利用特征线法求解方程ut＋b·Du＋cu＝f（x，t）的初值问题

本文研究具有初值条件u（x,0）＝g（x）的方程 ut＋b·Du＋cu＝f（x,t）的初值问题。方程ut＋b·Du＋cu＝f（x,t）是具有常系数的一阶非齐次线性偏微分方程,这类方程在变分法、质点力学和几何学中都出现过,因此研究这类方程的目的是更好地应用于这些学科。求解这类方程的最基本方法是特征线法。它是把偏微分方程转化为常微分方程或常微分方程组,通过求解这些常微分方程得到所要求的解。本文分别运用特征线法以及特征线法的特殊情况求解了该初值问题,两种方法所得到的解是一致的,都是u（x,t）＝g（x-bt）e-ct＋e-ct t0 ecu f（x＋b（u-t）,u）du。因此,有了通过特征线法所求得的该初值问题的解的公式,我们可以更好地研究相关的一些实际问题。     

一类三次非线性生态系统的极限环

应用数学生态学和微分方程定性理论,讨论了一类既相互干扰又具有密度制约的生态系统：dx/dt=x（r1x-r2x^2）-cxy,dy/dt=y（-d＋cex-by）,在给定参数满足一定的条件下,证明了该系统极限环的存在性和唯一性。     

信息与计算科学专业常微分方程教学改革初探

根据应用型本科院校的教学特点,结合实际,主要从教学内容、教学方法和加强学生创新能力的培养等方面,对信息与计算科学专业“常微分方程”课程教学改革进行了探索。     

偏微分方程的应用

本文在简要的介绍偏微分方程的发展历史的基础上，详细的讨论了其在弦振动及人口问题中的应用。其目的在于了解偏微分方程曲折的发展史及其广阔的应用前景，从而激励读者深入的学习和研究偏微分方程。     

基于LELAND-LOTT思想双币种期权定价

本文利用期权复制、无套利对冲原理、计价单位转换、随机微分方程等工具,对具有交易费用的双币种期权的定价进行了探讨。得到了支付交易费用的双币种期权所满足的偏微分方程和定价公式。     

变量代换法在求解微分方程问题中的应用

在常微分方程中,许多类型的常微分方程求解是依靠变量代换这一重要方法来完成的,文章就变量代换在几类微分方程中的应用进行探究。     

常微分方程双语教学的实践与探索

双语教学是培养高层次专业人才的重要的教学方法,是提高教学质量的重要手段之一。从多年的教学实践出发,对双语教学存在的问题进行探讨,研究如何进行常微分方程双语教学模式的创新与突破,做到既充分体现专业学科特色,又提高学生专业外语水平。     

阻滞增长模型在奥运会撑杆跳高冠军成绩预测中的应用

采用数学建模理论对历届奥运会男子撑杆跳高运动员的金牌成绩进行统计分析,运用拟合模型和常微分方程模型对未来撑杆跳高竞赛项目的最好成绩进行预测,以期为拓宽数学建模在体育领域的应用范围提供一定的依据。     

走跑健身的生理机制与影响因素分析

着重阐明了走路和跑步对减肥,健脑、防病治病、防腿老和消除烦脑的生理学机制。并对影响常走和常跑锻炼的因素进行了分析。提出了坚持常走和常跑锻炼的措施和方法。     

奥运会官方电影刍议

电影与奥运会已有100多年的历史,期间二者经历了不同的发展阶段,表现出了种种不同的特点.在考证了奥运会官方电影概念的基础上,对历届奥运会官方电影进行了回顾、归纳和总结,同时,对其发展现状和面临的问题进行了分析和讨论.     

Reliability and Validity of Self Report of Aerobic Activity: Family Health Project

Abstract

Two studies are presented which deal with the reliability and validity of self-reports of aerobic activity. The first study compared two forms of self-report data obtained as part of a study of intervention strategy. The two forms were daily self-report and weekly retrospective report. Analyses covering the overlapping time period revealed differences in mean minutes engaged in activity, but modest and statistically significant correlations between the two forms among adults participating in the intervention group. No meaningful results were obtained among adults in the control group, nor among children in either group. The need for the development and testing of self-report forms among children was noted, and was the subject of the second study.

In Study II, six different forms on which third to sixth grade children recorded their aerobic activity were compared against two days of continuous observations of their behavior. The six forms varied along two dimensions. The first dimension varied the time period of reporting: half the forms required reporting by segments of the day; the other half allowed for reporting of the day as a whole. The second dimension varied response format: one third of the forms asked for a dichotomous (yes; no) report; one third asked for a trichotomous (no; yes, but less than 20 min; yes, for 20 min or more) report; and one third asked for reporting of precise numbers of minutes. The segmented day forms resulted in significantly higher agreement with the observers' report of activity. This finding is interpreted to be congruent with recent research on the importance of context in the recall of behavior. No effect from parental assistance in child's form completion was detected.     

