Physical Parameters for the Afterglows of GRB 980703, 990123, 990510, and 991216 Determined from Modeling of Multi-Frequency Data

We model the radio, optical, and X-ray emission for the afterglows of GRB 980703, 990123, 990510, and 991216, within the framework of relativistic jets, to determine their physical parameters. The models that yield acceptable fits to the data have jet energies mostly between 10^{50} to 10^{51} erg and initial opening angles between 1 deg and 4 deg. The external medium density is uncertain by at least one order of magnitude in each case, being around 10^{-3}/cm^3 for GRB 980703 and 990123, ~0.1/cm^3 for GRB 990510, and ~3/cm^3 for GRB 991216. If the jets are uniform (i.e. there are no angular gradients of the energy per solid angle) then the 20 keV -- 1 MeV radiative efficiency during the GRB phase must have been at least 2-3% for GRB 990510, 20% for GRB 990123, and 30% for GRB 991216.Comment: accepted for publication by the ApJ, vol. 554. 11 pages, color figures. Last figures replaced with probability distributions of model parameter

Crystal structure of 4-(dimethylamino)-pyridinium 4-aminobenzoate dihydrate

Acknowledgements The authors thank SAIF, IIT, Madras for thedata collection.Peer reviewedPublisher PD

Spin-phonon coupling in multiferroic RCrO3_3 (R-Y, Lu, Gd, Eu, Sm): A Raman study

Raman study on a select few orthochromites, RCrO$_3$ (R = Y, Lu, Gd, Eu and Sm) shows that the phonon behavior at TN in compounds with magnetic R-ion (Gd and Sm) is remarkably different from that of non-magnetic R-ion (Y, Lu and Eu). While anomalies in most of the observed phonon frequencies in all these compounds may result from the distortion of CrO$_6$ octahedra due to size effect and magnetostriction arising from Cr-ordering, the anomalous behavior of their linewidths observed at TN for the compounds with only magnetic R-ion suggests spin-phonon coupling. The presence of spin-phonon coupling and the anomalies in the low frequency modes related to R-ion motion in orthochromites (R = Gd and Sm) support the suggestion that the coupling between 4f-3d moments play important role in inducing switchable electric polarization.Comment: 6 pages (two column format), 7 figures; The updated version of the manuscript can be found at Euro. Phys. Lett. 101, 17008 (2013

Birefringence analysis of multilayer leaky cladding optical fibre

We analyse a multilayer leaky cladding (MLC) fibre using the finite element method and study the effect of the MLC on the bending loss and birefringence of two types of structures: (i) a circular core large-mode-area structure and (ii) an elliptical-small-core structure. In a large-mode-area structure, we verify that the multilayer leaky cladding strongly discriminates against higher order modes to achieve single-mode operation, the fibre shows negligible birefringence, and the bending loss of the fibre is low for bending radii larger than 10 cm. In the elliptical-small-core structure we show that the MLC reduces the birefringence of the fibre. This prevents the structure from becoming birefringent in case of any departures from circular geometry. The study should be useful in the designs of MLC fibres for various applications including high power amplifiers, gain flattening of fibre amplifiers and dispersion compensation.Comment: 18 page