Time filter

Source Type

Llibre J.,Autonomous University of Barcelona | Ponce E.,Escuela Tecnica Superior de Ingenieria | Valls C.,University of Lisbon
Journal of Nonlinear Science | Year: 2015

Some techniques for proving the existence and uniqueness of limit cycles for smooth differential systems are extended to continuous piecewise linear differential systems with two and three zones and no symmetry. For planar systems with three linearity zones, the existence of two limit cycles surrounding the only equilibrium point at the origin is rigorously shown for the first time. The usefulness of the achieved analytical results is illustrated by considering non-symmetric memristor-based electronic oscillators. © 2015, Springer Science+Business Media New York. Source

Sarras I.,Free University of Colombia | Acosta J.A.,Escuela Tecnica Superior de Ingenieria | Ortega R.,Supelec | Mahindrakar A.D.,Indian Institute of Technology Madras
Automatica | Year: 2013

A constructive approach to stabilize a desired equilibrium for a class of underactuated mechanical systems, which obviates the solution of partial differential equations, is proposed. The Immersion & Invariance methodology is adopted, with the main result formulated in the Port-Hamiltonian framework, for both model and target dynamics. The procedure is applicable to mechanical systems with under-actuation degree larger than one, extending the results recently reported by some of the authors. The approach is successfully applied to two benchmark examples and some basic connections with the interconnection and damping assignment passivity-based control are revealed. An additional contribution of this work is the identification of a class of mechanical systems whose mechanical structure remains invariant under partial feedback linearization. © 2013 Elsevier Ltd. All rights reserved. Source

Novaes D.D.,Autonomous University of Barcelona | Novaes D.D.,University of Campinas | Ponce E.,Escuela Tecnica Superior de Ingenieria
International Journal of Bifurcation and Chaos | Year: 2015

Recently Braga and Mello conjectured that for a given n ∈ N there is a piecewise linear system with two zones in the plane with exactly n limit cycles. In this paper, we prove a result from which the conjecture is an immediate consequence. Several explicit examples are given where location and stability of limit cycles are provided. © 2015 World Scientific Publishing Company. Source

Orive J.,University of the Basque Country | Balda R.,Escuela Tecnica Superior de Ingenieria | Balda R.,Donostia International Physics Center | Fernandez J.,Escuela Tecnica Superior de Ingenieria | And 3 more authors.
Dalton Transactions | Year: 2013

M2(SeO3)F2 (M = Zn (1), Mn (2)) stoichiometric phases together with the Zn2-xMnx(SeO 3)F2 compound doped at various concentrations (x = 0.002-0.2) were synthesized by employing mild hydrothermal conditions. These compounds have been characterized by scanning electron microscopy (SEM), Rietveld refinement of the X-ray powder diffraction patterns, ICP-Q-MS, thermogravimetric and thermodiffractometric analyses, and IR, UV/vis and electron paramagnetic resonance (EPR) spectroscopies. Compounds 1 and 2 crystallize in the orthorhombic Pnma space group with lattice parameters: a = 7.27903(4), b = 10.05232(6) and c = 5.26954(3) Å for the zinc species and a = 7.50848(9), b = 10.3501(12) and c = 5.47697(6) Å for the manganese phase, with Z = 4. The crystal structures of these compounds are isotypic and are built up from a 3D framework constructed by (010) sheets of [MO 3F3] octahedra linked up by [SeO3] building units. Luminescence measurements of Mn2(SeO3)F2 were performed at different temperatures between 10 and 150 K. At 10 K, the emission spectrum consists of a broad band peaked at around 660 nm related to the 4T1g → 6A1g transition in octahedrically coordinated Mn2+. Moreover, the influence of temperatures up to 295 K and the Mn concentration on the luminescent properties of the Zn2-xMnx(SeO3)F2 system were systematically studied. Magnetic measurements of 2 show antiferromagnetic coupling as the major interactions exhibiting a spin canting at low temperature. © 2013 The Royal Society of Chemistry. Source

Llibre J.,Autonomous University of Barcelona | Ordonez M.,Escuela Tecnica Superior de Ingenieria | Ponce E.,Escuela Tecnica Superior de Ingenieria
Nonlinear Analysis: Real World Applications | Year: 2013

Some techniques to show the existence and uniqueness of limit cycles, typically stated for smooth vector fields, are extended to continuous piecewise-linear differential systems. New results are obtained for systems with three linearity zones without symmetry and having one equilibrium point in the central region. We also revisit the case of systems with only two linear zones giving shorter proofs of known results. A relevant application to the McKean piecewise linear model of a single neuron activity is included. © 2013 Elsevier Ltd. All rights reserved. Source

Discover hidden collaborations