基于Mathematica的变量带有上下界的丢番图方程组的简单实现

K.Aardal等人给出了一种求解变量有上下界的丢番图方程组的算法。文章利用Mathematica这门编程语言就可将该算法简单地实现。文中进行了相关的数值实验,说明了用Mathematica这门编程语言来求解变量有上下界的丢番图方程组的可行性和有效性。     

Forthcoming events

The aims of this study were to quantify the effects of factors such as mode of exercise, body composition and training on the relationship between heart rate and physical activity energy expenditure (measured in kJ?·?min^?1) and to develop prediction equations for energy expenditure from heart rate. Regularly exercising individuals (n = 115; age 18?–?45 years, body mass 47?–?120?kg) underwent a test for maximal oxygen uptake ([Vdot]O_2max test), using incremental protocols on either a cycle ergometer or treadmill; [Vdot]O_2max ranged from 27 to 81?ml?·?kg^?1?·?min^?1. The participants then completed three steady-state exercise stages on either the treadmill (10?min) or the cycle ergometer (15?min) at 35%, 62% and 80% of [Vdot]O_2max, corresponding to 57%, 77% and 90% of maximal heart rate. Heart rate and respiratory exchange ratio data were collected during each stage. A mixed-model analysis identified gender, heart rate, weight, [Vdot]_2max and age as factors that best predicted the relationship between heart rate and energy expenditure. The model (with the highest likelihood ratio) was used to estimate energy expenditure. The correlation coefficient (r) between the measured and estimated energy expenditure was 0.913. The model therefore accounted for 83.3% (R ²) of the variance in energy expenditure in this sample. Because a measure of fitness, such as [Vdot]O_2max, is not always available, a model without [Vdot]O_2max included was also fitted. The correlation coefficient between the measured energy expenditure and estimates from the mixed model without [Vdot]O_2max was 0.857. It follows that the model without a fitness measure accounted for 73.4% of the variance in energy expenditure in this sample. Based on these results, we conclude that it is possible to estimate physical activity energy expenditure from heart rate in a group of individuals with a great deal of accuracy, after adjusting for age, gender, body mass and fitness.     

Classification of Physical Activity Cut-Points and the Estimation of Energy Expenditure During Walking Using the GT3X+ Accelerometer in Overweight and Obese Adults

This study establishes tri-axial activity count (AC) cut-points for the GT3X+ accelerometer to classify physical activity intensity in overweight and obese adults. Further, we examined the accuracy of established and novel energy expenditure (EE) prediction equations based on AC and other metrics. Part 1: Twenty overweight or obese adults completed a 30 minute incremental treadmill walking protocol. Heart rate (HR), EE, and AC were measured using the GT3X+ accelerometer. Part 2: Ten overweight and obese adults conducted a self-paced external walk during which EE, AC, and HR were measured. Established equations (Freedson et al., 1998; Sasaki et al., 2011) overestimated EE by 40% and 31%, respectively (p < .01). Novel gender-specific prediction equations provided good estimates of EE during treadmill and outdoor walking (standard error of the estimate = .91 and .65, respectively). We propose new cut-points and prediction equations to estimate EE using the GT3X+ tri-axial accelerometer in overweight and obese adults.     

Confirmatory factor analysis of the Test of Performance Strategies (TOPS) among adolescent athletes

The aim of the present study was to examine the factorial validity of the Test of Performance Strategies (TOPS; Thomas et al., ) among adolescent athletes using confirmatory factor analysis. The TOPS was designed to assess eight psychological strategies used in competition (i.e. activation, automaticity, emotional control, goal-setting, imagery, negative thinking, relaxation and self-talk,) and eight used in practice (the same strategies except negative thinking is replaced by attentional control). National-level athletes (n?=?584) completed the 64-item TOPS during training camps. Fit indices provided partial support for the overall measurement model for the competition items (robust comparative fit index?=?0.92, Tucker-Lewis index?=?0.88, root mean square error of approximation?=?0.05) but minimal support for the training items (robust comparative fit index?=?0.86, Tucker-Lewis index?=?0.81, root mean square error of approximation?=?0.06). For the competition items, the automaticity, goal-setting, relaxation and self-talk scales showed good fit, whereas the activation, emotional control, imagery and negative thinking scales did not. For the practice items, the attentional control, emotional control, goal-setting, imagery and self-talk scales showed good fit, whereas the activation, automaticity and relaxation scales did not. Overall, it appears that the factorial validity of the TOPS for use with adolescents is questionable at present and further development is required.     

