Lluís Miquel Garcia Raffi | Universitat Politècnica de València (original) (raw)

Papers by Lluís Miquel Garcia Raffi

Applied General Topology, 2005

Using compactness properties of bounded subsets of spaces of vector measure integrable functions ... more Using compactness properties of bounded subsets of spaces of vector measure integrable functions and a representation theorem for q-convex Banach lattices, we prove a domination theorem for operators between Banach lattices. We generalize in this way several classical factorization results for operators between these spaces, as psumming operators.

Topology and its Applications, 2008

In this paper we analyze the existence of points of a subset S of a linear space X where the shor... more In this paper we analyze the existence of points of a subset S of a linear space X where the shortest distance to a point x of X with respect to an asymmetric norm q is attained (q-nearest points). Since the structure of an asymmetric norm do not provide in general uniqueness of such points-due to the fact that the separation properties in these spaces are in general weaker than in normed spaces-we develop a technique to find particular subsets of the set of q-nearest points-that we call optimal distance points-that are also optimal for the norm q s associated to the asymmetric norm.

Publications of the Research Institute for Mathematical Sciences, 2013

Sequences of real functions that are orthogonal with respect to a vector measure are a natural ge... more Sequences of real functions that are orthogonal with respect to a vector measure are a natural generalization of orthogonal systems with respect to a parametric measure. In this paper we develop a new procedure to construct non-linear approximations of functions by defining orthogonal series in spaces of square integrable functions with respect to a vector measure whose Fourier coefficients are also functions. We study the convergence properties of such series, defining a convenient approximation procedure for signal processing involving time dependence of the measure. Some examples involving classical orthogonal polynomials are given.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1995

An appropriate parameterization of the relation between the counting rate asymmetry and the degre... more An appropriate parameterization of the relation between the counting rate asymmetry and the degree of polarization is derived for Compton polarimeters not having orthogonal symmetry. The question of the usefulness of such polarimeters is addressed using the concept of merit and exemplified with the case of the EUROBALL CLUSTER detector.

The Journal of the Acoustical Society of America, 2006

A phenomenological model that simulates the acoustic attenuation behavior of sonic crystals is de... more A phenomenological model that simulates the acoustic attenuation behavior of sonic crystals is developed in this paper. The input of the model is a set of parameters that characterizes each experimental setup, and the output is a simulation of the associated attenuation spectrum. The model consists of a combination of a multiresolution analysis based on wavelet functions and a set of artificial neural networks. An optimized coupling of these tools allows us to drastically reduce the experimental data needed, and to obtain a fast computational model that can be used for technological purposes.

Applied Physics Letters, 2008

An improvement in the attenuation capabilities of acoustic metamaterials by means of the creation... more An improvement in the attenuation capabilities of acoustic metamaterials by means of the creation of defects is considered here as a multiobjective optimization problem. From this point of view, it is possible to define the optimum strategy in the creation of defects to achieve an important increase in acoustic attenuation in a predetermined range of frequencies. A powerful multiobjective optimization algorithm called evMOGA has been used to solve this problem. The study has been restricted to the case of a two-dimensional sonic crystal formed by rigid cylinders in air, the defects being vacancies in the initial structure.

Enseñanza de las Ciencias. Revista de investigación y experiencias didácticas, 1999

In this article we present a program of interdisciplinary practices for a first engineering cours... more In this article we present a program of interdisciplinary practices for a first engineering course. We followed this program during the course 1996-1997, and we give several examples of the kind of exercises that we used. We also present some remarks and conclusions that we have achieved in our experience. Our purpose is to introduce a teaching strategy for Mathematics and Physics at the University level.

PACS 43.20.+g-General linear acoustics PACS 43.35.+d-Ultrasonics, quantum acoustics, and physical... more PACS 43.20.+g-General linear acoustics PACS 43.35.+d-Ultrasonics, quantum acoustics, and physical effects of sound Abstract-The transmission of acoustic waves in a fractal distribution of rigid scatterers embedded in air is reported in this work. The Sierpinsky fractal is used to produce a compact small device containing several periodicities, therefore the fractal distribution contains several finite sonic crystals. The attenuation band produced by the fractal distribution results from the sum of the Bragg peaks of each periodicity. On the other hand, bandgaps of sonic crystal depend on the well-known filling fraction, thus the radii of the scatterers in the fractal distribution has been optimized using genetic algorithm in order to overlap the bandgaps of each periodicity obtaining a wide and full attenuation band.

Analysis of the wave propagation properties of a periodic array of rigid cylinders perpendicular ... more Analysis of the wave propagation properties of a periodic array of rigid cylinders perpendicular to a finite impedance surface This article has been downloaded from IOPscience. Please scroll down to see the full text article.

This work theoretically and experimentally reports the evanescent connections between propagating... more This work theoretically and experimentally reports the evanescent connections between propagating bands in periodic acoustic materials. The complex band structures obtained by solving for the k(ω) problem reveal a complete interpretation of the propagation properties of these systems. The prediction of evanescent modes, nonpredicted by classical ω( k) methods, is of interest for the understanding of these propagation properties. Complex band structures provide an interpretation of the evanescent coupling and the level repulsion states showing the possibility of controlling evanescent waves in periodic materials. DOI: 10.1103/PhysRevB.84.212302 PACS number(s): 43.20.Fn, 43.20.Gp, 43.20.Mv, 63.20.−e Propagation of waves in periodic structures is characterized by both propagating and evanescent waves. On one hand, the control of the propagation properties of periodic electromagnetic 1-3 and elastic 4-7 materials has revealed a huge number of physical phenomena in the last decades. On t...

