125 research outputs found

    Measuring Confidence of Assurance Cases in Safety-Critical Domains

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    Evaluation of assurance cases typically requires certifiers’ domain knowledge and experience, and, as such, most software certification has been conducted manually. Given the advancement in uncertainty theories and software traceability, we envision that these technologies can synergistically be combined and leveraged to offer some degree of automation to improve the certifiers’ capability to perform software certification. To this end, we present DS4AC, a novel confidence calculation framework that 1) applies the Dempster-Shafer theory to calculate the confidence between a parent claim and its children claims; and 2) uses the vector space model to evaluate the confidence for the evidence items using traceability information. We illustrate our approach on two different applications, where safety is the key property of interest for both systems. In both cases, we use the Goal Structuring Notation to represent the respective assurance cases and provide proof of concept results that demonstrate the DS4AC framework can automate portions of the evaluation of assurance cases, thereby reducing the burden of manual certification process

    Volume 36, issue 1

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    The mission of CJS is to contribute to the effective continuing medical education of Canadian surgical specialists, using innovative techniques when feasible, and to provide surgeons with an effective vehicle for the dissemination of observations in the areas of clinical and basic science research. Visit the journal website at http://canjsurg.ca/ for more.https://ir.lib.uwo.ca/cjs/1257/thumbnail.jp

    Historical data and analysis for the first five years of KSC STS payload processing

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    General and specific quantitative and qualitative results were identified from a study of actual operational experience while processing 186 science, applications, and commercial payloads for the first 5 years of Space Transportation System (STS) operations at the National Aeronautics and Space Administration's (NASA) John F. Kennedy Space Center (KSC). All non-Department of Defense payloads from STS-2 through STS-33 were part of the study. Historical data and cumulative program experiences from key personnel were used extensively. Emphasis was placed on various program planning and events that affected KSC processing, payload experiences and improvements, payload hardware condition after arrival, services to customers, and the impact of STS operations and delays. From these initial considerations, operational drivers were identified, data for selected processing parameters collected and analyzed, processing criteria and options determined, and STS payload results and conclusions reached. The study showed a significant reduction in time and effort needed by STS customers and KSC to process a wide variety of payload configurations. Also of significance is the fact that even the simplest payloads required more processing resources than were initially assumed. The success to date of payload integration, testing, and mission operations, however, indicates the soundness of the approach taken and the methods used

    Carbapenemase-Producing Enterobacterales

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    Carbapenem-resistant Enterobacterales (CRE) are a common cause of infections in both community and healthcare settings and have become an increasing threat to public health worldwide. The focus of this Special Issue includes aspects concerning plasmid-mediated antimicrobial resistance along with other carbapenem resistance mechanisms. Understanding the prevalence and routes of transmission of CRE is important in developing specific interventions for healthcare facilities, as well as the general impact of CRE circulation on the environment. Attention has also been focused on carbapenemase testing in order to provide advanced phenotypic and molecular assays for the identification of CRE, as a valid tool for active global surveillance, and from this perspective, the study of resistance mechanisms can provide significant support for the development of new and appropriate antimicrobial molecules. For all of these reasons, the phenomenon of carbapenem resistance deserves more attention, for the sake of public health

    Optimization of Parameters Used in Predictive Models for Respirator Cartridge Service Life for Toxic Organic Vapors

