Automating allocation of development assurance levels: An extension to HiP-HOPS

Controlling the allocation of safety requirements across a system's architecture from the early stages of development is an aspiration embodied in numerous major safety standards. Manual approaches of applying this process in practice are ineffective due to the scale and complexity of modern electronic systems. In the work presented here, we aim to address this issue by presenting an extension to the dependability analysis and optimisation tool, HiP-HOPS, which allows automatic allocation of such requirements. We focus on aerospace requirements expressed as Development Assurance Levels (DALs); however, the proposed process and algorithms can be applied to other common forms of expression of safety requirements such as Safety Integrity Levels. We illustrate application to a model of an aircraft wheel braking system

Assisted assignment of automotive safety requirements

ISO 26262, a functional-safety standard, uses Automotive Safety Integrity Levels (ASILs) to assign safety requirements to automotive-system elements. System designers initially assign ASILs to system-level hazards and then allocate them to elements of the refined system architecture. Through ASIL decomposition, designers can divide a function & rsquo;s safety requirements among multiple components. However, in practice, manual ASIL decomposition is difficult and produces varying results. To overcome this problem, a new tool automates ASIL allocation and decomposition. It supports the system and software engineering life cycle by enabling users to efficiently allocate safety requirements regarding systematic failures in the design of critical embedded computer systems. The tool is applicable to industries with a similar concept of safety integrity levels. © 1984-2012 IEEE

Frais de gestion de fortune: impact des nouvelles dipositions légales envers les acteurs de la prévoyance professionnelle

A l’heure où la sécurité sociale dépendait du bon vouloir des descendances et d’oeuvres charitables le système des trois piliers s’est mis en place au rythme du 20ème siècle. Plus précisément, la prévoyance professionnelle a connu ses premiers jours en 1985 dans le but de maintenir un niveau de vie décent aux personnes nécessiteuses. La loi sur la prévoyance et ses deux ordonnances répondent à ces attentes. Malgré un bon encadrement, plusieurs modifications ont été entreprises pour permettre une évolution et une meilleure adaptation aux nouvelles contraintes qui surviennent. La réforme de 2010 en est la preuve, celle-ci a su modifier et réadapter des articles afin de permettre une plus grande transparence sur ce marché. En 2012, le marché du deuxième pilier est composé de 2073 institutions de prévoyance pour une fortune globale d’environ 700 milliards de francs suisses. Les frais de gestion de fortune quant à eux s’élèvent à 853 millions, soit 0.14% de la fortune globale. Des frais qui d’après plusieurs cabinets de conseil se situent bien en-dessous des vrais montants. Une partie de la réforme 2010 a donc mis en place des mesures pour faire apparaître ces frais et permettre une plus grande visibilité des frais encourus par les institutions de prévoyance. Le but de ce travail est de vérifier que les leviers mis en place ont bien été respectés et qu’ils ont apporté des solutions à cette problématique. Dans ces principales lignes, en plus de devoir faire figurer le deuxième et le troisième niveau liés aux placements collectifs et aux produits structurés les caisses doivent dès à présent : déterminer un ratio de frais de gestion de fortune global, déterminer pour chaque placement collectif un indicateur des frais en francs suisses, calculer le taux de transparence et indiquer dans l’annexe aux comptes les placements considérés comme non transparents en matière de frais. Ces directives ont pour la plupart été correctement mises en place dans les comptes 2013. Néanmoins, certaines recommandations permettraient une meilleure lecture des comptes. Pour cela, il faudrait davantage détailler les frais de chaque placement collectif, indiquer la performance liée à chaque placement, exiger aux caisses d’expliciter dans l’annexe aux comptes certaines décisions de placement et interdire les placements dans des produits non transparents. Ces recommandations, au-delà du point de vue monétaire, apporteraient une plus grande protection aux investisseurs et veilleraient indirectement au bon fonctionnement des marchés financiers. Les années à venir nous donneront plus d’informations sur l’impact réel de ces directives car pour l’heure la réforme « prévoyance professionnelle 2020 » est déjà au centre des débats

A synthesis of logic and bio-inspired techniques in the design of dependable systems

Much of the development of model-based design and dependability analysis in the design of dependable systems, including software intensive systems, can be attributed to the application of advances in formal logic and its application to fault forecasting and verification of systems. In parallel, work on bio-inspired technologies has shown potential for the evolutionary design of engineering systems via automated exploration of potentially large design spaces. We have not yet seen the emergence of a design paradigm that effectively combines these two techniques, schematically founded on the two pillars of formal logic and biology, from the early stages of, and throughout, the design lifecycle. Such a design paradigm would apply these techniques synergistically and systematically to enable optimal refinement of new designs which can be driven effectively by dependability requirements. The paper sketches such a model-centric paradigm for the design of dependable systems, presented in the scope of the HiP-HOPS tool and technique, that brings these technologies together to realise their combined potential benefits. The paper begins by identifying current challenges in model-based safety assessment and then overviews the use of meta-heuristics at various stages of the design lifecycle covering topics that span from allocation of dependability requirements, through dependability analysis, to multi-objective optimisation of system architectures and maintenance schedules

