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Indian Institute of Science is a public university for scientific research and higher education located in Bengaluru , India. Established in 1899 with active support from Jamshetji Tata it is also locally known as the "Tata Institute". It acquired the status of a Deemed University in 1958. IISc is widely regarded as India's finest institution in its field, and has made significant contribution to advanced computing, space, and nuclear technologies. Wikipedia.

Ramaswamy S.,Indian Institute of Science
Annual Review of Condensed Matter Physics | Year: 2010

Active particles contain internal degrees of freedom with the ability to take in and dissipate energy and, in the process, execute systematic movement. Examples include all living organisms and their motile constituents such as molecular motors. This article reviews recent progress in applying the principles of nonequilibrium statistical mechanics and hydrodynamics to form a systematic theory of the behavior of collections of active particles - active matter - with only minimal regard to microscopic details. A unified view of the many kinds of active matter is presented, encompassing not only living systems but inanimate analogs. Theory and experiment are discussed side by side. Copyright © 2010 by Annual Reviews. All rights reserved.

Gandhi K.S.,Indian Institute of Science
Journal of Power Sources | Year: 2015

Electrical resistance of both the electrodes of a lead-acid battery increases during discharge due to formation of lead sulfate, an insulator. Work of Metzendorf [1] shows that resistance increases sharply at about 65% conversion of active materials, and battery stops discharging once this critical conversion is reached. However, these aspects are not incorporated into existing mathematical models. Present work uses the results of Metzendorf [1], and develops a model that includes the effect of variable resistance. Further, it uses a reasonable expression to account for the decrease in active area during discharge instead of the empirical equations of previous work. The model's predictions are compared with observations of Cugnet et al. [2]. The model is as successful as the non-mechanistic models existing in literature. Inclusion of variation in resistance of electrodes in the model is important if one of the electrodes is a limiting reactant. If active materials are stoichiometrically balanced, resistance of electrodes can be very large at the end of discharge but has only a minor effect on charging of batteries. The model points to the significance of electrical conductivity of electrodes in the charging of deep discharged batteries. © 2014 Elsevier B.V. All rights reserved.

Roychoudhury S.,Indian Institute of Science
World Journal of Gastroenterology | Year: 2015

Helicobacter pylori (H. pylori ) have long been associated with a spectrum of disease outcomes in the gastro-duodenal system. Heterogeneity in bacterial virulence factors or strains is not enough to explain the divergent disease phenotypes manifested by the infection. This review focuses on host genetic factors that are involved during infection and eventually are thought to influence the disease phenotype. We have summarized the different host genes that have been investigated for association studies in H. pylori mediated duodenal ulcer or gastric cancer. We discuss that as the bacteria co-evolved with the host; these host gene also show much variation across different ethnic population. We illustrate the allelic distribution of interleukin-1B, across different population which is one of the most popular candidate gene studied with respect to H. pylori infections. Further, we highlight that several polymorphisms in the pathway gene can by itself or collectively affect the acid secretion pathway axis (gastrin: somatostatin) thereby resulting in a spectrum of disease phenotype. © The Author(s) 2015. Published by Baishideng Publishing Group Inc. All rights reserved.

Joanny J.-F.,University Pierre and Marie Curie | Ramaswamy S.,Indian Institute of Science
Journal of Fluid Mechanics | Year: 2012

We study theoretically the hydrodynamics of a fluid drop containing oriented filaments endowed with active contractile or extensile stresses and placed on a solid surface. The active stresses alter qualitatively the wetting properties of the drop, leading to new spreading laws and novel static drop shapes. Candidate systems for testing our predictions include cytoskeletal extracts with motors and ATP, suspensions of bacteria or pulsatile cells, or fluids laden with artificial self-propelled colloids. © 2011 Cambridge University Press.

Lal S.,Indian Institute of Science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

We consider four-dimensional CFTs which admit a large-N expansion, and whose spectrum contains states whose conformal dimensions do not scale with N. We explicitly reorganise the partition function obtained by exponentiating the one-particle partition function of these states into a heat kernel form for the dual string spectrum on AdS(5). On very general grounds, the heat kernel answer can be expressed in terms of a convolution of the one-particle partition function of the light states in the four-dimensional CFT. © 2013 Elsevier B.V.

Khare A.,Indian Institute of Science | Saxena A.,Los Alamos National Laboratory
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2013

We demonstrate a kind of linear superposition for a large number of nonlinear equations which admit elliptic function solutions, both continuum and discrete. In particular, we show that whenever a nonlinear equation admits solutions in terms of Jacobi elliptic functions cn(x,m) and dn(x,m), then it also admits solutions in terms of their sum as well as difference, i.e. dn(x,m)±mcn(x,m). Further, we also show that whenever a nonlinear equation admits a solution in terms of dn2(x,m), it also has solutions in terms of dn2(x,m)±mcn(x,m)dn(x,m) even though cn(x,m)dn(x,m) is not a solution of that nonlinear equation. Finally, we obtain similar superposed solutions in coupled theories. © 2013 Elsevier B.V.

Cao L.,Zhejiang University | Bala G.,Indian Institute of Science | Caldeira K.,Carnegie Institution
Environmental Research Letters | Year: 2012

Recent studies show that fast climate response on time scales of less than a month can have important implications for long-term climate change. In this study, we investigate climate response on the time scale of days to weeks to a step-function quadrupling of atmospheric CO2 and contrast this with the response to a 4% increase in solar irradiance. Our simulations show that significant climate effects occur within days of a stepwise increase in both atmospheric CO2 content and solar irradiance. Over ocean, increased atmospheric CO2 warms the lower troposphere more than the surface, increasing atmospheric stability, moistening the boundary layer, and suppressing evaporation and precipitation. In contrast, over ocean, increased solar irradiance warms the lower troposphere to a much lesser extent, causing a much smaller change in evaporation and precipitation. Over land, both increased CO2 and increased solar irradiance cause rapid surface warming that tends to increase both evaporation and precipitation. However, the physiological effect of increased atmospheric CO2 on plant stomata reduces plant transpiration, drying the boundary layer and decreasing precipitation. This effect does not occur with increased solar irradiance. Therefore, differences in climatic effects from CO2 versus solar forcing are manifested within days after the forcing is imposed. © 2012 IOP Publishing Ltd.

Degottardi W.,University of Illinois at Urbana - Champaign | Sen D.,Indian Institute of Science | Vishveshwara S.,University of Illinois at Urbana - Champaign
Physical Review Letters | Year: 2013

We present a unified study of the effect of periodic, quasiperiodic, and disordered potentials on topological phases that are characterized by Majorana end modes in one-dimensional p-wave superconducting systems. We define a topological invariant derived from the equations of motion for Majorana modes and, as our first application, employ it to characterize the phase diagram for simple periodic structures. Our general result is a relation between the topological invariant and the normal state localization length. This link allows us to leverage the considerable literature on localization physics and obtain the topological phase diagrams and their salient features for quasiperiodic and disordered systems for the entire region of parameter space. © 2013 American Physical Society.

Bansal K.,Indian Institute of Science
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2013

Connection between junction impedance and modulated electroluminescence characteristics of light emitting devices of III-V compounds is probed at low frequencies (≤100 kHz). Negative capacitance effect is observed accompanied by the onset of qualitatively similar modulated light emission as a systematic function of modulation frequency. Interdependent optical and electrical response at such low frequencies is explained by the role of defects in charge recombination dynamics which can cause reduction of radiative recombination efficiency for high frequency applications. Time domain behaviour of the negative capacitance has also been studied. Occurrence of negative capacitance can be identified by the monotonically decreasing shape of the current transient derivative. The characterization techniques used here can be helpful in optimizing the design of devices based on nitrides of III-V compounds. However a more rigorous theoretical frame work is required for further analysis which may not follow the conventional semiconductor diode models based on depletion approximation and electrostatic description. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Iengar P.,Indian Institute of Science
Nucleic Acids Research | Year: 2012

Cancer-associated mutations in cancer genes constitute a diverse set of mutations associated with the disease. To gain insight into features of the set, substitution, deletion and insertion mutations were analysed at the nucleotide level, from the COSMIC database. The most frequent substitutions were c→t, g→a, g→t, and the most frequent codon changes were to termination codons. Deletions more than insertions, FS (frameshift) indels more than I-F (in-frame) ones, and single-nucleotide indels, were frequent. FS indels cause loss of significant fractions of proteins. The 5′-cut in FS deletions, and 5′-ligation in FS insertions, often occur between pairs of identical bases. Interestingly, the cut-site and 3′-ligation in insertions, and 3′-cut and join-pair in deletions, were each found to be the same significantly often (p<0.001). It is suggested that these features aid the incorporation of indel mutations. Tumor suppressors undergo larger numbers of mutations, especially disruptive ones, over the entire protein length, to inactivate two alleles. Proto-oncogenes undergo fewer, less-disruptive mutations, in selected protein regions, to activate a single allele. Finally, catalogues, in ranked order, of genes mutated in each cancer, and cancers in which each gene is mutated, were created. The study highlights the nucleotide level preferences and disruptive nature of cancer mutations. © The Author(s) 2012.

Mukhopadhyay B.,Indian Institute of Science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

String theory and gauge/gravity duality suggest the lower bound of shear viscosity (η) to entropy density (s) for any matter to be ̃μh/4πkB, when h and kB are reduced Planck and Boltzmann constants respectively and μ≤1. Motivated by this, we explore η/s in black hole accretion flows, in order to understand if such exotic flows could be a natural site for the lowest η/s. Accretion flow plays an important role in black hole physics in identifying the existence of the underlying black hole. This is a rotating shear flow with insignificant molecular viscosity, which could however have a significant turbulent viscosity, generating transport, heat and hence entropy in the flow. However, in presence of strong magnetic field, magnetic stresses can help in transporting matter independent of viscosity, via celebrated Blandford-Payne mechanism. In such cases, energy and then entropy produces via Ohmic dissipation. In addition, certain optically thin, hot, accretion flows, of temperature ≳109 K, may be favourable for nuclear burning which could generate/absorb huge energy, much higher than that in a star. We find that η/s in accretion flows appears to be close to the lower bound suggested by theory, if they are embedded by strong magnetic field or producing nuclear energy, when the source of energy is not viscous effects. A lower bound on η/s also leads to an upper bound on the Reynolds number of the flow. © 2013 Elsevier B.V.

Gautam S.,Indian Institute of Science
Modern Physics Letters B | Year: 2013

In this paper, we investigate the initiation and subsequent evolution of Crow instability in an inhomogeneous unitary Fermi gas using zero-temperature Galilei-invariant nonlinear Schrödinger equation. Considering a cigar-shaped unitary Fermi gas, we generate the vortex-antivortex pair either by phase-imprinting or by moving a Gaussian obstacle potential. We observe that the Crow instability in a unitary Fermi gas leads to the decay of the vortex-antivortex pair into multiple vortex rings and ultimately into sound waves. © 2013 World Scientific Publishing Company.

Paul A.,Indian Institute of Science
Philosophical Magazine | Year: 2013

Interdiffusion studies become increasingly difficult to perform with the increasing number of elements in a system. It is rather easy to calculate the interdiffusion coefficients for all the compositions in the interdiffusion zone in a binary system. The intrinsic diffusion coefficients can be calculated for the composition of Kirkendall marker plane in a binary system. In a ternary system, however, the interdiffusion coefficients can only be calculated for the composition where composition profiles from two different diffusion couples intersect. Intrinsic diffusion coefficients are possible to calculate when the Kirkendall markers are also present at that composition, which is a condition that is generally difficult to satisfy. In a quaternary system, the composition profiles for three different diffusion couples must intersect at one particular composition to calculate the diffusion parameters, which is a condition that is almost impossible to satisfy. To avoid these complications in a multicomponent system, the average interdiffusion coefficients are calculated. I propose a method of calculating the intrinsic diffusion coefficients and the variation in the interdiffusion coefficients for multicomponent systems. This method can be used for a single diffusion couple in a multicomponent pseudobinary system. The compositions of the end members of a diffusion couple should be selected such that only two elements diffuse into the interdiffusion zone. A few hypothetical diffusion couples are considered in order to validate and explain our method. Various sources of error in the calculations are also discussed. © 2013 Copyright Taylor and Francis Group, LLC.

Khare A.,Indian Institute of Science
Annals of Physics | Year: 2013

We demonstrate the existence of a novel set of discrete symmetries in the context of the N=2 supersymmetric (SUSY) quantum mechanical model with a potential function f(x) that is a generalization of the potential of the 1D SUSY harmonic oscillator. We perform the same exercise for the motion of a charged particle in the X-Y plane under the influence of a magnetic field in the Z-direction. We derive the underlying algebra of the existing continuous symmetry transformations (and corresponding conserved charges) and establish its relevance to the algebraic structures of the de Rham cohomological operators of differential geometry. We show that the discrete symmetry transformations of our present general theories correspond to the Hodge duality operation. Ultimately, we conjecture that any arbitrary N=2 SUSY quantum mechanical system can be shown to be a tractable model for the Hodge theory. © 2013 Elsevier Inc.

Jissy A.K.,Indian Institute of Science | Datta A.,Indian Association for The Cultivation of Science
Journal of Physical Chemistry Letters | Year: 2013

Recently, inorganic double-helical structures based on simple lithium and phosphorus salts have been demonstrated. We have analyzed the nature of bonding in these double helices of LinPn (n = 7-9). Similar to DNA, noncovalent interactions and cooperativity play an important role in stabilizing the inorganic double helices. Cooperativity imparts an additional stabilization of 4.5 to 10.1 kcal/mol per Li-P pair. In addition, the ionicity of Li-P units further augments the stability of these inorganic double-helix structures in contrast with the canonical base pairs in DNA, where noncovalent interactions determine the duplex stability. Unwinding is shown to be unfavorable, and cleavage of a few edge Li-P bonds leads to spontaneous self-healing into the intact double-helix tract. © 2013 American Chemical Society.

Marchetti M.C.,Syracuse Biomaterials Institute | Joanny J.F.,University Pierre and Marie Curie | Ramaswamy S.,Indian Institute of Science | Liverpool T.B.,University of Bristol | And 5 more authors.
Reviews of Modern Physics | Year: 2013

This review summarizes theoretical progress in the field of active matter, placing it in the context of recent experiments. This approach offers a unified framework for the mechanical and statistical properties of living matter: biofilaments and molecular motors in vitro or in vivo, collections of motile microorganisms, animal flocks, and chemical or mechanical imitations. A major goal of this review is to integrate several approaches proposed in the literature, from semimicroscopic to phenomenological. In particular, first considered are "dry" systems, defined as those where momentum is not conserved due to friction with a substrate or an embedding porous medium. The differences and similarities between two types of orientationally ordered states, the nematic and the polar, are clarified. Next, the active hydrodynamics of suspensions or "wet" systems is discussed and the relation with and difference from the dry case, as well as various large-scale instabilities of these nonequilibrium states of matter, are highlighted. Further highlighted are various large-scale instabilities of these nonequilibrium states of matter. Various semimicroscopic derivations of the continuum theory are discussed and connected, highlighting the unifying and generic nature of the continuum model. Throughout the review, the experimental relevance of these theories for describing bacterial swarms and suspensions, the cytoskeleton of living cells, and vibrated granular material is discussed. Promising extensions toward greater realism in specific contexts from cell biology to animal behavior are suggested, and remarks are given on some exotic active-matter analogs. Last, the outlook for a quantitative understanding of active matter, through the interplay of detailed theory with controlled experiments on simplified systems, with living or artificial constituents, is summarized. © 2013 American Physical Society.

Wen X.,University of Florida | Rangarajan G.,Indian Institute of Science | Ding M.,University of Florida
PLoS ONE | Year: 2013

Multivariate neural data provide the basis for assessing interactions in brain networks. Among myriad connectivity measures, Granger causality (GC) has proven to be statistically intuitive, easy to implement, and generate meaningful results. Although its application to functional MRI (fMRI) data is increasing, several factors have been identified that appear to hinder its neural interpretability: (a) latency differences in hemodynamic response function (HRF) across different brain regions, (b) low-sampling rates, and (c) noise. Recognizing that in basic and clinical neuroscience, it is often the change of a dependent variable (e.g., GC) between experimental conditions and between normal and pathology that is of interest, we address the question of whether there exist systematic relationships between GC at the fMRI level and that at the neural level. Simulated neural signals were convolved with a canonical HRF, down-sampled, and noise-added to generate simulated fMRI data. As the coupling parameters in the model were varied, fMRI GC and neural GC were calculated, and their relationship examined. Three main results were found: (1) GC following HRF convolution is a monotonically increasing function of neural GC; (2) this monotonicity can be reliably detected as a positive correlation when realistic fMRI temporal resolution and noise level were used; and (3) although the detectability of monotonicity declined due to the presence of HRF latency differences, substantial recovery of detectability occurred after correcting for latency differences. These results suggest that Granger causality is a viable technique for analyzing fMRI data when the questions are appropriately formulated. © 2013 Wen et al.

Raote I.,National Center for Biological science | Bhattacharyya S.,Indian Institute of Science | Panicker M.M.,National Center for Biological science
Molecular Pharmacology | Year: 2013

G protein-coupled receptor (GPCR) signaling is modulated by endocytosis and endosomal sorting of receptors between degradation and recycling. Differential regulation of these processes by endogenous ligands and synthetic drugs is a poorly understood area of GPCR signaling. Here, we describe remarkable diversity in the regulation of trafficking of GPCR induced by multiple ligands. We show that the serotonin receptor 2A (5-HT2A), a prototypical GPCR in the study of functional selectivity at a signaling receptor, is functionally selective in endocytosis and recycling in response to five ligands tested: endogenous agonists serotonin (5-HT) and dopamine (DA), synthetic agonist 1-(2,5-dimethoxy-4-iodophenyl)-aminopropane (DOI), antagonist ketanserin, and inverse agonist and antipsychotic drug clozapine. Only four ligands (5-HT, DA, DOI, and clozapine) bring about receptor endocytosis. As we have earlier described with 5-HT and DA, there is ligand-specific requirement for protein kinase C (PKC) in endocytosis. We now show 5-HT2A phosphorylation by PKC is necessary for 5-HT-mediated and DOI-mediated receptor endocytosis, but DA-mediated and clozapine-mediated internalization is not affected if PKC is inhibited. Internalized receptors are recycled to the cell surface, but there is variability in the time course of recycling. 5-HT- and DA-internalized receptors are recycled in 2.5 hours while agonist DOI and antagonist clozapine bring about recycling in 7.5 hours. Recycling in response to those ligands that require PKC activation to effect receptor endocytosis is dependent on receptor dephosphorylation by protein phosphatase 2A (PP2A). Thus, internalization and phosphorylation/dephosphorylation cycles may play a significant role in the regulation of 5-HT2A by functionally and therapeutically important ligands. Copyright © 2013 by The American Society for Pharmacology and Experimental Therapeutics.

Choudhuri A.R.,Indian Institute of Science
Pramana - Journal of Physics | Year: 2011

After summarizing the relevant observational data, we discuss how a study of flux tube dynamics in the solar convection zone helps us to understand the formation of sunspots. Then we introduce the flux transport dynamo model and assess its success in modelling both the solar cycle and its departures from strictly periodic behaviour. © Indian Academy of Sciences.

Kumar J.,Indian Institute of Science
Soil Dynamics and Earthquake Engineering | Year: 2011

A method has been presented to establish the theoretical dispersion curve for performing the inverse analysis for the Rayleigh wave propagation. The proposed formulation is similar to the one available in literature, and is based on the finite difference formulation of the governing partial differential equations of motion. The method is framed in such a way that it ultimately leads to an Eigen value problem for which the solution can be obtained quite easily with respect to unknown frequency. The maximum absolute value of the vertical displacement at the ground surface is formed as the basis for deciding the governing mode of propagation. With the proposed technique, the numerical solutions were generated for a variety of problems, comprising of a number of different layers, associated with both ground and pavements. The results are found to be generally satisfactory. © 2011 Elsevier Ltd.

Pai A.,Indian Institute of Science | Arun K.G.,Chennai Mathematical Institute
Classical and Quantum Gravity | Year: 2013

Various coefficients of the 3.5 post-Newtonian (PN) phasing formula of non-spinning compact binaries moving in circular orbits is fully characterized by the two component masses. If two of these coefficients are independently measured, the masses can be estimated. Future gravitational wave observations may measure most of the eight independent PN coefficients calculated to date. These additional measurements can be used to test the PN predictions of the underlying theory of gravity with a similar PN structure. Since all of these parameters are functions of the two component masses, there is a strong correlation between the parameters when treated independently. Using singular value decomposition of the Fisher information matrix, we remove these correlations and obtain a new set of parameters which are a linear combination of the original phasing coefficients. We show that the new set of parameters can be estimated with significantly improved accuracies which have implications for the ongoing efforts to implement parametrized tests of PN theory in the data analysis pipelines. © 2013 IOP Publishing Ltd.

Koteeswara Reddy N.,Indian Institute of Science
ECS Journal of Solid State Science and Technology | Year: 2013

In this article we have demonstrated the influence of growth-temperature on the morphology and orientation of SnS films deposited by thermal evaporation technique. While increasing the growth-temperature, the morphology of SnS films changed from flakes-like nanocrystals to regular cubes, whereas their orientation shifted from 〈111〉 to 〈040〉 direction. The chemical composition of SnS films gradually changed from sulfur-rich to tin-rich with the increase of growth-temperature. The structural analyzes reveal that the crystal structure of SnS films probably changes from orthorhombic to tetragonal at the growth-temperature of about 410°C. Raman studies show that SnS films grown at all temperatures consist of purely SnS phase, whereas the optical studies reveal that the direct optical bandgap of SnS films decreased with the increase of growth-temperature. From these results it has been emphasized that the morphology and orientation along with electrical and optical properties of nearly stoichiometric SnS films strongly depend on their growth-temperature. © 2013 The Electrochemical Society.

Rajagopal A.,Indian Institute of Science
Biopolymers | Year: 2012

Crystal structures of eight peptide β-hairpins in the sequence Boc-Leu-Phe-Val-Xxx-Yyy-Leu-Phe-Val-OMe revealed that the Phe(2) and Phe(7) aromatic rings are in close spacial proximity, with the centroid-centroid distance (R(cen)) of 4.4-5.4 Å between the two phenyl rings. Proton NMR spectra in chloroform and methanol solution reveal a significant upfield shift of the Phe(7) C(δ,δ') H(2) protons (6.65-7.04 ppm). Specific assignments of the aromatic protons have been carried out in the peptide Boc-Leu-Phe-Val-(D)Pro-(L)Pro-Leu-Phe-Val-OMe (6). The anticipated ring current shifts have been estimated from the aromatic ring geometrics observed in crystals for all eight peptides. Only one of the C(δ,δ') H proton lies in the shielding zone with rapid ring flipping, resulting in averaging between the two extreme chemical shifts. An approximate estimate of the population of conformations, which resemble crystal state orientation, may be obtained. Key nuclear Overhauser effects (NOEs) between facing Phe side chains provide support for close similarity between the solid state and solution conformation. Temperature dependence of aromatic ring proton chemical shift and line widths for peptide 6 (Boc-Leu-Phe-Val-(D)Pro-(L)Pro-Leu-Phe-Val-OMe) and the control peptide Boc-Leu-Val-Val-(D)Pro-Gly-Leu-Phe-Val-OMe establish an enhanced barrier to ring flipping when the two Phe rings are in proximity. Modeling studies suggest that small, conformational adjustment about C(α)-C(β) (χ(1) ) and C(β)-C(γ) (χ(2) ) bonds of both the Phe residues may be required in order to permit unhindered, uncorrelated flipping of both the Phe rings. The maintenance of the specific aromatic ring orientation in organic solvents provides evidence for significant stabilizing interaction. Copyright © 2012 Wiley Periodicals, Inc.

