113,453 research outputs found
Data-Driven Approach to Simulating Realistic Human Joint Constraints
Modeling realistic human joint limits is important for applications involving
physical human-robot interaction. However, setting appropriate human joint
limits is challenging because it is pose-dependent: the range of joint motion
varies depending on the positions of other bones. The paper introduces a new
technique to accurately simulate human joint limits in physics simulation. We
propose to learn an implicit equation to represent the boundary of valid human
joint configurations from real human data. The function in the implicit
equation is represented by a fully connected neural network whose gradients can
be efficiently computed via back-propagation. Using gradients, we can
efficiently enforce realistic human joint limits through constraint forces in a
physics engine or as constraints in an optimization problem.Comment: To appear at ICRA 2018; 6 pages, 9 figures; for associated video, see
https://youtu.be/wzkoE7wCbu
Relation between directed polymers in random media and random bond dimer models
We reassess the relation between classical lattice dimer models and the
continuum elastic description of a lattice of fluctuating polymers. In the
absence of randomness we determine the density and line tension of the polymers
in terms of the bond weights of hard-core dimers on the square and the
hexagonal lattice. For the latter, we demonstrate the equivalence of the
canonical ensemble for the dimer model and the grand-canonical description for
polymers by performing explicitly the continuum limit. Using this equivalence
for the random bond dimer model on a square lattice, we resolve a previously
observed discrepancy between numerical results for the random dimer model and a
replica approach for polymers in random media. Further potential applications
of the equivalence are briefly discussed.Comment: 6 pages, 3 figure
Hyperon Electromagnetic Properties in Two-Flavor Chiral Perturbation Theory
The pion mass dependence of hyperon electromagnetic properties is determined
using two-flavor heavy baryon chiral perturbation theory. Specifically we
compute chiral corrections to the charge radii, magnetic moments, and magnetic
radii of the spin one-half hyperons, as well as the charge radii, magnetic
moments, magnetic radii, electric quadrupole moments, and quadrupole radii of
the spin three-half hyperons. Results for the nucleon and delta are also
included. Efficacy of the two-flavor theory is investigated by analyzing the
role played by virtual kaons. For the electromagnetic properties of spin
one-half hyperons, kaon loop contributions are shown to be well described by
terms analytic in the pion mass squared. Similarly kaon contributions to the
magnetic moments of spin three-half hyperons are well described in the
two-flavor theory. The remaining electromagnetic properties of spin three-half
resonances can be described in two-flavor chiral perturbation theory, however,
this description fails just beyond the physical pion mass. For the case of
experimentally known hyperon magnetic moments and charge radii, we demonstrate
that chiral corrections are under reasonable control, in contrast to the
behavior of these observables in the three-flavor chiral expansion. The
formulae we derive are ideal for performing the pion mass extrapolation of
lattice QCD data obtained at the physical strange quark mass.Comment: 29 pages, 7 figures, v3: published versio
Hyperon Axial Charges in Two-Flavor Chiral Perturbation Theory
We use two-flavor heavy baryon chiral perturbation theory to investigate the
isovector axial charges of the spin one-half hyperons. Expressions for these
hyperon axial charges are derived at next-to-leading order in the chiral
expansion. We utilize phenomenological and lattice QCD inputs to assess the
convergence of the two-flavor theory, which appears to be best for cascades.Comment: 4 pages, 1 figures, published versio
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