Ultraviolet photodetectors have attracted significant research attention in recent years due to their potential applications in civilian and military fields. ZnO nanowires and nanorods have been regarded as the most potential candidates for ultraviolet photodetectors fabrication because of their peculiar characteristics and size effect, which are different from their bulk material. Recently, many novel routes and semiconductor features, such as the surface and interface engineering, the pryo-phototronic effect, the piezo-phototronic effect, the surface plasmon effect and the surface functionalization have been utilized to improve the photoelectric characteristics of ultraviolet photodetectors. Thus, the working mechanism of these effects existing in ZnO nanowires/nanorods-based ultraviolet photodetectors should be investigated in-depth. In this paper, firstly, the hydrothermal method and the chemical vapor deposition method, as two typical synthesis methods of ZnO nanowires are briefly reviewed. Secondly, we focus on reviewing the properties of varied ZnO nanowires/nanorods-based ultraviolet photodetectors constructed using the above mentioned semiconductor features with metal-semiconductor-metal structure, Schottky barrier structure, vertical p-n heterojunction structure and core-shell heterostructure. Furthermore, the most attractive self-powered ultraviolet photodetectors are systematically reviewed. For various ZnO nanowires/nanorods-based ultraviolet photodetectors, we put the emphasis on the working mechanism of semiconductor features to improve the properties of the photodetectors. Finally, we give an outlook on the future development of ZnO nanowires/nanorods-based ultraviolet photodetectors.

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Many previous researches have proved that foam can increase the sweep efficiency and control gas mobility, and thus increase oil recovery. However, research on the effects of reservoir conditions such as the permeability, reservoir heterogeneity, formation rhythm and the viscosity of prude oil remains incomplete. Therefore, it is significant to study the foam efficiency in different reservoir conditions for large scale application of foam flooding.The foaming agent was evaluated in laboratory and flooding experiments were conducted upon two groups of long real formation cores from Shengli oilfield to study foam flooding efficiencies. The effects of core permeability and gas liquid ratio on foam resistance factor were discussed. And then operating parameters including gas liquid injection ratio, injection rate and foam injection time were optimized and the influence of reservoir heterogeneity, the viscosity of crude oil and formation rhythm on nitrogen foam flooding efficiency were investigated at length by means of numerical simulation in the light of Shengli specific reservoir conditions.The results show that, nitrogen foam flooding has excellent blocking ability and the optimum ratio of gas to liquid is 1.5:1; and the optimum foam rate is0.2 pore volume; the best foam flooding time is when the water cut of production well is 85%~ 90%. Nitrogen foam flooding is more effective for heterogeneous formations rather than for homogeneous ones. Furthermore, the efficiency of the flooding system decreases with the increasing viscosity of crude oil and is better in regular rhythm formation than that in negative rhythm formation. Finally, some easy-to-use and practical charts are drawn to analyze the economic benefits of nitrogen foam flooding for the given reservoir.The study results provide a set of reservoir criteria that can be used as guidelines to choose potential reservoir candidates for nitrogen foam flooding.

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