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File sharing is the foundation of the Internet. But the traditional centralized service architecture will result in huge infrastructure costs and maintenance costs. Due to the lack of effective file management system, a lot of sensitive information is out of control and loss of confidentiality document has occur from time to time. In order to address the difficulty of tamper detection and the lack of supervision in the entire process of file transmission in the current Internet environment, this paper designs a block-chain-based system architecture for secure sharing of electronic documents. An efficient Blockchain model is used in our framework, and with the help of distributed storage system and asymmetric encryption technology, file sharing can be controlled, reliable and traceable in the transmission process.Referring to existing consensus mechanism, e.g., Delegated Proof of Stake (DPoS) and Practical Byzantine Fault Tolerance (PBFT), we propose a new consensus for efficient and secure file sharing.

The permafrost of Mohe County and its suburbs in the Daxing’an Mountains has been influenced by the urbanization. Remote sensing, GIS technology and numerical simulation was used to study the temperature variations of permafrost with the changes in surface vegetation that cover Mohe County and suburban areas, and the law of permafrost degradation on the study area was analyzed. The research results show that the urban area of the study area increased 114.42% from 2000 to 2016, and the urbanization process is continuing to accelerate. The Normalized Difference Vegetation Index map of 2017 in Mohe County and its suburbs was studied and the maximum proportion of vegetation coverage was different in the four seasons. The numerical calculation model results show that the permafrost temperature change in the study area cyclically fluctuates in a cosine form. The annual variation curve of permafrost temperature gradually decreased and its accompanying phase lag increased with depth. The annual temperature change value with the different depths of the town was greater than the natural ground. The maximum permafrost thawing depths of the town and natural ground were 4.2 m and 2.82 m in 50 a, and the degradation rates of the two permafrost are, respectively, 0.88 cm/a and 0.46 cm/a. These results show that urbanization has accelerated the degradation of permafrost.