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Unexpected thermal conductivity enhancement in aperiodic superlattices discovered using active machine learning

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npj Computational materials 2022年第1期8卷 99-105页

作者： Prabudhya Roy Chowdhury Xiulin ruan school of mechanical Engineering and the Birck Nanotechnology Center Purdue UniversityWest LafayetteIN47907-2088USA

While machine learning(mL)has shown increasing effectiveness in optimizing materials properties under known physics,its application in discovering new physics remains challenging due to its interpolative *** this work,we demonstrate a general-purpose adaptive mL-accelerated search process that can discover unexpected lattice thermal conductivity(κ_(l))enhancement in aperiodic superlattices(sLs)as compared to periodic superlattices,with implications for thermal management of multilayer-based electronic *** use molecular dynamics simulations for high-fidelity calculations ofκ_(l),along with a convolutional neural network(CNN)which can rapidly predictκ_(l)for a large number of *** ensure accurate prediction for the target unknown sLs,we iteratively identify aperiodic sLs with structural features leading to locally enhanced thermal transport and include them as additional training data for the *** identified structures exhibit increased coherent phonon transport owing to the presence of closely spaced interfaces.

关键词： thermal conductivity transport

Quantitative Characterizations of Bounded Compact Approximation Property by semi-Fredholm Operators

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Acta mathematica sinica,English series 2023年第6期39卷 1115-1128页

作者： Dong Yang CHEN Ying Bin ruan school of mathematical sciences Xiamen UniversityXiamen 361005P.R.China school of mathematics and statistics Fujian Normal UniversityFuzhou 350007P.R.China

Based on a characterization of upper semi-Fredholm operators due to *** and ***,we introduce and investigate a new quantity characterizing upper semi-Fredholm *** quantity and several well-known quantities are used to characterize bounded compact approximation ***,a new quantity characterizing lower semi-Fredholm operators is introduced,investigated and used to characterize the bounded compact approximation property for dual spaces.

关键词： Bounded compact approximation property compact operators upper semi-Fredholm operators lower semi-Fredholm operators

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Rheological behavior of paste in metal mines

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International Journal of minerals,metallurgy and materials 2022年第4期29卷 717-726页

作者： Aixiang Wu Zhuen ruan Jiandong Wang Key Laboratory of High-Efficient mining and safety of metal mines of the ministry of Education University of Science and Technology BeijingBeijing 100083China shunde Graduate school of University of science and Technology Beijing Foshan 528399China school of Civil and Resources Engineering University of Science and Technology BeijingBeijing 100083China

Cemented paste backfill(CPB)has been one of the best practical approaches for tailings management and underground goaf *** rheology is a science to study the flow and deformation behaviors of paste or filling body under the effects of stress,strain,temperature,and time during the CPB *** goal of studying paste rheology is to solve the engineering problems existing in four key processes;that is,paste rheology should meet the engineering demands of thickening,mixing,transportation,and ***,paste rheology is extremely complicated due to its high concentration,materials complexity,and engineering characteristics of non-stratification,nonsegregation,and *** rheological behavior of full tailings in deep thickening,rheological behavior of paste in mixing and pipeline transportation,and rheological behavior of filling body are introduced and discussed:(1)gel point,compressive yield stress,and the hindered settling function are adopted to characterize the rheological properties of full tailings in deep *** of Coe-Clevenger theory and Buscall-White theory can also analyze the thickening performance in the whole area of deep cone thickener;(2)yield stress and viscosity are consistent with the evolution trend of the relative structure coefficient of paste in mixing;(3)coupling effect of wall slip and time-temperature dependency has a significant influence on the rheological properties and pipeline transportation;(4)damage variable is introduced to the Burgers model to describe the creep damage of the filling ***,in-depth and systematic studies were still needed to establish a complete theoretical system of paste rheology in metal mines.

