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Journal of Advanced Ceramics 2022年第6期11卷 912-921页

作者： Xiuyuan FAN Guohua BAI Zhenhua ZHANG Qiming CHEN Jiaying JINa Jiafeng XUa Xuefeng ZHANG Mi YAN School of Materials Science and Engineering State Key Laboratory of Silicon MaterialsKey Laboratory of Novel Materials for Information Technology of Zhejiang ProvinceZhejiang UniversityHangzhou 310027China Institute of Advanced Magnetic Materials College of Materials&Environmental EngineeringHangzhou Dianzi UniversityHangzhou 310012China

High-frequency soft magnetic ferrite ceramics are desired in miniaturized and efficient power electronics but remain extremely challenging to deploy on account of the power loss(Pcv)at megahertz frequencies.Here,we prepared NiCuZn ferrite with superior high-frequency properties by V_(2)O_(5)and Bi_(2)O_(3)synergistic doping,which proves to be a potent pathway to reduce Pcv of the ferrite at megahertz frequencies.The sample doped with 800 ppm V_(2)O_(5)and 800 ppm Bi_(2)O_(3)yielded the most optimized magnetic properties with a Pcv of 113 kW/m^(3)(10 MHz,5 mT,25℃),an initial permeability(μi)of 89,and a saturation induction(Bs)of 340 mT,which is at the forefront of the reported results.These outstanding properties are closely related to the notable grain boundary structure,which features a new type of nano-Bi_(2)Fe_(4)O_(9)phase around ferrite grains and a Ca/Si/V/O amorphous layer.Our results indicate great strides in correlating the grain boundary structure with multiple-ion doping and set the scene for the developing high-frequency soft magnet ferrites.

关键词： NiCuZn ferrite megahertz application grain boundary Bi_(2)Fe_(4)O_(9) ion doping

On BiHom-L-R Smash Products

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代数集刊:英文版 2023年第2期30卷 245-262页

作者： jiafeng Lu Panpan Wang Ling Liu Department of Mathematics Zhejiang Normal University JinhuaZhejiang 321004China

Let(H,αH,βH,ψH,ωH,SH)be a BiHom-Hopf algebra and(A,αA,βA)be an(H,αH,βH,ψH,ωH)-BiHom-bimodule algebra,where the mapsαH,βH,ψH,ωH,αA,βA are bijective.We first prove the Maschke-type theorem for the BiHom-L-R smash product over a finite-dimensional semisimple BiHom-Hopf algebra.Next we give a Morita context between the BiHom-subalgebra A^(biH)and the BiHom-L-R smash product A#H.

关键词： BiHom-bimodule algebra BiHom-L-R smash product Maschke-type theorem Morita context

Positive Ground State Solutions for Schrodinger-Poisson System with General Nonlinearity and Critical Exponent

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Journal of Partial Differential Equations 2023年第1期36卷 68-81页

作者： CHEN Qingfang LIAO jiafeng School of Mathematics and Information China West Normal UniversityNanchong 637009China Nanchong NO.1 Middle School Nanchong 637000China College of Mathematics Education China West Normal UniversityNanchong 637009China

In this paper,we consider the following Schrodinger-Poisson system{-Δu+ηΦu=f(x,μ)+μ^(5),x∈Ω,-ΔФ=μ^(2),x∈Ω,μ=Φ=0,x∈■Ω,whereΩis a smooth bounded domain in R^(3),η=±1 and the continuous function f satisfies some suitable conditions.Based on the Mountain pass theorem,we prove the existence of positive ground state solutions.

关键词： Schrodinger-Poisson system Sobolev critical exponent positive ground state solu-tion Mountain pass theorem

State estimation and finite-frequency fault detection for interconnected switched cyber-physical systems

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Science China(Information Sciences) 2023年第9期66卷 194-212页

作者： Shenghui GUO Mingzhu TANG Darong HUANG jiafeng SONG School of Electronic and Information Engineering Suzhou University of Science and Technology School of Artificial Intelligence Anhui University Tsinghua University Suzhou Automobile Research Institute

For switched cyber-physical systems with disturbances and actuator faults, we address fault detection and isolation problems. First, the preconditions relative to subsystems are discussed in detail,and the original subsystems are turned into an overall system. Second, the frequency ranges of faults are considered to belong to the finite-frequency domain, and the observer, which makes the residual robust against disturbances and sensitive to faults, is designed by combining the finite-frequency H-technique with the mixed L2-L∞/H∞technique. Third, design conditions, which guarantee that the error system is stable and satisfies the mixed performance, are derived using the average dwell time method and Lyapunov functionals. Finally, a traffic density dynamic model is proposed to demonstrate the validity and effectiveness of the proposed method.

