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On similitude law of sub-systems

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Earthquake Engineering and Engineering Vibration 2006年第1期5卷 133-142页

作者： Zach liang George c.Lee Department of civil Structural and Environmental Engineering University at BuffaloState University of New YorkBuffaloNew YorkUSA Multidisciplinary center for Earthquake Engineering Research University at BuffaloState University of New YorkBuffaloNew YorkUSA

Based on Buckingham＇s π-Theorem, dimensional analysis has achieved considerable success over the past near-century. Model testing has long been a powerful tool in both scientific studies and engineering applications. However, the prototype objects are becoming more and more complicated nowadays, and many of the prototype systems can contain several sub-systems. The conventional theories on model-prototype similarity and dimensional analysis have only limited application since the π-Theorem itself does not distinguish between the original system and subsystems. This is particularly true in the field of structural dynamics, where the structure is often modeled as a multi-degree-of-freedom system. In this paper, we attempt to show that, if a system can be decoupled into several nontrivial subsystems, then, in each subsystem, the number of π-terms will be reduced and therefore simplify the model testing. On the other hand, if a system cannot be decoupled into subsystems, then using model testing with reduced π-term analysis, both experimentally and theoretically, may introduce severe errors.

关键词： similitude law Buckingham's π-theorem model testing sub-systems

Multiple sclerosis is at a checkpoint: advancing the program

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Neural Regeneration Research 2025年第3期20卷 811-812页

作者： Brandon c.Smith Jessica L.Williams Department of Neurosciences Lerner Research InstituteCleveland ClinicClevelandOHUSA Department of Biological Geologicaland Environmental SciencesCleveland State UniversityClevelandOHUSA

Multiple sclerosis(MS) is a chronic inflammatory and demyelinating disease of the central nervous system(cNS). Patients with MS experience sensory and motor function loss due to myelin and/or axon damage perpetuated b... 详细信息

关键词： Hauser sclerosis damage

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教学的文化实践属性及三个基本认识向度

新疆师范大学学报（哲学社会科学版） 2025年第2期46卷 137-143页

作者：程良宏王芸新疆师范大学教育科学学院新疆高等教育发展研究中心新疆乌鲁木齐830017

教学不仅是知识传递行为,而且是具有文化交往和文化生产属性的实践活动。文本认为,从教学目的、教学主体和教学内容入手探析教学在知识传递传承背后的文化实践特质,是理解教学具有文化交往和文化生产属性的三个基本认识向度。因此,要深... 详细信息

教学不仅是知识传递行为,而且是具有文化交往和文化生产属性的实践活动。文本认为,从教学目的、教学主体和教学内容入手探析教学在知识传递传承背后的文化实践特质,是理解教学具有文化交往和文化生产属性的三个基本认识向度。因此,要深入体认教学作为一种特殊的文化交往和生产实践形态,明晰以文化人、以文育人的导引和践行为目的指引,以教师与学生为文化交往和文化生产的实践主体,以教学过程中对教材与师生文化的理解再造为文化实践的基本内容。

关键词：教学实践教学的文化属性文化生产

Theoretical analysis of influencing factors on resistance in the process of gas migration in coal seams

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International Journal of Mining Science and Technology 2017年第2期27卷 315-319页

作者： Wang Kai Liu ang Zhou Aitao School of Resource and Safety Engineering China University of Mining and Technology State Key Laboratory of coal Resource and Mine Safety School of Resources and Safety Engineering

Inspired by previous resistance models for porous media, a resistance expression of gas migration within coal seams based on the ideal matchstick geometry, combined with the Darcy equation and the modified Poiseuille equation is proposed. The resistance to gas migration is generally dynamic because of the variations in adsorption swelling and matrix shrinkage. Due to the limitations of experimental conditions,only a theoretical expression of resistance to gas migration in coal is deduced, and the impacts of tortuosity, effective stress and pore pressure on the resistance are then considered. To validate the proposed expression, previous data from other researchers are adopted for the history matching exercise, and the agreement between the two is good.

