343 research outputs found
Interactions and star formation activity in Wolf-Rayet galaxies
We present the main results of the PhD Thesis carried out by
L\'opez-S\'anchez (2006), in which a detailed morphological, photometrical and
spectroscopical analysis of a sample of 20 Wolf-Rayet (WR) galaxies was
realized. The main aims are the study of the star formation and O and WR
stellar populations in these galaxies and the role that interactions between
low surface companion objects have in the triggering of the bursts. We analyze
the morphology, stellar populations, physical conditions, chemical abundances
and kinematics of the ionized gas, as well as the star-formation activity of
each system.Comment: 16 pages, 15 figure
The role of gas infall in the evolution of disc galaxies
Spiral galaxies are thought to acquire their gas through a protracted infall
phase resulting in the inside-out growth of their associated discs. For field
spirals, this infall occurs in the lower density environments of the cosmic
web. The overall infall rate, as well as the galactocentric radius at which
this infall is incorporated into the star-forming disc, plays a pivotal role in
shaping the characteristics observed today. Indeed, characterising the
functional form of this spatio-temporal infall in-situ is exceedingly
difficult, and one is forced to constrain these forms using the present day
state of galaxies with model or simulation predictions. We present the infall
rates used as input to a grid of chemical evolution models spanning the mass
spectrum of discs observed today. We provide a systematic comparison with
alternate analytical infall schemes in the literature, including a first
comparison with cosmological simulations. Identifying the degeneracies
associated with the adopted infall rate prescriptions in galaxy models is an
important step in the development of a consistent picture of disc galaxy
formation and evolution.Comment: 12 pages, 12 figures, MNRAS, accepte
Control difuso de la tasa de transferencia de extremo a extremo en protocolos de transporte de Internet
La dinámica del tráfico de extremo a extremo en Internet es un problema complejo para el cual los modelos disponibles son, en el mejor de los casos incompletos. Esta comunicación describe nuevos mecanismos para regulación de la tasa de transferencia de extremo a extremo en la capa de transporte por medio de sistemas difusos. Se describen una generalización basada en lógica difusa de los mecanismos de control de flujo y congestión de TCP (Transport Control Protocol), el diseño de un regulador difuso basado en mecanismo de ventana para TCP, así como la metodología de diseño empleada para simular e implementar de manera experimental el sistema. Se resume un estudio comparativo del regulador difuso presentado frente a los mecanismos tradicionales. El regulador difuso resulta útil como enfoque de modelado y proporciona significativas mejoras de prestaciones respecto a un conjunto de criterios.Ministerio de Educación y Ciencia TEC2005-04359/MICJunta de Amdalucía TIC2006-63
Open FPGA-based development platform for fuzzy systems with applications to communications
Soft computing techniques are gaining momentum as tools
for network traffic modeling, analysis and control. Efficient
hardware implementations of these techniques that can
achieve real-time operation in high-speed communications
equipment is however an open problem. This paper describes
a platform for the development of fuzzy systems with applications
to communications systems, namely network traffic
analysis and control. An FPGA development board with PCI
interface is employed to support an open platform that comprises
open CAD tools as well as IP cores. For the development
process, we set up a methodology and a CAD tools
chain that cover from initial specification in a high-level language
to implementation on FPGA devices. PCI compatible
fuzzy inference modules are implemented as SoPC based on
the open WISHBONE interconnection architecture. We outline
results from the design and implementation of fuzzy analyzers
and regulators for network traffic. These systems are
shown to satisfy operational and architectural requirements
of current and future high-performance routing equipment.Ministerio de Educación y Ciencia TEC2005-04359/MICJunta de Andalucía TIC2006-63
Control difuso de la tasa de transferencia de extremo a extremo en protocolos de transporte de Internet
La dinámica del tráfico de extremo a extremo en Internet es un problema complejo para el cual los modelos disponibles son, en el mejor de los casos incompletos. Esta comunicación describe nuevos mecanismos para regulación de la tasa de transferencia de extremo a extremo en la capa de transporte por medio de sistemas difusos. Se describen una generalización basada en lógica difusa de los mecanismos de control de flujo y congestión de TCP (Transport Control Protocol), el diseño de un regulador difuso basado en mecanismo de ventana para TCP, así como la metodología de diseño empleada para simular e implementar de manera experimental el sistema. Se resume un estudio comparativo del regulador difuso presentado frente a los mecanismos tradicionales. El regulador difuso resulta útil como enfoque de modelado y proporciona significativas mejoras de prestaciones respecto a un conjunto de criterios.Ministerio de Educación y Ciencia TEC2005-04359/MICJunta de Amdalucía TIC2006-63
On the 3D structure of the mass, metallicity, and SFR space for SF galaxies
We demonstrate that the space formed by the star-formation rate (SFR),
gas-phase metallicity (Z), and stellar mass (M), can be reduced to a plane, as
first proposed by Lara-Lopez et al. We study three different approaches to find
the best representation of this 3D space, using a principal component analysis,
a regression fit, and binning of the data. The PCA shows that this 3D space can
be adequately represented in only 2 dimensions, i.e., a plane. We find that the
plane that minimises the chi^2 for all variables, and hence provides the best
representation of the data, corresponds to a regression fit to the stellar mass
as a function of SFR and , M=f(Z,SFR). We find that the distribution
resulting from the median values in bins for our data gives the highest chi^2.
