Browsing by Issue Date, starting with "2016-06-09"
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- A comprehensive analysis of mechanical and morphological traits in temperate and tropical seagrass speciesPublication . de los Santos, Carmen B.; Onoda, Yusuke; Vergara, J.J.; Pérez-Lloréns, J. Lucas; Bouma, Tjeerd J.; La Nafie, Yayu A.; Cambridge, Marion L.; Brun, Fernando G.Knowledge of plant mechanical traits is important in understanding how plants resist abiotic and biotic forces and in explaining ecological strategies such as leaf lifespan. To date, these traits have not been systematically evaluated in seagrasses. We analysed mechanical (breaking force and tensile strength) and associated traits (thickness, width, length, fibre content, mass area, and lifespan) of leaves in 22 seagrass species (around one-third of all known seagrass species) to examine (1) the inter-specific variation of these traits in relation to growth form and bioregions, (2) the contribution of morphology to leaf breaking force, (3) how breaking force scales to leaf dimensions, and (4) how mechanical and structural traits correlate to leaf longevity. We also compared our seagrass dataset with terrestrial plant databases to examine similarities between them. Large variation in leaf breaking force was found among seagrass species but, on average, temperate species resisted higher forces than tropical species. Variation in leaf breaking force was largely explained by differences in leaf width rather than thickness, likely due to the benefits in leaf reconfiguration and light interception. Species of large dimensions (long leaves) typically had high leaf breaking force, plausibly to tolerate the drag forces they may experience, which are proportional to the leaf area. Leaves of long-lived species typically had high mass per leaf area and fibre content and they supported high breaking forces. Compared to terrestrial plants, seagrasses are short-lived species with moderately strong fibre-reinforced leaves, which probably evolved to withstand the hydrodynamic forces occurring in the sea, and in response to other environmental factors. Overall, our analysis provides new insights into the physical performance of seagrasses in the marine environment.
- Hybrid materials based on polyethylene and MCM-41 microparticles functionalized with silanes: catalytic aspects of in situ polymerization, crystalline features and mechanical propertiesPublication . Cerrada, M. L.; Bento, A.; Pérez, Ernesto; Lorenzo, V.; Lourenço, J. P.; Ribeiro, M. R.New nanocomposites based on polyethylene have been prepared by in situ polymerization of ethylene in presence of mesoporous MCM-41. The polymerization reactions were performed using a zirconocene catalyst either under homogenous conditions or supported onto mesoporous MCM-41 particles, which are synthesized and decorated post-synthesis with two silanes before polymerization in order to promote an enhanced interfacial adhesion. The existence of polyethylene chains able to crystallize within the mesoporous channels in the resulting nanocomposites is figured out from the small endothermic process, located at around 80 C, on heating calorimetric experiments, in addition to the main melting endotherm. These results indicate that polyethylene macrochains can grow up during polymerization either outside or inside the MCM-41 channels, these keeping their regular hexagonal arrangements. Mechanical response is observed to be dependent on the content in mesoporous MCM-41 and on the crystalline features of polyethylene. Accordingly, stiffness increases and deformability decreases in the nanocomposites as much as MCM-41 content is enlarged and polyethylene amount within channels is raised. Ultimate mechanical performance improves with MCM-41 incorporation without varying the final processing temperature.