91 research outputs found
The Extremely Luminous Quasar Survey in the Pan-STARRS 1 Footprint (PS-ELQS)
We present the results of the Extremely Luminous Quasar Survey in the
survey of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS;
PS1). This effort applies the successful quasar selection strategy of the
Extremely Luminous Survey in the Sloan Digital Sky Survey footprint
() to a much larger area
(). This spectroscopic survey targets the most
luminous quasars (; ) at intermediate redshifts
(). Candidates are selected based on a near-infrared JKW2 color cut
using WISE AllWISE and 2MASS photometry to mainly reject stellar contaminants.
Photometric redshifts () and star-quasar classifications for each
candidate are calculated from near-infrared and optical photometry using the
supervised machine learning technique random forests. We select 806 quasar
candidates at from a parent sample of 74318 sources. After
exclusion of known sources and rejection of candidates with unreliable
photometry, we have taken optical identification spectra for 290 of our 334
good PS-ELQS candidates. We report the discovery of 190 new quasars
and an additional 28 quasars at lower redshifts. A total of 44 good PS-ELQS
candidates remain unobserved. Including all known quasars at , our
quasar selection method has a selection efficiency of at least . At lower
declinations we approximately triple the known
population of extremely luminous quasars. We provide the PS-ELQS quasar catalog
with a total of 592 luminous quasars (, ). This unique
sample will not only be able to provide constraints on the volume density and
quasar clustering of extremely luminous quasars, but also offers valuable
targets for studies of the intergalactic medium.Comment: 34 pages, 10 figures, accepted to ApJ
Mathematical modelling of mass transfer in a multi-stage rotating disc contactor column
In this study, the development of an improved forward and inverse models for the mass transfer process in the Rotating Disc Contactor (RDC) column were carried out. The existing mass transfer model with constant boundary condition does not accurately represent the mass transfer process. Thus, a time-varying boundary condition was formulated and consequently the new fractional approach to equilibrium was derived. This derivation initiated the formulation of the modified quadratic driving force, called Time-dependent Quadratic Driving Force (TQDF). Based on this formulation, a Mass Transfer of A Single Drop (MTASD) Algorithm was designed, followed by a more realistic Mass Transfer of Multiple Drops (MTMD) Algorithm which was later refined to become another algorithm named the Mass Transfer Steady State (MTSS) Algorithm. The improved forward models, consisting of a system of multivariate equations, successfully calculate the amount of mass transfer from the continuous phase to the dispersed phase and was validated by the simulation results. The multivariate system is further simplified as the Multiple Input Multiple Output (MIMO) system of a functional from a space of functions to a plane. This system serves as the basis for the inverse models of the mass transfer process in which fuzzy approach was used in solving the problems. In particular, two dimensional fuzzy number concept and the pyramidal membership functions were adopted along with the use of a triangular plane as the induced output parameter. A series of algorithms in solving the inverse problem were then developed corresponding to the forward models. This eventually brought the study to the implementation of the Inverse Single Drop Multistage (ISDMS)-2D Fuzzy Algorithm on the Mass Transfer of Multiple Drops in Multistage System. This new modelling approach gives useful information and provides a faster tool for decision-makers in determining the optimal input parameter for mas
PAndromeda - first results from the high-cadence monitoring of M31 with Pan-STARRS 1
The Pan-STARRS 1 (PS1) survey of M31 (PAndromeda) is designed to identify
gravitational microlensing events, caused by bulge and disk stars
(self-lensing) and by compact matter in the halos of M31 and the Milky Way
(halo lensing, or lensing by MACHOs). With the 7 deg2 FOV of PS1, the entire
disk of M31 can be imaged with one single pointing. Our aim is to monitor M31
with this wide FOV with daily sampling (20 mins/day). In the 2010 season we
acquired in total 91 nights towards M31, with 90 nights in the rP1 and 66
nights in the iP1. The total integration time in rP1 and iP1 are 70740s and
36180s, respectively. As a preliminary analysis, we study a 40'\times40'
sub-field in the central region of M31, a 20'\times20' sub-field in the disk of
M31 and a 20'\times20' sub-field for the investigation of astrometric
precision. We demonstrate that the PSF is good enough to detect microlensing
events. We present light curves for 6 candidate microlensing events. This is a
competitive rate compared to previous M31 microlensing surveys. We finally also
present one example light curve for Cepheids, novae and eclipsing binaries in
these sub-fields.Comment: 41 pages, 19 figures, 4 tables. Published in A
Intelligent spatial decision support systems
This thesis investigates the conceptual and methodological issues for the development of
Intelligent Spatial Decision Support Systems (ISDSS). These are spatial decision support
systems (SDSS) integrating intelligent systems techniques (Genetic Algorithms, Neural
Networks, Expert Systems, Fuzzy Logic and Nonlinear methods) with traditional modelling and
statistical methods for the analysis of spatial problems.
The principal aim of this work is to verify the feasibility of heterogeneous systems for
spatial decision support derived from a combination of traditional numerical techniques and
intelligent techniques in order to provide superior performance and functionality to that achieved
through the use of traditional methods alone.
This thesis is composed of four distinct sections: (i) a taxonomy covering the
employment of intelligent systems techniques in specific applications of geographical
information systems and SDSS; (ii) the development of a prototype ISDSS; (iii) application of
the prototype ISDSS to modelling the spatiotemporal dynamics of high technology industry in
the South-East of England; and (iv) the development of ISDSS architectures utilising
interapplication communication techniques.
