检索结果-南通市图书馆

Periodicity and Stability in Periodic n-Species Lotka-Volterra Competition System with Feedback Controls and Deviating Arguments

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Mathematica Sinica,English Series 2003年第4期19卷 801-822页

作者： MengFAN kewang PatriciaJ.Y.WONG RaviP.AGARWAL DepartmentofMathematics KeyLaboratoryforVegetationEcologyoftheEducationMinistryofP.R.China NortheastNormalUniversity Changchun130024P.R.China SchoolofElectricalandElectronicEngineering NanyangTechnologicalUniversitySingapore639798Singapore DepartmentofMathematicalSciences FloridaInstituteofTechnologyMelbourneFlorida32901-6975USA

By using the method of coincidence degree and Lyapunov functional, a set ofeasily applicable criteria are established for the global existence and global asymptotic stabilityof strictly positive (componentwise) periodic solution of a periodic n-species Lotka-Volterracompetition system with feedback controls and several deviating arguments. The problem considered inthis paper is in many aspects more general and incorporate as special cases various problems whichhave been studied extensively in the literature. Moreover, our new criteria, which improve andgeneralize some well known results, can be easily checked.

关键词： strictly positive periodic solutions globally asymptotic stability Lotka-Volterra competition system feedback controls deviating arguments coincidence degree Lyapunov functional

Friction and wear properties of Cu-based self-lubricating composites in air and vacuum conditions

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2012年第5期25卷 391-400页

作者： Shiyin HUANG Yi FENG kewang DING Gang QIAN Hongjuan LIU Yang WANG Department of Material Science and Engineering Hefei University of Technology Hefei 230009 China

Cu-based self-lubricating materials containing two different solid lubricants （graphite and MoSs） were fabricated by P/M hot pressing techniques. Physical and mechan- ical properties of the samples were examined. The effects of graphite and MoSs contents on friction coefficient and wear rate were investigated by a ring-on-disc wear machine in air and vacuum conditions, respectively. Tribo-films formed on the worn surfaces were characterized by scanning electron microscopy （SEM） and X-ray photo- electron spectroscopy （XPS）. The results indicated that density, hardness and bending strength all increased with the increasing content of MoS2, while the relative density was opposite. Sample B containing 15 vol. pct graphite and 15 vol. pct MoS2 pos- sessed superior tribological properties both in air and vacuum conditions. However, the tribo-films formed on the worn surfaces of the sample B were greatly discrepant in composition at different testing conditions. In air, the volume ratio of MoS2 and graphite in the tribo-films is 0.31：1 whereas the ratio in vacuum is 1.07：1.

关键词： Self-lubricating composite Air and vacuum conditions Frictioncoefficient Wear rate Synergistic effect

Asplenium sanshuiense sp. nov.:the Lowest Latitude Fossil Record of the Genus

在线全文

学校读者我要写书评

暂无评论

Acta Geologica Sinica(English Edition) 2017年第4期91卷 1179-1189页

作者： XU kewang LIAO Wenbo JIN Jianhua LIU Xiaoyan State Key Laboratory of Biocontrol Guangdong Provincial Key Laboratory of Plant Resourcesand School of Life SciencesSun Yat-sen University State Key Laboratory of Palaeobiology and Stratigraphy(Nanjing Institute of Geology and Palaeontology CAS)

Extant Asplenium is one of the most widespread fern groups and occurs in the temperate and tropical regions. However, the fossil records of this genus are poorly documented, especially in the low latitudes. Here, a new species, Asplenium sanshuiense sp. nov. is described from the early Eocene of Sanshui Basin, Guangdong Province, South China. This is the lowest modern latitude fossil record of Asplenium and the first fossil assignment of A. section Darea （Jussieu） Bak., as well as the first fossil record of Asplenium reported from South China. This new species shows that Asplenium had already spread into South China by the early Eocene and the section Darea （Jussieu） Bak. was identifiable within the genus Asplenium during that time. This new species, combined with previous fossil spore-pollen records indicates a warm and humid climate in the Sanshui Basin of the early Eocene.

关键词： Asplenium early Eocene Phytogeographical implications Sanshui Basin

Effect of Electrical Current on the Tribological Behavior of the Cu-WS_2-G Composites in Air and Vacuum

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Mechanical Engineering 2013年第2期26卷 384-392页

作者： QIAN Gang FENG Yi LI Bin HUANG Shiyin LIU Hongjuan DING kewang School of Materials Science and Engineering Hefei University of Technology

