3,507 research outputs found
Enriched property ontology for knowledge systems : a thesis presented in partial fulfilment of the requirements for the degree of Master of Information Systems in Information Systems, Massey University, Palmerston North, New Zealand
"It is obvious that every individual thing or event has an indefinite number of properties or attributes observable in it and might therefore be considered as belonging to an indefinite number of different classes of things" [Venn 1876]. The world in which we try to mimic in Knowledge Based (KB) Systems is essentially extremely complex especially when we attempt to develop systems that cover a domain of discourse with an almost infinite number of possible properties. Thus if we are to develop such systems how do we know what properties we wish to extract to make a decision and how do we ensure the value of our findings are the most relevant in our decision making. Equally how do we have tractable computations, considering the potential computation complexity of systems required for decision making within a very large domain. In this thesis we consider this problem in terms of medical decision making. Medical KB systems have the potential to be very useful aids for diagnosis, medical guidance and patient data monitoring. For example in a diagnostic process in certain scenarios patients may provide various potential symptoms of a disease and have defining characteristics. Although considerable information could be obtained, there may be difficulty in correlating a patient's data to known diseases in an economic and efficient manner. This would occur where a practitioner lacks a specific specialised knowledge. Considering the vastness of knowledge in the domain of medicine this could occur frequently. For example a Physician with considerable experience in a specialised domain such as breast cancer may easily be able to diagnose patients and decide on the value of appropriate symptoms given an abstraction process however an inexperienced Physician or Generalist may not have this facility.[FROM INTRODUCTION
Infrared and Ultraviolet Observations of VIRGOHI 21 and NGC 4254's Outer Disk
We present the results of Spitzer and Galex observations of gas/dust and star formation activities in the extreme outer disk of Virgo galaxy NGC 4254 and its surrounding regions. These observations were motivated in part by the potential existence of a “dark galaxy” in the vicinity. In the intergalactic VIRGOHI 21 region where the free-floating HI gas is found, neither UV nor mid-IR shows corresponding emission, thus providing stringent upper limits on the stellar mass and star formation rate in these clouds.On the other hand, we find clearly discernible excess ultraviolet emission in parts of the extended disk of NGC 4254, which is yet unseen in the optical and infrared. These UV emission appears different from the so-called “XUV disks” of other nearby galaxies in both their distribution pattern and physical origin, which we suggest is directly related to the gas concentration of VIRGOHI 21
Neutral Hydrogen and Star Formation in the Coma-Abell1367 Supercluster
We present preliminary results of a multi-wavelength study focused on the
evolution of spiral galaxies in the UV-optical colour-magnitude (CM) diagram.
By combining HI, UV and optical observations of the Coma-Abell1367 supercluster
we are able to identify galaxies at different stages of their evolution: from
healthy star-forming galaxies, to blue HI-poor spirals and transition objects.
Our analysis shows that galaxies in the transition region are likely to be the
progeny of healthy spirals, whose star-formation has been quenched by the harsh
cluster environment. This result suggests that, at least in clusters of
galaxies, the migration of galaxies from the blue to the red sequence might be
due to environmental processes.Comment: To appear in AIP Conf. Proc., "The Evolution of Galaxies through the
Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, eds. R. Minchin & E.
Momjian. 4 pages, 2 figure
Star Formation in Massive Low Surface Brightness Galaxies
Massive low surface brightness galaxies have disk central surface
brightnesses at least one magnitude fainter than the night sky, but total
magnitudes and masses that show they are among the largest galaxies known. Like
all low surface brightness (LSB) galaxies, massive LSB galaxies are often in
the midst of star formation yet their stellar light has remained diffuse,
raising the question of how star formation is proceeding within these galaxies.
We have undertaken a multi-wavelength study to clarify the structural
parameters and stellar and gas content of these enigmatic systems. The results
of these studies, which include HI, CO, optical, near UV, and far UV images of
the galaxies will provide the most in depth study done to date of how, when,
and where star formation proceeds within this unique subset of the galaxy
population.Comment: to be published in proceeding of IAU 244 - Dark Galaxies and Lost
Baryons IAU Symposiu
Extragalactic HI Surveys at Arecibo: the Future
Starting in the 1970s, the Arecibo 305m telescope has made seminal
contributions in the field of extragalactic spectroscopy. With the Gregorian
upgrade completed in the late 1990s, the telescope acquired a field of view.
