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Performance analysis of a novel chip tracking loop used for regenerative pseudo-noise ranging clock recovery
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作者 张朝杰 金小军 +1 位作者 郁发新 金仲和 《Journal of Southeast University(English Edition)》 EI CAS 2007年第2期185-189,共5页
To improve the performance of composite pseudo-noise (PN) code clock recovery in a regenerative PN ranging system at a low symbol signal-to-noise ratio (SNR), a novel chip tracking loop (CTL) used for regenerati... To improve the performance of composite pseudo-noise (PN) code clock recovery in a regenerative PN ranging system at a low symbol signal-to-noise ratio (SNR), a novel chip tracking loop (CTL) used for regenerative PN ranging clock recovery is adopted. The CTL is a modified data transition tracking loop (DTTL). The difference between them is that the Q channel output of the CTL is directly multiplied by a clock component, while that of the DTTL is multiplied by the Ⅰ channel transition detector output. Under the condition of a quasi-squareware PN ranging code, the tracking ( mean square timing jitter) performance of the CTL is analyzed. The tracking performances of the CTL and the DTTL, are compared over a wide range of symbol SNRs. The result shows that the CTL and the DTTL have the same performance at a large symbol SNR, while at a low symbol SNR, the former offers a noticeable enhancement. 展开更多
关键词 clock recovery tracking loops pseudo-noise codes ranging data transition tracking loop chip tracking loop
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Preventing Data Leakage in a Cloud Environment
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作者 Fuzhi Cang Mingxing Zhang +1 位作者 Yongwei Wu Weimin Zheng 《ZTE Communications》 2013年第4期27-31,共5页
Despite the multifaceted advantages of cloud computing,concerns about data leakage or abuse impedes its adoption for security-sensi tive tasks.Recent investigations have revealed that the risk of unauthorized data acc... Despite the multifaceted advantages of cloud computing,concerns about data leakage or abuse impedes its adoption for security-sensi tive tasks.Recent investigations have revealed that the risk of unauthorized data access is one of the biggest concerns of users of cloud-based services.Transparency and accountability for data managed in the cloud is necessary.Specifically,when using a cloudhost service,a user typically has to trust both the cloud service provider and cloud infrastructure provider to properly handling private data.This is a multi-party system.Three particular trust models can be used according to the credibility of these providers.This pa per describes techniques for preventing data leakage that can be used with these different models. 展开更多
关键词 cloud computing data leakage data tracking data provenance homomorphic encryption
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Zenith Pass Problem of Inter-satellite Linkage Antenna Based on Program Guidance Method 被引量:1
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作者 翟坤 杨涤 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2008年第1期53-60,共8页
While adopting an elevation-over-azimuth architecture by an inter-satellite linkage antenna of a user satellite, a zenith pass problem always occurs when the antenna is tracing the tracking and data relay satellite (... While adopting an elevation-over-azimuth architecture by an inter-satellite linkage antenna of a user satellite, a zenith pass problem always occurs when the antenna is tracing the tracking and data relay satellite (TDRS). This paper deals with this problem by way of, firstly, introducing movement laws of the inter-satellite linkage to predict the movement of the user satellite antenna followed by analyzing the potential pass moment and the actual one of the zenith pass in detail. A number of specific orbit altitudes for the user satellite that can remove the blindness zone are obtained. Finally, on the base of the predicted results from the movement laws of the inter-satellite linkage, the zenith pass tracing strategies for the user satellite antenna are designed under the program guidance using a trajectory preprocessor. Simulations have confirmed the reasonability and feasibility of the strategies in dealing with the zenith pass problem. 展开更多
关键词 SATELLITE ANTENNA tracking and data relay satellite zenith pass program guidance
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A nowcasting model for the prediction of typhoon tracks based on a long short term memory neural network 被引量:21
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作者 GAO Song ZHAO Peng +5 位作者 PAN Bin LI Yaru ZHOU Min XU Jiangling ZHONG Shan SHI Zhenwei 《Acta Oceanologica Sinica》 SCIE CAS CSCD 2018年第5期8-12,共5页