Journal of Physics D: Applied Physics, 2021

We theoretically, numerically and experimentally report the localization of an acoustic wave at t... more We theoretically, numerically and experimentally report the localization of an acoustic wave at the interface between two one-dimensional hyperuniform materials of different geometrical representations. These materials suppress the acoustic scattering in the long wavelength regime, being rather disordered and degenerate, while possessing a wide band gap. In this work, these hyperuniform materials are made of an air-filled acoustic waveguide with rigid diaphragms acting as scatterers. A wide band gap and the emergence of the edge modes provide promising applications in wave control devices.

Zeitschrift Fur Physik a-Hadrons and Nuclei, 1997

Topology and Its Applications, 2008

A systematic study of precompact and compact subsets on asymmetric normed linear spaces is develo... more A systematic study of precompact and compact subsets on asymmetric normed linear spaces is developed, centering our attention in the case of linear lattices with an asymmetric norm.

Topology and Its Applications, 2009

It is well known that if (X, q) is an asymmetric normed linear space, then the function q s defin... more It is well known that if (X, q) is an asymmetric normed linear space, then the function q s defined on X by q s (x) = max{q(x), q(−x)}, is a norm on the linear space X. However, the lack of symmetry in the definition of the asymmetric norm q yields an algebraic asymmetry in the dual space of (X, q). This fact establishes a significant difference with the standard results on duality that hold in the case of locally convex spaces. In this paper we study some aspects of a reflexivity theory in the setting of asymmetric normed linear spaces. In particular, we obtain a version of the Goldstine Theorem to these spaces which is applied to prove, among other results, a characterization of reflexive asymmetric normed linear spaces.

New Journal of Physics, 2012

Spinal Cord, 2013

Objectives: The main goal of this study was to validate the use of accelerometers by means of mul... more Objectives: The main goal of this study was to validate the use of accelerometers by means of multiple linear models to estimate the O 2 consumption (VO 2) in paraplegic persons and, secondary, to determine the best placement for accelerometers on the human body. Setting: Non hospitalized paraplegics' community. Methods: A volunteer sample of participants (n=20, mean age = 40.03 years, mean weight = 75.8 kg and mean height = 1.76 m) completed a series of sedentary, propulsion and housework activities for 10 min each. A portable gas analyzer was used to record breath-by-breath VO 2. Additionally, four accelerometers (placed on the non-dominant chest, nondominant waist and both wrists) were used to collect second-by-second acceleration signals. Minute-by-minute VO 2 (ml•kg-1 •min-1) collected from minute 4 to minute 7 was used as the dependent variable. A total of 36 features extracted from the acceleration signals were used as independent variables. These variables were, for each axis including the resultant vector, the percentiles 10 th , 25 th , 50 th , 75 th and 90 th ; the autocorrelation with lag of 1

$Research paper thumbnail of Interferometric method of determining the refraction index of two-dimensional sonic crystals$

Physical Review B, 2007

Sonic crystals are defined as materials consisting of periodic distributions of acoustic scattere... more Sonic crystals are defined as materials consisting of periodic distributions of acoustic scatterers in another medium with different elastic properties. These materials present two main acoustical features: they present ranges of frequencies where the acoustic wave propagation is forbidden and, moreover, they can be used to construct acoustical refractive devices. We present here an interferometric method of characterizing directly the refraction index of these materials. We focused our research on sonic crystals constructed with a periodic distribution of rigid cylinders in air. The interferometric method used is based on the acoustical analog of an optical device called Fresnel's biprism. Our numerical predictions are in good agreement with the experimental results obtained and allow us to estimate the refraction index for very low frequencies. Moreover, in this range we show the nonlinear behavior in the dispersion relation refraction index versus frequency. Finally, we analyze the relationship between the refraction index and some typical sonic crystal parameters. In view of the results we can conclude that this method offers certain advantages with respect to the classical method used to obtain the refraction index in sonic crystals with airborne propagation: the phase delay method.

The Journal of the Acoustical Society of America, 2009

An exhaustive study has been made into the potential improvement in attenuation and focusing of p... more An exhaustive study has been made into the potential improvement in attenuation and focusing of phononic crystal arrays resulting from the deliberate creation of vacancies. Use is made of a stochastic search algorithm based on evolutionary algorithms called the epsilon variable multi-objective genetic algorithm which, in conjunction with the application of multiple scattering theory, enables the design of devices for effectively controlling sound waves. Several parameters are analyzed, including the symmetries used in the distribution of holes and the optimum number of holes. The validity and utility of the general rules obtained have been confirmed experimentally.

Journal of Sound and Vibration, 2013

An acoustic metamaterial made of a two-dimensional (2D) periodic array of multi-resonant acoustic... more An acoustic metamaterial made of a two-dimensional (2D) periodic array of multi-resonant acoustic scatterers is analysed in this paper. The building blocks consist of a combination of elastic beams of Low-Density Polyethylene Foam (LDPF) with cavities of known volume. Sound inside the structure can excite elastic resonances of the material as well as acoustic resonances in the cavities producing several attenuation peaks in the low-frequency range. Due to this behaviour at the subwavelength regime we can define this periodic array as a Locally Multi-Resonant Acoustic Metamaterial (LMRAM) presenting strong dispersive characteristics of the effective properties with subwavelength multi-resonant structural units. The results shown in this paper could be use to design effective Sonic Crystal Acoustic Barriers with wide tunable attenuation bands in the low-frequency range.