12,019 research outputs found
GRB000301C with peculiar afterglow emission
The CCD magnitudes in Johnson V and Cousins R and I photometric passbands are
determined for GRB 000301C afterglow starting ~ 1.5 day after the gamma-ray
burst. In fact we provide the earliest optical observations for this burst.
Light curves of the afterglow emissions in U, B, V, R, I, J and K' passbands
are obtained by combining the present measurements with the published data.
Flux decay shows a very uncommon variation relative to other well observed
GRBs. Overall, there is a steepening of the optical and near-infrared flux
decay caused by a geometric and sideways expanding jet. This is superimposed by
a short term variability especially during early time (Delta t < 8 days). The
cause of variability is not well understood, though it has occurred
simultaneously with similar amplitude in all the filters. We derive the early
and late time flux decay constants using jet model. The late time flux decay is
the steepest amongst the GRB OTs observed so far with alpha ~ 3. Steepening in
the flux decay seems to have started simultaneously around Delta t ~ 7.6 day in
all passbands. The value of spectral index in the optical-near IR region is ~
-1.0. Redshift determination with z=2.0335 indicates cosmological origin of the
GRB having a luminosity distance of 16.6 Gpc. Thus it becomes the second
farthest amongst the GRBs with known distances. An indirect estimate of the
fluence > 20 keV indicates, if isotropic,> =10^53 ergs of release of energy.
The enormous amount of released energy will be reduced, if the radiation is
beamed which is the case for this event. Using a jet break time of 7.6 days, we
infer a jet opening angle of ~ 0.15 radian. This means the energy released is
reduced by a factor of ~ 90 relative to the isotropic value.Comment: LaTeX file, 11 pages including 4 figures, uses psfig.sty, Bull.
Astron. Society of India(accepted, Sept, 2000 issue
Evidence for two spin-glass transitions with magnetoelastic and magnetoelectric couplings in the multiferroic (BiBa)(FeTi)O system
For disordered Heisenberg systems with small single ion anisotropy, two spin
glass transitions below the long range ordered phase transition temperature has
been predicted theoretically for compositions close to the percolation
threshold. Experimental verification of these predictions is still
controversial for conventional spin glasses. We show that multiferroic spin
glass systems can provide a unique platform for verifying these theoretical
predictions via a study of change in magnetoelastic and magnetoelectric
couplings, obtained from an analysis of diffraction data, at the spin glass
transition temperatures. Results of macroscopic and microscopic (x-ray and
neutron scattering) measurements are presented on disordered BiFeO3, a
canonical Heisenberg system with small single ion anisotropy, which reveal
appearance of two spin glass phases SG1 and SG2 in coexistence with the LRO
phase below the A-T and G-T lines. It is shown that the temperature dependence
of the integrated intensity of the antiferromagnetic peak shows dips with
respect to the Brillouin function behaviour around the SG1 and SG2 transition
temperatures. The ferroelectric polarisation changes significantly at the two
spin glass transition temperatures. These results, obtained using microscopic
techniques, clearly demonstrate that the SG1 and SG2 transitions occur on the
same magnetic sublattice and are intrinsic to the system. We also construct a
phase diagram showing all the magnetic phases in BF-xBT system. While our
results on the two spin glass transitions support the theoretical predictions,
it also raises several open questions which need to be addressed by revisiting
the existing theories of spin glass transitions by taking into account the
effect of magnetoelastic and magnetoelectric couplings as well as
electromagnons.Comment: 59 pages 21 figure
Recent Progress in Low Energy Neutrino Scattering Physics and Its Implications for the Standard and Beyond the Standard Model Physics
Neutrinos continue to provide a testing ground for the structure of the
standard model of particle physics as well as hints towards the physics beyond
the standard model. Neutrinos of energies spanning over several orders of
magnitude, originating in many terrestrial and astrophysical processes, have
been detected via various decay and interaction mechanisms. At MeV scales,
there has been one elusive process, until a few years ago, known as coherent
elastic neutrino-nucleus scattering (CEvNS) that was theoretically predicted
over five decades ago but was never observed experimentally. The recent
experimental observation of the CEvNS process by the COHERENT collaboration at
a stopped pion neutrino source has inspired physicists across many subfields.
This has vital implications for nuclear physics, high-energy physics,
astrophysics, and beyond. CEvNS, being a low-energy process, provides a natural
window to study light, weakly-coupled, new physics in the neutrino sector.
In this review, we intend to provide the current status of low energy
neutrino scattering physics and its implications for the standard and beyond
the standard model physics. We discuss the general formalism of calculating the
tree-level CEvNS cross section and present estimated theoretical uncertainties
on the CEvNS cross section stemming from different sources. We also discuss the
inelastic scattering of tens of MeV neutrinos that have implications for
supernova detection in future neutrino experiments. We discuss how the CEvNS
experiments can be used as a testing ground for the Standard Model (SM) weak
physics as well as in searching for the Beyond the Standard Model (BSM) physics
signals. Any deviation from the SM predicted event rate either with a change in
the total event rate or with a change in the shape of the recoil spectrum,
could indicate new contributions to the interaction cross-section.Comment: Invited review article for the Progress in Particle and Nuclear
Physics. Published version. 58 pages, 11 figures, 5 table
Phosphate uptake kinetics and its regulation in N2- fixing cyanobacterium Anabaena oryzae Fritsch under salt stress
Phosphorous (P) starved cells of the cyanobacterium Anabaena oryzae showed higher phosphate uptake rates than P-sufficient cells. The P-uptake obeyed saturation kinetics. The Km value for Pdeficientcells was lower (54.34 mM) than P-sufficient cells (82.64 mM) while Vmax was higher in Pdeficient and lower in P-sufficient cells. Salinity (NaCl) stimulated phosphate uptake significantly in thecyanobacterium which is followed by greater amount of P-accumulation in the form of polyphosphate bodies. Inhibition of P-uptake in P-deficient cells was 45% in dark grown compared to light grown cells.P-uptake was inhibited 52 and 85% in culture treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU; 10 mM) and carbonyl cyanide m-chloro phenylhydrazone (CCCP; 100 mM), respectively,suggesting that energy for uptake could be derived from oxidative phosphorylation and photophosphorelation
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