The distance-time relationship over a century of running Olympic performances: A limit on the critical speed concept     

Dekerle J  Nesi X  Carter H 《Journal of sports sciences》2006,24(11):1213-1221

We analyse the evolution of the slope (critical speed) and the y-intercept (anaerobic distance capacity) of the linear distance-time relationship over a century of Olympic running performances. The distance-time relationship of each Olympic Games (1920-2004) was plotted using the performances in the 800-, 1500- and 5000-m track events. Values for critical speed and anaerobic distance capacity were determined by linear modelling. Mean performances for the 800, 1500 and 5000 m were 104.9 +/- 1.5 s (1.4%), 217.2 +/- 2.8 s (1.3%) and 808.9 +/- 18.4 s (2.3%), respectively. Critical speed improved during the first three-quarters of the twentieth century to reach a plateau in 1984. This is in accordance with the literature (Peronnet & Thibault, 1989) and suggests that "human aerobic endurance" has improved within the century (+13.4%) and tends to stabilize. Anaerobic distance capacity was highly variable over the century (coefficient of variation = 9.4%) and did not show a linear improvement over the years as has previously been suggested (Peronnet & Thibault, 1989). This could be due to an artefact in the application of the two-parameter model to only three Olympic performances. A limitation to the use of this linear mathematical model to fit physiological data may have been demonstrated.  相似文献   

Assessing working students' college experiences: a grounded theory approach     

David X. Cheng  Lucia Alcántara 《Assessment & Evaluation in Higher Education》2007,32(3):301-311

This study explores working students' college experiences using the grounded theory approach. Focus groups were conducted to allow working students to elaborate on their college experiences, clarifying issues not easily addressed through surveys. Two theoretical propositions are offered to describe how working students are constantly searching for meaningful work as well as meaning in their work. It is important for institutions to consider work as an educationally purposeful activity outside classroom and to create job opportunities that benefit students academically, socially and financially.  相似文献   

浅议现金流量     

席庆荣  刘秋华  许文静 《北京工业职业技术学院学报》2006,5(1):117-120

现金流量是一家企业或某个特定项目在一定时期或现金流量计算期内的现金流入、流出的数量及其净额,无论是一家企业一定时期内的现金流量,还是一个特定投资项目计算期内的现金流量,一般都采用以年为单位计算现金流量的方法编制现金流量表.现金流量表分为企业现金流量表和投资项目现金流量表,二者具有相同点也有不同点.现金流量有其变化规律,认识现金流量的变化规律有重要意义.  相似文献   

A framework for the application of distributed broadband multimedia communication services in education and training     

CONSTANTINE A. Papandreou  DIONISIS X. Adamopoulos 《Education and Information Technologies》1997,2(3):207-218

This paper examines the influence of multimedia communication services in education and training. After a brief introduction in multimedia communication systems and an analysis of the learning process, a framework for the application of distributed, broadband multimedia communication services in education and training is proposed. Its main elements, which are a set of requirements, a generic layered model and a list of important related matters, are then discussed in considerable detail. Finally, the application of the proposed framework in the field of telecommunications training is suggested  相似文献   

Bilingualism Narrows Socioeconomic Disparities in Executive Functions and Self-Regulatory Behaviors During Early Childhood: Evidence From the Early Childhood Longitudinal Study     

Andree Hartanto  Wei X. Toh  Hwajin Yang 《Child development》2019,90(4):1215-1235

Socioeconomic status (SES) and bilingualism have been shown to influence executive functioning during early childhood. Less is known, however, about how the two factors interact within an individual. By analyzing a nationally representative sample of approximately 18,200 children who were tracked from ages 5 to 7 across four waves, both higher SES and bilingualism were found to account for greater performance on the inhibition and shifting aspects of executive functions (EF) and self-regulatory behaviors in classroom. However, only SES reliably predicted verbal working memory. Furthermore, bilingualism moderated the effects of SES by ameliorating the detrimental consequences of low-SES on EF and self-regulatory behaviors. These findings underscore bilingualism's power to enrich executive functioning and self-regulatory behaviors, especially among underprivileged children.  相似文献   

Local and teleconnected temperature effects of afforestation and vegetation greening in China     

Yue Li  Shilong Piao  Anping Chen  Philippe Ciais  Laurent Z X Li 《国家科学评论(英文版)》2020,7(5):897

