排序方式: 共有14条查询结果,搜索用时 16 毫秒
1.
Multipath arrivals at a receiving sensor are frequently encountered in many signal-processing areas, including sonar, radar, and communication problems. In underwater acoustics, numerous approaches to source localization, geoacoustic inversion, and tomography rely on accurate multipath arrival extraction. A novel method for estimation of time delays and amplitudes of arrivals with maximum a posteriori (MAP) estimation is presented here. MAP estimation is optimal if appropriate statistical models are selected for the data; implementation, requiring maximization of a multidimensional function, is computationally demanding. Gibbs sampling is proposed as an efficient means for estimating necessary posterior probability distributions, bypassing analytical calculations. The Gibbs sampler includes as unknowns time delays, amplitudes, noise variance, and number of arrivals. Through Monte Carlo simulations, the method is shown to have a performance very close to that of analytical MAP estimation. The method is also shown to be superior to expectation-maximization, which is often applied to time-delay estimation. The Gibbs sampling approach is demonstrated to be more informative than other time-delay estimation methods, providing complete posterior distributions compared to just point estimates; the distributions capture the uncertainty in the problem, presenting likely values of the unknowns that are different from simple point estimates. 相似文献
2.
Sinyukov AM Liu Z Hor YL Su K Barat RB Gary DE Michalopoulou ZH Zorych I Federici JF Zimdars D 《Optics letters》2008,33(14):1593-1595
Rapid voltage-controlled phase modulation of cw terahertz (THz) radiation is demonstrated. By transmitting an infrared beam through a lithium niobate phase modulator the phase of the THz radiation, which is generated by the photomixing of two infrared beams, can be directly modulated through a 2pi phase shift. The 100 kHz modulation rate that is demonstrated with this technique is approximately 3 orders of magnitude faster than what can be achieved by mechanical scanning. 相似文献
3.
A deep understanding of both guided propagating and evanescent waves is very essential for non-destructive evaluation. Guided propagating waves have received considerable attention, but the research on guided evanescent waves is quite limited, especially for functionally graded structures. This paper presents an analytical approach, based on the orthogonal function technique, to solve the evanescent waves in a spherical curved plate with functionally graded material in the radial direction. The proposed approach can obtain all the real, imaginary and complex solutions but without iterative process. The validity of the proposed approach is illustrated by comparison with available results. The convergence of the approach is also discussed through a numerical example. Dispersion characteristics of the guided waves in various graded spherical curved plates are studied and three dimensional dispersion curves are plotted in frequency-complex wavenumber space. The effects of different radius-thickness ratios and graded fields on the dispersion curves of the guided evanescent waves are illustrated. The displacement distributions are also discussed to analyze the characteristics of the guided evanescent waves. 相似文献
4.
The focus of this work is on arrival time and amplitude estimation from acoustic signals recorded at spatially separated hydrophones in the ocean. A particle filtering approach is developed that treats arrival times as "targets" and tracks their "location" across receivers, also modeling arrival time gradient. The method is evaluated via Monte Carlo simulations and is compared to a maximum likelihood estimator, which does not relate arrivals at neighboring receivers. The comparison demonstrates a significant advantage in using the particle filter. It is also shown that posterior probability density functions of times and amplitudes become readily available with particle filtering. 相似文献
5.
DTO体系分子反应动力学 总被引:6,自引:1,他引:5
基于DTO分子( 1A1)的氢同位素效应,得到修正的Born-Oppenheimer(B-O)理论下多体展式分析势能函数.用准经典的Monte-Carlo轨迹法研究了D+ TO(0 ,0)和T+ DO(0 ,0)的分子反应动力学过程.结果表明:在碰撞能量较低时( < 209.2 kJ. mol - 1 ),D+ TO(0 ,0)和T+DO(0,0)反应主要生成O+ DT,并且该反应是无阈能的;有少量的交换反应产物DO (TO)生成,并伴有极少量的络合物产生.碰撞能大于209.2kJ . mol - 1后,逐渐出现分子被完全碰散成D,T ,O 原子的情形.反应 D+TO(0 ,0) →OD + T和 T +DO(0 ,0) →OT + D是无热反应但是有阈能存在.由于D和T原子的同位素效应,置换产物轨线存在非一致性. 相似文献
6.
An image-processing method is proposed to obtain the distribution of the removal efficiency of particles on a plate by an
air jet. This method can be used to measure particle removal from a flat surface by processing the image of the reflected
light from the surface. Factors affecting the particle removal efficiency such as air pressure, distance between the nozzle
and the impinging surface and the impinging angle are discussed. Optimal conditions are determined to obtain the most effective
particle removal by the air jet.
Received: 10 April 2001 / Accepted: 2 August 2001 相似文献
7.
Michalopoulou V. Axiotis M. Chasapoglou S. Eleme Z. Gkatis G. Kalamara A. Kokkoris M. Lagoyannis A. Patronis N. Stamatopoulos A. Tsantiri A. Vlastou R. 《The European Physical Journal A - Hadrons and Nuclei》2021,57(9):1-18
The European Physical Journal A - The E1 contribution to the capture reaction $$^7\mathrm {Li}(n,\gamma )^8\mathrm {Li}$$ is calculated at low energies. We employ a coupled-channel... 相似文献
8.
Michalopoulou ZH Yardim C Gerstoft P 《The Journal of the Acoustical Society of America》2012,131(1):EL74-EL80
Seabed interface depths and fathometer amplitudes are tracked for an unknown and changing number of sub-bottom reflectors. This is achieved by incorporating conventional and adaptive fathometer processors into sequential Monte Carlo methods for a moving vertical line array. Sediment layering information and time-varying fathometer response amplitudes are tracked by using a multiple model particle filter with an uncertain number of reflectors. Results are compared to a classical particle filter where the number of reflectors is considered to be known. Reflector tracking is demonstrated for both conventional and adaptive processing applied to the drifting array data from the Boundary 2003 experiment. The layering information is successfully tracked by the multiple model particle filter even for noisy fathometer outputs. 相似文献
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