Barrier Lyapunov function-based adaptive prescribed performance control of the PMSM used in robots with full-state and input constraints

The permanent magnet synchronous motor is extensively used in robots due to its superior performances. However, robots mostly operate in unstructured and dynamically changing environments. Therefore, it is urgent and challenging to achieve high-performance control with high security and reliability. This paper investigates an accelerated adaptive fuzzy neural prescribed performance controller for the PMSM to solve chaotic oscillations, prescribed output performance constraint, full-state constraints, input constraints, uncertain time delays, and unknown external disturbances. First, for ensuring the permanent magnet synchronous motor with higher security, faster response speed, and lower tracking error simultaneously, a novel unified prescribed performance log-type barrier Lyapunov function is proposed to handle both prescribed output performance constraint and full-state constraints. Subsequently, a continuous differentiable constraint function-based model is introduced for solving input constraints nonlinearity. The Lyapunov–Krasovskii functions are utilized to compensate the uncertain time delays. Besides, a type-2 sequential fuzzy neural network is exploited to approximate unknown nonlinearities and unknown gain. For the “explosion of complexity” associated with backstepping, a tracking differentiator is integrated into this controller. Furthermore, a speed function is introduced in the backstepping technique for accelerated convergence. On the basis of above works, the accelerated adaptive backstepping controller is achieved. And the presented controller can ensure that all the closed-loop signals are ultimate boundedness, and all state variables are restricted in the prespecified regions and the permanent magnet synchronous motor successfully escapes from chaotic oscillations. Finally, the simulation results verify the effectiveness of the proposed controller.

New records in non-native vascular plants of Russian Lapland

The non-native vascular plants of Murmansk Region (European Russia) are under active investigation towards the compilation of the first complete checklist. This work is part of the project 'Flora of Russian Lapland', which ultimately aims at the complete inventory of the taxonomy, distribution and status of vascular plant species in Murmansk Region, based on the comprehensive database of herbarium specimens, field observations and literature. New territory-level records of non-native vascular plants emerged during our inventory of herbarium collections and recent fieldwork. Fourteen species (Anthemis ruthenica, Aruncus dioicus, Bromus commutatus, Chaerophyllum hirsutum, Galega orientalis, Geum aleppicum, Leonurus quinquelobatus, Lepidium densiflorum, Levisticum officinale, Myrrhis odorata, Phleum phleoides, Prunus armeniaca, Rorippa sylvestris, Senecio vernalis) are reported as new to Murmansk Region. The historical occurrences of alien plants appeared in the territory largely as contaminants (of seed or forage). In particular, Rorippa sylvestris and Senecio vernalis arrived with the forage imported during the Second World War. All recent occurrences originated by escape from confinement (ornamental purposes, horticulture, agriculture), reflecting a high diversity of the modern assortment of cultivated plants in commerce and private gardens. Regarding the invasion status, five alien species are considered casual and eight species are treated as locally established or persisting (for uncertain time). Only one species, Galega orientalis, is considered naturalised and capable of further spreading in the territory, although without invasive potential.

Stock Market Volatility during COVID-19 Pandemic

The study investigates the response of the stock market to the coronavirus pandemic. The economic consequences of the coronavirus (COVID-19) for the stock market are considerable for a developing country, like Pakistan, which was amongst the list of fifteen countries with the highest number of coronavirus cases in May 2020. The present study is aimed at finding the effect of an increase in the number of confirmed cases of coronavirus on the stock returns in the Pakistan stock market. Additionally, the study investigates the effect of an increase in the number of deaths on stock returns. The results show that an increase in the number of confirmed cases has a significant negative effect on the stock returns. While the increase in the number of deaths does not have a significant effect on the stock returns. The results are in line with the results of Ashraf (2020). The findings are important for the policymakers in formulating policies to safeguard the investors in the stock market during this uncertain time.

