A Vector Matroid-Theoretic Approach in the Study of Structural Controllability Over F(z)

In this paper, the structural controllability of the systems over F(z) is studied using a new mathematical method-matroids. Firstly, a vector matroid is defined over F(z). Secondly, the full rank conditions of [sI-A|B] are derived in terms of the concept related to matroid theory, such as rank, base and union. Then the sufficient condition for the linear system and composite system over F(z) to be structurally controllable is obtained. Finally, this paper gives several examples to demonstrate that the married-theoretic approach is simpler than other existing approaches

竞争战略与美国特朗普政府对华政策调整

The Competitive Strategy, which helped the US gain great advantages in competition with its major rivals, has played an important part in US foreign policy for a long time. The full use of it in the cold war with Soviet Union is the most significant case. In recent years, under the promotion of the academic circle and the strategic circle, the concept of a competitive strategy is rapidly returning into the US foreign strategy, becoming an important theoretical basis for the adjustment of the Trump Administration's China policy. Recently, the United States has taken multi-domain actions simultaneously to strengthen the strategic competition and containment policies against China, such as mobilizing public opinion, provoking China-related issues, creating new weaponized legislation and even increasingly making use of Taiwan and Hong Kong to contain China. Under this competition situation, China must balance the whole picture and the critical point, make proper adjustments accordingly while sticking to their bottom-line priorities. Only in this way can China relieve the pressure and gain the initiative to effectively manage competition with the US. During this course, China should make more effort in improving its capacity and level of governance, strengthening the domestic foundation of competition against the US. Meanwhile, China should also actively adapt itself to the changing world and make full use of the situation to guide the direction of the China-US relationship. Key Words: Strategic competition; China-US relationship; Competition management; Counterbalancing ability 竞争战略在美国对外政策中占有重要地位，尤其在和主要对手的较量中，美国善于运用这一战略并曾收到较大成效，其中最显著的案例就是在美苏冷战中的充分运用。在美国学界和战略界的推动下，竞争战略理念在美对外战略中快速回归，也成为特朗普政府对华政策调整的重要理论依据。近来美国不断强化对华战略竞争与遏制的舆论动员，设置涉华议题，为强化对华战略竞争与遏制提供法律依据，并在等多个领域出手，全面强化对华战略竞争压力，甚至更多地利用台湾、香港局势的发展变化来牵制中国。面对咄咄逼人的竞争态势，中国既需抓住关键也需把握全局，既要坚守底线也要进退有据，有效管控中美竞争，化解战略压力拓展战略主动；而在竞争中更须切实提升国家治理能力和水平，筑牢战略竞争的国内基础，同时也要积极顺应世界变局，因势利导努力牵引中美关系的发展方向。 【关键词】战略竞争 中美关系 竞争管控 制衡能力 因势利

Robust global sliding model control for water-hull-propulsion unit interaction systems - part 2: model validation

Unexpected severe hull deformation caused by wave loads poses alignment problem to the propulsion shaft line in large scale ships, which would significantly influence the dynamical performance of the marine propulsion system. How to suppress negative disturbance imposed by the interaction between water-hull-propulsion and ensure the normal operation of the marine propulsion system is a challenging task. To address this issue, a new global sliding model control (GSMC) for marine water-hull-propulsion unit systems is proposed and investigated to obtain more accurate control performance in a series of researches. In Part 1 the GSMC controller has been developed and the bounded nonlinear model uncertainties have been derived based on the experiments and sea trial. In this work the upper boundary of 1,85 % was introduced into the GSMC controller to derive the total control law realising the robust control of the marine propulsion system. Numerical simulations based on the real bulk carrier parameters show a high effectiveness of the GSMC for speed tracking, compared with the traditional sliding model controller and Proportional Integral Derivative (PID) controller. By the proposed and investigated control system in this paper may be developed a simple practical-effective robust control strategy for marine propulsion systems subject to some complex unknown uncertainties through further investigations, validations and modification

Recent Progress on Mechanical Condition Monitoring and Fault Diagnosis

AbstractMechanical equipments are widely used in various industrial applications. Generally working in severe conditions, mechanical equipments are subjected to progressive deterioration of their state. The mechanical failures account for more than 60% of breakdowns of the system. Therefore, the identification of impending mechanical fault is crucial to prevent the system from malfunction. This paper discusses the most recent progress in the mechanical condition monitoring and fault diagnosis. Excellent work is introduced from the aspects of the fault mechanism research, signal processing and feature extraction, fault reasoning research and equipment development. An overview of some of the existing methods for signal processing and feature extraction is presented. The advantages and disadvantages of these techniques are discussed. The review result suggests that the intelligent information fusion based mechanical fault diagnosis expert system with self-learning and self-updating abilities is the future research trend for the condition monitoring fault diagnosis of mechanical equipments

Achieving unidirectional propagation of twisted magnons in a magnetic nanodisk array

Twisted magnons (TMs) have great potential applications in communication and computing owing to the orbital angular momentum (OAM) degree of freedom. Realizing the unidirectional propagation of TMs is the key to design functional magnonics devices. Here we theoretically study the propagation of TMs in one-dimensional magnetic nanodisk arrays. By performing micromagnetic simulations, we find that the one-dimensional nanodisk array exhibits a few bands due to the collective excitations of TMs. A simple model by considering the exchange interaction is proposed to explain the emerging multiband structure and theoretical results agree well with micromagnetic simulations. Interestingly, for a zigzag structure, the dispersion curves and propagation images of TMs show obvious nonreciprocity for specific azimuthal quantum number ($l$), which originates from a geometric effect depending on the phase difference of TMs and the relative angle between two adjacent nanodisks. Utilizing this feature, one can conveniently realize the unidirectional propagation of TMs with arbitrary nonzero $l$. Our work provides important theoretical references for controlling the propagation of TMs.Comment: 7 pages, 6 figure

Evaluation of roadway spatial-temporal travel speed estimation using mapped low-frequency AVL probe data

© 2020 Elsevier Ltd The rapid increase in the number of vehicles equipped with GPS devices has resulted in using automatic vehicle location (AVL) data as probes to identify traffic flow status as well as route travel speed on a very fine spatial-temporal scale. However, these traffic monitoring approaches heavily rely on the widely distributed probe vehicles in the network and the high frequency of these probe samples, which are rarely implemented in the real world. This study aims to analyze the applicability of providing accurate traffic flow information from four types of low-frequency AVL data. Each data source is applied for speed estimation to develop guidelines on GPS data requirements for travel speed estimation. First, the probe sample size of each data source on each target corridor is studied to reveal the road segments that have the potential for speed estimation, along with the GPS sampling frequency of each data source. Second, the impact of probe vehicle types, sample sizes, and GPS sampling frequency is analyzed. This study offers guidance in using GPS data to conduct speed estimation in different scenarios, which can be further implemented in a prototype software tool for estimating the real-time travel speed. This study has shown the applicability for speed estimation from four types of GPS data, where the transit bus GPS data provides the best mean speed estimation. The speed estimation results are compared with loop detector data on a test road segment to evaluate its accuracy. The comparison results show that given the current GPS data sample size and updating frequency, the transit bus GPS data can provide a reasonably accurate estimation of the traffic flow speed with a mean absolute speed difference of 6.96 km/h