CFT in Conformally Flat Spacetimes

A new class of conformal field theories is presented, where the background gravitational field is conformally flat. Conformally flat (CF) spacetimes enjoy conformal properties quite similar to the ones of flat spacetime. The conformal isometry group is of maximal rank and the conformal Killing vectors in conformally flat coordinates are {\em exactly} the same as the ones of flat spacetime. In this work, a new concept of distance is introduced, the {\em conformal distance}, which transforms covariantly under all conformal isometries of the CF space. It is shown that precisely for CF spacetimes, an adequate power of the said conformal distance is a solution of the non-minimal d'Alembert equation.Comment: Minor changes and some clarifications added. Published version. 16 page

Weyl anomalies and the nature of the gravitational field

The presence of gravity generalizes the notion of scale invariance to Weyl invariance, namely, invariance under local rescalings of the metric. In this work, we have computed the Weyl anomaly for various classically scale or Weyl invariant theories, making particular emphasis on the differences that arise when gravity is taken as a dynamical fluctuation instead of as a non-dynamical background field. We find that the value of the anomaly for the Weyl invariant coupling of scalar fields to gravity is sensitive to the dynamical character of the gravitational field, even when computed in constant curvature backgrounds. We also discuss to what extent those effects are potentially observable.Comment: 37 pages, 1 tabl

Weighing the Vacuum Energy

We discuss the weight of vacuum energy in various contexts. First, we compute the vacuum energy for flat spacetimes of the form $\mathbb{T}^3 \times \mathbb{R}$, where $\mathbb{T}^3$ stands for a general 3-torus. We discover a quite simple relationship between energy at radius $R$ and energy at radius $\frac{l_s^2}{ R}$. Then we consider quantum gravity effects in the vacuum energy of a scalar field in $\mathbb{M}_3 \times S^1$ where $\mathbb{M}_3$ is a general curved spacetime, and the circle $S^1$ refers to a spacelike coordinate. We compute it for General Relativity and generic transverse {\em TDiff} theories. In the particular case of Unimodular Gravity vacuum energy does not gravitate.Comment: 32 pages. Minor correction

Massless Positivity in Graviton Exchange

We formulate Positivity Bounds for scattering amplitudes including exchange of massless particles. We generalize the standard construction through dispersion relations to include the presence of a branch cut along the real axis in the complex plane for the Maldestam variable $s$. In general, validity of these bounds require the cancellation of divergences in the forward limit of the amplitude, proportional to $t^{-1}$ and $\log(t)$. We show that this is possible in the case of gravitons if one assumes a Regge behavior of the amplitude at high energies below the Planck scale, as previously suggested in the literature, and that the concrete UV behaviour of the amplitude is uniquely determined by the structure of IR divergences. We thus extend previous results by including a sub-leading logarithmic term, which we show to be universal. The bounds that we present here have the potential of constraining very general models of modified gravity and EFTs of matter coupled to gravitation.Comment: 9 pages, 1 figure. Matches journal versio

