A Genetic Algorithm for Solving a Capacitated p-Median Problem

Facility-location problems have several applications, such as telecommunications, industrial transportation and distribution. One of the most well-known facility-location problems is the p-median problem. This work addresses an application of the capacitated p-median problem to a real-world problem. We propose a genetic algorithm (GA) to solve the capacitated p-median problem. The proposed GA uses not only conventional genetic operators, but also a new heuristic “hypermutation” operator suggested in this work. The proposed GA is compared with a tabu search algorithm.     

Precise bounds and asymptotics for the first Dirichlet eigenvalue of triangles and rhombi

We study the asymptotic expansion of the first Dirichlet eigenvalue of certain families of triangles and of rhombi as a singular limit is approached. In certain cases, which include isosceles and right triangles, we obtain the exact value of all the coefficients of the unbounded terms in the asymptotic expansion as the angle opening approaches zero, plus the constant term and estimates on the remainder. For rhombi and other triangle families such as isosceles triangles where now the angle opening approaches π, we have the first two terms plus bounds on the remainder. These results are based on new upper and lower bounds for these domains whose asymptotic expansions coincide up to the orders mentioned. Apart from being accurate near the singular limits considered, our lower bounds for the rhombus improve upon the bound by Hooker and Protter for angles up to approximately 22° and in the range (31°,54°). These results also show that the asymptotic expansion around the degenerate case of the isosceles triangle with vanishing angle opening depends on the path used to approach it.     

Basins of Attraction of Periodic Oscillations in Suspension Bridges

We consider the dynamics of the lowest order transversal vibration mode of a suspension bridge, for which the hangers are treated as one-sided springs, according to the model of Lazer and McKeena [SIAM Review 58, 1990, 537]. We analyze in particular the multi-stability of periodic attractors and the basin of attraction structure in phase space and its dependence with the model parameters. The parameter values used in numerical simulations have been estimated from a number of bridges built in the United States and in the United Kingdom, thus taking into account realistic, yet sometimes simplified, structural, aerodynamical, and physical considerations.     

Conformational and stereoelectronic investigation in 1,2-difluoropropane: The gauche effect

The effect of attaching an additional fluorine atom at C-2 in 1-fluoropropane (FP), giving 1,2-difluoropropane (DFP), on its conformational equilibrium, is theoretically evaluated. This substitution causes critical implications on the conformer stabilities of DFP (TG, GT and GG conformations) and the steric and electrostatic interactions should favor the conformer with fluorine atoms trans. However, the gauche effect plays a major role in describing the energies balance in DFP, shifting the equilibrium towards the conformation in which the two fluorine atoms are gauche. The origin of this effect is discussed through an NBO analysis, which allows the evaluation of both classical and non-classical (hyperconjugation and bent bonds) interactions as the prevailing factors governing the conformational equilibrium of molecules containing the 1,2-difluoroethane fragment.     

Fused pyrazolopyrimidines. I. Pyrazolo[4,3-e]-v-triazolo[1,5-a]pyrimidine. A new heterocyclic system

5-Azido-4-cyano-1-phenylpyrazole reacts with benzylcyanide in the presence of sodium methoxide to give the title ring system.     

Atmospheric selenium in an industrialized area of Portugal

Summary Selenium is determined by instrumental neutron activation analysis (INAA), based on measurement of the long-lived ⁷⁵Se nuclide. In the urban and industrialized areas of Portugal selenium contents have been found of the order of of 0.5-1 ng/m³ in PM10 and PM2.5, according to the data collected since 1994. From November 12, 2001 and for not more than 3 months, the Se contents in PM10 and PM2.5 increased by a factor of 1000 in the northern area of Lisbon. More than other nutrients, selenium illustrates the dichotomy between essentiality and toxicity. There is no legislation on Se for ambient air and on indoor ambient point threshold limit values (US and Germany legislation), were 100 times higher than the abnormal values found that winter. The increase was also visible for mercury although not to such an extent. Attempts were made to understand the trend, going into a study of the emission sources located in the area using both INAA and PIXE. It was concluded that the observation occurred due to abnormal meteorological wind direction, which pushed the pollutants towards the populated area, when usually they flow into the Tagus estuary.     

Nutrients and other elements in honey from Azores and mainland Portugal

The present study aims the identification and quantification of trace elements in samples of honey from the Azores and the Portuguese mainland. Elemental concentrations were determined for Al, Br, Cl, Cs, Cu, Eu, Fe, K, Mg, Mn, Na, Rb, Sb, and Zn. Some of these elements are essential dietary nutrients for humans. The essential elements, K and to a lesser extent Na and Cl were the most abundant in the honey samples. However, overall, the elemental content was very low, inferior to the recommended allowances for daily dietary intake (DDI), with the exception of Na whose concentration exceeded that of the recommended DDI. The results of the present investigation and data reported for other countries compare well. The honeys correlate much better when they are from Azores or from Portugal mainland, however, some good correlations were found between honeys from the islands and the mainland. The color of the honey, which depends of the flower-source, could have a role in the differences and similarities between the different honeys as suggested by the cluster analysis of the data. The correlation between honey, soil, tree bark and lichens, all collected in Azores, was poor.