MIMO离散非线性系统的自适应Backstepping控制

研究MIMO离散非线性系统的自适应Backstepping控制,对包含两个三阶子系统的MIMO系统推出稳定的自适应控制器设计,并利用关键性引理和投影算法的性质证明了闭环系统的所有信号有界和保证跟踪性能.     

沈从文的时间意识

沈从文的时间意识与死亡意识相生相成,构成沈从文“生命哲学”的重要而又特殊的组成部分。他认为时间的魔力巨大,能消融生命,能治疗痛苦,还能造就创作;他的时间意识停留在“过去”,具有“过去式”、“静态化”与“突变性”的特点。     

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

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.     

Predictive value of ventilatory inflection points determined under field conditions

The aim of this study was to evaluate the predictive potential provided by two ventilatory inflection points (VIP₁ and VIP₂) examined in field without using gas analysis systems and uncomfortable facemasks. A calibrated respiratory inductance plethysmograph (RIP) and a computerised routine were utilised, respectively, to derive ventilation and to detect VIP₁ and VIP₂ during a standardised field ramp test on a 400 m running track on 81 participants. In addition, average running speed of a competitive 1000 m run (S_1k) was observed as criterion. The predictive value of running speed at VIP₁ (S_VIP1) and the speed range between VIP₁ and VIP₂ in relation to VIP₂ (VIP_SPAN) was analysed via regression analysis. VIP_SPAN rather than running speed at VIP₂ (S_VIP2) was operationalised as a predictor to consider the covariance between S_VIP1 and S_VIP2. S_VIP1 and VIP_SPAN, respectively, provided 58.9% and 22.9% of explained variance in regard to S_1k. Considering covariance, the timing of two ventilatory inflection points provides predictive value in regard to a competitive 1000 m run. This is the first study to apply computerised detection of ventilatory inflection points in a field setting independent on measurements of the respiratory gas exchange and without using any facemasks.     

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

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.     

福州市中年人参加健身跑现状的调查研究

采用文献资料法、问卷调查法、数理统计法等,对福州市中年人参加健身跑的情况进行调查分析,明确健身跑运动对中年人身体健康的意义和作用,旨在为中年人更好地进行健身跑运动,提供参考。     

9.11事件后地缘政治观的反思

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。     

从认知语言学角度看英汉语时间概念隐喻的差异

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。     

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

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.     

How much does lower body strength impact Paralympic running performance?

Objectives: Development of evidence-based methods of Paralympic classification requires research quantifying the relative strength of association between ratio-scaled measures of impairment and athletic performance. The purpose of this study was to quantify the extent to which muscle strength affects running performance in runners with and without brain impairment. Design: Cross-sectional study. Methods: Participants were 41 male runners: 13 with brain impairments (RBI) and 28 non-disabled (NDR). All participants completed a maximal 60-m sprint and a novel battery of three lower limb isometric strength tests. Results: RBI showed significantly lower strength scores compared with NDR on the more affected side in leg flexion (176 vs. 243?N), leg extension (993 vs. 1661?N) and plantarflexion (824 vs. 1457?N). Significant differences were also seen on the less affected side in plantarflexion (1072 vs. 1508?N). RBI were significantly slower in the acceleration phase (0–15?m) (3.2?s?±?0.3?vs. 2.8?s?±?0.2) and top speed phase (30?60?m) (4.3?s?±?0.6?vs. 3.8?s?±?0.3). Correlation analysis showed stronger relationships between strength and running performance in RBI than NDR; however, the correlations were not significant. Conclusions: This study evaluated measures to assess strength for the purposes of classification and found that the measures were significantly different in RBI compared with NDR indicating the tests were able to capture strength impairment in this population. This study indicates that strength may be an important impairment type to assess in this population, as impairments of muscle strength may influence the outcome of running performance in athletes with more severe impairments.