平直界面一维晶体生长问题的相似解     

刘竞 《石家庄职业技术学院学报》2005,17(6):1-3

对于平直界面下由过冷边界开始的熔体的一维凝固过程，考虑液态中远场温度高于凝固温度，而底板温度低于凝固温度，利用相似性解法分别求解固液态温度，分析其结果，说明由低温区长入高温区的界面总是稳定的，从而更加完善了一维晶体生长理论．  相似文献   

指派问题在机械分配中的运用     

王刚 《襄樊职业技术学院学报》2006,5(3):9-10

在许多企业生产经营管理工作中。经常面临着给机械分派工作地点等问题，由于这类问题相关的效率统计资料是比较容易获得的，因此，可以应用指派问题解决机械分配的有关问题。通过例子介绍了有部分限制的匈牙利解法在机械分配中的运用。  相似文献   

Inter-participant variability in daily physical activity and sedentary time among male youth sport footballers: independent associations with indicators of adiposity and cardiorespiratory fitness     

Sally A. M. Fenton  Joan L. Duda  Timothy Barrett 《Journal of sports sciences》2016,34(3):239-251

Participation in youth sport is assumed to promote and contribute towards more physically active lifestyles among children and adolescents. The aim of this study was to examine inter-participant variability in objectively measured habitual physical activity (PA) behaviours and sedentary time among youth sport participants and their implications for health. One-hundred-and-eighteen male youth sport footballers (Mean ± s = 11.72 ± 1.60) wore a GT3X accelerometer for 7 days. Average daily PA [min · day^?1, in light (LPA), moderate (MPA), vigorous (VPA) and combined moderate-to-vigorous (MVPA)] and sedentary time were calculated. Participants’ body mass index adjusted for age and sex (BMI–standard deviation score), per cent body fat (BF%), waist circumference and cardiorespiratory fitness were assessed. Results revealed that variability in daily PA behaviours and sedentary time (min · day^?1) was associated with BMI–standard deviation score [VPA (?), MVPA (?)], BF% [sedentary time (+), VPA (?), MVPA (?)], waist circumference [sedentary time (+), LPA (?)] and cardiorespiratory fitness [sedentary time (?), MPA (+), VPA (+), MVPA (+)]. Whilst sedentary time and MVPA were not related to health outcomes independent of one another, associations with markers of adiposity and cardiorespiratory fitness were stronger for sedentary time. Sedentary time was also significantly positively related to waist circumference independent of VPA. Results demonstrate inter-participant variability in habitual PA and sedentary time among youth sport participants which holds implications for their health. Thus, promoting PA and, in particular, reducing sedentary time may contribute towards the prevention of adverse health consequences associated with a physically inactive lifestyle for children and adolescents active in the youth sport context.  相似文献   

Accelerometer data requirements for reliable estimation of habitual physical activity and sedentary time of children during the early years - a worked example following a stepped approach     

Daniel D. Bingham  Silvia Costa  Stacy A. Clemes  Ash C. Routen  Helen J. Moore  Sally E. Barber 《Journal of sports sciences》2016,34(20):2005-2010

This study presents a worked example of a stepped process to reliably estimate the habitual physical activity and sedentary time of a sample of young children. A total of 299 children (2.9 ± 0.6 years) were recruited. Outcome variables were daily minutes of total physical activity, sedentary time, moderate to vigorous physical activity and proportional values of each variable. In total, 282 (94%) provided 3 h of accelerometer data on ≥1 day and were included in a 6-step process: Step-1: determine minimum wear-time; Step-2: process 7-day-data; Step-3: determine the inclusion of a weekend day; Step-4: examine day-to-day variability; Step-5: calculate single day intraclass correlation (ICC) (2,1); Step-6: calculate number of days required to reach reliability. Following the process the results were, Step-1: 6 h was estimated as minimum wear-time of a standard day. Step-2: 98 (32%) children had ≥6 h wear on 7 days. Step-3: no differences were found between weekdays and weekend days (P ≥ 0.05). Step-4: no differences were found between day-to-day variability (P ≥ 0.05). Step-5: single day ICC’s (2,1) ranged from 0.48 (total physical activity and sedentary time) to 0.53 (proportion of moderate to vigorous physical activity). Step-6: to reach reliability (ICC = 0.7), 3 days were required for all outcomes. In conclusion following a 7 day wear protocol, ≥6 h on any 3 days was found to have acceptable reliability. The stepped-process offers researchers a method to derive sample-specific wear-time criterion.  相似文献   

