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A Local Implementation of the POD-Based Ensemble 4DVar with R-Localization

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Atmospheric and Oceanic Science Letters 2014年第1期7卷 11-16页

作者： tian xiang-Jun International Center for Climate and Environment Sciences Institute of Atmospheric PhysicsChinese Academy of Sciences State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of Sciences

The purpose of this paper is to provide a robust and flexible implementation of a proper orthogonal decomposition-based ensemble four-dimensional variational assimilation method(PODEn4DVar) through *** R-localization,the implementation of the local PODEn4DVar analysis can be coded for parallelization with enhanced assimilation *** feasibility and effectiveness of the PODEn4DVar local implementation with R-localization are demonstrated in a two-dimensional shallow-water equation model with simulated observations(OSSEs) in comparison with the original version of the PODEn4DVar with B-localization and that without *** performance of the PODEn4DVar with localization shows a significant improvement over the scheme with no localization,particularly under the imperfect model ***,the R-localization scheme is capable of outperforming the Blocalization case to a certain ***,the assimilation experiments also demonstrate that PODEn4DVar with R-localization is most efficient due to its easy parallel implementation.

关键词： PODEn4DVar R-localization local implementation

High efficient moving object extraction and classification in traffic video surveillance

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Journal of Systems Engineering and Electronics 2009年第4期20卷 858-868页

作者： Li Zhihua Zhou Fan tian xiang Chen Yaowu Inst. of Advanced Digital Technology and Instrument Zhejiang Univ. Hangzhou 310027 P. R. China

Moving object extraction and classification are important problems in automated video surveillance systems. A background model based on region segmentation is proposed. An adaptive single Gaussian background model is used in the stable region with gradual changes, and a nonparametric model is used in the variable region with jumping changes. A generalized agglomerative scheme is used to merge the pixels in the variable region and fill in the small interspaces. A two-threshold sequential algorithmic scheme is used to group the background samples of the variable region into distinct Gaussian distributions to accelerate the kernel density computation speed of the nonparametric model. In the feature-based object classification phase, the surveillance scene is first partitioned according to the road boundaries of different traffic directions and then re-segmented according to their scene localities. The method improves the discriminability of the features in each partition. AdaBoost method is applied to evaluate the relative importance of the features in each partition respectively and distinguish whether an object is a vehicle, a single human, a human group, or a bike. Experimental results show that the proposed method achieves higher performance in comparison with the existing method.

关键词： background model nonparametric model adaptive single Gaussian model object classification

Effects of material of metallic frame on the penetration resistances of ceramic-metal hybrid structures

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Defence Technology（防务技术） 2020年第1期16卷 77-87页

作者： Xuanyi An Chao tian Qitian Sun Yongxiang dong State Key Laboratory of Explosion Science and Technology Beijing Institute of TechnologyBeijing100081China

The effects of metallic material on the penetration resistances of ceramic-metal hybrid structures against vertical long-rod tungsten projectiles were studied by artillery-launched experiments and numerical *** structures with rectangular cores in transverse orthogonal arrangement and slidefitting ceramic inserts of zirconia toughened alumina prisms were fabricated with titanium alloy TC4(Ti6 Al4 V),AISI 4340 steel and 7075 aluminum alloy panels,*** results showed that the hybrid structure of Ti6A14V exhibited the highest penetration resistance,followed by that of 7075 aluminum alloy with the same area *** penetration resistance of the hybrid structure of AISI4340 steel was the *** underlying mechanisms showed that the metallic material of a ceramicmetal hybrid structure can directly affect its energy absorption from the impact projectile,which further affects its penetration *** metallic frames exhibited different failure characteristics,resulting in different constraint conditions or support conditions for ceramic *** high penetration resistance of the Ti6Al4V hybrid structure was due to its stronger back support to ceramic prisms as compared with that of AISI 4340 steel hybrid structure,and better constraint condition for ceramic prisms by metallic webs as compared with that of 7075 aluminum alloy hybrid *** results of mass efficiency and thickness efficiency showed that the Ti6Al4V hybrid structure has advantages in reducing both the thickness and the mass of protective *** addition,because the ceramic-metal hybrid structures in the present work were heterogeneous,impact position has slight influence on their penetration resistances.

