检索结果-南通市图书馆

Review of deployment technology for tethered satellite systems

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica sinica 2018年第4期34卷 754-768页

作者： B.s.Yu H.Wen D.P.Jin state Key Laboratory of Mechanics and Control of Mechanical structures Nanjing University of Aeronautics and Astronautics

Tethered satellite systems（Tsss） have attracted significant attention due to their potential and valuable applications for scientific research. With the development of various launched on-orbit missions, the deployment of tethers is considered a crucial technology for operation of a Tss. Both past orbiting experiments and numerical results have shown that oscillations of the deployed tether due to the Coriolis force and environmental perturbations are inevitable and that the impact between the space tether and end-body at the end of the deployment process leads to complicated nonlinear phenomena. Hence, a set of suitable control methods plays a fundamental role in tether deployment. This review article summarizes previous work on aspects of the dynamics, control, and ground-based experiments of tether deployment. The relevant basic principles, analytical expressions, simulation cases, and experimental results are presented as well.

关键词： Tethered satellite Deployment Dynamics Control Experiment

Asymptotic and numerical study of a surface breaking crack subject to a transient thermal loading

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica sinica 2006年第1期22卷 22-27页

作者： A.B. Movchan I.s. Jones ljmu.ac.uk Department of Mathematical sciencesUniversity of Liverpoo UK L69 3BX school of EngineeringJames Parsons BuildingJohn Moores UniversityByrom st.Liverpool UK. L3 3AF E-mail: i.s.jones

An asymptotic algorithm is applied to the problem of a finite, thermo-elastic solid containing a surface breaking crack, when the exterior surface is subjected to oscillatory thermal loading. This algorithm involves the study of a model problem. An analytical and numerical study of this model problem of a thermo-elastic half space containing a surface breaking crack and subjected to oscillatory thermal loading is presented. The crack surface is traction free. In particular, the amplitude of the stress intensity factor at the crack vertex is found as a function of the crack depth and the frequency of thermal oscillation.

关键词： Thermo-elasticity surface breaking crack Wiener-Hopf solution Weight function method

Creep Behavior and Microstructure Evolution of sand–Cast Mg–4Y–2.3Nd–1Gd–0.6Zr Alloy Crept at 523–573 K

在线全文

学校读者我要写书评

暂无评论

Journal of Materials science & Technology 2017年第1期33卷 79-89页

作者： Y.H.Kang H.Yan R.s.Chen The Group of Magnesium Alloys and Their Applications Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China University of the Chinese Academy of sciences Beijing 100049China

High temperature tensile-creep behavior of Mg-4Y-2.3Nd-IGd-O.6Zr （wt%, WE43（T6）） alloy at 523- 573 K was investigated. The creep stress exponent is equal to 4.6, suggesting the underlying dislocation creep mechanism. The activation energy is （199 _＋ 23） kJ/mol, which is higher than that for self- diffusion in Mg and is believed to be associated with precipitates coarsening or cross slip. The creep mechanism is further suggested to be dislocation climb at 523 K, while a cross slip at 573 K is possible. The metastable 13＇ and ~]1 phases in the WE43（T6） alloy were relatively thermal stable at 523 K and could be effective to hinder the dislocation climb, which contributed to its excellent creep resistance. However, at 573 K it readily transforms into equilibrium/3e phase and coarsens within two hours, thereby causing a decrease of creep resistance. In addition, precipitate free zones approximately normal to applied stress direction （directional PFZs） developed during the creep deformation, especially at 573 K. Those zones became preferential sites to nucleate, extend and connect microcracks and cavities, which lead to the intergranular creep fracture. Improving the thermal stability of precipitates or introducing thermally stable fine plate-shaped precipitates on the basal planes of Mg matrix could enhance the high temperature creep resistance.

关键词： WE43 alloy Creep PFZs Precipitate Fracture

Conversion of an atomic to a molecular argon ion and low pressure argon relaxation

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2016年第1期25卷 697-705页

作者： M N stankov A P Jovanovie V Lj Markovic s N stamenkovic Department of Physics Faculty of Sciences and MathematicsUniversity of Ni Viegradska 33Ni 18001Serbia

The dominant process in relaxation of DC glow discharge between two plane parallel electrodes in argon at pressure 200 Pa is analyzed by measuring the breakdown time delay and by analytical and numerical models. By using the approx- imate analytical model it is found that the relaxation in a range from 20 to 60 ms in afterglow is dominated by Ar＋ ions, produced by atomic-to-molecular conversion of Ar＋ ions in the first several milliseconds after the cessation of the discharge. This conversion is confirmed by the presence of double-Gaussian distribution for the formative time delay, as well as con- version maxima in a set of memory curves measured in different conditions. Finally, the numerical one-dimensional （1D） model for determining the number densities of dominant particles in stationary DC glow discharge and two-dimensional （2D） model for the relaxation are used to confirm the previous assumptions and to determine the corresponding collision and transport coefficients of dominant species and processes.

关键词： argon discharge afterglow relaxation fluid model plasma reactions

synthesis of ZnO Nanoparticles onto sepiolite Needles and Determination of Their sensitivity toward Humidity, NO_2 and H_2

在线全文

学校读者我要写书评

暂无评论

Journal of Materials science & Technology 2016年第6期32卷 573-582页

作者： M.Hassan Ahmed s.Afify J.M.Tulliani Department of Applied science and Technology Politecnico di Torino

This work investigated the sensitivity toward humidity, NO2 and H2 of ZnO modified sepiolite （si12Mg8O30（OH）4.（H2O）4.8H2O）. To this aim, sepiolite powder was first modified by leaching magnesium ions in HCI then by precipitating nano-sized Zn-based compounds under basic conditions. A subse- quent thermal treatment at 550 ℃ for 1 h was performed. The powders were characterized by X-ray diffraction （XRD）, specific surface area measurements, thermogravimetric and differential thermal anal- ysis and field emission scanning electron microscopy, as well as high resolution transmission electron microscopy. The XRD patterns showed that all leached heat treated samples were made of anhydrous sepiolite and of ZnO. sensors were then obtained by screen printing these materials onto commercial alumina substrates with Pt electrodes. All the investigated compositions were capable of detecting NO2 down to ppm level and 20 ppm H2, at an optimal working temperature of 300°C. These detection limits are in line with the current best results reported in literature.

