1,847 research outputs found
Folding model analysis of alpha radioactivity
Radioactive decay of nuclei via emission of particles has been
studied theoretically in the framework of a superasymmetric fission model using
the double folding (DF) procedure for obtaining the -nucleus
interaction potential. The DF nuclear potential has been obtained by folding in
the density distribution functions of the nucleus and the daughter
nucleus with a realistic effective interaction. The M3Y effective interaction
has been used for calculating the nuclear interaction potential which has been
supplemented by a zero-range pseudo-potential for exchange along with the
density dependence. The nuclear microscopic -nucleus potential thus
obtained has been used along with the Coulomb interaction potential to
calculate the action integral within the WKB approximation. This subsequently
yields microscopic calculations for the half lives of decays of
nuclei. The density dependence and the exchange effects have not been found to
be very significant. These calculations provide reasonable estimates for the
lifetimes of radioactivity of nuclei.Comment: 7 pages including 1 figur
Radio continuum and far-infrared emission from the galaxies in the Eridanus group
The Eridanus galaxies follow the well-known radio-FIR correlation. Majority
(70%) of these galaxies have their star formation rates below that of the Milky
Way. The galaxies having a significant excess of radio emission are identified
as low luminosity AGNs based on their radio morphologies obtained from the GMRT
observations. There are no powerful AGNs (L{20cm} > 10^{23} W Hz^{-1}) in the
group. The two most far-infrared and radio luminous galaxies in the group have
optical and HI morphologies suggestive of recent tidal interactions. The
Eridanus group also has two far-infrared luminous but radio-deficient galaxies.
It is believed that these galaxies are observed within a few Myr of the onset
of an intense star formation episode after being quiescent for at least a 100
Myr. The upper end of the radio luminosity distribution of the Eridanus
galaxies (L_{20cm} ~ 10^{22} W Hz^{-1}) is consistent with that of the field
galaxies, other groups, and late-type galaxies in nearby clusters.Comment: 16 pages; Accepted for publication in Journal of Astroph. & Astron.
March, 200
RBSC-NVSS Sample. I. Radio and Optical Identifications of a Complete Sample of 1500 Bright X-ray Sources
We cross-identified the ROSAT Bright Source Catalog (RBSC) and the NRAO VLA
Sky Survey (NVSS) to construct the RBSC-NVSS sample of the brightest X-ray
sources (>= 0.1 counts/s or ~1E-12 ergs/cm/cm/s in the 0.1-2.4 keV band) that
are also radio sources (S >= 2.5 mJy at 1.4 GHz) in the 7.8 sr of extragalactic
sky with |b| > 15 degrees. and delta > -40 degrees. The sky density of NVSS
sources is low enough that they can be reliably identified with RBSC sources
having average rms positional uncertainties = 10 arcsec. We used the more
accurate radio positions to make reliable X-ray/radio/optical identifications
down to the POSS plate limits. We obtained optical spectra for many of the
bright identifications lacking published redshifts. The resulting X-ray/radio
sample is unique in its size (N ~ 1500 objects), composition (a mixture of
nearly normal galaxies, Seyfert galaxies, quasars, and clusters), and low
average redshift ( ~ 0.1).Comment: 35 LaTeX pages including 6 eps figures + 40 LaTeX page table2
(landscape) w/ AASTeX 5.0; accepted to ApJ
The Deep SWIRE Field I. 20cm Continuum Radio Observations: A Crowded Sky
We present results from deep radio observations taken with the VLA at a
center frequency of 1400 MHz cover a region of the SWIRE Spitzer Legacy survey,
centered at 10 46 00, 59 01 00 (J2000). The reduction and cataloging of the
radio sources are described. The survey presented is the deepest so far in
terms of the radio source density on the sky. Perhaps surprisingly, the sources
down to the bottom of the catalog have median angular sizes greater than 1
arcsecond, like their cousins 10-100 times stronger. If the log N - log S
normalization remains constant at the lowest flux densities, there are about 6
sources per square arcminute down to 15 microJy at 20cm. Given the finite
source sizes this implies we may reach the natural confusion limit near 1
microJy.Comment: 29 pages, 11 figures, accepted A
Oxide nanotemplates for self-assembling "solid" building blocks
It is widely accepted that self-assembling building blocks is one of the
promising ways for engineering new materials. Recent years reveal substantial
progress in fabricating colloidal particles, polymer blocks and supramolecular
aggregates of organic molecules. Despite of substantial progress in molecular
self-assembly there is still a lack of simple blocks made of "solid matter"
(e.g. metals, oxides etc.) with well-defined crystal structure and spatial
order. Here we demonstrate that ordered arrays of metal nanoclusters can be
fabricated by self-assembly on a wide range of oxide templates. These
nano-templates are produced either by depositing an alien oxide film or by
oxidizing a metal/metal oxide substrate.Comment: 11 pages, 2 figures added DFT calculations and Fig.
