排序方式: 共有54条查询结果,搜索用时 15 毫秒
41.
月尘累积对太阳电池阵电帘除尘效率影响的实验研究 总被引:4,自引:0,他引:4
月尘在月球探测器太阳电池阵表面的累积将会导致其输出功率下降甚至功能失效。近年来,电帘除尘方法被认为是月尘清除防护的有效手段。文章实验研究了月尘累积对三结砷化镓太阳电池性能影响,拟合得到了月尘累积质量与太阳电池相对输出功率的数学模型;利用电帘除尘装置,研究了不同月尘累积质量下电帘的除尘效率。研究结果表明,6 mg/cm2月尘累积质量是太阳电池阵电帘除尘装置启动的最佳工作条件。该研究成果可为开发具有自适应除尘能力的太阳电池阵提供技术支持。 相似文献
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单级轴流压气机的旋转失速特性实验 总被引:2,自引:2,他引:2
以一台单级低速轴流压气机为研究对象,采用在压气机周向、轴向不同位置处布置多个动态压力传感器的方法,获取了压气机失速过程中不同位置动态压力信号的变化情况,通过对各测点的压力信号分别进行了时域、频域分析.结果表明:压气机在失速前出现尖脉冲型扰动;失速后的失速团的有分裂和合并的现象,个数在1和2之间相互转换,但退出失速时总是由两个合并成为一个,并且在几个转子周期内迅速退出;对失速时的压力信号频谱分析证明了对失速团个数判断的准确性. 相似文献
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A method of determining effective elastic properties of honeycomb cores based on equal strain energy
A computational homogenization technique (CHT) based on the finite element method (FEM) is discussed to predict the effective elastic properties of honeycomb structures. The need of periodic boundary conditions (BCs) is revealed through the analysis for in-plane and out-of-plane shear moduli of models with different cell numbers. After applying periodic BCs on the represen-tative volume element (RVE), comparison between the volume-average stress method and the boundary stress method is performed, and a new method based on the equality of strain energy to obtain all non-zero components of the stiffness tensor is proposed. Results of finite element (FE) analysis show that the volume-average stress and the boundary stress keep a consistency over different cell geometries and forms. The strain energy method obtains values that differ from those of the volume-average method for non-diagonal terms in the stiffness matrix. Analysis has been done on numerical results for thin-wall honeycombs and different geometries of angles between oblique and vertical walls. The inaccuracy of the volume-average method in terms of the strain energy is shown by numerical benchmarks. 相似文献
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为实现无人作战飞机(UCAV,Unmanned Combat Aerial Vehicle)认知导航的空间方位自主推算,提出了一种基于多尺度网格细胞的路径整合方法.该方法模拟背侧内嗅皮层(dMEC,dorsal Medial Entorhinal Cortex)的相同区域网格细胞放电特征相同、不同区域放电特征递增变化的特点,构建尺度递增的仿生多尺度网格图组,在各层中引入突触样式(synaptic pattern)计算各细胞权值,通过细胞的活跃度变化表征各网格层中位置的变化,并在各层分别实现路径整合,进而利用低尺度整合结果调整高尺度整合,提高空间位置的推算精度.实验结果表明,所提方法在一定的速度误差与方向误差范围内能够精确推算方位,具有较高的空间位置推算精度,并且方向误差值随运动方向变化呈锯齿状分布. 相似文献
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Alejandra Barrera Gonzalo Tejera Martin Llofriu Alfredo Weitzenfeld 《Spatial Cognition & Computation》2013,13(1):27-59
In his landmark article, Richard Morris (1981) introduced a set of rat experiments intended “to demonstrate that rats can rapidly learn to locate an object that they can never see, hear, or smell provided it remains in a fixed spatial location relative to distal room cues” (p. 239). These experimental studies have greatly impacted our understanding of rat spatial cognition. In this article, we address a spatial cognition model primarily based on hippocampus place cell computation where we extend the prior Barrera–Weitzenfeld model (2008) intended to allow navigation in mazes containing corridors. The current work extends beyond the limitations of corridors to enable navigation in open arenas where a rat may move in any direction at any time. The extended work reproduces Morris's rat experiments through virtual rats that search for a hidden platform using visual cues in a circular open maze analogous to the Morris water maze experiments. We show results with virtual rats comparing them to Morris's original studies with rats. 相似文献
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Daisuke Kitazawa Yutaka Miyazawa Nobuharu Fujii Eiji Nitasaka Hideyuki Takahashi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
In higher plants, gravity is a major environmental cue that governs growth orientation, a phenomenon termed gravitropism. It has been suggested that gravity also affects other aspects of morphogenesis, such as circumnutation and winding movements. Previously, we showed that these aspects of plant growth morphology require amyloplast sedimentation inside gravisensing endodermal cells. However, the molecular mechanism of the graviresponse and its relationship to circumnutation and winding remains obscure. Here, we have characterized a novel shoot gravitropic mutant of morning glory, weeping2 (we2). In the we2 mutant, the gravitropic response of the stem was absent, and hypocotyls exhibited a severely reduced gravitropic response, whereas roots showed normal gravitropism. In agreement with our previous studies, we found that we2 mutant has defects in shoot circumnutation and winding. Histological analysis showed that we2 mutant forms abnormal endodermal cells. We identified a mutation in the morning glory homolog of SHORT-ROOT (PnSHR1) that was genetically linked to the agravitropic phenotype of we2 mutant, and which may underlie the abnormal differentiation of endodermal cells in this plant. These results suggest that the phenotype of we2 mutant is due to a mutation of PnSHR1, and that PnSHR1 regulates gravimorphogenesis, including circumnutation and winding movements, in morning glory. 相似文献
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Electric and thermal power have to be available at the base site on the lunar surface before the first lunar crew arrives. Unlimited solar energy is available during the lunar day, but this must be stored for use during the lunar night unless nuclear energy systems are available. State-of-the-art candidate systems are reviewed and the production of solar cells on the moon is discussed. Various options for developing a lunar power plant are proposed. These must be simulated and optimized in a real lifecycle systems scenario to provide operations and cost data essential for choosing a strategy. 相似文献
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Swantje Hauschild Svantje Tauber Beatrice Lauber Cora S. Thiel Liliana E. Layer Oliver Ullrich 《Acta Astronautica》2014
Dating back to the Apollo and Skylab missions, it has been reported that astronauts suffered from bacterial and viral infections during space flight or after returning to Earth. Blood analyses revealed strongly reduced capability of human lymphocytes to become active upon mitogenic stimulation. Since then, a large number of in vitro studies on human immune cells have been conducted in space, in parabolic flights, and in ground-based facilities. It became obvious that microgravity affects cell morphology and important cellular functions. Observed changes include cell proliferation, the cytoskeleton, signal transduction and gene expression. This review gives an overview of the current knowledge of T cell regulation under altered gravity conditions obtained by in vitro studies with special emphasis on the cell culture conditions used. We propose that future in vitro experiments should follow rigorous standardized cell culture conditions, which allows better comparison of the results obtained in different flight- and ground-based experiment platforms. 相似文献