Articles de revues sur le sujet « Broadband Doppler effect »
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Albuquerque, Daniel F., José M. N. Vieira, Sérgio I. Lopes, Carlos A. C. Bastos et Paulo J. S. G. Ferreira. « Indoor acoustic simulator for ultrasonic broadband signals with Doppler effect ». Applied Acoustics 97 (octobre 2015) : 140–51. http://dx.doi.org/10.1016/j.apacoust.2015.04.010.
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Zhou, Y., J. Wang et M. Sawahashi. « Downlink Transmission of Broadband OFCDM Systems—Part II : Effect of Doppler Shift ». IEEE Transactions on Communications 54, no 6 (juin 2006) : 1097–108. http://dx.doi.org/10.1109/tcomm.2006.876872.
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Tian, Haopeng, et Benshuai Lyu. « Prediction of broadband noise from rotating blade elements with serrated trailing edges ». Physics of Fluids 34, no 8 (août 2022) : 085109. http://dx.doi.org/10.1063/5.0094423.
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This paper conducts a theoretical investigation into the prediction of broadband trailing-edge noise for rotating serrated blades. Lyu's semi-analytical noise prediction model for isolated flat plates is extended to rotating blades using Schlinker and Amiet's approach and applied to three test applications including a wind turbine, a cooling fan, and an open propeller. The model is validated by comparing the straight edge results with that presented in the work of Sinayoko et al., which shows an excellent agreement. The noise spectra obtained using different-order approximations show that the second-order solution yields a converged result. It is found that trailing-edge serrations can lead to noise reduction in the intermediate- and high-frequency ranges at an observer angle of 45° at low Mach numbers but may lead to noise increase in the intermediate-frequency range at high Mach numbers. The results show that the directivity patterns change due to the use of trailing-edge serrations and the directivity peaks are observed at high frequencies. A detailed analysis on the effects of rotation shows that for low-Mach number applications, the Doppler effect is weak and the peaky directivity pattern is mainly affected by the nonuniform directivity of an isolated flat plate at high frequencies. However, for high-Mach number applications, the Doppler effect is significant and also contributes to the final directivity pattern of rotating blades.
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Khokhlova, Tatiana D., Minho Song, Randall P. Williams, Joo Ha Hwang, Yak-Nam Wang et Oleg A. Sapozhnikov. « Passive and active Doppler methods and metrics to quantify inertial cavitation induced by pulsed focused ultrasound ». Journal of the Acoustical Society of America 152, no 4 (octobre 2022) : A215. http://dx.doi.org/10.1121/10.0016055.
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Inertial cavitation induced by pulses of nonlinearly distorted focused ultrasound (FUS) at moderate intensity can result in mild mechanical disruption of tissue, short of its complete mechanical disintegration—histotripsy. This effect can be used to enhance diffusion of subsequently systemically administered drugs or biologics. Previously, single-element passive cavitation detection (PCD) of broadband noise emissions was successfully used to quantify tissue disruption and enhancement in drug concentration. This metric, however, has limitations: minimal spatial resolution and challenges with calibration when used at large depths in acoustically variable tissue. To address this, we developed a combination of passive and active Doppler-based methods that relied on relative, rather than absolute signal metrics. Specifically, destructive cavitation behaviors were previously linked to substantial motion of the bubbles during the FUS pulse due to acoustic radiation force and shock scattering. This was reflected in the backscattered FUS harmonics as Doppler shift and measurable from PCD. The bubbles were observed to dissolve within milliseconds following each FUS pulse, thus their distribution could be visualized as an area of rapid change via fast plane wave Doppler ensemble following the FUS pulse. The Doppler power distribution was spatially correlated with the area of tissue disruption in the in vivo experiments. [Work supported by NIH R01CA154451, R01EB025187, and R01EB23910.]
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Bonnefous, O., et P. Pesqué. « Time Domain Formulation of Pulse-Doppler Ultrasound and Blood Velocity Estimation by Cross Correlation ». Ultrasonic Imaging 8, no 2 (avril 1986) : 73–85. http://dx.doi.org/10.1177/016173468600800201.
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The Doppler effect is usually described as a frequency shift of the backscattered signals from moving targets with respect to the frequency transmitted. Recently, real-time blood flow imaging has become possible thanks to the development of a new velocity estimator based on phase-shift measurements of successive echoes. However, this method suffers from the well-known limitations of pulse-Doppler instruments. A new formulation is presented which describes the pulse-Doppler effect on the successive echoes from a cloud of moving targets as a progressive translation in time due to the displacement of the scatterers between two excitations. This approach allows us to generate efficiently computer-simulated data in order to evaluate accurately the various processing techniques. Furthermore, it leads to a novel class of velocity estimators in the time domain which measure the time shifts which are proportional to the local blood velocity. Among them, the cross correlation of the received rf signals turns out to be well suited. A local cross-correlation function is first calculated from a consecutive pair of range-gated echoes and the time shift is then determined by searching for the time position with the maximum correlation. The time-correlation technique is shown to provide accurate velocity profiles with broadband transducers. Moreover, the classical velocity limitation of pulse-Doppler is overcome because there is no ambiguity in measuring a time shift instead of a phase shift. These major advantages should make quantitative flow mapping possible and more reliable.
