Search results for "VECTORS"
showing 10 items of 601 documents
Almost Planar Homoclinic Loops in R3
1996
AbstractIn this paper we study homoclinic loops of vector fields in 3-dimensional space when the two principal eigenvalues are real of opposite sign, which we call almost planar. We are interested to have a theory for higher codimension bifurcations. Almost planar homoclinic loop bifurcations generically occur in two versions “non-twisted” and “twisted” loops. We consider high codimension homoclinic loop bifurcations under generic conditions. The generic condition forces the existence of a 2-dimensional topological invariant ring (non necessarily unique), which is a topological cylinder in the “non-twisted” case and a topological Möbius band in the “twisted” case. If the third eigenvalue is…
Nonlinear nonhomogeneous Neumann eigenvalue problems
2015
We consider a nonlinear parametric Neumann problem driven by a nonhomogeneous differential operator with a reaction which is $(p-1)$-superlinear near $\pm\infty$ and exhibits concave terms near zero. We show that for all small values of the parameter, the problem has at least five solutions, four of constant sign and the fifth nodal. We also show the existence of extremal constant sign solutions.
Computation of a few smallest eigenvalues of elliptic operators using fast elliptic solvers
2001
The computation of a few smallest eigenvalues of generalized algebraic eigenvalue problems is studied. The considered problems are obtained by discretizing self-adjoint second-order elliptic partial differential eigenvalue problems in two- or three-dimensional domains. The standard Lanczos algorithm with the complete orthogonalization is used to compute some eigenvalues of the inverted eigenvalue problem. Under suitable assumptions, the number of Lanczos iterations is shown to be independent of the problem size. The arising linear problems are solved using some standard fast elliptic solver. Numerical experiments demonstrate that the inverted problem is much easier to solve with the Lanczos…
Could malaria and dengue reappear in Spain?
2010
El aumento de la inmigración durante los últimos años en España ha facilitado la importación de numerosas enfermedades tropicales. Entre ellas, las de transmisión vectorial son algunas de las más complicadas de estudiar por la complejidad que conlleva la participación de diversos hospedadores en los ciclos de transmisión, así como por la necesidad de conocer todos los parámetros fisiológicos, bioecológicos y biogeográficos relacionados con el organismo vector para poder inferir las posibilidades reales de la emergencia o la reemergencia de las enfermedades pertinentes. En estas circunstancias, el presente trabajo aporta información acerca de enfermedades importadas de incuestionable interés…
¿Pueden la malaria y el dengue reaparecer en España?
2010
ResumenEl aumento de la inmigración durante los últimos años en España ha facilitado la importación de numerosas enfermedades tropicales. Entre ellas, las de transmisión vectorial son algunas de las más complicadas de estudiar por la complejidad que conlleva la participación de diversos hospedadores en los ciclos de transmisión, así como por la necesidad de conocer todos los parámetros fisiológicos, bioecológicos y biogeográficos relacionados con el organismo vector para poder inferir las posibilidades reales de la emergencia o la reemergencia de las enfermedades pertinentes. En estas circunstancias, el presente trabajo aporta información acerca de enfermedades importadas de incuestionable …
¿Pueden la malaria y el dengue reaparecer en España? Could malaria and dengue reappear in Spain?
2010
El aumento de la inmigración durante los últimos años en España ha facilitado la importación de numerosas enfermedades tropicales. Entre ellas, las de transmisión vectorial son algunas de las más complicadas de estudiar por la complejidad que conlleva la participación de diversos hospedadores en los ciclos de transmisión, así como por la necesidad de conocer todos los parámetros fisiológicos, bioecológicos y biogeográficos relacionados con el organismo vector para poder inferir las posibilidades reales de la emergencia o la reemergencia de las enfermedades pertinentes. En estas circunstancias, el presente trabajo aporta información acerca de enfermedades importadas de incuestionable interés…
Pose classification using support vector machines
2000
In this work a software architecture is presented for the automatic recognition of human arm poses. Our research has been carried on in the robotics framework. A mobile robot that has to find its path to the goal in a partially structured environment can be trained by a human operator to follow particular routes in order to perform its task quickly. The system is able to recognize and classify some different poses of the operator's arms as direction commands like "turn-left", "turn-right", "go-straight", and so on. A binary image of the operator silhouette is obtained from the gray-level input. Next, a slice centered on the silhouette itself is processed in order to compute the eigenvalues …
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
2018
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually-unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generic…
Filter approach to the stochastic analysis of MDOF wind-excited structures
1999
Abstract In this paper, an approach useful for stochastic analysis of the Gaussian and non-Gaussian behavior of the response of multi-degree-of-freedom (MDOF) wind-excited structures is presented. This approach is based on a particular model of the multivariate stochastic wind field based upon a particular diagonalization of the power spectral density (PSD) matrix of the fluctuating part of wind velocity. This diagonalization is performed in the space of eigenvectors and eigenvalues that are called here wind-eigenvalues and wind-eigenvectors, respectively. From the examination of these quantities it can be recognized that the wind-eigenvectors change slowly with frequency while the first wi…
Multiplicity results for asymptotically linear equations, using the rotation number approach
2007
By using a topological approach and the relation between rotation numbers and weighted eigenvalues, we give some multiplicity results for the boundary value problem u′′ + f(t, u) = 0, u(0) = u(T) = 0, under suitable assumptions on f(t, x)/x at zero and infinity. Solutions are characterized by their nodal properties.