Estudo de novas aplicações da fibra de carbono nos materiais de construção

Dissertação de Mestrado em Engenharia Civil - Área de Especialização Materiais de ConstruçãoO crescente desenvolvimento e aplicação de novos materiais nas últimas décadas permitiram melhorar a qualidade de vida para o ser humano e consequentemente a sociedade em que está inserido. As fibras de carbono têm merecido uma atenção especial devido às suas características particulares, as quais se destacam a sua baixa densidade associada a uma elevada resistência mecânica assim com as suas propriedades eléctricas. Este trabalho apresenta um estudo sobre as propriedades eléctricas e piezoelectricas das fibras de carbono. Estudou-se a aplicação de uma nova base de suporte, o silicone, para o fabrico de um compósito com incorporação de fibras de carbono com vista a avaliar as suas propriedades piezoresistivas para funcionar como sensor. De modo a se poder avaliar adequadamente a capacidade sensitiva de cada um dos sensores, realizaram-se ensaios cíclicos e estáticos de deformação. O primeiro, visou o estudo da reversibilidade dos valores lidos assim como a extracção das curvas de calibração que permitam efectuar uma relação com a deformação que se encontra aplicada no sensor. Já o ensaio em condições estáticas permitiu avaliar a evolução das leituras em condições de deformação constante e assim verificar a sua estabilidade ao longo do tempo. O estudo ficou concluído com a avaliação da sua aplicabilidade prática em que se sujeitou os sensores às condições reais de obra, onde foram colocados nos solos das fundações das estruturas a construir, devidamente escolhidas para o efeito. Estudou-se igualmente as propriedades termoeléctricas das fibras de carbono quando incorporadas num material base de suporte com a finalidade de este poder actuar como um elemento capaz de produzir radiação térmica quando sujeito a uma corrente eléctrica. Foram desenvolvidas placas com incorporação de fibras de carbono em diferentes quantidades, que simularam um pavimento radiante. Estas placas serviram para quantificar o consumo energético e determinar poder calorífico radiante máximo. Por ultimo, foi realizada uma comparação quantitativa das placas desenvolvidas neste trabalho com as placas comercialmente disponíveis no mercado.The rapid development of new materials in the last few decades has allowed a significant improvement of the quality of life. Special attention has been given to carbon fibbers due to its unique properties; which combines the low density with high mechanical properties and interesting electrical properties. In this research work, a study was carried out to assess the electrical and piezoelectric properties of the carbon fibbers. A new composite, using a silicone rubber as binder, reinforced with carbon fibbers was developed that can act as a sensor. In order to properly evaluate the sensor sensitivity, a set of experimental tests was carried out in the laboratory. The sensors were submitted to compressive cyclic loading and to a prolonged constant deformation test. The first one aimed at studying the reversibility of the measurements under cycling loading in order to estimate the calibration curves, and establish a relationship between electrical resistance and the applied deformation. The constant deformation test allowed the evaluation of electrical resistance readings when submitted to constant deformation for a long period of time. Polymers are known to be sensitive to creep and as such this test was important for evaluating the practical application of the sensor. Furthermore, the sensors were applied in the real environment conditions on a construction site and their performance was monitored. Sensors were placed under the foundation and hence registered the real movements of the soil. Also in this research work, the thermoelectric properties of carbon string were studied when placed within gypsum and polymeric boards, so that the resulting composite could act as an element capable of thermal radiation, when plugged into an electric current. Boards were developed with deferent amounts of carbon strings simulating thermal radiation pavement and electrical consumptions were estimated. The results obtained indicate that it is possible to manufacture sensors using carbon fibre reinforced polymers for general application in construction industry. Furthermore, the gypsum and polymer reinforced with carbon strings can be used for thermal radiation pavements with lower energy consumption

Proposal of a New Parameter for the Weathering Characterization of Carbonate Flysch-Like Rock Masses: The Potential Degradation Index (PDI)

The susceptibility of clay bearing rocks to weathering (erosion and/or differential degradation) is known to influence the stability of heterogeneous slopes. However, not all of these rocks show the same behaviour, as there are considerable differences in the speed and type of weathering observed. As such, it is very important to establish relationships between behaviour quantified in a laboratory environment with that observed in the field. The slake durability test is the laboratory test most commonly used to evaluate the relationship between slaking behaviour and rock durability. However, it has a number of disadvantages; it does not account for changes in shape and size in fragments retained in the 2 mm sieve, nor does its most commonly used index (Id2) accurately reflect weathering behaviour observed in the field. The main aim of this paper is to propose a simple methodology for characterizing the weathering behaviour of carbonate lithologies that outcrop in heterogeneous rock masses (such as Flysch slopes), for use by practitioners. To this end, the Potential Degradation Index (PDI) is proposed. This is calculated using the fragment size distribution curves taken from material retained in the drum after each cycle of the slake durability test. The number of slaking cycles has also been increased to five. Through laboratory testing of 117 samples of carbonate rocks, extracted from strata in selected slopes, 6 different rock types were established based on their slaking behaviour, and corresponding to the different weathering behaviours observed in the field.This work was funded by the University of Alicante under the project GRE14–04, the Ministerio de Economía y Competitividad del Gobierno de España in the framework of the projects TIN2014-55413-C2-2-P and TEC2011-28201-C02-02

