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Aplicação da técnica de tecelagem de modelos na transformação de modelos na MDA.; Application of model weaving in model transformation in MDA.

Mignon, Alexandre dos Santos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 03/04/2007 PT
Relevância na Pesquisa
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Uma das principais atividades dos enfoques de desenvolvimento de software centrados em modelos, como por exemplo a Arquitetura Dirigida por Modelo (Model Driven Architecture - MDA), é o processo de transformação de modelos. Geralmente, um passo preliminar para a transformação dos modelos é o mapeamento dos elementos do meta-modelo fonte nos elementos do meta-modelo alvo. Este trabalho apresenta uma aplicação de uma técnica de mapeamento de modelos denominada tecelagem de modelos. Esta técnica permite ao usuário definir a semântica das ligações estabelecidas entre os elementos do meta-modelo fonte e os elementos do meta-modelo alvo. A semântica é definida através de tipos fortes associados às ligações. O presente trabalho analisa, através de dois experimentos, alguns aspectos da geração de modelos de transformação de modelos no arcabouço MDA, utilizando a técnica de tecelagem de modelos. A análise utiliza duas alternativas de especificação de transformação de modelos a título de comparação: a que usa somente uma linguagem de especificação de modelos de transformação e a que usa a técnica de tecelagem de modelos. Os aspectos analisados são: a reutilização de trechos de código escritos na linguagem de geração de especificações de transformação e a reutilização de decisões de projeto (design) no mapeamento entre dois meta-modelos distintos.; One of the main activities of the model-centric approaches of software development...

Efeitos do modelo na aprendizagem do nado sincronizado; Effects of model in the motor learning process of synchronized swimming skills

Fugita, Meico
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/03/2010 PT
Relevância na Pesquisa
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O objetivo do presente estudo foi investigar os efeitos do tipo de modelo, boneca e humano, na aprendizagem das habilidades motoras do nado sincronizado, mais especificamente na figura tina (Experimento 1), bem como os efeitos da ordem da apresentação do modelo, boneca-humano ou humano-boneca na aprendizagem da mesma figura (Experimento 2). Participaram do Experimento 1, 20 sujeitos, partindo dos seguintes critérios de inclusão: voluntários do sexo feminino, com idade média de 23,1 anos (DP= 4,1), adaptados ao meio aquático, capazes de deslocar-se na parte rasa da piscina, de flutuar com auxílio das mãos, sem experiência anterior com qualquer das habilidades do nado sincronizado. A tarefa consistiu na execução da tina, que compreende a execução de uma sequência composta por 3 posições e 2 movimentos de transição: (1) Posição Inicial; (2) Transição para a tina; (3) Posição de Tina; (4) Transição para a posição final; e, (5) Posição Final. Os sujeitos foram distribuídos em dois grupos de 10 participantes cada, o grupo modelo boneca (GB) e o grupo modelo humano (GH). Após um pré-teste composto de seis tentativas consecutivas de execução da tina a partir de instrução verbal, todos executaram 60 tentativas a partir de demonstração e instrução verbal. As demonstrações tanto do modelo boneca como do modelo humano foram fornecidas a cada tentativa...

Extração e verificação de modelos para sistemas em evolução; Model checking and model extraction during software

Freire, Matheus de Mello
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Trabalho de Conclusão de Curso Formato: application/pdf
POR
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Softwares estão sempre em constante evolução e atualização. Durante o ciclo de vida de um sistema, muitas modificações ocorrem, em relação às funcionalidades definidas em sua primeira especificação. É desejável que durante todo o ciclo de vida do sistema, o mesmo execute corretamente as funções para as quais foi projetado, mesmo na ocorrência de modificações. Para isto, o uso de verificação de modelos e teste de software tem desempenhado uma importante função na busca por melhor qualidade de software. Este trabalho busca utilizar técnicas de teste de software, verificação e extração de modelos para obter modelos os quais representem os comportamentos corretos de sistemas mesmo após modificações. O objetivo do trabalho é estabelecer um processo de validação de sistemas em relação a propriedades estabelecidas o qual permita não apenas verificar se as propriedades são preservadas em um modelo do sistema, mas também se o comportamento da implementação gerada corresponde ao definido no modelo. Utilizando uma modelagem manual a partir de um modelo pré-existente, é definida uma única propriedade, onde os comportamentos esperados do sistema em questão são englobados por esta propriedade. Após a modificação do código...

