Reasoning about the Reliability of Diverse Two-Channel Systems in which One Channel is "Possibly Perfect"

This paper considers the problem of reasoning about the reliability of fault-tolerant systems with two "channels" (i.e., components) of which one, A, supports only a claim of reliability, while the other, B, by virtue of extreme simplicity and extensive analysis, supports a plausible claim of "perfection." We begin with the case where either channel can bring the system to a safe state. We show that, conditional upon knowing pA (the probability that A fails on a randomly selected demand) and pB (the probability that channel B is imperfect), a conservative bound on the probability that the system fails on a randomly selected demand is simply pA.pB. That is, there is conditional independence between the events "A fails" and "B is imperfect." The second step of the reasoning involves epistemic uncertainty about (pA, pB) and we show that under quite plausible assumptions, a conservative bound on system pfd can be constructed from point estimates for just three parameters. We discuss the feasibility of establishing credible estimates for these parameters. We extend our analysis from faults of omission to those of commission, and then combine these to yield an analysis for monitored architectures of a kind proposed for aircraft

The safety case and the lessons learned for the reliability and maintainability case

This paper examine the safety case and the lessons learned for the reliability and maintainability case

Role of placement in determination of service quality measurement of higher education in India

In this research paper the methodological development of a new model, namely SQM-HEI (Service Quality Measurement in Higher Education in India) for the measurement of service quality in higher educational institutions is developed. Three dimensions are arrived namely Teaching Methodology(TM), Environmental Change in Study Factor (ECSF) and Disciplinary Action(DA). The Placement is considered as the mediating factor for the outcome of education. For conducting an empirical study, data were collected from final year students of higher educational institutions across Tamilnadu. 1600 valid questionnaires were used for the analysis. The SQM-HEI captures the authentic determinants of service quality within the higher education sector. The developed 30-item instrument has been empirically tested with AMOS 7.0. The developed model is tested for Structural Equation Model and Bayesian estimation and testing. The SEM model output reveals that the RMSEA=0.049, GFI= 0.987 and NFI = 0.928. all the fit indices concludes the best fit of the model. The results from the current study are crucial because previous studies have produced scales that bear a resemblance to the generic measures of service quality, which may not be totally adequate to assess the perceived quality in higher education.SQM-HEI, Service Quality, Higher Education, India

NASA Lewis Research Center Futuring Workshop

On October 21 and 22, 1986, the Futures Group ran a two-day Futuring Workshop on the premises of NASA Lewis Research Center. The workshop had four main goals: to acquaint participants with the general history of technology forecasting; to familiarize participants with the range of forecasting methodologies; to acquaint participants with the range of applicability, strengths, and limitations of each method; and to offer participants some hands-on experience by working through both judgmental and quantitative case studies. Among the topics addressed during this workshop were: information sources; judgmental techniques; quantitative techniques; merger of judgment with quantitative measurement; data collection methods; and dealing with uncertainty

Similarity Structure Analysis and Structural Equation Modeling in Studying Latent Structures: An Application to the Attitudes towards Portuguese Language Questionnaire

Several international studies such as PISA and PILRS (Progress in International Reading Literacy Study), have stressed the importance of positive attitudes and behaviours as facilitators of individuals reading literacy during the school years and throughout their lives. Considering that there are not available instruments for assessing attitudes Towards Portuguese Language, it was proposed the development of the Attitudes towards Portuguese Language Questionnaire – ATPLQ (Questionário de Atitudes Face à Língua Portuguesa: QAFLP, Neto et al., 2011; Rebelo, 2012). The questionnaire has 22 Likert-type items, with four levels of response (Strongly Disagree, Disagree, Agree, Strongly Agree), spread, through exploratory factor analysis (EFA), over three attitudinal dimensions: Behavioural, Affective, and Motivational.In this study we aimed to analyse the ATPLQ’s latent structure with a pooled sample data of 1441 participants, applying similarity structure analysis (SSA) and confirmatory factor analysis of ordinal data (CFA). The SSA was carried out with Hudap in order to identify the structural properties of the questionnaire and to assess its adequacy in a Portuguese population. The CFA was carried out with LISREL in order to assure structural validity, i.e., accounting for factorial validity, but also for factors’ convergent and discriminant validity, and composite reliability. These psychometric features allowed the comparison of both the EFA derived model and the SSA derived model. We justify the selection of the SSA’s model, and we discuss the similarities between the results generated by SSA and LISREL procedures, highlighting their use in modeling constructs with ordinal indicators

Evaluating the Differences of Gridding Techniques for Digital Elevation Models Generation and Their Influence on the Modeling of Stony Debris Flows Routing: A Case Study From Rovina di Cancia Basin (North-Eastern Italian Alps)

