Improving energy efficiency and reducing environmental pollution emissions are two important ways to alleviate energy problems. Despite the progress in energy efficiency, the growth in energy demand still exceeds the efficiency improvements. This study adopts nonparametric methods to estimate the total factor energy efficiency (TFEE) of 105 resource-based cities covering the period 2010-2016 in China and analyzes the spatiotemporal characteristics of changes in energy efficiency. Furthermore, panel quantile regression is applied to analyze the multiple impacts of economic level, industrial structure, resource endowment, energy price, government intervention and degree of openness on energy efficiency. The main findings are as follows. (1) Each determinant has a different influence on TFEE at different levels; among them, the influence of the fuel and energy price index show an inverted U-shaped distribution as the quantile increases, and that of the GDP per capita shows a stronger heterogeneity than those of other factors. (2) Resource-based cities with lower efficiency are more sensitive to government intervention than are cities with higher efficiency. (3) A city's openness has a negative effect on TFEE, which partly supports the pollution haven hypothesis: the more foreign investment a resource-based city receives, the lower its energy and technology efficiency. Finally, some practical suggestions for the sustainable development of resource-based cities are discussed.

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Electrically conductive composites have been intensively studied as the interconnects and the printed lines in the next generation of electrical devices. Silver fillers have been widely accepted as the key conductive filler material due to their excellent electrical conductivity, malleability, chemical and mechanical stability. Here we for the first time introduce a scalable synthesis of the mono-dispersed silver dendrites with 3-D micro-and nano-structures, and their uses as the conductive filler for the electrically conductive adhesives (ECAs) with ultralow silver content. These silver dendrites have a unique 3-D fractal structure, which are able to provide excellent low-temperature sintering ability due to the abundant nanostructures at the edge of the dendrite leaves. This feature renders them form excellent electrical percolation network with ultralow concentration (percolation threshold down to 20 wt%) in conventional engineering resins, which is currently the one with the lowest percolation threshold for the micro-metal-filler based ECAs. Thermal analysis (TGA/DSC) and scanning electron microscopy (SEM) suggest that the silver dendrite powders go through a sintering process at the temperature below 150 ºC, thus the adjacent dendrites are able to form effective ohmic conductance. Considering the low materials preparation cost and negligible environmental risk, this method suggests an effective way to develop environmentally benign materials for the flexible printed electronics devices.