融合模糊连通图和区域生长的MRI脑组织图像分割算法

针对磁共振脑组织图像中存在灰度不均匀,不利于分割的问题,提出了一种应用模糊连通图和区域生长的MRI(Magnetic Resonance Imaging)脑组织图像分割算法。首先用大津法对脑组织进行粗分割,得到脑白质部分的大致轮廓,。然后计算粗分割结构的中心点,根据中心点得到图像的模糊连通图。最后用区域生长算法对模糊连通图中的脑白质进行更精确的分割。试验结果表明,此方法能够精确的得到脑白质轮廓的边缘,并且大大降低了区域生长种子点位置和阈值选取对分割结果的影响。     

折叠超立方体的边邻域连通度

折叠超立方体是最受关注的网络模型之一.设e是图G的一条边, 如果从图G中删掉以e为中心的双星子图,则称e"倒戈".设S为一个边集, 如果S中的边全部倒戈, 若剩下的子图或者不连通, 或者是一个孤立点, 或者是空集, 则称S为G的割边策略.G的最小割边策略所含的边数为边邻域连通度.该文主要证明了折叠超立方体FQn的边邻域连通度为n.     

基于改进的抛物线方程方法求解棱边散射体

将抛物线算法应用于目标的电磁散射特性分析中;针对传统的抛物线算法在计算棱边散射体时误差较大这一问题,引入了棱边绕射对其进行修正;计算结果表明,与传统方法相比,该方法可以有效地提高棱边散射体的计算精度.     

一种新的彩色图像边缘检测算法

传统的边缘检测方法大都基于灰度图像,不能充分利用彩色图像的全部信息。针对已有算法中存在的像素点扩散、边缘定位不准确、边缘不连续等问题,提出了一种彩色图像边缘提取算法,基于图像自身梯度方向信息和多通道信息融合技术,将灰度边缘模板算子扩展应用到彩色图像的边缘检测中,在RGB空间中对原彩色图像进行多通道边缘检测;同时采用滤波来抑制噪声,依靠边缘生长保证检出边缘的连续性,并提出了自适应确定边缘提取门限值的方法。该文提出的彩色图像边缘检测算法计算量小,实验结果表明了其能充分利用图像的颜色和梯度信息,有效地消除噪声,提高边缘检测的准确性,保证边缘的连续性。     

Research progress in ZnO single-crystal: growth,scientific understanding,and device applications

Zinc oxide, a wide band-gap semiconductor, has shown extensive potential applications in high-efficiency semiconductor photoelectronic devices, semiconductor photocatalysis, and diluted magnetic semiconductors. Due to the undisputed lattice integrity, ZnO single crystals are essential for the fabrication of high-quality ZnO-based photoelectronic devices, and also believed to be ideal research subjects for understanding the underlying mechanisms of semiconductor photocatalysis and diluted magnetic semiconductors. This review, which is organized in two main parts, introduces the recent progress in growth, basic characterization, and device development of ZnO single crystals, and some related works in our group. The first part begins from the growth of ZnO single crystal, and summarizes the fundamental and applied investigations based on ZnO single crystals. These works are composed of the fabrication of homoepitaxial ZnO-based photoelectronic devices, the research on the photocatalysis mechanism, and dilute magnetic mechanism. The second part describes the fabrication of highly thermostable n-type ZnO with high mobility and high electron concentration through intentional doping. More importantly, in this part, a conceptual approach for fabricating highly thermostable p-type ZnO materials with high mobility through an integrated three-step treatment is proposed on the basis of the preliminary research.     

Structure characterization of melt drawn polyethylene ultrathin films

Highly oriented ultrathin polyethylene (PE) films were prepared by a melt-draw technique. Transmission electron microscopy study on the obtained ultrathin films indicates that the melt drawn PE thin films consist of highly oriented edge-on lamellae aligned perpendicular to the drawing direction. Electron diffraction confirms that the PE chains in crystal-line phase are highly oriented in film plane along the drawing direction, while only a random orientation of the crystallographic a-and b-axes can be described through electron diffraction. The IR results on the melt-drawn ultrathin PE films demonstrate that the PE molecular chains in both crystalline and amorphous phases of the melt drawn thin films are well oriented along the drawing direction. Moreover, the IR results indicate that in the crystalline phase, the crystallographic b-axis tend to lie in the thin film plane, while in the amorphous phase, the skeleton plane of some local chains prefers to parallel the film plane. The alignment of b-axis of PE crystals in ultrathin films originates from the fact that the b-axis is the fastest growth direction of the PE crystals.     