Debris \ufb02ows are among the most hazardous phenomena in mountain areas. To cope with debris \ufb02ow hazard, it is common to delineate the risk-prone areas through routing models. The most important input to debris \ufb02ow routing models are the topographic data, usually in the form of Digital Elevation Models (DEMs). The quality of DEMs depends on the accuracy, density, and spatial distribution of the sampled points; on the characteristics of the surface; and on the applied gridding methodology. Therefore, the choice of the interpolation method affects the realistic representation of the channel and fan morphology, and thus potentially the debris \ufb02ow routing modeling outcomes. In this paper, we initially investigate the performance of common interpolation methods (i.e., linear triangulation, natural neighbor, nearest neighbor, Inverse Distance to a Power, ANUDEM, Radial Basis Functions, and ordinary kriging) in building DEMs with the complex topography of a debris \ufb02ow channel located in the Venetian Dolomites (North-eastern Italian Alps), by using small footprint full- waveform Light Detection And Ranging (LiDAR) data. The investigation is carried out through a combination of statistical analysis of vertical accuracy, algorithm robustness, and spatial clustering of vertical errors, and multi-criteria shape reliability assessment. After that, we examine the in\ufb02uence of the tested interpolation algorithms on the performance of a Geographic Information System (GIS)-based cell model for simulating stony debris \ufb02ows routing. In detail, we investigate both the correlation between the DEMs heights uncertainty resulting from the gridding procedure and that on the corresponding simulated erosion/deposition depths, both the effect of interpolation algorithms on simulated areas, erosion and deposition volumes, solid-liquid discharges, and channel morphology after the event. The comparison among the tested interpolation methods highlights that the ANUDEM and ordinary kriging algorithms are not suitable for building DEMs with complex topography. Conversely, the linear triangulation, the natural neighbor algorithm, and the thin-plate spline plus tension and completely regularized spline functions ensure the best trade-off among accuracy and shape reliability. Anyway, the evaluation of the effects of gridding techniques on debris \ufb02ow routing modeling reveals that the choice of the interpolation algorithm does not signi\ufb01cantly affect the model outcomes

Conservative Claims for the Probability of Perfection of a Software-based System Using Operational Experience of Previous Similar Systems

We begin by briefly discussing the reasons why claims of probability of non-perfection ( pnp ) may sometimes be useful in reasoning about the reliability of software-based systems for safety-critical applications. We identify two ways in which this approach may make the system assessment problem easier. The first concerns the need t o assess the chance of lifetime freedom from failure of a single system . The second concerns the need to assess the reliability of multi-channel software-diverse fault tolerant systems – in this paper, 1-out-of-2 systems. In earlier work (Littlewood and Rushby 2012, Littlewood and Povyakalo 2013) it was proposed that, in certain applications, claims for possible perfection of one of the channels in such a system may be feasible. It was shown that in such a case there is a particularly simple conservative expression for system pfd (probability of failure on demand) , involving the pfd of one channel , and the pnp of the other. In this paper we address the problem of how to assess such a pnp . In previous work (Zhao 2015) we have addressed this problem when the evidence available is only extensive failure - free working of the system in question. Here we consider the case in which there is, in addition , evidence of the previous success of the software development procedures used to build the system: specifically, several previous similar systems built using the same process have exhibited failure -free working during extensive operational exposure

Doctor of Philosophy

dissertationWater resources are limited and disproportionately distributed in time and place. Moreover, complex interactions among different components of the water system, changes in population and urbanization growth rates, and climate change have increased the uncertainty influencing water resource planning. The ultimate question arising for water managers considering the complexity of water systems is how to determine if management strategies are effective and improve the performance of a water system. Generally, decision-makers assess the system’s condition based on a univariate measure of reliability or vulnerability. However, these measures do not deliver sufficient information, and present a limited view about the system’s performance. There is a known need to study water resources in an integrated fashion to effectively manage for the present and the future. In this dissertation, a new comprehensive integrated modeling and performance assessment framework is offered. First, a new approach is designed to assess vulnerability of a water system based on important factors including exposure, sensitivity, severity, potential severity, social vulnerability, and adaptive capacity. Then, instead of an individual metric, the joint probability distribution of reliability and vulnerability based on copula function is developed to estimate a new index, the Water System Performance Index (WSPI), to evaluate the reliability and vulnerability of a water system simultaneously. To test the effectiveness of the framework and demonstrate the advances of the new performance index, a practical application is conducted for the Salt Lake City Department of Public Utilities (SLCDPU) water system. For this purpose, an integrated water resource management (IWRM) model is developed using system dynamics approach for the case study. Management alternatives are incorporated into the model using a decision support tool designed for use by water managers and stakeholders. Results of the study show an inconsistency in the degree of vulnerability between traditionally used and the new vulnerability assessment approaches. The use of the integrated model and new vulnerability approach is also shown to provide more informative guidance for decision makers evaluating alternative management strategies during failure events. Furthermore, results illustrate the effectiveness of the WSPI to identify critical conditions when there is a need for a combined measure of performance. In terms of water management decision making, the final results of this dissertation indicate centralized water storage solutions improve water system performance better than rainwater harvesting for the Salt Lake City case study

