Showing papers by "Instituto Superior Técnico published in 2013"

Green composites: A review of adequate materials for automotive applications

Abstract: This study provides a bibliographic review in the broad field of green composites seeking-out for materials with a potential to be applied in the near future on automotive body panels. Hereupon, materials deriving from renewable resources will be preferred as opposed to the exhaustible fossil products. With the technical information of bio-polymers and natural reinforcements a database was created with the mechanical performance of several possible components for the prospect green composite. Following the review, an assessment is performed where aspects of suitability for the candidate elements in terms of mechanical properties are analyzed. In that section, renewable materials for matrix and reinforcement are screened accordingly in order to identify which hold both adequate strength and stiffness performance along with affordable cost so as to be a promising proposal for a green composite.

The Sol–Gel Route to Advanced Silica-Based Materials and Recent Applications

Abstract: Applications Rosaria Ciriminna,† Alexandra Fidalgo,‡ Valerica Pandarus, Franco̧is Beĺand, Laura M. Ilharco,*,‡ and Mario Pagliaro*,† †Istituto per lo Studio dei Materiali Nanostrutturati, CNR, via U. La Malfa 153, 90146 Palermo, Italy ‡Centro de Química-Física Molecular and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Tećnico, Complexo I, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal SiliCycle Inc., 2500, Parc-Technologique Boulevard, Quebec City, Quebec G1P 4S6, Canada

The O3N2 and N2 abundance indicators revisited: improved calibrations based on CALIFA and T e-based literature data

Abstract: The use of integral field spectroscopy is since recently allowing to measure the emission line fluxes of an increasingly large number of star-forming galaxies, both locally and at high redshift. Many studies have used these fluxes to derive the gas-phase metallicity of the galaxies by applying the so-called strong-line methods. However, the metallicity indicators that these datasets use were empirically calibrated using few direct abundance data points (T_e-based measurements). Furthermore, a precise determination of the prediction intervals of these indicators is commonly lacking in these calibrations. Such limitations might lead to systematic errors in determining the gas-phase metallicity, especially at high redshift, which might have a strong impact on our understanding of the chemical evolution of the Universe. The main goal of this study is to review the most widely used empirical oxygen calibrations, O3N2 and N2, by using new direct abundance measurements. We pay special attention to (1) the expected uncertainty of these calibrations as a function of the index value or abundance derived and (2) the presence of possible systematic offsets. This is possible thanks to the analysis of the most ambitious compilation of T_e-based H II regions to date. This new dataset compiles the Te-based abundances of 603 H II regions extracted from the literature but also includes new measurements from the CALIFA survey. Besides providing new and improved empirical calibrations for the gas abundance, we also present a comparison between our revisited calibrations with a total of 3423 additional CALIFA H II complexes with abundances derived using the ONS calibration from the literature. The combined analysis of T_e-based and ONS abundances allows us to derive their most accurate calibration to date for both the O3N2 and N2 single-ratio indicators, in terms of all statistical significance, quality, and coverage of the parameters space. In particular, we infer that these indicators show shallower abundance dependencies and statistically significant offsets compared to others'. The O3N2 and N2 indicators can be empirically applied to derive oxygen abundances calibrations from either direct abundance determinations with random errors of 0.18 and 0.16, respectively, or from indirect ones (but based on a large amount of data), reaching an average precision of 0.08 and 0.09 dex (random) and 0.02 and 0.08 dex (systematic; compared to the direct estimations), respectively.

Static, free vibration and buckling analysis of isotropic and sandwich functionally graded plates using a quasi-3D higher-order shear deformation theory and a meshless technique

Abstract: In this paper the authors derive a higher-order shear deformation theory for modeling functionally graded plates accounting for extensibility in the thickness direction. The explicit governing equations and boundary conditions are obtained using the principle of virtual displacements under Carrera’s Unified Formulation. The static and eigenproblems are solved by collocation with radial basis functions. The efficiency of the present approach is assessed with numerical results including deflection, stresses, free vibration, and buckling of functionally graded isotropic plates and functionally graded sandwich plates.

