排序方式: 共有21条查询结果,搜索用时 156 毫秒
11.
12.
13.
14.
Jenkin HL Dyde RT Zacher JE Zikovitz DC Jenkin MR Allison RS Howard IP Harris LR 《Acta Astronautica》2005,56(9-12):1025-1032
In order to measure the perceived direction of "up", subjects judged the three-dimensional shape of disks shaded to be compatible with illumination from particular directions. By finding which shaded disk appeared most convex, we were able to infer the perceived direction of illumination. This provides an indirect measure of the subject's perception of the direction of "up". The different cues contributing to this percept were separated by varying the orientation of the subject and the orientation of the visual background relative to gravity. We also measured the effect of decreasing or increasing gravity by making these shape judgements throughout all the phases of parabolic flight (0 g, 2 g and 1 g during level flight). The perceived up direction was modeled by a simple vector sum of "up" defined by vision, the body and gravity. In this model, the weighting of the visual cue became negligible under microgravity and hypergravity conditions. 相似文献
15.
相位梯度自聚焦(PGA)方法对多种成像情况和相位误差函数都具有稳健性,但要其收敛通常需要进行4-6次迭代。为了收敛于杂波干扰中的显著散射体上,同时能充分地获取模糊函数,必须进行迭代。在本文中,我们提出用选择性地增大高质量同步源集合的方法来加速估计收敛,且不受SAR图像的距离像素的限制。这是非常可能的,因为每个距离单元中都含有一个以上的、横跨积累孔径的显著散射体。使在一个距离门中所选择出的次最亮的散射体的能量(比另一个距离门中最大亮度散射体)更高也是很可能的。由于采用恰当的目标滤波方法对从大的散射体集合中选择出的高质量散射体进行滤波,且采用了更高阶的相位误差测量工具,新算法在不进行迭代的情况下就获得近收敛的聚焦质量。我们把这种解决方案叫作高质量PGA(QPGA)算法。 相似文献
16.
17.
DeWitt HL Hasenkopf CA Trainer MG Farmer DK Jimenez JL McKay CP Toon OB Tolbert MA 《Astrobiology》2010,10(8):773-781
The presence of sulfur mass-independent fractionation (S-MIF) in sediments more than 2.45?×?10(9) years old is thought to be evidence for an early anoxic atmosphere. Photolysis of sulfur dioxide (SO(2)) by UV light with λ?220?nm has been shown in models and some initial laboratory studies to create a S-MIF; however, sulfur must leave the atmosphere in at least two chemically different forms to preserve any S-MIF signature. Two commonly cited examples of chemically different sulfur species that could have exited the atmosphere are elemental sulfur (S(8)) and sulfuric acid (H(2)SO(4)) aerosols. Here, we use real-time aerosol mass spectrometry to directly detect the sulfur-containing aerosols formed when SO(2) either photolyzes at wavelengths from 115 to 400?nm, to simulate the UV solar spectrum, or interacts with high-energy electrons, to simulate lightning. We found that sulfur-containing aerosols form under all laboratory conditions. Further, the addition of a reducing gas, in our experiments hydrogen (H(2)) or methane (CH(4)), increased the formation of S(8). With UV photolysis, formation of S(8) aerosols is highly dependent on the initial SO(2) pressure; and S(8) is only formed at a 2% SO(2) mixing ratio and greater in the absence of a reductant, and at a 0.2% SO(2) mixing ratio and greater in the presence of 1000?ppmv CH(4). We also found that organosulfur compounds are formed from the photolysis of CH(4) and moderate amounts of SO(2). The implications for sulfur aerosols on early Earth are discussed. Key Words: S-MIF-Archean atmosphere-Early Earth-Sulfur aerosols. 相似文献
18.
19.
20.