Population of that field of view with a seven-feed array at L-band (ALFA)
increased by nearly one order of magnitude its survey speed. As a result, much
of the extragalactic astronomy time of the telescope is now allocated to survey
projects, which are briefly discussed. The next technical development stage for
the 305m telescope is foreseen as that of a 40 beam system that would take
advantage of phased array technology: AO40. This would further speed up the
survey performance of the telescope. It is shown how the figure of merit for
survey speed of AO40 would be comparable with that of SKA-precursor facilities,
planned for operation in the next decade. A number of scientifically desirable
new surveys that would become possible with AO40 are briefly discussed.Comment: To appear in AIP Conference Proceedings, "The Evolution of Galaxies
through the Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, Puerto Rico,
eds. R. Minchin & E. Momjian. 6 pages including 1 figur
Conference Summary: HI Science in the Next Decade
The atomic hydrogen (HI) 21cm line measures the gas content within and around
galaxies, traces the dark matter potential and probes volumes and objects that
other surveys do not. Over the next decade, 21cm line science will exploit new
technologies, especially focal plane and aperture arrays, and will see the
deployment of Epoch of Reionization/Dark Age detection experiments and Square
Kilometer Array (SKA) precursor instruments. Several experiments designed to
detect and eventually to characterize the reionization history of the
intergalactic medium should deliver first results within two-three years time.
Although "precision cosmology" surveys of HI in galaxies at z ~ 1 to 3 require
the full collecting area of the SKA, a coherent program of HI line science
making use of the unique capabilities of both the existing facilities and the
novel ones demonstrated by the SKA precursors will teach us how many gas rich
galaxies there really are and where they reside and will yield fundamental
insight into how galaxies accrete gas, form stars and interact with their
environment.Comment: To appear in AIP Conference Proceedings, "The Evolution of Galaxies
through the Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, Puerto Rico,
eds. R. Minchin & E. Momjian. 8 page
HI Structure Observations of Reionization and Dark Energy
This proceeding concentrates on the BAO signature of dark energy, and how the
SKA dark energy case has been complicated by the emergence of HI structure
experiments modeled after the Epoch of Reionization observatories. The purpose
of the conference talk was to review the current status of the Murchison
Widefield Array (MWA), and show the applications of HI structure observations
for both reionization and dark energy measurements. Since the status of the MWA
is changing weekly, please see the website www.haystack.mit.edu/ast/arrays/mwa/
for the current status. This proceedings will instead concentrate on HI
structure observations, their applicability to reionization and cosmography,
and the implications for the SKA and future HI structure observations of dark
energy.Comment: Proceeding from The Evolution of Galaxies through the Neutral
Hydrogen Window, Arecibo, 2008, AIP Conference Proceedings, Volume 103
Can galaxy growth be sustained through HI-rich minor mergers?
Local galaxies with specific star-formation rates (star-formation rate per
unit mass; sSFR~0.2-10/Gyr) as high as distant galaxies (z~1-3), are very rich
in HI. Those with low stellar masses, log M_star (M_sun)=8-9, for example, have
M_HI/M_star~5-30. Using continuity arguments of Peng et al. (2014), whereby the
specific merger rate is hypothesized to be proportional to the specific
star-formation rate, and HI gas mass measurements for local galaxies with high
sSFR, we estimate that moderate mass galaxies, log M_star (M_sun)=9-10.5, can
acquire sufficient gas through minor mergers (stellar mass ratios ~4-100) to
sustain their star formation rates at z~2. The relative fraction of the gas
accreted through minor mergers declines with increasing stellar mass and for
the most massive galaxies considered, log M_star (M_sun)=10.5-11, this
accretion rate is insufficient to sustain their star formation. We checked our
minor merger hypothesis at z=0 using the same methodology but now with
relations for local normal galaxies and find that minor mergers cannot account
for their specific growth rates, in agreement with observations of HI-rich
satellites around nearby spirals. We discuss a number of attractive features,
like a natural down-sizing effect, in using minor mergers with extended HI
disks to support star formation at high redshift. The answer to the question
posed by the title, "Can galaxy growth be sustained through \HI-rich minor
mergers?", is maybe, but only for relatively low mass galaxies and at high
redshift.Comment: 6 pages, 3 figures; in final acceptance by A&
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