An Atom is Known by the Company it Keeps: A Constructionist Learning Environment for Materials Science Using Agent-Based Modeling

This article reports on “MaterialSim”, an undergraduate-level computational materials science set of constructionist activities which we have developed and tested in classrooms. We investigate: (a) the cognition of students engaging in scientific inquiry through interacting with simulations; (b) the effects of students programming simulations as opposed to only interacting with ready-made simulations; (c) the characteristics, advantages, and trajectories of scientific content knowledge that is articulated in epistemic forms and representational infrastructures unique to computational materials science, and (d) the principles which govern the design of computational agent-based learning environments in general and for materials science in particular. Data sources for the evaluation of these studies include classroom observations, interviews with students, videotaped sessions of model-building, questionnaires, and analysis of artifacts. Results suggest that by becoming ‘model builders,’ students develop deeper understanding of core concepts in materials science, and learn how to better identify unifying principles and behaviors within the content matter.     

From Global to National Comprehensive Models: A Developing Country Perspective on Global Modelling in Transition

Journal of the Operational Research Society - This paper examines experience with two decades of global model-building efforts, focusing on their impact and on methodological issues. Adopting a...     

Field theoretical Lie symmetry analysis: The Möbius group,exact solutions of conformal autonomous systems,and predictive model-building

We study single and coupled first-order differential equations (ODEs) that admit symmetries with tangent vector fields, which satisfy the N-dimensional Cauchy–Riemann equations. In the two-dimensional case, classes of first-order ODEs which are invariant under Möbius transformations are explored. In the N dimensional case we outline a symmetry analysis method for constructing exact solutions for conformal autonomous systems. A very important aspect of this work is that we propose to extend the traditional technical usage of Lie groups to one that could provide testable predictions and guidelines for model-building and model-validation. The Lie symmetries in this paper are constrained and classified by field theoretical considerations and their phenomenological implications. Our results indicate that conformal transformations are appropriate for elucidating a variety of linear and nonlinear systems which could be used for, or inspire, future applications. The presentation is pragmatic and it is addressed to a wide audience.     

Valuation of sinking-fund bonds in the Vasicek and CIR frameworks∗Financial support from Murst Fondo 40% on ‘Modelli di struttura a termine dei tassi d'interesse’ is gratefully acknowledged.

In a sinking-fund bond, the issuer is required to retire portions of the bond prior to maturity, with the option of doing so either by calling the bonds by lottery, or by buying them back at their market value. This paper discusses the valuation of a default-free sinking-fund bond issue in the Vasicek (1977) and, alternatively, the Cox, Ingersoll and Ross (CIR) (1985) frameworks. We show in particular that, calling the bond issue without the delivery option ‘corresponding serial’, and the one without the prepayment feature ‘corresponding coupon’, under no-arbitrage a sinking-fund bond can be priced either in terms of the corresponding coupon bond and a bond call option, or in terms of the corresponding serial and a bond put option. We also present a detailed comparative-statics analysis of our valuation model, where we show that a sinking-fund bond has a stochastic duration intermediate between the ones of the corresponding serial and coupon bonds. We argue that such a feature gives a further rational for the presence of the delivery option. Moreover, we compare our results with the ones of Ho (1985), who has previously discussed the valuation problem under scrutiny.     

Parsimonious modelling and forecasting of seasonal time series

Some seasonal time series models are considered which are appropriate for the univariate modelling and forecasting of many time series. The equivalent ARIMA forms of these models provide the basis for a critical examination of the Box-Jenkins approach to seasonal model-building. It is concluded that this approach is unsatisfactory and in particular can often result in over-differencing and the adoption of an inappropriate model. Two main reasons for this are discussed: (a) the inadequate class of models considered which rests on a restricted view of parsimony, and (b) the shortcomings of the basic approach to model identification.     

从双层规划的角度看道德风险理论的一阶条件方法

本文首先对双层规划的一个特殊例子即道德风险模型中使用的一阶条件方法（FOA）做简要的梳理，然后提出一种更为一般的使FOA有效的原则与方法。新方法主要依赖于代理人对委托人设置的目标的最优反应映射是否存在不动点，这个性质不要求原问题与用一阶条件放松以后的问题之间的约束集等价，从而也不要求代理人的期望效用对行动具有全局凹性。在新方法下，可以用较为简单的方法证明FOA在以下两种情形之一有效，即如果分布函数是概率分布的凸组合或者分布函数来自某些特殊的指数族分布。     

