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991.
光学成像系统自身通常都具有一定的偏振效应,严重影响仪器偏振测量精度,而提高仪器中偏振片绝对角度精度能提高偏振定标精度,对校正光学系统自身的偏振特性具有重要的意义。对偏振片直线透光轴Raw图像高精度边缘定位和直线检测是偏振片绝对角度计算的关键步骤。针对传统LOG算子各向同性及虚假边缘与边缘定位精度相矛盾的缺陷,提出改进型一阶导阈值旋转式椭圆对称LOG算子。该算子不仅保留了经典LOG算子的优点,还具有对不同角度的边缘更加有效地进行检测,在保持边缘定位精度下,减少虚假边缘的特点。在处理得到的边缘二值图像上,进行直线检测求出偏振片绝对角度,通过对比分析最小二乘法线性拟合和霍夫变换的直线检测效果,得出霍夫变换能精确计算出偏振片绝对角度。实验证明改进型LOG算子与霍夫变换相结合提高了偏振片绝对角度测量精度,对偏振定标精度具有很大的提高。 相似文献
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属性约简是粗糙集理论的重要研究内容之一。在Pawlak粗糙集模型中,正区域大小随着属性增多而变大,呈现单调性。然而,在决策粗糙集模型中,概率正区域与属性集之间不具有单调性,从而产生各种属性约简定义。为此,深入研究了决策粗糙集属性约简问题,阐述了几种约简定义之间的关系,证明了保持局部最大概率正区域的约简具有较大的代价,指出了保持所有对象的正决策不变的约简呈现稳定性和存在属性核。 相似文献
993.
HTTP-flooding attack is a much stealthier distributed denial of service (DDoS) attack, challenging the survivability of the web services seriously. Observing the web access behavior, we find that the surfing preference of normal users is much more consistent with the webpage popularity than that of malicious users. Based on this observation, this paper proposes a novel detection scheme for HTTP-flooding (HTTP-SoLDiER). Specifically, HTTP-SoLDiER first quantifies the consistency between web users surfing preference and the web- page popularity with large-deviation principle. Then HTTP-SoLDiER distinguishes the malicious users from normal ones according to the large-deviation probability. In practice, the webpage popularity plays a key role in attack detection of HTTP-SoLDiER. Due to the never-ending updating of the webpage content and the disturbance induced by attackers, the webpage popularity often varies over time. Thus, it is critical for HTTP-SoLDiER to dynamically update the webpage popularity. We design a reversible exponentially weighted moving average (EWMA) algorithm to solve the problem. Finally, we evaluate the effectiveness of this scheme in terms of true positive (TF) and false positive (FP) probabilities with NS-3 simulations. The simulation results show that HTTP-SoLDiER can detect all random HTTP-flooding attackers and most of the perfect-knowledge HTTP-flooding attackers at little false positive. 相似文献
994.
Seong Ik Yoo Tae Yeon Lee Jin‐San Yoon Ik‐Mo Lee Mal‐Nam Kim Han Sup Lee 《应用聚合物科学杂志》2002,83(4):767-776
The interfacial reaction of the polyethylene (PE)/starch blend system containing the reactive compatibilizer maleated polyethylene (m‐PE) was directly characterized by Fourier transform infrared (FTIR) spectroscopy. A significant amount of anhydride groups on m‐PE existed as hydrolyzed forms, resulting in a large amount of carboxyl groups. Using a vacuum‐heating‐cell designed in the laboratory, the carboxyl groups were successfully transformed into the dehydrolyzed state (i.e., anhydride group). This result enabled the direct spectroscopic observation of chemical reaction occurring at the interface. For the PE/starch blend system containing m‐PE, the chemical reaction at the interface was verified by the evolution of ester and carboxyl groups in the FTIR spectra. The effect of the reactive compatibilizer on the interfacial morphology was also examined by scanning electron micrography (SEM). Enhanced interfacial adhesion was clearly observed for the blend system containing reactive compatibilizer. Tensile strengths of blend systems containing m‐PE also increased noticeably compared with the corresponding system without compatibilizer. A similar observation was made for the breaking elongation data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 767–776, 2002 相似文献
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从481—2B型废催化剂中回收钼工艺述评 总被引:2,自引:0,他引:2
钼酸铵是一种主要的化工原料,本文对从工业生产的废催化剂中回收钼的工艺进行了比较系统的概括,对各种工艺进行了比较,并给出了最佳的工艺条件。 相似文献
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A thermally labile polymer, poly(propylene glycol), was modified to obtain PPG having an amino end group. PPG was incorporated into a partially aliphatic polyimide based on an alicyclic dianhydride, and this afforded triblock copolymers containing various amounts of PPG blocks. The thermal properties of the copolymers were investigated by thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the PPG block in the copolymers was carried out at 240°C under various pressures to obtain porous polyimide films. The pores remained during the thermolysis under a reduced pressure of 710 mmHg, whereas they collapsed under (near) atmospheric pressure. The pore size increased as the amount of the PPG block in the copolymers increased. The dielectric constants of the porous polyimides varied from 2.60 to 2.42 with the original copolymer composition. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 532–538, 2006 相似文献