185 research outputs found
Implementation of Classification Technique for Mammogram Image
Abstract: Mammography is an important research field. Mammography Image classification is an area of interest to most of the researchers today. The aim of this paper is to detect the Mammography image for its malignancy. Different methods can be used to detect the malignancy. This paper represents GLDM feature extraction method and SVM classifier. Experiments were conducted on MIAS database. The results show that combination of GLDM feature extractor with SVM classifier is found to give appropriate results
Global spiral modes in multi-component disks
We performed two-dimensional non-linear hydrodynamical simulations of
two-component gravitating disks aimed at studying stability properties of these
systems. In agreement with previous analytical and numerical simulations, we
find that the cold gas component strongly affects the growth rates of the
unstable global spiral modes in the disk. Already a five percent admixture of
cold gas increases approximately two-fold the growth rate of the most unstable
global mode while a twenty percent gas admixture enhances the modal growth rate
by a factor of four. The local stability properties of a two-component disk
coupled by self-gravity are governed by a stability criterion similar to
Toomre's Q-parameter derived for one-component systems. Using numerical
simulations, we analyse the applicability of a two-component local stability
criterion for the analysis of the stability properties of global modes. The
comparison of non-linear simulations with the analytical stability criterion
shows that the two-component disks can be globally unstable while being stable
to the local perturbations. The minimum value of the local stability criterion
provides, however, a rough estimate of the global stability properties of
two-component systems. We find that two-component systems with a content of
cold gas of ten percent or less are globally stable, if the minimum value of
the stability parameter exceeds about 2.5.Comment: 7 pages, with 8 postscript figures, accepted for publication by
Astronomy & Astrophysic
Periodic Pattern in the Residual-Velocity Field of OB Associations
An analysis of the residual-velocity field of OB associations within 3 kpc of
the Sun has revealed periodic variations in the radial residual velocities
along the Galactic radius vector with a typical scale length of
lambda=2.0(+/-0.2) kpc and a mean amplitude of fR=7(+/-1) km/s. The fact that
the radial residual velocities of almost all OB-associations in rich
stellar-gas complexes are directed toward the Galactic center suggests that the
solar neighborhood under consideration is within the corotation radius. The
azimuthal-velocity field exhibits a distinct periodic pattern in the region
0<l<180 degrees, where the mean azimuthal-velocity amplitude is ft=6(+/-2)
km/s. There is no periodic pattern of the azimuthal-velocity field in the
region 180<l<360 degrees. The locations of the Cygnus arm, as well as the
Perseus arm, inferred from an analysis of the radial- and azimuthal-velocity
fields coincide. The periodic patterns of the residual-velocity fields of
Cepheids and OB associations share many common features.Comment: 21 page
Rotating Nuclear Rings and Extreme Starbursts in Ultraluminous Galaxies
New high resolution interferometer data of 10 IR ultraluminous galaxies shows
the molecular gas is in rotating nuclear rings or disks with radii 300 to 800
pc. Most of the CO flux comes from a moderate-density, warm, intercloud medium
rather than self-gravitating clouds. Gas masses of ~ 5 x 10^9 Msun, 5 times
lower than the standard method are derived from a model of the molecular disks.
The ratio of molecular gas to dynamical mass, is M_gas/M_dyn ~ 1/6 with a
maximum ratio of gas to total mass surface density of 1/3. For the galaxies
VIIZw31, Arp193, and IRAS 10565+24, there is good evidence for rotating
molecular rings with a central gap. In addition to the rotating rings a new
class of star formation region is identified which we call an Extreme
Starburst. They have a characteristic size of only 100 pc., about 10^9 Msun of
gas and an IR luminosity of ~3 x 10^11 Lsun. Four extreme starbursts are
identified in the 3 closest galaxies in the sample Arp220, Arp193 and Mrk273.
They are the most prodigious star formation events in the local universe, each
representing about 1000 times as many OB stars as 30 Doradus. In Arp220, the CO
and 1.3 mm continuum maps show the two ``nuclei'' embedded in a central ring or
disk and a fainter structure extending 3 kpc to the east, normal to the nuclear
disk. There is no evidence that these sources really are the pre-merger nuclei.
They are compact, extreme starburst regions containing 10^9 Msun of dense
molecular gas and new stars, but no old stars. Most of the dust emission and
HCN emission arises in the two extreme starbursts. The entire bolometric
luminosity of Arp~220 comes from starbursts, not an AGN. In Mrk231, the disk
geometry shows that the molecular disk cannot be heated by the AGN; the far IR
luminosity of Mrk~231 is powered by a starburst, not the AGN. (Abridged)Comment: 97 pages Latex with aasms.sty, including 29 encapsulated Postscript
figures. Figs 18 and 23 are GIFs. 31 figures total. Text and higher quality
versions of figures available at
http://sbastk.ess.sunysb.edu/www/RINGS_ESB_PREPRINT.html To be published in
Ap. J., 10 Nov. 199
Minimum Velocity Dispersion in Stable Stellar Disks. Numerical Simulations
N-body dynamical simulations are used to analyze the conditions for the
gravitational stability of a three-dimensional stellar disk in the
gravitational field of two rigid spherical components--a bulge and a halo whose
central concentrations and relative masses vary over wide ranges. The number of
point masses N in the simulations varies from 40 to 500 thousands and the
evolution of the simulated models is followed over 10--20 rotation periods of
the outer edge of the disk. The initially unstable disks are heated and, as a
rule, reach a quasi-stationary equilibrium with a steady-state radial-velocity
dispersion over five to eight periods of rotation. The radial behavior of
the Toomre stability parameter for the final state of the disk is
estimated. Numerical models are used to analyze the dependence of the
gravitational stability of the disk on the relative masses of the spherical
components, disk thickness, degree of differential rotation, and initial state
of the disk. Formal application of existing, analytical, local criteria for
marginal stability of the disk can lead to errors in radial velocity dispersion
of more than a factor of 1.5. It is suggested that the approximate
constancy of for (where L
is the radial scale of disk surface density), valid for a wide range of models,
can be used to estimate upper limits for the mass and density of a disk based
on the observed distributions of the rotational velocity of the gaseous
component and of the stellar velocity dispersion.Comment: 33 pages, 8 Figs. Published in Astronomy Reports,2003,v.47,p.357 The
paper may also be found at http://neptun.sai.msu.su/~zasov/articles/k_z.zi
The 'K' selected oligophilic bacteria: a key to uncultured diversity?
