Instituto Superior Técnico

About: Instituto Superior Técnico is a based out in . It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 10085 authors who have published 30226 publications receiving 667524 citations. The organization is also known as: IST & Instituto Superior Tecnico.

The nature of LINER galaxies: - Ubiquitous hot old stars and rare accreting black holes

Abstract: Context. Galaxies, which often contain ionised gas, sometimes also exhibit a so-called low-ionisation nuclear emission line region (LINER). For 30 years, this was attributed to a central mass-accreting supermassive black hole (more commonly known as active galactic nucleus, AGN) of low luminosity, making LINER galaxies the largest AGN sub-population, which dominate in numbers over higher luminosity Seyfert galaxies and quasars. This, however, poses a serious problem. While the inferred energy balance is plausible, many LINERs clearly do not contain any other independent signatures of an AGN. Aims. Using integral field spectroscopic data from the CALIFA survey, we compare the observed radial surface brightness profiles with what is expected from illumination by an AGN. Methods. Essential for this analysis is a proper extraction of emission lines, especially weak lines, such as Balmer H beta lines, which are superposed on an absorption trough. To accomplish this, we use the GANDALF code, which simultaneously fits the underlying stellar continuum and emission lines. Results. For 48 galaxies with LINER-like emission, we show that the radial emission-line surface brightness profiles are inconsistent with ionisation by a central point-source and hence cannot be due to an AGN alone. Conclusions. The most probable explanation for the excess LINER-like emission is ionisation by evolved stars during the short but very hot and energetic phase known as post-AGB. This leads us to an entirely new interpretation. Post-AGB stars are ubiquitous and their ionising effect should be potentially observable in every galaxy with the gas present and with stars older than ~1 Gyr unless a stronger radiation field from young hot stars or an AGN outshines them. This means that galaxies with LINER-like emission are not a class defined by a property but rather by the absence of a property. It also explains why LINER emission is observed mostly in massive galaxies with old stars and little star formation.

On the planning and analysis of Integrated Community Energy Systems: A review and survey of available tools

Abstract: Highly Integrated Community Energy Systems (ICES) greatly but not solely dependent on combined heat and power (CHP) sources are a viable approach for dealing effectively with the new set of global threats which Mankind is facing, such as Climate Change, Global Warming and Extreme Poverty. ICES are capable of delivering sustainable electricity, heat and cold to small communities and of working as grid-connected or islanded microgrids, adding technical, economical, environmental and social benefits to populations. The impacts of introducing ICES in current distribution networks can be analyzed at different scales due to the wide range of influence exerted not only at the local but also at regional and global levels. For these reasons, there is increased need for appropriate modeling of ICES for the vital purposes of planning and analysis of these systems. An overview on the available bottom-up tools for the optimization planning and analysis of ICES is done in this paper. The survey shows that DER-CAM can be considered an appropriate tool for the purpose of ICES design modeling due to the robust and flexible three-level optimization algorithm, hourly time step and other scale considerations but particularly due to the several successful applications with modeling microgrid systems. Additionally there is research experience on expanding the objective function for environmental concerns and also with EV battery storage interactions. Finally, GAMS DER-CAM's base language, is a widely known package for allowing changes to be made in model specifications simply and safely. In that sense, there is potential in exploring such tool for the design of ICES. Furthermore, it is found that MARKAL/TIMES, also a GAMS/CPLEX based tool, has scale flexibility which enables it for analyzing the long-term deployment of ICES in time. There is opportunity in this field for further work exploring the sustainability-sound modeling for optimal design of ICES and deployment scenario options evaluation, through long-term time horizons consideration.

Speciation Studies of Bifunctional 3-Hydroxy-4-Pyridinone Ligands in the Presence of Zn2+ at Different Ionic Strengths and Temperatures.

Abstract: The acid–base properties of two bifunctional 3-hydroxy-4-pyridinone ligands and their chelating capacity towards Zn2+, an essential bio-metal cation, were investigated in NaCl aqueous solutions by potentiometric, UV-Vis spectrophotometric, and 1H NMR spectroscopic titrations, carried out at 0.15 ≤ I/mol −1 ≤ 1.00 and 288.15 ≤ T/K ≤ 310.15. A study at I = 0.15 mol L−1 and T = 298.15 K was also performed for other three Zn2+/Lz− systems, with ligands belonging to the same family of compounds. The processing of experimental data allowed the determination of protonation and stability constants, which showed accordance with the data obtained from the different analytical techniques used, and with those reported in the literature for the same class of compounds. ESI-MS spectrometric measurements provided support for the formation of the different Zn2+/ligand species, while computational molecular simulations allowed information to be gained on the metal–ligand coordination. The dependence on ionic strength and the temperature of equilibrium constants were investigated by means of the extended Debye–Huckel model, the classical specific ion interaction theory, and the van’t Hoff equations, respectively.