Baswana S.,Indian Institute of Technology Kanpur | Kavitha T.,Indian Institute of Science
SIAM Journal on Computing | Year: 2010

Let G = (V, E) be a weighted undirected graph having nonnegative edge weights. An estimate δ̂(u, v) of the actual distance δ(u, v) between u, v ∈ V is said to be of stretch t if and only if δ(u, v) ≤ δ̂(u, v) ≤ t · δ(u, v). Computing all-pairs small stretch distances efficiently (both in terms of time and space) is a well-studied problem in graph algorithms. We present a simple, novel, and generic scheme for all-pairs approximate shortest paths. Using this scheme and some new ideas and tools, we design faster algorithms for all-pairs t-stretch distances for a whole range of stretch t, and we also answer an open question posed by Thorup and Zwick in their seminal paper [J. ACM, 52 (2005), pp. 1-24]. © 2010 Society for Industrial and Applied Mathematics.

Ramakrishnan T.V.,Indian Institute of Science | Ramakrishnan T.V.,Banaras Hindu University
Annual Review of Condensed Matter Physics | Year: 2016

This is an account of a professional life in the field that was generally known as solid-state physics when I started working in it; India and the United States of America are the countries in which this life was largely played out. My attempts to understand various things in condensed matter physics, and efforts to put together people and activities in India in this field, are mainly the story. © Copyright 2016 by Annual Reviews. All rights reserved.

Chakrabarty R.,University of Utah | Mukherjee P.S.,Indian Institute of Science | Stang P.J.,University of Utah
Chemical Reviews | Year: 2011

Early coordination-driven self-assembly paradigms and more complex and discrete 2D and 3D supramolecular ensembles are reviewed. Work in this field focused on the development of rational methodologies for the self-assembly of predesigned systems along with their characterization. Multinuclear, high-resolution NMR and electrospray mass spectrometry are the primary and essential tools for proper characterization along with X-ray and more recently synchrotron X-ray methods. The most recent and arguably interesting applications have been in catalysis, use as microreactors and biological applications. Raymond and Bergman have exploited the cavities of self-assembled 3D cages for enzyme-like catalysis. Coordination-driven self-assembly will continue to be an active area of research and an important component of supramolecular chemistry and nanoscience.

Pradhan N.,Indian Association for The Cultivation of Science | Sarma D.D.,Indian Institute of Science
Journal of Physical Chemistry Letters | Year: 2011

Insertion of just a few impurity atoms in a host semiconductor nanocrystal can drastically alter its phase, shape, and physical properties. Such doped nanomaterials now constitute an important class of optical materials that can provide efficient, stable, and tunable dopant emission in visible and NIR spectral windows. Selecting proper dopants and inserting them in appropriate hosts can generate many new series of such doped nanocrystals with several unique and attractive properties in order to meet current challenges in the versatile field of luminescent materials. However, the synthesis of such doped nanomaterials with a specific dopant in a predetermined host at a desired site leading to targeted optical properties requires fundamental understanding of both the doping process as well as the resulting photophysical properties. Summarizing up to date literature reports, in this Perspective we discuss important advances in synthesis methods and in-depth understanding of the optical properties, with an emphasis on the most widely investigated Mn-doped semiconductor nanocrystals. © 2011 American Chemical Society.

Choudhury A.,Indian Institute of Science
Transactions of the Indian Institute of Metals | Year: 2015

Eutectic growth is an interesting example for exploring the topic of pattern-formation in multi-phase systems, where the growth of the phases is coupled with the diffusive transport of one or more components in the melt. While in the case of binary alloys, the number of possibilities are limited (lamellae, rods, labyrinth etc.), their number rapidly increases with the number of components and phases. In this paper, we will investigate pattern formation during three-phase eutectic solidification using a state-of-the art phase-field method based on the grand-canonical density formulation. The major aim of the study is to highlight the role of two properties, which are the volume fraction of the solid phases and the solid–liquid interfacial energies, in the self-organization of the solid phases during directional growth. Thereafter, we will show representative phase-field simulations of a micro-structure in a real alloy (Ag–Al–Cu) using an asymmetric phase diagram as well as interfacial properties. © 2015, The Indian Institute of Metals - IIM.

Mondal S.,Indian Association for The Cultivation of Science | Sen D.,Indian Institute of Science | Sengupta K.,Indian Association for The Cultivation of Science | Shankar R.,Chennai Mathematical Institute
Physical Review Letters | Year: 2010

We study the transport properties of the Dirac fermions with a Fermi velocity vF on the surface of a topological insulator across a ferromagnetic strip providing an exchange field J over a region of width d. We show that the conductance of such a junction, in the clean limit and at low temperature, changes from oscillatory to a monotonically decreasing function of d beyond a critical J. This leads to the possible realization of a magnetic switch using these junctions. We also study the conductance of these Dirac fermions across a potential barrier of width d and potential V0 in the presence of such a ferromagnetic strip and show that beyond a critical J, the criteria of conductance maxima changes from χ=eV0d/□vF=nπ to χ=(n+1/2)π for integer n. We point out that these novel phenomena have no analogs in graphene and suggest experiments which can probe them. © 2010 The American Physical Society.

Khan S.H.,Wayne State University | Matei G.,Wayne State University | Patil S.,Indian Institute of Science | Hoffmann P.M.,Wayne State University
Physical Review Letters | Year: 2010

Mechanical properties of nanoconfined water layers are still poorly understood and continue to create controversy, despite their importance for biology and nanotechnology. We report on dynamic nanomechanical measurements of water films compressed to a few single molecular layers. We show that the mechanical properties of nanoconfined water layers change significantly with their dynamic state. In particular, we observed a sharp transition from viscous to elastic response even at extremely slow compression rates, indicating that mechanical relaxation times increase dramatically once water is compressed to less than 3-4 molecular layers. © 2010 The American Physical Society.

Chanda R.,Indian Institute of Science
Globalization and Health | Year: 2011

Background: India and the EU are currently negotiating a Trade and Investment Agreement which also covers services. This paper examines the opportunities for and constraints to India-EU relations in health services in the context of this agreement, focusing on the EU as a market for India's health services exports and collaboration. The paper provides an overview of key features of health services in the EU and India and their bearing on bilateral relations in this sector.Methods: Twenty six semi-structured, in-person, and telephonic interviews were conducted in 2007-2008 in four Indian cities. The respondents included management and practitioners in a variety of healthcare establishments, health sector representatives in Indian industry associations, health sector officials in the Indian government, and official representatives of selected EU countries and the European Commission based in New Delhi. Secondary sources were used to supplement and corroborate these findings.Results: The interviews revealed that India-EU relations in health services are currently very limited. However, several opportunity segments exist, namely: (i) Telemedicine; (ii) Clinical trials and research in India for EU-based pharmaceutical companies; (iii) Medical transcriptions and back office support; (iv) Medical value travel; and (v) Collaborative ventures in medical education, research, training, staff deployment, and product development. However, various factors constrain India's exports to the EU. These include data protection regulations; recognition requirements; insurance portability restrictions; discriminatory conditions; and cultural, social, and perception-related barriers. The interviews also revealed several constraints in the Indian health care sector, including disparity in domestic standards and training, absence of clear guidelines and procedures, and inadequate infrastructure.Conclusions: The paper concludes that although there are several promising areas for India-EU relations in health services, it will be difficult to realize these opportunities given the pre-dominance of public healthcare delivery in the EU and sensitivities associated with commercializing healthcare. Hence, a gradual approach based on pilot initiatives and selective collaboration would be advisable initially, which could be expanded once there is demonstrated evidence on outcomes. Overall, the paper makes a contribution to the social science and health literature by adding to the limited primary evidence base on globalization and health, especially from a developing-developed country and regional perspective. © 2011 Chanda; licensee BioMed Central Ltd.

Anandhakumar S.,SRM University | Raichur A.M.,Indian Institute of Science
Acta Biomaterialia | Year: 2013

We demonstrate a nanoparticle loading protocol to develop a transparent, multifunctional polyelectrolyte multilayer film for externally activated drug and protein delivery. The composite film was designed by alternate adsorption of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on a glass substrate followed by nanoparticle synthesis through a polyol reduction method. The films showed a uniform distribution of spherical silver nanoparticles with an average diameter of 50 ± 20 nm, which increased to 80 ± 20 nm when the AgNO3 concentration was increased from 25 to 50 mM. The porous and supramolecular structure of the polyelectrolyte multilayer film was used to immobilize ciprofloxacin hydrochloride (CH) and bovine serum albumin (BSA) within the polymeric network of the film. When exposed to external triggers such as ultrasonication and laser light the loaded films were ruptured and released the loaded BSA and CH. The release of CH is faster than that of BSA due to a higher diffusion rate. Circular dichroism measurements confirmed that there was no significant change in the conformation of released BSA in comparison with native BSA. The fabricated films showed significant antibacterial activity against the bacterial pathogen Staphylococcus aureus. Applications envisioned for such drug-loaded films include drug and vaccine delivery through the transdermal route, antimicrobial or anti-inflammatory coatings on implants and drug-releasing coatings for stents. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Mukherjee A.,Indian Institute of Science
Journal of Physical Chemistry Letters | Year: 2011

The interplay of entropy components in a molecular recognition process is complex but intriguing. In this study, we probed into the origin of this interplay among the drug, DNA, and water entropy in the intercalation process (free → minor groove-bound → intercalation) of an anticancer drug daunomycin, resulting in small entropy difference (+1.1 kcal/mol) in excellent agreement with experiment (-1.1 kcal/mol). Using extensive all-atom simulations (>0.6 μs in total), followed by quasi-harmonic entropy calculation (with prior permutation reduction for water) and rigorous anharmonic and mutual information corrections, this study captures differing trends of drug and DNA entropy in different bound states. Overall water entropy change is positive although somewhat controlled due to the formation of bigger solvation layer in the bound states. This study encompasses for the first time all of the different entropy contributions including water in a biomolecular recognition process depicting entropy compensation similar to the ubiquitous enthalpy/entropy compensation prevalent in chemistry. © 2011 American Chemical Society.

Bhatnagar S.,Indian Institute of Science
Systems and Control Letters | Year: 2011

In this paper, we give a generalization of a result by Borkar and Meyn (2000) [1], on the stability and convergence of synchronous-update stochastic approximation algorithms, to the case of asynchronous stochastic approximations with delays. We then describe an interesting application of the result to asynchronous distributed temporal difference (TD) learning with function approximation and delays. © 2011 Elsevier B.V. All rights reserved.

Donthi S.N.,Broadcom Communications Technologies Private Ltd | Mehta N.B.,Indian Institute of Science
IEEE Transactions on Vehicular Technology | Year: 2011

Frequency-domain scheduling and rate adaptation enable next-generation orthogonal frequency-division multiple access (OFDMA) cellular systems such as Long-Term Evolution (LTE) to achieve significantly higher spectral efficiencies. LTE uses a pragmatic combination of several techniques to reduce the channel-state feedback that is required by a frequency-domain scheduler. In the subband-level feedback and user-selected subband feedback schemes specified in LTE, the user reduces feedback by reporting only the channel quality that is averaged over groups of resource blocks called subbands. This approach leads to an occasional incorrect determination of rate by the scheduler for some resource blocks. In this paper, we develop closed-form expressions for the throughput achieved by the feedback schemes of LTE. The analysis quantifies the joint effects of three critical components on the overall system throughput-scheduler, multiple-antenna mode, and the feedback schemeand brings out its dependence on system parameters such as the number of resource blocks per subband and the rate adaptation thresholds. The effect of the coarse subband-level frequency granularity of feedback is captured. The analysis provides an independent theoretical reference and a quick system parameter optimization tool to an LTE system designer and theoretically helps in understanding the behavior of OFDMA feedback reduction techniques when operated under practical system constraints. © 2010 IEEE.

Ubaidulla P.,Sudan University of Science and Technology | Chockalingam A.,Indian Institute of Science
IEEE Transactions on Signal Processing | Year: 2011

In this paper, we consider robust joint designs of relay precoder and destination receive filters in a nonregenerative multiple-input multiple-output (MIMO) relay network. The network consists of multiple source-destination node pairs assisted by a MIMO-relay node. The channel state information (CSI) available at the relay node is assumed to be imperfect. We consider robust designs for two models of CSI error. The first model is a stochastic error (SE) model, where the probability distribution of the CSI error is Gaussian. This model is applicable when the imperfect CSI is mainly due to errors in channel estimation. For this model, we propose robust minimum sum mean square error (SMSE), MSE-balancing, and relay transmit power minimizing precoder designs. The next model for the CSI error is a norm-bounded error (NBE) model, where the CSI error can be specified by an uncertainty set. This model is applicable when the CSI error is dominated by quantization errors. In this case, we adopt a worst-case design approach. For this model, we propose a robust precoder design that minimizes total relay transmit power under constraints on MSEs at the destination nodes. We show that the proposed robust design problems can be reformulated as convex optimization problems that can be solved efficiently using interior-point methods. We demonstrate the robust performance of the proposed design through simulations. © 2011 IEEE.

Choudhury J.,Indian Institute of Science
Angewandte Chemie - International Edition | Year: 2011

Pince me: N-heterocyclic nitrenium cations have been framed into pincer motifs to explore their unprecedented ligand behavior to transition metals. This work fills a long-standing gap in the series of main-group N-heterocyclic carbene(NHC)-type ligands (see picture). Reasonable π-acceptor and weak σ-donor properties of these new ligands are expected to play a pivotal role in many organometallic reactions and in catalysis in the near future. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kumar J.,Indian National Institute for Interdisciplinary Science and Technology | Thomas K.G.,Indian National Institute for Interdisciplinary Science and Technology | Thomas K.G.,Indian Institute of Science
Journal of Physical Chemistry Letters | Year: 2011

Raman signal enhancement of two analyte molecules, containing bipyridine and phenyl moieties, were investigated by linking them (i) onto the edges of Au nanorods using monothiol derivatives and (ii) at the junctions of two Au nanorods using dithiol derivatives. Edges of Au nanorods are regions of high electric field, and specific interaction of the thiol molecules on the {111} planes at the edges resulted in an enhanced Raman signal. When two Au nanorods are brought together in a linear fashion through dithiol linkages, their longitudinal plasmon oscillations couple each other, creating regions of enhanced electric field (hot spots) at the junctions. Interestingly, dimerization leads to a spontaneous enhancement in the intensity of Raman signals (enhancement factor of ∼1.4 × 10 5) due to the localization of molecules at the junctions of Au nanorod dimers. © 2011 American Chemical Society.

Sekar S.,Indian Institute of Science
Journal of Animal Ecology | Year: 2012

1.Dispersal ability of a species is a key ecological characteristic, affecting a range of processes from adaptation, community dynamics and genetic structure, to distribution and range size. It is determined by both intrinsic species traits and extrinsic landscape-related properties. 2.Using butterflies as a model system, the following questions were addressed: (i) given similar extrinsic factors, which intrinsic species trait(s) explain dispersal ability? (ii) can one of these traits be used as a proxy for dispersal ability? (iii) the effect of interactions between the traits, and phylogenetic relatedness, on dispersal ability. 3.Four data sets, using different measures of dispersal, were compiled from published literature. The first data set uses mean dispersal distances from capture-mark-recapture studies, and the other three use mobility indices. Data for six traits that can potentially affect dispersal ability were collected: wingspan, larval host plant specificity, adult habitat specificity, mate location strategy, voltinism and flight period duration. Each data set was subjected to both unifactorial, and multifactorial, phylogenetically controlled analyses. 4.Among the factors considered, wingspan was the most important determinant of dispersal ability, although the predictive powers of regression models were low. Voltinism and flight period duration also affect dispersal ability, especially in case of temperate species. Interactions between the factors did not affect dispersal ability, and phylogenetic relatedness was significant in one data set. 5.While using wingspan as the only proxy for dispersal ability maybe problematic, it is usually the only easily accessible species-specific trait for a large number of species. It can thus be a satisfactory proxy when carefully interpreted, especially for analyses involving many species from all across the world. © 2011 The Author. Journal of Animal Ecology © 2011 British Ecological Society.

Bhattacherjee B.,University of Tokyo | Bhattacherjee B.,Indian Institute of Science | Choudhury A.,Harish Chandra Research Institute
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Measurement of the self-coupling of the 125 GeV Higgs boson is one of the most crucial tasks for a high luminosity run of the LHC, and it can only be measured in the di-Higgs final state. In the minimal supersymmetric standard model, heavy CP even Higgs (H) can decay into a lighter 125 GeV Higgs boson (h) and, therefore, can influence the rate of di-Higgs production. We investigate the role of single H production in the context of measuring the self-coupling of h. We have found that the H→hh decay can change the value of Higgs (h) self-coupling substantially, in a low tanβ regime where the mass of the heavy Higgs boson lies between 250 and 600 GeV and, depending on the parameter space, it may be seen as an enhancement of the self-coupling of the 125 GeV Higgs boson. © 2015 American Physical Society.

Desiraju G.R.,Indian Institute of Science
Angewandte Chemie - International Edition | Year: 2011

Speak not against my bond: Another definition of the hydrogen bond? Strong hydrogen bonds satisfy all current definitions of this phenomenon, but as weaker interactions X-H⋯Y-Z have been brought into the scope of hydrogen bonding, the definitions have had to change. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Brahma S.,Indian Institute of Science
Thin Solid Films | Year: 2010

We report a method for the deposition of thin films and thick coatings of metal oxides through the liquid medium, involving the microwave irradiation of a solution of a metal-organic complex in a suitable dielectric solvent. The process is a combination of sol-gel and dip-coating methods, wherein coatings can be obtained on nonconducting and semiconducting substrates, within a few minutes. Thin films of nanostructured ZnO (würtzite) have been obtained on Si(100), glass and polymer substrates, the nanostructure determined by process parameters. The coatings are strongly adherent and uniform over 15 mm × 15 mm, the growth rate ∼ 0.25 μm/min. Coatings of nanocrystalline Fe 2O3 and Ga2O3 have also been obtained. The method is scalable to larger substrates, and is promising as a low temperature technique for coating dielectric substrates, including flexible polymers. © 2010 Elsevier B.V. All rights reserved.

Dasappa S.,Indian Institute of Science
Energy for Sustainable Development | Year: 2011

The paper explores the biomass based power generation potential of Africa. Access to electricity in sub-Saharan Africa (SSA) is about 26% and falls to less than 1% in the rural areas. On the basis of the agricultural and forest produce of this region, the residues generated after processing are estimated for all the countries. The paper also addresses the use of gasification technology - an efficient thermo-chemical process for distributed power generation - either to replace fossil fuel in an existing diesel engine based power generation system or to generate electricity using a gas engine. This approach enables the implementation of electrification programs in the rural sector and gives access to grid quality power. This study estimates power generation potential at about 5000. MW and 10,000. MW by using 30% of residues generated during agro processing and 10% of forest residues from the wood processing industry, respectively. A power generation potential of 15000. MW could generate 100. terawatt-hours (TWh), about 15% of current generation in SSA. The paper also summarizes some of the experience in using the biomass gasification technology for power generation in Africa and India. The paper also highlights the techno economics and key barriers to promotion of biomass energy in sub-Saharan Africa. © 2011 International Energy Initiative.

Medepally B.,Ericsson AB | Mehta N.B.,Indian Institute of Science
IEEE Transactions on Wireless Communications | Year: 2010

The use of energy harvesting (EH) nodes as cooperative relays is a promising and emerging solution in wireless systems such as wireless sensor networks. It harnesses the spatial diversity of a multi-relay network and addresses the vexing problem of a relay's batteries getting drained in forwarding information to the destination. We consider a cooperative system in which EH nodes volunteer to serve as amplify-and-forward relays whenever they have sufficient energy for transmission. For a general class of stationary and ergodic EH processes, we introduce the notion of energy constrained and energy unconstrained relays and analytically characterize the symbol error rate of the system. Further insight is gained by an asymptotic analysis that considers the cases where the signal-to-noise-ratio or the number of relays is large. Our analysis quantifies how the energy usage at an EH relay and, consequently, its availability for relaying, depends not only on the relay's energy harvesting process, but also on its transmit power setting and the other relays in the system. The optimal static transmit power setting at the EH relays is also determined. Altogether, our results demonstrate how a system that uses EH relays differs in significant ways from one that uses conventional cooperative relays. © 2010 IEEE.

Bhatnagar S.,Indian Institute of Science
Systems and Control Letters | Year: 2010

We develop in this article the first actor-critic reinforcement learning algorithm with function approximation for a problem of control under multiple inequality constraints. We consider the infinite horizon discounted cost framework in which both the objective and the constraint functions are suitable expected policy-dependent discounted sums of certain sample path functions. We apply the Lagrange multiplier method to handle the inequality constraints. Our algorithm makes use of multi-timescale stochastic approximation and incorporates a temporal difference (TD) critic and an actor that makes a gradient search in the space of policy parameters using efficient simultaneous perturbation stochastic approximation (SPSA) gradient estimates. We prove the asymptotic almost sure convergence of our algorithm to a locally optimal policy. © 2010 Elsevier B.V. All rights reserved.

