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A 3D finite element (FE) model based on the double ellipsoidal heat source was developed to investigate the evolution of temperature and stress fields during the multilayer and multi-pass wire and arc additive manufacturing (WAAM) process. This paper aims to investigate the evolution of temperature and stress fields during the multilayer and multi-pass wire and arc additive manufacturing (WAAM) process by developing a 3D finite element (FE) model based on the double ellipsoidal heat source.

Experimental thermal cycle curves and residual stresses were obtained by thermocouples and X-ray diffraction, respectively. The validity of the model was verified by the corresponding experimental results.

The deposition process of the upper pass led to the partial remelting of the lower deposited pass. The thermal process of the current-deposited pass alleviated the stress concentration in the previous-formed passes. A more uniform temperature distribution could be obtained by using the reciprocating deposition path. Compared to the reciprocating deposition path, the peak values of the transverse and longitudinal tensile residual stresses of the deposited sample under the unidirectional deposition path were reduced by 15 MPa and increased by 13 MPa, respectively. The heat conduction in the deposited passes could be improved by extending the inter-pass cooling time appropriately. With an increase in the inter-pass cooling time, the longitudinal residual stress in the middle region of sample along longitudinal and transverse directions showed increase and decrease–increase trends, respectively, while the transverse residual stress exhibited decrease trend.

This study enhances the understanding of temperature and stress fields evolution during the multilayer and multi-pass cold metal transfer-WAAM processes of magnesium alloy and provides the reference for parameter optimization.

Carbon reduction in the construction industry is related to the achievement of carbon emission peaks and carbon neutrality targets. Therefore, exploring the influence of current carbon reduction policies on the construction industry is necessary. China’s low-carbon pilot (LCP) policy has been extensively studied, while LCPs mechanism and effectiveness on carbon reduction in the construction industry remain to be explored.

This study selected four provincial LCP regions as case studies and adopted the grounded theory method for case studies to analyze the implementation mechanism of the LCP policy on carbon reduction in the construction industry. Then, this study adopted the propensity score matching and difference-in-differences regression (PSM-DID) approach to evaluate the influence of the LCP policy on carbon intensity (CI) in the construction industry by using panel data taken from 30 provinces in China between 2008 and 2017.

The authors found that (1) the LCP policy promotes carbon reduction in the construction industry through the crossing implementation mechanism of five vertical support approaches and five horizontal support approaches. (2). The LCP policy can significantly reduce CI in the construction industry.

The study not only explored how is the LCP policy implemented, but also examined the effectiveness of the LCP policy in the construction industry. The policy implications of this study can help policy-makers better achieve low-carbon development targets in the construction industry.

Vegetable e-commerce is of great significance for improving the efficiency of vegetable circulation, and for solving the problems of high circulation cost and poor connection between production and marketing. The purpose of this study is to explore the key factors that influence consumers’ vegetable e-commerce adoption willingness, behavior, and willingness-behavior consistency.

A total of 427 valid questionnaires were collected from 16 districts of Beijing in 2019 via the internet, yielding a response rate of 94.9%. Bivariate probit and binary logistic regression were used for analysis.

The results show that 62.84% of vegetable e-commerce consumers have the same willingness and behavior, and 37.16% of consumers have a deviation of willingness and behavior; the key factors influencing the willingness, behavior, and willingness-behavior consistency of vegetable e-commerce consumers are different. The three variables of usefulness perception, logistics service quality perception, and nearest vegetable market distance have significant effects on and are positively correlated with the adoption willingness, behavior, and willingness-behavior consistency of vegetable e-commerce consumers.

Consumers in Beijing, a first-tier city, were taken as the research object in this study. Second-tier and even third-tier cities can be investigated as comparative studies in a follow-up study. In addition, the key factors that affect the differences in the willingness and behavior of vegetable e-commerce adoption can be studied.

The results obtained in the present study and their implications could aid in vegetable e-commerce optimization, and contribute to the understanding of how to improve consumers’ awareness and participation in vegetable e-commerce. The suggestions of this study could also be used for the improvement of vegetable e-commerce in other cities facing similar issues.