Mean drift forces on arrays of bodies due to incident long waves

The scattering of long water waves by an array of bodies is investigated using the method of matched asymptotic expansions. Two particular geometries are considered, these are a group of vertical cylinders extending throughout the depth and a group of floating hemispheres. From these solutions, the low-frequency limit of the ratio of the mean drift force on a group of N bodies to that on a single body is calculated. For a wide range of circumstances this drift force ratio is N2 which is in agreement with previous numerical work. Further drift force enhancement is possible for certain configurations of vertical cylinders

NASA control research overview

An overview of NASA research activities related to the control of aeronautical vehicles is presented. A groundwork is laid by showing the organization at NASA Headquarters for supporting programs and providing funding. Then a synopsis of many of the ongoing activities is presented, some of which will be presented in greater detail elsewhere. A major goal of the workshop is to provide a showcase of ongoing NASA sponsored research. Then, through the panel sessions and conversations with workshop participants, it is hoped to glean a focus for future directions in aircraft controls research

Sherlock Is Law Abiding

An approach to the semantics of fiction that uses the tools of truth relativism provides an alternative to Meinongian and pretence-based approaches. The approach is consistent with the deep motivations of John Wood's Truth in Fiction

An expectation transformer approach to predicate abstraction and data independence for probabilistic programs

In this paper we revisit the well-known technique of predicate abstraction to characterise performance attributes of system models incorporating probability. We recast the theory using expectation transformers, and identify transformer properties which correspond to abstractions that yield nevertheless exact bound on the performance of infinite state probabilistic systems. In addition, we extend the developed technique to the special case of "data independent" programs incorporating probability. Finally, we demonstrate the subtleness of the extended technique by using the PRISM model checking tool to analyse an infinite state protocol, obtaining exact bounds on its performance

Spontaneity and Materiality: What Photography Is in the Photography of James Welling

Images are double agents. They receive information from the world, while also projecting visual imagination onto the world. As a result, mind and world tug our thinking about images, or particular kinds of images, in contrary directions. On one common division, world traces itself mechanically in photographs, whereas mind expresses itself through painting.1 Scholars of photography disavow such crude distinctions: much recent writing attends in detail to the materials and processes of photography, the agency of photographic artists, and the social determinants of the production and reception of photographs. As such writing makes plain, photographs cannot be reduced to mechanical traces.2 Yet background conceptions of photography as trace or index persist almost by default, as no framework of comparable explanatory power has yet emerged to replace them. A conception of photography adequate to developments in recent scholarship is long overdue. Rather than constructing such a conception top-down, as philosophers are wont to do, this paper articulates it by examining selected works by James Welling.3 There are several reasons for this: Welling’s practice persistently explores the resources and possibilities of photography, the effect of these explorations is to express a particular metaphysics of the mind’s relation to its world, and appreciating why this metaphysics is aptly expressed by exploring photography requires a revised conception of what photography is. In as much as it provides a framework for a richer interpretation of Welling, the new conception is also capable of underwriting a wide range of critical and historical approaches to photography

Probabilistic Rely-guarantee Calculus

Jones' rely-guarantee calculus for shared variable concurrency is extended to include probabilistic behaviours. We use an algebraic approach which combines and adapts probabilistic Kleene algebras with concurrent Kleene algebra. Soundness of the algebra is shown relative to a general probabilistic event structure semantics. The main contribution of this paper is a collection of rely-guarantee rules built on top of that semantics. In particular, we show how to obtain bounds on probabilities by deriving rely-guarantee rules within the true-concurrent denotational semantics. The use of these rules is illustrated by a detailed verification of a simple probabilistic concurrent program: a faulty Eratosthenes sieve.Comment: Preprint submitted to TCS-QAP