Papers by Hector Huayta Espinoza
Anales de la Facultad de Medicina, 2013
Introducción: Debido a la gran diversidad de patologÃa quirúrgica de la glándula tiroides y su al... more Introducción: Debido a la gran diversidad de patologÃa quirúrgica de la glándula tiroides y su alta frecuencia en nuestro medio, creemos conveniente presentar nuestra experiencia en esta patologÃa. Objetivos: Conocer la incidencia de la patologÃa quirúrgica de la glándula tiroides, según diagnóstico anatomopatológico, en pacientes operados. Diseño: Estudio retrospectivo, observacional y descriptivo. Lugar: Servicio de cirugÃa de cabeza y cuello, Hospital Dos de Mayo, Lima, Perú, hospital de enseñanza médica. Participantes: Pacientes operados de la glándula tiroides. Intervenciones: Se revisó las historias clÃnicas de pacientes operados de la glándula tiroides, desde enero de 1997 hasta diciembre de 2006. Principales medidas de resultados: Resultados anatomopatológicos en los especÃmenes de glándula tiroides. Resultados: Hubo 274 casos operados, de los cuales 81,4% del total correspondió al sexo femenino; 56,9% de los casos provenÃa de fuera de Lima y Callao, con edades que fluctuaba...
Valor diagnóstico de la gamagrafÃa en tiroides
Cir Rev Soc Cir Peru, Dec 1, 1987
Science Journal of Public Health, Oct 29, 2014
To evaluate the risk of Anisakiasis in the population, a common zoonotic disease worldwide caused... more To evaluate the risk of Anisakiasis in the population, a common zoonotic disease worldwide caused by ingestion of larvae (L3) of the nematode family anisakidae (Anisakis spp, Contracaecum spp, Pseudoterranova spp) present in raw fish or undercooked constitute a health risk that should not be underestimated; fish caught in the area Golfete of Coro, Venezuela Falcòn state. Artisanal trawling shore and depth serve as financial support to numerous fishing villages located along the western coast of the isthmus of dunes, the Peninsula Paraguana where trade in species of different orders of zoological scale marine fauna existing there. A study was conducted to determine the degree of parasitism by anisakidae family, using a non-probability purposive sampling 90 specimens were purchased directly from fishermen, giving prevalence to the lowest economic value, which also are used for family consumption as: mullet (Mugil Mugil curema or incilis), mullet (Mugil liza), crappie (Eugerres plumieri) and catfish (Ictalurus punctatus) among others. They moved to the laboratory for: evisceration, debridement and muscle dissection seeking parasites. Nematodes of the family anisakidae identified in the sample were Contracaecum spp. 97% and pseudoterranova spp. 3%, and those with high degree of infestation were 88.8% and mojarra smooth 80% with parasite loads ranging from seven to nine parasites per specimen, demonstrating a high parasitism.
Acta Acustica united with Acustica, 2016
Working with the wave equation in mixed rather than irreducible form allows one to directly accou... more Working with the wave equation in mixed rather than irreducible form allows one to directly account for both, the acoustic pressure field and the acoustic particle velocity field. Indeed, this becomes the natural option in many problems, such as those involving waves propagating in moving domains, because the equations can easily be set in an arbitrary Lagrangian-Eulerian (ALE) frame of reference. Yet, when attempting a standard Galerkin finite element solution (FEM) for them, it turns out that an inf-sup compatibility constraint has to be satisfied, which prevents from using equal interpolations for the approximated acoustic pressure and velocity fields. In this work it is proposed to resort to a subgrid scale stabilization strategy to circumvent this condition and thus facilitate code implementation. As a possible application, we address the generation of diphthongs in voice production.
El agotamiento de los combustibles fósiles y la contaminación producida por la utilización de los... more El agotamiento de los combustibles fósiles y la contaminación producida por la utilización de los mismos, ha hecho que se desarrollen fuentes de energÃa alternativas, especialmente las energÃas renovables. El viento es una forma de energÃa renovable, aunque de baja concentración, y para su aprovechamiento es necesaria la utilización de turbinas de viento o aerogeneradores. El estudio de la aerodinámica de los aerogeneradores es de suma importancia para el eficiente aprovechamiento de la energÃa eólica. Para realizar el estudio aerodinámico existen básicamente tres caminos: estudios de campo o laboratorio, modelos semi-empÃricos y modelos que utilizan las ecuaciones de Navier-Stokes resueltas mediante métodos numéricos (CFD). De los métodos anteriormente citados, el más exacto y confiable son las mediciones de campo; pero al mismo tiempo resulta costoso y complejo. Esto ha hecho que en la actualidad se utilice mucho la Dinámica de Fluidos Computacional (CFD) para resolver estos probl...
