土壤初始含水量对注射灌土壤水分运移分布 特性影响试验研究

通过室内不同土壤初始含水量的注射灌水分入渗试验,研究了土壤初始含水量对注射灌土壤水分运移分布特性影响。研究表明：注射灌的累积入渗量与时间呈幂函数关系,土壤初始含水量越大,相同入渗时间的累积入渗量越大。在出水口下方土壤水分湿润范围较大,土壤含水量也较大,而在出水口上方则相反。土壤初始含水量越大,土壤湿润范围越大,距离出水口相同距离的土壤含水量越大。以上研究可为进一步补充注射灌理论技术提供基础。     

A parameter uniform B-spline collocation method for solving singularly perturbed turning point problem having twin boundary layers

A numerical scheme is proposed to solve singularly perturbed two-point boundary value problems with a turning point exhibiting twin boundary layers. The scheme comprises B-spline collocation method on a non-uniform mesh of Shishkin type. Asymptotic bounds are established for the derivative of the analytical solution of a turning point problem. The present method is boundary layer resolving as well as second-order accurate in the maximum norm. A brief analysis has been carried out to prove the uniform convergence with respect to the singular perturbation parameter ? by decomposing the solution into smooth and singular components. Some relevant numerical examples are also illustrated to verify computationally the theoretical aspects.     

大型室内游乐场人员疏散运动时间的模拟

针对大型室内游乐场人员疏散运动时间的问题,分析了游乐场人员构成、人员步速和肩宽及其分布与人员疏散运动时间的关系,采用Pathfinder模拟了该运动时间与其影响因素间的关系.模拟结果表明:对于特定的大型室内游乐场,在外界环境和人员密度不变的条件下,人员疏散运动时间随人员步速的增大而减少,随人员肩宽的增大而增大,随儿童比例的增大而增大;人员步速和肩宽均服从常值分布时的疏散运动时间最短,服从均匀分布时的疏散运动时间最长,服从正态分布时的疏散运动时间介于二者之间.     

基于半转机构的类两足步行机构相对运动空间分析

基于半转机构的类两足步行机构是一种新型单自由度行走机构,适用于步行车的移动系统。针对类两足步行机构运行过程中有着不同于传统腿式步行机构的扫略规律,在给出类两足步行机构基本构型和行走原理的基础上,以机架为参考系,解析一级转臂、二级转臂、腿杆和弯头定位杆等重要组件在运动过程中外轮廓形成规律,综合获得类两足步行机构相对运动空间。研究结果为防止步行车行走机构与机身发生干涉、以及实现步行车相关结构精准化设计奠定理论基础。     

闸后水流运动的SPH法数值模拟

在对光滑离子流体动力学(SPH)法的基本原理、核函数及控制方程离散格式、边界处理方法等进行介绍的基础上建立了数值水槽模型,成功模拟了闸门开启后水流的界面变形、界面破碎、气泡的生成及溃灭,以及涌浪的生成过程。结果表明SPH法能够捕捉到流体的飞溅及融合现象,适于模拟具有瞬时极大变形等水流运动。     

Sequential ballistic movement

Studies of sequential ballistic movements showed that strong interaction occurs between components of a complex movement task. Within an individual component of the motion, a good predictor of movement time was the square root of the movement amplitude. There was a statistically significant influence of the preceding amplitude on the movement time, apart from the first component where the movement time was dependent on the immediate subsequent movement amplitude. Models for movement times are proposed for the different components of sequential movements.     

Development and validation of a biodynamic model for predicting multi-finger movements in cylinder-grasping tasks †

This article describes the development and validation of a model for predicting multi-finger movements in grasping activities. The model builds upon a newly proposed approach that incorporates forward dynamics and a system identification procedure, and is amenable to empirical tests. A database of multi-fingered grasping movements performed by 28 subjects was established and divided into four sets, one for model development and three for model validation. In the development phase, model parameter values were estimated by the iterative system identification procedure through a physics-based heuristic algorithm. The estimated parameter values were then statistically synthesised and integrated into the prediction model. In the validation phase, the model was applied to three novel datasets containing different grasping movements involving objects of varied sizes and different subjects. The results demonstrated the model's ability to predict hand prehensile movements with error magnitudes comparable to the inter-person variability in performing such movements. New insights into the control of multi-fingered hand prehensile movements at the systems and joint levels emerged from the model development and validation process. The current study contributes to building a foundation for long-term development of realistic biodynamic simulation of multi-finger hand movements. Such simulation capabilities will aid in design of hand-operated tools, devices or hand-intensive work for proactive ergonomics and in evaluation as well as treatment of functional impairment of the hand.     

Capture of shrinking targets

‘Shrinking targets’ are targets whose size diminishes with time. The task studied is a modification of Fitts' (1954 Fitts, P. M. 1954. The information capacity of the human motor system in controlling the amplitude of movement. Journal of Experimental Psychology, 67(6): 381–391. [Crossref] , [Google Scholar]) paradigm, with the difference that, as soon as the movement is started, the target size reduces at a constant rate until it finally vanishes. Very little research has been reported on this problem apart from Johnson and Hart (1987 Johnson, W. W. and Hart, S. G. Step tracking shrinking targets. Proceedings of the Human Factors Society 31st annual meeting. October1987, New York City. pp.248–252. Santa Monica, CA: HFES.  [Google Scholar]) and Hancock and Caird (1993 Hancock, P. A. and Caird, J. K. 1993. Experimental evaluation of a model of mental workload. Human Factors, 35(3): 413–429. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). Two experiments are reported aimed at determining the parameters that affect the movement time and the probability of capturing a target when there are different amplitudes of movement, target widths and shrink rates. A multiplicative model is required to describe movement time data, which is dependent on Fitts' Index of Difficulty, the shrink rate and the product of these two variables. An alternative model describes the critical movement time, for a specified probability of target capture, in a modified form of Fitts' Law.

Statement of Relevance: Modifications of Fitts' Law have been developed for many different movement tasks. Shrinking targets occur in circumstances such as gunnery and in computer games, where a target is moving away from the person. An expression is developed for the critical time to capture the target in terms of a modified form of Fitts' Law.     

Does fatigue exist in a quantitative measurement of eye movements?

Abstract

The measurement system for quantitative analysis of eye movements and distribution of eye fixation points was developed through the study. Experiments on physiological fatigue characteristics of eye movements were studied using the system. The subjects involved in the study were six young males. No significant change was quantitatively found in saccadic eye movements during and/or after five hours of rapid eye tracking tasks. The saccadic velocity of two subjects were found in binocular decreased temporarily. The maximum velocity of eye movements obtained in the present experiment was ascertained in order to produce a scale for various visual work as an ergonomic index.