The Business Model Canvas

Business Model Foundry
Fonte: Universidade Federal de Santa Catarina Publicador: Universidade Federal de Santa Catarina
Tipo: Outros
EN
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Painel do The Business Model generation; The Business Model Canvas

One-dimensional viscoelastic fluid model where viscosity and normal stress coeffients depend on the shear rate

Carapau, Fernando
Fonte: F. Carapau, "One-dimensional viscoelastic fluid model where viscosity and normal stress coeffients depend on the shear rate",Nonlinear Analysis:Real World Applications, Volume 11, Issue 5, pp. 4342-4354, 2010. Publicador: F. Carapau, "One-dimensional viscoelastic fluid model where viscosity and normal stress coeffients depend on the shear rate",Nonlinear Analysis:Real World Applications, Volume 11, Issue 5, pp. 4342-4354, 2010.
Tipo: Artigo de Revista Científica
POR
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Westudy the unsteady motion of a viscoelastic fluid modeled by a second-order fluid where normal stress coefficients and viscosity depend on the shear rate by using a power-law model. To study this problem, we use the one-dimensional nine-director Cosserat theory approach which reduces the exact three-dimensional equations to a system depending only on time and on a single spatial variable. Integrating the equation of conservation of linear momentum over the tube cross-section, with the velocity field approximated by the Cosserat theory, we obtain a one-dimensional system. The velocity field approximation satisfies both the incompressibility condition and the kinematic boundary condition exactly. From this one-dimensional system we obtain the relationship between average pressure and volume flow rate over a finite section of the tube with constant and variable radius. Also, we obtain the correspondent equation for the wall shear stress which enters directly in the formulation as a dependent variable. Attention is focused on some numerical simulation of unsteady/steady flows for average pressure, wall shear stress and on the analysis of perturbed flows.

Using Model-Data Fusion to Interpret Past Trends, and Quantify Uncertainties in Future Projections, of Terrestrial Ecosystem Carbon Cycling

Keenan, Trevor; Richardson, Andrew; Moffat, Antje; Munger, William; Davidson, Eric
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
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Uncertainties in model projections of carbon cycling in terrestrial ecosystems stem from inaccurate parameterization of incorporated processes (endogenous uncertainties) and processes or drivers that are not accounted for by the model (exogenous uncertainties). Here, we assess endogenous and exogenous uncertainties using a model-data fusion framework benchmarked with an artificial neural network (ANN). We used 18 years of eddy-covariance carbon flux data from the Harvard forest, where ecosystem carbon uptake has doubled over the measurement period, along with 15 ancillary ecological data sets relative to the carbon cycle. We test the ability of combinations of diverse data to constrain projections of a process-based carbon cycle model, both against the measured decadal trend and under future long-term climate change. The use of high-frequency eddy-covariance data alone is shown to be insufficient to constrain model projections at the annual or longer time step. Future projections of carbon cycling under climate change in particular are shown to be highly dependent on the data used to constrain the model. Endogenous uncertainties in long-term model projections of future carbon stocks and fluxes were greatly reduced by the use of aggregated flux budgets in conjunction with ancillary data sets. The data-informed model...

Coordinating Agile Systems through the Model-based Execution of Temporal Plans

Leaute, Thomas
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 155 p.; 41524644 bytes; 17696521 bytes; application/postscript; application/pdf
EN_US
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Agile autonomous systems are emerging, such as unmanned aerial vehicles (UAVs), that must robustly perform tightly coordinated time-critical missions; for example, military surveillance or search-and-rescue scenarios. In the space domain, execution of temporally flexible plans has provided an enabler for achieving the desired coordination and robustness, in the context of space probes and planetary rovers, modeled as discrete systems. We address the challenge of extending plan execution to systems with continuous dynamics, such as air vehicles and robot manipulators, and that are controlled indirectly through the setting of continuous state variables.Systems with continuous dynamics are more challenging than discrete systems, because they require continuous, low-level control, and cannot be controlled by issuing simple sequences of discrete commands. Hence, manually controlling these systems (or plants) at a low level can become very costly, in terms of the number of human operators necessary to operate the plant. For example, in the case of a fleet of UAVs performing a search-and-rescue scenario, the traditional approach to controlling the UAVs involves providing series of close waypoints for each aircraft, which incurs a high workload for the human operators...