It is of vital importance to reduce injuries and economic losses by accurate forecasts of typhoon tracks. A huge amount of typhoon observations have been accumulated by the meteorological department, however, they are... It is of vital importance to reduce injuries and economic losses by accurate forecasts of typhoon tracks. A huge amount of typhoon observations have been accumulated by the meteorological department, however, they are yet to be adequately utilized. It is an effective method to employ machine learning to perform forecasts. A long short term memory(LSTM) neural network is trained based on the typhoon observations during 1949–2011 in China's Mainland, combined with big data and data mining technologies, and a forecast model based on machine learning for the prediction of typhoon tracks is developed. The results show that the employed algorithm produces desirable 6–24 h nowcasting of typhoon tracks with an improved precision. 展开更多
关键词 typhoon tracks machine learning LSTM big data
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Overall test evaluation based on trajectory tracking data 被引量:1
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作者 王正明 段晓君 《Science China(Technological Sciences)》 SCIE EI CAS 2001年第2期149-157,共9页
According to the trajectory characteristics of ballistic missile, a reduced parameter model is constructed based on difference between telemetry trajectory and trajectory tracking data. By virtue of Bayesian theory an... According to the trajectory characteristics of ballistic missile, a reduced parameter model is constructed based on difference between telemetry trajectory and trajectory tracking data. By virtue of Bayesian theory and data fusion technique, a new test evaluation method is put forth, which can make full use of the trajectory tracking data, shooting range test data and relevant information. Since the impact point can be derived from trajectory difference and its kinetic characteristics, evaluation of the impact point is a special case of this method. The accurate evaluation and the accuracy of evaluation results can be provided by the new method. 展开更多
关键词 test evaluation tracking data parameterized technique Bayesian theory data fusion
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Comparison between several satellite constellation schemes for MEO-TDRSS of China 被引量:2
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作者 Wu Tingyong Wu Shiqi 《Journal of Systems Engineering and Electronics》 SCIE EI CSCD 2008年第5期907-913,共7页
The satellite constellation classes, which are suitable for the medium earth orbit tracking and data relay satellite system (MEO-TDRSS) of China, are investigated. On the basis of the functionality and the traffic d... The satellite constellation classes, which are suitable for the medium earth orbit tracking and data relay satellite system (MEO-TDRSS) of China, are investigated. On the basis of the functionality and the traffic distribution characteristic of MEO-TDRSS, the coverage performance and inter-satellite link properties of four different constellation schemes are compared by simulations. Simulation results indicate that the rosette and common-track constellations, whose satellites are distributed on the celestial sphere more uniformly, are appropriate for the implementation of MEO-TDRSS of China. 展开更多
关键词 medium earth orbit tracking and data relay satellite system (MEO-TDRSS) satellite constellation inter-satellite links.
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Feedforward attitude control for a TDRS with mobile antennas
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作者 姜文辉 曹喜滨 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2006年第1期54-58,共5页
In this paper, feedforward attitude control law for a Tracking and Data Relay Satellite (TDRS) with mobile antennas is proposed. To track or point the target spacecraft with median/law orbit, the large mobile antenn... In this paper, feedforward attitude control law for a Tracking and Data Relay Satellite (TDRS) with mobile antennas is proposed. To track or point the target spacecraft with median/law orbit, the large mobile antennas have to move in a wide range. The movement of such mobile antennas disturbs the satellite attitude conscquently. Conventionally, the main body of thc satellitc and the mobile antennas are controlled independently. The proposed controller first estimates the angular momentum which the mobile antennas will produce based on tiLe momentum conservation equation. Next, it computes the desired velocity of reaction wheels to compensate the disturbance due to the antenna motion. It then adds the errnr of the wheels' velocity between a desired one and a current value as a feedforward signal to the control system. The proposed controller is demonstrated using a mathematical simulation, of which these results coincide well with analytical results. 展开更多
关键词 tracking and data relay satellite ANTENNA attitude control angular momentuml FEEDFORWARD
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Why Did the Reform Fail?The Impact of the Personnel System Reform on Teachers in Jia County of China
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作者 ZHAO Qian JIAO Xinran LIANG Yuwei 《Sino-US English Teaching》 2019年第12期491-509,共19页
