Catalogue of the morphological features in the Spitzer Survey of Stellar Structure in Galaxies (S4^4G)

A catalogue of the morphological features for the complete Spitzer Survey of Stellar Structure in Galaxies (S$^4$G), including 2352 nearby galaxies, is presented. The measurements are made using 3.6 $\mu$m images, largely tracing the old stellar population; at this wavelength the effects of dust are also minimal. The measured features are the sizes, ellipticities, and orientations of bars, rings, ringlenses, and lenses. Measured in a similar manner are also barlenses (lens-like structures embedded in the bars), which are not lenses in the usual sense, being rather the more face-on counterparts of the boxy/peanut structures in the edge-on view. In addition, pitch angles of spiral arm segments are measured for those galaxies where they can be reliably traced. More than one pitch angle may appear for a single galaxy. All measurements are made in a human-supervised manner so that attention is paid to each galaxy. We used isophotal analysis, unsharp masking, and fitting ellipses to measured structures. We find that the sizes of the inner rings and lenses normalized to barlength correlate with the galaxy mass: the normalized sizes increase toward the less massive galaxies; it has been suggested that this is related to the larger dark matter content in the bar region in these systems. Bars in the low mass galaxies are also less concentrated, likely to be connected to the mass cut-off in the appearance of the nuclear rings and lenses. We also show observational evidence that barlenses indeed form part of the bar, and that a large fraction of the inner lenses in the non-barred galaxies could be former barlenses in which the thin outer bar component has dissolved.Comment: 17 pages, 12 figures, accepted for publication in A&

Wetting phenomenon in the liquid-vapor phase coexistence of a partially miscible Lennard-Jones binary mixture

We have carried out extensive equilibrium molecular dynamics (MD) simulations to study the structure and the interfacial properties in the liquid-vapor (LV) phase coexistence of partially miscible binary Lennard-Jones (LJ) mixtures. By analyzing the structural properties as a function of the miscibility parameter, $\alpha$, we found that at relatively low temperatures the system separates forming a liquid A-liquid B interface in coexistence with the vapor phase. At higher temperatures and, $0<\alpha\leq 0.5$, we found a temperature range, $T^{*}_{w}(\alpha) \leq T^{*} < T^{*}_{cons}(\alpha)$, where the liquid phases are wet by the vapor phase. Here, $T^{*}_{w}(\alpha)$ represents the wetting transition temperature (WTT) and $T^{*}_{cons}(\alpha)$ is the consolute temperature of the mixture. However, for $0.5< \alpha < 1$, no wetting phenomenon occurs. For the particular value, $\alpha=0.25$, we analyzed quantitatively the $T^{*}$ versus $\rho^{*}$, and $P^{*}$ versus $T^{*}$ phase diagrams and found, $T^{*}_{c}\simeq 1.25$, and $T^{*}_{cons}\simeq1.25$. We also studied quantitatively, as a function of temperature, the surface tension and the adsorption of molecules at the liquid-liquid interface. It was found that the adsorption shows a jump from a finite negative value up to minus infinity, when the vapor wets the liquid phases, suggesting that the wetting transition (WT) is of first order. The calculated phase diagram together with the wetting phenomenon strongly suggest the existence of a tricritical point. These results agree well with some experiments carried out in fluid binary mixtures.Comment: Enlarged version that include results of more extensive simulations. A total of 24 LaTeX pages that include 12 encapsulated poscript figures. To appear in PRE, Vol. 70, issue Sept. 1st (2004

Annual Legumes as an Alternative for Animal Feeding in Cuba

Studies conducted in Cuba have demonstrated the importance of the agronomic and nutritional performance of the species Vigna unguiculata (cowpea), Canavalia ensiformis (jackbean), Stizolobium niveum (mucuna), Lablab purpureus (dolicho) and Glycine max (soybean) as feed sources for non-ruminant species. Under Cuban tropical conditions, and with minimum agricultural inputs, jackbean, dolicho and mucuna have attained forage yields between 4 and 6 t dry matter (DM)/ha and grain yields between 2.57 and 3.41 t/ha and cowpea and soybean have given yields of between 1 and 2 t/ha (Díaz 2000). This study was carried out to determine the chemical composition of grains and forages of these annual legumes in relation to their use in animal feeding

Vivências e envolvimento acadêmico de estudantes universitários : adaptação e validação de escalas para a sua avaliação

