基于模型约简和GPU加速的软组织实时仿真

为了得到虚拟外科手术中人体软组织的实时变形仿真,采用了基于模态分析的模型约简方法,同时结合了GPU加速技术,实现了人体软组织的实时仿真计算,为虚拟手术提供了良好的人机交互.模型约简以有限元理论为基础,将软组织模型的动力学方程投射到约筒子空间,减少系统自由度.在实时仿真过程中,首先需在子空间中对低维动力学模型进行数值计算,然后利用GPU通用计算技术来加速重建原始空间中的形变向量.以心脏大变形实时仿真为例,验证方法的性能,实验结果表明心脏的变形仿真可以在很高的刷新率下运行.提出的模型约简和GPU加速方法,为人体软组织的变形实现了实时仿真,为虚拟手术提供了理论基础和技术支撑.     

实时交互式软组织切割与变形计算模型

为提高虚拟手术模拟的交互性与实时性,提出一种软组织实时切割与变形计算模型.该模型以混合有限元模型为基础,根据手术过程中不同区域的交互特点,利用GPU加速手术区域的切割与变形计算;同时,对非手术区域的软组织因交互而引起的实时变形可通过选择性相乘的方法快速实现.实验结果充分证明,该计算模型可以灵活有效地实现实时软组织的交互切割与变形模拟.     

一种基于弹簧振子模型的颅面软组织仿真算法

软组织仿真研究是利用计算机技术对真实软组织进行模拟以便研究,为医学工作者提供辅助和帮助科研工作者更好地进行虚拟手术.这方面的研究在国外已经较为普及,在国内尚处于起步阶段.软组织仿真算法已有多种成熟模型,其中较为代表性的有弹簧振子模型(MSS)和有限元模型(FEM).在参阅了前人的研究基础上,选取了弹簧振子模型作为软组织仿真的物理形变模型,并对仿真算法进行编码和仿真实验,进而对实验效果进行分析,并提出改进之处.实验发现基于弹簧振子模型的软组织较好地实现了形变仿真的效果.     

虚拟手术实时物体碰撞检测和软组织变形研究

针对虚拟手术系统中实时碰撞检测和软组织变形的问题进行了研究。对于实时碰撞检测,使用了包围盒检测结合三角面片检测的方法来检测物体之间的碰撞,并且找到相互碰撞的两个三角面片。对于软组织变形,使用了一种基于胡克定律的弹簧质点模型来虚拟仿真变形,并提供了控制点移动的方法。采用优化虚拟手术中的物体碰撞检测方法,减少了不必要的计算和增强了系统的精确度;简化了软组织变形的算法,相对加快了有限元模型运算速度。对推动虚拟手术的发展具有积极的意义和作用。     

用于三维软组织实时切割的混合凝聚有限元模型

随着近几年来微创外科的迅速发展，虚拟内窥镜手术模拟系统作为手术训练、规划的有效手段，已逐渐成为研究的热点。根据实际手术的需要，虚拟手术系统应该不仅能够实时模拟软组织的变形，而且也同样可以对软组织的切割、缝合操作进行实时模拟。该文提出了一个用于虚拟手术模拟、三维软组织变形以及切割的有限元模型－混合凝聚有限元模型。该模型的显著优点在于其可以在当前的PC机平台上有效地对软组织变形及具有拓扑改变的切割操作进行实时模拟。     

实时力反馈技术在手术仿真中的实现与应用

文章介绍了一种应用于手术仿真中的实时力反馈技术。主要讨论了其实现的步骤过程和系统仿真结构,分析了其采用的质点-弹簧-阻尼器物理仿真模型,并描述了手术仿真中虚拟手术器械挤压软组织模型的面弹力和在软组织表面上的粘滞摩擦力的实现原理和方法,同时,为手术仿真中实时力反馈的实现和应用提出了一种解决的方案。     

一种基于弹簧振子模型的颅面软组织仿真算法

软组织仿真研究是利用计算机技术对真实软组织进行模拟以便研究,为医学工作者提供辅助和帮助科研工作者更好地进行虚拟手术。这方面的研究在国外已经较为普及,在国内尚处于起步阶段。软组织仿真算法已有多种成熟模型,其中较为代表性的有弹簧振子模型（MSS）和有限元模型（FEM）。在参阅了前人的研究基础上,选取了弹簧振子模型作为软组织仿真的物理形变模型,并对仿真算法进行编码和仿真实验,进而对实验效果进行分析,并提出改进之处。实验发现基于弹簧振子模型的软组织较好地实现了形变仿真的效果。     

基于移动最小二乘法的无网格肝脏形变研究

在手术虚拟仿真对软组织形变研究中,采用传统的网格形变方法,由于出现网格畸变、网格重构会影响形变效果的问题.针对手术虚拟仿真要求尽可能逼真地模拟形变以达到良好的真实感,提出了一种基于移动最小二乘法的无网格方法对以肝脏为对象的软组织进行形变研究,考虑肝脏软组织生物力学特性,采用Voigt模型对肝脏软组织进行物理建模.同时,针对无网格肝脏模型的碰撞检测,提出AABB包围盒与八叉树空间分割相结合的碰撞检测算法,在肝脏模型体节点的合理布局基础上可以对碰撞进行有效准确的检测.实验结果表明,无网络方法实现简单且具有较好的形变真实感,对虚拟手术中软组织形变研究具有重要的指导意义.     

新一代火箭卫星整流罩的模态特性分析、试验与模型修正

针对全透波段非金属夹层结构的新一代运载火箭卫星整流罩,建立有限元模型,计算了半罩在不同边界条件下的模态特性.地面模态试验中,采用垂直悬挂和置于海绵垫上多种方式模拟自由边界条件,基于频响函数和特征值、特征向量辨识半罩模态,基于试验结果采用模型缩聚迭代算法对仿真计算模型进行模型修正,得到高精度的可供全箭动力学分析和整流罩分离分析使用的有限元模型.     

虚拟针刺人体软组织建模仿真

针刺人体软组织是医疗诊断中比较普遍使用的治疗手段,然而细微的针刺操作对医生的能力提出较高的要求.医生可采用虚拟现实技术来进行大量的训练,获得宝贵的经验.虚拟针刺过程中的软组织变形是重要研究内容.文章采用有限元方法建立软组织模型,使用GPU加速仿真的方法,实现针刺软组织的仿真.实验结果表明,软组织模型在针刺作用下,能产生...     

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).