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Room-temperature ferromagnetism and piezoelectricity in metalfree 2D semiconductor crystalline carbon nitride

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Nano Research 2024年第6期17卷 5670-5679页

作者： Yong Wang Dingyi Yang wei xu Yongjie xu Yu Zhang Zixuan Cheng Yizhang Wu xuetao Gan wei Zhong Yan Liu Genquan Han yue Hao Wide Bandgap Semiconductor Technology Disciplines State Key Laboratory School of MicroelectronicsAcademy of Advanced Interdisciplinary ResearchXidian UniversityXi’an 710071China Emerging Device and Chip Laboratory Hangzhou Institute of TechnologyXidian UniversityHangzhou 311200China INRS Centre for Energy Materials and Telecommunications1650 Boul.Lionel BouletVarennesQC J3X 1P7Canada National Laboratory of Solid State Microstructures Collaborative Innovation Center of Advanced Microstructures and Jiangsu Provincial Key Laboratory for NanotechnologyNanjing UniversityNanjing 210093China School of Education Jiangsu Open UniversityNanjing 210036China department of Physics Shaanxi University of Science and TechnologyXi’an 710021China department of applied Physical Sciences The University of North Carolina at Chapel HillChapel HillNC 27514USA Key Laboratory of Light Field Manipulation and Information Acquisition Ministry of Industry and Information Technologyand Shaanxi Key Laboratory of Optical Information TechnologySchool of Physical Science and TechnologyNorthwestern Polytechnical UniversityXi'an 710129 China

Two-dimensional(2D)materials that combine ferromagnetic,semiconductor,and piezoelectric properties hold significant potential for both fundamental research and spin electronic ***,the majority of reported 2D ferromagnetic-semiconductor-piezoelectric materials rely on d-electron systems,which limits their practical applications due to a Curie temperature lower than room temperature(RT).Here,we report a high-crystallinity carbon nitride(CCN)material based on sp-electrons using a chemical vapor deposition *** exhibits a band gap of 1.8 eV and has been confirmed to possess substantial in-plane and out-of-plane ***,we acquired clear evidences of ferromagnetic behavior at room *** structural characterizations combined with theoretical calculations reveal that incorporating structural oxygen into the highly ordered heptazine structure causes partial substitution of nitrogen sites,which is primarily responsible for generating room-temperature ferromagnetism and *** a result,the strain in wrinkles can effectively modulate the domain behavior and piezoelectric potential at room *** addition of RT ferromagnetic-semiconductor-piezoelectric material based on sp-electrons to the family of two-dimensional materials opens up numerous possibilities for novel applications in fundamental research and spin electronic devices.

关键词： crystallinity carbon nitride room-temperature ferromagnetism piezoelectricity magnetic force microscopy density functional theory(DFT)calculations

Delay induced transitions in an asymmetry bistable system and stochastic resonance

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Science china(Physics,Mechanics & Astronomy) 2010年第4期53卷 745-750页

作者： ZHANG HuiQing , xu wei, xu Yong & ZHOU BingChang department of {4. mathematics, Northwestern Polytechnical University, xi’an 710072, {4. 1. department of applied mathematics Northwestern Polytechnical University Xi’an 710072 China

The delay Fokker-Planck equation is given for an asymmetry bistable system with correlated Gaussian white noises. The small delay approximation based on the probability density approach is used and the approximate stationary probability density function is obtained. The phenomenon of delay induced transitions is found. When a weak periodic signal is added, the phenomenon of stochastic resonance is investigated. Expression of the signal-to-noise ratio (SNR) is obtained by using the two-state theory. It is shown that the time delay can suppress or promote the stochastic resonance phenomenon.

关键词： stochastic resonance time-delayed asymmetry bistable system correlated noises

Analysis of application range of simplified models for field to thermo-field to thermionic emission processes from the cathode

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Plasma Science and Technology 2024年第9期26卷 51-60页

作者： Li SUN Zhuo DAI Ming xu wei WANG Zengyao LI applied Physics department Xi’an University of TechnologyXi’an 710048People’s Republic of China Key Laboratory of Thermo-Fluid Science and Engineering Ministry of EducationSchool of Energy and Power EngineeringXi’an Jiaotong UniversityXi’an 710049People’s Republic of China

