Results for "Fernando A. Oliveira"

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Growth exponents of the etching model in high dimensionsJul 18 2017In this work we generalize the etching model (Mello et al 2001 Phys. Rev. E 63 041113) to d + 1 dimensions. The dynamic exponents of this model are compatible with those of the Kardar-Parisi-Zhang universality class. We investigate the roughness dynamics ... More
Thermodynamics aspects of noise-induced phase synchronizationJan 17 2016In this article, we present an approach for the thermodynamics of phase oscillators induced by an internal multiplicative noise. We analytically derive the free energy, entropy, internal energy, and specific heat. In this framework, the formulation of ... More
C2 densely the 2-sphere has an elliptic closed geodesicNov 29 2003We prove that a riemannian metric on the 2-sphere or the projective plane can be C2-approximated by a smooth metric whose geodesic flow has an elliptic closed geodesic.
Pendular behavior of public transport networksJul 18 2017In this paper, we propose a methodology that bears close resemblance to the Fourier analysis of the first harmonic to study networks subjected to pendular behavior. In this context, pendular behavior is characterized by the phenomenon of people's dislocation ... More
An analytical formulation for roughness based on celular automataAug 24 2012Aug 29 2012We present a method to derive the analytical expression of the roughness of a fractal surface whose dynamics is ruled by cellular automata. Starting from the automata, we write down the the time derivative of the height's average and variance. By assuming ... More
Anomalous diffusion: A basic mechanism for the evolution of inhomogeneous systemsFeb 08 2019In this article we review classical and recent results in anomalous diffusion and provide mechanisms useful for the study of the fundamentals of certain processes, mainly in condensed matter physics, chemistry and biology. Emphasis will be given to some ... More
Breakdown of the Fluctuation-Dissipation Theorem for fast superdiffusionJul 30 2002We study anomalous diffusion for one-dimensional systems described by a generalized Langevin equation. We show that superdiffusion can be classified in slow superdiffusion and fast superdiffusion. For fast superdiffusion we prove that the Fluctuation-Dissipation ... More
Intermediate dynamics between Newton and LangevinDec 04 2006A dynamics between Newton and Langevin formalisms is elucidated within the framework of the generalized Langevin equation. For thermal noise yielding a vanishing zero-frequency friction the corresponding non-Markovian Brownian dynamics exhibits anomalous ... More
A Formal Evaluation of PSNR as Quality Measurement Parameter for Image Segmentation AlgorithmsMay 23 2016Quality evaluation of image segmentation algorithms are still subject of debate and research. Currently, there is no generic metric that could be applied to any algorithm reliably. This article contains an evaluation for the PSRN (Peak Signal-To-Noise ... More
Flow in Rough Self-Affine Fractures JointsAug 30 2006We investigate viscous and non-viscous flow in two-dimensional self-affine fracture joints through direct numerical simulations of the Navier-Stokes equations. As a novel hydrodynamic feature of this flow system, we find that the effective permeability ... More
A counterexample to a conjecture of Larman and Rogers on sets avoiding distance 1Aug 22 2018Mar 11 2019For $n \geq 2$ we construct a measurable subset of the unit ball in $\mathbb{R}^n$ that does not contain pairs of points at distance 1 and whose volume is greater than $(1/2)^n$ times the volume of the ball. This disproves a conjecture of Larman and Rogers ... More
On the integrality gap of the maximum-cut semidefinite programming relaxation in fixed dimensionAug 07 2018We describe a factor-revealing convex optimization problem for the integrality gap of the maximum-cut semidefinite programming relaxation: for each $n \geq 2$ we present a convex optimization problem whose optimal value is the largest possible ratio between ... More
Analysis of etching at a solid-solid interfaceJul 18 2017We present a method to derive an analytical expression for the roughness of an eroded surface whose dynamics are ruled by cellular automaton. Starting from the automaton, we obtain the time evolution of the height average and height variance (roughness). ... More
