Finding exact periodic solutions in Lure systems through periodic signal mapping

A solution of the periodic problem in a nonlinear system comprising a single-valued symmetric nonlinearity (Lure system) and linear dynamics is presented. The solution is designed as an iterative application of Periodic Signal Mapping to refine the approximate solution obtained through the describing function method. The algorithm is based upon the transformation of the original nonlinear system into an equivalent nonlinear system for which the filtering hypothesis is satisfied exactly, and for that reason the latter being suitable for application of the developed algorithm. The solution sought for is a fixed point of the periodic signal mapping. Conditions of asymptotic convergence of the proposed algorithm are given. The proposed approach is illustrated by two examples of analysis of periodic motions in a relay feedback system and chattering in a terminal sliding mode.     

面向关联数据的高校机构知识库构建方法研究

[目的/意义]针对当前我国高校机构知识库研究与应用离真正的开放互连、知识集成、知识检索还有较大差距的问题,提出一种面向关联数据的机构知识库构建方法,该方法覆盖机构知识库构建的整个过程,并支持机构知识的资源整合、语义检索、知识推理和关联数据发布,为各高校机构知识库建设提供参考。[方法/过程]调研和剖析国内外典型的机构知识库,将机构知识库构建方法分为5个步骤,包括:①评价和选择有价值的信息资源;②建立机构知识库概念模型;③进行语义描述和关联设置;④发现并创建关联化数据环境下的语义推理规则;⑤设计系统架构,并通过西南科技大学机构知识库构建实例来验证该方法的有效性。[结果/结论]实例验证表明,面向关联数据的机构知识库构建方法具有合理性和有效性,起到了降低机构知识库开发难度和缩短开发周期的作用,对于其他机构知识库的建设具有参考价值。     

Designing discipline-specific roles for interdisciplinary learning: two comparative cases in an afterschool STEM + L programme

The current K-12 educational system often does not engage students in interdisciplinary learning. To address this need, we developed an integrated STEM?+?L (Science, Technology, Engineering, Math, and Digital Literacies) afterschool programme in which middle school students took discipline-specific roles (writer, scientist, artist, and engineer) and worked in small groups to produce multimodal science fictions. The study aims to investigate the effect of discipline-specific roles on students’ interdisciplinary and collaborative learning processes. Two groups were chosen as comparison cases because their final products indicated low and high levels in integrating science and literacy respectively. Analysing and visualising students’ individual role-changing patterns and examining their discourse in role-specific interactions revealed the following features for high-quality interdisciplinary learning: (1) Students need to be willing and able to enact not only expected roles, but also other roles; (2) Students need to develop awareness of their own and others’ role enactment; (3) Collaboration between students with different roles may follow a possible trajectory from solo-construction, to co-construction, to re-construction. This study also proposes instructional strategies related to the design of discipline-specific roles to facilitate interdisciplinary learning in STEM education.     

The Tyranny of the Empty Frame

This study explores the notion of the “tyranny of the empty frame” within the online departments of the two leading Slovenian newspapers, Delo and Dnevnik, where online journalists—newsworkers with little or no training or experience in photojournalism—are required to provide each news item with at least one photograph. By adopting newsroom observation and in-depth interviews with online journalists working for Delo and Dnevnik, we investigate paradoxes associated with this imperative. Despite often being faced with a desperate search for “any image,” online journalists at both institutions are reluctant to use citizen-produced photographs—their use appears to be an aberration rather than a norm. Instead, they frequently resort to using what they refer to as a “symbolic photograph” to overcome the lack of visual material originating from the reported event. This move from indexical–iconic nexus to metaphoric visual communication signals challenges to the dominant paradigm of press photography. At the same time, we suggest that we should not view the phenomena of citizen photojournalism as a radical break with the past but as the latest development in a series of interrelated processes, intellectual projects of modernity, such as ocularcentrism, journalism, capitalism and the nation state.     