Estatística Espacial para Gestão de Dádivas de Sangue em Portugal

A doação de sangue é indispensável para salvar vidas, sendo em algumas situações inevitável a transfusão. Em Portugal todos os dias são necessárias entre 900 e 950 unidades de sangue nos hospitais e tendo em conta que os componentes sanguíneos têm um prazo de validade é de extrema importância manter a regularidade das colheitas, sendo as dádivas regulares essenciais para garantir a estabilidade das reservas e o funcionamento do sistema de saúde. A pouca disponibilidade de ferramentas que possibilitem o estudo geográfico destes fenómenos, dificulta o planeamento de sessões de colheita. Face a estes dados é fundamental que haja na área da saúde, sistemas de informação (SI) que permitam uma boa gestão das sessões de colheita de forma a contribuir para uma eficaz racionalização de recursos. Este estágio teve por objetivo principal os seguintes pontos de atuação: i) identificação geográfica das sessões de colheita de sangue; ii) análise da distribuição geográfica dos diferentes grupos sanguíneos. Neste trabalho é construído um dashboard que permite auxiliar o Instituto Português do Sangue e Transplantação (IPST) no planeamento de sessões de colheita. De forma a facilitar a construção e o acesso do dashboard foi utilizado o software Power BI, que não só facilita a introdução de novos registos, como permite que a informação esteja sempre atualizada. Inicialmente procedeu-se à recolha e tratamento de dados com o intuito de criação e estruturação de uma base de dados em Excel. Posteriormente realizou-se a geocodificação das sessões de colheita de sangue. Preparada a informação, pretende-se compreender as dinâmicas espaciais da dádiva de sangue, desse modo aplicaram-se métodos estatísticos, nomeadamente o Índice de Moran e análise de Hot Spot, com vista a identificar padrões espaciais e constatar se a distribuição espacial é aleatória ou aglomerada. De modo a observar de forma coesa a densidade de brigadas móveis, procedeu-se à aplicação do método da densidade de Kernel. Foi também realizada uma análise de potencial, recorrendo ao método Regressão Linear Múltipla (RLM), como forma de perspetivar se alguns aspetos populacionais influenciam o número de dádivas. Por fim, através da aplicação Power BI procedeu-se à criação de um dashboard que foi apresentado e disponibilizado ao IPST.Blood donation is essential to save lives, and in some situations, transfusion is unavoidable. In Portugal, between 900 and 950 units of blood are needed every day in hospitals and, taking into account that blood components have an expiration date, it is extremely important to maintain the regularity of collections, with regular donations being essential to guarantee the stability of reserves and the functioning of the health system. The limited availability of tools that allow the geographical study of these phenomena makes it difficult to plan collection sessions. In view of these data, it is essential that there are information systems in the health area that allow for a good management of collection sessions in order to contribute to an effective rationalization of resources. The main objective of this internship was the following points of action: i) geographical identification of the blood collection sessions; ii) analysis of the geographic distribution of the different blood groups. In this work, a dashboard is built that helps the Portuguese Institute of Blood and Transplantation (IPST) in the planning of harvesting sessions. In order to facilitate the construction and access of the dashboard, the Power BI software was used, which not only facilitates the introduction of new records, but also allows the information to be always updated. Initially, data was collected and processed with the aim of creating and structuring a database in Excel. Subsequently, the geocoding of the blood collection sessions was carried out. Having prepared the information, it is intended to understand the spatial dynamics of blood donation, in this way statistical methods were applied, namely the Moran Index and Hot Spot analysis, in order to identify spatial patterns and verify if the spatial distribution is random or agglomerated. In order to, cohesively observe the density of mobile brigades, the Kernel density method was applied. A potential analysis was also carried out, using the Multiple Linear Regression (MLR) method, as a way of envisioning whether some population aspects influence the number of donations. Finally, through the Power BI application, a dashboard was created that was presented and made available to the IPST

avaliação da textura de uvas de diferentes variedades

O objectivo deste trabalho foi avaliar as propriedades reológicas de diferentes variedades de uvas para vinificar. Foram estudadas as variedades brancas Siria, Antão Vaz, Perrum, Rabo de Ovelha e Arinto e as variedades tintas Trincadeira, Aragonez, Tinta Caiada, Moreto e Castelão. Para se avaliar da existência ou não de diferenças entre as variedades, foram efectuados testes em 200 bagos de cada variedade, nomeadamente a compressão do bago inteiro e a resistência da pelicula (pericarpo) e da polpa (mesocarpo) à penetração. Um segundo objectivo deste trabalho foi seleccionar os métodos e parâmetros que melhor caracterizam as variedades reologicamente, por forma a reduzir o tempo de análise e simplificar a metodologia de análise. Foram encontradas diferenças significativas entre as variedades para todos os parâmetros reológicos estudados. Os valores elevados de firmeza (F) obtidos pela máxima força durante a compressão do bago inteiro, pela máxima força durante o teste de penetração da película, e pela força a 3 mm de deformação da polpa, demostraram serem bons indicadores para serem usados em trabalhos futuros

Multi-hazard Susceptibility Assessment for Land Use Planning in the Lisbon Metropolitan Area

The Lisbon Metropolitan Area is a risk hotspot in Portugal due to excessive exposure to natural and environmental hazards. In this work, a multi-hazard susceptibility assessment is performed for the 118 parishes that constitute the study area, considering the spatial incidence of seven hazardous processes: earthquakes, tsunami, beach erosion and coastal flooding, coastal erosion and cliff retreat, landslides, floods, and forest fires. The relative importance of hazardous processes was established through the Analytic Hierarchy Process (AHP), based on the frequency-magnitude relationship of each process and its damage capacity. All the parishes exhibiting very high multi-hazard susceptibility have high earthquake susceptibility and most are located in riverine or coastal zones, thus subjected to floods and/or coastal erosion (affecting beaches and/or cliffs).info:eu-repo/semantics/publishedVersio