A quantitative version of Steinhaus' theorem for compact, connected, rank-one symmetric spacesMay 04 2010Jan 10 2013Let $d_1$, $d_2$, ... be a sequence of positive numbers that converges to zero. A generalization of Steinhaus' theorem due to Weil implies that, if a subset of a homogeneous Riemannian manifold has no pair of points at distances $d_1$, $d_2$, ... from ... More
Computing upper bounds for the packing density of congruent copies of a convex bodyAug 22 2013Jul 06 2016In this paper we prove a theorem that provides an upper bound for the density of packings of congruent copies of a given convex body in $\mathbb{R}^n$; this theorem is a generalization of the linear programming bound for sphere packings. We illustrate ... More
Fourier analysis, linear programming, and densities of distance avoiding sets in R^nAug 13 2008Dec 02 2008In this paper we derive new upper bounds for the densities of measurable sets in R^n which avoid a finite set of prescribed distances. The new bounds come from the solution of a linear programming problem. We apply this method to obtain new upper bounds ... More
Solving Irregular Strip Packing Problems With Free Rotations Using Separation LinesJul 22 2017Solving nesting problems or irregular strip packing problems is to position polygons in a fixed width and unlimited length strip, obeying polygon integrity containment constraints and non-overlapping constraints, in order to minimize the used length of ... More
Torelli theorem for the moduli spaces of rank 2 quadratic pairsJun 18 2012Feb 01 2014Let $X$ be a smooth projective complex curve. We prove that a Torelli type theorem holds, under certain conditions, for the moduli space of $\alpha$-polystable quadratic pairs on $X$ of rank 2.
A Federated Lightweight Authentication Protocol for the Internet of ThingsJul 12 2019Considering the world's IoT development and market, it is necessary to guarantee the security of the developed IoT applications as well as the privacy of their end users. In this sense, Federated Identity Management (FIdM) systems can be of great help ... More
Accuracy of generalized gradient approximation functionals for density functional perturbation theory calculationsSep 18 2013We assess the validity of various exchange-correlation functionals for computing the structural, vibrational, dielectric, and thermodynamical properties of materials in the framework of density-functional perturbation theory (DFPT). We consider five generalized-gradient ... More
A variational problem associated to a hyperbolic Caffarelli--Kohn--Nirenberg inequalityNov 16 2017We prove a Caffarelli--Kohn--Nirenberg inequality in the hyperbolic space. For a semilinear elliptic equation involving the associated weighted Laplace--Beltrami operator, we establish variationally the existence of positive radial solutions in the subcritical ... More
The positive semidefinite Grothendieck problem with rank constraintOct 30 2009May 03 2010Given a positive integer n and a positive semidefinite matrix A = (A_{ij}) of size m x m, the positive semidefinite Grothendieck problem with rank-n-constraint (SDP_n) is maximize \sum_{i=1}^m \sum_{j=1}^m A_{ij} x_i \cdot x_j, where x_1, ..., x_m \in ... More
Minkowski structure for purity and entanglement of Gaussian bipartite statesOct 24 2013The relation between the symplectic and Lorentz groups is explored to investigate entanglement features in a two-mode bipartite Gaussian state. We verify that the correlation matrix of arbitrary Gaussian states can be associated to a hyperbolic space ... More
Improving the semidefinite programming bound for the kissing number by exploiting polynomial symmetrySep 16 2016The kissing number of $\mathbb{R}^n$ is the maximum number of pairwise-nonoverlapping unit spheres that can simultaneously touch a central unit sphere. Mittelmann and Vallentin (2010), based on the semidefinite programming bound of Bachoc and Vallentin ... More
Positive solutions of quasilinear elliptic equations with exponential nonlinearity combined with convection termAug 27 2018We establish the existence of positive solutions for a nonlinear elliptic Dirichlet problem in dimension $N$ involving the $N$-Laplacian. The nonlinearity considered depends on the gradient of the unknown function and an exponential term. In such case, ... More
