Patterns of commutativity: the commutant of the full pattern

Identified are a number of conditions on square patterns that are closely related to allowing commutativity with the full pattern. Implications and examples that show non-implications are given, along with a graph that summarizes the provided information. A complete description of commutativity with the full pattern is given in both the irreducible case and the reducible case in which there are two irreducible components.info:eu-repo/semantics/publishedVersio

Optical tomography using the SCIRun problem solving environment: Preliminary results for three-dimensional geometries and parallel processing

We present a 3D implementation of the UCL imaging package for absorption and scatter reconstruction from time-resolved data (TOAST), embedded in the SCIRun interactive simulation and visualization package developed at the University of Utah. SCIRun is a scientific programming environment that allows the interactive construction, debugging, and steering of large-scale scientific computations. While the capabilities of SCIRun's interactive approach are not yet fully exploited in the current TOAST implementation, an immediate benefit of the combined TOAST/SCIRun package is the availability of optimized parallel finite element forward solvers, and the use of SCIRun's existing 3D visualisation tools. A reconstruction of a segmented 3D head model is used as an example for demonstrating the capability of TOAST/SCIRun of simulating anatomically shaped meshes

Why do juvenile fish utilise mangrove habitats?

Three hypotheses to discern the strong positive association between juvenile fish and mangrove habitat were tested with field and laboratory experiments. Artificial mangrove structure in the field attracted slightly more juvenile fish than areas without structure. Artificial structure left to accumulate fouling algae attracted four-times the total number of juvenile fish than areas without structure or areas with clean structure. Community composition of fish attracted to structure with fouling algae was different when compared with areas with no structure or clean structure; five species were attracted by structure with fouling algae whilst two species were associated with structure regardless of fouling algae. Algae were linked to increased food availability and it is suggested that this is an important selection criteria for some species. Other species were apparently attracted to structure for different reasons, and provision of shelter appears to be important. Predation pressure influenced habitat choice in small juvenile fish in laboratory experiments. In the absence of predators, small juveniles of four out of five species avoided shelter but when predators were introduced all species actively sought shelter. Large fish were apparently less vulnerable to predators and did not seek shelter when predators were added to their tank. Feeding rate was increased in the mangrove habitat for small and medium-sized fish compared with seagrass beds and mudflats indicating increased food availability or foraging efficiency within this habitat. Larger fish fed more effectively on the mudflats with an increased feeding rate in this habitat compared with adjacent habitats. The most important aspect of the mangrove habitat for small juvenile fish is the complex structure that provides maximum food availability and minimises the incidence of predation. As fish grow a shift in habitat from mangroves to mudflat is a response to changes in diet, foraging efficiency and vulnerability to predators

Nutrient inputs from seabirds and humans on a populated coral cay

Inputs of inorganic nutnents in 1992 from seabirds (white-capped noddy and wedgetail shearwater, maximum of ca 80 000 breeding pairs) are compared to inputs from humans (97 700 person days) on Heron Island at the southern end of the Great Barrier Reef, Australia. We estimated that nod- dies deposited ca 107 t and shearwaters ca 22 t, of fresh guano The composition of fresh noddy guano was 7.3 % nitrogen 1.5 % phosphorus. 60 % moisture and 31.2 % other substances. Assuming a similar composition for shearwaters the total annual deposition of guano contained 9.4 t nitrogen and 1.9 t phosphorus. Experiments examining effects of ageing of guano indicated a large decrease in total nitrogen in guano under humid conditions over 4 d as a result of volatilisation of NH3. Under natural conditions most of the deposited nitrogen is likely to be lost as NH, and a relatively small fraction ot the soluble component leached into the cay, but the precise dynamics will depend on ramfall and wind patterns. Phosphorus was not volatilised from guano under any expenmental conditions. Although inputs of nitrogen and phosphorus from human sewage into the cay system (ca 0.3 t of each) were much less than that from birds, all nutrients from humans are released in liquid form and percolate directly into the cay. Significant seasonal and tidal variations in standing concentratlons of NH3 oxidised forms of nitrogen (NO2,+NO3), and PO4, were detected in the water column around the island. Trends of higher mean concentrations of all nutrients in summer than in winter, and higher concentrations at low tide than at high tide except at sites close to the Island where nutrient levels were high independent of tide suggest that nutrients may be transported from guano on Heron Island into the water immediately surrounding the island The exact fate and mechanisms of transport of all nutnents require further attention