正入射时二维空气孔结构正方形和三角形光子晶体的带隙结构

 利用平面波展开法推导出光在光子晶体中传播时的本征方程及其矩阵表达形式,数值求解了圆形空气孔结构的正方形光子晶体和三角形结构光子晶体的色散曲线,给出了不同空气孔结构下的色散曲线。计算分析发现,在<11>方向上,二维正方形结构的光子晶体E波的第一带隙与H波的第一带隙完全分开。在<10>方向上,E波的第一带隙比H波略窄,两者的变化趋势也不尽相同。对E波来说,第一带隙随着空气孔径的增大而增宽;但对H波来说,第一带隙先增宽再变窄。与正方形结构光子晶体不同的是,二维三角形结构光子晶体在<11>方向的第一带隙边缘位置并不在M（1,1）点,而是出现在（0.5,0.5）点,其中心频率比<10>方向的小,但其带隙宽度较正方形结构的大。在<10>方向上,E波的第一带隙比H波的略宽,且两者的变化趋势完全相反。对E波来说,第一带隙先增宽再变窄;但对H波来说,第一带隙随着空气孔径的增大而增宽。     

基于小波变换和模糊算法医学图像边缘检测算法

在医学图像三维显示技术中，需要得到单像素级的清晰轮廓线。为了适应这种需求，提出了一种边缘检测算法。它基于Mallat小波模极大值边缘检测方法，同时应用模糊算法构造相应的隶属函数，再对得到的极大值进行进一步筛选，最终可以得到单像素级的边缘。实验结果证明了该算法的可行性。     

有旋转六角洞的光子晶体的最大绝对带隙和缺陷模

研究有旋转六角洞的三角点阵二维光子晶体的带结构,探索单元核几何对称性减少对绝对带隙值和局域缺陷模频率值的影响。对洞的中等旋转角,我们揭示此结构的最大绝对带隙可以获得,且该角依赖于洞的半径和背景材料的折射指数。我们也研究了由洞的缺失产生的缺陷模的特点,讨论了此结构模的可调性。     

Magnetite defines a vertebrate magnetoreceptor

The key behavioural, physiological and anatomical components of a magnetite-based magnetic sense have been demonstrated in rainbow trout (Oncorhynchus mykiss). Candidate receptor cells located within a discrete sub-layer of the olfactory lamellae contained iron-rich crystals that were similar in size and shape to magnetite crystals extracted from salmon. Here we show that these crystals, which mapped to individual receptors using confocal and atomic force microscopy, are magnetic, as they are uniquely associated with dipoles detected by magnetic force microscopy. Analysis of their magnetic properties identifies the crystals as single-domain magnetite. In addition, three-dimensional reconstruction of the candidate receptors using confocal and atomic force microscopy imaging confirm that several magnetic crystals are arranged in a chain of about 1 microm within the receptor, and that the receptor is a multi-lobed single cell. These results are consistent with a magnetite-based detection mechanism, as 1-microm chains of single-domain magnetite crystals are highly suitable for the behavioural and physiological responses to magnetic intensity previously reported in the trout.     

基于小波变换的多尺度图像边缘检测

边缘作为图像的最主要特征,成为图像信息获取的重要内容.而小波变换具有检测局域突变的能力,而且可以结合多尺度信息进行检测,因此成为图像信息边缘检测的优良工具.文章首先构造了高斯多尺度边界检测算子,然后根据信号边界与噪声边界的小波变换模值跨尺度传递的不同特性,讨论了不同尺度的检测算子检测的边缘所具有的特点,在此基础上提出由边缘传递、继承和生长构成的多尺度边缘关联融合算法.实验结果说明这种特征提取方法不仅有效地降低了噪声,而且融合的边界比较完整,定位准确.     

Dynamic instabilities and memory effects in vortex matter

The magnetic flux line lattice in type II superconductors serves as a useful system in which to study condensed matter flow, as its dynamic properties are tunable. Recent studies have shown a number of puzzling phenomena associated with vortex motion, including: low-frequency noise and slow voltage oscillations; a history-dependent dynamic response, and memory of the direction, amplitude duration and frequency of the previously applied current; high vortex mobility for alternating current, but no apparent vortex motion for direct currents; and strong suppression of an a.c. response by small d.c. bias. Taken together, these phenomena are incompatible with current understanding of vortex dynamics. Here we report a generic mechanism that accounts for these observations. Our model, which is derived from investigations of the current distribution across single crystals of NbSe2, is based on a competition between the injection of a disordered vortex phase at the sample edges, and the dynamic annealing of this metastable disorder by the transport current. For an alternating current, only narrow regions near the edges are in the disordered phase, while for d.c. bias, most of the sample is in the disordered phase--preventing vortex motion because of more efficient pinning. The resulting spatial dependence of the disordered vortex system serves as an active memory of the previous history.     

等规聚苯乙烯单链单晶的结构和耐辐照性能

利用电子衍射（ED）和高分辨电子显微（HREM）技术，研究等规聚苯乙烯（i－PS）单链单晶的结构．纳米级的单链单晶具有很强的耐电子辐照性能．按照i－PS的晶胞能对ED图中的衍射环和HREM像中的晶格条纹进行晶面指标化，但发现低指数衍射缺失．由于单链单晶的尺寸很小，电子辐照所产生的次级电子可以逸出晶体，使辐照损伤大大减小．另外，单链单晶存在着较少的低指数晶面，未能产生足够的衍射强度，使低指数晶面的衍射缺失．单链单晶对电子辐照稳定，在室温下，可得到高分辨晶格条纹象，这为研究高分子晶体的结构开辟了新的实验方法．     

