4,525 research outputs found
Introducción de las técnicas de modelización para el estudio de la física y de las matemáticas en los primeros cursos de las carreras técnicas
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
Introducción de las técnicas de modelización para el estudio de la física y de las matemáticas en los primeros cursos de las carreras técnicas
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
Evidences of evanescent Bloch waves in Phononic Crystals
We show both experimentally and theoretically the evanescent behaviour of
modes in the Band Gap (BG) of finite Phononic Crystal (PC). Based on
experimental and numerical data we obtain the imaginary part of the wave vector
in good agreement with the complex band structures obtained by the Extended
Plane Wave Expansion (EPWE). The calculated and measured acoustic field of a
localized mode out of the point defect inside the PC presents also evanescent
behaviour. The correct understanding of evanescent modes is fundamental for
designing narrow filters and wave guides based on Phononic Crystals with
defects.Comment: 8 pages, 3 figure
Self-organization of ultrasound in viscous fluids
We report the theoretical and experimental demonstration of pattern formation
in acoustics. The system is an acoustic resonator containing a viscous fluid.
When the system is driven by an external periodic force, the ultrasonic field
inside the cavity experiences different pattern-forming instabilities leading
to the emergence of periodic structures. The system is also shown to possess
bistable regimes, in which localized states of the ultrasonic field develop.
The thermal nonlinearity in the viscous fluid, together with the
far-from-equilibrium conditions, are is the responsible of the observed
effects
Bistable and dynamic states of parametrically excited ultrasound in a fluid-filled cavity
In this paper we have considered the problem of parametric sound generation
in an acoustic resonator flled with a fluid, taking explicitely into account
the influence of the nonlinearly generated second harmonic. A simple model is
presented, and its stationary solutions obtained. The main feature of these
solutions is the appearance of bistable states of the fundamental field
resulting from the coupling to the second harmonic. An experimental setup was
designed to check the predictions of the theory. The results are consistent
with the predicted values for the mode amplitudes and parametric thresholds. At
higher driving values a self-modulation of the amplitudes is observed. We
identify this phenomenon with a secondary instability previously reported in
the frame of the theoretical model.Comment: 5 figures. Submitted to JAS
From stationary to remote: Employee risks at pandemic migration of workplaces
The first lockdown due to COVID-19 in the year 2020 created a particular scenario that forced a change to telework among diverse professions and social groups. This article presents the results of research carried out among samples of Polish, Lithuanian and Spanish remote workers concerning working conditions in organizations and at home, and the potential impact of some professional hazards from home-based telework. On the contrary to earlier published papers on pandemic-induced telework that focused on how the limitations at home of first-time remote workers impacted on their well-being and work–family balance, our research contributes to a more recent endeavor that focuses the analysis on the work design perspective. The results of the survey indicate that employees felt more stressed and in conflict at their remote workstations when they had to telework during the lockdown, and that this negative output was significantly related to the deterioration of some working dimensions like space, quality and design but not to the perception of professional hazards from home-based telework. According to our research, the forced situation seemed not to be a favorable factor for implementing changes in light of the insufficient technical and organizational preparation of employers as well as the employees’ mental preparation. It should be necessary to update sequentially the results of the epidemic-induced telework and conduct research for various stages of the pandemic and the subsequent economic recovery. This could help popularize remote work as one of the tools of the labor market in the future and as a tool for treating labor resources as an element of sustainable development. © 2021 by the authors. Licensee MDPI, Basel, Switzerland
Evanescent modes in Sonic Crystals: Complex relation dispersion and supercell approximation
Evanescent modes in complete sonic crystals (SC) and SC with point defects
are reported both theoretically and experimentally in this paper. Plane wave
expansion (PWE) and, in general, methods have been used to
calculate band structures showing gaps that have been interpreted as ranges of
frequencies where no real exists. In this work, we extend PWE to solve the
complex problem applied to SC, introducing the supercell
approximation for studying one vacancy. Explicit matrix formulation of the
equations is given. This method enables the calculation of complex
band structures, as well as enabling an analysis of the propagating modes
related with real values of the function , and the evanescent modes
related with imaginary values of . This paper shows theoretical
results and experimental evidences of the evanescent behavior of modes inside
the SC band gap. Experimental data and numerical results using the finite
elements method are in very good agreement with the predictions obtained using
the method.Comment: 15 pages, 3 figure
Wave focusing using symmetry matching in axisymmetric acoustic gradient index lenses
Copyright 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.
