Browsing by Issue Date, starting with "2011-08"
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- Using multitable techniques for assessing the temporal variability of species–environment relationship in a copepod community from a temperate estuarine ecosystemPublication . Cotrim Marques, Sónia; Pardal, Miguel Ângelo; MENDES, SUSANA; Azeiteiro, Ulisses Manuel de MirandaThis study investigated copepod assemblages' distribution patterns and determined the main hydrological and physical factors structuring it at different temporal scales. Copepod and hydrographic surveys were conducted seasonally during a one-year period, at a fixed station in Mondego estuary. Hourly samples were collected, during a diel cycle from sub-surface and 1m above the bottom, at spring tides. Temporal variability of copepod community was analyzed using the STATICO method. Seasonal variability of the environmental conditions, linked with periods of higher freshwater flow, were the main drivers responsible for copepod community structure observed. Seasonal changes related to environmental factors showed to be strongest in spring and in winter, which accounted with higher species density. Marine and estuarine copepods showed maximal abundance in spring and summer, while the period of higher river flow, coincidently with autumn and winter, imposed changes in the copepods composition, emphasizing the changes in saline zonation within the estuary due to regime of river discharge. STATICO also emphasized the effects of physical forcing at short-term temporal scales. The stable part of the species–environment relationships resulted from the combination of a salinity gradient linked to a fresh, brackish- and marine species gradient, which was dependent on tidal cycle. The STATICO method proved to be a valuable statistical tool to get a clear representation of temporal organization of the copepod assemblages.
- A simple scattering model for tree trunksPublication . Leonor, Nuno; Ferreira, David; Caldeirinha, Rafael; Fernandes, Telmo, Telmo Rui Carvalhinho Cunha, Telmo R.; Ferreira, DavidThis paper presents the work carried out in an effort of modelling the scattering and absorption effects of single tree trunks with application to the discrete Radiative Energy Transfer (dRET) based model applications. The assessment of the proposed empirical model was performed against measurements of both metallic and dielectric cylinders, mimicking tree trunks, at several micro- and millimetre wave frequencies, i.e. 9.4, 18.8 and 37.6 GHz. These were carried out in a controlled environment, i.e. an anechoic chamber, so that frequency dependent effects could be evaluated.
- Investigation of a time-variant dRET model in vegetation: XXIXth URSI general assembly to be held in Chicago, IL, USA, August 7–16, 2008Publication . Morgadinho, Sergio; Richter, Juergen; Caldeirinha, Rafael; Fernandes, Telmo, Telmo Rui Carvalhinho Cunha, Telmo R.In this paper, the discrete Radiative Energy Transfer is investigated as an effective mean to model wind induced time-variant vegetative radio channels. The investigated model will make use of the input parameters time-variation properties to achieve channel dynamics modeling. Analysis of both the foliated channel statistics and model performance against measured data, at 20 GHz, will be presented.
- Analysis of friction in the ejection of thermoplastic mouldingsPublication . Correia, Mário Simões; Miranda, Antonio Sousa; Oliveira, Marta Cristina; Capela, Carlos Alexandre; Pouzada, Antonio SergioThe ejection force of injection-moulded thermoplastics depends on the contact conditions at the moment of ejection. Replication of the polymer part surface occurs onto the mould surface during injection of the melt. Ejection takes place in a very short time, hence the static coefficient of friction must be considered for modelling the ejection process. To understand the contribution of the mechanisms involved in the friction during the ejection stage, a mixed approach was followed: analytical simulation of the ploughing, numerical simulation of the deformation, and experimental inference of the adhesion. The relevance of roughness, temperature and contact pressure in the coefficient of friction was evidenced.