Este artículo describe los procesos preliminares de adaptación y validación de dos instrumentos diseñados para describir Vivencias Académicas (centradas en la satisfacción) y la Implicación Académica (centrada en el compromiso) en estudiantes universitarios. De acuerdo con la literatura científica en el área, las vivencias y la implicación académica se encuentran asociadas con las dificultades relacionadas al abandono de los alumnos. Para este estudio se aplicaron dos cuestionarios a 261 estudiantes pertenecientes a la Universidad de Concepción, Campus Los Ángeles, Chile. Ambos instrumentos mostraron niveles adecuados de homogeneidad o consistencia interna en los ítems repartidos para las subescalas de cada cuestionario. Paralelamente, se calcularon las correlaciones entre las dimensiones de ambos cuestionarios, siendo los coeficientes obtenidos adecuados para los constructos evaluados. Estos antecedentes permiten el comienzo de la validación de los cuestionarios en estudio.This paper presents preliminary findings regarding the adaptation and validation of two instruments designed to measure Academic Experiences (centred on satisfaction) and Academic Involvement in university students. Previous research has shown that academic experience and involvement are strongly correlated with student drop-out rates. For the present study, the two surveys were administered to 261 students at the University of Concepción, Chile, on the Los Ángeles campus. Both instruments showed suitable levels of reliability and internal consistency on the subscales. Furthermore, the correlation coefficients obtained when comparing dimensions on each survey were acceptable for the constructs being evaluated. These findings allow for a preliminary validation of the two questionnaires included in the study.Descrevem-se os processos preliminares de adaptação e validação de dois instrumentos voltados para a avaliação das Vivências Acadêmicas (centradas na satisfação) e da Implicação Acadêmica (centrada no compromisso) de estudantes universitários. Conforme a literatura científica na área, vivências e implicação acadêmica encontram-se associadas às dificuldades relacionadas ao abandono dos alunos. Este estudo envolveu a aplicação dos dois questionários a 261 estudantes da Universidade de Concepción, campos Los Angeles, Chile. Ambos os instrumentos mostram níveis adequados de homogeneidade ou consistência interna dos itens divididos em subescalas, em cada questionário. Paralelamente, calculam-se as correlações entre as dimensões dos questionários, sendo os coeficientes obtidos adequados aos constructos avaliados. Estes antecedentes permitem o início da validação dos questionários em estudo.Red de Revistas Científicas de América Latina, el Caribe, España y Portugal Sistema de Información CientíficaUniversidad Austral de Chile Valdivia, Chil

Characterization of galactic bars from 3.6 μ m S 4 G imaging

Context. Stellar bars play an essential role in the secular evolution of disk galaxies because they are responsible for the redistribution of matter and angular momentum. Dynamical models predict that bars become stronger and longer in time, while their rotation speed slows down. Aims. We use the Spitzer Survey of Stellar Structure in Galaxies (S4G) 3.6 μm imaging to study the properties (length and strength) and fraction of bars at z = 0 over a wide range of galaxy masses (M∗ ≈ 108−1011 M⊙) and Hubble types (−3 ≤ T ≤ 10).Methods. We calculated gravitational forces from the 3.6 μm images for galaxies with a disk inclination lower than 65°. We used the maximum of the tangential-to-radial force ratio in the bar region (Qb) as a measure of the bar-induced perturbation strength for a sample of ~600 barred galaxies. We also used the maximum of the normalized m = 2 Fourier density amplitude (A2max) to characterize the bar. Bar sizes were estimated i) visually; ii) from ellipse fitting; iii) from the radii of the strongest torque; and iv) from the radii of the largest m = 2 Fourier amplitude in the bar region. By combining our force calculations with the H i kinematics from the literature, we estimated the ratio of the halo-to-stellar mass (Mh/M∗) within the optical disk and by further using the universal rotation curve models, we obtained a first-order model of the rotation curve decomposition of 1128 disk galaxies. Results. We probe possible sources of uncertainty in our Qb measurements: the assumed scale height and its radial variation, the influence of the spiral arms torques, the effect of non-stellar emission in the bar region, and the dilution of the bar forces by the dark matter halo (our models imply that only ~10% of the disks in our sample are maximal). We find that for early- and intermediate-type disks (−3 ≤ TQb by about 10−15%, which is of the same order as the uncertainty associated with estimating the vertical scale height. The halo correction on Qb becomes important for later types, implying a reduction of ~20−25% for T = 7−10. Whether the halo correction is included or not, the mean Qb shows an increasing trend with T. However, the mean A2max decreases for lower mass late-type systems. These opposing trends are most likely related to the reduced force dilution by bulges when moving towards later type galaxies. Nevertheless, when treated separately, both the early- and late-type disk galaxies show a strong positive correlation between Qb and A2max. For spirals the mean ε ≈ 0.5 is nearly independent of T, but it drops among S0s (≈0.2). The Qb and ε show a relatively tight dependence, with only a slight difference between early and late disks. For spirals, all our bar strength indicators correlate with the bar length (scaled to isophotal size). Late-type bars are longer than previously found in the literature. The bar fraction shows a double-humped distribution in the Hubble sequence (~75% for Sab galaxies), with a local minimum at T = 4 (~40%), and it drops for M∗ ≲ 109.5−10 M⊙. If we use bar identification methods based on Fourier decomposition or ellipse fitting instead of the morphological classification, the bar fraction decreases by ~30−50% for late-type systems with T ≥ 5 and correlates with Mh/M∗. Our Mh/M∗ ratios agree well with studies based on weak lensing analysis, abundance matching, and halo occupation distribution methods, under the assumption that the halo inside the optical disk contributes roughly a constant fraction of the total halo mass (~4%). Conclusions. We find possible evidence for the growth of bars within a Hubble time; as (1) bars in early-type galaxies show larger density amplitudes and disk-relative sizes than their intermediate-type counterparts; and (2) long bars are typically strong. We also observe two clearly distinct types of bars, between early- and intermediate-type galaxies (T</p

