Dichotomy for tree-structured trigraph list homomorphism problems

Trigraph list homomorphism problems (also known as list matrix partition problems) have generated recent interest, partly because there are concrete problems that are not known to be polynomial time solvable or NP-complete. Thus while digraph list homomorphism problems enjoy dichotomy (each problem is NP-complete or polynomial time solvable), such dichotomy is not necessarily expected for trigraph list homomorphism problems. However, in this paper, we identify a large class of trigraphs for which list homomorphism problems do exhibit a dichotomy. They consist of trigraphs with a tree-like structure, and, in particular, include all trigraphs whose underlying graphs are trees. In fact, we show that for these tree-like trigraphs, the trigraph list homomorphism problem is polynomially equivalent to a related digraph list homomorphism problem. We also describe a few examples illustrating that our conditions defining tree-like trigraphs are not unnatural, as relaxing them may lead to harder problems

Transitions in the cryptocurrency market during the COVID-19 pandemic: A network analysis

In this letter, we identify the transitions of the cryptocurrency market during the pandemic by means of a network analysis. This method allows us to observe that COVID-19 significantly affected cryptocurrencies during a short period of financial panic, from 12 March 2020 to 1 April 2020, giving rise to a remarkable increase of market synchronisation. However, since April 2020, the cryptocurrency market progressively recovered its initial state, since the strong synchronisation, observed as a consequence of COVID-19, continuously disappeared. Therefore, our analysis highlights different market phases, which can be related to some of the phenomena reported in the existing literature

The illusion of the metaverse and meta-economy

This paper provides (i) a review of the existing literature on the metaverse and (ii) an empirical assessment of the current state of the Web3 meta-economy, with the focus on economic governance and metaverse commerce. We have analysed the entire Web3 metaverse niche, i.e. both the 196 available metaverse fungible tokens and all the non-fungible token (NFT) transactions belonging to the metaverse marketplace. Our results showed that economic governance is based on metaverse tokens that cannot be defined as reliable virtual currencies due to their explosive behaviour, negative performance, and higher volatility compared to traditional alternatives. Paradoxically, fiat currencies and stablecoins could be more appropriate candidates for the payment infrastructure. Moreover, we also observed that NFT prices are affected by the cryptocurrency market, which highlights the risk of metaverse commerce. For future research, developers and scholars must assess the different alternatives and infrastructures that can make the metaverse a persistent reality with a proper virtual economy. However, at present, it seems that the hype has run far ahead of reality

The diffusion of Internet: a cross-country analysis

This paper analyzes the process of Internet diffusion across the world using a panel of 214 countries during the period 1990-2004. Countries are classified as low and high-income and it is shown that the diffusion process is characterized by a different S-shape in each group. The estimated diffusion curves provide evidence of very slow "catching up". The paper also explores the determinants of Internet diffusion and shows that network effects are crucial to explain this process. One important finding is that the degree of competition in the provision of Internet contributes positively to its diffusion.Technological diffusion, Internet, S-shape curve, Network externalities, Digital divide

