MPC-based dual control with online experiment design

We present two dual control approaches to the model maintenance problem based on adaptive model predictive control (mpc). The controllers employ systematic self-excitation and design experiments that are performed under normal operation, resulting in improved control performance with smaller output variance and less control effort. Our control formulations offer a novel approach to the question of how to excite the plant input to generate informative data within the context of mpc and adaptive control. One controller actively tries to reduce the parameter-estimate error covariances; the other controller maximizes the information in the signals for enhanced learning. Our approach differs from existing ones in that we let our controllers converge to standard certainty equivalence (ce) mpc when the parameter uncertainty decreases or more information is generated, and as a result we avoid plant excitation when the uncertainty is low or enough information has been generated. We demonstrate that the controllers work well with a large number of tuning configurations and also address the issue of models that are not admissible for control design.     

基于移动应用层组播终端主动反馈的自适应负载均衡机制研究

在移动应用层组播通信中,热点地区可能会因用户过多而导致用户流服务满意度降低,非热点地区却可能会出现资源浪费现象,引起整个系统性能下降.提出了一种基于移动终端主动反馈的自适应负载均衡机制(Adaptive Load Balancing Mechanism based Mobile Terminal Active Feedback,ALBM-MTAF).ALBM-MTAF利用网络相关性能指标模拟移动终端(用户)所获得的流媒体服务满意度(Streaming Media Service Satisfaction,SMSS),通过终端用户主动反馈SMSS不断进行自适应的调整,将SMSS较差地域的子节点切换到SMSS较好的父节点上,从而实现整个系统的负载均衡.模拟实验表明,该机制具有良好的负载均衡效果,并能保证通信的质量.     

基于半监督聚类的文档敏感信息推导方法

针对当前多文档聚合推导引起的敏感信息泄露问题存在风险大、隐蔽性高的特点,提出了一种基于半监督聚类的文档敏感信息推导方法。首先,为确保在较小的时间开销下获得高质量的约束信息,设计了一种新颖的二阶约束主动学习算法,它通过选择不确定性最大的样本点来生成信息量最大的约束闭包;然后,在引入约束信息的基础上结合DBSCAN提出一种新的半监督聚类算法,它能够有效解决DBSCAN算法存在的边界模糊问题,提高文档聚类准确性;最后,在半监督聚类结果的基础上,对相似文档进行敏感信息可能性测度。实验表明,半监督聚类算法准确率提升明显,推导方法能够有效推导出敏感信息。     

一种基于AOS格式的多相水平集快速分割方法

采用迎风格式的水平集算法实现需要在曲线演化过程中重新初始化水平集函数的要求,为保证算法的稳定,时间步长选取较小值,算法运行速度较慢。文中基于无须重新初始化的水平集方法,在算法数值实现中引入AOS半隐格式,对基于不同统计模型的水平集分割算法给出统一的数值实现。以二相水平集分割算法为基础提出一种新的多相水平集分割方法。该方法采用一个水平集函数进行多次演化实现多区域分割,其优点包括：1)采用AOS半隐格式,该格式无条件稳定,可采用较大的时间步长;2)对多个统计模型进行统一处理;3)采用单一的水平集函数进行演化,减少水平集演化方程的数量,算法更加灵活。实验结果表明,该方法具有较快的分割速度,对具有多个区域的图像能够进行较准确的分割。     

The frequency partitioned block modified filtered-x NLMS with orthogonal correction factors for multichannel Active Noise Control

