基于自适应纹理复杂度的仿生视觉导航方法研究

针对稠密光流在低纹理复杂度时精度较低的问题,提出了一种自适应纹理复杂度的稠密光流优化方法,以提升光流导航精度。根据三种不同大气条件下三种不同图像模糊程度的图像光流精度与纹理复杂度的统计图,推断稠密光流的精度与图像的纹理复杂度呈线性关系。通过建立图像纹理复杂度和稠密光流精度之间的直接联系,利用灰度共生矩阵的对比度参数评价图像纹理复杂度,采用最小二乘法拟合图像纹理复杂度和光流真值优化系数的函数关系,获得自适应纹理复杂度的稠密光流优化模型。基于该优化模型设计了仿真实验,实验结果表明,基于该模型可有效提升稠密光流在低纹理复杂度时的计算精度。     

基于纹理边界检测的航天器椭圆特征提取方法

为确定失效航天器等非合作目标的相对位姿，提出一种通过纹理边界检测的椭圆特征提取方法。该方法假设椭圆特征是航天器表面两种不同纹理的边界，利用上一时刻相对位姿信息，将对接环离散几何模型投影到像平面，并沿各离散点的法向方向通过概率方法检测纹理边界点。利用随机抽样一致(RANSAC)方法剔除边界点中的粗大误差，进而拟合出椭圆参数。纹理特征对光照变化具有鲁棒性，因此该方法能够在变光照、星体表面反光不均匀等复杂情况下快速准确地提取图像中的椭圆特征。本文以对接环图像特征提取为例进行仿真校验，分析了算法参数和噪声对提取椭圆精度和时间的影响。利用真实图像与基于梯度边缘的椭圆提取方法进行对比，结果表明，所提出的算法具有较高的精度和速度。     

Electrochemical micromachining of micro-dimple arrays on cylindrical inner surfaces using a dry-film photoresist

The application of surface textures has been employed to improve the tribological performance of various mechanical components. Various techniques have been used for the application of surface textures such as micro-dimple arrays, but the fabrication of such arrays on cylindrical inner surfaces remains a challenge. In this study, a dry-film photoresist is used as a mask during through-mask electrochemical micromachining to successfully prepare micro-dimple arrays with dimples 94 lm in diameter and 22.7 lm deep on cylindrical inner surfaces, with a machining time of 9 s and an applied voltage of 8 V. The versatility of this method is demonstrated, as are its potential low cost and high efficiency. It is also shown that for a fixed dimple depth, a smaller dimple diameter can be obtained using a combination of lower current density and longer machining time in a passivating sodium nitrate electrolyte.     

基于纹理的活动轮廓三维图像分割研究

对具高噪声和低对比度三维图像的识别和分割算法进行了研究。基于活动轮廓模型,用Gabor变换提取图像的纹理特征,根据统计学信息假设,通过偏微分方程水平集和窄带方法求解,获得较基本活动轮廓的算法分割更光滑精确的物体轮廓。实验结果表明:改进模型算法的效率和准确度达到预期效果。     

从图像工程角度看CBERS-1卫星图像

文章从图像工程角度从灰度、纹理和边缘3个方面对CBERS -1卫星的图像进行了量化评价 ,并与同一地区的TM图像进行了比较 ,客观地反映了CBERS-1卫星的图像质量 ,提出了CBERS-1卫星图像的优势和需改进的方面。     

基于纹理特征多分辨双Markov-GAR模型的SAR图像分割

为了提高SAR图像分割精度,提出在以灰度共生矩阵产生的纹理统计量为特征所生成的图像上,同时考虑SAR图像像素间空间分布特征和局部灰度均值和方差等统计量给出多分辨双Markov框架下的GAR模型,采用多分辨MPM的参数估计方法及对应的无监督分割算法,对SAR图像进行纹理分割。实验结果表明该方法用于一些高分辨SAR图像,与基于灰度图像上的多分辨双Markov-GAR模型纹理分割相比,在分割精度上能降低分割时的错分率。     