关键词： paste rheology cemented paste backfill thickening mixing pipeline transportation

Electromagnetic-Thermo-mechanical Coupling Behavior of Cu/si Layered Thin Plate Under Pulsed magnetic Field

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Acta mechanica solida sinica 2022年第1期35卷 90-100页

作者： Qicong Li Linli Zhu Haihui ruan Department of Engineering mechanics and Key Laboratory of Soft Machines and Smart Devices of Zhejiang ProvinceZhejiang UniversityHangzhou 310027China Department of mechanical Engineering The Hong Kong Polytechnic UniversityHong KongChina

semiconductor-based electronic devices usually work under multiphysics fields rendering complex electromagnetic-thermo-mechanical *** this work,we develop a penalty function method based on a finite element analysis to tackle this coupling behavior in a metal/semiconductor bilayer plate-the representative unit of semiconductor antenna,which receives strong and pulsed electromagnetic *** these pulses,eddy current is generated,of which the magnitude varies remarkably from one plate to another due to the difference in electrical *** the concerned system,the metal layer generates much larger current,resulting in the large temperature rise and the nonnegligible Lorentz force,which could lead to delamination and failure of the semiconductor-based electronic *** study provides theoretical guidance for the design and protection of semiconductor-based electronic devices in complex environments.

关键词： Electromagnetic-thermo-mechanical coupling behavior Finite element method Pulse magnetic field Eddy current Delamination

Enhanced Thermal Conductivities of Liquid Crystal Polyesters from Controlled structure of molecular Chains by Introducing Different Dicarboxylic Acid monomers

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Research 2022年第4期2022卷 507-517页

作者： Xiao Zhong Kunpeng ruan Junwei Gu Research Development Institute of Northwestern Polytechnical University ShenzhenGuangdong 518057China shanxi Key Laboratory of macromolecular sCcience and Technology School of Chemistry and Chemical EngineeringNorthwestern Polytechnical UniversityXi'anShaanxi 710072China

Enhancing thermal conductivity coefficient (λ) of liquid crystal polyesters would further widen their application in electronics and electricals. In this work, a kind of biphenyl-based dihydroxy monomer is synthesized using 4, 4’-biphenyl (BP) and triethylene glycol (TEG) as raw material, which further reacts with three different dicarboxylic acids (succinic acid, p-phenylenediacetic acid, and terephthalic acid, respectively) by melt polycondensation to prepare intrinsically highly thermally conductive poly 4’, 4”’-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) succinate (PEOs), poly 4’, 4”’-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) p-phenyldiacetate (PEOP) and poly 4’, 4”’-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) terephthalate (PEOT), collectively called biphenyl-based liquid crystal polyesters (B-LCPE). The results show that B-LCPE possess the desired molecular structure, exhibit smectic phase in liquid crystal range and semicrystalline polymers at room temperature, and possess excellent intrinsic thermal conductivities, thermal stabilities, and mechanical properties. λ of PEOT is 0.51 W/(m·K), significantly exceeds that of polyethylene terephthalate (0.15 W/(m·K)) which has similar molecular structure with PEOT, and also higher than that of PEOs (0.32 W/(m·K)) and PEOP (0.38 W/(m·K)). The corresponding heat resistance index (THRI), elasticity modulus, and hardness of PEOT are 174.6℃, 3.6 GPa, and 154.5 mPa, respectively, and also higher than those of PEOs (162.2℃, 1.8 GPa, and 83.4 mPa) and PEOP (171.8℃, 2.3 GPa, and 149.6 mPa).

关键词： properties ethane polyester

Quasi-Newton-type optimized iterative learning control for discrete linear time invariant systems

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Control Theory and Technology 2015年第3期13卷 256-265页

作者： Yan GENG Xiaoe ruan school of mathematics and statistics Xi'an Jiaotong University

In this paper, a quasi-Newton-type optimized iterative learning control （ILC） algorithm is investigated for a class of discrete linear time-invariant systems. The proposed learning algorithm is to update the learning gain matrix by a quasi-Newton-type matrix instead of the inversion of the plant. By means of the mathematical inductive method, the monotone convergence of the proposed algorithm is analyzed, which shows that the tracking error monotonously converges to zero after a finite number of iterations. Compared with the existing optimized ILC algorithms, due to the superlinear convergence of quasi-Newton method, the proposed learning law operates with a faster convergent rate and is robust to the ill-condition of the system model, and thus owns a wide range of applications. Numerical simulations demonstrate the validity and effectiveness.

