论计算机图形学的画法几何方法

在计算机图形学中,相对于矩阵变换法,画法几何法简单而直观,是一种很有前途的新方法。以作者多年从事画法几何计算机化的研究成果,用对比的方式,扼要论述画几法的特点。     

利用VGA接口测量笔记本电脑电池供电时间

利用VGA接口在笔记本运行时的电气特性,结合GPIB488数据接口的数字万用表的自动测量系统,介绍了实现笔记本电池供电运行时长的自动化测量的方法。     

Computers and computer graphics in the teaching of field phenomena

The use of computers and computer graphics in the teaching of sophomore/junior level students majoring in electrical engineering and computer engineering is discussed. Any previous study of electromagnetic fields is presumed to have been limited to a brief exposure in freshman physics. The author has been using both instructor-written and student-written programs in teaching various topics in the fields area for many years. The major part of the discussion concerns static field phenomena, since the basic introductory concepts taught to these student begins with static phenomena and since the physical meaning of many field quantities can best be understood in terms of static fields. Some of the ways the author is implementing the use of computers and computer graphics in his electromagnetics classes are described     

Interactive relay coordination using microcomputer graphics

A computer procedure is presented which enables the power system designer to interactively determine tap and time dial settings of overcurrent relays for the protection of industrial power systems. The user enters data about the power system, and a fault analysis is performed. Current transformer ratios, relay types, and load currents are then input to the program and the user selects tripping times or coordinating time intervals. Computer graphics techniques are then used to display the coordination curves and settings may be changed, if necessary, until the desired protection characteristics are achieved. An example of protection design for a sample industrial power system is provided to show the procedures for program use and demonstrate its capabilities.     

Visualizations of the integral forms of Maxwell's equations throughinteractive computer graphics

The author describes educational software which provides students with tools for visualizing the significance of the integral laws which underlie applied electromagnetics, and for obtaining insights into interrelationships between electric and magnetic fields and their sources. EILP, the electric integral law program, allows the student to specify positions and magnitudes of line charges using a mouse. The program computes and draws equipotential lines and electric field lines corresponding to the specified source configuration. The problem then allows the student to specify a closed surface and corresponding closed contour within the field solution, and plots accumulated normal electric flux and tangential electric field line integral as a marker makes its way around the surface/contour, demonstrating the specific implications of Gauss' law for electric field and the electroquasistatic Faraday law     

基于LabVIEW的数采卡(DAQ)驱动程序设计

介绍了在ＬａｂＶＩＥＷ５．０环境下通过ＣＩＮ（代码接口结点）即利用其与Ｃ语言的接口扩展功能的方法。给出了在Ｗｉｎ９５环境下开发自制数采卡驱动程序的实例。     

虚拟数字存储示波器高速数据采集卡的设计与实现

介绍了一种采样速度可达50Msps的用于虚拟数字存储示波器的高速数据采集卡硬件设计方案,着重讨论了方案主要涉及的DMA控制电路。     

Teaching computer design using virtual prototyping

The rapid increase in complexity and size of digital systems has reduced the effectiveness of old design methodologies based on physical prototyping. Prototyping via simulation must be used to achieve design cost and time-to-market goals when designing large digital systems. This virtual prototyping design methodology often permits the first physical prototype to be a manufacturable product. A two-course sequence has been developed to introduce students to this design paradigm. These courses teach virtual prototyping techniques and allow the students to use these techniques to develop a simple computer. The students simulate their designs, and then they implement their designs in hardware using field programmable hardware. This allows the students to complete an entire design cycle from idea to actual hardware implementation and compare their physical results to their simulated results.     