Upper bounds for packings of spheres of several radiiJun 12 2012We give theorems that can be used to upper bound the densities of packings of different spherical caps in the unit sphere and of translates of different convex bodies in Euclidean space. These theorems extend the linear programming bounds for packings ... More
Complete positivity and distance-avoiding setsApr 24 2018Mar 11 2019We introduce the cone of completely-positive functions, a subset of the cone of positive-type functions, and use it to fully characterize maximum-density distance-avoiding sets as the optimal solutions of a convex optimization problem. As a consequence ... More
Transição de fase no sistema de Hénon-Heiles (Phase transition in the Henon-Heiles system)Nov 22 2017The Henon-Heiles system was originally proposed to describe the dynamical behavior of galaxies, but this system has been widely applied in dynamical systems by exhibit great details in phase space. This work presents the formalism to describe Henon-Heiles ... More
A Conforming Primal-Dual Mixed Formulation for the 2D Multiscale Porous Media Flow ProblemJan 04 2017Oct 02 2018In this paper a new primal-dual mixed finite element method is introduced, aimed to model multiscale problems with several geometric subregions in the domain of interest. In each of these regions porous media fluid flow takes place, but governed by physical ... More
The asymptotic analysis of a Darcy-Stokes system coupled through a curved interfaceFeb 22 2019The asymptotic analysis of a Darcy-Stokes system modeling the fluid exchange between a narrow channel (Stokes) and a porous medium (Darcy) coupled through a $ C^{2} $ curved interface, is presented. The channel is a cylindrical domain between the interface ... More
Finite-Size Effects in the Absorption Spectra of a Single-Wall Carbon NanotubeDec 13 2017The determination of the optical spectrum of single-wall carbon nanotubes (SWCNTs) is essential for the development of opto-electronic components and sensors with application in many fields. Real SWCNTs are finite, but almost all the studies performed ... More
Canonical formulation of Poincare BFCG theory and its quantizationSep 12 2014Mar 29 2015We find the canonical formulation of the Poincare BFCG theory in terms of the spatial 2-connection and its canonically conjugate momenta. We show that the Poincare BFCG action is dynamically equivalent to the BF action for the Poincare group and we find ... More
Charmonium and Bottomonium from Classical SU(3) Gauge ConfigurationsOct 31 2006The charmonium and bottomonium spectra computed from a potential defined from a single gauge configuration, obtained from solving the classical field equations, is discussed. The theoretical spectra shows good agreement with the measured states. A discussion ... More
Heavy Quarkonia from Classical SU(3) Yang-Mills ConfigurationsOct 11 2006A generalized Cho-Faddeev-Niemi ansatz for SU(3) Yang-Mills is investigated. The corresponding classical field equations are solved for its simplest parametrization. From these solutions it is possible to define a confining central non-relativistic potential ... More
Charmonium from Classical Pure SU(3) Yang-Mills ConfigurationsMar 06 2006Jul 29 2006A generalized Faddeev-Niemi ansatz for the gluon field is discussed. In its simplest parametrization, the ansatz allows a solution of the classical SU(3) Yang-Mills equations. From these solutions a confining potential for heavy quarkonia is defined. ... More
Classical Solutions of SU(2) and SU(3) Pure Yang-Mills Theories and Heavy Quark SpectrumMay 28 2003Sep 11 2003In this paper we compute classical Minkowsky spacetime solutions of pure SU(2) and SU(3) gauge theories, in Landau gauge. The solutions are regular everywhere except at the origin and/or infinity, are characterized by a four momentum $k$ such that $k^2 ... More
Classical Solutions of SU(3) Pure Yang-Mills TheoryJan 24 2002Apr 30 2002Regular classical solutions of pure SU(3) gauge theories, in Minkowsky spacetime, are computed in the Landau gauge. The classical fields have an intrinsic energy scale and produce quark confinement if interpreted in the sense of a nonrelativistic potential. ... More
