1,720,968 research outputs found
Quantitative analysis of dynamic safety-critical systems using temporal fault trees
Get PDFEmerging technological systems present complexities that pose new risks and hazards. Some of these systems, called safety-critical systems, can have very disastrous effects on human life and the environment if they fail. For this reason, such systems may feature multiple modes of operation, which may make use of redundant components, parallel architectures, and the ability to fall back to a degraded state of operation without failing completely. However, the introduction of such features poses new challenges for systems analysts, who need to understand how such systems behave and estimate how reliable and safe they really are.Fault Trees Analysis (FTA) is a technique widely accepted and employed for analysing the reliability of safety-critical systems. With FTA, analysts can perform both qualitative and quantitative analyses on safety-critical systems. Unfortunately, traditional FTA is unable to efficiently capture some of the dynamic features of modern systems. This problem is not new; various efforts have been made to develop techniques to solve it. Pandora is one such technique to enhance FTA. It uses new 'temporal' logic gates, in addition to some existing ones, to model dynamic sequences of events and eventually produce combinations of basic events necessary and sufficient to cause a system failure. Until now, Pandora was not able to quantitatively evaluate the probability of a system failure. This is the motivation for this thesis.This thesis proposes and evaluates various techniques for the probabilistic evaluation of the temporal gates in Pandora, enabling quantitative temporal fault tree analysis. It also introduces a new logical gate called the 'parameterised Simultaneous-AND' (pSAND) gate. The proposed techniques include both analytical and simulation-based approaches. The analytical solution supports only component failures with exponential distribution whilst the simulation approach is not restricted to any specific component failure distribution. Other techniques for evaluating higher order component combinations, which are results of the propagation of individual gates towards a system failure, have also been formulated. These mathematical expressions for the evaluation of individual gates and combinations of components have enabled the evaluation of a total system failure and importance measures, which are of great interest to system analysts
Quantitative analysis of dynamic safety-critical systems using temporal fault trees
Get PDFEmerging technological systems present complexities that pose new risks and hazards. Some of these systems, called safety-critical systems, can have very disastrous effects on human life and the environment if they fail. For this reason, such systems may feature multiple modes of operation, which may make use of redundant components, parallel architectures, and the ability to fall back to a degraded state of operation without failing completely. However, the introduction of such features poses new challenges for systems analysts, who need to understand how such systems behave and estimate how reliable and safe they really are.Fault Trees Analysis (FTA) is a technique widely accepted and employed for analysing the reliability of safety-critical systems. With FTA, analysts can perform both qualitative and quantitative analyses on safety-critical systems. Unfortunately, traditional FTA is unable to efficiently capture some of the dynamic features of modern systems. This problem is not new; various efforts have been made to develop techniques to solve it. Pandora is one such technique to enhance FTA. It uses new 'temporal' logic gates, in addition to some existing ones, to model dynamic sequences of events and eventually produce combinations of basic events necessary and sufficient to cause a system failure. Until now, Pandora was not able to quantitatively evaluate the probability of a system failure. This is the motivation for this thesis.This thesis proposes and evaluates various techniques for the probabilistic evaluation of the temporal gates in Pandora, enabling quantitative temporal fault tree analysis. It also introduces a new logical gate called the 'parameterised Simultaneous-AND' (pSAND) gate. The proposed techniques include both analytical and simulation-based approaches. The analytical solution supports only component failures with exponential distribution whilst the simulation approach is not restricted to any specific component failure distribution. Other techniques for evaluating higher order component combinations, which are results of the propagation of individual gates towards a system failure, have also been formulated. These mathematical expressions for the evaluation of individual gates and combinations of components have enabled the evaluation of a total system failure and importance measures, which are of great interest to system analysts
An evaluation framework and selection tool for education apps usability, with a case study from health education apps
Get PDFMobile apps for health education are commonly utilised to support different users. The development of these apps is increasing rapidly. A critical evaluation framework is needed to ensure the usability and reliability of Mobile Health Education Applications (MHEAs) to save time and effort for stakeholders. This project aims to assist the evaluation of MHEAs through development of an evaluation framework, which includes suitable metrics, an efficient hybrid utilizing Heuristic Evaluation (HE) and Usability Evaluation (UE). This framework determines the usefulness and usability of MHEAs, in order to improve the software engineering to create more effective ways to evaluate such software. In this framework, the Medical Apps Selection Tool (MAST) has been developed in which performance helps to select suitable MHEAs, assisting stakeholders to choose MHEAs that meet their requirements.The thesis employs two methods to make the evaluation framework capable of performing qualitative and quantitative data analysis. The first is a qualitative method, involving interviews based on proposed selected hybrid metrics from HE and UE, with three kinds of stakeholders: Patients, Health Professionals and Software Developers, to identify specific relevant selected hybrid metrics to measure usability in MHEAs. These metrics are deployed to measure usability in different MHEAs based on ranking these apps within the evaluation framework. These metrics were converted into an evaluation questionnaire, which has been applied to several MHEAs. The second method is the translation of the outcomes form the first method to measure the usability of MHEAs and determine what stakeholders require from using MHEAs. For this purpose, it categorises stakeholders with different needs from MHEAs; this reflected in the MAST, based on matching different stakeholders with different MHEAs.The findings of the study indicate that the evaluation framework is able to evaluate MHEAs and record usability problems. Furthermore, this evaluation framework leads to selection of the most appropriate apps by developing the MAST for stakeholders. The framework is expected to be applicable to other domains and platforms
