Black Hole Emission Rates and the AdS/CFT Correspondence

We study the emission rates of scalar, spinor and vector particles from a 5 dimensional black hole for arbitrary partial waves. The solution is lifted to 6 dimensions, and the near horizon $BTZ \times S^3$ geometry of the black hole solution is probed to determine the greybody factors. We show that the exact decay rates can be reproduced from a $(1+1)$-dimensional conformal field theory which lies on the boundary of the near horizon geometry. The AdS/CFT correspondence is used to determine the dimension of the CFT operators corresponding to the bulk fields. These operators couple to plane waves incident on the CFT from infinity to produce emission in the bulk.Comment: 37 pages, minor modifications; to be published in JHE

The Influence of Environmental Factors and Landcover Change on the Distribution and Metacommunity Structure of Upper Montane (Shola) Forests in the Western Ghats

Tropical montane cloud forests are unique habitats with great ecological and hydrological significance. In the Western Ghats, these upper montane forests (also known as sholas) and associated grassland habitats form approximately 1% of the land area but harbour disproportionately high numbers of endemic taxa. Despite their great conservation significance, little is known about how patterns of tree and shrub species composition vary across space, how environmental factors such as soil, climate and topography affect tree and shrub community composition, and how widespread conversion of surrounding grasslands to tea and exotic tree plantations has affected shola forest communities. The naturally fragmented nature of shola communities, which display patchiness at hierarchically nested scales, also makes them an ideal system in which to study metacommunity structure as species distributions, interactions and ecological processes, within and across fragments are likely to have equilibrated over many hundreds of generations (for trees). Hence the central underlying assumption of the species sorting perspective of the metacommunity framework, (i.e. that local community dynamics are at equilibrium) is more likely to be met in such a system. Further, recent conversion of the natural grassland matrix to exotic tree plantations and tea estates, is likely to have disrupted this equilibrium in complex and unpredictable ways, which can provide greater insights into mechanisms driving metacommunities dynamics in general and effects of landscape matrix conversion on plant communities in particular. In this thesis I attempt to understand the patterns of distribution and plant community composition of shola forests and their drivers at different spatial scales. I investigate the topographic and bioclimatic determinants of vegetation pattern within shola-grassland mosaics across their distribution in the central and southern Western Ghats. I then focus on studying the distribution and metacommunity patterns of shola tree and shrub species at the landscape scale in the southern and western Upper Nilgiris Plateau. I identify important environmental gradients structuring tree and shrub metacommunities, and determine the extent to which the latter are influenced by abiotic factors such as climate, topography and soil versus biotic factors such as dispersal. I also examine effects of grassland conversion to tea and exotic tree plantations on the structure, composition and regeneration of shola forest fragments. In order to fulfil these objectives, I use various analytic approaches including conditional inference classification trees, generalized linear models with an information theoretic framework, spatial eigenvectors and variation partitioning. I also develop a novel approach to modelling spatial connectivity created by dispersal processes in topographically heterogeneous terrain using a combination of spatial eigenvectors derived from a Circuit Theory approach. I find that both vegetation pattern within shola-grassland mosaics in general, and the shola tree and shrub metacommunity in particular, are strongly structured by the elevation gradient. In particular, above approximately 2000m elevation, there appear to be shifts in both the distribution of forest and grassland within these mosaics, as well as large changes in community composition within shola fragments. The shola metacommunity in the Upper Nilgiris primarily exhibits a Clemenstian pattern of species distribution along an elevation gradient with high turnover and significant clumping of range boundaries. Spatially structured environmental variability, accounts for much of the explained variation in shola tree and shrub abundances, while dispersal limitation accounts for about 10% of explained variation. Approximately half of the variation in tree and shrub communities remains unexplained by the environmental, historical and spatial predictors considered. Finally, sholas located within a landscape matrix of grassland differ significantly in terms of structure, composition as well as regeneration levels from those located within an altered landscape matrix of tea plantations and wattle (Acacia mearnsii), indicating that landscape matrix conversion has affected the structure and dynamics of vegetation in sholas. I present a synthesis of the main results and conclusions with a discussion of potential climate change impacts on shola forests and further research priorities. The specific conservation and management implications emerging from this study are also highlighted

Can Extremal Black Holes Have Non-Zero Entropy ?

We give several pieces of evidence to show that extremal black holes cannot be obtained as limits of non-extremal black holes. We review arguments in the literature showing that the entropy of extremal black holes is zero, while that of near-extremal ones obey the Bekenstein-Hawking formula. However, from the counting of degeneracy of quantum (BPS) states of string theory the entropy of extremal stringy black holes obeys the area law. An attempt is made to reconcile these arguments.Comment: 18 pages, RevTEX; last section modified, version to appear in Mod. Phys. Lett.