Feature Selection for Microarray Gene Expression Data using Simulated Annealing guided by the Multivariate Joint EntropyFeb 07 2013In this work a new way to calculate the multivariate joint entropy is presented. This measure is the basis for a fast information-theoretic based evaluation of gene relevance in a Microarray Gene Expression data context. Its low complexity is based on ... More
Atomic topology and radial distribution functions of a-SiNxOct 17 2001We report a new approach to simulate amorphous networks of covalently bonded materials that leads to excellent radial distribution functions and realistic atomic arrangements. We apply it to generate the first ab initio structures of nitrogen-doped silicon, ... More
Robust Output Regulation of Linear Passive Systems with Multivalued Upper Semicontinuous ControlsDec 05 2014The use of multivalued controls derived from a special maximal monotone operator are studied in this note. Starting with a strictly passive linear system (with possible parametric uncertainty and external disturbances) a multivalued control law is derived, ... More
There is no anomaly in the nonlocality of two entangled qutritsApr 07 2015Sep 04 2015There is no doubt about the fact that entanglement and nonlocality are distinct resources. It is acknowledged that a clear illustration of this point is the difference between maximally entangled states and states that maximally violate a Bell inequality. ... More
Flag Algebras: A First GlanceJul 16 2016The theory of flag algebras, introduced by Razborov in 2007, has opened the way to a systematic approach to the development of computer-assisted proofs in extremal combinatorics. It makes it possible to derive bounds for parameters in extremal combinatorics ... More
Mass and Extremals Associated with the Hardy-Schrödinger Operator on Hyperbolic SpaceOct 03 2017Apr 05 2018We consider the Hardy-Schr\"odinger operator $ -\Delta_{\mathbb{B}^n}-\gamma{V_2}$ on the Poincar\'e ball model of the Hyperbolic space ${\mathbb{B}^n}$ ($n \geq 3$). Here $V_2$ is a well chosen radially symmetric potential, which behaves like the Hardy ... More
$k$-point semidefinite programming bounds for equiangular linesDec 14 2018In this paper we derive a hierarchy of $k$-point semidefinite programming upper bounds for the maximum number of equiangular lines in $n$-dimensional Euclidean space. We apply symmetry reduction techniques for invariant semidefinite programs to compute ... More
On bicluster aggregation and its benefits for enumerative solutionsJun 02 2015Biclustering involves the simultaneous clustering of objects and their attributes, thus defining local two-way clustering models. Recently, efficient algorithms were conceived to enumerate all biclusters in real-valued datasets. In this case, the solution ... More
Surface and bulk properties of ballistic deposition models with bond breakingAug 08 2012Feb 17 2013We introduce a new class of growth models, with a surface restructuring mechanism in which impinging particles may dislodge suspended particles, previously aggregated on the same column in the deposit. The flux of these particles is controlled through ... More
Lower bounds for measurable chromatic numbersJan 07 2008Jul 17 2009The Lovasz theta function provides a lower bound for the chromatic number of finite graphs based on the solution of a semidefinite program. In this paper we generalize it so that it gives a lower bound for the measurable chromatic number of distance graphs ... More
Evolution of Collective Behaviors for a Real Swarm of Aquatic Surface RobotsNov 10 2015Feb 02 2016Swarm robotics is a promising approach for the coordination of large numbers of robots. While previous studies have shown that evolutionary robotics techniques can be applied to obtain robust and efficient self-organized behaviors for robot swarms, most ... More
Turbulent channel flow perturbed by triangular ripplesFeb 28 2018Mar 15 2018This paper presents an experimental investigation of the perturbation of a turbulent closed-conduit flow by two-dimensional triangular ripples. Two ripple configurations were employed: one single asymmetric triangular ripple, and two consecutive asymmetric ... More
Better bounds for planar sets avoiding unit distancesDec 31 2014Oct 26 2015A $1$-avoiding set is a subset of $\mathbb{R}^n$ that does not contain pairs of points at distance $1$. Let $m_1(\mathbb{R}^n)$ denote the maximum fraction of $\mathbb{R}^n$ that can be covered by a measurable $1$-avoiding set. We prove two results. First, ... More
