关于加加速度的若干机械运动分析及MATLAB模拟

分析了和加加速度有关的若干机械运动的运动特点,并用MATLAB作了计算机模拟。     

MATLAB在刚体运动教学中的应用

刚体运动问题是大学物理教学中较抽象的重要知识点。本文应用MATLAB对大学物理的刚体运动学问题进行求解,直观体现物理量之间的关系,让学生更好地理解和掌握物理规律,增加学生学习物理的兴趣。     

Phase separation driven by density-dependent movement: A novel mechanism for ecological patterns

Many ecosystems develop strikingly regular spatial patterns because of small-scale interactions between organisms, a process generally referred to as spatial self-organization. Self-organized spatial patterns are important determinants of the functioning of ecosystems, promoting the growth and survival of the involved organisms, and affecting the capacity of the organisms to cope with changing environmental conditions. The predominant explanation for self-organized pattern formation is spatial heterogeneity in establishment, growth and mortality, resulting from the self-organization processes. A number of recent studies, however, have revealed that movement of organisms can be an important driving process creating extensive spatial patterning in many ecosystems. Here, we review studies that detail movement-based pattern formation in contrasting ecological settings. Our review highlights that a common principle, where movement of organisms is density-dependent, explains observed spatial regular patterns in all of these studies. This principle, well known to physics as the Cahn–Hilliard principle of phase separation, has so-far remained unrecognized as a general mechanism for self-organized complexity in ecology. Using the examples presented in this paper, we explain how this movement principle can be discerned in ecological settings, and clarify how to test this mechanism experimentally. Our study highlights that animal movement, both in isolation and in unison with other processes, is an important mechanism for regular pattern formation in ecosystems.     

气顶油藏油气界面移动距离的计算

针对带地层倾角的气顶油藏,利用跟踪质点的拉格朗日法描述油气界面移动的力学特性;借助油气渗流的基本微分方程组,并假设油气界面呈平直线移动,求解气井和油井单独定流量生产时的油气界面移动;将计算模型进行实例计算.结果表明:随着地层压力的降低,油气界面上气相势的下降要比油相势大很多;油井单独生产时,油气界面偏向油井方向移动,而气井单独生产时,油气界面偏向气井方向移动;合理的控制采油采气速度,可以较好地保持油气界面的稳定.     

Simulating train movement in railway traffic using a car-following model

Based on a car-following model, in this paper, we propose a new traffic model for simulating train movement in railway traffic. In the proposed model, some realistic characteristics of train movement are considered, such as the distance headway and the safety stopping distance. Using the proposed traffic model, we analyse the space-time diagram of traffic flow, the trajectory of train movement, etc. Simulation results demonstrate that the proposed model can be successfully used for simulating the train movement. Some complex phenomena can be reproduced, such as the complex acceleration and deceleration of trains and the propagation of train delay.     

An Improved Walk Model for Train Movement on Railway Network

In this paper, we propose an improved walk model for simulating the train movement on railway network. In the proposed method, walkers represent trains. The improved walk model is a kind of the network-based simulation analysis model. Using some management rules for walker movement, walker can dynamically determine its departure and arrival times at stations. In order to test the proposed method, we simulate the train movement on a part of railway network. The numerical simulation and analytical results demonstrate that the improved model is an effective tool for simulating the train movement on railway network. Moreover, it can well capture the characteristic behaviors of train scheduling in railway traffic.     

Calibrating the X‐ray attenuation of liquid water and correcting sample movement artefacts during in operando synchrotron X‐ray radiographic imaging of polymer electrolyte membrane fuel cells

Synchrotron X‐ray radiography, due to its high temporal and spatial resolutions, provides a valuable means for understanding the in operando water transport behaviour in polymer electrolyte membrane fuel cells. The purpose of this study is to address the specific artefact of imaging sample movement, which poses a significant challenge to synchrotron‐based imaging for fuel cell diagnostics. Specifically, the impact of the micrometer‐scale movement of the sample was determined, and a correction methodology was developed. At a photon energy level of 20 keV, a maximum movement of 7.5 µm resulted in a false water thickness of 0.93 cm (9% higher than the maximum amount of water that the experimental apparatus could physically contain). This artefact was corrected by image translations based on the relationship between the false water thickness value and the distance moved by the sample. The implementation of this correction method led to a significant reduction in false water thickness (to ～0.04 cm). Furthermore, to account for inaccuracies in pixel intensities due to the scattering effect and higher harmonics, a calibration technique was introduced for the liquid water X‐ray attenuation coefficient, which was found to be 0.657 ± 0.023 cm^?1 at 20 keV. The work presented in this paper provides valuable tools for artefact compensation and accuracy improvements for dynamic synchrotron X‐ray imaging of fuel cells.     

