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Since the reform and opening up, the urbanization rate in China has risen about 40% from 1978 to 2016, and it has been rapidly advancing at a rate of 0.5 percentage points higher than the world average each year. In the process of city booming, there inevitably exist problems such as extensive land use, urban sprawl and excessive energy consumption. In recent years, environmental pollution such as haze caused by excessive energy consumption has impacted seriously on the life quality of urban residents, and the problem is even more serious in large cities. In western countries, it has been proved that compact city is an effective development mode in alleviating energy shortage and environmental pollution in large cities. However, the concept of compact city has not been given enough attention in China. In this paper, we focused on the relationship between energy efficiency and compactness. The energy efficiency and compactness of 29 large cities during 2003- 2014 were measured with superefficiency- DEA model and entropy value method, and then quadrant map approach was introduced to explore the relationship between urban compactness and energy efficiency. The results showed that energy efficiency was relatively low but was increasing slowly. The regional disparities of the relationship between urban compactness and energy efficiency were significant. The eastern part of China mainly had high coordination relationship, while the middle and western part of China mostly had low coordination relationship. From the perspective of the scale of cities, larger cities had higher energy efficiency. As the city size increased, the proportion of high coordination type became higher and higher. Megacities mostly fell into the categories of high coordination, and small cities mostly fell into the categories of low coordination. The quadrant diagram analysis after eliminating other possible affecting factors showed more obvious result that more compact city had higher energy efficiency. To improve the energy efficiency, multi-functional composite utilization of economy humanity and ecology should be realized by putting more investment into the construction of public service facilities and infrastructure, intensifying industrial land use and perfecting the functional system of cities. [ABSTRACT FROM AUTHOR]

Life cycle assessment analysis method was used to establish the life-cycle energy consumption and emission inventory, and evaluate the environmental impacts of bioethanol production produced from sweet potato with two different fertilization modes, that is, conventional fertilization mode and soil testing & formulating fertilization mode. The sweet potato based ethanol production system was divided into three subsystems, including crop cultivation, feedstock transport and ethanol conversion. The energy consumption and pollutant emission inventory of sweet potato based ethanol was established with the unit of 1 000 L ethanol production. The results show that the energy efficiencies of the two sweet potato based ethanol production systems were 1.41 and 1.43. The main environmental impacts of ethanol produced from sweet potato with conventional fertilization practice are human toxicity, eutrophication, acidification, freshwater ecotoxicity, energy depletion and global warming, their environmental impact potentials accounting for 40%, 40%, 31%, 29%, 25% and 20% of relevant environmental potential per capita in 2000. The soil test & formulating fertilization practice reduced the usage of chemical nitrogen and phosphate fertilizers and increased the fertilizer utilization efficiency and sweet potato yielding, so the environmental impact indexes of eutrophication, freshwater ecotoxicity, acidification and global warming were decreased by 31%, 15%, 9% and 7%, respectively. Therefore, soil testing & formulating fertilization mode can improve life-cycle energy efficiency of the sweet potato based bioethanol and significantly alleviate its negative environmental impacts. [ABSTRACT FROM AUTHOR]