水声信号稀疏重构的高阶累积量波达方向估计

高阶累积量具有高斯噪声抑制和阵元扩展特性,将高阶累积量引入水声信号的方位估计中,提出了离格稀疏贝叶斯学习重构的高阶累积量测向算法。该方法利用高阶累积量对高斯噪声的自然盲性,计算阵列信号四阶累积量来滤除高斯噪声,使阵元在原来的结构上扩展了一倍;并构造出选择矩阵剔除了四阶累积量中的冗余项,能再一次的扩展阵元,得到的新观测模型具有更好的统计性能;最后利用空域稀疏性,推导出四阶累积量下的离格稀疏表示模型,采用贝叶斯学习解算出源信号的最大后验概率,实现了目标方位估计。数值仿真和海试实验数据表明,该方法在相邻声源方位间隔为4°的情况下分辨概率可达到95%以上,在信噪比大于-5 dB时目标方位估计的均方根误差在1°以内,可显著抑制背景噪声干扰,在多声源密集分布条件下也能准确、稳健的对水声目标方位进行估计。      

Array gain of fourth-order cumulants beamforming under typical probability density background

The fourth-order cumulant of zero mean Gaussian distribution noise always equals to zero theoretically.In practice the probability density of noise and reverberation is the key problem to performance of the fourth-order cumulant beamforming technique.In this paper,the array gain functions of the fourth-order cumulant beamforming are deducted considering the instantaneous amplitude distribution of the ambient sea noise and bottom reverberation respectively.And the relationships are determined between array gain and the factors including the number of the array elements,the fourth-order and second-order statistical properties of the noise and reverberation,and the input signal-to-noise ratio.It is also verified that there is a critical signal-to-interference ratio and the fourth-order cumulant beamforming can obtain higher gain and resolution than the conventional beamforming method when the ratio is larger than it.The results of experiment data processing demonstrate that the gain and the resolution of the fourth-order cumulant beamforming coincide with the theoretic.     

典型概率密度背景下四阶累积量波束形成的阵增益

在理论上零均值高斯分布噪声的四阶累积量恒等于零,而实际噪声和混响的概率密度是影响四阶累积量波束形成技术性能的关键问题。本文针对海洋环境噪声与海底混响的瞬时幅度分布,分别推导了四阶累积量波束形成阵增益函数;建立了阵增益与阵元数、海洋环境噪声和海底混响统计特性的四阶矩和二阶矩及输入信噪比的关系;确定了与常规波束形成阵增益之间存在临界信噪比,高于临界信干比时四阶累积量波束形成可以获得比常规波束形成更高的阵增益与分辨率。实验数据处理结果验证了四阶累积量波束形成阵增益和分辨率理论结果的一致性。      

噪声对超导量子比特测量系统的影响

详细介绍了噪声对超导量子比特测量系统的影响。测量系统通过对时间的测量来获得单个约瑟夫森结跳变电流统计分布P(I)。在测量电路中采取了一系列的降噪措施,使得实验所能测到的约瑟夫森结的最低等效温度进一步的降低。     

A novel algorithm for underwater moving-target dynamic line enhancement

When we use a traditional adaptive line enhancer (ALE) algorithm to detect an underwater moving target, there are two disadvantages: the ability to suppress colored Gaussian noise is low and the lower the SNR is, the worse the performance of the ALE algorithm. In order to greatly overcome these disadvantages, we take full advantage of the capability of higher order cumulants to alleviate the effect of colored Gaussian noise and develop a fourth order cumulant non-diagonal slice-based adaptive dynamic line enhancer (FOCNDSBADLE) algorithm and fourth order cumulant diagonal slice-based adaptive dynamic line enhancer (FOCDSBADLE) algorithm. The adaptive filtering coefficients of these algorithms are indirectly updated by the instantaneous fourth order cumulant slices. It is shown that these slices are comprised of noiseless sinusoids if the input signals are comprised of sinusoids corrupted by Gaussian noise. Therefore these algorithms are fit to handle highly colored Gaussian noise. Simulation tests are carried out using the measured data radiated by the underwater moving target. Simulation results have shown that the FOCNDSBADLE algorithm and FOCDSBADLE algorithm outperform the ALE algorithm and that the FOCNDSBADLE algorithm outperforms the FOCDSBADLE algorithm in the case of Gaussian noise.     

Rigorous field-theoretical approach to the contact mechanics of rough elastic solids

A statistical field theory is formulated, which allows one to calculate the pressure distribution Pr(p) in a contact formed by an elastic body and a rigid counter face of arbitrary topography. It is a cumulant expansion, which contains Persson's contact mechanics theory as the leading-order term. Our approach provides a framework with which corrections can now be derived systematically. As an example, Pr(p) is calculated to high accuracy for exponentially repulsive solids. Non-Gaussian tails in Pr(p) can be rationalized for surfaces whose height spectra differ from colored noise.     