关键词： Hybrid structures Zirconia toughened alumina Penetration resistance Long-rod projectile Metallic frame

Magnetometer Compensation Scheme and Experimental Results on ZDPS-1A Pico-satellite

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Chinese Journal of Aeronautics 2012年第3期25卷 430-436页

作者： HAN Ke WANG Hao xiang tian JIN Zhonghe Department of Information Science and Electronic Engineering Zhejiang University Hangzhou 310027China

In a pico-satellite with small volume, measurements from on-board three-axis magnetometer （TAM） are not accurate, as it can be easily disturbed by other electronic systems. To improve its accuracy, a scheme of compensation methods is introduced in this article. The scheme is based on an improved meast, rement model of pico-satellite TAM, and it mainly consists of three steps. First, in satellite design stage, several techniques are recommended to simplify the afterwards compensations. Then after satellite assembly, TAM ground tests and pre-launch calibration with least-square batch filter are introduced to improve magnetometer performance. At the end, a post-launch calibration with unscented Kalman filter （UKF） is implemented with in-orbit data. The compensation scheme is used in the development of Chinese pico-satellite ZDPS-1A made by Zhejiang University. Results show that with the introduced compensation scheme, the maximum error of ZDPS-1A TAM can be reduced from 80 mG to 6 naG （1 G=10^-4T）.

关键词： pico-satellite magnetometers calibration: least-square filter Kalman filter

SPURIOUS NUMERICAL SOLUTIONS OF DELAY DIFFERENTIAL EQUATIONS

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Journal of Computational Mathematics 2006年第2期24卷 181-192页

作者： Hong-jiong tian Li-qiang Fan Yuan-ying Zhang Jia-xiang xiang Department of Mathematics Shanghai Normal University Division of Computational Science E-Institute of Shanghai Universities Shanghai 200234 China Department of Mathematics Shanghai Normal University Shanghai 200234 China

This paper deals with the relationship between asymptotic behavior of the numerical solution and that of the true solution itself for fixed step-sizes. The numerical solution is viewed as a dynamical system in which the step-size acts as a parameter. We present a unified approach to look for bifurcations from the steady solutions into spurious solutions as step-size varies.

关键词： Spurious solution Asymptotic behavior Delay differential equation.

Test Verification and Design of the Bicycle Frame Parameters

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Chinese Journal of Mechanical Engineering 2015年第4期28卷 716-725页

作者： ZHANG Long xiang Zhongxia LUO Huan tian Guan Key Laboratory of Mechanism Theory and Equipment Design of Education Tianjin University

Research on design of bicycles is concentrated on mechanism and auto appearance design, however few on matches between the bike and the rider. Since unreasonable human-bike relationship leads to both riders＇ worn-out joints and muscle injuries, the design of bicycles should focus on the matching. In order to find the best position of human-bike system, simulation experiments on riding comfort under different riding postures are done with the lifemode software employed to facilitate the cycling process as well as to obtain the best position and the size function of it. With BP neural network and GA, analyzing simulation data, conducting regression analysis of parameters on different heights and bike frames, the equation of best position of human-bike system is gained at last. In addition, after selecting testers, customized bikes based on testers＇ height dimensions are produced according to the size function. By analyzing and comparing the experimental data that are collected from testers when riding common bicycles and customized bicycles, it is concluded that customized bicycles are four times even six times as comfortable as common ones. The equation of best position of human-bike system is applied to improve bikes＇ function, and the new direction on future design of bicycle frame parameters is presented.

关键词： bike modeling data mining fatigue dynamics simulation oxygen uptake

A Local Region Molecular Dynamics Simulation Method for Nanoscale Sliding Contacts

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Chinese Journal of Mechanical Engineering 2018年第5期31卷 119-126页

作者： Rui-Ting Tong Geng Liu tian-xiang Liu Shaanxi Engineering Laboratory for Transmissions and Controls Northwestern Polytechnical University Xi’an 710072 China Institute for Mechanics and Fluid Dynamics TU Bergakademie Freiberg Lampadiusstr. 4 09596 Freiberg Germany

Computational e ciency and accuracy always conflict with each other in molecular dynamics(MD) simulations. How to enhance the computational e ciency and keep accuracy at the same time is concerned by each corresponding researcher. However, most of the current studies focus on MD algorithms, and if the scale of MD model could be reduced, the algorithms would be more meaningful. A local region molecular dynamics(LRMD) simulation method which can meet these two factors concurrently in nanoscale sliding contacts is developed in this paper. Full MD simulation is used to simulate indentation process before sliding. A criterion called contribution of displacement is presented, which is used to determine the e ective local region in the MD model after indentation. By using the local region, nanoscale sliding contact between a rigid cylindrical tip and an elastic substrate is investigated. Two two?dimensional MD models are presented, and the friction forces from LRMD simulations agree well with that from full MD simulations, which testifies the e ectiveness of the LRMD simulation method for two?dimensional cases. A three?dimensional MD model for sliding contacts is developed then to show the validity of the LRMD simulation method further. Finally, a discussion is carried out by the principles of tribology. In the discussion, two two?dimensional full MD models are used to simulate the nanoscale sliding contact problems. The results indicate that original smaller model will induce higher equivalent scratching depth, and then results in higher friction forces, which will help to explain the mechanism how the LRMD simulation method works. This method can be used to reduce the scale of MD model in large scale simulations, and it will enhance the computational e ciency without losing accuracy during the simula?tion of nanoscale sliding contacts.