An approach for characterising the weathering behaviour of Flysch slopes applied to the carbonatic Flysch of Alicante (Spain)

Various studies indicate that most of the slope instabilities affecting Flysch heterogeneous rock masses are related to differential weathering of the lithologies that make up the slope. Therefore, the weathering characteristics of the intact rock are of great importance for the study of these types of slopes and their associated instability processes. The main aim of this study is to characterise the weathering properties of the different lithologies outcropping in the carbonatic Flysch of Alicante (Spain), in order to understand the effects of environmental weathering on them, following slope excavation. To this end, 151 strata samples obtained from 11 different slopes, 5–40 years old, were studied. The lithologies were identified and their mechanical characteristics obtained using field and laboratory tests. Additionally, the slaking properties of intact rocks were determined, and a classification system proposed based on the first and fifth slake cycles (Id1 and Id5 respectively) and an Index of Weathering (IW5), defined in the study. Information obtained from the laboratory and the field was used to characterise the weathering behaviour of the rocks. Furthermore, the slaking properties determined from laboratory tests were related to the in-situ weathering properties of rocks (i.e., the weathering profile, patterns and length, and weathering rate). The proposed relationship between laboratory test results, field data, and in-situ observations provides a useful tool for predicting the response of slopes to weathering after excavation during the preliminary stages of design.This work was partially funded by the University of Alicante under the projects vigrob-157 uausti10–18, uausti11–11 and gre09–40 and by the Generalitat Valenciana within project gv/2011/044

Will otas expansion be a threat to the hotel industry?

This dissertation studies essentially how Airbnb and Google could change the current paradigm of online travel agents’ industry (OTAs), in the sense that, these entrances would erode the duopoly from Booking.com and Expedia, a duopoly that has been increasing the commissions percentage and controlling the hotel booking process. With the OTAs market gaining relevance and representing more than 50% of total hotel revenue in 2019, this is a sensible market for the hotel industry. To measure the direct effects of these OTAs’ market expansion on hotel industry, specifically on NH Hotel Group’s value drivers three cases were analyzed: Scenario 1a, where Airbnb would enter in the market with reduced commissions (4%) and gaining 10% of OTAs’ market share; Scenario 1b, where Airbnb would enter in the same conditions but now gaining 25% of OTAs’ market share; Scenario 2, where Google would enter in the market and reduce commissions absolute amount in 25%. I concluded that the direct effects of any of these scenarios would not be a threat to NH since it leads to a better position of NH versus OTAs’ market, revealing an increase in the return to NH Hotel Group’sshareholders from the previously expected 19.9% (base case) to 66.3%

SecRush – New Generation Vulnerability Management Framework

Tese de Mestrado, Segurança Informática, 2022, Universidade de Lisboa, Faculdade de CiênciasVulnerabilities have been increasing over the years without signs of decreasing soon. With this ex ponential growth, it is important for organizations to define a vulnerability management plan to proceed with what should be done if they encounter a vulnerability. However, existing plans and metrics do not fit the current reality. Existing plans are not independent of vulnerability detection tools. The classifica tion systems currently used (the most common is CVSS) fail to provide information on the variation of risk that a particular vulnerability entails for the organization. As this is not constant, being exception ally high when there is a form of active exploitation, as well as its location in the network and business needs. SecRush presents itself as a new vulnerability management framework with a new risk-based vulnerability management process. It has a set of procedures inspired by agile methodologies to mitigate vulnerabilities and a new classification system - SecScore – able to provide a prioritization in context with the organization. SecScore varies its ranking through temporal factors (specific risk index depend ing on the organization’s risk appetite and the availability of an exploit) and environmental factors (asset visibility to the external network and importance of the asset to the organization’s mission). This project intends not only to contribute with a set of procedures independent of the security tools used but also to improve the currently existing classification systems for prioritization, which cannot adapt to the different contexts in which they are found

Saint Sebastian. An iconographic study: From painting to film

Este artículo busca una primera aproximación que permita una mejor comprensión sobre la iconografía de San Sebastián tomando, en primer lugar, como referencia lo que sobre él recogen las fuentes literarias tales como la Passio y su reflejo en el arte. En segundo lugar, se analiza la evolución de la iconografía de este santo militar hasta el arte contemporáneo, partiendo de las fuentes escritas, así como la influencia de su modelo iconográfico y su primer martirio en los medios audiovisuales actuales, tomando como ejemplo una gran cantidad de obras representativas entre las que se destacan seis pinturas medievales, siete pinturas renacentistas, un grabado del siglo XV, una escultura renacentista, cinco pinturas barrocas, dos dibujos del siglo XX, dos ejemplospictóricos siglo XXI y cuatro fotogramas de películas representativas, tanto de su contexto europeo como americano.This ’article aims to show a first approximation which allows a better understanding of the iconography of St Sebastian. Firstly, it will be considered what literary sources such as Passio refers about him. Secondly, this thesis will analyze the evolution of the iconography of this military saint until Contemporary art, taking into account some written sources. Finally, it will be given consideration to the influence of his iconographic model and his first martyrdom in audiovisual media, taking as an example a large number of representative works, among which six medieval paintings, seven Renaissance paintings, a fifteenth-century engraving, a Renaissance sculpture, five baroque paintings, two twentieth-century drawings, two XXI-century pictorial examples and four stills stand out. of representative films, both from its European and American context