Browsing by Issue Date, starting with "2005-09"
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- A análise input-output na avaliação do impacte económico das universidadesPublication . Silva, João Albino; Santos, Sérgio Pereira dosO papel das instituições de ensino superior no desenvolvimento económico das regiões onde se localizam é amplamente reconhecido e a sua quantificação tem sido objecto de análise de vários estudos ao longo das últimas três décadas. Não obstante o interesse suscitado, não existe actualmente uma metodologia universalmente aceite para a realização de estudos nesta área de investigação. Constitui objectivo principal do presente artigo contribuir para a discussão e reflexão sobre este tema através da revisão da literatura e discussão de alguns dos aspectos metodológicos fundamentais subjacentes à avaliação do impacte económico das instituições de ensino superior, com particular ênfase para a análise input-output. Pretende-se também com este esforço definir os principais procedimentos metodológico a adoptar na avaliação do impacte económico da Universidade do Algarve na economia regional.
- Ion binding to natural organic matter: General considerations and the NICA-Donnan modelPublication . Koopal, L. K.; Saito, T.; Pinheiro, J. P.; Van Riemsdijk, W. H.The general principles of cation binding to humic matter and the various aspects of modeling used in general-purpose speciation programs are discussed. The discussion will focus on (1) the discrimination between chemical and electrostatic interactions, (2) the binding site heterogeneity, (3) the models for the electrostatic interactions, such as the Donnan model and (4) the complications inherent to ion binding in multi-component systems, including a different stoichiometry for different ions. The basic NICA (non ideal competitive adsorption) model addresses issues (1), (2) and (4) and ensures thermodynamic consistency. The electrostatic interactions (3) can be included using the ion activity adjacent to the binding sites. To compute this activity it is necessary to use an electrostatic model that relates the particle charge and the characteristic particle potential. Several simplifications to arrive at such a relation are analyzed. The Donnan model is proposed as the most convenient model. A short derivation of the NICA–Donnan model is presented to illustrate that the derivation is quite straightforward once it is clear which assumptions should be made. The main parameters of the NICA model are the site density, the median affinity constants for the different ions, the ion stoichiometry and the width of the generic affinity distribution. All these parameters are intrinsic properties that are independent of pH, salt concentration or metal concentration. The key parameter of the Donnan model is the Donnan volume, for which an empirical relation with one adjustable parameter is advised. The NICA–Donnan model has been used in several studies. To illustrate the capabilities of the model some results obtained for purified humic acid are presented together with model predictions. Key features of the model are its ability to adjust to different heterogeneities and binding stoichiometries and its predictive abilities with respect to metal ion–proton and metal–metal ion competition. With the application the model should be regarded as semi-empirical because assumptions have been made for its derivation that are not met in practice. Both for this reason and since it is difficult, if not impossible, to find a unique set of parameters for a given system the interpretation of the parameter values may be difficult. A brief discussion is given on the generic NICA–Donnan description of fulvic and humic acids presented by Milne et al. [C.J. Milne, D.G. Kinniburgh, E. Tipping, Environ. Sci. Technol. 35 (2001) 2049; C.J. Milne, D.G. Kinniburgh, W.H. van Riemsdijk, E. Tipping, Environ. Sci. Technol. 37 (2003) 958]. Finally a brief literature review is presented on the use of the NICA–Donnan model for other heterogeneous natural sorbent systems.
- Microplankton composition, production and upwelling dynamics in Sagres (SW Portugal) during the summer of 2001Publication . Loureiro, S.; Newton, Alice; Icely, J. D.Microplankton community, production, and respiration were studied alongside physical and chemical conditions at Sagres (SW Portugal) during the upwelling season, from May to September 2001. The sampling station was 5 km east of the upwelling centre off Cabo S. Vicente, and 2 km west of an offshore installation for bivalve aquaculture. Three major periods were distinguished according to sea surface temperature (SST): period I (Pl; May and June), characterised by high temperature values (17.0 +/- 1.8 degrees C); period 2 (P2; July), characterised by lower temperatures (14.6 +/- 0.3 degrees C), identified as an upwelling-blooming stage; and period 3 (P3; August), characterised by a high temperature pattern (16.25 +/- 1.14 degrees C). Chaetoceros spp., Thalassiosira spp., Lauderia spp., Detonula spp. and Pseudo-nitzschia spp. were the major taxa contributing to the dissimilarities between P2 (July) and the other periods. In July (P2), the average gross production (GP; 52.5 +/- 12.3 mu M O-2 d(-1)) and net community production (NCP; 46.9 +/- 15.3 mu M O-2 d(-1)) peaked with the maximal concentrations of diatom-chl a. Dark community respiration (DCR) remained low and more constant throughout (4.6 +/- 3.6 mu M O-2 d(-1)). The plankton assemblage was dominated by diatoms throughout the survey. Physical events were the primary factors determining the microplankton structure and distribution at this location.
- Unit root tests for panel data: a survey and an applicationPublication . Barreira, Ana Paula; Rodrigues, Paulo M. M.The importance of a priori check of the existence of unit roots in the panel data comes from the already known effect that the presence of unit roots in time series may cause a misinterpretation of estimated results. Adding the cross-section dimension to the time series dimension offers an advantage in testing for nonstationary and cointegration since cross-section increases the data set used in those tests, thus improving their power. However, the cross-section dimension also brings some new problems into question, namely the existence of cross-section dependency which can bias usual panel data unit root test results in small samples. This paper presents a survey of panel unit root tests, evidencing the most recent developments on the issue, including those that account for the presence of contemporaneous cross-correlation as well as for the presence of heterogeneous serial correlation. Parallel to the developments of panel unit root tests, great attention has also been given to cointegration tests. We briefly review the most widely referred cointegration tests. We apply the reviewed panel unit root tests on an EU social variable which represents the population weight over than 65 years of age. We consider data running from 1970 to 2001. The panel unit root test results reveal to be sensitive to the prior assumptions regarding contemporaneous cross-correlation and heterogeneous serial correlation in small samples. The usual battery of panel unit root tests appear not to be adequate when a panel is composed by a mix of a stationary and nonstationary time series.
- Contributos da Internet para a cidadania na perspectiva dos formadores de T.I.C.: estudo de casoPublication . Silva, Natércia Maria Guerreiro Pereira da; Carioca, Vito José de JesusCom o presente trabalho pretende-se a construção de um instrumento de observação e análise que permita observar e analisar os comportamentos de cidadania que devem ser adoptados quando se utiliza a Internet, colocando em evidência a necessidade de desenvolver e promover práticas de cidadania na aprendizagem da Internet, como meio de contribuir para que os seus utilizadores continuem a ser conscientes e participativos, e ao mesmo tempo que partilham o conhecimento adquirido.
- Behavioural endocrinology: no hormonal response in tied fightsPublication . Oliveira, R. F.; Carneiro, L. A.; Canario, Adelino V. M.Fish androgens may start to surge only when there seems to be a good chance of winning a contest. Duel action: a cichlid attacks its reflection. Androgens are the principal sex steroids controlling reproduction and aggression in male fish1, but their production can also be affected by social interactions2, 3. Here we show that androgen concentrations are not significantly increased in cichlid fish (Oreochromis mossambicus) that are fighting their own image in a mirror, despite their aggressive behaviour towards the virtual intruder. Our results indicate that the hormonal response normally triggered in male contests is not induced under these circumstances by the act of fighting itself, and that it may therefore depend on some indicator of relative fighting ability that cannot be delivered by a mirror-image challenger.