关键词： Local region molecular dynamics simulation Nanoscale Sliding contacts Contribution of displacement

Effects of annealing temperature and cooling rate on microstructures of a novel titanium alloy Ti-6Al-2V-1.5Mo-0.5Zr-0.3Si manufactured by laser additive manufacturing

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Journal of Iron and Steel Research International 2018年第4期25卷 442-452页

作者： Guo-chao Li Xu Cheng xiang-jun tian National Engineering Laboratory of Additive Manufacturing for Large Metallic Components and Engineering Research Center of Ministry of Education on Laser Direct Manufacturing for Large Metallic Components School of Materials Science and Engineering Beihang University Beijing 100091 China

The microstructure changes of Ti-6Al-2V-1.5Mo-0.5Zr-0.3Si alloy manufactured by laser additive manufacturing （LAM） are systematically investigated with statistical analysis of primary α phase （αp） and secondary α phase （αs） under different annealing conditions. Results indicate that, with the increase in holding temperature, the content of αp lamellas decreases with the increasing αs content, maintaining the total α phases concentration stabilized. The width of αp lamellas and the nominal specific surface area of α phase both exhibit positive correlation with the temperature, while the increment of αp and the widths of αs lamellas show an increase-decrease tendency. Besides, with the decrease in cooling rate, the total content of α and the width of αp lamellas increase, while the nominal specific surface area of α phase shows no significant change. The results indicate that, in the annealing process, the holding temperature determines the surplus and growth interfaces of % lamellas, and the cooling rate influences the nucleation quantity of c^s in unit time. During the cooling stage, the αp lamellas grow initially, and then, the nucleation and crab-like structure growth occur followed by those of the αs lamellas. The time intervals among them are influenced by cooling rate. The mechanism of microstructure formation of the LAMed titanium alloy during annealing stage was discussed, which would guide for the heat treatment method to achieve required microstructure.

关键词： Novel titanium alloy Annealing Microstructure statistics Holding temperature Cooling rate

Increase in yield and nitrogen use efficiency of double rice with long-term application of controlled-release urea

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Journal of Integrative Agriculture 2022年第7期21卷 2106-2118页

作者： tian Chang SUN Ming-xue ZHOU Xuan LI Juan XIE Gui-xian YANG xiang-dong PENG Jian-wei College of Resources and Environment Hunan Agricultural University/National Engineering Laboratory for Efficient Utilization of Soil and Fertilizer ResourcesChangsha 410128P.R.China Institute of Agricultural Resources and Regional Planning Chinese Academy of Agricultural Sciences/Key Laboratory of Plant Nutrition and FertilizerMinistry of Agriculture and Rural AffairsBeijing 100081P.R.China Institute of Soil and Fertilizer Hunan Academy of Agricultural SciencesChangsha 410125P.R.China

Controlled-release urea(CRU)has better characteristics than conventional urea for synchronizing nitrogen(N)release with plant *** the effects of CRU on crop yield and N use efficiency(NUE)has long been the key to evaluate the performance of CRU.A long-term experiment over five consecutive years was conducted in Changsha,Hunan Province,China,to investigate the effects of polyethylene-coated urea with a 90-d release period on the yield and NUE of double rice(early and late crops are grown in the same year),the amount of residual soil mineral N and the soil–plant N balance,as well as on the economic *** N fertilizer treatments including CK(no N fertilizer),U(conventional urea),CRU1(polyethylene-coated urea with equal N application rate to U)and CRU2(20%reduction in N application rate of CRU1)were *** results indicated that CRU1 application increased the yield and NUE of double rice by 11.0 and 13.5%,respectively,compared with *** yield and NUE of late rice were found than in early rice in CRU *** with conventional U,the yield and NUE of early rice in the CRU1 treatment were increased by 6.0 and 10.2%,respectively,and those of late rice were increased by 15.4 and 13.8%,*** was no significant difference between CRU1 and CRU2 in double rice ***,CRU treatments(including CRU1 and CRU2)had higher apparent residual Nmin rate(ARNR)and apparent N recovery rate(ANRR),but lower apparent N loss(NS)than the conventional U *** of NH_(4)^(+)-N and NO_(3)^(-)-N were greater in the surface soil(0–20 cm)and lower in the deeper soil layer(40–60 cm)with CRU treatments than in the U treatment after ***,CRU application produced a greater economic benefit than conventional U *** general,CRU outperformed U fertilizer in terms of rice yield,NUE,soil–plant N balance,economic benefit,and CRU2 provided greater comprehensive benefits than *** is suggested that C

关键词： controlled-release urea rice yield nitrogen use efficiency