Abstract
For a spatial stochastic epidemic model we investigate in the pair approximation scheme the differential equations for the moments. The basic reinfection model of susceptible-infected-recovered-reinfected or SIRI type is analysed, its phase transition lines calculated analytically in this pair approximation.

Abstract
Ubiquitous Computing Systems are characterized by a collection of devices working together autonomically. Due to the fact that these systems are composed by a high number of devices, several problems arise. These problems range from management, compatibility to economic costs. In this paper some essential characteristics of sensors and actuators are proposed in order to allow them to be included in a Ubiquitous Computing System. It is also presented a way to build ubiquitous systems by integration of several independent systems, creating one system with new features that could not be found in the original Ubiquitous Systems.

Abstract
The use of the scintillation produced in the charge avalanches in GEM holes as signal amplification and readout is investigated for xenon. A VUV-sensitive avalanche photodiode has been used as photosensor. Detector gains of about 4 x 104 are achieved in scintillation readout mode, for GEM voltages of 490 V and for a photosensor gain of 150. Those gains are more than one order of magnitude larger than what is obtained using charge readout. In addition, the energy resolutions achieved with the scintillation readout are lower than those achieved with charge readout. The GEM scintillation yield in xenon was measured as a function of GEM voltage, presenting values that are about a half of those achieved for the charge yield, and reach about 730 photons per primary electron at GEM voltages of 490 V.

Abstract

Abstract
The xenon secondary scintillation yield was studied as a function of the electric field in the scintillation region, in a gas proportional scintillation counter operated at room temperature. A large area avalanche photodiode was used for the readout of the VUV secondary scintillation produced in the gas, together with the 5.9 keV x-rays directly absorbed in the photodiode. The latter was used as a reference for the determination of the number of charge carriers produced by the scintillation pulse and, thus, the number of VUV photons impinging the photodiode. A value of 140 photons/kV was obtained for the scintillation amplification parameter. The attained results are in good agreement with those predicted, for room temperature, by Monte Carlo simulation and Boltzmann calculations, as well as with those obtained for saturated xenon vapour, at cryogenic temperatures, and are about a factor of two higher than former results measured at room temperature.

Abstract
The first's library projects occur some years ago with digitization, but just in 1996, the first's web archive initiatives start occurring. Such, was based in the Internet growth and in its increasing use, items that revealed to be an opportunity to transform and readapt the traditional library services. In this context, search engines play a fundamental role of support to the new paradigm of knowledge, by capturing, storing and providing access to the resources, allowing the existence of a digital library in each computer with internet access. In this article we analyze the ways of developing a digital library, taking higher attention to the web harvesting technique, and presenting digital libraries capabilities and limitations. Then we fully summarize relevant projects and initiatives, to finally study the role of search engines in what concerns to, digital preservation, access and information diffusion.