Background： Many studies examining individual-level correlates in youth utilize self-report rather than objective measures of physical activity （PA）. This utilization of self-report may result in associations that ...Background： Many studies examining individual-level correlates in youth utilize self-report rather than objective measures of physical activity （PA）. This utilization of self-report may result in associations that are not present when examining objectively measured PA. The present study investigates the relationship between hypothesized correlates of PA with objectively and subjectively measured PA. Methods： Participating children （n 232, 101 males, mean age - 12.3 years） provided a minimum of four monitored days of PA （via accelerometer） and completed a survey assessing moderate-to-vigorous physical activity （MVPA）, sport competence, appearance, enjoyment, and self-efficacy. Height and weight were measured and body mass index （BMI） was calculated. Results： Hierarchical regression models controlling for sex, race, and BMI Z-score showed that only sex and BMI Z-score were significant correlates of objective MVPA while only sex was a significant correlate of objective total PA. However, in a separate model examining the relationship with subjective MVPA, enjoyment of PA and self-efficacy for PA were the only significant correlates of self-reported PA. Conclusion： Measuring MVPA via self-report versus accelerometry produces considerably different results in a sample of young adolescents. Future studies should use caution when selecting outcome measures if the intent is to identify modifiable correlates of MVPA in youth.展开更多
文摘随着多能源混合储能技术的快速发展,氢电混合储能系统将成为解决可再生能源并网发电间歇性、波动性问题的重要途径。运用热力学原理推导了质子交换膜(proton exchange membrane,PEM)电解制氢的输出电压,建立了符合制氢电压输出特性的电化学模型;然后,分析了氢电混合储能微网的典型架构,提出了考虑蓄电池荷电状态(state of charge,SOC)的指数型下垂控制策略,在维持微网母线电压稳定的同时,解决了蓄电池并联充放电的SOC均衡问题;最后,结合光伏和电解制氢单元的适应性控制方法,根据蓄电池充放电状态将微网划分为4种工作模式,并进行了仿真分析。结果表明考虑蓄电池SOC的指数型下垂控制策略能够控制微网实现工作模式之间平滑过渡,当光伏发电供能产生变化时,可进行适应性功率分配,有效提升了系统经济性与能源利用效率。
基金funded by the Centers for Disease Control and Prevention(K01-DP001126)
文摘Background： Many studies examining individual-level correlates in youth utilize self-report rather than objective measures of physical activity （PA）. This utilization of self-report may result in associations that are not present when examining objectively measured PA. The present study investigates the relationship between hypothesized correlates of PA with objectively and subjectively measured PA. Methods： Participating children （n 232, 101 males, mean age - 12.3 years） provided a minimum of four monitored days of PA （via accelerometer） and completed a survey assessing moderate-to-vigorous physical activity （MVPA）, sport competence, appearance, enjoyment, and self-efficacy. Height and weight were measured and body mass index （BMI） was calculated. Results： Hierarchical regression models controlling for sex, race, and BMI Z-score showed that only sex and BMI Z-score were significant correlates of objective MVPA while only sex was a significant correlate of objective total PA. However, in a separate model examining the relationship with subjective MVPA, enjoyment of PA and self-efficacy for PA were the only significant correlates of self-reported PA. Conclusion： Measuring MVPA via self-report versus accelerometry produces considerably different results in a sample of young adolescents. Future studies should use caution when selecting outcome measures if the intent is to identify modifiable correlates of MVPA in youth.