High energy effects on D-brane and black hole emission rates

Sherpa Romeo green journal. Permission to archive final published version.We study the emission of scalar particles from a class of near-extremal five-dimensional black holes and the corresponding D-brane configuration at high energies. We show that the distribution functions and the black hole greybody factors are modified in the high energy tail of the Hawking spectrum in such a way that the emission rates exactly match. We extend the results to charged scalar emission and to four dimensions.Ye

Patterns and consequences of invasion of tropical montane forests by Cestrum aurantiacum Lindl. in the Western Ghats

In the montane forest-grassland mosaics of the Western Ghats, land cover conversion to silviculture and agriculture over the last five decades has resulted in both loss of natural habitats and widespread invasion of remnant habitat patches. While invasion of the grassland habitats of the mosaic has been relatively well studied, there have been few attempts to understand the extent to which forest habitats (locally known as sholas) have been affected by the spread of exotic species. Here we examine the patterns and impacts of invasion of shola forest understoreys by Cestrum aurantiacum Lindl., an exotic shrub species. At the landscape scale, we demonstrate that the presence and abundance of this invasive in shola understories is negatively related to distance from tea plantations. Further, the intensity of invasion is higher in areas with greater seasonality of temperature and lower mean annual precipitation. At the patch scale, invasion is greatest at shola edges and away from stream courses. We find that C. aurantiacum abundance has negatively affected the regeneration of native shola tree species as well as the abundance of native shola understorey shrubs. Fifty three percent of invaded plots had no native shrubs present. In plots where both C. aurantiacum and native shrubs were present in large enough numbers, we found evidence of negative spatial dependence between stem locations of C. aurantiacum and native shrubs. Our findings have important implications for the management and conservation of these mosaics

Vitamin D Deficiency Eradication: A National Priority

Vitamin D Deficiency Eradication: A National Priorit

A Novel Threshold Detection Technique for the Automatic Construction of Attribute Profiles in Hyperspectral Images

Attribute profiles are well-acknowledged as one of the most significant techniques to characterize spectral-spatial properties of a hyperspectral image. The spectral-spatial content of an attribute profile is influenced by the threshold values considered during its construction. In this article, we propose a robust method to detect the threshold values automatically by overcoming the limitations of the existing techniques. The proposed method employs a tree structure representing the connected components of the image and evaluates attribute values at each node. Then, a total characteristic function (TCF) is defined that represents these attribute values in a nondecreasing order. The defined TCF is analyzed using a novel technique to detect a few informative thresholds for the construction of a low-dimensional attribute profile representing substantial spectral-spatial information. The proposed threshold detection method is computationally efficient. To assess the effectiveness of the proposed technique experiments are conducted on three real hyperspectral datasets using six different attributes and the results are compared to the recent state-of-the-art method. The results demonstrate that the proposed method has several advantages over the existing state-of-the-art method

Planckian scattering of D-branes

Sherpa Romeo green journal. Open access article. Creative Commons Attribution License (CC BY) applies.We consider the gravitational scattering of point particles in four dimensions, at Planckian centre of mass energy and low momentum transfer, or the eikonal approximation. The scattering amplitude can be exactly computed by modelling point particles by very generic metrics. A class of such metrics are black hole solutions obtained from dimensional reduction of p-brane solutions with one or more Ramond-Ramond charges in string theory. At weak string coupling, such black holes are replaced by a collection of wrapped D-branes. Thus, we investigate eikonal scattering at weak coupling by modelling the point particles by wrapped D-branes and show that the amplitudes exactly match the corresponding amplitude found at strong coupling. We extend the calculation for scattering of charged particles.Ye

Topographic and Bioclimatic Determinants of the Occurrence of Forest and Grassland in Tropical Montane Forest-Grassland Mosaics of the Western Ghats, India

The objective of this analysis was to identify topographic and bioclimatic factors that predict occurrence of forest and grassland patches within tropical montane forest-grassland mosaics. We further investigated whether interactions between topography and bioclimate are important in determining vegetation pattern, and assessed the role of spatial scale in determining the relative importance of specific topographic features. Finally, we assessed the role of elevation in determining the relative importance of diverse explanatory factors. The study area consists of the central and southern regions of the Western Ghats of Southern India, a global biodiversity hotspot. Random forests were used to assess prediction accuracy and predictor importance. Conditional inference classification trees were used to interpret predictor effects and examine potential interactions between predictors. GLMs were used to confirm predictor importance and assess the strength of interaction terms. Overall, topographic and bioclimatic predictors classified vegetation pattern with approximately 70% accuracy. Prediction accuracy was higher for grassland than forest, and for mosaics at higher elevations. Elevation was the most important predictor, with mosaics above 2000m dominated largely by grassland. Relative topographic position measured at a local scale (within a 300m neighbourhood) was another important predictor of vegetation pattern. In high elevation mosaics, northness and concave land surface curvature were important predictors of forest occurrence. Important bioclimatic predictors were: dry quarter precipitation, annual temperature range and the interaction between the two. The results indicate complex interactions between topography and bioclimate and among topographic variables. Elevation and topography have a strong influence on vegetation pattern in these mosaics. There were marked regional differences in the roles of various topographic and bioclimatic predictors across the range of study mosaics, indicating that the same pattern of grass and forest seems to be generated by different sets of mechanisms across the region, depending on spatial scale and elevation