This thesis deals with a common cause failure analysis (CCF) for space devices. This analysis belongs among dependability analyses, which have not been sufficiently developed in a field of space industry in corresponding technical and normative documents. Therefore, we focused on devising a new procedure of a qualitative and quantitative common cause failure analysis for the space applications herein. This new procedure of the qualitative and quantitative CCF analysis was applied on redundant systems of a special space device microaccelerometer (ACC), which was developed in VZLÚ. Performance of the qualitative CCF analysis can lead to recommendations to change design of the system, making the system less susceptible to the common cause failures. Performance of the quantitative CCF analysis and its inclusion into the computation of the system reliability can lead to a more accurate estimation of the reliability (in most cases it leads to decreasing the system reliability). During the development of the ACC there were not defined any requirements to perform the CCF analysis within general dependability requirements (defined by the customer and by ECSS standards). Hence, we compared computations of the ACC reliability with and without considering the CCFs. When the CCFs were considered, the reliability of the ACC was decreased according to our assumption. On our example of the ACC we showed advantages of the performance of the CCF analysis within the dependability analyses during development of the space devices.

<p> In the field of Reliability, a new concept is introduced. The Combined Dependability theory is put forth in this thesis. </p> <p> Attempts are made to prove this theory experimentally by use of accelerated failure tests of GE-47 miniature lamps. The lamps are tested individually and ten in series. The individual lamp test results are then used for the prediction of the reliability of the ten lamps in series.</p> <p> The ten lamps in series simulate a machine with ten components. A failure of one of the components will produce a failure of the machine. The reliability of the machine can be found if the reliability of each part is known. The single part when tested individually must be subjected to the same stresses and conditions that it would encounter when operating in the machine. If this is not accomplished, the machine's calculation of reliability is invalid.</p> / Thesis / Master of Engineering (MEngr)

Currently, the development of high-integrity embedded component-based software systems is not supported by well-integrated means allowing for quality evaluation and design support within a development process. Quality, especially dependability, is very important for such systems. The CHESS (Composition with Guarantees for High-integrity Embedded Software Components Assembly) project aims at providing a new systems development methodology to capture extra-functional concerns and extend Model Driven Engineering industrial practices and technology approaches to specifically address the architectural structure, the interactions and the behavior of system components while guaranteeing their correctness and the level of service at run time. The CHESS methodology is expected to be supported by a tool-set which consists of a set of plug-ins integrated within the Eclipse IDE. In the framework of the CHESS project, this thesis addresses the lack of well integrated means concerning quality evaluation and proposes an integrated framework to evaluate the dependability of high-integrity embedded systems. After a survey of various failure behavior analysis techniques, a specific technique, called Failure Propagation and Transformation Calculus (FPTC), is selected and a plug-in, called CHESS-FPTC, is developed within the CHESS tool-set. FPTC technique allows users to calculate the failure behavior of the system from the failure behavior of its building components. Therefore, to fully support FPTC, CHESS-FPTC plug-in allows users to model the failure behavior of the building components, perform the analysis automatically and get the analysis results back into their initial models. A case study about AAL2 Signaling Protocol is presented to illustrate and evaluate the CHESS-FPTC framework. / CHESS Project - http://chess-project.ning.com/

High-stakes testing is used for the purposes of providing results that have important consequences such as certifications, licensing, or credentialing. The purpose of this study was to examine aspects of an exam recently written by flight paramedics for recertification and make recommendations for development of future exams. In 2008, an unexpectedly high failure led to revisions in the exam development process for flight paramedics. Using principles of classical test theory and generalizability theory, I examined the decision consistency and dependability of the examination and found the decision consistency for dichotomous items to be within acceptable limits, yet the dependability was low. Discrimination was strong at the cut-score. An in-depth look into the process used to set the exam, as well as the psychometric properties of the exam and the items have led to recommendations that will contribute to future development of dependable exams in the industry that result in more valid interpretations with respect to paramedic competence. / Thesis (Master, Education) -- Queen's University, 2012-09-06 22:41:41.552