Multi-Model Parallel Programming

Marsh, Brian D. ; LeBlanc, Thomas J.
Fonte: University of Rochester. Computer Science Department. Publicador: University of Rochester. Computer Science Department.
Tipo: Thesis; Technical Report
ENG
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Thesis (Ph. D.)--University of Rochester. Dept. of Computer Science, 1992. Simultaneously published in the Technical Report series.; Multi-model parallel programming is the simultaneous use of different programming models, either within a single program or in separate programs. A variety of programming models is best implemented in runtime libraries, yet current operating systems are not designed to support user-level implementations of processes and communication. Even if an efficient implementation of a programming model can be constructed in user space, interaction with other programming models is complicated by the lack of a common communication mechanism. The thesis of this dissertation is that in order to support multi-model parallel programming, an operating system must provide first-class user-level processes and model-independent communication. First-class user-level processes support the construction of multiple models by allowing flexibility and efficiency of user-level implementations to be combined with the control over resource allocation traditionally enjoyed only by kernel-level implementations. Model-independent communication supports the integration of multiple models into a single application by eliminating model dependencies from the data transfer and concurrency control mechanisms used for communication. Together...

Melhoria de processos de tecnologia da informação multi-modelo; Multi-model information techonology process im-provement

MENDES, Fabiana Freitas
Fonte: Universidade Federal de Goiás; BR; UFG; Mestrado em Ciência da Computação; Ciências Exatas e da Terra - Ciências da Computação Publicador: Universidade Federal de Goiás; BR; UFG; Mestrado em Ciência da Computação; Ciências Exatas e da Terra - Ciências da Computação
Tipo: Dissertação Formato: application/pdf
POR
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To use just one quality model in a Information Technology Process Improvement (ITPI) iniciative means just one: language, thought about how to fit organization needs, and way to conduct improvements and appraisals. Despite, to use just one model also means it could exist other ways to deal with ITIPI needs, but this is not going to be considered. To use more than one model, hence, means to model a best solution. Mono-Model ITPI initiatives have similar nature if compared with multi-model initiatives. However, there are multi-model specific challenges like: integration of improvement initiatives, of appraisals, and of quality model. Despite of being possible to model better solutions through multi model ITPI, there are little works about it. This research review works related to this subject, presents challenges multi-model list, and comes up with an approach to deal with these challenges. This approach has the advantage to be independent of the conduct method of improvement, quality model or project improvement phase.; Utilizar um único modelo de qualidade em uma iniciativa de Melhoria de Processos de TI (MPTI) em uma organização significa também única: linguagem, maneira de pensar sobre como atender as necessidades de MPTI, e maneira de conduzir as melhorias e as avaliações. Apesar disso...

The development and assessment of the semantic fields model of visual salience.

Stone, Benjamin
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2010
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The present thesis describes the development and assessment of the Semantic Fields Model of visual salience. The Semantic Fields model provides estimates of visual salience in relation to goal-oriented Web site search tasks. The development and assessment of this model is reported over seven studies that are presented in two journal articles and two peer-reviewed conference papers. In Paper 1 (N=50), pupil dilation is validated as a measure of cognitive load for use in later studies. While it has been found previously that a participant’s pupil dilation will be larger during more complex tasks, these experiments have not generally been conducted under the environmental condition of light radiated from a computer monitor. The findings of this experiment indicate that computer monitor radiance in our experimental setting did not interfere with the ability to discriminate successfully between task-related pupil dilation. Paper 2 (N=49) introduces the Semantic Fields model for estimating the visual salience of different areas displayed on a Web page. Latent Semantic Analysis and the Touchstone Applied Science Associates (TASA) corpus were used to calculate Semantic Field values for any (x, y) coordinate point on a Web page based on the structure of that Web page. These Semantic Field values were then used to estimate eye-tracking data that was collected from participants’ goal-oriented search tasks on a total of 1842 Web pages. Semantic Field values were found to predict the participants’ eye-tracking data. In Paper 3 (N=100)...

A prognostic model for priority public dental care.

