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Search Results: 1 - 10 of 51658 matches for " Carlos Vasquez "
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Construcción de un magnetómetro elemental
Carlos Alberto Vasquez
Revista Eureka sobre Ense?anza y Divulgación de las Ciencias , 2007,
Abstract: Earth Magnetic Field; cheap magnetometer
Three-dimensional Ising model confined in low-porosity aerogels: a Monte Carlo study
Ricardo Paredes,Carlos Vasquez
Physics , 2006, DOI: 10.1103/PhysRevB.74.054201
Abstract: The influence of correlated impurities on the critical behaviour of the 3D Ising model is studied using Monte Carlo simulations. Spins are confined into the pores of simulated aerogels (diffusion limited cluster-cluster aggregation) in order to study the effect of quenched disorder on the critical behaviour of this magnetic system. Finite size scaling is used to estimate critical couplings and exponents. Long-range correlated disorder does not affect critical behavior. Asymptotic exponents differ from those of the pure 3D Ising model (3DIS), but it is impossible, with our precision, to distinguish them from the randomly diluted Ising model (RDIS).
Right-handed lepton mixings at the LHC
Juan Carlos Vasquez
Physics , 2014,
Abstract: We study how the elements of the leptonic right-handed mixing matrix can be determined at the LHC in the minimal Left-Right symmetric extension of the standard model. We do it by explicitly relating them with physical quantities of the Keung-Senjanovi\'c process and the lepton number violating decays of the right doubly charged scalar. We also point out that the left and right doubly charged scalars can be distinguished at the LHC, without measuring the polarization of the final state leptons coming from their decays.
Effects of aerogel-like disorder on the critical behavior of O(m)-vector models. Recent simulations and experimental evidences
Carlos Vasquez,Ricardo Paredes
Physics , 2006,
Abstract: We review some results on the effect of a specific type of quenched disorder on well known O(m)-vector models in three dimension. Evidences of changes of criticality in both systems, when confined in aerogel pores, are briefly referenced. The 3DXY model (m=2) represents the universality class to which the \lambda-transition of bulk superfluid $^4$He belongs. Experiments report changes of critical exponents for this transition, when superfluid $^4$He is confined in aerogels. Numerical results of the 3DXY model, confined in aerogel-like structures, are in agreement with experiments. Both results seem to contradict Harris criterion: being the specific heat exponent negative for the pure system, changes must be explained in terms of the extended criterion due to Weinrib and Halperin, which requires disorder to be long-range correlated (LRC) at all scales. Aerogels are fractal through some decades only, and present crossovers to homogeneous regimes at finite scales, so the violation to Harris criterion persists. The apparent violation has been explained in terms of hidden LRC subsets within aerogels $[$Phys. Rev. Lett., 2003, {\bf 90}, 170602$]$. On the other hand, experiments on the liquid-vapor (LV) transition of $^4$He and N$_2$ confined in aerogels, also showed changes in critical-point exponents. Being the LV critical-point in the O(1) universality class, criticality may be affected by both, short-range correlated (SRC) and LRC subsets ofdisorder. Simulations of the 3DIS in DLCA aerogels can corroborate experimental results. Experiments and simulations both suggest a shift in critical exponents to values closer to the SRC instead of those of the LRC fixed point.
On the abundance of non-zero central Lyapunov exponents, physical measures and stable ergodicity for partially hyperbolic dynamics
Vitor Araujo,Carlos H. Vasquez
Mathematics , 2010,
Abstract: We show that the time-1 map of an Anosov flow, whose strong-unstable foliation is $C^2$ smooth and minimal, is $C^2$ close to a diffeomorphism having positive central Lyapunov exponent Lebesgue almost everywhere and a unique physical measure with full basin, which is $C^r$ stably ergodic. Our method is perturbative and does not rely on preservation of a smooth measure.
Réplica: meningite após técnica combinada para analgesia de parto. Relato de caso
Vasquez Carlos Escobar,Pereira Raquel da Rocha
Revista Brasileira de Anestesiologia , 2002,
A variational principle for impulsive semiflows
Jose F. Alves,Maria Carvalho,Carlos Vasquez
Mathematics , 2014,
Abstract: We consider impulsive semiflows defined on compact metric spaces and deduce a variational principle. In particular, we generalize the classical notion of topological entropy to our setting of discontinuous semiflows.
Spike trains statistics in Integrate and Fire Models: exact results
Bruno Cessac,Hassan Nasser,Juan-Carlos Vasquez
Physics , 2010,
Abstract: We briefly review and highlight the consequences of rigorous and exact results obtained in \cite{cessac:10}, characterizing the statistics of spike trains in a network of leaky Integrate-and-Fire neurons, where time is discrete and where neurons are subject to noise, without restriction on the synaptic weights connectivity. The main result is that spike trains statistics are characterized by a Gibbs distribution, whose potential is explicitly computable. This establishes, on one hand, a rigorous ground for the current investigations attempting to characterize real spike trains data with Gibbs distributions, such as the Ising-like distribution, using the maximal entropy principle. However, it transpires from the present analysis that the Ising model might be a rather weak approximation. Indeed, the Gibbs potential (the formal "Hamiltonian") is the log of the so-called "conditional intensity" (the probability that a neuron fires given the past of the whole network). But, in the present example, this probability has an infinite memory, and the corresponding process is non-Markovian (resp. the Gibbs potential has infinite range). Moreover, causality implies that the conditional intensity does not depend on the state of the neurons at the \textit{same time}, ruling out the Ising model as a candidate for an exact characterization of spike trains statistics. However, Markovian approximations can be proposed whose degree of approximation can be rigorously controlled. In this setting, Ising model appears as the "next step" after the Bernoulli model (independent neurons) since it introduces spatial pairwise correlations, but not time correlations. The range of validity of this approximation is discussed together with possible approaches allowing to introduce time correlations, with algorithmic extensions.
Stochastic stability of diffeomorphisms with dominated splitting
Jose F. Alves,Vitor Araujo,Carlos H. Vasquez
Mathematics , 2004,
Abstract: We prove that the statistical properties of random perturbations of a nonuniformly hyperbolic diffeomorphism are described by a finite number of stationary measures. We also give necessary and sufficient conditions for the stochastic stability of such dynamical systems. We show that a certain $C^2$-open class of nonuniformly hyperbolic diffeomorphisms introduced in [Alves, J; Bonatti, C. and Viana, V., SRB measures for partially hyperbolic systems with mostly expanding central direction, Invent. Math., 140 (2000), 351-398] are stochastically stable. Our setting encompasses that of partially hyperbolic diffeomorphisms as well. Moreover, the techniques used enable us to obtain SRB measures in this setting through zero-noise limit measures.
Multicriteria Analysis for Improving the Innovation Capability in Small and Medium Enterprises in Emerging Countries  [PDF]
Juan Sepúlveda, Elizardo Vasquez
American Journal of Industrial and Business Management (AJIBM) , 2014, DOI: 10.4236/ajibm.2014.44027

In this paper we describe an analytical model to determine the innovation capability of a small and medium enterprise (SME) as the first step towards the continuous improvement of performance in such a dimension of an organization. The model first assesses organizational variables and classifies companies by using the Flowsort? multicriteria method. As second step, the classification module categorizes SMEs into four classes of companies: passive, reactive, proactive, proactive. From this sorting and the subsequent analysis of the variables measured by the survey, it is determined the set of best management practices for innovation that the company needs to implement in order to increase their level of performance. The application of the model to nine companies in Chile is shown along with numerical results. Evaluations show that the classification is consistent with expert judgment and that effectively identifies those areas that contribute most to the increase of the innovation capability in the SMEs.

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