关键词： Clay minerals Gas sensor sensitivity Hydrogen sensor Nitrogen Oxide

A comparative study on polypropylene separators coated with different inorganic materials for lithium-ion batteries

在线全文

学校读者我要写书评

暂无评论

Frontiers of Chemical science and Engineering 2017年第3期11卷 346-352页

作者： Linghui Yu Jiansong Miao Yi Jin Jerry Y.s. Lin school for Engineering of Matter Transport and Energy Arizona State University Tempe AZ 85287 USA state Key Laboratory of Operation and Control of Renewable Energy & storage systems China Electric Power Research Institute Beijing 100192 China

Coating commercial porous polyolefin separators with inorganic materials can improve the thermal stability of the polyolefin separators and hence improve the safety of lithium-ion batteries. several different inorganic materials have been studied for the coating. However, there lacks a study on how different the properties of separators, in inorganic materials affect terms of thermal stability and cell performance. Herein, we present such a study on coating a commercial polypropylene separator with four inorganic materials, i.e., Al2O3, siO2, ZrO2 and zeolite. All inorganic coatings have improved thermal stability of the separators although with differences. The coating layers add 28%-45% of electrical resistance compared with the pure polypropylene separator, but all the cells prepared with the coated polypropylene separators have the same electrical chemical performance as the uncoated separator in terms of rate capability and capacities at different temperatures.

关键词： lithium-ion battery battery safety composite separator porosity tortuosity

Moisture effect on the combustion of a single copper concentrate particle in a flash smelting furnace

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

International Journal of Minerals,Metallurgy and Materials 2014年第3期21卷 251-258页

作者： E.Hassan Zaim s.H.Mansouri A.Arab solghar Department of Mechanical Engineering School of Engineering Shahid Bahonar University Department of Mechanical Engineering School of Engineering Vali-e-Asr University

A mathematical model has been presented to study the combustion of a single copper concentrate particle with high moisture content. By using the presented model, the effect of particle moisture content on particle temperature, sulfur oxidation, and combustion heat generation has been evaluated. The mineralogical composition of the commonly used concentrate at Khatoonabad flash smelting furnace has been used in this study. It was found that the particle moisture content is removed in the sub-second time range and thus the moisture has marginal impact on the variation of particle temperature and on the reaction rate when the gas temperature is assumed to be constant in the reaction shaft. When a concentrate with high moisture content is charged, the particle size enlargement due to the agglomeration of concentrate particles causes an abrupt fall in the particle reaction rate.

关键词： flash smelting furnaces copper smelting moisture combustion

Investigation on the dissolution of η phase in a cast Ni-based superalloy

在线全文

学校读者我要写书评

暂无评论

International Journal of Minerals,Metallurgy and Materials 2013年第1期20卷 42-48页

作者： M.R. Jahangiri H. Arabi s.M.A. Boutorabi school of Metallurgy and Materials Engineering Iran University of Science and Technology Metallurgy Department Niroo Research Institute Center of Excellence for Advanced Materials & Processing Iran University of Science and Technology

The dissolution behavior of rI phase has been investigated in a cast Ni-based superalloy. The results showed that the platelets and blocks of η phase were formed within the interdendritic regions of the microstructure. Applying standard solution annealing at 1150-1160℃ for a period of 4 h did not result in the complete dissolution of η phase. For the complete dissolution of η phase without residual incipient melting, a 2-step solution annealing has been recommended. After dissolution at high tem- peratures, the TI phase transforms to two MC-type carbides： one is enriched in Ti, Nb, and Ta, and the other is of （Zr,Ti）C type.

关键词： superalloys nickel alloys phase transitions dissolution heat treatment carbides

Cattaneo-Christov heat and mass flux model for 3D hydrodynamic flow of chemically reactive Maxwell liquid

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and Mechanics(English Edition) 2017年第10期38卷 1347-1356页

作者： s.A.sHEHZAD T.HAYAT A.ALsAEDI M.A.MERAJ Department of Mathematics COMSATS Institute of Information Technology Department of Mathematics Quaid-i-Azam University Nonlinear Analysis and Applied Mathematics (NAAM) Research Group Faculty of ScienceKing Abdulaziz University

This research focuses on the Cattaneo-Christov theory of heat and mass flux for a three-dimensional Maxwell liquid towards a moving surface. An incompressible laminar flow with variable thermal conductivity is considered. The flow generation is due to the bidirectional stretching of sheet. The combined phenomenon of heat and mass transport is accounted. The Cattaneo-Christov model of heat and mass diffusion is used to develop the expressions of energy and mass species. The first-order chemical reaction term in the mass species equation is considered. The boundary layer assumptions lead to the governing mathematical model. The homotopic simulation is adopted to visualize the results of the dimensionless flow equations. The graphs of velocities, temperature, and concentration show the effects of different arising parameters. A numerical benchmark is presented to visualize the convergent values of the computed results. The results show that the concentration and temperature fields are decayed for the Cattaneo^Christov theory of heat and mass diffusion.

关键词： Cattaneo-Christov theory chemical reactive flow temperature-dependentconductivity Maxwell liquid