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Conditions for polynomial Liénard centers

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Science China Mathematics 2016年第3期59卷 411-424页

作者： YU zhiheng ZHANG WeiNian School of Mathematics Sichuan University

In 1999, Christopher gave a necessary and sufficient condition for polynomial Li′enard centers, which requires coupled functional equations, where the primitive functions of the damping function and the restoring function are involved, to have polynomial solutions. In order to judge whether the coupled functional equations are solvable, in this paper we give an algorithm to compute a Gr¨obner basis for irreducible decomposition of algebraic varieties so as to find algebraic relations among coefficients of the damping function and the restoring function. We demonstrate the algorithm for polynomial Li′enard systems of degree 5, which are divided into 25 cases. We find all conditions of those coefficients for the polynomial Li′enard center in 13 cases and prove that the origin is not a center in the other 12 cases.

关键词： center polynomial Liénard system Grobner basis variety decomposition

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农村人力资本结构高级化对乡村振兴的影响

华东经济管理 2025年第1期39卷 52-62页

作者：徐增阳杜亚楠杜猛华中师范大学公共管理学院湖北武汉430079

优化农村人力资本结构对有效实施乡村振兴战略具有深远的意义。文章基于2012—2023年中国30个省份的面板数据,运用固定效应模型、调节效应模型和门槛效应模型实证分析农村人力资本结构高级化对乡村振兴的影响。研究发现:农村人力资本结... 详细信息

优化农村人力资本结构对有效实施乡村振兴战略具有深远的意义。文章基于2012—2023年中国30个省份的面板数据,运用固定效应模型、调节效应模型和门槛效应模型实证分析农村人力资本结构高级化对乡村振兴的影响。研究发现:农村人力资本结构高级化促进乡村振兴,但存在区域异质性;科技创新在农村人力资本结构高级化对乡村振兴的影响中所起的调节作用因经济社会发展水平不同而有差异;农村人力资本结构高级化对乡村振兴存在单一门槛效应,对外开放跨过门槛值9.386后,农村人力资本结构高级化对乡村振兴的促进作用减弱。由此得出分类施策促进农村人力资本结构高级化、营造创新环境、处理好农产品外贸出口与内销的关系等政策启示。

关键词：农村人力资本结构乡村振兴共同富裕科技创新对外开放

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Influences of cavity leakage on the design of low flow coefficient centrifugal impeller

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Science China(Technological Sciences) 2011年第2期54卷 311-317页

作者： WANG zhiheng XI Guang School of Energy and Power Engineering Xi 'an Jiaotong University Xi'an 710049 China

The low flow coefficient centrifugal impeller(LFCCI)gives a relatively low efficiency and a special treatment is required for the design of this kind of *** paper investigates the influences of cavity leakage on the performance prediction and design of LFCCI based on Computational Fluid Dynamics(CFD)*** results show that,the reduction in the effi-ciency of impeller due to the introduction of cavity leakage varies with the blade shape of impeller in a wide range since there is a strong and complex interaction of main flow and leakage flow in the *** get a credible optimization result,the backside and foreside cavities should be considered in the CFD-based design of LFCCI.

关键词： cavity leakage optimization design low flow coefficient impeller

Performance enhancement of perovskite solar cells with Cs2PtI6-xBrx absorber layer based on numerical simulation

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Optoelectronics Letters 2025年

作者： du Zuyan Yuan Yujie Hou Guofu Xin Yupeng Bi Jinlian Li Wei Tianjin Key Laboratory of Film Electronic and Communication Devices， School of Integrated Circuit Science and Engineering， Tianjin University of Technology Institute of Photoelectronic Thin Film Devices and Technology， Nankai University

Cs2TiBr6， characterized as a lead-free vacancy-ordered double perovskite material， demonstrates notable stability and photoelectric performance， rendering it suitable for application in perovskite solar cells. However， the experimental efficiency of this material is currently limited， achieving only 3.12%. This efficiency limitation primarily stems from the material’s wide bandgap， which results in insufficient light absorption. To address this issue， this study utilized Cs2PtI6-xBrxfor band structure fine-tuning. By adjusting the bandgap of Cs2PtI6-xBrxthrough Br-doping， not only was the alignment of the energy bandgap in the absorption layer effectively adjusted， but the cutoff range of light absorption was also significantly expanded. Setting the Cs2PtI6-xBrxbandgap to 1.4 eV resulted in optimal device performance. Additionally， comparative analyses aimed at boosting solar cell efficiency were performed on both hole transport and electron transport layer materials. Subsequently， the structure of the perovskite solar cell was optimized using an FTO/TiO2/Cs2TiBr6/Cs2PtI6-xBrx/Cu2O/Au configuration. Furthermore， the influence of the absorber layer thickness and defect density on device performance was studied. Ultimately， this configuration enabled the Cs2TiBr6/Cs2PtI6-xBrxsolar cell to achieve a peak conversion efficiency of 29.69%.

