The Effect of Recency to Human Mobility

In recent years, we have seen scientists attempt to model and explain human dynamics and, in particular, human movement. Many aspects of our complex life are affected by human movements such as disease spread and epidemics modeling, city planning, wireless network development, and disaster relief, to name a few. Given the myriad of applications it is clear that a complete understanding of how people move in space can lead to huge benefits to our society. In most of the recent works, scientists have focused on the idea that people movements are biased towards frequently-visited locations. According to them, human movement is based on an exploration/exploitation dichotomy in which individuals choose new locations (exploration) or return to frequently-visited locations (exploitation). In this work, we focus on the concept of recency. We propose a model in which exploitation in human movement also considers recently-visited locations and not solely frequently-visited locations. We test our hypothesis against different empirical data of human mobility and show that our proposed model is able to better explain the human trajectories in these datasets

Estimating Ambient Air Pollution Using Structural Properties of Road Networks

In recent years, the world has become increasingly concerned with air pollution. Particularly in the global north, countries are implementing systems to monitor air pollution on a large scale to aid decision-making, focusing on urban areas. Such efforts are essential but costly and are difficult to implement expediently. In this paper, we demonstrate that we can estimate air pollution using open-source information about the structural properties of roads within the United Kingdom. Our approach makes it possible to implement an inexpensive method of estimating air pollution in the United Kingdom to an accuracy level that can underpin policymakers' decisions while providing an estimate in all regions in the UK, not just urban areas. Impact Statement. We show that a linear regression model using a single structural property -- length of the track and unclassified road network within 0.5\% of districts within England and Wales -- can accurately estimate which regions of the UK are the most polluted. The model presents a low-cost yet effective alternative to more expensive models such as the one currently used by DEFRA in the UK. The model has apparent practical uses for policymakers who want to pursue clean-air initiatives but lack the capital to invest in comprehensive monitoring networks. Its low implementation cost, accessible model design, and worldwide coverage of the dataset provide a basis for implementing systems to estimate air pollution levels in low-income countries.Comment: Main File 19 pages, 10 Figures, 4 Tables. Supplementary File 17 pages, 13 figures, 14 tables. Edited to fix TeX issue

Um estudo sobre modelos de computação paralela

Orientador: João Carlos SetubalDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Ciencia da ComputaçãoResumo: Modelos de Computação são uma ferramenta muito importante para um bom desenvolvimento de algoritmos. Em geral, eles visam facilitar o trabalho de projetistas abstraindo diversos fatores existentes nas máquinas reais. Em computação paralela, a necessidade de um modelo é extrema devido a grande variedade de arquiteturas. O surgimento de um modelo de computação paralela poderia impulsionar ainda mais o crescimento da área que já é bastante acentuado, devido a limitações físicas existentes em computadores seqüenciais. Nesta dissertação fazemos um estudo de modelos de computação paralela sob o ponto de vista de projeto de algoritmos e com enfoque na computação paralela derivada da arquitetura de von Neumann. Para tanto, começamos por estudar um conjunto de máquinas paralelas para que suas diferenças fiquem claras. Escolhemos as máquinas paralelas mais conhecidas, ou mais difundidas, como: CM-2, Sequent Symmetry, MasPar MP-l, CM-5, entre outras. Após este estudo de máquinas, partimos diretamente para os modelos de computação paralela. Escolhemos três como base. Tais modelos apresentam características bem distintas quanto a simplicidade e realismo. Os modelos estudados são PRAM, BSP [Val90] e LogP [CKP+93]. Muitos defendem que continuemos usando o modelo PRAM , pois este, apesar de ser muito abstrato, facilita bastante o trabalho dos projetistas. A proposta do modelo BSP é um pouco mais ousada pois Valiant tenta, com seu modelo, influenciar as áreas de hardware e software da mesma forma que a arquitetura von Neumann fez com a computação seqüencial. Já a proposta do modelo LogP é bastante imediatista, visto que tenta resolver o problema atual de dificuldade de projeto de algoritmos. Para que pudéssemos avaliar um modelo sob o ponto de vista de projeto de algoritmos, fizemos um estudo de casos com os problemas de Transformada de Fourier e Eliminação de Gauss. Com este estudo de casos pudemos avaliar quão fácil ou difícil é projetar algoritmos em cada um dos modelos.Abstract: Models of Computation are one of most important tools in algorithm design With these models, the work of an algorithm designer becomes easier, because these models leave out many characteristics of real machines. In parallel computing there is a great need for a general model, because we have many different parallel machines. The advent of a parallel computing model could make the area grow more than it is already growing. In this dissertation we study some parallel computing models. First we take a look at a representative set of parallel machines, in order to learn the differences between each architecture. Our set of machines contains some of the most important commercial machines such as: CM-2, Sequent Symmetry, MasPar MP-l and CM-5. After this, we study the models themselves. The models chosen were: PRAM, BSP [Va190] and LogP [CKP+93]. Many researchers argue that the PRAM is the best model for algorithm design although it is not realistic. The proposal of the BSP mo dei is bold, since it also seeks to influence parallel architecture design The proposal of LogP model although similar to the BSP, does not require parallel machines to have synchronization mechanisms. This makes LogP the most realistic but also the most difficult model to use. We evaluate these models based on the problems of Fourier Transform and Gaussian Elimination. After this study we made an evaluation of the three models.MestradoMestre em Ciência da Computaçã

Differences in the spatial landscape of urban mobility: gender and socioeconomic perspectives

In society, many of our routines and activities are linked to our ability to move; be it commuting to work, shopping for groceries, or meeting friends. Yet, factors that limit the individuals' ability to fully realise their mobility needs will ultimately affect the opportunities they can have access to (e.g. cultural activities, professional interactions). One important aspect frequently overlooked in human mobility studies is how gender-centred issues can amplify other sources of mobility disadvantages (e.g. socioeconomic inequalities), unevenly affecting the pool of opportunities men and women have access to. In this work, we leverage on a combination of computational, statistical and information-theoretical approaches to investigate the existence of systematic discrepancies in the mobility diversity (i.e.the diversity of travel destinations) of (1) men and women from different socioeconomic backgrounds, and (2) work and non-work travels. Our analysis is based on datasets containing multiple instances of large-scale, official, travel surveys carried out in three major metropolitan areas in South America: Medell\'in and Bogot\'a in Colombia, and S\~ao Paulo in Brazil. Our results indicate the presence of general discrepancies in the urban mobility diversities related to the gender and socioeconomic characteristics of the individuals. Lastly, this paper sheds new light on the possible origins of gender-level human mobility inequalities, contributing to the general understanding of disaggregated patterns in human mobility

O caso da extração de imagens de satélite Landsat

UID/SOC/04647/2013As tecnologias de informação alteraram a dinâmica da sociedade. A forma como se ensina, aprende e se utilizam os seus benefícios. A velocidade com que a informação é gerada tem de ser acompanhada pelo ritmo da sua assimilação. A disseminação da informação é fundamental para gerar conhecimento. A sua utilização num processo de análise espacial é tanto mais eficaz, quanto mais ágeis forem as várias etapas que o compõem. A deteção remota tem tido, em complementaridade com os SIG, uma evolução notável, quer pelo aumento da resolução, quer pelo avanço dos algoritmos de análise espacial. No entanto, ela não tem sido, em muitos casos, acompanhada por formas expeditas de extração da informação, criando inércia nos processos de disseminação da informação. Esta comunicação pretende assim demonstrar a versatilidade de uma plataforma, criada “de raíz”, em linguagem R, que agiliza um conjunto de operações: pesquisa, recolha, organização, integração e tratamento das imagens.publishersversionpublishe