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Parametric Optimization of Wheel Spoke Structure for Drag Reduction of an Ahmed Body

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Computer Modeling in Engineering & Sciences 2024年第4期139卷 955-975页

作者： Huihui Zhai Dongqi jiao Haichao zhou Institute of Electrical and Information Engineering Zhenjiang CollegeZhenjiang212028China School of Automotive and Traffic Engineering Jiangsu UniversityZhenjiang212013China

The wheels have a considerable influence on the aerodynamic properties and can contribute up to 25%of the total drag on modern *** this study,the effect of the wheel spoke structure on the aerodynamic performance of the isolated wheel is ***,the 35°Ahmed body with an optimized spoke structure is used to analyze the flow behavior and the mechanism of drag *** Fluent software is employed for this investigation,with an inlet velocity of 40 m/*** accuracy of the numerical study is validated by comparing it with experimental results obtained from the classical Ahmed *** gain a clearer understanding of the effects of the wheel spoke parameters on the aerodynamics of both the wheel and Ahmedmodel,and five design variables are proposed:the fillet angleα,the inside arc radius R1,the outside radius R2,and the same length of the chord L1 and *** variables characterize the wheel spoke *** Optimal Latin Hypercube designmethod is utilized to conduct the experimental *** on the simulation results of various wheel spoke designs,the Kriging model and the adaptive simulated annealing algorithm is selected to optimize the design *** objective is to achieve the best combination for maximum drag *** is indicated that the optimized spoke structure resulted in amaximum drag reduction of 5.7%and 4.7%for the drag coefficient of the isolated wheel and Ahmed body,*** drag reduction is primarily attributed to changes in the flow state around the wheel,which suppressed separation ***,it influenced the boundary layer thickness around the car body and reduced the turbulent kinetic energy in the wake *** effects collectively contributed to the observed drag reduction.

关键词： Ahmed body wheel spoke design parameter optimization drag reduction numerical simulation

General properties of the spectral form factor in open quantum systems

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Frontiers of physics 2024年第3期19卷 229-237页

作者： Yi-Neng zhou tian-Gang zhou Pengfei Zhang Institute for Advanced Study Tsinghua UniversityBeijing 100084China Department of Physics Fudan UniversityShanghai 200438China

The spectral form factor(SFF)can probe the eigenvalue statistic at different energy scales as its time variable *** closed quantum chaotic systems,the SFF exhibits a universal dip-ramp-plateau behavior,which reflects the spectrum rigidity of the *** this work,we explore the general properties of SFF in open quantum *** find that in open systems the SFF first decays exponentially,followed by a linear increase at some intermediate time scale,and finally decreases to a saturated plateau *** derive general relations between(i)the early-time decay exponent and Lindblad operators;(ii)the long-time plateau value and the number of steady *** also explain the effective field theory perspective of general *** verify our theoretical predictions by numerically simulating the Sachdev−Ye−Kitaev(SYK)model,random matrix theory(RMT),and the Bose−Hubbard model.

关键词： spectral form factor open quantum system quantum chaos

Parametric formation control of multiple nanosatellites for cooperative observation of China Space Station

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Astrodynamics 2024年第1期8卷 77-95页

作者： Hao zhou Bohan jiao Zhaohui Dang Jianping Yuan School of Astronautics Northwestern Polytechnical UniversityXi’an710072China National Key Laboratory of Aerospace Flight Dynamics Northwestern Polytechnical UniversityXi’an710072China

This study proposes a parametric formation control method for the cooperative observation of the China Space Station(CSS)using multiple ***,a simplified geometrical model of the CSS is constructed using fundamental solids,such as the capsule body and ***,the spacecraft formation configuration for the observation mission is characterized by a three-dimensional(3D)Lissajous curve using related design parameters under the full-coverage observation requirements of specific parts,such as the CSS connecting section and collision avoidance ***,a double-layer control law is designed for each nanosatellite,in which the upper layer is a distributed observer for recognizing the target formation configuration parameters,and the lower layer is a trajectory-tracking controller to make the nanosatellite converge to its temporary target position calculated from the upper layer’s *** closed-loop control stability is proven under the condition that the communication network topology of the nanosatellite cluster contains a directed spanning ***,the control method is verified by numerical simulation,where the CSS connecting section is selected as the observation target,and ten small nanosatellites are assumed to perform the cooperative observation *** simulation results demonstrate that the double-layer control law is robust to single-point communication failures and suitable for the accompanying missions of large space objects with multiple nanosatellites.

