Repositório IC-Online
Repositório Científico da Instituição
Entradas recentes
Structure development during additive manufacturing
Publication . Tojeira, A.; Biscaia, S.; Viana, T.; Bártolo, P. J.; Mitchell, G. R.
Additive manufacturing involves the shaping of a product through the use of a liquid phase which is subsequently transformed to the solid state by cooling or through the use of chemical cross-linking reactions. Of particular note is the fused deposition modeling which utilizes semi-crystalline polymers such as poly(ε-caprolactone) or poly(lactic acid) and has been employed in CDRsp to prepare highly porous scaffolds for Tissue Engineering. We show that the crystallization process amplifies small levels of molecular anisotropy introduced in the additive writing process. We show that the level of anisotropy is significantly dependent on the process parameters such as temperature, write speed, and flow rate. The differences in the crystalline morphology introduced by changing these process parameters will have a marked impact on the mechanical properties. This in turn will alter the growth of tissue on such scaffold structures. As with other polymer processing procedures, tuning the process parameters provides a route to controlling and defining the structure and morphology of the scaffold and the properties exhibited by that scaffold.
Natural establishment of Eucalyptus globulus Labill. in burnt stands in Portugal
Publication . Águas, Ana; Ferreira, António; Maia, Paula; Fernandes, Paulo M.; Roxo, Luís; Keizer, Jan; Silva, Joaquim S.; Rego, Francisco C.; Moreira, Francisco
Exotic tree species are increasingly common in many regions of the world and at least some species are becoming naturalized in the regions where they were introduced. Disturbances like fire may be at the origin or accelerate the naturalization of these species. Portugal holds one of the largest areas of exotic Eucalyptus globulus plantations in the world and is one of the countries most affected by forest fires. These two facts have triggered the present research. This study aimed at characterising medium-term natural establishment of E. globulus plants originated from seeds under natural conditions in burnt planted forests (pure E. globulus stands, pure Pinus pinaster stands, and mixed stands of both species), and at analysing factors associated with this establishment. Occurrence, abundance and height of naturally established E. globulus plants were characterized in 284 sites distributed in burnt areas, across Central and Northern Portugal, 5–7 years after wildfire. Generalized linear models were used to assess the influence of stand type, regional productivity potential, and post-fire management practices on occurrence probability, density, and median height of sampled E. globulus individuals. The influence of these explanatory variables on the structure (in terms of size class distribution) of naturally established E. globulus cohort was examined using analysis of similarity and non-metric multidimensional scaling. Naturally established E. globulus plants were present in 93.1%, 19.0% and 98.6% of samples in pure E. globulus, pure P. pinaster and mixed stands, respectively. Cohort median density was 0.20 plants m−2 and maximum density was 4.55 plants m−2. Median height of plants was 2.0 m and 95.3% of them had h >1.30 m and DBH ⩽5 cm. Establishment probability, density and median height were highest in the most productive regions. Three post-fire management operations had a significant influence on the response variables: (i) salvage logging was associated with a higher density; (ii) tillage was associated with a lower density and a smaller median height; (iii) understorey removal was associated with a lower occurrence probability. Tillage was the only studied factor influencing the size structure of spontaneously established cohort, eliminating larger plants. This study showed that stand type, productivity region and post-fire management operations might have significantly influenced the natural establishment of E. globulus in burnt areas, and consequently the species naturalization process in Portugal. The implications of these findings for management are discussed.
Innovative developments on Agile-CAD system
Publication . Gaspar, M.; Alves, N.; Martins-Ferreira, N.; Bártolo, P.
Agile-CAD is a reverse engineering computer tool that allows the recovering of outer and inner 3D shapes of existing objects of revolution with constant thickness, using silhouettes computed from one or two digital views. In this context, some improved algorithms were developed in order to provide more accurate and robust tridimensional reconstruction when using a single digital image as source. Experimental results based on real images are presented, demonstrating the good performance of this computer tool.
Temporal changes in macrofauna as response indicator to potential human pressures on sandy beaches
Publication . Bessa, Filipa; Gonçalves, Sílvia C.; Franco, João N.; André, José N.; Cunha, Pedro P.; Marques, João Carlos
Sandy beaches are natural dynamic ecosystems, which are becoming worldwide increasingly disturbed by intensive human direct use, coastal development and erosive evolution. In this study, we have examined whether ten years of potential increased human pressures have resulted in significant changes in the macrofaunal assemblages’ structure and composition of two mesotidal sandy beaches (Cabedelo – urban beach, and Quiaios – rural beach) on the European Atlantic coast (Portugal). Seasonal macrofauna collections were performed at both beaches in two different periods, one in 1999–2000 and another in 2010–2011. The physical variables did not change significantly in both beaches throughout the studied periods, however, the urban beach was subject to an increase of human pressures (tourism and shoreline modifications) over the 10-years interval considered when compared with the rural beach. The univariate community descriptors (total density, species richness and diversity) did not differ significantly among periods for the rural beach. In contrast, temporal differences were found at the most urbanised beach, principally regarding the abundances of the amphipod Talitrus saltator and the isopod Tylos europaeus, two of the most abundant species at both beaches. PERMANOVA tests enhanced these temporal variations and the SIMPER analysis attributed to these species the main differences found between periods in this beach. Since the physical environment was similar in both periods, the ecological changes were most likely attributed to the increased human pressures observed at the urban beach. Nevertheless, this study highlights the need of further robust and effective impact assessments and long-term studies to better discern between natural and human induced changes on sandy beaches.
Bidentate Urea Derivatives of p-tert-Butyldihomooxacalix[4]arene: Neutral Receptors for Anion Complexation
Publication . Marcos, Paula M.; Teixeira, Filipa A.; Segurado, Manuel A. P.; Ascenso, José R.; Bernardino, Raul J.; Michel, Sylvia; Hubscher-Bruder, Véronique
Three new bidentate ureidodihomooxacalix[4]- arene derivatives (phenyl 5a, n-propyl 5b, and tert-butyl 5c) were synthesized in four steps from the parent compound ptert- butyldihomooxacalix[4]arene and obtained in the cone conformation, as shown by NMR studies. The binding ability of these neutral receptors toward spherical, linear, trigonal planar, and tetrahedrical anions was assessed by 1H NMR and UV-vis titrations. The structures and complexation energies of some complexes were also studied by DFT methods. The data showed that the association constants are strongly dependent on the nature of the substituent (aryl/alkyl) at the urea moiety. In general, for all the receptors, the association constants decrease with decrease of anion basicity. Ph-urea 5a is the best anion receptor, showing the strongest complexation for F- (log Kassoc = 3.10 in CDCl3) and also high binding affinity for the carboxylates AcO- and BzO-. Similar results were obtained by UV-vis studies and were also corroborated by DFT calculations.