In recent years,with the rapid development of cross-border e-commerce,international postal parcels have been increasing sharply,thus giving rise to a new way for alien biological invasion.According to the"animal ...In recent years,with the rapid development of cross-border e-commerce,international postal parcels have been increasing sharply,thus giving rise to a new way for alien biological invasion.According to the"animal and plant quarantine information platform"of the General Adminis-tration of Customs,postal inspection system intercepted a total of 4975 harmful organisms nationwide.There were 219 quarantine organisms,including 142 insects,27 weeds,12 nematodes,29 fungi,1 bacterium and 8 viruses.Insects accounted for 64.84%of the quarantine organisms,among which Hypothenemus hampei had the highest interception frequency.Up to 71.36%of those harmful organisms were from seedlings,yet47.31%organisms came from products exported from India.These analyses indicate the direction of future portal quarantine work and lay a theoret-ical foundation for better guarding the biological security.展开更多
The Chinese Area Positioning System (CAPS) is based on communication satellites with integrated capability, which is different from the Global Positioning System (GPS), the International Maritime Satellite Organizatio...The Chinese Area Positioning System (CAPS) is based on communication satellites with integrated capability, which is different from the Global Positioning System (GPS), the International Maritime Satellite Organization (Inmarsat) and so on. CAPS works at C-band, and its navigation information is not directly generated from the satellite, but from the master control station on the ground and transmitted to users via the satellite. The slightly inclined geostationary-satellite orbit (SIGSO) satellites are adopted in CAPS. All of these increase the difficulty in the design of the system and terminals. In this paper, the authors study the CAPS configuration parameters of the navigation master control station, information transmission capability, and the selection of the antenna aperture of the communication center station, as well as the impact of satellite parameters on the whole communication system from the perspective of the transmission link budget. The conclusion of availability of the CAPS navigation system is achieved. The results show that the CAPS inbound communication system forms a new low-data-rate satellite communication system, which can accommodate mass communication terminals with the transmission rate of no more than 1 kbps for every terminal. The communication center station should be configured with a large-aperture antenna (about 10-15 m); spread spectrum com- munication technology should be used with the spreading gain as high as about 40 dB; reduction of the satellite transponder gain attenuation is beneficial to improving the signal-to-noise ratio of the system, with the attenuation value of 0 or 2 dB as the best choice. The fact that the CAPS navigation system has been checked and accepted by the experts and the operation is stable till now clarifies the rationality of the analysis results. The fact that a variety of experiments and applications of the satellite communication system designed according to the findings in this paper have been successfully carried out confirms the correctness of the study results.展开更多
基金Supported by Public Welfare Project of Ningbo City(2019C10087)。
文摘In recent years,with the rapid development of cross-border e-commerce,international postal parcels have been increasing sharply,thus giving rise to a new way for alien biological invasion.According to the"animal and plant quarantine information platform"of the General Adminis-tration of Customs,postal inspection system intercepted a total of 4975 harmful organisms nationwide.There were 219 quarantine organisms,including 142 insects,27 weeds,12 nematodes,29 fungi,1 bacterium and 8 viruses.Insects accounted for 64.84%of the quarantine organisms,among which Hypothenemus hampei had the highest interception frequency.Up to 71.36%of those harmful organisms were from seedlings,yet47.31%organisms came from products exported from India.These analyses indicate the direction of future portal quarantine work and lay a theoret-ical foundation for better guarding the biological security.
基金Supported by the National Basic Research and Development Program of China (Grant No. 2007CB815504)the Technology Research and Development Pro-gram of China (Grant No. 2007AA12z343)
文摘The Chinese Area Positioning System (CAPS) is based on communication satellites with integrated capability, which is different from the Global Positioning System (GPS), the International Maritime Satellite Organization (Inmarsat) and so on. CAPS works at C-band, and its navigation information is not directly generated from the satellite, but from the master control station on the ground and transmitted to users via the satellite. The slightly inclined geostationary-satellite orbit (SIGSO) satellites are adopted in CAPS. All of these increase the difficulty in the design of the system and terminals. In this paper, the authors study the CAPS configuration parameters of the navigation master control station, information transmission capability, and the selection of the antenna aperture of the communication center station, as well as the impact of satellite parameters on the whole communication system from the perspective of the transmission link budget. The conclusion of availability of the CAPS navigation system is achieved. The results show that the CAPS inbound communication system forms a new low-data-rate satellite communication system, which can accommodate mass communication terminals with the transmission rate of no more than 1 kbps for every terminal. The communication center station should be configured with a large-aperture antenna (about 10-15 m); spread spectrum com- munication technology should be used with the spreading gain as high as about 40 dB; reduction of the satellite transponder gain attenuation is beneficial to improving the signal-to-noise ratio of the system, with the attenuation value of 0 or 2 dB as the best choice. The fact that the CAPS navigation system has been checked and accepted by the experts and the operation is stable till now clarifies the rationality of the analysis results. The fact that a variety of experiments and applications of the satellite communication system designed according to the findings in this paper have been successfully carried out confirms the correctness of the study results.
