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在观测空间碎片时,受碎片结构紧凑、组成材料复杂,以及地基观测设备空间分辨率的限制,同一像元中通常会包含多种材料的信息,即产生"混合像元"。目前国内外对混合像元的研究主要集中在获取混合像元的纯物质光谱以及丰度上,往往忽略了高光谱数据中纯物质个数的确定对于没有任何先验信息的混合像元分析是至关重要的。如果估计的材料数目过少,将会导致解混出的材料光谱仍然是混合状态的像元;如果估计的材料数目过多,提取出的端元中将很有可能包含冗余噪声成分。基于光谱线性混合模型,提出一种改进的p范数纯像元辨识算法。主要利用光谱数据具有近似于低维流形的特性,首先采用正交投影的原理,将提取的端元扩充至正交投影算子中,然后分析投影后各个像元向量的p范数值,最终将p范数值高于阈值的向量个数作为材料种类数目。对实测碎片常用材料和美国地质勘测局数据库分别进行仿真实验,实验结果表明:提出的方法在估计材料种类数目的同时,还能提取出目标所包含的材料光谱,这在一定程度上提高混合光谱分解过程的自动化程度;相对于现有的一些主流算法,该方法有较强的鲁棒性,并且在信噪比不高的情况下仍能正确地估计空间碎片材料种类数目。 相似文献
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Yuqiang GUO;Qionghua WANG 《光子学报》2022,51(7):271-288
At present, Liquid Crystal Display （LCD） has become an important display technology, especially in the large-size display field. Since the liquid crystal is optically anisotropic materials, LCD has inherent viewing angle-related problems, which is increasingly becoming a bottleneck restricting its further development. In this case, LCD needs to constantly innovate to cope with the fierce competition with other display technologies and the increasing performance demands from consumers. In recent years, some technologies that can improve the LCD’s viewing angle problem have been proposed. In order to make the researchers quickly find out the relevant technical progress, we summarize some research on improving the viewing angle-related performance in recent years. This overview can be divided into the following three parts： LCD structure and display mode, the research progress of viewing angle-related performance, and special viewing angle control technology. 1） LCD structure and display mode. The basic structure and display principle of LCD are first introduced, and four common display modes, including twisted nematic, vertical alignment, in-plane switching, and fringe-field switching, are described in the order in which they were proposed. We then describe the spatial positions of the electrode structures and the initial liquid crystal orientation in the four display modes. Besides, the specific display principles of the different display modes are explained in detail. Then, the advantages and disadvantages of the different display modes and their suitable applicable fields are briefly introduced. As we know, the viewing angle problems of different display modes are different, and thus the corresponding improvement measures are also different. 2） Research progress of viewing angle-related performance. Among the many display performances, some performances have the dependence on viewing angle. Here, we introduce the properties related to viewing angle, such as brightness, contrast, grayscale, color, and color gamut. Representative improvement methods are pointed out at these performances, and the advantages and disadvantages of different methods are analyzed. In terms of brightness, several methods that can improve the brightness at the full viewing angle are introduced, such as high brightness backlight, narrow electrode technology, and field sequential color technology. We introduce the wide viewing angle compensation film, regional dimming technology, dual-cell display technology, and surface anti-reflection structure to improve the contrast. In terms of the grayscale and color performance, we introduce the use of light scattering films, single-domain and multi-domain electrode structures, and optimized driving methods to reduce the gamma shift and color difference. In addition, the methods to improve the color gamut of LCD are pointed out, such as high color gamut backlights and broadband optical filters. Each of the above methods has an important reference value for improving the viewing angle-related performance of LCD, but each approach focuses on a different viewing angle problem, and each method has its advantages and disadvantages. Therefore, researchers need to choose the appropriate methods to solve their specific problems. 