关键词： China Space Station(CSS) cooperative observation parametric formation 3D Lissajous curve double-layer system

Hollow Ni Mo-based nitride heterojunction with super-hydrophilic/aerophobic surface for efficient urea-assisted hydrogen production

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Journal of Energy Chemistry 2024年第8期95卷 428-439,I0009页

作者： Yuying Fan Ying Gu Dongxu Wang Yanqing jiao Aiping Wu Chungui tian Key Laboratory of Functional Inorganic Material Chemistry Ministry of Education of the People’s Republic of ChinaHeilongjiang UniversityHarbin 150080HeilongjiangChina College of Chemistry Chemical Engineering and Resource UtilizationNortheast Forestry UniversityHarbin 150040HeilongjiangChina

Hydrogen evolution reaction(HER)and urea oxidation reaction(UOR)are key reactions of the watercycling associated catalytic process/*** design of catalysts with a super-hydrophilic/aerophobic structure and optimized electron distribution holds great ***,we have designed a threedimensional(3D)hollow Ni/NiMoN hierarchical structure with arrayed-sheet surface based on a onepot hydrothermal route for efficient urea-assisted HER based on a simple hydrothermal *** Ni/NiMoN catalyst exhibits super-hydrophilic/aerophobic properties with a small droplet contact angle of 6.07°and an underwater bubble contact angle of 155.7°,thus facilitating an escape of bubbles from the *** functional theory calculations and X-ray photoelectron spectroscopy results indicate the optimized electronic structure at the interface of Ni and NiMoN,which can promote the adsorption/desorption of reactants and *** virtues combining with a large specific surface area endow Ni/NiMoN with efficient catalytic activity of low potentials of 25 mV for HER and 1.33 V for UOR at10 mA cm^(-2).The coupled HER and UOR system demonstrates a low cell voltage of 1.42 V at 10 mA cm^(-2),which is approximately 209 mV lower than water electrolysis.

关键词： Hydrogen evolution Transition metal nitrides Hollow heterojunctions Urea electrooxidation Super hydrophilic/aerophobic

Integrated interconnected porous and lamellar structures realized fast ion/electron conductivity in high-performance lithium-sulfur batteries

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Chinese Chemical Letters 2024年第6期35卷 161-167页

作者： Ya Song Mingxia zhou Zhu Chen Huali Nie jiao-Jing Shao Guangmin zhou School of Materials and Metallurgy Guizhou UniversityGuiyang 550025China Medical College of Guizhou University Guiyang 550025China College of Biological Science and Medical Engineering Donghua UniversityShanghai 201620China Shenzhen Geim Graphene Center Tsinghua Shenzhen International Graduate SchoolTsinghua UniversityShenzhen 518055China

The practical application of high-energy-density lithium-sulfur(Li-S)batteries have been highly praised for energy storage devices,while are largely hindered by the“shuttling effect”.Herein,core-shell carbon spheres composed of interlinked porous core and lamellar shell were designed to restrain the polysulfide *** microporous structure with pore size of around 1 nm effectively trap lithium ***,the interconnected porous core shortens the ion transfer distance and the lamellar carbon shell endows the carbon spheres with fast electron conduction,finally facilitating polysulfide conversion ***,the Li-S batteries with the carbon spheres as the interlayer show high discharge specific capacity of 1002 m Ah/g at 2 C with 574 m Ah/g remaining after 600 cycles,and high areal capacity of 5.48 m Ah/cm^(2) with sulfur loading of 4.67 mg/cm^(2) at 0.1 *** corresponding pouch cells also exhibit stable cycling stability with an initial discharge specific capacity of 1082 m Ah/g at 0.1 C.

关键词： Interlayer Shuttle effect Strong adsorption Porous carbon spheres Lithium-sulfur batteries

Properties of Ultra-low Thermal Expansion LAS Transparent Glass-ceramics Prepared by Spodumene

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Journal of Wuhan University of Technology(Materials Science) 2024年第3期39卷 541-550页

作者：何峰何子君 zhou Zhiqiang tian Yingliang ZHAO Zhiyong School of Materials Science and Engineering Beijing University of TechnologyBeijing 100124China Department of Functional Material Research Central Iron and Steel Research InstituteBeijing 100081China School of Materials Science and Engineering Wuhan University of TechnologyWuhan 430070China National Engineering Research Center of FPD Glass Technology Xianyang 712000China

The glass-ceramics were prepared with the spodumene mineral as the main raw material,and the effects of ZrO_(2)replacing TiO_(2)on the samples were systematically *** results show that the substitution of ZrO_(2)for TiO_(2)is not conductive to precipitate𝛽β-quartz solid solution phase,but can improve the transparency and flexural strength of *** the glass-ceramic with the highest visible light transmittance(87%)and flexural strength(231.80 MPa)exhibits an ultra-low thermal expansion of-0.028×10^(-7)K^(-1)in the region of 30-700℃.

