A importância da permeabilidade na avaliação do desempenho de sistemas de ventilação

A permeabilidade da envolvente é um parâmetro fundamental na avaliação do desempenho energético dos edifícios, uma vez que permite avaliar as trocas de ar não controladas. O parâmetro mais utilizado para quantificar a permeabilidade é o número de renovações horárias para um diferencial de pressão de 50 Pa (n50), que pode ser determinado experimentalmente com recurso a uma porta ventiladora. No âmbito do Regulamento de Desempenho Energético dos Edifícios de Habitação (REH), o Laboratório Nacional de Engenharia Civil (LNEC) desenvolveu uma folha de cálculo que permite avaliar o desempenho dos sistemas de ventilação, determinando, entre outros parâmetros, a taxa de renovação de ar da fração na estação de aquecimento e na de arrefecimento. Para o cálculo é necessário caracterizar a permeabilidade ao ar da envolvente, nomeadamente através da indicação do valor do n50. Pretende-se com este artigo apresentar os resultados de uma análise de sensibilidade cujo objetivo é avaliar a importância da permeabilidade no desempenho dos sistemas de ventilação. Para tal, utilizou-se a ferramenta de cálculo desenvolvida pelo LNEC, estudando-se o impacto do clima exterior, da geometria do edifício e do sistema de ventilação. Alterações na estanquidade de uma dada envolvente podem ter uma influência relevante nos padrões de fluxo de ar e na taxa de renovação do ar interior. Dos cenários considerados, a maior variação da taxa de renovação de ar verificada foi de 2.73 h-1 entre um n50 medido de 0.6 e 10 h-1. Esta variação representa cerca de 6.8 e 4.5 vezes os valores de referência para a estação de aquecimento, 0.4 h-1, e a estação de arrefecimento, 0.6 h-1, respetivamente. Para determinados cenários o aumento da permeabilidade da envolvente esteve associado à criação de fluxos de ar por ventilação cruzada. O efeito do vento e geometria da envolvente têm um impacto preponderante relativamente ao efeito da impulsão térmica em Portugal continental no referente à regulação das taxas de renovação de ar. Consequentemente as variações na estanquidade da envolvente implicam oscilações mais pronunciadas nas primeiras em sistemas predominantemente influenciados por diferenciais de pressão decorrentes do efeito do vento e geometria da edificação em estudo. Bolsa de Doutoramento PD/BD/135162/2017, através do Programa Doutoral EcoCoRe. Este trabalho foi suportado financeiramente pelo: Projecto POCI-01-0145-FEDER-007457 - CONSTRUCT - Institute of R&D In Structures and Construction com apoio financeiro do FEDER através do COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) – e por fundos nacionais através da FCT

Crystal ball, virtual gallery C reation system for immersive environments

This paper presents a concept and a tool suite for authoring, configuring, organizing and displaying 3D virtual galleries, depicting multimedia content, like art, picture, movie or any other kind of media, which are appropriate for large-scale immersive virtual environments such as the CAVE™. A comparison was established by the authors with standard PC environments while experimenting virtual environments produced by Crystal Ball, showing the superior experience obtained by an installation of the type of CAVE™ that is in operation at Lousal, south of Portugal.info:eu-repo/semantics/publishedVersio

Diluted antiferromagnet in a ferromagnetic enviroment

The question of robustness of a network under random ``attacks'' is treated in the framework of critical phenomena. The persistence of spontaneous magnetization of a ferromagnetic system to the random inclusion of antiferromagnetic interactions is investigated. After examing the static properties of the quenched version (in respect to the random antiferromagnetic interactions) of the model, the persistence of the magnetization is analysed also in the annealed approximation, and the difference in the results are discussed

Fish-based groups for ecological assessment in rivers: the importance of environmental drivers on taxonomic and functional traits of fish Assemblages

The use of river-types is of practical value, serving as groups for which assessment procedures can be developed and applied. An abiotic typology was set by the Portuguese Water Agency, mainly based on 6 major morphoclimatic regions. However, to be biologically meaningful, this typology should fit the distribution patterns of the biological quality elements communities proposed in Water Framework Directive under the lowest possible human pressure. This study aimed to identify and characterize fish-based geographical groups for continental Portugal and their environmental and geographical discriptors, using taxonomic and functional traits. Sampling took place between 2004 and 2006 during Spring. Fish fauna from 155 reference sites was analysed using a multivariate approach. Cluster Analysis on fish composition identified 10 fish-groups, expressing a clear correspondence to the river basin level, due to the restrict basin distribution of many species. Groups showed a wider aggregation in 4 regions with a larger geographical correspondence, statistically supported by Similarity Analysis, both on fish composition and mostly on fish metrics/guilds. Principal Components Analysis revealed major environmental drivers associated to fish-groups and fish-regions. Fish-groups were hierarchically grouped over major and local regions, expressing a large-scale response to a North-South environmental gradient defined by temperature, precipitation, mineralization and altitude, and a regional scale response mainly to drainage area and flow discharge. From North to South, fish-regions were related to the morphoclimatic regions. Results contributed to reduce redundance in abiotic river-types and set the final typology for Portuguese rivers, constituting a fundamental tool for planning and managing water resources

Frequency up- and down-conversions in two-mode cavity quantum electrodynamics

In this letter we present a scheme for the implementation of frequency up- and down-conversion operations in two-mode cavity quantum electrodynamics (QED). This protocol for engineering bilinear two-mode interactions could enlarge perspectives for quantum information manipulation and also be employed for fundamental tests of quantum theory in cavity QED. As an application we show how to generate a two-mode squeezed state in cavity QED (the original entangled state of Einstein-Podolsky-Rosen)

Truncated states obtained by iteration

Quantum states of the electromagnetic field are of considerable importance, finding potential application in various areas of physics, as diverse as solid state physics, quantum communication and cosmology. In this paper we introduce the concept of truncated states obtained via iterative processes (TSI) and study its statistical features, making an analogy with dynamical systems theory (DST). As a specific example, we have studied TSI for the doubling and the logistic functions, which are standard functions in studying chaos. TSI for both the doubling and logistic functions exhibit certain similar patterns when their statistical features are compared from the point of view of DST. A general method to engineer TSI in the running-wave domain is employed, which includes the errors due to the nonidealities of detectors and photocounts.Comment: 10 pages, 22 figure