Many HCI applications, such as volume adjustment in a gaming system, require quantitative gesture measurement for metrics such as movement distance and direction. In this paper, we propose QGesture, a gesture recognition system that uses CSI values provided by COTS WiFi devices to measure the movement distance and direction of human hands. To achieve high accuracy in measurements, we first use phase correction algorithm to remove the phase noise in CSI measurements. We then propose a robust estimation algorithm, called LEVD, to estimate and remove the impact of environmental dynamics. To separate gesture movements from daily activities, we design simple gestures with unique characteristics as preambles to determine the start of the gesture. Our experimental results show that QGesture achieves an average accuracy of 3 cm in the measurement of movement distance and more than 95% accuracy in the movement direction detection in the one-dimensional case. Furthermore, it achieves an average absolute direction error of 15 degrees and an average accuracy of 3.7 cm in the measurement of movement distance in the two-dimensional case.

Physical inactivity and sedentary behavior (SB) have attracted growing attention globally since they relate to noninfectious chronic diseases (NCDs) and could further result in the loss of life. This systematic literature review aimed to identify existing evidence on the efficacy of mobile health (mHealth) technology in inducing physical activity and reducing sedentary behavior for physically inactive people. Studies were included if they used a smartphone app in an intervention to improve physical activity and/or sedentary behavior for physically inactive individuals. Interventions could be stand-alone interventions or multi-component interventions, including an app as one of several intervention components. A total of nine studies were included, and all were randomized controlled trials. Two studies involved interventions delivered solely via a mobile application (stand-alone intervention) and seven studies involved interventions that used apps and other intervention strategies (multi-component intervention). Methodological quality was assessed, and the overall quality of the studies was ensured. The pooled data favored intervention in improving physical activity and reducing sedentary behavior. This review provided evidence that mobile health intervention improved physical activity and reduced sedentary behavior among inactive individuals. More beneficial effects can be guaranteed when interventions include multiple components. Further studies that maintain the effectiveness of such interventions are required to maximize user engagement and intervention efficacy.

DC microgrids (MGs) have gained significant attention for its remarkable advantages of integrating renewable energy sources (RESs) and electronic loads. In order to improve the operational performance of the DC MG in both steady and transient states, a fully distributed fixed-time based secondary controller is proposed to remove the DC voltage deviation and provide proportional current sharing simultaneously. The secondary control of each DG consists of a fixed-time consensus-based current and voltage regulators that use relative information from the neighboring DGs through a sparse communication network. In contrast to the existing controllers, the proposed controller is distinguished with its accelerated convergence time which does not rely on the initial values. Besides, the stability of the proposed method is verified through the Lyapunov function. A simulation model is built in PLECS to prove the effectiveness of the proposed control strategy. Some scenarios are introduced to validate the link-failure resiliency, plug and play capability, the scalability, and the feasibility under various time delays. Meanwhile, a DC MG experimental prototype is built to verify the controller performance.

This paper addresses a fully distributed hierarchical coordination controller, which minimizes the global total generation cost (TGC) for a cluster of DC microgrids (MGs) through handling the optimal power-sharing between MGs. It consists of local and global tertiary controllers, in which a two-layer communication network is modeled to share information with a reduced complexity as one or some distributed generators (DGs) of each MG are pinned from the local network to broadcast the information between MGs at the global network. Under this control structure, the global tertiary controllers, based on dynamic consensus technique, generate the global optimum incremental cost (IC) reference to attain the entire cluster's economic operation. Moreover, using pinning-based leader-follower consensus algorithm, the local tertiary controllers assign MG average voltage reference at which the ICs of all DGs are matched at the global reference to ensure optimal operation of the cluster with considering DGs generation boundaries. Finally, the nominal voltage set points of each DG can be determined by the secondary controller to guarantee the generation-demand power balance. The feasibility of the proposed controller is demonstrated by simulation and experiment under various test scenarios.

In order to improve the performance of traditional phase-shifted full-bridge converters and reduce the output current ripple, an improved zero voltage and zero current switching phase-shifted full-bridge PWM converter is proposed in this article. By adding a simple auxiliary circuit, the leading-leg switches realize zero voltage switching and the lagging-leg switches realize zero current switching. The primary current is reset during the freewheeling period, so the efficiency of the converter is improved. What is more, the improved converter can effectively reduce the output current ripple. The added auxiliary circuit does not include any lossy components or saturable reactors. The improved phase-shifted full-bridge converter has many advantages, including simple circuit topology, easy implementation of soft switching, high efficiency, and low output current ripple. The operational principle and analysis of the proposed converter are presented in this article. An 800 W experimental prototype is built for experimental verification.