Optimal Connected Cruise Control Design with Time-Varying Leader Velocity and Delays

With the development of intelligent transportation system (ITS), owing to its flexible connectivity structures and communication network topologies, connected cruise control (CCC), increasing the situation awareness of the autonomous vehicle without redesigning the other vehicles, is an advanced cruise control technology attracted extensive attention. However, due to the uncertain traffic environment and the movement of the connected vehicles, the leader speed is typically highly dynamic. In this paper, taking the uncertain time-varying leading vehicle velocity and communication delays into consideration, an optimal CCC algorithm is proposed for both near-static case and general dynamic control cases. First, the analysis for discrete-time error dynamics model of the longitudinal vehicle platoon is performed. Then, in order to minimize the error between the desired and actual states, a linear quadratic optimization problem is formulated. Subsequently, in near-static control case, an efficient algorithm is proposed to derive the solution of the optimization problem by two steps. Specifically, the online step calculates the optimal control scheme according to the current states and previous control signals, and the off-line step calculates the corresponding control gain through backward recursion. Then, the results are further extended to the general dynamic control case where the leader vehicle moves at an uncertain time-varying velocity. Finally, simulation results verify the effectiveness of the proposed CCC algorithm.

Additive Mixed Sensitivity Design of PID Controllers for Continuous-Time System with Uncertain Time-Delay

This paper presents an algorithm for all achievable coefficients of Proportional Integral Derivative (PID) controllers in an integral-derivative plane that stabilizes and satisfies additive mixed sensitivity constraint with an uncertain time delay for a continuous-time system. This algorithm solves the singularity problem of designing PID controllers in the integral and derivative plane and estimates achievable ranges of proportional gain of the PID controllers. A numerical cascaded ball and beam with unity feedback control of an SRV-DC motor and uncertain communication time delays in the system process demonstrate the application of this methodology. In this application, the additive weight bounds the additive errors for the cascaded ball and beam and the closed-loop SRV-DC motor system transfer function with the internal communication time delays

Uncertain Time: Precarious Schedules and Job Turnover in the US Service Sector

The authors develop a model of cumulative disadvantage relating three axes of disadvantage for hourly workers in the US retail and food service sectors: schedule instability, turnover, and earnings. In this model, exposure to unstable work schedules disrupts workers’ family and economic lives, straining the employment relation and increasing the likelihood of turnover, which can then lead to earnings losses. Drawing on new panel data from 1,827 hourly workers in retail and food service collected as part of the Shift Project, the authors demonstrate that exposure to schedule instability is a strong, robust predictor of turnover for workers with relatively unstable schedules (about one-third of the sample). Slightly less than half of this relationship is mediated by job satisfaction and another quarter by work–family conflict. Job turnover is generally associated with earnings losses due to unemployment, but workers leaving jobs with moderately unstable schedules experience earnings growth upon re-employment.

Phenomenological Study of Muslim Nurses’ Experience During End-Of-Life Decision Making

<p class="paragraph" align="center">ABSTRACT</p><p class="paragraph"><strong>Objectives</strong>: This study examines the significance of Muslim nurses' lived experiences in the Intensive Care Unit (ICU) when it comes to End-of-Life (EOL) decisions (ICU)</p><p class="paragraph"><strong>Methods</strong>: The research was carried out at an intensive care unit (ICU) of a government hospital in Central Java, Indonesia. Fourteen nurses were chosen as participants after meeting the inclusion criteria: Muslims with at least three years of experience in the ICU and experienced to involved in end of life decision making process in an ICU. Data were gathered using in-depth interview. The result the transcribed and analyzed by using van Manen’s hermeneutic phenomenological approach. Trustworthiness was established following Lincoln and Guba's criteria.</p><p class="paragraph"><strong>Results: </strong>Four theme themes emerged from nurses' engagement in EOL decision-making. Feeling dilemma, being in uncertain time, receiving overwhelming role, and evading the process. Van Manen's four lived world of body, time, relation, and space are reflected in these subjects.</p><p class="paragraph"><strong>Conclusion</strong>: The purpose of this study was to illustrate the meaning of Muslim nurses' EOL decision-making in the ICU and to affect nursing policy addressing EOL decision-making education in ICU settings.</p>