The following article appeared in Romero García, V.; Cebrecos Ruiz, A.; Picó Vila, R.; Sánchez Morcillo, VJ.; García-Raffi, LM.; Sánchez Pérez, JV. (2013). Wave focusing using symmetry matching in axisymmetric acoustic gradient index lenses. Applied Physics Letters. 103(26):264106-264106. doi:10.1063/1.4860535 and may be found at http://scitation.aip.org/The symmetry matching between the source and the lens results in fundamental interest for lensing applications. In this work, we have modeled an axisymmetric gradient index (GRIN) lens made of rigid toroidal scatterers embedded in air considering this symmetry matching with radially symmetric sources. The sound amplification obtained in the focal spot of the reported lens (8.24 dB experimentally) shows the efficiency of the axisymmetric lenses with respect to the previous Cartesian acoustic GRIN lenses. The axisymmetric design opens new possibilities in lensing applications in different branches of science and technology.The work was supported by Spanish Ministry of Science and Innovation and European Union FEDER through Project Nos. FIS2011-29734-C02-01 and -02 and PAID 2012/253. V. R. G. is grateful for the support of post-doctoral contracts of the UPV CEI-01-11.Romero García, V.; Cebrecos Ruiz, A.; Picó Vila, R.; Sánchez Morcillo, VJ.; García-Raffi, LM.; Sánchez Pérez, JV. (2013). Wave focusing using symmetry matching in axisymmetric acoustic gradient index lenses. Applied Physics Letters. 103(26):264106-264106. https://doi.org/10.1063/1.4860535S26410626410610326John, S. (1987). Strong localization of photons in certain disordered dielectric superlattices. Physical Review Letters, 58(23), 2486-2489. doi:10.1103/physrevlett.58.2486Yablonovitch, E. (1987). Inhibited Spontaneous Emission in Solid-State Physics and Electronics. 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Physical Review B, 84(2). doi:10.1103/physrevb.84.024305Li, Y., Liang, B., Tao, X., Zhu, X., Zou, X., & Cheng, J. (2012). Acoustic focusing by coiling up space. Applied Physics Letters, 101(23), 233508. doi:10.1063/1.4769984Yang, S., Page, J. H., Liu, Z., Cowan, M. L., Chan, C. T., & Sheng, P. (2004). Focusing of Sound in a 3D Phononic Crystal. Physical Review Letters, 93(2). doi:10.1103/physrevlett.93.024301Luo, C., Johnson, S. G., Joannopoulos, J. D., & Pendry, J. B. (2002). All-angle negative refraction without negative effective index. Physical Review B, 65(20). doi:10.1103/physrevb.65.201104Ke, M., Liu, Z., Qiu, C., Wang, W., Shi, J., Wen, W., & Sheng, P. (2005). Negative-refraction imaging with two-dimensional phononic crystals. Physical Review B, 72(6). doi:10.1103/physrevb.72.064306SAMIMY, M., KIM, J.-H., KEARNEY-FISCHER, M., & SINHA, A. (2010). Acoustic and flow fields of an excited high Reynolds number axisymmetric supersonic jet. Journal of Fluid Mechanics, 656, 507-529. doi:10.1017/s0022112010001357Choe, Y., Kim, J. W., Shung, K. K., & Kim, E. S. (2011). Microparticle trapping in an ultrasonic Bessel beam. Applied Physics Letters, 99(23), 233704. doi:10.1063/1.3665615Baac, H. W., Ok, J. G., Maxwell, A., Lee, K.-T., Chen, Y.-C., Hart, A. J., … Guo, L. J. (2012). Carbon-Nanotube Optoacoustic Lens for Focused Ultrasound Generation and High-Precision Targeted Therapy. Scientific Reports, 2(1). doi:10.1038/srep00989Chang, T. M., Dupont, G., Enoch, S., & Guenneau, S. (2012). Enhanced control of light and sound trajectories with three-dimensional gradient index lenses. New Journal of Physics, 14(3), 035011. doi:10.1088/1367-2630/14/3/035011Sanchis, L., Yánez, A., Galindo, P. L., Pizarro, J., & Pastor, J. M. (2010). Three-dimensional acoustic lenses with axial symmetry. Applied Physics Letters, 97(5), 054103. doi:10.1063/1.3474616Gomez-Reino, C., Perez, M. V., & Bao, C. (2002). 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