Temperature-dependent third cumulant of tunneling noise

Poisson statistics predicts that the shot noise in a tunnel junction has a temperature independent third cumulant e(2)I, determined solely by the mean current I. Experimental data, however, show a puzzling temperature dependence. We demonstrate theoretically that the third cumulant becomes strongly temperature dependent and may even change sign as a result of feedback from the electromagnetic environment. In the limit of a noninvasive (zero-impedance) measurement circuit in thermal equilibrium with the junction, we find that the third cumulant crosses over from e(2)I at low temperatures to -e(2)I at high temperatures.     

An Accurate Method for Determining the IF Noise in SIS Heterodyne Receivers

We present a new method to determine the contribution of the IF-amplifier chain to the overall noise performance of an SE-based receiver. Using simulated I-V and IF power characteristics, we show that the standard method used to date to evaluate the IF noise can underestimate the contribution because of non-negligible curvature in the post-gap SIS I-V characteristic. We demonstrate that the new method is not susceptible to the post-gap curvature, and discuss its benefits and limitations to the accurate and precise evaluation of IF noise contributions.     

On the Domain of Hyperbolicity of the Cumulant Equations

In this article we consider the influence of non-equilibirum values of classical variables on the eigenvalues of the advection part of the cumulant equations. Real and finite eigenvalues are a neccessary condition for the cumulant equations to be hyperbolic which can be used to obtain estimates on admissible deviations from equilibrium for a model of particular order still to be valid. We find that this condition puts no constraints on velocity and shear stress values, but specific energy must be positive, normal stress must be bounded by specific energy and heat flux not be too large.     

Application of Electron-Beam Ionized Discharges to Switches?a Comparison of Experiment with Theory

A theoretical investigation of high-pressure discharges ionized by an external electron beam (e-beam) was conducted. Only when secondary emission from the cathode and electron-impact ionization of metastable states were included in the analysis did calculated current-voltage (I-V) characteristics for argon and methane discharges compare well with experimental data. The I-V characteristics obtained reveal a sharp rise in the current at a certain threshold voltage. This threshold voltage and the entire I-V characteristic are shifted to lower voltages when metastable ionization is significant. Below the threshold voltage and at low external ionization source strengths, a region of negative differential conductivity is obtained. In the high-current region, the I-V slope is controlled by the secondary emission coefficient. The additional cathode sheath ionization from secondary emission and ionization from metastable states significantly reduces the discharge voltage. This important effect can be used to reduce e-beam switch losses and increase lifetime through judicious gas mixture selection and proper cathode conditioning.     

DOA estimation for uniform circular array without the source number based on beamspace transform and higher-order cumulant

Fourth-order cumulant is one of most widely used high-order cumulant for direction of arrival (DOA) estimation due to its ability of expanding the virtual array aperture as well as suppressing Gaussian noise. To address the two-dimensional (2D) DOA estimation problem, we propose a modified MUSIC scheme for uniform circular array (UCA) in this paper. Firstly, the fourth-order cumulant of UCA is considered to construct a new propagator, resulting in the elimination of a priori knowledge of the number of signals. Secondly, the UCA is transformed by beamspace transformation, reducing the time computational complexity of the algorithm since the two-dimensional grid search and singular value decomposition are avoided. And finally a low-rank recovery algorithm is adopted to improve the accuracy regarding the limited snapshots scenario. The numerical simulations validate the superiority of the proposed method.     

Spin relaxation. The renormalized operator cumulant approach

Two-level systems under the influence of external noise are generic models of quantum relaxation processes. The spin 1/2 particle in a stochastic magnetic field is one of the best known examples. Interesting effects are observed if the noise is colored as is the case in most applications. The time-ordered operator cumulant expansion forms a convenient approach to this problem. Recently, a renormalization procedure has been proposed which corresponds to a partial summation of the naive expansion and hence constitutes an essential improvement over the second cumulant considered usually. For colored noise of intermediate strength and correlation time this approach is used to derive renormalized expressions for the transverse (T ₂) and longitudinal (T ₁) relaxation time and the frequency shift. In this parameter region, the ratioT ₁/T ₂= is found to deviate substantially from its value =2 valid for white noise exactly and for colored noise in the second cumulant approximation. This corroborates and extends results of Budimir and Skinner obtained by including the second and fourth cumulant only. However, their truncated expansion is shown to lead to unphysical results in the intermediate parameter region treated still correctly by the renormalized expansion.     

Magnetic-field-induced non-Gaussian fluctuations in macroscopic equilibrium systems

We calculate the magnetic-field-dependent nonlinear conductance and noise in a two-dimensional macroscopic inhomogeneous system. If the system does not possess a specific symmetry, the magnetic field induces a nonzero third cumulant of the current even at equilibrium. This cumulant is related to the first and second voltage derivatives of the spectral density and average current in the same way as for mesoscopic quantum-coherent systems, but these quantities may be much larger. The system provides a robust test of a nonequilibrium fluctuation relation.     

