Discretization and resolution of the (<Emphasis Type="Italic">r</Emphasis>|<Emphasis Type="Italic">X</Emphasis><Subscript><Emphasis Type="Italic">p</Emphasis></Subscript>)-medianoid problem involving quality criteria

In this paper an extension of the (r|X _p )-medianoid on networks introduced by Hakimi (1983) is studied. In this extension the customer considers not only the distance but some characteristics of the facilities such as store size, quality of service and parking space. A new firm wants to establishr new facilities which have to compete with thep facilities that already exist in the market. The entry firm wants to find their locations and characteristics to maximize profits. Three different customer choice rules (binary, partially binary and proportional preferences) are considered. Some discretization results are obtained and a resolution procedure is proposed. The problem is solved combining a global search algorithm based on a branch and bound procedure with some combinatorial heuristics (greedy, interchange, and tabu search). Some computational experiences are presented. Partially supported by Ministerio de Ciencia y Tecnología (Spain) and FEDER, grant BFM2002-04525-C02-01.     

A duopolistic spatial competition model with non-zero conjectural variation

Consider a two-stage non-cooperative Cournot game with location choice involving two firms. There aren spatially separated markets located at the vertices of a network. Each firm, first selects the location of a facility and then selects the quantities to supply to the markets in order to maximize its profit. Non-zero conjectural variation at the second stage is studied. Equilibrium in the quantities offered by each firm in the markets exists. Furthermore, when the demand in each market is sufficiently large, each firm chooses to locate its facility at the vertices. Partially financed by FEDER and Ministerio de Ciencia y Tecnología, grant BFM2002-04525-C02-01, and Universidad de Las Palmas de Gran Canaria, grant UNI2004/12     

Electrochemical properties of mesoporous iron phosphate in lithium batteries

Mesoporous iron phosphate containing CTAB as templating agent was synthesized and characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy and TGA techniques. The mesoporous material shows a highly ordered structure, that collapses when submitted to extraction with acetate ions. The treatment of the exchanged samples at 573 K under nitrogen atmosphere leads to amorphous phases with an electrochemical behaviour typical of carbon-coated iron phosphate electrodes. The existence of this coating, proceeding from incomplete pyrolysis of the organic exchange agent, enhances the electronic properties of the system, as evidenced by galvanostatic experiments and impedance spectroscopy measurements.     

Pareto Optimal Allocation and Price Equilibrium for a Duopoly with Negative Externality

A spatial competition model involving decisions made by consumers and firms is proposed. A regulating agent assigns the demand, taking into account the price, transport and externality cost, and minimizing the joint consumer cost to obtain a Pareto optimal allocation. Assuming the Pareto optimal allocation, firms fix prices in order to maximize the profit. An equilibrium problem is studied and some results are presented. The problem and results are illustrated with an example.     

Mg2Si and MSi2 (M=Ca, Fe) silicon alloys as possible anodes for lithium batteries

Several silicon alloys Mg₂Si and MSi₂ (M=Ca, Fe) in powder form have been tested as possible anodes in two electrode cells. These alloys react with lithium to form Li-Si alloys as detected by the X-ray diffraction. However, the initial uptake of lithium is poorer than expected, corresponding to 690, 250 and 100 mAh/g for the Mg, Ca and Fe systems, respectively. All the electrodes exhibit a drastic capacity fade upon cycling. X-Rays diffraction analysis correlated to the galvanostatic tests indicating that there is a mechanical disintegration of the electrode due to the impressive volume changes upon cycling and the lack of a suitable matrix to absorb the mechanical stress. Finally, we have observed that the lithium diffusion coefficients, calculated by the potentiostatic method, are in the order of 10⁻⁹ cm²/s in the initial reduction step of all the systems which is not a limiting factor for using Mg₂Si and MSi₂ (M=Ca, Fe) alloys as possible negative electrodes for Li-ion cells. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Comparison of the electrochemical behaviour of SnO2 and PbO2 negative electrodes for lithium ion batteries

In this paper we report our structural and electrochemical investigations of tin dioxide and lead dioxide electrodes in order to highlight the difference observed between them. The electrochemical reactions of these two oxides are known: the reduction of the metal oxide and the reversible formation/decomposition of the lithium-metal alloys. The reversible capacity of these systems is based on the alloy formation. The first reaction is supposedly irreversible (formation of Li₂O), but the X-ray diffraction analysis and especially¹¹⁹Sn Mössbauer spectrometry show a possible re-oxidation of the metal particles in the case of tin dioxide electrodes. However, this reaction is not fully reversible and occurs at a high potential vs. Li. For lead dioxide electrodes, the re-oxidation of the metal particles seems more difficult in spite of the similar structure of both oxides.