As the traditional graphite-based composites cannot meet the requirement of rapid developing modern industry, novel sliding electrical contact materials with high self-lubricating performance in multiple environments are eagerly required. Herein a copper-based composite with WS2 and graphite as solid lubricant are fabricated by powder metallurgy hot-pressed method. The friction and wear behaviors of the composites with and without current are investigated under the condition with sliding velocity of 10 m/s and normal load of 2.5N/cm 2 in both air and vacuum. Morphologies of the worn surfaces are observed by optical microscope and compositions of the lubricating films are analyzed by XPS. Surface profile curves and roughness of the worn surfaces are obtained by 2205 surface profiler. The results of wear tests show that the friction coefficient and wear volume loss of the composites with current are greater than that without current in both air and vacuum due to the adverse effects of electrical current which damaged the lubricating film partially and roughed the worn surfaces. XPS results demonstrate that the lubricating film formed in air is composed of oxides of Cu, WS2 , elemental S and graphite, while the lubricating film formed in vacuum is composed of Cu, WS2 and graphite. Because of the synergetic lubricating action of oxides of Cu, WS2 and graphite, the composites show low friction coefficient and wear volume loss in air condition. Owing to the fact that graphite loses its lubricity which makes WS2 become the only lubricant, severe adhesive and abrasive wear occur and result in a high value of wear rate in vacuum condition. The formation of the lubricating film on the contact interface between the brush and ring is one of the factors which can greatly affect the wear performance of the brushes. The low contact voltage drop of the composites in vacuum condition is attributed to the high content of Cu in the surface film. This study fabricated a kind of new sli

关键词： Cu-WS2-G composites electrical current air and vacuum environments friction and wear contact voltage drop

Relaxor-like dielectric behavior and its effect on energy storage performance in P(TFE-HFP-VDF) terpolymers

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2020年第2期63卷 150-153页

作者： kewang Yi Jie Liu Yang Zhou XinPing Hu ShiHai Zhang BaoJin Chu CAS Key Laboratory of Materials for Energy Conversion Department of Materials Science and EngineeringUniversity of Science and Technology of ChinaHefei 230026China PolyK Technologies LLCState CollegePennsylvania 16801USA

Capacitors are critical components in many advanced electronic and electrical systems,such as pulse power systems,due to their fast charging-discharging speed and high power density[1-4].The ever-increasing demand for compact energy storage devices requires the dielectrics,which are the energy storage materials in capacitors,to have a higher energy density and low dielectric loss[2,3].Furthermore,a stable high-temperature performance is another important parameter to be considered for some applications in which high-temperature conditions are present,such as hybrid vehicles[4-7].

关键词： dielectric energy performance

Advanced heterostructure of Pd nanosheets@Pt nanoparticles boosts methanol electrooxidation

在线全文

学校读者我要写书评

暂无评论

Journal of Energy Chemistry 2023年第10期85卷 430-438,I0012页

作者： Jie Li Cheng Wang Yuefan Zhang Shinichi Hata kewang Zhang Changqing Ye Yukihide Shiraishi Yukou Du College of Chemistry Chemical Engineering and Materials ScienceSoochow UniversitySuzhou 215123JiangsuChina Jiangsu Key Laboratory for Environment Functional Materials School of Materials Science and EngineeringSuzhou University of Science and TechnologySuzhou 215009JiangsuChina Department of Applied Chemistry Faculty of EngineeringSanyo-Onoda City UniversitySanyo-OnodaYamaguchi 756-0884Japan School of Optical and Electronic Information Suzhou City UniversitySuzhou 215104JiangsuChina

Heterostructures have emerged as elaborate structures to improve catalytic activity owing to their combined surface and distinct inverse ***,fabricating advanced nanocatalysts with facetdependent interface remains an unexploited and promising ***,we render the controlled growth of Pt nanoparticles(NPs)on Pd nanosheets(NSs)by regulating the reduction kinetics of Pt^(2+)with ***,the fast reduction kinetic makes the Pt NPs uniformly deposited on the Pd NSs(U-Pd@Pt HS),while the slow reduction kinetic leads to the preferential growth of Pt NPs on the edge of the Pd NSs(E-Pd@Pt HS).Density functional theory calculations demonstrate that Pd(111)-Pt interface in U-Pd@Pt HS induces the electron-deficient status of Pd substrates,triggering the d-band center downshift and amplifying the Pd-Pt intermetallic *** synergy between the electronic effect and interfacial effect facilitates the removal of poisonous intermediates on U-Pd@Pt *** virtue of the Pd NSs@Pt NPs interface,the heterostructure achieves exceptional methanol oxidation reaction activity as well as improved *** study innovatively proposes heterostructure engineering with facetdependent interfacial modulation,offering instructive guidelines for the rational design of versatile heterocatalysts.

