Safety Case Patterns: Theory and Applications

We develop the foundations for a theory of patterns of safety case argument structures, clarifying the concepts involved in pattern specification, including choices, labeling, and well-founded recursion. We specify six new patterns in addition to those existing in the literature. We give a generic way to specify the data required to instantiate patterns and a generic algorithm for their instantiation. This generalizes earlier work on generating argument fragments from requirements tables. We describe an implementation of these concepts in AdvoCATE, the Assurance Case Automation Toolset, showing how patterns are defined and can be instantiated. In particular, we describe how our extended notion of patterns can be specified, how they can be instantiated in an interactive manner, and, finally, how they can be automatically instantiated using our algorithm

Automating the Generation of Heterogeneous Aviation Safety Cases

A safety case is a structured argument, supported by a body of evidence, which provides a convincing and valid justification that a system is acceptably safe for a given application in a given operating environment. This report describes the development of a fragment of a preliminary safety case for the Swift Unmanned Aircraft System. The construction of the safety case fragment consists of two parts: a manually constructed system-level case, and an automatically constructed lower-level case, generated from formal proof of safety-relevant correctness properties. We provide a detailed discussion of the safety considerations for the target system, emphasizing the heterogeneity of sources of safety-relevant information, and use a hazard analysis to derive safety requirements, including formal requirements. We evaluate the safety case using three classes of metrics for measuring degrees of coverage, automation, and understandability. We then present our preliminary conclusions and make suggestions for future work

Change in Mental Models of ADAS in Relation to Quantity and Quality of Exposure

69A3551747131Given the importance of mental models towards safe interaction with Advanced Driver Assistance Systems (ADAS) and the various human factors challenges regarding ADAS such as miscalibrated trust and the effect on workload, it is important to understand how different types of driving experiences and exposures affect drivers\u2019 mental models about ADAS. The objective of this study was to examine how the frequency and quality of exposure (exposure defined as driving through events or situations that have some bearing on the functions of the Adaptive Cruise Control (ACC)) affect drivers\u2019 mental models about ACC, their trust, workload, and their use of the systems as measured by their behaviors around disengaging ACC

Role of twins in peak effect phenomenon observed at microwave frequencies in high Tc superconductor thin films

Measurements of microwave surface resistance, Rs, at subcritical currents as a function of temperature with varying dc magnetic field upto 0.8 T have shown peak effect (PE) in epitaxial DyBa2Cu3O7-δ (DBCO) and YBa2Cu3O7-δ (YBCO) thin films grown by pulsed laser deposition on <100> LaAlO3 substrates. Microwave measurements were performed on microstrip resonators as test vehicles. Occurrence of a peak in Rs in dc magnetic field is governed by the nature and concentration of defects. Evidence shows that thinner films with a higher ratio of areal density of extended defects, ne (such as twin boundaries), to the areal density of point defects, np, show PE at the measurement frequencies 4.88 and 9.55 GHz; whereas, thicker films (≥3000 Å) with a smaller ne/np ratio do not show PE. 2500 Å thick YBCO film shows a double peak structure at 9.55 GHz, thereby suggesting two sets of twin boundaries in this film having different κp values. Measurements carried out on low-twinned LaAlO3 substrates show that 2400 Å thick DBCO film does not exhibit the PE phenomenon at 4.88 GHz upto to an applied field of 0.8 T; this indicates that twins propagated from the LaAlO3 substrates are responsible for the occurrence of PE at microwave frequencies. Oxygen ion irradiation (90 MeV, 3 × 10^13 ions/cm2) of 2500 Å DBCO film has been found to shift the peak to lower temperature at 4.88 GHz, but significantly suppress the peak at 9.55 GHz. Depinning frequency, ωp vs. T plot obtained for the 2400 Å DBCO film shows a peak due to the peak in its Rs vs. T plots.