Hydrogen production by alkaline water electrolysis

Abstract: Water electrolysis is one of the simplest methods used for hydrogen production. It has the advantage of being able to produce hydrogen using only renewable energy. To expand the use of water electrolysis, it is mandatory to reduce energy consumption, cost, and maintenance of current electrolyzers, and, on the other hand, to increase their efficiency, durability, and safety. In this study, modern technologies for hydrogen production by water electrolysis have been investigated. In this article, the electrochemical fundamentals of alkaline water electrolysis are explained and the main process constraints (e.g., electrical, reaction, and transport) are analyzed. The historical background of water electrolysis is described, different technologies are compared, and main research needs for the development of water electrolysis technologies are discussed.

Mass-metallicity relation explored with CALIFA I. Is there a dependence on the star-formation rate?

Abstract: We studied the global and local ℳ-Z relation based on the first data available from the CALIFA survey (150 galaxies). This survey provides integral field spectroscopy of the complete optical extent of each galaxy (up to 2−3 effective radii), with a resolution high enough to separate individual H II regions and/or aggregations. About 3000 individual H II regions have been detected. The spectra cover the wavelength range between [OII]3727 and [SII]6731, with a sufficient signal-to-noise ratio to derive the oxygen abundance and star-formation rate associated with each region. In addition, we computed the integrated and spatially resolved stellar masses (and surface densities) based on SDSS photometric data. We explore the relations between the stellar mass, oxygen abundance and star-formation rate using this dataset. We derive a tight relation between the integrated stellar mass and the gas-phase abundance, with a dispersion lower than the one already reported in the literature (σ_Δlog (O/H) = 0.07 dex). Indeed, this dispersion is only slightly higher than the typical error derived for our oxygen abundances. However, we found no secondary relation with the star-formation rate other than the one induced by the primary relation of this quantity with the stellar mass. The analysis for our sample of ~3000 individual H II regions confirms (i) a local mass-metallicity relation and (ii) the lack of a secondary relation with the star-formation rate. The same analysis was performed with similar results for the specific star-formation rate. Our results agree with the scenario in which gas recycling in galaxies, both locally and globally, is much faster than other typical timescales, such like that of gas accretion by inflow and/or metal loss due to outflows. In essence, late-type/disk-dominated galaxies seem to be in a quasi-steady situation, with a behavior similar to the one expected from an instantaneous recycling/closed-box model.

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.

3D deflagration simulations leaving bound remnants: a model for 2002cx-like Type Ia supernovae

Abstract: cx-like supernovae are a sub-class of sub-luminous Type Ia supernovae. Their light curves and spectra are characterized by distinct features that indicate strong mixing of the explosion ejecta. Pure turbulent deagrations have been shown to produce such mixed ejecta. Here, we present hydrodynamics, nucleosynthesis and radiative transfer calculations for a 3D full-star deagration of a Chandrasekhar-mass white dwarf. Our model is able to reproduce the characteristic observational features of SN 2005hk (a proto-typical 2002cx-like supernova), not only in the optical, but also in the near- infrared. For that purpose we present, for the rst time, ve near-infrared spectra of SN 2005hk from 0:2 to 26:6 days with respect to B-band maximum. Since our model burns only small parts of the initial white dwarf, it fails to completely unbind the white dwarf and leaves behind a bound remnant of 1.03 M { consisting mainly of unburned carbon and oxygen, but also enriched by some amount of intermediate-mass and iron-group elements from the explosion products that fall back on the remnant. We discuss possibilities for detecting this bound remnant and how it might inuence the late-time observables of 2002cx-like SNe.

The influence of empathy in human-robot relations

Abstract: The idea of robotic companions capable of establishing meaningful relationships with humans remains far from being accomplished. To achieve this, robots must interact with people in natural ways, employing social mechanisms that people use while interacting with each other. One such mechanism is empathy, often seen as the basis of social cooperation and prosocial behaviour. We argue that artificial companions capable of behaving in an empathic manner, which involves the capacity to recognise another's affect and respond appropriately, are more successful at establishing and maintaining a positive relationship with users. This paper presents a study where an autonomous robot with empathic capabilities acts as a social companion to two players in a chess game. The robot reacts to the moves played on the chessboard by displaying several facial expressions and verbal utterances, showing empathic behaviours towards one player and behaving neutrally towards the other. Quantitative and qualitative results of 31 participants indicate that users towards whom the robot behaved empathically perceived the robot as friendlier, which supports our hypothesis that empathy plays a key role in human-robot interaction.

Systematic study of the thermophysical properties of imidazolium-based ionic liquids with cyano-functionalized anions.