关键词： switched system fault detection and isolation mixed L 2 − L ∞ / H ∞ , H − technique

Research on Facial Expression Capture Based on Two-Stage Neural Network

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Computers, Materials & Continua 2022年第9期72卷 4709-4725页

作者： Zhenzhou Wang Shao Cui Xiang Wang jiafeng Tian School of Information Science and Engineering Hebei University of Science and TechnologyShijiazhuang050000China School of Engineering Newcastle UniversityNewcastle Upon TyneNE98United Kingdom

To generate realistic three-dimensional animation of virtual character,capturing real facial expression is the primary task.Due to diverse facial expressions and complex background,facial landmarks recognized by existing strategies have the problem of deviations and low accuracy.Therefore,a method for facial expression capture based on two-stage neural network is proposed in this paper which takes advantage of improved multi-task cascaded convolutional networks(MTCNN)and high-resolution network.Firstly,the convolution operation of traditional MTCNN is improved.The face information in the input image is quickly filtered by feature fusion in the first stage and Octave Convolution instead of the original ones is introduced into in the second stage to enhance the feature extraction ability of the network,which further rejects a large number of false candidates.The model outputs more accurate facial candidate windows for better landmarks recognition and locates the faces.Then the images cropped after face detection are input into high-resolution network.Multi-scale feature fusion is realized by parallel connection of multi-resolution streams,and rich high-resolution heatmaps of facial landmarks are obtained.Finally,the changes of facial landmarks recognized are tracked in real-time.The expression parameters are extracted and transmitted to Unity3D engine to drive the virtual character’s face,which can realize facial expression synchronous animation.Extensive experimental results obtained on the WFLW database demonstrate the superiority of the proposed method in terms of accuracy and robustness,especially for diverse expressions and complex background.The method can accurately capture facial expression and generate three-dimensional animation effects,making online entertainment and social interaction more immersive in shared virtual space.

关键词： Facial expression capture facial landmarks multi-task cascaded convolutional networks high-resolution network animation generation

Koszul property of a class of graded algebras with nonpure resolutions

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Frontiers of Mathematics in China 2016年第4期11卷 985-1002页

作者： jiafeng LU Junling ZHENG Department of Mathematics Zhejiang Normal University Jinhua 321004 China

给任何整数一， b ， c ，和 d 与一> 1 ， c 0 ， b + c ，和 d b + c ，观点(一， b ， c ， d ) -Koszul 代数学被介绍，它是有 nonpure 分辨率的标准分级的代数学的另一个类，并且包括许多 Artin-Schelter 低全球尺寸的常规代数... 详细信息

给任何整数一， b ， c ，和 d 与一> 1 ， c 0 ， b + c ，和 d b + c ，观点(一， b ， c ， d ) -Koszul 代数学被介绍，它是有 nonpure 分辨率的标准分级的代数学的另一个类，并且包括许多 Artin-Schelter 低全球尺寸的常规代数学同样特定的例子。一些基本性质(一， b， c， d )-Koszul 代数学 / 模块被给，并且为一个标准的几个标准分级代数学是(一， b， c， d )-Koszul 被提供。

关键词：分次代数财产标准整数低维

A Hierarchical Scheme for Video-Based Person Re-identification Using Lightweight PCANet and Handcrafted LOMO Features

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Chinese Journal of Electronics 2021年第2期30卷 289-295页

作者： LI Youjiao ZHUO Li LI jiafeng ZHANG Jing Beijing Key Laboratory of Computational Intelligence and Intelligent System Beijing University of Technology Faculty of Information Technology College of Micro-electronics Beijing University of Technology College of Computer Science and Technology Shandong University of Technology

A two-level hierarchical scheme for video-based person re-identification(re-id) is presented, with the aim of learning a pedestrian appearance model through more complete walking cycle extraction. Specifically,given a video with consecutive frames, the objective of the first level is to detect the key frame with lightweight Convolutional neural network(CNN) of PCANet to reflect the summary of the video content. At the second level, on the basis of the detected key frame, the pedestrian walking cycle is extracted from the long video sequence. Moreover,local features of Local maximal occurrence(LOMO) of the walking cycle are extracted to represent the pedestrian’s appearance information. In contrast to the existing walking-cycle-based person re-id approaches, the proposed scheme relaxes the limit on step number for a walking cycle, thus making it flexible and less affected by noisy frames. Experiments are conducted on two benchmark datasets: PRID 2011 and i LIDS-VID. The experimental results demonstrate that our proposed scheme outperforms the six state-of-art video-based re-id methods, and is more robust to the severe video noises and variations in pose,lighting, and camera viewpoint.

