Viscothermal Losses in Double-Negative Acoustic Metamaterials

[EN] The influence of losses in double-negative metamaterial slabs recently introduced by Graciá-Salgado et al. [Phys. Rev. B 88, 224305 (2013)] is comprehensively studied. Viscous and thermal losses are considered in the linearized Navier-Stokes equations with no flow. Despite the extremely low thicknesses of boundary layers associated with each type of losses, the double-negative behavior is totally suppressed for the rigid structures under analysis. In other words, almost 100% of the energy transmitted into the slab is dissipated by viscothermal effects, in agreement with experimental data. Simulations undertaken for larger structures, using scale factors of up to 20 times, show that double-negative behavior is never recovered. The huge dissipation obtained by these structures leads us to propose them as interesting alternatives to conventional absorbers for specific situations, e.g., when treating low frequencies or when the excitation is narrow banded.V. M. G.-C. and J. S.-D. acknowledge the support from the Spanish Ministerio de Economia y Competitividad (MINECO), and the European Union Fondo Europeo de Desarrollo Regional (FEDER) through Project No. TEC 2014-53088-C3-1-R.Cutanda-Henriquez, V.; Garcia Chocano, VM.; Sánchez-Dehesa Moreno-Cid, J. (2017). Viscothermal Losses in Double-Negative Acoustic Metamaterials. Physical Review Applied. 8(1):014029-1-014029-12. doi:10.1103/PhysRevApplied.8.014029S014029-1014029-128

Comparative analysis and fusion of spatiotemporal information for footstep recognition

Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. R. Vera-Rodriguez, J. S. D. Mason, J. Fierrez, and J. Ortega-Garcia, "Comparative analysis and fusion of spatiotemporal information for footstep recognition", Pattern Analysis and Machine Intelligence, IEEE Transaction, vol. 35, no. 4, pp. 823-834, August 2012Footstep recognition is a relatively new biometric which aims to discriminate people using walking characteristics extracted from floor-based sensors. This paper reports for the first time a comparative assessment of the spatiotemporal information contained in the footstep signals for person recognition. Experiments are carried out on the largest footstep database collected to date, with almost 20,000 valid footstep signals and more than 120 people. Results show very similar performance for both spatial and temporal approaches (5 to 15 percent EER depending on the experimental setup), and a significant improvement is achieved for their fusion (2.5 to 10 percent EER). The assessment protocol is focused on the influence of the quantity of data used in the reference models, which serves to simulate conditions of different potential applications such as smart homes or security access scenarios.Ruben Vera-Rodriguez, Julian Fierrez and Javier Ortega Garcia are supported by projects Contexts (S2009/TIC-1485), Bio-Challenge (TEC2009-11186), TeraSense (CSD2008-00068) and ‘Catedra UAM-Telefonica’

Perdas na colheita na cultura da soja.

bitstream/item/79567/1/comunicado-271.pd

Design of a transverse flux machine for power generation from seawaves

In this paper, we present a transverse flux linear generator. We investigate the possibility to use this generator to extract energy from seawaves. We propose an optimization procedure that allows us to obtain an optimized design of the generator. The optimized design of the converter shows a power generation capability index much higher than other renewable systems

Redirection and Splitting of Sound Waves by a Periodic Chain of Thin Perforated Cylindrical Shells

[EN] The scattering of sound by finite and infinite chains of equally spaced perforated metallic cylindrical shells in an ideal (inviscid) and viscous fluid is theoretically studied using rigorous analytical and numerical approaches. Because of perforations, a chain of thin shells is practically transparent for sound within a wide range of frequencies. It is shown that strong scattering and redirection of sound by 90° may occur only for a discrete set of frequencies (Wood¿s anomalies) where the leaky eigenmodes are excited. The spectrum of eigenmodes consists of antisymmetric and symmetric branches with normal and anomalous dispersion, respectively. The antisymmetric eigenmode turns out to be a deaf mode, since it cannot be excited at normal incidence. However, at slightly oblique incidence, both modes can be resonantly excited at different but close frequencies. The symmetric mode, due to its anomalous dispersion, scatters sound in the ¿wrong¿ direction. This property may find an application for the splitting of the two resonant harmonics of the incoming signal into two beams propagating along the chain in the opposite directions. A chain of perforated cylinders may also be used as a passive antenna that detects the direction to the incoming signal by measuring the frequencies of the waves excited in the chain. Calculations are presented for aluminum shells in viscous air where the effects of anomalous scattering, redirection, and signal splitting are well manifested.A. K. acknowledges support from Programa de Apoyo a la Investigacion y Desarrollo (PAID-02-15) de la Universitat Politecnica de Valencia. A. B., F. C., and J. S.-D. acknowledge the support by the Ministerio de Economia y Competitividad of the Spanish government and the European Union Fondo Europeo de Desarrollo Regional (FEDER) through Project No. TEC2014-53088-C3-1-R. The authors are thankful to Michael R. Haberman for fruitful discussion regarding possible applications of the periodic chain of a perforated shell in the processing of acoustic signals.Bozhko, A.; Sánchez-Dehesa Moreno-Cid, J.; Cervera Moreno, FS.; Krokhin, A. (2017). Redirection and Splitting of Sound Waves by a Periodic Chain of Thin Perforated Cylindrical Shells. Physical Review Applied. 7(6):064034-1-064034-13. doi:10.1103/PhysRevApplied.7.064034S064034-1064034-137

Avaliação da incidência de vírus em acessos de pimenta em campo.

Resumo 854-