The Structure of the Vortex Liquid at the Surface of a Layered Superconductor

A density-functional approach is used to calculate the inhomogeneous vortex density distribution in the flux liquid phase at the planar surface of a layered superconductor, where the external magnetic field is perpendicular to the superconducting layers and parallel to the surface. The interactions with image vortices are treated within a mean field approximation as a functional of the vortex density. Near the freezing transition strong vortex density fluctuations are found to persist far into the bulk liquid. We also calculate the height of the Bean-Livingston surface barrier.Comment: 8 pages, RevTeX, 2 figure

Metastable liquid lamellar structures in binary and ternary mixtures of Lennard-Jones fluids

We have carried out extensive equilibrium molecular dynamics (MD) simulations to investigate the Liquid-Vapor coexistence in partially miscible binary and ternary mixtures of Lennard-Jones (LJ) fluids. We have studied in detail the time evolution of the density profiles and the interfacial properties in a temperature region of the phase diagram where the condensed phase is demixed. The composition of the mixtures are fixed, 50% for the binary mixture and 33.33% for the ternary mixture. The results of the simulations clearly indicate that in the range of temperatures $78 < T < 102 ^{\rm o}$K, --in the scale of argon-- the system evolves towards a metastable alternated liquid-liquid lamellar state in coexistence with its vapor phase. These states can be achieved if the initial configuration is fully disordered, that is, when the particles of the fluids are randomly placed on the sites of an FCC crystal or the system is completely mixed. As temperature decreases these states become very well defined and more stables in time. We find that below $90 ^{\rm o}$K, the alternated liquid-liquid lamellar state remains alive for 80 ns, in the scale of argon, the longest simulation we have carried out. Nonetheless, we believe that in this temperature region these states will be alive for even much longer times.Comment: 18 Latex-RevTex pages including 12 encapsulated postscript figures. Figures with better resolution available upon request. Accepted for publication in Phys. Rev. E Dec. 1st issu

Explainable Artificial Intelligence (XAI): Concepts, Taxonomies, Opportunities and Challenges toward Responsible AI

In the last few years, Artificial Intelligence (AI) has achieved a notable momentum that, if harnessed appropriately, may deliver the best of expectations over many application sectors across the field. For this to occur shortly in Machine Learning, the entire community stands in front of the barrier of explainability, an inherent problem of the latest techniques brought by sub-symbolism (e.g. ensembles or Deep Neural Networks) that were not present in the last hype of AI (namely, expert systems and rule based models). Paradigms underlying this problem fall within the so-called eXplainable AI (XAI) field, which is widely acknowledged as a crucial feature for the practical deployment of AI models. The overview presented in this article examines the existing literature and contributions already done in the field of XAI, including a prospect toward what is yet to be reached. For this purpose we summarize previous efforts made to define explainability in Machine Learning, establishing a novel definition of explainable Machine Learning that covers such prior conceptual propositions with a major focus on the audience for which the explainability is sought. Departing from this definition, we propose and discuss about a taxonomy of recent contributions related to the explainability of different Machine Learning models, including those aimed at explaining Deep Learning methods for which a second dedicated taxonomy is built and examined in detail. This critical literature analysis serves as the motivating background for a series of challenges faced by XAI, such as the interesting crossroads of data fusion and explainability. Our prospects lead toward the concept of Responsible Artificial Intelligence, namely, a methodology for the large-scale implementation of AI methods in real organizations with fairness, model explainability and accountability at its core. Our ultimate goal is to provide newcomers to the field of XAI with a thorough taxonomy that can serve as reference material in order to stimulate future research advances, but also to encourage experts and professionals from other disciplines to embrace the benefits of AI in their activity sectors, without any prior bias for its lack of interpretability