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601.
混杂纤维复合材料的界面 总被引:2,自引:0,他引:2
本文首先揭示和分析了混杂复合材料的特异现象—混杂效应,并认为混杂效应产生的主要原因是混杂界面。从而对混杂界面进行了研究和论述。指出混杂界面层与单一纤维复合材料界面层不同,为更加不均匀过渡,并以多相、多层次方式存在使混杂复合材料得以多种功能综合于一体。 相似文献
602.
关于我国低空空域管理问题的思考 总被引:1,自引:0,他引:1
低空空域管理的目的是为了在确保国家安全的前提下,更好地开发利用空域这个重要的国家资源,在避免影响军事航空、公共运输航空飞行的基础上,尽可能满足并促进通用航空的发展。因此,我们从低空空域使用者的需求特点和发展需求入手,借鉴航空发达国家的先进经验,从国家空域系统的发展方向进行分析,阐述了实现上述低空空域管理目标的设想。一、低空空域与通用航空(一)低空空域属性空域是国家重要资源,其资源价值体现在为公共运输、通用航空和军事航空(包括警用飞行)服务。低空空域是国家空域体系的重要组成部分,按照国际民航组织的空域分类标准,… 相似文献
603.
张山 《南京航空航天大学学报》2018,13(1):87-97
落儿岭-土地岭断裂是东大别地区重要的发震构造,然而限于自然地理条件等因素,前人对其的研究并不充分。本文以发生多次中强地震的落儿岭-土地岭断裂为研究对象,在高精度卫星影像解译的基础上,通过详细的野外地质地貌调查,尤其是对典型断层剖面进行分析,研究落儿岭-土地岭断裂的断错地质地貌特征、几何结构及活动特征。通过野外调查并结合其他资料分析认为落儿岭-土地岭断裂为发育于大别造山带内部的一条走向NE、向NW陡倾的断裂带。依据地质地貌特征及地震活动性,断裂可以划分为杨树沟-黑石渡段和黑石渡-横塘岗乡段两个几何段落。断裂最新活动时代为中更新世晚期—晚更新世早期,断裂最新活动继承了中生代以来的运动方式,以兼具右旋走滑的拉张正断为主。 相似文献
604.
605.
Young-Joo Song Sang-Young Park Kyu-Hong Choi Eun-Sup Sim 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
A design technique for a near optimal, Earth–Moon transfer trajectory using continuous variable low thrust is proposed. For the Earth–Moon transfer trajectory, analytical and numerical methods are combined to formulate the trajectory optimization problem. The basic concept of the proposed technique is to utilize analytically optimized solutions when the spacecraft is flying near a central body where the transfer trajectories are nearly circular shaped, and to use a numerical optimization method to match the spacecraft’s states to establish a final near optimal trajectory. The plasma thruster is considered as the main propulsion system which is currently being developed for crewed/cargo missions for interplanetary flight. The gravitational effects of the 3rd body and geopotential effects are included during the trajectory optimization process. With the proposed design technique, Earth–Moon transfer trajectory is successfully designed with the plasma thruster having a thrust direction sequence of “fixed-varied-fixed” and a thrust acceleration sequence of “constant-variable-constant”. As this strategy has the characteristics of a lesser computational load, little sensitivity to initial conditions, and obtaining solutions quickly, this method can be utilized in the initial scoping studies for mission design and analysis. Additionally, derived near optimal trajectory solution can be used as for initial trajectory solution for further detailed optimization problem. The demonstrated results will give various insights into future lunar cargo trajectories using plasma thrusters with continuous variable low thrust, establishing approximate costs as well as trajectory characteristics. 相似文献
606.
607.
Yang Wei-hua Cao Jun Shi Rui Hao Xu-sheng Song Shuang-wen 《Acta Astronautica》2011,68(11-12):1782-1789
A new series of test pieces with different geometrical configuration and geometry dimensions are designed to experimentally investigate on impingement-effusion cooling behavior in curve effusion wall of combustion chamber. The test results show that the discharge coefficient increased with the increasing blowing ratio. The effusion hole–hole spacing has an effect on the discharge coefficient and the discharge coefficient commonly decreased with the increment of effusion hole–hole spacing. The blowing ratio greatly effects cooling behavior. The bigger blowing ratio is favorable for improving cooling characters. At the curved effusion wall, to begin with, cooling effectiveness increased slowly and kept a steady value in subsequence. But, for the rear end of curved effusion wall, it decreased slowly. With decreasing of effusion hole angle and effusion hole–hole spacing, cooling effectiveness is enhanced. Meanwhile, blowing ratio, effusion angle and effusion hole–hole spacing take an evident effect on the discharge coefficient. 相似文献
608.
609.
Mingkun Su Yanxi Yang Lei Qiao Xuyang Teng Huina Song 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(2):868-882
This study proposes an enhanced multipath mitigation method based on multi-resolution carrier-to-noise-ratio (CNR) model and adaptive statistical test strategy for real-time kinematic precise point positioning (PPP) applications. The multi-resolution CNR model is established with GPS observation data collected from DOY 152 to 181 of 2019 by 230 globally distributed IGS stations, which used to analyze the relevant factors affecting CNR. Statistical results indicate that the CNR is not only related to the satellite elevation, but also closely related to the receiver types and specific satellite. The maximum difference between different receivers can reach 20 dB for the same satellite at the same elevation. In addition, the performance of the CNR is also obviously different between each satellite, and the maximum difference between different satellites is about 10 dB for the same receiver at the same elevation. Hence, in terms of the method which is based on CNR information for multipath detection and mitigation, the independence of receiver types, satellite and frequency must be considered. With the above analysis, this study developed a multi-resolution CNR model based on different receiver types, different satellites and different elevation firstly. Then, combined with the adaptive statistical test strategy which is based on the difference of CNR between inter-frequency and the difference of CNR between adjacent epochs, the multipath can be detected effectively. For the epoch which affected by multipath, the down-weighted strategy based on CNR is adopted to mitigate the influence of multipath on positioning. Real-time kinematic PPP data are collected to assess the proposed method, and the results demonstrate that the proposed method can detect the multipath effectively, and the detection rate can reach 90.28%. Moreover, after adopting the mitigation strategy, the RMS bias of the east, north and up components are improved about 19.95%, 17.89% and 23.07% compared to the original results, respectively. It is worth noting that this proposed method is also suitable for other GNSS, such as GLONASS and BDS, but the corresponding CNR model must be established simultaneously. 相似文献