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1,204 results on '"Zhang, Yamei"'

26. Teaching Presence Predicts Cyberloafing during Online Learning: From the Perspective of the Community of Inquiry Framework and Social Learning Theory

Author

Zhang, Yamei, Tian, Yuan, Yao, Liangshuang, Duan, Changying, Sun, Xiaojun, and Niu, Gengfeng

Abstract

Background: Cyberloafing exists extensively in online learning and impairs learning, yet little is known about how course-related factors affect it. The community of inquiry framework maintains that learning is affected by teaching presence, according to which, we assume that teaching presence impacts cyberloafing, which is mediated by social presence, cognitive presence, and lack of attention, and moderated by normative influence. Aims: This study examined the effect of teaching presence on cyberloafing and its underlying mechanisms -- the mediating roles of social presence, cognitive presence and lack of attention, and the moderating roles of normative influence. Sample: Participants were 814 university students who were taking video-centric asynchronous online courses. Methods: Self-report instruments were adopted, and data were analysed using structural equation modelling. Results: Teaching presence was negatively associated with cyberloafing. Social presence (positively), cognitive presence (negatively), and lack of attention (negatively) mediated the relation, respectively. Social presence, cognitive presence and lack of attention were also serial mediators of the association (i.e., teaching presence [right arrow] social presence [right arrow] cognitive presence [right arrow] cyberloafing; teaching presence [right arrow] cognitive presence [right arrow] lack of attention [right arrow] cyberloafing; teaching presence [right arrow] social presence [right arrow] cognitive presence [right arrow] lack of attention [right arrow] cyberloafing), and these sequential mediating effects were negative. Moreover, normative influence could aggravate the negative effect of cognitive presence on lack of attention, the positive effect of social presence on cyberloafing, and the positive effect of lack of attention on cyberloafing. Conclusions Theoretical and practical implications of the findings for learning and teaching are discussed.

Published
2022
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43. Microwave Photonic Imaging Radar with a Millimeter-level Resolution

Author

Ma, Cong, Yang, Yue, Liu, Ce, Fan, Beichen, Ye, Xingwei, Zhang, Yamei, Wang, Xiangchuan, and Pan, Shilong

Subjects
Electrical Engineering and Systems Science - Signal Processing
Abstract

Microwave photonic radars enable fast or even real-time high-resolution imaging thanks to its broad bandwidth. Nevertheless, the frequency range of the radars usually overlaps with other existed radio-frequency (RF) applications, and only a centimeter-level imaging resolution has been reported, making them insufficient for civilian applications. Here, we propose a microwave photonic imaging radar with a millimeter-level resolution by introducing a frequency-stepped chirp signal based on an optical frequency shifting loop. As compared with the conventional linear-frequency modulated (LFM) signal, the frequency-stepped chirp signal can bring the system excellent capability of anti-interference. In an experiment, a frequency-stepped chirp signal with a total bandwidth of 18.2 GHz (16.9 to 35.1 GHz) is generated. Postprocessing the radar echo, radar imaging with a two-dimensional imaging resolution of ~8.5 mm$\times$~8.3 mm is achieved. An auto-regressive algorithm is used to reconstruct the disturbed signal when a frequency interference exists, and the high-resolution imaging is sustained.

Published
2020
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