课程文献中心 更多>>

关键词： 航空湿式离合器   轴心供油冷却   摩擦副   瞬态流场   CFD  

摘要： 以航空湿式离合器为研究对象,通过数值仿真得出摩擦片输出转速曲线和对偶钢片轴向移动曲线,采用最小二乘法拟合出输出转速曲线公式和钢片轴向移动公式,获得接合过程中时变的摩擦片输出转速和钢片轴向移动位移。基于计算流体动力学(CFD)方法,运用Fluent仿真技术,采用动网格方法,对轴心供油冷却方式下摩擦副的不同接合时间下的瞬态流场进行仿真分析,研究该润滑方式下瞬态油液的速度分布规律和压力分布规律。研究结果表明:摩擦副半径越大处,油液流速越大,润滑油在油液离心力的作用下,高速排出,部分油液不断被搅动,再次进入摩擦副片间润滑摩擦副;在该轴心润滑方式下,随着接合时间增大,油液所受的油膜承载力越大,油压分布越均匀,接合面的油压几乎呈对称分布,润滑效果好。

关键词： Harmonic generation   Parametric down conversion   Phase matching   Phase velocity   Scanning electron microscopy   Second harmonic generation  

摘要： We theoretically and experimentally investigate type II second harmonic generation in III-V-on-insulator wire waveguides. We show that the propagation direction plays a crucial role and that longitudinal field components can be leveraged for robust and efficient conversion. We predict that the maximum theoretical conversion is larger than that of type I second harmonic generation for similar waveguide dimensions and reach an experimental conversion efficiency of 12%/W, limited by the propagation loss. (C) 2021 Optical Society of America

关键词： 13-catenin   Dickkopf-1   Fracture healing   Substance P   Type 1 diabetes   Wnt signalling  

摘要： Diabetes mellitus is an ill-famed metabolic disorder with varied repercussions including delayed fracture healing. Wnt/13-catenin axis is known to play a tight pivotal role in the bone healing process. Substance P (SubP) is a neuropeptide with established positive modulatory functions in fracture healing and associated neuronal milieu. In this study, we performed local delivery of recombinant adenovirus of Dickkopf-1 (DKK1) into the fracture site to understand the antagonizing the role of DKK1 against substance P. Rats were segregated into 4 groups: (i) Fractured non-diabetic rats;(ii) Fractured T1D rats;T1D was provoked by using STZ 50 mg/kg for 5 consecutive days;(iii) Fractured T1D + SubP (50 mg/ml/Kg;i.p.;30 min prior to fracture procedure);(iv) Fractured T1D + SubP + Ad-DKK1. Bone radiographs were taken using a Faxitron X-ray machine and the residual gap size was measured using an electric caliper. Western blotting was also performed to determine the protein expression levels of osteogenic markers (RUNX2, OSTX and OSTC) bone resorption markers (OPG, RANKL and RANK) and also Wnt-signalling markers (13-catenin, LRP5 and GSK-313). We observed that SubP promoted osteogenesis (as indicated by RUNX2, OSTX and OSTC upregulation) and mitigated the bone resorption (as indicated by optimized OPG/RANKL/RANK axis) via activated Wnt signalling (manifested by upmodulated 13-catenin and LRP5, with downmodulated GSK-313 levels. Activation of endogenous SubP or administration of exogenous mimics might counterprotect the fractured bone against the deforming effects of T1D. @& nbsp;2021 The Author(s). Published by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://***/licenses/by-nc-nd/4.0/).

关键词： Magnetorheological fluid (MRF)   Magnetorheological clutch (MRC)   Electric vehicle   Correlation analysis, Uncertainty analysis  

摘要： This work makes an effort to explore a magnetorheological clutch (MRC) prototype for a two-wheeled electric vehicle owing to its quick response, accurate torque transmission control by varying the magnetic field;and electro-mechanical interface. A design variation 'MRC with-slits' is proposed to enhance the torque transmission capacity and compared with `MRC without-slits'. The torque transmitting capability of the MRC with and without-slits is evaluated analytically and experimentally with respect to input parameters viz. current and speeds. The rise in torque transmission due to the presence of slits and thermal behavior is validated experimentally. Correlation and uncertainty analysis are used to confirm the findings. The weight and size of the MRC remains a major challenge for its successful integration with a two-wheeled electric vehicle application.