Male fertility and type 2 diabetes mellitus: effect of white tea

Diabetes mellitus (DM) is one of the major public health problems and its increase incidence is closely related with a decrease in birth rates. Male infertility related with type 2 DM (T2DM) has been linked to reactive oxygen species (ROS) overproduction and increased testicular oxidative stress (OS). Tea is one of the most widely consumed beverages and its antihyperglycemic and antioxidant potential has been reported. Herein, we hypothesized that White Tea (WTEA) consumption by T2DM rats could prevent testicular OS preserving sperm quality. For that purpose, we used a neonatal STZ-induced diabetic rat model. At one month of age, water was substituted by WTEA during two months and testicular antioxidant potential and OS were evaluated, as well as sperm parameters in normal and T2DM rats drinking water or WTEA. WTEA consumption improved glucose tolerance and insulin sensitivity in T2DM rats. WTEA consumption restored protein oxidation and lipid peroxidation to normal levels. Testicular antioxidant potential was increased by WTEA consumption in T2DM, while testicular OS was decreased. Nevertheless, glutathione content and redox state was not altered. After WTEA consumption by T2DM rats, sperm concentration was improved while sperm motility, viability and the abnormal spermatozoa reached normal values evidencing that epididymal sperm quality was restored. Overall, our results show that WTEA consumption causes an important improvement in sperm parameters and thus in male T2DM reproductive function, due to a significant decrease in testes ROS production. WTEA consumption can be a natural, economical and good strategy to counteract the deleterious effects of T2DM in male reproductive function.A diabetes mellitus é um dos principais problemas de saúde pública e seu aumento de incidência está intimamente relacionado com a diminuição das taxas de natalidade. A infertilidade masculina relacionada com a diabetes tipo 2 tem sido associada ao aumento de produção de espécies reactivas de oxigénio e ao aumento do stress oxidativo testicular. O chá é uma das bebidas mais consumidas no mundo e o seu potencial anti hiperglicémico e antioxidante tem sido descrito em diversos estudos. Com este trabalho pretende-se investigar se o consumo de chá branco por ratos diabéticos tipo 2 pode prevenir o stress oxidativo testicular e assim preservar a qualidade espermática. Para essa finalidade, utilizou-se um modelo de rato diabético tipo 2 induzido por streptozotocina. Em animais com um mês de idade, a água foi substituída por chá branco durante dois meses e após esse período o potencial antioxidante e o stress oxidativo nos testículos foi avaliado, bem como os parâmetros espermáticos em ratos normais e em ratos diabéticos tipo 2 que consumiram água ou chá branco. O consumo de chá branco melhorou a tolerância à glucose e a sensibilidade à insulina em ratos diabéticos tipo 2. Restaurou ainda os níveis de oxidação proteica e de peroxidação lipídica para níveis presentes em ratos controlo. O potencial antioxidante testicular foi aumentado pelo consumo de chá branco em ratos diabéticos tipo 2, enquanto o stress oxidativo testicular foi diminuído. No entanto, o teor de glutationa e o seu estado redox não foram alterados. Após o consumo de chá branco por ratos diabéticos tipo 2, a concentração espermática foi aumentada, enquanto a motilidade, a viabilidade e o número de espermatozóides anormais atingiram valores normais, evidenciando que a qualidade dos espermatozóides epididimais foi restaurada. No geral, estes resultados mostram que o consumo de chá branco provoca uma melhoria acentuada nos parâmetros espermáticos e, portanto, na função reprodutora masculina em diabetes tipo 2, devido a uma diminuição significativa na produção de espécies reactivas de oxigénio nos testículos. O consumo de chá branco pode ser uma estratégia natural e económica para neutralizar os efeitos deletérios da diabetes tipo 2 na função reprodutiva masculina

Gestão sustentável e segura de fluxos de passageiros no corredor suburbano Aveiro – Porto