Jones, Kelly
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2013
Relevância na Pesquisa
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Excess demand over the service capacity of public dental services has resulted in ad hoc rationing of access to services. As a result a significant proportion of public dental service patients receive only same-day or priority dental care. However, many such appointments are of low urgency, an outcome which is facilitated by lack of a standardised method to determine access for those seeking priority dental care. Aim: This thesis aimed to develop, validate and trial the implementation of a prognostic model for urgent dental care. Methods: This was a multi-phased research study. The first phase, the Parent study, collected psychosocial data on people seeking emergency dental care in SA and NSW and dentists‟ assessment of urgency. Two sequential prognostic models for urgency of dental care were developed as preliminary research. As further development of the models was to occur only in SA, the sequential prognostic models were examined separately in SA and NSW. The next phase involved testing the validity of the models on patients accessing urgent dental care at two new SA sites over an eight month period in 2004. This led to the development of a single model, the Composite model, and testing of its accuracy. The Composite model was then tested in a 28-week intervention trial in four SA Dental Service clinics in 2006. Both quantitative outcomes and qualitative outcomes were assessed. Results: The Parent study included 839 people seeking urgent dental care. Two sequential logistic regression models were developed to predict dentists assessed urgency of < 48 hours vs 2+ days...

Staatszerfall in Kolumbien und Angola? Über die Erklärung und Prognostizierbarkeit von Staatszerfall anhand des Global Model; State failure in Colombia and Angola? Explaining and forecasting state failure by means of the Global Model

Warweg, Florian
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Masterarbeit
DE_DE
Relevância na Pesquisa
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Das bis heute umfangreichste Projekt, Staatszerfall wissenschaftlich aufzuarbeiten, stellt das im Frühjahr 1994 durch den damalige Vizepräsidenten der Vereinigten Staaten von Amerika, Al Gore, zusammen mit der Central Intelligence Agency (CIA) initiierte State Failure Project (SFP) dar. Kernstück der Forschungsbemühungen war die Entwicklung eines quanitativen Frühwarnsystems für Staatszerfall, des sogenannten Global Forecasting Model of Political Instability, kurz Global Model (GM). Basierend auf der im Mai 2006 erstmals erfolgten Veröffentlichung eines Großteils der Daten und Ergebnisse des Projekts, unternimmt die vorliegende Arbeit eine kritische Analyse des GM. Zunächst wird, nach einer Einführung in die State Failure Debatte sowie die Frühwarnforschung, das GM auf methodologische, theoretische und analytische Schwächen im Bereich der Makroebene des Modells untersucht. Dies beinhaltet eine detaillierte Exploration der vorgenommenen Definitionen, der Datenauswahl sowie Modellbildung mit Fokus auf der abhängigen Variable. In einem zweiten Schritt werden die durch das GM selektionierten fünf unabhängigen Schlüsselvariablen auf ihre Konsistenz mit anderen Forschungsergebnissen, ihre statistische Signifikanz und ihre Verortung im kausalen Gefüge geprüft. Im Anschluss daran erfolgt eine Evaluierung der gezogenen kausalen Schlüsse sowie der generellen Vorhersage- und Erklärungsperformanz des Modells. Um das Vorhersage- und Erklärungspotenzial des Modells im konkreten Einzelfall zu testen...

Über die Anwendung und Modifikation des Hillschen Muskelmodells in der Biomechanik; The application and modification of a Hill-type muscle model in biomechanics

Schmitt, Syn
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
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Die vorliegende Arbeit “Über die Anwendung und Modifikation des Hillschen Muskelmodells in der Biomechanik” beschäftigt sich zunächst mit der Anwendung des Hillschen Muskelmodells bei Computersimulationen eines Mehrkörper - Muskel - Skelett - Systems (MKS). Konkret wird beispielhaft gezeigt, welche Arbeitsschritte notwendig sind, um eine Simulation eines menschlichen Sprungs aus der Hocke getrieben durch Muskelkräfte Hillscher Muskeln zu simulieren und welche zusätzlichen Fragen die Computersimulation hierbei beantworten kann. Anschließend werden die vorgestellten Arbeitsschritte angewandt, um ein valideres Computermodell des Hillschen Muskels zu erstellen, das ein bekanntes Defizit (Auftreten hochfrequenter Schwingungen) beseitigt. Dabei müssen Modifikationen am Standardmuskelmodell (Hill, 1938; van Soest und Bobbert, 1993) vorgenommen werden, um im Vergleich mit dem Experiment am isolierten Muskel konsistente Ergebnisse zu erzielen. In dieser Arbeit wird der vorwärts-dynamische Ansatz zur Computersimulation gewählt. Im ersten Teil der vorliegenden Arbeit wurde ein Hillsches Standardmuskelmodell zur Simulation eines menschlichen Sprungs aus der Hocke angewendet. Die Grundlage der Simulation war das MKS-Modell von Günther und Ruder (2003). Ziel der Untersuchung war es...