Exploring the impact of different cost heuristics in the allocation of safety integrity levels

Contemporary safety standards prescribe processes in which system safety requirements, captured early and expressed in the form of Safety Integrity Levels (SILs), are iteratively allocated to architectural elements. Different SILs reflect different requirements stringencies and consequently different development costs. Therefore, the allocation of safety requirements is not a simple problem of applying an allocation "algebra" as treated by most standards; it is a complex optimisation problem, one of finding a strategy that minimises cost whilst meeting safety requirements. One difficulty is the lack of a commonly agreed heuristic for how costs increase between SILs. In this paper, we define this important problem; then we take the example of an automotive system and using an automated approach show that different cost heuristics lead to different optimal SIL allocations. Without automation it would have been impossible to explore the vast space of allocations and to discuss the subtleties involved in this problem

Possibilities for recycling cellulases after use in celllase processing - part I: effects of end-product inhibition, thermal and mechanical deactivation, and cellulase depletion by adsorption

Preliminary recycling experiments with cellulase enzymes after cotton treatments at 50°C showed that activity remaining in the treatment liquors was reduced by about 80% after five recycling steps. The potential problems of end-product inhibition, thermal and mechanical deactivation, and the loss of some components of the cellulase complex by preferential and or irreversible adsorption to cotton substrates were studied. End-product inhibition studies showed that the build-up of cellobiose and glucose would be expected to cause no more than 40% activity loss after five textile treatment cycles. Thermal and mechanical treatments of cellulases suggested that the enzymes start to be deactivated at 60°C and agitation levels similar to those used in textile processing did not cause significant enzyme deactivation. Analysis of cellulase solutions, by fast protein liquid chromatography, before and after adsorption on cotton fabrics, suggested that the cellobiohydrolase II (Cel6A) content of the cellulase complex was reduced, relative to the other components, by preferential adsorption. This would lead to a marked reduction in activity after several treatment cycles and top-up with pure cellobiohydrolase II would be necessary unless this component is easily recoverable from the treated fabric

Possibilities for recycling cellulases after use in cotton processing - part II: Separation of cellulases from reaction products and released dyestuffs by ultrafiltration

The adsorption and activity of a total cellulase (Trichoderma reesei) was measured and compared on undyed and dyed cotton fabrics. Recovery of enzymes from the reaction mixture and by desorption from the cotton substrate was evaluated. About 80% of the initial protein could be recovered. The removal of released products (soluble reducing sugars and dyes) from the treatment liquor and subsequent concentration of cellulase proteins was performed using an ultrafiltration membrane. Strong protein-dye interactions made it impossible to separate efficiently the dyes from the enzymecontaining treatment liquors. The use of surfactants did not enhance cellulase desorption from cotton fabric. Although anionic surfactants have a deactivating effect on cellulases, this effect seems to be reversible, since after ultrafiltration the cellulase activity was similar to that of enzymes desorbed with buffer only. Humicola insolens cellulases were shown to be much more sensitive to anionic surfactant than T. reesei cellulases. The use of cellulases that bind reversibly to cellulose is suggested for achieving more efficient cellulase recycling and for reducing backstaining by dye-cellulase complexes

Effects of agitation level on the adsorption, desorption, and activities on cotton fabrics of full length and core domains of EGV(humicola insolens) and CenA (cellulomonas fimi)

The activities (at pH 7 and 50 degrees C) of purified EGV (Humicola insolens) and CenA (Cellulomonas fimi) were determined on cotton fabrics at high and low levels of mechanical agitation. Similar activity measurements were also made by using the core domains of these cellulases. Activity experiments suggested that the presence of cellulose binding domains (CBDs) is not essential for cellulase performance in the textile processes, where high levels of mechanical agitation are applied. The binding reversibilities of these cellulases and their cores were studied by dilution of the treatment liquor after equilibrium adsorption. EGV showed low percentage of adsorption under both levels of agitation. It was observed that the adsorption/desorption processes of cellulases are enhanced by higher mechanical agitation levels and that the binding of cellulase with CBD of family I (EGV) is more reversible than that of CBD of the cellulase of family II (CenA). (C) 2000 Elsevier Science Inc. All rights reserved