Banerjee N.,Indian Institute of Technology Kharagpur | Sharma P.,Indian Institute of Science
Monthly Notices of the Royal Astronomical Society | Year: 2014

We study the interplay between turbulent heating, mixing, and radiative cooling in an idealized model of cool cluster cores. Active galactic nuclei (AGN) jets are expected to drive turbulence and heat cluster cores. Cooling of the intracluster medium (ICM) and stirring by AGN jets are tightly coupled in a feedback loop. We impose the feedback loop by balancing radiative cooling with turbulent heating. In addition to heating the plasma, turbulence also mixes it, suppressing the formation of cold gas at small scales. In this regard, the effect of turbulence is analogous to thermal conduction. For uniform plasma in thermal balance (turbulent heating balancing radiative cooling), cold gas condenses only if the cooling time is shorter than the mixing time. This condition requires the turbulent kinetic energy to be ≳ the plasma internal energy; such high velocities in cool cores are ruled out by observations. The results with realistic magnetic fields and thermal conduction are qualitatively similar to the hydrodynamic simulations. Simulations where the runaway cooling of the cool core is prevented due to mixing with the hot ICM show cold gas even with subsonic turbulence, consistent with observations. Thus, turbulent mixing is the likely mechanism via which AGN jets heat cluster cores. The thermal instability growth rates observed in simulations with turbulence are consistent with the local thermal instability interpretation of cold gas in cluster cores. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Sathiya M.,CSIR - Central Electrochemical Research Institute | Prakash A.S.,CSIR - Central Electrochemical Research Institute | Ramesha K.,CSIR - Central Electrochemical Research Institute | Tarascon J.-M.,CNRS Laboratory of Chemistry and Reactivity of Solids | Shukla A.K.,Indian Institute of Science
Journal of the American Chemical Society | Year: 2011

Functionalized multiwalled carbon nanotubes (CNTs) are coated with a 4-5 nm thin layer of V2O5 by controlled hydrolysis of vanadium alkoxide. The resulting V2O5/CNT composite has been investigated for electrochemical activity with lithium ion, and the capacity value shows both faradaic and capacitive (nonfaradaic) contributions. At high rate (1 C), the capacitive behavior dominates the intercalation as 2/3 of the overall capacity value out of 2700 C/g is capacitive, while the remaining is due to Li-ion intercalation. These numbers are in agreement with the Trasatti plots and are corroborated by X-ray photoelectron spectroscopy (XPS) studies on the V2O5/CNTs electrode, which show 85% of vanadium in the +4 oxidation state after the discharge at 1 C rate. The cumulative high-capacity value is attributed to the unique property of the nano V2O 5/CNTs composite, which provides a short diffusion path for Li +-ions and an easy access to vanadium redox centers besides the high conductivity of CNTs. The composite architecture exhibits both high power density and high energy density, stressing the benefits of using carbon substrates to design high performance supercapacitor electrodes. © 2011 American Chemical Society.

Mandal T.,Indian Institute of Science
Applied Physics Letters | Year: 2012

Using all-atom molecular dynamics simulation, we have studied the effect of size and temperature on the strain induced phase transition of wurtzite CdSe nanowires. The wurtzite structure transforms into a five-fold coordinated structure under uniaxial strain along the c axis. Our results show that lower temperature and smaller size of the nanowires stabilize the five-fold coordinated phase which is not a stable structure in bulk CdSe. High reversibility of this transformation with a very small heat loss will make these nanowires suitable for building efficient nanodevices. © 2012 American Institute of Physics.

Ghosh C.,Indian Institute of Science
Intermetallics | Year: 2010

Solid state reactive diffusion in binary Au-Sn system has been studied using the diffusion couple consisting of pure elements Au and Sn annealed in the temperature range of 180-100°C for 25 h. Interdiffusion zone consists of four intermetallic phases Au5Sn, AuSn, AuSn2, and AuSn4. Activation energy for parabolic growth constant and integrated diffusivity for each phase has been calculated to indicate about the possible mechanism for diffusion controlled growth process. Parabolic growth constant of individual phases has also been compared. Kirkendall marker plane position has been indicated in the interdiffusion zone and furthermore the ratio of intrinsic diffusivities of species has also been determined. © 2010 Elsevier Ltd. All rights reserved.

Das M.,Indian Institute of Science
Journal of Chemical Physics | Year: 2010

We studied the nature of the ground and low-lying excited states of poly-fused thiophene oligomers within long-range Pariser-Parr-Pople (PPP) model Hamiltonian with up to 14 monomers using symmetrized density matrix renormalization group technique. Our results show that the lowest dipole-allowed state lies below the lowest dipole forbidden two-photon state, indicating that poly-fused thiophenes are strongly fluorescent. The lowest triplet state lies below the two-photon state, which is in agreement with the general trend in conjugated polymers. The charge density and bond order calculations of three low-lying excited states, along with the ground state of fused thiophene oligomers, show a significant transfer of charge from sulfur to adjacent carbon atom in the middle of the largest system size and these excitations are localized. The charge density and bond order calculations on singly and doubly doped states show that bipolarons are not stable entity in these systems. The calculations of low-lying excitations on radical cation and anion of fused thiophene oligomers show a new energy band in the low energy region, which is strongly coupled to its hole and electron conductivity. This implies that poly-fused thiophenes posses novel field-effect transistor properties. © 2010 American Institute of Physics.

Shao Z.,Yale University | Negi A.S.,Indian Institute of Science | Osuji C.O.,Yale University
Soft Matter | Year: 2013

We use rheological measurements to examine the yielding behavior of a microgel system spanning the range from soft jammed glassy suspensions dominated by inter-particle repulsion to colloidal gels produced by attractive interactions. Under repulsive conditions, the suspensions display a prototypical soft glassy yielding response in which the shear loss modulus exhibits a single peak on increasing strain during the crossover from elastic to viscous behavior. By contrast, under fully attractive conditions the colloidal gel displays a more complex yielding, with two distinct peaks in the loss modulus in the vicinity of the yield strain. It is apparent that the gels yield initially by network rupture, followed by shear induced densification which leads to the formation of compact clusters. We show that the second peak in the loss modulus is consistent with the subsequent breakup of these dense clusters. We quantitatively map the steady progression from simple glassy yielding to the more complex gel response on increasing attraction strength by the evolution of peak locations, magnitudes and frequency dependencies. Notably, the peak locations diverge as the network becomes more fragile and spatially heterogeneous with increasing attraction strength. There is little frequency dependence in the peak positions, but the amplitude of the second yielding peak shows a non-monotonic dependence with a maximum near 5 rad s-1. Time-resolved measurements and decreasing strain sweeps highlight pronounced differences in the reversibility of the network rupture and cluster breakup processes. Correspondingly, the linear viscoelastic properties of the gel are strongly dependent on mechanical history whereas the glass exhibits no such dependence. © 2013 The Royal Society of Chemistry.

Guchhait B.,se National Center For Basic Science | Biswas R.,se National Center For Basic Science | Ghorai P.K.,Indian Institute of Science
Journal of Physical Chemistry B | Year: 2013

Here a combined dynamic fluorescence and all-atom molecular dynamics simulation study of aqueous pool-size dependent solvation energy and rotational relaxations of a neutral dipolar solute, C153, trapped in AOT (charged) and IGPAL (neutral) reverse micelles (RMs) at 298 K, is described. RMs in simulations have been represented by a reduced model where SPC/E water molecules interact with a trapped C153 that possesses realistic charge distributions for both ground and excited states. In large aqueous pools, measured average solvation and rotation rates are smaller for the neutral RMs than those in charged ones. Interestingly, while the measured average solvation and rotation rates increase with pool size for the charged RMs, the average rotation rates for the neutral RMs exhibit a reverse dependence. Simulations have qualitatively reproduced this experimental trend and suggested interfacial location for the solute for all cases. The origin for the subnanosecond Stokes shift dynamics has been investigated and solute-interface interaction contribution quantified. Simulated layer-wise translational and rotational diffusions of water molecules re-examine the validity of the core-shell model and provide a resolution to a debate regarding the origin of the subnanosecond solvation component in dynamic Stokes shift measurements with aqueous RMs but not detected in ultrafast IR measurements. © 2013 American Chemical Society.

Gadagkar R.,Indian Institute of Science
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2016

Ropalidia marginata is a primitively eusocial wasp widely distributed in peninsular India. Although solitary females found a small proportion of nests, the vast majority of newnests are founded bysmall groups of females. In suchmultiple foundress nests, a single dominant female functions as the queen and lays eggs, while the rest function as sterile workers and care for the queen’s brood. Previous attempts to understand the evolution of social behaviour and altruism in this species have employed inclusive fitness theory (kin selection) as a guiding framework. Although inclusive fitness theory is quite successful in explaining the high propensity of the wasps to found nests in groups, several features of their social organization suggest that forces other than kin selection may also have played a significant role in the evolution of this species. These features include lowering of genetic relatedness owing to polyandry and serial polygyny, nest foundation by unrelated individuals, acceptance of young non-nest-mates, a combination ofwell-developed nest-mate recognition and lack of intra-colony kin recognition, a combination of meek and docile queens and a decentralized self-organized work force, long reproductive queues with cryptic heir designates and conflict-free queen succession, all resulting in extreme intra-colony cooperation and inter-colony conflict. © 2016 The Author(s) Published by the Royal Society. All rights reserved.

Aliam M.M.,Indian Institute of Science
Journal of Sound and Vibration | Year: 2010

Seismic structural design is essentially the estimation of structural response to a forced motion, which may be deterministic or stochastic, imposed on the ground. The assumption that the same ground motion acts at every point of the base of the structure (or at every support) is not always justifiable; particularly in case of very large structures when considerable spatial variability in ground motion can exist over significant distances-example long span bridges. This variability is partly due to the delay in arrival of the excitation at different supports (which is called the wave passage effect) and due to heterogeneity in the ground medium which results in incoherency and local effects. The current study examines the influence of the wave passage effect (in terms of delay in arrival of horizontal ground excitation at different supports and neglecting transmission through the structure) on the response of a few open-plane frame building structures with soil-structure interaction. The ground acceleration has been modeled by a suitably filtered white noise. As a special case, the ground excitation at different supports has also been treated as statistically independent to model the extreme case of incoherence due to local effects and due to modifications to the ground motion resulting from wave reflections and refractions in heterogeneous soil media. The results indicate that, even for relatively short spanned building frames, wave passage effect can be significant. In the absence of soil-structure interaction, it can significantly increase the root mean square (rms) value of the shear in extreme end columns for the stiffer frames but has negligible effect on the flexible frames when total displacements are considered. It is seen that pseudo-static displacements increasingly contribute to the rms value of column shear as the time delay increases both for the stiffer and for the more flexible frames. When soil-structure interaction is considered, wave passage effect (in terms of total displacements) is significant only for low soil shear modulus, G s, values (where soil-structure interaction significantly lowers the fundamental frequency) and for stiff frames. The contribution of pseudo-static displacement to these rms values is found to decrease with increase in G S. In general, wave passage effect for most interactive frames is insignificant compared to the attenuating effect a decrease in Gs has on the response of the interactive structure to uniform support excitation. When the excitations at different supports are statistically independent, it is seen that for both the stiff and flexible frames, the rms value of the column shear in extreme end columns is several times larger (more for the stiffer frames) than the value corresponding to uniform base excitation with the pseudo-static displacements contributing over 99% of the rms value of column shear. Soil-structure interaction has an attenuating effect on the rms value of the column shear, the effect decreasing with increase in GS. Here too, the pseudo-static displacements contribute very largely to the column shear. The influence of the wave passage effect on the response of three 2-bay frames with and without soil-structure interaction to a recorded horizontal accelerogram is also examined. © 2010 Elsevier Ltd. All rights reserved.

Bhowmick S.,Indian Institute of Science | Waghmare U.V.,Jawaharlal Nehru Centre for Advanced Scientific Research
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Stone-Wales (SW) defects, analogous to dislocations in crystals, play an important role in mechanical behavior of s p2 -bonded carbon based materials. Here, we show using first-principles calculations that a marked anisotropy in the interaction among the SW defects has interesting consequences when such defects are present near the edges of a graphene nanoribbon: depending on their orientation with respect to edge, they result in compressive or tensile stress, and the former is responsible to depression or warping of the graphene nanoribbon. Such warping results in delocalization of electrons in the defect states. © 2010 The American Physical Society.

Bala G.,Indian Institute of Science | Caldeira K.,Carnegie Institution | Nemani R.,NASA
Climate Dynamics | Year: 2010

Recent studies have shown that changes in global mean precipitation are larger for solar forcing than for CO2 forcing of similar magnitude. In this paper, we use an atmospheric general circulation model to show that the differences originate from differing fast responses of the climate system. We estimate the adjusted radiative forcing and fast response using Hansen's "fixed-SST forcing" method. Total climate system response is calculated using mixed layer simulations using the same model. Our analysis shows that the fast response is almost 40% of the total response for few key variables like precipitation and evaporation. We further demonstrate that the hydrologic sensitivity, defined as the change in global mean precipitation per unit warming, is the same for the two forcings when the fast responses are excluded from the definition of hydrologic sensitivity, suggesting that the slow response (feedback) of the hydrological cycle is independent of the forcing mechanism. Based on our results, we recommend that the fast and slow response be compared separately in multi-model intercomparisons to discover and understand robust responses in hydrologic cycle. The significance of this study to geoengineering is discussed. © 2009 Springer-Verlag.

David J.R.,Indian Institute of Science | Sahoo B.,International Center for Theoretical Physics
Journal of High Energy Physics | Year: 2010

We show that integrability and symmetries of the near horizon geometry of the D1-D5 system determine the S-matrix for the scattering of magnons with polarizations in AdS 3 × S 3 completely up to a phase. Using semi-classical methods we evaluate the phase to the leading and to the one-loop approximation in the strong coupling expansion. We then show that the phase obeys the unitarity constraint implied by the crossing relations to the one-loop order. We also verify that the dispersion relation obeyed by these magnons is one-loop exact at strong coupling which is consistent with their BPS nature. © SISSA 2010.

Aggarwal L.,Indian Institute of Science
Nature Materials | Year: 2015

Three-dimensional (3D) Dirac semimetals exist close to topological phase boundaries which, in principle, should make it possible to drive them into exotic new phases, such as topological superconductivity, by breaking certain symmetries. A practical realization of this idea has, however, hitherto been lacking. Here we show that the mesoscopic point contacts between pure silver (Ag) and the 3D Dirac semimetal Cd3As2 (ref. ) exhibit unconventional superconductivity with a critical temperature (onset) greater than 6 K whereas neither Cd3As2 nor Ag are superconductors. A gap amplitude of 6.5 meV is measured spectroscopically in this phase that varies weakly with temperature and survives up to a remarkably high temperature of 13 K, indicating the presence of a robust normal-state pseudogap. The observations indicate the emergence of a new unconventional superconducting phase that exists in a quantum mechanically confined region under a point contact between a Dirac semimetal and a normal metal. © 2015 Nature Publishing Group

Mukherjee R.,Ecole Polytechnique Federale de Lausanne | Chatterji D.,Indian Institute of Science
IUBMB Life | Year: 2012

Species of opportunistic mycobacteria are the major causative agent for disseminating pulmonary infections in immuno-compromised individuals. These naturally resistant strains recruit a unique type of glycolipid known as glycopeptidolipids (GPLs), noncovalently attached to the outer surface of their thick lipid rich cell envelope. Species specific GPLs constitute the chemical determinants of most nontuberculous mycobacterial serotypes, and their absence from the cell surface confers altered colony morphology, hydrophobicity, and inability to grow as biofilms. The objective of this review is to present a comprehensive account and highlight the renewed interest on this much neglected group of pleiotropic molecules with respect to their structural diversity and biosynthesis. In addition, the role of GPLs in mycobacterial survival, both intracellular and in the environment is also discussed. It also explores the possibility of identifying new targets for intervening Mycobacterium avium complex-related infections. These antigenic molecules have been considered to play a pivotal role in immune suppression and can also induce various cytokine mediated innate immune responses, the molecular mechanism of which remains obscure. Copyright © 2012 Wiley Periodicals, Inc.

Hanawal M.K.,French Institute for Research in Computer Science and Automation | Sundaresan R.,Indian Institute of Science
IEEE Transactions on Information Theory | Year: 2011

The problem of guessing a random string is revisited. A close relation between guessing and compression is first established. Then it is shown that if the sequence of distributions of the information spectrum satisfies the large deviation property with a certain rate function, then the limiting guessing exponent exists and is a scalar multiple of the Legendre-Fenchel dual of the rate function. Other sufficient conditions related to certain continuity properties of the information spectrum are briefly discussed. This approach highlights the importance of the information spectrum in determining the limiting guessing exponent. All known prior results are then re-derived as example applications of our unifying approach. © 2006 IEEE.

Anilkumar P.,Indian National Institute for Interdisciplinary Science and Technology | Jayakannan M.,Indian Institute of Science
Journal of Physical Chemistry B | Year: 2010

We report a unique supramolecular organogel template approach for conducting polyaniline nanomaterials. A novel organogel based on sulfonic acid dopant was designed and developed from renewable resource 3-pentadecyl phenol via ring-opening of 1, 4-butane sultone. The amphiphilic dopant molecule formed thermoreversible supramolecular organogel in highly polar solvents like alcohols. The self-assembled fibril network morphology of the gel was confirmed by scanning electron microscopy (SEM) and atomic force microscopy. Transmission electron microscopy (TEM) revealed that the inner part of the fibrous gel is nanotubular with the pore diameter of ∼75 nm. The organogel nanotubular morphology was retained even in the presence of aniline+dopant complex, and the aniline monomers occupied the hydrophobic nanopockets provided by the amphiphilic dopant. The chemical oxidative polymerization of the dopant+aniline organogel template produced well-defined polyaniline nanofibers. The polymerization was carried out at various temperatures to establish the role of the physical state and stability of the organogel on the morphology. The sulfonic acid molecule acts both as self-assembled molecular template for the synthesis of polymer nanomaterial as well as anionic counterpart for stabilizing the positively charged conducting polymer chains. The gel template played a pivotal role in directing polyaniline chains to form nanofibers and also manipulating the number of other properties such as conductivity, solubility, percent crystallinity, and solid-state ordering, etc. Temperature-dependent electrical conductivity measurements revealed that the nanomaterials showed typical linear ohmic behavior and also followed the 3-D VRH model at elevated temperatures. © 2010 American Chemical Society.

Bhadra K.,Indian Institute of Science
Mini reviews in medicinal chemistry | Year: 2010

Alkaloids are a group of natural products with unmatched chemical diversity and biological relevance forming potential quality pools in drug screening. The molecular aspects of their interaction with many cellular macromolecules like DNA, RNA and proteins are being currently investigated in order to evolve the structure activity relationship. Isoquinolines constitute an important group of alkaloids. They have extensive utility in cancer therapy and a large volume of data is now emerging in the literature on their mode, mechanism and specificity of binding to DNA. Thermodynamic characterization of the binding of these alkaloids to DNA may offer key insights into the molecular aspects that drive complex formation and these data can provide valuable information about the balance of driving forces. Various thermal techniques have been conveniently used for this purpose and modern calorimetric instrumentation provides direct and quick estimation of thermodynamic parameters. Thermal melting studies and calorimetric techniques like isothermal titration calorimetry and differential scanning calorimetry have further advanced the field by providing authentic, reliable and sensitive data on various aspects of temperature dependent structural analysis of the interaction. In this review we present the application of various thermal techniques, viz. isothermal titration calorimetry, differential scanning calorimetry and optical melting studies in the characterization of drug-DNA interactions with particular emphasis on isoquinoline alkaloid-DNA interaction.

Lenka N.K.,Indian Institute of Science | Lal R.,Ohio State University
Soil and Tillage Research | Year: 2012

Mulching effect on carbon (C) sequestration depends on soil properties, mulch material, and the rate and duration of application. Thus, rate of soil C sequestration was assessed on a 15 year field study involving three levels of wheat straw at 0 (M 0), 8 (M 8) and 16 (M 16) Mgha -1yr -1, at two levels (244kgNha -1yr -1, F 1 and without, F 0) of supplemental N. Soil C concentration was assessed in relation to aggregation and occlusion in aggregates of a silt loam Alfisol under a no-till (NT) and crop-free system in central Ohio. In comparison to control, soil organic carbon (SOC) concentration in the 0-10cm depth of bulk soil increased by 32% and 90% with M 8 and M 16 treatments with a corresponding increase in the SOC stock by 21-25% and 50-60%, respectively. With increase in rate of residue mulch, proportion of water stable aggregates (small macroaggregates, >250μm size) increased by 1.4-1.8 times and of microaggregates (53-250μm) by 1.4 times. Fertilizer N significantly increased the SOC concentration of small macroaggregates under M 16 treatments only. Ultra-sonication showed that 12-20% of SOC occluded in the inter-microaggregate space of small macroaggergates, was a function of both mulch and fertilizer rates. Significantly higher and positive correlation of greenhouse gases (GHGs), CO 2, CH 4 and N 2O flux was observed with C and N concentrations of small macroaggregates and also of the occluded fraction of small macroaggregates. The higher correlation coefficient indicated the latter to be prone to microbial attack. On the contrary, non-significant relationship with C and N concentrations of microaggregates indicate a possible protection of microaggregate C. The diurnal fluxes of CO 2, CH 4 and N 2O were the lowest under bare soil and the highest under high mulch rate with added N, with values ranging from 1.51 to 2.31gm -2d -1, -2.79 to 3.15mgm -2d -1 and 0.46 to 1.02mgm -2d -1, respectively. Mulch rate affected the GHGs flux more than did the fertilizer rates. The net global warming potential (GWP) was higher for high mulch (M 16) than low mulch (M 8) rates, with values ranging from 0.46 to 0.57 Mg CO 2 equivalent - Cha -1yr -1 (M 8) and 1.98 to 3.05Mg CO 2 equivalent - Cha -1yr -1 (M 16). In general, mulch rate determined the effect of fertilizers. The study indicated that over long-term, a mulch rate between 8 and 16Mgha -1yr -1 may be optimal for Alfisols in Central Ohio. © 2012 Elsevier B.V.

Shenoy V.B.,Indian Institute of Science | Ho T.-L.,Ohio State University
Physical Review Letters | Year: 2011

We generalize the Noziéres-Schmitt-Rink method to study the repulsive Fermi gas in the absence of molecule formation, i.e., in the so-called "upper branch." We find that the system remains stable except close to resonance at sufficiently low temperatures. With increasing scattering length, the energy density of the system attains a maximum at a positive scattering length before resonance. This is shown to arise from Pauli blocking which causes the bound states of fermion pairs of different momenta to disappear at different scattering lengths. At the point of maximum energy, the compressibility of the system is substantially reduced, leading to a sizable uniform density core in a trapped gas. The change in spin susceptibility with increasing scattering length is moderate and does not indicate any magnetic instability. These features should also manifest in Fermi gases with unequal masses and/or spin populations. © 2011 American Physical Society.

Rajan G.S.,India Ltd | Rajan B.S.,Indian Institute of Science
IEEE Transactions on Information Theory | Year: 2010

In this paper, collocated and distributed space-time block codes (DSTBCs) which admit multigroup maximum-likelihood (ML) decoding are studied. First, the collocated case is considered and the problem of constructing space-time block codes (STBCs) which optimally tradeoff rate and ML decoding complexity is posed. Recently, sufficient conditions for multigroup ML decodability have been provided in the literature and codes meeting these sufficient conditions were called Clifford unitary weight (CUW) STBCs. An algebraic framework based on extended Clifford algebras (ECAs) is proposed to study CUW STBCs and using this framework, the optimal tradeoff between rate and ML decoding complexity of CUW STBCs is obtained for few specific cases. Code constructions meeting this tradeoff optimally are also provided. The paper then focuses on multigroup ML decodable DSTBCs for application in synchronous wireless relay networks and three constructions of four-group ML decodable DSTBCs are provided. Finally, the orthogonal frequency-division multiplexing (OFDM)-based Alamouti space-time coded scheme proposed by LiXia for a 2-relay asynchronous relay network is extended to a more general transmission scheme that can achieve full asynchronous cooperative diversity for arbitrary number of relays. It is then shown how differential encoding at the source can be combined with the proposed transmission scheme to arrive at a new transmission scheme that can achieve full cooperative diversity in asynchronous wireless relay networks with no channel information and also no timing error knowledge at the destination node. Four-group decodable DSTBCs applicable in the proposed OFDM-based transmission scheme are also given. © 2006 IEEE.