Electron emission plays a dominant role in plasma-cathode interactions and is a key factor in many plasma phenomena and industrial *** is necessary to illustrate the various electron emission mechanisms and the corresponding applicable description models to evaluate their impacts on discharge *** this study,detailed expressions of the simplified formulas valid for field emission to thermo-field emission to thermionic emission typically used in the numerical simulation are proposed,and the corresponding application ranges are determined in the framework of the Murphy-Good theory,which is commonly regarded as the general model and to be accurate in the full range of conditions of the validity of the *** parameterization was used to evaluate the emission current density of the Murphy-Good formula,and a deviation factor was defined to obtain the application ranges for different work functions(2.5‒5 eV),cathode temperatures(300‒6000 K),and emitted electric fields(10^(5) to 10^(10) V·m^(-1)).The deviation factor was shown to be a nonmonotonic function of the three parameters.A comparative study of particle number densities in atmospheric gas discharge with a tungsten cathode was performed based on the one-dimensional implicit particle-in-cell(PIC)with the Monte Carlo collision(MCC)method according to the aforementioned application *** was found that small differences in emission current density can lead to variations in the distributions of particle number density due to changes in the collisional *** study provides a theoretical basis for selecting emission models for subsequent numerical simulations.

关键词： electron emission processes application range Murphy-Good theory implicit particlein-cell Monte Carlo collision method

Stochastic response analysis of noisy system with non-negative real-power restoring force by generalized cell mapping method

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applied mathematics and Mechanics(English Edition) 2015年第3期36卷 329-336页

作者： Qun HAN wei xu xiaole yue department of applied mathematics Northwestern Polytechnical University

The stochastic response of a noisy system with non-negative restoring force is investigated. The generalized cell mapping （GCM） method compute the transient and stationary probability density functions （PDFs） real-power is used to Combined with the global properties of the noise-free system, the evolutionary process of the tran- sient PDFs is revealed. The results show that stochastic P-bifurcation occurs when the system parameter varies in the response analysis and the stationary PDF evolves from bimodal to unimodal along the unstable manifold during the bifurcation.

关键词： stochastic response probability density function (PDF) generalized cell mapping (GCM) method real-power restoring force bifurcation

Stochastic bifurcations in the SD (smooth and discontinuous) oscillator under bounded noise excitation

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Science china(Physics,Mechanics & Astronomy) 2013年第5期56卷 1010-1016页

作者： yue xiaole xu wei WANG Liang department of applied mathematics Northwestern Polytechnical University

Stochastic bifurcations of the SD （smooth and discontinuous） oscillator with additive and/or multiplicative bounded noises are studied by the generalized cell mapping method using digraph analysis algorithm. From the global viewpoint, stochastic bifur- cation can be described as a sudden change in shape and size of a random attractor as the system parameter valies. The evolu- tionary process of stochastic bifurcation in the SD oscillator is shown in detail. Meanwhile, we show the phenomenon that un- der stochastic excitation the shape and size of random attractor and random saddle change along with the direction of unstable manifold. A plane stochastic bifurcation diagram is included.

关键词： stochastic bifurcation SD oscillator generalized cell mapping method bounded noise

Global analyses of crisis and stochastic bifurcation in the hardening Helmholtz-Duffing oscillator

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中国科学:技术科学 2010年第2期 213-213页

作者： xu wei & yue xiaole department of applied mathematics, Northwestern Polytechnical University, xi’an 710072, china

Crisis and stochastic bifurcation of the hardening Helmholtz-Duffing oscillator are studied by means of the generalized cell mapping method using digraph. For the system subject to a single deterministic harmonic excitation, our study reveals that a series of crisis phenomena can occur when the system parameter passes through different critical values, including chaotic boundary crisis, regular boundary crisis and interior crisis. A chaotic boundary crisis due to the collision of regular attractor with chaotic saddle embedded in a fractal basin boundary and an interior crisis due to the collision of regular attractor with chaotic saddle of its attraction basin are discovered. A new phenomenon, namely the global properties of dynamical system show symmetric as system parameter is varied, can be also revealed according to our analysis. For the system subject to a combination of a deterministic harmonic excitation and a random excitation, it is found that stochastic bifurcation, defined as a sudden change in character of a stochastic attractor, can occur one after another when the noise intensity passes through different critical values. This kind of stochastic bifurcation corresponds to stochastic crisis essentially. Our study also reveals that the generalized cell mapping method using digraph is a powerful tool not only for the crisis behavior analysis of deterministic system, but also for the global property analysis of stochastic bifurcation.

