Limits on the AGN activities in X-ray underluminous galaxy groups

We have observed four X-ray underluminous groups of galaxies using the Giant Meterwave RadioTelescope. The groups NGC 524, 720, 3607, and 4697 are underluminous in relation to the extrapolation of the Lx - T relation from rich clusters and do not show any evidence of current AGN activities that can account for such a departure. The GMRT observations carried out at low frequencies (235 and 610 MHz) were aimed at detecting low surface brightness, steep-spectrum sources indicative of past AGN activities in these groups. No such radio emissions were detected in any of these four groups. The corresponding upper limits on the total energy in relativistic particles is about 3 X 10$^{57}$ erg. This value is more than a factor of 100 less than that required to account for the decreased X-ray luminosities (or, enhanced entropies) of these four groups in the AGN-heating scenario. Alternatively, the AGN activity must have ceased about 4 Gyr ago, allowing the relativistic particles to diffuse out to such a large extent (about 250 kpc) that their radio emission could have been undetected by the current observations. If the latter scenario is correct, the ICM was pre-heated before the assembly of galaxy clusters.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letter

A phenomenological model for magnetoresistance in granular polycrystalline colossal magnetoresistive materials: the role of spin polarised tunnelling at the grain boundaries

It has been observed that in bulk and polycrystalline thin films of collossal magnetoresistive (CMR) materials the magnetoresistance follows a different behaviour compared to single crystals or single crystalline films below the ferromagnetic transition temperature Tc. In this paper we develop a phenomenological model to explain the magnetic field dependence of resistance in granular CMR materials taking into account the spin polarised tunnelling at the grain boundaries. The model has been fitted to two systems, namely, La0.55Ho0.15Sr0.3MnO3 and La1.8Y0.5Ca0.7Mn2O7. From the fitted result we have separated out, in La0.55Ho0.15Sr0.3MnO3, the intrinsic contribution from the intergranular contribution to the magnetoresistance coming from spin polarised tunnelling at the grain boundaries. It is observed that the temperature dependence of the intrinsic contribution to the magnetoresistance in La0.55Ho0.15Sr0.3MnO3 follows the prediction of double exchange model for all values of field.Comment: 14 pages + 5 figures, postscript (to appear in Journal of Applied Physics

Stock Market Integration and Volatility Spillover:India and its Major Asian Counterparts

Return and volatility spillover among Indian stock market with that of 12 other developed and emerging Asian countries over a period from November 1997 to April 2008 is studied. Daily opening and closing prices of all major equity indices from the sample countries are examined by applying the GARCH model [Engle (1982) and Bollerslev (1986)] to explore the possibility of stock market integration and volatility spillover among India and its major Asian counterparties. Apart from different degrees of correlations, both in terms of return and squared return series, among Indian stock market with that of other Asian countries, the contemporaneous intraday return spillover among India and almost all the sample countries are found to be positively significant and bi-directional. More specifically, Hong Kong, Korea, Singapore and Thailand are found to be the four Asian markets from where there is a significant flow of information in India. Similarly, among others, stock markets in Pakistan and Sri Lanka are found to be strongly influenced by movements in Indian market. Though most of the information gets transmitted among the markets without much delay, some amount of information still remains and can successfully transmit as soon as the market opens in the next day.Asian stock markets; Integration; Information spillover; GARCH model

The Role of Δ(1232)\Delta(1232) in Two-pion Exchange Three-nucleon Potential

In this paper we have studied the two-pion exchange three-nucleon potential $(2\pi E-3NP)$ using an approximate $SU(2) \times SU(2)$ chiral symmetry of the strong interaction. The off-shell pion-nucleon scattering amplitudes obtained from the Weinberg Lagangian are supplemented with contributions from the well-known $\sigma$-term and the $\Delta(1232)$ exchange. It is the role of the $\Delta$-resonance in $2\pi E-3NP$, which we have investigated in detail in the framework of the Lagrangian field theory. The $\Delta$-contribution is quite appreciable and, more significantly, it is dependent on a parameter Z which is arbitrary but has the empirical bounds $|Z| \leq 1/2$. We find that the $\Delta$-contribution to the important parameters of the $2\pi E-3NP$ depends on the choice of a value for Z, although the correction to the binding energy of triton is not expected to be very sensitive to the variation of Z within its bounds.Comment: 14 pages, LaTe

Reclamation of Model Wastewater Containing Rhodamine B by Electrochemical Fenton (ECF) process

624-628Treatment of the Synthetic Rhodamine B (RhB) wastewater by Electrochemical Fenton (ECF) processes for colour removal in batch mode using commercially available iron plates as electrodes was studied. Colour removal efficiency was determined for the ECF process by considering the effects of different variables such as pH, current density, RhB concentration and temperature. Improvement in colour removal efficiency was obtained when H2O2 was added as an oxidizing agent. The colour removal efficiency reached 94.89 % at the optimum experimental conditions (pH 3.0, 100 A/m2, 50 mg/l RhB concentration, 5 minutes, 30oC and dosage of 0.2 M H2O2). Electrical energy consumption was calculated as 2.09 KWh/m3. The ECF process was found capable to achieve the higher colour removal efficiencies with potential for wastewater treatment

Predictions in SU(5) Supergravity Grand Unification with Proton Stability and Relic Density Constraints

It is shown that in the physically interesting domain of the parameter space of SU(5) supergravity GUT, the Higgs and the Z poles dominate the LSP annihilation. Here the naive analyses on thermal averaging breaks down and formulae are derived which give a rigorous treatment over the poles. These results are then used to show that there exist significant domains in the parameter space where the constraints of proton stability and cosmology are simultaneously satisfied. New upper limits on light particle masses are obtained.Comment: (An error in the reheating factor is corrected, strengthening the conclusions, i.e. the region in parameter space where the relic density constraints are satisfied is enlarged.