Economic efficiency is the key issue of sustainable development in urban agglomerations. To date, more attention has been paid to the estimates of productivity gains from urban agglomerations. Differing from the previous studies, this paper focuses on the influencing factors and mechanisms of the economic efficiency of urban agglomerations, and check the effects of three different externalities (industrial specialization, industrial diversity and industrial competition) on the economic efficiency of urban agglomerations. The selected samples are multiple urban agglomerations, and the economic efficiency of urban agglomerations includes single factor productivity and total factor productivity. China’s top 10 urban agglomerations are selected as the case study and their differences in economic efficiency are portrayed comparatively. Firstly, a theoretical analysis framework for three different externalities effect mechanisms on the economic efficiency of urban agglomerations is incorporated. Secondly, economic efficiency measurement index system composes of labor productivity, capital productivity, land productivity and total factor productivity, and the impact of various factors on the economic efficiency of urban agglomerations is tested. The results confirm some phenomena (MAR externality, Jacobs externality and Porter externality) discussed or mentioned in the literature and some new findings regarding the urban agglomerations, derive policy implications for improving economic efficiency and enhancing the sustainability of urban agglomerations, and suggest some potentials for improving the limitations of the research.

In response to concern by the U.S. Environmental Protection Agency (EPA) about the health effects of farmworker exposure to 2,4-D and the phenoxy class of herbicides, the U.S. Department of Agriculture (USDA) initiated a benefits assessment in 1993 to determine the economic implications of a complete ban of these materials in agricultural and nonagricultural uses. About 55 million pounds of phenoxy herbicides are used annually in the United States, with 2,4-D comprising 86% of total use or about 47 million pounds of acid equivalent. The severest economic effects would be felt in major field crop applications and in alfalfa forage uses. The total loss of phenoxy herbicides in field crop applications could result in net societal losses, which combine producer and consumer effects of yield, cost, and price changes, approaching $1.2 billion. Greatest yield losses averaged over total planted acres under a total phenoxy herbicide loss scenario would be seen in peanut (13%), alfalfa (5.2%), barley (3.8%), sorghum (2.4%), and wheat (2.2%). Producers of orchard, vineyard, soft fruit, and nut crops could incur losses of $105 million. The estimated aggregate economic impact of losing phenoxy herbicides in the applications included in this paper is a loss of $1.3 billion. These estimates describe the yield and financial impacts of the initial production year after a cancellation. Subsequent years' losses and financial impacts would be less as farmers and markets adjust to the new production situation.

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The identification of a sustainable competitive position in enterprises is a common concern of information science and sustainable development research. Achievement of sustainable competitive position and superior performance is the first priority of business organizations. However, the existing research focuses on technology competition and light market competition. The research proposes a comprehensive framework for identifying an enterprise's sustainable competitive position based on a two-dimensional perspective of insiders (enterprise self-positioning) and outsiders (public cognition), including enterprise technology competition identification based on technology proximity, and enterprise market competition identification based on URL co-occurrence analysis. Based on the patents collected using the Derwent Innovation Index (DII) and the URL data collected from the Internet, the sustainable competitive position of mobile communication companies is identified from two dimensions of insiders and outsiders. QAP (quadratic assignment procedure) correlation analysis shows that these two dimensions are complementary. The two-dimensional perspective is integrated to comprehensively analyze the sustainable competitive position of Huawei, and thus obtain valuable information. In order to achieve the sustainability of competitive position in the industry, mobile communication enterprises must improve their management level (marketing characteristics of management and low cost structure), and must also have the ability to break through the governance system (rigid characteristics of governance) in a timely manner, and gain the ability to create value for customers in the long run (enhancement of public cognition and public image, and customer loyalty). Meanwhile, the mobile communication industry is a typical network externality market. If the companies want to obtain a sustainable competitive position in the competitive landscape, they need to manage user's expectations, expand the foundation of users, achieve extensive cooperation and alliances with manufacturers of complementary products, and improve the quality and reputation of their brands.

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