Abstract: In the past few years, ionic liquids (ILs) with cyano-functionalized anions have shown to be improved candidates for electrochemical and separation applications. Nevertheless, only scattered data exist hitherto and a broad analysis of their structure–property relationship has yet to be attempted. Therefore, in this work, a systematic study of the densities, viscosities and refractive indices of imidazolium-based ILs with cyano-functionalized anions was carried out at 0.1 MPa within a broad temperature range (from 278 to 363 K). The ILs under study are based on 1-alkyl-3-methylimidazolium cations (alkyl = ethyl, butyl and hexyl) combined with the [SCN]−, [N(CN)2]−, [C(CN)3]− and [B(CN)4]− anions. The selected matrix of cation/anion combinations allows us to provide a detailed and comprehensive investigation of the influence of the −CN group through an analysis of the thermophysical properties of the related ILs. The results show that, regardless of the cation, the densities decrease with an increase in the...

Influence of curing conditions on the durability-related performance of concrete made with selected plastic waste aggregates

Abstract: The effect of curing conditions on the durability of concrete mixes containing selected plastic waste aggregates was investigated. Concrete mixes were prepared in which 0%, 7.5% and 15% of natural aggregates were replaced by plastic – polyethylene terephthalate (PET) – aggregate. The effects of fine and coarse aggregates, used separately, as well as of their shape were also investigated. The manufactured concrete specimens were subjected to outdoor environment, laboratory environment and wet chamber curing regimes. Tests for shrinkage, water absorption by immersion, water absorption by capillarity action, carbonation and chloride penetration were carried out. The test results showed a decline in the properties of concrete made with plastic aggregates, in terms of durability, compared with conventional concrete. All specimens performed worse when subjected to drier curing regimes. However, sensitivity analyses showed that the properties of concrete mixes containing plastic aggregates generally deteriorate less than those of conventional concrete, when subjected to progressively drier curing regimes.

Free vibration analysis of functionally graded shells by a higher-order shear deformation theory and radial basis functions collocation, accounting for through-the-thickness deformations

Abstract: This paper deals with free vibration problems of functionally graded shells. The analysis is performed by radial basis functions collocation, according to a higher-order shear deformation theory that accounts for through-the-thickness deformation. The equations of motion and the boundary conditions are obtained by Carrera’s Unified Formulation resting upon the principle of virtual work, and further interpolated by collocation with radial basis functions. Numerical results include spherical as well as cylindrical shell panels with all edges clamped or simply supported and demonstrate the accuracy of the present approach.

Pervasive Aeolian Activity Along Rover Curiosity's Traverse in Gale Crater, Mars

Abstract: The NASA Mars Science Laboratory (MSL) rover, Curiosity, has safely landed near a 35-km-long dark dune field in Gale Crater on Mars. This dune field crosses the landing site from the northeast to the southwest and lies along Curiosity’s traverse to Aeolis Mons. Here we present the first evidence of recent aeolian activity in the form of ripple and dune migration, and further estimate wind directions within the dune field through analysis of ripple and dune morphologies and the Mars Regional Atmospheric Modeling System (MRAMS). We measured a minimum ripple migration rate of 0.66 m per Earth year, and dune migration rate of 0.4 m per Earth year, in the southwest portion of the field. A strongly bidirectional ripple crestline orientation, nearly orthogonal dune slipfaces, and linear seif or oblique dunes indicate a bidirectional wind regime with winds mainly coming from the ENE and from the northwest; however, MRAMS results indicate primary winds from the ENE. Our constraints on the wind regime provide the unique opportunity to use ground measurements from MSL to test the accuracy of winds predicted from orbital data.