关键词： Porous media Gas Resistance Tortuosity Effective stress Pore pressure

Separate control of High Frequency Electro-hydraulic Vibration Exciter

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chinese Journal of Mechanical Engineering 2011年第2期24卷 293-302页

作者： JIA Wen＇ang RUAN Jian REN Yan The Key Laboratory of Mechanical Manufacture and Automation of Ministry of Education Zhejiang University of Technology Hangzhou 310032 China

The working frequency of the conventional electro-hydraulic vibration exciters,which consist of a servo valve and a hydraulic cylinder,is generally restricted within a narrow range due to limited frequency response capability of the servo valve *** counteract such restriction,a novel scheme for an electro-hydraulic vibrator,controlled by a two-dimensional valve（2D valve） and a bias valve in parallel,is therefore *** frequency,amplitude and offset are independently controlled by rotary speed,axial sliding of the spool of the 2D valve and axial sliding of the spool of the bias *** principle of separate control was presented and the regulation approach of frequency,amplitude and offset was discussed.A mathematical model of the hydraulic power mechanism for the proposed vibration exciter was established to investigate the relationship between the amplitude and the axial sliding of the 2D valve＇ spool,as well as that between the offset and the axial sliding of the bias valve＇s spool at various *** experimental system was built to validate the theoretical *** is verified that the 2D exciter is capable of working smoothly in a frequency range of 5- 200 *** its frequency,amplitude and offset can be controlled respectively by either closed loop or open loop *** is a linear relationship between the output amplitude and the spool axial opening of the 2D valve until a point when the flow rate becomes saturate and the amplitude remains *** offset displacement of the cylinder＇s piston is linearly proportional to the axial displacement of the spool of the bias valve,when the valve opening is less than 25%.Thereafter,the slop of the offset curve decreases and tends to *** proposed electro-hydraulic vibration controlled by the 2D valve not only facilitates the realization of high-frequency electro-hydraulic vibration,the high-accuracy of vibration can also be achieved by means of independent controls to the freque

关键词： control valves electro-hydraulic system vibration exciter dynamics characteristics

Understanding yields in alley cropping maize (Zea mays L.) and cassia siamea Lam. under semi-arid conditions in Machakos, Eastern Kenya

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Journal of Environmental Sciences 2001年第3期13卷 291-298页

作者： DNMungai cJStigter cLcoulson JKNg’ang’A GWSNetondo GOUmaya TTMI Project University of NairobiP.O.Box 30197NairobiKenya Department of Geography Department of Botany Department of Meteorology TTMI-Project Department of Environmental SciencesCT.de Wit Graduate School of Production Ecology and Resource ConservationWageningen UniversityDuivendaal 26701 AP WageningenThe Netherlands.

Six seasons of experiments in Machakos, Kenya, revealed that above about 150 mm of rainfall, maize yields per row in alley cropped “replacement” agroforestry (AF) plots, of cassia siamea Lam. and maize ( Zea mays, cv. Katumani composite B), may be expected to exceed those in the control (sole maize) plots. Such yields were insufficient to compensate for the area “lost” to the hedgerows. Below about 150 mm the control plots may be expected to perform better. This result was due to competition for water. Greater association of the fine roots of cassia and maize was observed in the middle of the alleys than near the hedgerows. Photosynthetic consequences of shading were insignificant relative to other factors. In the alleys, reductions of soil temperature due to shade in the western and eastern maize rows were higher than in the middle row. Soil moisture extraction was higher in the AF than in the control plots. In the AF plots, moisture extraction was greater under the central maize rows than under those nearest the cassia. Yield patterns followed such soil temperature and soil moisture patterns. Maize transpiration and photosynthetic rates were significantly higher in the control than in the AF plots during a below average rainy season but not during above average rainy seasons. It is concluded that alley cropping under semi arid conditions should be approached differently from the system worked on. It must at least provide strong physical protection of crops and/or soils and have a strong economic incentive to be of interest to the farmers.

关键词： alley cropping cassia siamea competition Kenya maize yields microclimate mulching semi arid conditions

Output Waveform Analysis of an Electro-hydraulic Vibrator controlled by the Multiple Valves

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chinese Journal of Mechanical Engineering 2014年第1期27卷 186-197页

作者： REN Yan RUAN Jian JIA Wen'ang college of Mechanical & Electrical Engineering Wenzhou University Key Laboratory of Special Purpose Equipment and Advanced Machining Technology Ministry of Education & Zhejiang Province Zhejiang University of Technology

