Wave-generated flow on coral reefs - an analysis for two-dimensional horizontal reef-tops with steep faces

Waves breaking on the seaward rim of a coral reef generate a flow of water from the exposed side of the reef to the sheltered side and/or to either channels through the reef-rim or lower sections of the latter. This wave-generated flow is driven by the water surface gradient resulting from the wave set-up created by the breaking waves. This paper reviews previous approaches to modelling wave-generated flows across coral reefs and discusses the influence of reef morphology and roughness upon these flows. Laboratory measurements upon a two-dimensional horizontal reef platform with a steep reef face provide the basis for extending a previous theoretical analysis for wave set-up on a reef in the absence of a flow [Gourlay, M.R., 1996b. Wave set-up on coral reefs. 2. Set-up on reefs with various profiles. Coastal Engineering 28, 1755] to include the interaction between a unidirectional flow and the wave set-up. The laboratory model results are then used to demonstrate that there are two basic reef-top flow regimes-reef-top control and reef-rim control. Using open channel flow theory, analytical relationships are derived for the reef-top current velocity in terms of the offreef wave conditions, the reef-top water depth and the physical characteristics of the reef-top topography. The wave set-up and wave-generated flow relationships are found to predict experimental values with reasonable accuracy in most cases. The analytical relationships are used to investigate wave-generated flows into a boat harbour channel on Heron Reef in the southern Great Barrier Reef. (c) 2005 Elsevier B.V. All rights reserved.

A probabilistic switch model of information flow in social networks: Application for virtual circuits to organizational design

Network building and exchange of information by people within networks is crucial to the innovation process. Contrary to older models, in social networks the flow of information is noncontinuous and nonlinear. There are critical barriers to information flow that operate in a problematic manner. New models and new analytic tools are needed for these systems. This paper introduces the concept of virtual circuits and draws on recent concepts of network modelling and design to introduce a probabilistic switch theory that can be described using matrices. It can be used to model multistep information flow between people within organisational networks, to provide formal definitions of efficient and balanced networks and to describe distortion of information as it passes along human communication channels. The concept of multi-dimensional information space arises naturally from the use of matrices. The theory and the use of serial diagonal matrices have applications to organisational design and to the modelling of other systems. It is hypothesised that opinion leaders or creative individuals are more likely to emerge at information-rich nodes in networks. A mathematical definition of such nodes is developed and it does not invariably correspond with centrality as defined by early work on networks.