Hybrid galaxy evolution modelling: Monte Carlo Markov Chain parameter estimation in semi-analytic models of galaxy formation

We introduce a statistical exploration of the parameter space of the Munich semi-analytic model built upon the Millennium dark matter simulation. This is achieved by applying a Monte Carlo Markov Chain (MCMC) method to constrain the 6 free parameters that define the stellar mass function at redshift zero. The model is tested against three different observational data sets, including the galaxy K-band luminosity function, B −V colours, and the black hole-bulge mass relation, to obtain mean values, confidence limits and likelihood contours for the best fit model. We discuss how the model parameters affect each galaxy property and find that there are strong correlations between them. We analyze to what extent these are simply reflections of the observational constraints, or whether they can lead to improved understanding of the physics of galaxy formation. When all the observations are combined, the need to suppress dwarf galaxies requires the strength of the supernova feedback to be significantly higher in our best-fit solution than in previous work. We interpret this fact as an indication of the need to improve the treatment of low mass objects. As a possible solution, we introduce the process of satellite disruption, caused by tidal forces exerted by central galaxies on their merging companions. We apply similar MCMC sampling techniques to the new model, which allows us to discuss the impact of disruption on the basic physics of the model. The new best fit model has a likelihood four times better than before, reproducing reasonably all the observational constraints, as well as the metallicity of galaxies and predicting intra-cluster light. We interpret this as an indication of the need to include the new recipe. We point out the remaining limitations of the semi-analytic model and discuss possible improvements that might increase its predictive power in the future

Gestão de conteúdos digitais em múltiplos monitores

With the generalized use of systems for digital contents dissemination arises the opportunity for implementing solutions capable of evaluating audience reaction. This dissertation reflects the implementation of one of those solutions. To this end, the development involved adapting a previously functional digital signage system. In this sense, digital cameras were paired to the content display terminals in order to capture information from the area in front of them. Using computer vision technologies, the terminals detect, in real time, people who appear in the cameras’ field of view, and this information is communicated to a server for data extraction. On the server, methods are used to perform face and emotion recognition, and also to extract data indicating the position of the head, which allows the calculation of an attention coefficient. The data is stored in a relational database, and can be consulted through a web platform, where they are presented associated with the contents corresponding to the moment of their capture and extraction. This solution thus allows the evaluation of the impact of the digital contents presented by the system.Com a utilização generalizada de sistemas de disseminação de conteúdos digitais, surge a oportunidade de implementar soluções capazes de avaliar a reacção do público. Esta dissertação reflete a implementação de uma dessas soluções. Para isso, o desenvolvimento passou pela adaptação de um sistema de sinalização digital previamente funcional. Neste sentido, aos terminais de exposição de conteúdos, foram emparelhadas câmaras digitais de modo a permitir a captação de informação da área à frente destes. Com recurso a tecnologias de visão de computador, os terminais fazem, em tempo real, deteção de pessoas que apareçam no campo de visão das câmaras, sendo esta informação comunicada a um servidor para extração de dados. No servidor, são utilizados métodos para realização de reconhecimento de faces e emoções, e também é feita extração de dados indicadores da posição da cabeça, o que permite o cálculo de um coeficiente de atenção. Os dados são guardados numa base de dados relacional e podem ser consultados através de uma plataforma web, onde são apresentados associados aos contéudos correspondentes ao momento de captação e extração destes. Esta solução, permite, assim, a avaliação do impacto dos conteúdos digitais apresentados pelo sistema.Mestrado em Engenharia de Computadores e Telemátic

Monte Carlo Markov Chain parameter estimation in semi-analytic models of galaxy formation

We present a statistical exploration of the parameter space of the De Lucia and Blaizot version of the Munich semi-analytic (SA) model built upon the Millennium dark matter simulation. This is achieved by applying a Monte Carlo Markov Chain method to constrain the six free parameters that define the stellar and black hole mass functions at redshift zero. The model is tested against three different observational data sets, including the galaxy K-band luminosity function, B - V colours and the black hole-bulge mass relation, separately and combined, to obtain mean values, confidence limits and likelihood contours for the best-fitting model. Using each observational data set independently, we discuss how the SA model parameters affect each galaxy property and find that there are strong correlations between them. We analyse to what extent these are simply reflections of the observational constraints, or whether they can lead to improved understandings of the physics of galaxy formation. When all the observations are combined, we find reasonable agreement between the majority of the previously published parameter values and our confidence limits. However, the need to suppress dwarf galaxy formation requires the strength of the supernova feedback to be significantly higher in our best-fitting solution than in previous work. To balance this, we require the feedback to become ineffective in haloes of lower mass than before, so as to permit the formation of sufficient high-luminosity galaxies: unfortunately, this leads to an excess of galaxies around L*. Although the best fit is formally consistent with the data, there is no region of parameter space that reproduces the shape of galaxy luminosity function across the whole magnitude range. For our best fit, we present the model predictions for the bJ-band luminosity and stellar mass functions. We find a systematic disagreement between the observed mass function and the predictions from the K-band constraint, which we explain in light of recent works that suggest uncertainties of up to 0.3 dex in the mass determination from stellar population synthesis models. We discuss modifications to the SA model that might simultaneously improve the fit to the observed mass function and reduce the reliance on excessive supernova feedback in small haloes