We also show that the empirical calibrations to the oxygen abundance used to
derive the Fundamental Metallicity Relation (Nagao et al.) have important
limitations, which contribute to the apparent inconsistencies. The main problem
is that these empirical calibrations do not consider the ionization degree of
the gas. Furthermore, the use of the N2 index to estimate oxygen abundances
cannot be applied for ~8.8 because of the saturation of the [NII]6584 line in
the high-metallicity regime. Finally we provide an update of the Fundamental
Plane derived by Lara-Lopez et al.Comment: ApJ, accepted. 15 pages, 13 figure
The role of gas infall in the evolution of disc galaxies
Spiral galaxies are thought to acquire their gas through a protracted infall phase resulting in the inside-out growth of their associated discs. For field spirals, this infall occurs in the lower density environments of the cosmic web. The overall infall rate, as well as the galactocentric radius at which this infall is incorporated into the star-forming disc, plays a pivotal role in shaping the characteristics observed today. Indeed, characterising the functional form of this spatio-temporal infall in-situ is exceedingly difficult, and one is forced to constrain these forms using the present day state of galaxies with model or simulation predictions. We present the infall rates used as input to a grid of chemical evolution models spanning the mass spectrum of discs observed today. We provide a systematic comparison with alternate analytical infall schemes in the literature, including a first comparison with cosmological simulations. Identifying the degeneracies associated with the adopted infall rate prescriptions in galaxy models is an important step in the development of a consistent picture of disc galaxy formation and evolution
Properties of the outer regions of spiral disks: Abundances, colors and ages
© 2017 International Astronomical Union. We summarize the results obtained from our suite of chemical evolution models for spiral disks, computed for different total masses and star formation efficiencies. Once the gas, stars and star formation radial distributions are reproduced, we analyze the Oxygen abundances radial profiles for gas and stars, in addition to stellar averaged ages and global metallicity. We examine scenarios for the potential origin of the apparent flattening of abundance gradients in the outskirts of disk galaxies, in particular the role of molecular gas formation prescriptions
Dense circum-nuclear molecular gas in starburst galaxies
We present results from a study of the dense circum-nuclear molecular gas of
starburst galaxies. The study aims to investigate the interplay between
starbursts, active galactic nuclei and molecular gas. We characterise the dense
gas traced by HCN, HCO and HNC and examine its kinematics in the
circum-nuclear regions of nine starburst galaxies observed with the Australia
Telescope Compact Array. We detect HCN (10) and HCO (10) in seven
of the nine galaxies and HNC (10) in four. Approximately 7 arcsec resolution
maps of the circum-nuclear molecular gas are presented. The velocity integrated
intensity ratios, HCO (10)/HCN (10) and HNC (10)/HCN (10),
are calculated. Using these integrated intensity ratios and spatial intensity
ratio maps we identify photon dominated regions (PDRs) in NGC 1097, NGC 1365
and NGC 1808. We find no galaxy which shows the PDR signature in only one part
of the observed nuclear region. We also observe unusually strong HNC emission
in NGC 5236, but it is not strong enough to be consistent with X-ray dominated
region (XDR) chemistry. Rotation curves are derived for five of the galaxies
and dynamical mass estimates of the inner regions of three of the galaxies are
made.Comment: Accepted for publication in MNRAS, 22 December 2015. Main manuscript
is 13 pages, containing 3 figures. Also has 4 appendices of 13 pages total
containing numerous figures and details of calculation
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