关键词： Aerospace   “   Cradle-type”   five-axis machining center   Error accuracy   Measuring method  

摘要： This study mainly measures the accuracy of closed impeller machining machines in aerospace. However, this machining center is different from others and belongs to a "cradle type" five-axis machining center. The measuring difficulty of cradle-type five-axis machining center is that the error accuracy of X, Y, Z, B, and C axes can meet the requirements when the Y-axis moving speed reaches 80 m/min and the maximum acceleration is 10 m/s(2);and the C-axis maximum angular acceleration is 1.25 rad/s2;and the maximum angular velocity is 60 rpm. Therefore, the 24 theoretical models of accuracy error measurement for cradle type are derived at first. Combined with the theoretical model, the straightness of X, Y, and Z and the positioning accuracy of X, Y, Z, B, and C axes are measured by laser interferometer. In X, Y, Z, and C axes detection, two methods are adopted and compared. Then, the overall processing accuracy is measured through trial-cutting parts. The measurement results show that the second way (with temperature sensor) is better than the first measurement. Compared with the device without normal temperature sensor, the measurement of X-axis repeated positioning accuracy and positioning accuracy are improved by 8.5% and 23.6%, respectively. The positioning accuracy of Y-axis is improved by 16.7%. The repeated positioning accuracy and positioning accuracy of Z-axis are improved by 78.9% and 72.1%, respectively. The repeated positioning accuracy and positioning accuracy of the C-axis are improved by 20.4% and 7%, respectively. At the same time, it is also measured that the repeated positioning accuracy of B-axis is 15 mu m. Finally, through the processing and testing of the trial-cutting parts, the processing error of the inclined cone table profile is 20 mu m, which is far less than the design parameters of the original cradle-type five-axis machine tool. It provides efficient theoretical guidance and practical reference for similar five-axis machine tool measuremen

关键词： Wind energy   Vertical axis wind turbine (VAWT)   Aerodynamics   Parameters  

摘要： The high emission of fossil fuels are major driving forces in renewable energy technology development. In response, the lift-type vertical axis wind turbines (VAWT) is experiencing a renewed interest for large-scale offshore wind energy generation and also for small-scale urban devices. Significant research has been published on the aerodynamic design and optimisation of VAWTs. In this paper, an attempt is made to review the aerodynamic design parameters which influence the VAWT's aerodynamic efficiency. Each parameter is discussed in detail regarding their advantages and disadvantages. A baseline VAWT design has been put forward from this literature review to support VAWT aerodynamic analysis. Furthermore, areas of future research requiring attention have been identified to further progress the aerodynamic design and development of VAWTs.

关键词： Aix sponsa   brood parasitism   clutch size evolution   incubation temperature   life-history   offspring number versus quality   wood duck  

摘要： Elucidating factors that limit the number of offspring produced is fundamental to understanding life-history evolution. Here, we examine the hypothesis that parental ability to maintain an optimal physical developmental environment for all offspring constrains clutch size via effects on offspring quality. Experimental laboratory studies of birds have shown that a <1 degrees C difference in average incubation temperature has diverse effects on fitness-related post-hatching offspring phenotypes. Thus, the inability of parents to maintain optimal incubation temperatures could constrain clutch sizes. A fundamental question that has not been sufficiently addressed is whether larger clutch sizes lead to within nest variation in egg temperature that is large enough to produce offspring with different phenotypes within a brood. This could lead to differential survival among offspring, and could create a trade-off between offspring number and quality. We manipulated clutch size in nests of free-living wood ducks and measured incubation temperature among and within clutches using multiple temperature loggers. As clutch size increased, average incubation temperatures were lower and more variable, and eggs took longer to hatch. Notably, the range in average incubation temperature among eggs within nests increased with clutch size and exceeded 1 degrees C in large clutches. Clutch size did not affect hatch success. In conjunction with our companion laboratory studies that used artificial incubation to document the effects of temperature variation on fitness-related traits in this species, our work suggests that suboptimal incubation temperatures could be a factor that limits clutch size through diminishing returns on post-hatch offspring quality. A free Plain Language Summary can be found within the Supporting Information of this article.

关键词： 16W10   17A01   17D99  

摘要： We construct a new series of n(2)-dimensional axial algebras of Monster type (2 eta, eta). They arise as subalgebras A of the Matsuo algebras M-eta(-O-n+1(+)(3)), generated by single and double axes. Also, we address the question of when these algebras are simple. While we do not solve this question, we formulate three concrete conjectures based on the calculation, using the computer algebra system GAP, of the roots of the determinant of the Gram matrix of the Frobenius form on A for several small values of n.

关键词： 离合器   弹簧   力学分析   钢球   过载保护   扭矩  

摘要： 在航空微型传动机构领域中，常规安全离合器由于扭矩较大不能满足使用要求，因此需要研制小扭矩安全离合器。基于钢球式离合器模型，采用三维建模仿真计算方法，设计一种小型钢球式离合器，并对其进行传递扭矩、弹簧弹力、结构件强度等有限元分析计算和结构件静动态特性分析；进行优化设计计算后，将该小型过载保护离合器搭载到航空驱动机构上进行试验验证。结果表明：该小型钢球离合器的传递扭矩在一定范围内可调，传递扭矩范围小于0.57 N·m，使用寿命达到3 000 h，具有过载保护功能，可用于航空刚性机械传动系统中。