This study examined the differential effects of teachers' first language (L1) use and second language (L2)‐only explanations on Chinese‐speaking adults' acquisition of concrete and abstract English words. A quasi‐experimental research design was used, in which 50 participants were assigned to an L1‐use condition, 50 participants were assigned to an L2‐only use condition, and another 48 participants served as a comparison group. Assessed with a pre‐test, immediate post‐test, and delayed post‐test, each group's knowledge of the target words was compared with that of the other groups over time. The results suggest that teachers' L1 use, compared to L2‐only explanations, might lead to greater vocabulary gains in immediate and delayed recall. Possible explanations for these findings are proposed.

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This paper addresses the control design for an upper limb exoskeleton in the presence of input saturation. An adaptive controller employing the neural network technology is proposed to approximate the uncertain robotic dynamics. Also, an auxiliary system is designed to deal with the effect of input saturation. Furthermore, we develop both the state feedback and the output feedback control strategies, which effectively estimates the uncertainties online from the measured feedback errors, instead of the model-based control. In addition to the proposed control, a disturbance observer is designed to reject the unknown disturbance online for achieving the trajectory tracking. The method requires a minimal amount of a priori knowledge of system dynamics. Subsequently, the principle of Lyapunov synthesis ensures the stability of the closed-loop system. Finally, the experimental studies are carried out on this robotic exoskeleton.

Abstract:Methane emissions from hydroelectric reservoirs can comprise a considerable portion of anthropogenic methane. However, lack of data on CH 4 emissions in different geographical regions and high spatial-temporal variability in the emission rates of reservoirs has led to uncertainties regarding regional emission estimates of CH 4 . In the subtropical plateau climate region, we used the Ertan hydroelectric reservoir as a study area. The CH 4 flux at the air-water interface was assessed by floating chambers and factors influencing emissions, including the distance from the dam, water depth, seasonal variation in wet and dry season, air-water temperature gradient and wind speed, and was also studied through a year-long systematic sampling and monitoring experiment. The results showed that the surface of the reservoir was a source of CH 4 during the sampling period and the annual average CH 4 flux was 2Ð80 š 1Ð52 mg m 2 d 1 . CH 4 flux (and its variation) was higher in the shallow water areas than in the deep-water areas. CH 4 flux near the dam was significantly higher than that of other locations farther from the dam in the dry season. The seasonal variations of CH 4 emission in wet and dry seasons were minor and significant diurnal variations were observed in wet and dry seasons. Exponential relationships between the CH 4 flux and air-water temperature gradient were found. Air-water temperature gradient was an important factor influencing diurnal variations of CH 4 flux in the Ertan hydroelectric reservoir. These results indicate that systematic sampling is needed to better estimate CH 4 flux through coverage of the spatial variation of different water depths, measuring-point distance from the dam, seasonal variation in wet and dry seasons and changes in climate factors (such as air-water temperature gradient). Our results also provide a fundamental parameter for CH 4 emission estimation of global reservoirs.

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