المؤلفون: Skelton, E. A.¹ e.a.skelton@imperial.ac.uk, Craster, R. V.¹ r.craster@imperial.ac.uk, AColombi, A.¹ a.colombi@imperial.ac.uk, Colquitt, D. J.² d.colquitt@liverpool.ac.uk

المصدر: New Journal of Physics. May2018, Vol. 20 Issue 5, p1-13. 13p.

مصطلحات موضوعية: *ELASTIC plates & shells, *ELASTIC wave propagation, *BIFUNCTIONAL catalysis, *DISPERSION (Atmospheric chemistry), *ATMOSPHERIC chemistry

مستخلص: Weconsider the propagation and mode conversion of flexural-acoustic waves along a fluid-loaded graded array of elastic resonators, forming a metasurface. The multi-physics nature of the problem, coupling two disparate physical systems, brings both challenges and novel features not previously seen in so-called bifunctional metamaterials. In particular, by using an appropriately designed graded array of resonators, we show that it is possible to employ our metasurface to mode-convert sub-sonic surface flexural waves into bulk acoustic waves and vice-versa; transferring energy between two very different physical systems. Whilst the sub-sonic mechanical surface wave is dispersive, the bulk acoustic wave is dispersionless and radiates energy at infinity. We also show that this bifunctional metasurface is capable of exhibiting the classical effect of rainbow trapping for sub-sonic surface waves. [ABSTRACT FROM AUTHOR]

المؤلفون: Furutani, K, Tononi, A, Salasnich, L

المصدر: New Journal of Physics; Apr2021, Vol. 23 Issue 4, p1-10, 10p

مصطلحات موضوعية: BOSE-Einstein gas, SUPERFLUIDITY, SPEED of sound, TRANSITION temperature, ACOUSTIC wave propagation, SOUND measurement

مستخلص: We theoretically investigate sound modes in a weakly-interacting collisional Bose gas in D dimensions. Using the Landau's two-fluid hydrodynamics and working within the Bogoliubov theory, we observe the hybridization of the first and second sound modes for D ⩾ 2. To model the recent measurements of the sound velocities in 2D, obtained in the weakly-interacting regime and around the Berezinskii–Kosterlitz–Thouless transition temperature, we derive a refined calculation of the superfluid density, finding a fair agreement with the experiment. In the 1D case, for which experimental results are currently unavailable, we find no hybridization, triggering the necessity of future investigations. Our analysis provides a systematic understanding of sound propagation in a collisional weakly-interacting Bose gas in D dimensions. [ABSTRACT FROM AUTHOR]

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المؤلفون: Matheus I N Rosa, Massimo Ruzzene

المصدر: New Journal of Physics, Vol 22, Iss 5, p 053004 (2020)

مصطلحات موضوعية: meta materials, non-Hermitian systems, wave amplification, non-reciprocal wave propagation, topological modes, Science, Physics, QC1-999

الوصف: We investigate non-Hermitian elastic lattices characterized by non-local feedback interactions. In one-dimensional lattices, proportional feedback produces non-reciprocity associated with complex dispersion relations characterized by gain and loss in opposite propagation directions. For non-local controls, such non-reciprocity occurs over multiple frequency bands characterized by opposite non-reciprocal behavior. The dispersion topology is investigated with focus on winding numbers and non-Hermitian skin effect, which manifests itself through bulk modes localized at the boundaries of finite lattices. In two-dimensional lattices, non-reciprocity is associated with directional wave amplification. Moreover, the combination of skin effect in two directions produces modes that are localized at the corners of finite two-dimensional lattices. Our results describe fundamental properties of non-Hermitian elastic lattices, and suggest new possibilities for the design of meta materials with novel functionalities related to selective wave filtering, amplification and localization. The considered non-local lattices also provide a platform for the investigation of topological phases of non-Hermitian systems.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1367-2630Test

الوصول الحر: https://doaj.org/article/86fb2bf83b3047ff86c5f3acd609f899Test

المؤلفون: G Corona-Patricio, U Kuhl, F Mortessagne, P Vignolo, L Tessieri

المصدر: New Journal of Physics, Vol 21, Iss 7, p 073041 (2019)