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Zhuravleva, L. M., M. A. Nilov, V. L. Loshkarev et V. V. Levshunov. « Evaluation of the Impact of Doppler Effect on Quality of HSR Radiocommunications ». World of Transport and Transportation 18, no 4 (5 janvier 2021) : 54–71. http://dx.doi.org/10.30932/1992-3252-2020-18-54-71.
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The article proposes a methodology for evaluating radio signal distortions caused by Doppler effect (DE; also, Doppler shift) under the conditions of highspeed train traffic (HSR, high-speed rail). The objective of the work is to develop criteria for assessing quality of radiocommunications with moving objects in HSR environment. For this, a technique is proposed for calculating the probability of an error arising from Doppler effect. A rationale for relevance of the topic is that radiocommunications are used on railways for controlling train traffic and ensuring safety and achieving required quality of radio signals is a major challenge. Quality assessment is especially important for organization of broadband communication channels with locomotive drivers using mobile networks. To solve this problem, a model for assessing quality of radiocommunication influenced by DE is considered. Distortions of signals in a radio channel due to DE are proposed to be estimated using the reduced dispersion of the total error, which consists of two components: dynamic and interference. Calculations of the total reduced signal error and the error probability for speeds above 100 km/h are described. Estimates of the effect of DE on a coherent receiver, in which errors may occur due to changes in duration of radio pulses, are suggested. Effectiveness of the receiver’s automatic frequency control (AFC) system is analysed as a means of challenging DE. For this, the concept of an instantaneous spectrum of parasitic frequency modulation due to DE was introduced and quality of radio communication was calculated using the reduced dispersion of the total error. The efficiency of using AFC has been proven after comparing the evaluations of reception quality with and without AFC in the form of the ratio of error probabilities. The features of the use of mobile communications on railways under the conditions of DE are formulated.
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Orta, Adil Han, Mathias Kersemans et Koen Van Den Abeele. « On the Identification of Orthotropic Elastic Stiffness Using 3D Guided Wavefield Data ». Sensors 22, no 14 (15 juillet 2022) : 5314. http://dx.doi.org/10.3390/s22145314.
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Scanning laser Doppler vibrometry is a widely adopted method to measure the full-field out-of-plane vibrational response of materials in view of detecting defects or estimating stiffness parameters. Recent technological developments have led to performant 3D scanning laser Doppler vibrometers, which give access to both out-of-plane and in-plane vibrational velocity components. In the present study, the effect of using (i) the in-plane component; (ii) the out-of-plane component; and (iii) both the in-plane and out-of-plane components of the recorded vibration velocity on the inverse determination of the stiffness parameters is studied. Input data were gathered from a series of numerical simulations using a finite element model (COMSOL), as well as from broadband experimental measurements by means of a 3D infrared scanning laser Doppler vibrometer. Various materials were studied, including carbon epoxy composite and wood materials. The full-field vibrational velocity response is converted to the frequency-wavenumber domain by means of Fourier transform, from which complex wavenumbers are extracted using the matrix pencil decomposition method. To infer the orthotropic elastic stiffness tensor, an inversion procedure is developed by coupling the semi-analytical finite element (SAFE) as a forward method to the particle swarm optimizer. It is shown that accounting for the in-plane velocity component leads to a more accurate and robust determination of the orthotropic elastic stiffness parameters.
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Fedorenko, A. K., A. V. Bespalova, O. K. Cheremnykh et E. I. Kryuchkov. « A dominant acoustic-gravity mode in the polar thermosphere ». Annales Geophysicae 33, no 1 (27 janvier 2015) : 101–8. http://dx.doi.org/10.5194/angeo-33-101-2015.
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Abstract. The article presents a summary of the main findings of the systematic study of acoustic-gravity waves (AGWs) in the polar thermosphere. This study was based on the in situ measurements made by the Dynamics Explorer 2 (DE2) spacecraft late in its mission when it descended low enough (250–400 km). It was found out that AGWs in the polar thermosphere are observed within a narrow frequency band close to the Brunt–Väisälä frequency and with horizontal wavelengths about 500–600 km. The broadband spectrum of travelling ionospheric disturbance (TID) frequencies observed by radars is caused by the Doppler effect. The AGW amplitudes do not depend on the altitude, but grow almost linearly with the wind velocity. They propagate towards the wind.
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Hou, Jiacheng, et Zhongquan Charlie Zheng. « Simulation of near-ground signals from a flying source on UAV over a building structure ». Journal of the Acoustical Society of America 151, no 4 (avril 2022) : A36. http://dx.doi.org/10.1121/10.0010577.
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Acoustic signals near the ground generated by a moving source on a fly-by UAV are simulated around a house. The simulation is carried out using a time-domain acoustics solver that can simulate acoustic propagations with the specified moving source, ground properties, and building geometries. The source on a UAV is approximated by a broadband source moving at a constant speed. The long-range three-dimensional computation is developed with a ground as a rigid or porous medium and a residential house with realistic geometries. Time histories and histograms of the near-ground sensors at different locations around the house are analyzed with their different behaviors due to Doppler shift, ground effect, and acoustic interference from the house structures. Comparisons will be made with literature results and available measured data.
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Prokopovich, V. V., et A. V. Shafranyuk. « Model of Signal Mark Detection in a Passive Sonar System ». IOP Conference Series : Materials Science and Engineering 1215, no 1 (1 janvier 2022) : 012009. http://dx.doi.org/10.1088/1757-899x/1215/1/012009.
