固体材料导热系数的分子动力学模拟

采用分子动力学方法对金属和非金属材料薄膜的导热系数进行数值模拟. 非金属材料氩的粒子间相互作用势采用12/6 L-J势能模型,金属材料钨使用MEAM势能模型. 模拟结果表明,非金属材料氩的导热系数与已有实验结果符合较好,但金属材料钨的导热系数结果较实验结果小1~2个数量级. 研究结果表明,引入自由电子导热模型能较准确预测金属材料钨的导热系数变化规律.     

科学知识增长过程中系统自组织创生模式研究

[目的/意义]通过微观层面上个体的因果相互作用来阐述信息计量领域宏观幂律分布现象形成的必然性,将其从随机性的统计规律转变成为必然性的动力学规律。[方法/过程]在幂律分布必然性的揭示上,抛弃粗糙的机械还原论视角,而将其放在更加精密的复杂系统的分析框架下。数学论证上以普赖斯引文网络为实例,运用主方程、隐马尔科夫链推导出双参数广义普赖斯定理β函数数学描述并进一步推导出3条数学性质。[结果/结论]将信息计量领域普遍存在的偏态随机性统计规律发展成为确定性的系统动力学规律,即在简单线性累加优势规则而非马太效应规则的约束下,通过最细粒度层级上的因果二元组的多次正向性互动反馈,经由临界涨落和对称性打破,根据严谨的网络动力学数学语言描述出系统的自组织有序性稳态建构。     

Mechanical power output in rowing should not be determined from oar forces and oar motion alone

Mechanical power output is a key performance-determining variable in many cyclic sports. In rowing, instantaneous power output is commonly determined as the dot product of handle force moment and oar angular velocity. The aim of this study was to show that this commonly used proxy is theoretically flawed and to provide an indication of the magnitude of the error. To obtain a consistent dataset, simulations were performed using a previously proposed forward dynamical model. Inputs were previously recorded rower kinematics and horizontal oar angle, at 20 and 32 strokes?min^?1. From simulation outputs, true power output and power output according to the common proxy were calculated. The error when using the common proxy was quantified as the difference between the average power output according to the proxy and the true average power output (P?_residual), and as the ratio of this difference to the true average power output (ratio_res./rower). At stroke rate 20, P?_residual was 27.4 W and ratio_res./rower was 0.143; at stroke rate 32, P?_residual was 44.3 W and ratio_res./rower was 0.142. Power output in rowing appears to be underestimated when calculated according to the common proxy. Simulations suggest this error to be at least 10% of the true power output.     

Hip joint kinetics in the table tennis topspin forehand: relationship to racket velocity

The purpose of this study was to determine hip joint kinetics during a table tennis topspin forehand, and to investigate the relationship between the relevant kinematic and kinetic variables and the racket horizontal and vertical velocities at ball impact. Eighteen male advanced table tennis players hit cross-court topspin forehands against backspin balls. The hip joint torque and force components around the pelvis coordinate system were determined using inverse dynamics. Furthermore, the work done on the pelvis by these components was also determined. The peak pelvis axial rotation velocity and the work done by the playing side hip pelvis axial rotation torque were positively related to the racket horizontal velocity at impact. The sum of the work done on the pelvis by the backward tilt torques and the upward joint forces was positively related to the racket vertical velocity at impact. The results suggest that the playing side hip pelvis axial rotation torque exertion is important for acquiring a high racket horizontal velocity at impact. The pelvis backward tilt torques and upward joint forces at both hip joints collectively contribute to the generation of the racket vertical velocity, and the mechanism for acquiring the vertical velocity may vary among players.     