Learning to Race through Coordinate Descent Bayesian OptimisationFeb 17 2018In the automation of many kinds of processes, the observable outcome can often be described as the combined effect of an entire sequence of actions, or controls, applied throughout its execution. In these cases, strategies to optimise control policies ... More
Improving Graphene-metal Contacts: Thermal Induced PolishingJan 15 2018Graphene is a very promising material for nanoelectronics applications due to its unique and remarkable electronic and thermal properties. However, when deposited on metallic electrodes the overall thermal conductivity is significantly decreased. This ... More
Spectral bounds for the independence ratio and the chromatic number of an operatorJan 06 2013Jun 19 2013We define the independence ratio and the chromatic number for bounded, self-adjoint operators on an L^2-space by extending the definitions for the adjacency matrix of finite graphs. In analogy to the Hoffman bounds for finite graphs, we give bounds for ... More
Open string with a background B-field as the first order mechanics and noncommutativityOct 19 2001To study noncommutativity properties of the open string with constant B-field we construct a mechanical action which reproduces classical dynamics of the string sector under consideration. It allows one to apply the Dirac quantization procedure for constrained ... More
Using the Galileoscope in astronomical observationsJan 28 2015This project aims to attract school students and teachers from the state education system from Ca\c{c}apava do Sul - RS to Sciences and specially to Astronomy. We made astronomical observations using a Galileoscope choosing the Moon as a primary target. ... More
On the generation of bipartite grids with controlled regularity for 2-D and 3-D simply connected domainsDec 25 2013We present a procedure to generate bipartite grids for simply connected domains in 2-D and 3-D of prescribed size and controlled regularity elements. The mesh elements $K$ of the triangulation satisfy $\zeta_{K} \leq C$ where $\zeta_{K}$ is the regularity ... More
On the Implementation and Assessment of several Divide & Conquer Matheuristic Strategies for the solution of the Knapsack ProblemJan 04 2019We introduce and asses a Divide \& Conquer heuristic method, aimed to solve large instances of the Knapsack Problem. The method subdivides a large problem in two smaller ones (or recursive iterations of the same principle), to lower down the global computational ... More
Asymptotic behavior of Boussinesq system of KdV-KdV typeSep 18 2017This work deals with the local rapid exponential stabilization for a Boussinesq system of KdV-KdV type introduced by J. Bona, M. Chen and J.-C. Saut. This is a model for the motion of small amplitude long waves on the surface of an ideal fluid. Here, ... More
Spin Dependence of Heavy Quark FragmentationFeb 28 2007We propose that the non-perturbative fragmentation functions describing the transition from a heavy quark to a heavy meson is proportional to the square of the produced meson wave function at the origin. We analyze the effects of this proposal on the ... More
Learning Attribute Representation for Human Activity RecognitionFeb 02 2018Attribute representations became relevant in image recognition and word spotting, providing support under the presence of unbalance and disjoint datasets. However, for human activity recognition using sequential data from on-body sensors, human-labeled ... More
Fifty Shades of Congestion Control: A Performance and Interactions EvaluationMar 09 2019Congestion control algorithms are crucial in achieving high utilization while preventing overloading the network. Over the years, many different congestion control algorithms have been developed, each trying to improve in specific situations. However, ... More
On the Stability of the Cauchy Problem of Timoshenko Thermoelastic Systems with Past History: Cattaneo and Fourier LawAug 26 2018In this paper, we investigate the decay properties of the thermoelastic Timoshenko system with past history in the whole space where the thermal effects are given by Cattaneo and Fourier laws. We obtain that both systems, Timoshenko-Fourier and Timoshenko-Cattaneo, ... More
