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The development of Power Internet of Things has brought a variety of access requirements for massive collecting terminals. Based on the characteristics of security attributes of Power Internet of Things, this paper proposes a secure access protocol based on symmetric cryptographic algorithm for the large number of collecting terminals with limited manufacturing cost, computing power and storage resources. This protocol only uses the symmetric cryptographic algorithm which has the fast computing speed and low resource consumption, and the protocol can realize two-way identity authentication between the collecting terminal and master station. At the same time, combined with the historical access mechanism, it improves the access efficiency of the collecting terminals, and realizes the safe and fast access of the collecting terminal. Finally, compared with other protocols, the proposed protocol is also effective in security and performance.

The “GF-4” satellite is China’s first high resolution geostationary optical remote sensing satellite. It has the unique advantages of short imaging time interval (20s) and high resolution (50m). In order to analyze the effect of GF-4 satellite image registration accuracy on sea ice drift in Bohai Sea, firstly, the orthorectification of the 28 image data available from August 2016 to March 2018 in the Bohai Sea area was carried out. Then we selected the sea-land edge points as control points, and registration of two images which have the same time interval. Next, we recorded the marked same name points which searched from the bottom of Liaodong bay, east of Liaodong bay and west of Liaodong bay respectlly. We statisticed the direction and frequency of land point offset sub-regionally, then we created the rose plots and maked histogram of the offset of land point. The results show that, when the time interval is 4 hours and 24 hours, the dominant migration direction in the three regions in Liaodong bay is east; when the time interval is 1 minute, the dominant migration direction in Liaodong Bay bottom and Liaodong Bay west coast land is south, Followed by east and southeast respectively; the dominant migration in Liaodong Bay East Coast is north, followed by east; When the time interval is 3 hours, the dominant migration direction in west of Liaodong Bay, bottom of Liaodong Bay and east of Liaodong bay are east, west and south respectively, followed by southeast, east, southeast respectively. The land offset in three regions is major centralized distribution in a range which is from 60m to 80m. That is to say, the offset of land is basically equal to 1.2 times of pixels, and the maximum land offset is less than 2 times of pixels. Through statistical analysis, it can be seen that with the increase of time interval, the land offset will not change much. This study also paves the way for the study of the drift of sea ice.

The Severn Estuary has the second largest tidal range in the world and full of potential tidal power. The estuary area has great ecological value due to its nature conservation sites, biological habitats and unique coastal ecological system. Various kinds of plans and projects about exploiting the Severn Estuary have been proposed by many organizations for years. Giving the consideration of electricity generating efficiency, financial costs and especially environmental impacts, it is reasonable to believe that the application of a tidal lagoon system in the estuary area is the most suitable choice among all the options, which has the features of eco-friendly, effective, predictable and flood defending. The implementation of the Severn Estuary tidal lagoon system can be a long-term and stable renewable energy source for UK and will provide reference value for the development of other coastal area.