Quantum Tunneling, Blackbody Spectrum and Non-Logarithmic Entropy Correction for Lovelock Black Holes

We show, using the tunneling method, that Lovelock black holes Hawking radiate with a perfect blackbody spectrum. This is a new result. Within the semiclassical (WKB) approximation the temperature of the spectrum is given by the semiclassical Hawking temperature. Beyond the semiclassical approximation the thermal nature of the spectrum does not change but the temperature undergoes some higher order corrections. This is true for both black hole (event) and cosmological horizons. Using the first law of thermodynamics the black hole entropy is calculated. Specifically the $D$-dimensional static, chargeless black hole solutions which are spherically symmetric and asymptotically flat, AdS or dS are considered. The interesting property of these black holes is that their semiclassical entropy does not obey the Bekenstein-Hawking area law. It is found that the leading correction to the semiclassical entropy for these black holes is not logarithmic and next to leading correction is also not inverse of horizon area. This is in contrast to the black holes in Einstein gravity. The modified result is due to the presence of Gauss-Bonnet term in the Lovelock Lagrangian. For the limit where the coupling constant of the Gauss-Bonnet term vanishes one recovers the known correctional terms as expected in Einstein gravity. Finally we relate the coefficient of the leading (non-logarithmic) correction with the trace anomaly of the stress tensor.Comment: minor modifications, two new references added, LaTeX, JHEP style, 34 pages, no figures, to appear in JHE

Study of Dissipative Collisions of 20^{20}Ne (∼\sim7-11 MeV/nucleon) + 27^{27}Al

The inclusive energy distributions of complex fragments (3 $\leq$Z $\leq$ 9) emitted in the reactions $^{20}$Ne (145, 158, 200, 218 MeV) + $^{27}$Al have been measured in the angular range 10$^{o}$ - 50$^{o}$. The fusion-fission and the deep-inelastic components of the fragment yield have been extracted using multiple Gaussian functions from the experimental fragment energy spectra. The elemental yields of the fusion-fission component have been found to be fairly well exlained in the framework of standard statistical model. It is found that there is strong competition between the fusion-fission and the deep-inelastic processes at these energies. The time scale of the deep-inelastic process was estimated to be typically in the range of $\sim$ 10$^{-21}$ - 10$^{-22}$ sec., and it was found to decrease with increasing fragment mass. The angular momentum dissipations in fully energy damped deep-inelastic process have been estimated from the average energies of the deep-inelastic components of the fragment energy spectra. It has been found that, the estimated angular momentum dissipations, for lighter fragments in particular, are more than those predicted by the empirical sticking limit.Comment: 16 pages, 9 figure

Electrical transport across Au/Nb:SrTiO3 Schottky interface with different Nb doping

We have investigated electron transport in Nb doped SrTiO$_3$ single crystals for two doping densities. We find that the resistivity and mobility are temperature dependent in both whereas the carrier concentration is almost temperature invariant. We rationalize this using the hydrogenic theory for shallow donors. Further, we probe electrical transport across Schottky interfaces of Au on TiO$_2$ terminated n-type SrTiO$_3$. Quantitative analysis of macroscopic I-V measurements reveal thermionic emission dominated transport for the low doped substrate whereas it deviates from such behavior for the high doped substrate. This work is relevant for designing devices to study electronic transport using oxide-semiconductors.Comment: 10 Pages, 3 Figure

Studies on Glass Reinforced Epoxy Resin Using Vulkadur- A as Crosslinking Agent both in Presence and Absence of Carbon Black and other Non black Fillers

Epoxy resin can be reinforced with glass (fabric form) in presence of Vulkadur-A, a phenol formaldehyde resin containing a hardening agent. Overall enhancement in mechanical properties has been found stocks cured with Vulkadur-A containing 2.5 parts of carbon black as filler

Characterization of fragment emission in ^{20}Ne (7 - 10 MeV/nucleon) + ^{12}C reactions

The inclusive energy distributions of the complex fragments (3 $\leq$ Z $\leq$ 7) emitted from the bombardment of ^{12}C by ^{20}Ne beams with incident energies between 145 and 200 MeV have been measured in the angular range 10$^{o} \leq \theta_{lab} \leq$ 50^{o}. Damped fragment yields in all the cases have been found to be the characteristic of emission from fully energy equilibrated composites. The binary fragment yields are compared with the standard statistical model predictions. Enhanced yields of entrance channel fragments (5 $\leq$ Z $\leq$ 7) indicate the survival of orbiting-like process in ^{20}Ne + ^{12}C system at these energies.Comment: 18 pages, 13 figure

Digitized archive of the Kodaikanal images: Representative results of solar cycle variation from sunspot area determination

Photographic images are valuable data resources for studying long term changes in the solar magnetic field and its influence on the Earth's climate and weather. We digitized more than 100 years of white light images stored in photographic plates and films that are available at Kodaikanal observatory starting from 1904. The digitized images were calibrated for relative plate density and aligned in such a way that the solar north is in upward direction. A semi-automated sunspot detection technique was used to identify the sunspots on the digitized images. In addition to describing the calibration procedure and availability of the data, we here present preliminary results on the sunspot area measurements and their variation with time. The results show that the white-light images have a uniform spatial resolution throughout the 90 years of observations. However, the contrast of the images decreases from 1968 onwards. The images are circular and do not show any major geometrical distortions. The measured monthly averaged sunspot areas closely match the Greenwich sunspot area over the four solar cycles studied here. The yearly averaged sunspot area shows a high degree of correlation with the Greenwich sunspot area. Though the monthly averaged sunspot number shows a good correlation with the monthly averaged sunspot areas, there is a slight anti-correlation between the two during solar maximum The Kodaikanal data archive is hosted at http://kso.iiap.res.in. The long time sequence of the Kodaikanal white light images provides a consistent data set for sunspot areas and other proxies. Many studies can be performed using Kodaikanal data alone without requiring intercalibration between different data sources.Comment: 9 pages, A&A(accepted

Substrate rigidity deforms and polarizes active gels

We present a continuum model of the coupling between cells and substrate that accounts for some of the observed substrate-stiffness dependence of cell properties. The cell is modeled as an elastic active gel, adapting recently developed continuum theories of active viscoelastic fluids. The coupling to the substrate enters as a boundary condition that relates the cell's deformation field to local stress gradients. In the presence of activity, the coupling to the substrate yields spatially inhomogeneous contractile stresses and deformations in the cell and can enhance polarization, breaking the cell's front-rear symmetry.Comment: 6 pages, 4 figures, EPL forma