Search results for " acoustic"

The Soliton Concept in Lattice Dynamics

1996

In previous chapters we have considered nonlinear waves in the macroworld. We have examined different systems which provide the simplest examples of onedimensional systems or devices, where the localized waves or pulses called solitons can be simply and coherently created, easily observed, and manipulated on a macroscopic scale. At the microscopic level the localized nonlinear wave modes have a spatial extension ranging from less than a few microns to a few angstroms. These excitations, which correspond to large-amplitude atomic or molecular motions, are mainly created by thermal processes, sometimes by some external stimulus; their experimental manifestation is indirect; their observation …

Spatiotemporal carrier dynamics in quantum wells under surface acoustic waves

2004

We present a theoretical study of transport and recombination of electrons and holes in quantum wells under the piezoelectric field induced by a surface acoustic wave (SAW). Our model calculations, which include free carriers and excitons in the framework of the drift-diffusion equations, describe the spatial and time dependences of the photoluminescence intensity on excitation density and SAW amplitude, and show overall agreement with recent microphotoluminescence experiments performed on GaAs/(Al,Ga)As quantum wells and quantum wires.

Rich dynamics and anticontrol of extinction in a prey-predator system

2019

This paper reveals some new and rich dynamics of a two-dimensional prey-predator system and to anticontrol the extinction of one of the species. For a particular value of the bifurcation parameter, one of the system variable dynamics is going to extinct, while another remains chaotic. To prevent the extinction, a simple anticontrol algorithm is applied so that the system orbits can escape from the vanishing trap. As the bifurcation parameter increases, the system presents quasiperiodic, stable, chaotic and also hyperchaotic orbits. Some of the chaotic attractors are Kaplan-Yorke type, in the sense that the sum of its Lyapunov exponents is positive. Also, atypically for undriven discrete sys…

Modeling vibrating panels excited by a non-homogeneous turbulent boundary layer

2021

Abstract Predicting the vibration response of an elastic structure excited by a turbulent flow is of interest for the civil and military transportation sector. The models proposed in the literature are generally based on the assumption that the turbulent boundary layer (noted TBL in the following) exciting the structure is spatially homogeneous. However, this assumption is not always fulfilled in practice, in particular when the excited area is close to the starting point of the TBL or with curved structures. To overcome this issue, this work proposes to extend two approaches generally used for dealing with homogeneous TBL, namely the spatial and the wavenumber approaches. The extension of …

Acoustic phonons for coherent photon control in semiconductor structures

2007

We present a novel concept for acousto-optical modulation in waveguide (WG) structures using coherent phonons in the form of surface acoustic waves (SAWs). Here, a SAW impinging perpendicular to a waveguide structure induces a change in phase of the light propagating through it, which is translated into a transmission intensity modulation by using the WG as an arm of a Mach-Zehnder interferometer (MZI). We show that the modulation becomes strongly enhanced if the SAW induces phase changes of opposite sign in the MZI arms. Very compact modulators with an interaction length between the optical and acoustic waves of approx. 15 µm have been fabricated using focusing acoustic transducers to gene…

A general nonexistence result for inhomogeneous semilinear wave equations with double damping and potential terms

2021

Abstract We investigate the large-time behavior of solutions for a class of inhomogeneous semilinear wave equations involving double damping and potential terms. Namely, we first establish a general criterium for the absence of global weak solutions. Next, some special cases of potential and inhomogeneous terms are studied. In particular, when the inhomogeneous term depends only on the variable space, the Fujita critical exponent and the second critical exponent in the sense of Lee and Ni are derived.

Approximate analytical mean-square response of an impacting stochastic system oscillator with fractional damping

2017

The paper deals with the stochastic dynamics of a vibroimpact single-degree-of-freedom system under a Gaussian white noise. The system is assumed to have a hard type impact against a one-sided motionless barrier, located at the system's equilibrium. The system is endowed with a fractional derivative element. An analytical expression for the system's mean squared response amplitude is presented and compared with the results of numerical simulations.

Adiabatic charge pumping in carbon nanotube quantum dots.

2008

We investigate charge pumping in carbon nanotube quantum dots driven by the electric field of a surface acoustic wave. We find that, at small driving amplitudes, the pumped current reverses polarity as the conductance is tuned through a Coulomb blockade peak using a gate electrode. We study the behavior as a function of wave amplitude, frequency, and direction and develop a model in which our results can be understood as resulting from adiabatic charge redistribution between the leads and quantum dots on the nanotube.

Erratum: “Technique for routine output verification of Leipzig applicators with a well chamber” [Med. Phys. 33, 16-20 (2006)]

2006

New constraints on coupled dark energy from the Planck satellite experiment

2013

We present new constraints on coupled dark energy from the recent measurements of the cosmic microwave background anisotropies from the Planck satellite mission. We found that a coupled dark energy model is fully compatible with the Planck measurements, deriving a weak bound on the dark matter-dark energy coupling parameter xi = -0.49(-0.31)(+0.19) at 68% C.L. Moreover if Planck data are fitted to a coupled dark energy scenario, the constraint on the Hubble constant is relaxed to H-0 = 72.1(-2.3)(+3.2) km/s/Mpc, solving the tension with the Hubble Space Telescope (HST) value. We show that a combined PLANCK + HST analysis provides significant evidence for coupled dark energy finding a nonzer…