Existing approaches for implementing modelling tools within SDSS and GIS generally
fall into one of two schemes - loose coupling or tight coupling - both of which involve a tradeoff
between generality and speed of data interchange. In addition, these schemes offer little use
of distributed processing resources.
A prototype ISDSS was developed in collaboration with KPMG Peat Marwick's High
Technology Practice as a general purpose spatiotemporal analysis tool with particular regard to
modelling high technology industry. The GeoAnalyser system furnishes the user with animation
and time plotting tools for observing spatiotemporal dynamics; such tools are typically not found
in existing SDSS or GIS. Furthermore, GeoAnalyser employs the client/server model of
distributed computing to link the front end client application with the back end modelling
component contained within the server application. GeoAnalyser demonstrates a hybrid approach
to spatial problem solving - the application utilises a nonlinear model for the temporal evolution
of spatial variables and a genetic algorithm for calibrating the model in order to establish a good
fit for the dataset under investigation.
Several novel architectures are proposed for ISDSS based on existing distributed systems
technologies. These architectures are assessed in terms of user interface, data and functional
integration. Implementation issues are also discussed.
The research contributions of this work are four-fold: (i) it lays the foundation for ISDSS
as a distinct type of system for spatial decision support by examining the user interface,
performance and methodological requirements of such systems; (ii) it explores a new approach
for linking modelling techniques and SDSS; (iii) it investigates the possibility of modelling high
technology industry; and (iv) it details novel architectures for ISDSS based on distributed
systems
RR Lyrae in XSTPS: The halo density profile in the North Galactic Cap
We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt
Telescope Photometric Survey (XDSS). The area we consider is located in the
North Galactic Cap, covering 376.75 sq deg at RA 150 deg and Dec
27 deg down to a magnitude limit of i 19. Using the
variability information afforded by the multi-epoch nature of our XDSS data,
combined with colors from the Sloan Digital Sky Survey, we are able to identify
candidate RRLs. We find 318 candidates, derive distances to them and estimate
the detection efficiency. The majority of our candidates have more than 12
observations and for these we are able to calculate periods. These also allows
us to estimate our contamination level, which we predict is between 30% to 40%.
Finally we use the sample to probe the halo density profile in the 9-49 kpc
range and find that it can be well fitted by a double power law. We find good
agreement between this model and the models derived for the South Galactic Cap
using the Watkins et al. (2009) and Sesar et al. (2010) RRL data-sets, after
accounting for possible contamination in our data-set from Sagittarius stream
members. We consider non-spherical double power law models of the halo density
profile and again find agreement with literature data-sets, although we have
limited power to constrain the flattening due to our small survey area. Much
tighter constraints will be placed by current and future wide-area surveys,
most notably ESA's astrometric Gaia mission. Our analysis demonstrates that
surveys with a limited number of epochs can effectively be mined for RRLs. Our
complete sample is provided as accompanying online material.Comment: 14 pages, ApJ (in press
Stellar Stream and Halo Structure in the Andromeda Galaxy From a Subaru/Hyper Suprime-Cam Survey
We present wide and deep photometry of the northwest part of the halo of the
Andromeda galaxy (M31) using Hyper Suprime-Cam on the Subaru Telescope. The
survey covers 9.2 deg field in the , , and bands and shows
a clear red giant branch (RGB) of M31's halo stars and a pronounced red clump
(RC) feature. The spatial distribution of RC stars shows a prominent stream
feature, the North Western (NW) Stream, and a diffuse substructure in the south
part of our survey field. We estimate the distances based on the RC method and
obtain = 24.63(random)(systematic) and 24.29(random)(systematic) mag for the NW stream and diffuse
substructure, respectively, implying that the NW Stream is located behind M31,
whereas the diffuse substructure is located in front. We also estimate
line-of-sight distances along the NW Stream and find that the south part of the
stream is 20 kpc closer to us relative to the north part. The distance to
the NW Stream inferred from the isochrone fitting to the color-magnitude
diagram favors the RC-based distance, but the TRGB-based distance estimated for
-selected RGB stars does not agree with it. The surface number density
distribution of RC stars across the NW Stream is found to be approximately
Gaussian with a FWHM of 25 arcmin (5.7 kpc), with a slight skew to the
south-west side. That along the NW Stream shows a complicated structure
including variations in number density and a significant gap in the stream.Comment: 24 pages, 18 figures, accepted for publication in Ap
Invasive Species Forecasting System: A Decision Support Tool for the U.S. Geological Survey: FY 2005 Benchmarking Report v.1.6
The National Institute of Invasive Species Science (NIISS), through collaboration with NASA's Goddard Space Flight Center (GSFC), recently began incorporating NASA observations and predictive modeling tools to fulfill its mission. These enhancements, labeled collectively as the Invasive Species Forecasting System (ISFS), are now in place in the NIISS in their initial state (V1.0). The ISFS is the primary decision support tool of the NIISS for the management and control of invasive species on Department of Interior and adjacent lands. The ISFS is the backbone for a unique information services line-of-business for the NIISS, and it provides the means for delivering advanced decision support capabilities to a wide range of management applications. This report describes the operational characteristics of the ISFS, a decision support tool of the United States Geological Survey (USGS). Recent enhancements to the performance of the ISFS, attained through the integration of observations, models, and systems engineering from the NASA are benchmarked; i.e., described quantitatively and evaluated in relation to the performance of the USGS system before incorporation of the NASA enhancements. This report benchmarks Version 1.0 of the ISFS
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