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A set of microstructure-based constitutive equations in hot forming of a titanium alloy

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Journal of University of Science and Technology Beijing 2006年第5期13卷 435-441页

作者： xiaoli li Miaoquan li College of Materials Science ＆ Engineering Northwestern Polytechnical University Xi＇an 710072 China

A physical model of microstructure evolution including dislocation density rate and grain growth rate was established based on the deformation mechanism for the hot forming of a class of two-phase titanium alloys. Further, a set of mechanism-based constitutive equations were proposed, in which the microstructure variables such as grain size and dislocation density were taken as internal state variables for characterizing the current material state. In the set of constitutive equations, the contributions of different mechanisms and individual phase to the deformation behavior were analyzed. The present equations have been applied to describe a correlation of the flow stress with the microstructure evolution of the TC6 alloy in hot forming.

关键词： titanium alloy constitutive equations microstructure evolution grain size dislocation density

FLOCKING OF MULTI-AGENT DYNAMIC SYSTEMS WITH GUARANTEED GROUP CONNECTIVITY

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Journal of Systems Science & Complexity 2008年第3期21卷 337-346页

作者： xiaoli li Yugeng XI Department of Automation Shanghai Jiao Tong University Shanghai 200240 China

This paper investigates distributed flocking problem where the information exchange among agents is modeled by the communication topology changing with time. Previous research on this problem establishes group stabilization by assuming that the dynamic topology is connected all the time, which however cannot be guaranteed by most proposed distributed control laws. In this paper, a distributed algorithm to distill a necessary subgraph of the initial communication topology is presented. This subgraph covers all the vertices of the communication topology and is proved to be connected as long as the initial communication topology is connected. A distributed control law is then designed to pursue the flocking motion while preserving all the edges in this subgraph. In this way, connectivity can be preserved all the time, and flocking problem is thus solved only provided the initial communication topology of multi-agent system is connected.

关键词： Connectivity distributed control flocking multi-agent system

Electron microprobe analysis of Hf and Ti in ultrahigh temperature zircon:Optimized approaches and perspectives

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Science China Earth Sciences 2023年第5期66卷 985-996页

作者： xiaoli li Bin WANG Chunjing WEI Key Laboratory of Orogenic Belts and Crustal Evolution MOE School of Earth and Space SciencesPeking UniversityBeijing100871China

Zircon as a multi-objective typomorphic mineral commonly contains diverse trace elements with specific petrogenetic *** Hf abundance in zircon is sensitively indicative of melt fractionation during zircon growth on one hand,and on another,the Ti content is a robust temperature sensor of zircon crystallization and has been effectively u tilized in thermometric estimation.A Hf-Ti negative correlation was previously reported in igneous zircons,and thus a potential Hf thermometry was then *** this work,we performed reliable electron microprobe(EMP)measurements of Hf and Ti in ultrahigh temperature(UHT)zircons from the North China Craton,in optimizing point,line and grid *** EMP contents of Hf and Ti both show a wide range of fluctuation owing to the smaller probe spot,and some of them are higher than the LAICPMS *** Hf-Ti correlation in UHT zircons displays dual and thus complicated patterns in contrast with the previous consideration,which implicates some other factors controlling the geochemical behaviors of Hf and Ti in ***,the estimated Ti temperatures based on the EMP analyses are obviously higher than the LA-ICPMS outcomes,but are well consistent with the actual peak condition of the parent *** explains the common underestimation of Ti temperatures in hightemperature metamorphic rocks,by using LA-ICPMS analyses.

关键词： Ultrahigh-temperature Zircon Hf content Ti content Electron microprobe

BLOCK-CENTERED FINITE DIFFERENCE METHODS FOR NON-FICKIAN FLOW IN POROUS MEDIA

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Journal of Computational Mathematics 2018年第4期36卷 492-516页

作者： xiaoli li Hongxing Rui School of Mathematics Shandong University Jinan Shandong 250100 China

In this article, two block-centered finite difference schemes are introduced and analyzed to solve the parabolic integro-differential equation arising in modeling non-Fickian flow in porous media. One scheme is Euler backward scheme with first order accuracy in time increment while the other is Crank-Nicolson scheme with second order accuracy in time increment. Stability analysis and second-order error estimates in spatial meshsize for both pressure and velocity in discrete L^2 norms are established on non-uniform rectangular grid. Numerical experiments using the schemes show that the convergence rates are in agreement with the theoretical analysis.

关键词： Block-centered finite difference Parabolic integro-differential equation Nonuniform Error estimates Numerical analysis

Efficient linear and unconditionally energy stable schemes for the modified phase field crystal equation

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Science China Mathematics 2022年第10期65卷 2201-2218页

作者： xiaoli li Jie Shen School of Mathematics Shandong UniversityJinan 250100China Department of Mathematics Purdue UniversityWest LafayetteIN 47907USA

In this paper,we construct efficient schemes based on the scalar auxiliary variable block-centered finite difference method for the modified phase field crystal equation,which is a sixth-order nonlinear damped wave *** schemes are linear,conserve mass and unconditionally dissipate a pseudo *** prove rigorously second-order error estimates in both time and space for the phase field variable in discrete *** also present some numerical experiments to verify our theoretical results and demonstrate the robustness and accuracy.