Erstellung eines komplexen Muskel-Skelett-Modells zur Berechnung der Druckbelastung in Gelenken bei vorwärtsdynamisch simulierten Bewegungsformen; Creation of a complex muscle skeleton model for calculation of the pressure distribution in joints unter forward dynamic generated motion patterns

Prochel, Anton
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
35.738567%
In der vorliegenden Arbeit wurde ein dreidimensionales Computermodell erstellt, mit welchem die Berechnung der Druckverteilung auf den menschlichen Hüftgelenkflächen unter synthetisch generierter Bewegung mittels realitätsnah modellierter Muskel möglich ist. Damit wurde die Druckverteilung für den geregelten Zweibeinstandes berechnet. Da dafür kein geeignetes Modell existierte, lag die Hauptaufgabe in der Erstellung eines komplexen, biomechanischen Menschmodells (Anthropion), das die geforderten Funktionalitäten umfasste. In der Vergangenheit wurden zwar viele biomechanische Modelle entwickelt, diese konzentrieren sich aber meistens auf die Beschreibung eines eng umrissenen Aspekts des biomechanischen Gesamtsystems und sind komplett unabhängig voneinander. Allgemeinere Modelle, die einen weiteren Bereich des biomechanischen Gesamtsystems abdecken, existieren kaum bzw. waren zur Bearbeitung der vorliegenden Fragestellung nicht geeignet. Daher erfolgte im Zuge dieser Arbeit die Integration mehrerer dieser speziellen Modelle zu dem komplexen, biomechanischen Muskel-Skelett-Menschmodell Anthropion mit Bewegungskontrolle und realitätsnah arbeitenden Muskeln. Die Basis dieses als Computersimulation realisierten Modells ist ein dreidimensionales Mehr-Körper-System-Modell des Menschen mit Segmenten...

Smoothing Functional Data with a Bayesian Hierarchical Model and Robust Fitting of a Weibull Model with Optional Censoring

Yang, Jingjing
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
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In this dissertation, I investigated two independent problems: smoothing functional data with a hierarchical Bayesian model, and robust fitting of a Weibull model for lifetime data with optional right-hand censoring. In the first project, a Bayesian hierarchical model is developed for smoothing functional data. Functional data, with basic data unit being function evaluations (e.g. curves or surfaces) over a continuum, have been frequently encountered in nowadays. While many functional data analysis tools are now available, the issue of simultaneous smoothing is less emphasized. Some methods treat functional data as fully observed while ignoring the measurement noise, others perform smoothing to each functional observation independently thus fail to borrow strength across replications from the same stochastic process. In the first part of this dissertation, a Bayesian hierarchical model is proposed to smooth all functional observations simultaneously. The proposed method relies on priors with data-driven hierarchical parameters, which automatically determine the amount of smoothness. It also provides simultaneous estimates for the mean function and covariance. Case studies of simulated and real data demonstrate that this Bayesian method produces more accurate signal estimates and smooth covariance estimate. In the second project...

Variability and evolution in model-based engineering of embedded systems

Botterweck, Goetz; Polzer, Andreas; Kowalewski, Stefan
Fonte: MBEES 2010 - Model-Based Development of Embedded Systems 2010 Publicador: MBEES 2010 - Model-Based Development of Embedded Systems 2010
Tipo: Conference item; all_ul_research; ul_published_reviewed; none
ENG
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peer-reviewed; In this paper, we report on techniques for variability and evolution in Model-based Engineering of Embedded Systems. The techniques are based on an integration of domain-specific languages for embedded systems with model-driven techniques for Software Product Lines. In particular, we discuss (1) product configuration with interactive tools, (2) product derivation with model transformations, and (3) first steps towards feature-oriented evolution planning.

Data driven model selection and parameter estimation using semi-automatic approximate Bayesian computation to reconstruct population dynamics from ancient DNA.

