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SEMI-IMPLICIT SPECTRAL DEFERRED CORRECTION METHODS BASED ON SECOND-ORDER TIME INTEGRATION SCHEMES FOR NONLINEAR PDES

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Journal of Computational Mathematics 2024年第1期42卷 111-133页

作者： Ruihan Guo yan xu School of Mathematics and Statistics Zhengzhou UniversityZhengzhou 450001China School of Mathematical Sciences University of Science and Technology of ChinaHefei 230026China

In[20],a semi-implicit spectral deferred correction(SDC)method was proposed,which is efficient for highly nonlinear partial differential equations(PDEs).The semi-implicit SDC method in[20]is based on first-order time integration methods,which are corrected iteratively,with the order of accuracy increased by one for each additional *** this paper,we will develop a class of semi-implicit SDC methods,which are based on second-order time integration methods and the order of accuracy are increased by two for each additional *** spatial discretization,we employ the local discontinuous Galerkin(LDG)method to arrive at fully-discrete schemes,which are high-order accurate in both space and *** experiments are presented to demonstrate the accuracy,efficiency and robustness of the proposed semi-implicit SDC methods for solving complex nonlinear PDEs.

关键词： Spectral deferred correction method Nonlinear PDEs Local discontinuous Galerkin method Second-order scheme

Malware Evasion Attacks Against IoT and Other Devices: An Empirical Study

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Tsinghua Science and Technology 2024年第1期29卷 127-142页

作者： yan xu Deqiang Li Qianmu Li Shouhuai xu School of Computer Science and Engineering Nanjing University of Science and TechnologyNanjing 210094China School of Computer Science Nanjing University of Posts and TelecommunicationsNanjing 210023China Department of Computer Science University of Colorado Colorado SpringsColorado SpringsCO 80918USA

The Internet of Things(loT)has grown rapidly due to artificial intelligence driven edge *** enabling many new functions,edge computing devices expand the vulnerability surface and have become the target of malware ***,attackers have used advanced techniques to evade defenses by transforming their malware into functionality-preserving *** systematically analyze such evasion attacks and conduct a large-scale empirical study in this paper to evaluate their impact on *** specifically,we focus on two forms of evasion attacks:obfuscation and adversarial *** the best of our knowledge,this paper is the first to investigate and contrast the two families of evasion attacks *** apply 10 obfuscation attacks and 9 adversarial attacks to 2870 malware *** obtained findings are as follows.(1)Commercial Off-The-Shelf(COTS)malware detectors are vulnerable to evasion attacks.(2)Adversarial attacks affect COTS malware detectors slightly more effectively than obfuscated malware examples.(3)Code similarity detection approaches can be affected by obfuscated examples and are barely affected by adversarial attacks.(4)These attacks can preserve the functionality of original malware examples.

关键词： Android malware obfuscation adversarial examples

High-Order Decoupled and Bound Preserving Local Discontinuous Galerkin Methods for a Class of Chemotaxis Models

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Communications on Applied Mathematics and Computation 2024年第1期6卷 372-398页

作者： Wei Zheng yan xu School of Mathematical Sciences University of Science and Technology of ChinaHefei230026AnhuiChina

In this paper,we explore bound preserving and high-order accurate local discontinuous Galerkin(LDG)schemes to solve a class of chemotaxis models,including the classical Keller-Segel(KS)model and two other density-dependent *** use the convex splitting method,the variant energy quadratization method,and the scalar auxiliary variable method coupled with the LDG method to construct first-order temporal accurate schemes based on the gradient flow structure of the *** semi-implicit schemes are decoupled,energy stable,and can be extended to high accuracy schemes using the semi-implicit spectral deferred correction *** bound preserving DG discretizations are only worked on explicit time integration methods and are difficult to get high-order *** overcome these difficulties,we use the Lagrange multipliers to enforce the implicit or semi-implicit LDG schemes to satisfy the bound constraints at each time *** bound preserving limiter results in the Karush-Kuhn-Tucker condition,which can be solved by an efficient active set semi-smooth Newton *** numerical experiments illustrate the high-order accuracy and the effect of bound preserving.

