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Integrating BDS and GPS for precise relative orbit determination of LEO formation flying

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Chinese Journal of Aeronautics 2018年第10期31卷 2013-2022页

作者： Bin yi Defeng GU Xiao CHANG kai SHAO College of Liberal Arts and Sciences National University of Defense Technology

Low-Earth-Orbit（LEO） formation-flying satellites have been widely applied in many kinds of space geodesy. Precise Relative Orbit Determination（PROD） is an essential prerequisite for the LEO formation-flying satellites to complete their mission in space. The contribution of the BeiDou Navigation Satellite System（BDS） to the accuracy and reliability of PROD of LEO formation-flying satellites based on a Global Positioning System（GPS） is studied using a simulation method. Firstly, when BDS is added to GPS, the mean number of visible satellites increases from9.71 to 21.58. Secondly, the results show that the 3-Dimensional（3 D） accuracy of PROD, based on BDS-only, GPS-only and BDS ＋ GPS, is 0.74 mm, 0.66 mm and 0.52 mm, respectively. When BDS co-works with GPS, the accuracy increases by 29.73%. Geostationary-Earth-Orbit（GEO） satellites and Inclined Geosynchronous-Orbit（IGSO） satellites are only distributed over the Asia-Pacific region; however, they could provide a global improvement to PROD. The difference in PROD results between the Asia-Pacific region and the non-Asia-Pacific region is not apparent. Furthermore, the value of the Ambiguity Dilution Of Precision（ADOP）, based on BDS ＋ GPS, decreases by 7.50% and 8.26%, respectively, compared with BDS-only and GPS-only. Finally, if the relative position between satellites is only a few kilometres, the effect of ephemeris errors on PROD could be ignored. However, for a several-hundred-kilometre separation of the LEO satellites, the SingleDifference（SD） ephemeris errors of GEO satellites would be on the order of centimetres. The experimental results show that when IGSO satellites and Medium-Earth-Orbit（MEO） satellites co-work with GEO satellites, the accuracy decreases by 17.02%.

关键词： Ambiguity Dilution Of Precision BeiDou Navigation Satellite System Geostationary-Earth-Orbit Global Positioning System LEO formation flying Precise Relative Orbit Determination

Inseparable Criterion and Bell Inequality

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Communications in Theoretical Physics 2005年第3X期44卷 451-454页

作者： WEI kai-yi WU Xiao-hua Department of Physics Sichuan University Chengdu 610064 China

In this letter, we shall show how to construct constrained Bell-type inequality for a generaltwo-party system, and violating this inequality is equivalent to being inseparable. For 2 (×) 2 system, the maximum violati... 详细信息

关键词： Bell inequality inseparable criterion

The Optimal Policy for Insurance Company Under Consideration of Internal Competition and the Time Value of Ruin

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Acta Mathematicae Applicatae Sinica 2014年第3期30卷 807-818页

作者： Wei LIU yi-jun hu School of Mathematics and System Sciences Xinjiang University School of Mathematics and Statistics Wuhan University

This paper considers the dividend optimization problem for an insurance company under the consideration of internal competition between different units inside the company. The objective is to find a reinsurance policy and a dividend payment scheme so as to maximize the expected discounted value of the dividend payment, and the expected present value of an amount which the insurer earns until the time of ruin. By solving the corresponding constrained Hamilton-Jacobi-Bellman （HJB） equation, we obtain the value function and the optimal reinsurance policy and dividend payment.

关键词： dividend payment proportional reinsurance internal competition Hamilton-Jacobi-Bellman (HJB)equation

Smoothing methods comparison for CMB E-and B-mode separation

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Research in Astronomy and Astrophysics 2016年第4期16卷 55-62页

作者： yi-Fan Wang kai Wang Wen Zhao CAS Key Laboratory for Research in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China

The anisotropies of the B-mode polarization in the cosmic microwave background radiation play a crucial role in the study of the very early Universe. However, in real observations, a mixture of the E- mode and B-mode can be caused by partial sky surveys, which must be separated before being applied to a cosmological explanation. The separation method developed by Smith （2006） has been widely adopted, where the edge of the top-hat mask should be smoothed to avoid numerical errors. In this paper, we compare three different smoothing methods and investigate leakage residuals of the E-B mixture. We find that, if less information loss is needed and a smaller region is smoothed in the analysis, the sin- and cos-smoothing methods are better. However, if we need a cleanly constructed B-mode map, the larger region around the mask edge should be smoothed. In this case, the Gaussian-smoothing method becomes much better. In addition, we find that the leakage caused by numerical errors in the Gaussian-smoothing method is mostly concentrated in two bands, which is quite easy to reduce for further E-B separations.

关键词： cosmic microwave background radiation -- polarization -- statistics

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Chinese Journal of Electronics 2024年第3期33卷 672-682页

作者： yi ZHANG kai ZHANG Ting CUI PLA SSF Information Engineering University

Related-key model is a favourable approach to improve attacks on block ciphers with a simple key ***,to the best of our knowledge,there are a few results in which zero-correlation linear attacks take advantage of the related-key *** ascribe this phenomenon to the lack of consideration of the key input in zerocorrelation linear *** on the linear key schedule of a block cipher,we generalize the zero-correlation linear attack by using a related-key ***,we propose the creation of generalized linear hulls(GLHs)when the key input is involved;moreover,we indicate the links between GLHs and conventional linear hulls(CLHs).Then,we prove that the existence of zero-correlation GLHs is completely determined by the corresponding CLHs and the linear key *** addition,we introduce a method to construct zero-correlation GLHs by CLHs and transform them into an integral *** correctness is verified by applying it to SIMON16/16,a SIMON-like toy *** on our method,we find 12/13/14/15/15/17/20/22-round related-key zero-correlation linear distinguishers of SIMON32/64,SIMON48/72,SIMON48/96,SIMON64/96,SIMON64/128,SIMON96/144,SIMON128/192 and SIMON 128/256,*** far as we know,these distinguishers are one,two,or three rounds longer than current best zero-correlation linear distinguishers of SIMON.

