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Influences of the Texture Characteristic and Interdendritic LPSO Phase Distribution on the Tensile Properties of Mg–Gd–Y–Zn–Zr Sheets Through Hot Rolling

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Acta Metallurgica Sinica(English Letters) 2021年第8期34卷 1051-1064页

作者： Bing Li ji wu Bugang Teng School of Materials Science and Engineering Harbin Institute of TechnologyHarbin 150001China National Key Laboratory for Precision Hot Processing of Metals Harbin Institute of TechnologyHarbin 150001China

The Mg–Gd–Y–Zn–Zr alloy sheets with different texture characteristics and distribution of the interdendritic long periodstacking ordered(LPSO) phases were fabricated through altering the final rolling reduction(FRR). The results showed that the texture characteristic was closely related to FRR and affected the tensile properties of the resulted sheets to some extent. The Schmid factor(SF) of the basal 〈a〉 slip improved with further FRR, which was ascribed to that the dynamic recrystallization(DRX) grains expand into the deformed grains with basal texture. However, the improvement of the tensile yield strength(TYS) with further FRR indicates that the strengthening effect from DRX grains surpasses the weakening effect from the elevated SF. The formation of the line-distributed interdendritic 14 H-LPSO phases can also affect the tensile properties of the resulted sheets. The line-distributed interdendritic 14 H-LPSO phases along rolling direction(RD) can act as reinforcing fiber and contribute to the higher TYS along RD and 45° to some extent, which resulted in the higher TYS along 45° compared with that along transverse direction(TD) for each resulted sheet under the circumstance of approximate basal 〈a〉 and pyramid 〈c + a〉 friction stress. Thus, the tensile yield strength is not only related to the texture, but also depends on the grain size and line-distributed interdendritic LPSO phases. The micro-cracks spread perpendicular to the tension direction, and thus, the larger cracks form within the line-distributed 14 H-LPSO phases during tension along TD, which accounts for the lower fracture elongation along TD.

关键词： Final rolling reduction Texture characteristic Interdendritic 14H-LPSO phases distribution Tensile property

Effect of charge on the stability of single-walled carbon nanotubes

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Science China(Physics,Mechanics & Astronomy) 2004年第6期47卷 685-693页

作者： LUO ji wu jinlei Department of Electronics Peking University Beijing 100871 China Department of Electronics Peking University Beijing 100871 China

By using density-functional-theory based DMol3 code, the structure optimizations are performed on a short charged single-walled carbon nanotube. Results show that the total energy of the nanotube exhibits a parabolic variation with respect to the amount of extra charge, and one negatively charged nanotube has the lowest total energy; thus the carbon nanotube has a positive electron affinity. When the charge is small, the variation of the atomic structure of the nanotube is also small, and neglecting the atomic structure variation leads to the qualitatively correct properties of the total energy and the energy of the highest occupied molecular orbital. When the extra charge is large, the end structure of the nanotube will be first affected and form into a trumpet shape. With the increasing of the extra charge, the nanotube end gradually becomes unstable, and this may lead to the ultimate destruction of the nanotube.

关键词： carbon nanotube, density-functional theory, charge, stability.

Weak Solutions to the Cahn–Hilliard Equation with Degenerate Diffusion Mobility in R^N

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Acta Mathematica Sinica,English Series 2019年第10期35卷 1629-1654页

作者： ji Hui wu Lei LU College of Mathematics Physics and StatisticsShanghai University of Engineering ScienceShanghai 201620P.R.China College of Sciences Shanghai UniversityShanghai 200444P.R.China College of Mechanical Engineering Beijing University of TechnologyBeijing 100124P.R.China

This paper is concerned with a popular form of Cahn-Hilliard equation which plays an important role in understanding the evolution of phase separation. We get the existence and regularity of a weak solution to nonlinear parabolic, fourth order Cahn-Hilliard equation with degenerate mobility M(u)= u^m(1-u)^m which is allowed to vanish at 0 and 1. The existence and regularity of weak solutions to the degenerate Cahn-Hilliard equation are obtained by getting the limits of Cahn-Hilliard equation with non-degenerate mobility. We explore the initial value problem with compact support and obtain the local non-negative result. Further, the above derivation process is also suitable for the viscous Cahn–Hilliard equation with degenerate mobility.

