13,321 research outputs found
Field theoretic calculation of scalar turbulence
The cascade rate of passive scalar and Bachelor's constant in scalar
turbulence are calculated using the flux formula. This calculation is done to
first order in perturbation series. Batchelor's constant in three dimension is
found to be approximately 1.25. In higher dimension, the constant increases as
.Comment: RevTex4, publ. in Int. J. Mod. Phy. B, v.15, p.3419, 200
Calculation of renormalized viscosity and resistivity in magnetohydrodynamic turbulence
A self-consistent renormalization (RG) scheme has been applied to nonhelical
magnetohydrodynamic turbulence with normalized cross helicity and
. Kolmogorov's 5/3 powerlaw is assumed in order to compute the
renormalized parameters. It has been shown that the RG fixed point is stable
for . The renormalized viscosity and resistivity
have been calculated, and they are found to be positive for all
parameter regimes. For and large Alfv\'{e}n ratio (ratio of
kinetic and magnetic energies) , and . As
is decreased, increases and decreases, untill where both and are approximately zero. For large ,
both and vary as . The renormalized parameters for
the case are also reported.Comment: 19 pages REVTEX, 3 ps files (Phys. Plasmas, v8, 3945, 2001
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
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
Energy fluxes in helical magnetohydrodynamics and dynamo action
Renormalized viscosity, renormalized resistivity, and various energy fluxes
are calculated for helical magnetohydrodynamics using perturbative field
theory. The calculation is to first-order in perturbation. Kinetic and magnetic
helicities do not affect the renormalized parameters, but they induce an
inverse cascade of magnetic energy. The sources for the the large-scale
magnetic field have been shown to be (1) energy flux from large-scale velocity
field to large-scale magnetic field arising due to nonhelical interactions, and
(2) inverse energy flux of magnetic energy caused by helical interactions.
Based on our flux results, a premitive model for galactic dynamo has been
constructed. Our calculations yields dynamo time-scale for a typical galaxy to
be of the order of years. Our field-theoretic calculations also reveal
that the flux of magnetic helicity is backward, consistent with the earlier
observations based on absolute equilibrium theory.Comment: REVTEX4; A factor of 2 corrected in helicit
Sequencing of the non-transcribed spacer region of the ribosomal RNA genes of Neurospora crassa
The nontranscribed spacer (NTS) region of the ribosomal RNA (rRNA) genes is the most important region of the rDNA because it contains the nucleotide sequences that trigger and/or terminate transcription. To understand the structural organization of the NTS region of Neurospora crassa rDNA we have cloned and sequenced the complete NTS region and compared it with the corresponding sequences from other organisms
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
Large-Eddy Simulations of Fluid and Magnetohydrodynamic Turbulence Using Renormalized Parameters
In this paper a procedure for large-eddy simulation (LES) has been devised
for fluid and magnetohydrodynamic turbulence in Fourier space using the
renormalized parameters. The parameters calculated using field theory have been
taken from recent papers by Verma [Phys. Rev. E, 2001; Phys. Plasmas, 2001]. We
have carried out LES on grid. These results match quite well with direct
numerical simulations of . We show that proper choice of parameter is
necessary in LES.Comment: 12 pages, 4 figures: Proper figures inserte
What do school children and teachers in rural Maharashtra think of AIDS and sex?
This paper discusses findings on issues related to sex and AIDS based on focus-group discussions conducted among students and teachers in the rural areas of Maharashtra. Most students were not sure whether AIDS could affect them, or how it could be contracted; some standard IX girl students stated the need for sex education at early ages. Most teachers did not want to talk about sex or student sexual behaviour; they stressed moral issues
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