Funcionalização de nanofibras de carbono em fase gasosa

Dissertação para obtenção do Grau de Mestre em Engenharia Química e Bioquímica

Compact ion-source based on superionic rubidium silver iodide (RbAg4I5) solid electrolyte

Dissertação para obtenção do Grau de Mestre em Engenharia Física

Politicization of non-political events

Spatial analysis and social network analysis typically take into consideration social processes in specific contexts of geographical or network space. The research in political science increasingly strives to model heterogeneity and spatial dependence. To better understand and geographically model the relationship between “non-political” events, streaming data from social networks, and political climate was the primary objective of the current study. Geographic information systems (GIS) are useful tools in the organization and analysis of streaming data from social networks. In this study, geographical and statistical analysis were combined in order to define the temporal and spatial nature of the data eminating from the popular social network Twitter during the 2014 FIFA World Cup. The study spans the entire globe because Twitter’s geotagging function, the fundamental data that makes this study possible, is not limited to a geographic area. By examining the public reactions to an inherenlty non-political event, this study serves to illuminate broader questions about social behavior and spatial dependence. From a practical perspective, the analyses demonstrate how the discussion of political topics fluсtuate according to football matches. Tableau and Rapidminer, in addition to a set basic statistical methods, were applied to find patterns in the social behavior in space and time in different geographic regions. It was found some insight into the relationship between an ostensibly non-political event – the World Cup - and public opinion transmitted by social media. The methodology could serve as a prototype for future studies and guide policy makers in governmental and non-governmental organizations in gauging the public opinion in certain geographic locations.

Ion-beam sources based on superionic solid electrolytes

An ion emitter consisting of a sharp silver tip covered in RbAg4I5 solid electrolyte film has been developed and studied. An accelerating potential is applied and Ag+ ions are emitted from the tip’s apex by field evaporation. The emitted ions are collected by a Faraday cup, producing a current on the pico/nanoampere level which is read by an electrometer. The tips were produced mechanically by sandpaper polishing. The sharpest tip produced had a 2:4 m apex radius. Two deposition methods were studied: thermal vacuum and pulsed laser deposition. The best tip produced a peak current value of 96nA at 180oC, and a quasi-stable 4nA emission current at 160oC, both using an extraction potential of 10kV . The emission dependence on time, temperature and accelerating potential has been studied. Deposited films were characterized by X-ray diffraction (XRD), profilometry, optical and Scanning Electron Microscope (SEM) and Secondary Ion Mass Spectroscopy (SIMS) measurements. Several ion emitters were developed, the latter ones were all able to maintain stable high ion emissions for long periods of time. This investigation was a continuation of an ongoing project backed by the European Space Agency, with the objective of making a proof of concept of this kind of ion emitter with potential application on ion thrusters for orbiting satellites. Going forward, it would be interesting to make a finer analysis of the electrolyte’s conductivity at high temperatures, explore Wien Effect-based emission and to further develop a multi-tip ion emitter prototype.