基于系统动力学的建筑废弃物管理模型研究

运用系统动力学理论方法研究建筑废弃物现场管理问题,分析影响建筑废弃物现场管理的主要因素及相互关系,建立包括废弃物产生、现场分类分拣和废弃物处理3个子系统的建筑废料现场管理模型,同时借助软件Vensim进行模拟评估。实证结果表明:基于系统动力学构建的建筑废弃物现场管理模型能够有效模拟施工阶段建筑废弃物的产生与处理,通过减少设计变更、提高减量化意识以及施工现场分类分拣等操作,都可以有效减少废弃物的产生及其处理成本。该方法可用于项目管理人员对管理效果进行模拟及预测。     

基于系统动力学的冷链物流配送效率因素分析及提升策略

为探索冷链物流配送影响因素,提高企业配送效率,从冷链企业、冷鲜产品及客户三方面分析冷链物流配送影响因素及相互关系,据此构建冷链配送系统及其子系统因果关系图;以冷鲜肉配送为例,将实载率、流通损失率、准时交货率等作为配送效率量化指标,同时特别考虑车辆调度、装车以及运输过程中的不确定性因素,构建配送效率影响因素系统动力学模型。利用该模型对系统进行投资分析、供需分析、载货分析,并依据分析结果提出合理的配送效率提升策略。     

基于系统动力学的移动电子商务产业演化研究

近年来我国移动电子商务产业规模迅速扩大。从系统的角度出发,移动电子商务产业可看作由经济、政策、移动技术和产业链4个相互关联的子系统构成,根据各子系统的内在因果关系,运用Vensim软件构建移动电子商务产业的系统动力学模型;在检验模型有效性的基础上,对我国移动电子商务产业的演化趋势进行仿真,并在政策和技术的不同投入力度场景下分析系统行为的变化。仿真结果表明,在适度的政策引导下,协同移动技术和产业链的发展能有效促进我国移动电子商务产业健康、可持续发展。     

创新网络与企业技术创新动态能力协同演进研究——基于系统动力学的分析_*

本研究利用系统动力学方法,从知识流动的角度描述、量化、模拟企业创新网络与企业技术创新动态能力协同演进的过程。模型分析结果表明当前企业创新绩效取决于技术创新动态能力与创新网络协同演进路径：技术创新动态能力→创新网络构建与演化→外部知识内化→创新绩效→技术创新动态能力。在协同演进的过程中随着企业技术创新的发展,在创新绩效驱动三要素中,动态能力以及创新网络知识内化对创新绩效提升具有边际递增的效应,同时创新战略、产业政策平台和管理平台对企业技术创新都存在显著影响,但这种影响作用存在较大差异。     

基于图书借阅的人类行为标度律分析

通过研究两所大学图书馆数据库中的真实资料,从群体和个体两个层面分析一次借阅过程中图书的借阅时间和用户连续两次借阅或还回图书的时间间隔等统计特征。结果表明,群体行为与个体行为表现出不同的统计特征,除群体行为的借阅时间表现为指数分布外,其它统计量都服从指数范围为1至3的幂律分布。研究说明,人类行为在群体和个体层面上具有不同的多重标度特性。     

Interpersonal coordination tendencies supporting the creation/prevention of goal scoring opportunities in futsal

Abstract

Research on 1vs1 sub-phases in team sports has shown how one player coordinates his/her actions with his/her opponent and the location of a target/goal to attain performance objectives. In this study, we extended this approach to analysis of 5vs5 competitive performance in the team sport of futsal to provide a performance analysis framework that explains how players coordinate their actions to create/prevent opportunities to score goals. For this purpose, we recorded all 10 futsal matches of the 2009 Lusophony Games held in Lisbon. We analysed the displacement trajectories of a shooting attacker and marking defender in plays ending in a goal, a goalkeeper's save, and a defender's interception, at four specific moments during performance: (1) assisting attacker's ball reception and (2) moment of passing, (3) shooter's ball reception, and (4), shot on goal. Statistical analysis showed that when a goal was scored, the defender's angle to the goal and to the attacker tended to decrease, the attacker was able to move to the same distance to the goal alongside the defender, and the attacker was closer to the defender and moving at the same velocity (at least) as the defender. This study identified emergent patterns of coordination between attackers and defenders under key competitive task constraints, such as the location of the goal, which supported successful performance in futsal.