Dual closed-loops current controller for a 4-leg shunt APF based on repetitive control

ABSTRACT

Current repetitive control strategy for a 4-leg APF is usually of a poor speed in responding to the drastic changes in load harmonic profile. In this paper, a dual closed-loop current controller composed of a repetitive control-based outer loop and a PI-based inner loop is proposed to improve the performance of a 4-leg APF, with a focus on response speed and harmonic current compensation gain. The principle of the dual loop controller is explained in detail, and the stability of the system is analysed thoroughly. To further decrease the inherent time delay associated with the PWM strategy, a zero-sequence-voltage-based PWM strategy is proposed to solve the complexity in the implementation of 3D-SVPWM methods. By formulating the relationship between the duty ratio of the neutral leg control pulse and the zero-sequence-component of the reference voltages, the duty ratios of the other three legs can be calculated conveniently. The simulation and lab experiment results are provided to verify the correctness and effectiveness of the proposed dual closed-loop current controller and the zero-sequence-voltage-based PWM strategy.     

Improved non-maximum suppression for object detection using harmony search algorithm

Non-maximum suppression (NMS) plays a key role in many modern object detectors. It is responsible to remove detection boxes that cover the same object. NMS greedily selects the detection box with maximum score; other detection boxes are suppressed when the degree of overlap between these detection boxes and the selected box exceeds a predefined threshold. Such a strategy easily retain some false positives, and it limits the ability of NMS to perceive nearby objects in cluttered scenes. This paper proposes an effective method combining harmony search algorithm and NMS to alleviate this problem. This method regards the task of NMS as a combination optimization problem. It seeks final detection boxes under the guidance of an objective function. NMS is applied to each harmony to remove imprecise detection boxes, and the remaining boxes are used to calculate the fitness value. The remaining detection boxes in a harmony with highest fitness value are chosen as the final detection results. The standard Pattern Analysis, Statistical Modeling and Computational Learning Visual Object Classes dataset and the Microsoft Common Objects in Context dataset are used in all of the experiments. The proposed method is applied to two popular detection networks, namely Faster Region-based Convolutional Neural Networks and Region-based Fully Convolutional Networks. The experimental results show that the proposed method improves the average precision of these two detection networks. Moreover, the location performance and average recall of these two detectors are also improved.     

Backtracking search optimization heuristics for nonlinear Hammerstein controlled auto regressive auto regressive systems

In this work, novel application of evolutionary computational heuristics is presented for parameter identification problem of nonlinear Hammerstein controlled auto regressive auto regressive (NHCARAR) systems through global search competency of backtracking search algorithm (BSA), differential evolution (DE) and genetic algorithms (GAs). The mean squared error metric is used for the fitness function of NHCARAR system based on difference between actual and approximated design variables. Optimization of the cost function is conducted with BSA for NHCARAR model by varying degrees of freedom and noise variances. To verify and validate the worth of the presented scheme, comparative studies are carried out with its counterparts DE and GAs through statistical observations by means of weight deviation factor, root of mean squared error, and Thiel’s inequality coefficient as well as complexity measures.     

结合公钥加密和关键字可搜索加密的加密方案

带关键字搜索的公钥加密(PEKS)是一种有用的加密原语，它允许用户将在加密数据上搜索的功能委托给不可信的第三方服务器，而不影响原始数据的安全性和隐私性。但是，由于缺乏对于数据的加密以及解密能力，PEKS方案不能单独进行使用，必须与标准的公钥加密方案(PKE)相结合。因此，Baek等人在2006年引入了一种新的加密原语，称为结合PKE和PEKS的加密方案(PKE+PEKS)，它同时提供了PKE和PEKS的功能。目前，已有文献提出了几种PKE+PEKS方案。然而，他们都没有考虑关键字猜测攻击的问题。本文提出一个新的高效且能够抵抗关键字猜测攻击的PKE+PEKS方案，与已有方案相比，该方案在性能上有很大的提升，并且在生成关键字和数据密文时，不需要使用双线性对，极大地降低了计算和存储成本。安全性分析表明，本文中所提出的方案能够满足密文隐私安全性、陷门不可区分性和抗关键字猜测攻击的安全性。效率分析表明，本分提出的方案更加高效。     

Too big to surveil: the fourth amendment illuminated by ‘modern lights’ and shadowed by obsta principiis in a post-Carpenter world concerned with privacy