Using vegetation indices and texture measures to estimate vegetation fractional coverage (VFC) of planted and natural forests in Nanjing city,China

Vegetation fractional coverage (VFC) is an important vegetation parameter affecting exchanges of carbon, water, energy between the atmosphere and surface. In this study, the applicability of tonal and texture measures calculated using an IKONOS_2 image in retrieving VFC of forests was investigated in the urban area of Nanjing city, China. Four spectral vegetation indices (VI) and six texture measures (TEX) were related to VFCs acquired from in situ measurements. Models for estimating VFC based on VIs or/and TEXs were established and validated for planted low broad-leaf forest plots (PLB), planted mature forest plots (PMF), natural broad-leaf forest plots (NBF), and all forest plots (ALLv), respectively. The results show that high spatial resolution remote sensing data is applicable to estimate VFC in urban areas, and TEXs may act as effective supplements of vegetation indices (VIs) for the retrieval of VFC. VIs are suitable for VFC estimation of mature forests (such as NBF and PMF) with high vegetation density, and TEXs can yield a more accurate estimate for planted forests (such as PLB and PMF) with regular spatial distribution if they are calculated with proper parameters, such as window size. The combination of VIs and TEXs improve the estimation of VFC if forest types are not previously differentiated. The results can be used as a reference for determining effective spectral or texture parameters in VFC estimation under similar environmental conditions according to vegetation maturity and regularity.     

电子束增材制造γ-TiAl显微组织调控与拉伸性能研究

研究了电子束选区熔化增材制造Ti-48A1-2Cr-2Nb合金的显微组织与拉伸性能.A1含量的烧损导致显微组织呈现不均匀性,沉积态材料由较大的γ晶粒和被α2晶粒钉扎的链状细小γ晶粒组成.γ相占据89％的体积,但并未显示出明显织构;而α2相显示出14.1倍随机值的(0001)织构,其c轴与沉积方向平行.沉积态材料的室温抗拉强度达到503MPa,而塑性为0.热等静压与热处理后的材料强度稍有下降,但延伸率获得较大改善.直到800℃,双态组织TiAl-4822材料的抗拉强度仍在460MPa以上,而全片层组织材料则维持在400MPa以上.     

Dynamic tensile behavior of AZ31B magnesium alloy at ultra-high strain rates

The samples having {0001} parallel to extruding direction(ED) present a typical true stress–true strain curve with concave-down shape under tension at low strain rate. Ultra-rapid tensile tests were conducted at room temperature on a textured AZ31 B magnesium alloy. The dynamic tensile behavior was investigated. The results show that at ultra-high strain rates of 1.93 · 102 s 1and 1.70 · 103 s 1, the alloy behaves with a linear stress–strain response in most strain range and exhibits a brittle fracture. In this case, {10-12} 10-11 extension twinning is basic deformation mode. The brittleness is due to the macroscopic viscosity at ultra-high strain rate, for which the external critical shear stress rapidly gets high to result in a cleavage fracture before large amounts of dislocations are activated. Because {10-12} tension twinning, {10-11} compressive twinning,basal a slip, prismatic a slip and pyramidal c + a slip have different critical shear stresses(CRSS), their contributions to the degree of deformation are very differential. In addition,Schmid factor plays an important role in the activity of various deformation modes and it is the key factor for the samples with different strain rates exhibit various mechanical behavior under dynamic tensile loading.     

微织构刀具切削钛合金的研究进展

针对钛合金切削加工过程中切削力大、切削温度高和刀具磨损严重等问题,近年学者们尝试采用微织构刀具来解决。本文综述了微织构刀具在钛合金切削加工中的应用,分析了微织构刀具在改善表面质量,降低切削力、刀具磨损、摩擦因数和切削温度等方面的切削机理,并指出微织构刀具切削钛合金存在的问题。