4,054 research outputs found
Study of stellar populations in the bulges of barred galaxies
We have obtained long-slit spectroscopy for a sample of 20 early-type barred
galaxies to study the influence of bars in the building of galaxy bulges. Line
strength indices were measured and used to derive age and metallicity gradients
in the bulge region by comparing with stellar population models. The same
analysis was also carried out with similar data of unbarred galaxies taken from
the literature. The bulges of barred galaxies seem to be more metal rich, at a
given velocity dispersion (sigma), than the bulges of unbarred galaxies, as
measured by some metallicity sensitive indices. There are indications that the
ratio of relative abundance of alpha-elements with respect to iron, [E/Fe],
derived for the bulges of barred galaxies tend to lie above the values of the
unbarred galaxies at a given sigma. The metallicity gradients for the majority
of the bulges are negative, less metal rich towards the end of the bulge. The
gradient values show a large scatter for galaxies with sigma below 150 km/s.
The age distribution is related to the presence of bulge substructure such as a
nuclear ring or an inner disk. The metallicity of both the bulge and the bar
are very well correlated indicating a close link between the enrichment
histories of both components. Bulges of barred early type galaxies might have
suffered a different chemical enrichment compared to the bulges of unbarred
galaxies of the same morphological type, same central velocity dispersion and
low inclination angles. The hinted stellar populations differences separating
the bulges of barred and unbarred galaxies and the strong link existing between
the metallicity of the bulge and the presence of a bar points to scenarios were
they both form simultaneously in processes leading to rapid and massive
episodes of star formation, possibly linked to the bar formation.Comment: Accepted for publication in Astronomy and Astrophysic
Performance of a New Enhanced Topological Decision-Rule Map-Matching Algorithm for Transportation Applications
Indexación: Web of Science; ScieloMap-matching problems arise in numerous transportation-related applications when spatial data is collected using inaccurate GPS technology and integrated with a flawed digital roadway map in a GIS environment. This paper presents a new enhanced post-processing topological decision-rule map-matching algorithm in order to address relevant special cases that occur in the spatial mismatch resolution. The proposed map-matching algorithm includes simple algorithmic improvements: dynamic buffer that varies its size to snap GPS data points to at least one roadway centerline; a comparison between vehicle heading measurements and associated roadway centerline direction; and a new design of the sequence of steps in the algorithm architecture. The original and new versions of the algorithm were tested on different spatial data qualities collected in Canada and United States. Although both versions satisfactorily resolve complex spatial ambiguities, the comparative and statistical analysis indicates that the new algorithm with the simple algorithmic improvements outperformed the original version of the map-matching algorithm.El problema de la ambigüedad espacial ocurre en varias aplicaciones relacionadas con transporte, especÃficamente cuando existe inexactitud en los datos espaciales capturados con tecnologÃa GPS o cuando son integrados con un mapa digital que posee errores en un ambiente SIG. Este artÃculo presenta un algoritmo nuevo y mejorado basado en reglas de decisión que es capaz de resolver casos especiales relevantes en modo post-proceso. El algoritmo propuesto incluye las siguientes mejoras algorÃtmicas: un área de búsqueda dinámica que varÃa su tamaño para asociar puntos GPS a al menos un eje de calzada, una comparación entre el rumbo del vehÃculo y la dirección del eje de calzada asignada, y un nuevo diseño de la secuencia de pasos del algoritmo. Tanto el algoritmo original como el propuesto fueron examinados con datos espaciales de diferentes calidades capturados en Canadá y Estados Unidos. Aunque ambas versiones resuelven satisfactoriamente el problema de ambigüedad espacial, el análisis comparativo y estadÃstico indica que la nueva versión del algoritmo con las mejoras algorÃtmicas entrega resultados superiores a la versión original del algoritmo.http://ref.scielo.org/9mt55
Un modelo para resolver el problema dinámico de despacho de vehÃculos con incertidumbre de clientes y con tiempos de viaje en arcos
