Oscillating non-singular relativistic spherical model

A particular choice of the time function in the recently presented spherical solution by Dadhich [1] leads to a singularity free cosmological model which oscillates between two regular states. The energy-stress tensor involves anisotropic pressure and a heat flux term but is consistent with the usual energy conditions (strong, weak and dominant). By choosing the parameters suitably one can make the model consistent with observational data. An interesting feature of the model is that it involves blue shifts as in the quasi steady state model [2] but without violating general relativity.Comment: 6 pages, REVTEX versio

Study of the local field distribution on a single-molecule magnet-by a single paramagnetic crystal; a DPPH crystal on the surface of an Mn12-acetate crystal

The local magnetic field distribution on the subsurface of a single-molecule magnet crystal, SMM, above blocking temperature (T >> Tb) detected for a very short time interval (~ 10-10 s), has been investigated. Electron Paramagnetic Resonance (EPR) spectroscopy using a local paramagnetic probe was employed as a simple alternative detection method. An SMM crystal of [Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O (Mn12-acetate) and a crystal of 2,2- diphenyl-1-picrylhydrazyl (DPPH) as the paramagnetic probe were chosen for this study. The EPR spectra of DPPH deposited on Mn12-acetate show additional broadening and shifting in the magnetic field in comparison to the spectra of the DPPH in the absence of the SMM crystal. The additional broadening of the DPPH linewidth was considered in terms of the two dominant electron spin interactions (dipolar and exchange) and the local magnetic field distribution on the crystal surface. The temperature dependence of the linewidth of the Gaussian distribution of local fields at the SMM surface was extrapolated for the low temperature interval (70-5 K)

Non-singular black-holes on the brane

We investigate the possibility of obtaining non-singular black-hole solutions in the brane world model by solving the effective field equations for the induced metric on the brane. The Reissner-Nordstrom solution on the brane was obtained by Dadhich etal by imposing the null energy condition on the 3-brane for a bulk having non zero Weyl curvature. In this work, we relax the condition of vanishing scalar curvature $R$, however, retaining the null condition. We have shown that it is possible to obtain class of static non-singular spherically symmetric brane space-times admitting horizon. We obtain one such class of solution which is a regular version of the Reissner-Nordstrom solution in the standard general relativity.Comment: 8 pages, References added, Version to appear in Int. J. Mod. Phys.

Focusing versus defocusing properties of truly naked black holes

We study the properties of the congruence of null geodesics propagating near the so-called truly naked horizons (TNH) - objects having finite Kretschmann scalar but with diverging tidal acceleration for freely falling observers. The expansion of outgoing rays near the future horizon always tends to vanish for the non-extremal case but may be non-zero for the distorted (ultra)extremal one. It tends to diverge for the ingoing ones if the the null energy condition (NEC) is satisfied in the vicinity of the horizon outside. However, it also tends to zero for NEC violating cases except the remote horizons. We also discuss the validity of test particle approximation for TNHs and find the sufficient condition for backreaction remaining small.Comment: 16 pages. To appear in IJMP

Schwarzschild black hole with global monopole charge

We derive the metric for a Schwarzschild black hole with global monopole charge by relaxing asymptotic flatness of the Schwarzschild field. We then study the effect of global monopole charge on particle orbits and the Hawking radiation. It turns out that existence, boundedness and stability of circular orbits scale up by $(1-8 \pi\eta^2)^{-1}$, and the perihelion shift and the light bending by $(1-8 \pi\eta^2)^{-3/2}$, while the Hawking temperature scales down by $(1 - 8 \pi \eta^2)^2$ the Schwarzschild values. Here $\eta$ is the global charge.Comment: 12 pages, LaTeX versio

Effect of age of plantation on seed characters and growth performance of Tokopatta (Livistona jinkensiana Griff.) seedling

Tokopatta palm (Livistona jinkensiana) is a valuable non timber multiple end uses forest species of Arunachal Pradesh. In order to establish improved plantation, the production of quality seedling of this species is essential. The present study was undertaken to determine tree age effects on seed characters, seed germination and performance of seedlings. The 500 seeds sample from each plantations aged 18, 25, 35, 45, 54, 63 and 74 years old around Pasighat town under East Siang district, Arunachal Pradesh, India were taken to see the effect of tree ageon seed morphological characters, seed germination and seedling performance. Significant variation was observed for seed diameter and seed weight between plantations of different ages. The age effect was also seen in the germination patterns with middle aged plantations producing most superior seeds in terms of seed morphological parameters and germination behavior. Seedling attributes after 12 months showed that seedling obtained from young and middle aged plantations (between 18 to 45 years) performed better than those beyond 50 years