مصطلحات موضوعية: Anderson localization, wave propagation, bi-dimensional systems, electronic transmission, Science, Physics, QC1-999

الوصف: We consider two bidimensional random models characterised by the following features: (a) their Hamiltonians are separable in polar coordinates and (b) the random part of the potential depends either on the angular coordinate or on the radial one, but not on both. The disorder correspondingly localises the angular or the radial part of the eigenfunctions. We analyse the analogies and the differences which exist between the selected 2D models and their 1D counterparts. We show how the analogies allow one to use correlated disorder to design a localisation length with pre-defined energy dependence and to produce directional localisation of the wavefunctions in models with angular disorder. We also discuss the importance of finite-size and resonance effects in shaping the eigenfunctions of the model with angular disorder; for the model with disorder associated to the radial variable we show under what conditions the localisation length coincides with the expression valid in the 1D case.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1367-2630Test

الوصول الحر: https://doaj.org/article/9ac4e47f6ef04aa5b48f592641839b2aTest

المؤلفون: A Nguyen, P González de Alaiza Martínez, I Thiele, S Skupin, L Bergé

المصدر: New Journal of Physics, Vol 20, Iss 3, p 033026 (2018)

مصطلحات موضوعية: terahertz generation, chirp, plasma, filamentation, wave propagation, 42.65.Re, Science, Physics, QC1-999

الوصف: We numerically study the influence of chirping and delaying several ionizing two-color light pulses in order to engineer terahertz (THz) wave generation in air. By means of comprehensive 3D simulations, it is shown that two chirped pulses can increase the THz yield when they are separated by a suitable time delay for the same laser energy in focused propagation geometry. To interpret these results, the local current theory is revisited and we propose an easy, accessible all-optical criterion that predicts the laser-to-THz conversion efficiencies given any input laser spectrum. In the filamentation regime, numerical simulations display evidence that a chirped pulse is able to produce more THz radiation due to propagation effects, which maintain the two colors of the laser field more efficiently coupled over long distances. A large delay between two pulses promotes multi-peaked THz spectra as well as conversion efficiencies above 10 ^−4 .

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1367-2630Test

الوصول الحر: https://doaj.org/article/bf176ae1bb4a481eb2d27385a41bc41dTest

المؤلفون: Wiktor Walasik, Chicheng Ma, Natalia M Litchinitser

المصدر: New Journal of Physics, Vol 19, Iss 7, p 075002 (2017)

مصطلحات موضوعية: waveguides, couplers, and arrays, wave propagation, transmission and absorption, charge conjugation, Science, Physics, QC1-999

الوصف: Despite the benefits which the directional couplers based on parity-time symmetric systems may offer to the field of integrated optics, the realization of such couplers relies on rather strict design constraints on the waveguide parameters. Here, we analytically and numerically investigate directional couplers built of dissimilar waveguides that do not fulfill the parity-time symmetry. Nevertheless, we demonstrate that for properly designed parameters, at least one mode of such couplers shows a behavior similar to the one observed in parity-time symmetric systems. We find an analytical condition relating the gain and loss that enables such a behavior. Moreover, if the individual waveguides composing the dissimilar coupler are designed such that the propagation constants of their modes are identical, the behavior of both super-modes supported by the coupler resembles that of the parity-time symmetric systems.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1367-2630Test

الوصول الحر: https://doaj.org/article/1b330e0e8eca466d9b86fae32b3e964eTest

المؤلفون: Y Liu, B Vial, S A R Horsley, T G Philbin, Y Hao

المصدر: New Journal of Physics, Vol 19, Iss 7, p 073010 (2017)

مصطلحات موضوعية: inverse problem, wave optics, electromagnetic wave propagation, 41.20.Jb, 42.25.-p, 02.30.Zz, Science, Physics, QC1-999

الوصف: In this article we propose a new design methodology allowing us to control both amplitude and phase of electromagnetic waves from a cylindrical incident wave. This results in isotropic materials and does not resort to transformation optics or its quasi-conformal approximations. Our method leads to two-dimensional isotropic, inhomogeneous material profiles of permittivity and permeability, to which a general class of scattering-free wave solutions arise. Our design is based on the separation of the complex wave solution into amplitude and phase. We give two types of examples to validate our methodology.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1367-2630Test

