Asynchronous Systems Research Articles

Event-Triggered Distributed Fusion Estimator for Asynchronous Markov Jump Systems with Correlated Noises and Fading Measurements.

In this study, we investigate event-triggered distributed fusion estimation for asynchronous Markov jump systems subject to correlated noises and fading measurements. The measurement noises are interrelated, and they are simultaneously coupled with the system noise. The sensor samples measurements uniformly, and the sampling rates of the sensors are different. First, the asynchronous system is synchronized at state update points; then, the local filter is obtained. Furthermore, a variance-based event-triggered strategy is introduced between the local estimator and the fusion center to decrease the energy consumption of network communication. Then, a distributed fusion estimation algorithm is proposed using a matrix-weighted fusion criterion. Finally, the effectiveness of the algorithm is verified using computer simulations.

Formation of the Spectral Composition of the Output Voltage of Converters for Nuclear Magnetic Resonance

In this paper, we consider the construction of an asynchronous control system for semiconductor converters for nuclear magnetic resonance. The relevance of research in this direction, main problems that arise during the construction of these systems are shown. Derived the mathematical model of the inverter, on the basis of which a control system with asynchronous pulse-width modulation is constructed. Proposed an equivalent converter circuit with a constant structure, constant parameters, and an equivalent EMF generator. Established correspondence between the equivalent circuit of the converter and its mathematical model in the form of differential equations. On the basis of mathematical equations, a structural diagram of the converter with a control system was developed and the principle of operation of the device was described according to it. To develop an algorithm for the control system, the dependence of the frequency change relative to the resonant frequency on the phase shift between the current through the filter and the voltage on the antenna circuit is determined. For which the model was built in Simulink and the corresponding simulation was carried out. Numerical dependences of reference signal frequency change and phase shift were obtained. The increase in efficiency of device for nuclear magnetic resonance is considered due to the use of multilevel inverters with tuning the frequency of operation to the frequency of the resonant circuit. Simulation of a three-level diode-clamped inverter showed that when the capacitance of the resonant circuit changes and, therefore, the resonant frequency of the circuit, the input current increases. The work obtained specific numerical dependencies. Time diagrams of voltages and currents on the main elements of the converter are given, which illustrate the implementation asynchronous pulse-width modulation in the control system. After working out the automatic frequency control algorithm, the increase in current consumption can be leveled off. The simulation results also show that it is possible to reduce the amplitude of the third harmonic. The disadvantages of the proposed system include the fact that the frequency of the converter is adjusted at each subsequent period of its operation. At the same time, the parameters of the filter can change again, which leads us to believe that adjusting the frequency will never give a 100% result, but will only allow to get as close as possible to the set parameters of the sounding signal. The work also indicates that it is possible to improve the spectral composition of the probing voltage generated by the converter by using more levels of a diode-clamped multi-level inverter. However, increasing the number of levels reduces the action speed of the system and complicates the control system itself. Therefore, the need to maintain a balance between the number of levels of the inverter and the complexity of the system is indicated.

Performance Bounds for Passive Sensing in Asynchronous ISAC Systems

Performance Bounds for Passive Sensing in Asynchronous ISAC Systems

Comparing Synchronous and Asynchronous Task Delivery in Mixed Reality Environments.

Asynchronous digital communication is a widely applied and well-known form of information exchange. Most pieces of technology make use of some variation of asynchronous communication systems, be it messaging or email applications. This allows recipients to process digital messages immediately (synchronous) or whenever they have time (asynchronous), meaning that purely digital interruptions can be mitigated easily. Mixed Reality systems have the potential to not only handle digital interruptions but also interruptions in physical space, e.g., caused by co-workers in workspaces or learning environments. However, the benefits of such systems previously remained untested in the context of Mixed Reality. We conducted a user study ($\mathrm{N}=26$) to investigate the impact that the timing of task delivery has on the participants' performance, workflow, and emotional state. Participants had to perform several cognitively demanding tasks in a Mixed Reality workspace. Inside the virtual workspace, we simulated in-person task delivery either during tasks (i.e., interrupting the participant) or between tasks (i.e., delaying the interruption). Our results show that delaying interruptions has a significant impact on subjective metrics like the perceived performance and workload.

Sparse representation based motor imagery EEG classification towards asynchronous BCI systems

Sparse representation based motor imagery EEG classification towards asynchronous BCI systems

Sparse representation-based motor imagery EEG classification towards asynchronous BCI systems

Sparse representation-based motor imagery EEG classification towards asynchronous BCI systems

An Asynchronous Training-free SSVEP-BCI Detection Algorithm for Non-Equal Prior Probability Scenarios.