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    Les appareils de protection respiratoire munis de cartouches chimiques contenant du charbon actif, sont les appareils les plus utilisĂ©s en milieu de travail pour protĂ©ger les travailleurs contre les vapeurs organiques toxiques. Cependant, Ă©tant donnĂ© que les indicateurs de fin de service pour les cartouches ne sont pas encore au point, il est recommandĂ© d’utiliser des modĂšles de prĂ©diction pour estimer la durĂ©e de vie des cartouches. Dans le cas des mĂ©langes, ces modĂšles de prĂ©diction ne tiennent pas compte de la toxicitĂ© des contaminants. Ainsi, l’objectif principal de cette thĂšse fut d’optimiser les modĂšles thĂ©oriques de prĂ©diction Ă  partir de rĂ©alisation de trois sujets de recherche : (1) le dĂ©veloppement d’une mĂ©thode expĂ©rimentale pour caractĂ©riser la microstructure des charbons actifs dans des conditions environnementales semblables Ă  celles de leur utilisation; (2) la conception d’une approche expĂ©rimentale dans un montage rĂ©duit avec une cartouche miniature (Mini) permettant de mieux contrĂŽler les conditions environnementales et de rĂ©duire la quantitĂ© de solvants utilisĂ©s lors des essais ; et (3) l’intĂ©gration d’une approche toxicologique qui applique le principe de l’indice de risque (HI) aux mĂ©langes pour l’utilisation sĂ©curitaire des cartouches. En ce qui concerne la caractĂ©risation de la microporositĂ© des charbons, il a Ă©tĂ© dĂ©montrĂ© qu’il Ă©tait possible d’obtenir des isothermes d’adsorption de type I en exposant les charbons Ă  des vapeurs organiques diffĂ©rentes, ayant des rapports de tensions de vapeurs variant de 0.001 Ă  0.1. Ces isothermes ont permis d’obtenir les microporositĂ©s des charbons et, Ă  l’aide de lâ€˜Ă©quation de Dubinin-Radushkevich, de calculer les capacitĂ©s d’adsorption des charbons des cartouches chimiques qui sont semblables aux valeurs expĂ©rimentales. La mise au point d’un systĂšme rĂ©duit a dĂ©montrĂ© qu’une cartouche Mini reprĂ©sentant une section de la cartouche de taille rĂ©elle Ă©tait capable de reproduire les temps de claquage Ă  10% d’un contaminant et la capacitĂ© d’adsorption de la cartouche tout en reproduisant des courbes de claquages parfaitement symĂ©triques. Cette approche a permis de mieux contrĂŽler les paramĂštres expĂ©rimentaux (tempĂ©rature, humiditĂ© et dĂ©bit d’air) et de diminuer la quantitĂ© de solvants utilisĂ©s pour les essais, tout en obtenant des rĂ©sultats plus fiables. L’étude sur les mĂ©langes de vapeurs comprenant un contaminant trĂšs volatil et peu toxique a dĂ©montrĂ© que l’intĂ©gration de l’indice de risque dans le calcul du temps de service pour les mĂ©langes permettait une utilisation efficace et sĂ©curitaire des cartouches. Cette approche est valable lorsque la concentration du contaminant le plus volatil est < 50 ppm et que le rapport des concentrations du contaminant volatil au moins volatil est infĂ©rieur Ă  2. Ces travaux ont dĂ©montrĂ©, dans l’ensemble, l’amĂ©lioration de l’approche expĂ©rimentale et thĂ©orique, ce qui apporte une plus haute prĂ©cision des paramĂštres des modĂšles de prĂ©diction du temps de service des cartouches chimiques et par consĂ©quent, une meilleure protection des travailleurs.Air-purifying respirators equipped with activated carbon cartridges are among the most widely used respirators in the workplace to protect against toxic organic vapors. Because end-of-service-life-indicators (ESLI) are limited for organic vapors, mathematical models are recommended to yield the cartridge service life (CSL). Moreover, in the case of mixture contaminants, the toxicity of the breakthrough vapors is not even considered in the estimation of CSL. Hence, the main objective of this study was to improve predictive models by investigating three research topics: (1) developing an experimental approach to characterize the pore structure of activated carbons in respirator cartridges using adsorption isotherms obtained with different organic vapors of different vapor pressure at environmental conditions similar to the ones found in the workplace; (2) designing a miniaturized (Mini) cartridge device to allow better control of environmental conditions and reducing the amount of solvent used while providing reliable data; (3) integrating a toxicological approach in the estimation of CSL for vapor mixtures by using the Hazard Index (HI) principle to indicate the safe use of respirators. The characterisation of the microporous structure of the activated carbons showed that a type I characteristic multi-vapor adsorption isotherm can be obtained with organic vapors of relative vapor pressures ranging from 0.001 to 0.1. The obtained micropore values were used in the Dubinin-Radushkevich equation to calculate the micropore volumes and the adsorption capacities of the activated carbons, which showed agreement with the experimental data. The Mini cartridge device was designed to reproduce a small section of a given respirator cartridge and have the same carbon bed thickness as the full size respirator cartridge. The Mini was able to reproduce symmetrical breakthrough curves of the full size cartridge and gave results comparable to the 10% breakthrough times and adsorption capacities of the cartridges. This efficient approach provided better control over environmental conditions (temperature, humidity, and flow) in breakthrough tests to obtain reliable data, and reduced the amount of solvent used. The study on vapor mixtures involving a volatile and low toxic component showed that applying the Hazard Index (HI) was suitable for optimal and safe use of respirator cartridges. This approach was reliable at low concentrations of acetone (< 50 ppm) and when the ratio of the contaminants of the volatile to the less volatile was < 2. Overall, this thesis has showed that the experimental and theoretical approaches have improved the predictive models for cartridge the service life by improving the precision of the intrinsic parameters of these models to better protect the workers

