被动声纳方位估计的宽带盲源分离算法

针对实际被动声纳信号宽带非平稳且统计特性无法预知的特点,由宽带卷积混合模型,建立了融合时间延迟结构与非参数化特性的代价函数,通过核密度技术同时估计目标源的概率密度函数和解混矩阵,并对估计的最优解混矩阵与目标源信号求取每个频点内方位能量谱,最后累加所有子带构成宽带方位能量谱。宽带仿真结果与实际海试表明该方法在方位分辨率和估计精度方面接近最小方差无失真响应(Minimum Variance Distortionless Response,MVDR)和多重信号分类(Multiple Signal Classification,MUSIC)算法,在弱目标检测方面具有一定优势。

Decay rates and time lags of heat conduction in building construction under field conditions

The field measurements of decay rates and time lags of heat conduction in a building construction taken in Nanjing during the summer of 2001 are presented.The decay rates and time lags are calculated according to the frequency responses of the heat absorbed by the room＇s internal surfaces,inside surface temperature,indoor air temperature and outdoor synthetic temperature.The measured results match very well with the theoretical results of the zeroth and the first order values of the decay rates and time lags of heat conduction in the building construction,but the difference between the measured values and the theoretical values for the second order is too great to be accepted.It is therefore difficult to accurately test the second order value.However,it is still advisable to complete the analysis using the zeroth-and the first-orders values of the decay rates and time lags of heat conduction in building construction under field conditions,because in these cases the decay rates of heat conduction reach twenty which meets the requirements of engineering plans.

Characteristic Analysis of Underwater Acoustic Scattering Echoes in the Wavelet Transform Domain

Underwater acoustic scattering echoes have time–space structures and are aliasing in time and frequency domains. Different series of echoes properties are not identified when incident angle is unknown. This article investigates variations in target echoes of monostatic sonar to address this problem. The mother wavelet with similar structures has been proposed on the basis of preprocessing signal waveform using matched filter, and the theoretical expressions between delay factor and incident angle are derived in the wavelet domain. Analysis of simulation data and experimental results in free-field pool show that this method can effectively separate geometrical scattering components of target echoes. The time delay estimation obtained from geometrical echoes at a single angle is consistent with target geometrical features, which provides a basis for object recognition without angle information. The findings provide valuable insights for analyzing elastic scattering echoes in actual ocean environment.

A New Experimental Method for Investigations on Microstructure of Liquid-Vapor Interface

Many physical,chemical,and biological processes happen in liquid-vapor interface and are profoundly influenced with the local microstructures.In contrast to the liquid bulk,molecular orientation is the remarkable one of asymmetric structural features of the interface.Here we report an experimental method,namely,electron-impact time-delayed mass spectrometry and give a Ion Detector Time-of-Flight Tub*Liquid Microjet Ion Attrac Liq Electron Multiplier Quadrupole Mass Filter Bender j id Beai Electrons Liquid Dump Pulsed Electron Gun brief review about our recent progresses.This brand-new method not only enables us to have more insights into the interfacial structures,as done with small-angle X-ray and neutron scatterings and vibrational sum frequency generation spectroscopy,but also provides opportunity to explore the electron-driven chemical reactions therein.

Clustered trajectories anonymity in wireless sensor networks

This paper proposes a clustered trajectories anonymity scheme （CTA） that enhances the kano nymity scheme to provide the intended level of source location privacy in mobile event monitoring when a global attacker is assumed. CTA applies isomorphic property of rotation to create traces of the fake sources distributions which are similar to those of the real sources. Thus anonymity of each trajectory and that of the clustered is achieved. In addition, location kdiversity is achieved by dis tributing fake sources around the base station. To reduce the time delay, tree rooted at the base sta tion is constructed to overlap part of the beacon interval of the nodes in the hierarchy. Both the ana lytical analysis and the simulation results prove that proved energy overhead and time delay. our scheme provides perfect anonymity with improved energy overhead and time delay.

Coefficient of retardation time found out by polynomial fitting to predict creep behaviour of polystyrene

The universal creep function is successful in relating the creep （ε） to the ageing time （ta）, coefficient of retardation time （β）, and intrinsic time （t0）. The relation was used to treat the creep experimental data for polystyrene （PS） specimens at a given aged time and different stress levels. Comparing with “middle-point” method reported in the literatures, β is found out by another method “polynomial fitting” in this work. Then unified master lines were constructed with the treated data and curves according to the universal equation. The master lines can be used to predict the long-term creep behaviour and lifetime by extrapolating to a required ultimate strain.

Synchronization Research of a Modified Time-Delayed Multi-agent Network Model

The synchronization of time-delayed multi-agent networks with connected and directed topology is studied. Based on the correlative work about the agent synchronization, a modified model is presented, in which each communication receiver is distributed a delay 7. In addition, a proportional term k is introduced to modulate the delay range and to guarantee the synchronization of each agent. Two new parameters mentioned above are only correlative to the network topology, and a theorem about their connections is derived by both frequency domain method and geometric method. Finally, the theoretical result is illustrated by numerical simulations.

OUTPUT VARIABLE STRUCTURE CONTROL FOR TIME-INVARIANT LINEAR TIME-DELAY SINGULAR SYSTEM

Synthesis and design of output variable structure controller for time-invariant linear timedelay singular system are studied. In the case that the system is regular and the system index is one, switching function with integral compensator and variable structure controller are designed, which guarantee that the sliding mode is asymptotically stable and the solution trajectory of the system arrives at the switching manifold in limited time. The design method is applicable to the systems which can be regularized. Finally, a numerical example is given to demonstrate effectiveness and simplicity of the design method.

Dynamic analysis of a stage-structured predator-prey system with disturbed time delay and birth pulse

In this paper, a stage-structured predator prey system with birth pulse and disturbed time delay is investigated. The conditions of the prey-extinction periodic solution of the system which are globally attractive have been obtained. Furthermore, the sufficient corlditions for the permanence of the system are established. Finally, numerical analysis is given to confirm the theoretical results.