Seyfert星系NGC4151宽线区的Reverberation Mapping分析

本文利用我们所参与的1993年的国际联测光学资料，对NGC4151的BLR进行了后续ReverberationMapping分析，其中包括a）Monte-Carlo数值模拟检验谱线光变对连续谱光变响应的最可靠的延时时标，b）用正则线性化反演方法解出BLR的转移函数．我们分析并具体解释了对NGC4151的BLR尺度的最新测量结果同1988年的测量结果存在极其显著差别的原因．

Method of reverberation ray matrix for static analysis of planar framed structures composed of anisotropic Timoshenko beam members

Based on the method of reverberation ray matrix（MRRM）, a reverberation matrix for planar framed structures composed of anisotropic Timoshenko（T） beam members containing completely hinged joints is developed for static analysis of such structures.In the MRRM for dynamic analysis, amplitudes of arriving and departing waves for joints are chosen as unknown quantities. However, for the present case of static analysis, displacements and rotational angles at the ends of each beam member are directly considered as unknown quantities. The expressions for stiffness matrices for anisotropic beam members are developed. A corresponding reverberation matrix is derived analytically for exact and unified determination on the displacements and internal forces at both ends of each member and arbitrary cross sectional locations in the structure. Numerical examples are given and compared with the finite element method（FEM） results to validate the present model. The characteristic parameter analysis is performed to demonstrate accuracy of the present model with the T beam theory in contrast with errors in the usual model based on the Euler-Bernoulli（EB） beam theory. The resulting reverberation matrix can be used for exact calculation of anisotropic framed structures as well as for parameter analysis of geometrical and material properties of the framed structures.

Research of Underwater Bottom Object and Reverberation in Feature Space

The critical technical problem of underwater bottom object detection is founding a stable feature space for echo signals classification. The past literatures more focus on the characteristics of object echoes in feature space and reverberation is only treated as interference. In this paper, reverberation is considered as a kind of signal with steady characteristic, and the clustering of reverberation in frequency discrete wavelet transform （FDWT） feature space is studied. In order to extract the identifying information of echo signals, feature compression and cluster analysis are adopted in this paper, and the criterion of separability between object echoes and reverberation is given. The experimental data processing results show that reverberation has steady pattern in FDWT feature space which differs from that of object echoes. It is proven that there is separability between reverberation and object echoes.

A Space-Time Reverberation Model for Moving Target Detection

In recent years,moving target detection methods based on low-rank and sparse matrix decomposition have been developed,and they have achieved good results.However,there is not enough interpretation to support the assumption that there is a high correlation among the reverberations after each transmitting pulse.In order to explain the correlation of reverberations,a new reverberation model is proposed from the perspective of scattering cells in this paper.The scattering cells are the subarea divided from the detection area.The energy fluctuation of a scattering cell with time and the influence of the neighboring cells are considered.Key parameters of the model were analyzed by numerical analysis,and the applicability of the model was verified by experimental analysis.The results showed that the model can be used for several simulations to evaluate the performance of moving target detection methods.

Distant Bottom Reverberation in Shallow Water

The method of coupled mode is introduced for investigation of bi-static distant bottom reverberation of impulsive source in shallow water, which will not contradict with principle of reciprocity in all cases. And the method of multi-pole for directional source is also introduced. It shows that in case of layered medium, intensity of bi-static bottom reverberation will decease according to the cubic power of receiving time t, and the transverse spatial correlation of bottom reverberation is a little greater than longitudinal correlation for equal separation of receivers, and both vary in form with the receiving time.

A Study of Oceanic Reverberation Modeling Based on a Nonlinear Low-Dimensional Dynamic System

Acoustic reverberation signals generated by an experimental explosive source are analyzed by nonlinear dynamical methods. Three characteristic parameters, i.e., the correlation dimension, the largest Lyapunov exponent, and the Kolmogorov en- tropy, are estimated in the reconstructed phase space. The results indicate that the reverberation signals are nonlinear. The Volterra adaptive prediction method is introduced to model the oceanic reverberation signals. The reverberation time series can be predicted in short term with small prediction errors. A preliminary conclusion can be reached that the nonlinear low-dimensional dynamic sys- tem model is more suitable for modeling oceanic reverberation than the classical random AR model.