الوصول الحر: https://doaj.org/article/5034f39b453143f3bf037bfb3d410bc8Test

المؤلفون: Xin Fang, Jihong Wen, Bernard Bonello, Jianfei Yin, Dianlong Yu

المصدر: New Journal of Physics, Vol 19, Iss 5, p 053007 (2017)

مصطلحات موضوعية: nonlinear acoustic metamaterial, wave propagation, band structure, nonlinear dynamics, chaos, Science, Physics, QC1-999

الوصف: The propagation of waves in nonlinear acoustic metamaterial (NAM) is fundamentally different from that in conventional linear ones. In this article we consider two one-dimensional (1D) NAM systems featuring respectively a diatomic and a tetratomic meta unit-cell. We investigate the attenuation of waves, band structures, and bifurcations to demonstrate novel nonlinear effects, which can significantly expand the bandwidth for elastic wave suppression and cause nonlinear wave phenomena. The harmonic averaging approach, continuation algorithm, and Lyapunov exponents (LEs) are combined to study the frequency responses, nonlinear modes, bifurcations of periodic solutions, and chaos. The nonlinear resonances are studied, and the influence of damping on hyperchaotic attractors is evaluated. Moreover, a ‘quantum’ behavior is found between the low-energy and high-energy orbits. This work provides a theoretical base for furthering understandings and applications of NAMs.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1367-2630Test

الوصول الحر: https://doaj.org/article/a6db674b73724cc596a49c0871fe3e9dTest

المؤلفون: Armen G Hayrapetyan, S P Klevansky, Jörg B Götte

المصدر: New Journal of Physics, Vol 19, Iss 10, p 105002 (2017)

مصطلحات موضوعية: amplitude and frequency modulations, PT symmetry in optics, time-varying wave propagation, analytical solutions to Maxwell’s equations, Science, Physics, QC1-999

الوصف: We study the impact of a spatially homogeneous yet non-stationary dielectric permittivity on the dynamical and spectral properties of light. Our choice of potential is motivated by the interest in ${ \mathcal P }{ \mathcal T }$ -symmetric systems as an extension of quantum mechanics. Because we consider a homogeneous and non-stationary medium, ${ \mathcal P }{ \mathcal T }$ symmetry reduces to time-reversal symmetry in the presence of balanced gain and loss. We construct the instantaneous amplitude and angular frequency of waves within the framework of Maxwell’s equations and demonstrate the modulation of light amplification and attenuation associated with the well-defined temporal domains of gain and loss , respectively. Moreover, we predict the splitting of extrema of the angular frequency modulation and demonstrate the associated shrinkage of the modulation period. Our theory can be extended for investigating similar time-dependent effects with matter and acoustic waves in ${ \mathcal P }{ \mathcal T }$ -symmetric structures.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1367-2630Test

الوصول الحر: https://doaj.org/article/210be308292d4eb686f078ef32016de6Test

المؤلفون: Peter Hansinger, Philipp Töpfer, Nikolay Dimitrov, Daniel Adolph, Dominik Hoff, Tim Rathje, A Max Sayler, Alexander Dreischuh, Gerhard G Paulus

المصدر: New Journal of Physics, Vol 19, Iss 2, p 023040 (2017)

مصطلحات موضوعية: wave propagation, optical and dielectric properties, ultrafast processes, photoionization, carrier-envelope phase, refractive index dispersion, Science, Physics, QC1-999

الوصف: We introduce a novel method for direct and accurate measurement of refractive index dispersion based on carrier-envelope phase detection of few-cycle laser pulses, exploiting the difference between phase and group velocity in a dispersive medium. In a layout similar to an interferometer, two carrier-envelope phasemeters are capable of measuring the dispersion of a transparent or reflective sample, where one phasemeter serves as the reference and the other records the influence of the sample. Here we report on proof-of-principle measurements that already reach relative uncertainties of a few 10 ^−4 . Further development is expected to allow for unprecedented precision.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1367-2630Test

الوصول الحر: https://doaj.org/article/565392ca034a487c9bd17b1e82c4eed5Test