Comparative Performance of Tabu Search and Simulated Annealing Heuristics for the Quadratic Assignment Problem

For almost two decades the question of whether tabu search (TS) or simulated annealing (SA) performs better for the quadratic assignment problem has been unresolved. To answer this question satisfactorily, we compare performance at various values of targeted solution quality, running each heuristic at its optimal number of iterations for each target. We find that for a number of varied problem instances, SA performs better for higher quality targets while TS performs better for lower quality targets

An Efficient Implementation of the Robust Tabu Search Heuristic for Sparse Quadratic Assignment Problems

We propose and develop an efficient implementation of the robust tabu search heuristic for sparse quadratic assignment problems. The traditional implementation of the heuristic applicable to all quadratic assignment problems is of O(N^2) complexity per iteration for problems of size N. Using multiple priority queues to determine the next best move instead of scanning all possible moves, and using adjacency lists to minimize the operations needed to determine the cost of moves, we reduce the asymptotic complexity per iteration to O(N log N ). For practical sized problems, the complexity is O(N)

Non-Newtonian ice rheology and the retention of craters on Ganymede

Calculations carried out for craters of varying sizes in a medium with constant temperature T = 173 K yield values for the crater relaxation time t sub e (defined as the time required for the crater depth to become 1/e of its original value) that appear to be too small to account for the observed retention of craters on Ganymede and the other icy satellites. Such a calculation is seriously in conflict with the observed crater population of the surfaces of the icy satellites. In an attempt to reconcile this conflict, possible explanations for the much slower relaxation rate of craters on the icy satellites are considered. It is possible that an admixture of silicates in the surface ice regions of the icy satellites may raise the viscosity to some extent. This possible explanation and others are briefly discussed

A degenerate PCR-based strategy as a means of identifying homologues of aminoglycoside and ß-lactam resistance genes in the gut microbiota

peer-reviewedBackground: The potential for the human gut microbiota to serve as a reservoir for antibiotic resistance genes has been the subject of recent discussion. However, this has yet to be investigated using a rapid PCR-based approach. In light of this, here we aim to determine if degenerate PCR primers can detect aminoglycoside and β-lactam resistance genes in the gut microbiota of healthy adults, without the need for an initial culture-based screen for resistant isolates. In doing so, we would determine if the gut microbiota of healthy adults, lacking recent antibiotic exposure, is a reservoir for resistance genes. Results: The strategy employed resulted in the identification of numerous aminoglycoside (acetylation, adenylation and phosphorylation) and β-lactam (including bla OXA, bla TEM, bla SHV and bla CTX-M) resistance gene homologues. On the basis of homology, it would appear that these genes originated from different bacterial taxa, with members of the Enterobacteriaceae being a particularly rich source. The results demonstrate that, even in the absence of recent antibiotic exposure, the human gut microbiota is a considerable reservoir for antibiotic resistance genes. Conclusions: This study has demonstrated that the gut can be a significant source of aminoglycoside and β-lactam resistance genes, even in the absence of recent antibiotic exposure. The results also demonstrate that PCR-based approaches can be successfully applied to detect antibiotic resistance genes in the human gut microbiota, without the need to isolate resistant strains. This approach could also be used to rapidly screen other complex environments for target genes.Fiona Fouhy is in receipt of an Irish Research Council EMBARK scholarship and is a Teagasc Walsh fellow. Research in the PDC laboratory is also supported by the Irish Government under the National Development Plan through the Science Foundation Ireland Investigator award 11/PI/113

1977 performance of commercial soybeans in Illinois / 1152

Chiefly tables.Cover title

The AC field effect in germanium whiskers

Call number: LD2668 .T4 1966 H326Master of Scienc