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Abstract Modeling of broadband and narrowband signal mark detection is widely used for sonar and radar systems. In this work, the problem is considered in relation to hydroacoustics. The paper describes the formation of a stream of correctly detected and false signal marks and calculation of estimates of their parameters, taking into account the antenna characteristics as well as the processing parameters of the system being simulated. Also considered are the realistic distribution of false signal marks by heading angles and the influence of the Doppler effect on the estimation of the mark parameters. The resulting model can be used in simulation systems, in the formation of a stream of detected signal marks, and the development of tracking algorithms. The model can be also used for predictive calculations that determine the probability of detecting signal sources and their characteristics
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Gu, Yong Hong, Rui Min Lu et Shi Jun Xie. « System Design Considerations for Satellite Communications on the Move ». Advanced Materials Research 748 (août 2013) : 1015–19. http://dx.doi.org/10.4028/www.scientific.net/amr.748.1015.
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Communications on the Move (COTM) has gained a great deal of attention recently. The need for broadband connectivity from a moving vehicle has increased dramatically in the past few years for both commercial and military applications. This paper will discuss elements and considerations of providing satellite communications on a moving platform from a system perspective. It will focus on Internet Protocol (IP) over satellite since IP has become the dominant protocol for newly deployed voice and video applications. A global COMT network has much great degree of complexity than a regional network since it will require beam switchover and IP routing re-convergence as a vehicle moves from one satellite beam to another. This paper will present some approaches to COTM system design including antenna size and link budget, spectral density, the Doppler effect, beam and teleport switchover.
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Kuang, Lei, Shouzheng Zhu, Jianjun Gao, Zhengqi Zheng et Danan Dong. « A Numerical Method for Analyzing Electromagnetic Scattering Properties of a Moving Conducting Object ». International Journal of Antennas and Propagation 2014 (2014) : 1–9. http://dx.doi.org/10.1155/2014/386315.
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A novel numerical approach is developed to analyze electromagnetic scattering properties of a moving conducting object based on the finite-difference time-domain (FDTD) algorithm. Relativistic boundary conditions are implemented into the FDTD algorithm to calculate the electromagnetic field on the moving boundary. An improved technique is proposed to solve the scattered field in order to improve the computational efficiency and stability of solutions. The time-harmonic scattered field from a one-dimensional moving conducting surface is first simulated by the proposed approach. Numerical results show that the amplitude and frequency of the scattered field suffer a modulation shift. Then the transient scattered field is calculated, and broadband electromagnetic scattering properties of the moving conducting surface are obtained by the fast Fourier transform (FFT). Finally, the scattered field from a two-dimensional moving square cylinder is analyzed. The numerical results demonstrate the Doppler effect of a moving conducting object. The simulated results agree well with analytical results.
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Pozdniakov, V., et M. Buhaiov. « ACOUSTIC SIGNALS ANALYSIS OF AERIAL ATTACK WEAPON ». Проблеми створення, випробування, застосування та експлуатації складних інформаційних систем, no 25 (I) (25 décembre 2023) : 58–75. http://dx.doi.org/10.46972/2076-1546.2023.25.06.
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This paper analyzes the acoustic signals of aerodynamic aerial attack weapons used by the Russian Federation during a full-scale invasion. These include strike unmanned aerial vehicles, cruise missiles, jet and turboprop aircraft, and helicopters. It has been established that the time for observing an acoustic signal is limited by the speed of the vehicle. For high-speed targets (cruise missiles, airplanes), it averages 10 s, and for slower targets, 40-50 s. The Welch periodogram method was used to extract the spectral characteristics of acoustic signals. It is shown that the acoustic signal of propeller-driven vehicles is the sum of harmonic and noise-like broadband components, and that of turbojet-powered vehicles has a predominantly noise-like structure with several narrowband components. It was found that at the moment of maximum convergence, the signal spectrum has the greatest width. The characteristic change in the frequency of harmonic components associated with the Doppler effect is investigated. It can be used to estimate the parameters of motion and identify the vehicle. By correlation analysis of acoustic signals, it was found that broadband components have a noise-like structure. An acoustic signal for the case of simultaneous over flight of different types of vehicles was formed by adding records of different acoustic signals. It is shown that the characteristic spectral characteristics of all objects are preserved on the frequency-time plane. The results of the analysis can be used to build mathematical models of acoustic signals and to develop methods for processing signals of aerial attack weapons in an acoustic airspace monitoring system. Keywords: aerial attack weapons; acoustic signal; spectrogram; acoustic monitoring system; harmonic component.
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Shen, Zhiyuan, Thomas R. Neil, Daniel Robert, Bruce W. Drinkwater et Marc W. Holderied. « Biomechanics of a moth scale at ultrasonic frequencies ». Proceedings of the National Academy of Sciences 115, no 48 (12 novembre 2018) : 12200–12205. http://dx.doi.org/10.1073/pnas.1810025115.