mixed wave equation, stabilized finite element methods, numerical analysis, Fourier analysis, von... more mixed wave equation, stabilized finite element methods, numerical analysis, Fourier analysis, von Neuman analysis, dispersion, dissipation, stability, convergence, voice simulation
Computer Methods in Applied Mechanics and Engineering, 2015
In this paper we analyze time marching schemes for the wave equation in mixed form. The problem i... more In this paper we analyze time marching schemes for the wave equation in mixed form. The problem is discretized in space using stabilized finite elements. On the one hand, stability and convergence analyses of the fully discrete numerical schemes are presented using different time integration schemes and appropriate functional settings. On the other hand, we use Fourier techniques (also known as von Neumann analysis) in order to analyze stability, dispersion and dissipation. Numerical convergence tests are presented for various time integration schemes, polynomial interpolations (for the spatial discretization), stabilization methods, and variational forms. To analyze the behavior of the different schemes considered, a 1D wave propagation problem is solved.
Waves in time dependent domains
Wave equations usually arise from the manipulation of conservation laws, such as linearization or... more Wave equations usually arise from the manipulation of conservation laws, such as linearization or time derivation of these. In particular, the classical irreducible hyperbolic wave equation of second order in space and time is often obtained from a combination of two equations in two independent unknowns, of first order both in space and time. These equations constitute the so called mixed form of the wave problem. The mixed wave equation we consider has one scalar variable and a vector one, while the irreducible form can be written in terms of the scalar variable only. Using the former instead of the latter may be due to the wish of obtaining a better approximation for the vector field. However, there is one case in which the irreducible form cannot be obtained, and the mixed one is mandatory; this happens when the domain in which the problem is posed is time dependent. For example, if an Arbitrary Lagrangian-Eulerian (ALE) formulation is used, the two equations of the mixed form o...
Approximation of waves written in mixed form in time dependent domains
Stabilized finite element formulation for the mixed convected wave equation in domains with driven flexible boundaries
A stabilized finite element (FEM) formulation for the wave equation in mixed form with convection... more A stabilized finite element (FEM) formulation for the wave equation in mixed form with convection is presented, which permits using the same interpolation fields for the acoustic pressure and the acoustic particle velocity. The formulation is based on a variational multiscale approach, in which the problem unknowns are split into a large scale component that can be captured by the computational mesh, and a small, subgrid scale component, whose influence into the large scales has to be modelled. A suitable option is that of taking the subgrid scales, or subscales, as being related to the finite element residual by means of a matrix of stabilization parameters. The design of the later turns to be the key for the good performance of the method. In addition, the mixed convected wave equation has been set in an arbitrary Lagrangian-Eulerian (ALE) frame of reference to account for domains with moving boundaries. The movement of the boundaries in the present work consists of two components...
Numerical analysis and benchmarking of a Sommerfeld-type non-reflecting boundary condition for the wave equation in mixed form
In this paper we investigate a non-reflecting boundary condition (NRBC) of Sommerfeld type for th... more In this paper we investigate a non-reflecting boundary condition (NRBC) of Sommerfeld type for the wave equation in mixed form in time domain. We apply the NRBC for three variational forms of the equation. Special emphasis is put in the spaces where the solution belongs, in particular the regularity required on the boundary. Then stabilized finite element methods are described. Stability and convergence analysis of stabilized finite element formulations including the NRBC are presented. Additionally, numerical convergence test are evaluated for various polynomial interpolations , stabilization methods and variational forms. Finally, several benchmark problems are solved to determine the accuracy of the NRBC in 2D and 3D.
Multi-Objective Design Optimisation of Stamping Process for Advanced High Strength Steels
ABSTRACT The paper investigates the multi-objective design optimisation of stamping process to co... more ABSTRACT The paper investigates the multi-objective design optimisation of stamping process to control both the shape and quality of final Advanced High Strength Steels (AHSSs) in terms of springback and safety using Distributed Multi-Objective Evolutionary Algorithm (DMOGA) coupled with Finite Element Analysis (FEA) based stamping analyser. The design problem of stamping process is formulated to minimise the difference between the desired shape and the final geometry obtained by a numerical simulation accounting elastic springback. In addition, the final product quality is maximised by improving safety factor without winkling, thinning, or failure. Numerical results show that a proposed methodology improves the final product quality while reducing its springback.
