基于K均值聚类的传输函数设计方法

在直接体绘制中,传输函数定义了从体数据属性到光学属性的映射关系,直接决定了体绘制的效果,是体绘制研究的关键技术之一。传统的多维传输函数是基于体数据和梯度体数据进行设计的,本文提出基于K均值聚类的传输函数设计方法,并在此基础上进行气象数据的分类方法研究,实现基于GPU的气象台风数据的直接体绘制。     

基于多维传输函数的三维医学图像系统研究

传输函数是直接体绘制的基础,传输函数的设计是体视化结果的关键。本文在传输函数的定义上,讨论了将体数据标量值和梯度模值作为定义域的多维传输函数的原理及实现方法。针对传输函数与位置无关,难以提取感兴趣的区域(Region Of Interest 简称ROI),提出了基于三切面交互式体数据的切割方法,从而有效的提取感兴趣区域。最后,设计和实现了一个基于多维传输函数的三维医学图像系统,获得了很好的体绘制效果。     

特征抽象的直接体绘制方法

直接体绘制需要借助于传输函数,而设计一个有效的传输函数非常耗时且需要具备丰富的经验.为此提出一种不透明度自动调节的可视化方法.通过分析采样光线提取出数据的特征,并将这些特征抽象为不同层次的采样点,抽象采样点的不透明度根据采样光线上特征数的变化而改变;在保证最远抽象采样点可见度最大的前提下,推导并修改传统体绘制积分方程,得到基于抽象采样点的体绘制积分方程.实验结果表明,该方法不依赖于传输函数,能有效地展示体数据中的特征信息.     

一种快速的体数据特征增强可视化算法

传输函数是实现体数据特征分类与可视化的重要手段,随着维度的升高,传输函数设计过程趋于复杂且难以实时交互;而在基于视线方向上特征分析的体数据特征可视化方法中,复杂的特征分析过程占用GPU硬件资源,降低了体绘制效率.为此提出一种快速的、不完全依赖于传输函数设计的体数据特征增强可视化算法.利用视线方向上采样点标量值变化率,快速识别视线方向上的重要特征,通过降低不重要特征的不透明度以增强重要特征在绘制结果图像中的可见性;引入反锐化掩模技术对视线方向上重要特征进行加权处理,在保证体绘制效率的同时增强了体数据特征的视觉感知.在绘制过程中,文中算法利用简单而有效的特征分析操作,在传输函数映射的基础上对感兴趣特征的视觉元素再次优化,实现不完全依赖于复杂传输函数设计的体数据特征增强可视化.最后通过大量实验,进一步验证了该算法的有效性与实用性.     

基于样例图像的颜色传输函数设计

体绘制是颜色混合的过程,用户很难通过直接编辑颜色传输函数来得到期望的颜色混合效果.为了能更直观地为体绘制图像设置颜色,提出一种基于样例图像的颜色传输函数设计方法.首先使用颜色迁移方法,基于样例图像对初始体绘制图像进行颜色迁移,使得迁移后的体绘制图像与样例图像有类似的着色风格;然后还原体绘制的颜色混合过程,使用最优化的框架将迁移后的体绘制图像反推到三维建立颜色传输函数,在该颜色传输函数下的绘制结果与样例图像尽可能保持一致,样例图像可以是任意符合用户期望颜色效果的图像.与传统的传输函数设计方法相比,文中方法利用了已有图像资源和人类对图像的感知能力,更简单直观,易于使用,且该方法是有效的.     

基于体数据分类的直接体绘制传输函数研究

直接体绘制是形成于20世纪80年代后期的一个新研究领域,本论文提出了一种基于体数据的标量值和梯度的分类方法,采用该方法可获得体数据重要的信息,从而帮助研究人员准确地设置传输函数的不透明度和颜色参数,使绘制的图像更加清晰。     

局部特征加强的体绘制算法

最大强度差值累积结合了直接体绘制和最大强度值投影的优势,但其在累积过程中会遗漏一些局部特征.为了绘制体数据中局部特征信息,提出一种局部特征加强的直接体绘制方法.通过查找采样光线上特征边界点来确定局部最大强度的区域,利用局部差值累积的方法加强特征区域的绘制;为了提高特征分界点的查找精度,引入移动最小二乘法来平滑采样光线上的标量值,并利用用户自定义的阈值函数来控制特征的绘制;在绘制过程中,采用特征分析的表面光照模型增强绘制特征的三维立体感,引入深度信息对局部特征累积算法进行优化,并引入了Tone衰减方法使累积颜色值处于正常显示范围.实验结果表明,文中方法可在不需要传输函数的前提下绘制体数据中的特征信息.     

基于梯度特征的医学体绘制传输函数曲线拟合方法

医学体绘制的精度和实时性取决于传输函数曲线的精度和生成过程的运算开销.典型体绘制的传输函教生成方法是通过灰度映射来生成分段线性函数,精度低、耗时长.本文针对该问题.提出了一种基于体数据梯度特征的传输函数曲线拟舍方法.该方法根据体数据集的梯度变化特点,利用数据值、梯度和沿梯度方向的二阶导数拟合曲线函数来生成传输函数.实验结果表明:在使用规则俸数据时,本方法可有效实现医学可视化.     

面向爆炸压力场的体绘制自动传输函数设计

直接体绘制广泛应用于可视化领域,其中传输函数决定了最终绘制的效果。大规模爆炸数据属于复杂的时变数据,其压力场的取值范围和分布会随时间剧烈变化。为了实现对冲击波传播特征的连续跟踪,提出了一种基于标量-时间梯度（scalar-temporal gradient,STG）二维空间的自动传输函数设计方法。结合爆炸过程中的物理规律,将STG空间划分为多种状态并总结了状态之间的转移规律。将冲击波的传播特征编码为一段一定长度的状态转移链（state transitions chain,STC）,称为时变特征。传输函数中颜色以时变特征为单位,基于完全状态转移链自动分配。传输函数中的不透明度采用基于压强变化速率的分段非线性曲线,凸显压强变化剧烈的特征。选取了两类典型的大规模爆炸场景对方法进行了验证,绘制结果中都包含了丰富的明显可区分的冲击波传播特征。结果表明,生成的传输函数在整个时间维度上都能稳定、准确地捕捉冲击波的传播特征。     

基于GPU的三维医学图像混合可视化系统

研究并实现了一个基于GPU的医学图像混合可视化系统，该系统采用三维纹理映射的方法实现直接体绘制，利用GPU的可编程特性完成体绘制方法中的插值后分类算法和传输函数的传递及实时修改，采用OpenGL技术实现表面的绘制，并基于场景图结构实现时表面数据的管理。面绘制和体绘制部分都采用OpenGL实现，运用OpenGL的融合机制，系统实现了面绘制和体绘制的混合显示。本系统大大提高了体绘制的速度，有效地保留了面绘制和体绘制的优势，在保证绘制速度的基础上丰富了图像信息。     

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).