Geodesic acoustic mode oscillation in the low frequency range

We studied the amplitude modulation of the radial electric field constructed from the Langmuir probe plasma potential measurements at the edge of the mega-ampere spherical tokamak (MAST). The Empirical Mode Decomposition (EMD) technique was applied, which allowed us to extract fluctuations on temporal scales of plasma turbulence, the Geodesic Acoustic Mode (GAM), and those associated with the residual poloidal flows. This decomposition preserved the nonlinear character of the signal. Hilbert transform (HT) was then used to obtain the amplitude modulation envelope of fluctuations associated with turbulence and with the GAM. We found significant spectral coherence at frequencies between 1–5 kHz, in the turbulence and the GAM envelopes and for the signal representing the low frequency zonal flows (LFZFs). We present the evidence of local and nonlocal, in frequency space, three wave interactions leading to coupling between the GAM and the low frequency (LF) part of the spectrum.

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Evaluation of Special Hearing Aids for Deaf Children

Journal of Speech and Hearing Disorders ◽

10.1044/jshd.3604.527 ◽

1971 ◽

Vol 36 (4) ◽

pp. 527-537 ◽

Cited By ~ 1

Author(s):

Norman P. Erber

Keyword(s):

Hearing Aids ◽

High Frequency ◽

Hearing Aid ◽

Low Frequency ◽

Acoustic Stimulation ◽

Deaf Children ◽

Frequency Range ◽

Frequency Limit ◽

Unpublished Studies ◽

Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

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Dynamic Damping and Stiffness Characteristics of the Rolling Tire

Tire Science and Technology ◽

10.2346/1.2135243 ◽

2001 ◽

Vol 29 (4) ◽

pp. 258-268 ◽

Cited By ~ 12

Author(s):

G. Jianmin ◽

R. Gall ◽

W. Zuomin

Keyword(s):

Dynamic Behavior ◽

Variable Parameter ◽

Low Frequency ◽

Vertical Load ◽

Frequency Range ◽

Inflation Pressure ◽

Vehicle Simulation ◽

Dynamic Damping ◽

Speed Range ◽

Stiffness Characteristics

Abstract A variable parameter model to study dynamic tire responses is presented. A modified device to measure terrain roughness is used to measure dynamic damping and stiffness characteristics of rolling tires. The device was used to examine the dynamic behavior of a tire in the speed range from 0 to 10 km/h. The inflation pressure during the tests was adjusted to 160, 240, and 320 kPa. The vertical load was 5.2 kN. The results indicate that the damping and stiffness decrease with velocity. Regression formulas for the non-linear experimental damping and stiffness are obtained. These results can be used as input parameters for vehicle simulation to evaluate the vehicle's driving and comfort performance in the medium-low frequency range (0–100 Hz). This way it can be important for tire design and the forecasting of the dynamic behavior of tires.

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Sound transmission loss through double glazing windows in low frequency range: comparison between finite element and experimental results

10.26678/abcm.diname2019.din2019-0014 ◽

2019 ◽

Author(s):

Jean-François Deü ◽

Rubens Sampaio

Keyword(s):

Finite Element ◽

Transmission Loss ◽

Low Frequency ◽

Sound Transmission ◽

Experimental Results ◽

Sound Transmission Loss ◽

Frequency Range

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Evaluation of the acoustic performance of polyurethane foams embedded with rock wool fibers at low-frequency range; design and construction

Applied Acoustics ◽

10.1016/j.apacoust.2021.108223 ◽

2021 ◽

Vol 182 ◽

pp. 108223

Author(s):

Behzad Mohammadi ◽

Abdolrasoul Safaiyan ◽

Peymaneh Habibi ◽

Gholamreza Moradi

Keyword(s):

Low Frequency ◽

Polyurethane Foams ◽

Frequency Range ◽

Acoustic Performance ◽

Wool Fibers ◽

Rock Wool ◽

Design And Construction

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An Improved Time Integration Method Based on Galerkin Weak Form with Controllable Numerical Dissipation

Applied Sciences ◽

10.3390/app11041932 ◽

2021 ◽

Vol 11 (4) ◽

pp. 1932

Author(s):

Weixuan Wang ◽

Qinyan Xing ◽

Qinghao Yang

Keyword(s):

High Frequency ◽

Integration Method ◽

Time Integration ◽

Low Frequency ◽

Weak Form ◽

High Accuracy ◽

Numerical Dissipation ◽

Frequency Range ◽

Time Integration Method ◽

Numerical Damping

Based on the newly proposed generalized Galerkin weak form (GGW) method, a two-step time integration method with controllable numerical dissipation is presented. In the first sub-step, the GGW method is used, and in the second sub-step, a new parameter is introduced by using the idea of a trapezoidal integral. According to the numerical analysis, it can be concluded that this method is unconditionally stable and its numerical damping is controllable with the change in introduced parameters. Compared with the GGW method, this two-step scheme avoids the fast numerical dissipation in a low-frequency range. To highlight the performance of the proposed method, some numerical problems are presented and illustrated which show that this method possesses superior accuracy, stability and efficiency compared with conventional trapezoidal rule, the Wilson method, and the Bathe method. High accuracy in a low-frequency range and controllable numerical dissipation in a high-frequency range are both the merits of the method.