关键词： Heterostructure engineering Facet-dependent interfacial modulation Methanol oxidation reaction

Tofukasu-derived biochar with interconnected and hierarchical pores for high efficient removal of Cr (Ⅵ)

在线全文

学校读者我要写书评

暂无评论

Biochar 2023年第1期5卷 1189-1201页

作者： Liang Fang Wei Yang Jianhua Hou kewang Zheng Asif Hussain Yongcai Zhang Zhenhua Hou Xiaozhi Wang School of Environmental Science and Engineering Yangzhou UniversityYangzhou 225000People’s Republic of China Beijing System Design Institute of Electro-Mechanic Engineering Beijing 100005People’s Republic of China Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization Nanjing 210095People’s Republic of China School of Chemistry and Materials Science Hubei Engineering UniversityXiaoganPeople’s Republic of China Jiangxi Xinda Hangke New Materials Technology Co. LtdNanchang 330096People’s Republic of China

Herein,we report the synthesis of interconnected hierarchical pore biochar(HTB)via an ice-templating strategy using bio-waste(tofukasu).The abundance of N-and O-containing functional groups in tofukasu makes it easy to form hydrogen bonds with water molecules and water clusters,resulting in nano-micro structures like ice clusters and snow crystals during freezing *** importantly,tofukasu will be squeezed by micron-scale snow crystals to form coiled sheet-like structures,and its surface and interior will be affected by needle-like ice nanocrystals from several nanometers to tens of nanometers to form transverse groove needles and *** ice crystals are then removed by sublimation with tofukasu,leaving the interconnected pore structure ***,the ice template synthesis strategy endowed the interconnected hierarchical pore structure of HTB with a large specific surface area(SBET,733 m^(2)⋅g^(−1))and hierarchical porosity(30.30%for mesopores/total pore volume ratio),which is significantly higher than the normal dry treated tofukasu biochar(TB),which had a SBET of 436 m^(2)⋅g^(−1) and contained 1.53%*** addition,the sheet-like structure with interconnected pores of HTB favors high exposure of active sites(N-and O-containing functional groups),and a fast electron transport *** a result,HTB had an excellent adsorption capacity of 159.65 mg⋅g^(−1),which is 4.7 times that of typical block biochar of TB(33.89 mg⋅g^(−1))according to Langmuir *** characterization,FTIR and XPS analysis showed that the mechanism of Cr(Ⅵ)removal by HTB included electrostatic attraction,pore filling,reduction and surface complexation.

关键词： Chromium adsorption Tofukasu Ice template Biochar Hierarchical pore structure Mesopores

Polymer passivation of defects in inorganic perovskite solar cells

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Optoelectronics Letters 2022年第6期18卷 338-342页

作者： ZHANG Meng ZHANG Fanghui SHI kewang ZHANG Wenxi HUANG Jin QIU Huimin School of Electrical and Control Engineering Shaanxi University of Science&TechnologyXi'an 710021China School of Electronic Information and Artificial Intelligence Shaanxi University of Science and TechnologyXi'an 710021China

Inorganic perovskite solar cells(IPSCs)have attained attention due to their excellent thermal and phase *** this work,we demonstrate a novel approach for fabricating IPSCs,using the strategies of interface passivation and anti-solvent before spin-coating ***(methyl methacrylate)(PMMA)and chlorobenzene(CB)are used as passivator and anti-solvent,*** CB improves the perovskite crystal ***,PMMA passivates the defects between poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)and perovskite layer,thus increasing the short-circuit ***,we find that PMMA benefits the grain boundaries(GBs)of perovskite,which makes it more humidity-resistant,increasing the stability of perovskite ***,PMMA mitigates interfacial charge losses,and the devices based on CsPbI_(3-x)Br_(x)passivated by PMMA exhibit the power conversion efficiency(PCE)much higher than those based on pure CsPbI_(3-x)Br_(x).

关键词： perovskite humidity interfacial

The first mitogenome of Lauraceae(Cinnamomum chekiangense)

在线全文

学校读者我要写书评

暂无评论

Plant Diversity 2024年第1期46卷 144-148页

作者： Changwei Bi Ning Sun Fuchuan Han kewang Xu Yong Yang David K.Ferguson State Key Laboratory of Tree Genetics and Breeding Co-Innovation Center for Sustainable Forestry in Southern ChinaKey Laboratory of Tree Genetics and Biotechnology of Educational Department of ChinaKey Laboratory of Tree Genetics and Silvicultural Sciences of Jiangsu ProvinceNanjing Forestry UniversityNanjing 210037China College of Information Science and Technology Nanjing Forestry UniversityNanjing 210037China Research Institute of Subtropical Forestry Chinese Academy of ForestryHangzhou 311400China Co-Innovation Center for Sustainable Forestry in Southern China College of Life SciencesNanjing Forestry UniversityNanjing 210037China Department of Paleontology University of ViennaViennaAustria

There are three distinct genetic systems in higher plants,the dominant nuclear genome and the semi-autonomous organelle genomes(plastids and mitochondria).In contrast to the conserved plastid genome(plastome),the plant mitochondrial genome(mitogenome)is characterized by an intriguing“evolutionary paradox”distinguished by a remarkably low mutation rate but with a significantly high rearrangement rate(Palmer and Herbon,1988;Lai et al.,2022).

关键词： autonomous distinguished Palmer