Linear Waves in Mixed Form: Functional Setting and Stabilized Finite Element Approximation
A stabilized Arbitrary Lagrangian Eulerian Finite Element Method for the mixed wave equation with application to diphthong production
ABSTRACT Though most engineering problems in acoustics directly deal with the wave equation in it... more ABSTRACT Though most engineering problems in acoustics directly deal with the wave equation in its irreducible form, in many situations it becomes interesting to consider it in mixed form, so as to directly account for both, the acoustic pressure and the acoustic velocity fields. A particular case is that of waves propagating in domains with moving boundaries. When attempting a finite element solution to such problems, the mixed formulation naturally allows to set the equations in an arbitrary Lagrangian-Eulerian (ALE) framework. This results in the appearance of some extra terms involving the scalar product of the mesh velocity and the gradient of the pressure and velocity fields. As known, the finite element solution to the mixed wave equation needs to be stabilized so as to use equal interpolation for the pressure and velocity fields. Following the lines in, where algebraic and orthogonal subgrid stabilization were used, in this work a stabilized finite element method is proposed for the ALE wave equation in mixed form. As an application, we face the problem of the numerical generation of diphthongs. Much numerical work has recently been done with regard to static vocal tract acoustics i.e., generation of vowels and related phenomena, but little has been reported on dynamic vocal tract acoustics, most efforts being placed to date in the simulation of phonation. As a first step towards the generation of diphthongs, some 2D simulations will be presented based on simplified vocal tract geometries, which can be tuned to exhibit a 3D behavior.
Wave Equation in Mixed Form: Stability and Convergence Estimates using Stabilized Finite Element Methods
ABSTRACT The wave equation in mixed form is considered and its weak formulations analyzed. Each w... more ABSTRACT The wave equation in mixed form is considered and its weak formulations analyzed. Each weak formulation requires certain regularity on the unknowns depending on the integration by parts performed which leads to different functional settings. The problem is discretized in space using stabilized finite element methods and is left as continuous in time. We refer to it as the semi-discrete problem. The stabilized finite element methods used are Algebraic Sub-Grid Scales Method (ASGS) and Orthogonal Sub-Scales Method (OSS). Length scales associated to the unknowns are introduced in the stabilized finite element methods. These length scales allow us to handle all weak formulations in a unified manner. Additionally, they allow certain control of the gradient of the scalar unknown or the divergence of the vector unknown as shown in the stability analysis. Furthermore, they establish a certain convergence rate depending on the weak formulation as shown in the convergence analysis. Stability of the finite element methods is proven in certain working norms involving the unknowns, the gradient of the scalar unknown and the divergence of the vector unknown. Additionally, convergence in space of the semi-discrete problem is analyzed. Finally, numerical performance of the formulations is assesed via numerical tests and compared to the theoretical results. Additionally, the work is complemented with numerical examples.
Stability, convergence, and accuracy of stabilized finite element methods for the wave equation in mixed form
ABSTRACT In this paper we propose two stabilized finite element methods for different functional ... more ABSTRACT In this paper we propose two stabilized finite element methods for different functional frameworks of the wave equation in mixed form. These stabilized finite element methods are stable for any pair of interpolation spaces of the unknowns. The variational forms corresponding to different functional settings are treated in a unified manner through the introduction of length scales related to the unknowns. Stability and convergence analysis is performed together with numerical experiments. It is shown that modifying the length scales allows one to mimic at the discrete level the different functional settings of the continuous problem and influence the stability and accuracy of the resulting methods.
Computer Methods in Applied Mechanics and Engineering, 2014
In this paper we develop numerical approximations of the wave equation in mixed form supplemented... more In this paper we develop numerical approximations of the wave equation in mixed form supplemented with non-reflecting boundary conditions (NRBCs) of Sommerfeld-type on artificial boundaries for truncated domains. We consider three different variational forms for this problem, depending on the functional space for the solution, in particular, in what refers to the regularity required on artificial boundaries. Then, stabilized finite element methods that can mimic these three functional settings are described. Stability and convergence analyses of these stabilized formulations including the NRBC are presented. Additionally, numerical convergence test are evaluated for various polynomial interpolations, stabilization methods and variational forms. Finally, several benchmark problems are solved to determine the accuracy of these methods in 2D and 3D.
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Papers by Hector Huayta Espinoza