13,448 research outputs found
Incompressible Turbulence as Nonlocal Field Theory
It is well known that incompressible turbulence is nonlocal in real space
because sound speed is infinite in incompressible fluids. The equation in
Fourier space indicates that it is nonlocal in Fourier space as well. Contrast
this with Burgers equation which is local in real space. Note that the sound
speed in Burgers equation is zero. In our presentation we will contrast these
two equations using nonlocal field theory. Energy spectrum and renormalized
parameters will be discussed.Comment: 7 pages; Talk presented in Conference on "Perspectives in Nonlinear
Dynamics (PNLD 2004)" held in Chennai, 200
Efficient absolute aspect determination of a balloon borne far infrared telescope using a solid state optical photometer
The observational and operational efficiency of the TIFR 1 meter balloon
borne far infrared telescope has been improved by incorporating a multielement
solid state optical photometer (SSOP) at the Cassegrain focus of the telescope.
The SSOP is based on a 1-D linear photo diode array (PDA). The online and
offline processing schemes of the PDA signals which have been developed, lead
to improvement in the determination of absolute telescope aspect (
0\farcm8), which is very crucial for carrying out the observations as well as
offline analysis. The SSOP and its performance during a recent balloon flight
are presented here.Comment: To appear in the February 2000 issue of the PAS
Potential fishery resources, their exploitation and utilisation
Over the years various estimates have been made of the maximum sustainable yield of the total fish resources in the
Indian waters. These estimates are by fisheries experts, exploratory teams, trial fishings conducted by independent agencies and Fisheries Survey of, India. While the estimates vary from 2.4 to 6 million tonnes annually, there is a near unanimity in the projection of an annual yield of 4.5 million tonnes from our EEZ, which remains largely unexploited. It is well-known that the marine resources exploitation in the Indian Ocean have stagnated at the level of 1.5 million tonnes for move than a
decade. While there has been some increase in the value of exports, and this has been largely due to the better international
prices and greater quality control, the annual quantitative catch has remained almost the same, and there is also not much
diversification achieved. Our fishing attitudes remain shrimp oriented only and we have made no tangible headway in increasing
the production of various other varieties as has been the case in other countries. Hence, the attention of the planners should
be focussed to tap this additional resource potential of the EEZ, which is 3.0 million tonnes over the psesent annual catch of
1,6 million tonnes
Local shell-to-shell energy transfer via nonlocal Interactions in fluid turbulence
In this paper we analytically compute the strength of nonlinear interactions
in a triad, and the energy exchanges between wavenumber shells in
incompressible fluid turbulence. The computation has been done using
first-order perturbative field theory. In three dimension, magnitude of triad
interactions is large for nonlocal triads, and small for local triads. However,
the shell-to-shell energy transfer rate is found to be local and forward. This
result is due to the fact that the nonlocal triads occupy much less Fourier
space volume than the local ones. The analytical results on three-dimensional
shell-to-shell energy transfer match with their numerical counterparts. In
two-dimensional turbulence, the energy transfer rates to the near-by shells are
forward, but to the distant shells are backward; the cumulative effect is an
inverse cascade of energy.Comment: 10 pages, Revtex
Star formation activity in the southern Galactic HII region G351.63-1.25
The southern Galactic high mass star-forming region, G351.6-1.3, is a HII
region-molecular cloud complex with a luminosity of 2.0 x 10^5 L_sun, located
at a distance of 2.4 kpc. In this paper, we focus on the investigation of the
associated HII region, embedded cluster and the interstellar medium in the
vicinity of G351.6-1.3. We address the identification of exciting source(s) as
well as the census of stellar populations. The ionised gas distribution has
been mapped using the Giant Metrewave Radio Telescope (GMRT), India at three
continuum frequencies: 1280, 610 and 325 MHz. The HII region shows an elongated
morphology and the 1280 MHz map comprises six resolved high density regions
encompassed by diffuse emission spanning 1.4 pc x 1.0 pc. The zero age
main-sequence (ZAMS) spectral type of the brightest radio core is O7.5. We have
carried out near-infrared observations in the JHKs bands using the SIRIUS
instrument on the 1.4 m Infrared Survey Facility (IRSF) telescope. The
near-infrared images reveal the presence of a cluster embedded in nebulous
fan-shaped emission. The log-normal slope of the K-band luminosity function of
the embedded cluster is found to be 0.27 +- 0.03 and the fraction of the
near-infrared excess stars is estimated to be 43%. These indicate that the age
of the cluster is consistent with 1 Myr. The champagne flow model from a flat,
thin molecular cloud is used to explain the morphology of radio emission with
respect to the millimetre cloud and infrared brightness.Comment: 18 pages, 8 figures, To be published in MNRA
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