Performance Evaluation and Effectiveness of the Reverberation Room

This research presents a thorough evaluation of the reverberation room at Acoustics Laboratory in National Institute of Standards(NIS)according to the related international standards.The evaluation aims at examining the room performance and exploring its effectiveness in the frequency range from 125 Hz to 10000 Hz according to the international standard requirements.The room,which was designed and built several years ago,is an irregular rectangular shape free from diffusers.Its volume is about 158.84 m^(3),which meets the requirement of the ISO 354 standard Lmax<1.9V^(1/3).Cut-off frequencies of one and one-third octave are 63 Hz and 100 Hz respectively;however Schroder frequency is 400 Hz.Calculations of cut-off frequency and modal density showed adequate modes that give acceptable uniformity starting comfortably from frequency of 125 Hz.The room has a reverberation time that is suitable for its size over the frequency range of interest.The room sound absorption surface area and its sound absorption coefficient satisfy the criteria given in ISO 3741 and ISO 354.There is an accepted diffuse sound field inside the room due to the standard deviation of measured sound level,which is less than 1.5 dB over all the frequency range.The only exception was 125 Hz which may be due to a lack of diffusivity of the sound field at this frequency.The evaluation proves that the NIS reverberation room is in full agreement with the international standards,which in turns qualifies the room to host measurements inside without concerns.

A procedure of the method of reverberation ray matrix for the buckling analysis of a thin multi-span plate

A procedure of the method of reverberation ray matrix(MRRM)is developed to perform the buckling analysis of thin multi-span rectangular plates having internal line supports or stiffeners.A computation algorithm for the reverberation ray matrix in the MRRM is derived to determine the buckling loading.Specifically,the analytical solutions are presented for the buckling of the structure having two opposite simply-supported or clamped-supported edges with spans,while the constraint condition of two remaining edges may be in any combination of free,simply-supported,and clamped boundary conditions.Furthermore,based on the analysis of matrices relating to the unknown coefficients in the solution form for the deflection in terms of buckling modal functions,some recursive equations(REs)for the MRRM are introduced to generate a reduced reverberation ray matrix with unchanged dimension when the number of spans increases,which promotes the computation efficiency.Several numerical examples are given,and the present results are compared with the known solutions to illustrate the validity and accurateness of the MRRM for the buckling analysis.

Novel Way to Suppress Reverberation Based on Fractional Fourier Transform

A novel method of anti-reverberation based on the fractional Fourier transformation is presented. By virtue of the fact that it has a good focus property in the fractional Fourier domain, the linearly frequency modulation (LFM) signal can be seperated from the reverberation through a swept-frequency filter. With the actual reverberation data and the LFM pulse for seperation, the good results are obtained: the reverbareation is largely removed, and relatively the better performance is shown under the lower signal reverberation ratio (SRR). Based on the theorical analyses and simulation results, two schemes for detecting targets are provided: one is the detection of the LFM echo from the target with a threshold by means of this method directly; the other is to detect the target by means of other methods, with this method performing pre-process to increase SRR, which need enough large SRR.

A Deep-Water Bottom Reverberation Model Based on Ray Theory

Ocean reverberation is an important issue in underwater acoustics due to the significant influence on working performance of the active sonars. In this paper, a uniform bottom-reverberation model is proposed based on ray theory, which can calculate monostatic and bistatic reverberation intensity and explain the generation process of deep-water reverberation. The mesh meth-od is firstly used in this model by dividing bottom scatterers into a number of grids. Then reverberation is calculated based on the exact time of scattering signal generated on each grid. Due to exact arrival time, the presented model can provide more accurate result than classical models, in which scatterers are usually treated as circular rings or elliptical rings. Numerical results are compared with reverberation data collected from the South China Sea deep-water experiment with different receiving distances and depths. The simulated and experimental results agree well overall.

The Effect of Television Decors on the Change of Reverberation Time of the Studio

Reverberation time within studio’s decor is changed because of addition of its surface to the overall surfaces of the studio and also the additional absorption of its materials. It seems reverberation time changes due to studio’s decor is little because surface of the decor is small in comparison with the overall surfaces of the studio and surface has an important role in room constant and therefore in reverberation time. But these changes do not only depend on added surfaces and their absorption. Reverberation time is also dependent on shape of the decor and sometimes. It can decrease the effects of added surfaces which are used to increase the reverberation time. In this paper, a standard television studio is designed and implemented by using ODEON and 12 different decor which their dimensions and materials are similar to the actual ones, are applied inside the studio. Then studio’s decor effects on reverberation time of the studio are computed, compared and analyzed.

