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为了改善天然橡胶的热氧老化性能,试验了防老剂D提纯品和工业品对天然橡胶(NR)热氧老化性能的影响,测试了其热氧化诱导期、热失重、热老化的性能变化。结果表明:含杂少纯度高的防老剂D使天然橡胶的抗热氧老化得到改善。 相似文献
73.
The effect of a non-uniform basic temperature gradient on the onset of convection driven by surface tension in a horizontal layer of a Boussinesq fluid with suspended particles confined between an upper free, constant heat flux boundary and a lower rigid isothermal boundary is considered. The microrotation is assumed to vanish at the boundaries. A linear stability analysis is performed. The Rayleigh–Ritz technique is used to obtain the eigenvalues. The influence of various parameters on the onset of convection has been analyzed. Six different non-uniform basic state temperature profiles are considered and their comparative influence on onset is discussed. It is observed that the fluid layer with suspended particles heated from below is more stable compared to the classical fluid layer without suspended particles. The problem has possible applications in microgravity situations. 相似文献
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ABSTRACTShadows have long been a challenging topic for computer vision. This challenge is made even harder when we assume that the camera is moving, as many existing shadow detection techniques require the creation and maintenance of a background model. This article explores the problem of shadow modelling from a moving viewpoint (assumed to be a robotic platform) through comparing shadow-variant and shadow-invariant image features — primarily color, texture and edge-based features. These features are then embedded in a segmentation pipeline that provides predictions on shadow status, using minimal temporal context. We also release a public dataset of shadow-related image sequences, to help other researchers further develop shadow detection methods and to enable benchmarking of techniques. 相似文献
75.
The aim of this paper is to provide a comprehensive comparison of the thermal insulation and heat transfer performance for Kagome truss-cored lattice along two perpendicular orientations OA and OB. Three test conditions are conducted under forced air convection for the titanium sandwich panel fabricated by 3 D printing technology. The thermo-fluidic characteristics are further explored by numerical simulation to reveal the underlying mechanisms of heat transfer enhancement.The results indicate that the orientation OB exhibits better thermal insulation than orientation OA under the identical temperature loading, while the latter outperforms the former by up to 20% higher overall heat transfer performance. In particular, the endwalls and lattice core in orientation OA achieve 9.7% and 22.5% higher area-averaged Nusselt number respectively than that in orientation OB for a given Reynolds number. The heat transfer superiority of orientation OA comes from the unique topology which induces the large scale spiral primary flows, facilitating the heat exchange between the cooling air and the surfaces of sandwich panel. However, the complex flow mixing leads to a maximum of 20% higher friction factor in orientation OA than that in orientation OB. 相似文献
76.
Masaya Kimura Masanori Kawamura Katsuhiko Yamada 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(3):1336-1346
An analytical expression for distant retrograde orbits (DROs) is obtained in this study. Owing to the fact that a planar DRO is a closed orbit and can be expressed as an approximately elliptical orbit, respective geometries and periods of DROs are analytically calculated. A switching point, where various properties of planar DROs change abruptly with an increase in the orbital radius, is determined. The Mars–Deimos system is taken as a case study in this work. The proposed method can be applied to cases where the Hill’s approximation of the restricted three-body problem is valid. Numerical calculations are performed to validate the proposed method. 相似文献
77.
《中国航空学报》2023,36(1):324-341
Based on the growth mechanism of natural biological branching systems and inspiration from the morphology of plant root tips, a bionic design method called Improved Adaptive Growth Method (IAGM) has been proposed in the authors’ previous research and successfully applied to the reinforcement optimization of three-dimensional box structures with respect to natural frequencies. However, as a kind of ground structure methods, the final layout patterns of stiffeners obtained by using the IAGM are highly subjected to their ground structures, which restricts the optimization effect and freedom to further improve the dynamic performance of structures. To solve this problem, a novel post-processing geometry and size optimization approach is proposed in this article. This method takes the former layout optimization result as start, and iteratively finds the optimal layout angles, locations, and lengths of stiffeners with a few design variables by optimizing the positions of some specific node lines called active node lines. At the same time, thicknesses of stiffeners are also optimized to further improve natural frequencies of three-dimensional box structures. Using this method, stiffeners can be successfully separated from their ground structures and further effectively improve natural frequencies of three-dimensional box structures with less material consumption. Typical numerical examples are illustrated to validate the effectiveness and advantages of the suggested method. 相似文献
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通过对多种典型型号湿度传感器在不同空气流速条件下对同一相对湿度测量结果的变化的实验研究,得出了0~1.5 m/s流速范围内湿度传感器的示值随流速的变化趋势,即示值随流速增大而增大,总变化量最大达2%RH以上,且变化主要发生0.5 m/s以下的低流速情况下,同时传感器表面温度随流速增大而降低,两者变化趋势相互吻合。进一步分析表明,上述现象是湿度传感器的自热效应和空气与传感器之间的对流换热效应共同作用的结果,它给湿度传感器的测量结果带来新增不确定度。 相似文献