The role of translational invariance in non linear gauge theories of gravity

The internal structure of the tetrads in a Poincar\'e non linear gauge theory of gravity is considered. Minkowskian coordinates becomes dynamical degrees of freedom playing the role of Goldstone bosons of the translations. A critical length allowing a covariant expansion similar to the weak field approach is deduced, the zeroth order metric being maximally symmetric (Minkowskian in some cases).Comment: 17 pages, LaTe

Cosmology without inflation

We propose a new cosmological paradigm in which our observed expanding phase is originated from an initially large contracting Universe that subsequently experienced a bounce. This category of models, being geodesically complete, is non-singular and horizon-free, and can be made to prevent any relevant scale to ever have been smaller than the Planck length. In this scenario, one can find new ways to solve the standard cosmological puzzles. One can also obtain scale invariant spectra for both scalar and tensor perturbations: this will be the case, for instance, if the contracting Universe is dust-dominated at the time at which large wavelength perturbations get larger than the curvature scale. We present a particular example based on a dust fluid classically contracting model, where a bounce occurs due to quantum effects, in which these features are explicit.Comment: 8 pages, no figur

Development of an applicattion to improve traceability and food safety management

Food safety has become an important food quality attribute within the last decade. Facing recent food scandals taken up by the media, consumers are more and more concerned about and interested in the provenance and authenticity of their food. Both food industry and authorities need to be able to trace back and to authenticate food products and raw materials used for food production to comply with legislation and to meet the food safety and food quality requirements as well as the increasing consumer demand. Therefore, food companies are faced with the problem of defining and implementing a series of procedures, controls and measures. Moreover, it is necessary to define an application method which is both rigorous and economically sustainable in order to guarantee the safe production of food and to be able to trace it along the food chain. The application was designed to manage traceability as well as to help in the quality control and production improvement, using an user-friendly interface. This application was developed in Visual Basic over an SQL database and its main features are: to register quality control parameters of raw materials, in-course products and final products; to manage reception, production and expedition orders; to analyse production costs, productivity, raw materials and products’ consumptions; to define and print labels containing lot information and other relevant data; to trace products during the food chain (from raw materials to final client). All these informations are accessible either from pre-defined reports either exported to intranet based on Internet Explorer or other browser. Usually the process to assure traceability, specially in food products (due to the large number of ingredients involved in a single formulation) is very time-consuming, involves lots of paperwork and consequently a large number of resources are expended in this laborious task. This application can minimize efforts involved in traceability and managing food quality and safety systems.Fundação para a Ciência e a Tecnologia (FCT)

Locating the Source of Diffusion in Large-Scale Networks

How can we localize the source of diffusion in a complex network? Due to the tremendous size of many real networks--such as the Internet or the human social graph--it is usually infeasible to observe the state of all nodes in a network. We show that it is fundamentally possible to estimate the location of the source from measurements collected by sparsely-placed observers. We present a strategy that is optimal for arbitrary trees, achieving maximum probability of correct localization. We describe efficient implementations with complexity O(N^{\alpha}), where \alpha=1 for arbitrary trees, and \alpha=3 for arbitrary graphs. In the context of several case studies, we determine how localization accuracy is affected by various system parameters, including the structure of the network, the density of observers, and the number of observed cascades.Comment: To appear in Physical Review Letters. Includes pre-print of main paper, and supplementary materia

The use of TIC’s as a managing tool for traceability in the food industry

Food safety has become an important food quality attribute. Both food industry and authorities need to be able to trace back and to authenticate food products and raw materials used for food production to comply with legislation and to meet the food safety and food quality requirements. PaniGest is a user-friendly computer package designed to manage traceability and help in the quality control and production improvement. This application was developed in Visual Basic language over an SQL database and its main features are: to register quality control parameters of raw materials, in-course products and final products; to manage reception, production and expedition orders; to analyse production costs, productivity, raw materials and products’ consumptions; to trace products during the food chain. It runs on a personal computer over Windows 95/98 or Windows 2000/XP operating system. The program also uses common Internet Browsers to make information available to users.Fundação para a Ciência e a Tecnologia (FCT)

Chemical Evolution of the Galaxy Based on the Oscillatory Star Formation History

We model the star formation history (SFH) and the chemical evolution of the Galactic disk by combining an infall model and a limit-cycle model of the interstellar medium (ISM). Recent observations have shown that the SFH of the Galactic disk violently variates or oscillates. We model the oscillatory SFH based on the limit-cycle behavior of the fractional masses of three components of the ISM. The observed period of the oscillation ($\sim 1$ Gyr) is reproduced within the natural parameter range. This means that we can interpret the oscillatory SFH as the limit-cycle behavior of the ISM. We then test the chemical evolution of stars and gas in the framework of the limit-cycle model, since the oscillatory behavior of the SFH may cause an oscillatory evolution of the metallicity. We find however that the oscillatory behavior of metallicity is not prominent because the metallicity reflects the past integrated SFH. This indicates that the metallicity cannot be used to distinguish an oscillatory SFH from one without oscillations.Comment: 21 pages LaTeX, to appear in Ap

Perspectiva biomimética do ninho de andorinha-dos-beirais

A terra é um material natural, ecológico, reciclável e abundante e, como tal, foi sempre e volta agora a ser considerado como sendo um dos materiais/soluções de construção de eleição, com enorme potencial. Na construção tradicional portuguesa encontram-se várias soluções construtivas recorrendo ao uso da terra crua, com uma importante expressão. Este património construído necessita de ser conservado. Neste contexto, o presente trabalho tem como principal objectivo dar um contributo na temática das soluções de melhoramento do comportamento e reforço de elementos construtivos em terra a partir do estudo biomimético de um ninho de andorinha-dos-beirais. De modo a identificar a eventual existência de algum fenómeno de aglutinação ocorrido durante o processo de construção de um ninho de andorinha-dos-beirais, procedeu-se a um trabalho experimental de caracterização a partir de amostras recolhidas em diferentes ninhos encontrados na zona de Vila Real. Para a identificação da composição química inorgânica e mineralógica das amostras recolhidas realizaram-se análises em Scanning Electron Microscopy / Energy Dispersive Spectroscopy (SEM/EDS) e por difracção de raios-X. Para a identificação da composição orgânica das amostras recolhidas foi feita a quantificação colorimétrica do teor de proteínas pelo método de biureto, e do teor de polissacarídeos/açucares pelo método dos açúcares totais. Os resultados experimentais relativos às amostras retiradas dos ninhos quando comparados com resultados similares relativos a amostras de argila recolhidas na mesma zona de origem dos ninhos, são muito semelhantes, destacando-se apenas a presença de polissacarídeos/açucares nas amostras de ninho. Pretende-se que a partir dos resultados da caracterização do material constituinte dos ninhos se possam retirar sugestões para o desenvolvimento de soluções de estabilização e de melhoramento de elementos construtivos existentes de terra crua

The motion of two masses coupled to a massive spring

We discuss the classical motion of a spring of arbitrary mass coupled to two arbitrary massive blocks attached at its ends. A general approach to the problem is presented and some general results are obtained. Examples for which a simple elastic function can be inferred are discussed and the normal modes and normal frequencies obtained. An approximation procedure to the evaluation of the normel frequencies in the case of uniform elastic function and mass density is also discussed.Comment: Standard Latex file plus three eps figure