SSVEP-based brain-computer interface (BCI) systems have received a lot of attention due to their relatively high Signal to Noise Ratio (SNR) and less training requirements. Most of the existing steady-state visual evoked potential (SSVEP) detection algorithms treat the prior probability of each alternative target being selected as equal. In this study, the prior probability distribution of alternative targets was introduced into the SSVEP recognition algorithm, and an asynchronous training-free SSVEP-BCI detection algorithm for non-equal prior probability scenarios was proposed. This algorithm is based on the Spatio-temporal equalization multi-window technique (STE-MW) and introduces the Maximum A Posteriori criterion (MAP), which makes full use of prior information to improve the performance of the asynchronous training-free BCI system. In addition, we proposed a mutual information-based performance evaluation metric called Mutual information rate (MIR) specifically for non-equal prior probability scenarios. This evaluation framework is designed to provide a more accurate estimation of the information transmission performance of BCI systems in such scenarios. A 10-target simulated vehicle control offline experiment involving 17 subjects showed that the proposed method improved the average MIR by 6.48%. Online free control experiments involving 12 subjects showed that the proposed method improved the average MIR by 14.93%, and significantly reduced the average instruction time. The proposed algorithm is more suitable for practical engineering application scenarios that are asynchronous and training-free; the extremely high accuracy is guaranteed while maintaining a low false alarm rate, which can be applied to asynchronous BCI systems that require high stability.

Electromechanical Transient Modeling of the Low-Frequency AC System With Modular Multilevel Matrix Converter Stations

This paper studies the electromechanical transient modeling of a low-frequency AC (LFAC) system with modular multilevel matrix converter (M3C) stations. Firstly, the mathematical model of the M3C and its equivalent circuits are established. Then, an iterative power flow calculation algorithm for AC systems integrated with the M3C-LFAC system is developed. The dynamic model of the M3C for electromechanical transient simulation is studied and implemented in PSS/E. Based on a test system consisting of two asynchronous AC systems with an embedded M3C-LFAC system, comparisons between the electromechanical transient simulation results from PSS/E and the electromagnetic transient simulation results from PSCAD are conducted. The results from PSS/E and PSCAD coincide with each other well, and the validity of the established electromechanical transient model is proved. Lastly, a stability study of a modified New England 39-bus system with an embedded M3C-LFAC system is executed, and the characteristics of the M3C-LFAC system are presented.

Stability of Asynchronous Networked Linear Control Systems with Direct-Feedthrough Terms and Scheduling Protocols

Stability of Asynchronous Networked Linear Control Systems with Direct-Feedthrough Terms and Scheduling Protocols

High-Frequency Discrete-Interval Binary Sequence in Asynchronous C-VEP-Based BCI for Visual Fatigue Reduction.

In code-modulated visual evoked potential (c-VEP) based BCI systems, flickering visual stimuli may result in visual fatigue. Thus, we introduced a discrete-interval binary sequence (DIBS) as visual stimulus modulation, with its power spectrum optimized to emphasize high-frequency components (40 Hz-60 Hz). 8 and 17 subjects participated, respectively, in offline and online experiments on a 4-target asynchronous c-VEP-based BCI system designed to realize a high positive predictive value (PPV), a low false positive rate (FPR) during idle states, and a high true positive rate (TPR) in control states, while minimizing visual fatigue level. Two visual stimuli modulations were introduced and compared: a maximum length sequence (m-sequence) and the high-frequency discrete-interval binary sequence (DIBS). The decoding algorithm was compared among the canonical correlation analysis (CCA), the task-related component analysis (TRCA), and two approaches of sub-band component weight calculation (the traditional method and the proportional method) for FBCCA and FBTRCA. In the online experiments, the average PPV, FPR and TPR achieved, respectively [Formula: see text], [Formula: see text], [Formula: see text] with m-sequence, while [Formula: see text], [Formula: see text] and [Formula: see text] with DIBS. Estimated by objective eye-related metrics and a subjective questionnaire, the visual fatigue in DIBS cases is significantly smaller than that in m-sequence cases. In this study, the feasibility of a novel modulation approach for visual fatigue reduction was proved in an asynchronous c-VEP system, while maintaining comparable performance to existing methods, which provides further insights towards enhancing this field's long-term viability and user-friendliness.

