Modeling Worldwide Highway Networks

This letter addresses the problem of modeling the highway systems of different countries by using complex networks formalism. More specifically, we compare two traditional geographical models with a modified geometrical network model where paths, rather than edges, are incorporated at each step between the origin and destination nodes. Optimal configurations of parameters are obtained for each model and used in the comparison. The highway networks of Brazil, the US and England are considered and shown to be properly modeled by the modified geographical model. The Brazilian highway network yielded small deviations that are potentially accountable by specific developing and sociogeographic features of that country.Comment: 5 pages, 3 figures, 1 tabl

RetScan: efficient fovea and optic disc detection in retinographies

Dissertação de mestrado em Engenharia de InformáticaThe Fovea and Optic Disc are relevant anatomical eye structures to diagnose various diseases. Its automatic detection can provide both a cost reduction when analysing large populations and improve the effectiveness of ophthalmologists and optometrists. This dissertation describes a methodology to automatically detect these structures and analyses a, CPU only, MATLAB implementation of this methodology. RetScan is a port to a freeware environment of this methodology, its functionality and performance are evaluated and compared to the original. The results of both evaluations lead to a discussion on possible improvements in the metodology that influence the functionality and performance. The resulting improvements are implemented and integrated in RetScan. To further improve performance, a parallelization of RetScan to take advantage of a multi-core architecture or a CUDA-enabled accelerator was designed, coded and evaluated.This evaluation reveals that RetScan achieves its best throughput efficiency using a multi-core architecture only and analysing several images at once. For one image usage, using multi-core only is also the best solution, but with a small speed-up. The usage of CUDA-enabled accelerators is not recommended for this scope as the images are small and the cost of the data transfer to and from the accelerator has a severe impact on performance.A Fóvea e o Disco Ótico são estruturas oculares importantes quando se procura diagnosticar doenças no olho. A sua deteção automática permite reduzir o custo de um rastreio a grandes populações e também aumentar a eficácia de oftalmologistas e optometristas. Nesta dissertação é descrita uma metodologia para detetar estas estruturas automaticamente e é analisada uma implementação em MATLAB desta metodologia. RetScan é o resultado do porte para um ambiente de desenvolvimento com ferramentas livres (open source) desta metodologia. O RetScan é avaliado quer em funcionalidade, quer em performance. Os resultados da avaliação levam a uma reflexão sobre mudanças a realizar à metodologia para melhorar os resultados em ambas as avaliações. Estas melhorias são implementadas e integradas no RetScan. Para melhorar a sua performance é também realizada um paralelização do RetScan de forma a que tire partido de uma arquitetura multi-core ou de um acelerador compatível com CUDA. Após realizar uma nova avaliação conclui-se que o RetScan atinge o seu melhor débito de dados (throughput) quando usa apenas os CPUs numa arquitetura multi-core e analisando várias imagens em paralelo. Para a análise de uma só imagem, o uso apenas de CPUs numa arquitetura multi-core também é o melhor resultado, embora tenha um ganho (speed up) reduzido. O uso de aceleradores compatíveis com CUDA não é recomendado neste âmbito pois as imagens têm um tamanho reduzido e o custo da transferência de e para estes aceleradores tem um grande impacto no tempo tota

Border trees of complex networks

The comprehensive characterization of the structure of complex networks is essential to understand the dynamical processes which guide their evolution. The discovery of the scale-free distribution and the small world property of real networks were fundamental to stimulate more realistic models and to understand some dynamical processes such as network growth. However, properties related to the network borders (nodes with degree equal to one), one of its most fragile parts, remain little investigated and understood. The border nodes may be involved in the evolution of structures such as geographical networks. Here we analyze complex networks by looking for border trees, which are defined as the subgraphs without cycles connected to the remainder of the network (containing cycles) and terminating into border nodes. In addition to describing an algorithm for identification of such tree subgraphs, we also consider a series of their measurements, including their number of vertices, number of leaves, and depth. We investigate the properties of border trees for several theoretical models as well as real-world networks.Comment: 5 pages, 1 figure, 2 tables. A working manuscript, comments and suggestions welcome

A Systems Approach to Test the Usefulness of a Model to Challenge Organisational Change

The impact of a proposition concerning the split of the structure of a precision engineering company into two clusters was holistically analysed and verified for consistency, as regards the structure design parameters. A conceptual model supported by both the schools of strategists and structuralists was used as an audit tool for ordered questioning, debate, learning and dialectical discussion. Moreover, the Soft Systems Methodology (SSM), provided orientation to theoretical validation of the model whose outcomes identified the potential, desirable and feasible change of both manufacturing systems and production planning and control (PPC). A situational, hermeneutics, interpretivist, learning oriented process of enquiry, rather different from best practice views, was shown adequate to the problem nature and to the case study confirming the interest of the two clusters. Thus, formal planning and control procedures exhibited a very weak stand requiring both development in line with the contingency factors and complementarity with the other work co-ordination mechanisms. This holistic, systemic, strategic and structured approach produced the reviewing and reformatting of the manufacturing strategy decision areas and recommended that PPC procedures should be further analysed in detail, in order to fit the two clusters. To sum up, the audit tool was found useful and it was also able to identify potential change in a credible way, to classify it as desirable/undesirable by following a learning process and, to discuss its feasibility in the context of a specific organisational culture. Thus, SSM provided an original contribution to Operations Research through the design of complex organisations under a systems view

Analysing Symbolic Regression Benchmarks under a Meta-Learning Approach

The definition of a concise and effective testbed for Genetic Programming (GP) is a recurrent matter in the research community. This paper takes a new step in this direction, proposing a different approach to measure the quality of the symbolic regression benchmarks quantitatively. The proposed approach is based on meta-learning and uses a set of dataset meta-features---such as the number of examples or output skewness---to describe the datasets. Our idea is to correlate these meta-features with the errors obtained by a GP method. These meta-features define a space of benchmarks that should, ideally, have datasets (points) covering different regions of the space. An initial analysis of 63 datasets showed that current benchmarks are concentrated in a small region of this benchmark space. We also found out that number of instances and output skewness are the most relevant meta-features to GP output error. Both conclusions can help define which datasets should compose an effective testbed for symbolic regression methods.Comment: 8 pages, 3 Figures, Proceedings of Genetic and Evolutionary Computation Conference Companion, Kyoto, Japa

Mudanças climáticas e seus reflexos na paisagem do quaternário: primeiras Reflexões.

bitstream/item/107273/1/Doc-157-Mudancas-Quaternario.pd

Leques aluviais pleistocênicos da regiao costeira da Bahia : implicaçoes paleoclimaticas

Les auteurs présentent une étude sédimentologique des dépôts de sables du Pleistocène localisés le long de la côte de l'Etat de Bahia (Brésil). Leur mise en place serait liée à la dernière grande période de climat aride ayant caractérisé cette région

Análise de solos coesos do litoral Norte da Bahia utilizando a granulometria a laser.

Uma das características mais conspícuas dos solos dos Tabuleiros Costeiros é a coesão manifestada em horizontes subsuperficiais (horizontes coesos). Alguns autores defendem que a gênese dos horizontes coesos está relacionada a iluviação de argila muito fina, enquanto que outros relatam a importância da boa distribuição granulométrica. Visando contribuir para o entendimento dos horizontes coesos, foram realizados estudos em três perfis de solos utilizando um granulômetro a laser. O trabalho não comprovou a relação entre a translocação de argila muito fina e os horizontes coesos, contudo sugere que a boa distribuição granulométrica e a argiluviação favoreceram a constituição e evolução da coesão