Analysing Symbolic Regression Benchmarks under a Meta-Learning ApproachMay 25 2018The definition of a concise and effective testbed for Genetic Programming (GP) is a recurrent matter in the research community. This paper takes a new step in this direction, proposing a different approach to measure the quality of the symbolic regression ... More
Optical Pumping of TeH+: Implications for the Search for Varying mp/meJul 11 2018Sep 20 2018Molecular overtone transitions provide optical frequency transitions sensitive to variation in the proton-to-electron mass ratio ($\mu\equiv m_p/m_e$). However, robust molecular state preparation presents a challenge critical for achieving high precision. ... More
Hamiltonian analysis of the BFCG theory for the Poincare 2-groupAug 23 2015Feb 25 2016We perform the full Hamiltonian analysis of the topological BFCG action based on the Poincare 2-group. The Hamiltonian of the theory is constructed, and the algebra of constraints is computed. The Dirac brackets are evaluated, and the second class constraints ... More
Hamiltonian analysis of the BFCG formulation of General RelativityJul 17 2018Dec 03 2018We perform the complete Hamiltonian analysis of the BFCG action for General Relativity. We determine all the constraints of the theory and classify them into the first-class and the second-class constraints. We also show how the canonical formulation ... More
Human Dynamics: The Correspondence Patterns of Darwin and EinsteinNov 01 2005While living in different historical era, Charles Darwin (1809-1882) and Albert Einstein (1879-1955) were both prolific correspondents: Darwin sent (received) at least 7,591 (6,530) letters during his lifetime while Einstein sent (received) over 14,500 ... More
Soft and hard X-ray dips in the light curves of gamma CassiopeiaeJul 26 2019We have examined soft (<2keV) "dips" in six archival XMM-Newton observations of gamma Cas (B0.5IV e) for "soft dips" (< 2keV) in X-ray light curves. We find that such events are sometimes accompanied by minor, near-simultaneous dips in the hard X-ray ... More
Dynamical Lower Bounds for 1D Dirac OperatorsAug 07 2007Quantum dynamical lower bounds for continuous and discrete one-dimensional Dirac operators are established in terms of transfer matrices. Then such results are applied to various models, including the Bernoulli-Dirac one and, in contrast to the discrete ... More
Vacuum energy density and pressure of a massive scalar fieldDec 29 2014Apr 03 2015With a view toward application of the Pauli-Villars regularization method to the Casimir energy of boundaries, we calculate the expectation values of the components of the stress tensor of a confined massive field in 1+1 space-time dimensions. Previous ... More
A semiclassical trace formula for the canonical partition function of one dimensional systemsJul 20 2006Sep 05 2006We present a semiclassical trace formula for the canonical partition function of arbitrary one-dimensional systems. The approximation is obtained via the stationary exponent method applied to the phase-space integration of the density operator in the ... More
Torsion effects on Condensed Matter: like a magnetic field but not so muchJan 07 2017In this work, we study the effects of torsion due to a uniform distribution of topological defects (screw dislocations) on free spin/carrier dynamics in elastic solids. When a particle moves in such a medium, the effect of the torsion associated to the ... More
Min-max piecewise constant optimal control for multi-model linear systemsDec 12 2014The present work addresses a finite-horizon linear-quadratic optimal control problem for uncertain systems driven by piecewise constant controls. The precise values of the system parameters are unknown, but assumed to belong to a finite set (i.e., there ... More
CAL 87 - an evolved wind-driven supersoft X-ray binaryJul 23 2007Compact binary supersoft X-ray sources (CBSS) are explained as being associated with hydrostatic nuclear burning on the surface of a white dwarf with high accretion rate. This high mass transfer rate has been suggested to be caused by dynamical instability, ... More
Mass Terms in Two-Higgs Doublet ModelsDec 14 2001Feb 11 2003We take a closer look at the mass terms of all renormalizable and CP conserving two-Higgs doublet models (THDM). We show how some of the dimension two parameters in the potential can be set equal to zero leading to relations among the tree-level parameters ... More