An evaluation framework and selection tool for education apps usability, with a case study from health education apps
No full textMobile apps for health education are commonly utilised to support different users. The development of these apps is increasing rapidly. A critical evaluation framework is needed to ensure the usability and reliability of Mobile Health Education Applications (MHEAs) to save time and effort for stakeholders. This project aims to assist the evaluation of MHEAs through development of an evaluation framework, which includes suitable metrics, an efficient hybrid utilizing Heuristic Evaluation (HE) and Usability Evaluation (UE). This framework determines the usefulness and usability of MHEAs, in order to improve the software engineering to create more effective ways to evaluate such software. In this framework, the Medical Apps Selection Tool (MAST) has been developed in which performance helps to select suitable MHEAs, assisting stakeholders to choose MHEAs that meet their requirements.The thesis employs two methods to make the evaluation framework capable of performing qualitative and quantitative data analysis. The first is a qualitative method, involving interviews based on proposed selected hybrid metrics from HE and UE, with three kinds of stakeholders: Patients, Health Professionals and Software Developers, to identify specific relevant selected hybrid metrics to measure usability in MHEAs. These metrics are deployed to measure usability in different MHEAs based on ranking these apps within the evaluation framework. These metrics were converted into an evaluation questionnaire, which has been applied to several MHEAs. The second method is the translation of the outcomes form the first method to measure the usability of MHEAs and determine what stakeholders require from using MHEAs. For this purpose, it categorises stakeholders with different needs from MHEAs; this reflected in the MAST, based on matching different stakeholders with different MHEAs.The findings of the study indicate that the evaluation framework is able to evaluate MHEAs and record usability problems. Furthermore, this evaluation framework leads to selection of the most appropriate apps by developing the MAST for stakeholders. The framework is expected to be applicable to other domains and platforms
An exploration of graph algorithms and graph databases
No full textWith data becoming larger in quantity, the need for complex, efficient algorithms to solve computationally complex problems has become greater. In this thesis we evaluate a selection of graph algorithms; we provide a novel algorithm for solving and approximating the Longest Simple Cycle problem, as well as providing novel implementations of other graph algorithms in graph database systems.The first area of exploration is finding the Longest Simple Cycle in a graph problem. We propose two methods of finding the longest simple cycle. The first method is an exact approach based on a flow-based Integer Linear Program. The second is a multi-start local search heuristic which uses a simple depth-first search as a basis for a cycle, and improves this with four perturbation operators.Secondly, we focus on implementing the Minimum Dominating Set problem into graph database systems. An unoptimised greedy heuristic solution to the Minimum Dominating Set problem is implemented into a client-server system using a declarative query language, an embedded database system using an imperative query language and a high level language as a direct comparison. The performance of the graph back-end on the database systems is evaluated. The language expressiveness of the query languages is also explored. We identify limitations of the query methods of the database system, and propose a function that increases the functionality of the queries
An exploration of graph algorithms and graph databases
Get PDFWith data becoming larger in quantity, the need for complex, efficient algorithms to solve computationally complex problems has become greater. In this thesis we evaluate a selection of graph algorithms; we provide a novel algorithm for solving and approximating the Longest Simple Cycle problem, as well as providing novel implementations of other graph algorithms in graph database systems.The first area of exploration is finding the Longest Simple Cycle in a graph problem. We propose two methods of finding the longest simple cycle. The first method is an exact approach based on a flow-based Integer Linear Program. The second is a multi-start local search heuristic which uses a simple depth-first search as a basis for a cycle, and improves this with four perturbation operators.Secondly, we focus on implementing the Minimum Dominating Set problem into graph database systems. An unoptimised greedy heuristic solution to the Minimum Dominating Set problem is implemented into a client-server system using a declarative query language, an embedded database system using an imperative query language and a high level language as a direct comparison. The performance of the graph back-end on the database systems is evaluated. The language expressiveness of the query languages is also explored. We identify limitations of the query methods of the database system, and propose a function that increases the functionality of the queries
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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