The relationship between game-based performance indicators and developmental level in junior Australian football: Implications for coaching

Identifying performance differences between juniors at different stages of a talent pathway may assist with the development of prospective talent. This study investigated the relationship between game-based performance indicators and developmental level in junior Australian football (AF). Players were categorised into 2 groups according to developmental level; U16 and U18. Physical and technical skill performance indicators were collated for all U16 (n = 200) and U18 (n = 244) participants of their respective 2014 national championships. Data were acquired from all 28 games (12 U16, 16 U18); resulting in 1360 player observations (568 U16, 792 U18). Microtechnology and a commercial provider facilitated the quantification of 15 performance indicators. Generalised estimating equations (GEEs) modelled the extent to which these performance indicators were associated with developmental level. The GEE model revealed that “contested marks” and “contested possessions” had the strongest association with the U16 level, while “total marks” and “clearances” had the strongest association with the U18 level. The remaining performance indicators were not developmentally discriminant. These results indicate that there are distinctive features of gameplay more associated with the U16 and U18 levels in AF. Coaches may wish to consider these results when constructing training drills designed to minimise developmental gaps.     

Two tests of approach-iron golf skill and their ability to predict tournament performance

Abstract

The aim of this study was to investigate the convergent and predictive validity of two skill tests that examine the ability of golfers to hit accurate approach-iron shots. Twenty-four high-level golfers (handicap = 2.6 ± 1.7) performed the Nine-Ball Skills Test (assesses the ability to shape/control ball trajectory with high accuracy) and the Approach-Iron Skill Test (assesses the ability to hit straight shots from varying distances with high accuracy). Participants then completed at least eight rounds of tournament golf over the following 90 days and reported an indicator of approach-iron accuracy (per cent error index). A moderate correlation (r = 0.50, P < 0.05) was noted between scores for both tests. Generalised estimating equations, using two covariates (lie of the ball and distance to hole), were used to determine model fit and the amount of variance explained for tournament per cent error index. Results showed that the Approach-Iron Skill Test was the slightly stronger predictor of on-course per cent error index. With both test scores considered together, a minimal amount of additional variance was explained. These findings suggest that either of the tests used individually or combined may be used to predict tournament approach iron performance in high-level golfers.     

Body fat measurement in elite sport climbers: Comparison of skinfold thickness equations with dual energy X-ray absorptiometry

Abstract

The aim of this study was to compare equations for estimating percentage body fat from skinfold thickness in elite sport climbers by assessing their agreement with percentage body fat measured using dual-energy X-ray absorptiometry (DXA). Skinfold thickness was measured in a convenience sample of 19 elite sport climbers [9 women and 10 men; mean age 31.2 years (s = 5.0) and 28.6 years (s = 3.6), respectively]. Percentage body fat was estimated using 17 different equations, and it was also measured by DXA. A significant inter-methods difference was observed for all equations, except for Durnin's equation in men (inter-methods difference: ?0.57% and ?0.29%; 1.96 s: 5.56 and 5.23 for Siri's and Brozek's equation, respectively) and women (inter-methods difference: ?0.67% and ?1.29% for Siri's and Brozek's equation, respectively), and for Wilmore's equation using Siri's body fat equation in women (inter-methods difference: ?1.86%). In women, the limits of agreement were lower when using Durnin's equation compared with Wilmore's equation (1.96 s: 3.86% and 5.13%, respectively). In conclusion, of the 17 studied equations, Durnin's equation was the most accurate in estimating percentage body fat in both male and female elite climbers. Therefore, Durnin's equation could be used to assess percentage body fat in elite sport climbers if more accurate methods are not available. The generalizability of the results is limited by the fact that the sample was not selected at random.     

高校体育舞蹈运动开展的受制因素分析及对策研究

体育舞蹈是一门新兴的体育运动项目,具有很高的审美价值和健身娱乐价值,深受高校学生的喜爱。体育舞蹈在我国的普及推广过程中,受到诸多因素的影响,通过调查访问法,并结合体育舞蹈的项目特点,以及在我国开展的现状,对体育舞蹈在高校开展的四大受制因素进行了剖析,并提出了相应的对策,以期能促进该项目在高校蓬勃开展。     

Integrating different tracking systems in football: multiple camera semi-automatic system,local position measurement and GPS technologies

Abstract

During the past decade substantial development of computer-aided tracking technology has occurred. Therefore, we aimed to provide calibration equations to allow the interchangeability of different tracking technologies used in soccer. Eighty-two highly trained soccer players (U14–U17) were monitored during training and one match. Player activity was collected simultaneously with a semi-automatic multiple-camera (Prozone), local position measurement (LPM) technology (Inmotio) and two global positioning systems (GPSports and VX). Data were analysed with respect to three different field dimensions (small, <30 m² to full-pitch, match). Variables provided by the systems were compared, and calibration equations (linear regression models) between each system were calculated for each field dimension. Most metrics differed between the 4 systems with the magnitude of the differences dependant on both pitch size and the variable of interest. Trivial-to-small between-system differences in total distance were noted. However, high-intensity running distance (>14.4 km · h^?1) was slightly-to-moderately greater when tracked with Prozone, and accelerations, small-to-very largely greater with LPM. For most of the equations, the typical error of the estimate was of a moderate magnitude. Interchangeability of the different tracking systems is possible with the provided equations, but care is required given their moderate typical error of the estimate.