Afforestation in China provides carbon sequestration and prevents soil erosion, but its remote impacts on climate in other regions via the coupling of forest energy fluxes with atmospheric circulation are largely unknown. Here, we prescribe inventory-based forest cover change and satellite-observed leaf area index from 1982 to 2011 in a coupled land-atmosphere model to simulate their biophysical climate effects. Both local and global surface air temperatures show a seasonal contrast in response to past vegetation cover expansion over China: a phenomenon we primarily attribute to a variation of seasonality of vegetation greening. A large cooling in spring results in concurrent decreases in geopotential height over China and zonal wind over Mongolia, causing a dipole structure in the upper troposphere over the Arctic. This accounts for ∼58% of simulated spring warming over the Russian Arctic and ∼61% of simulated spring cooling over the Canadian Artic. Our results imply that spring vegetation dynamics in China may affect climate in northern high latitudes.  相似文献   

Optofluidic planar reactors for photocatalytic water treatment using solar energy     

Lei L  Wang N  Zhang XM  Tai Q  Tsai DP  Chan HL 《Biomicrofluidics》2010,4(4):43004

Optofluidics may hold the key to greater success of photocatalytic water treatment. This is evidenced by our findings in this paper that the planar microfluidic reactor can overcome the limitations of mass transfer and photon transfer in the previous photocatalytic reactors and improve the photoreaction efficiency by more than 100 times. The microreactor has a planar chamber (5 cm×1.8 cm×100 μm) enclosed by two TiO(2)-coated glass slides as the top cover and bottom substrate and a microstructured UV-cured NOA81 layer as the sealant and flow input∕output. In experiment, the microreactor achieves 30% degradation of 3 ml 3×10(-5)M methylene blue within 5 min and shows a reaction rate constant two orders higher than the bulk reactor. Under optimized conditions, a reaction rate of 8% s(-1) is achieved under solar irradiation. The average apparent quantum efficiency is found to be only 0.25%, but the effective apparent quantum efficiency reaches as high as 25%. Optofluidic reactors inherit the merits of microfluidics, such as large surface∕volume ratio, easy flow control, and rapid fabrication and offer a promising prospect for large-volume photocatalytic water treatment.  相似文献   

String vibration dampers do not reduce racket frame vibration transfer to the forearm     

Li FX  Fewtrell D  Jenkins M 《Journal of sports sciences》2004,22(11-12):1041-1052

In this study, we examined the effect of string vibration damping devices on reducing racket frame vibration transfer to the forearm. Twenty participants volunteered to hold a tennis racket stationary in a forehand and backhand stroking position while tennis balls were fired at 20 m x s(-1) towards two impact locations, the node of vibration and the dead spot. A three-way analysis of variance with repeated measures on damping condition, impact location and stroke condition was performed on the data. The resonant frequency of the hand-held racket was found to be approximately 120 Hz. No significant differences in amplitude of vibration at the resonant frequency were found for the wrist or the elbow when damped and non-damped impacts were compared. Impacts at the dead spot produced greater amplitudes of vibration (P < 0.01) but no interaction between impact location and string dampers was evident. The string dampers had no effect on the grip force used or the muscle electrical activity in the forearm after impact. In conclusion, we found that string dampers do not reduce the amount of racket frame vibration received at the forearm. We suggest that string dampers remain a popular accessory among tennis players because of their acoustic effects and psychological support rather than any mechanical advantage.  相似文献   

对我国学生体质状况的灰色关联聚类分析   总被引：1，自引：0，他引：1  

郑旗 《体育科学》1998,(2):38

以灰色系统理论中的关联分析方法为基础,建立了基于关联度的聚类分析方法,对1995年全国汉族7～22岁男性学生的体质进行了聚类评价。结果表明:我国大学阶段各年龄组学生群体体质处于最优这一层次;高中阶段各年龄组学生群体体质处于最差层次;初中阶段各年龄组学生群体体质处于中等层次;小学阶段的各年龄组学生群体体质分属于优、中、劣之间。同时显示出,基于灰色关联度聚类的方法计算简捷,结果直观清晰,从而为群体体质的综合评价提供了一种新的量化方法。  相似文献   

Program of the 1962 convention of the central states speech association     

Frank E. X. Dance 《Communication Studies》2013,64(3):189-208

This investigation explored the use of generalized semantic differential scales for measuring organizational credibility. Findings revealed that this use is questionable, but that such findings may be the product of factors such as ego‐involvement and knowledge of a specific organization.  相似文献