In 2019 the transport sector was responsible for 25.8% of EU-27 greenhouse gas (GHG) emissions. While urban transport has received much attention from policy makers and the scientific community, intercity passenger transport has not received as much attention. In 2019, intercity trips accounted for 65% of the total kilometres travelled in Portugal and contributed to more than 55% of carbon dioxide (CO₂) and nitrogen oxide (NOᵪ) emissions. The COVID-19 pandemic has negatively affected mobility due to people’s fear of infection and government restrictions and recommendations. The main objectives of this dissertation are to model the supply and demand of passenger transport in the suburban corridor between Aveiro and Porto, determination of the COVID-19 pandemic impact on travelling behaviour and mode choice for different socio-economic levels and travel purposes and estimate the emissions and the impact per passenger before and during the pandemic. An online survey was designed to understand travelling behaviour and preferences and how these factors changed towards the pandemic. Transport was modelled recurring to a logit model based on the utilities of each transport mode, which were calculated considering the mode choice, travel time, and travel cost of each alternative. The output of the transport modelling was the modal split. The impacts considered were CO₂, NOᵪ, PM₂﮳5, PM₁₀, VOC, NMVOC and CO emissions. The emission values were estimated using the fleet characteristics and average speed as input. Results from the survey show a 70% reduction in travel frequency during the pandemic, with teleworking and online classes being the main reasons for this decrease. Before the pandemic, 65% of trips were made by train and 31% by car. During the pandemic, these shares shifted to 37% and 60%, respectively, and 27% of participants stopped travelling. The logit model was revealed to be a helpful tool for transport modelling. However, the network characteristics, availability of transport modes and sample size limited the statistical significance and accuracy of the model. Air pollution costs decreased by about 53% during the pandemic, primarily due to a decrease in travel frequency.Em 2019, o sector dos transportes foi responsável por 25,8% das emissões de gases com efeito de estufa (GEE) da UE-27. Embora os transportes urbanos tenham recebido muita atenção dos decisores políticos e da comunidade científica, o transporte interurbano de passageiros não tem recebido tanta atenção. Em 2019, as viagens em estradas rurais e autoestradas representaram 65% do total de quilómetros percorridos em Portugal e contribuíram para mais de 55% das emissões de dióxido de carbono (CO₂) e óxidos de azoto (NOᵪ). A pandemia COVID-19 afetou negativamente a mobilidade devido ao medo de infeção das pessoas e restrições e recomendações governamentais. Os principais objetivos desta dissertação são modelar a oferta e a procura de transporte de passageiros no corredor suburbano entre Aveiro e Porto, a determinação do impacto da pandemia COVID-19 nos hábitos de deslocações e escolha de modo para diferentes níveis socioeconómicos e propósitos de deslocação e estimar as emissões e o impacto por passageiro por passageiro antes e durante a pandemia. Um inquérito online foi concebido para compreender os hábitos e preferências de transporte, e como estes fatores mudaram durante a pandemia. O transporte foi modelado recorrendo a um modelo logit baseado nas utilidades de cada modo de transporte, que foram calculados considerando a escolha do modo, o tempo de viagem e o custo de viagem de cada alternativa. O produto desta modelação de transportes foi a distribuição modal. Os impactos considerados foram as emissões de CO₂, NOᵪ, PM₂﮳5, PM₁₀, VOC, NMVOC e CO. As emissões foram estimadas utilizando como dados as características da frota e a velocidade média. Os resultados do inquérito mostram uma redução de 70% na frequência de deslocações durante a pandemia, sendo o teletrabalho e as aulas online as principais razões desta diminuição. Antes da pandemia, 65% das viagens eram feitas de comboio e 31% de carro. Durante a pandemia, estas percentagens mudaram para 37% e 60%, respetivamente, e 27% dos participantes deixaram de viajar. O modelo logit foi revelou-se uma ferramenta útil para a modelação de transporte. No entanto, as características da rede, a disponibilidade de modos de transporte e o tamanho da amostra limitaram a significância estatística e a precisão do modelo. Os custos da poluição atmosférica diminuíram cerca de 53% durante a pandemia, principalmente devido à diminuição da frequência de viagem.Mestrado em Engenharia Mecânic

The emptying of the metanarratve: Foucault´s archaeology and genealogy in the study of normativity

The twenty-first century is characterized by drastic changes in epistemology, as a result of academical shifts in important fields since the 60s. The decline of metanarratives – defined by Lyotard as grand-narratives about narratives (which, in turn, legitimate historically-situated events) – provided a fertile research ground for new methodological practices based on sharp critiques of Enlightenment rationality. One of the founding authors of the “postmodern condition” (as Lyotard labels it) is Michel Foucault. Foucault’s archaeological and genealogical project regarding epistemology redefined our conceptual approach to knowledge and its legitimation, by situating both concepts in specific historical contexts, at specific historical times. Recurring themes in the Foucauldian project involve skepticism about objective truths, anti-historicism and subjectivity. In this dissertation, I seek to answer the question “Why is Foucauldian methodology relevant in the (post-)modern world, especially in light of the decline of metanarratives?”. The main goal is to address the role of Foucault’s works in the rethinking of historically given narratives and expose the contingency of practices embroiled in power-knowledge relations, while keeping in mind the dispersibility of the origins of those narratives. This is particularly relevant under the framework of an emptying of over-arching narratives about knowledge and the human condition, i.e., the Lyotardian metanarrative. Human societies are usually seen in a context of a larger narrative to which each of our lives in an element. The metanarrative serves as an umbrella for smaller narratives in which other epistemic and moral narratives find their place. There seems to be a clear intersection in Lyotard and Foucault’s works: the former studies the conditions in which the metanarratives empty themselves, while the latter occupies himself with the archaeological/genealogical study of the narratives within the metanarratives that, in turn, occupy the vacuum left by the original metanarrative. There is, nonetheless, a distinction between both authors: while Lyotard sees this replacement as normative-laden, Foucault focuses on a strictly analytical view of discourse and practice

Equity research: valuation of farfetch - the rise of farfetch in luxury e-commerce

This final work project forecasts Farfetch’s results, analyzing its business and position in the luxury market. The COVID-19 pandemic brought good things for the company, experiencing a high in new active consumers. This allied with the new focus on brand development brings great prospects for the revenues’ growth. Following our assumptions and calculations, we forecast a price target of US$70,33 for FY21, resulting in a return of 10% for the shareholders, giving a HOLD recommendation