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关于无公度线段存在的问题的叙述一向是联系着欧几里得算法,这样就在教学中引起了一些困难,在这篇文章里,建议不引用欧几里得的算法而只是依据线段与正有理数相乘积的概念来证明。下文中,我们以位于线段两端的大写字母在字头上注上一横线(或以小写字母上面也注上一横线),来表示线段如AB,a等。 相似文献
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OBJECTIVES: To establish reliable estimates of the proportion of books available in formats accessible to visually impaired people; to recommend a practical method of updating the estimates. METHODS: The project had two stages. Stage one estimated the overall availability of all categories of books. The British National Bibliography (BNB) for 1999-2003 was chosen as the sampling frame. A sample of 2069 titles over the 5 years was selected using a systematic sample design. These titles were then checked for availability against the catalogues of four major producer/suppliers of materials in accessible formats. The second stage involved checking the availability of books in six genres; about 400 titles for each genre were examined. RESULTS: Of the titles selected for the overall estimate, 92 (4.4%) were found to be available in one or more accessible formats. Availability of titles in accessible formats varied greatly between categories. Adult fiction had the highest number of available publications (26.3%), least represented were cookery (1.9%) and gardening (1.8%). CONCLUSIONS: This study provided baseline figures and a methodology for the Right to Read Alliance to monitor their progress in campaigning for more books to be accessible to visually impaired people. 相似文献
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This study examined the reliability of a retrospective recall methodology for providing evidence of deliberate imagery practice. A secondary purpose was to determine which imagery activities constituted the sport-specific definition of deliberate practice (Starkes, Deakin, Allard, Hodges, & Hayes, 1996). Ninety-three Canadian athletes from one of three different competitive levels (regional, provincial, and national) completed the Deliberate Imagery Practice Recall Questionnaire, which was specifically designed for the present study. The athletes also completed a 1-week imagery diary to assess their use of 14 different imagery activities. The results of the study indicated that the athletes were able to reliably estimate their use of imagery over a short recall interval. Four imagery activities were also determined to fulfill the sport specific definition of deliberate practice. 相似文献
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Hertogh C Chamari K Damiani M Martin R Hachana Y Blonc S Hue O 《Journal of sports sciences》2005,23(9):937-942
In this study, we examined the effects of a prior run-up on intermittent maximal vertical jump performance. Seven regionally ranked male volleyball players volunteered to participate in the study. They performed three randomized tests: (1) six repeated intermittent maximal jumps (jump condition), (2) six repeated intermittent run-ups (run-up condition), and (3) six repeated run-ups followed by maximal jumps (run-up plus jump condition). All performances were assessed and blood lactate concentration and heart rate were measured before and after each of the tests. Mean ( +/- ) jump performance (64.7 +/- 2.3 cm) increased significantly (P = 0.02) over the course of the jump condition and was significantly higher (P < 0.001) than for the run-up plus jump condition (58.0 +/- 3.2 cm), which tended to decrease with repetition. Blood lactate concentration was significantly higher in the run-up plus jump condition (3.73 +/- 0.24 mmol . l(-1)) than in the jump (2.61 +/- 0.26 mmol . l(-1), P = 0.02) and run-up (2.86 +/- 0.18 mmol . l(-1), P = 0.03) conditions. The increase in heart rate was significantly higher both in the run-up plus jump condition (33 +/- 6 beats . min(-1), P = 0.05) and run-up condition (33 +/- 4 beats . min(-1), P = 0.02) than in the jump condition (21 +/- 3 beats . min(-1)). The results indicate that the addition of run-ups probably impeded performance in the repetition of vertical jumps. 相似文献
180.
Ring C Carroll D Hoving J Ormerod J Harrison LK Drayson M 《Journal of sports sciences》2005,23(5):501-508
It has been suggested that the psychological stress associated with competitive sports events may help to explain the increased susceptibility to respiratory infections due to reductions in secretory immunity. In the current study, we investigated the influence of competitive exercise and psychological stress on secretory immunoglobulin A (s-IgA). Salivary s-IgA and heart rate were measured in 62 healthy young recreationally active men at rest and, in a between-subjects design, following one of four 8-min tasks: mental arithmetic, cycling at workloads of 60 to 180 W (mean = 146 W), mental arithmetic while cycling, or competitive cycling. Mental arithmetic was associated with significant increases in s-IgA concentration (mean = 49 microg.min(-1)) and s-IgA secretion rate (mean = 25 microg.ml(-1)) compared with rest, while mental arithmetic combined with exercise was associated with a significant increase in s-IgA concentration only (mean = 124 microg.min(-1)). In contrast, competitive exercise and exercise alone did not influence s-IgA concentration or secretion rate. Heart rate increased modestly to mental arithmetic (mean = 7 beats.min(-1)) and substantially, and similarly, to the three exercise tasks (mean = 56(62 beats.min(-1)). The hypothesis that the psychological stress of competitive exercise contributes to increased susceptibility to infection via reductions in s-IgA requires further investigation. 相似文献