50,849 research outputs found
Large joints in graphs
We show that if G is a graph of sufficiently large order n containing as many
r-cliques as the r-partite Turan graph of order n; then for some C>0 G has more
than Cn^(r-1) (r+1)-cliques sharing a common edge unless G is isomorphic to the
the r-partite Turan graph of order n. This structural result generalizes a
previous result that has been useful in extremal graph theory.Comment: 9 page
Modeling Stiffness and Damping in Rotational Degrees of Freedom Using Multibond Graphs
A contribution is proposed for the modeling of mechanical systems using multibond graphs. When modeling a physical system, it may be needed to catch the dynamic behavior contribution of the joints between bodies of the system and therefore to characterize the stiffness and damping of the links between them. The visibility of where dissipative or capacitive elements need to be implemented to represent stiffness and damping in multibond graphs is not obvious and will be explained. A multibond graph architecture is then proposed to add stiffness and damping in hree rotational degrees of freedom. The resulting joint combines the spherical joint multibond graph relaxed causal constraints while physically representing three concatenated revolute joints. The mathematical foundations are presented, and then illustrated through the modeling and simulation of an inertial navigation system; in which stiffness and damping between the gimbals are taken into account. This method is particularly useful when modeling and simulating multibody systems using Newton-Euler formalism in multibond graphs. Future work will show how this method can be extended to more complex systems such as rotorcraft blades' connections with its rotor hub.Fondation Airbus Grou
Skeleton-based Action Recognition of People Handling Objects
In visual surveillance systems, it is necessary to recognize the behavior of
people handling objects such as a phone, a cup, or a plastic bag. In this
paper, to address this problem, we propose a new framework for recognizing
object-related human actions by graph convolutional networks using human and
object poses. In this framework, we construct skeletal graphs of reliable human
poses by selectively sampling the informative frames in a video, which include
human joints with high confidence scores obtained in pose estimation. The
skeletal graphs generated from the sampled frames represent human poses related
to the object position in both the spatial and temporal domains, and these
graphs are used as inputs to the graph convolutional networks. Through
experiments over an open benchmark and our own data sets, we verify the
validity of our framework in that our method outperforms the state-of-the-art
method for skeleton-based action recognition.Comment: Accepted in WACV 201
Combinatorial models of rigidity and renormalization
We first introduce the percolation problems associated with the graph
theoretical concepts of -sparsity, and make contact with the physical
concepts of ordinary and rigidity percolation. We then devise a renormalization
transformation for -percolation problems, and investigate its domain of
validity. In particular, we show that it allows an exact solution of
-percolation problems on hierarchical graphs, for . We
introduce and solve by renormalization such a model, which has the interesting
feature of showing both ordinary percolation and rigidity percolation phase
transitions, depending on the values of the parameters.Comment: 22 pages, 6 figure
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