抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

A heuristic method has been developed for registering two sets of 3-D curves obtained by using an edge-based stereo system, or two dense 3-D maps obtained by using a correlation-based stereo system. Geometric matching in general is a difficult unsolved problem in computer vision. Fortunately, in many practical applications, some a priori knowledge exists which considerably simplifies the problem. In visual navigation, for example, the motion between successive positions is usually approximately known. From this initial estimate, our algorithm computes observer motion with very good precision, which is required for environment modeling (e.g., building a Digital Elevation Map). Objects are represented by a set of 3-D points, which are considered as the samples of a surface. No constraint is imposed on the form of the objects. The proposed algorithm is based on iteratively matching points in one set to the closest points in the other. A statistical method based on the distance distribution is used to deal with outliers, occlusion, appearance and disappearance, which allows us to do subset-subset matching. A least-squares technique is used to estimate 3-D motion from the point correspondences, which reduces the average distance between points in the two sets. Both synthetic and real data have been used to test the algorithm, and the results show that it is efficient and robust, and yields an accurate motion estimate.

/pdf/iterative-point-matching-for-registration-of-free-form-5fl1ftde76.pdf

Iterative point matching for registration of free-form curves and surfaces

A scheme is developed for classifying the types of motion perceived by a humanlike robot. It is assumed that the robot receives visual images of the scene using a perspective system model. Equations, theorems, concepts, clues, etc., relating the objects, their positions, and their motion to their images on the focal plane are presented. >

http://ieeexplore.ieee.org/iel2/815/3148/00100651.pdf

Robot vision

Geometric matching in general is a difficult unsolved problem in computer vision. Fortunately, in many pratical applications, some a priori knowledge exists which considerably simplifies the problem. In visual navigation, for example, the motion between successive positions is usually either small or approximately known, but a more precise registration is required for environment modeling. The algorithm described in this report meets this need. Objects are represented by free-form curves, i.e., arbitrary spaces curves of the type found in practice. A curve is available in the form of a set of chained points. The proposed algorithm is based on iteratively matching points on one curve to the closest points on the other. A least-squares technique is used to estimate 3-D motion from the point correspondences, which reduces the average distance between curves in two sets. Both synthetic and real data have been used to test the algorithm, and the results show that it is efficient and robust, and yields an accurate motion estimate. The algorithm can be easily extended to solve similar problems such as 2-D curve matching and 3-D surface matching.

/pdf/iterative-point-matching-for-registration-of-free-form-b0pre910b7.pdf

Iterative point matching for registration of free-form curves

In many areas of industry, it is desirable to create geometric models of existing objects for which no such model is available. This paper reviews the process of reverse engineering of shapes. After identifying the purpose of reverse engineering and the main application areas, the most important algorithmic steps are outlined and various reconstruction strategies are presented. Pros and cons of various data acquisition techniques are described with related problems of boundary representation model construction. Specific issues addressed include characterization of geometric models and related surface representations, segmentation and surface fitting for simple and free-form shapes, multiple view combination and creating consistent and accurate B-rep models. The limitations of currently known solutions are also described, and we point out areas in which further work is required before reverse engineering of shape becomes a practical, widely-available engineering tool.

Reverse engineering of geometric models—an introduction

The authors present an optimal match scheme that aligns the measurement data with the design data in CAD-directed dimensional inspection. The principle of this scheme is to determine the actual measured points on the nominal surface by minimizing the sum of the squared distances of the measurement data from the surface with respect to the parameters of a rigid body transformation. Its computational efficiency and robustness against singularity are discussed. Two applications are examined. The first is determining the design coordinate system with respect to a machine coordinate system. The second is comparative analysis for precision measurement. For determining the design coordinate system, a sensitivity measure is proposed and confirmed experimentally. For error comparative analysis, a statistical model is developed to determine the minimum number of required measurement points so that the sampled points can closely represent the entire population. >

Automated precision measurement of surface profile in CAD-directed inspection

The selection of measurement configurations in robot cali bration is investigated. The goal is to select a set of robot measurement configurations that will yield maximum ob servability of the error parameters in a defined position error model so that the effect of noise in parameter estimation can be minimized. The noise considered in this paper includes both measurement and modeling errors. An observability measure is used as a criterion for selecting measurement configurations for calibration. Experimental studies are per formed to demonstrate the importance of observability to parameter estimation and to verify its implications in robot calibration. Based on the defined observability measure, the optimal measurement configurations for robot calibration are determined for general open-loop planar mechanism and PUMA type robots.

Determination of optimal measurement configurations for robot calibration based on observability measure

The influence of microslip on vibratory response, part I: A new microslip model

The paper identifies the steps involved in the reverse-engineering process. The procedure begins with the division of the whole array of measurement data points into regions, according to shape-change detection. In each region, points are parameterized, and knots are selected. Smooth parametric surface approximation is obtained by the least-square fitting of B-splines. Nonlinear least-square minimization is applied for parameter optimization with simple bounds on the parameter values. The objective function minimized is the explicit error expression for the sum of the squares of error values at the data points.

Smooth-surface approximation and reverse engineering

In this paper, the classical Preisach independent domain model is used to capture the essential characteristics of hysteresis nonlinearity in electromagnetic (EM) actuators made of soft ferromagnetic material. Experimental results demonstrate its ability to accurately model electromagnetic hysteresis for variations in input current, airgap, and orientation. The Preisach model is then inverted and incorporated in an open-loop control strategy that regulates the EM actuator and compensates for hysteretic effects; hysteresis-free regulation of the EM actuator is obtained, for variations in input current, airgap, and orientation. Hysteresis is also effectively compensated for desired force trajectories of frequencies up to 100 Hz. Thus, the experimental results demonstrate consistent performance of the open-loop control strategy based on Preisach model inversion, in satisfactorily regulating the output of the EM actuator to the desired trajectories.

Chia-Hsiang Menq

Papers

Automated precision measurement of surface profile in CAD-directed inspection

Determination of optimal measurement configurations for robot calibration based on observability measure

The influence of microslip on vibratory response, part I: A new microslip model

Smooth-surface approximation and reverse engineering

Hysteresis compensation in electromagnetic actuators through Preisach model inversion