基于多分类器组合择优方法的主题爬行分类策略

针对主题爬行技术中的单一分类算法在面对多主题Web抓取和分类需求时泛化能力不强的局限,设计一种利用多种强分类算法形成的分类器组合,主题爬行器根据当前主题任务在线评估并为分类器排名,从中选择最优分类器分类的策略,并开展在多个主题抓取任务下的分类实验,比较每种分类算法的准确率和组合后的平均分类准确率以及对分类效率等评价指标的综合分析,结果证明该策略对领域局域性有所克服,普适性较强。     

网球拍弦磅数变化对优秀网球职业运动员底线击球效果的研究

为研究优秀的网球职业运动员是否对球拍拍弦磅数变化有更好的区分能力以及拍弦磅数变化是否会影响到击球效果,本研究使用网球发球机发球,让18名优秀的网球职业运动员参加一个用不同拍弦磅数球拍的(从47磅~64磅)击球测试。从实验结果来看,61%测试者不能准确的区分6磅的拍弦磅数变化,击球后球飞行的平均速度是117 km/h,击球平均速度与落点失误数都与球拍拍弦磅数不存在显著性差异。研究结果表明,优秀网球职业运动员对网球拍弦磅数变化的分辨能力与敏感度较低;优秀的网球职业运动员击球的落点与球拍磅数不存在显著性相关;在底线击球中优秀的网球职业运动员对使用不同磅数的球拍有着很强的适应能力与控制能力。     

Differences in ball speed and accuracy of tennis groundstrokes between elite and high-performance players

Abstract

The main aim of this study was to identify and compare ball speed and hitting accuracy of forehand and backhand groundstrokes between ATP professionals (elite) and high-performance youth players when shots were played cross-court and down the line to a target square. Six elite and seven high-performance tennis players volunteered to participate in the study. A Doppler-radar device and a digital video camera, operating at 120 frames per second, were used to measure ball speed and accuracy of forehand and backhand groundstrokes in the respective situation (cross-court and down the line). The results of 1040 measured groundstrokes indicate that the ball speed of the forehand and the backhand ground stroke was higher in the elite group when analysing (1) all valid shots, (2) the six fastest shots, and (3) the six most accurate shots (all P < 0.05). In addition, all players achieved a higher forehand speed compared with their backhand when balls were directed cross-court (P < 0.01). The participants demonstrated similar ability when considering accuracy of their groundstrokes (P > 0.05). However, a group difference for accuracy was identified when considering the six fastest forehand shots (P<0.05), and the forehand cross-court stroke was played more accurately than the backhand cross-court stroke by both groups (valid shots and six most accurate shots, P<0.05). Moreover, there was no evidence that players who impacted the ball faster were any less accurate than those who impacted the ball more slowly. Analyses for participants actually revealed a negative correlation between ball speed and mean radial error (accuracy) for the backhand down the line (r= ? 0.77, P<0.01). According to the results of this study, ball speed seems to be the determining factor that separates elite from sub-elite tennis players.     

Competition and Instructional Set Effects On the Speed and Accuracy of a Throwing Task

Abstract

Two experiments were conducted to investigate the effects of competition and instructional sets on the speed and accuracy of a dart-throwing task. In both experiments individuals competed against another subject on one day, and performed under noncompetitive conditions on a second day. The five distinct instructional sets varied from extreme emphasis on speed to extreme emphasis on accuracy. Multivariate analyses of variance revealed main effects for instructional sets on speed and accuracy in both experiments. Strong tradeoffs occurred with speed slowing and accuracy improving as the instructional emphasis changed from speed to accuracy. A competition by instructional sets interaction in Experiment 2 indicated that competition facilitated speed when speed was important, but when instructions emphasized accuracy, speed was slower in competition than in noncompetition. Accuracy was not affected by competition.     

有关口语报告法效度的几个争议问题

尽管口语报告法在当前心理学、教育学以及认知科学的研究中被广泛使用,但关于其效度的争议依然存在。这些争议主要包括:第一,口语报告的准确性,即口语报告能否准确地反映我们的思维内容?第二,口语报告的完整性,即搜集到的口语报告能否为我们了解被试的认知过程提供足够的信息?第三,口语报告的反应性,即口语报告是否会影响思维的正常进程?文章对这些问题进行了较为深入的分析和思考,并指出了对口语报告法进行研究的几个新趋势。     

浅析说明文中的美育因素

说明文中蕴含有真知美、形式与内容高度统一的和谐美、语言上的准确美、简明美、生动美 ,教师应认识并利用这些美育因素 ,搞好说明文教学。     

基于FPGA的磁定位技术研究与实现

在磁定位技术应用过程中,为解决数据处理过程复杂、计算量大导致实时性无法满足问题,利用FPGA的并行结构,设计实现了一种基于FPGA平台的磁定位方案。实验结果表明,磁矩为0.1255[A?m2]的永磁体在距离磁传感器高度在20cm以内时,定位精度能达到毫米级,定位速度比通用计算机提升了一倍以上,可以满足绝大多数实时性要求,更有利于永磁体定位技术产业化,应用前景广阔。     

What History Can Teach Us About Science: Theory and Experiment, Data and Evidence

Scientists often use more than the results of experiment to arrive at a result; they use anticipation and analogy to arrive at the results that fit their theories, and sometimes they correct results in the light of analogy. They also need to be clear about the difference between accuracy and precision. They do all this using not only theories, but also apparatus, and the interplay between apparatus and the development of concepts and theories is often crucial. Historians of chemistry (notably including the recent work of Usselman, Rocke, and Holmes) furnish us with plenty of examples of such interplay, and of the selection of data in the light of theory. Lavoisier, Dalton, and Liebig can each teach us a good deal about the way that good scientists arrive at reproducible results.     

基于激光干涉仪的机床精度检测及误差补偿创新实验设计

利用引进的ML10激光干涉仪,进行适用于本科实验教学的创新实验设计,开发了基于激光干涉仪的创新实验——数控机床精度检测与误差补偿实验。结果表明,此类实验的开设不仅大大增强科研设备的利用率,而且对创新本科实验教学、提高学生专业技能有很大帮助。     

汉语母语和二语书面表现的对比分析——以小学高年级中国学生和大学高年级越南学生的同题汉语作文为例

本研究以小学高年级中国学生和大学高年级越南学生的同题汉语作文为例,从流利性、准确性、复杂性和多样性四个维度,对上述两组被试的书面语言表现进行了测量。统计结果显示,中国学生组的流利性和准确性各项指标均高于越南学生组,尤其在流利性及词汇与句法准确性方面,两组之间存在统计意义上的显著差异;在复杂性方面,两组被试的汉字和词语复杂性测量数据差别不明显,但越南学生组在以T单位长度为指标的句法复杂性方面显著高于中国学生组;在多样性方面,越南学生组的各项指标均高于中国学生组,不过两组之间只在词语多样性方面存在显著差异。这些发现揭示了汉语母语和二语书面表现的不同发展特点．