关键词： crisis stochastic bifurcation hardening Helmholtz-Duffing oscillator generalized cell mapping method using digraph

Extreme parameter sensitivity of transient persistence in spatially coupled ecological systems

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Theoretical & applied Mechanics Letters 2011年第6期1卷 51-56页

作者： Lin Du, wei xu,) and Zhanguo Li department of applied {4., Northwestern Polytechnical University, xi’an 710072, {4. department of applied mathematics Northwestern Polytechnical University Xi'an 710072 China

This paper investigates persistence of transient dynamics depending on parameters in spatially coupled ecological systems. We emphasis that the persistence time can be obtained by populations of species or Lyapunov exponents of transient dynamics. It is found that extreme sensitive dependence of persistence on parameters occurs commonly in ecological models. A non-zero uncertainty exponent is used to characterize the high sensitivity in a reasonable parameter region. The result of a small uncertainty exponent indicates a fractal structure of transient persistence in the two-dimensional parameter space. In spite of different methods of measurement, the fractal dimensions have a good consistency. Since populations of natural communities with many coupled oscillators are often affected by disturbance of migration rates, the large probability of error in estimating persistence of transients should be concerned.

关键词： transient dynamics predator-prey systems persistence sensitivity uncertainty exponents fractal dimensions

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气流作用下气道组织变形的流固耦合研究

力学学报 2024年第2期56卷 472-481页

作者：秦源陈茜魏东任晓勇徐光魁西安交通大学航天航空学院多尺度力学-医学交叉实验室西安710049 西安交通大学第二附属医院耳鼻咽喉头颈外科西安710004 空气动力学国家重点实验室四川绵阳621000

悬雍垂腭咽成形术(UPPP)是一种治疗阻塞性睡眠呼吸暂停(OSA)的常规外科手术,然而由于手术作用机制仍不清楚,手术成功率较低.现有的研究大多忽略了患者上气道的具体形态以及呼吸作用下气道软组织的弹性变形,不足以有效指导手术治疗.文章... 详细信息

悬雍垂腭咽成形术(UPPP)是一种治疗阻塞性睡眠呼吸暂停(OSA)的常规外科手术,然而由于手术作用机制仍不清楚,手术成功率较低.现有的研究大多忽略了患者上气道的具体形态以及呼吸作用下气道软组织的弹性变形,不足以有效指导手术治疗.文章基于OSA患者在术前、术后的CT扫描图像,构建了精确的三维上气道模型,通过双向流固耦合(FSI)计算,模拟研究了呼吸作用下上气道软组织的弹性变形和气道内气流流动情况.比较手术成功案例和失败案例中OSA患者上气道的流速、压力分布及气道弹性变形情况,从气道流体流动状态和气道软组织变形的角度解释了OSA的发生原因与手术作用机制.结果表明,最小横截面积尺寸并不是UPPP手术成功与否的决定性因素,成功的手术应当是减轻气道壁负压力程度、降低气道进出口之间的压降.此外,使用双向FSI方法,文章进一步构建了简化的人体二维软腭模型,探究了软腭弹性模量对吸气过程的影响,发现当软腭的弹性模量在0.5~1.5 MPa的范围内时,刚度更小的软腭会改善流场的流动情况,但也更易发生变形塌陷.文章所发展的流固模型为个性化预测手术效果提供了研究工具.

关键词：上气道阻塞性睡眠呼吸暂停双向流固耦合压降数值模拟

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基于复合胞化空间的图胞映射方法

物理学报 2008年第7期57卷 4021-4028页

作者：贺群徐伟李爽肖玉柱西北工业大学理学院成用数学系西安710072

为了提高计算的准确性和效率,通过引入复合胞化空间概念,构建了一种迭代的图胞映射方法.该方法能够对任意感兴趣的空间区域进行细化处理,细化过程采用代数运算完成不会额外增加计算机内存且能保持细化前后图动力系统性质不变.为了便于... 详细信息

为了提高计算的准确性和效率,通过引入复合胞化空间概念,构建了一种迭代的图胞映射方法.该方法能够对任意感兴趣的空间区域进行细化处理,细化过程采用代数运算完成不会额外增加计算机内存且能保持细化前后图动力系统性质不变.为了便于计算机实施,也给出了相应的有效算法.通过对典型例子Henon映射的应用分析,证实了该方法的有效性.

关键词：图胞映射方法迭代方法 Henon映射