A Novel Data Augmentation Approach Using Mask Encoding for Deep Learning-Based Asynchronous SSVEP-BCI.

Deep learning (DL)-based methods have been successfully employed as asynchronous classification algorithms in the steady-state visual evoked potential (SSVEP)-based brain-computer interface (BCI) system. However, these methods often suffer from the limited amount of electroencephalography (EEG) data, leading to overfitting. This study proposes an effective data augmentation approach called EEG mask encoding (EEG-ME) to mitigate overfitting. EEG-ME forces models to learn more robust features by masking partial EEG data, leading to enhanced generalization capabilities of models. Three different network architectures, including an architecture integrating convolutional neural networks (CNN) with Transformer (CNN-Former), time domain-based CNN (tCNN), and a lightweight architecture (EEGNet) are utilized to validate the effectiveness of EEG-ME on publicly available benchmark and BETA datasets. The results demonstrate that EEG-ME significantly enhances the average classification accuracy of various DL-based methods with different data lengths of time windows on two public datasets. Specifically, CNN-Former, tCNN, and EEGNet achieve respective improvements of 3.18%, 1.42%, and 3.06% on the benchmark dataset as well as 11.09%, 3.12%, and 2.81% on the BETA dataset, with the 1-second time window as an example. The enhanced performance of SSVEP classification with EEG-ME promotes the implementation of the asynchronous SSVEP-BCI system, leading to improved robustness and flexibility in human-machine interaction.

Innovation of Learning Management System in Mathematics Education Study Program as MBKM Supporting Media

The main objective of this research is to produce an LMS that can support synchronous, asynchronous and blended learning systems, especially in the Mathematics Education study program at Universitas Sembilanbelas November Kolaka (USN Kolaka). This is very important because USN Kolaka currently does not have an independent LMS while the existence of an LMS greatly supports the implementation of MBKM, especially in lecture programs outside the University. The LMS that will be created is an opensource-based LMS that also supports the use of the Woocommerce system. Specifically, the course that will be included in the system is the Mathematics Learning Media course. However, if possible, this LMS will be developed into an online mathematics learning center throughout Indonesia, starting from elementary school to university level. To develop this LMS requires several stages. The first stage is to analyze what essential materials will be included in the system first. Second, designing or designing the LMS interface, menu layout, including how to deliver the material, The third stage realizes what has been planned. The realization stage consists of product trials, evaluation and revision. The last stage is the implementation stage. This stage of development is known as the plompt model. From these stages, an opensource LMS is obtained that is suitable for use as an online learning platform. It can include various lesson materials. Especially for this research, the teaching materials included have also gone through a validation process so that both the material and the media are ready to be used for the teaching and learning process.

Design and Evaluation of an Asynchronous VR Exploration System for Architectural Design Discussion Content

Design discussion is crucial in the architectural design process. To enhance the spatial understanding of 3D space and discussion effectiveness, recently, some systems have been proposed to support design discussion interactively in an immersive virtual environment. The entire design discussion can be archived and potentially become course materials for future learners. In this paper, we propose an asynchronous VR exploration system that aims to help learners explore content effectively and efficiently anywhere and at any time. To improve effectiveness and efficiency, we also propose a summarization-to-detail approach with the application space by which students can observe the visualization of spatial summarization of actions and participants’ dwell time or the temporal distribution of dialogues and then locate the important or interesting region or dialogue for further exploration. To further explore the discussion content, students can call the preview to see the time-lapse animation of the object operation to understand the change in models or playback to view the discussion details. We conducted an exploratory user study with 10 participants to evaluate user experience, user impression, and effectiveness of learning the design discussion course content using our asynchronous VR design discussion content exploration system. The results indicate that the interactive VR exploration system presented can help learners study the design discussion content effectively. Participants also provided some positive feedback and confirmed the usefulness and value of the system presented. Our applications and lessons learned have implications for future asynchronous VR exploration systems, not only for architectural design discussion content, but also for other applications, such as industrial visual inspections and educational visualizations of design discussions.

