Search results for "ACOUSTIC"
showing 10 items of 1590 documents
Microscopic carrier dynamics in quantum wells modulated by high-frequency lateral fields
2002
Abstract We have investigated the dynamics of photogenerated carriers in GaAs quantum wells under the influence of high-frequency fields produced by metal gratings and by surface acoustic waves (SAW's) using spatially and time-resolved photoluminescence (PL). The frequency and phase of the PL oscillations induced by the high-frequency field yield information about the spatial distribution of the carriers and, in the case of SAW's, about the band-gap modulation induced by the SAW strain.
Acoustic Wave Properties in Footpoints of Coronal Loops in 3D MHD Simulations
2021
Acoustic waves excited in the photosphere and below might play an integral part in the heating of the solar chromosphere and corona. However, it is yet not fully clear how much of the initially acoustic wave flux reaches the corona and in what form. We investigate the wave propagation, damping, transmission, and conversion in the lower layers of the solar atmosphere using 3D numerical MHD simulations. A model of a gravitationally stratified expanding straight coronal loop, stretching from photosphere to photosphere, is perturbed at one footpoint by an acoustic driver with a period of 370 seconds. For this period acoustic cutoff regions are present below the transition region (TR). About 2% …
A dynamical dark energy model with a given luminosity distance
2011
It is assumed that the current cosmic acceleration is driven by a scalar field, the Lagrangian of which is a function of the kinetic term only, and that the luminosity distance is a given function of the red-shift. Upon comparison with Baryon Acoustic Oscillations (BAOs) and Cosmic Microwave Background (CMB) data the parameters of the models are determined, and then the time evolution of the scalar field is determined by the dynamics using the cosmological equations. We find that the solution is very different than the corresponding solution when the non-relativistic matter is ignored, and that the universe enters the acceleration era at larger red-shift compared to the standard $\Lambda CD…
Acousto-optical multiple interference switches
2007
The authors introduce an alternative approach for acousto-optical light control based on the interference of light propagating through several waveguides, each subjected to a periodic refractive index modulation induced by a surface acoustic wave. The feasibility of the concept is demonstrated by the realization of an optical switch for arbitrary time intervals with an on/off contrast ratio of 20.
Lärm als Umweltproblem
1976
Noise as an Environmental Problem. Anatomical structure and physiological function of the human ear are described. It is shown that constant noise stress leads to damage of certain parts of the inner ear. These damages proceed characteristically and may be diagnosed relatively early by means of audiometric tests. VDI-instructions 2058 (sheet 2) prescribes screening-tests for an earliest possible detection of incipient noise damage. In addition to ear-damaging effects of noise there have also been recorded physiological reactions under noise influence. Such disturbances, however, cannot as yet be described as an “Extraaural disease”. On the other hand, the fact that high sound intensities of…
High-overtone bulk acoustic resonator as passive ground penetrating RADAR cooperative targets
2013
International audience; RAdio-frequency Detection And Ranging instruments—RADARs—are widely used for applications aimed at measuring passive target velocity or ranging for various metrology applications such as ground position and localization. Within the context of using piezoelectric acoustic passive sensors as cooperative targets to RADARs probed through a radiofrequency link, this paper reports on investigating the compatibility of narrowband resonator architectures with the classical operation mode of wideband RADAR instruments. Since single mode resonators are hardly compatible due to the limited bandwidth of their spectrum, the investigation has been extended to High-overtone Bulk Ac…
Mechanical models of amplitude and frequency modulation
2005
This paper presents some mechanical models for amplitude and frequency modulation. The equations governing both modulations are deduced alongside some necessary approximations. Computer simulations of the models are carried out by using available educational software. Amplitude modulation is achieved by using a system of two weakly coupled pendulums, whereas the frequency modulation is obtained by using a pendulum of variable length. Under suitable conditions (small oscillations, appropriate initial conditions, etc) both types of modulation result in significantly accurate and visualized simulations.
Current-induced H-shaped-skyrmion creation and their dynamics in the helical phase
2021
Abstract Inevitable for the basic principles of skyrmion racetrack-like applications is not only their confined motion along one-dimensional channels but also their controlled creation and annihilation. Helical magnets have been suggested to naturally confine the motion of skyrmions along the tracks formed by the helices, which also allow for high-speed skyrmion motion. We propose a protocol to create topological magnetic structures in a helical background. We furthermore analyse the stability and current-driven motion of the skyrmions in a helical background with in-plane uniaxial anisotropy fixing the orientation of the helices.
Waveguide-QED-based measurement of a reservoir spectral density
2015
The spectral density (SD) function has a central role in the study of open quantum systems (OQSs). We discover a method allowing for a "static" measurement of the SD - i.e., it requires neither the OQS to be initially excited nor its time evolution tracked in time - which is not limited to the weak-coupling regime. This is achieved through one-dimensional photon scattering for a zero-temperature reservoir coupled to the OQS via the rotating wave approximation. We find that the SD profile is a universal simple function of the photon's reflectance and transmittance. As such, it can be straightforwardly inferred from photon's reflection and transmission spectra.
Resonance energy transfer between two atoms in a conducting cylindrical waveguide
2018
We consider the energy transfer process between two identical atoms placed inside a perfectly conducting cylindrical waveguide. We first introduce a general analytical expression of the energy transfer amplitude in terms of the electromagnetic Green's tensor; we then evaluate it in the case of a cylindrical waveguide made of a perfect conductor, for which analytical forms of the Green's tensor exist. We numerically analyse the energy transfer amplitude when the radius of the waveguide is such that the transition frequency of both atoms is below the lower cutoff frequency of the waveguide, so that the resonant photon exchange is strongly suppressed. We consider both cases of atomic dipoles p…