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Bidder collusion seriously undermines the fair competition of the construction project market, and effective identification of collusion behaviors is of vital importance to the implementation of proactive regulation and supervision. In this paper, the data of construction project bidders from 2011 to 2018 are selected in Shaanxi Province, China, and a bidder network of construction projects is constructed. The collusion suspicion of bidders is analyzed from the macro-, meso-, and microlevels. The results show that the bidder network has features as small world at macrolevels, and it is easy for bidders to involve in collusion. The network community formed by construction, supervision, and survey and design bidding enterprises is analyzed at the mesolevel, and the collusion of supervision enterprises is found to have the highest suspicion At the microlevel, the characteristic value judgment and community division are adopted to analyze the collusion suspicion, which is divided into high, medium, and low according to the possibility. Through a comparison with the actual data, it is found that the method proposed in this paper can effectively identify the collusion behavior of construction project bidders. This paper proposes red, yellow, and green warning mechanism and formulates hierarchical accurate management preparedness, which can provide some suggestions to help prevent bidders from colluding. [ABSTRACT FROM AUTHOR]

The method for the determination of calcium content is optimized to establish the effective method to determine the content of Danba (measured by calcium ion). The difference between high temperature and microwave digestion for sample preparation method was compared. The EDTA titration method was improved. The content of calcium ion was determined by ion chromatography and EDTA titration at the same time in the salted aconite root rinse. Microwave digestion method is more advantage than high temperature in pretreating samples, and taking replace the high temperature method as a new method for sample treatment in titration method. Titration method that adding tartaric acid as a masking agent is more accurate than others in determining the quality of calcium ion concentration. The result of titration is 2.17~3.32 mg/mL, the result of ion chromatography is 1.90 ~ 3.27 mg/mL. Two methods have no obvious difference, they are the effective methods. The optimized method is efficient, rapid, accurate, reliable and can be used as a determination method for the contents of Danba in the process of washing salted aconite root. It's the first time to establish ion chromatography method and microwave digestion joint EDTA titration method for the determination of calcium ion. [ABSTRACT FROM AUTHOR]