209 research outputs found
2D Bayesian automated tilted-ring fitting of disk galaxies in large HI galaxy surveys: 2DBAT
We present a novel algorithm based on a Bayesian method for 2D tilted-ring
analysis of disk galaxy velocity fields. Compared to the conventional
algorithms based on a chi-squared minimisation procedure, this new
Bayesian-based algorithm suffers less from local minima of the model parameters
even with highly multi-modal posterior distributions. Moreover, the Bayesian
analysis, implemented via Markov Chain Monte Carlo (MCMC) sampling, only
requires broad ranges of posterior distributions of the parameters, which makes
the fitting procedure fully automated. This feature will be essential when
performing kinematic analysis on the large number of resolved galaxies expected
to be detected in neutral hydrogen (HI) surveys with the Square Kilometre Array
(SKA) and its pathfinders. The so-called '2D Bayesian Automated Tilted-ring
fitter' (2DBAT) implements Bayesian fits of 2D tilted-ring models in order to
derive rotation curves of galaxies. We explore 2DBAT performance on (a)
artificial HI data cubes built based on representative rotation curves of
intermediate-mass and massive spiral galaxies, and (b) Australia Telescope
Compact Array (ATCA) HI data from the Local Volume HI Survey (LVHIS). We find
that 2DBAT works best for well-resolved galaxies with intermediate inclinations
(20 deg < i < 70 deg), complementing three-dimensional techniques better suited
to modelling inclined galaxies.Comment: Accepted for publication in MNRAS; 46 pages, 33 figure
Seeing things
This paper is concerned with the problem of attaching meaningful symbols to aspects of the visible environment in machine and biological vision. It begins with a review of some of the arguments commonly used to support either the 'symbolic' or the 'behaviourist' approach to vision. Having explored these avenues without arriving at a satisfactory conclusion, we then present a novel argument, which starts from the question : given a functional description of a vision system, when could it be said to support a symbolic interpretation? We argue that to attach symbols to a system, its behaviour must exhibit certain well defined regularities in its response to its visual input and these are best described in terms of invariance and equivariance to transformations which act in the world and induce corresponding changes of the vision system state. This approach is illustrated with a brief exploration of the problem of identifying and acquiring visual representations having these symmetry properties, which also highlights the advantages of using an 'active' model of vision
Going beyond semantic image segmentation, towards holistic scene understanding, with associative hierarchical random fields
In this thesis we exploit the generality and expressive power of the Associative Hierarchical
Random Field (AHRF) graphical model to take its use beyond that of semantic image segmentation,
into object-classes, towards a framework for holistic scene understanding. We provide a
working definition for the holistic approach to scene understanding, which allows for the integration
of existing, disparate, applications into an unifying ensemble. We believe that modelling
such an ensemble as an AHRF is both a principled and pragmatic solution. We present a hierarchy
that shows several methods for fusing applications together with the AHRF graphical model.
Each of the three; feature, potential and energy, layers subsumes its predecessor in generality
and together give rise to many options for integration. With applications on street scenes we
demonstrate an implementation of each layer. The first layer application joins appearance and
geometric features. For our second layer we implement a things and stuff co-junction using
higher order AHRF potentials for object detectors, with the goal of answering the classic questions:
What? Where? and How many? A holistic approach to recognition-and-reconstruction
is realised within our third layer by linking two energy based formulations of both applications.
Each application is evaluated qualitatively and quantitatively. In all cases our holistic approach
shows improvement over baseline methods
Made to measure: An introduction to quantifying microscopy data in the life sciences
Images are at the core of most modern biological experiments and are used as a major source of quantitative information. Numerous algorithms are available to process images and make them more amenable to be measured. Yet the nature of the quantitative output that is useful for a given biological experiment is uniquely dependent upon the question being investigated. Here, we discuss the 3 main types of information that can be extracted from microscopy data: intensity, morphology, and object counts or categorical labels. For each, we describe where they come from, how they can be measured, and what may affect the relevance of these measurements in downstream data analysis. Acknowledging that what makes a measurement 'good' is ultimately down to the biological question being investigated, this review aims at providing readers with a toolkit to challenge how they quantify their own data and be critical of conclusions drawn from quantitative bioimage analysis experiments
Relation between parameters of dust and parameters of molecular and atomic gas in extragalactic star-forming regions
The relationships between atomic and molecular hydrogen and dust of various
sizes in extragalactic star-forming regions are considered, based on
observational data from the Spitzer and Herschel infrared space telescopes, the
Very Large Array (atomic hydrogen emission) and IRAM (CO emission). The source
sample consists of approximately 300 star-forming regions in 11 nearby
galaxies. Aperture photometry has been applied to measure the fluxes in eight
infrared bands (3.6, 4.5, 5.8, 8, 24, 70, 100, and 160m), the atomic
hydrogen (21cm) line and CO (2--1) lines.