Molecular techniques have made it increasingly clear that a large proportion of bacterial diversity in natural habitats is uncultured and therefore unexplored. We suggest and give evidence in support of a hypothesis that a large proportion, if not all, of the uncultured diversity from a variety of aquatic and terrestrial habitats are oligophilic (oligotrophic) bacteria. Oligophilic bacteria grow only on dilute nutrient media and form small or microscopic colonies. A technique to cultivate and isolate the moderately oligophilic bacteria was developed and 90 cultures isolated, The twelve bacterial cultures characterized showed high growth yield coefficients and carbon conversion efficiencies at low substrate concentrations and progressively decreased with increasing substrate concentrations. Most of the growth yields were substantially higher than those reported in the literature and lie near the theoretical maximum. Slow growth rates and high yields indicate that they are 'K' selected species. 16S rDNA partial sequence analysis of the isolates indicates that it is a novel as well as diverse group
Results from PAMELA, ATIC and FERMI : Pulsars or Dark Matter ?
It is well known that the dark matter dominates the dynamics of galaxies and
clusters of galaxies. Its constituents remain a mystery despite an assiduous
search for them over the past three decades. Recent results from the
satellite-based PAMELA experiment detect an excess in the positron fraction at
energies between 10-100 GeV in the secondary cosmic ray spectrum. Other
experiments namely ATIC, HESS and FERMI show an excess in the total electron
(\ps + \el) spectrum for energies greater 100 GeV. These excesses in the
positron fraction as well as the electron spectrum could arise in local
astrophysical processes like pulsars, or can be attributed to the annihilation
of the dark matter particles. The second possibility gives clues to the
possible candidates for the dark matter in galaxies and other astrophysical
systems. In this article, we give a report of these exciting developments.Comment: 27 Pages, extensively revised and significantly extended, to appear
in Pramana as topical revie
Partial Volume Segmentation of Brain MRI Scans of any Resolution and Contrast
Partial voluming (PV) is arguably the last crucial unsolved problem in
Bayesian segmentation of brain MRI with probabilistic atlases. PV occurs when
voxels contain multiple tissue classes, giving rise to image intensities that
may not be representative of any one of the underlying classes. PV is
particularly problematic for segmentation when there is a large resolution gap
between the atlas and the test scan, e.g., when segmenting clinical scans with
thick slices, or when using a high-resolution atlas. In this work, we present
PV-SynthSeg, a convolutional neural network (CNN) that tackles this problem by
directly learning a mapping between (possibly multi-modal) low resolution (LR)
scans and underlying high resolution (HR) segmentations. PV-SynthSeg simulates
LR images from HR label maps with a generative model of PV, and can be trained
to segment scans of any desired target contrast and resolution, even for
previously unseen modalities where neither images nor segmentations are
available at training. PV-SynthSeg does not require any preprocessing, and runs
in seconds. We demonstrate the accuracy and flexibility of the method with
extensive experiments on three datasets and 2,680 scans. The code is available
at https://github.com/BBillot/SynthSeg.Comment: accepted for MICCAI 202
Bulge growth through disk instabilities in high-redshift galaxies
The role of disk instabilities, such as bars and spiral arms, and the
associated resonances, in growing bulges in the inner regions of disk galaxies
have long been studied in the low-redshift nearby Universe. There it has long
been probed observationally, in particular through peanut-shaped bulges. This
secular growth of bulges in modern disk galaxies is driven by weak,
non-axisymmetric instabilities: it mostly produces pseudo-bulges at slow rates
and with long star-formation timescales. Disk instabilities at high redshift
(z>1) in moderate-mass to massive galaxies (10^10 to a few 10^11 Msun of stars)
are very different from those found in modern spiral galaxies. High-redshift
disks are globally unstable and fragment into giant clumps containing 10^8-10^9
Msun of gas and stars each, which results in highly irregular galaxy
morphologies. The clumps and other features associated to the violent
instability drive disk evolution and bulge growth through various mechanisms,
on short timescales. The giant clumps can migrate inward and coalesce into the
bulge in a few 10^8 yr. The instability in the very turbulent media drives
intense gas inflows toward the bulge and nuclear region. Thick disks and
supermassive black holes can grow concurrently as a result of the violent
instability. This chapter reviews the properties of high-redshift disk
instabilities, the evolution of giant clumps and other features associated to
the instability, and the resulting growth of bulges and associated sub-galactic
components.Comment: 37 pages, 9 figures. Invited refereed review to appear in "Galactic
Bulges", E. Laurikainen, D. Gadotti, R. Peletier (eds.), Springe
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