Continuous probability distributions in model-based specification languages

PhD ThesisModel-based speci cation languages provide a means for obtaining assurance of dependability of complex computer-based systems, but provide little support for modelling and analysing fault behaviour, which is inherently probabilistic in nature. In particular, the need for a detailed account of the role of continuous probability has been largely overlooked. This thesis addresses the role of continuous probability in model-based speci cation languages. A model-based speci cation language (sGCL) that supports continuous probability distributions is de ned. The use of sGCL and how it interacts with engineering practices is also explored. In addition, a re nement ordering for continuous probability distributions is given, and the challenge of combining non-determinism and continuous probability is discussed in depth. The thesis is presented in three parts. The rst uses two case studies to explore the use of probability in formal methods. The rst case study, on ash memory, is used to present the capabilities of probabilistic formal methods and to determine the kinds of questions that require continuous probability distributions to answer. The second, on an emergency brake system, illustrates the strengths and weaknesses of existing languages and provides a basis for exploring a prototype language that includes continuous probability. The second part of the thesis gives the formal de nition of sGCL's syntax and semantics. The semantics is made up of two parts, the proof theory (transformer semantics) and the underpinning mathematics (relational semantics). The additional language constructs and semantical features required to include non-determinism as well as continuous probability are also discussed. The most challenging aspect lies in proving the consistency of the semantics when non-determinism is also included. The third part uses a nal case study, on an aeroplane pitch monitor, to demonstrate the use of sGCL. The new analysis techniques provided by sGCL, and how they t in with engineering practices, are explored.EPSRC: The School of Computing Science, Newcastle University: DEPLOY project

The ReSIST Resilience Knowledge Base

We describe a prototype knowledge base that uses semantic web technologies to provide a service for querying a large and expanding collection of public data about resilience, dependability and security. We report progress and identify opportunities to support resilience-explicit computing by developing metadata-based descriptions of resilience mechanisms that can be used to support design time and, potentially, run-time decision making

The Dogrib Birchbark Canoe Project

The Dogrib are one of the Athapaskan, or Dene groups occupying the Mackenzie Valley area in the Northwest Territories (see map). Their hunting canoes, though engineered for traversing a rugged landscape, had elegant and flowing lines. ... Although there is a reasonably good collection of archival photographs of Dogrib canoes, mostly due to the efforts of the anthropologist J. Alden Mason ..., the historical record has preserved little knowledge pertinent to canoe construction and use, and only a small number of canoes have survived in museum collections. During our recent archaeological research on two important Dogrib canoe routes, however, we recorded the remains of nearly 30 hunting canoes .... Today, in the Dogrib communities of Snare Lake, Rae Lakes, Wha Ti and Rae-Edzo, the oral tradition is full of canoeing and canoe-related stories and remembrances, although very few surviving elders actually built one in their youth. This fact, and the large number of canoes recorded in our research, gave us a new appreciation of the importance and role they had played in travel, and led to an exciting cultural revival project: to build and document a Dogrib birchbark canoe. ... [This article briefly describes the canoe project, sharing some of what the elders taught us about Dogrib hunting canoes.

The growth of faults and fracture networks in a mechanically evolving, mechanically stratified rock mass : a case study from Spireslack Surface Coal Mine, Scotland

Fault architecture and fracture network evolution (and resulting bulk hydraulic properties) are highly dependent on the mechanical properties of the rocks at the time the structures developed. This paper investigates the role of mechanical layering and pre-existing structures on the evolution of strike–slip faults and fracture networks. Detailed mapping of exceptionally well exposed fluvial–deltaic lithologies at Spireslack Surface Coal Mine, Scotland, reveals two phases of faulting with an initial sinistral and later dextral sense of shear with ongoing pre-faulting, syn-faulting, and post-faulting joint sets. We find fault zone internal structure depends on whether the fault is self-juxtaposing or cuts multiple lithologies, the presence of shale layers that promote bed-rotation and fault-core lens formation, and the orientation of joints and coal cleats at the time of faulting. During ongoing deformation, cementation of fractures is concentrated where the fracture network is most connected. This leads to the counter-intuitive result that the highest-fracture-density part of the network often has the lowest open fracture connectivity. To evaluate the final bulk hydraulic properties of a deformed rock mass, it is crucial to appreciate the relative timing of deformation events, concurrent or subsequent cementation, and the interlinked effects on overall network connectivity

Core surprise : Characterising the internal structure of an ancient plate boundary fault in Scotland

Knowledge of the structure and rheology of large, earthquake-hosting plate boundary faults is lacking as they are normally poorly exposed or difficult to find on the surface. Recently, several drilling projects have been undertaken to explore the internal structure of active plate boundary fault zones at depth to understand how this constrains seismic slip behaviour. All of these projects highlight the presence and importance of clay-rich rocks within the fault core in controlling slip behaviour along these large faults. The Highland Boundary fault (HBF) in Scotland, provides a rare opportunity to study the internal fault architecture of a well-exposed along-strike section of an ancient plate boundary fault. The HBF extends for over 240 km, however, is only well-exposed along a 560 m section at Stonehaven. Here, serpentinite juxtaposes quartzofeldspathic crustal rocks, a common feature at many plate boundaries (e.g., sections of the San Andreas fault and Alpine fault, New Zealand). We collected six across-fault transects aiming to capture the internal structure of the HBF and its along-strike variability. Within the fault core we discover four mechanically and chemically distinct clay-rich units, which have sharp contacts. Despite evidence of internal strain within the clay-rich fault rocks, relatively intact clasts of wall rock and microfossils are preserved. From mineralogical observations it can be interpreted that the clay-rich rocks along this section of the HBF, formed through fluid-assisted, shear-enhanced chemical reactions between wall rocks of contrasting chemistry. Our field evidence also demonstrates that plate boundary faults can be structurally variable along strike at various scales. The total thickness of the fault core varies from 3 to 10.7 m over an along strike distance of 560 m. Not every unit is laterally continuous along strike, and each unit varies in thickness. We compare our observations with studies on other plate boundary systems. For example, the HBF has analogous thickness and mineralogy to drill core recovered from the San Andreas fault. Highly variable fault core structures and related properties such as mineralogy, may exert significant control on earthquake rupture and slip behaviour at large plate boundaries