158 research outputs found
A comparison of daylight measurement using radiance
This dissertation compares the daylight coefficient approach for predicting time varying illuminance to a new method formulated by Peter J. Raynham based on the sunlight and daylight factors. The accuracy of the daylight coefficient derived illuminance predictions was verified by John Mardaljevic using the BRE-IDMP validation datasheet. The prediction tool used for all the work described here is the Radiance lighting simulation system. Hourly predictions of daylight illuminance over a period of one year under variable sky and sun conditions were carried out for a full-size office space using both methods. The total annual klux-hours were then calculated, providing a simple metric to compare the two methods. It has been demonstrated that Raynham's method and that of Mardaljevic diverge in terms of their results, with the difference becoming much more significant further away from the windows. It can therefore be deduced that Raynham's method can not be used to predict hourly internal illuminance levels. Raynham's source of error is that he assumes an overcast sky to determine the diffuse component which has a dark horizon and brighter zenith with ratio of about 1 to 3. Thus, his method puts a lot of light higher in the sky as opposed to the ground as is the case of a clear sky. It is impractical to also assume that the daylight coefficient approach is the ideal standard by which any potential method for predicting time varying illuminance should be compared against. The accuracy of this method is based on one set of results, and there are various sources of imprecision which could prove to be significant when the daylight coefficient approach is examined for a different locale
The SVD-Fundamental Theorem of Linear Algebra
Given an m × n matrix A, with m ≥ n, the four subspaces associated with it are shown in Fig. 1 (see [1]).
Fig. 1. The row spaces and the nullspaces of A and AT; a1 through an and h1 through hm are abbreviations of the alignerframe and hangerframe vectors respectively (see [2]).
The Fundamental Theorem of Linear Algebra tells us that N(A) is the orthogonal complement of R(AT). These four subspaces tell the whole story of the Linear System Ax = y. So, for example, the absence of N(AT) indicates that a solution always exists, whereas the absence of N(A) indicates that this solution is unique. Given the importance of these subspaces, computing bases for them is the gist of Linear Algebra. In “Classical” Linear Algebra, bases for these subspaces are computed using Gaussian Elimination; they are orthonormalized with the help of the Gram-Schmidt method. Continuing our previous work [3] and following Uhl’s excellent approach [2] we use SVD analysis to compute orthonormal bases for the four subspaces associated with A, and give a 3D explanation. We then state and prove what we call the “SVD-Fundamental Theorem” of Linear Algebra, and apply it in solving systems of linear equations
Detection of new point-sources in WMAP Cosmic Microwave Background (CMB) maps at high Galactic latitude. A new technique to extract point sources from CMB maps
In experimental microwave maps, point-sources can strongly affect the
estimation of the power-spectrum and/or the test of Gaussianity of the Cosmic
Microwave Background (CMB) component. As a consequence, their removal from the
sky maps represents a critical step in the analysis of the CMB data. Before
removing a source, however, it is necessary to detect it and source extraction
consists of a delicate preliminary operation. In the literature, various
techniques have been presented to detect point-sources in the sky maps. The
most sophisticated ones exploit the multi-frequency nature of the observations
that is typical of the CMB experiments. These techniques have "optimal"
theoretical properties and, at least in principle, are capable of remarkable
performances. Actually, they are rather difficult to use and this deteriorates
the quality of the obtainable results. In this paper, we present a new
technique, the "weighted matched filter" (WMF), that is quite simple to use and
hence more robust in practical applications. Such technique shows particular
efficiency in the detection of sources whose spectra have a slope different
from zero. We apply this method to three Southern Hemisphere sky regions - each
with an area of 400 square degrees - of the seven years Wilkinson Microwave
Anisotropy Probe (WMAP) maps and compare the resulting sources with those of
the two seven-year WMAP point-sources catalogues. In these selected regions we
find seven additional sources not previously listed in WMAP catalogues and
discuss their most likely identification and spectral properties.Comment: Astronomy and Astrophysics, 2011, in pres
Identification of discrete chaotic maps with singular points
We investigate the ability of artificial neural networks to reconstruct discrete chaotic maps with singular points. We use as a simple test model the Cusp map. We compare the traditional Multilayer Perceptron, the Chebyshev Neural Network and the Wavelet Neural Network. The numerical scheme for the accurate determination of a singular point is also developed. We show that combining a neural network with the numerical algorithm for the determination of the singular point we are able to accurately approximate discrete chaotic maps with singularities
A Complete Catalog of Swift GRB Spectra and Durations: Demise of a Physical Origin for Pre-Swift High-Energy Correlations
We calculate durations and spectral paramaters for 218 Swift bursts detected
by the BAT instrument between and including GRBs 041220 and 070509, including
77 events with measured redshifts. Incorporating prior knowledge into the
spectral fits, we are able to measure the characteristic spectral
peak energy and the isotropic equivalent energy
(1-- keV) for all events. This complete and rather extensive catalog,
analyzed with a unified methodology, allows us to address the persistence and
origin of high-energy correlations suggested in pre-Swift observations. We find
that the - correlation is present in the Swift
sample; however, the best-fit powerlaw relation is inconsistent with the
best-fit pre-Swift relation at >5 sigma significance. Moreover, it has a factor
>~ 2 larger intrinsic scatter, after accounting for large errors on . A large fraction of the Swift events are hard and subluminous
relative to (and inconsistent with) the pre-Swift relation, in agreement with
indications from BATSE GRBs without redshift. Moreover, we determine an