An Analysis of Challenges Faced by Academics During the Transition from Contact to Online Learning

The Coronavirus (Covid-19) pandemic affected many lives and sectors across the world. In the higher education sector, Covid-19 caused a drastic shift from contact learning to multiple forms of online learning. It is in this context that the paper undertook a critical analysis of the challenges experienced by academics because of Covid-19. A comprehensive literature search was conducted on 6 databases (Google Scholar, ScienceDirect, Jstor, Academic Search Complete, SpringerLink, and SAGE Journals) for relevant studies published from the year 2019 to 2022. Moreover, further relevant studies were retrieved from the reference list of studies identified from the initial search. The search terms employed by the researchers were COVID-19, remote learning, e-learning, online learning, higher education, information technology and asynchronous learning systems. For the selection of the most relevant articles for the final review, the researchers employed inclusion and exclusion criteria. Studies that addressed higher education online learning and the challenges encountered by higher education due to Covid-19 were eligible for inclusion. The findings revealed that academics encountered multiple challenges during the transition from contact learning to online learning, these include the academic’s limited experience and lack of training in the pedagogy of online learning, challenges related to planning and adaptability, issues of network and connectivity, insufficient teaching and learning resources, workload, and stress along with the unconducive physical spaces and environment. Based on the findings presented, this study recommended that the pedagogical strategies must be revised. Furthermore, necessary adjustments in infrastructure in higher education institutions must also be made. This will ensure the smooth running of the teaching and learning process. Moreover, the systematic flaws and transformation gaps in higher education institutions have been made clear by the shift from contact learning to online learning. Thus, this study concludes that blended learning may emerge as the default teaching mode in higher learning institutions, this ensures the maximisation of efficiency. Keywords: Covid-19, Online Teaching, Contact Or Face-To-Face Education, Higher Education, Technology.

Improved results of asynchronous mixed [formula omitted] and passive control for discrete-time linear switched system with mode-dependent average dwell time

This paper primarily discusses the hybrid H∞ and passive control problems of asynchronous discrete-time switching systems based on mode-dependent average dwell time. In the process of analysis, we divide the running time of the subsystem into two cases: matching and not matching the controller. Firstly, we employ the method of mode-dependent average dwell time to model the system and derive a suitable switching signal, ensuring the system is global uniform asymptotic stability. Meanwhile, the weighted hybrid H∞ and passivity are achieved. Then, according to the different performance parameters of each subsystem, the appropriate controller is designed using the form of linear matrix inequalities to improve the stability of the system. Finally, the effectiveness of the proposed method is demonstrated by a numerical example and a population ecosystem.

FOPID controlled PV based QBC fed gamma Z-source inverter applicable for pump operations in an induction motor drive

<span lang="EN-US">A closed loop current mode-fractional-order-PID (CM-FOPID) controlled and PV based quadratic-boost-converter (QBC) fed gamma Z-Source Inverter with Induction motor system (PV-QBC-GZSI-IMS) for pump operation is proposed here. This work recommends a combination of QBC with gamma Z-source-inverter between the DC link source and asynchronous motor system. This will reduce the voltage rating of PV panel and its initial cost. GZSI reduces the current spikes in stator current. The objective of this research work is to regulate the speed of PV-QBC-GZSI-IMS. This effort deals with the closed loop response of PV-QBC-GZSI-IMS accompanied by current-mode-proportional integral (CM-PI) and CM-FOPID controllers. The performance investigations are analyzed with the control of QBC fed Gamma Z-source inverter with motor load using CM-PI and CM-FOPID controllers and the detailed comparison has been presented. MATLAB/Simulink outputs obtained with their respective speed and torque characteristics in time domain have been depicted. The closed loop CM-FOPID control of PV-QBC-GZSI-IMS is superior to the closed loop CM-PI control of PV-QBC-GZSI-IMS. The proposed QBC-converter reduces the voltage rating of PV panel and GZSI reduces current spikes in motor. The novelty of the article is to enhance the dynamic response of PV-QBC-GZSI-IMS using FOPID. The steady state error in torque is reduced to 0.52 N-m using FOPID.</span>

Результаты исследований высших гармоник при эксплуатации судовых частотно-регулируемых асинхронных электроприводов

