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991.
992.
Research on lamellar structure and micro-hardness of directionally solidified Sn-58Bi eutectic alloy
In this work,the Sn-58Bi(weight percent) eutectic alloy was directionally solidified at a constant temperature gradient(G = 12 K.mm-1) with different growth rates using a Bridgman type directional solidification furnace.A lamellar microstructure was observed in the Sn-58Bi samples.The lamellar spacing and micro-hardness of longitudinal and transversal sections were measured.The values of lamellar spacing of both longitudinal and transversal sections decrease with an increase in growth rate.The microhardness increases with an increase in the growth rate and decreases with an increase in the lamellar spacing.The dependence of lamellar spacing on growth rate,and micro-hardness on both growth rate and lamellar spacing were obtained by linear regression analysis.The relationships between the lamellar spacing and growth rate,microhardness and growth rate,and micro-hardness and lamellar spacing for transversal and longitudinal sections of Sn-58Bi eutectic alloy were given.The fitted exponent values obtained in this work were compared with the previous similar experimental results and a good agreement was obtained. 相似文献
993.
Fei Ai Hong Li Quan Wang Wang Zhang Yuan Xiaoyong Chen Libin Yang Junhong Zhao Yongming Zhang 《Journal of Materials Science》2012,47(12):5030-5040
Poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) membranes have important applications as biomaterials. In this study, PVDF/PMMA with varying ratios is blown into membranes, the surface property and blood compatibility of which are thoroughly investigated. Membrane surface characteristics including composition and topography exert considerable influence on the blood compatibility. Introduction of PMMA disturbs PVDF crystallization, however, favors the β phase crystal formation. PVDF content, crystallization ability, and surface enrichment have decisive effects on the membrane surface composition. Meanwhile, with increased PMMA fraction, the membrane surface roughness is also increased, and subsequently results in decreased hemocompatibility. While the membranes with PMMA content lower than 30 wt% show good blood compatibility, those with higher PMMA fraction exhibit obvious platelet adhesion to the surface. Thermal annealing promotes the formation of β phase PVDF and generates much smoother surface, thus endowing the membranes with greatly enhanced blood compatibility. These results show the prospect for optimization of processability, surface property, and blood compatibility of PVDF/PMMA membranes through facile modulation of PMMA content and fabrication process. 相似文献
994.
Audio information hiding has attracted more attentions recently. Spread spectrum (SS) technique has developed rapidly in this area due to the advantages of good robustness and immunity to noise attack. Accordingly detecting the SS hiding effectively and verifying the presence of the secrete message are important issues. In this paper we present two steganalysis algorithms for SS hiding. Both the two methods are based on machine learning theory and discrete wavelet transform (DWT). In the algorithm I, we introduce Gaussian mixture model (GMM) and generalize Gaussian distribution (GGD) to character the probability distribution of wavelet sub-band. Then the absolute probability distribution function (PDF) moment is extracted as feature vectors. In the algorithm II, we propose distance metric between GMM and GGD of wavelet sub-band to distinguish cover and stego audio. Four distance metrics (Kullback-Leibler Distance, Bhattacharyya Distance, Earth Mover’s Distance, L2 Distance) are calculated as feature vectors. The support vector machine (SVM) classifier is utilized for classification. The experiment results of both two proposed algorithms can achieve better detecting performance. Even when embedding strength gets 0.0005, the correct detection rate can reach up to 90%. Its simplicity and extensibility indicate further application in other audio steganalysis. 相似文献
995.
L BG算法作为矢量量化的基本算法具有经典意义 ,但由于在训练图象中 ,总存在少量的离群矢量 ,使得在训练码书时 ,码字的分布受到影响 ,进而使得压缩性能下降 ,因而不能充分体现出矢量量化的优越性能 .而运用基于稳健统计的方法来设计矢量量化器 ,由于减少了码书中的离群矢量 ,同时加强了中心矢量在码书中的权重 ,因而不仅能够尽量减少码书的冗余 ,而且能大幅度提高压缩性能 .实验结果显示 ,用基于稳健统计的设计方法设计的码书 ,其压缩性能比传统的 L BG算法有了较大的改善 ,且恢复图象的主观、客观效果都是令人满意的 . 相似文献
996.
为了弥补传统体绘制静止画面时,不能明确判断场值集中部位的不足,提出了一种快速体绘制算法,针对大坝地震反应有限元计算数据场,根据每个单元法线与视线夹角最小的表面来选择剖切方向,将单元剖切成多个四边形面后进行颜色融合和叠加,大大提高了体绘制速度,实现了动态观察体绘制图,从而清楚地分析场值集中部位。 相似文献
997.
三维真实感图形是科学可视化、计算机动画、虚拟现实的技术核心,也是时空一体化地理信息系统的关键技术,而OpenGL又是目前最新的三维图形国际标准,为了实现地形的真实感显示,讨论了三维真实感地形表现在OpenGL支持下的地形模型映、遥感影象与地形的融合、专题信息与地形的融合、以及动画与虚拟现实等技术实现方法,并在荆江分洪区洪水演进模拟系统等开发中得到应用。 相似文献
998.
999.
针对航空发动机在台架试车中出现的传感器温漂故障,提出了基于经验模式分解(EMD)和Hilbert变换的航空发动机传感器数据有效性验证方法。首先,介绍了航空发动机传感器常见的失效模式以及EMD分解和Hilbert变换方法,并将其引入航空发动机传感器信号分析领域;然后,利用该方法对传感器故障信号进行分解,提取航空发动机传感器故障信号特征,通过故障信号重构和残差向量分析判断故障的严重程度,将原始信号中的故障信号予以剔除;最后,重构有效的信息成分,实现对数据的有效性验证。实例计算与分析验证了该方法在航空发动机传感器温漂数据有效性验证方面是有效的。 相似文献
1000.
Shao Yang Zhang Ai Jiao Xue Xue Feng Jin Wei Ping Chen Zhi Gang Li Yan Ping Liu Hai Bo Wang 《Tribology Letters》2012,45(1):29-36
Semi-interpenetrating network composite containing 33 vol% ceramics (5Al2O3·8SiO2) and 67 vol% Al-alloy dry sliding against Cr12 cold-work die steel was measured on a SRV4 testing machine. The test procedures
include the load sensitivities of the friction and wear at 70 °C and 270 °C. Test results show that the friction and wear
decreased with the increase of load, whereas the specific energy conversion per countermaterial surface unit increased. The
friction level and the specific energy conversion at 70 °C were superior to those at 270 °C. Scanning electron microscopy
and energy dispersive X-ray spectroscopy analysis revealed at 270 °C the existence of the thicker tribofilms and, with them,
more Fe oxides and less Al oxide at the worn composite surfaces in comparison with those at 70 °C. A good accordance was obtained
between test and analysis results. 相似文献