Supermassive black holes as the regulators of star formation in central galaxies

We present a relationship between the black hole mass, stellar mass, and star formation rate of a diverse group of 91 galaxies with dynamically-measured black hole masses. For our sample of galaxies with a variety of morphologies and other galactic properties, we find that the specific star formation rate is a smoothly decreasing function of the ratio between black hole mass and stellar mass, or what we call the specific black hole mass. In order to explain this relation, we propose a physical framework where the gradual suppression of a galaxy's star formation activity results from the adjustment to an increase in specific black hole mass and, accordingly, an increase in the amount of heating. From this framework, it follows that at least some galaxies with intermediate specific black hole masses are in a steady state of partial quiescence with intermediate specific star formation rates, implying that both transitioning and steady-state galaxies live within this region known as the "green valley." With respect to galaxy formation models, our results present an important diagnostic with which to test various prescriptions of black hole feedback and its effects on star formation activity.Comment: 15 pages, 4 figures, 2 tables. Accepted for publication in The Astrophysical Journa

Directa, de Nuno Bragança: questões de tempo

Tese de mestrado, Literatura Portuguesa Contemporânea, Universidade de Lisboa, Faculdade de Letras, 2009Este trabalho é uma, entre inúmeras possíveis, análise do tempo, não só como categoria narrativa, a par do espaço e das personagens, mas também como tema, em Directa, de Nuno Bragança. Se por um lado, se fez uma exegese cuidada de problemas literariamente canónicos como o tempo da narrativa, da história e da narração, por outro lado, tentou-se mostrar como a História, enquanto discurso sobre o tempo, se imiscui e estrutura, não só a narrativa, mas também a história do romance. Além disto, não foi ignorada a necessidade de esclarecer o que é o tempo, sendo que o termo ganha definições distintas dependendo do paradigma que a ele se associe. O tempo físico é distinto do tempo psicológico e estes dois divergem do seu congénere literário. Numa dissertação sobre o tempo dedica-se um capítulo a questões de índole religiosa e política, porque se entendeu que a matriz judaico-cristã e o marxismo são elementos estruturantes da concepção de tempo do narrador e, por conseguinte, da história, na medida que todas esta ideologias podem ser interpretadas, entre muitas outras coisas, como ideias fazedoras de tempo. Mais do que um trabalho extraordinariamente coeso, do ponto de vista temático, pretende-se apresentar um conjunto de textos que alumie de forma original e profunda o problema exegético que o tempo constitui em Directa, de Nuno Bragança.In this dissertation time will be analysed not only as category of narrative fiction, but also as a main subject in the novel Directa by Nuno Bragança. On the one hand, canonical literary problems such as time of narrative and time of story were thoroughly examined; on the other hand the structuring role of History in the text was severely discussed. Furthermore the polysemy of the concept of time was explained. Though time is the main subject of this thesis, a whole chapter was dedicated to questions related to religion and politics, because the Jewish, Christian and Marxist ideologies were regarded as concepts of time. The main goal of this dissertation is to present a variety of original texts that shed some light on the chosen subject time in the novel Directa by Nuno Bragança

Transplant Open Registry Initiative

Health data science aims to extract knowledge from data allowing better decision-making, using multidisciplinary approaches from fields such as computation, statistics, epidemiology, and several medical knowledge domains. We live in the ‘big data’ era, with a growing availability of health data, in volume, variety, and velocity, also for tasks such as kidney transplantation. Hereby, secondary use of this health data must be encouraged to improve patient care planning, disease research, and policymaking around transplantation. This article presents the Transplant Open Registry (TxOR) website where some health data science applications on kidney transplantation are available. With it, we try to answer, some of the remaining questions on kidney transplantation in Portugal, with a new approach.This project received the “Antonio Morais Sar- mento” research grant from the Portuguese Society of Transplantation.info:eu-repo/semantics/publishedVersio