Novel model reference adaptive control laws for improved transient dynamics and guaranteed saturation constraints

In classical model reference adaptive control (MRAC), the adaptive rates must be tuned to meet multiple competing objectives. Large adaptive rates guarantee rapid convergence of the trajectory tracking error to zero. However, large adaptive rates may also induce saturation of the actuators and excessive overshoots of the closed-loop system’s trajectory tracking error. Conversely, low adaptive rates may produce unsatisfactory trajectory tracking performances. To overcome these limitations, in the classical MRAC framework, the adaptive rates must be tuned through an iterative process. Alternative approaches require to modify the plant’s reference model or the reference command input. This paper presents the first MRAC laws for nonlinear dynamical systems affected by matched and parametric uncertainties that constrain both the closed-loop system’s trajectory tracking error and the control input at all times within user-defined bounds, and enforce a user-defined rate of convergence on the trajectory tracking error. By applying the proposed MRAC laws, the adaptive rates can be set arbitrarily large and both the plant’s reference model and the reference command input can be chosen arbitrarily. The user-defined rate of convergence of the closed-loop plant’s trajectory is enforced by introducing a user-defined auxiliary reference model, which converges to the trajectory tracking error obtained by applying the classical MRAC laws before its transient dynamics has decayed, and steering the trajectory tracking error to the auxiliary reference model at a rate of convergence that is higher than the rate of convergence of the plant’s reference model. The ability of the proposed MRAC laws to prescribe the performance of the closed-loop system’s trajectory tracking error and control input is guaranteed by barrier Lyapunov functions. Numerical simulations illustrate both the applicability of our theoretical results and their effectiveness compared to other techniques such as prescribed performance control, which allows to constrain both the rate of convergence and the maximum overshoot on the trajectory tracking error of uncertain systems.     

“系统动力学基础”本科课程教学思考与实践

"系统动力学基础"是系统科学理论与建模仿真实践紧密结合的一门课程。本文从课堂讲授、实验教学、答疑考核角度出发,提出在课堂讲授方面需要精心准备课件,激发学员的主体意识,综合运用多种教学方法;在实验教学方面需要正确认识实验教学的作用,精心设计理论验证型实验和实际应用型实验;在答疑考核方面需要师生互动,教学相长。最后探讨了课程实施遇到的问题以及改进提高的方法。     

Impact of age on haematological markers pre- and post-marathon running

This study investigated whether haematological markers differ between young and masters marathon participants, running at similar performance levels. Nine young (31.89 ± 4.96 years) and eight masters (63.13 ± 4.61 years) runners participated. At five time points (pre-race through 54 h post-race), a complete blood cell count, basic metabolic panel and creatine kinase (CK) isoenzyme panel were assessed. Race performance was standardised using the World Masters Association Age Grading Performance Tables. Total CK levels were elevated for all participants at all time points post-race (P < 0.001). The CK-isoenzyme MB% was elevated across groups at 6, 30 and 54 h post-race (P < 0.01, P < 0.01 and P < 0.05), with masters runners having a higher CK-MB% at 30 and 54 h (P < 0.05, P < 0.05). Total white blood cell and neutrophil counts were elevated through 6 h post-race (P < 0.001), with higher levels found in younger runners (P < 0.001). When considering all blood work, masters runners had a higher number of abnormal values at 6, 30 and 54 h post-race (P < 0.05, P < 0.01 and P < 0.05). In conclusion, masters runners demonstrated sustained CK-MB elevation, which may suggest greater cardiac stress. However, future studies using additional cardiac markers should be completed to confirm these findings. In addition, masters runners showed an increased number of laboratory values outside normal range, indicating the body’s reduced capacity to respond to marathon running.     

Archipelagic rhetoric: remapping the Marianas and challenging militarization from “A Stirring Place”

Engaging critical rhetorical fieldwork in the Mariana Islands archipelago, this article destabilizes colonial naming projects and US federal control that dispossess island places from Indigenous peoples. On Euro-American and military maps, archipelagoes are depicted as distant, tiny, empty, or merely (is)lands for US geostrategic control. I argue for a remapping of the Marianas as expansive, oceanic sites of resistance to colonial cartographic violence and US militarization. Fieldwork in the Marianas demonstrates how Indigenous epistemologies function as archipelagic rhetoric enacted through a Chamoru sense of place. I examine these fluid relational connections to place and their implications for decolonization.     

Informational Sources,Social Media Use,and Race in the Flint,Michigan, Water Crisis

Safe, clean water is necessary for health and well-being. Water issues affect minority and vulnerable populations at disproportionate rates, including the poor and racial and ethnic minorities. An investigation of the relationships of race, social media use, and informational sources during the municipal water crisis in Flint, Michigan, reflects an instrumental view of communication and uses and gratifications theory in this study. Data from 208 Flint residents in 2016 indicated that African American respondents favored interpersonal networks and resources and were more likely than other racial groups to obtain current information about the water crisis via Instagram. Preferred channels and sources to receive additional crisis information varied on the basis of race.     

Transforming education systems: comparative and critical perspectives on school leadership

The centrality of education in the pursuit of better economic and social prosperity is now well established. The dominance of human capital theory, which provides a strong argument for better education as a key factor in fuelling economic growth, has encouraged policy makers, in various countries, to focus on education reform as a key priority and to borrow policy solutions from other countries. This special edition explores one policy solution in depth. It investigates the preparation and training of school leaders in very different countries and takes a comparative perspective. This article argues that the limitations of standardized strategies are clearly visible when taking a comparative view and, most importantly, that context matters significantly in shaping, defining and explaining differential educational performance.     

Comparing performance: a cross-national investigation into the teaching of mathematics in primary classrooms in England and China

This article presents initial findings from an empirical study of the effectiveness of mathematics teaching (EMT). The article explores the teaching of mathematics in two very different contexts: England and China. Within each country, the target cohort of pupils were those aged 9–10 and overall, 19 teachers, 10 from England and nine from China, participated in the study together with their pupils (n = 562). Two internationally validated instruments were used to collect the data and teacher behaviours were also measured systematically. In addition, structured observation was undertaken in classrooms in both countries. The results show that, on average, Chinese teachers scored higher on effective teaching measures and Chinese pupils outscored their English peers in the tests that were part of the study. This research project is currently collecting qualitative data but its findings, to date, reinforce the findings from previous research studies suggesting that certain teacher behaviours and classroom factors work effectively to improve student learning outcomes.