Separability and Nonseparability of Elastic States in Arrays of One-Dimensional Elastic Waveguides

We show that the directional projection of longitudinal waves propagating in a parallel array of N elastically coupled waveguides can be described by a nonlinear Dirac-like equation in a 2N dimensional exponential space. This space spans the tensor product Hilbert space of the two-dimensional subspaces of N uncoupled waveguides grounded elastically to a rigid substrate (called φ -bits). The superposition of directional states of a φ -bit is analogous to that of a quantum spin. We can construct tensor product states of the elastically coupled system that are nonseparable on the basis of tensor product states of N φ -bits. We propose a system of coupled waveguides in a ring configuration that supports these nonseparable states

Acoustic channel drop tunneling in a phononic crystal

International audienceWe study both theoretically and experimentally the possibility of resonant tunneling of acoustic waves between two parallel guides created in a phononic crystal composed of steel cylinders in water. In the absolute bandgap of the phononic crystal, ranging from 250 to 325 kHz, a full transmission band exits for propagation inside a straight wave guide. We show that the transfer of a particular wavelength can occur between two parallel wave guides coupled together through an appropriate coupling structure. The latter is composed of isolated cavities interacting with stubs located at the sides of the wave guides

Level repulsion and evanescent waves in sonic crystals

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(¿) problem reveal a complete interpretation of the propagation properties of these systems. The prediction of evanescent modes, nonpredicted by classical ¿(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. © 2011 American Physical Society.V.R.G. and L.M.G.R. would like to thank the facilities provided by the IEMN UMR CNRS 8520. L.M.G.R. would like to thank the UPV for Grant No. PAID-00-11. V.R.G. is grateful for the support contracts of the UPV CEI-01-11. This work was supported by MCI Secretaria de Estado de Investigacion (Spanish government) and the FEDER funds, under Grant No. MAT2009-09438.Romero García, V.; Vasseur, J.; Hladky Hennion, AC.; García Raffi, LM.; Sánchez Pérez, JV. (2011). Level repulsion and evanescent waves in sonic crystals. Physical Review B. 84:2123021-2123024. https://doi.org/10.1103/PhysRevB.84.212302S212302121230248

Neutrality and the Response of Rare Species to Environmental Variance

Neutral models and differential responses of species to environmental heterogeneity offer complementary explanations of species abundance distribution and dynamics. Under what circumstances one model prevails over the other is still a matter of debate. We show that the decay of similarity over time in rocky seashore assemblages of algae and invertebrates sampled over a period of 16 years was consistent with the predictions of a stochastic model of ecological drift at time scales larger than 2 years, but not at time scales between 3 and 24 months when similarity was quantified with an index that reflected changes in abundance of rare species. A field experiment was performed to examine whether assemblages responded neutrally or non-neutrally to changes in temporal variance of disturbance. The experimental results did not reject neutrality, but identified a positive effect of intermediate levels of environmental heterogeneity on the abundance of rare species. This effect translated into a marked decrease in the characteristic time scale of species turnover, highlighting the role of rare species in driving assemblage dynamics in fluctuating environments

Multiwavelength laser sources for broadband optical access networks

The objective of the proposed research is to develop multiwavelength lasers as cost-efficient sources for broadband optical access networks. Todays telecommunications networks have widely adopted optical fiber as the backbone transmission medium. Optical fiber systems are promising candidates for the broadband access networks to offer high-speed and future-proof services. To harness the available bandwidth in fiber and to meet the ever-growing bandwidth demand, wavelength division multiplexing (WDM) techniques have been investigated. There have been intense research activities for the creation of new low-cost laser sources for such emerging applications. In this context, multiwavelength fiber ring lasers have been significantly investigated as they present many advantages, including simple structure, low-cost, and selectable multiwavelength operation. We propose a new laser system architecture that emits alternate multiwavelength picosecond pulses operating at room temperature. Optical signal generation is based on a single active component, an unbalanced Mach-Zehnder interferometer, inserted in an actively mode-locked erbium-doped fiber ring laser to provide both intensity modulation and wavelength-selective filtering. Time and frequency controls of the light emission are reached by inserting an additional modulator and a periodic filter in the cavity. This approach focuses on the application of multiwavelength lasers as sources for WDM passive optical networks.Ph.D.Committee Chair: Gee-Kung Chang; Committee Co-Chair: John Barry; Committee Member: Ali Adibi; Committee Member: Rick Trebino; Committee Member: Steve McLaughlin; Committee Member: William Rhode

Elastic wave propagation along waveguides in three-dimensional phononic crystals

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Concurrent multiscale model of an atomic crystal coupled with elastic continua

International audienceA methodology based on a Green’s function formalism, which enables the coupling between atomic and continuous systems, is employed to evaluate the dynamical properties of concurrent elastic multiscale models. Boundary conditions satisfying the continuity of displacement and stress across interfaces between a harmonic crystal and continua are insufficient to establish seamless coupling at high frequency. The elastic mismatch in coupled discrete/continuous models is inherently linked to the difference in dispersion of the constitutive media

Second-order sound field during megasonic cleaning of patterned silicon wafers: Application to ridges and trenches

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Acoustic band gaps in fibre composite materials of boron nitride structure

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