On the spectrum and weakly effective operator for Dirichlet Laplacian in thin deformed tubesMar 15 2011We study the Laplacian in deformed thin (bounded or unbounded) tubes in ?$\R^3$, i.e., tubular regions along a curve $r(s)$ whose cross sections are multiplied by an appropriate deformation function $h(s)> 0$. One the main requirements on $h(s)$ is that ... More
Quantum Hamiltonians with Quasi-Ballistic Dynamics and Point SpectrumJan 04 2007Consider the family of Schr\"odinger operators (and also its Dirac version) on $\ell^2(\mathbb{Z})$ or $\ell^2(\mathbb{N})$ \[ H^W_{\omega,S}=\Delta + \lambda F(S^n\omega) + W, \quad \omega\in\Omega, \] where $S$ is a transformation on (compact metric) ... More
Retinal vessel segmentation based on Fully Convolutional Neural NetworksDec 18 2018Dec 19 2018The retinal vascular condition is a reliable biomarker of several ophthalmologic and cardiovascular diseases, so automatic vessel segmentation may be crucial to diagnose and monitor them. In this paper, we propose a novel method that combines the multiscale ... More
Reliability of digitized quantum annealing and the decay of entanglementNov 01 2016We performed a banged-digital-analog simulation of a quantum annealing protocol in a two-qubit Nuclear Magnetic Resonance (NMR) quantum computer. Our experimental simulation employed up to 235 Trotter steps, with more than 2000 gates (pulses), and we ... More
An elementary approach to certain bilinear estimatesFeb 11 2016We prove L2 x L2 to weak L1 estimates for some novel bilinear maximal operators of Kakeya and lacunary type thus extending to this setting, the works of Cordoba and of Nagel, Stein and Wainger.
Multiresolution Division Multiplex (MRDM): A New Wavelet-based Multiplex SystemFeb 12 2015An original multiplex scheme is introduced, which is based on Mallat's multiresolution formulation of wavelet systems. This system is adaptable and its implementation is well matched to digital signal processors and computers. The approach termed multiresolution ... More
Aspects of Wave Turbulence in PreheatingJun 04 2014In this work we have studied the nonlinear preheating dynamics of the $\frac{1}{4} \lambda \phi^4$ inflationary model. It is well established that after a linear stage of preheating characterized by the parametric resonance, the nonlinear dynamics becomes ... More
Aspects of wave turbulence in preheating II: Rebirth of the nonminimal coupled modelsMay 31 2019We study the nonlinear stage of preheating in a model consisting of a single inflaton field $\phi$ nonminimally coupled to the spacetime curvature and considering a self-coupling quartic potential V ($\phi$) = $\lambda \phi^4/4$. As the first motivation, ... More
Dynamical Delocalization for the 1D Bernoulli Discrete Dirac OperatorJan 21 2005An 1D tight-binding version of the Dirac equation is considered; after checking that it recovers the usual discrete Schr?odinger equation in the nonrelativistic limit, it is found that for two-valued Bernoulli potentials the zero mass case presents absence ... More
The Kramers problem for SDEs driven by small, accelerated Lévy noise with exponentially light jumpsApr 03 2019We establish Freidlin-Wentzell results for a nonlinear ordinary differential equation starting close to a stable state subject to a perturbation by a stochastic integral driven by an $\varepsilon$-small and $(1/\varepsilon)$-accelerated L\'evy process ... More
A Darcy-Brinkman Model of Fractures in Porous MediaNov 16 2016For a fully-coupled Darcy-Stokes system describing the exchange of fluid and stress balance across the interface between a saturated porous medium and an open very narrow channel, the limiting problem is characterized as the width of the channel converges ... More
Power law Kohn anomaly in undoped graphene induced by Coulomb interactionsSep 29 2011Feb 14 2012Phonon dispersions generically display non-analytic points, known as Kohn anomalies, due to electron-phonon interactions. We analyze this phenomenon for a zone boundary phonon in undoped graphene. When electron-electron interactions with coupling constant ... More
Predictions Based on the Clustering of Heterogeneous Functions via Shape and Subject-Specific CovariatesMay 11 2015We consider a study of players employed by teams who are members of the National Basketball Association where units of observation are functional curves that are realizations of production measurements taken through the course of one's career. The observed ... More