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The wings of moths and butterflies are densely covered in scales that exhibit intricate shapes and sculptured nanostructures. While certain butterfly scales create nanoscale photonic effects, moth scales show different nanostructures suggesting different functionality. Here we investigate moth-scale vibrodynamics to understand their role in creating acoustic camouflage against bat echolocation, where scales on wings provide ultrasound absorber functionality. For this, individual scales can be considered as building blocks with adapted biomechanical properties at ultrasonic frequencies. The 3D nanostructure of a full Bunaea alcinoe moth forewing scale was characterized using confocal microscopy. Structurally, this scale is double layered and endowed with different perforation rates on the upper and lower laminae, which are interconnected by trabeculae pillars. From these observations a parameterized model of the scale’s nanostructure was formed and its effective elastic stiffness matrix extracted. Macroscale numerical modeling of scale vibrodynamics showed close qualitative and quantitative agreement with scanning laser Doppler vibrometry measurement of this scale’s oscillations, suggesting that the governing biomechanics have been captured accurately. Importantly, this scale of B. alcinoe exhibits its first three resonances in the typical echolocation frequency range of bats, suggesting it has evolved as a resonant absorber. Damping coefficients of the moth-scale resonator and ultrasonic absorption of a scaled wing were estimated using numerical modeling. The calculated absorption coefficient of 0.50 agrees with the published maximum acoustic effect of wing scaling. Understanding scale vibroacoustic behavior helps create macroscopic structures with the capacity for broadband acoustic camouflage.
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BOIKO, JULIY, ILYA PYATIN et IGOR PARKHOMEY. « SIGNAL PROCESSING AND SYNCHRONIZATION TECHNIQUE IN SOFTWARE-DEFINED RADIO SYSTEMS WITH OFDM ». Herald of Khmelnytskyi National University. Technical sciences 307, no 2 (2 mai 2022) : 123–32. http://dx.doi.org/10.31891/2307-5732-2022-307-2-123-132.
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The article describes modern concepts for the development of Software-defined Radio (SDR) technology. A functional diagram of a software-defined radio station using the method of transmitting information with modulation based on Orthogonal Frequency Division Multiplexing (OFDM) is proposed. The conditions for ensuring symbol synchronization of OFDM signals are investigated. It is determined that the disruption of the orthogonality of OFDM symbols is accompanied by such phenomena as the occurrence of inter-symbol interference and inter-channel interference. The method of constellation diagrams was used to study the effect of errors caused by interference on the quality of processing of multiposition signals. The effect of interference in a channel from OFDM on the phase of signals during their processing is estimated. Mathematical models of signals with OFDM in the presence of interference effects are obtained. Two types of errors are considered, which are caused by carrier distortion. In particular, the occurrence of phase noise is possible, the cause of which is associated with the instability of the generating equipment of the carrier signals both on the transmitting and on the receiving side. Another factor is carrier offset due to Doppler frequency. The proposed SDR receiver structure is based on the digital IF architecture. This architecture has more flexibility than traditional RF architectures and is not sensitive to DC offset, LO leakage, etc. Moreover, since the I/Q up/down conversion is done digitally in the IF stage, the negative effects caused by I/Q imbalance will be minimized. The SDR consists of a small piece of hardware at the RF input, i.e., an antenna and a high-rate ADC capable of capturing and digitizing broadband radio signals. To increase the communication range in SDR, we use amplifiers in front of two DAC/ADC stages. The receiver has a low-noise amplifier to reduce the quantization noise of the transducer and increase the Signal-to-noise Ratio (SNR). The data is then processed on specialized computational units within the embedded system, enabling important demodulation, synchronization, and decoding techniques to be implemented.
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Lin, Lupin Chun-Che, Chin-Ping Hu, Jumpei Takata, Kwan-Lok Li, C. Y. Hui et A. K. H. Kong. « Investigation of the Timing and Spectral Properties of an Ultraluminous X-Ray Pulsar NGC 7793 P13 ». Astrophysical Journal 924, no 2 (1 janvier 2022) : 65. http://dx.doi.org/10.3847/1538-4357/ac32b9.
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Abstract We perform both timing and spectral analyses using the archival X-ray data taken with Swift, XMM-Newton, NICER, and NuSTAR from 2016 to 2020 to study an ultraluminous pulsar, NGC 7793 P13, that showed a long period of super-Eddington accretion. We use the Rayleigh test to investigate the pulsation at different epochs, and confirm the variation of the pulse profile with finite Gaussian mixture modeling and a two-sample Kuiper test. Taking into account the periodic variation of the spin periods caused by the orbital Doppler effect, we further determine an orbital period of ∼65 days and show that no significant correlation can be detected between the orbital phase and the pulsed fraction. The pulsed spectrum of NGC 7793 P13 in the 0.5–20 keV range can be simply described using a power law with a high-energy exponential cutoff, while the broadband phase-averaged spectrum of the same energy range requires two additional components to account for the contribution of a thermal accretion disk and the Comptonization photons scattered into the hard X-rays. We find that NGC 7793 P13 stayed in the hard ultraluminous state and the pulsed spectrum was relatively soft when the source was faint at the end of 2019. Moreover, an absorption feature close to 1.3 keV is marginally detected from the pulsed spectra and it is possibly associated with a cyclotron resonant scattering feature.
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PHAM, HIEU T., SUTANU SARKAR et KYLE A. BRUCKER. « Dynamics of a stratified shear layer above a region of uniform stratification ». Journal of Fluid Mechanics 630 (10 juillet 2009) : 191–223. http://dx.doi.org/10.1017/s0022112009006478.