Tunneling in submicron CMOS single-photon avalanche diodes

Tunneling is studied in two main single-photon avalanche diode （SPAD） topologies, which are r~-tub guard ring （NTGR） and p-tub guard ring （PTGR）. Device sinmlation, I - V measurements, and dark count calculations and measurements demonstrate that tunneling is the main source of noise in NTGR, but it is less dominant in PTGR SPADs. All structures are characterized with respect to dark noise, photon detection probability, tinting jitter, afterpulsing probability, and breakdown voltage. Noise performmme is disturbed because of tunneling, whereas jitter performance is disturbed because of the short diffusion time of photo-generated minority carriers in NTGR SPADs. The maximum photon detection probability is enhanced because of an improvement in absorption thickness.     

Langmuir单探针诊断射频辉光放电等离子体及其数据处理

Langmuir探针是诊断等离子体参数的重要手段.报道了在氩气射顿(13.56MHz)辉光放电等离子体中使用调谐单探针进行诊断,对探针I-V特性曲线的统计噪声进行了数字滤波的光滑化处理,而后求二次微商.在相同的放电条件下,使用自行设计的微分电路,对探针特性二次微商进行在线测量.这两种方法得到的二次微商结果能够较好地符合. 关键词： Langmuir探针 二次微商 数值滤波 微分电路     

Localisation of moving sources in a multipath propagation environment

A new algorithm is presented for tracking correlated narrow-band sources in the presence of colored Gaussian noise. A fast cumulant-based preprocessing method is used to remove unknown noise and a Kalman filtering is used to track the source parameters. The use of a Kalman filtering avoids the data association problem and improves the tracking performance for crossing tracks. It is applied to the outputs of Newton’s algorithm to track moving sources. In this paper, the algorithm is developed for the special case in which the updated cumulant matrix is obtained by substituting a new matrix of the current data. The rank tracking problem is not considered in this study.We demonstrate the performance of the proposed algorithm by computer simulations of the tracking of moving targets emitting correlated signals, we also tested the proposed algorithm on the real data recorded during an underwater acoustic experiments.     

强噪声中的光散射通信信号检测

针对光散射通信存在严重的多径衰落及噪声干扰,提出了一种基于空间分集接收,并采用三阶累积量及互相关滤波的信号检测方法。该方法使用两路探测器同时接收信号,并分别计算采集信号的自三阶累积量对角切片,之后对两路信号进行互相关滤波。实验结果表明,在接收信号信噪比低至-25dB时,该方法仍可抑制噪声干扰,正确提取信号频率特征,且对设备要求不高,操作简便,能够实现强噪声中的实时光散射信号的检测。     

Place specific influences on the wave I to V interpeak latency of the auditory brain-stem response.

There is controversy over whether the wave I to V interpeak latency (I-V IPL) of the auditory brain-stem response can be manipulated by cochlear processing. In this study, a forward masking paradigm was used to test the predictions of two contrasting models of I-V IPL generation. The paradigm was designed to determine if the I-V IPL can be affected by masking selected portions of the cochlear response region. The results from ten normal hearing subjects suggest that: (1) waves I and V can be masked semi-independent of each other, and (2) the I-V IPL can be shortened or prolonged by masking the basal or apical portion of the cochlear response region respectively. These findings support the hypothesis that, at least in normal hearing subjects, wave V is biased to reflect more apical cochlear events than wave I. Additionally, they offer tentative support for anecdotal reports of shortened I-V IPLs in the presence of high-frequency hearing loss.     

匹配场处理舰船辐射噪声级估计方法

针对水声信道对舰船辐射噪声声传播的影响,进而导致声源级测量结果不准确的问题,提出了基于匹配场处理的舰船辐射噪声级估计方法。在海洋环境噪声为空间均匀高斯白噪声的假设下,当海洋环境参数已知、信噪比满足一定要求时,匹配场处理能有效地给出被测噪声源的位置信息及该位置处的能量响应。从能量估计角度出发,推导了声源位置处匹配场输出响应的能量修正因子计算公式,从理论上证明了匹配场处理在被测声源位置处输出响应与能量修正因子的乘积为真实声源级的最小方差无偏(MVU)估计。该方法首先选择合适的声场计算模型计算拷贝场向量,对接收到的辐射噪声信号进行匹配场处理,得出接收信号级和被测声源位置;其次利用该位置所对应的拷贝场向量替换能量修正因子公式中的真实信道传输函数以计算能量修正因子的估计值;最后由接收信号级与能量修正因子估计值相乘得出舰船辐射噪声声源级的MVU估计。针对典型的浅海水声信道,进行了计算机仿真试验,结果表明:该方法能有效地进行舰船辐射噪声测量,当信噪比满足一定要求时,测量得到的声源级与实际声源级相比,误差小于1 dB。