment: 18 pages, Latex. Some formulas are added. Final version to appear in
Nucl. Phys.
Rolling friction of a hard cylinder on a viscous plane
The resistance against rolling of a rigid cylinder on a flat viscous surface
is investigated. We found that the rolling-friction coefficient reveals
strongly non-linear dependence on the cylinder's velocity. For low velocity the
rolling-friction coefficient rises with velocity due to increasing deformation
rate of the surface. For larger velocity, however, it decreases with velocity
according to decreasing contact area and deformation of the surface.Comment: 7 pages, 3 figure
Coefficient of Restitution as a Fluctuating Quantity
The coefficient of restitution of a spherical particle in contact with a flat
plate is investigated as a function of the impact velocity. As an experimental
observation we notice non-trivial (non-Gaussian) fluctuations of the measured
values. For a fixed impact velocity, the probability density of the coefficient
of restitution, , is formed by two exponential functions (one
increasing, one decreasing) of different slope. This behavior may be explained
by a certain roughness of the particle which leads to energy transfer between
the linear and rotational degrees of freedom.Comment: 4 pages, 4 figure
Virtual Organization as a Source of Competitive Advantage: A Framework from the Resource-Based View
A framework is developed for viewing the centralization issues of organizations to consider to what degree a virtual organization may help a firm obtain competitive advantage. Utilizing the concepts of flexibility and synergy, the framework can serve as a guide for practitioners to help determine what degree of synergy and flexibility a given organizational form would bring and what its suggested category of competitive advantage would be. Implications and suggestions for future research are also discussed
Coefficient of tangential restitution for the linear dashpot model
The linear dashpot model for the inelastic normal force between colliding
spheres leads to a constant coefficient of normal restitution,
const., which makes this model very popular for the investigation
of dilute and moderately dense granular systems. For two frequently used models
for the tangential interaction force we determine the coefficient of tangential
restitution , both analytically and by numerical integration of
Newton's equation. Although const. for the linear-dashpot model,
we obtain pronounced and characteristic dependencies of the tangential
coefficient on the impact velocity . The
results may be used for event-driven simulations of granular systems of
frictional particles.Comment: 12 pages, 12 figure
Guarantees on Robot System Performance Using Stochastic Simulation Rollouts
We provide finite-sample performance guarantees for control policies executed
on stochastic robotic systems. Given an open- or closed-loop policy and a
finite set of trajectory rollouts under the policy, we bound the expected
value, value-at-risk, and conditional-value-at-risk of the trajectory cost, and
the probability of failure in a sparse rewards setting. The bounds hold, with
user-specified probability, for any policy synthesis technique and can be seen
as a post-design safety certification. Generating the bounds only requires
sampling simulation rollouts, without assumptions on the distribution or
complexity of the underlying stochastic system. We adapt these bounds to also
give a constraint satisfaction test to verify safety of the robot system.
Furthermore, we extend our method to apply when selecting the best policy from
a set of candidates, requiring a multi-hypothesis correction. We show the
statistical validity of our bounds in the Ant, Half-cheetah, and Swimmer MuJoCo
environments and demonstrate our constraint satisfaction test with the Ant.
Finally, using the 20 degree-of-freedom MuJoCo Shadow Hand, we show the
necessity of the multi-hypothesis correction.Comment: Submitted to IEEE-TR
Teachers' Perceptions of Sae Programs and Benefits for Students with Special Needs in Oklahoma
Agricultural Education, Communications, and 4-H Youth Developmen
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