TOFPET ASIC for PET applications

Abstract: A 64-channel ASIC for Time-of-Flight Positron Emission Tomography (TOF PET) imaging has been designed and simulated. The circuit is optimized for the readout of signals pro- duced by the scintillation of a L(Y)SO crystal optically coupled to a silicon photomultiplier (SiPM). Developed in the framework of the EndoTOFPET-US collaboration (1), the ASIC is integrated in the external PET plate and performs timing, digitization and data transmission for 511 keV and lower-energy events due to Compton scattering. Multi-event buffering capability allows event rates up to 100 kHz per channel. The channel cell includes a low input impedance low-noise current conveyor and two trans-impedance amplifier branches separately optimized for energy and time resolution. Two voltage mode discriminators generate respectively a fast trigger for accurate timing and a signal for time-over-threshold calcu- lation, used for charge measurement. The digitization of these signals is done by two low-power TDCs, providing coarse and fine time stamps that are saved into a local register and later managed by a global controller, which builds-up the 40-bit event data and runs the interface with the data acquisition back-end. Running at 160 MHz the chip yields a 50 ps time binning and dissipates u 7 mW per channel (simulated for 40 kHz event rate p/channel) for high capacitance photodetectors (9 mm 2 active area Silicon Photomultiplier with 320 pF terminal capacitance). The minimum SNR of 23.5 dB expected with this capacitance should allow triggering on the first photoelectron to achieve the envisaged timing performance for a TOF-PET system.

Nebular emission and the Lyman continuum photon escape fraction in CALIFA early-type galaxies

Abstract: PP is supported by Ciencia 2008 Contract, funded by FCT/MCTES (Portugal) and POPH/FSE (EC), and J.M.G. by a Post-Doctoral grant, funded by FCT/MCTES (Portugal) and POPH/FSE (EC). P.P. and J.M.G. acknowledge support by the Fundacao para a Ciencia e a Tecnologia (FCT) under project FCOMP-01-0124-FEDER-029170 (Reference FCT PTDC/FIS-AST/3214/2012), funded by FCT-MEC (PIDDAC) and FEDER (COMPETE). I.M. acknowledges support from Spanish grant AYA2010-15169 and the Junta de Andalucia through TIC-114 and the Excellence Project P08-TIC-03531. J.F.-B. from the Ramon y Cajal Program, grants AYA2010-21322-C03-02 and AIB-2010-DE-00227 from the Spanish Ministry of Economy and Competitiveness (MINECO), as well as from the FP7 Marie Curie Actions of the European Commission, via the Initial Training Network DAGAL under REA grant agreement n° 289313.

Nano-segregation in ionic liquids: scorpions and vanishing chains.

Abstract: The present study analyses the large structural differences, first observed using X-ray diffraction, between 1-alkyl-3-methylimidazolium-based ionic liquids, [Cnmim][Ntf2] (n = 3, 6, 9), and their counterparts with ether-substituted alkyl side chains, [(C1OC1)(n/3)mim][Ntf2] (n = 3, 6, 9). The MD simulations—obtained using a non-polarizable atomistic force-field to model the ionic liquids under discussion—demonstrate that the suppression of the nanostructured nature in the ionic liquids with ether chains is persistent along the entire series and it is not due to any modification of the polar network of the ionic liquid but rather due to the different morphologies of the non-polar regions that surround it. The modification of the non-polar regions—shift from bulky segregated domains in [Cnmim][Ntf2] to thin enveloping ones in [(C1OC1)(n/3)mim][Ntf2]—are caused by the inability of the oxygen-substituted alkyl side chains to pack effectively side by side, the existence of kinks along the chain that lead eventually to intra-molecular, scorpion-like interactions between the chains and the imidazolium ring, and by their stronger interactions with the cations of the polar network via the lone electron pairs of the ether oxygen atoms.

Carotenoid and lipid production by the autotrophic microalga Chlorella protothecoides under nutritional, salinity, and luminosity stress conditions

Abstract: Today microalgae represent a viable alternative source for high-value products. The specie Chlorella protothecoides (Cp), heterotrophically grown, has been widely studied and provides a high amount of lutein and fatty acids (FA) and has a good profile for biodiesel production. This work studies carotenoid and FA production by autotrophic grown Cp. Cp was grown until the medium’s nitrogen was depleted, then diluted in NaCl solution, resulting in nutritional, luminosity, and salinity stresses. Different NaCl concentrations were tested (10, 20, 30 g/L) at two different dilutions. After dilution, a color shifting from green to orange-red was noticed, showing carotenoid production. The best production of both carotenoids and FA was attained with a 20 g/L NaCl solution. The total carotenoid content was 0.8 % w/w (canthaxanthin (23.3 %), echinenone (14.7 %), free astaxanthin (7.1 %), and lutein/zeaxanthin (4.1 %)). Furthermore, the total lipid content reached 43.4 % w/w, with a FA composition of C18:1 (33.64 %), C16:0 (23.30 %), C18:2 (11.53 %), and less than 12 % of C18:3, which is needed to fulfill the biodiesel quality specifications (EN 14214).