The parameters of the dust in the starforming regions were determined via
synthetic-spectra fitting, such as the total dust mass, the fraction of
polycyclic aromatic hydrocarbons (PAHs), etc. Comparison of the observed fluxes
with the measured parameters shows that the relationships between atomic
hydrogen, molecular hydrogen, and dust are different in low- and
high-metallicity regions. Low-metallicity regions contain more atomic gas, but
less molecular gas and dust, including PAHs. The mass of dust constitutes about
of the mass of molecular gas in all regions considered. Fluxes produced
by atomic and molecular gas do not correlate with the parameters of the stellar
radiation, whereas the dust fluxes grow with increasing mean intensity of
stellar radiation and the fraction of enhanced stellar radiation. The ratio of
the fluxes at 8 and 24m, which characterizes the PAH content, decreases
with increasing intensity of the stellar radiation, possibly indicating
evolutionary variations of the PAH content. The results confirm that the
contribution of the 24m emission to the total IR luminosity of
extragalactic star-forming regions does not depend on the metallicity.Comment: Published in Astronomy Reports, 2017, vol. 61, issue
A Search for correlations between turbulence and star formation in LITTLE THINGS dwarf irregular galaxies
Turbulence has the potential for creating gas density enhancements that
initiate cloud and star formation (SF), and it can be generated locally by SF.
To study the connection between turbulence and SF, we looked for relationships
between SF traced by FUV images, and gas turbulence traced by kinetic energy
density (KED) and velocity dispersion () in the LITTLE THINGS sample
of nearby dIrr galaxies. We performed 2D cross-correlations between FUV and KED
images, measured cross-correlations in annuli to produce correlation
coefficients as a function of radius, and determined the cumulative
distribution function of the cross correlation value. We also plotted on a
pixel-by-pixel basis the locally excess KED, , and HI mass surface
density, , as determined from the respective values with the
radial profiles subtracted, versus the excess SF rate density , for all regions with positive excess . We found that
and KED are poorly correlated. The excess KED associated
with SF implies a % efficiency for supernova energy to pump local HI
turbulence on the scale of resolution here, which is a factor of too
small for all of the turbulence on a galactic scale. The excess in
SF regions is also small, only km s. The local excess in
corresponding to an excess in is
consistent with an HI consumption time of Gyr in the inner parts of
the galaxies. The similarity between this timescale and the consumption time
for CO implies that CO-dark molecular gas has comparable mass to HI in the
inner disks.Comment: In press in the Astronomical Journa
A Search for Correlations between Turbulence and Star Formation in LITTLE THINGS Dwarf Irregular Galaxies
Turbulence has the potential for creating gas density enhancements that initiate cloud and star formation (SF), and it can be generated locally by SF. To study the connection between turbulence and SF, we looked for relationships between SF traced by FUV images, and gas turbulence traced by kinetic energy density (KED) and velocity dispersion (v disp) in the LITTLE THINGS sample of nearby dIrr galaxies. We performed 2D cross-correlations between FUV and KED images, measured cross-correlations in annuli to produce correlation coefficients as a function of radius, and determined the cumulative distribution function of the cross-correlation value. We also plotted on a pixel-by-pixel basis the locally excess KED, v disp, and H i mass surface density, ΣHI, as determined from the respective values with the radial profiles subtracted, versus the excess SF rate density ΣSFR, for all regions with positive excess ΣSFR. We found that ΣSFR and KED are poorly correlated. The excess KED associated with SF implies a ∼0.5% efficiency for supernova energy to pump local H i turbulence on the scale of the resolution here, which is a factor of ∼2 too small for all of the turbulence on a galactic scale. The excess v disp in SF regions is also small, only ∼0.37 km s-1. The local excess in ΣHI corresponding to an excess in ΣSFR is consistent with a H i consumption time of ∼1.6 Gyr in the inner parts of the galaxies. The similarity between this timescale and the consumption time for CO implies that CO-dark molecular gas has comparable mass to H i in the inner disks
Enhancing information-based spaces using IoT and multimedia visualization - a case study
O principal objetivo desta pesquisa é fazer uma exploração em torno das estruturas conceituais, estado da arte e aplicações plausíveis da Internet de Coisas Multimédia em serviços distribuídos com para a criação de ambientes aumentados que contribuam a melhorar a experiência coletiva e participação das pessoas assistentes a conferências profissionais, reuniões grupais e espaços públicos em geral. Assim, a metodologia será baseada em uma revisão do estado da arte das tecnologias de IoT aplicáveis a coisas de multimédia e visualização de informação, especialmente no contexto de espaços públicos aumentados, onde o acesso a informação de alta qualidade possa ser possível sem influenciar negativamente a interação no mundo real entre os participantes, assim como melhorar a experiência global dos mesmos, considerando também soluções tecnológicas projetadas para os eventos de prazos limitados.The main objective of this research is to make an exploration around conceptual frameworks, state of the art and plausible applications of the Internet of Multimedia Things in distributed services for creating augmented environments that contribute to enhance the collective experience and participation of people attending professional conferences, group meetings and public spaces in general. Thus, the methodology will be based on a review of the state of the art of IoT technologies applicable for multimedia things and information visualization, specially in the context of augmented public spaces, where the access of high-quality data can be possible without preventing real-world interaction among attendants, as well as improving the overall experience of participants, considering also technological solutions designed for the events of limited time-frames
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