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61.
The World Wide Web is a popular “tool” for companies. It can be used as a method of communication between companies and their customers; it also allows organizations to setup virtual storefronts that can be accessed by customers from all over the world. The ability to understand customers’ behavior is extremely important as companies strive to increase the usability and profitability of their web service. The concept of a session is a popular unit of measurement used to analyze recorded information. However, this concept is currently rather abstract and lacks definition. How we measure a session is a fundamental question for web services utilizing this concept. Currently, this question has no real answer. This paper presents a session timeout threshold model based on empirical observations as an initial answer to this question. The model seeks to provide accurate session data with respect to individual web services. 相似文献
62.
This study determines the optimal vascular designs for perfusing engineered tissues. Here, "optimal" describes a geometry that minimizes vascular volume fraction (the fractional volume of a tissue that is occupied by vessels) while maintaining oxygen concentration above a set threshold throughout the tissue. Computational modeling showed that optimal geometries depended on parameters that affected vascular fluid transport and oxygen consumption. Approximate analytical expressions predicted optima that agreed well with the results of modeling. Our results suggest one basis for comparing the effectiveness of designs for microvascular tissue engineering. 相似文献
63.
James Hartley 《中国科技期刊研究》2004,15(2):127-129
参考文献表的编排有多种体例形式,并且不同体例中参考文献各著录项的表达也不尽相同。由于期刊大都倾向于采用自己所特定的参考文献著录格式,因而目前已有的参考文献软件并不能给予作者很多帮助,即作者如果将其稿件由某期刊改投到另一种期刊,通常需要改动其中的参考文献表格式和正文中的相关部分。在众多的参考文献表格式中,有两种最为主要。其一是在人文科学中较为常用的哈佛体系(即著者一出版年体系),该体系规定正文中给出引文的作者和出版年,文献书目中的引文按著者姓名的字母顺序和出版年的先后排列。另外一种主要的参考文献表是数字体系(顺序编码制),即正文中给出引文的序号,参考文献表中的各篇文献按其在正文中出现的先后顺序排列。科技论文和医学论文多采用该种体例。本文列举了上述两种体例的格式,并对比了二者的优缺点,认为著者.出版年体系可以使学术论文的读者很方便地了解作者所引用的工作是由谁完成的,而数字体系(顺序编码制)因为简洁,从而可以使读者更为通畅地阅读论文。 相似文献
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65.
James H. Dugdale Calum A. Arthur Dajo Sanders Angus M. Hunter 《European Journal of Sport Science》2019,19(6):745-756
This study aimed to establish between-day reliability and validity of commonly used field-based fitness tests in youth soccer players of varied age and playing standards, and to discriminate between players without (“unidentified”) or with (“identified”) a direct route to professional football through their existing club pathway. Three-hundred-and-seventy-three Scottish youth soccer players (U11–U17) from three different playing standards (amateur, development, performance) completed a battery of commonly used generic field-based fitness tests (grip dynamometry, standing broad jump, countermovement vertical jump, 505 (505COD) and T-Drill (T-Test) change of direction and 10/20 m sprint tests) on two separate occasions within 7–14?days. The majority of field-based fitness tests selected within this study proved to be reliable measures of physical performance (ICC?=?0.83–0.97; p?.01). However, COD tests showed weaker reliability in younger participants (ICC?=?0.57–0.79; p?.01). The field-based fitness testing battery significantly discriminated between the unidentified and identified players; χ2 (7)?=?101.646, p?.001, with 70.2% of players being correctly classified. We have shown field-based fitness tests to be reliable measures of physical performance in youth soccer players. However, results from the 505COD and T-Test change of direction tests may be more variable in younger players, potentially due to complex demands of these tests and the limited training age established by these players. While the testing battery selected in this study was able to discriminate between unidentified and identified players, findings were inconsistent when attempting to differentiate between individual playing standards within the “identified” player group (development vs. performance). 相似文献
66.
