概率加权测地距离的脑部MR图像超像素分割

超像素是一种重要的图像过分割,因为医学图像具有边界模糊、不同组织的灰度范围互相重叠的特点,为超像素分割带来极大困难.针对脑部MR图像超像素生成问题,从脑部MR图像的特点出发,充分利用脑部MR图像表达先验知识,结合脑部MR图像的一般结构,定义每个像素属于脑组织中一个类别的概率,并基于分类概率提出一种有效的边界梯度计算方法;在此基础上,提出一种概率密度加权的测地距离脑部MR图像超像素分割算法;最后应用模糊C均值聚类算法作为后续分割处理,获得脑部MR图像的组织分类.与现有算法在分割性能上进行定量比较的实验结果表明,文中算法能够产生更准确的分割边界.     

脑部MR图像的Sigma-IFCM分割算法

受成像原理、设备及环境的影响,脑部MR图像一般都有大量的噪声,给图像分割造成很大困难。在IFCM算法的基础上通过引用Sigma过滤器原理,改变邻居像素点的计算方法,对分割后的图像进行去毛刺和边部光滑处理,并在模拟的脑部MR图像上进行分割实验。     

基于改进的Snake模型的脑部MR图像分割方法*

为实现对脑部磁共振图像的分割,提出了一种改进Snake模型的图像分割方法。通过引入轮廓中心的概念,在贪婪Snake模型的能量函数中增加距离势能作为外部约束能量,增大了外能的吸引范围,使分割结果不依赖于初始轮廓;对各能量项进行归一化操作,并以归一化扩散方程各分量的梯度矢量流代替MR图像的梯度,提高了模型处理弱边界和深度凹陷区域的能力;对各能量函数的离散化和参数的选择进行了阐述。实验结果表明,该算法是一种有效的分割脑部MR图像的方法。     

基于高斯混合模型的脑部MR图像自动分割

将脑部组织从MR图像中提取出来是脑部图像处理的一个重要环节,如何精确地将脑组织从非脑组织中分离出来成为研究的难点。传统的水平集方法仅依赖梯度信息,由于脑部图像含有噪音、过度区域等因素的影响,使得分割效果不是很理想。文章提出了一种脑部MR图像的自动分割方法,它利用模糊各向异性扩散方法对图像进行平滑,结合直方图分析得到了图像的全局信息自动构造初始曲线,并利用高斯混合模型构造水平集演化的速度函数,得到较好的分割结果。对脑部MR图像分割的实验表明该方法准确度高、抗噪性能良好。     

非局部降噪快速模糊C-均值聚类算法

传统的模糊C-均值聚类算法未利用图像的空间信息,在分割迭加了噪声的MR图像时分割精度较差。采用了既能有效去除噪声又能较好地保持图像边缘特征的非局部降噪方法,结合基于图像灰度直方图聚类分析的快速模糊C-均值聚类算法,得到了一种具有较高分割精度的图像快速分割算法。通过对模拟图像、仿真脑部MR图像和临床脑部MR图像的分割实验,表明提出的新算法比已有的快速模糊C-均值聚类算法有更精确的图像分割能力。     

基于MS-FCM算法的MR图像分割方法

针对传统模糊C-均值(FCM)聚类算法在分割低信噪比图像时准确性较差的问题,提出一种用于MR图像分割的改进算法MS-FCM。针对脑部MR图像相邻像素属于同一分类的模糊隶属度相近的特性,在迭代过程中对隶属度数据集进行滤波,以降低噪声对聚类精度的影响。模拟脑部MR图像和临床脑部MR图像的分割实验证明,该算法可以提高图像分割精度。     

基于模糊马尔可夫场的脑部MR图像分割算法

在传统马尔可夫场模型的基础上,建立了模糊马尔可夫场模型。通过对模型的分析得出图像像素对不同类的隶属度计算公式,提出了一种高效、无监督的图像分割算法,从而实现了对脑部MR图像的精确分割。通过对模拟脑部MR图像和临床脑部MR图像分割实验,表明新算法比传统的基于马尔可夫场的图像分割算法和模糊C-均值等图像分割算法有更精确的图像分割能力。     

基于水平集的三维脑部肿瘤分割

脑部肿瘤的分割在临床的诊断、治疗以及研究方面都有很重要的作用,但是由于脑肿瘤的大小、类型、位置等的多变性,脑部肿瘤分割一直是一个难点问题.根据脑肿瘤在核磁共振图像上的梯度以及图像中点的强度分布提出了一种新的基于水平集的分割方法.算法定义了一个新的能量函数,更好地匹配图像中肿瘤区域的强度分布.在实际的脑部核磁共振图像上进行实验,文中算法可以准确地分割出脑部肿瘤.与传统的水平集方法比较,该算法分割结果更加准确.     

基于NL-Means的双水平集脑部MR图像分割算法

针对脑部MR图像中通常伴有灰度不均、高噪声的缺点,且传统水平集无法有效分割的问题,提出了一种基于NL-Means的双水平集算法。首先,利用改进型NL-Means算法对带有噪声的医学图像进行去噪处理,再通过双水平集算法对图像进行分割,提取多目标区域,为了去除医学图像中灰度不均对分割效果的影响,所提算法引入了偏移场拟合项,进一步改进了双水平集模型,进而对去噪图像分割效果进行了优化处理。实验结果表明,所提算法能有效地解决灰度不均与高噪声的问题,能够将伴有灰度不均的高噪声脑部MR图像完全分割出来,从而获得预期的分割效果。     

融合稀疏表示和字典学习的脑部MR图像分割

针对脑部磁共振图像中白质、灰质和脑脊液的分割精度问题,提出一种融合稀疏表示和字典学习的图像分割方法。首先,利用基于块的输入数据来训练过完备字典;然后,根据学习到的字典获得最优稀疏表示的高维特征;最后,结合每个像素局部和非局部重构误差实现分割。在模拟和真实图像数据库上的实验结果表明,该方法能利用带有距离因子和稀疏因子的公式准确分割MR图像,在稳定性方面优于其他MR分割方法。     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).