Current Issue : April - June Volume : 2018 Issue Number : 2 Articles : 5 Articles
Underwater acoustic channel (UAC) is one of the most challenging communication channels in the world, owing to\nits complex multi-path and absorption as well as variable ambient noise. Although adaptive equalization could\neffectively eliminate the inter-symbol interference (ISI) with the help of training sequences, the convergence rate of\nequalization in sparse UAC decreased remarkably. Besides, channel estimation algorithms could roughly figure out\nchannel impulse response and other channel parameters through several specific mathematical criterions. In this\npaper, a typical channel estimation method, least square (LS) algorithm, is applied in adaptive equalization to obtain\nthe initial tap weights of least mean square (LMS) algorithm. Simulation results show that the proposed method\nsignificantly enhances the convergence rate of the LMS algorithm....
To explore the failure precursors of hard rock, a series of triaxial loading and unloading experiments were carried out on sandstone\nsample using the acoustic emission systems.Theextreme-point symmetricmode decomposition method (ESMDmethod) was used\nto denoise and reconstruct the AE data.The AE quiet period in Scheme I becomes much more obvious with the confining pressure\nincreasing, which can be regarded as the precursor information of the sample failure under conventional triaxial compression.\nUnlike Scheme I, there are no obvious precursory characteristics before failure in Schemes II and III, and the count rate reaches\nthe maximum at the peak point. When the stress ratio ranges from 0.8 to 1.0, the fractal values of acoustic emission can be used\nto investigate the failure precursors of samples at a lower confining pressure.When the time ratio is greater than 0.8 under higher\nconfining pressures, the fractal values of sandstone samples under unloading paths are rapidly reduced,which can be used to predict\nrock failure at higher confining pressures....
We investigate longitudinal near-field coupling between acoustic resonators grafted along\na waveguide. Experiments are performed in the audible range with a simple acoustic system\ncomposed of a finite aperiodic sequence of air resonators. Transmission typically shows a zero around\na resonance frequency of a single resonator, as is well known. When two identical resonators are\nbrought in close proximity, however, we observe that longitudinal near-field coupling strongly\ninfluences the acoustic transmission. When the separation between resonators is increased so\nthat they can be considered in the far field of one another, we further observe the appearance\nof Fano-like transmission profiles. We explain this observation by the formation of locally resonant\nFabry-Perot interferometers from every pair of resonators. All experimental results are compared to\nthree-dimensional finite element analysis of the acoustic system....
The application of Acoustic Doppler Current Profiler (ADCP) can be used not only for measuring ocean currents, but also for\nquantifying suspended sediment concentrations (SSC) from acoustic backscatter strength based on sonar principle. Suspended\nsediment has long been recognized as the largest sources of sea contaminant and must be considered as one of the important\nparameters in water quality of seawater. This research was to determine SSC from measured acoustic backscattered intensity of\nstatic and mobile ADCP. In this study, vertically mounted 400 kHz and 750 kHz static ADCP were deployed in Lembeh Strait,\nNorth Sulawesi. A mobile ADCP 307.2 kHz was also mounted on the boat and moved to the predefined cross-section, accordingly.\nThe linear regression analysis of echo intensity measured by ADCP and by direct measurement methods showed that ADCP is a\nreliable method to measure SSC with correlation coefficient (...
Thanks, the terrorist attacks on the worldwide interest in the design of structures for\nfire greatly increased. One of the advantages of concrete over other building materials is its\ninherent fire-resistive properties. The concrete structural components still must be able to\nwithstand dead and live loads without collapse even though the rise in temperature causes a\ndecrease in the strength and modulus of elasticity for concrete and steel reinforcement. In\naddition, fully developed fires cause expansion of structural components and the resulting\nstresses and strains must be resisted. This paper reports the results of measurements by Impactecho\nmethod and measurement by ultrasound. Both methods are based on the acoustic\nproperties of the material which are dependent on its condition. These acoustic methods allow\nidentifying defects and are thus suitable for monitoring the building structure condition. The\nresults are obtained in the laboratory during the degradation of composite materials based on\ncement by high-temperature....
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