This study investigated the impact of a chatbot-based micro-learning system on students’ learning motivation and performance. A quasi-experiment was conducted with 99 first-year students taking part in a basic computer course on number system conversion. The students were assigned to a traditional learning group or a chatbot-based micro-learning group. After the experiment, both groups achieved a comparable performance, suggesting that students are sufficiently competent to learn independently in the chatbot-based learning environment without the need for continuous face-to-face delivery. Moreover, students in the chatbot learning group attained significantly higher intrinsic motivation than the traditional learning group with perceived choice and perceived value as core predictors of intrinsic motivation. Further analysis with the Johnson-Neyman procedure revealed differences on interaction between the perceived choice and the learning environments. For students with a high initial perceived choice (>=5.1), chatbot-based learning further enhances their post choice motivation whereas for students with a low initial perceived choice (<=3.0), the traditional classroom is more suitable to enhance their post choice motivation. The implications of the findings can help instructors to incorporate chatbot-based learning in the classroom.

Infrared studies of the initial cure and post-cure of RP-46 resin, a nadic end-capped polyimide and a model bisnadimide compound N, N' -(oxydi-3,4 phenylene) di-5,6-norbornene-2,3-dicarboximide (Bis-nadic-3,4'-ODA) were conducted at 316, 325 and 350° C for various time periods. Infrared studies of another model compound, N-phenylnadimide, were conducted at lower temperatures, from 100 to 270° C. N-Phenylnadimide cures at much lower temperatures than Bis-nadic-3,4 -ODA and RP-46. The crosslinking reaction was followed by monitoring the absorption peaks at 841 and 785 cm-1, the endo and exo bands in the 2,3 positions of the nadic end caps and cyclo-aliphatic and cyclo-olefinic peaks on the region 1000 to 600 cm-1 associated with the nadic end-cap curing reaction. Weight losses and changes in the glass transition temperature of the RP-46 resin due to cure and post-cure, were also examined. The infrared changes suggest that complete cross-linking requires a temperature of 325° C or above, and that several new infrared bands are generated in the process. The simple thermally induced reverse Diels–Alder cyclopentadiene N-substituted maleimide recombination reaction or norbornene to norbornene, norbornene to cyclopentadiene or norbornene to substituted maleimide addition reactions may adequately define the cross-linked products derived from the initial cross-linking reaction at 316° C for 1 to 2 h. However, postcure of RP-46 resin or the nadic-3,4 -ODA model compound at 325 or 350° C for several hours generates additional infrared bands in the cyclo-aliphatic and cyclo-olefinic regions (1000–600 cm-1), which are absent in material cured at 316° C for 1 to 2 h. Therefore, completely cured resin consists of simple addition reaction products from the initial cure at 316° C and more complex products from the elevated temperature post-cures. A post-cure at 325° C for about 8 h or at 350° C for 2 h is required for a maximum Tgof 391° C. This is accompanied by a stabilization weight loss of about 2–3%. The weight loss and Tgdata are supporting evidence for the infrared studies.

The 2019 novel coronavirus pandemic (COVID-19) negatively affected global public health and socioeconomic development. Lockdowns and travel restrictions to contain COVID-19 resulted in reduced human activity and decreased anthropogenic emissions. However, the secondary effects of these restrictions on the biophysical environment are uncertain. Using remotely sensed big data, we investigated how lockdowns and traffic restrictions affected China’s spring vegetation in 2020. Our analyses show that travel decreased by 58% in the first 18 days following implementation of the restrictions across China. Subsequently, atmospheric optical clarity increased and radiation levels on the vegetation canopy were augmented. Furthermore, the spring of 2020 arrived 8.4 days earlier and vegetation 17.45% greener compared to 2015–2019. Reduced human activity resulting from COVID-19 restrictions contributed to a brighter, earlier, and greener 2020 spring season in China. This study shows that short-term changes in human activity can have a relatively rapid ecological impact at the regional scale.

ABSTRACT:Microwave energy was investigated to cure nadic-end-capped polyimide precursors (RP-46 resin) using a Cober Electronics Model LBM 1.2A/7703 microwave oven at a frequency of 2.45 GHz. Both neat resin samples and glass cloth and hybrid glass cloth-graphite cloth-RP-46 resin composites were studied. For the resin studies, the effect of various parameters, such as power level, sample size, processing temperature, time, and graphite fiber absorber, were investigated. The variables investigated with the composite study were the power level, mold material, vacuum, and low pressure. The results showed that microwave energy was effective in curing both neat resin samples and composite specimens. The presence of a small quantity of absorber (chopped carbon fiber) accelerates the cure dramatically. Moreover, soapstone mold material was found to be an efficient absorber for glass and glass-graphite composite processing, causing an effective cure in less than 1 h. Glass and glass-graphite hybrid composites with flexural strengths of 372-588 MPa (54 -85 ksi) and moduli of 28.7-31.7 GPa (4.2-4.6 Msi) have been fabricated. This is equivalent to 50 to 80% of the properties of composites fabricated by conventional means.