On a fundamental physical principle underlying the point locationalgorithm in computer graphics [for EM field theory]

The issue of point location is an important problem in computer graphics and the study of efficient data structures and fast algorithms is an important research area for both computer graphics and computational geometry disciplines. When filling the interior region of a planar polygon in computer graphics, it is necessary to identify all points that lie within the interior region and those that are outside. Sutherland and Hodgman are credited for designing the first algorithm to solve the problem. Their approach utilizes vector construction and vector cross products, and forms the basis of the “odd parity” rule. To verify whether a test point is within or outside a given planar polygon, a ray from the test point is drawn extending to infinity in any direction without intersecting a vertex. If the ray intersects the polygon outline an odd number of times, the region is considered interior. Otherwise, the point is outside the region. In three-dimensional space (3-space), Lee and Preparata propose an algorithm but their approach is limited to point location relative to convex polyhedrons with vertices in 3-space. Although it is rich on optimal data structures to reduce the storage requirement and efficient algorithms for fast execution, a proof of correctness of the algorithm, applied to the general problem of point location relative to any arbitrary surface in 3-space, is absent in the literature. This paper argues that the electromagnetic field theory and Gauss's Law constitute a fundamental basis for the “odd parity” rule and shows that the “odd parity” rule may be correctly extended to point location relative to any arbitrary closed surface in 3-space     

采用FPGA的双通道500 MHz的数据采集卡

对于高速数据采集系统设计而言,除了器件的处理速度之外,如何协调地解决总线控制逻辑、如何进行高速存储以及如何方便地与主机进行交换数据等一直是高速数据采集系统设计的难题。针对这些问题,本文介绍了一种基于FPGA实现的设计思想和方法。这种设计经过实际验证,工作稳定,能很好地达到预期要求。     

A computer architecture laboratory course using programmable logic

This paper describes the software and hardware developed for the laboratory component of a junior/senior level computer architecture course. The principal feature of this course is that students are required to design and build their own computers using programmable logic devices (PLDs). The students use a simple register transfer language (CURTL) with a simulator and commercial PLD tools for their design activity. A graphical PC based debugging tool provides the I/O and main memory for the student built computers     

Teaching computer networking fundamentals using practical laboratory exercises

Motivating students to learn computer networking concepts is often difficult because many students find the subject rather technical, dry, and boring. To overcome this problem, the author has prepared some practical laboratory exercises (practicals) and other materials. They are designed around a network operating system and a multiuser, multitasking operating system and are suitable for classroom use in undergraduate computer networking courses. The effectiveness of these practicals has been evaluated both formally by students and informally in discussion within the teaching team. The implementation of the practicals was judged to be successful because of the positive student feedback and also because students scored better in the final exam. This paper describes the practicals, their overall effectiveness, and plans for further projects. The impact of practicals on student learning and comprehension is also discussed.     

Three-dimensional simulation of field emission triode structure using carbon-nanotube emitters

Field emission (FE) triode arrays with the anodic aluminum oxide (AAO) template carbon nanotubes (CNTs) as the field emitters are successfully fabricated and analyzed. Both the experimental measurement and numerical calculation are conducted to examine the electron conduction properties of AAO-CNTs. Using a three-dimensional finite-difference time-domain particle-in-cell method, a set of Maxwell equations and Lorentz equation is solved self-consistently, where the FE current is computed with Fowler–Nordheim equation. We explore the FE characteristics of AAO-CNTs in the triode structure. After calibration with the measured data, we study the evolution of current density and the convergence of the electron beams on anode plate with different gate voltages, anode heights, and SiO₂ thickness. The current density and focus performance maintain a trade-off relationship, where a larger current density accompanies more divergent electron beam.     

利用单片机实现空间矢量调制算法

介绍一种用8位专用单片机内部结构特征而设计的空间矢量调制算法,不但具有电压利用率高、谐波损耗小等优点,还具有计算速度快、过调制处理方法简洁、性能价格比高等优点。     

A course on computer modeling for second or third year engineeringundergraduates

A course on computer modeling for sophomores and juniors at Harvey Mudd College is described. The rationale for such a course is three fold: it teaches students the role of computation in engineering problem solving; fills the present hiatus between the freshman year, where programming is taught, and the senior year, where attempts are made, after many students have forgotten the programming they learned, to use those skills in coursework; and provides a means of introducing the student to the design cycle of testing through analysis and changing designs, until performance criteria are met     

利用工控机实现神经网络式距离保护的研究

提出了神经网络式距离保护的新原理,提出基于工控机的微机保护是继电保护发展的一个新方向.对利用工控机实现神经网络式距离保护进行了研究.试验结果表明,利用工控机实现神经网络式距离保护能够满足微机保护的要求.     

