61,262 research outputs found
The lightcurve reconstruction method for measuring the time delay of gravitational lens systems
We propose a new technique to measure the time delay of radio-loud
gravitational lens systems, which does not rely on the excessive use of
interferometric observations. Instead, the method is based on single-dish flux
density monitoring of the (unresolved) lens system's total lightcurve, combined
with additional interferometric measurements of the flux density ratio at a few
epochs during that monitoring period. The basic idea of the method is to
reconstruct the individual image lightcurves from the observed total lightcurve
by assuming a range of potential values for the time delay and the
magnification ratio of the images. It is then possible to single out the
correct reconstruction, and therefore determine the time delay, by checking the
consistency of the reconstructed individual lightcurves with the additional
interferometric observations. We performed extensive numerical simulations of
synthetic lightcurves to investigate the dependence of the performance of this
method on various parameters which are involved in the problem. Probably the
most promising candidates for applying the method (and also for determining the
Hubble constant) are lens systems consisting of multiply imaged compact sources
and an Einstein ring, such as B0218+357 from which some of the parameters used
for our simulations were adopted.Comment: 26 pages, LaTex, including 23 figures; submitted to Monthly Notices
of the Royal Astronomical Society; a version with a higher quality for some
of the figures is available at
http://www.mpa-garching.mpg.de/Lenses/Preprints/LightCrv.ps.g
Fuzzy techniques for noise removal in image sequences and interval-valued fuzzy mathematical morphology
Image sequences play an important role in today's world. They provide us a lot of information. Videos are for example used for traffic observations, surveillance systems, autonomous navigation and so on.
Due to bad acquisition, transmission or recording, the sequences are however usually corrupted by noise, which hampers the functioning of many image processing techniques. A preprocessing module to filter the images often becomes necessary.
After an introduction to fuzzy set theory and image processing, in the first main part of the thesis, several fuzzy logic based video filters are proposed: one filter for grayscale video sequences corrupted by additive Gaussian noise and two color extensions of it and two grayscale filters and one color filter for sequences affected by the random valued impulse noise type.
In the second main part of the thesis, interval-valued fuzzy mathematical morphology is studied. Mathematical morphology is a theory intended for the analysis of spatial structures that has found application in e.g. edge detection, object recognition, pattern recognition, image segmentation, image magnificationâŠ
In the thesis, an overview is given of the evolution from binary mathematical morphology over the different grayscale morphology theories to interval-valued fuzzy mathematical morphology and the interval-valued image model. Additionally, the basic properties of the interval-valued fuzzy morphological operators are investigated.
Next, also the decomposition of the interval-valued fuzzy morphological operators is investigated. We investigate the relationship between the cut of the result of such operator applied on an interval-valued image and structuring element and the result of the corresponding binary operator applied on the cut of the image and structuring element. These results are first of all interesting because they provide a link between interval-valued fuzzy mathematical morphology and binary mathematical morphology, but such conversion into binary operators also reduces the computation.
Finally, also the reverse problem is tackled, i.e., the construction of interval-valued morphological operators from the binary ones. Using the results from a more general study in which the construction of an interval-valued fuzzy set from a nested family of crisp sets is constructed, increasing binary operators (e.g. the binary dilation) are extended to interval-valued fuzzy operators
Gravitational Microlensing of a Reverberating Quasar Broad Line Region - I. Method and Qualitative Results
The kinematics and morphology of the broad emission line region (BELR) of
quasars are the subject of significant debate. The two leading methods for
constraining BELR properties are microlensing and reverberation mapping. Here
we combine these two methods with a study of the microlensing behaviour of the
BELR in Q2237+0305, as a change in continuum emission (a "flare") passes
through it. Beginning with some generic models of the BELR - sphere, bicones,
disk - we slice in velocity and time to produce brightness profiles of the BELR
over the duration of the flare. These are numerically microlensed to determine
whether microlensing of reverberation mapping provides new information about
the properties of BELRs. We describe our method and show images of the models
as they are flaring, and the unlensed and lensed spectra that are produced.
Qualitative results and a discussion of the spectra are given in this paper,
highlighting some effects that could be observed. Our conclusion is that the
influence of microlensing, while not strong, can produce significant observable
effects that will help in differentiating the properties of BELRs.Comment: 17 pages, 14 low resolution figures, 1 table, accepted for MNRAS. v2:
Corrected velocities p16, 8 to 0.08, 9 to 0.0
Statistics of Magnification Perturbations by Substructure in the Cold Dark Matter Cosmological Model
We study the statistical properties of magnification perturbations by
substructures in strong lensed systems using linear perturbation theory and an
analytical substructure model including tidal truncation and a continuous
substructure mass spectrum. We demonstrate that magnification perturbations are
dominated by perturbers found within a tidal radius of an image, and that
sizable magnification perturbations may arise from small, coherent
contributions from several substructures within the lens halo. We find that the
root-mean-square (rms) fluctuation of the magnification perturbation is 10% to
20% and both the average and rms perturbations are sensitive to the mass
spectrum and density profile of the perturbers. Interestingly, we find that
relative to a smooth model of the same mass, the average magnification in
clumpy models is lower (higher) than that in smooth models for positive
(negative) parity images. This is opposite from what is observed if one assumes
that the image magnification predicted by the best-fit smooth model of a lens
is a good proxy for what the observed magnification would have been if
substructures were absent. While it is possible for this discrepancy to be
resolved via nonlinear perturbers, we argue that a more likely explanation is
that the assumption that the best-fit lens model is a good proxy for the
magnification in the absence of substructure is not correct. We conclude that a
better theoretical understanding of the predicted statistical properties of
magnification perturbations by CDM substructure is needed in order to affirm
that CDM substructures have been unambiguously detected.Comment: ApJ accepted, minor change
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