Hundi R.S.,Indian Institute of Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

The Large Hadron Collider has recently discovered a Higgs-like particle having a mass around 125 GeV and also indicated that there is an enhancement in the Higgs to diphoton decay rate as compared to that in the standard model. We have studied implications of these discoveries in the bilinear R-parity violating supersymmetric model, whose main motivation is to explain the nonzero masses for neutrinos. The R-parity violating parameters in this model are Ïμ and bÏμ, and these parameters determine the scale of neutrino masses. If the enhancement in the Higgs to diphoton decay rate is true, then we have found Ïμ0.01 GeV and bÏμ∼1 GeV2 in order to be compatible with the neutrino oscillation data. Also, in the above mentioned analysis, we can determine the soft masses of sleptons (m L) and CP-odd Higgs boson mass (mA). We have estimated that mL300 GeV and mA700 GeV. We have also commented on the allowed values of Ïμ and bÏμ, in case there is no enhancement in the Higgs to diphoton decay rate. Finally, we present a model to explain the smallness of Ïμ and bÏμ. © 2013 American Physical Society.

Narayanan R.,Indian Institute of Science | Johnston D.,University of Texas at Austin
Journal of Neurophysiology | Year: 2012

The presence and plasticity of dendritic ion channels are well established. However, the literature is divided on what specific roles these dendritic ion channels play in neuronal information processing, and there is no consensus on why neuronal dendrites should express diverse ion channels with different expression profiles. In this review, we present a case for viewing dendritic information processing through the lens of the sensory map literature, where functional gradients within neurons are considered as maps on the neuronal topograph. Under such a framework, drawing analogies from the sensory map literature, we postulate that the formation of intraneuronal functional maps is driven by the twin objectives of efficiently encoding inputs that impinge along different dendritic locations and of retaining homeostasis in the face of changes that are required in the coding process. In arriving at this postulate, we relate intraneuronal map physiology to the vast literature on sensory maps and argue that such a metaphorical association provides a fresh conceptual framework for analyzing and understanding single-neuron information encoding. We also describe instances where the metaphor presents specific directions for research on intraneuronal maps, derived from analogous pursuits in the sensory map literature. We suggest that this perspective offers a thesis for why neurons should express and alter ion channels in their dendrites and provides a framework under which active dendrites could be related to neural coding, learning theory, and homeostasis. © 2012 the American Physiological Society.

Kenfack A.,Free University of Berlin | Singh K.P.,Indian Institute of Science
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

We study onset and control of stochastic resonance (SR) phenomenon in two driven bistable systems, mutually coupled and subjected to independent noises, taking into account the influence of both the inertia and the coupling. In the absence of coupling, we found two critical damping parameters: one for the onset of SR and another for which SR is optimum. We then show that in weakly coupled systems, emergence of SR is governed by chaos. A strong coupling between the two oscillators induces coherence in the system; however, the systems do not synchronize no matter what the coupling is. Moreover, a specific coupling parameter is found for which the SR of each subsystem is optimum. Finally, a scheme for controlling SR in such coupled systems is proposed by introducing a phase difference between the two coherent driving forces. © 2010 The American Physical Society.

Johal R.S.,Indian Institute of Science
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

If the work per cycle of a quantum heat engine is averaged over an appropriate prior distribution for an external parameter a, the work becomes optimal at Curzon-Ahlborn (CA) efficiency. More general priors of the form Π (a) ∝1/ aγ yield optimal work at an efficiency which stays close to CA value, in particular near equilibrium the efficiency scales as one-half of the Carnot value. This feature is analogous to the one recently observed in literature for certain models of finite-time thermodynamics. Further, the use of Bayes' theorem implies that the work estimated with posterior probabilities also bears close analogy with the classical formula. These findings suggest that the notion of prior information can be used to reveal thermodynamic features in quantum systems, thus pointing to a connection between thermodynamic behavior and the concept of information. © 2010 The American Physical Society.

Mukherjee A.J.,Indian Institute of Technology Bombay | Zade S.S.,Indian Institute of Science | Singh H.B.,Indian Institute of Technology Bombay | Sunoj R.B.,Indian Institute of Technology Bombay
Chemical Reviews | Year: 2010

Recent developments in the field of organoselenium chemistry with a focus on hypervalent nature of selenium is studied. Study of crystal structure of p-ethoxyphenyl-2-(2-pyridyl) phenyl selenide showed that the compound has a suitably positioned nitrogen atom to form a five-membered chelate ring. A study of X-ray crystal structure of areneselenenyl chloride stabilized by the stereoelectronic effect of an intramolecular nitrogen atom found that the electronic structure around the selenium atom is similar to second-order nucleophilic substitution transition state at a divalent selenium. Synthesis and characterization of selenenyl chloride and azide using diselenide as a precursor showed that organoselenium azides are extremely temperature-sensitive materials. Ferrocenyl selenides are also synthesized by lithiation of N,N-diisopropyl ferrocenecarboxamide followed by quenching with appropriate aryl/alkyl diselenide.

Jatkar D.P.,Harish Chandra Research Institute | Sinha A.,Indian Institute of Science
Physical Review Letters | Year: 2011

We show that the recently proposed Dirac-Born-Infeld extension of new massive gravity emerges naturally as a counterterm in four-dimensional anti-de Sitter space (AdS4). The resulting on-shell Euclidean action is independent of the cutoff at zero temperature. We also find that the same choice of counterterm gives the usual area law for the AdS4 Schwarzschild black hole entropy in a cutoff-independent manner. The parameter values of the resulting counterterm action correspond to a c=0 theory in the context of the duality between AdS3 gravity and two-dimensional conformal field theory. We rewrite this theory in terms of the gauge field that is used to recast 3D gravity as a Chern-Simons theory. © 2011 American Physical Society.

Reddy A.L.M.,Rice University | Gowda S.R.,Rice University | Shaijumon M.M.,Indian Institute of Science | Ajayan P.M.,Rice University
Advanced Materials | Year: 2012

Materials engineering plays a key role in the field of energy storage. In particular, engineering materials at the nanoscale offers unique properties resulting in high performance electrodes and electrolytes in various energy storage devices. Consequently, considerable efforts have been made in recent years to fulfill the future requirements of electrochemical energy storage using these advanced materials. Various multi-functional hybrid nanostructured materials are currently being studied to improve energy and power densities of next generation storage devices. This review describes some of the recent progress in the synthesis of different types of hybrid nanostructures using template assisted and non-template based methods. The potential applications and recent research efforts to utilize these hybrid nanostructures to enhance the electrochemical energy storage properties of Li-ion battery and supercapacitor are discussed. This review also briefly outlines some of the recent progress and new approaches being explored in the techniques of fabrication of 3D battery structures using hybrid nanoarchitectures. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mir R.,Indian Institute of Science
Oncogene | Year: 2015

The chromatin organizer SATB1 has been implicated in the development and progression of multiple cancers including breast and colorectal cancers. However, the regulation and role of SATB1 in colorectal cancers is poorly understood. Here, we demonstrate that expression of SATB1 is induced upon hyperactivation of Wnt/β-catenin signaling and repressed upon depletion of TCF7L2 (TCF4) and β-catenin. Using several colorectal cancer cell line models and the APC min mutant zebrafish in vivo model, we established that SATB1 is a novel target of Wnt/β-catenin signaling. We show that direct binding of TCF7L2/β-catenin complex on Satb1 promoter is required for the regulation of SATB1. Moreover, SATB1 is sufficient to regulate the expression of β-catenin, members of TCF family, multiple downstream effectors and mediators of Wnt pathway. SATB1 potentiates the cellular changes and expression of key cancer-associated genes in non-aggressive colorectal cells, promotes their aggressive phenotype and tumorigenesis in vivo. Conversely, depletion of SATB1 from aggressive cells reprograms the expression of cancer-associated genes, reverses their cancer phenotype and reduces the potential of these cells to develop tumors in vivo. We also show that SATB1 and β-catenin bind to the promoters of TCF7L2 and the downstream targets of Wnt signaling and regulate their expression. Our findings suggest that SATB1 shares a feedback regulatory network with TCF7L2/β-catenin signaling and is required for Wnt signaling-dependent regulation of β-catenin. Collectively, these results provide unequivocal evidence to establish that SATB1 reprograms the expression of tumor growth- and metastasis-associated genes to promote tumorigenesis and functionally overlaps with Wnt signaling critical for colorectal cancer tumorigenesis.Oncogene advance online publication, 13 July 2015; doi:10.1038/onc.2015.232. © 2015 Macmillan Publishers Limited

Roy A.K.,Indian Institute of Science
International Journal of Quantum Chemistry | Year: 2014

Bound-state spectra of shifted Deng-Fan oscillator potential are studied by means of a generalized pseudospectral method. Very accurate results are obtained for both low as well as high states by a nonuniform optimal discretization of the radial Schrödinger equation. Excellent agreement with literature data is observed in both s-wave and rotational states. Detailed variation of energies with respect to potential parameters is discussed. Application is made to the ro-vibrational levels of representative diatomic molecules (H2, LiH, HCl, CO). Nine states having {n,ℓ}=0,1,2 are calculated with good accuracy along with 15 other higher states for each of these molecules. Variation of energies with respect to state indices n, ℓ show behavior similar to that in the Morse potential. Many new states are reported here for the first time. In short, a simple, accurate, and efficient method is presented for this and other similar potentials in molecular physics. © 2013 Wiley Periodicals, Inc.

Maiti R.,Indian Institute of Science
International Journal of Industrial Ergonomics | Year: 2014

A controlled laboratory experiment was carried out on forty Indian male college students for evaluating the effect of indoor thermal environment on occupants' response and thermal comfort. During experiment, indoor temperature varied from 21°C to 33°C, and the variables like relative humidity, airflow, air temperature and radiant temperature were recorded along with subject's physiological parameters (skin (Tsk) and oral temperature (Tc)) and subjective thermal sensation responses (TSV). From Tsk and Tc, body temperature (Tb) was evaluated. Subjective Thermal Sensation Vote (TSV) was recorded using ASHRAE 7-point scale. In PMV model, Fanger's Tsk equation was used to accommodate adaptive response. Stepwise regression analysis result showed Tb was better predictor of TSV than Tsk and Tc. Regional skin temperature response, suppressed sweating without dipping, lower sweating threshold temperature and higher cutaneous threshold for sweating were observed as thermal adaptive responses. These adaptive responses cannot be considered in PMV model. To incorporate subjective adaptive response, mean skin temperature (Tsk) is considered in dry heat loss calculation. Along with these, PMV-model and other two methodologies are adopted to calculate PMV values and results are compared. However, recent literature is limited to measure the sweat rate in Indians and consideration of constant Ersw in PMV model needs to be corrected. Using measured Tsk in PMV model (Method1), thermal comfort zone corresponding to 0.5≤PMV≤0.5 was evaluated as (22.46-25.41) °C with neutral temperature of 23.91°C, similarly while using TSV response, wider comfort zone was estimated as (23.25-26.32) °C with neutral temperature at 24.83°C, which was further increased to with TSV-PPDnew relation. It was observed that PMV-model overestimated the actual thermal response. Interestingly, these subjects were found to be less sensitive to hot but more sensitive to cold. A new TSV-PPD relation (PPDnew) was obtained from the population distribution of TSV response with an asymmetric distribution of hot-cold thermal sensation response from Indians. The calculations of human thermal stress according to steady state energy balance models used on PMV model seem to be inadequate to evaluate human thermal sensation of Indians. Relevance to industry: The purpose of this paper is to estimate thermal comfort zone and optimum temperature for Indians. It also highlights that PMV model seems to be inadequate to evaluate subjective thermal perception in Indians. These results can be used in feedback control of HVAC systems in residential and industrial buildings. © 2014 Elsevier B.V.

Mukherjee A.,Indian Institute of Science
Monthly Notices of the Royal Astronomical Society | Year: 2016

This work is based upon a parametric reconstruction of the effective or total equation of state in a model for the Universe with accelerated expansion. The constraints on the model parameters are obtained by maximum-likelihood analysis using the supernova distance modulus data, observational Hubble data, baryon acoustic oscillation data and cosmic microwave background shift parameter data. For statistical comparison, the same analysis has also been carried out for the ω cold dark matter (ωCDM) dark energy model. Different model selection criteria (Akaike information criterion and Bayesian information criterion) give the clear indication that the reconstructed model is well consistent with the ωCDM model. Then both the models [ωeff(z) model and ωCDM model] have also been presented through (q0,j0) parameter space. Tighter constraint on the present values of dark energy equation of state parameter (ωDE(z = 0)) and cosmological jerk (j0) have been achieved for the reconstructed model. © 2016 The Author. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Uberoi C.,Indian Institute of Science
Eos | Year: 2012

Sunspotsvisibly dark spots on the Sun's surface caused by intense magnetic activityare very active regions of the Sun. The Sun is referred to as quiet during the sunspot minima, when very few sunspots are seen; the activity of the Sun increases with higher numbers of sunspots. The variation in the number of sunspots during the solar minima and maxima shows a cyclic behavior with a period of about 11 years. © 2012. American Geophysical Union. All Rights Reserved.

Karak B.B.,Indian Institute of Science
Astrophysical Journal | Year: 2010

Meridional circulation is an important ingredient in flux transport dynamo models. We have studied its importance on the period, the amplitude of the solar cycle, and also in producing Maunder-like grand minima in these models. First, we model the periods of the last 23 sunspot cycles by varying the meridional circulation speed. If the dynamo is in a diffusion-dominated regime, then we find that most of the cycle amplitudes also get modeled up to some extent when we model the periods. Next, we propose that at the beginning of the Maunder minimum the amplitude of meridional circulation dropped to a low value and then after a few years it increased again. Several independent studies also favor this assumption. With this assumption, a diffusion-dominated dynamo is able to reproduce many important features of the Maunder minimum remarkably well. If the dynamo is in a diffusion-dominated regime, then a slower meridional circulation means that the poloidal field gets more time to diffuse during its transport through the convection zone, making the dynamo weaker. This consequence helps to model both the cycle amplitudes and the Maunderlike minima. We, however, fail to reproduce these results if the dynamo is in an advection-dominated regime. © 2010. The American Astronomical Society.

Raman K.V.,Indian Institute of Science
Applied Physics Reviews | Year: 2014

Molecular spintronics, a field that utilizes the spin state of organic molecules to develop magneto-electronic devices, has shown an enormous scientific activity for more than a decade. But, in the last couple of years, new insights in understanding the fundamental phenomena of molecular interaction on magnetic surfaces, forming a hybrid interface, are presenting a new pathway for developing the subfield of interface-assisted molecular spintronics. The recent exploration of such hybrid interfaces involving carbon based aromatic molecules shows a significant excitement and promise over the previously studied single molecular magnets. In the above new scenario, hybridization of the molecular orbitals with the spin-polarized bands of the surface creates new interface states with unique electronic and magnetic character. This study opens up a molecular-genome initiative in designing new handles to functionalize the spin dependent electronic properties of the hybrid interface to construct spin-functional tailor-made devices. Through this article, we review this subject by presenting a fundamental understanding of the interface spin-chemistry and spin-physics by taking support of advanced computational and spectroscopy tools to investigate molecular spin responses with demonstration of new interface phenomena. Spin-polarized scanning tunneling spectroscopy is favorably considered to be an important tool to investigate these hybrid interfaces with intra-molecular spatial resolution. Finally, by addressing some of the recent findings, we propose novel device schemes towards building interface tailored molecular spintronic devices for applications in sensor, memory, and quantum computing. © 2014 U.S. Government.

Zade S.S.,Indian Institute of Science | Zamoshchik N.,Weizmann Institute of Science | Bendikov M.,Weizmann Institute of Science
Accounts of Chemical Research | Year: 2011

Given their utility in a variety of electronic devices, conjugated oligomers and polymers have attracted considerable research interest in recent years. Because polymeric materials consist of very large molecules with a range of molecular weights (that is, they are polydisperse), predicting their electronic properties is a complicated task. Accordingly, their properties are typically estimated by extrapolation of oligomeric properties to infinite chain lengths. In this Account, we discuss the convergence behavior of various electronic properties of conjugated oligomers, often using thiophene oligomers as a representative example. We have observed some general trends in our studies, which we briefly summarize below for five properties. Most of the calculated values are method dependent: the absolute values can be strongly dependent on the computational level used. Band Gap. The generally accepted approximation used to estimate polymer band gap, whereby a plot of HOMO - LUMO gap versus 1/n (where n is the number of monomer units) is extrapolated to infinite n, fails for long oligomers, because convergence behavior is observed for band gaps. At the B3LYP/6-31G(d) level, it is possible to extrapolate oligomer HOMO - LUMO gaps with a second-order polynomial equation. Alternatively, PBC/B3LYP/6-31G(d) is a very good method to reliably predict the band gap of conjugated polymers. Reorganization Energy. Values of the internal reorganization energy (λ) do not scale linearly with 1/n, instead exhibiting an inverse correlation with the square-root of the number of monomer units for n = 2 - 12. For larger n (10 - 50), a linear relationship is observed between reorganization energy and the reciprocal chain length, and the extrapolation approaches λ ≈ 0 for infinite numbers of oligomer rings. Ionization Potential. The relationship between the first adiabatic ionization potential IP1a of oligothiophenes and oligoselenophenes and chain length linearly correlates with an empirically obtained value of 1/(n 0.75). The first vertical ionization potential (IP1v) linearly correlates with a similarly empirically obtained value of 1/(n 0.70). Polaron - Bipolaron Balance. The contribution of a polaron pair to the electronic structure of the short oligothiophene dication is small; for medium-length oligothiophene chains, the contribution from the polaron pair state begins to become significant. For longer (above 20-mer) oligothiophenes, the polaron pair state dominates. A similar picture was observed for multications as well as doped oligomers and polymers. The qualitative polaron - bipolaron picture does not change when a dopant is introduced; however, quantitatively, the bipolaron - polaron pair equilibrium shifts toward the bipolaron state. Disproportionation Energy. The stability of a single oligothiophene dication versus two cation radical oligothiophene molecules increases with increasing chain length, and there is an excellent correlation between the relative disproportionation energy and the inverse of chain length. A similar trend is observed in the disproportionation energies of oligothiophene polycations as well as doped oligomer and polymers. We also examine doped oligothiophenes (with explicitly included counterions) and polymers with a repeating polar unit. From our experience, it is clear that different properties converge in different ways, and long oligomers (having about 50 double bonds in the backbone) must often be used to correctly extrapolate polymer properties. © 2010 American Chemical Society.

Khurana S.,Indian Institute of Science
Developmental Dynamics | Year: 2016

In most of the mammalian tissues, homeostasis as well as injury repair depend upon a small number of resident adult stem cells. The decline in tissue/organ function in aged organisms has been directly linked with poorly functioning stem cells. Altered function of hematopoietic stem cells (HSCs) is at the center of an aging hematopoietic system, a tissue with high cellular turnover. Poorly engrafting, myeloid-biased HSCs with higher levels of DNA damage accumulation are the hallmark features of an aged hematopoietic system. These cells show a higher proliferation rate than their younger counterparts. It was proposed that quiescence of these cells over long period of time leads to accumulation of DNA damage, eventually resulting in poor function/pathological conditions in hematopoietic system. However, various mouse models with premature aging phenotype also show highly proliferative HSCs. This review examines the evidence that links proliferation of HSCs with aging, which leads to functional changes in the hematopoietic system. © 2016 Wiley Periodicals, Inc.

Mukhopadhyay B.,Indian Institute of Science
Physical Review Letters | Year: 2014

A Comment on the Letter by F. Iocco and M. Pato, Phys. Rev. Lett. 109, 021102 (2012)PRLTAO0031-900710.1103/PhysRevLett.109.021102. The authors of the Letter offer a Reply. © 2014 American Physical Society.

Antony M.J.,Indian National Institute for Interdisciplinary Science and Technology | Jayakannan M.,Indian Institute of Science
Langmuir | Year: 2011

Biologically important analytes such as cysteine and vitamin-C were detected by electron transfer (ET) via naked eye colorimetric sensing using a tailor-made watersoluble vself-doped polyaniline (PSPANa) as a substrate. Monomer (N-3-sulfopropylaniline) was synthesized via ring-opening of propane sultone with excess aniline and polymerized in water using ammoniumpersulfate to obtain green water-soluble polymer. Vitamin-C (ascorbic acid) and cysteine showed unexpected sharp and instantaneous color change from blue to colorless sensing action. The stoichiometry of the analyte to polymer was determined as 3:2 and 4:1 with association (or binding) constants of K = 2.1 × 10 3 and 1.5 × 103 M-1 for vitamin-C and cysteine, respectively. Efficient electron transfer from vitamin-C (also cysteine) to the quinoid unit of the polyaniline base occurred in solution; as a result, the color of the solution changed from deep blue to colorless. Cyclic voltammetry analysis of PSPANa showed the disappearance of the cathodic peak at -0.21 V upon the addition of analytes (vitamin-C and cysteine) and confirms the electron transfer from the analyte to the polymer backbone. Dynamic light scattering (DLS) and zeta potential techniques were utilized to trace the molecular interactions in the electron transfer process. DLS histograms of the polymer samples confirmed the existence of nanoaggregates of 8-10 nm in diameter. The polymers possessed typical amphiphilic structure to produce micellar aggregates which facilitate the efficient electron transfer occurred between the analyte and polyaniline backbone. © 2011 American Chemical Society.

Caldeira K.,Carnegie Institution for Science | Bala G.,Indian Institute of Science | Cao L.,Zhejiang University
Annual Review of Earth and Planetary Sciences | Year: 2013

Carbon dioxide emissions from the burning of coal, oil, and gas are increasing atmospheric carbon dioxide concentrations. These increased concentrations cause additional energy to be retained in Earth's climate system, thus increasing Earth's temperature. Various methods have been proposed to prevent this temperature increase either by reflecting to space sunlight that would otherwise warm Earth or by removing carbon dioxide from the atmosphere. Such intentional alteration of planetary-scale processes has been termed geoengineering. The first category of geoengineering method, solar geoengineering (also known as solar radiation management, or SRM), raises novel global-scale governance and environmental issues. Some SRM approaches are thought to be low in cost, so the scale of SRM deployment will likely depend primarily on considerations of risk. The second category of geoengineering method, carbon dioxide removal (CDR), raises issues related primarily to scale, cost, effectiveness, and local environmental consequences. The scale of CDR deployment will likely depend primarily on cost. © Copyright ©2013 by Annual Reviews. All rights reserved.