Beamforming Algorithm for Multiuser Wideband Millimeter-Wave Systems with Hybrid and Subarray ArchitecturesMay 10 2019We present a beamforming algorithm for multiuser wideband millimeter wave (mmWave) communication systems where one access point uses hybrid analog/digital beamforming while multiple user stations have phased-arrays with a single RF chain. The algorithm ... More
Determinantal point process mixtures via spectral density approachMay 15 2017We consider mixture models where location parameters are a priori encouraged to be well separated. We explore a class of determinantal point process (DPP) mixture models, which provide the desired notion of separation or repulsion. Instead of using the ... More
Tangential Fluid flow within 3D narrow fissures: Conservative velocity fields on associated triangulations and transport processesNov 28 2016Oct 02 2018For a fissured medium with uncertainty in the knowledge of fractures' geometry, a conservative tangential flow field is constructed, which is consistent with the physics of stationary fluid flow in porous media and an interpolated geometry of the cracks. ... More
On the Suitability of PLC Pulses for Power Line Fault Sensing via Time-Domain ReflectometryJan 23 2019This work discusses the suitability of typical power line communication (PLC) pulses for fault sensing in power lines via pulse-compression time-domain reflectometry (TDR). For this purpose, we first carefully outline a TDR system operating over a power ... More
Video-based computer aided arthroscopy for patient specific reconstruction of the Anterior Cruciate LigamentJul 25 2018The Anterior Cruciate Ligament (ACL) tear is a common medical condition that is treated using arthroscopy by pulling a tissue graft through a tunnel opened with a drill. The correct anatomical position and orientation of this tunnel is crucial for knee ... More
Reliability of digitized quantum annealing and the decay of entanglementNov 01 2016Jun 29 2017We performed a banged-digital-analog simulation of a quantum annealing protocol in a two-qubit Nuclear Magnetic Resonance (NMR) quantum computer. Our experimental simulation employed up to 235 Trotter steps, with more than 2000 gates (pulses), and we ... More
Magnetic hyperfine field at \textit{s-p} impurities on Laves phase compoundsNov 16 2011Recent experimental results for the magnetic hyperfine field B_{\rm hf} at the nuclei of \textit{s-p} impurities such as ${}^{119}$Sn in intermetallic Laves phases RM_2 (R = Gd, Tb, Dy, Ho, Er; M = Fe, Co) and ${}^{111}$Cd in RCo_{2}, the impurity occupying ... More
Real-space grids and the Octopus code as tools for the development of new simulation approaches for electronic systemsJan 22 2015Real-space grids are a powerful alternative for the simulation of electronic systems. One of the main advantages of the approach is the flexibility and simplicity of working directly in real space where the different fields are discretized on a grid, ... More
Quantum corral wave function engineeringAug 26 2004We present a theoretical method for the design and optimization of quantum corrals with specific electronic properties. Taking advantage that spins are subject to a RKKY interaction that is directly controlled by the scattering of the quantum corral, ... More
Noncommutative cosmological models coupled to a perfect fluid and a cosmological constantNov 23 2011In this work we carry out a noncommutative analysis of several Friedmann-Robert-Walker models, coupled to different types of perfect fluids and in the presence of a cosmological constant. The classical field equations are modified, by the introduction ... More
Tidal Forces in Reissner-Nordström SpacetimesFeb 23 2016We analyze the tidal forces produced in the spacetime of Reissner-Nordstr\"om black holes. We point out that the radial component of the tidal force changes sign just outside the event horizon if the charge-to-mass ratio is close to $1$ unlike in Schwarzschild ... More
Noncommutativity in the early UniverseJan 07 2014May 04 2016In the present work, we study the noncommutative version of a quantum cosmology model. The model has a Friedmann-Robertson-Walker geometry, the matter content is a radiative perfect fluid and the spatial sections have zero constant curvature. In this ... More