Three-dimensional echo-planar cine imaging of cerebral blood supply using arterial spin labeling

Objective

Echo-planar imaging (EPI) with CYlindrical Center-out spatiaL Encoding (EPICYCLE) is introduced as a novel hybrid three-dimensional (3D) EPI technique. Its suitability for the tracking of a short bolus created by pseudo-continuous arterial spin labeling (pCASL) through the cerebral vasculature is demonstrated.

Materials and methods

EPICYCLE acquires two-dimensional planes of k-space along center-out trajectories. These “spokes” are rotated from shot to shot about a common axis to encode a k-space cylinder. To track a bolus of labeled blood, the same subset of evenly distributed spokes is acquired in a cine fashion after a short period of pCASL. This process is repeated for all subsets to fill the whole 3D k-space of each time frame.

Results

The passage of short pCASL boluses through the vasculature of a 3D imaging slab was successfully imaged using EPICYCLE. By choosing suitable sequence parameters, the impact of slab excitation on the bolus shape could be minimized. Parametric maps of signal amplitude, transit time, and bolus width reflected typical features of blood transport in large vessels.

Conclusion

The EPICYCLE technique was successfully applied to track a short bolus of labeled arterial blood during its passage through the cerebral vasculature.

     

基于强度折减法的高土石坝三维抗震稳定分析

在边坡稳定性分析中,虽然极限平衡法因为简单易行而广泛使用,但在处理三维稳定问题时还面临很多困难,而有限元强度折减法处理三维问题要方便得多。本文以应用广泛的岩土工程三维数值模拟工具———FLAC3 D为计算平台,以混凝土面板堆石坝和黏土心墙堆石坝两种坝型为研究对象,在强度折减法基础上采用拟静力方法研究高土石坝坝坡在不同坝高、坝坡坡度、地震烈度以及岸坡坡度条件下的稳定安全系数以及最危险滑裂面的位置和形状。计算结果表明,随着坝高的增加、坝坡的变陡、地震烈度的提高以及岸坡坡度的变缓,坝坡的稳定安全系数均降低。安全系数与坝坡坡比近似呈线性关系,与坝高、地震烈度、岸坡坡度等因素呈非线性特性。基于计算结果,文中给出了安全系数与影响因素之间的经验拟合公式。同时发现,地震烈度和岸坡坡度对面板堆石坝的滑裂面位置和形状有较大影响,而地震烈度对心墙堆石坝滑裂面形状和位置的影响较小。     

Three-dimensional black-blood multi-contrast carotid imaging using compressed sensing: a repeatability study

Objective

The purpose of this work is to evaluate the repeatability of a compressed sensing (CS) accelerated multi-contrast carotid protocol at 3 T.

Materials and methods

Twelve volunteers and eight patients with carotid disease were scanned on a 3 T MRI scanner using a CS accelerated 3-D black-blood multi-contrast protocol which comprises T ₁w, T ₂w and PDw without CS, and with a CS factor of 1.5 and 2.0. The volunteers were scanned twice, the lumen/wall area and wall thickness were measured for each scan. Eight patients were scanned once, the inter/intra-observer reproducibility of the measurements was calculated.

Results

In the repeated volunteer scans, the interclass correlation coefficient (ICC) for the wall area measurement using a CS factor of 1.5 in PDw, T ₁w and T ₂w were 0.95, 0.81, and 0.97, respectively. The ICC for lumen area measurement using a CS factor of 1.5 in PDw, T ₁w and T ₂w were 0.96, 0.92, and 0.96, respectively. In patients, the ICC for inter/intra-observer measurements of lumen/wall area, and wall thickness were all above 0.81 in all sequences.

Conclusion

The results show a CS accelerated 3-D black-blood multi-contrast protocol is a robust and reproducible method for carotid imaging. Future protocol design could use CS to reduce the scanning time.