Karanth K.P.,Indian Institute of Science
Journal of Genetics | Year: 2010

Numerous morphology-based classification schemes have been proposed for langurs and leaf monkeys of South Asia but there is very little agreement between them. An incorrect classification scheme when used as a basis for biogeographic studies can support erroneous hypotheses. Further, lack of taxonomic resolution will also confound conservation efforts, given that conservation biologists use traditional morphology-based-classification schemes to prioritize species for conservation. Here, I have revisited recent molecular phylogenetic studies done on langurs and leaf monkeys of South Asia. Results from these studies are in turn used to derive a rational and scientific basis for prioritizing species for conservation. Molecular data support the classification of langurs of the Indian subcontinent-Hanuman, Nilgiri and purple-faced langurs-in the genus Semnopithecus, whereas Phayre's leaf monkey along with other Southeast Asian leaf monkeys form another distinct clade (Trachypithecus). The phylogenetic position of capped and golden langurs remains unresolved. Molecular data suggest that they are closely related to each other but this group might have evolved through past hybridization between Semnopithecus and Trachypithecus. Additionally, genetic data also support the splitting of the so-called Hanuman langurs into at least three species. The scores for taxonomic uniqueness of langurs and leaf monkeys of South Asia were revised using this molecular phylogeny-based classification. According to the revised scores, Phayres leaf monkey and golden langur are priority species for conservation followed by capped and Nilgiri langurs. © 2010 Indian Academy of Sciences.

Roy A.,Physical Research Laboratory | Gautam S.,Indian Institute of Science | Angom D.,Physical Research Laboratory
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We show that the third Goldstone mode, which emerges in binary condensates at phase separation, persists to higher interspecies interaction for density profiles where one component is surrounded on both sides by the other component. This is not the case with symmetry-broken density profiles where one species is entirely to the left and the other is entirely to the right. We, then, use Hartree-Fock-Bogoliubov theory with Popov approximation to examine the mode evolution at T≠0 and demonstrate the existence of mode bifurcation near the critical temperature. The Kohn mode, however, exhibits deviation from the natural frequency at finite temperatures after the phase separation. This is due to the exclusion of the noncondensate atoms in the dynamics. © 2014 American Physical Society.

Jena H.S.,Indian Institute of Technology Guwahati | Jena H.S.,Indian Institute of Science
RSC Advances | Year: 2014

Diastereoselective self-assembly of Zn(ii) heterochiral complexes of racemic Schiff bases L1H and L2H (where L1H = 2-((phenyl(2-pyridyl)methylimino)- methyl)phenol; L2H = 1-((phenyl(2-pyridyl)methylimino)methyl)-2-naphthol) in a chiral self-discriminating process are reported. Complexes 1-6 are synthesized using ligand L1H (1-3), L2H (4-6), Zn(NO3)2·6H 2O, and co-ligands such as N3 - or NCS - and are conclusively structurally characterized. Determination of molecular structures of 1-5 confirmed the presence of a di-metallic core constructed by monochelated tridentate ligands with an inversion centre located directly between the two zinc ions. In 1-5, within one centrosymmetric dimer one of the ligands possessed R configuration whereas other possessed S configuration resulting a heterochiral dimerization of ligands around the Zn(ii) centre in a chiral self-discriminating manner. Complex 6 is mononuclear having R configuration of ligand L2 and linked through a C-H⋯O interaction with the nearby mononuclear Zn(ii) centre having S configuration of ligand L2 and consequently a heterochiral dimer. The plausible mechanism for the chiral self-discrimination is revealed which makes it clear that trans oriented anions direct the phenyl group appended to the asymmetric carbon atoms to be trans due to steric congestion and consequently the heterochiral dimerization configuration. The effects of different non-covalent interactions to self-assemble the heterochiral dimers to 1D chain having the sequence ⋯RS⋯RS⋯RS⋯ or ⋯RS⋯SR⋯RS⋯ or ⋯R⋯S⋯R⋯ and to transfer the stereochemical information of the heterochiral dimers throughout the chain are studied. Also the effects of the anions on the isotactic and syndiotactic arrangements of coordination complex are studied. The results demonstrate that ligand modification, anions and non-covalent interactions play a domino role on controlling the solid state structural rearrangements and photoluminescence properties of the synthesized complexes. © 2014 The Royal Society of Chemistry.

Raney J.R.,California Institute of Technology | Misra A.,Indian Institute of Science | Daraio C.,California Institute of Technology
Carbon | Year: 2011

We synthesize vertically aligned arrays of carbon nanotubes (CNTs) in a chemical vapor deposition system with floating catalyst, using different concentrations of hydrogen in the gas feedstock. We report the effect of different hydrogen concentrations on the microstructure and mechanical properties of the resulting material. We show that a lower hydrogen concentration during synthesis results in the growth of stiffer CNT arrays with higher average bulk density. A lower hydrogen concentration also leads to the synthesis of CNT arrays that can reach higher peak stress at maximum compressive strain, and dissipate a larger amount of energy during compression. The individual CNTs in the arrays synthesized with a lower hydrogen concentration have, on average, larger outer diameters (associated with the growth of CNTs with a larger number of walls), but present a less uniform diameter distribution. The overall heights of the arrays and their strain recovery after compression have been found to be independent of the hydrogen concentration during growth. © 2011 Elsevier Ltd. All rights reserved.

Majumder B.,Indian Institute of Science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

Recently Ali et al. (2009) proposed a Generalized Uncertainty Principle (or GUP) with a linear term in momentum (accompanied by Plank length). Inspired by this idea here we calculate the quantum corrected value of a Schwarzschild black hole entropy and a Reissner-Nordström black hole with double horizon by utilizing the proposed generalized uncertainty principle. We find that the leading order correction goes with the square root of the horizon area contributing positively. We also find that the prefactor of the logarithmic contribution is negative and the value exactly matches with some earlier existing calculations. With the Reissner-Nordström black hole we see that this model-independent procedure is not only valid for single horizon spacetime but also valid for spacetimes with inner and outer horizons. © 2011 Elsevier B.V.

Majumder B.,Indian Institute of Science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

Recently Ali et al. (2009) [13] proposed a Generalized Uncertainty Principle (or GUP) with a linear term in momentum (accompanied by Planck length). Inspired by this idea we examine the Wheeler-DeWitt equation for a Schwarzschild black hole with a modified Heisenberg algebra which has a linear term in momentum. We found that the leading contribution to mass comes from the square root of the quantum number n which coincides with Bekenstein's proposal. We also found that the mass of the black hole is directly proportional to the quantum number n when quantum gravity effects are taken into consideration via the modified uncertainty relation but it reduces the value of mass for a particular value of the quantum number. © 2011 Elsevier B.V.

Bhattacharyya A.J.,Indian Institute of Science
Journal of Physical Chemistry Letters | Year: 2012

"Soggy sand" electrolyte, which essentially consists of oxide dispersions in nonaqueous liquid salt solutions, comprises an important class of soft matter electrolytes. The ion transport mechanism of soggy sand electrolyte is complex. The configuration of particles in the liquid solution has been observed to depend in a nontrivial manner on various parameters related to the oxide (concentration, size, surface chemistry) and solvent (dielectric constant, viscosity) as well as time. The state of the particles in solution not only affects ionic conductivity but also effectively the mechanical and electrochemical properties of the solid-liquid composite. Apart from comprehensive understanding of the underlying phenomena that govern ion transport, which will benefit design of better electrolytes, the problem has far-reaching implications in diverse fields such as catalysis, colloid chemistry, and biotechnology. © 2012 American Chemical Society.

Kumar G.V.P.,Indian Institute of Science
Applied Optics | Year: 2010

The Pascal triangle is a geometric representation of binomial coefficients in triangular form. We utilize this formalism to deterministically arrange silver nanocylinders of different sizes (30, 60, and 90 nm) on a triangle and numerically study their near-field optical properties.We show that near-field intensities at specific points on this triangle depend on the wavelength and angle of incidence. From the wavelengthdependent studies at various junctions of nanocylinders, we obtain maximum near-field intensity at 350 and 380 nm. By varying the angle of incidence of the TM-polarized plane wave, we find systematic variation in the near-field intensity at different junctions of the geometry. Our study will lead to insights in designing controllable electromagnetic hot spots for chip-based plasmonic devices. © 2010 Optical Society of America.

Patil D.V.,Indian Institute of Science
Physica A: Statistical Mechanics and its Applications | Year: 2013

The classical Chapman-Enskog expansion is performed for the recently proposed finite-volume formulation of lattice Boltzmann equation (LBE) method [D.V. Patil, K.N. Lakshmisha, Finite volume TVD formulation of lattice Boltzmann simulation on unstructured mesh, J. Comput. Phys. 228 (2009) 5262-5279]. First, a modified partial differential equation is derived from a numerical approximation of the discrete Boltzmann equation. Then, the multi-scale, small parameter expansion is followed to recover the continuity and the Navier-Stokes (NS) equations with additional error terms. The expression for apparent value of the kinematic viscosity is derived for finite-volume formulation under certain assumptions. The attenuation of a shear wave, Taylor-Green vortex flow and driven channel flow are studied to analyze the apparent viscosity relation. © 2013 Elsevier B.V. All rights reserved.

Das Sarma J.,Indian Institute of Science
Journal of NeuroVirology | Year: 2014

Microglia, the major resident immune cells in the central nervous system (CNS) are considered as the key cellular mediators of neuroinflammatory processes. In the past few years, microglial research has become a main focus in cellular neuroimmunology and neuroinflammation. Chronic/remitting neurological disease such as multiple sclerosis (MS) has long been considered an inflammatory autoimmune disease with the infiltration of peripheral myelin-specific T cells into the CNS. With the rapid advancement in the field of microglia and astrocytic neurobiology, the term neuroinflammation progressively started to denote chronic CNS cell-specific inflammation in MS the direct glial responses in MS are different from conventional peripheral immune responses. This review attempts to summarize current findings of neuroinflammatory responses within the CNS by direct infection of neural cells by mouse hepatitis virus (MHV) and the mechanisms by which glial cell responses ultimately contribute to the neuropathology on demyelination. Microglia can be persistently infected by MHV. Microglial activation and phagocytosis are recognized to be critically important in the pathogenesis of demyelination. Emerging evidence for the pathogenic role of microglia and the activation of inflammatory pathways in these cells in MHV infection supports the concept that microglia induced neuroinflammation is an amplifier of virus-induced neuropathology. © 2013 Journal of NeuroVirology, Inc.

Kumar G.V.P.,Indian Institute of Science
Journal of Nanophotonics | Year: 2012

Surface enhanced Raman scattering (SERS) is an optical spectroscopy technique with single molecule sensitivity and chemical specificity. The electromagnetic enhancement mechanism of SERS is facilitated by the localized surface plasmons of metallic nanostructures utilized in experiments. The magnitude of the local optical field created by the plasmonic nanostructure depends on parameters such as size, shape, morphology, arrangement, and local environment of the nanostructure. By tuning these parameters, electromagnetic hot spots can be created to facilitate ultra-sensitive, subwavelength SERS detection platforms. In recent years, there have been a number of innovations in nanofabrication and synthesis of plasmonic nanostructures. This has led to a variety of plasmonic nano-architectures that can be harnessed for SERS. Recently investigated plasmonic nanostructures in the context of SERS include nanosphere dimers, individual nanocubes, nanotriangular arrays, nano-pyramid shells, individual and assembly of nanorods, nanowires, and nanotips, and some unconventional nano-architectures. Challenges in fundamental and application aspects of SERS remain for future research. © 2012 Society of Photo-Optical Instrumentation Engineers.

Chopra D.,Indian Institute of Science
Crystal Growth and Design | Year: 2012

The covalent chemistry of the main group element fluorine is well understood. In contrast, its noncovalent chemistry, which forms the pillar of the paradigm of supramolecular chemistry, is still in its infancy. The latter involves a complete understanding of the different interactions (both intermolecular and intramolecular) involving donor and acceptor atoms. This perspective highlights the recent developments in the understanding of noncovalent interactions in relation to organic fluorine (partially fluorinated compounds) and the versatility and importance of such interactions to the scientific community. © 2011 American Chemical Society.

Chopra D.,Indian Institute of Science
Journal of Physical Chemistry A | Year: 2012

The development of charge density analysis has undergone a major renaissance in the last two decades. In recent years, the characterization of bonding features associated with atoms in molecules and in crystals has been explored using high-resolution X-ray diffraction data (laboratory or synchrotron) complemented by high level ab initio theoretical calculations. The extraction of one electron topological properties, namely, electrostatic charges, dipole moment and higher moments, electrostatic potential, electric field gradients, in addition to evaluation of the local kinetic and potential energy densities, have contributed toward an understanding of the electron density distributions in molecular solids. New topological descriptors, namely, the source function (SF) and electron localization function (ELF) provide additional information as regards characterization of the topology of the electron density. In addition, delocalization indices have also been developed to account for bonding features pertinent to M-M bonds. The evaluation of these properties have contributed significantly toward the understanding of intra-and intermolecular bonding features in organic, inorganic, and biomolecules in the crystalline phase, with concomitant applications in the understanding of chemical reactivity and material/biological properties. In recent years, the focus has strongly shifted toward the understanding of structure-property relationships in organometallic complexes containing labile M-C bonds in the crystal structure with subsequent implications in catalysis. This perspective aims to highlight the major developments in electron density measurements in the past few years and provides pointers directed toward the potential use of this technique in future applications for an improved understanding of chemical bonding in systems that have been unexplored. © 2012 American Chemical Society.

Ganganagappa N.,Federal University of Rio Grande do Sul | Siddaramanna A.,Indian Institute of Science
Materials Characterization | Year: 2012

One of the metastable phases of vanadium dioxide, VO 2(B) bundles of nanorods and microspheres have been synthesized through a simple hydrothermal method by dispersing V 2O 5 in aqueous quinol. The obtained products were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and electrochemical discharge-charge test for lithium battery. It was found that the morphologies of the obtained VO 2(B) can be tuned by manipulating the relative amount of quinol. The electrochemical test found that the bundles of nanorods exhibit an initial discharge capacity of 171 mAh g - 1 and its almost stabilized capacity was reached to 108 mAh g - 1 after 47 cycles at a current density of 0.1 mA g - 1. The formation mechanism of the VO 2(B) bundles of nanorods and microspheres was also discussed. © 2012 Elsevier Inc. All rights reserved.

Shenoy V.B.,Indian Institute of Science
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We study the Feshbach resonance of spin-12 particles in a uniform synthetic non-Abelian gauge field that produces spin-orbit coupling and constant spin potentials. We develop a renormalizable quantum field theory including the closed-channel boson which engenders the resonance. We show that the gauge field shifts the Feshbach field where the low-energy scattering length diverges. In addition the Feshbach field is shown to depend on the center-of-mass momentum of the particles. For high-symmetry gauge fields which produce a Rashba spin coupling, we show that the system supports two bound states over a regime of magnetic fields when the background scattering length is negative and the resonance width is comparable to the energy scale of the spin-orbit coupling. We discuss interesting consequences useful for future theoretical and experimental studies, even while our predictions are in agreement with recent experiments. © 2014 American Physical Society.

Myers R.C.,Perimeter Institute for Theoretical Physics | Sinha A.,Perimeter Institute for Theoretical Physics | Sinha A.,Indian Institute of Science
Journal of High Energy Physics | Year: 2011

We re-examine holographic versions of the c-theorem and entanglement entropy in the context of higher curvature gravity and the AdS/CFT correspondence. We select the gravity theories by tuning the gravitational couplings to eliminate non-unitary operators in the boundary theory and demonstrate that all of these theories obey a holographic c-theorem. In cases where the dual CFT is even-dimensional, we show that the quantity that flows is the central charge associated with the A-type trace anomaly. Here, unlike in conventional holographic constructions with Einstein gravity, we are able to distinguish this quantity from other central charges or the leading coefficient in the entropy density of a thermal bath. In general, we are also able to identify this quantity with the coefficient of a universal contribution to the entanglement entropy in a particular construction. Our results suggest that these coefficients appearing in entanglement entropy play the role of central charges in odd-dimensional CFT's. We conjecture a new c-theorem on the space of odd-dimensional field theories, which extends Cardy's proposal for even dimensions. Beyond holography, we were able to show that for any even-dimensional CFT, the universal coefficient appearing the entanglement entropy which we calculate is precisely the A-type central charge. © SISSA 2011.

Majumder B.,Indian Institute of Science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

A spatially flat Friedmann-Robertson-Walker (FRW) cosmological model with generalized Chaplygin gas is studied in the context of scalar-metric formulation of cosmology. Schutz's mechanism for the perfect fluid is applied with generalized Chaplygin gas and the classical and quantum dynamics for this model is studied. It is found that the only surviving matter degree of freedom played the role of cosmic time. For the quantum mechanical description it is possible to find the wave packet which resulted from the linear superposition of the wave functions of the Schrödinger-Wheeler-DeWitt (SWD) equation, which is a consequence of the above formalism. The wave packets show two distinct dominant peaks and propagate in the direction of increasing scale factor. It may happen that our present universe originated from one of those peaks. The many-world and ontological interpretation of quantum mechanics is applied to investigate about the behavior of the scale factor and the scalar field (considered for this model). In both the cases the scale factor avoids singularity and a bouncing non-singular universe is found. © 2011 Elsevier B.V.

Sharma U.K.,Astrazeneca | Chatterji D.,Indian Institute of Science
FEMS Microbiology Reviews | Year: 2010

During active growth of Escherichia coli, majority of the transcriptional activity is carried out by the housekeeping sigma factor (σ70), whose association with core RNAP is generally favoured because of its higher intracellular level and higher affinity to core RNAP. In order to facilitate transcription by alternative sigma factors during nutrient starvation, the bacterial cell uses multiple strategies by which the transcriptional ability of σ70 is diminished in a reversible manner. The facilitators of shifting the balance in favour of alternative sigma factors happen to be as diverse as a small molecule (p)ppGpp (represents ppGpp or pppGpp), proteins (DksA, Rsd) and a species of RNA (6S RNA). Although 6S RNA and (p)ppGpp were known in literature for a long time, their role in transcriptional switching has been understood only in recent years. With the elucidation of function of DksA, a new dimension has been added to the phenomenon of stringent response. As the final outcome of actions of (p)ppGpp, DksA, 6S RNA and Rsd is similar, there is a need to analyse these mechanisms in a collective manner. We review the recent trends in understanding the regulation of σ70 by (p)ppGpp, DksA, Rsd and 6S RNA and present a case for evolving a unified model of RNAP redistribution during starvation by modulation of σ70 activity in E. coli. © 2010 Federation of European Microbiological Societies.

Chakrabarti R.,Indian Institute of Science
Physica A: Statistical Mechanics and its Applications | Year: 2012

Based on the Wilemski-Fixman approach [G. Wilemski, M. Fixman, J. Chem. Phys. 60 (1974) 866], we show that, for a flexible chain in θ solvent, hydrodynamic interaction treated with a pre-averaging approximation makes ring closing faster if the chain is not very short. We also show that the ring closing time for a long chain with hydrodynamic interaction in θ solvent scales with the chain length (N) as N 1.5, in agreement with the previous renormalization group calculation based prediction by Freidman and O'Shaughnessy [B. Friedman, B. O'Shaughnessy, Phys. Rev. A 40 (1989) 5950]. © 2012 Elsevier B.V. All rights reserved.

Sengupta S.,University of Wurzburg | Sengupta S.,Indian Institute of Science | Wurthner F.,University of Wurzburg
Accounts of Chemical Research | Year: 2013

Among the natural light-harvesting (LH) systems, those of green sulfur and nonsulfur photosynthetic bacteria are exceptional because they lack the support of a protein matrix. Instead, these so-called chlorosomes are based solely on "pigments". These are self-assembled bacteriochlorophyll c, d, and e derivatives, which consist of a chlorophyll skeleton bearing a 3 1-hydroxy functional group. Chemists consider the latter as an essential structural unit to direct the formation of light-harvesting self-assembled dye aggregates with J-type excitonic coupling. The intriguing properties of chlorosomal J-type aggregates, particularly narrow red-shifted absorption bands, compared with monomers and their ability to delocalize and migrate excitons, have inspired intense research activities toward synthetic analogues in this field. The ultimate goal of this research field is the development of (opto-)electronic devices based on the architectural principle of chlorosomal LH systems. In this regard, the challenge is to develop small, functional building blocks with appropriate substituents that are preprogrammed to self-assemble across different length scales and to emulate functions of natural LH systems or to realize entirely new functions beyond those found in nature. In this Account, we highlight our achievements in the past decade with semisynthetic zinc chlorins (ZnChls) as model compounds of bacteriochlorophylls obtained from the naturally most abundant chlorin precursor: chlorophyll a.To begin, we explore how supramolecular strategies involving π-stacking, hydrogen bonding, and metal-oxygen coordination can be used to design ZnChl-based molecular stack, tube, and liquid crystalline assemblies conducive to charge and energy transport. Our design principle is based on the bioinspired functionalization of the 31-position of ZnChl with a hydroxy or methoxy group; the former gives rise to tubular assemblies, whereas the latter induces stack assemblies. Functionalization of the 172-position with esterified hydrophilic or hydrophobic chains, dendron-wedge substituents, and chromophores having complementary optical properties such as naphthalene bisimides (NBIs) is used to modulate the self-assembly of ZnChl dyes. The resulting assemblies exhibit enhanced charge transport and energy transfer abilities. We have used UV/vis, circular dichroism (CD), fluorescence spectroscopy, and dynamic light scattering (DLS) for the characterization of these assemblies in solution. In addition, we have studied assembly morphologies by atomic force microscopy (AFM), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), and cryogenic-TEM. Crystallographic techniques such as powder X-ray and solid-state NMR have been used to explain the precise long- and short-range packing of dyes in these assemblies. Finally, functional properties such as charge and energy transport have been explored by pulse radiolysis time-resolved microwave conductivity (PR-TRMC), conductive AFM, and time-resolved fluorescence spectroscopy. The design principles discussed in this Account are important steps toward the utilization of these materials in biosupramolecular electronics and photonics in the future. © 2013 American Chemical Society.

Shenoy V.B.,Indian Institute of Science
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

Recent experiments on fermions in synthetic gauge fields result in systems with a spin-orbit coupling along one spatial axis, a detuning field, and a Zeeman field. We show theoretically that the presence of all three results in interesting and unusual phenomena in a system of interacting fermions (interactions described by a scattering length). For two fermions, bound states appear only over a certain range of the center-of-mass momenta. The deepest bound state appears at a nonzero center-of-mass momentum. For center-of-mass momenta without a bound state, the gauge field induces a resonance-like feature in the scattering continuum resulting in a large scattering phase shift. In the case of many particles, we demonstrate that the system, in a parameter range, shows flow-enhanced pairing, i.e., a Fulde-Farrell-Larkin-Ovchnnikov superfluid state made of robust pairs with a finite center-of-mass momentum. Yet another regime of parameters offers the opportunity to study strongly interacting normal states of spin-orbit-coupled fermionic systems utilizing the resonance-like feature induced by the synthetic gauge field. © 2013 American Physical Society.

