Computer Simulations and Computational Models in Science

Author(s):  
Cyrille Imbert
Episteme ◽  
2009 ◽  
Vol 6 (2) ◽  
pp. 145-163 ◽  
Author(s):  
Alexander Riegler ◽  
Igor Douven

ABSTRACTIn recent years, various computational models have been developed for studying the dynamics of belief formation in a population of epistemically interacting agents that try to determine the numerical value of a given parameter. Whereas in those models, agents’ belief states consist of single numerical beliefs, the present paper describes a model that equips agents with richer belief states containing many beliefs that, moreover, are logically interconnected. Correspondingly, the truth the agents are after is a theory (a set of sentences of a given language) rather than a numerical value. The agents epistemically interact with each other and also receive evidence in varying degrees of informativeness about the truth. We use computer simulations to study how fast and accurately such populations as wholes are able to approach the truth under differing combinations of settings of the key parameters of the model, such as the degree of informativeness of the evidence and the weight the agents give to the evidence.


Author(s):  
Peter R. Monge ◽  
Noshir Contractor

Computer simulations have long been used as an effective tool in engineering, economics, psychology, and a number of other social sciences. Engineers typically use simulations to predict performance of a system that has known dynamic characteristics. These characteristics are typically obtained from theory and are then articulated in the simulation as difference or differential equations. The goal of engineering simulation is then to assess the dynamic performance of a system based on a priori knowledge of the dynamic relationships among the various elements of the system. Forrester (1961, 1973) was one of the earliest and most influential advocates of simulation modeling of dynamic social systems. Forrester advocated this approach as a way to model and assess the dynamics of industrial and world phenomena. Sterman (2000) provides a recent review of research on dynamics simulation from this tradition. While this approach has produced a considerable number of studies, it too is based on the assumption that the researcher has a priori knowledge of the dynamic relationships among elements of the system. Indeed, many of the results of these models have been criticized for specifying relationships that were at best untested and at worst flawed. In response to these criticisms, more recent interest has focused on redefining the utility of simulations in the social sciences. Rather than using simulations to test the long-term dynamics of systems with known interrelationships, theorists (Carley & Prietula, 1994; Contractor, 1994; Hanneman, 1988) have suggested that social scientists should use simulations to help construct theory, to identify the heretofore-unknown interrelationships. This section describes the traditional use of computer simulations as well as the adaptation of this approach toward theory construction and testing in the social sciences. Later sections will apply these general approaches to the computational modeling of networks in particular. Carley and Prietula (1994) suggest that the emergence of the new field of computational organizational theory (COT) signals the growing interest in the construction of computational models to augment and assist theory building. Most social science theories are richly evocative but highly abbreviated (Poole, 1997), that is, they offer explanations that suggest complex interrelationships but do not provide precise, falsifiable mathematical formalizations of the theory.


Author(s):  
Giuseppe Primiero

This chapter further investigates the constitutive elements of the experimental foundation of computing. It first introduces the different notions of models, then overviews the types of computer simulations from the literature, and finally explores the various purposes attached to their use as implementations of computational models.


2015 ◽  
Vol 732 ◽  
pp. 267-274
Author(s):  
Pavel Polach ◽  
Jaroslav Václavík

Fibres, cables and wires can play an important role in design of many machines. One of the most interesting applications is replacement of chosen rigid elements of a manipulator or a mechanism by fibres. Dynamic behaviour of fibres in simplified mechanical systems was investigated. In the first step the computational investigation of a fibre dynamic behaviour in the system of an inverted pendulum attached to two fibres and driven by them was performed. Then experiments and computer simulations with two simple laboratory mechanical systems followed. The first system consisted of a weight moving on an inclined plane and of one fibre, the second one contained a drive and a pulley in addition to it. The results of experimental measurements serve for tuning the computational models. The simulation aim is to create a phenomenological model of a fibre.


1999 ◽  
Vol 121 (03) ◽  
pp. 68-69
Author(s):  
Michelle Perkins

A model from Los Alamos studies the deformation of a hypothetical nuclear device when it collides with a steel plate. This shows that simulations play a key role in establishing the reliability of nuclear weapons. The scientists at Los Alamos, Sandia, and Lawrence Livermore labs are turning to huge computers and advanced visualization software to test virtual models. Visualizing and analyzing the data generated by the computational models overwhelm traditional scientific visualization methods. Scientists at Sandia National Laboratories are using computer simulations to test whether the Navy’s W76 nuclear warhead could still function amid blasts of X-rays on a nuclear battlefield. The simulations try to mathematically predict what real X-rays would do as they go through the W76's electronic circuits. Real world tests are run with weaker X-rays and the results are compared with the computer simulations. Data from old underground nuclear tests are also used to validate the computer tests.


Author(s):  
R. Gronsky

The phenomenon of clustering in Al-Ag alloys has been extensively studied since the early work of Guinierl, wherein the pre-precipitation state was characterized as an assembly of spherical, ordered, silver-rich G.P. zones. Subsequent x-ray and TEM investigations yielded results in general agreement with this model. However, serious discrepancies were later revealed by the detailed x-ray diffraction - based computer simulations of Gragg and Cohen, i.e., the silver-rich clusters were instead octahedral in shape and fully disordered, atleast below 170°C. The object of the present investigation is to examine directly the structural characteristics of G.P. zones in Al-Ag by high resolution transmission electron microscopy.


Author(s):  
R. Herrera ◽  
A. Gómez

Computer simulations of electron diffraction patterns and images are an essential step in the process of structure and/or defect elucidation. So far most programs are designed to deal specifically with crystals, requiring frequently the space group as imput parameter. In such programs the deviations from perfect periodicity are dealt with by means of “periodic continuation”.However, for many applications involving amorphous materials, quasiperiodic materials or simply crystals with defects (including finite shape effects) it is convenient to have an algorithm capable of handling non-periodicity. Our program “HeGo” is an implementation of the well known multislice equations in which no periodicity assumption is made whatsoever. The salient features of our implementation are: 1) We made Gaussian fits to the atomic scattering factors for electrons covering the whole periodic table and the ranges [0-2]Å−1 and [2-6]Å−1.


Author(s):  
Vladimir Yu. Kolosov ◽  
Anders R. Thölén

In this paper we give a short overview of two TEM applications utilizing the extinction bend contour technique (BC) giving the advantages and disadvantages; especially we consider two areas in which the BC technique remains unique. Special attention is given to an approach including computer simulations of TEM micrographs.BC patterns are often observed in TEM studies but are rarely exploited in a serious way. However, this type of diffraction contrast was one of the first to be used for analysis of imperfections in crystalline foils, but since then only some groups have utilized the BC technique. The most extensive studies were performed by Steeds, Eades and colleagues. They were the first to demonstrate the unique possibilities of the BC method and named it real space crystallography, which developed later into the somewhat similar but more powerful convergent beam method. Maybe, due to the difficulties in analysis, BCs have seldom been used in TEM, and then mainly to visualize different imperfections and transformations.


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