Dealing properly with electronics and software will be a strong competitive advantage in the automotive sector in the near future. Electronics are driving current innovations and are at the same time becoming a larger part of the cost of the vehicle. In order to be successful as an automotive manufacturer, innovations must be introduced in the vehicle without compromising the final price tag. Also, the electronics has to compete with, and win over, the dependability of well known and proven mechanical solutions. Structure related costs can be reduced by designing a modular system, volume related costs can be reduced by utilizing fewer electronic control units that shares software performing a variety of functions. To achieve a modular system careful consideration must be applied in the architecture design process. Architecting is commonly referred to as an art, performed in a qualitative manner. This thesis provides a quantitative method for architecture design and evaluation targeting modular architectures. The architecture design method is based on a simple underlying information model. This model is extended through practical experiences in case studies to include support for configuration and documentation. An information model is a key enabler for managing the increasing complexity of automotive embedded systems. The model provides the basis for establishing the analyzable documentation that is required to ensure the dependability of the systems, specifically in terms of need for reliability, maintainability and safety. An information model supports traceability both within the product, across components, and also between different organizational units using different views of the product throughout the lifecycle. Further, some general issues of systems engineering and model based development related to the engineering of automotive embedded systems are discussed. Considerations for introducing a model based development process are covered. Also, the maturity of development processes and requirements on tools in an automotive context are evaluated. The ideas and methods presented in this thesis have been developed and tried in an industrial setting through a range of case studies. / QC 20101027

Given the increasing influence of technology and the explosion in data collection demands, the acceptance and assimilation of new paradigms and technologies require today’s educators, researchers, and evaluators to select appropriate tools and apply them effectively. One of these technologies—handheld computers—makes the benefits of computerized data collection more accessible to field-based researchers. Three related studies were conducted to evaluate handheld-based data collection system for use in special education settings and to highlight the acceptability factors to effectively use this emerging technology. The first study reviewed the recent literature on the dependability and willingness of teachers to adopt handheld data collection systems and emphasized five important factors: (1) perceived ease of use; (2) perceived usefulness; (3) intention to use; (4) dependability; and (5) subjective norms. The second study discussed the dependability of handheld computers used by special education teachers for collecting self-report data by addressing four dependability attributes: reliability, maintainability, availability, and safety. Data were collected from five sources: (1) self-reports of time use by 19 special education teachers using Pocket PC computers, (2) observations of time use from eight external data collectors, (3) teacher interviews, (4) technical reports prepared by the researcher, and (5) teacher satisfaction. Results indicated that data collection via handheld computers yielded accurate, complete, and timely data, and was appropriate for these four dependability attributes. The last study investigated teachers’ acceptance of handheld computer use by testing the relationship among five factors that influence intention to use this technology which was based on a modified version of the technology acceptance model using the handheld computer acceptance survey responses from 45 special education teachers. The results showed that intention to use handheld computer was directly affected by the devices’ perceived usefulness and perceived ease of use. The issue of dependability had a direct and indirect statistically significant effect on perceived ease of use and usefulness, and intention to use a handheld computer, respectively. Overall, three studies demonstrated that handheld computers can be effectively used in the direct observation of behavior in a school environment, without requirements of any settings.

<p>COM+ and Enterprise JavaBeans are two component-based technologies that can be used to build enterprise systems. These are two competing technologies in the software industry today and choosing which technology a company should use to build their enterprise system is not an easy task. There are many factors to consider and in this project we evaluate these two technologies with focus on scalability and the dependability aspects security, availability and reliability. Independently, these technologies are theoretically evaluated with the criteria in mind.</p><p>We use a 4-tier architecture for the evaluation and the center of attention is a persistence layer, which typically resides in an application server, and how it can be realized using the technologies. This evaluation results in a recommendation about which technology is a better approach to build a scalable and dependable distributed system. The results are that COM+ is considered a better approach to build this kind of multi-tier distributed systems.</p>

<p>Dealing properly with electronics and software will be a strong competitive advantage in the automotive sector in the near future. Electronics are driving current innovations and are at the same time becoming a larger part of the cost of the vehicle. In order to be successful as an automotive manufacturer, innovations must be introduced in the vehicle without compromising the final price tag. Also, the electronics has to compete with, and win over, the dependability of well known and proven mechanical solutions.</p><p>Structure related costs can be reduced by designing a modular system, volume related costs can be reduced by utilizing fewer electronic control units that shares software performing a variety of functions. To achieve a modular system careful consideration must be applied in the architecture design process. Architecting is commonly referred to as an art, performed in a qualitative manner. This thesis provides a quantitative method for architecture design and evaluation targeting modular architectures.</p><p>The architecture design method is based on a simple underlying information model. This model is extended through practical experiences in case studies to include support for configuration and documentation.</p><p>An information model is a key enabler for managing the increasing complexity of automotive embedded systems. The model provides the basis for establishing the analyzable documentation that is required to ensure the dependability of the systems, specifically in terms of need for reliability, maintainability and safety. An information model supports traceability both within the product, across components, and also between different organizational units using different views of the product throughout the lifecycle.</p><p>Further, some general issues of systems engineering and model based development related to the engineering of automotive embedded systems are discussed. Considerations for introducing a model based development process are covered. Also, the maturity of development processes and requirements on tools in an automotive context are evaluated. The ideas and methods presented in this thesis have been developed and tried in an industrial setting through a range of case studies.</p>