3） Special viewing angle control technology. In some special application fields, the wide viewing angle technology is no longer applicable, such as business mobile phones, bank automated teller machines, ciphers, and aviation display that require privacy protection. In order to address the needs of the above fields, several special viewing angle control technologies are introduced, including narrow viewing angle, specified viewing angle, and viewing angle controllable technologies. In the aspect of narrow viewing angle technology, two commonly used methods of shading privacy film and viewing angle compensation film are introduced. In terms of the more special non-face-to-view display field, the specified viewing angle display technology based on the viewing angle deflection film is introduced. Besides, several viewing angle controllable technologies are introduced, such as dual-pixel structure, dual-cell device structure, electrode bias method. These methods can make LCD exhibit the viewing angle performance different from the common LCD with wide viewing angle, and they have the application value for some application fields with special viewing angle requirements. In different practical situations, relevant researchers should select out the appropriate technical solutions according to the actual needs, so as to solve the specific viewing angle problems in the design and manufacturing processes.Due to the limited space of this overview, the research on the various viewing angle performances cannot be summed up in all. And thus, only some representative research works are reviewed. It should be noted that, in addition to the viewing angle-related performance introduced in this overview, LCD needs to be continuously optimized in terms of flexible display, reducing the motion picture response time, and reducing the power consumption, etc. Driven by market competition, consumers pay more attention to the comprehensive performances of display technology, thus we should not sacrifice other performances just to improve one performance of LCD. In fact, how to realize the “multi-parameter linkage optimization” has become an important task to improve the comprehensive performance of LCD, which also poses a greater challenge to future research works. At present, LCD is still a relatively important display technology. From the perspective of development trends, the overall display performance of LCD based on the Mini LED backlight and regional dimming is excellent. It has the advantages of a million-level dynamic contrast ratio, more than 2 000 nits peak brightness, and ultra-high color gamut. Therefore, Mini LED LCD is an important display technology in the future, the methods mentioned in the paper are also effective in improving the viewing angle-related performance of LCD. 相似文献
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可控/“活性”自由基聚合(CLRP)可以用于制备分子量分布窄、分子链缺陷少的聚合物,如聚乙烯(PE)、聚氯乙烯(PVC)、聚偏氯乙烯(PVDC)和聚偏氟乙烯(PVDF),且易控制上述单体与其他单体共聚得到嵌段聚合物。本文调研了近年来可控/“活性”自由基聚合(如碘转移聚合(ITP)、氮氧稳定自由基聚合(NMP)、可逆加成断裂链转移(RAFT)聚合和金属催化的活性自由基聚合(OMRP)等)制备聚乙烯和聚卤代烯烃等方面的工作,并指出了未来的发展方向。 相似文献
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通过熔体快淬的方法制备出Pr9-xDyxFe86B5和Pr9-xDyxFe84.4-yCoyGa1Mn0.6B5(x=0～2.0;y=0～15)薄带样品,利用X射线衍射和振动样品磁强计进行了相成分分析和磁性能研究.对不同成分的样品磁性能进行分析比较,发现用Co替代Fe、用Dy替代Pr可以明显改善Pr2Fe14B/α-Fe型纳米复合稀土永磁材料的室温和高温磁性能.适当的Co和Dy联合添加时,材料表现出很好的高温永磁性能,其中Pr8Dy1Fe76.4Co8Ga1Mn0.6B5样品在550 K时仍具有5.0 MGOe的最大磁能积,显示出很好的高温应用前景. 相似文献
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报道了N-{4-{N-甲基-N-[2-羟基-3-(2,4-二氧代-1,2,3,4-四氢嘧啶-5-基)氨基]丙基}氨基-3-溴}苯甲酰基-L-谷氨酸二乙酯及其衍生物的简便合成方法. 分别以4-氨基苯甲酸乙酯和4-氨基苯甲酰基-L-谷氨酸二乙酯为起始物, 经甲基化、烯丙基化、溴羟基化、环氧化、开环、脱保护等反应首次合成了6个新型5-取代氨基嘧啶类化合物, 并通过1H NMR, 13C NMR 和MS对其化学结构进行了表征. 初步生物活性结果表明, 苯环侧链的L-谷氨酸酯部分是此类化合物抑制人重组二氢叶酸还原酶的必需结构. 相似文献
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采用单室、三电极体系,通过希瓦氏菌(Shewanella)还原氧化石墨烯(GO)膜,制备了石墨烯(rGO)薄膜,并通过X射线衍射(XRD)和拉曼光谱(Raman)等手段表征了GO还原前后的结构和性质,证明了Shewanella菌可以有效将GO膜还原为rGO.以该生物还原得到的rGO薄膜为工作电极,可以有效改善Shewanella菌的胞外电子转移(EET).与空白的氧化铟锡(ITO)电极相比,rGO电极的阳极输出电流增大了13%,电量增加90%.该Shewanella还原法是一种温和制备rGO膜的方法,制得的rGO膜改善了微生物的EET效率. 相似文献
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耗散粒子动力学是一种粗粒化的计算模拟方法,在微米和纳米流体力学中有着广泛的应用.由于界面在微小体积流体中的重要性,边界条件的选取在微米和纳米流体的研究中起到了关键性的作用.我们简单地介绍了耗散粒子动力学的模拟方法,并以此为基础,介绍了能够实现纳维边界条件的可调滑移长度的边界条件模拟方法.通过条纹状图案修饰的超疏水表面的流体力学行为研究,和高分子链在微米纳米流体器件中的运动研究2个例子,耗散粒子动力学结合纳维边界条件的模拟方法的实用性和可靠性得到了证实. 相似文献