Reasoning About the Reliability of Multi-version, Diverse Real-Time Systems

This paper is concerned with the development of reliable real-time systems for use in high integrity applications. It advocates the use of diverse replicated channels, but does not require the dependencies between the channels to be evaluated. Rather it develops and extends the approach of Little wood and Rush by (for general systems) by investigating a two channel system in which one channel, A, is produced to a high level of reliability (i.e. has a very low failure rate), while the other, B, employs various forms of static analysis to sustain an argument that it is perfect (i.e. it will never miss a deadline). The first channel is fully functional, the second contains a more restricted computational model and contains only the critical computations. Potential dependencies between the channels (and their verification) are evaluated in terms of aleatory and epistemic uncertainty. At the aleatory level the events ''A fails" and ''B is imperfect" are independent. Moreover, unlike the general case, independence at the epistemic level is also proposed for common forms of implementation and analysis for real-time systems and their temporal requirements (deadlines). As a result, a systematic approach is advocated that can be applied in a real engineering context to produce highly reliable real-time systems, and to support numerical claims about the level of reliability achieved

Learning 101: The untaught basics

Despite the accessibility of a wealth of information in the current era-books, universities, and online massive open online courses (MOOCs)-well-intentioned and hard-working students often fail to learn effectively due to deficient learning techniques or improper mind-sets. Two things, in particular, hinder students from achieving their potential. First, the students' intuition regarding how learning works is often flawed and counterproductive; second, despite significant progress in the research discipline of "learning sciences," these hard-earned scientific insights have not yet filtered their way through the research community to the students who stand to benefit most from this knowledge

The use of proofs in diversity arguments

The limits to the reliability that can be claimed for a design-diverse fault-tolerant system are mainly determined by the dependence that must be expected in the failure behaviours of the different versions: claims for independence between version failure processes are not believable. In this note we examine a different approach, in which a simple secondary system is used as a back-up to a more complex primary. The secondary system is sufficiently simple that claims for its perfection (with respect to design faults) are possible, but there is not complete certainty about such perfection. It is shown that assessment of the reliability of the overall fault-tolerant system in this case may take advantage of claims for independence that are more plausible than those involved in design diversity

Empty, Useless, and Dangerous? Recent Kantian Replies to the Empty Formalism Objection

Like two heavyweight boxers exchanging punches, but neither landing the knock-out blow, Kantians and Hegelians seem to be in a stand-off on what in contemporary parlance is known as the Empty Formalism Objection. Kant?s ethics is charged with being merely formal and thereby failing to provide the kind of specific guidance that any defensible ethical system should have the resources to provide. Hegel is often credited with having formulated this objection in its most incisive way, and a wealth of Kantian responses has been deployed to answer it. In this paper, I take up the objection as it appears in �135R of Elements of the Philosophy of Right in order to scrutinise the contemporary debate between the two camps. I propose that there are, in fact, three different, albeit connected objections and examine (what I take to be) the best Kantian replies to them. I will not adjudicate which of these replies is the most accurate interpretation of Kant?s texts, nor trace the particular historical context in which Hegel takes up Kant?s ethics, nor the way the Empty Formalism Objection fits into Hegel?s wider system. This is partly because of constraints of space, and partly because many of the contemporary Kantian replies ? for better or for worse ? treat the Empty Formalism Objection as a self-standing philosophical problem, irrespective of its historical context or systematic place in Hegel?s theory. My limited aim here is to show that, even if one grants ? for argument?s sake ? the legitimacy of such a non-contextual approach, significant difficulties remain

The Nature and Nurture of Sports Performance, Blog 6

Student blog posts from the Great VCU Bike Race Book

Reasoning about the Reliability of Diverse Two-Channel Systems in which One Channel is "Possibly Perfect"

This paper considers the problem of reasoning about the reliability of fault-tolerant systems with two "channels" (i.e., components) of which one, A, supports only a claim of reliability, while the other, B, by virtue of extreme simplicity and extensive analysis, supports a plausible claim of "perfection." We begin with the case where either channel can bring the system to a safe state. We show that, conditional upon knowing pA (the probability that A fails on a randomly selected demand) and pB (the probability that channel B is imperfect), a conservative bound on the probability that the system fails on a randomly selected demand is simply pA.pB. That is, there is conditional independence between the events "A fails" and "B is imperfect." The second step of the reasoning involves epistemic uncertainty about (pA, pB) and we show that under quite plausible assumptions, a conservative bound on system pfd can be constructed from point estimates for just three parameters. We discuss the feasibility of establishing credible estimates for these parameters. We extend our analysis from faults of omission to those of commission, and then combine these to yield an analysis for monitored architectures of a kind proposed for aircraft