2,446 research outputs found

    User's guide for NETS/PROSSS

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    Expensive analysis programs are often combined with optimization procedures to solve engineering problems. To obtain an optimal solution requires numerous iterations between the analysis program and the optimizer. This often becomes prohibitive due to the cost and amount of computer time needed to converge to an optimal solution. NETS/PROSSS was developed to address this problem. The purpose of this paper is to serve as a user's guide for NETS/PROSSS. The key features include the neural network, determining the training pairs for the neural network, and the approximated analysis/optimization process. A small problem is given to serve as an example of how to apply the system

    HAZOP: Our Primary Guide in the Land of Process Risks: How can we improve it and do more with its results?

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    PresentationAll risk management starts in determining what can happen. Reliable predictive analysis is key. So, we perform process hazard analysis, which should result in scenario identification and definition. Apart from material/substance properties, thereby, process conditions and possible deviations and mishaps form inputs. Over the years HAZOP has been the most important tool to identify potential process risks by systematically considering deviations in observables, by determining possible causes and consequences, and, if necessary, suggesting improvements. Drawbacks of HAZOP are known; it is effort-intensive while the results are used only once. The exercise must be repeated at several stages of process build-up, and when the process is operational, it must be re-conducted periodically. There have been many past attempts to semi- automate the HazOp procedure to ease the effort of conducting it, but lately new promising developments have been realized enabling also the use of the results for facilitating operational fault diagnosis. This paper will review the directions in which improved automation of HazOp is progressing and how the results, besides for risk analysis and design of preventive and protective measures, also can be used during operations for early warning of upcoming abnormal process situations

    How to Treat Expert Judgment? With certainty it contains uncertainty!

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    PresentationTo be acceptably safe one must identify the risks one is exposed to. It is uncertain whether the threat really will materialize, but determining the size and probability of the risk is also full of uncertainty. When performing an analysis and preparing for decision making under uncertainty, quite frequently failure rate data, information on consequence severity or on a probability value, yes, even on the possibility an event can or cannot occur is lacking. In those cases, the only way to proceed is to revert to expert judgment. Even in case historical data are available, but one should like to know whether these data still hold in the current situation, an expert can be asked about their reliability. Anyhow, expert elicitation comes with an uncertainty depending on the expert’s reliability, which becomes very visible when two or more experts give different answers or even conflicting ones. This is not a new problem, and very bright minds have thought how to tackle it. But so far, however, the topic has not been given much attention in process safety and risk assessment. The paper has a review character and will present various approaches with detailed explanation and examples

    Can we verify and intrinsically validate risk assessment results? What progress is being made to increase QRA trustworthiness?

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    PresentationThe purpose of a risk assessment is to make a decision whether the risk of a given situation is acceptable, and, if not, how we can reduce it to a tolerable level. For many cases, this can be done in a semi-quantitative fashion. For more complex or problematic cases a quantitative approach is required. Anybody who has been involved in such a study is aware of the difficulties and pitfalls. Despite proven software many choices of parameters must be made and many uncertainties remain. The thoroughness of the study can make quite a difference in the result. Independently, analysts can arrive at results that differ orders of magnitude, especially if uncertainties are not included. Because for important decisions on capital projects there are always proponents and opponents, there is often a tense situation in which conflict is looming. The paper will first briefly review a standard procedure introduced for safety cases on products that must provide more or less a guarantee that the risk of use is below a certain value. Next will be the various approaches how to deal with uncertainties in a quantitative risk assessment and the follow-on decision process. Over the last few years several new developments have been made to achieve, to a certain extent, a hold on so-called deep uncertainty. Expert elicitation and its limitations is another aspect. The paper will be concluded with some practical recommendations

    Stochastic oscillations of adaptive networks: application to epidemic modelling

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    Adaptive-network models are typically studied using deterministic differential equations which approximately describe their dynamics. In simulations, however, the discrete nature of the network gives rise to intrinsic noise which can radically alter the system's behaviour. In this article we develop a method to predict the effects of stochasticity in adaptive networks by making use of a pair-based proxy model. The technique is developed in the context of an epidemiological model of a disease spreading over an adaptive network of infectious contact. Our analysis reveals that in this model the structure of the network exhibits stochastic oscillations in response to fluctuations in the disease dynamic.Comment: 11 pages, 4 figure

    Uncoupling of T Cell Receptor Zeta Chain Function during the Induction of Anergy by the Superantigen, Staphylococcal Enterotoxin A

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    Staphylococcus aureus enterotoxins have immunomodulatory properties. In this study, we show that Staphylococcal enterotoxin A (SEA) induces a strong proliferative response in a murine T cell clone independent of MHC class II bearing cells. SEA stimulation also induces a state of hypo-responsiveness (anergy). We characterized the components of the T cell receptor (TCR) during induction of anergy by SEA. Most interestingly, TCR zeta chain phosphorylation was absent under SEA anergizing conditions, which suggests an uncoupling of zeta chain function. We characterize here a model system for studying anergy in the absence of confounding costimulatory signals

