Analyzing Differences between Online Learner Groups during the COVID-19 Pandemic through K-Prototype Clustering

Online learning is a very important means of study, and has been adopted in many countries worldwide. However, only recently are researchers able to collect and analyze massive online learning datasets due to the COVID-19 epidemic. In this article, we analyze the difference between online learner groups by using an unsupervised machine learning technique, i.e., k-prototypes clustering. Specifically, we use questionnaires designed by domain experts to collect various online learning data, and investigate students’ online learning behavior and learning outcomes through analyzing the collected questionnaire data. Our analysis results suggest that students with better learning media generally have better online learning behavior and learning result than those with poor online learning media. In addition, both in economically developed or undeveloped regions, the number of students with better learning media is less than the number of students with poor learning media. Finally, the results presented here show that whether in an economically developed or an economically undeveloped region, the number of students who are enriched with learning media available is an important factor that affects online learning behavior and learning outcomes.

Molecular mechanisms underlying heat or tetracycline treatments for citrus HLB control

Huanglongbing(HLB),a destructive plant bacterial disease,severely impedes worldwide citrus production.In our previous reports,we revealed the molecular mechanisms of host plant responses that underlie thermotherapy against HLB.In this study,we investigated the molecular mechanism underlying heat or tetracycline treatments on the HLB bacterium,‘Candidatus Liberibacter asiaticus’(Las)by focusing on Las prophage/phage conversion under stress conditions.By comparing the prophage FP1 and FP2 copy number to the copy number of 16S rDNA in HLB-affected plants,we found that the relative copy number of both FP1 and FP2 increased significantly,ranging from 3.4-to 6.7-fold change when Las-infected samples underwent a temperature shift from 23 to 37,42 or 45°C.When treated with tetracycline at 50–150 and 200–250µg/ml,respectively,the relative copy number of both FP1 and FP2 increased by 3.4-to 6.0-fold.In addition,analyses of Las prophage structural gene and antirepressor gene copy numbers showed similar trends for all treatments.Furthermore,transmission electron microscopy provided direct evidence of lysogenic to lytic conversion upon temperature increase.These results not only provide new insight into the molecular mechanisms underlying heat or tetracycline treatment but also suggest a novel HLB control strategy by enhancing the endogenous conversion from Las prophages to phages.

Solar thermotherapy reduces the titer of Candidatus Liberibacter asiaticus and enhances canopy growth by altering gene expression profiles in HLB-affected citrus plants

Huanglongbing(HLB),a systemic and destructive disease of citrus,is associated with‘Candidatus Liberibacter asiaticus’(Las)in the United States.Our earlier work has shown that Las bacteria were significantly reduced or eliminated when potted HLB-affected citrus were continuously exposed to high temperatures of 40 to 42°C for a minimum of 48 h.To determine the feasibility and effectiveness of solar thermotherapy in the field,portable plastic enclosures were placed over commercial and residential citrus,exposing trees to high temperatures through solarization.Within 3–6 weeks after treatment,most trees responded with vigorous new growth.Las titer in new growth was greatly reduced for 18–36 months after treatment.Unlike with potted trees,exposure to high heat did not eradicate the Las population under field conditions.This may be attributed to reduced temperatures at night in the field compared to continuous high temperature exposure that can be maintained in growth chambers,and the failure to achieve therapeutic temperatures in the root zone.Despite the presence of Las in heat-treated commercial citrus,many trees produced abundant flush and grew vigorously for 2 to 3 years after treatment.Transcriptome analysis comparing healthy trees to HLB-affected citrus both before and after heat treatment demonstrated that post-treatment transcriptional expression patterns more closely resembled the expression patterns of healthy controls for most differentially expressed genes and that genes involved with plant-bacterium interactions are upregulated after heat treatment.Overall,these results indicate that solar thermotherapy can be an effective component of an integrated control strategy for citrus HLB.

