A comprehensive investigation was carried out to determine the changes that occurred in water-stressed cucumber (Cucumis sativus L.) in response to melatonin treatment. We examined the potential roles of melatonin during seed germination and root generation and measured its effect on reactive oxygen species (ROS) levels, antioxidant enzyme activities, and photosynthesis. Melatonin alleviated polyethylene glycol induced inhibition of seed germination, with 100 μm melatonin-treated seeds showing the greatest germination rate. Melatonin stimulated root generation and vitality and increased the root:shoot ratio; therefore, melatonin may have an effect on strengthening cucumber roots. Melatonin treatment significantly reduced chlorophyll degradation. Seedlings treated with 100 μm melatonin clearly showed a higher photosynthetic rate, thus reversing the effect of water stress. Furthermore, the ultrastructure of chloroplasts in water-stressed cucumber leaves was maintained after melatonin treatment. The antioxidant levels and activities of the ROS scavenging enzymes, i.e., superoxide dismutase, peroxidase, and catalase, were also increased by melatonin. These results suggest that the adverse effects of water stress can be minimized by the application of melatonin.

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Future wireless networks have a substantial potential in terms of supporting a broad range of complex compelling applications both in military and civilian fields, where the users are able to enjoy high-rate, low-latency, low-cost and reliable information services. Achieving this ambitious goal requires new radio techniques for adaptive learning and intelligent decision making because of the complex heterogeneous nature of the network structures and wireless services. Machine learning (ML) algorithms have great success in supporting big data analytics, efficient parameter estimation and interactive decision making. Hence, in this article, we review the thirty-year history of ML by elaborating on supervised learning, unsupervised learning, reinforcement learning and deep learning. Furthermore, we investigate their employment in the compelling applications of wireless networks, including heterogeneous networks (Het-Nets), cognitive radios (CR), Internet of things (IoT), machine to machine networks (M2M), and so on. This article aims for assisting the readers in clarifying the motivation and methodology of the various ML algorithms, so as to invoke them for hitherto unexplored services as well as scenarios of future wireless networks.

COVID-19 vaccines have been conditionally used in a few countries, including China since December 2020. The present study aimed to examine whether the acceptance of COVID-19 vaccination changed in different COVID-19 epidemic phases in China. Two consecutive surveys were conducted among Chinese adults in March (n = 2058) (severe epidemic phase) and November–December (n = 2013) (well-contained phase, right before the COVID-19 vaccine was conditionally approved) 2020, and 791 respondents were longitudinally followed-up. The attitude, acceptance, and preferences for future COVID-19 vaccination were compared between two epidemic phases. Multivariate logistic regression was used to identify influencing factors of acceptance. Among the 791 respondents longitudinally followed, 91.9% in March and 88.6% of them in November–December 2020 would like to get COVID-19 vaccination in China. In March 58.3% wished to get vaccinated immediately, but the proportion declined to 23.0% in November–December 2020, because more respondents wanted to delay vaccination until the vaccine’s safety was confirmed. Similar results were found by comparing all respondents from the two cross-sectional surveys in different epidemic phases. The risk perception, attitude for the importance of vaccination against COVID-19, vaccination history, valuing doctor’s recommendations, vaccination convenience, or vaccine price in decision-making had impacts on respondents’ intention for immediate vaccination. The public acceptance for COVID-19 vaccination in China sustained at a high level in different COVID-19 epidemic phases. However, the intention of immediate vaccination declined substantially due to concerns about the vaccine’s safety. Information about vaccination safety from authoritative sources, doctor’s recommendations, and vaccination convenience were important in addressing vaccine hesitancy and promoting successful herd immunity for the general population in China.

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