Over recent years,the reform-driven development of education has been one primary idea of the Chinese government under the leadership of Xi Jinping.Above all,the reform of the personnel system,closely related to the i... Over recent years,the reform-driven development of education has been one primary idea of the Chinese government under the leadership of Xi Jinping.Above all,the reform of the personnel system,closely related to the interests of teachers,becomes the most sensitive link in the educational reform.To root out the restriction of education system on teachers and enhance their enthusiasm for work,Jia County carried out a reform of teacher personnel system from 2013 to 2016,including breaking the hierarchical restriction on teachers’administrative promotion,decentralizing the power of confirming the teachers’professional titles,eliminating the teachers with the worst performances,practicing performance salary,and other measures.In this study,we tracked 627 teachers regarding their work enthusiasm and stress during the three-year reform,analyzed the data through the Hierarchical Linear Model(HLM),and found that:(1)The teachers’enthusiasm for work increased over time,but did not significantly change with the consideration of the influence of the principals’leadership in teaching.The personnel system reform aiming at motivating teachers failed to work as expected.(2)The teachers’work stress still increased year by year.Therefore,this study concludes that the reform in Jia County failed to fulfill its goals and that the vigorous top-down reform did not lead to ideal results.A reason might be that the reform damaged the vested interests of teachers who represent the deep-rooted nepotism typically in the Chinese education community.Reforms of educational personnel system should give schools a full play regarding educational governance in the future. 展开更多
关键词 county-level reform teacher work stress teacher work enthusiasm tracking data
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Software Backdoor Analysis Based on Sensitive Flow Tracking and Concolic Execution 被引量:3
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作者 XU Xin WANG Jiajie +2 位作者 CHENG Shaoyin ZHANG Tao JIANG Fan 《Wuhan University Journal of Natural Sciences》 CAS CSCD 2016年第5期421-427,共7页
In order to effectively detect and analyze the backdoors this paper introduces a method named Backdoor Analysis based on Sensitive flow tracking and Concolic Execution(BASEC).BASEC uses sensitive flow tracking to ef... In order to effectively detect and analyze the backdoors this paper introduces a method named Backdoor Analysis based on Sensitive flow tracking and Concolic Execution(BASEC).BASEC uses sensitive flow tracking to effectively discover backdoor behaviors, such as stealing secret information and injecting evil data into system, with less false negatives. With concolic execution on predetermined path, the backdoor trigger condition can be extracted and analyzed to achieve high accuracy. BASEC has been implemented and experimented on several software backdoor samples widespread on the Internet, and over 90% of them can be detected. Compared with behavior-based and system-call-based detection methods, BASEC relies less on the historical sample collections, and is more effective in detecting software backdoors, especially those injected into software by modifying and recompiling source codes. 展开更多
关键词 software backdoor detection data flow tracking concolic execution malware detection
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Type synthesis of 2-DoF rotational parallel mechanisms actuating the inter-satellite link antenna 被引量:4
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作者 Song Yimin Qi Yang +1 位作者 Dong Gang Sun Tao 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2016年第6期1795-1805,共11页
This paper focuses on the type synthesis of two degree-of-freedom(2-DoF) rotational parallel mechanisms(RPMs) that would be applied as mechanisms actuating the inter-satellite link antenna. Based upon Lie group theory... This paper focuses on the type synthesis of two degree-of-freedom(2-DoF) rotational parallel mechanisms(RPMs) that would be applied as mechanisms actuating the inter-satellite link antenna. Based upon Lie group theory, two steps are necessary to synthesize 2-DoF RPMs except describing the continuous desired motions of the moving platform. They are respectively generation of required open-loop limbs between the fixed base and the moving platform and definition of assembly principles for these limbs. Firstly, all available displacement subgroups or submanifolds are obtained readily according to that the continuous motion of the moving platform is the intersection of those of all open-loop limbs. These subgroups or submanifolds are used to generate all the topology structures of limbs. By describing the characteristics of the displacement subgroups and submanifolds intuitively through employing simple geometrical symbols, their intersection and union operations can be carried out easily. Based on this, the assembly principles of two types are defined to synthesize all 2-DoF RPMs using obtained limbs. Finally, two novel categories of 2-DoF RPMs are provided by introducing a circular track and an articulated rotating platform,respectively. This work can lay the foundations for analysis and optimal design of 2-DoF RPMs that actuate the inter-satellite link antenna. 展开更多
关键词 Articulated rotating platform Assembly principle Circular track Lie group theory Rotational parallel mechanism tracking and data relay satellite Type synthesis
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