关键词： Video-based person re-identification Convolutional neural network Key frame detection Walking cycle extraction

The influence of surface roughness on cloud cavitation flow around hydrofoils

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Acta Mechanica Sinica 2018年第1期34卷 10-21页

作者： jiafeng Hao Mindi Zhang Xu Huang School of Mechanical Engineering Beijing Institute of Technology

The aim of this study is to investigate experimentally the effect of surface roughness on cloud cavitation around Clark-Y hydrofoils. High-speed video and particle image velocimetry(PIV) were used to obtain cavitation patterns images(Prog. Aerosp. Sci. 37: 551–581, 2001), as well as velocity and vorticity fields. Results are presented for cloud cavitating conditions around a Clark-Y hydrofoil fixed at angle of attack of α = 8? for moderate Reynolds number of Re = 5.6 × 10~5. The results show that roughness had a great influence on the pattern, velocity and vorticity distribution of cloud cavitation. For cavitating flow around a smooth hydrofoil(A) and a rough hydrofoil(B), cloud cavitation occurred in the form of finger-like cavities and attached subulate cavities, respectively. The period of cloud cavitation around hydrofoil A was shorter than for hydrofoil B.Surface roughness had a great influence on the process of cloud cavitation. The development of cloud cavitation around hydrofoil A consisted of two stages:(1) Attached cavities developed along the surface to the trailing edge;(2) A reentrant jet developed, resulting in shedding and collapse of cluster bubbles or vortex structure. Meanwhile, its development for hydrofoil B included three stages:(1) Attached cavities developed along the surface to the trailing edge, with accumulation and rotation of bubbles at the trailing edge of the hydrofoil affecting the flow field;(2) Development of a reentrant jet resulted in the first shedding of cavities. Interaction and movement of flows from the pressure side and suction side brought liquid water from the pressure side to the suction side of the hydrofoil, finally forming a reentrant jet. The jet kept moving along the surface to the leading edge of the hydrofoil, resulting in large-scale shedding of cloud bubbles. Several vortices appeared and dissipated during the process;(3) Cavities grew and shed again.

关键词： Surface roughness Experiments Cloud cavitation Hydrofoils

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Study on Quantitative Precipitation Estimation by Polarimetric Radar Using Deep Learning

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Advances in Atmospheric Sciences 2024年第6期41卷 1147-1160页

作者： Jiang HUANGFU Zhiqun HU jiafeng ZHENG Lirong WANG Yongjie ZHU State Key Lab of Severe Weather Chinese Academy of Meteorological SciencesBeijing 100081China Meteorological observatory of Jiangxi Province Nanchang 330096China Hebei Meteorological Disaster Prevention and Environmental Meteorological Center Shijiazhuang 050021China School of Atmospheric Sciences Chengdu University of Information TechnologyChengdu 610225China

Accurate radar quantitative precipitation estimation(QPE)plays an essential role in disaster prevention and mitigation.In this paper,two deep learning-based QPE networks including a single-parameter network and a multi-parameter network are designed.Meanwhile,a self-defined loss function(SLF)is proposed during modeling.The dataset includes Shijiazhuang S-band dual polarimetric radar(CINRAD/SAD)data and rain gauge data within the radar’s 100-km detection range during the flood season of 2021 in North China.Considering that the specific propagation phase shift(KDP)has a roughly linear relationship with the precipitation intensity,KDP is set to 0.5°km^(-1 )as a threshold value to divide all the rain data(AR)into a heavy rain(HR)and light rain(LR)dataset.Subsequently,12 deep learning-based QPE models are trained according to the input radar parameters,the precipitation datasets,and whether an SLF was adopted,respectively.The results suggest that the effects of QPE after distinguishing rainfall intensity are better than those without distinguishing,and the effects of using SLF are better than those that used MSE as a loss function.A Z-R relationship and a ZH-KDP-R synthesis method are compared with deep learning-based QPE.The mean relative errors(MRE)of AR models using SLF are improved by 61.90%,51.21%,and 56.34%compared with the Z-R relational method,and by 38.63%,42.55%,and 47.49%compared with the synthesis method.Finally,the models are further evaluated in three precipitation processes,which manifest that the deep learning-based models have significant advantages over the traditional empirical formula methods.

关键词： polarimetric radar quantitative precipitation estimation deep learning single-parameter network multi-parameter network

A reciprocating motion-driven rotation mechanism for the ATP synthase

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Science China(Life Sciences) 2016年第1期59卷 44-48页

作者： jiafeng Liu Xinmiao Fu Zengyi Chang State Key Laboratory of Protein and Plant Gene Research School of Life Sciences Peking University Center for Protein Science Peking University

The ATP synthase(having a typical subunit composition of ?3?3???ab2c8-15) employs an intriguing rotary mechanism for the generation of ATP from ADP and Pi, using energy stored in a transmembrane proton gradient. The conventional rotary model, although being generally accepted, remains difficult to explain certain experimental observations. Here we propose an alternative rotary model for the ATP synthase such that what rotates is the catalytic ?3?3 cylinder rather than the central stalk and the membrane-embedded c-ring. Specifically, the membrane translocation of protons would induce a cycled conformational change in the c-ring, leading to a reciprocating motion of the attached central stalk, which in turn drives the unidirectional rotation of the ?3?3 cylinder. Such a reciprocating motion-driven rotation mechanism is somehow analogous to the working mechanism of a retractable click ballpoint pen. Our new model not only explains the experimental observations that have been difficult to reconcile with the conventional model but also avoids its theoretical illogicality.

关键词：旋转机构往复运动旋转机械驱动 ATP合成酶旋转模型质子梯度实验观察

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