关键词： Degenerate non-degenerate viscous convergence

The Maximum Principle for One Kind of Stochastic Optimization Problem and Application in Dynamic Measure of Risk

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Acta Mathematica Sinica,English Series 2007年第12期23卷 2189-2204页

作者： Shao Lin ji Zhen wu School of Mathematics and Systems Science Shandong University Jinan 250100 P. R. China

The authors get a maximum principle for one kind of stochastic optimization problem motivated by dynamic measure of risk. The dynamic measure of risk to an investor in a financial market can be studied in our framewor... 详细信息

关键词： backward stochastic differential equation perturbation method Ekeland's variational principle dynamic measure of risk

Aircraft safety analysis based on differential manifold theory and bifurcation method

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Frontiers of Information Technology & Electronic Engineering 2019年第2期20卷 292-299页

作者： Chi ZHOU Ying-hui LI wu-ji ZHENG Peng-wei wu School of Aeronautics and Astronautics Engineering Air Force Engineering University

Loss of control(LOC) is considered one of the leading causes of fatal aircraft accidents worldwide. Reducing LOC is critical to improve flight safety. Although it is still vaguely defined, LOC is generally associated with a flight state that is outside the safety envelope, with nonlinear influences of aircraft dynamics and incorrect handling by the flight crew. We have studied how nonlinear factors and pilot operations contribute to LOC. In this study, the stall point and bifurcation point are confirmed using the bifurcation analysis, and the results show that the aircraft will stall when excessive elevator movement is commanded. Moreover, even though there may be an equilibrium state in one of the elevator deflections, the flight state may still be outside the flight safety envelope. When the flight state is near the edge of the flight safety envelope, the strategy to regulate the elevator deflection is super-sensitive, and a slight change in the elevator deflection may contribute to a flight state outside the safety envelope. To solve this issue, the differential manifold theory is introduced to determine the safety envelope. Examples are provided using NASA's generic transport model.

关键词： Loss of control Safety envelope Aircraft dynamic Bifurcation analysis Differential manifold theory

A NONOVERLAPPING DOMAIN DECOMPOSITION METHOD FOR EXTERIOR 3-D PROBLEM

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Journal of Computational Mathematics 2001年第1期19卷 77-86页

作者： De-hao Yu ji-ming wu State Key Laboratory of Scientific and Engineering Computing Institute of Computational Mathematics and Scientific/Engineering ComputingChinese Academy of SciencesBeijing 100080China Laboratory of Computational Physics Institute of Applied Physics and Computational MathematicsBeijing 100088China

Examines a nonoverlapping domain decomposition method based on the natural boundary reduction. Development of the D-N alternating algorithm; Studies the convergence of the D-N method for exterior spherical domain; Dis... 详细信息

关键词： domain decomposition D-N algorithm exterior 3-D problem

Application of ensemble H-infinity filter in aquifer characterization andcomparison to ensemble Kalman filter

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Water Science and Engineering 2017年第1期10卷 25-35页

作者： Tong-chao Nan ji-chun wu State Key Laboratory of Pollution Control and Resources Reuse Nanjing UniversityNanjing 210093China Department of Hydrosciences School of Earth Sciences and EngineeringNanjing UniversityNanjing 210093China