    Accurate aeroacoustic measurements in closed-section hard-walled wind tunnels

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    Noise emissions from aircraft are of major concern to aircraft manufacturers. There are various analytical, empirical and numerical tools to help in the design of quieter aircraft, however aeroacoustic measurements in wind tunnels are still required. There is a growing interest in simultaneous aerodynamic and aeroacoustic measurements in hard-walled closed-section wind tunnels. The research hypothesis of this work is whether accurate aeroacoustic measurements are possible in this type of wind tunnel. Two issues are of particular concern: the reverberation sound field and high background noise levels. De-reverberation, based on an Image Source Model (ISM), is proposed to tackle the first issue by incorporating the reflections in the focused beamformer. This technique is computationally fast and easy to implement. Source Power Integration and deconvolution techniques are shown to be still valid in de-reverberation. Measurements in a closed section wind tunnel have shown that an ISM gives a better estimate of the Green's functions, when compared to free-space Green's functions. Furthermore de-reverberation yielded more accurate source strength estimates from the beamformer. Qualitatively, de-convolved results were no different than when using free-space Green's functions. Simulations have shown that the ISM can become unstable at high frequencies if position errors are present. It is therefore recommended to limit the application of the ISM to frequencies below 10 kHz. At low frequencies the accuracy of beamforming levels is highly dependent on the level of noise contamination of the input data. Removing the diagonal of the cross spectral matrix might not be sufficient to eliminate this noise

    SSL: A software specification language

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    SSL (Software Specification Language) is a new formalism for the definition of specifications for software systems. The language provides a linear format for the representation of the information normally displayed in a two-dimensional module inter-dependency diagram. In comparing SSL to FORTRAN or ALGOL, it is found to be largely complementary to the algorithmic (procedural) languages. SSL is capable of representing explicitly module interconnections and global data flow, information which is deeply imbedded in the algorithmic languages. On the other hand, SSL is not designed to depict the control flow within modules. The SSL level of software design explicitly depicts intermodule data flow as a functional specification

    Study of geometry effects on local corrosion rates for Lbe loop

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    Corrosion is an extremely important issue in nuclear cooling system applications. Many scientific and engineering efforts have contributed to the research of finding an ideal material, which has resistance to corrosive Lead Bismuth Eutectic (LBE). A Delta Loop was designed and constructed in Los Alamos National Lab (LANL) to obtain the experimental data. This loop is a multi-section closed system that differs in diameter from one part to another. As a result, an intensive study on the geometry effect is necessary and valuable. In this thesis, this problem was simulated by commercial software STAR-CD. Results provide a good prediction where the highest corrosion rate might occur and how geometry will affect the local corrosion phenomenon. A simple study on reactive flow was carried out by using STAR-CD + CHEMKIN, which is designed for solving reactions both in flow and on surface. In addition, a self-developed code using the finite difference method was employed to reveal how mass transfer is affected by geometry and flow. A parametric study on several factors was carried out

    An acoustic charge transport imager for high definition television applications

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    This report covers: (1) invention of a new, ultra-low noise, low operating voltage APD which is expected to offer far better performance than the existing volume doped APD device; (2) performance of a comprehensive series of experiments on the acoustic and piezoelectric properties of ZnO films sputtered on GaAs which can possibly lead to a decrease in the required rf drive power for ACT devices by 15dB; (3) development of an advanced, hydrodynamic, macroscopic simulator used for evaluating the performance of ACT and CTD devices and aiding in the development of the next generation of devices; (4) experimental development of CTD devices which utilize a p-doped top barrier demonstrating charge storage capacity and low leakage currents; (5) refinements in materials growth techniques and in situ controls to lower surface defect densities to record levels as well as increase material uniformity and quality
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