13,986 research outputs found
Gap Processing for Adaptive Maximal Poisson-Disk Sampling
In this paper, we study the generation of maximal Poisson-disk sets with
varying radii. First, we present a geometric analysis of gaps in such disk
sets. This analysis is the basis for maximal and adaptive sampling in Euclidean
space and on manifolds. Second, we propose efficient algorithms and data
structures to detect gaps and update gaps when disks are inserted, deleted,
moved, or have their radius changed. We build on the concepts of the regular
triangulation and the power diagram. Third, we will show how our analysis can
make a contribution to the state-of-the-art in surface remeshing.Comment: 16 pages. ACM Transactions on Graphics, 201
Disk Loss and Disk Renewal Phases in Classical Be Stars I: Analysis of Long-Term Spectropolarimetric Data
(Abridged) Classical Be stars occasionally transition from having a gaseous
circumstellar disk (''Be phase'') to a state in which all observational
evidence for the presence of these disks disappears (''normal B-star phase'').
We present one of the most comprehensive spectropolarimetric views to date of
such a transition for two Be stars, pi Aquarii and 60 Cygni. 60 Cyg's disk loss
episode was characterized by a monotonic decrease in emission strength over a
time-scale of 1000 days, consistent with the viscous time-scale of the disk,
assuming alpha is 0.14. pi Aqr's disk loss was episodic in nature and occurred
over a time-scale of 2440 days. An observed time lag between the behavior of
the polarization and H-alpha in both stars indicates the disk clearing
proceeded in an ''inside-out'' manner. We determine the position angle of the
intrinsic polarization to be 166.7 +/- 0.1 degrees for pi Aqr and 107.7 +/- 0.4
degrees for 60 Cyg, and model the observed polarization during the quiescent
diskless phase of each star to determine the interstellar polarization along
the line of sight. Minor outbursts observed during the quiescent phase of each
star shared similar lifetimes as those previously reported for mu Cen,
suggesting that the outbursts represent the injection and subsequent viscous
dissipation of individual blobs of material into the inner circumstellar
environments of these stars. We also observe deviations from the mean intrinsic
polarization position angle during polarization outbursts in each star,
indicating deviations from axisymmetry. We propose that these deviations might
be indicative of the injection (and subsequent circularization) of new blobs
into the inner disk, either in the plane of the bulk of the disk material or in
a slightly inclined (non-coplanar) orbit.Comment: 30 pages, 14 figures; accepted in Ap
Image Sampling with Quasicrystals
We investigate the use of quasicrystals in image sampling. Quasicrystals
produce space-filling, non-periodic point sets that are uniformly discrete and
relatively dense, thereby ensuring the sample sites are evenly spread out
throughout the sampled image. Their self-similar structure can be attractive
for creating sampling patterns endowed with a decorative symmetry. We present a
brief general overview of the algebraic theory of cut-and-project quasicrystals
based on the geometry of the golden ratio. To assess the practical utility of
quasicrystal sampling, we evaluate the visual effects of a variety of
non-adaptive image sampling strategies on photorealistic image reconstruction
and non-photorealistic image rendering used in multiresolution image
representations. For computer visualization of point sets used in image
sampling, we introduce a mosaic rendering technique.Comment: For a full resolution version of this paper, along with supplementary
materials, please visit at
http://www.Eyemaginary.com/Portfolio/Publications.htm
Autocalibrating and Calibrationless Parallel Magnetic Resonance Imaging as a Bilinear Inverse Problem
Modern reconstruction methods for magnetic resonance imaging (MRI) exploit
the spatially varying sensitivity profiles of receive-coil arrays as additional
source of information. This allows to reduce the number of time-consuming
Fourier-encoding steps by undersampling. The receive sensitivities are a priori
unknown and influenced by geometry and electric properties of the (moving)
subject. For optimal results, they need to be estimated jointly with the image
from the same undersampled measurement data. Formulated as an inverse problem,
this leads to a bilinear reconstruction problem related to multi-channel blind
deconvolution. In this work, we will discuss some recently developed approaches
for the solution of this problem.Comment: 3 pages, 3 figures, 12th International Conference on Sampling Theory
and Applications, Tallinn 201
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