A Note on Multi-Issue Bargaining with a Finite Set of Alternatives

We extend the results of van Damme et al. (1990) and Muthoo (1991) to two bilateral multi-issue bargaining)procedures with complete information and endogenous agenda, where each issue is associated with a finite set of alternatives. We show that in the first procedure (issue-by-issue bargaining), the stationary subgame perfect equilibria alone may support a large multiplicity of inefficient agreements. Confronting a recent study, the results for the second procedure imply that it is not necessary to appeal to “strictly controversial” issues in a bargaining problem in order to find multiplicity and delay in agreements     

可计算一般均衡求解中多要素CES函数的线性化表达

CES函数的线性化是可计算一般均衡求解过程中不可绕开的问题.在Gohin和Hertel(2003)给出的两要素(n=2)CES函数线性化的基础上,基于成本最小化的一阶条件,推导了两个及两个以上要素(n≥2)情况下CGE函数的线性化过程,进而在替代弹性趋近于1和0的条件下,分别得到了多要素CD函数和Leontief函数的线性化表达.所得到的表达方式更为简洁和一般化,能够提高CGE建模效率.     

Mechanics of complex bodies: comments on the unified modeling of active substructures

Basic issues of the general model-building framework of the mechanics of complex bodies are discussed. Attention is focused on the representation of the material elements, the conditions for the existence of ground states of elastic complex bodies and their consequences on the interpretation of the nature of the various balance laws occurring. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Micro-simulation of Markets

This paper attempts to give an integrated presentation of the application of micro-simulation to the study of markets, based on the purchase behaviour of individual consumers. We emphasize the methodological considerations which should govern the use of the approach, and in particular the need for evolutionary model-building; the technical problems which are only rarely specified in the literature; and the need to be eclectic in the selection of sub-model formulations. Case-studies are reported, and information is given on the scale of resources required for such projects. The presentation is backed with full references to relevant published work, to provide a practical aid to workers in the field. Much of the discussion is also relevant to the simulation of social systems other than markets.     

The graph limit of the minimizer of the Onsager-Machlup functional and its computation

The Onsager-Machlup(OM) functional is well known for characterizing the most probable transition path of a diffusion process with non-vanishing noise. However, it suffers from a notorious issue that the functional is unbounded below when the specified transition time T goes to infinity. This hinders the interpretation of the results obtained by minimizing the OM functional. We provide a new perspective on this issue. Under mild conditions, we show that although the infimum of the OM functional becomes unbounded when T goes to infinity, the sequence of minimizers does contain convergent subsequences on the space of curves. The graph limit of this minimizing subsequence is an extremal of the abbreviated action functional, which is related to the OM functional via the Maupertuis principle with an optimal energy. We further propose an energy-climbing geometric minimization algorithm(EGMA) which identifies the optimal energy and the graph limit of the transition path simultaneously. This algorithm is successfully applied to several typical examples in rare event studies. Some interesting comparisons with the Freidlin-Wentzell action functional are also made.     

Contract type and decision right of sales promotion in supply chain management with a capital constrained retailer

From the practices of Chinese consumer electronics market, we find there are two key issues in supply chain management: The first issue is the contract type of either wholesale price contracts or consignment contracts with revenue sharing, and the second issue is the decision right of sales promotion (such as advertising, on-site shopping assistance, rebates, and post-sales service) owned by either manufacturers or retailers. We model a supply chain with one manufacturer and one retailer who has limited capital and faces deterministic demand depending on retail price and sales promotion. The two issues interact with each other. We show that only the combination (called as chain business mode) of a consignment contract with the manufacturer’s right of sales promotion or a wholesale price contract with the retailer’s right of sales promotion is better for both members. Moreover, the latter chain business mode is realized only when the retailer has more power in the chain and has enough capital, otherwise the former one is realized. But which one is preferred by customers? We find that the former is preferred by customers who mainly enjoy low price, while the latter is preferred by those who enjoy high sales promotion level.     

Bank-office Process Management in the Financial Services: a Simulation Approach Using a Model Generator

For the last ten years or so, developments in simulation software and methodology have been focused in two areas: (1) automating the model-building process; and (2) interfacing with other techniques and systems. That both academic and commercial research continues to be carried out in these areas is evidence of the continued popularity of the simulation technique. The most popular application areas where simulation modelling is used include manufacturing (engineering and process), warehousing and communications; not surprisingly, research and developments have therefore been concentrated in these areas. This paper describes the development of a simulation model generator for a different application area, that of clerical office processing of paper and documents for financial service companies. It outlines the reasons why there is a need for such a model generator and discusses the initial design requirements. The paper goes on to detail the developments and re-defined criteria required as the model generator brief changes as a result of practical applications.     

