Three-dimensional ray tracing of the Jovian magnetosphere in the low-frequency range

In order to solve the problem of strong penetration and difficult attenuation of low-frequency sound wave in traditional materials, several three-dimensional acoustic black hole superstructures are designed. First of all, multi-stage acoustic black holes are designed. It is found that their sound insulation coefficient is about 0.9 in the frequency range of 50–1600 Hz when the ration of the outlet tip diameter to the inlet diameter is [Formula: see text]. Then, the acoustic black hole thin and light superstructure was designed by embedding many acoustic black hole units in an array on the 10 mm thick plate. The sound insulation coefficient of two samples embedded 81 or 144 acoustic black holes is above 0.96 in the frequency range of 50–1600 Hz. To facilitate processing and engineering applications, we designed acoustic black hole wedge-shaped plate superstructures, and found that the average sound insulation of these acoustic black hole superstructures is 30 dB in the frequency range of 50–1600 Hz. These superstructures will be widely used in anechoic rooms, factories and aviation.

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An Elementary Study of SPH-Based Simulations for Free Surface Flows With Gravity and Compressibility Effects in Cylindrical Confinement

Volume 4: Fluid-Structure Interaction ◽

10.1115/pvp2009-77469 ◽

2009 ◽

Author(s):

Guillaume Oger ◽

Erwan Jacquin ◽

David Le Touze ◽

Bertrand Alessandrini ◽

Jean-Franc¸ois Sigrist

Keyword(s):

Free Surface ◽

High Frequency ◽

Seismic Analysis ◽

Three Dimensional ◽

Low Frequency ◽

Free Surface Flows ◽

Frequency Range ◽

Surface Flows ◽

Particle Hydrodynamics ◽

Compressibility Effects

The design of nuclear pressure vessel requires the description of various dynamic effects, among which fluid-structure interaction. In some configurations, gravity effects (in the low frequency range) and compressibility effects (in the high frequency range) are of paramount importance and have therefore to be accounted for. The present paper is concerned with the description of free surface flows with gravity and compressibility effects, using a SPH (Smoothed Particle Hydrodynamics) method in circular confinement, with expected applications to the dynamic analysis of auxiliary nuclear component for naval propulsion. For the system under concern, the range of dynamic solicitation extends from low frequency (for seismic analysis of grounded prototype) to high frequency (for shock analysis of embarked reactors); it is therefore of particle interest to employ a numerical techniques which allows the description of linear and non-linear free surface effects, which can be expected in both cases. SPH method gives promising perspective for simulation of sloshing flows in various configurations; the present paper investigates the use of such a technique in the context of three-dimensional problems with cylindrical confinement.

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Wide-Frequency-Range Dielectric Tuning of BaTiO3 by Embedding Metal Nanocrystals

10.21203/rs.3.rs-99563/v1 ◽

2020 ◽

Author(s):

Deli SHI ◽

Leiming FANG ◽

Xiaoqiang Zhang ◽

Jinlong TANG ◽

Jun LI ◽

...

Keyword(s):

High Frequency ◽

Dielectric Response ◽

Inductive Effect ◽

Three Dimensional ◽

Low Frequency ◽

Wide Frequency Range ◽

Frequency Range ◽

Rectification Effect ◽

Metal Nanocrystals ◽

Nanocomposite System

Abstract The Fe nanocrystals (NCs) were embedded into the epitaxial BaTiO 3 (BTO) matrix. According to optimize growth processes, a novel nanocomposite system was constructed, which consist of well epitaxial BTO layer and three-dimensional Fe NCs. Based on this, the different dielectric response in the regions of low temperature-high frequency and low frequency-high temperature were revealed by the contribution of hopping and interfacial polarizations, respectively. With the increased amount of Fe NCs, the obvious enhancement of low-frequency conductivity, middle frequency capacitance and high-frequency inductive effect was found. The metal NC embedding plays an important role in tuning the dielectric behaviors and ac conductivity of oxide dielectrics. This significant rectification effect in the wide-frequency ranges opens up a new direction for the designing of embedded nano-capacitors.