AN EXAMINATION OF VALUE ENHANCING ENTERPRISE RISK MANAGEMENT IMPLEMENTATION FRAMEWORK FOR MALAYSIAN PUBLIC LISTED COMPANIES

Enterprise risk management or ERM is fast ascending the corporate agenda globally. Its relevancy and popularity as a management technique are abetted by the changing business practices and burgeoning regulatory requirements on risk management. ERM is defined as the process of identifying and analyzing risk from an integrated, company-wide perspective in a structured and disciplined approach in aligmng strategy, processes, people, technology and knowledge with a purpose of evaluating and managing the uncertainties facing the enterprise as it creates value. ERM essentially lays concern for managing the firm's specific risk apart from the systematic risks. However, the neo-classical finance theory (NCFT) postulates that managing firm-specific risk is irrelevant. Nonetheless, this notion is in stark contrast to the phenomenon of increased acceptance of ERM by industry practitioners. As such, this thesis attempts to propose an ERM implementation framework to theorize a model that captures the causal relationships of the risks that are strategically associated with the firms' business performance and the cost of capital, e.g. risk premium. This thesis highlights the notion of managing firms' unsystematic (specific) risk via an ERM implementation framework that leads to the enhancement of shareholders' value. The mechanism through which the firms' value enhancement takes place is theorized by a strategic conceptualization of risk premium model. The model cites managing the firm's three classes of unsystematic risk, namely tactical risk, strategic risk, and normative risk. The specific aims of this thesis are fourfold: (i) to examine the depth of penetration of ERM practices among the public listed companies in Malaysia; (ii) to examine how an effective impiementation process of ERM will bring about value-enhancing outcome to Malaysia public listed companies (PLCs); (iii) to analyze the value proposition hypotheses of corporate risk management as the determinants for ERM practices; and (iv) to investigate the validity of the theorized value creation transmission mechanism of the proposed ERM framework via the strategic conceptualization of risk premium model. The data is collected through questionnaires survey from 128 PLCs on the Malaysian stock exchange. Variables in the questionnaire are measured in 5-point Likert's scale. The analyses encompass factor analysis and structural equation modeling (SEM). Outcomes of the factor analysis provide inputs (the measurement model) for the SEM analysis. The SEM validates the theorized causal relationships among the three constructs, i.e. ERM implementation challenge, ERM implementation intensity, andperceivedERM benefitmeasures: The modified model incorporates a second-order factor model which presents improved overall goodness-of-fit values than the proposed model. Apart from that, the analytic also comprises bivariate correlation analysis of hypotheses testing in relation to the various aspects of: (i) the value maximization theory of ERM practices; and (ii) the value creation transmission mechanism of the proposed ERM implementation framework. The analysis results conclude the following: (i) that all causal relationships (structural model) under SEM examination indicate significant parameters; (ii) that ERM implementation has significant positive associations with value maximization theories of risk management; (iii) that ERM implementation has significant positive effects in reducing the firm's tactical and strategic risks with the consequence of lowering the firm's risk premium

Partial Least Squares Structural Equation Modeling (PLS-SEM) Using R

Partial least squares structural equation modeling (PLS-SEM) has become a standard approach for analyzing complex inter-relationships between observed and latent variables. Researchers appreciate the many advantages of PLS-SEM such as the possibility to estimate very complex models and the method’s flexibility in terms of data requirements and measurement specification. This practical open access guide provides a step-by-step treatment of the major choices in analyzing PLS path models using R, a free software environment for statistical computing, which runs on Windows, macOS, and UNIX computer platforms. Adopting the R software’s SEMinR package, which brings a friendly syntax to creating and estimating structural equation models, each chapter offers a concise overview of relevant topics and metrics, followed by an in-depth description of a case study. Simple instructions give readers the “how-tos” of using SEMinR to obtain solutions and document their results. Rules of thumb in every chapter provide guidance on best practices in the application and interpretation of PLS-SEM