对“巴伦布朗特挟沙水流时均运动方程”的讨论

本文通过推导证明:认为巴伦布朗特的挟沙水流运动方程,采用了液体不均质性只影响重力项的假定后,使时间平均运动方程难于成立.本文同时给出了挟沙水流时间平均运动方程的准确形式.     

Optimization of the motion in a resistant medium of a body with a movable internal mass

The motion, in a resistant medium, of a system consisting of a rigid body and movable internal mass is considered. The external medium acts on the body by a force that piecewise linearly depends on its speed. The class of periodic motions of the internal mass for which the speed of this mass relative to the body is piecewise constant is studied. It is shown that, under certain conditions, the forward movement of the whole system in the medium is possible. The average speed of this movement over a period is determined. Optimal parameters of the motion of the internal mass for which the average speed of the system movement is maximal are found.     

An analysis of file movement under Dynamic File Management strategies

This paper addresses the data file movement inherent in Dynamic File Management (DFM) strategies. The goal of this data movement is to enhance the throughput of a computer system with a many level store by keeping the most active data near the top of the store. This paper does not address the criteria for file movement; rather the manner of file movement. The two DFM move primitivesT andP are defined functionally. This is followed by a careful analysis of the hole selection strategies employed to find valid destinations for the two DFM move primitives. Some additional DFM enhancements are clarified for better understanding of the DFM strategies. It is shown that the DFM move primitives are sufficient to implement a DFM. Simulation results verify the utility of DFM strategies.     

金融资产收益分布的混合高斯分析

本文研究了金融资产收益的混合高斯分布模型 ,给出了混合高斯分布的 Kolmogorov-Smirnov检验的方法 ,分析了金融资产收益的非高斯性及市场价格运动的有效性 .此外 ,用成分数目 K*、拟合误差 DK*n和主成分系数 p*k 描述金融资产收益的性质 ,对外汇银行同业拆借市场和中国股票市场实证分析     

Exploring affordances and limitations of between-group movement in elementary mathematics classrooms

In this exploratory study, we examine how between-group movement, as an autonomy-promoting practice, might incentivize or disincentivize sixth-grade students’ engagement in two mathematical practices: (1) making sense of problems and persevering in solving them; and (2) constructing viable arguments and critiquing the reasoning of others. Between-group movement refers to a pedagogical strategy wherein teachers allow groups to physically move within the classroom while problem-solving to discuss strategies, ask for help, or check their work with other groups. Exploring both the affordances and limitations of between-group movement, we found that between-group movement supported groups to construct viable justifications, among other sense-making mathematical practices. However, we also found that some groups over-scaffolded during between-group conversations which disincentivized meaningful engagement in mathematical practices. Furthermore, between-group movement revealed some equity concerns in relation to status-based privileges. The findings imply that between-group movement can be a constructive pedagogical practice under specific conditions.     

重物落水后运动过程的数学建模

分析了影响重物落水运动过程的主要因素,根据各因素权重关系及相关物理理论建立了多因素融合的大实心方砖落水过程模型,对重物在水中的运动分成部分浸入水中和重物完全浸入水体两个阶段.定性描述了两连接物体落水后耦合运动过程,并与实测数据进行拟合,根据对比的结果,实现了误差分析,根据误差原因优化模型以提高其准确度和适用性,并对未来的试验和研究工作提出了一些建议,以提高试验数据的质量.     

Valuation of European options in the market with daily price limit

A valuation problem of the European style contingent claim in the market with daily price movement limit is studied. Unlike the one leading to the well known Black-Scholes formula, this problem depicts considerable conceptual difficulty and anomaly created by the presence of various arbitrage opportunities inherently built in the model due to the daily price movement limit. The presence of arbitrage makes it go against the grain of the well established arbitrage pricing theory. In this paper, how these complications arise are discussed and then a valuation approach devised, which is called the ‘vanishing transaction cost technique,’ of getting around the difficulty.     

Competition of three species in an advective environment

Individuals in advective environments, for example rivers, coastlines, or the gut, are subject to movement with directional bias. We study how this movement bias shapes community composition by considering how the strength of movement bias affects the outcome of competition among three species. Our model is a system of three reaction-advection-diffusion equations with Danckwerts boundary conditions. Our key tool in this study is to use the dominant eigenvalue of the diffusion-advection operator in order to reduce the spatially explicit model to a spatially implicit ordinary differential equation model. After an in-depth analysis of the implicit model, we use numerical simulations of the explicit model to test the predictions obtained from the analysis. In general, we find a good qualitative agreement between the explicit and the implicit model. We find that varying the strength of advection can fundamentally alter the outcome of competition between the three species, and we characterize the possible transitions. In particular, water extraction and flow control can destabilize existing species communities or facilitate invasions of non-native species.     

位移和速度反馈的数学模型及实现方法

本文提出了位移和速度同时反馈的数学模型 .并给出了位移和速度反馈的实现方法 ,该方法用传统的差动变压器实现了位移和速度的同时反馈     

Time-delayed model of the unbiased movement of Tetrahymena Pyriformis

In our paper we investigate the unbiased movement of the unicellular eukaryotic ciliate Tetrahymena Pyriformis. We use a time-delayed version of the previously known model to describe the specific movement of this species. With the help of semi-discretization, we state analytic results for the model.     

