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.     

基于体数据空间相似性的传输函数优化设计方法

传输函数设计是体数据可视化流程的重要环节,高效的传输函数设计方法是提升体数据可视化效率的关键.在传统传输函数设计的基础上,该文以提升体数据特征可视化及分析效率为目标,提出一种基于体数据空间相似性的传输函数优化设计方法.在特征空间分析过程中,结合体数据空间位置信息,定义特征空间相似性度量标准,对一维传输函数特征空间进行自适应划分;在光学参数映射过程中,定义能量方程描述感兴趣特征的可见性分布与目标可见性分布的差异,近似求解能量方程的梯度,加速光学参数向量的迭代优化,以高效地实现光学参数优化设计.相比于传统的传输函数设计方法,该方法有效耦合特征空间分析及光学参数映射过程,可以帮助用户快速地实现体数据中感兴趣特征的分析与可视化.大量的实验结果、效率对比及用户体验反馈信息进一步验证了该文算法的有效性与实用性.     

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.     

非对称高斯函数的时变体数据特征跟踪及可视化

目的 在传统基于时序曲线的时变体数据特征的识别与跟踪过程中,不仅需要用户具备丰富的先验知识来确定感兴趣特征的时序曲线形状,而且时序曲线段的匹配和抽取过程亦复杂,难以交互,这一定程度上降低了时变体数据可视化及分析效率.提出了一种新的基于高斯时序曲线的时变体数据可视化及分析方法.方法 首先,对时序曲线进行低通滤波,准确地查找极小值点,对时序曲线进行分段;进而,引入非对称高斯函数对时序曲线段进行拟合获得高斯时序曲线;为了进一步方便用户识别感兴趣特征,观察特征在时间域上的演变过程,提供一种便捷的交互技术,由用户单击任一时间步绘制结果图像中感兴趣的特征信息,分析视线方向上的特征可见性,以确定感兴趣特征及其对应的高斯曲线,进而由参数匹配获得所有时间步中感兴趣特征信息.结果 为了验证本文算法的高效性与可行性,对时序仿真的飓风数据进行特征跟踪与交互式可视化,可以看出,本文算法不仅可以准确跟踪飓风中心特征,而且特征分析与可视化效率亦大大提升.结论 相比于传统的时变体数据可视化方法,本文算法不需要用户先验知识的前提下,利用非对称高斯模拟时序曲线变化,进而由高斯参数匹配代替复杂的时序曲线匹配过程,有效地提升了时变体数据可视化及分析效率.     

在连续框架下利用拓扑特征增强的体数据可视化

传统体绘制方法难以清晰地展现体数据的内部结构,本文提出了基于连续框架的利用数据拓扑特征增强体绘制的新方法.该方法首先利用7方向box样条拟插值对离散数据进行连续重建,然后通过求解多项式系统得到数据场中的特征点分布;从鞍点出发可以在连续模型上计算出鞍极曲线,本文提出以鞍极曲线长度给特征点值分布加权得到含权特征点直方图,并依据直方图信息重新设计体绘制的传输函数来增强体绘制.实验结果表明,与离散框架的方法相比,文中方法更加简单可靠,且可视化结果具有更好的平滑性,能清晰地反映体数据内部的细微结构.     

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.     

基于视觉感知增强的最大密度投影算法

提出一种基于视觉感知增强的最大密度投影算法,无需调节复杂的传输函数,就可以有效增强体数据内部最大密度特征的深度感知和形状感知.在传统的最大密度投影算法的基础上,利用梯度模属性精确查找特征或相似特征的边界,以确定最佳法向特征;利用最佳法向特征的深度信息自适应地修改局部光照系数,进而对最大密度特征进行光照处理,以获得视觉感知增强的可视化结果;采用基于密度值和三维空间距离的双阈值区域增长策略,动态区分感兴趣区域和背景区域,交互地实现特征突出显示.实验结果表明,该算法在传统算法的基础上进一步增强了最大密度特征的视觉感知,并提供了丰富的形状信息和背景补偿信息,具有较强的实用性.     

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。     

基于梯度模分布的视点选择

在三维体数据的可视化中,信息的获取不仅与传输函数的设置有关,而且与用户观察的视点有关.提出一种新的应用直接体绘制来可视化体数据时最佳视点的选择算法,通过计算梯度模在图像上的分布,寻找梯度模分布最为均匀且投影面积最大的视点方向,同时,在视域球上离散采样得到初始视点墒分布后,使用自适应步长的梯度下降法来优化全局最佳视点方向.实验结果证实了所提出方法能够有效地找到最佳视点.     

一种改进的基于CUDA的纹理映射和光线投射结合的体绘制算法

针对传统的基于GPU的光线投射算法绘制效率较低的问题,利用CUDA架构的并行计算特性和对三维纹理的处理能力进行改进和优化.将体数据映射为三维纹理,利用CUDA三维数组进行存储与绑定,纹理拾取的浮点返回值利用线性滤波进行平滑.在传输函数的设计中引入中心差分梯度幅值增强对体数据边界面的绘制效果.每条光线的求交及颜色积累采用并行计算,按照由前向后进行颜色及不透明度累积.设置不透明度阈值,采用不透明度提前终止加速绘制.实验结果表明,绘制速度较传统的基于GPU算法有10％的速度提升,绘制效果也有很大的改善.     

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).