关键词： ultra-low thermal expansion LAS transparent glass-ceramics substitution of ZrO_(2)for TiO_(2) spodumene mineral

Electrochemical oxidation of perfluoroalkyl and polyfluoroalkyl substances: Mechanisms, implications, and challenges

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Science China Technological Sciences 2024年第10期67卷 2972-2990页

作者： zhou XuDong ZHONG YaShi tian XiaoChun ZHAO Feng CAS Key Laboratory of Urban Pollutant Conversion Institute of Urban EnvironmentChinese Academy of Sciences University of Chinese Academy of Sciences College of Environment & Safety Engineering Fuzhou University

Perfluoroalkyl and polyfluoroalkyl substances(PFASs) have recently gained considerable attention due to their potential risks to human health and ecosystems. The response to these concerns has led to regulations and bans on legacy PFASs, such as perfluorooctanoic acid and perfluorooctane sulfonic acid. Thus, fluoride production has shifted toward short-chain PFASs and emerging fluorinated alternatives. Several technologies are available for PFAS degradation, among which electrochemical oxidation(EO) is a promising method to mineralize legacy PFASs and other emerging fluorinated alternatives in water *** review provides an overview of the recent advancements in EO, comprehensively elucidating PFAS degradation mechanisms at the anode and exploring key factors that influence PFAS removal efficiency, such as anode materials as well as reactor designs and configurations. Moreover, the review elucidates the impact of operating conditions and parameters, including current density, electrolytes, pH, initial PFAS concentrations, and other coexisting pollutants, on the EO process. Finally, the constraints in the EO process are discussed when considering practical implementations, including undesired by-product generation, incomplete mineralization resulting in the accumulation of short-chain PFASs, and low PFAS concentrations in the natural environment leading to mass transfer limitations and low defluorination efficiency. Consequently, this review provides a perspective on potential solutions integrating the pre-concentration steps and EO process for effective PFAS remediation.

关键词： electrochemical oxidation legacy PFASs fluorinated alternatives degradation mechanisms influencing factors

Data-driven rational design of single-atom materials for hydrogen evolution and sensing

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Nano Research 2024年第4期17卷 3352-3358页

作者： Lei zhou Pengfei tian Bowei Zhang Fu-Zhen Xuan Shanghai Key Laboratory of Intelligent Sensing and Detection Technology East China University of Science and TechnologyShanghai 200237China School of Mechanical and Power Engineering East China University of Science and TechnologyShanghai 200237China Key Laboratory of Pressure Systems and Safety of Ministry of Education East China University of Science and TechnologyShanghai 200237China

Herein we proposed a data-driven high-throughput principle to screen high-performance single-atom materials for hydrogen evolution reaction(HER)and hydrogen sensing by combing the theoretical computations and a topology-based multi-scale convolution kernel machine learning *** the rational training by 25 groups of data and prediction of all 168 groups of single-atom materials for HER and sensing,respectively,a high prediction accuracy(>0.931 R^(2) score)was achieved by our *** show that the promising HER catalysts include Pt atoms in C_(4) and Sc atoms in C_(1)N_(3) coordination ***,Y atoms in C_(4) coordination environment and Cd atoms in C_(2)N_(2)-ortho coordination environment were predicted with great potential as hydrogen sensing *** method provides a way to accelerate the discovery of innovative materials by avoiding the time-consuming empirical principles in experiments.

关键词： machine learning single-atom materials sensing hydrogen evolution

Analysis on unit maximum capacity of orthogonal multiple watermarking for multimedia signals in B5G wireless communications

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Digital Communications and Networks 2024年第1期10卷 38-44页

作者： Mianjie Li Senfeng Lai jiao Wang Zhihong tian Nadra Guizani Xiaojiang Du Chun Shan School of Electronics and Information Guangdong Polytechnic Normal UniversityGuangzhou510665China Cyberspace Institute of Advanced Technology Guangzhou UniversityGuangzhou510006China Schoolof Electrical Engineering and Computer Science Washington State UniversityPullmanWA99164USA Department of Computer and Information Science Temple UniversityPhiladelphiaPA19122USA

Beyond-5G(B5G)aims to meet the growing demands of mobile traffic and expand the communication *** that intelligent applications to B5G wireless communications will involve security issues regarding user data and operational data,this paper analyzes the maximum capacity of the multi-watermarking method for multimedia signal hiding as a means of alleviating the information security problem of *** multiwatermarking process employs spread transform dither *** the watermarking procedure,Gram-Schmidt orthogonalization is used to obtain the multiple spreading ***,multiple watermarks can be simultaneously embedded into the same position of a multimedia ***,the multiple watermarks can be extracted without affecting one another during the extraction *** analyze the effect of the size of the spreading vector on the unit maximum capacity,and consequently derive the theoretical relationship between the size of the spreading vector and the unit maximum capacity.A number of experiments are conducted to determine the optimal parameter values for maximum robustness on the premise of high capacity and good imperceptibility.

关键词： B5G Multimedia information security Spread transform dither modulation Spreading vector measurement Unit maximum capacity