A fraud-alert model for credit cards during the authorization process

^*Correspondence regarding this paper should be addressed to the first author In this paper, we set forth an expert-system model to help alertbanks and other financial institutions to fraudulent usage ofconsumer credit during the authorization process. The paperfirst addresses the model-building process, then briefly describesprototype development, and finally presents results from analysisof real data from a Canadian bank.     

Supporting mathematical literacy: examples from a cross-curricular project

Mathematical literacy implies the capacity to apply mathematical knowledge to various and context-related problems in a functional, flexible and practical way. Improving mathematical literacy requires a learning environment that stimulates students cognitively as well as allowing them to collect practical experiences through connections with the real world. In order to achieve this, students should be confronted with many different facets of reality. They should be given the opportunity to participate in carrying out experiments, to be exposed to verbal argumentative discussions and to be involved in model-building activities. This leads to the idea of integrating science into maths education. Two sequences of lessons were developed and tried out at the University of Education Schwäbisch Gmünd integrating scientific topics and methods into maths lessons at German secondary schools. The results show that the scientific activities and their connection with reality led to well-based discussions. The connection between the phenomenon and the model remained remarkably close during the entire series of lessons. At present the sequences of lessons are integrated in the European ScienceMath project, a joint project between universities and schools in Denmark, Finland, Slovenia and Germany (see www.sciencemath.ph-gmuend.de).     

Mathematical programming in human geography

A survey of mathematical programming in human geography is undertaken. To demonstrate its relevance in this field, particular attention focuses on model-building aspects rather than solution techniques per se. After a brief discussion of their underlying rationale, optimisation, a variety of aspects of mathematical programming such as linear programming, non-linear programming, duality, parametric and sensitivity analysis, and the temporal dimension, are considered.     

Robustness of perturbation analysis estimators for queueing systems with unknown distributions

Sample-path-based stochastic gradient estimators for performance measures of queueing systems rely on the assumption that a probability distribution of the random vector of interest (e.g., a service or interarrival time sequence) is given. In this paper, we address the issue of dealing with unknown probability distributions and investigate the robustness of such estimators with respect to possibly erroneous distribution choices. We show that infinitesimal perturbation analysis (IPA) can be robust in this sense and, in some cases, provides distribution-independent estimates. Comparisons with other gradient estimators are provided, including experimental results. We also show that finite perturbation analysis (FPA), though only providing gradient approximations, possesses some attractive robustness properties with respect to unknown distribution parameters. An application of FPA estimation is included for a queueing system performance optimization problem involving customers with real-time constraints.This work was supported in part by the National Science Foundation Grant ECS-88-01912 and by the Office of Naval Research Contract N00014-87-K-0304.The authors wish to thank Dr. Jack Holtzman for several useful comments and suggestions.     

证券交易印花税对证券市场资源配置影响实证研究

证券交易印花税对证券市场资源配置效率的影响一直是理论界争论的热点问题.综合证券市场资源配置的三个主要方面:流动性、波动性和有效性,通过印花税对这三方面影响的实证检验,来全面清晰的反应印花税在我国证券市场中所起到的作用.实证结果表明:征收证券交易印花税,对我国证券市场的流动性影响有限,但是会增加市场有效性;上调印花税率会增加证券市场的波动性,下调对波动性影响有限.     

Summability for Nonunital Spectral Triples

This paper examines the issue of summability for spectral triples for the class of nonunital algebras introduced in [23]. For the case of (p, )-summability, we prove that the Dixmier trace can be used to define a (semifinite) trace on the algebra of the spectral triple. We show this trace is well-behaved, and provide a criteria for measurability of an operator in terms of zeta functions. We also show that all our hypotheses are satisfied by spectral triples arising from geodesically complete Riemannian manifolds. In addition, we indicate how the Local Index Theorem of Connes-Moscovici extends to our nonunital setting.     

On when to stop sampling for the maximum

Suppose a sequential sample is taken from an unknown discrete probability distribution on an unknown range of integers, in an effort to sample its maximum. A crucial issue is an appropriate stopping rude determining when to terminate the sampling process. We approach this problem from a Bayesian perspective, and derive stopping rules that minimize loss functions which assign a loss to the sample size and to the deviation between the maximum in the sample and the true (unknown) maximum. We will show that our rules offer an extremely simple approximate solution to the well-known problem to terminate the Multistart method for continuous global optimization.