Learning to Recognize Patterns: Changes in the Visual Field with Familiarity

Two studies were conducted to investigate changes which take place in the visual information processing of novel stimuli as they become familiar. Japanese writing characters (Hiragana and Kanji) which were unfamiliar to two native English speaking subjects were presented using a moving window technique to restrict their visual fields. Study time for visual recognition was recorded across repeated sessions, and with varying visual field restrictions. The critical visual field was defined as the size of the visual field beyond which further increases did not improve the speed of recognition performance. In the first study, when the Hiragana patterns were novel, subjects needed to see about half of the entire pattern simultaneously to maintain optimal performance. However, the critical visual field size decreased as familiarity with the patterns increased. These results were replicated in the second study with more complex Kanji characters. In addition, the critical field size decreased as pattern complexity decreased. We propose a three component model of pattern perception. In the first stage a representation of the stimulus must be constructed by the subject, and restricting of the visual field interferes dramatically with this component when stimuli are unfamiliar. With increased familiarity, subjects become able to reconstruct a previous representation from very small, unique segments of the pattern, analogous to the informativeness areas hypothesized by Loftus and Mackworth [J. Exp. Psychol., 4 (1978) 565].Inquiries or requests for reprints may be directed to any of the authors. Authors’ current addresses are: James M. Bebko, Department of Psychology, York University, 4700 Keele Street, North York, Ontario, Canada M3J 1P3; Keiji Uchikawa, Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226 Japan; Shinya Saida, Biosignaling Department, National Institute of Bioscience and Human-Technology, 1-1 Higashi, Tsukuba, Ibaraki 305 Japan; Mitsuo Ikeda, Department of Architecture, Kyoto University, Sakyo-ku, Kyoto 606 Japan.This research was conducted while the first author was supported by a Government of Japan Monbusho Research Fellowship at Tokyo Institute of Technology.     

Distortion of Visual Space During Pursuit Eye Movements

We measured perceived positions of flash stimuli arranged two-dimensionally in the peripheral visual field during pursuit eye movement to examine the influence of displacement of the eye position on localization in the peripheral visual field. The horizontal mislocalization of the flash stimulus during the horizontal pursuit eye movement was found toward the pursuit direction. The magnitude of this mislocalization was asymmetrical around the central visual field, and the asymmetry depended on the pursuit direction. As the eye position changed, the magnitude of the horizontal mislocalization gradually decreased. It was also observed that the vertical mislocalization of the flash stimulus was constant regardless of the eye position displacement. These results show that the visual space during the horizontal pursuit eye movement is expanded horizontally and then gradually returns to the normal state. It is suggested that the visual space is dynamically distorted during the pursuit eye movement.     

Multicriteria movement synchronization scheduling problems and algorithms

This article deals with multicriteria optimization models and algorithms of movement scheduling for many objects to synchronize their movement (2CMSS problem). The model consists of two parts: (1) node–disjoint path planning visiting specified nodes for K objects with a given vector of intermediate nodes for each one (NDSP problem); (2) movement synchronization in some intermediate nodes (MS problem). For synchronous movement, two categories of criteria are defined: time of movement and ‘distance’ of K-moved objects from the movement pattern. We defined the problem as a discrete-continuous, non-linear, two-criteria mathematical programming problem. We proposed to use a two-stage algorithm to solve the 2CMSS problem (as lexicographic solution): At first we have to find the vector of node–disjoint shortest paths for K objects visiting intermediate nodes to set optimal paths under the assumption that we use maximal possible velocities on each arc belonging to a path for each object (solution of the NDSP problem), and next we try to decrease the values of velocities to optimize the second criterion (synchronization, solution of the MS problem). Experimental analyses of effectiveness and complexity of the algorithms are presented.