Rohrlach, Adam Benjamin
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2014
Relevância na Pesquisa
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Population genetics is a discipline within the biological sciences that is concerned with the change in frequency of types of individuals in a population due to natural selection, mutation, genetic drift and gene flow. Genetic drift is the part of this process explained by random sampling. Important to the process of genetic drift is population structure and so we focus on the recovery of population sizes over time, given a set of DNA sequences. With recent advances in computational power and a growth in the amount of data available, increasingly powerful techniques are being developed for the study of sequence data. Key advances in the early 1980's centred around `the coalescent', a continuous time approximation to the Wright-Fisher model of reproduction, and these advances resulted in Skyline Plot methods for recovering population size estimates over time. Skyline Plots suffer from large variances for the `coalescent' event times, and sources of error common to DNA sequence sampling schemes. Approximate Bayesian Computation (ABC) is a class of likelihood-free methods for statistical inference. ABC techniques can trace their genesis back to the biological sciences due to the complexity of the models for reproduction (and hence the intractability of likelihood calculations). Unfortunately...

A Mutation Analysis Based Model Clone Detector Evaluation Framework

Stephan, MATTHEW
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
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Model-Driven Engineering is becoming increasingly prevalent and mature. As software projects developed through this methodology age, the need for analysis of Model-Driven projects becomes imperative. One form of analysis is Model Clone Detection, which involves finding similar or identical model fragments in a given context. There are a number of techniques intended for Model Clone Detection and for different types of models. One hindrance to the growth of this field is the ability to objectively and quantitatively compare different model clone detectors and settings of the same detector. In this thesis, our original contribution to knowledge includes a framework utilizing Mutation Analysis to evaluate and compare model clone detectors. It is our proposition that, through distinguishing edit operations on models as mutations, we can create such a framework. In order to demonstrate the plausibility of our framework, we develop a Simulink implementation of the framework. We begin by outlining our initial, qualitative, attempts evaluating our Simulink model clone detector. This includes challenges encountered that are addressed by our framework. We outline the framework and describe each step in its process in an example-driven manner through creation of a framework prototype that works on Simulink model clone detectors. We choose Simulink because it is the most mature form of Model Clone Detection...

The estimation and use of predictions for the assessment of model performance using large samples with multiply imputed data

Wood, Angela M.; Royston, Patrick; White, Ian R.
Fonte: Wiley Publicador: Wiley
Tipo: Article; published version
EN
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This is the final version. It was first published by Wiley at http://onlinelibrary.wiley.com/doi/10.1002/bimj.201400004/abstract;jsessionid=144424FA52D50041821329D8A7741BFD.f02t01; Multiple imputation can be used as a tool in the process of constructing prediction models in medical and epidemiological studies with missing covariate values. Such models can be used to make predictions for model performance assessment, but the task is made more complicated by the multiple imputation structure. We summarise various predictions constructed from covariates, including multiply imputed covariates, and either the set of imputation-specific prediction model coefficients or the pooled prediction model coefficients. We further describe approaches for using the predictions to assess model performance. We distinguish between ideal model performance and pragmatic model performance, where the former refers to the model?s performance in an ideal clinical setting where all individuals have fully observed predictors and the latter refers to the model?s performance in a real-world clinical setting where some individuals have missing predictors. The approaches are compared through an extensive simulation study based on the UK700 trial. We determine that measures of ideal model performance can be estimated within imputed datasets...

Uncertainty in the Bifurcation Diagram of a Model of Heart Rhythm Dynamics

Ring, Caroline
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2014
Relevância na Pesquisa
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To understand the underlying mechanisms of cardiac arrhythmias, computational models are used to study heart rhythm dynamics. The parameters of these models carry inherent uncertainty. Therefore, to interpret the results of these models, uncertainty quantification (UQ) and sensitivity analysis (SA) are important. Polynomial chaos (PC) is a computationally efficient method for UQ and SA in which a model output Y, dependent on some independent uncertain parameters represented by a random vector ξ, is approximated as a spectral expansion in multidimensional orthogonal polynomials in ξ. The expansion can then be used to characterize the uncertainty in Y.

PC methods were applied to UQ and SA of the dynamics of a two-dimensional return-map model of cardiac action potential duration (APD) restitution in a paced single cell. Uncertainty was considered in four parameters of the model: three time constants and the pacing stimulus strength. The basic cycle length (BCL) (the period between stimuli) was treated as the control parameter. Model dynamics was characterized with bifurcation analysis, which determines the APD and stability of fixed points of the model at a range of BCLs, and the BCLs at which bifurcations occur. These quantities can be plotted in a bifurcation diagram...