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Weak feedback self-mixing interference fringe slope discrimination method based on deep learning

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Optoelectronics Letters 2025年

作者： ZHAO Yan LIN Maohua du Shengzhi TONG Jigang LIU Bin HAN Fangfang School of Electrical Engineering and Automation， Tianjin University of Technology Tianjin Key Laboratory for Control Theory and Applications in Complicated Systems Department of Electrical Engineering， Tshwane University of Technology

In order to identify the tilt direction of the self-mixing interference (SMI) signals under weak feedback regime interfered by noise， a deep learning method is proposed. The one-dimensional U-Net (1D U-Net) neural network can discriminate the direction of self-mixing fringes accurately and quickly. For experimental SMI signals， the 1D U-Net can be used for discriminant direction after a one-step normalization. Simulation and experimental results show that the proposed method is suitable for SMI signals with noise within the whole weak feedback regime， and can maintain a high discrimination accuracy for signals interfered by 5dB noise. Combined with fringe counting method， accurate and rapid SMI signal displacement reconstruction can be realized.

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Aerodynamic effects of impeller-diffuser axial misalignment in low-flow-coefficient centrifugal compressor

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Science China(Technological Sciences) 2015年第1期58卷 29-36页

作者： WANG zhiheng XI Guang LIU QingFang School of Energy and Power Engineering Xi'an Jiaotong University School of Mathmatics and Statistics Xi'an Jiaotong University

A numerical investigation on the aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor is conducted through three-dimensional CFD *** results show that the flow,especially near the diffuser inlet,is influenced by the axial misalignment *** the impeller offsets to one side,the pressure at diffuser inlet close to this side will descend,and the vortex in the cavity on the other side will partially enter the diffuser and then result in the back *** performances of the stage and its components also change with the impeller-diffuser axial *** exists an optimum offset making the efficiency maximum at a given operating ***,the effect of impeller-diffuser axial misalignment on the axial thrust is *** axial thrust is nearly increased linearly with the increase of axial *** aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor behaves more remarkably at the large flow *** alleviate the aerodynamic effects of impeller-diffuser misalignment,a rounding in the meridional plane at the diffuser inlet can be applied.

关键词： misalignment compressor low flow coefficient impeller

Construction of compact RBF network by refining coarse clusters and widths

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Journal of Systems Engineering and Electronics 2009年第6期20卷 1309-1315页

作者： Zeng Delu Zhou zhiheng Xie Shengli School of Electronic and Information Engineering South China Univ. of Technology Guangzhou 510641 P. R. China

It is known that centers, widths, and weights are three mainly considered factors in constructing a radial basis function（RBF） *** paper aims at constructing a compact RBF network with two main *** the first step, the coarse clusters computed from triangle inequalities are refined to obtain the locations of centers by the defined maximum degree spanning tree（MDST）.Meanwhile the coarse widths are *** the second step, a learning algorithm referred to as anisotropic gradient descent method is presented to further refine the above coarse *** of the proposed algorithm show its great performance in times series prediction and classification.

关键词： clustering anisotropic gradient descent radial basis function time series prediction boundary extraction.

The effects of gas models on the predicted performance and flow of a centrifugal refrigeration compressor stage

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Science China(Technological Sciences) 2008年第8期51卷 1160-1168页

作者： WANG zhiheng XI Guang School of Energy and Power Engineering Xi’an Jiaotong UniversityXi’an 710049China

In this paper three perfect gas models with constant specific heat or with variable specific heat and one real gas model based on the gas property tables are respec- tively considered to implement into the three-dimensional CFD (computational fluid dynamics) analysis of a centrifugal refrigeration compressor stage. The results show that the gas models applied to the CFD code have significant influences on the performance of stage and the flow structures in the stage. Although the ther- modynamics operating condition of evolving fluid in the centrifugal refrigeration compressor has a significant deviation from the perfect gas, the perfect gas model with the modified value of gas constant and the variable specific heat offers a good prediction of stage performance. To predict some basic fluid flow parameters and flow structure accurately, the real gas effects should be considered and the rea- sonably accurate thermodynamic properties based on the analytical gas equation of state or numerical interpolation of gas tables should be applied to the CFD code.

关键词： gas model numerical analysis centrifugal refrigeration compressor

A conductive anionic Co-MOF cage with zeolite framework for supercapacitors

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Chinese Chemical Letters 2020年第9期31卷 2309-2313页

作者： Wei du Yue-Ling Bai Zhen Yang Runlong Li Dan Zhang zhiheng Ma Anbao Yuan Jiaqiang Xu College of Science Shanghai UniversityShanghai 200444China

Conductive MOFs could exhibit full potential as integrated electrode materials for supercapacitors without interference from additional conductive *** we report an anionic Co-MOF cage with zeolite framework,which was balanced by the redox-active guest [Co(H2O)6]2+ and protonated[(CH3)2NH2]2+ *** from the unique ion skeleton structure,Co-MOF exhibits a conductivity higher than most of reported MOFs with the value of 1.42 × 10^-3 S/cm,which can be directly fabricated as electrode for supercapacitors.A maximum specific capacitance of 236.2 F/g can be achieved at a current density of 1 A/g of ***,the electric performance and morphology of this Co-MOF can be modified by cetyltrimethylammonium bromide(CTAB) and the maximum specific capacitance could increase up to 334 F/g at 1 A/g when the ratio of ligand and CTAB is 1:6(Co-MOF-6).Furthermore,the specific capacitance can retain at 64.04% and 77.92% of the initial value after 3000 cycles of Co-MOF and Co-CTAB-6,***,the addition of CTAB further improves both capacitance and cycle stability.

关键词： Metal organic frameworks Supercapacitors Cetyltrimethylammonium bromide In-situ growth Redox-active guest