The existing research of the electro-hydraulic vibrator mainly focuses on system stability, working frequency width and output waveform distortion. However, this high frequency performance of the electro-hydraulic vibrator is difficult to be improved greatly due to fast insufficiently frequency response of the servo valve itself and limited compensation capability of the control structure in the vibrator system. In this paper, to realize high frequency vibration, an improved two-dimensional valve （here within defined as a 2D valve） as a main control component is adopted to the parallel connection with a servo valve to control the electro-hydraulic vibrator, Because the output waveforms of this electro-hydraulic vibrator are incapable to be verified through timely feedback as in the conventional electro-hydraulic servo system, the analysis to the output waveform becomes crucial to the design and control of the electro-hydraulic vibrator. The mathematical models of hydraulic actuation mechanism and the orifice area of the parallel valves connection are established first. And then the vibration process is divided into two sections in terms of the direction of the flow, the analytical expression of the excited waveform is solved. Based on relationships exist between working states and the control parameters the analytical results, the vibration boundary positions and the are derived. Finally an experimental system was built to validate the theoretical analysis. It is verified that this electro-hydraulic vibration system could achieve high working frequency, up to 2 000 Hz. The excited waveform is similar to the sinnsoidal waveform. And the ascent and decent slopes of the waveforms are somewhat asymmetrical. This asymmetry is not only caused by the c.ange of the direction of the elastic force but also dependent on the bias position of the vibration. consequentky the distortion of effective working waveform is less tha~ 10%. This electro-hydraulic vibrator controlled by t

关键词： 2D valves hydraulic multiple-valve system electro-hydraulic vibrator excited waveform

Flight trajectory optimization of sun-tracking solar aircraft under the constraint of mission region

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chinese Journal of Aeronautics 2021年第11期34卷 140-153页

作者： Mingjian WU Zhiwei SHI Tianhang XIAO Haisong ang School of Mechanical Engineering Nanjing University of Science and TechnologyNanjing 210094China School of Aerospace Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016China

The optimal yawing angle of sun-tracking solar aircraft is tightly related to the solar azimuth angle,which results in a large arc flight path to dynamically track the sun ***,the limited detection range of payload usually requires solar aircraft to loiter over areas of interest for persistent surveillance *** large arc sun-tracking flight may cause the target area on the ground to be outside the maximum coverage area of *** present study therefore develops an optimal flight control approach for planning the flight path of sun-tracking solar aircraft within a mission *** proposed method enables sun-tracking solar aircraft to maintain the optimal yawing angle most of the time during daylight flight,except when the aircraft reverses its direction by turning *** a circular region with a mission radius of 50km,the optimal flight trajectory and controls of an example K-shaped sun-tracking solar aircraft are investigated *** demonstrate the effectiveness of the proposed approach to optimize the flight path of the sun-tracking aircraft under the given circular region while maximizing the battery input ***,the effects of varying the mission radius on energy performance are explored *** has been proved that both net energy and energy balance remain nearly constant as the radius constraint varies,which enables the solar aircraft to achieve perpetual flight at almost the same latitude as the large arc *** method and results presented in this paper can provide reference for the persistent operation of sun-tracking solar aircraft within specific mission areas.

关键词： Energy performance Mission region Optimal yawing angle Perpetual operation Sun-tracking solar aircraft Trajectory optimization

Effect of cooling Rates on Solidification Microstructures and Tensile Property of a Novel Wrought Superalloy

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Journal of Wuhan University of Technology(Materials Science) 2023年第4期38卷 903-910页

作者：李鑫旭 JIA chonglin YU ang JIang Zhouhua Beijing Baimtec Material co. LtdBeijing100095China Aero Engine corporation of china Beijing Institute of Aeronautical MaterialsBeijing100095China School of Metallurgy Northeastern UniversityShenyang110819China

The effects of cooling rates on solidification behaviors,segregation characteristics and tensile property of GH4151 alloy were investigated using microstructure characterization and tensile ***,a relationship between the secondary dendrite arm spacing and cooling rate was determined and it was confirmed to be ***,it can be found from microstructure observations that the morphology of(Nb,Ti)c carbides transits from blocky and script type to fine script type and spotty type,and the refinedγ'phase was observed due to decrease of segregation with increasing cooling ***,the solidification microstructures of the industrial-scale samples were *** morphology ofηphase c.anges from indistinguishable shape,fine needle-like shape to large block-like shape with increasing ingot *** a result,the mechanical properties of alloy decrease due to increase of brittle *** experimental results show that the precipitation behavior of GH4151 is affected by segregation degree of elements,and the segregation degree is determined by solute distribution process and solid back-diffusion process.

关键词： GH4151 superalloy solidification segregation cooling rate tensile properties