James Rhodes Barry Mason Bertrand Perrat Martin Smith 《Journal of sports sciences》2013,31(17):1639-1647
AbstractThe aim of the current study was to investigate the validity and reliability of a radio frequency-based system for accurately tracking athlete movement within wheelchair court sports. Four wheelchair-specific tests were devised to assess the system during (i) static measurements; (ii) incremental fixed speeds; (iii) peak speeds; and (iv) multidirectional movements. During each test, three sampling frequencies (4, 8 and 16 Hz) were compared to a criterion method for distance, mean and peak speeds. Absolute static error remained between 0.19 and 0.32 m across the session. Distance values (test (ii)) showed greatest relative error in 4 Hz tags (1.3%), with significantly lower errors seen in higher frequency tags (<1.0%). Relative peak speed errors of <2.0% (test (iii)) were revealed across all sampling frequencies in relation to the criterion (4.00 ± 0.09 m · sˉ1). Results showed 8 and 16 Hz sampling frequencies displayed the closest-to-criterion values, whilst intra-tag reliability never exceeded 2.0% coefficient of variation (% CV) during peak speed detection. Minimal relative distance errors (<0.2%) were also seen across sampling frequencies (test (iv)). To conclude, the indoor tracking system is deemed an acceptable tool for tracking wheelchair court match play using a tag frequency of 8 or 16 Hz. 相似文献
67.
Issues associated with school absenteeism have attracted considerable attention and have long been one of the focal points of government strategies for school improvement. Pupil non-attendance is not a new phenomenon and featured prominently in Her Majesty’s Inspectors’ reports from 1839. This paper outlines the patterns of and influences on elementary education in early Victorian industrial Monmouthshire during the period 1839–1865. The twin problems of irregular attendance and early withdrawal of pupils are discussed together with the limitations and unreliability of contemporary statistics. An examination of the reasons for absence is then discussed together with the remedies proposed to alleviate the problem with particular reference to the contribution of the Prize Schemes. The paper illustrates the disadvantages of basing an educational system on voluntary endeavour and enlightened self-interest and highlights the paradox that, despite the introduction of mandatory attendance, the problem is still persistent and protracted and finding definitive solutions still remains elusive. 相似文献
68.
Are students’ mathematical procedures as unstable as they seem? Students often produce different errors in response to the same kind of problems on different testing occasions. This finding is puzzling. Past research has shown that students induce overly general procedures from worked-out examples during learning, which lead to a host of predictable errors on new problems. Do students create rule-based errors only to then switch between them at random? In this paper, we show that seemingly diverse errors on two different testing episodes may result from the same underlying stable procedure and are part of the same error category. These findings suggest that students’ errors are more stable on a category vs. on an individual level. The current study consists of teaching students addition in a new number system, called NewRoman, and analyzing students’ solution strategies in detail. Implications for teaching are discussed. 相似文献
69.
James L. Dolby 《Information processing & management》1977,13(1):69-77
One of the fundamental problems in information science is to distinguish various objects (such as books or journal articles) on the basis of associated values (such as authors and titles). Where the values fail to distinguish two distinct objects we say that the objects are ambigious under the given value assignment. To obtain a measure of ambiguity, it is only necessary to count the number of ways that the objects can be arranged for each set of ambiguous objects, multiply these counts and take logarithms. It is shown that such an approach leads to a measure in the formal sense and that the measure depends only on the definition of equality of values so that it can be simply extended to sets of values and ordered sets of values. It is also shown that it is possible to construct a function of ambiguity that one can call “information” and that the information loss that occurs when distinct values are grouped into equivalence classes (as in the use of search and sort keys) is also a measure. Finally, it is shown that ambiguity and information as here defined are directly related to Shannon's definition of “information” thus tieing this approach to that portion of information theory associated with the derivation of optimal distributions frequently used in information science models. 相似文献
70.