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Direct numerical simulations (DNS) are performed to investigate the behaviour of a weakly stratified shear layer in the presence of a strongly stratified region beneath it. Both, coherent Kelvin–Helmholtz (KH) rollers and small-scale turbulence, are observed during the evolution of the shear layer. The deep stratification measured by the Richardson number Jd is varied to study its effect on the dynamics. In all cases, a pycnocline is found to develop at the edges of the shear layer. The region of maximum shear shifts downward with increasing time. Internal waves are excited, initially by KH rollers, and later by small-scale turbulence. The wave field generated by the KH rollers is narrowband and of stronger amplitude than the broadband wave field generated by turbulence. Linear theory based on Doppler-shifted frequency of the KH mode is able to predict the angle of the internal wave phase lines during the direct generation of internal waves by KH rollers. Waves generated by turbulence are relatively weaker with a broader range of excitation angles which, in the deep region, tend towards a narrower band. The linear theory that works for the internal waves excited by KH rollers does not work for the turbulence generated waves. The momentum transported by the internal waves into the interior can be large, about 10% of the initial momentum in the shear layer, when Jd ≃ 0.25. Integration of the turbulent kinetic energy budget in time and over the shear layer thickness shows that the energy flux can be up to 17% of the turbulent production, 33% of the turbulent dissipation rate and 75% of the buoyancy flux. These numbers quantify the dynamical importance of internal waves. In contrast to linear theory where the effect of deep stratification on the shear layer instabilities has been found to be weak, the present nonlinear simulations show that the evolution of the shear layer is significantly altered because of the significant momentum and energy carried away by the internal waves.
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Lozovskiy, I. F. « The use of pseudonoise phase modulation broadband signals in radar surveys ». Journal of «Almaz – Antey» Air and Space Defence Corporation, no 3 (30 septembre 2019) : 30–40. http://dx.doi.org/10.38013/2542-0542-2019-3-30-40.
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The paper focuses on the problems of the use of pseudonoise phase modulation broadband signals in the radar survey. The average correlation characteristics of these signals in the Doppler frequency range and the structure of the processing system, including a multi-channel frequency matched filter, are determined. Methods of protecting the signal detection systems from the effects of narrow-band impulse and passive interference are proposed
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Meng, Han, Dimitrios Chronopoulos, Nick Bailey et Lei Wang. « Investigation of 2D Rainbow Metamaterials for Broadband Vibration Attenuation ». Materials 13, no 22 (19 novembre 2020) : 5225. http://dx.doi.org/10.3390/ma13225225.
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Phononic crystals (PnCs) and metamaterials are widely investigated for vibration suppression owing to the bandgaps, within which, wave propagation is prohibited or the attenuation level is above requirements. The application of PnCs and metamaterials is, however, limited by the widths of bandgaps. The recently developed rainbow structures consisting of spatially varied profiles have been shown to generate wider bandgaps than periodic structures. Inspired by this design strategy, rainbow metamaterials composed of nonperiodic mass blocks in two-dimensional (2D) space were proposed in the present study. The blocks were connected by curved beams and tessellated with internal voids to adjust their masses. In order to demonstrate the effects of the rainbow design, two 2D metamaterials, with periodic and nonperiodic units, respectively, were investigated and manufactured using additive manufacturing technologies. Receptance functions, i.e., displacement frequency response functions, of the manufactured metamaterials were calculated with finite element models and measured with a testing system containing a mechanical shaker, an impedance head, and a laser Doppler vibrometer. The obtained numerical and experimental results showed that the metamaterial with rainbow blocks has extended bandgaps compared with the periodic metamaterial.
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Smith, Kevin B., et Richard Ead. « Computing rough surface Doppler effects on broadband pulse propagation using a split‐step Fourier parabolic equation model ». Journal of the Acoustical Society of America 113, no 4 (avril 2003) : 2185–86. http://dx.doi.org/10.1121/1.4780104.
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Xiang, Ning, Jack Taylor et Max Miller. « Laser Doppler vibrometry-based measurements on viscoelastic panels for flexural damping properties ». Journal of the Acoustical Society of America 153, no 3_supplement (1 mars 2023) : A239. http://dx.doi.org/10.1121/10.0018766.
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Bending wave propagation is of central importance when enhancing sound transmission losses of sandwiched wall board systems incorporating viscoelastic panels as constrained damping layers. The damping properties of constrained damping layers made of viscoelastic materials can often be characterized by bending wave excitations. However, the multifactor, dispersive nature of the bending waves leads to challenges in reliable dynamic material characterization. To better understand the damping mechanism of the constrained damping layers, an experimental methodology employing complex bending wave theory has been developed to determine these flexural wave properties, including the loss factor and the bending stiffness of highly viscous panels. Relying on a transfer function from the experimentally measured bending velocities between two locations radially away from a flexural wave exciter on the viscoelastic panel under test, this methodology yields the broadband bending loss factor, the bending phase speed, and the bending stiffness. This paper discusses the experimental method for characterizing the above properties from laser Doppler vibrometry-based measurements of bending velocities. This paper also discusses the challenges with this method as well as an approach to mitigate the challenging effects and improve measurement accuracy.
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Higgins, Alex, et Martin Siderius. « Acoustic scattering from dynamic rough ocean surfaces using finite-difference time-domain modeling techniques ». Journal of the Acoustical Society of America 152, no 4 (octobre 2022) : A252—A253. http://dx.doi.org/10.1121/10.0016183.