Though the ensemble Kalman filter （EnKF） has been successfully applied in many areas, it requires explicit and accurate model and measurement error information, leading to difficulties in practice when only limited information on error mechanisms of observational in-struments for subsurface systems is accessible. To handle the uncertain errors, we applied a robust data assimilation algorithm, the ensemble H-infinity filter （EnHF）, to estimation of aquifer hydraulic heads and conductivities in a flow model with uncertain/correlated observational errors. The impacts of spatial and temporal correlations in measurements were analyzed, and the performance of EnHF was compared with that of the EnKF. The results show that both EnHF and EnKF are able to estimate hydraulic conductivities properly when observations are free of error; EnHF can provide robust estimates of hydraulic conductivities even when no observational error information is provided. In contrast, the estimates of EnKF seem noticeably undermined because of correlated errors and inaccurate error statistics, and filter divergence was observed. It is concluded that EnHF is an efficient assimilation algorithm when observational errors are unknown or error statistics are inaccurate.

关键词： Data assimilation Hydraulic parameter estimation Ensemble H-Infinity filter Ensemble Kalman filter Hydraulic conductivity Robustness

State of health estimation for lithium-ion batteries in real-world electric vehicles

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Science China(Technological Sciences) 2023年第1期66卷 47-56页

作者： wu ji FANG LeiChao DONG GuangZhong LIN MingQiang School of Automotive and Transportation Engineering Hefei University of TechnologyHefei 2300o9China Engineering Research Center for Intelligent Transportation and Cooperative Vehicle-Infrastructure of Anhui Province Hefei 230009China School of Mechanical Engineering and Automation Harbin Institute of TechnologyShenzhen 518055China Quanzhou Institute of Equipment Manufacturing Fujian Institute of Research on the Structure of MatterChinese Academy of SciencesJinjiang362200China

The state of health(SOH) plays a significant role in the mileage and safety of an electric vehicle(EV). In recent years, many methods based on data-driven analysis and laboratory measurements have been developed for SOH estimation. However, most of these proposed methods cannot be applied to real-world EVs. Here, we present a method for SOH estimation based on realworld EV data. A battery-aging evaluation health index(HI) with a strong correlation to the SOH is retrieved from battery-aging data and then modified with thermal factors to depict the former SOH. Afterward, a local weighted linear-regression algorithm is used to qualitatively characterize the declining trend of the HI, which eliminates the local HI fluctuation caused by data ***, a series of features-of-interest(FOIs) is extracted according to the battery consistency, cell-voltage extrema, and cumulative mileage, and validated using the grey relational analysis. Finally, a battery-degradation model is built using the extreme gradient-boosting algorithm with the selected FOIs. The experimental results from real-world data indicate that the proposed method has high estimation accuracy and generalization, and the maximum error is around 2% for batteries in realworld EVs.

关键词： electric vehicle state of health extreme gradient boosting battery consistency

Entrance-channel dynamics in the reaction 40Ca+208Pb

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Science China(Physics,Mechanics & Astronomy) 2019年第12期62卷 34-40页

作者： Xiao Yu Li Zhen ji wu Lu Guo School of Nuclear Science and Technology University of Chinese Academy of SciencesBeijing J00049China Institute of Theoretical Physics Chinese Academy of SciencesBeijing 100190China

The entrance-channel dynamics including capture, fusion, and quasifission processes for the reaction ^40Ca+^208Pb is investigated in the fully microscopic time-dependent Hartree-Fock(TDHF) theory. The calculations are performed in three-dimensional Cartesian coordinate without any symmetry restrictions, in which the full Skyrme energy functional SLy4d and SLy5 are *** study the energy dependence of capture cross sections, and find that the experimental data are well reproduced by the TDHF calculations. Both fusion and quasifission events are observed in the reaction ^40Ca+^208Pb. The contact time, mass and charge of quasifission fragments show a wide distribution in SLy4d compared with SLy5, implying that more nucleons are transferred in the SLy4d calculations. We find that the total kinetic energy of quasifission fragments in the TDHF calculations is distributed around Viola systematics, indicating that most of the relative kinetic energy is dissipated in quasifission dynamics.

关键词： capture fusion quasifission TDHF