关键词： Iterative learning control optimization quasi-Newton method inverse plant

Performance-based global reliability assessment of a high-rise frame-core tube structure subjected to multi-dimensional stochastic earthquakes

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Earthquake Engineering and Engineering Vibration 2022年第2期21卷 395-415页

作者： Liu Zhangjun ruan Xinxin Liu Zixin school of Civil Engineering and Architecture Wuhan Institute of TechnologyWuhan 430074China Key Laboratory of Building Collapse mechanism and Disaster Prevention Institute of Disaster PreventionChina Earthquake AdministrationSanhe 065201China

When evaluating the seismic safety and reliability of complex engineering structures,it is a critical problem to reasonably consider the randomness and multi-dimensional nature of ground *** this end,a proposed modeling strategy of multi-dimensional stochastic earthquakes is addressed in this *** improved seismic model has several merits that enable it to better provide seismic analyses of ***,at first,the ground motion model is compatible with the design response ***,the evolutionary power spectrum involved in the model and the design response spectrum are constructed accordingly with sufficient consideration of the correlation between different seismic ***,the random function-based dimension-reduction representation is applied,by which seismic modeling is established,with three elementary random *** simulations of multi-dimensional stochastic ground motions in a specific design scenario indicate the effectiveness of the proposed modeling ***,the multi-dimensional seismic response and the global reliability of a high-rise frame-core tube structure is discussed in detail to further illustrate the engineering applicability of the proposed *** analytical investigations demonstrate that the suggested stochastic model of multi-dimensional ground motion is available for accurate seismic response analysis and dynamic reliability assessment of complex engineering structures for performance-based seismic resistance design.

关键词： multi-dimensional stochastic ground motion dimension-reduction representation frame-core tube structure global dynamic reliability performance-based seismic design

Comparison of daylight simulation methods for reflected sunlight from curtain walls

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Building simulation 2021年第3期14卷 549-564页

作者： Jun Wang minchen Wei Xiukai ruan Department of Building services Engineering The Hong Kong Polytechnic UniversityHung HornKowloonHong KongChina Wenzhou University Wenzhou CityZhejiang ProvinceChina

Curtain walls are more and more commonly used as building *** allow a better daylight availability and a direct connection to exterior ***,due to the high specular reflections,they may also introduce negative impacts,such as glare and urban heat island effects,to the surround,especially in dense and urban ***,it is important to effectively characterize the reflected sunlight from curtain *** study aimed to compare how different simulation methods can be used to characterize the reflected sunlight from curtain *** was found that the modeling of the sun and sky,ambient calculation,and the modeling of the building facade significantly affected the simulation results.A combination of forward and backward ray-tracing is recommended,with forward ray-tracing for identifying the curtain wall areas reflecting sunlight and backward ray-tracing for calculating illuminance due to reflected sunlight.A follow-up work is planned to investigate how different parameters will affect the simulation results and which method can produce similar results as field measurements.

关键词： daylighting reflected sunlight daylight simulation ray-tracing

Cavity length below chute aerators

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science China(Technological sciences) 2008年第2期51卷 170-178页

作者： WU JianHua ruan shiPing College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing 210098China

It is proved that air entrainment is one of the efficient measures dealing with cavi-tation control for the release works of hydropower projects. There are many factors to be considered in designing a chute aerator. One of the most important factors concerns the cavity length below the aerator,which has outstanding effects on air entrainment against cavitation damage. It is crucial to determine reasonable emergence angle for the calculation of the cavity length. In the present paper the overall effects of structural and hydraulic parameters on the emergence angle of the flow from the aerator were analyzed. Four improved expressions of the emer-gence angle with weight coefficient were investigated through experimental data of 68 points observed from 12 aerators of 6 hydropower projects,of both model and prototype,on the basis of error theory. A method to calculate the cavity length be-low aerators was suggested,which considers overall effects of the above men-tioned parameters. Comparison between the method in this paper and the other five methods of calculating the cavity length showed that the present method is much more reliable than the existing methods while the mean error of the method is less than others.

关键词： aerator air entrainment cavitation damage cavity length emergence angle flow depth transverse fluctua-ting velocity