关键词： Schedules Ciphers Analytical models Toy manufacturing industry Force Linear approximation Transforms

Joint Pilot Design and Beamforming Optimization in Massive MIMO Surveillance Systems

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China Communications 2022年第4期19卷 83-97页

作者： Caihong kai Xiangru Zhang Xinyue hu Wei huang School of Computer Science and Information Engineering Hefei University of TechnologyHefei 230601China Intelligent Interconnected Systems Laboratory of Anhui Province Hefei University of TechnologyHefei 230601China School of Electronics and Information Engineering Anhui UniversityHefei 230601China

This paper proposes a novel joint channel estimation and beamforming scheme for the massive multiple-input-multiple-output(MIMO)frequency-division duplexing(FDD) wireless legitimate surveillance system. With the proposed scheme,the monitor with the full duplex capability realizes the proactive eavesdropping of the suspicious link by leveraging the pilot attack approach. Specifically, exploiting the effective eavesdropping rate and the mean square error as performance metrics and setting a total power budget at the training and transmission phases,while guaranteeing the information from suspicious source can be successfully decode, joint pilot design,power allocation and beamforming strategy are formulated as optimization problems for the two objective functions: MSE and effective eavesdropping rate. A closed-form expression of the optimal pilot with the limited length can be obtained via the channel correlation. The optimal power problem at the training phase can be solved by a simple bisection method. Then,based on the obtained imperfect estimated channel,the jamming beamforming at monitor optimization algorithm is proposed by utilizing the convex Semidefinite Programming approach to maximize the effective eavesdropping rate. Numerical results show that the proposed joint pilot design, power allocation and beamforming optimization scheme can improve the surveillance performance of the legitimate monitor as compared to the existing passive eavesdropping and jamming-assisted eavesdropping.

关键词： proactive eavesdropping massive MIMO channel estimation pilot contamination beamforming

Soil Enzyme Activity Changes in Different-Aged Spruce Forests of the Eastern Qinghai-Tibetan Plateau

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Pedosphere 2004年第3期14卷 305-312页

作者： ZHANGYong-Mei ZHOUGuo-yi WUNing BAOWei-kai SouthChinaInstituteofBotany ChineseAcademyofSciencesGuangzhou510650（China） ChengduInstituteofBiology ChineseAcademyofSciencesChengdu610041（China）

Activities of selected soil enzymes (invertase, acid phosphatase, proteinase,catalase, peroxidase and polyphenoloxi-dase) were determined under different spruce forests withrestoration histories of 5, 13, 18, 23, 27 years and an old growth forest over 400 years old in theeastern Qinghai-Tibetan Plateau, China, and their possible use as indicators of ecosystems healthwere analyzed. Plots 10 X 10 m with 4 replications were established to investigate three hypotheses:soil enzyme activities a) would increase with the restoration process; b) would be greater insurface soils than at lower depths; and c) would be correlated to selected physicochemicalproperties. Results showed that as the forests developed after restoration, invertase and peroxidaseactivities usually increased up to the 23 year point. Also soil enzyme activities were associatedwith surface soils and decreased with depths, suggesting that in earlier restoration stages surfaceaddition of organic fertilizer to soils might be more effective than additions at depth. In the 0-20cm soil, there were significant correlations (P < 0.01 or < 0.05) between some soil enzymeactivities and some selected chemical properties. Therefore, temporal changes in enzyme activitiesshould be included as an indicator when evaluating sustainable forest management practices.

关键词： acid phosphatase catalase invertase peroxidase spruce forest (picea spp.)

Comparison of fatigue property between friction stir and TIG welds

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Journal of University of Science and Technology Beijing 2008年第3期15卷 280-284页

作者： Xunhong Wang Kuaishe Wang Yang Shen kai hu Cold Rolling Plant Baosteel Branch Shanghai 200941 China School of Metallurgy Engineering Xi＇an University of Architecture and Technology Xi＇an 710055 China Xi＇an Aero Engine （Group） Ltd. Xi＇an 710021 China

The alloy 5052 was welded by friction stir welding （FSW） and tungsten inert gas （TIG） welding. The effect of welding processes （FSW and TIG） on the fatigue properties of 5052 aluminum-welded joints was analyzed based on fatigue testing, and the S-N curve of the joints were established. The results show that the fatigue properties of FSW welded joints are better than those of TIG welded joints. The fatigue strength is determined as 65 MPa under 106 cycling of fatigue life. The microstructure of joints is fine grains and narrow HAZ zone in FSW welds, which inhibit the growth of cracks and produce high fatigue life compared with that of TIG welds. Fracture morphologies also show that the fatigue fracture results from weld defects.

关键词： friction stir welding TIG welding fatigue property S-N curve fatigue fracture

Science Letters:Multi-frequency proportional-resonant (MFPR) current controller for PWM VSC under unbalanced supply conditions

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第10期8卷 1527-1531页

作者： hu Jia-bing HE yi-kang Sehool of Eleetrieal Engineering Zhejiang University Hangzhou 310027 China

This letter presents a multi-frequency proportional-resonant （MFPR） current controller developed for PWM voltage source converter （VSC） under the unbalanced supply voltage conditions. The delta operator is used in place of the shift operator for the implementation of MFPR by using a low-cost fixed-point DSE The experimental results with an alternative control strategy validated the feasibility of the proposed MFPR current controller for the PWM VSC during voltage unbalance.

关键词： PWM VSC Multi-frequency proportional-resonant (MFPR) Voltage unbalance