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- Energy scenarios: Toward a new energy paradigmPublication . Devezas, Tessaleno; LePoire, David; Matias, João; Silva, AbílioPrimary energy sources exhibited regular long-term logistic substitution trends from the mid-19th century through the third quarter of the 20th century. This analysis, based on an extension of the Fisher–Pry substitution model, accounted for the observed historical shifts of primary energy use from sources of wood, coal, oil, natural gas, and nuclear. In the mid1980s the substitution dynamics was replaced by a relatively constant contribution from oil, natural gas, coal, nuclear power, and hydropower. However, a major factor in energy use dynamics in this recent period was substitution of conservation and efficiency for actual fuel use. The energy efficiency is measured as the ratio of economic activity to the rate of energy use (energy intensity). To incorporate these data into the logistic analysis, a method for estimating the fraction of energy saved by the increased efficiency was used. With this interpretation, energy efficiency fits within the substitution model. Furthermore, to identify indications of future energy scenarios, as well as to test the logistic substitution analysis, another statistical approach using ternary diagrams was developed. The consistent results from both logistic substitution and statistical analysis are compared with recent energy projections, trends in decarbonization, Kondratieff waves, and other efficiency measures. While the specific future mix of renewables and nuclear energy sources is uncertain, the more general logistic dynamics pattern of the energy system seems to be continuing as it has for about 150 years now.
- Mechanical Characterization of Composites with Embedded Optical FibersPublication . Silva, José M.A.; Devezas, Tessaleno; Silva, Abílio; Ferreira, José A. M.The purpose of this investigation is to evaluate quantitatively and comparatively the effect of embedding optical fibers (OF) on the mechanical behavior of a carbon fiber-epoxy composite in order to verify whether their presence can possibly degrade the mechanical performance of the host material. The existing literature on this subject is not conclusive about the nature and intensity of this effect. Adding more reliable data to our systematic study contributes to this discussion favoring the conclusion about a harmful influence as a consequence of optical fiber embedment. Three kinds of mechanical tests have been performed in this work: impact tests, static flexural tests, and fatigue tests. The results of some experiments point to a possible detrimental influence related to the presence of the OF, being it different in nature and intensity for each of these tests. The mechanical behavior in static loading conditions seems to be not significantly affected as a consequence of the presence of the OF, while that in impact and fatigue tests are strongly affected, even though this influence being physically distinct from each other. Based on these results, some discussion is made about the possible failure mechanisms that can explain the detected differences.