Survey study and experimental investigation on the local behavior of pedestrian groups

Current research on pedestrian dynamics mainly focuses on the interactions among isolated individuals, the impact of the presence of groups is not fully considered. In recent 5 years, researchers have started to investigate pedestrian group movement. The aim of this work is to explore the local behavior of pedestrian groups by questionnaires and field observation. Survey study focused on pedestrians' psychology when walking in groups, which included five parts: group size, interpersonal distance, spatial relationship among group members, speed adjustment of group members, information transmission, and acid action among group members. Meantime a field observation was carried out to study group movement characteristics, which contained speed, step frequency, offset angle and interpersonal distance. The survey results show that group members have a closer interpersonal distance, faster information transmission and plenty of acid action. Conversely, group walking has a negative influence on pedestrian's speed, step frequency by comparing with the way isolated pedestrian walks. In addition, it is found that for a certain group, the group members are able to keep movement consistent. Also there exists obvious movement diversity among different group types (male dyads, female dyads, couple groups, and ordinary‐friend groups) because of different gender and social relationship. Ultimately the results will be more promising for helping to model the movement of pedestrian groups. © 2014 Wiley Periodicals, Inc. Complexity 20: 87–97, 2015     

Problem difficulty of real instances of convoy planning

Moving men and materials in large numbers and quantities is a long-standing military problem faced by all arms. An important part of this is the routing of convoys so that they reach their correct destinations in the shortest time. The optimization problem at the heart of this problem is referred to as the convoy movement problem. Previous work on the convoy movement problem has made the assumption that the problem is difficult in practice because of the NP-hardness of the problem in combination with the limited success of early approaches based on genetic algorithms. As a result subsequent work has focused on mathematical programming-based methods, principally Lagrangian relaxation. In this paper, we demonstrate that a straightforward reformulation of the problem renders the real-world like instances, used to benchmark previous approaches, amenable to solution by simple heuristics. The main lessons learnt from this work is that analysis of the problem in conjunction with simple algorithms can, in practice, yield surprisingly effective solutions.     

SIMULATIONS TO INVESTIGATE ANIMAL MOVEMENT EFFECTS ON POPULATION DYNAMICS

Abstract Movement of organisms will influence their ecology and demographics. Animal movements are often characterized by path structures with directional persistence. The extent to which this impacts on population dynamics is investigated in this paper using theoretical simulations. The effects of different movement strategies on variations in visits to individual patches across a forage area are discussed. Variations in resource biomass across patches are shown to persist after long simulations. Consumer resource equations with movement are used to show how heterogeneity in resources caused by these variations can affect global population dynamics. With directional movements (random or persistent), dynamics change from limit cycles to stable equilibrium solutions. It is suggested that this effect has the potential to increase survival because perturbations from unforeseen factors (like drought) are less likely to crash populations.     

A New Series: Blacks and Colleges: 1: The Dot and The Elephant

As recently as last year, I thought that “education”—the discipline—was too tiresome a subject to sustain my interest for more than a moment or two. I hastily abandoned this conviction after five minutes in front of a classroom. As a teacher, or as someone trying to teach, education became for me a living thing.

By happy, unplanned circumstance, my teaching and the research for this project began at the same time. The two assignments have dovetailed in a way that no amount of planning could have forecast.

This article is written from a black perspective—something which does not necessarily reside within a black skin. Retaining this perspective, particularly as a writer, requires among other things an agonizing bending of the mind. One is constantly obliged to see and weigh things including black education—from several points of view and finally to ask: “What does this or that event mean for black people at large—for ‘the movement’?“

The necessity for all of this is not readily understood by white people. The fact is that to be black in this country is to be part of “the movement.” Whether one is conscious of this fact or not, whether one rushes out to “join” something or not, matters little. One belongs whether one is male or female, unemployed, skilled in carpentry, or deep in clinical psychology. One “withdraws” from the movement only at great psychic cost. To be in it is painfully expensive as well, but this pain is offset by that particular joy that comes from embracing one's own people.     

Spatial Spread of Rabies in China

The reported data on human rabies in China in the past 10 years demonstrate that the number of counties with human rabies cases has increased dramatically and the disease has spread from southern provinces to northern provinces. The aim of this paper is to study how the movement of dogs impacts the spatial spread of rabies and to find effective strategies for controlling rabies. We firstly construct a reaction-diffusion model for dogs and humans and obtain the minimal wave speed. Then we consider the existence of traveling waves and the influences of parameters on human rabies cases and the minimal wave speed by numerical simulations. Lastly, we discuss the local stability of the endemic equilibrium. Our analysis indicates that dog movement leads to the traveling wave of dog and human rabies and has a large influence on the minimal wave speed. Thus restricting the movement of dogs, in particular the exposed and infected dogs, is an effective way to prevent the spatial spread of rabies.     

一个物理问题的建模及解答

对一个实际物理问题,构造相应的模型,得到描述其运动状态的常微分方程组.利用数学软件M ap le辅助,求解该方程组,从而准确刻画相应时刻物体的位置.     

城市地下水资源可持续开发利用模型研究

根据地下水可持续开发利用原则,运用系统分析方法建立了地下水可持续开发利用模型,首先,运用有限元分析法对地下水运动偏微分方程进行离散,导出了地下水运动的数值方程,使得地下水运动方程能够与系统分析方法相结合建立城市地下水可持续开发利用模型;然后,以地下水位下降最小为目标函数,以各井的出水能力及时段内的需水量作为约束条件,建立了城市地下水优化利用模型,为城市地下水资源可持续开发利用提供新的规划管理方法.     

Hard times and statistics

Hard times is a satire against mid-Victorian statisticians, those whom Dickens called ‘the representatives of the wickedest and most enormous vice of this time’. Historians of mathematics have seen the novel as a cruel parody of statistical determinism, a fatalistic movement which swept the continent in the 1860s and 1870s. But to see it as such is to credit Dickens with a better understanding of contemporary mathematics than he in fact possessed. The statistics in Hard times are not the probabilistic theories of continental academics. They are the mundane facts and figures of the much more prosaic English statistical movement.