Majumder B.,Indian Institute of Science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

Very recently Ali et al. (2009) [5] proposed a new Generalized Uncertainty Principle (or GUP) with a linear term in Plank length. In this Letter the effect of this GUP is studied in quantum cosmological models with dust and cosmic string as the perfect fluid. For the quantum mechanical description it is possible to find the wave packet which resulted from the superposition of the stationary wave functions of the Wheeler-deWitt equation. However the norm of the wave packets turned out to be time dependent and hence the model became non-unitary. The loss of unitarity is due to the fact that the presence of the linear term in Plank length in the Generalized Uncertainty Principle made the Hamiltonian non-Hermitian. © 2011 Elsevier B.V.

DeGottardi W.,University of Illinois at Urbana - Champaign | Sen D.,Indian Institute of Science | Vishveshwara S.,University of Illinois at Urbana - Champaign
New Journal of Physics | Year: 2011

We explore the salient features of the 'Kitaev ladder', a two-legged ladder version of the spin-1/2 Kitaev model on a honeycomb lattice, by mapping it to a one-dimensional fermionic p-wave superconducting system. We examine the connections between spin phases and topologically non-trivial phases of non-interacting fermionic systems, demonstrating the equivalence between the spontaneous breaking of global Z2 symmetry in spin systems and the existence of isolated Majorana modes. In the Kitaev ladder, we investigate topological properties of the system in different sectors characterized by the presence or absence of a vortex in each plaquette of the ladder. We show that vortex patterns can yield a rich parameter space for tuning into topologically non-trivial phases. We introduce and employ a new topological invariant for explicitly determining the presence of zero energy Majorana modes at the boundaries of such phases. Finally, we discuss dynamic quenching between topologically non-trivial phases in the Kitaev ladder and, in particular, the post-quench dynamics governed by tuning through a quantum critical point. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Raju T.S.,Temple City Institute of Technology and Engineering | Panigrahi P.K.,Indian Institute of Science
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We analytically explore a wide class of optical similariton solutions to the nonlinear Schrödinger equation appropriately modified to model beam propagation in a tapered, graded-index nonlinear-fiber amplifier with an external source. Under certain physical conditions, we reduce the coupled nonlinear Schrödinger equations to a single-wave equation that aptly describes similariton propagation through asymmetric twin-core fiber amplifiers. The asymmetric twin-core fiber is composed of two adjoining, closely spaced, single-mode fibers in which the active one is a tapered, graded-index nonlinear-fiber and the passive one is a step-index fiber. We obtain these self-similar waves for different choices of tapered index profile, using a Möbius transformation. Our procedure is applicable for both self-focusing and self-defocusing nonlinearities. © 2011 American Physical Society.

Zade S.S.,Indian Institute of Science | Bendikov M.,Weizmann Institute of Science
Journal of Physical Organic Chemistry | Year: 2012

Acenes are polycyclic aromatic hydrocarbons consisting of linearly fused benzene rings. These compounds are currently the subject of great interest from both fundamental and applied perspectives, particularly for use in organic electronics. This review highlights the computational studies carried out to understand acene reactivity, their reaction mechanisms, and the relationship of the latter to acene length. Generally, as acene length increases, the reactivity of acenes increases, and a greater tendency towards a biradical mechanism is observed. For example, an interesting change in mechanism (from concerted to biradical) is observed for the reaction of acenes (benzene through pentacene) with molecular oxygen. A computational study of the addition of HCl (which behaves as an electrophile) and water (which behaves mostly as a nucleophile) to acenes revealed that acene reactivity increases along the series up to hexacene and remains constant from hexacene and above because of the biradical character of the ground state of higher acenes. Although the exothermicity of the addition of water and HCl to acene is similar, the activation barrier for the addition of water is significantly higher than that for HCl. There is a substantial substituent effect on the energy barriers for electrophilic and nucleophilic reactions. Phenyl substitution at the most reactive meso-carbon atoms of the central ring of acene blocks dimerization through this ring but does not efficiently prevent dimerization through other rings. With respect to the self-reactivity (such as dimerization, etc.) of acenes, a computational study showed that the preferred pathways are the formation of acene dimers via a central benzene ring and the formation of acene-based polymers. Interestingly, longer acenes are predicted to self-react to form polymers, rather than acene dimers, as the thermodynamically preferred product. These findings invite experimentalists to reinvestigate the dimerization of long unsubstituted acenes. Given that computational studies directly relate to the gas phase reactivity of acenes, whereas long acenes find application in organic semiconductor devices as solids, the next research challenge is to obtain an understanding of the solid state reactivity of long acenes. Copyright © 2012 John Wiley & Sons, Ltd.

Desiraju G.R.,Indian Institute of Science
Journal of Chemical Sciences | Year: 2010

Crystal structures of organic and metal-organic compounds have been determined in enormous numbers over the past century, and at the time of writing this review, the Cambridge Structural Database has just crossed the half million mark. The possibility of designing a particular crystal packing is, however, of more recent origin and the subject of crystal engineering has addressed this possibility, more or less systematically, during the past 30 years. Crystal engineering demands a detailed and thorough knowledge of intermolecular interactions, which act as the supramolecular glue that binds molecules into crystals. It also requires systematic strategies for the design of a crystal, the architectural blueprint as it were. Finally, this enterprise needs to be geared towards a useful property in that the crystal that is being designed is a functional one. All these features of the subject are directly or indirectly connected with the fact that there is a very large database of known crystal structures that is available to the crystal engineer. This review attempts to briefly survey the current scenario in this expanding subject. © Indian Academy of Sciences.

Vidya Sagar R.,Indian Institute of Science
Construction and Building Materials | Year: 2016

This article reports on the influence of (i) concrete compressive strength (ii) specimen geometry (iii) change in rate of loading (iv) percentage of steel reinforcement [area of steel reinforcement as a percentage of the effective area of reinforced concrete (RC) structural member's cross section] (v) mode of failure on the relaxation ratio parameter (Colombo et al., 2005a, 2005b) of acoustic emissions (AE) released during fracture process in reinforced concrete (RC) flanged beam specimens. The aim is to study the feasibility of relaxation ratio analysis of AE signals for damage assessment in RC beams. The beam specimens were tested in the laboratory under incremental cyclic loading. The loading cycle first entered into the relaxation dominant phase in the relaxation ratio plot was equal or close to the loading cycle entering first into the heavy damage zone in the NDIS-2421 damage assessment plot proposed by Japanese society for nondestructive inspection. Further, the lowest AE based b-value was observed at the same or nearer loading cycle. Relaxation ratio analysis of AE signals is a useful method to assess the current load carrying capacity of a structure and state of damage in concrete structures in-situ. © 2016 Elsevier Ltd. All rights reserved.

Barpanda P.,Indian Institute of Science
Israel Journal of Chemistry | Year: 2015

Rechargeable batteries based on Li and Na ions have been growing leaps and bounds since their inception in the 1970s. They enjoy significant attention from both the fundamental science point of view and practical applications ranging from portable electronics to hybrid vehicles and grid storage. The steady demand for building better batteries calls for discovery, optimisation and implementation of novel positive insertion (cathode) materials. In this quest, chemists have tried to unravel many future cathode materials by taking into consideration their eco-friendly synthesis, material/process economy, high energy density, safety, easy handling and sustainability. Interestingly, sulfate-based cathodes offer a good combination of sustainable syntheses and high energy density owing to their high-voltage operation, stemming from electronegative SO42- units. This review delivers a sneak peak at the recent advances in the discovery and development of sulfate-containing cathode materials by focusing on their synthesis, crystal structure and electrochemical performance. Several family of cathodes are independently discussed. They are 1) fluorosulfates [AMSO4F], 2) bihydrated fluorosulfates [AMSO4F2H2O], 3) hydroxysulfate [AMSO4OH], 4) bisulfates [A2M(SO4)2], 5) hydrated bisulfates [A2M(SO4)2 nH2O], 6) oxysulfates [Fe2(SO4)2O] and 7) polysulfates [A2M2(SO4)3]. A comparative study of these sulfate-based cathodes has been provided to offer an outlook on the future development of high-voltage polyanionic cathode materials for next-generation batteries. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Srivastava C.,Indian Institute of Science
Materials Letters | Year: 2012

The present report illustrates the phenomenon of phase separation leading to the splitting of solid solution structured Ag-Co nanoparticles into pure Ag and pure Co nanoparticles upon isothermal annealing inside a transmission electron microscope. In bulk, Ag-Co system shows negligible mutual solubility into a single phase solid solution structure upto a very high temperature. The Ag-Co nanoparticle splitting revealed that room temperature, solid solution atomic configuration, between bulk immiscible Ag and Co atoms co-existing in a nano-sized particle, is a kinetically frozen atomic arrangement and not a thermodynamically stable structure. The observed phase separation behavior resulting in particle splitting at high temperatures can be used to produce devices for sensor applications. © 2011 Elsevier B.V. All rights reserved.

Bhattacharyya P.,Indian Institute of Science
IEEE Transactions on Device and Materials Reliability | Year: 2014

Micromachined silicon platforms, owing to some of its inherent advantages including miniaturized dimensions, ultralow power consumption, reduced batch fabrication cost, long-term reliability, and compatibility with standard CMOS fabrication technology, attracted the attention of solid-state gas sensor researchers, particularly since the last decade. As the semiconducting gas sensing thin film on top of micromachined platforms often needs an elevated temperature to activate the sensing mechanism, the suitable electrothermal and structural design of a microheater, i.e., having fast response, uniform temperature distribution over sensing area, and minimal residual/thermal-stress- induced membrane deflection, are of prime concern. In this paper, the technological developments related to the various designs and geometries of microheaters and their fabrication technology employing different suitable heating materials, for closed- and suspended-type silicon membranes have been discussed critically with particular emphasis on the relative merits and demerits with reference to heater parameters such as power consumption, temperature distribution, response time, and mechanical stability/reliability. © 2001-2011 IEEE.

Singh A.K.,Indian Institute of Science
Optik | Year: 2013

In contemporary world optoelectronics materials are used in daily life owing to its verity of applications. Utility of these materials makes them attractive for investigations. Specifically study regarding optical properties of recent developed materials is worth for technical uses. Therefore, this work demonstrates a comparative study of extinction coefficient (K), real dielectric (ε′) and imaginary dielectric (ε′′) constants, refractive index (n) and optical energy band gap (Eg) with structural unit for Se98-xZn2Inx (0 ≤ X In ≤ 10) and Se93-yZn2Te5In y (0 ≤ YIn ≤ 10) chalcogenide glasses. Fixed amount of Te with increasing In concentration as cost of Se is largely influence the optical parameters of the materials. Values of optical parameters are obtained higher and lower respectively at thresholds structural units values. This comparative study demonstrates that enhanced values of optical parameters have been obtained for Te containing Se-Zn-In glasses. © 2012 Elsevier GmbH. All rights reserved.

Deshpande N.G.,University of Oregon | Garg S.K.,Indian Institute of Science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

We investigate e +e -→γγ process within the Seiberg-Witten expanded noncommutative standard model (NCSM) scenario in the presence of anomalous triple gauge boson couplings. This study is done with and without initial beam polarization and we restrict ourselves to leading order effects of noncommutativity i.e. O(Θ). The noncommutative (NC) corrections are sensitive to the electric component (Θ→E) of NC parameter. We include the effects of Earth's rotation in our analysis. This study is done by investigating the effects of noncommutativity on different time averaged cross section observables. We have also defined forward backward asymmetries which will be exclusively sensitive to anomalous couplings. We have looked into the sensitivity of these couplings at future experiments at the International Linear Collider (ILC). This analysis is done under realistic ILC conditions with the center of mass energy (c.m.) s=800 GeV and integrated luminosity L=500 fb -1. The scale of noncommutativity is assumed to be Λ=1 TeV. The limits on anomalous couplings of the order 10 -1 from forward backward asymmetries while much stringent limits of the order 10 -2 from total cross section are obtained if no signal beyond SM is seen. © 2012 Elsevier B.V..

Jissy A.K.,Indian Institute of Science | Datta A.,Indian Association for The Cultivation of Science
ChemPhysChem | Year: 2012

The structure and electronic properties of guanine oligomers and π stacks of guanine quartets (G-quartets) with circulene are investigated under an external field through first-principles calculations. An electric field induces nonplanarity in the guanine aggregates and also leads to an increase in the H-bond distances. The calculations reveal that the binding energy of the circulenes with G-quartets increases on application of an electric field along the stacking direction. The HOMO-LUMO gap decreases substantially under the influence of an external field. The contribution of a simple dipole-dipole interaction to the stability of the stacked system is also analyzed. The electric field along the perpendicular axis increases the dipole moments of the guanine dimer, trimer, and quartet. Such an increase in the dipole moment facilitates stacking with circulenes. The stability of G-quartet-circulene π stacks depends on the phase of the dipole moment (in-phase or out-of-phase) induced by an external electric field. The stability of stacks of bowl-shaped circulenes with G-quartets depends on the direction of the applied field. Making a stack: An external electric field helps stacking of guanine quartets with disklike molecules such as circulenes to facilitate molecular recognition by DNA quadruplexes (see picture). The stability of stacks of bowl-shaped circulenes with G-quartets depends on the direction of the applied field. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mondal B.,Indian Institute of Science
Oncogene | Year: 2016

An integrative functional genomics study of multiple forms of data are vital for discovering molecular drivers of cancer development and progression. Here, we present an integrated genomic strategy utilizing DNA methylation and transcriptome profile data to discover epigenetically regulated genes implicated in cancer development and invasive progression. More specifically, this analysis identified fibromodulin (FMOD) as a glioblastoma (GBM) upregulated gene because of the loss of promoter methylation. Secreted FMOD promotes glioma cell migration through its ability to induce filamentous actin stress fiber formation. Treatment with cytochalasin D, an actin polymerization inhibitor, significantly reduced the FMOD-induced glioma cell migration. Small interfering RNA and small molecule inhibitor-based studies identified that FMOD-induced glioma cell migration is dependent on integrin-FAK-Src-Rho-ROCK signaling pathway. FMOD lacking C-terminus LRR11 domain (ΔFMOD), which does not bind collagen type I, failed to induce integrin and promote glioma cell migration. Further, FMOD-induced integrin activation and migration was abrogated by a 9-mer wild-type peptide from the FMOD C-terminus. However, the same peptide with mutation in two residues essential for FMOD interaction with collagen type I failed to compete with FMOD, thus signifying the importance of collagen type I–FMOD interaction in integrin activation. Chromatin immunoprecipitation–PCR experiments revealed that transforming growth factor beta-1 (TGF-β1) regulates FMOD expression through epigenetic remodeling of FMOD promoter that involved demethylation and gain of active histone marks with a simultaneous loss of DNMT3A and EZH2 occupancy, but enrichment of Sma- and Mad-related protein-2 (SMAD2) and CBP. FMOD silencing inhibited the TGF-β1-mediated glioma cell migration significantly. In univariate and multivariate Cox regression analysis, both FMOD promoter methylation and transcript levels predicted prognosis in GBM. Thus, this study identified several epigenetically regulated alterations responsible for cancer development and progression. Specifically, we found that secreted FMOD as an important regulator of glioma cell migration downstream of TGF-β1 pathway and forms a potential basis for therapeutic intervention in GBM.Oncogene advance online publication, 23 May 2016; doi:10.1038/onc.2016.176. © 2016 Macmillan Publishers Limited

Kanti Kole A.,National Institute of Technology Durgapur | Sekhar Tiwary C.,Indian Institute of Science | Kumbhakar P.,National Institute of Technology Durgapur
Journal of Materials Chemistry C | Year: 2014

A controllable synthesis of phase pure wurtzite (WZ) ZnS nanostructures has been reported in this work at a low temperature of ∼220 °C using ethylenediamine as the soft template and by varying the molar concentration of zinc to sulphur precursors as well as by using different precursors. A significant reduction in the formation temperature required for the synthesis of phase pure WZ ZnS has been observed. A strong correlation has been observed between the morphology of the synthesized ZnS nanostructures and the precursors used during synthesis. It has been found from Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) image analyses that the morphology of the ZnS nanocrystals changes from a block-like to a belt-like structure having an average length of ∼450 nm when the molar ratio of zinc to sulphur source is increased from 1:1 to 1:3. An oriented attachment (OA) growth mechanism has been used to explain the observed shape evolution of the synthesized nanostructures. The synthesized nanostructures have been characterized by the X-ray diffraction technique as well as by UV-Vis absorption and photoluminescence (PL) emission spectroscopy. The as-synthesized nanobelts exhibit defect related visible PL emission. On isochronal annealing of the nanobelts in air in the temperature range of 100-600 °C, it has been found that white light emission with a Commission Internationale de I'Eclairage 1931 (CIE) chromaticity coordinate of (0.30, 0.34), close to that of white light (0.33, 0.33), can be obtained from the ZnO nanostructures obtained at an annealing temperature of 600 °C. UV light driven degradation of methylene blue (MB) dye aqueous solution has also been demonstrated using as-synthesized nanobelts and ∼98% dye degradation has been observed within only 40 min of light irradiation. The synthesized nanobelts with visible light emission and having dye degradation activity can be used effectively in future optoelectronic devices and in water purification for cleaning of dyes. © 2014 the Partner Organisations.

Majumder B.,Indian Institute of Science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

In this Letter we study the effects of the Modified Uncertainty Principle as proposed in Ali et al. (2009) [7] on the inflationary dynamics of the early universe in both standard and Randall-Sundrum type II scenarios. We find that the quantum gravitational effect increase the amplitude of density fluctuation, which is oscillatory in nature, with an increase in the tensor-to-scalar ratio. © 2012 Elsevier B.V.

Tomar D.,Indian Institute of Science | Tomar D.,University of Bordeaux 1 | Singh R.,M. S. University of Baroda
Biology of the Cell | Year: 2015

The nuclear factor κB (NF-κB) transcription factor family plays a key role in regulation of the inflammatory pathway in response to different physiological stimuli starting from development to ageing. The dysregulation of NF-κB has been associated with many pathological conditions like inflammatory diseases, neurodegeneration, metabolic diseases and various kinds of malignancies. The NF-κB pathway is regulated by number of post-translational modifications, including phosphorylation and ubiquitination. Ubiquitin (Ub) E3 ligases are key regulators of the process of ubiquitination and provide specificity to the pathway as they recognise the substrate and determine the topology of ubiquitination. TRIMs, members of RING family of Ub E3 ligases, are characterised by the presence of three conserved domains, RING, B-Box and coiled-coil (RBCC). Emerging evidence suggests that TRIMs regulate innate immune signalling during infection and different pathological conditions. The studies have demonstrated the role of TRIMs in regulation of inflammatory pathways including NF-κB. Recent reports suggest that TRIMs play a critical role in regulation of the NF-κB pathway by ubiquitinating proteins at different steps. In the current review, we discuss the role of TRIMs as novel NF-κB regulators and their role in different pathophysiological conditions. © 2014 Société Française des Microscopies and Société de Biologie Cellulaire de France. Published by John Wiley & Sons Ltd.

Roy S.,Indian Institute of Science
CrystEngComm | Year: 2014

Polyoxometalates (POMs), as the name suggests, are single molecular charged or uncharged clusters comprising many metal centres and oxygen atoms. They are crystalline. On the other hand, recently, a class of macroionic, superstructured assemblies of POMs has been found which is reminiscent of soft matter and has been proposed to be called Softoxometalates (SOMs). This highlight gives a personal account of our work with SOMs. Starting with a brief background and history of SOMs, we explore the reasons for their formation. Thereafter, we discuss the charge regulation mechanism for the stabilization of SOMs. A few case studies for the directed formation of large surface area, mesoscopic SOMs are also discussed. Thereafter, we discuss the effects of sound and light on SOMs. This highlight finally ends with a discussion on self-assembled pattern formation with oxometalates. © 2014 the Partner Organisations 2014.

Rigney D.A.,Ohio State University | Karthikeyan S.,Indian Institute of Science
Tribology Letters | Year: 2010

This brief introductory article summarizes key findings from experiments and from computer simulations concerning the dramatic changes that commonly occur adjacent to sliding interfaces. We conclude that a wide range of observed features depends on a few basic processes (plastic deformation, interactions with the environment (including the counterface) and mechanical mixing) and that sliding leads to flow patterns similar to those expected in fluid flow. © 2009 Springer Science+Business Media, LLC.

Ganesan S.,Indian Institute of Science | Tobiska L.,Otto Von Guericke University of Magdeburg
Journal of Computational Physics | Year: 2012

A finite-element scheme based on a coupled arbitrary Lagrangian-Eulerian and Lagrangian approach is developed for the computation of interface flows with soluble surfactants. The numerical scheme is designed to solve the time-dependent Navier-Stokes equations and an evolution equation for the surfactant concentration in the bulk phase, and simultaneously, an evolution equation for the surfactant concentration on the interface. Second-order isoparametric finite elements on moving meshes and second-order isoparametric surface finite elements are used to solve these equations. The interface-resolved moving meshes allow the accurate incorporation of surface forces, Marangoni forces and jumps in the material parameters. The lower-dimensional finite-element meshes for solving the surface evolution equation are part of the interface-resolved moving meshes. The numerical scheme is validated for problems with known analytical solutions. A number of computations to study the influence of the surfactants in 3D-axisymmetric rising bubbles have been performed. The proposed scheme shows excellent conservation of fluid mass and of the total mass of the surfactant. © 2012 Elsevier Inc.

Purkayastha P.,Indian Institute of Science
Journal of Photochemistry and Photobiology A: Chemistry | Year: 2010

Compounds like trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) take part in compound induced cyclodextrin (CD) nanotubular suprastructure formation. The molecule undergoes differential encapsulation inside the CD cavities of different sizes and hence experience restricted freedom in its movement. DMASBT is capable of undergoing intramolecular charge transfer in the excited state in polar media. This physical phenomenon has been exploited to study the Cu2+ sensing capability of encapsulated DMASBT. The intramolecular charge transfer is found to get switched on employment of Cu2+ ions with the proper choice of cyclodextrin molecules for encapsulation. The differential encapsulation of the compound inside the CD cavities is held to be responsible for this behavior. The complexation takes place in the ground state and because of the difference in charge density on the ligating centers; the system is capable to show a switching behavior in the twisted intramolecular charge transfer (TICT) emission of the guest molecule inside the various cyclodextrin moieties. © 2010 Elsevier B.V. All rights reserved.

