Simulation of microalgal growth in a continuous photobioreactor with sedimentation and partial biomass recycling

Microalgae are considered as promising feedstocks for the third generation of biofuels. They are autotrophic organisms with high growth rate and can stock an enormous quantity of lipids (about 20 \u2013 40% of their dried cellular weight). This work was aimed at studying the cultivation of Scenedesmus obliquus in a two-stage system composed of a photobioreactor and a settler to concentrate and partially recycle the biomass as a way to enhance the microalgae cellular productivity. It was attempted to specify by simulation and experimental data a relationship between the recycling rate, kinetic parameters of microalgal growth and photobioreactor operating conditions. Scenedesmus obliquus cells were cultivated in a lab-scale flat-plate reactor, homogenized by aeration, and running in continuous flow with a residence time of 1.66 day. Experimental data for the microalgal growth were used in a semi-empirical simulation model. The best results were obtained for Fw = 0.2FI , when R = 1 and kd = 0 and 0.05 day-1, with the biomass production in the reactor varying between 8 g L -1 and 14 g L-1, respectively. The mathematical model fitted to the microalgal growth experimental data was appropriate for predicting the efficiency of the reactor in producing Scenedesmus obliquus cells, establishing a relation between cellular productivity and the minimum recycling rate that must be used in the system

Multi-phase semicrystalline microstructures drive exciton dissociation in neat plastic semiconductors

The optoelectronic properties of macromolecular semiconductors depend fundamentally on their solid-state microstructure. For example, the molecular-weight distribution influences polymeric- semiconductor properties via diverse microstructures; polymers of low weight-average molecular weight (Mw) form unconnected, extended-chain crystals, usually of a paraffinic structure. Because of the non-entangled nature of the relatively short-chain macromolecules, this leads to a polycrystalline, one-phase morphology. In contrast, with high-Mw materials, where average chain lengths are longer than the length between entanglements, two-phase morphologies, comprised of crystalline moieties embedded in largely unordered (amorphous) regions, are obtained. We investigate charge photogeneration processes in neat regioregular poly(3-hexylthiophene) (P3HT) of varying Mw by means of time-resolved photoluminescence (PL) spectroscopy. At 10 K, PL originating from recombination of long-lived charge pairs decays over microsecond timescales. Both the amplitude and decay rate distribution depend strongly on Mw. In films with dominant one-phase chain-extended microstructures, the delayed PL is suppressed as a result of a diminished yield of photoinduced charges, and its decay is significantly faster than in two-phase microstructures. However, independent of Mw, charge recombination regenerates singlet excitons in torsionally disordered chains forming more strongly coupled photophysical aggregates than those in the steady-state ensemble, with delayed PL lineshape reminiscent of that in paraffinic morphologies at steady state. We conclude that highly delocalized excitons in disordered regions between crystalline and amorphous phases dissociate extrinsically with yield and spatial distribution that depend intimately upon microstructure.Comment: 19 pages, 4 figure

Redes de Formação Profissional : uma dinâmica de participação e cidadania

O presente artigo reflecte sobre a dinâmica sócio-organizacional de entidades que desenvolvem acções de formação profissional no Alentejo Central (Portugal). O seu principal enfoque assenta no quadro de relacionamentos entre as entidades que promovem as acções de formação profissional, conduzindo a mecanismos de estruturação da acção colectiva, nomeadamente factores de confiança ou relações de «confiança desconfiante».This paper reflects on the social-organizational dynamics of institutions wich develops several vocational training actions in Alentejo Central (Portugal). Its main purpose settles on the relationships among these institutions that promote vocational training actions, leading to mechanisms of stucturing the collective action, mainly factors of confidence or relations of "untrusting confidence"

User behavior impact on IPTV platform performance

Tese de mestrado em Segurança Informática, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2010As plataformas de IPTV têm sido introduzidas pelos prestadores de serviços de rede e de telecomunicações como forma de competir com os operadores de cabo e satélite, impulsionando a receita por utilizador e simultaneamente reduzindo, na medida do possível, os custos associados à exploração de infra-estrutura legada. Através da análise de métricas de desempenho relativas ao funcionamento interno de um sistema complexo procuramos revelar padrões e ocorrências isoladas que possam indicar a existência de problemas de desempenho. Usando esta informação, analisámos também as características da actividade dos utilizadores. A hipótese subjacente é que deve ser possível correlacionar o desempenho de um sistema ou sub-sistema tendo por base o comportamento dos utilizadores, mesmo que estes não interajam directamente com o referido sub-sistema. Adicionalmente, esta correlação deve seguir regras que possam ser usadas, por exemplo, para redefinir a arquitectura do sistema ou detectar anomalias proactivamente. Neste projecto analisámos métricas de desempenho dos Servidores de Distribuição e dos Servidores de VOD. De seguida estudámos os Registos de Actividade das STB de forma a caracterizar as acções dos utilizadores que têm maior influência no desempenho da plataforma de IPTV. Demonstrámos que estas análises em domínios distintos (utilizadores/STB e servidores internos) pode convergir e possibilitar a activação de alarmes quando a probabilidade de ocorrência de problemas de desempenho é elevada.IPTV platforms are being introduced by many network operators in order to compete with cable and satellite operators, increasing the average revenue per user, while taking advantage and reducing as much as possible the losses associated with legacy infra-structure. By analyzing performance metrics regarding the inner works of complex systems we aimed at unveiling patterns and identifying outlier occurrences that indicate actual or potential problems. Using such information we analyzed user activity information seeking to match the identified outlier patterns with characteristic user activity. The broader underlying hypothesis is that it is possible to correlate a system, or system’s performance problem based on the behavior of the end users even if they do not interact with it. Furthermore, we assume that this correlation follow rules which could thereafter be used for architecture redesign and proactive anomaly detection. In this project, we examined performance metrics of the Distribution Servers and VOD Servers. We then used STB activity logs to characterize the user actions with greater influence on the IPTV platform. We showed that these analyzes of multiple domains (user/STB and internal servers) can be merged enabling to raise alerts whenever there is high probability of occurring efficiency problems in the system

Diagnóstico social no terceiro setor. A radiografia das Misericórdias do distrito de Évora

Resumo: Este artigo é uma súmula de um diagnóstico social, coordenado pelos autores, que teve como objetivo compreender as dinâmicas e as relações inter e intra organizacionais das Misericórdias do distrito de Évora. O trabalho desenvolvido tem por base uma metodologia de diagnóstico desenvolvida pelos autores deste artigo, tendo como estratégia analítica a análise de redes sociais e a análise prospetiva, através das quais se elabora um quadro sobre o estado atual das Misericórdias, procede-se a um mapeamento da rede e perspetivam-se estratégias de ação coletiva para as instituições. Palavras-Chave: Misericórdias, diagnóstico social, estratégias de ação coletiva. Abstract: This article is a summary of a social diagnosis, coordinated by the authors, which aimed to understand the dynamics and inter and intra organizational relationships of the Mercies of the Évora district. The work is based on a diagnostic methodology developed by the authors of this article, the analytical strategy to social network analysis and prospective analysis, through which draw up a picture of the current state of Mercies, proceed to a mapping network and perspetivam up collective action strategies for the institutions. Keywords: Mercies, social diagnosis, collective action strategies