Indexación: Web of Science; ScieloIn a real world case scenario, customer demands are requested at any time of the day requiring services that are not known in advance such as delivery or repairing equipment. This is called Dynamic Vehicle Routing (DVR) with customer uncertainty environment. The link travel time for the roadway network varies with time as traffic fluctuates adding an additional component to the dynamic environment. This paper presents a model for solving the DVR problem while combining these two dynamic aspects (customer uncertainty and link travel time). The proposed model employs Greedy, Insertion, and Ant Colony Optimization algorithms. The Greedy algorithm is utilized for constructing new routes with existing customers, and the remaining two algorithms are employed for rerouting as new customer demands appear. A real world application is presented to simulate vehicle routing in a dynamic environment for the city of Taipei, Taiwan. The simulation shows that the model can successfully plan vehicle routes to satisfy all customer demands and help managers in the decision making process.En un escenario real, los pedidos de los clientes son solicitados a cualquier hora del dÃa requiriendo servicios que no han sido planificados con antelación tales como los despachos o la reparación de equipos. Esto es llamado ruteo dinámico de vehÃculos (RDV) considerando un ambiente con incertidumbre de clientes. El tiempo de viaje en una red vial varÃa con el tiempo a medida que el tráfico vehicular fluctúa agregando una componente adicional al ambiente dinámico. Este artÃculo propone un modelo para resolver el problema RDV combinando estos dos aspectos dinámicos. El modelo propuesto utiliza los algoritmos Greedy, Inserción y optimización basada en colonias de hormigas. El algoritmo Greedy es utilizado para construir nuevas rutas con los clientes existentes y los otros dos algoritmos son usados para rutear vehÃculos a medida que surjan nuevos clientes con sus respectivos pedidos. Además, se presenta una aplicación real para simular el ruteo vehicular en un ambiente dinámico para la ciudad de Taipei, Taiwán. Esta simulación muestra que el modelo es capaz de planificar exitosamente las rutas vehiculares satisfaciendo los pedidos de los clientes y de ayudar los gerentes en el proceso de toma de decisiones.http://ref.scielo.org/3ryfh
The UV-upturn in brightest cluster galaxies
This paper is part of a series devoted to the investigation of a large sample
of brightest cluster galaxies (BCGs), their properties and the relationships
between these and the properties of the host clusters. In this paper, we
compare the stellar population properties derived from high signal-to-noise,
optical long-slit spectra with the GALEX ultraviolet (UV) colour measurements
for 36 nearby BCGs to understand the diversity in the most rapidly evolving
feature in old stellar systems, the UV-upturn. We investigate: (1) the possible
differences between the UV-upturn of BCGs and those of a control sample of
ordinary ellipticals in the same mass range, as well as possible correlations
between the UV-upturn and other general properties of the galaxies; (2)
possible correlations between the UV-upturn and the properties of the host
clusters; (3) recently proposed scenarios where helium-sedimentation in the
cluster centre can produce an enhanced UV-upturn. We find systematic
differences between the UV-colours of BCGs and ordinary ellipticals, but we do
not find correlations between these colours and the properties of the host
clusters. Furthermore, the observations do not support the predictions made by
the helium-sedimentation model as an enhancer of the UV-upturn.Comment: 12 pages, accepted for publication in MNRA
Modeling of macro fiber composite actuated laminate plates and aerofoils
© 2019 Sage Publications . The final, definitive version of this paper has been published in the Journal of Intelligent Material Systems and Structures by Sage Publications Ltd. All rights reserved. It is available at: https://doi.org/10.1177/1045389X19888728This article investigates the modeling of macro fiber composite-actuated laminate plates with distributed actuator patches. The investigation details an analytical and finite element modeling, with experimental validation of the bending strain and deflection of an epoxy E-glass fiber composite laminate. An analytical approach is also developed to estimate the plate deflection from the experimental strain measurements. The analytical method uses direct integration of single dimensional plate bending moments obtained by strain-induced shear moments from the macro fiber composite actuators. Finite element analysis software was used with the composite laminate modeled in ANSYS ACP. The results from both analytical and numerical models show good agreement with the experimental results, with strain values agreeing within 20 ppm and the maximum difference in deflection not exceeding 0.1 mm between models. Finally, an application of the analytical model for developing morphing aerofoil designs is demonstrated.Peer reviewe
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