The Fourth Amendment to the U.S. Constitution functions as a shield against excess governmental or police power by prohibiting unreasonable searches and seizures. Since its ratification, legal challenges have tempered this shield by frequently disputing the application of investigative processes and tools, including those that bypass the traditional – and simpler – analysis that focused on physical trespass. But recent technological advancements have prompted novel challenges and have forced the U.S. Supreme Court to adopt a parallel inquiry that evaluates society’s expectations of privacy as an alternate path to invoke the Fourth Amendment’s protections apart from any physical trespass. As revolutionary technology continues to present unique issues, this 200-year-old shield manifests a reflective luster as if polished by years of legal discourse that reveals the priorities of those who would interpret its text. Viewing the Fourth Amendment’s shield as a mirror illustrates not only the thoughts of the drafters that revolved primarily around protecting property interests but also the expectations of modern society with its insistence on promoting privacy. And where the drafters channeled their outrage against the loathsome writs of assistance in colonial times, later Americans continued to denounce the similarly invasive general warrants and attempts by investigators to expand the tools in their arsenal beyond constitutional bounds, especially in the surveillance context. Yet, the problems posed by new technology upon privacy concerns are best resolved by relying on the core principles supporting the Fourth Amendment, previous U.S. Supreme Court precedent, and current societal perspectives regarding privacy as a top priority proven by recently enacted legislation both foreign and domestic.

By applying a similar method to address advancing communication technology and its use as a surveillance tool in Carpenter v. United States, the Court turned this shield-become-mirror upon society to conclude that cell phone location information deserves Fourth Amendment protection because of its untiring comprehensiveness and its uniquely detailed nature. Moreover, nearly every American adult carries a cell phone with them almost all the time, making it possible to create a time-stamped map of any cell-phone-carrying-individual’s movements reaching back years and years. Unfortunately, the Carpenter Court did not extend this crucial protection far enough to protect all cell phone location data, and the unmistakable gap in its holding leaves a potential privacy vulnerability the exploitation of which could cause greater harm than all previously disputed surveillance technology combined because of cell phone usage’s general – near universal – applicability. Allowing cell phone location information to be obtained without probable cause and a proper search warrant not only fails to meet the spirit of the Fourth Amendment, it also begins to tarnish that shield such that it no longer reflects historical or current societal values, reducing its goal of protecting Americans to a hollow incantation of words left to languish as time (and technology) marches on.     

上游泵送机械密封多目标多工况优化研究

为了获得具有较强适应工况变化能力的上游泵送机械密封,以微间隙内流场的CFD计算为基础,建立涉及多工况的多目标优化数学模型,综合分析相关研究成果和密封特性确定了优化变量及其取值范围、工况参数取值范围和优化目标。应用模糊集理论确定不同工况下的液膜刚度和泄漏量的权重因子,并研究人工神经网络模型对优化结果的影响。基于穷尽搜索法和遗传算法对密封进行优化设计,对比分析2种优化方法得到的优化结果,并对优化前后的密封润滑膜流场特性进行BVF诊断分析。优化研究表明:人工神经网络模型很好地拟合了液膜刚度、泄漏量随槽型参数变化的函数关系;2种优化方法都能提高密封性能,但遗传算法优化比穷尽搜索法优化能获得更好的优化结果。     

User-friendly search interface for older adults: supporting search goal refreshing in working memory to improve information search strategies

ABSTRACT

This study investigates how a search interface that displays users’ ultimate query (i.e. users’ current search goal) can cope with the age-related decrease of fluid abilities and support older users’ search behaviours. 30 young and 18 older adults completed 9 search problems with a regular web browser or with the experimental search interface. Results showed that older adults spent longer time on the search engine result pages, they needed more time to reformulate, and they had more difficulties exploring the search paths elaborated. Age-differences also appeared as soon as the beginning of the search. The support tool helped older users reformulate their queries more rapidly and elaborate more flexible search strategies at the beginning of the activity. Indeed, older adults who interacted with the support tool switched to the processing of a new search path more rapidly instead of exploiting their initial query (i.e. they visited fewer websites for the initial query produced and reformulated a query instead of keeping on conducting a deeper investigation of the search results provided in the search engine result page). Implications of these findings for the design of effective support tools for older users are discussed.     

Enriching Context Information for Entity Linking with Web Data

Journal of Computer Science and Technology - Entity linking (EL) is the task of determining the identity of textual entity mentions given a predefined knowledge base (KB). Plenty of existing...     

Conditional Preference Networks with User's Genuine Decisions

User's choices involve habitual behavior and genuine decision. Habitual behavior is often expressed using preferences. In a multiattribute case, the Conditional Preference Network (CP-net) is a graphical model to represent user's conditional ceteris paribus (all else being equal) preference statements. Indeed, the CP-net induces a strict partial order over the outcomes. By contrast, we argue that genuine decisions are environmentally influenced and introduce the notion of “comfort” to represent this type of choices. In this article, we propose an extension of the CP-net model that we call the CP-net with Comfort (CPC-net) to represent a user's comfort with preferences. Given that preference and comfort might be two conflicting objectives, we define the Pareto optimality of outcomes when achieving outcome optimization with respect to a given CPC-net. Then, we propose a backtrack search algorithm to find the Pareto optimal outcomes. On the other hand, two outcomes can stand in one of six possible relations with respect to a CPC-net. The exact relation can be obtained by performing dominance testing in the corresponding CP-net and comparing the numeric comforts.