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Established models for underwater acoustic propagation and scattering typically assume the sea-surface to be either perfectly smooth or rough but static in time. When the sea-surface is rough and moving, received signals show anomalies such as additional transmission losses (due to scattering) and Doppler effects (due to surface motion). Understanding the mechanisms behind these anomalies leads to better sonar system designs without having to perform expensive at-sea experiments. The Finite-Difference Time-Domain (FDTD) method is ideal to predict these physical phenomena. This work presents a FDTD method implemented to model the impact of both sea-surface roughness and motion on underwater acoustic propagation. The FDTD method allows an arbitrary function to define the rough sea-surface and its time evolution. The surface characteristics are modeled using a Pierson-Moskowitz (PM) frequency spectrum. The PM surface model is simple to implement and fully defined by wind speed and direction. Time-domain results from FDTD simulations of static rough sea-surfaces are compared to an established Helmholtz integral equation (HIE) method to establish the validity of the approach. Broadband signals are used as the source waveform. Results demonstrate the anomalous transmission loss and Doppler in received signals. [Work supported by the Office of Naval Research.]
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Molina, E., S. del Palacio et V. Bosch-Ramon. « A model for high-mass microquasar jets under the influence of a strong stellar wind ». Astronomy & ; Astrophysics 629 (septembre 2019) : A129. http://dx.doi.org/10.1051/0004-6361/201935960.
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Context. High-mass microquasars (HMMQs) are systems from which relativistic jets are launched. At the scales of several times the binary system size, the jets are expected to follow a helical path caused by the interaction with a strong stellar wind and orbital motion. Such a trajectory has its influence on the non-thermal emission of the jets, which also depends strongly on the observing angle due to Doppler boosting effects. Aims. We explore how the expected non-thermal emission of HMMQ jets at small scales is affected by the impact of the stellar wind and the orbital motion on the jet propagation. Methods. We studied the broadband non-thermal emission, from radio to gamma rays, produced in HMMQ jets up to a distance of several orbital separations, taking into account a realistic jet trajectory, different model parameters, and orbital modulation. The jet trajectory is computed by considering momentum transfer with the stellar wind. Electrons are injected at the position where a recollimation shock in the jets is expected due to the wind impact. Their distribution along the jet path is obtained assuming local acceleration at the recollimation shock, and cooling via adiabatic, synchrotron, and inverse Compton processes. The synchrotron and inverse Compton emission is calculated taking into account synchrotron self-absorption within the jet, free-free absorption with the stellar wind, and absorption by stellar photons via pair production. Results. The spectrum is totally dominated by the jet over the counter-jet due to Doppler boosting. Broadband emission from microwaves to gamma rays is predicted, with radio emission being totally absorbed. This emission is rather concentrated in the regions close to the binary system and features strong orbital modulation at high energies. Asymmetric light curves are obtained owing to the helical trajectory of the jets. Conclusions. The presence of helical shaped jets could be inferred from asymmetries in the light curves, which become noticeable only for large jet Lorentz factors and low magnetic fields. Model parameters could be constrained if accurate phase-resolved light curves from GeV to TeV energies were available. The predictions for the synchrotron and the inverse Compton radiation are quite sensitive of the parameters determining the wind-jet interaction structure.
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Ahn, C. J., et I. Sasase. « The effects of modulation combination, target BER, Doppler frequency, and adaptation interval on the performance of adaptive OFDM in broadband mobile channel ». IEEE Transactions on Consumer Electronics 48, no 1 (février 2002) : 167–74. http://dx.doi.org/10.1109/tce.2002.1010107.
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Chen, Zhixiong, Xiushu Qie, Juanzhen Sun, Xian Xiao, Yuxin Zhang, Dongjie Cao et Jing Yang. « Evaluation of Fengyun-4A Lightning Mapping Imager (LMI) Performance during Multiple Convective Episodes over Beijing ». Remote Sensing 13, no 9 (30 avril 2021) : 1746. http://dx.doi.org/10.3390/rs13091746.
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This study investigates the characteristics of space-borne Lightning Mapping Imager (LMI) lightning products and their relationships with cloud properties using ground-based total lightning observations from the Beijing Broadband Lightning Network (BLNET) and cloud information from S-band Doppler radar data. LMI showed generally consistent lightning spatial distributions with those of BLNET, and yielded a considerable lightning detection capability over regions with complex terrain. The ratios between the LMI events, groups and flashes were approximately 9:3:1, and the number of LMI-detected flashes was roughly one order of magnitude smaller than the number of BLNET-detected flashes. However, in different convective episodes, the LMI detection capability was likely to be affected by cloud properties, especially in strongly electrified convective episodes associated with frequent lightning discharging and thick cloud depth. As a result, LMI tended to detect lightning flashes located in weaker and shallower cloud portions associated with fewer cloud shielding effects. With reference to the BLNET total lightning data as the ground truth of observation (both intra-cloud lightning and cloud-to-ground lightning flashes), the LMI event-based detection efficiency (DE) was estimated to reach 28% under rational spatiotemporal matching criteria (1.5 s and 65 km) over Beijing. In terms of LMI flash-based DE, it was much reduced compared with event-based DE. The LMI flash-based ranged between 1.5% and 3.5% with 1.5 s and 35–65 km matching scales. For 330 ms and 35 km, the spatiotemporal matching criteria used to evaluate Geostationary Lightning Mapper (GLM), the LMI flash-based DE was smaller (<1%).