关键词： modified phase field crystal scalar auxiliary variable energy stability error estimate numerical experiments

Internal state variable models for micro-structure in high temperature deformation of titanium alloys

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Science China(Technological Sciences) 2008年第11期51卷 1921-1929页

作者： LUO Jiao li MiaoQuan li xiaoli School of Materials Science and Engineering Northwestern Polytechnical UniversityXi’an 710072China

There exists an interaction between microstructural evolution and deformation behavior in high temperature deformation of titanium alloys. And the microstruc- ture of titanium alloys is very sensitive to the process parameters of plastic de- formation process. In this paper, on the basis of plastic deformation mechanism of metals and alloys, a microstructural model including dislocation density rate equa- tion and grain growth rate equation is established with the dislocation density rate being an internal state variable. Applying the model to the high temperature de- formation process of Ti60 titanium alloy, the average relative errors of grain sizes between the experiments and the predictions are 9.47% for sampled data, and 13.01% for non-sampled data.

关键词： titanium alloy grain size dislocation density models parameter recognition

ESTIMATION AND INFERENCE FOR VARYING-COEFFICIENT REGRESSION MODELS WITH ERROR-PRONE COVARIATES

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Journal of Systems Science & Complexity 2014年第6期27卷 1263-1285页

作者： XU Yongqing li xiaoli CHEN Gemai School of Statistics and Management Shanghai University of Finance and Economics Department of Mathematics & Statistics University of CalgaryCalgaryAlberta T2N1N4Canada

This paper studies the estimation and inference for a class of varying-coefficient regression models with error-prone *** authors focus on the situation where the covariates are unobserved,there are no repeated measurements,and the covariance matrix of the measurement errors is unknown,but some auxiliary information is *** authors propose an instrumental variable type local polynomial estimator for the unknown varying-coefficient functions,and show that the estimator achieves the optimal nonparametric convergence rate,is asymptotically normal,and avoids using undersmoothing to allow the bandwidths to be selected using data-driven methods.A simulation is carried out to study the finite sample performance of the proposed estimator,and a real date set is analyzed to illustrate the usefulness of the developed methodology.

关键词： Error-prone covariate instrumental variable local polynomial efficient estimation varying-coefficient.

Stochastically Perturbed Parameterizations for the Process-Level Representation of Model Uncertainties in the CMA Global Ensemble Prediction System

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Journal of Meteorological Research 2022年第5期36卷 733-749页

作者： Fei PENG xiaoli li Jing CHEN CMA Earth System Modeling and Prediction Centre China Meteorological Administration(CMA)Beijing 100081 State Key Laboratory of Severe Weather China Meteorological AdministrationBeijing 100081 National Meteorological Centre China Meteorological AdministrationBeijing 100081

To represent model uncertainties at the physical process level in the China Meteorological Administration global ensemble prediction system(CMA-GEPS),a stochastically perturbed parameterization(SPP)scheme is developed by perturbing 16 parameters or variables selected from three physical parameterization schemes for the planetary boundary layer,cumulus convection,and cloud *** chosen quantity is perturbed independently with temporally and spatially correlated perturbations sampled from log-normal *** of the SPP scheme on CMA-GEPS are investigated comprehensively by using the stochastically perturbed parametrization tendencies(SPPT)scheme as a *** the absence of initial-condition perturbations,perturbation structures introduced by the two schemes are investigated by analyzing the ensemble spread of three forecast variables’physical tendencies and perturbation energy in ensembles generated by the separate use of SPP and *** is revealed that both schemes yield different perturbation structures and can simulate different sources of model *** initialcondition perturbations are activated,the influences of the two schemes on the performance of CMA-GEPS are assessed by calculating verification scores for both upper-air and surface *** improvements in ensemble reliability and probabilistic skill introduced by SPP and SPPT are mainly located in the ***,the vast majority of the reliability improvements(including increases in ensemble spread and reductions in outliers)are statistically significant,and a smaller proportion of the improvements in probabilistic skill(i.e.,decreases in continuously ranked probability score)reach statistical *** with SPPT,SPP generally has more beneficial impacts on200-hPa and 2-m temperature,along with 925-hPa and 2-m specific humidity,during the whole 15-day forecast *** other examined variables,such as 850-hPa zonal wind,850-hPa temperature,and

关键词： model uncertainty global ensemble forecast stochastic physics parameter perturbation perturbation structure

Stabilization of Networked Control Systems Using a Mixed-Mode Based Switched Delay System Method

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IEEE/CAA Journal of Automatica Sinica 2018年第6期5卷 1089-1098页

作者： Qing-Kui li xiaoli li Jiuhe Wang Shengli Du School of Automation Beijing Information Science and Technology UniversityBeijing 100192China Faculty of Information Technology Beijing University of TechnologyBeijing 100124China

The phenomenon of mixed-mode is one of the most important characteristics of switched delay systems. If a networked control system(NCS) with network induced delays and packet dropouts(NIDs & PDs) is recast as a switched delay system, it is imperative to consider the effects of mixed-modes in the stability analysis for an NCS. In this paper, with the help of the interpolatory quadrature formula and the average dwell time method, stabilization of NCSs using a mixed-mode based switched delay system method is investigated based on a novel constructed Lyapunov-Krasovskii functional. With the Finsler's lemma, new exponential stabilizability conditions with less conservativeness are given for the NCS. Finally, an illustrative example is provided to verify the effectiveness of the developed results.

关键词： Interpolatory quadrature formula mixed-mode networked control system (NCS) switched delay system