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In terms of the collaborative utilization of residual energy and space resources in abandoned mines, under the framework of a green low-carbon multi-energy complementary system, a multi-energy complementary DC microgrid integrating wind-solar-gas-storage for residual CBM drainage in abandoned mine was proposed and constructed with the consideration of both the electricity demand of coalbed methane (CBM) in the abandoned mine goaf and the power generation potential of renewable energies in coal mining subsidence areas, as well as the low-concentration gas power generation and energy storage as supplements. Compared with the common DC microgrids, the superposition of multiple unfavorable factors such as low system inertia, weak grid connection, random changes in distributed power generation and large fluctuations in periodically variable working condition load makes the stable operation of the multi-energy complementary DC microgrid for residual CBM drainage face become a more severe challenges. Therefore, it is necessary to systematically discuss and investigate the key technologies and bottlenecks involved in the multi-energy complementary DC microgrid for residual CBM drainage in abandoned mine which is a potential scenario of collaborative utilization of residual energy and space resources in abandoned mines. First, the topology and components of a multi-energy complementary DC microgrid for residual CBM drainage were described, and the constraints that need to be considered in the system capacity optimization were discussed based on an energy flow model. Then, the key technologies including periodically variable working condition load analysis of CBM pumping motor, coupling of gas-electric conversion link of low-concentration gas generator, voltage stabilization control and system coordinated operation involved in achieving reliable, stable and coordinated operation of multi-energy complementary DC microgrid for residual CBM drainage in abandoned mine were concluded. The recent research progresses were summarized and reviewed, the difficulties and problems existed in the current work were analyzed, and some possible solutions and suggestions for following work were discussed. Furthermore, it is pointed out that it is urgent to address the bottleneck issues behind the key technologies such as the joint modeling method of both gas-electric coupling long-time scale of the low-concentration gas generator and short-time scale of wind-solar-storage, as well as the bus voltage oscillation mechanism caused by multiple unfavorable factors such as low inertia, weak connection and large disturbance. Finally, the feasibility and application prospect of constructing a multi-energy complementary DC microgrid for residual CBM drainage in abandoned mine were prospected from the aspects of existing work basis, research progress and economic benefits assessment.

Electronic resources represented by databases have become an important part of library collection development. Database acquisition involves not only huge amounts of library budget but also complicated legal issues. Negotiation with database vendors mainly based on inherent experiences and industry practice is usually the way of current databases acquisition of university libraries, while understanding of database acquisition issues from legal perspective is rather rare. Based on this, the article aims to provide a reference for library database acquisition, arouse the legal consciousness of librarians, and use legal weapons and legal thinking to avoid legal risks, while striving for the interests of libraries and readers to the greatest extent. It uses methods of survey and case analysis to investigate typical cases and identify bottle necks in the library database acquisition process, and points out the methods to solve these problems under the existing legal system framework in our country. By strengthening the legal literacy training of acquisition librarians, and soliciting opinions from legal experts, we hope to improve the library's awareness and ability to handle legal issues in the database acquisition. [ABSTRACT FROM AUTHOR]

The reactive extrusion for the polymerization of olefins based on the classic theory of anionic polymerization was briefly introduced. Its application value in the industrial fields and theoretical contribution to the anionic polymerization were mainly expressed. Then, the development of olefin anionic polymerization in 60 years, especially, most of the studies in this field over the past decade, were reviewed. Based on this, the 5 pieces of suspense and 2 major bottlenecks of the development remained in the anionic polymerization of olefins were pointed out. Through citing the researches of our team in recent 20 years, the interpretation of the suspense and the breakthrough in the bottlenecks were discoursed. [ABSTRACT FROM AUTHOR]