Antenas e superfícies seletivas de freqüência reconfiguráveis para sistemas de comunicação sem fio

This work aims to present how the reconfigurable microstrip antennas and frequency selective surfaces can be used to operate at communication systems that require changing their operation frequency according to system requirements or environmental conditions. The main purpose is to present a reconfigurable circular microstrip antenna using a parasitic ring and a reconfigurable dipole frequency selective surface. Thereupon there are shown fundamental topics like microstrip antennas, PIN diodes and the fundamental theory of reconfigurable antennas and frequency selective surfaces. There are shown the simulations and measurements of the fabricated prototypes and it is done an analysis of some parameters like the bandwidth and radiation pattern, for the antennas, and the transmission characteristics, for the frequency selective surface. Copper strips were used in place of the diodes for proof of the reconfigurability concept

Desenvolvimento e caracterização de nanocompósito de resina epóxi com nanopartículas de sílica para revestimento de dutos para transporte de petróleo

The use of polymer based coatings is a promising approach to reduce the corrosion problem in carbon steel pipes used for the transport of oil and gas in the oil industry. However, conventional polymer coatings offer limited properties, which often cannot meet design requirements for this type of application, particularly in regard to use temperature and wear resistance. Polymer nanocomposites are known to exhibit superior properties and, therefore, offer great potential for this type of application. Nevertheless, the degree of enhancement of a particular property is greatly dependent upon the matrix/nanoparticle material system used, the matrix/nanoparticle interfacial bonding and also the state of dispersion of the nanoparticle in the polymer matrix. The objective of the present research is to develop and characterize polymer based nanocomposites to be used as coatings in metallic pipelines for the transportation of oil and natural gas. Epoxy/SiO2 nanocomposites with nanoparticle contents of 2, 4, and 8 wt % were processed using a high-energy mill. Modifications of the SiO2 nanoparticles‟ surfaces with two different silane agents were carried out and their effect on the material properties were investigated. The state of dispersion of the materials processed was studied using Scanning and Transmission Electron Microscopy (SEM and TEM) micrographs. Thermogravimetric analysis (TG) were also conducted to determine the thermal stability of the nanocomposites. In addition, the processed nanocomposites were characterized by dynamic mechanical analysis (DMA) to investigate the effect of nanoparticles content and silane treatment on the viscoelastic properties and on the glass transition temperature. Finally, wear tests of the pin-on-disc type were carried out to determine the effects of the nanoparticles and the silane treatments studied. According to the results, the addition of SiO2 nanoparticles treated with silane increased the thermal stability, the storage modulus and Tg of the epoxy resin and decreased wear rate. This confirms that the interaction between the nanoparticles and the polymer chains plays a critical role on the properties of the nanocomposites

Mecanismos de desgaste, história térmica e ciclo de vida de componentes de um motor de combustão interna de aeromodelo

We developed an assay methodology that considered the temperature variation and the scanning electron microscopy as a method to quantify and characterize respectively the consumption evolution in three 46 LA machines, with internal combustion and two-stroke engines, 7.64 cm3 cylinder capacity, 23.0 millimeters diameter and 18.4 millimeters course, RPM service from 2.000 to 16.000 rpm, 1.2 HP power, and 272 grams weight. The investigated engines components were: (1) head of the engine (Al-Si alloy), (2) piston (Al-Si alloy) and (3) piston pin (AISI 52100 steel). The assays were carried out on a desktop; engines 1 and 2 were assayed with no load, whereas in two assays of engine 3 we added a fan with wind speed that varied from 8.10 m/s to 11.92 m/s, in order to identify and compare the engine dynamic behavior as related to the engines assayed with no load. The temperatures of the engine s surface and surroundings were measured by two type K thermopairs connected to the assay device and registered in a microcomputer with data recording and parameters control and monitoring software, throughout the assays. The consumed surface of the components was analyzed by scanning electron microscopy (SEM) and microanalysis-EDS. The study was complemented with shape deformation and mass measurement assays. The temperature variation was associated with the oxides morphology and the consumption mechanisms were discussed based on the relation between the thermal mechanical effects and the responses of the materials characterization

Reformas administrativas no Brasil: o caso do governo do estado do Piauí

From the 1980s, with technological development, globalization, and in a context of increasingly urgent demands, there is an international movement to modernize the state structures. Being driven by the victory of conservative governments in Britain and the U.S., this speech reform comes only to Brazil in the 1990s, the government of Fernando Henrique Cardoso. Thus, in view of the recent movement of states to implement this reform agenda in their structures this research was to identify the elements that made it possible to attempt to modernize the administrative structure of the state of Piauí in 2003, in view of the political and administrative career in which the state was entered. Seeking to clarify the problem studied here, through a case study carried out a descriptive and exploratory, using a technique of gathering data to document research and interviews semi-structured. As the lens of analysis for this study used the neo-historical and sociological institutionalism, through which it sought to identify the critical moment in which they gave the Administrative Reform of Piaui, the process of breaking with the political and administrative career that previously had being followed, and the isomorphic mechanisms that enabled this speech reform comes up to this state, mechanisms that allow the homogenization of the organizational field. In general it appears that the search for new patterns and new technologies for management by the states in Brazil is due to the context of fiscal crisis in which the states were entered, forcing them to seek alternative models of management . The process of diffusion of New Public Management agenda for the states became possible, among other factors, due to the new scenario in which was inserted into the Brazilian federal system in the second half of the 1990s, characterized by a greater articulation between the horizontalstates, where through the mechanisms of isomorphic institutional change was made possible by the absorption of the speech states reformer of the 1990s. However, due to the specificities of each region is given the experiences state unevenly. In the case of Piauí Administrative Reform only became possible due to the rearrangement of political forces in the state and the mechanisms of isomorphic institutional change, which allowed, in 2003, the state government to absorb the speech reformer

A relação entre o microcrédito e o capital social : o caso do CEAPE PI

This study consists of a study on the presence of relationship between social capital and solidarity groups to endorse the Center for Support to Small Businesses - CEAPE - PI, the capital was measured by confidence levels and associations, considering trust as the expectations want, and learned associations between people and how the interactions among members within a group and between groups. The central research question seeks to identify whether there are linkages between the levels of social capital and the profile of members of the solidarity group CEAPE-PI. The overall objective is to analyze the level of social capital and whether these vary with the change in the profile of the solidarity group members. The method adopted in perspective cross-examined the level of social capital found in 300 of solidarity group members, collected through a survey research related to the profile of the solidarity group members, obtained with the CEAPEPI. The data show that micro-credit groups have relatively high levels for most variables, but to relate to the profile of microcredit results demonstrate the interesting points of analysis