浅析“换元法”在含有根式函数一阶求导过程中的应用     

李春锋 《河西学院学报》2004,20(5):20-22

本文针对《高等数学》中含有根式的函数的一、二阶求导问题采用了较为简便的“换元法”进行求导计算的方法,基本解决了在复杂函数的求导过程中令人困扰的化简、计算容易出错的不利因素.为学生后期的进一步学习和踏上工作岗位后在实践过程中对导数在具体工程实践中的应用提供了一些帮助.  相似文献   

9.11事件后地缘政治观的反思   总被引：1，自引：0，他引：1  

赵为民 《洛阳师范学院学报》2002,21(6):26-28

地缘政治这一传统观念在经济全球化、政治趋向多极化的背景下,遇到了强有力的挑战。9.11事件后美国政府正在重构其地缘逻辑思维。适时提出“时缘政治”和“人缘政治”概念,全面审视世界政治格局。我国应从国家利益出发,积极重构地缘战略格局。  相似文献   

马克思价值转形问题上中国人数学解法的无效创意     

陈勇勤 《南阳师范学院学报》2007,6(11):32-43

转形问题长期陷入数学求证困境,所得到的各种结果与中外研究者所投入的时间和精力不能成正比。本文列举的中国人的三种解法,各有其特点。既要识别真伪性,也要识别合理性与不合理性。三种解法都以"西方构思"为本源,做出一点点创新(新的未必就不是伪的或不合理的),但都没有突破"西方构思"的基本框架。西方学者刻意追求数学证明,往往又止步在证伪"两个等于"。数学求证有一定的局限性。突破其局限性,不是数学技巧问题,而是数学思维问题。但是,改变数学思维终归替代不了从数学求证转换到非数学求证。  相似文献   

从认知语言学角度看英汉语时间概念隐喻的差异     

龚萍 《荆州师范学院学报》2005,28(4):104-106

英汉语在“时间是空间”、“时间流逝是运动”、“时间是金钱”、“时间是实体”等主要时间概念隐喻及相应的语言表达形式中虽有很多相同之处，但也存在着差异。这些差异来源于英汉不同的认知和社会文化背景。  相似文献   

Effects of environmental intervention on sedentary time,musculoskeletal comfort and work ability in office workers     

Ying Gao  Nina Nevala  Neil J. Cronin  Taija Finni 《European Journal of Sport Science》2016,16(6):747-754

Sit–stand workstations offer a potential strategy to reduce prolonged occupational sitting. This controlled intervention study examined the effects of an environmental intervention on occupational sedentary time, musculoskeletal comfort and work ability, and the usability of sit–stand workstations in office work via a self-reported questionnaire. The intervention group (n?=?24) used sit–stand workstations during the 6-month intervention period, and the control group (n?=?21) used traditional sitting workstations. The results showed that working at sit–stand workstations can reduce sitting time significantly compared to control workstations (?6.7% vs. 5.0%, p?=?.019), which is reallocated mostly to standing (r?=??0.719, p?p?=?.028), as well as work ability (p?=?.022). The majority of intervention subjects rated sit–stand workstation adjustability as good (83.3%), and 75.0% were satisfied with the workstation. About 41.7% of the intervention participants, who were exclusively female, used the sit–stand function on a daily basis. While the environmental change alone was effective, it is likely that promoting the daily use of sit–stand workstations with counselling would lead to even more substantial positive effects.  相似文献   

One hundred and fifty years of sprint and distance running – Past trends and future prospects     

Martin Weiss  Alexandra Newman  Ceri Whitmore  Stephan Weiss 《European Journal of Sport Science》2016,16(4):393-401

Sprint and distance running have experienced remarkable performance improvements over the past century. Attempts to forecast running performances share an almost similarly long history but have relied so far on relatively short data series. Here, we compile a comprehensive set of season-best performances for eight Olympically contested running events. With this data set, we conduct (1) an exponential time series analysis and (2) a power-law experience curve analysis to quantify the rate of past performance improvements and to forecast future performances until the year 2100. We find that the sprint and distance running performances of women and men improve exponentially with time and converge at yearly rates of 4% ± 3% and 2% ± 2%, respectively, towards their asymptotic limits. Running performances can also be modelled with the experience curve approach, yielding learning rates of 3% ± 1% and 6% ± 2% for the women's and men's events, respectively. Long-term trends suggest that: (1) women will continue to run 10–20% slower than men, (2) 9.50 s over 100 m dash may only be broken at the end of this century and (3) several middle- and long-distance records may be broken within the next two to three decades. The prospects of witnessing a sub-2 hour marathon before 2100 remain inconclusive. Our results should be interpreted cautiously as forecasting human behaviour is intrinsically uncertain. The future season-best sprint and distance running performances will continue to scatter around the trends identified here and may yield unexpected improvements of standing world records.  相似文献