One of the directions of scientific and technological progress at sea-based facilities is the use of electrical technologies based on nonlinear elements. It is revealed that the use of such technologies leads to a deterioration in the quality of electricity, mainly due to higher harmonic. The results of theoretical and experimental studies of the higher harmonic components of voltage and current occurring during the operation of ship frequency-controlled asynchronous electric drives are presented. During operation of a frequency-controlled electric drive high current harmonics of mainly 5, 7, 11, 13 orders are emitted into the power supply network, which is due to the presence of a six-phase rectifier. This leads to distortion of the sinusoid of the supply voltage, since the higher harmonic components of the current, propagating through the electrical network, create corresponding voltage drops on its elements. Along with the main harmonic of the voltage of a given frequency, the higher harmonic components of the voltage flow from the autonomous voltage inverter to the stator winding of the asynchronous electric motor, which causes the higher current harmonics and torques of the forward and reverse current sequences in the stator and rotor windings. As a result additional heating of the stator and rotor windings occurs and vibrations of the asynchronous motor shaft at frequencies of 300 and 600 Hz occur. A method for measuring the vibration of a frequency-controlled asynchronous electric drive from the interaction of the moments of the reverse and forward sequences has been developed and experimentally confirmed. A method for calculating the intrinsic frequency of oscillations of the asynchronous motor-load machine system is proposed, confirmed by the example of a laboratory installation. To accurately calculate the natural frequency of the oscillatory system, it is necessary to experimentally measure the moments of inertia of the rotor of an asynchronous motor and the armature of a DC motor.

Learner satisfaction with synchronous and asynchronous virtual learning systems during the COVID-19 pandemic in Tehran university of medical sciences: a comparative analysis

BackgroundThe need for electronic learning and its systems, especially during specific circumstances and crises, is crucial and fundamental for users in universities. However, what is even more important is the awareness and familiarity of learners with different systems and their appropriate use in e-learning. Therefore, the present study was conducted to determine the satisfaction of learners with synchronous and asynchronous electronic learning systems during the COVID-19 period at Tehran University of Medical Sciences.MethodsThe present study was a descriptive-analytical study conducted cross-sectionally from the first semester of 2019–2020 academic year until the end of the second semester of 2021–2022 academic year, coinciding with the COVID-19 pandemic. The sample size was determined to be 370 students and 650 staff members using the Krejcie and Morgan table. The face validity and reliability of the research tool, which was a researcher-made questionnaire, was confirmed. Considering a response rate of 75%, 280 completed questionnaires were received from students, and 500 completed questionnaires were collected from employees. For data analysis, absolute and relative frequencies, as well as independent t-test, analysis of variance (ANOVA), and Post Hoc tests in the SPSS software were utilized.ResultsDuring the COVID-19 pandemic, both students and staff members at Tehran University of Medical Sciences showed a relatively decreasing level of satisfaction with electronic learning. There was a significant difference in satisfaction between these two groups of learners regarding electronic learning (P = 0/031). Learners were relatively more satisfied with the offline system called “Navid” compared to online learning systems. Among the online systems, the highest level of satisfaction was observed with the Skype platform.ConclusionAlthough learners expressed relative satisfaction with electronic learning during the COVID-19 period, it is necessary to strengthen infrastructure and provide support services, technical assistance, and continuous updates for electronic learning platforms. This can contribute to more effective and efficient utilization of electronic learning, especially during particular circumstances and crises, or in hybrid models combining online and face to face education and training.

Breathable and impact-resistant shear thickening gel based three-dimensional woven fabric composites constructed by an efficient weaving strategy for wearable protective equipment

External low-velocity impacts (LVI) inevitably endanger human body health, yet attaining wear comfort and impact resistance simultaneously in protective equipment is challenging. Herein, flock-reinforced shear thickening gel (FRSTG) was demonstrated to display exceptional shear thickening behavior above the critical shear frequency (80.5 Hz). Three-dimensional (3D) shaped woven fabrics with folded structures were efficiently realized on a modified loom assembled with double warp beams and asynchronous self-reversal let-off systems, then 3D FRSTG/woven fabric composites were manufactured through a facile inclusion procedure. The “sizing effect” of FRSTG on the yarns resulted in enhanced mechanical properties of the composites. Attributed to the folded structures, the composites exhibited desired flexibility and innovatively achieved breathability (79.473 mm/s). They also performed responsive LVI resistance owing to the shear thickening effect of FRSTG and structural advantages of 3D shaped woven fabric. Furthermore, wearable protective applications based on those composites were evidenced to integrate breathability and LVI resistance.

Stability and Performance of Asynchronous Sampled-Data Interconnected Systems: An Integral Approach

In this paper, we focus on the stability of asynchronous sampled-data interconnected systems and the evaluation of how asynchronous sampling and time delays degrade the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {L}_{2}$</tex-math></inline-formula> gains from exogenous inputs to controlled outputs. To judge the stability and evaluate the performance of systems, an integral approach is proposed and it combines a revised form of ISS (input-to-state stability) Lyapunov conditions with an integral description of bounded measurement errors. Practical procedures for the application of the approach are further presented. In the case with shared sampling periods, a time-translation approach is introduced to investigate the relationship between asynchronous sampling and time delays.