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Yang, Gui-Ying, John Methven, Steve Woolnough, Kevin Hodges et Brian Hoskins. « Linking African Easterly Wave Activity with Equatorial Waves and the Influence of Rossby Waves from the Southern Hemisphere ». Journal of the Atmospheric Sciences 75, no 6 (17 mai 2018) : 1783–809. http://dx.doi.org/10.1175/jas-d-17-0184.1.
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Abstract A connection is found between African easterly waves (AEWs), equatorial westward-moving mixed Rossby–gravity (WMRG) waves, and equivalent barotropic Rossby waves (RWs) from the Southern Hemisphere (SH). The amplitude and phase of equatorial waves is calculated by projection of broadband-filtered ERA-Interim data onto a horizontal structure basis obtained from equatorial wave theory. Mechanisms enabling interaction between the wave types are identified. AEWs are dominated by a vorticity wave that tilts eastward below the African easterly jet and westward above: the tilt necessary for baroclinic wave growth. However, a strong relationship is identified between amplifying vorticity centers within AEWs and equatorial WMRG waves. Although the waves do not phase lock, positive vorticity centers amplify whenever the cross-equatorial motion of the WMRG wave lies at the same longitude in the upper troposphere (southward flow) and east of this in the lower troposphere (northward flow). Two mechanisms could explain the vorticity amplification: vortex stretching below the upper-tropospheric divergence and ascent associated with latent heating in convection in the lower-tropospheric moist northward flow. In years of strong AEW activity, SH and equatorial upper-tropospheric zonal winds are more easterly. Stronger easterlies have two effects: (i) they Doppler shift WMRG waves so that their period varies little with wavenumber (3–4 days) and (ii) they enable westward-moving RWs to propagate into the tropical waveguide from the SH. The RW phase speeds can match those of WMRG waves, enabling sustained excitation of WMRG. The WMRG waves have an eastward group velocity with wave activity accumulating over Africa and invigorating AEWs at similar frequencies through the vorticity amplification mechanism.
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Tang, Ziyi, Zhenyu Wan, Han Cao, Yize Liang, Wei Zhou, Yuchen Zhang, Liang Fang et Jian Wang. « Fiber-based broadband detection of a rotational object with superposed vortices ». APL Photonics 8, no 12 (1 décembre 2023). http://dx.doi.org/10.1063/5.0167478.
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Recently, the rotational Doppler effect has attracted broad attention in detecting rotational motion. However, the presently proposed detection techniques based on the rotational Doppler effect are generally configured relying on discrete components in free space, resulting in cumbersome and inflexible systems, which brings challenges to practical applications. In this paper, we demonstrate a fiber-based configuration on rotational Doppler measurements for the detection of a rotational object using an ultra-broadband mode-selective coupler to convert the superposed vortices. Remarkably, the results show the broadband operating range of the fiber-based measurement system intuitively through wavelength scanning. The refinement of rotational Doppler detection techniques is of great significance for lowering the cost, reducing system complexity, improving system integration, and industrial manufacturing. This fiber-based scheme might be a promising candidate for facilitating the rotational Doppler effect applied as novel motion monitoring and sensing equipment in engineering and industry.
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Zhang, Xiaozheng, Yinlong Li, Yongbin Zhang, Chuanxing Bi, Jinghao Li et Liang Xu. « An Improved Time-Domain Inverse Technique for Localization and Quantification of Rotating Sound Sources ». Chinese Journal of Mechanical Engineering 36, no 1 (7 novembre 2023). http://dx.doi.org/10.1186/s10033-023-00958-7.
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AbstractThe time-domain inverse technique based on the time-domain rotating equivalent source method has been proposed to localize and quantify rotating sound sources. However, this technique encounters two problems to be addressed: one is the time-consuming process of solving the transcendental equation at each time step, and the other is the difficulty of controlling the instability problem due to the time-varying transfer matrix. In view of that, an improved technique is proposed in this paper to resolve these two problems. In the improved technique, a de-Dopplerization method in the time-domain rotating reference frame is first applied to eliminate the Doppler effect caused by the source rotation in the measured pressure signals, and then the restored pressure signals without the Doppler effect are used as the inputs of the time-domain stationary equivalent source method to locate and quantify sound sources. Compared with the original technique, the improved technique can avoid solving the transcendental equation at each time step, and facilitate the treatment of the instability problem because the transfer matrix does not change with time. Numerical simulation and experimental results show that the improved technique can eliminate the Doppler effect effectively, and then localize and quantify the rotating nonstationary or broadband sources accurately. The results also demonstrate that the improved technique can guarantee a more stable reconstruction and compute more efficiently than the original one.
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Li, Mu, Jie Gao, Yongqi Wu, Rui Zhu, Qiang Gao et Yungang Zhang. « Study on temperature effect of broadband absorption spectroscopy based on Doppler broadening combined with multi-line shape superposition ». Optics Letters, 20 octobre 2023. http://dx.doi.org/10.1364/ol.503855.
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Abdulkarim, Yadgar I., Ayesha Mohanty, Om Prakash Acharya, Bhargav Appasani, Mohammad S. Khan, S. K. Mohapatra, Fahmi F. Muhammadsharif et Jian Dong. « A Review on Metamaterial Absorbers : Microwave to Optical ». Frontiers in Physics 10 (29 avril 2022). http://dx.doi.org/10.3389/fphy.2022.893791.