The Normalized Least Mean Square (NLMS) algorithm with a filtered-x structure (FxNLMS) is a widely used adaptive algorithm for Active Noise Control (ANC) due to its simplicity and ease of implementation. One of the major drawbacks is its slow convergence. A modified filtered-x structure (MFxNLMS) can be used to moderately improve the speed of convergence, but it does not offer a huge improvement. A greater increase in the speed of convergence can be obtained by using the MFxNLMS algorithm with orthogonal correction factors (M-OCF), but the usage of orthogonal correction factors also increases the computational complexity and limits the usage of the M-OCF in massive real-time applications. However, Graphics Processing Units (GPUs) are well known for their potential for highly parallel data processing. Therefore, GPUs seem to be a suitable platform to ameliorate this computational drawback. In this paper, we propose to derive the M-OCF algorithm to a partitioned block-based version in the frequency domain (FPM-OCF) for multichannel ANC systems in order to better exploit the parallel capabilities of the GPUs. The results show improvements in the convergence rate of the FPM-OCF algorithm in comparison to other NLMS-type algorithms and the usefulness of GPU devices for developing versatile, scalable, and low-cost multichannel ANC systems.     

On ADRC for non-minimum phase systems: canonical form selection and stability conditions

Active disturbance rejection control (ADRC), as proposed by Prof. Jingqing Han, reduces first the plant dynamics to its canonical form, normally in the form of cascade integrators, for which the standard controller can be employed to meet the design specifications. This paper concerns with the selection of the canonical form for non-minimum phase systems. In particular, it is shown that, by employing the well known controllable canonical form, the uncertainties of such systems can be divided into two terms in the state space model, one in the control channel and the other in the output channel. The necessary and sufficient condition is obtained for the stability of the closed-loop system with the proposed canonical form and ADRC. Also, by showing the necessity of the detectability of the extended system as well as certain information of the systemˉs “zeros”, we present the fundamental guidelines of design ADRC for non-minimum phase uncertain systems.     

Active disturbance rejection control: between the formulation in time and the understanding in frequency

With the rapid deployments of the active disturbance rejection control (ADRC) as a bonafide industrial technology in the background, this paper summarizes some recent results in the analysis of linear ADRC and offers explanations in the frequency response language with which practicing engineers are familiar. Critical to this endeavor is the concept of bandwidth, which has been used in a more general sense. It is this concept that can serve as the link between the otherwise opaque state space formulation of the ADRC and the command design considerations and concerns shared by practicing engineers. The remarkable characteristics of a simple linear ADRC was first shown in the frequency domain, followed by the corresponding analysis in time domain, where the relationship between the tracking error and the ADRC bandwidth is established. It is shown that such insight is only possible by using the method of solving linear differential equations, instead of the more traditional techniques such as the Lyapunov methods, which tend to be more conservative and difficult to grasp by engineers. The insight obtained from such analysis is further demonstrated in the simulation validation.     

E-ARK: Harmony of Social/Cultural Records Across Europe

E-ARK (European Archiving of Records and Knowledge Preservation) is currently introducing standardization, new tools, and infrastructure into pan-European digital archival systems. The results of this pilot project can be applied to higher education where research data centers are required to preserve data for re-use in accordance with new open policies.

We elucidate how the E-ARK best practice survey has informed the development of new information packages for ingest, preservation, and re-use, and show how these can be applied to the Arts, Humanities, and Social Sciences with practical exemplars such as census data.     

Segmentation of the left ventricle in cardiac cine MRI using a shape-constrained snake model

Segmentation of the left ventricle (LV) is a hot topic in cardiac magnetic resonance (MR) images analysis. In this paper, we present an automatic LV myocardial boundary segmentation method using the parametric active contour model (or snake model). By convolving the gradient map of an image, a fast external force named gradient vector convolution (GVC) is presented for the snake model. A circle-based energy is incorporated into the GVC snake model to extract the endocardium. With this prior constraint, the snake contour can conquer the unexpected local minimum stemming from artifacts and papillary muscle, etc. After the endocardium is detected, the original edge map around and within the endocardium is directly set to zero. This modified edge map is used to generate a new GVC force filed, which automatically pushes the snake contour directly to the epicardium by employing the endocardium result as initialization. Meanwhile, a novel shape-similarity based energy is proposed to prevent the snake contour from being strapped in faulty edges and to preserve weak boundaries. Both qualitative and quantitative evaluations on our dataset and the publicly available database (e.g. MICCAI 2009) demonstrate the good performance of our algorithm.