Ghosh N.,Indian Institute of Science
Journal of biomedical optics | Year: 2011

Polarimetry has a long and successful history in various forms of clear media. Driven by their biomedical potential, the use of the polarimetric approaches for biological tissue assessment has also recently received considerable attention. Specifically, polarization can be used as an effective tool to discriminate against multiply scattered light (acting as a gating mechanism) in order to enhance contrast and to improve tissue imaging resolution. Moreover, the intrinsic tissue polarimetry characteristics contain a wealth of morphological and functional information of potential biomedical importance. However, in a complex random medium-like tissue, numerous complexities due to multiple scattering and simultaneous occurrences of many scattering and polarization events present formidable challenges both in terms of accurate measurements and in terms of analysis of the tissue polarimetry signal. In order to realize the potential of the polarimetric approaches for tissue imaging and characterization/diagnosis, a number of researchers are thus pursuing innovative solutions to these challenges. In this review paper, we summarize these and other issues pertinent to the polarized light methodologies in tissues. Specifically, we discuss polarized light basics, Stokes-Muller formalism, methods of polarization measurements, polarized light modeling in turbid media, applications to tissue imaging, inverse analysis for polarimetric results quantification, applications to quantitative tissue assessment, etc.

Misra A.,Indian Institute of Science
AIP Advances | Year: 2012

Electron beam irradiation induced, bending of Iron filled, multiwalled carbon nanotubes is reported. Bending of both the carbon nanotube and the Iron contained within the core was achieved using two approaches with the aid of a high resolution electron microscope (HRTEM). In the first approach, bending of the nanotube structure results in response to the irradiation of a pristine kink defect site, while in the second approach, disordered sites induce bending by focusing the electron beam on the graphite walls. The HRTEM based in situ observations demonstrate the potential for using electron beam irradiation to investigate and manipulate the physical properties of confined nanoscale structures. © 2012 Author(s).

Aulakh C.S.,Panjab University | Garg S.K.,Panjab University | Garg S.K.,Indian Institute of Science
Nuclear Physics B | Year: 2012

The supersymmetric SO(10) GUT based on the 210⊕10⊕120⊕126⊕126̄ Higgs system provides a minimal framework for the emergence of the R-parity exact MSSM at low energies and a viable supersymmetric seesaw explanation for the observed neutrino masses and mixing angles. We present formulae for MSSM decomposition of the superpotential invariants, tree level light charged fermion effective Yukawa couplings, Weinberg neutrino mass generation operator, and the d=5, δB=δL≠0 effective superpotential in terms of GUT parameters. We use them to determine fits of the 18 available fermion mass-mixing data in terms of the superpotential parameters of the NMSGUT and SUGRY (NUHM) type soft supersymmetry breaking parameters ({mf~,m1/2,A0,MH,H̄2}) specified at the MSSM one-loop unification scale MX0=1016.33GeV. Our fits are compatible with electroweak symmetry breaking and Unification constraints and yield right-handed neutrino masses in the leptogenesis relevant range: 10 8-10 13GeV. Matching the SM data requires lowering the strange and down quark Yukawas in the MSSM via large tanβ driven threshold corrections and characteristic soft Susy breaking spectra. The standard model Higgs mass emerges less than 130 GeV. The Susy spectra have light pure Bino LSP, heavy exotic Higgs(inos) and large μ, A 0, MH,H̄ parameters ~100 TeV. Typically third generation sfermions are much heavier than the first two generations. The smuon is often the lightest charged sfermion thus offering a Bino-CDM co-annihilation channel. The parameter sets obtained are used to calculate B violation rates which are found to be generically much faster (~10 -28yr -1) than the current experimental limits. Improvements which may allow acceptable B violation rates are identified. © 2011 Elsevier B.V.

Mikelsons K.,Georgetown University | Freericks J.K.,Georgetown University | Krishnamurthy H.R.,Indian Institute of Science
Physical Review Letters | Year: 2012

We use a self-consistent strong-coupling expansion for the self-energy (perturbation theory in the hopping) to describe the nonequilibrium dynamics of strongly correlated lattice fermions. We study the three-dimensional homogeneous Fermi-Hubbard model driven by an external electric field showing that the damping of the ensuing Bloch oscillations depends on the direction of the field and that for a broad range of field strengths a long-lived transient prethermalized state emerges. This long-lived transient regime implies that thermal equilibrium may be out of reach of the time scales accessible in present cold atom experiments but shows that an interesting new quasiuniversal transient state exists in nonequilibrium governed by a thermalized kinetic energy but not a thermalized potential energy. In addition, when the field strength is equal in magnitude to the interaction between atoms, the system undergoes a rapid thermalization, characterized by a different quasiuniversal behavior of the current and spectral function for different values of the hopping. © 2012 American Physical Society.

Tibrewala R.,Indian Institute of Science
Classical and Quantum Gravity | Year: 2012

Effects of inverse triad corrections and (point) holonomy corrections, occurring in loop quantum gravity, are considered on the properties of Reissner-Nordström black holes. The version of inverse triad corrections with unmodified constraint algebra reveals the possibility of occurrence of three horizons (over a finite range of mass) and also shows a mass threshold beyond which the inner horizon disappears. For the version with modified constraint algebra, coordinate transformations are no longer a good symmetry. The covariance property of spacetime is regained by using a quantum notion of mapping from phase space to spacetime. The resulting quantum effects in both versions of these corrections can be associated with renormalization of either mass, charge or wavefunction. In neither of the versions, Newtons constant is renormalized. (Point) Holonomy corrections are shown to preclude the undeformed version of constraint algebra as also a static solution, though time-independent solutions exist. A possible reason for difficulty in constructing a covariant metric for these corrections is highlighted. Furthermore, the deformed algebra with holonomy corrections is shown to imply signature change. © 2012 IOP Publishing Ltd.

Nanda K.K.,Indian Institute of Science
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2012

We discuss the size-dependent density of nanoparticles and nanostructured materials keeping the recent experimental results in mind. The density is predicted to increase with decreasing size for nanoparticles but it can decrease with size for nanostructured materials that corroborates the experimental results reported in the literature. © 2012 Elsevier B.V.

Ananth S.,Indian Institute of Science
Journal of High Energy Physics | Year: 2012

It is shown that the coefficient of the cubic interaction vertex, in higher spin Lagrangians, has a very simple form when written in terms of spinor helicity products. The result for a higher-spin field, of spin λ, is equal to the corresponding Yang-Mills coefficient raised to the power λ. Among other things, this suggests perturbative ties, similar to the KLT relations, between higher spin theories and pure Yang-Mills. This result is obtained in four-dimensional flat spacetime. © SISSA 2012.

Gavara M.,Indian Institute of Science
Numerical Heat Transfer; Part A: Applications | Year: 2012

Laminar forced convection of nanofluids in a vertical channel with symmetrically mounted rib heaters on surfaces of opposite walls is numerically studied. The fluid flow and heat transfer characteristics are examined for various Reynolds numbers and nanoparticles volume fractions of water-Al 2O 3 nanofluid. The flow exhibits various structures with varying Reynolds number. Even though the geometry and heating is symmetric with respect to a channel vertical mid-plane, asymmetric flow and heat transfer are found for Reynolds number greater than a critical value. Introduction of nanofluids in the base fluid delays the flow solution bifurcation point, and the critical Reynolds number increases with increasing nanoparticle volume fraction. A skin friction coefficient along the solid-fluid interfaces increases and decreases sharply along the bottom and top faces of the heaters, respectively, due to sudden acceleration and deceleration of the fluid at the respective faces. The skin friction coefficient, as well as Nusselt numbers in the channel, increase with increasing volume fraction of nanoparticles. Copyright © 2012 Taylor and Francis Group, LLC.

Gavara M.,Indian Institute of Science
Numerical Heat Transfer; Part A: Applications | Year: 2012

Laminar natural convection in a series of thermally interacting cavities is numerically studied. Each cavity consists of a conducting bottom wall with a surface mounted heater. The side walls of the cavities are isothermally cooled. Each cavity thermally interacts with its adjacent cavities through the conducting walls. Flow and heat transfer characteristics are studied in detail for various Rayleigh numbers. The convection characteristics in multiple cavities are compared with those in single independent cavity. The thermal interaction between the cavities results in lower temperatures compared with those in independent cavities. While heat is rejected into the adjacent upper cavity through some portion of the conducting wall, heat is received from the adjacent cavity through the remaining portion of the wall. The influence of substrate conductivity on heat exchange between adjacent cavities are examined. Substrate conductivity shows strong effect on temperature distribution. When cooling at both vertical sides is changed to one side cooling, the heat transfer characteristics are changed drastically and many interesting flow features are observed. Effects of cavity aspect ratio is studied and higher heat transfer rates are observed at higher aspect ratios. Correlations for dimensionless temperature maximum and average Nusselt number are presented in terms of Rayleigh number. Copyright © 2012 Taylor and Francis Group, LLC.

Nanda K.K.,Indian Institute of Science
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2012

Based on the liquid-drop model, we have evaluated the Tolman length and surface energy of nanoparticles for different elements and compared with other theoretical models as well as the available simulated data. The predictions of the model show good agreement with the simulated results. Like the cohesive energy and melting temperature, the size-dependency of surface energy is also shape-dependent. © 2012 Elsevier B.V.

Kumar G.V.P.,Indian Institute of Science
Journal of the Optical Society of America B: Optical Physics | Year: 2012

Sharp geometrical features in crescent-shaped plasmonic nanostructures facilitate electromagnetic hot spots that can be harnessed for sensitive detection of molecules and nanomaterials. For a given geometry of nanocrescent cylinder, the near-field optical resonance and enhancement are constants. It is desirable to tune this resonance and enhancement without altering the geometry of the nanocrescent cylinder. Herein, we numerically show how the near-field resonance and enhancement at the tip of a nanocrescent cylinder can be proximally tuned by incorporating a plasmonic nanostrip in the vicinity. Geometrical parameters, such as the nanocrescent cylinder-nanostrip distance (g) and length (l) of the nanostrip, were varied to tune the near-field optical properties. Our analysis revealed (i) an increment in near-field enhancement at the tip of the nanocrescent cylinder in the presence of a plasmonic nanostrip; (ii) a redshift in the dipolar plasmon mode accompanied by an increase in the nearfield enhancement by decreasing g and increasing l, independently; and (iii) variation in the near-field enhancement of plasmonic modes as a function of the excitation angle. Such tunable plasmonic configurations offer capabilities to design wavelength-tuned optical devices without altering the base geometry. © 2012 Optical Society of America.

Sonowal R.,Indian Institute of Science
Proceedings. Biological sciences / The Royal Society | Year: 2013

Bacteria present in natural environments such as soil have evolved multiple strategies to escape predation. We report that natural isolates of Enterobacteriaceae that actively hydrolyze plant-derived aromatic β-glucosides such as salicin, arbutin and esculin, are able to avoid predation by the bacteriovorous amoeba Dictyostelium discoideum and nematodes of multiple genera belonging to the family Rhabditidae. This advantage can be observed under laboratory culture conditions as well as in the soil environment. The aglycone moiety released by the hydrolysis of β-glucosides is toxic to predators and acts via the dopaminergic receptor Dop-1 in the case of Caenorhabditis elegans. While soil isolates of nematodes belonging to the family Rhabditidae are repelled by the aglycone, laboratory strains and natural isolates of Caenorhabditis sp. are attracted to the compound, mediated by receptors that are independent of Dop-1, leading to their death. The β-glucosides-positive (Bgl(+)) bacteria that are otherwise non-pathogenic can obtain additional nutrients from the dead predators, thereby switching their role from prey to predator. This study also offers an evolutionary explanation for the retention by bacteria of 'cryptic' or 'silent' genetic systems such as the bgl operon.

Konar A.D.,Indian Institute of Science
CrystEngComm | Year: 2013

Two enantiomeric pseudopeptides I & II, comprising a single pyridinedicarboxylic acid and a flexible dipeptidyl fragment H-Xaa-mABA-OMe (Xaa: l-Ala, pseudopeptide I; d-Ala, pseudopeptide II, mABA: meta aminobenzoic acid), have been synthesized using Boc chemistry. X-ray crystallographic analysis reveals that in the solid state, both the enantiomers form a dimeric unit stabilized by intermolecular hydrogen bonding interactions. Interestingly, these dimeric subunits self-assemble to form a supramolecular double helical architecture using various noncovalent interactions. To date, significant examples are documented in the literature where DNA analogues/derivatives or several rigid templates have been employed as synthons for double helical self assembly. However, to the best of our knowledge, this novel example represents one of the very few reports of a supramolecular double helix design resulting from the self assembly of a flexible dimeric peptidyl unit, solely nucleated by the conformational features, of the peptides. Concentration and temperature dependant NMR experiments were performed for pseudopeptide I (one of the enantiomers) to decipher the existence of the dimeric unit in solution. Pseudopeptide II (one of the enantiomers) was subjected to iodine and gas absorption studies, which demonstrates its candidature in the design of nanoporous materials. This journal is © The Royal Society of Chemistry 2013.

Sureshan K.M.,Indian Institute of Science | Gonnade R.G.,CSIR - National Chemical Laboratory
CrystEngComm | Year: 2013

We report crystallographic evidence for the significance of C-H⋯π hydrogen bonds in the crystal stabilization of 1,4-di-O-benzoyl-myo-inositol. The strength of this otherwise weak hydrogen bond matches with the strength of O-H⋯O hydrogen bonds. This journal is © The Royal Society of Chemistry.

Narendar S.,Indian Defence Research And Development Laboratory | Gopalakrishnan S.,Indian Institute of Science
Acta Mechanica | Year: 2012

This article presents the buckling analysis of orthotropic nanoplates such as graphene using the two-variable refined plate theory and nonlocal small-scale effects. The two-variable refined plate theory takes account of transverse shear effects and parabolic distribution of the transverse shear strains through the thickness of the plate, hence it is unnecessary to use shear correction factors. Nonlocal governing equations of motion for the monolayer graphene are derived from the principle of virtual displacements. The closed-form solution for buckling load of a simply supported rectangular orthotropic nanoplate subjected to in-plane loading has been obtained by using the Navier's method. Numerical results obtained by the present theory are compared with first-order shear deformation theory for various shear correction factors. It has been proven that the nondimensional buckling load of the orthotropic nanoplate is always smaller than that of the isotropic nanoplate. It is also shown that small-scale effects contribute significantly to the mechanical behavior of orthotropic graphene sheets and cannot be neglected. Further, buckling load decreases with the increase of the nonlocal scale parameter value. The effects of the mode number, compression ratio and aspect ratio on the buckling load of the orthotropic nanoplate are also captured and discussed in detail. The results presented in this work may provide useful guidance for design and development of orthotropic graphene based nanodevices that make use of the buckling properties of orthotropic nanoplates. © Springer-Verlag 2011.

Bhattacharyya S.,Indian Institute of Science
Journal of Physical Chemistry C | Year: 2015

Magnetic nanoparticles (NPs) are prominent in various fields of scientific research and applications such as magnetic energy storage, magnetic fluids, biomedical fields, and catalysis. Metallic Fe NPs are difficult to protect from air oxidation, and iron oxide NPs suff er from reduced magnetization. Iron nitrides have the advantage of retaining high saturation magnetization (MS); for example, α″-Fe16N2 and γ′-Fe4N have average magnetic moments of 2.9 and 2 μB/Fe, respectively, which are comparable to 2.2 μB/Fe for α-Fe. The iron nitrides are ferromagnetic (FM) up to a maximum lattice dilution of 25% nitrogen for ε-Fe3N. Even though Fe-N NPs are extremely attractive as magnetic materials, the focus has been majorly on the bulk powders and thin films. This review provides a comprehensive overview of the crystal structures, nitriding kinetics, and synthesis methodologies of binary, doped, and ternary nanostructures, thin films, and bulk materials and their magnetism. Substitution of Fe by any other metal atom in the doped and ternary nanostructures breaks the long-range FM ordering but equally provides interesting low-temperature magnetic ordering such as spin glass and exchange bias. The dopant concentration dependence of the magnetic properties of the hybrid systems is discussed. (Chemical Equation Presented). © 2014 American Chemical Society.

McConkey K.R.,Indian Institute of Science | O'Farrill G.,University of Toronto
Trends in Ecology and Evolution | Year: 2015

The essential functional roles performed by animal species are lost when they become locally extinct, and ecosystems are critically threatened by this decline in functional diversity. Theory that links function, diversity, and ecosystem stability exists but fails to assess function loss that occurs in species with persistent populations. The entire functional role of a species, or a critical component of it, can be lost following large population declines (functional extinction), following population increase, or after behavioural adaptations to changes in the population, community, habitat, or climate. Here, we provide a framework that identifies the scenarios under which 'cryptic' function loss can occur in persistent populations. Cryptic function loss is potentially widespread and critically threatens ecosystem stability across the globe. © 2015 Elsevier Ltd.

Harshan J.,Monash University | Rajan B.S.,Indian Institute of Science
IEEE Transactions on Wireless Communications | Year: 2013

Constellation Constrained (CC) capacity regions of two-user Gaussian Multiple Access Channels (GMAC) have been recently reported, wherein an appropriate angle of rotation between the constellations of the two users is shown to enlarge the CC capacity region. We refer to such a scheme as the Constellation Rotation (CR) scheme. In this paper, we propose a novel scheme called the Constellation Power Allocation (CPA) scheme, wherein the instantaneous transmit power of the two users are varied by maintaining their average power constraints. We show that the CPA scheme offers CC sum capacities equal (at low SNR values) or close (at high SNR values) to those offered by the CR scheme with reduced decoding complexity for QAM constellations. We study the robustness of the CPA scheme for random phase offsets in the channel and unequal average power constraints for the two users. With random phase offsets in the channel, we show that the CC sum capacity offered by the CPA scheme is more than the CR scheme at high SNR values. With unequal average power constraints, we show that the CPA scheme provides maximum gain when the power levels are close, and the advantage diminishes with the increase in the power difference. © 2012 IEEE.

Jacob K.T.,Indian Institute of Science
ECS Transactions | Year: 2011

A new type of solid oxide fuel cell (SOFC) is presented which can convert heat absorbed from a high-temperature source to electricity bypassing the Carnot limitation and use solid carbon as the fuel. The essential cell reaction is the partial oxidation of carbon to carbon monoxide, unlike in the case of conventional SOFC where oxidation of hydrogen and carbon monoxide to water vapour and carbon dioxide are the main reactions. The fuel cell is endothermic and absorbs heat from an external source and converts it to electricity. The theoretical basis of the new fuel cell is explained and some preliminary experimental results are presented. A liquid metal is used as the medium for the carbon-oxygen reaction generating carbon monoxide. There is no violation of the second law of thermodynamics since the theoretically loss free conversion of heat to electricity is accompanied by a chemical reaction. ©The Electrochemical Society.

Patel A.,Indian Institute of Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

The flux tube model offers a pictorial description of what happens during the deconfinement phase transition in QCD. The three-point vertices of a flux tube network lead to formation of baryons upon hadronization. Therefore, correlations in the baryon number distribution at the last scattering surface are related to the preceding pattern of the flux tube vertices in the quark-gluon plasma, and provide a signature of the nearby deconfinement phase transition. I discuss the nature of the expected signal, and how to extract it from the experimental data for heavy ion collisions at RHIC and LHC. © 2012 American Physical Society.

Jassal H.K.,Indian Institute of Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

Dark energy perturbation affects the growth of matter perturbations even in scenarios with noninteracting dark energy. We investigate the integrated Sachs-Wolfe effect in various canonical scalar field models with perturbed dark energy. We do this analysis for models belonging to the thawing and freezing classes, which are classes based on the way the equation of state evolves with time. For thawing models, the dark energy equation of state remains the same as that of a cosmological constant and deviates from this value at late times. In freezing models, the equation of state evolves in the opposite manner, namely it "freezes" to cosmological constant-type behavior at late times. We show that between these classes there is no clear difference for the Sachs-Wolfe effect. We show that on taking perturbations into account, the contribution due to different models is closer to each other and to the cosmological constant model than it is to the case of an unperturbed scalar field, i.e., the dark energy component is homogeneous. Therefore, considering dark energy to be homogeneous gives an overestimate in distinction between different models. However, the difference between contribution to the angular power spectrum due to different models remains large, and future observations pertaining to growth of perturbations may be able to distinguish between these. © 2012 American Physical Society.

Guharoy S.,Qualcom India Pvt. Ltd. | Mehta N.B.,Indian Institute of Science
IEEE Transactions on Vehicular Technology | Year: 2013

Orthogonal frequency-division multiple access (OFDMA) systems divide the available bandwidth into orthogonal subchannels and exploit multiuser diversity and frequency selectivity to achieve high spectral efficiencies. However, they require a significant amount of channel state feedback for scheduling and rate adaptation and are sensitive to feedback delays. We develop a comprehensive analysis for OFDMA system throughput in the presence of feedback delays as a function of the feedback scheme, frequency-domain scheduler, and rate adaptation rule. Also derived are expressions for the outage probability, which captures the inability of a subchannel to successfully carry data due to the feedback scheme or feedback delays. Our model encompasses the popular best-n and threshold-based feedback schemes and the greedy, proportional fair, and round-robin schedulers that cover a wide range of throughput versus fairness tradeoff. It helps quantify the different robustness of the schedulers to feedback overhead and delays. Even at low vehicular speeds, it shows that small feedback delays markedly degrade the throughput and increase the outage probability. Further, given the feedback delay, the throughput degradation depends primarily on the feedback overhead and not on the feedback scheme itself. We also show how to optimize the rate adaptation thresholds as a function of feedback delay. © 2012 IEEE.

Ray S.,Indian Institute of Science
Current Opinion in Neurobiology | Year: 2015

Brain signals often show fluctuations in particular frequency bands, which are highly conserved across species and are associated with specific behavioural states. Such rhythmic patterns can be captured in the local field potential (LFP), which is obtained by low-pass filtering the extracellular signal recorded from microelectrodes. However, LFP also captures other neural processes that are associated with spikes, such as synaptic events preceding a spike, low-frequency component of the action potential ("spike bleed-through") and spike afterhyperpolarization, which pose difficulties in the estimation of the amplitude and phase of the rhythm with respect to spikes. Here we discuss these issues and different techniques that have been used to dissociate the rhythm from other neural events in the LFP. © 2014.

Vijayakumar K.,Indian Institute of Science
AIAA Journal | Year: 2011

The layerwise theory of bending of symmetric laminates with isotropic plies is discussed. The plate is subjected to asymmetric load and zero shear stress along the top and bottom faces of the plate. The stress components are expressed in terms of displacements through six stress-strain constitutive relations and six strain-displacement relations in displacement-based models. The vertical deflections in the case of homogeneous plate are the same for the top and neutral planes, which is physically not correct because of the use of an integration constant to satisfy face shear conditions in the top ply. Two-dimensional variables in the in-plane displacements are added as corrections to distributions of the corresponding variables obtained from the iterative method.