氯化钠型结构有限晶格振动

编制了氯化钠型结构各种晶体的晶格振动通用程序;它适用于循环或自由边界条件。令体系原子总数由少至多地分别计算得到了趋向于宏观尺寸极限的零维、一维、二维和三维体系的结果。体系的键角和键长力系数之比增大时,晶化模软化使结构不稳定,导致其升华或熔解。比较了两种边界条件所得到的完全不同的结果。在自由边界条件下简谐模频谱分布随结构中重和轻原子重比增大而分裂成三支;低频、中频和高频之间共出现两个禁区。低频支主要是重原子的振动;高频支重原子大致不动;中频支两种原子都振动。     

基于权函数法的含裂纹叶片的应力强度因子研究

基于两个已知的参考应力强度因子和权函数的基本特性,分别计算了含单边裂纹、双边裂纹和中心裂纹的有限宽板的权函数。然后,将所计算的权函数分别用于确定含单边、双边及中心裂纹的旋转平板叶片的裂尖应力强度因子K。最后,在线弹性断裂力学范围内由断裂准则KKIC分别对含单边、双边和中心裂纹的平板叶片的临界转速进行了估算。研究结果表明:旋转平板叶片所含的裂纹深度越深、裂纹位置距旋转轴越近,所引起的裂尖应力强度因子就越大,所允许的临界转速就越低。     

融合边缘信息的合成孔径雷达图像超像素分割算法

针对简单线性迭代聚类(simple linear iterative cluste, SLIC)对含有乘性相干斑噪声的合成孔径雷达(synthetic aperture radar, SAR)图像边缘分割不理想的问题,本文在SLIC基础上提出了一种融合边缘信息的SAR图像超像素分割算法。首先,利用高斯方向平滑对SAR图像进行预处理,从而在抑制乘性相干斑噪声的同时有效保护边缘细节;其次,提出了一种基于指数加权平均比率(ratio of exponential weighted average, ROEWA)算子的改进相似度测量参量,以提高SAR图像的分割精度;最后,采用六边形初始化聚类中心与圆形区域的搜索方式进行局部区域聚类,从而保证了算法复杂度增加的同时,算法的运行时间不会明显变化。实验结果表明,与四种经典超像素算法相比,本文算法生成的超像素边缘更加贴合SAR图像的真实边缘且得到的超像素大小较为均匀。     

深井采空区宽条带煤柱受力状态研究

为研究深井采空区宽条带煤柱受力状态,对唐口矿千米深矿井宽条带开采采空区煤柱受力状态进行了实际观测和分析.结果表明:距煤柱边缘6～8m区域为压力峰值区,距边缘10m区域承载附加应力较小;在锚网带支护系统作用下,煤壁边缘并不完全坍塌垮落;越靠近煤柱内部,其实际支撑能力越大,在距边缘1m区域的煤柱实际强度约为10.2MPa;深井覆岩外应力拱所需承载的覆岩重量要比浅井大得多,煤柱外应力场峰值和影响范围都明显大于浅井.     

基于边分类的三维模型外轮廓线抽取算法

根据三维模型面片的方向性对边进行分类，筛选出轮廓边即共享可见面与不可见面的边，大幅度地排除那些不可能成为轮廓线的边，筛选过程只是一种比较运算。算法L利用外轮廓线的连通性递归搜索邻接的轮廓边得到若干闭合回路和分离的轮廓边，最终得到外轮廓线，并且自动决定的闭合回路方向和回路之间位置关系决定了回路是否属于外轮廓线；对那些精度不高而可能造成闭合回路搜索失败的三维模型，算法C利用遮挡关系由模型的前向面片对轮廓边进行裁剪得到三维模型的外轮廓线。用四叉树结构对模型投影区域进行划分，尽可能地排除那些不可能对轮廓边有遮挡关系的前向面片，减少裁剪的比较范围，降低算法的复杂度。本文的方法快速准确，适应各类二维流形模型。     

图像边缘检测中的改进算法

针对传统的蚁群边缘检测算法存在耗时长和易受噪声影响的缺点,提出了一种改进的蚁群边缘检测算法.该算法对蚂蚁路径选择中的启发式信息值的计算方法进行改进,使其计算基于邻域中节点的梯度,能更好地引导蚂蚁向边缘节点进行移动.通过仿真实验表明:该算法与传统的蚁群算法相比,能够减少耗时、抑制噪声及准确快速地检测出图像边缘.     

PE,PP晶格内应力和晶胞参数变化的关系

高聚物在纺丝及后拉伸过程中,由于大分子运动缓慢,有相当一部分内应力尚未得到松弛,即被冻结在里面。本文以 PE 和 PP 为对象,采用声速法、TMA 法、密度梯度法、WAXS 法和计算机分峰技术,对这两种纤维进行分析,发现 PE 与 PP 的晶格应变相差很大。主要原因是 PE 的理论模量比 PP 大一个数量级。本文计算了 PP 的晶区模量,并与文献报道的理论模量作比较,发现有两种因素影响结晶尺寸和结晶度。本文得到的结论与文献报道的 PET,PPTA 研究结果极为相似。作者认为:品格内应力存在于各种高分子材料中,它是造成品格应变的主要原因。