296,160 research outputs found
VLBA images of High Frequency Peakers
We propose a morphological classification based on the parsec scale structure
of fifty-one High Frequency Peakers (HFPs) from the ``bright'' HFP sample. VLBA
images at two adjacent frequencies (chosen among 8.4, 15.3, 22.2 and 43.2 GHz)
have been used to investigate the morphological properties of the HFPs in the
optically thin part of their spectrum. We confirm that there is quite a clear
distinction between the pc-scale radio structure of galaxies and quasars: the
78% of the galaxies show a ``Double/Triple'' morphology, typical of Compact
Symmetric Objects (CSOs), while the 87% of the quasars are characterised by
Core-Jet or unresolved structure. This suggests that most HFP candidates
identified with quasars are likely blazar objects in which a flaring
self-absorbed component at the jet base was outshining the remainder of the
source at the time of the selection based on the spectral shape. Among the
sources classified as CSOs or candidates it is possible to find extremely young
radio sources with ages of about 100 years or even less.Comment: 21 pages, 8 figures; accepted for pubblication in A&A. Paper version
with full resolution images is available at
http://www.ira.inaf.it/~ddallaca/orienti.p
Multipolar Planetary Nebulae: Not as Geometrically Diversified as Thought
Planetary nebulae (PNe) have diverse morphological shapes, including
point-symmetric and multipolar structures. Many PNe also have complicated
internal structures such as torus, lobes, knots, and ansae. A complete
accounting of all the morphological structures through physical models is
difficult. A first step toward such an understanding is to derive the true
three-dimensional structure of the nebulae. In this paper, we show that a
multipolar nebula with three pairs of lobes can explain many of such features,
if orientation and sensitivity effects are taken into account. Using only six
parameters - the inclination and position angles of each pair - we are able to
simulate the observed images of 20 PNe with complex structures. We suggest that
the multipolar structure is an intrinsic structure of PNe and the statistics of
multipolar PNe has been severely underestimated in the past.Comment: 36 pages, 5 figures, 2 table
Combining Undersampled Dithered Images
Undersampled images, such as those produced by the HST WFPC-2, misrepresent
fine-scale structure intrinsic to the astronomical sources being imaged.
Analyzing such images is difficult on scales close to their resolution limits
and may produce erroneous results. A set of ``dithered'' images of an
astronomical source generally contains more information about its structure
than any single undersampled image, however, and may permit reconstruction of a
``superimage'' with Nyquist sampling. I present a tutorial on a method of image
reconstruction that builds a superimage from a complex linear combination of
the Fourier transforms of a set of undersampled dithered images. This method
works by algebraically eliminating the high order satellites in the periodic
transforms of the aliased images. The reconstructed image is an exact
representation of the data-set with no loss of resolution at the Nyquist scale.
The algorithm is directly derived from the theoretical properties of aliased
images and involves no arbitrary parameters, requiring only that the dithers
are purely translational and constant in pixel-space over the domain of the
object of interest. I show examples of its application to WFC and PC images. I
argue for its use when the best recovery of point sources or morphological
information at the HST diffraction limit is of interest.Comment: 22 pages, 9 EPS figures, submitted to PAS
PathologyGAN: Learning deep representations of cancer tissue
We apply Generative Adversarial Networks (GANs) to the domain of digital
pathology. Current machine learning research for digital pathology focuses on
diagnosis, but we suggest a different approach and advocate that generative
models could drive forward the understanding of morphological characteristics
of cancer tissue. In this paper, we develop a framework which allows GANs to
capture key tissue features and uses these characteristics to give structure to
its latent space. To this end, we trained our model on 249K H&E breast cancer
tissue images, extracted from 576 TMA images of patients from the Netherlands
Cancer Institute (NKI) and Vancouver General Hospital (VGH) cohorts. We show
that our model generates high quality images, with a Frechet Inception Distance
(FID) of 16.65. We further assess the quality of the images with cancer tissue
characteristics (e.g. count of cancer, lymphocytes, or stromal cells), using
quantitative information to calculate the FID and showing consistent
performance of 9.86. Additionally, the latent space of our model shows an
interpretable structure and allows semantic vector operations that translate
into tissue feature transformations. Furthermore, ratings from two expert
pathologists found no significant difference between our generated tissue
images from real ones. The code, generated images, and pretrained model are
available at https://github.com/AdalbertoCq/Pathology-GANComment: MIDL 2020 final versio
Fragmentation and Limits to Dynamical Scaling in Viscous Coarsening: An Interrupted in situ X-Ray Tomographic Study
X-Ray microtomography was used to follow the coarsening of the structure of a
ternary silicate glass experiencing phase separation in the liquid state. The
volumes, surfaces, mean and Gaussian curvatures of the domains of minority
phase were measured after reconstruction of the 3D images and segmentation. A
linear growth law of the characteristic length scale was
observed. A detailed morphological study was performed. While dynamical scaling
holds for most of the geometrical observables under study, a progressive
departure from scaling invariance of the distributions of local curvatures was
evidenced. The latter results from a gradual fragmentation of the structure in
the less viscous phase that also leads to a power-law size distribution of
isolated domains
Optical multiband surface photometry of a sample of Seyfert galaxies. I. Large-scale morphology and local environment analysis of matched Seyfert and inactive galaxy samples
Parallel analysis of the large-scale morphology and local environment of
matched active and control galaxy samples plays an important role in studies of
the fueling of active galactic nuclei. We carry out a detailed morphological
characterization of a sample of 35 Seyfert galaxies and a matched sample of
inactive galaxies in order to compare the evidence of non-axisymmetric
perturbation of the potential and, in the second part of this paper, to be able
to perform a multicomponent photometric decomposition of the Seyfert galaxies.
We constructed contour maps, BVRcIc profiles of the surface brightness,
ellipticity, and position angle, as well as colour index profiles. We further
used colour index images, residual images, and structure maps, which helped
clarify the morphology of the galaxies. We studied the presence of close
companions using literature data. By straightening out the morphological status
of some of the objects, we derived an improved morphological classification and
built a solid basis for a further multicomponent decomposition of the Seyfert
sample. We report hitherto undetected (to our knowledge) structural components
in some Seyfert galaxies - a bar (Ark 479), an oval/lens (Mrk 595), rings (Ark
120, Mrk 376), a nuclear bar and ring (Mrk 352), and nuclear dust lanes (Mrk
590). We compared the large-scale morphology and local environment of the
Seyfert sample to those of the control one and found that (1) the two samples
show similar incidences of bars, rings, asymmetries, and close companions; (2)
the Seyfert bars are generally weaker than the bars of the control galaxies;
(3) the bulk of the two samples shows morphological evidence of
non-axisymmetric perturbations of the potential or close companions; (4) the
fueling of Seyfert nuclei is not directly related to the large-scale morphology
and local environment of their host galaxies.Comment: Accepted for publication in A&
Design and implementation of a real-time morphological image processor prototype
Morphology, the study of form and structure, is also a method used for processing images. Morphological image processing can be used for many purposes, including edge detection, shape recognition, smoothing, and enhancement of images. A prototype for a real-time Morphological Image Processor has been developed to process 512 x 512 extended 8-bit gray scale images, using a 7 x 7 extended 8-bit gray scale mask. This prototype processor was developed jointly with another M.S. thesis candidate, Jeffrey Hanzlik. Software was also developed to allow the user to conveniently use a personal computer to transfer images to and from the Morphological Image Processor prototype and to perform a variety of image processing operations. Field programmable gate arrays have been used for the prototype, and implementing the same architecture in VLSI will allow for real-time processing of images
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