experimental threshold for the BAT detector and show how the -- correlation arises artificially due to partial
correlation with the threshold. We show that pre-Swift correlations found by
Amati et al.(2002), Yonetoku et al. (2004), Firmani et al.(2006) (and
independently by others) are likely unrelated to the physical properties of
GRBs and are likely useless for tests of cosmology. Also, an explanation of
these correlations in terms of a detector threshold provides a natural and
quantitative explanation for why short-duration GRBs and events at low redshift
tend to be outliers to the correlations.Comment: 25 pages, 9 figures, 2 tables, Accepted to Ap
The origins of X-ray emission from the hotspots of FRII radio sources
We use new and archival Chandra data to investigate the X-ray emission from a
large sample of compact hotspots of FRII radio galaxies and quasars from the 3C
catalogue. We find that only the most luminous hotspots tend to be in good
agreement with the predictions of a synchrotron self-Compton model with
equipartition magnetic fields. At low hotspot luminosities inverse-Compton
predictions are routinely exceeded by several orders of magnitude, but this is
never seen in more luminous hotspots. We argue that an additional synchrotron
component of the X-ray emission is present in low-luminosity hotspots, and that
the hotspot luminosity controls the ability of a given hotspot to produce
synchrotron X-rays, probably by determining the high-energy cutoff of the
electron energy spectrum. It remains plausible that all hotspots are close to
the equipartition condition.Comment: 49 pages, 16 figures. ApJ accepted. Revised version fixes a typo in
one of the Tables and corrects a statement about 3C27
The AGN fraction - velocity dispersion relation in clusters of galaxies
Some previous investigations have found that the fraction (f_AGN) of active
galactic nuclei (AGNs) is lower in clusters than in the field. This can result
from the suppression of galaxy-galaxy mergers in high-velocity dispersion
(sigma_v) clusters, if the formation and/or fueling of AGNs is directly related
to the merging process. We investigate the existence of a relation between
f_AGN and sigma_v in galaxy clusters in order to shed light on the formation
and evolution processes of AGNs and cluster galaxies. Using data from the Sloan
Digital Sky Survey we determine f_AGN and sigma_v for the clusters in two
samples, extracted from the catalogs of Popesso et al. (2006a) and Miller et
al. (2005), and excluding clusters with significant evidence for substructures.
We find a significant f_AGN-sigma_v anti-correlation. Clusters with sigma_v
lower and, respectively, higher than 500 km/s have AGN fractions of and , on average. The f_AGN-sigma_v relation can be
described by a model that assumes f_AGN is proportional to the galaxies merging
rate, plus a constant. Since f_AGN increases with decreasing sigma_v, AGNs are
likely to have played a significant role in heating the intra-cluster medium
and driving galaxy evolution in cluster precursors and groups.Comment: 4 pages, 3 figures, A&A Letter accepted for publicatio
The Peculiar Motions of Early-Type Galaxies in Two Distant Regions VI: The Maximum Likelihood Gaussian Algorithm
The EFAR project is designed to measure the properties and peculiar motions
of early-type galaxies in two distant regions. Here we describe the maximum
likelihood algorithm we developed to investigate the correlations between the
parameters of the EFAR database. One-, two-, and three-dimensional gaussian
models are constructed to determine the mean value and intrinsic spread of the
parameters, and the slopes and intrinsic parallel and orthogonal spread of the
Mgb'-Mg2, Mg2-sigma, Mgb'-sigma relations, and the Fundamental Plane. In the
latter case, the cluster peculiar velocities are also determined. We show that
this method is superior to ``canonical'' approaches of least-squares type,
which give biased slopes and biased peculiar velocities. We test the algorithm
with Monte Carlo simulations of mock EFAR catalogues and derive the systematic
and random errors on the estimated parameters. We find that random errors are
always dominant. We estimate the influence of systematic errors due to the way
clusters were selected and the hard limits and uncertainties in the selection
function parameters for the galaxies. We explore the influence of uniform
distributions in the Fundamental Plane parameters and the errors. We conclude
that the mean peculiar motions of the EFAR clusters can be determined reliably.
In particular, the placement of the two EFAR sample regions relative to the
Lauer and Postman dipole allows us to strongly constrain the amplitude of the
bulk motion in this direction.Comment: 43 pages, 19 figures, accepted for publication in MNRA
Testing Black Hole Jet Scaling Relations in Low Luminosity AGN
We present the results of the analysis of a sample of 17 low-luminosity (L_x
< 1e42 erg/s), radio loud AGNs in massive galaxies. The sample is extracted
from the SDSS database and it spans uniformly a wide range in optical [OIII]
emission line and radio luminosity, but within a narrow redshift range (0.05 <
z < 0.11) and a narrow super massive black hole mass range (~ 1e8 M_sun). For
these sources we measured core X-ray emission with the Chandra X-ray telescope
and radio emission with the VLA. Our main goal is to establish which emission
component, if any, can be regarded as the most reliable accretion/jet-power
estimator at these regimes. In order to do so, we studied the correlation
between emission line properties, radio luminosity, radio spectral slopes and
X-ray luminosity, as well as more complex multi-variate relations involving
black hole mass, such as the fundamental plane of black hole activity. We find
that 15 out of 17 sources of our sample can be classified as Low-Excitation
Galaxies (LEG) and their observed properties suggest X-ray and radio emission
to originate from the jet basis. We also find that X-ray emission does not
appear to be affected by nuclear obscuration and can be used as a reliable
jet-power estimator. More generally, X-ray, radio and optical emission appear
to be related, although no tight correlation is found. In accordance with a
number of recent studies of this class of objects these findings may be
explained by a lack of cold (molecular) gaseous structures in the innermost
region of these massive galaxies.Comment: 11 pages, 6 figures, published in MNRA
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