高职院校关于订单培养协议的几个问题

订单培养订单培养模式是高职院校人才培养的重要特色之一。但对于订单培养协议的签定和履行不管是在认识上,还是在操作上都还存在着一些问题。正确理解和认识订单培养协议所体现的法律关系,提高对学生主体地位的认识,加强对学生的宣传和教育工作,准确把握协议内容,明确各方责、权、利,提高预见性,防范违约情况的发生,争取企业的全面支持,是提高订单培养质量的重要措施。     

Frequency domain precision analysis and design of sliding mode observers

Estimation precision and bandwidth of sliding mode (SM) observers are analyzed in the frequency domain for different settings of the observer design parameters. It was shown previously that the SM observer could be analyzed as a relay feedback-feedforward system. It is feedback with respect to the measured variable of the system being observed, and feedforward with respect to the control applied to the system being observed. This approach is now further extended to analysis of effects of design parameter change on observer performance. An example of SM observer design for estimation of DC motor speed from the measurements of armature current is considered in the paper. The input-output properties of observer dynamics are analyzed with the use of the locus of a perturbed relay system (LPRS) method.     

基于GA-BP神经网络的扬声器音盆性能预测技术

在电声零器件制造行业中,扬声器音盆的性能好坏直接关系到扬声器产品的质量.本文提出用遗传算法(GA)优化BP神经网络模型对扬声器音盆性能进行预测.在分析了BP神经网络原理的基础上,主要阐述了如何应用遗传算法优化BP神经网络,以改进BP神经网络收敛速度慢、易陷入局部极小值的缺点.针对音盆产品特点,建立音盆性能的GA-BP神...     

Biomechanical jumping differences among elite female handball players with and without previous anterior cruciate ligament reconstruction: a novel inertial sensor unit study

Persistent biomechanical and jumping capacity alterations have been observed among female athletes who have sustained anterior cruciate ligament (ACL) injuries. The purpose of this study was to examine if biomechanical jumping differences persist among a cohort of elite female handball players with previous ACL reconstruction several years after return to top-level competition. In order to achieve this goal, a direct mechanics simplified analysis by using a single Inertial Sensor Unit (IU) was used. Twenty-one elite female (6 anterior cruciate ligament reconstructed and 15 uninjured control players) handball players were recruited and evaluated 6.0 ± 3.5 years after surgical anterior cruciate ligament reconstruction. Bilateral and unilateral vertical jumps were performed to evaluate the functional performance and a single inertial sensor unit was employed in order to collect 3D acceleration and 3D orientation data. Previously ACL-reconstructed analysed athletes demonstrated significant (p < 0.05) alterations in relation to the three-dimensional axis (X–Y–Z) supported accelerations and differing jump phase durations, including jumping performance values, in both bilateral and unilateral jumping manoeuvres several years after ACL reconstruction. Identification of the encountered deficits through the use of an IU devise could provide clinicians with a new reliable tool for movement analysis in a clinical setting.     

平稳增长条件下中国各省市自治区的排放需求估算

文章运用碳排放经济动力学模型,分析了中国各省市自治区2009—2050年的能源碳排放需求量和减排可能性。结果表明:(1)我国大多数地区节能减排处在良性发展阶段,我国的哥本哈根承诺在发展低碳技术的前提下可以满足;(2)2020年以前,按照平稳增长要求,我国西部地区不可能达到减排40%—45%的平均减排目标,因此东部地区在未来的减排过程中需要承担更多责任;(3)以上海为代表的传统工业省区,以及经济正在起飞的中部省区,不宜大规模降低能源消费,因此需加大对这些地区的产业机构进步投资和能源结构优化,以降低碳排放;(4)经济欠发达的西部省区内蒙古、宁夏、青海、贵州及云南地区,节能减排压力大,需重点加快技术进步投资和改进生产模式,以保障实现最优的平稳增长。     

Algorithm for adaptively smoothing the log-periodogram

We use the principle of minimum cross entropy (MCE) to build a non-parametric adaptive algorithm for smoothing the log-transformed periodogram, and construct an optimal estimate for the spectral density function of a process. We show that this estimate minimizes the cross-entropy with the log-transformed spectral density function of the process. The method is non-parametric and performs very well for the case of processes having rapidly changing spectra that exhibits a variable order of smoothness. The algorithm is locally based on linearly approximating the information present in the process, and uses this approximation to allow the bandwidth of the spectral window in the smoothed log-periodogram to vary. We extend the algorithm empirically for better application to processes having mixed, narrow-band spectra. Comparisons with other currently used procedures are performed through the means of simulated examples.