Max-balanced flows in oriented matroids

Let M=(E,O) be an oriented matroid on the ground set E. A real-valued vector x defined on E is a max-balanced flow for M if for every signed cocircuit Y∈O⊥, we have maxeεY+Xe=maxeεY−Xe. We extend the admissibility and decomposition theorems of Hamacher from regular to general oriented matroids in the case of max-balanced flows, which gives necessary and sufficient conditions for the existence of a max-balanced flow x satisfying l⩽×⩽u. We further investigate the semilattice of such flows under the usual coordinate partial order, and obtain structural results for the minimal elements. We also give necessary and sufficient conditions for the existence of such a flow when we are allowed to reverse the signs on a subset F⊆E. The proofs of all of our results are constructive, and yield polynomial algorithms in case M is coordinatized by a rational matrix A. In this same setting, we describe a polynomial algorithm that for a given vector w defined on E, either finds a potential p such that w′=w+pA is max-balanced, or a certificate that M has no max-balanced flow

Integral bases and p-twisted digraphs

AbstractA well-known theorem in network flow theory states that for a strongly connected digraph D = (V, A) there exists a set of directed cycles the incidence vectors of which form a basis for the circulation space of D and integrally span the set of integral circulations; that is, every integral circulation can be written as an integral combination of these vectors. In this paper, we extend this result to general digraphs. Following a definition of Hershkowitz and Schneider, we call a digraph p-twisted if each pair of vertices is contained in a closed (undirected) walk with the property that as the walk is traversed there are no more than p changes in the orientations of the arcs. We show that for every p-twisted digraph there exists a set of p-twisted cycles the incidence vectors of which form a basis for the circulation space and integrally span the set of integral circulations. We show that such a set can be computed in O(|||) time

Integral bases and p-twisted digraphs

A well-known theorem in network flow theory states that for a strongly connected digraph D = (V, A) there exists a set of directed cycles the incidence vectors of which form a basis for the circulation space of D and integrally span the set of integral circulations; that is, every integral circulation can be written as an integral combination of these vectors. In this paper, we extend this result to general digraphs. Following a definition of Hershkowitz and Schneider, we call a digraph p-twisted if each pair of vertices is contained in a closed (undirected) walk with the property that as the walk is traversed there are no more than p changes in the orientations of the arcs. We show that for every p-twisted digraph there exists a set of p-twisted cycles the incidence vectors of which form a basis for the circulation space and integrally span the set of integral circulations. We show that such a set can be computed in O(|||) time

Workshop on Techtonic Evolution of Greenstone Belts

Topics addressed include: greenstone belt externalities; boundaries; rock terranes; synthesis and destiny; tectonic evolution; rock components and structure; sedimentology; stratigraphy; volcanism; metamorphism; and geophysics

Tectonic evolution of greenstone belts

Topics addressed include: greenstone belt externalities; boundaries; rock terranes; synthesis and destiny; tectonic evolution; rock components and structure; sedimentology; stratigraphy; volcanism; metamorphism; and geophysics.edited by M.J. deWit and Lewis D. Ashwal.Early Precambrian crustal evolution of South India / Srinivasan, R. -- New insights into typical Archean structures in greenstone terranes of western Ontario / Schwerdtner, W.M. -- Rainy Lake wrench zone: An example of an Archean subprovince boundary in northwestern Ontario / Poulsen, K.H. -- Polyphase thrust tectonics in the Barberton greenstone belt / Paris, I. -- Thermal implications of metamorphism in greenstone belts and the hot asthenosphere-thick continental lithosphere paradox / Morgan,

Foundations of secure computation

Issued as Workshop proceedings and Final report, Project no. G-36-61

Future Computer Requirements for Computational Aerodynamics

Recent advances in computational aerodynamics are discussed as well as motivations for and potential benefits of a National Aerodynamic Simulation Facility having the capability to solve fluid dynamic equations at speeds two to three orders of magnitude faster than presently possible with general computers. Two contracted efforts to define processor architectures for such a facility are summarized

Cinesonica: Sounding the Audiovisuality of Film and Video

The dissertation presents an exploration of neglected and under-theorised aspects of film and video sound. In doing so, the study proposes a sounding of the cinesonic; that is, it considers the deployment of sound within an audiovisual context. The key concern of this dissertation is how we might map and negotiate the materiality of film and video sound both beyond, and in relation to, its signitive dimensions, and what might be at stake in a critical engagement with that materiality. In particular, this sounding engages with the inscription of difference that is common to Saussurian linguistics, signitive formulations of sound-image relations, and notions of what might constitute the properly 'political' in an audiovisual poetics founded on modernist paradigms. The research demonstrates that any coming-to-terms with film and video's materiality needs to be informed by the idea that the material events we term 'the film' or 'the video' are marked by a relationship between sound and image. Thus the dissertation negotiates a sounding of these media in relation to that materiality best described as audiovisuality. The dissertation opens with a consideration of the way in which sound is commonly conceptualised in terms of its relationship with an object source, and how the formulation of sound as signifier militates against an engagement with its material dimensions. The following chapters explore neglected aspects of film and video sound by drawing on a range of theoretical resources predominantly - but not exclusively - derived from the work of Gilles Deleuze, with detailed case study analyses of specific film and video texts, and interviews with filmmakers. The topics covered in these chapters include the phenomenon of optical crackle, electronic sounds, the correspondence of sound and image pejoratively termed 'mickey-mousing', and the organisation and manipulation of sounds in British Scratch Video of the 1980s