消力戽在低佛氏数水流中的应用

结合左江水利枢纽的兴建时消力戽进行了研究和实践，介绍低佛氏数水流特点和低佛氏数水流消能工的研究现状，左江工程的运行资料证明消力戽应用于低佛氏数水流消能是成功的。     

Synthesizing plans that contain actions with context-dependent effects1

This paper presents a method of solving planning problems that involve actions whose effects change according to the situations in which they are performed. The approach is an extension of the conventional planning methodology in which plans are constructed through an iterative process of scanning for goals that are not yet satisfied, inserting actions to achieve them, and introducing subgoals to these actions. This methodology was originally developed under the assumption that one would be dealing exclusively with actions that produce the same effects in every situation. The extension involves introducing additional subgoals to actions above and beyond the preconditions of execution normally introduced. These additional subgoals, called secondary preconditions, ensure that the actions are performed in contexts conducive to producing the effects we desire. This paper defines and analyzes secondary preconditions from a mathematically rigorous standpoint and demonstrates how they can be derived from regression operators.     

Bridging the generation gap between text planning and linguistic realization

Text planning is traditionally done as a separate process, independent of linguistic realization. However, I show in this paper that it is essential for a text planner to know the linguistic consequences of its actions. The choice of how to realize an element affects how much information is conveyed (e.g., “Floyd arrived safely in Boston” vs. “Floyd landed safely at Logan”) and what other information can be added (e.g., “Peter was deciding for an hour” vs. *“Peter made a decision for an hour”). The choice of realization also affects how the relative salience of the elements being expressed will be perceived (e.g., “The green car is in the garage” vs. “The car in the garage is green”). I have defined an intermediate level of representation for text planning, called the Text Structure. It is an abstract linguistic level that reflects germane linguistic constraints while abstracting away from syntactic detail. This representation allows the text planner to have greater control over the decisions, so that it can take advantage of the expressiveness of language to convey subtleties of meaning. More importantly, the Text Structure allows the generation process overall to be incremental, since it ensures that the text plan being composed will always be expressible in the language. La planification de textes est habituellement réalisée séparément, sans tenir compte de la réalisation linguistique. Cependant, ľauteur demontre dans cet article qu'il est essentiel à un planificateur de textes de connai̊tre les conséquences linguistiques de ses actions. Le choix de la méhode de réalisation ?un élément influe sur la quantité?informations qui est transmise (par ex.: 〈〈 Floyd est arrivé sain et sauf à Boston 〉〉 et 〈〈 Floyd a atterri sain et sauf àľaéroport Logan 〉〉) et sur quelle autre information peut ětre ajoutée. Le choix de la méthode de réalisation influe également sur la façon dont les caractères saillants des ééments qui sont exprimés seront perçus (par ex.: 〈〈 la voiture verte est dans le garage 〉〉 et 〈〈 la voiture dans le garage est verte 〉〉). L'auteur a défini un niveau intérmediaire de représentation pour la planification de textes qu'il a appelé structure de texte. Il; s'agit ?'un niveau linguistique abstrait qui refléte les contraintes linguistiques appropriées tout en s'éloignant du détail syntaxique. Cette représentation permet au planificateur de textes ?avoir un meilleur contrǒle des décisions, et done de tirer profit de la force ?expression du langage afin de tenir compte des subtiliés de sens. Plus important encore, la structure de texte permet au processus de génération ?ětre incrémentiel, car elle s'assure que le plan de texte en voie de composition soit toujours exprimable dans le langage.     

Logarithmic Singularity of Specific Heat in Liquid Helium II at the λ Point

The experimental width of the second sound peak in Brillouin scattering is less than the instrumental width. It is also less than the width of the first sound peak near the λ point. The theoretical width of the second sound peak becomes infinitely large at the λ point in the traditional viewpoint. This discrepancy suggests that the second sound peak detected in Brillouin scattering is an elementary excitation. We calculate the specific heat of liquid helium near the λ point by considering the second sound peak. The calculated temperature-dependence of the specific heat has a logarithmic divergence at the λ point. Furthermore, the calculated values of the specific heat agree well with data derived from experiments.     

双参数Bézier曲线的升二次扩展

本文以二次Bernstein基函数为例,首次提出了含双参数基函数的新扩展——αβQ—Bern-stein基函数,此类基函数具有新的特点,即基函数的扩展次数一次性升高两次,且包含了二次多项式和带一个参数的三次多项式基函数的所有性质。基于这组基函数定义了αβQ—Bézier曲线,该曲线也含有参数,具有形状可调性,当α与β取某些值时曲线能达到C4连续或在某个端点处C0连续。最后与含两个参数的升一次Bézier曲线进行比较,该曲线具有调节范围广、灵活性更强的优势。     

自适应布谷鸟搜索算法

为了使布谷鸟搜索算法(Cuckoo Search,CS)在保持强大的全局搜索能力的同时,尽可能地提高局部搜索能力,在深入分析CS算法机理的基础上,将CS算法中影响布谷鸟搜索路径步长的参数β和布谷鸟蛋被发现(淘汰)的概率p_a由固定值改为随搜索过程自适应变化的动态参数,将越界的鸟窝折返回边界内、在当前代最优鸟窝附近的区域随机建立1个新的鸟窝、而非折返回边界上重新建立鸟窝,以提高算法的局部搜索能力和收敛速度。改进后的CS算法称为自适应布谷鸟搜索算法(Adaptive Cuckoo Search,ACS)。通过8个标准测试函数分别测试了CS算法和ACS算法的性能,结果表明,无论是简单的单峰函数还是复杂的多峰函数,无论是小型的低维函数还是大型的高维函数,ACS算法的寻优性能均超过CS算法。     

电力电子实验装置中的晶闸管保护

在晶闸管变流电路中,应对晶闸管设置必要的过压保护、过流保护、di／dt保护、du／dt保护电路,以保证变流装置的正常运行．电力电子实验装置中虽对晶闸管设置了一定的保护措施,但晶闸管依然经常损坏．分析了这种保护措施的可靠性及晶闸管损坏的原因,并提供了解决问题的方法．     

三次Bézier曲线的α扩展

利用一个对称的调配函数,结合NURBS曲线中权的思想,在曲线控制顶点处引进调配参数,将三次Bézier曲线进行扩展,得到的新曲线比原来的曲线有更强的描述能力,并且包含了原曲线形式。讨论了扩展曲线的基表示及曲线的性质,调配参数可以用来控制曲线的局部形状,特别适用于自由曲线曲面的设计,在CAD/CAM中具有很好的应用前景。     

带有给定切线多边形的G2连续Bézier闭曲线

描述了一种与给定多边形相切的五次Bézier曲线的算法。在算法中,所有的五次Bézier曲线的控制点可以通过对多边形的顶点简单计算产生。所构造的曲线对多边形具有保形性,曲线可以局部修改,最后给出了一个算例。