Abstract. Software safety cases encourage developers to carry out only those safety activities that actually reduce risk. In practice this is not always achieved. To help remedy this, the SSEI at the University of York has developed a set of software safety argument patterns. This paper reports on using the patterns in two real-world case studies, evaluating the patterns' use against criteria that includes flexibility, ability to reveal assurance decits and ability to focus the case on software contributions to hazards. The case studies demonstrated that the safety patterns can be applied to a range of system types regardless of the stage or type of development process, that they help limit safety case activities to those that are significant for achieving safety, and that they help developers nd assurance deficits in their safety case arguments. The case study reports discuss the difficulties of applying the patterns, particularly in the case of users who are unfamiliar with the approach, and the authors recognise in response the need for better instructional material. But the results show that as part of the development of best practice in safety, the patterns promise signicant benets to industrial safety case creators.
Abstract. We report for the first time on finding shortest path solutions for the travelling salesman problem (TSP) using hybrid "in materio" computation: a technique that uses search algorithms to configure materials for computation. A single-walled carbon nanotube (SWCNT) / polymer composite material deposited on a micro-electrode array is configured using static voltages so that voltage output readings determine the path order in which to visit cities in a TSP. Our initial results suggest that the hybrid computation with the SWCNT material is able to solve small instances of the TSP as efficiently as a comparable evolutionary search algorithm performing the same computation in software. Interestingly the results indicate that the hybrid system's search performance on TSPs scales linearly rather than exponentially on these smaller instances. This exploratory work represents the first step towards building SWCNT-based electrode arrays in parallel so that they can solve much larger problems.
Model Based Systems Engineering (MBSE) has encouraged the use of a single systems model in languages such as SysML that fully specify the system and which form the basis of all development effort. However, using SysML models for safety analysis has been restricted by the lack of defined modelling standards for analytical techniques like Fault Tree Analysis (FTA). In lieu of such standards, the ENCASE project has formulated a simple SysML profile that captures the information required to represent fault trees and which enables the linkage of failure modes to other parts of the SysML model. Unlike traditional fault trees that can be difficult to validate against a system design, associating failure modes with system functions and hardware components means that consistency checks between the two models are possible, and changes to the SysML design are easier to identify against the corresponding fault tree model. Common definitions of the system specification improves the quality of both safety analysis and assurance, and the alignment of the two models enables us to make the first steps towards the automatic translation of parts of the system design into fault trees.
We present what we believe is the first attempt to physically reconstruct the exploratory mechanism of genetic regulatory networks. Feedback plays a crucial role during developmental processes and its mechanisms have recently become much clearer due to evidence from evolutionary developmental biology. We believe that without similar mechanisms of interaction and feedback, digital genomes cannot guide themselves across functional search spaces in a way that fully exploits a domain's resources, particularly in the complex search domains of real-world physics. Our architecture is designed to let evolution utilise feedback as part of its mechanism of exploration.
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