Spirograph theory: a framework for calculations on digitized straight lines

Using diagrams called ``spirographs' a general theory is developed with which one can easily perform calculations on various aspects of digitized straight lines. The mathematics of the theory establishes a link between digitized straight lines and the theory of numbers (Farey series, continued fractions). To show that spirograph theory is a useful unification, we derive two previously known advanced results within the framework of the theory, and new results concerning the accuracy in position of a digitized straight line as a function of its slope and length.     

Searching for names in two city street maps

Two experiments investigated the speed with which names could be found on maps from two London street atlases. Differences in grid referencing between the maps accounted for large differences in search times. However, small statistically significant differences were still present when grid references were not being used, and these cannot be explained in terms of map scale, nor in terms of greater familiarity with the faster map. Several design differences could have contributed to this effect and it is likely that the use of lower case type on the faster map was an important factor. Implications for the map designer are discussed.     

Estimating time and time-lag in time-of-flight velocimetry

Estimating time and time-lag in time-of-flight velocimeters is investigated. Statistics of a filtered Poisson point process is given. A Maximum Likelihood Estimator is compared with suboptimum estimators in terms of robustness. For a dominating background combined spatial and temporal processing can improve the robustness compared with purely temporal processing. Schemes for the spatial filters are given.     

发展中国家水生态系统服务的经济价值评估研究

为保障发展中国家的用水需求,需要正确评估水生态系统服务的经济价值。基于近年来发展中国家在水生态系统服务经济评估方面的文献资料,指出"市场价格"法是进行经济评估最为普遍的方法;当水生态系统的服务功能非市场化时,"成本计算"等评估方法也较为常见。回顾以往评估研究,总结分析了发展中国家水生态系统服务经济价值评估方面的经验,并指出评估研究现状和所面临的主要挑战。结果表明,其经济价值各不相同,年均30～3 000美元/hm2不等。评估结果对发展中国家制定相关科学决策至关重要。     

SVD-based Preisach hysteresis identification and composite control of piezo actuators

In this paper, the singular value decomposition (SVD) based identification and compensation of the hysteretic phenomenon in piezo actuators are addressed using a Preisach model. First, this paper presents an SVD-based least squares algorithm and a revision approach of the identification through updating the SVD. With the identified parameters and a log of the memory curve, a Preisach-based inversion compensator is constructed which is complemented with a feedback controller to address the inevitable and residual modeling errors. Experimental results are furnished for both the identification and compensation approaches. The Preisach-based feedforward controller significantly improves the tracking performance and reduces the root-mean-square (RMS) tracking error of a PID controller by 76.7% and 89% at 1 Hz and 25 Hz, respectively. With the proposed composite controller, the percent-RMS errors at 1 Hz and 25 Hz are reduced to 0.035% and 0.31%, respectively.     

Production and acceleration of ion beams by laser ablation

In this work, we present a new pulsed laser ablation technique to obtain energetic ion beams. The accelerator we made is a compact device able to extract and accelerate the ionic components of plasma up to 160 keV per charge state. It is composed by a generating chamber containing an expansion chamber used like first electrode. Next, a second electrode connected to ground and a third electrode connected to negative voltage are used. The third electrode is used also as Faraday cup. By the analysis of the ion signals we studied the plume parameters such as TOF accelerated signals, charge state, and divergence.