关键词： Chemotaxis models Local discontinuous Galerkin(LDG)scheme Convex splitting method Variant energy quadratization method Scalar auxiliary variable method Spectral deferred correction method

Upconversion-based chiral nanoprobe for highly selective dual-mode sensing and bioimaging of hydrogen sulfide in vitro and in vivo

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Light(Science & Applications) 2024年第9期13卷 1878-1887页

作者： yang Lu xu Zhao Dongmei yan Yingqian Mi Peng Sun xu yan Xiaomin Liu Geyu Lu State Key Laboratory of Integrated Optoelectronics College of Electronic Science and EngineeringJilin University130012 ChangchunChina Department of Immunology College of Basic Medical SciencesJilin University130021 ChangchunChina

Chiral assemblies have become one of the most active research areas due to their versatility,playing an increasingly important role in bio-detection,imaging and *** this work,chiral UCNPs/CuxOS@ZIF nanoprobes are prepared by encapsulating upconversion nanoparticles(UCNPs)and CuxOS nanoparticles(NPs)into zeolitic imidazolate framework-8(ZIF-8).The novel excited-state energy distribution-modulated upconversion nanostructure(NaYbF4@-NaYF4:Yb,Er)is selected as the fluorescence source and energy donor for highly efficient fluorescence resonance energy transfer(FRET).CuxOS NP is employed as chiral source and energy acceptor to quench upconversion luminescence(UCL)and provide circular dichroism(CD)*** the natural adsorption and sorting advantages of ZIF-8,the designed nanoprobe can isolate the influence of other common disruptors,thus achieve ultra-sensitive and highly selective UCL/CD dual-mode quantification of H2S in aqueous solution and in living ***,the nanoprobe is also capable of in vivo intra-tumoral H2S *** work highlights the multifunctional properties of chiral nanocomposites in sensing and opens a new vision and idea for the preparation and application of chiral nanomaterials in biomedical and biological analysis.

关键词： chiral sulfide donor

Energy absorption behaviors of a novel buffer lander-leg with Yoshimura core

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Chinese Journal of Aeronautics 2024年第4期37卷 333-342页

作者： yan xu He HUANG Chao ZHANG Rongji FU School of Aeronautics and Astronautics Zhejiang UniversityHangzhou 310027China School of Mechanics Civil Engineering and Architecture Northwestern Polytechnical UniversityXi’an 710072China

In the current soft-landing system,the lander-leg and the buffer are two independent parts which may cause weight *** traditional mechanical buffers also have their own shortcomings such as small buffer stroke and being non-reusable.A Novel Buffer Lander-leg with Yoshimura core (NBLY) is proposed in this paper,inspired by the Buckling Restrained Brace(BRB).The design details of NBLY and parameter definitions of the core are *** finite element analysis modes have been employed to analyze the nonlinear mechanical behaviors of NBLY subjected to the cyclic *** with four different core styles of hexagon,octagon,dodecagon and hexadecagon are analyzed and *** restraining ratio and cumulative dissipation energy ratio have been obtained to evaluate the energy absorption *** results show that the origami pattern has significant influences on the deformation ductility,plastic energy absorbing and axial load transferring to the *** NBLY with octagon core has outstanding properties,especially the hysteretic energy dissipation and enhancement of compression *** interaction mechanism between the core and encasing member constrains the deformation extensions and contributes to the frictional energy dissipation of the *** paper provides a new conceptual design of buffer lander-leg for soft-landing *** can realize the reuse function as a buffer lander-leg with better loading-bearing and energy absorption behaviors.

关键词： Lander-leg structure Origami Energy absorption Cyclic loading Finite element analysis

Joint Planning of Active Distribution Network and EV Charging Stations Considering Vehicle-to-Grid Functionality and Reactive Power Support

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CSEE Journal of Power and Energy Systems 2024年第5期10卷 2100-2113页

作者： Yongheng Wang Xinwei Shen yan xu Institute for Tsinghua Shenzhen International Graduate School Tsinghua UniversityShenzhen 518055China School of Electrical and Electronic Engineering Nanyang Technological UniversitySingapore

This paper proposes a collaborative planning model for active distribution network(ADN)and electric vehicle(EV)charging stations that fully considers vehicle-to-grid(V2G)function and reactive power support of EVs in different *** paper employs a sequential decomposition method based on physical characteristics of the problem,breaking down the holistic problem into two sub-problems for *** I optimizes the charging and discharging behavior of autopilot electric vehicles(AEVs)using a mixed-integer linear programming(MILP)*** II uses a mixed-integer secondorder cone programming(MISOCP)model to plan ADN and retrofit or construct V2G charging stations(V2GCS),as well as multiple distributed generation resources(DGRs).The paper also analyzes the impact of bi-directional active-reactive power interaction of V2GCS on ADN *** presented model is tested in the 47-node ADN in Longgang District,Shenzhen,China,and the IEEE 33-node ADN,demonstrating that decomposition can significantly improve the speed of solving large-scale problems while maintaining accuracy with low AEV penetration.