Frequency-selective attenuation of sound propagation and reverberation in shallow water

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Improving sound diffusion in a reverberation tank using a randomly fluctuating surface

Underwater reverberation environments that satisfy the conditions of uniformity and isotropy of the diffuse field can be used to measure the acoustic characteristics of underwater targets.This study combines two practical indicators—the standard deviation of the absolute sound pressure field(to indicate uniformity)and the analysis of the wavenumber spectrum in the spherical harmonics domain(to indicate isotropy)—for an accurate evaluation of the diffusion of the sound field in a reverberation tank.A method is proposed that can improve the narrow-band diffusion of the sound field by employing a randomly fluctuating surface.An acoustic experiment was performed in a reverberation water tank(1.2 m×1 m×0.8 m),where a randomly fluctuating surface was generated by making waves.The experimental results show that as the wave motion contributes effectively to the random reflection of sound rays in all directions,the uniformity and isotropy are improved significantly when the surface is fluctuating randomly.This work helps to ensure accurate measurements of the characteristics of underwater targets in reverberation tanks.

Numerical Simulation on the Extraction of Modal Back-Scattering Matrix from Reverberation Data for High Frequency Cases

The modal back-scattering matrix can be extracted from reverberation data. For high frequency cases the ’window smoothed’ processing has been proposed by E. C. Shang, T. F. Gao and D. J. Tang (2002) to extract the ’window averaged’ back-scattering matrix. It is pointed out in this paper that in order to inverse the ’window averaged’ back-scattering matrix by changing the source depth data we have to assume that the matrix is not related to the source depth, and the numerical simulation on the question has been conducted.

Nonlinear Acoustic Shadow Method to Reduce Reverberation Artifact

A novel technique for reducing reverberation artifact in acoustic shadow imaging using nonlinear ultrasound interaction, called nonlinear acoustic shadow method, has been developed and experimentally studied. In this technique, the conventional acoustic shadow method is modified by using the secondary wave generated by nonlinear interaction of two primary sound waves emitted from parametric array. Either conventional or nonlinear acoustic shadow imaging is carried out for aluminum square cylinder and the size of the shadow is compared. The result shows that the nonlinear acoustic shadow method reduces reverberation artifact inside the square cylinder and has better accuracy in the size measurement than conventional acoustic shadow method.

Determined Reverberant Blind Source Separation of Audio Mixing Signals

Audio signal separation is an open and challenging issue in the classical“Cocktail Party Problem”.Especially in a reverberation environment,the separation of mixed signals is more difficult separated due to the influence of reverberation and echo.To solve the problem,we propose a determined reverberant blind source separation algorithm.The main innovation of the algorithm focuses on the estimation of the mixing matrix.A new cost function is built to obtain the accurate demixing matrix,which shows the gap between the prediction and the actual data.Then,the update rule of the demixing matrix is derived using Newton gradient descent method.The identity matrix is employed as the initial demixing matrix for avoiding local optima problem.Through the real-time iterative update of the demixing matrix,frequency-domain sources are obtained.Then,time-domain sources can be obtained using an inverse short-time Fourier transform.Experi-mental results based on a series of source separation of speech and music mixing signals demonstrate that the proposed algorithm achieves better separation performance than the state-of-the-art methods.In particular,it has much better superiority in the highly reverberant environment.

Reverberation Chamber技术应用于手机OTA量测

一般混响室多用于EMC测试中,文章针对手机的OTA全辐射功率与全性灵敏度在混响室中测试方法提出说明,并针对小型的多输入多输出天线于多重路径环境测试测试方式说明。

弹簧地基上大直径单桩海上风机的一阶自振频率

自振频率是海上风机前期动力设计的主要难点之一,计算精度要求极高,而桩-土相互作用对自振频率影响显著。目前,针对桩-土相互作用普遍采用弹簧地基简化模型,为对比分析不同弹簧地基简化模型的准确性和精度,本文采用回传射线矩阵法,建立固定端、单弹簧、双弹簧和三弹簧这4种地基简化模型,基于Bernoulli-Euler梁理论和Timoshenko梁理论,求解风机系统的自振频率,并与风机基频实测值作对比,进一步分析三弹簧简化地基模型中地基旋转刚度、地基耦合刚度和地基水平刚度对风机系统基频的影响。研究结果表明,桩-土相互作用不可忽略,三弹簧地基简化模型计算风机系统基频精度最高;地基刚度对风机系统基频的敏感性次序为,地基耦合刚度>地基旋转刚度>地基水平刚度;当地基旋转(水平)刚度较小时,地基耦合刚度与地基旋转(水平)刚度的耦合效应对风机系统的基频影响较大;地基耦合刚度与地基旋转刚度的耦合效应对风机系统基频的影响程度大于地基耦合刚度与地基水平刚度的耦合效应。