Observations of the bright radio sources in the North Celestial Pole region at the RATAN-600 radio telescope
A survey of the North Celestial Pole region using the RATAN-600 radio
telescope at five frequencies in the range 2.3 to 21.7 GHz is described.
Sources were chosen from the NVSS catalogue. The flux densities of 171 sources
in the Declination range +75 to +88 are presented; typical flux density errors
are 5-10 percent including calibration errors. About 20 percent of the sources
have flat spectra or a flat component.Comment: 21 pages, 7 figures; to be published in Astronomy and Astrophysics
(without last figure with the spectra of the observed sources
Implications of non-feasible transformations among icosahedral orbitals
The symmetric group that permutes the six five-fold axes of an
icosahedron is introduced to go beyond the simple rotations that constitute the
icosahedral group . Owing to the correspondence , the
calculation of the Coulomb energies for the icosahedral configurations
based on the sequence can be brought
to bear on Racah's classic theory for the atomic d shell based on . Among the elements of is the kaleidoscope
operator that rotates the weight space of SO(5) by . Its use
explains some puzzling degeneracies in d^3 involving the spectroscopic terms
^2P, ^2F, ^2G and ^2H.Comment: Tentatively scheduled to appear in Physical Preview Letters Apr 5,
99. Revtex, 1 ps figur
GMRT observations of NGC 2997 and radio detection of the circumnuclear ring
We present high-resolution, high-sensitivity radio continuum observations of
the nearby spiral galaxy NGC 2997 at 332, 616 and 1272 MHz using the Giant
Metrewave Radio Telescope (GMRT). The integrated spectrum of this galaxy has a
spectral index of -0.92 () and we place an upper
limit to the thermal fraction at 1272 MHz of ~ 10 per cent. Our multi-frequency
study shows a relatively flat spectrum source ( ~ -0.6) at the centre
of the galaxy. This leads to radio detection of a circumnuclear ring in the
high resolution map at 1272 MHz. We detect five hotspots in the ring, with
average star formation rate of ~ 0.024 , a median SN rate
of ~ 0.001 and luminosity of W Hz. We estimate an
equipartition field in the central nuclear region of diameter ~ 750 pc to be
about G. We also report several interesting features along the spiral
arms. In this paper, we present the low frequency radio continuum maps, the
spectral index distribution, the circumnuclear ring and the derived physical
properties.Comment: 10 pages, 9 Figures, accepted in MNRAS journal on 2011 May 1
VLA 1.4 GHz Catalogs of the Abell 370 and Abell 2390 Cluster Fields
We present 1.4 GHz catalogs for the cluster fields Abell 370 and Abell 2390
observed with the Very Large Array. These are two of the deepest radio images
of cluster fields ever taken. The Abell 370 image covers an area of 40'x40'
with a synthesized beam of ~1.7" and a noise level of ~5.7 uJy near field
center. The Abell 2390 image covers an area of 34'x34' with a synthesized beam
of ~1.4" and a noise level of ~5.6 uJy near field center. We catalog 200
redshifts for the Abell 370 field. We construct differential number counts for
the central regions (radius < 16') of both clusters. We find that the faint
(S_1.4GHz < 3 mJy) counts of Abell 370 are roughly consistent with the highest
blank field number counts, while the faint number counts of Abell 2390 are
roughly consistent with the lowest blank field number counts. Our analyses
indicate that the number counts are primarily from field radio galaxies. We
suggest that the disagreement of our counts can be largely attributed to cosmic
variance.Comment: 13 pages, accepted for publication in ApJ
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