闪电快电场信号时频特性的小波分析

应用小波变换方法将具有短时非平稳特点的闪电快电场时域波形信号转换到二维的时频平面,从时间和频率上同时描述闪电快电场信号的电场强度或相对能量分布,揭示其所包含的不同频率分量及其随时间变化的特性.分析结果表明,基于小波变换的闪电快电场信号时频特性分析可以挖掘闪电电场更深层次的变化规律和特征;也为闪电放电类型的识别研究提供了新的思路.     

An interactive approach based on a discrete differential evolution algorithm for a class of integer bilevel programming problems

This paper presents an interactive approach based on a discrete differential evolution algorithm to solve a class of integer bilevel programming problems, in which integer decision variables are controlled by an upper-level decision maker and real-value or continuous decision variables are controlled by a lower-level decision maker. Using the Karush--Kuhn–Tucker optimality conditions in the lower-level programming, the original discrete bilevel formulation can be converted into a discrete single-level nonlinear programming problem with the complementarity constraints, and then the smoothing technique is applied to deal with the complementarity constraints. Finally, a discrete single-level nonlinear programming problem is obtained, and solved by an interactive approach. In each iteration, for each given upper-level discrete variable, a system of nonlinear equations including the lower-level variables and Lagrange multipliers is solved first, and then a discrete nonlinear programming problem only with inequality constraints is handled by using a discrete differential evolution algorithm. Simulation results show the effectiveness of the proposed approach.     

A two-stage approach in solving the state probabilities of the multi-queue M/G/1 model

The M/G/1 model is the fundamental basis of the queueing system in many network systems. Usually, the study of the M/G/1 is limited by the assumption of single queue and infinite capacity. In practice, however, these postulations may not be valid, particularly when dealing with many real-world problems. In this paper, a two-stage state-space approach is devoted to solving the state probabilities for the multi-queue finite-capacity M/G/1 model, i.e. q-M/G/1/K_i with K_i buffers in the ith queue. The state probabilities at departure instants are determined by solving a set of state transition equations. Afterward, an embedded Markov chain analysis is applied to derive the state probabilities with another set of state balance equations at arbitrary time instants. The closed forms of the state probabilities are also presented with theorems for reference. Applications of Little's theorem further present the corresponding results for queue lengths and average waiting times. Simulation experiments have demonstrated the correctness of the proposed approaches.     

ADRC Law of Spacecraft Rendezvous and Docking in Final Approach Phase

This article addresses the high-precision coordinated control problem of spacecraft autonomous rendezvous and docking, which couple the relative position and attitude in the final approach phase. The coupled dynamics equations of the tracking-target spacecrafts is derived by using dual quaternions. Then, a cascade Active Disturbance Rejection Controller is proposed, by which the extended state observer and nonlinear error feedback law is designed, the virtual value on which the actual control volume tracking is calculated to ensure the finite time convergence of the relative position and attitude tracking errors in spite of parametric uncertainties and external disturbances. Finally, numerical simulations are performed to demonstrate that the proposed approaches, which can avoid the coupling effect and restrain the interference, can track the target spacecraft in a relatively short period of time, and the control precision can satisfy the requirements of docking.     

An iterative approach for sparse direction-of-arrival estimation in co-prime arrays with off-grid targets

This paper addresses the problem of direction of arrival (DOA) estimation by exploiting the sparsity enforced recovery technique for co-prime arrays, which can increase the degrees of freedom. To apply the sparsity based technique, the discretization of the potential DOA range is required and every target must fall on the predefined grid. Off-grid target can highly deteriorate the recovery performance. To the end, this paper takes the off-grid DOAs into account and reformulates the sparse recovery problem with unknown grid offset vector. By introducing a convex function majorizing the given objective function, an iterative approach is developed to gradually amend the offset vector to achieve final DOA estimation. Numerical simulations are provided to verify the effectiveness of the proposed method in terms of detection ability, resolution ability and root mean squared estimation error, as compared to the other state-of-the-art methods.     

The EU data protection reform and the challenges of big data: remaining uncertainties and ways forward

As the first broad reform of the EU data protection legislation is being achieved, and notwithstanding EU institutions’ confident discourse, scepticism remains about the reform’s ability to safeguard the fundamental right to data protection in the face of evolving data processing techniques underlying so-called big data. Yet, one might wonder whether the cause for this difficulty should be ascribed mainly to technological progresses that the law finds it hard to deal with or rather to the policy choices embedded in the legal reform itself. Indeed, a new data protection enforcement model is being adopted, which relies heavily on risk assessment and management by the data controllers themselves. Likewise, data protection authorities see their supervisory role significantly weakened. These developments and the underlying rationality are discussed. Given the limitations of the risk-based approach as currently devised, we suggest that it be reappraised in consideration of risk regulatory experiences in other domains.     

Set-membership estimation from poor quality data sets: Modelling ammonia volatilisation in flooded rice systems

A set-membership (bounded-error) estimation approach can handle small and poor quality data sets as it does not require testing of statistical assumptions which is possible only with large informative data sets. Thus, set-membership estimation can be a good tool in the modelling of agri-environmental systems, which typically suffers from limited and poor quality observational data sets. The objectives of the paper are (i) to demonstrate how six parameters in an agri-environmental model, developed to estimate NH₃ volatilisation in flooded rice systems, were estimated based on two data sets using a set-membership approach, and (ii) to compare the set-membership approach with conventional non-linear least-squares methods. Results showed that the set-membership approach is efficient in retrieving feasible parameter-vectors compared with non-linear least-squares methods. The set of feasible parameter-vectors allows the formation of a dispersion matrix of which the eigenvalue decomposition reflects the parameter sensitivity in a region.     

面向系统能力的形式化分析和测试方法

国内软件业界实施系统测试时,大部分采用对系统规格说明描述的功能点进行逐一测试的方法,很少从系统能力的角度进行测试,难以充分说明系统软件产品满足系统能力需求的要求。同时,系统规格说明使用自然语言进行描述,存在语义不准确的现象,直接影响系统测试的质量。针对上述问题,提出了一种面向系统能力的形式化分析和测试方法。通过该方法,测试工程师可得到语义清晰的系统能力需求描述,并实施面向系统能力的系统测试,有效地提高系统测试的充分性和准确性,从而提高系统软件质量。     

基于morlet小波与模态分析的突发型声发射源定位研究

在建立基于声发射技术的裂纹产生与拓展检测系统的基础上.以薄钢板为实验对象,研究了Lamb波在薄板中传播的频散及多模态特性,并结合morlet小波时频联合分析方法,提出了一种针对声发射信号在薄板中传播时产生的不同模态进行识别的方法.通过提取不同模态波到达同一传感器的时间差并依据不同模态波对应的波速实现对出现裂纹的位置进行定位.经过实验研究表明,运用该方法不仅能准确地识别A0、S0模态波并实现对声发射源进行精确定位.     

非平稳信号度量方法综述

非平稳性度量是非平稳信号处理中的重要课题。尽管已有的度量方法在原理上有较大差异,缺少统一的理论框架和度量标准,但这些非平稳信号度量方法都在其相应领域发挥了重要作用。本文对随机信号非平稳度量方法进行了综述,系统地总结、归纳了不同领域现有的随机信号非平稳性度量方法,包括基于统计量和动力学参数的时域方法、时频域参数方法、信号建模参数方法以及特定类别信号的非平稳性度量方法,给出了各种度量方法的应用,并展望了非平稳性度量的未来发展方向。