Customers make a lot of reviews on online shopping websites every day, e.g., Amazon and Taobao. Reviews affect the buying decisions of customers, meanwhile, attract lots of spammers aiming at misleading buyers. Xianyu, the largest second-hand goods app in China, suffering from spam reviews. The anti-spam system of Xianyu faces two major challenges: scalability of the data and adversarial actions taken by spammers. In this paper, we present our technical solutions to address these challenges. We propose a large-scale anti-spam method based on graph convolutional networks (GCN) for detecting spam advertisements at Xianyu, named GCN-based Anti-Spam (GAS) model. In this model, a heterogeneous graph and a homogeneous graph are integrated to capture the local context and global context of a comment. Offline experiments show that the proposed method is superior to our baseline model in which the information of reviews, features of users and items being reviewed are utilized. Furthermore, we deploy our system to process million-scale data daily at Xianyu. The online performance also demonstrates the effectiveness of the proposed method.
This study considers an original equipment manufacturer (OEM) who (a) relies on a contract manufacturer (CM) to produce its new products, and (b) engages the CM again or an independent remanufacturer (IR) to perform the remanufacturing operations of branded patented products through either authorization or outsourcing. This study chiefly investigates the optimal remanufacturing engagement strategy (i.e., engage a CM or an IR) and remanufacturing mode (i.e., authorization and outsourcing) that should be taken by an OEM. This paper derives the optimal responses of the three parties (i.e., OEM, CM, and IR) by comparing the outcomes of different remanufacturing engagement strategies and remanufacturing modes under two settings, depending on whether the wholesale price is exogenously or endogenously given. The results suggest that the OEM is better off adopting the authorization remanufacturing mode by either working with the CM or the IR when the wholesale price is exogenously given. When the wholesale price is endogenously determined by the CM, the best strategy for the OEM is to work with the IR using the outsourcing approach. The CM and the IR also show different preferences between the two modes. The IR or CM that engages in remanufacturing always prefers the outsourcing mode than the authorization mode in the two settings. However, when the CM does not engage in remanufacturing, it is better off adopting the authorization mode when the wholesale price is exogenously given or when the remanufacturing cost is relatively low in the endogenized wholesale price setting.
Many original equipment manufacturers (OEMs) face the choice of whether to license an independent remanufacturer (IR) to remanufacture their used products. In this paper, we develop closed-loop supply chain models with licensed and unlicensed remanufacturing operations to analyze the competition and cooperation between an OEM and an IR. The OEM sells new products and collects used products through trade-ins, while the IR intercepts the OEM's cores to produce remanufactured products and sell them in the same market. We derive optimal decisions for each of the two types of firms in licensed and unlicensed remanufacturing scenarios and identify conditions under which the OEM and the IR would be most likely to cooperate with each other in implementing remanufacturing. The results show although it is beneficial for an OEM to license an IR to remanufacture its cores, it is not always necessary for an IR to accept OEM's authorization. Moreover, we contrast the result for licensed remanufacturing scenario in the decentralized system with that in the centrally coordinated system to quantify potential inefficiency resulting from decentralization of decision making.
Remanufacturing plays an important role in a circular economy, by shifting supply chains from linear to closed loop. However, the development of the remanufacturing industry faces many challenges. Consumers’ uncertainty about the quality of remanufactured products can hamper their decision to make a purchase (i.e., uncertainty behavior). Such uncertainty can be reduced when they learn that more consumers are purchasing remanufactured products (i.e., network externality behavior). Considering the aforementioned behaviors, this paper investigates how a government could set the optimal subsidy level to maximize the sales quantity of remanufactured products with a limited budget. We modeled a Stackelberg game between the government and an original equipment manufacturer, under two settings, over two periods. Setting 1 only considers an original equipment manufacturer that produces remanufactured products, and Setting 2 considers an original equipment manufacturer that produces both new and remanufactured products. We show that the original equipment manufacturer should adjust its pricing strategy (i.e., markup vs. markdown) according to the subsidy levels. Our analysis on the government budget constraint shows that an original equipment manufacturer earns more profits in Setting 1 than Setting 2, only when the budget constraint is high, and less profits when budget constraint is low.
Elevated levels of total dissolved gas (TDG) may occur downstream of dams during the spill process. These high levels would increase the incidence of gas bubble disease in fish and cause severe environmental impacts. With increasing numbers of cascade hydropower stations being built or planned, the cumulative effects of TDG supersaturation are becoming increasingly prominent. The TDG saturation distribution in the downstream reaches of the Jinsha River was studied to investigate the cumulative effects of TDG supersaturation resulting from the cascade hydropower stations. A comparison of the effects of the joint operation and the single operation of two hydropower stations (XLD and XJB) was performed to analyze the risk degree to fish posed by TDG supersaturation. The results showed that water with supersaturated TDG generated at the upstream cascade can be transported to the downstream power station, leading to cumulative TDG supersaturation effects. Compared with the single operation of XJB, the joint operation of both stations produced a much higher TDG saturation downstream of XJB, especially during the non-flood discharge period. Moreover, the duration of high TDG saturation and the lengths of the lethal and sub-lethal areas were much higher in the joint operation scenario, posing a greater threat to fish and severely damaging the environment. This work provides a scientific basis for strategies to reduce TDG supersaturation to the permissible level and minimize the potential risk of supersaturated TDG.
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