There is currently much UK government and industry interest towards the integration of complex computer-based systems, including those in the military domain. These systems can include both mission critical and safety critical applications, and therefore require the dependable communication of data. Current modular military systems requiring such performance guarantees are mostly based on parameters and system states fixed during design time, thus allowing a predictable estimate of performance. These systems can exhibit a limited degree of reconfiguration, but this is typically within the constraints of a predefined set of configurations. The ability to reconfigure systems more dynamically, could lead to further increased flexibility and adaptability, resulting in the better use of existing assets. Current software architecture models that are capable of providing this flexibility, however, tend to lack support for dependable performance. This thesis explores the benefits for the dependability of future dynamic systems, built on a publish/subscribe model, from using Quality of Service (QoS) methods to map application level data communication requirements to available network resources. Through this, original contributions to knowledge are created, including; the proposal of a QoS framework that specifies a way of defining flexible levels of QoS characteristics and their use in the negotiation of network resources, a simulation based evaluation of the QoS framework and specifically the choice of negotiation algorithm used, and a test-bed based feasibility study. Simulation experimentation conducted comparing different methods of QoS negotiation gives a clear indication that the use of the proposed QoS framework and flexible negotiation algorithm can provide a benefit in terms of system utility, resource utilisation, and system stability. The choice of negotiation algorithm has a particularly strong impact on these system properties. The cost of these benefits comes in terms of the processing power and execution time required to reach a decision on the acceptance of a subscriber. It is suggested, given this cost, that when computational resources are limited, a simpler priority based negotiation algorithm should be used. Where system resources are more abundant, however, the flexible negotiation algorithm proposed within the QoS framework can offer further benefits. Through the implementation of the QoS framework within an existing military avionics software architecture based emulator on a test-bed, both the technical challenges that will need to be overcome and, more importantly, the potential viability for the inclusion of the QoS framework have been demonstrated.

Made available in DSpace on 2014-06-12T15:58:19Z (GMT). No. of bitstreams: 2 arquivo3464_1.pdf: 2672787 bytes, checksum: 9bee33c2153182c2ce64b9027453243a (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Sistemas computacionais estão em constante evolução para satisfazer crescimentos na demanda, ou novas exigências dos usuários. A administração desses sistemas requer decisões que sejam capazes de prover o nível mais alto nas métricas de desempenho e dependabilidade, com mudanças mínimas `a configuração existente. É comum realizar análises de desempenho, confiabilidade, disponibilidade e performabilidade de sistemas através de modelos analíticos, e as cadeias de Markov representam um dos formalismos matemáticos mais utilizados, permitindo estimar algumas métricas de interesse, dado um conjunto de parâmetros de entrada. No entanto, a análise de sensibilidade, quando feita, é executada simplesmente variando o conjunto de parâmetros dentro de suas faixas de valores e resolvendo repetidamente o modelo escolhido. A análise de sensibilidade diferencial permite a quem está modelando encontrar gargalos de uma maneira mais sistemática e eficiente. Este trabalho apresenta uma abordagem automatizada para análise de sensibilidade, e almeja guiar a melhoria de sistemas computacionais. A abordagem proposta é capaz de acelerar o processo de tomada de decisão, no que se refere a optimização de ajustes de hardware e software, além da aquisição e substituição de componentes. Tal metodologia usa as cadeias de Markov como técnica de modelagem formal, e a análise de sensibilidade desses modelos, preenchendo algumas lacunas encontradas na literatura sobre análise de sensibilidade. Por fim, a análise de sensibilidade de alguns sistemas distribuídos selecionados, conduzida neste trabalho, destaca gargalos nestes sistemas e fornece exemplos da acurácia da metodologia proposta, assim como ilustra sua aplicabilidade