    A representation of the natural numbers by means of cycle-numbers, with consequences in number theory

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    In this paper we give rules for creating a number triangle T in a manner analogous to that for producing Pascal’s arithmetic triangle; but all of its elements belong to {0, 1}, and cycling of its rows is involved in the creation. The method of construction of any one row of T from its preceding rows will be defined, and that, together with starting and boundary conditions, will suffice to define the whole triangle, by sequential continuation. We shall use this triangle in order to define the so-called cycle-numbers, which can be mapped to the natural numbers. T will be called the ‘cyclenumber triangle’. First we shall give some theorems about relationships between the cyclenumbers and the natural numbers, and discuss the cycling of patterns within the triangle’s rows and diagonals. We then begin a study of figures (i.e. (0,1)patterns, found on lines, triangles and squares, etc.) within T. In particular, we shall seek relationships which tell us something about the prime numbers. For our later studies, we turn the triangle onto its side and work with a doubly-infinite matrix C. We shall find that a great deal of cycling of figures occurs within T and C, and we exploit this fact whenever we can. The phenomenon of cycling patterns leads us to muse upon a ‘music of the integers’, indeed a ‘symphony of the integers’, being played out on the cycle-number triangle or on C. Like Pythagoras and his ‘music of the spheres’, we may well be the only persons capable of hearing it! Keywords: cycle-number triangle, cycle-number, prime cycle-number

    A principled approach to the measurement of situation awareness in commercial aviation

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    The issue of how to support situation awareness among crews of modern commercial aircraft is becoming especially important with the introduction of automation in the form of sophisticated flight management computers and expert systems designed to assist the crew. In this paper, cognitive theories are discussed that have relevance for the definition and measurement of situation awareness. These theories suggest that comprehension of the flow of events is an active process that is limited by the modularity of attention and memory constraints, but can be enhanced by expert knowledge and strategies. Three implications of this perspective for assessing and improving situation awareness are considered: (1) Scenario variations are proposed that tax awareness by placing demands on attention; (2) Experimental tasks and probes are described for assessing the cognitive processes that underlie situation awareness; and (3) The use of computer-based human performance models to augment the measures of situation awareness derived from performance data is explored. Finally, two potential example applications of the proposed assessment techniques are described, one concerning spatial awareness using wide field of view displays and the other emphasizing fault management in aircraft systems

    FEMA's Integration of Preparedness and Development of Robust Regional Offices

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    In October 2006, Congress enacted major legislation to reform the function and organization of the Federal Emergency Management Agency (FEMA) in response to the recognized failures in preparation for and response to Hurricane Katrina. The Post-Katrina Emergency Management Reform Act of 2006 (PKEMRA) focused national preparedness responsibilities within FEMA and directed additional resources and responsibilities to FEMA's ten regional offices. Directed by Congress, in October 2008 a National Academy Panel began an independent assessment of FEMA's integration of preparedness functions and progress in development of robust regional offices.Main FindingsOver the past three years, FEMA has taken significant steps in an effort to integrate preparedness and develop more robust regional offices. These efforts, undertaken by both the previous and current Administrations, are documented throughout this report and should be recognized and applauded. However, FEMA has yet to define specific goals and outcomes that would permit it, Congress or the public to determine when preparedness has been fully integrated into all aspects of FEMA's work and whether the development and ongoing operation of robust regional offices has been achieved. In the absence of well-defined, measurable outcome indicators, the National Academy Panel relied upon the assessments of FEMA leaders and staff, documentation provided by FEMA, and a review of secondary sources material to inform its findings and recommendations. Based upon this evidence, the Panel has concluded that, while progress has been made: (1) preparedness is not fully integrated across FEMA, (2) FEMA's regional offices do not yet have the capacity required to ensure the nation is fully prepared, (3) stakeholders are not yet full partners with FEMA in national preparedness, and (4) FEMA has ineffective internal business practices, particularly with regard to human resource management. The Panel made seven recommendations for FEMA:Establish a cross-organizational process, with participation from internal and external stakeholders, to develop a shared understanding of preparedness integrationEstablish a robust set of outcome metrics and standards for preparedness integration, as well as a system to monitor and evaluate progress on an ongoing basisWork to eliminate organizational barriers that are adversely impacting the full integration of preparedness across the agencyContinue to build regional office capacity and monitor implementation consistent with the Administrator's recent policy guidanceUndertake steps to improve the ongoing working relationship between headquarters and the regions in accord with Panel-identified principlesTake steps to improve stakeholder engagement and relationships at all levels in accord with Panel-identified principles; andStrengthen internal business practices, especially in the area of human capital planning
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