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A waveform inversion technique for measuring elastic wave attenuation in cylindrical bars

Geophysics ◽

10.1190/1.1443299 ◽

1992 ◽

Vol 57 (6) ◽

pp. 854-859 ◽

Cited By ~ 6

Author(s):

Xiao Ming Tang

Keyword(s):

Elastic Wave ◽

Wave Attenuation ◽

Waveform Inversion ◽

Finite Size ◽

Low Frequency ◽

Frequency Range ◽

Multiple Reflections ◽

Low Frequencies ◽

The Time Domain ◽

Attenuation Values

A new technique for measuring elastic wave attenuation in the frequency range of 10–150 kHz consists of measuring low‐frequency waveforms using two cylindrical bars of the same material but of different lengths. The attenuation is obtained through two steps. In the first, the waveform measured within the shorter bar is propagated to the length of the longer bar, and the distortion of the waveform due to the dispersion effect of the cylindrical waveguide is compensated. The second step is the inversion for the attenuation or Q of the bar material by minimizing the difference between the waveform propagated from the shorter bar and the waveform measured within the longer bar. The waveform inversion is performed in the time domain, and the waveforms can be appropriately truncated to avoid multiple reflections due to the finite size of the (shorter) sample, allowing attenuation to be measured at long wavelengths or low frequencies. The frequency range in which this technique operates fills the gap between the resonant bar measurement (∼10 kHz) and ultrasonic measurement (∼100–1000 kHz). By using the technique, attenuation values in a PVC (a highly attenuative) material and in Sierra White granite were measured in the frequency range of 40–140 kHz. The obtained attenuation values for the two materials are found to be reliable and consistent.

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A Compact Four-Port Coplanar Antenna Based on an Excitation Switching Reconfigurable Mechanism for Cognitive Radio Applications

Applied Sciences ◽

10.3390/app9153157 ◽

2019 ◽

Vol 9 (15) ◽

pp. 3157 ◽

Cited By ~ 1

Author(s):

O ◽

Jin ◽

Choi

Keyword(s):

Cognitive Radio ◽

High Frequency ◽

Coplanar Waveguide ◽

Low Frequency ◽

Loop Antenna ◽

Ultra Wideband ◽

Frequency Range ◽

Uwb Antenna ◽

High Isolation ◽

Loop Antennas

In this paper, we propose a compact four-port coplanar antenna for cognitive radio applications. The proposed antenna consists of a coplanar waveguide (CPW)-fed ultra-wideband (UWB) antenna and three inner rectangular loop antennas. The dimensions of the proposed antenna are 42 mm × 50 mm × 0.8 mm. The UWB antenna is used for spectrum sensing and fully covers the UWB spectrum of 3.1–10.6 GHz. The three loop antennas cover the UWB frequency band partially for communication purposes. The first loop antenna for the low frequency range operates from 2.96 GHz to 5.38 GHz. The second loop antenna is in charge of the mid band from 5.31 GHz to 8.62 GHz. The third antenna operates from 8.48 GHz to 11.02 GHz, which is the high-frequency range. A high isolation level (greater than 17.3 dB) is realized among the UWB antenna and three loop antennas without applying any additional decoupling structures. The realized gains of the UWB antenna and three loop antennas are greater than 2.7 dBi and 1.38 dBi, respectively.

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Acoustic source localization using the open spherical microphone array in the low-frequency range

MATEC Web of Conferences ◽

10.1051/matecconf/201928304001 ◽

2019 ◽

Vol 283 ◽

pp. 04001

Author(s):

Boquan Yang ◽

Shengguo Shi ◽

Desen Yang

Keyword(s):

Source Localization ◽

Generalized Inverse ◽

Microphone Array ◽

Low Frequency ◽

Poor Performance ◽

Microphone Arrays ◽

Three Dimension ◽

Frequency Range ◽

Array Aperture ◽

Regularization Matrix

Recently, spherical microphone arrays (SMA) have become increasingly significant for source localization and identification in three dimension due to its spherical symmetry. However, conventional Spherical Harmonic Beamforming (SHB) based on SMA has limitations, such as poor resolution and high side-lobe levels in image maps. To overcome these limitations, this paper employs the iterative generalized inverse beamforming algorithm with a virtual extrapolated open spherical microphone array. The sidelobes can be suppressed and the main-lobe can be narrowed by introducing the two iteration processes into the generalized inverse beamforming (GIB) algorithm. The instability caused by uncertainties in actual measurements, such as measurement noise and configuration problems in the process of GIB, can be minimized by iteratively redefining the form of regularization matrix and the corresponding GIB localization results. In addition, the poor performance of microphone arrays in the low-frequency range due to the array aperture can be improved by using a virtual extrapolated open spherical array (EA), which has a larger array aperture. The virtual array is obtained by a kind of data preprocessing method through the regularization matrix algorithm. Both results from simulations and experiments show the feasibility and accuracy of the method.

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