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Phononic metastructures with ultrawide low frequency three-dimensional bandgaps as broadband low frequency filter

Scientific Reports ◽

10.1038/s41598-021-86520-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Muhammad ◽

C. W. Lim

Keyword(s):

Passive Control ◽

Noise Control ◽

Three Dimensional ◽

Low Frequency ◽

Resonant Mode ◽

Frequency Range ◽

Research Activities ◽

Vibration Attenuation ◽

Mass Spring ◽

Broadband Frequency

AbstractVibration and noise control are among the classical engineering problems that still draw extensive research interest today. Multiple active and passive control techniques to resolve these problems have been reported, however, the challenges remain substantial. The recent surge of research activities on acoustic metamaterials for vibration and noise control are testimony to the fact that acoustic metamaterial is no longer limited to pure theoretical concepts. For vibration and noise control over an ultrawide frequency region, 3-D metastructures emerge as a novel solution tool to resolve this problem. In that context, the present study reports a novel proposal for 3-D monolithic phononic metastructures with the capability to induce low frequency ultrawide three-dimensional bandgaps with relative bandwidth enhancements of 157.6% and 160.1%. The proposed monolithic metastructure designs consist of elastic frame assembly that is connected with the rigid cylindrical masses. Such structural configuration mimics monoatomic mass-spring chain where an elastic spring is connected with a rigid mass. We develop an analytical model based on monoatomic mass-spring chain to determine the acoustic mode frequency responsible for opening the bandgap. The wave dispersion study reveals the presence of ultrawide bandgaps for both types of metastructures. The modal analysis shows distribution of vibration energy in the bandgap opening (global resonant mode) and closing (local resonant mode) bounding edges. We further analyze the band structures and discuss the physical concepts that govern such ultrawide bandgap. Vibration attenuation inside the bandgap frequency range is demonstrated by frequency response studies conducted by two different finite element models. Thanks to additive manufacturing technology, 3-D prototypes are prepared and low amplitude vibration test is performed to validate the numerical findings. Experimental results show the presence of an ultrawide vibration attenuation zone that spreads over a broadband frequency spectrum. The bandgaps reported by the proposed metastructures are scale and material independent. The research methodology, modelling and design strategy presented here may pave the way for the development of novel meta-devices to control vibration and noises over a broadband frequency range.

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Stochastic BEM for the Vibroacoustic Analysis of Three-Dimensional Structures

Advances in Acoustics and Vibration ◽

10.1155/2011/952407 ◽

2011 ◽

Vol 2011 ◽

pp. 1-12 ◽

Cited By ~ 2

Author(s):

R. D'Amico ◽

A. Pratellesi ◽

M. Pierini ◽

N. Baldanzini

Keyword(s):

Crucial Role ◽

Three Dimensional ◽

Low Frequency ◽

Wide Frequency Range ◽

Frequency Range ◽

Small Perturbations ◽

Low Frequencies ◽

Response Sensitivity ◽

Basic Assumptions ◽

Prediction Reliability

Nowadays, extending the NVH prediction reliability to the whole frequency range is an attractive goal of vibroacoustics. Deterministic methodologies are well established for the low-frequency range, but, decreasing the wavelength, energy-based methods are necessary. In such a range, a crucial role is played by small perturbations which highly influence the response sensitivity. Moreover, taking into account these variations allows to make the product design more robust and even quicker. Introducing geometrical uncertainties within the classic BEM formulation allows to obtain the so-called stochastic BEM. As a result, the solution shows deterministic behaviour at low frequencies; decreasing the wavelength, the effect of the uncertainties smooths the response. Consequently, it is possible to obtain an averaged trend over the whole frequency range which asymptotically tends to the deterministic one. In this paper, we deal with three-dimensional acoustic SBEM. First, the formulation and its basic assumptions are presented. Secondly, they are applied to academic cases to show its potentialities in predicting vibroacoustic behaviour over a wide frequency range.

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Density-based discrimination of protein and RNA in the ribosome

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100122721 ◽

1992 ◽

Vol 50 (1) ◽

pp. 464-465

Author(s):

Joachim Frank

Keyword(s):

Transfer Function ◽

Spatial Frequency ◽

Three Dimensional ◽

Wiener Filter ◽

Dark Field Image ◽

Dark Field ◽

Frequency Range ◽

Bright Field ◽

Contrast Transfer Function ◽

Pass Filter

Cryo-electron microscopy combined with single-particle reconstruction techniques has allowed us to form a three-dimensional image of the Escherichia coli ribosome.In the interior, we observe strong density variations which may be attributed to the difference in scattering density between ribosomal RNA (rRNA) and protein. This identification can only be tentative, and lacks quantitation at this stage, because of the nature of image formation by bright field phase contrast. Apart from limiting the resolution, the contrast transfer function acts as a high-pass filter which produces edge enhancement effects that can explain at least part of the observed variations. As a step toward a more quantitative analysis, it is necessary to correct the transfer function in the low-spatial-frequency range. Unfortunately, it is in that range where Fourier components unrelated to elastic bright-field imaging are found, and a Wiener-filter type restoration would lead to incorrect results. Depending upon the thickness of the ice layer, a varying contribution to the Fourier components in the low-spatial-frequency range originates from an “inelastic dark field” image. The only prospect to obtain quantitatively interpretable images (i.e., which would allow discrimination between rRNA and protein by application of a density threshold set to the average RNA scattering density may therefore lie in the use of energy-filtering microscopes.

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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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