Beneficial horticultural responses from the application of solar thermotherapy to mature Huanglongbing-affected citrus trees

The detrimental effects of Huanglongbing(HLB)on citrus are well known and so is the need for effective methods to combat this disease.Solar thermotherapy(ST),one of the management methods to help alleviate some of the negative effects of HLB,is the process of heating trees to therapeutic temperatures by encompassing the tree within a plastic structure(Visqueen)to harness the sun’s natural energy.ST was applied to mature‘Valencia’citrus trees in three locations.Tree vigor,yield,and Candidatus Liberibacter asiaticus(Las)titer in leaves were monitored for two consecutive seasons post ST treatment,while fruit and juice quality were evaluated at the end of the second season.ST promoted an increase in canopy density in most groves tested and did not have a significant effect on fruit quantity,despite the prolonged exposure of the trees to increased temperatures.Moreover,Las titer was reduced in both leaves and juice processed from affected trees post ST.With respect to fruit quality,the ratio of total soluble solids to titratable acidity was higher post ST compared to controls as was the sucrose content of the juice in most treated groves,whereas limonin was higher in juice from control trees.Principal components analysis of aroma volatiles showed significant differences between juice from treated versus control trees with volatiles imparting top-note and freshness to orange juice,such as acetaldehyde,hexanal,Z-3-hexenol and linalool,being higher in juice fromtreated trees.Taste panels confirmed that flavor differences existed,ultimately showing that ST resulted in improved juice flavor in well-managed groves.Although the effects of ST on the trees appear temporary,such outcomes emphasize its utility when used as part of an integrated management strategy for HLB-affected citrus,imparting beneficial horticultural responses with minimal to positive effects on subsequent juice flavor.

Building a Neural Network Model to Analyze Teachers’ Satisfaction with Online Teaching during the COVID-19 Ravages

The ravages of COVID-19 have forced schools in countries around the world to make a temporary shift from traditional, face-to-face teaching to online teaching. Are teachers in schools prepared to deal with this change? We conducted a survey in which we distributed questionnaires to primary and secondary school teachers in Guangdong Province, China, asking them about their views on various aspects of online education. We received 498,481 questionnaires back, and over 80% of teachers were satisfied with the online resources, and over 68% of teachers were satisfied with the online platform and software. Immediately afterward, we analyzed the differences between urban and rural teachers on specific issues using cross-sectional analysis and chi-square tests and built a neural network model to achieve predictions of teacher satisfaction with an accuracy of nearly 90%. Finally, we analyzed the features that influence the decisions of the neural network. This epidemic has prompted the widespread use of online learning, and the insights we gain today will be helpful in the future.

An error analysis and optimization method for combined measurement with binocular vision

The accurate measurement of surfaces of large aviation components is vital for the assessment of manufacturing and assembly quality of such components.To satisfy the measurement requirement of large-size components,most current researches pay more attention to combined measurement methods utilizing different measuring instruments,but the related researches on error analysis and optimization methods are not taken enough attention.This paper proposes a combined laser-assisted measurement method with feature enhancement techniques,and it also develops an error propagation model of the main factors affecting the overall measurement error in detail.Firstly,the surface of a large-size component is measured by the measurement system at multiple stations.Secondly,a control point coordinate system is established as a bridge to unify all local measurement data into the global coordinate system.To improve the overall measurement accuracy,the pixel extraction error as a key factor causing the overall measurement error is analyzed in detail.Next,the error propagation model is established,and some optimization strategies of layout for minimizing measurement error and transformation error are researched.Finally,experiments are carried out to verify the effectiveness of the proposed method.The results show that the measurement error of the proposed method reaches 0.073%and 0.14%with a 1 D standard ruler and a flat plate,respectively.

Effects of eggshell addition on calcium-deficient acid soils contaminated with heavy metals

In this study, effects of water conditions （flooded, wet, or dry） and eggshell dosages （0, 0.1, 1.0, and 10.0 g/kg soil, respectively） on pH variation, content of unavailable state of heavy metals, form of heavy metals, and available nutritious element calcium （Ca） in acid soils contaminated with heavy metals were investigated, respectively. The soil samples were continuously cultivated indoors and analyzed by toxicity characteristic leaching procedure and community bureau of reference （BCR） sequential extraction procedure. The results showed that the addition of eggshell could effectively improve the pH of acid soil and increase it to neutral level. Moreover, the contents of unavailable state of heavy metals Cu, Zn, and Cd increased significantly. Furthermore, when the soil was cultivated under the flooded condition with 1.0 g/kg eggshell, the unavailable state ofCu, Zn, and Cd increased the most, and these heavy metals were transformed into residual state. On the other hand, the amount of available state of Ca increased to 432.19 from 73.34 mg/kg with the addition of 1.0 g/kg eggshell, which indicated that the addition of eggshell dramatically improved the available state of Ca. Therefore, eggshell could ameliorate the soil environment as it led to the decrease of available heavy metals and improvement of fertilization effectively. In a word, this study indicates that the addition of eggshell would be a new potential method for remediation of acid field soils contaminated with heavy metals.