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Metamaterials (MM) are artificially designed materials that possess unique properties due to their geometrical design. They also display some peculiar properties, such as negative refractive index, Snell’s law reversal, Doppler effect reverse, and left-handed behavior. MMs are used in a myriad of applications, including invisibility cloaking, perfect lensing, perfect absorption, and sensing. In this review article, the property of electromagnetic absorption by structures known as metamaterial absorbers (MMAs) is discussed. An MMA is a composite made up of many layers of metallic patterns separated by dielectric. This novel device helps in achieving near-unity absorption by various mechanisms, which are investigated in this article. The MMAs are classified based on their absorption characteristics, such as polarization tunability, broadband operation, and multiband absorption, in different frequency regimes.
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Li, Yuhong, Han Wu, Hanbo Jiang, Siyang Zhong et Xin Zhang. « Computational Aeroacoustics Study of Propellers with Vibrational Motion ». AIAA Journal, 10 juin 2023, 1–17. http://dx.doi.org/10.2514/1.j062370.
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In this work, we conduct a numerical investigation of aerodynamics and aeroacoustics of propeller blades with vibrations, which could occur in practical unmanned aerial vehicles as the blades are often made of lightweight materials. The simulations resolve the sound generation from the unsteady turbulent flows using an acoustic-wave preserved artificial compressibility method. Then, the sound projection to the far-field observers is made using an integral solution of the Ffowcs-Williams and Hawkings equation. The study shows that periodic blade vibrations with small amplitudes can lead to aerodynamic thrust fluctuations. The blade vibration also affects the generation of tip vortices and the near-blade flow structures due to the periodic change of the effective angle of attack. Consequently, significant tonal noise at the harmonics of rotational frequency is produced, and the noise can propagate to both upstream and downstream directions of the rotor disc plane. A noise source analysis is performed to identify the contribution of different noise components. Results show that the extra tonal noise is mainly caused by the Doppler effect due to the blade axial motion and the influence of the thrust fluctuations. Moreover, the study also suggests that the high-frequency broadband noise seems to be insensitive to the blade vibration.
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Zhai, S. L., X. P. Zhao, S. Liu, F. L. Shen, L. L. Li et C. R. Luo. « Inverse Doppler Effects in Broadband Acoustic Metamaterials ». Scientific Reports 6, no 1 (31 août 2016). http://dx.doi.org/10.1038/srep32388.
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Xiao, Tong, Xiaojun Qiu et Benjamin Halkon. « Ultra-broadband local active noise control with remote acoustic sensing ». Scientific Reports 10, no 1 (27 novembre 2020). http://dx.doi.org/10.1038/s41598-020-77614-w.
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AbstractOne enduring challenge for controlling high frequency sound in local active noise control (ANC) systems is to obtain the acoustic signal at the specific location to be controlled. In some applications such as in ANC headrest systems, it is not practical to install error microphones in a person’s ears to provide the user a quiet or optimally acoustically controlled environment. Many virtual error sensing approaches have been proposed to estimate the acoustic signal remotely with the current state-of-the-art method using an array of four microphones and a head tracking system to yield sound reduction up to 1 kHz for a single sound source. In the work reported in this paper, a novel approach of incorporating remote acoustic sensing using a laser Doppler vibrometer into an ANC headrest system is investigated. In this “virtual ANC headphone” system, a lightweight retro-reflective membrane pick-up is mounted in each synthetic ear of a head and torso simulator to determine the sound in the ear in real-time with minimal invasiveness. The membrane design and the effects of its location on the system performance are explored, the noise spectra in the ears without and with ANC for a variety of relevant primary sound fields are reported, and the performance of the system during head movements is demonstrated. The test results show that at least 10 dB sound attenuation can be realised in the ears over an extended frequency range (from 500 Hz to 6 kHz) under a complex sound field and for several common types of synthesised environmental noise, even in the presence of head motion.
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Highton, David, Matthew Caldwell, Ilias Tachtsidis, Clare E. Elwell, Martin Smith et Chris E. Cooper. « The influence of carbon dioxide on cerebral metabolism and oxygen consumption : combining multimodal monitoring with dynamic systems modelling ». Biology Open 13, no 1 (5 janvier 2024). http://dx.doi.org/10.1242/bio.060087.
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ABSTRACT Hypercapnia increases cerebral blood flow. The effects on cerebral metabolism remain incompletely understood although studies show an oxidation of cytochrome c oxidase, Complex IV of the mitochondrial respiratory chain. Systems modelling was combined with previously published non-invasive measurements of cerebral tissue oxygenation, cerebral blood flow, and cytochrome c oxidase redox state to evaluate any metabolic effects of hypercapnia. Cerebral tissue oxygen saturation and cytochrome oxidase redox state were measured with broadband near infrared spectroscopy and cerebral blood flow velocity with transcranial Doppler ultrasound. Data collected during 5-min hypercapnia in awake human volunteers were analysed using a Fick model to determine changes in brain oxygen consumption and a mathematical model of cerebral hemodynamics and metabolism (BrainSignals) to inform on mechanisms. Either a decrease in metabolic substrate supply or an increase in metabolic demand modelled the cytochrome oxidation in hypercapnia. However, only the decrease in substrate supply explained both the enzyme redox state changes and the Fick-calculated drop in brain oxygen consumption. These modelled outputs are consistent with previous reports of CO2 inhibition of mitochondrial succinate dehydrogenase and isocitrate dehydrogenase. Hypercapnia may have physiologically significant effects suppressing oxidative metabolism in humans and perturbing mitochondrial signalling pathways in health and disease.