关键词： Active distribution network large-scale problem reactive power support sequential decomposition V2G charging station

A calibration and compensation method for an industrial robot with high accuracy harmonic reducers

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Science China(Technological Sciences) 2024年第3期67卷 725-739页

作者： ZHAO Yiyang LIU xun CAO JiaBin LIU JinYu xu yan yan WeiXin School of Mechanical Engineering Shanghai Jiao Tong UniversityShanghai 200240China College of Computer and Control Engineering Northeast Forestry UniversityHarbin 150040China

Industrial serial robots need high stiffness to keep absolute pose accuracy and meet the requirements in practical applications. However, the weak stiffness feature of robot joints and the payloads affected on robot end-effector, which will also increase the pose error of robot. Especially, the existing calibration methods often consider under no-payload condition without discussing the payload state. In this paper, we report a new industrial serial robot composed by a new harmonic reducer: Model-Y, based on high accuracy and high stiffness, and a kinematic parameter calibration algorithm which is based on a harmonic reducer forcedeformation model. To decrease the accuracy effects of payload, an iterative calibration method for kinematic parameters with payload situation was proposed. Simulation and experiments are conducted to verify the effectiveness of the proposed calibration method using the self-developed industrial serial robot. The results show a remarkably improved accuracy in absolute position and orientation with the robot's payload range. The position mean error has 70% decreased to 0.1 mm and the orientation mean error diminished to less than 0.01° after calibration with compensation. Additionally, online linear and circular tests are carried out to evaluate the position error of the robot during large-scale spatial and low-speed continuous movement. The accuracy is consistent with the previous calibration results, indicating the effectiveness and advantages of the proposed strategy in this article.

关键词： industrial serial robot Model-Y harmonic calibration stiffness model online compensation

Numerical simulation on directional solidification and heat treatment processes of turbine blades

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China Foundry 2024年第5期21卷 476-490页

作者： Ye-yuan Hu Ju-huai Ma Qing-yan xu School of Materials Science and Engineering Tsinghua UniversityKey Laboratory for Advanced Materials Processing TechnologyMinistry of EducationBeijing 100084China

Study on turbine blades is crucial due to their critical role in ensuring the efficient and reliable operation of aircraft ***-based single crystal superalloys are extensively used in the hot manufacturing of turbine blades due to their exceptional high-temperature mechanical *** hot manufacturing of single crystal blades involves directional solidification and heat *** manufacturing of these blades is time-consuming,capital-intensive,and often insufficient to meet industrial *** simulation techniques have gained widespread acceptance in blade manufacturing research due to their low energy consumption,high efficiency,and rapid turnaround *** article introduces the modeling and simulation of hot manufacturing in single crystal *** discussion outlines the prevalent mathematical models employed in numerical simulations related to blade hot *** encapsulates the advancements in research concerning macro to micro-level numerical simulation techniques for directional solidification and heat treatment ***,potential future trajectories for the numerical simulation of single crystal blade hot manufacturing are also discussed.

关键词： single crystal blades Ni-based superalloy directional solidification heat treatment numerical simulation

Spherical Confinement Generates Entropic Force to Accelerate Polymer Chain Detachment

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Chinese Journal of Polymer Science 2024年第3期42卷 407-416,I0010页

作者： Yu-Shan Zheng Jian-Ping Zhou yan xu Kai Li Mechanical Engineering Xinjiang UniversityUrumqi 830002China

To understand the dynamic process of polymer detachment, it is necessary to determine the mean detachment time of a single breakable link, which is modeled as a spring. Normally, this time can be viewed as the escape of a Brownian particle from the potential well of the spring. However, as the free dangling length of the polymer chain increases, the conformational entropy of the chain is affected by geometric confinement. It means that the wall exerts a repulsive force on the chain, resulting in accelerated link detachment from a macroscopic perspective. In this work, we investigate the effect of entropy on the detachment rate in the case where the substrate is spherical. We demonstrate that spherical confinement accelerates chain detachment both inside and outside the sphere. An analytical expression for the mean detachment time of breakable links is given, which includes an additional pre-factor that is related to the partition function. Additionally, we analyze the expressions for entropic forces inside the sphere, outside the sphere, and on a flat wall, comparing their magnitudes to explain the difference in mean detachment time.

关键词： Polymer detachment Breakable link Entropic force Mean first passage time