1,720,955 research outputs found
The development of a hybrid simulation modelling approach based on agents and discrete-event modelling
No full textThis thesis initially presents the work carried out on the research hypothesis –agent-based simulation is better than traditional discrete-event modelling. To test this assertion, a comparison of these two modelling approaches is made by way of a case study. The scenario, a global repair operation of a fleet of civil jet engines, is a real lifecycle costing example which involves logistics and is typical of problems commonly modelled using either of these paradigms.To carry out the comparison, the method involved building a discrete-event model which matched the functions of an existing agent-based model as closely as
possible. Rigorous control was applied during its implementation phase by way of formal code walkthroughs and model dynamic testing. Among the internal metrics, lines of code provided an estimate for model size while the McCabe Cyclomatic
Number measured structural complexity. The external software quality of maintainability was derived from these metrics and estimated by modelling experts through Delphi sessions. The dynamic performance of each model was determined
by the execution times of successfully completed simulation runs over a range of engine fleet sizes.This research went on to develop a hybrid approach (which is currently the subject of a Rolls-Royce patent application) which draws on the strengths of both agent and discrete-event paradigms. In order to combine agent roles and discrete event processes, a new model was implemented using a three-layered architecture. A full fleet simulation was developed using this hybrid approach. Although the code size is slightly larger and run times slightly longer than the conventional model, the thesis argues that, crucially, it is more maintainable as it reduces the conceptual gap between problem and model
Characterising the convergence of a stochastic simulation model using the bootstrap method
No full textAccepting that all models are wrong, whilst some are useful (G.E.P. Box), this paper will describe how the bootstrap technique has been applied to forecasting for Rolls-Royce, in order to develop a more robust decision support framework that can deliver on the promise of being more useful.Practically speaking, the computational cost of large simulation studies may seem prohibitive, but large enough samples are often required to ensure both the accuracy and precision necessary for unambiguous experimentation. In order to appropriately prioritise opportunities, it is crucially important that an analyst can distinguish the sample differences that are due to experimental changes, rather than imprecise estimates.To illustrate this issue, the bootstrap method has been applied to a complex model of engine maintenance operations to show a clear relationship between sample size, computational power, and precision. As example, all metric means in this case study were shown to have reached an acceptable level of precision within 1024 runs, or one hour of computation time, however, one hour per trial is considered impractically slow with respect to an experimental study requiring upwards of 350 trials. In showing that 25 of 198 tracked metric values require more than 1024 iterations to achieve acceptable levels of precision, this paper illustrates the need to trade off computation time against computation power, thus enabling the sorts of experimentation that usefully prioritise the exploitation of profitable opportunities
Approaches to modeling the gas-turbine maintenance process
Full text linkDiscrete-event modeling has long been used for logistics and scheduling problems, while multi--agent modelling closely matches human decision-making process. In this paper a metric-based comparison between the traditional discrete-event and the emerging agent-based modeling approaches is reported. The case study involved the implementation of two functionally identical models based on a realistic, non-trivial, civil aircraft gas turbine global repair operation. The size, structural complexity, and coupling metrics from the two models were used to gauge the benefits and drawbacks of each modeling paradigm. The agent-based model was significantly better than the discrete-event model in terms of execution times, scalability, understandability, modifiability, and structural flexibility. In contrast, and importantly in an engineering context, the discrete-event model guaranteed predictable and repeatable results and was comparatively easy to test because of its single-threaded operation. However, neither modeling approach on its own possesses all these characteristics nor can each handle the wide range of resolutions and scales frequently encountered in problems exemplified by the case study scenario. It is recognized that agent-based modeling can emulate high-level human decision-making and communication closely while discrete-event modeling provides a good fit for low-level sequential processes such as those found in manufacturing and logistics
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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