Ray S.,Indian Institute of Science | Maunsell J.H.R.,University of Chicago
Trends in Cognitive Sciences | Year: 2015

Gamma rhythm (which has a center frequency between 30 and 80. Hz) is modulated by cognitive mechanisms such as attention and memory, and has been hypothesized to play a role in mediating these processes by supporting communication channels between cortical areas or encoding information in its phase. We highlight several issues related to gamma rhythms, such as low and inconsistent power, its dependence on low-level stimulus features, problems due to conduction delays, and contamination due to spike-related activity that makes accurate estimation of gamma phase difficult. Gamma rhythm could be a potentially useful signature of excitation-inhibition interactions in the brain, but whether it also provides a mechanism for information processing or coding remains an open question. © 2014 Elsevier Ltd.

Sukhatme J.,Indian Institute of Science
Quarterly Journal of the Royal Meteorological Society | Year: 2013

Intraseasonal time-scales play an important role in tropical variability. Two modes that contribute significantly to tropical intraseasonal variability (ISV) are the eastward-propagating Madden-Julian Oscillation (MJO), and westward-moving moist equatorial Rossby waves. This note reports on a correspondence between the longitudinal gradient of mean tropical precipitable water (PW), and the geographical regions of genesis, and convective activity, of both these large-scale tropical systems. Our finding is based on an analysis of PW from the MERRA reanalysis product. The data indicate that the mean tropical PW has a dominant wavenumber two (three) structure in longitude in the Northern (Southern) Hemisphere. Departures from a longitudinally homogeneous state are attributed to the influence of subtropical anticyclones, and are accentuated by monsoonal regions of both hemispheres. This mean structure results in a sharply localized longitudinal gradient of PW. Remarkably, regions with positive gradients (such as the Northern and Southern Hemisphere western Indian Ocean), i.e. they have larger PW to the east, are the very zones that are implicated in the formation, and show high levels of convective activity, of the eastward-moving MJO. On the other hand, regions with negative gradients (such as the Southern Hemisphere central Pacific) are the very regions where genesis, and maxima in variance, of westward-moving moist equatorial Rossby waves are known to occur. Apart from providing a first-order longitudinal footprint of the convective phase of these systems, this correspondence reinforces the role of the mean climatic state in tropical ISV. © 2012 Royal Meteorological Society.

Rangarajan A.,Indian Institute of Science
BMC cancer | Year: 2014

BACKGROUND: The Bmi1 polycomb ring finger oncogene, a transcriptional repressor belonging to the Polycomb group of proteins plays an important role in the regulation of stem cell self-renewal and is elevated in several cancers. In the current study, we have explored the role of Bmi1 in regulating the stemness and drug resistance of breast cancer cells.METHODS: Using real time PCR and immunohistochemistry primary breast tissues were analyzed. Retro- and lentiviruses were utilized to overexpress and knockdown Bmi1, RT-PCR and Western blot was performed to evaluate mRNA and protein expression. Stemness properties were analyzed by flow cytometry and sphere-formation and tumor formation was determined by mouse xenograft experiments. Dual luciferase assay was employed to assess promoter activity and MTT assay was used to analyze drug response.RESULTS: We found Bmi1 overexpression in 64% of grade III invasive ductal breast adenocarcinomas compared to normal breast tissues. Bmi1 overexpression in immortalized and transformed breast epithelial cells increased their sphere-forming efficiency, induced epithelial to mesenchymal transition (EMT) with an increase in the expression of stemness-related genes. Knockdown of Bmi1 in tumorigenic breast cells induced epithelial morphology, reduced expression of stemness-related genes, decreased the IC50 values of doxorubicin and abrogated tumor-formation. Bmi1-high tumors showed elevated Nanog expression whereas the tumors with lower Bmi1 showed reduced Nanog levels. Overexpression of Bmi1 increased Nanog levels whereas knockdown of Bmi1 reduced its expression. Dual luciferase promoter-reporter assay revealed Bmi1 positively regulated the Nanog and NFκB promoter activity. RT-PCR analysis showed that Bmi1 overexpression activated the NFκB pathway whereas Bmi1 knockdown reduced the expression of NFκB target genes, suggesting that Bmi1 might regulate Nanog expression through the NFκB pathway.CONCLUSIONS: Our study showed that Bmi1 is overexpressed in several high-grade, invasive ductal breast adenocarcinomas, thus supporting its role as a prognostic marker. While Bmi1 overexpression increased self-renewal and promoted EMT, its knockdown reversed EMT, reduced stemness, and rendered cells drug sensitive, thus highlighting a crucial role for Bmi1 in regulating the stemness and drug response of breast cancer cells. Bmi1 may control self-renewal through the regulation of Nanog expression via the NFκB pathway.

Ravikant V.,Indian Institute of Science | Wu F.-Y.,CAS Institute of Geology and Geophysics | Ji W.-Q.,CAS Institute of Geology and Geophysics
Earth and Planetary Science Letters | Year: 2011

The Subhimalaya of NW India exposes a well developed marine to continental foreland sequence preserving sediments shed from the tectonically evolving Cenozoic Himalayan orogen. Detrital zircon U-Pb ages and their Hf isotopic compositions, of seven samples, were analyzed from the Subathu sub-basin foreland formations to constrain sediment provenance. The detrital zircon U-Pb age spectra yielded a similar pattern, for all foreland formations, with major peaks clustered at ~. 500-650. Ma, 900-1000. Ma and ~. 2500. Ma, corresponding to (indistinguishable) Tethyan Himalaya and Higher Himalayan Crystalline sources and those at ~. 1800-1900. Ma corresponding to lower a Lesser Himalayan arc source. Comparison of the foreland detrital zircon U-Pb age spectra with Himalayan lithotectonic source units, in conjunction with their Hf isotopes and previously determined sediment petrography and age constraints, suggest that the sediments to the flysch marine Subathu Formation (~65 to >41. Ma) were sourced from a positive-relief area of the Tethyan Himalaya mixed with detritus from lower Lesser Himalaya and additional cratonic northern Indian Precambrian rocks. No Cretaceous to Eocene-aged detrital zircons, contributed by eroding Ladakh batholith north of the Indus Tsangpo suture zone, were recorded in the Palaeogene-aged foreland samples. The younger synorogenic continental Dagshai Formation (<30 to <22. Ma) sediments were sourced from the very low-grade Tethyan Himalaya, whereas the alluvial-facies Kasauli Formation (<22 to 13. Ma) began to receive sediments additionally from erosion of the medium-grade metamorphic rocks of the Higher Himalayan Crystalline and the lower Lesser Himalaya. The Lower Siwalik Formation sediments (~13-11.5. Ma) were derived from the low-grade rocks of the Tethyan Himalaya, both the upper and lower Lesser Himalaya and additionally from the eroding high-grade migmatitic gneisses of the Higher Himalayan Crystalline. Thus, from the similar detrital zircon age spectra of the foreland formations, we infer that differences in the continental sediment detritus into the foreland basin reflect a straightforward sediment mixture of variable proportions from fixed Himalayan lithotectonic sources which progressively shifted towards the foreland with development of the orogen. © 2011 Elsevier B.V.

Dasgupta S.,Indian Institute of Science | Bose S.,Presidency University of India | Das K.,Bengal Engineering and Science University | Das K.,Hiroshima University
Precambrian Research | Year: 2013

We present possible tectonic models for two crustal domains of the Proterozoic Eastern Ghats Belt, India based on recent petrological, geophysical and geochronological data. Although both the domains presently expose deep crustal sections, they evolved in two distinct time segments of the Precambrian through accretion-collision processes. This is why we argue that no unique model can explain the complexities of the belt. The southern part of the belt evolved through subduction-dominated accretionary processes encompassing India, east Antarctica, Australia and Laurentia as part of supercontinent Columbia during the span of ca. 1.90-1.60. Ga. To the contrary, the central domain witnessed a prolonged accretion-collision history initiated at ca. 1.50. Ga and culminated at ca. 0.90. Ga with the formation of supercontinent Rodinia. The latter united cratonic India with east Antarctica as a separate continent Enderbia that existed until about ca. 0.50. Ga. The pre-1.50. Ga history of this domain is ambiguous at the present state of knowledge. The northern domain has a much younger (ca. 0.90-0.50. Ga) tectonothermal history which is unrelated to either of the studied domains. The present models explain the reported petrotectonic processes including the ultra high temperature metamorphism in both the domains. The episodic growth of the Eastern Ghats Belt matches with Proterozoic supercontinent cycles. © 2012 Elsevier B.V.

Paikaray S.,Indian Institute of Science
Mine Water and the Environment | Year: 2015

Due to geochemical similarity between arsenic and sulphur, polymetallic sulphide deposits and pyrite/arsenopyrite-bearing coal beds often contain exceptionally high concentrations of arsenic. Arsenic release from mine waste occurs after oxidative dissolution of sulphide minerals. Both arsenite and arsenate forms coexist in many mine drainage localities, with the latter oxidation state more common. The rate of arsenite oxidation to arsenate in such environments is mostly controlled by the availability of oxygen and arsenic-oxidizing microbes. Most released arsenic gets naturally attenuated within few meters downstream by adsorption and co-precipitation; amorphous precipitates such as schwertmannite or hydrous ferric oxides are better sinks than crystalline counterparts, such as goethite and jarosite. Because arsenate has a stronger affinity than arsenite for sorbents at acidic pH, arsenate-dominated mine water often contains lower levels of arsenic than arsenite-dominated mine water. Secondary mineral precipitation is largely controlled by distribution of acid-neutralizing minerals, such as carbonates and aluminosilicates. In addition to natural attenuation, active and passive treatment of mine water can lower arsenic levels to meet legal limits. © 2014, Springer-Verlag Berlin Heidelberg.

Rayasam G.V.,CSIR - Central Electrochemical Research Institute | Balganesh T.S.,Indian Institute of Science
Trends in Pharmacological Sciences | Year: 2015

host-directed need for treatment of drug-resistant tuberculosis (TB) is to find novel therapies that are efficacious, safe, and shorten the duration of treatment. Drug discovery approaches for TB primarily target essential genes of the pathogen Mycobacterium tuberculosis (Mtb) but novel strategies such as host-directed therapies and nonmicrobicidal targets are necessary to bring about a paradigm shift in treatment. Drugs targeting the host pathways and nonmicrobicidal proteins can be used only in conjunction with existing drugs as adjunct therapies. Significantly, host-directed adjunct therapies have the potential to decrease duration of treatment, as they are less prone to drug resistance, target the immune responses, and act via novel mechanism of action. Recent advances in targeting host-pathogen interactions have implicated pathways such as eicosanoid regulation and angiogenesis. Furthermore, several approved drugs such as metformin and verapamil have been identified that appear suitable for repurposing for the treatment of TB. These findings and the challenges in the area of host- and/or pathogen-directed adjunct therapies and their implications for TB therapy are discussed. © 2015 Elsevier Ltd.

Sarma J.D.,Indian Institute of Science
Interdisciplinary Perspectives on Infectious Diseases | Year: 2010

Myelin forms an insulating sheath surrounding axons in the central and peripheral nervous systems and is essential for rapid propagation of neuronal action potentials. Demyelination is an acquired disorder in which normally formed myelin degenerates, exposing axons to the extracellular environment. The result is dysfunction of normal neuron-to-neuron communication and in many cases, varying degrees of axonal degeneration. Numerous central nervous system demyelinating disorders exist, including multiple sclerosis. Although demyelination is the major manifestation of most of the demyelinating diseases, recent studies have clearly documented concomitant axonal loss to varying degrees resulting in long-term disability. Axonal injury may occur secondary to myelin damage (outside-in model) or myelin damage may occur secondary to axonal injury (inside-out model). Viral induced demyelination models, has provided unique imminent into the cellular mechanisms of myelin destruction. They illustrate mechanisms of viral persistence, including latent infections, virus reactivation and viral-induced tissue damage. These studies have also provided excellent paradigms to study the interactions between the immune system and the central nervous system (CNS). In this review we will discuss potential cellular and molecular mechanism of central nervous system axonal loss and demyelination in a viral induced mouse model of multiple sclerosis. Copyright © 2010 Jayasri Das Sarma.

Karak B.B.,Indian Institute of Science | Petrovay K.,Eotvos Lorand University
Solar Physics | Year: 2013

The compatibility of the fast-tachocline scenario with a flux-transport dynamo model is explored. We employ a flux-transport dynamo model coupled with simple feedback formulae relating the thickness of the tachocline to the amplitude of the magnetic field or to the Maxwell stress. The dynamo model is found to be robust against the nonlinearity introduced by this simplified fast-tachocline mechanism. Solar-like butterfly diagrams are found to persist and, even without any parameter fitting, the overall thickness of the tachocline is well within the range admitted by helioseismic constraints. In the most realistic case of a time- and latitude-dependent tachocline thickness linked to the value of the Maxwell stress, both the thickness and its latitudinal dependence are in excellent agreement with seismic results. In nonparametric models, cycle-related temporal variations in tachocline thickness are somewhat larger than admitted by helioseismic constraints; we find, however, that introducing a further parameter into our feedback formula readily allows further fine tuning of the thickness variations. © 2012 Springer Science+Business Media Dordrecht.

Seshadri A.K.,Indian Institute of Science
Climate Dynamics | Year: 2016

Monsoons involve increases in dry static energy (DSE), with primary contributions from increased shortwave radiation and condensation of water vapor, compensated by DSE export via horizontal fluxes in monsoonal circulations. We introduce a simple box-model characterizing evolution of the DSE budget to study nonlinear dynamics of steady-state monsoons. Horizontal fluxes of DSE are stabilizing during monsoons, exporting DSE and hence weakening the monsoonal circulation. By contrast latent heat addition (LHA) due to condensation of water vapor destabilizes, by increasing the DSE budget. These two factors, horizontal DSE fluxes and LHA, are most strongly dependent on the contrast in tropospheric mean temperature between land and ocean. For the steady-state DSE in the box-model to be stable, the DSE flux should depend more strongly on the temperature contrast than LHA; stronger circulation then reduces DSE and thereby restores equilibrium. We present conditions for this to occur. The main focus of the paper is describing conditions for bifurcation behavior of simple models. Previous authors presented a minimal model of abrupt monsoon transitions and argued that such behavior can be related to a positive feedback called the ‘moisture advection feedback’. However, by accounting for the effect of vertical lapse rate of temperature on the DSE flux, we show that bifurcations are not a generic property of such models despite these fluxes being nonlinear in the temperature contrast. We explain the origin of this behavior and describe conditions for a bifurcation to occur. This is illustrated for the case of the July-mean monsoon over India. The default model with mean parameter estimates does not contain a bifurcation, but the model admits bifurcation as parameters are varied. © 2016 Springer-Verlag Berlin Heidelberg

Roychowdhury D.,Indian Institute of Science
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

In this paper, based on the principles of gauge/gravity duality and considering the so called hydrodynamic limit we compute various charge transport properties for a class of strongly coupled non-relativistic CFTs corresponding to z = 2 fixed point whose dual gravitational counter part could be realized as the consistent truncation of certain non-relativistic Dp branes in the non-extremal limit. From our analysis we note that unlike the case for the AdS black branes, the charge diffusion constant in the non-relativistic background scales differently with the temperature. This shows a possible violation of the universal bound on the charge conductivity to susceptibility ratio in the context of non-relativistic holography. © 2015 The Author.

Surana P.,National Center for Biological science | Satchidanandam V.,Indian Institute of Science | Nair D.T.,National Center for Biological science
Nucleic Acids Research | Year: 2014

Flaviviral RNA-dependent RNA polymerases (RdRps) initiate replication of the single-stranded RNA genome in the absence of a primer. The template sequence 5′-CU-3′ at the 3′-end of the flaviviral genome is highly conserved. Surprisingly, flaviviral RdRps require high concentrations of the second incoming nucleotide GTP to catalyze de novo template-dependent RNA synthesis. We show that GTP stimulates de novo RNA synthesis by RdRp from Japanese encephalitis virus (jRdRp) also. Crystal structures of jRdRp complexed with GTP and ATP provide a basis for specific recognition of GTP. Comparison of the jRdRpGTP structure with other viral RdRp-GTP structures shows that GTP binds jRdRp in a novel conformation. Apo-jRdRp structure suggests that the conserved motif F of jRdRp occupies multiple conformations in absence of GTP. Motif F becomes ordered on GTP binding and occludes the nucleotide triphosphate entry tunnel. Mutational analysis of key residues that interact with GTP evinces that the jRdRpGTP structure represents a novel pre-initiation state. Also, binding studies show that GTP binding reduces affinity of RdRp for RNA, but the presence of the catalytic Mn2+ ion abolishes this inhibition. Collectively, these observations suggest that the observed pre-initiation state may serve as a checkpoint to prevent erroneous template-independent RNA synthesis by jRdRp during initiation. © 2013 The Author(s). Published by Oxford University Press.

Raghavan S.,Indian Institute of Science
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

A kinetic model has been developed for dislocation bending at the growth surface in compressively stressed low-mobility films such as III-V nitrides. It is based on a reduction in the number of atoms at the growth surface. Stress and nonstress sources of driving force for such a reduction are discussed. A comparison between the derived equations and experimentally measured stress evolution data yields good agreement between the predicted and observed angles through which dislocations bend. © 2011 American Physical Society.

Paul A.,Indian Institute of Science
Journal of Materials Science: Materials in Electronics | Year: 2011

Often, wrong conclusions about the mobilities of species are drawn from the position of the Kirkendall marker plane or voids in the interdiffusion zone. To clarify, I have discussed the growth mechanism of the phases and the position of the marker plane depending on the relative mobilities of the species. The formation of different kinds of voids in the interdiffusion zone is discussed. Further, the microstructure that could be found because of the Kirkendall effect is also explained.© Springer Science+Business Media, LLC 2010.

Evnin O.,Chulalongkorn University | Evnin O.,Vrije Universiteit Brussel | Krishnan C.,Indian Institute of Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Recent investigations have revealed powerful selection rules for resonant energy transfer between modes of nonlinear perturbations in global anti-de Sitter (AdS) space-time. It is likely that these selection rules are due to the highly symmetric nature of the underlying AdS background, though the precise relation has remained unclear. In this article, we demonstrate that the equation satisfied by the scalar field mode functions in AdSd+1 has a hidden SU(d) symmetry, and explicitly specify the multiplets of this SU(d) symmetry furnished by the mode functions. We also comment on the role this structure might play in explaining the selection rules. © 2015 American Physical Society.

Dutta J.,Indian Institute of Science
Astrophysical Journal | Year: 2015

The collapse of the primordial gas in the density regime ∼108-1010 cm-3 is controlled by the three-body H2 formation process, in which the gas can cool faster than free-fall time - a condition proposed as the chemothermal instability. We investigate how the heating and cooling rates are affected during the rapid transformation of atomic to molecular hydrogen. With a detailed study of the heating and cooling balance in a 3D simulation of Pop III collapse, we follow the chemical and thermal evolution of the primordial gas in two dark matter minihalos. The inclusion of sink particles in modified Gadget-2 smoothed particle hydrodynamics code allows us to investigate the long-term evolution of the disk that fragments into several clumps. We find that the sum of all the cooling rates is less than the total heating rate after including the contribution from the compressional heating (pdV). The increasing cooling rate during the rapid increase of the molecular fraction is offset by the unavoidable heating due to gas contraction. We conclude that fragmentation occurs because H2 cooling, the heating due to H2 formation and compressional heating together set a density and temperature structure in the disk that favors fragmentation, not the chemothermal instability. © 2015. The American Astronomical Society. All rights reserved..

Govindu V.M.,Indian Institute of Science | Pooja A.,Amazon
IEEE Transactions on Image Processing | Year: 2014

In this paper, we present an extension of the iterative closest point (ICP) algorithm that simultaneously registers multiple 3D scans. While ICP fails to utilize the multiview constraints available, our method exploits the information redundancy in a set of 3D scans by using the averaging of relative motions. This averaging method utilizes the Lie group structure of motions, resulting in a 3D registration method that is both efficient and accurate. In addition, we present two variants of our approach, i.e., a method that solves for multiview 3D registration while obeying causality and a transitive correspondence variant that efficiently solves the correspondence problem across multiple scans. We present experimental results to characterize our method and explain its behavior as well as those of some other multiview registration methods in the literature. We establish the superior accuracy of our method in comparison to these multiview methods with registration results on a set of well-known real datasets of 3D scans. © 2013 IEEE.

Rangaprakash D.,Indian Institute of Science
Computers in Biology and Medicine | Year: 2014

Real world biological systems such as the human brain are inherently nonlinear and difficult to model. However, most of the previous studies have either employed linear models or parametric nonlinear models for investigating brain function. In this paper, a novel application of a nonlinear measure of phase synchronization based on recurrences, correlation between probabilities of recurrence (CPR), to study connectivity in the brain has been proposed. Being non-parametric, this method makes very few assumptions, making it suitable for investigating brain function in a data-driven way. CPR's utility with application to multichannel electroencephalographic (EEG) signals has been demonstrated. Brain connectivity obtained using thresholded CPR matrix of multichannel EEG signals showed clear differences in the number and pattern of connections in brain connectivity between (a) epileptic seizure and pre-seizure and (b) eyes open and eyes closed states. Corresponding brain headmaps provide meaningful insights about synchronization in the brain in those states. K-means clustering of connectivity parameters of CPR and linear correlation obtained from global epileptic seizure and pre-seizure showed significantly larger cluster centroid distances for CPR as opposed to linear correlation, thereby demonstrating the superior ability of CPR for discriminating seizure from pre-seizure. The headmap in the case of focal epilepsy clearly enables us to identify the focus of the epilepsy which provides certain diagnostic value. © 2013 Elsevier Ltd.

Banerjee S.,Harish Chandra Research Institute | Mitra M.,Indian Institute of Science | Spannowsky M.,Durham University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We study the discovery prospects of a heavy neutral scalar arising from a U(1)B-L extension of the Standard Model (SM) during the Large Hadron Collider's high luminosity runs (HL-LHC). This heavy neutral scalar mixes with the SM Higgs boson through a Higgs portal and interacts with the SM particles with an interaction strength proportional to the sine of the mixing angle. The mixing between the two Higgs bosons is constrained by direct and indirect measurements. We choose an experimentally viable mixing angle and explore in detail the ZZ and WW decay modes of the heavy Higgs boson. For the ZZ case, we focus on the cleanest 4 and 2 2j final states and find that a heavy Higgs boson of mass smaller than 500 GeV can be discovered at the HL-LHC. For the WW decay mode, we analyze the jjET signature. We implement novel background reduction techniques in order to tackle the huge background by performing both cut-based and multivariate analyses. However, large backgrounds render this channel challenging. We briefly discuss the discovery prospects of the heavy Z′-boson arising in this model. © 2015 American Physical Society.

Das D.,University of California at San Diego | Datta S.,Indian Institute of Science
Physical Review Letters | Year: 2015

We show the presence of universal features in the entanglement entropy of regularized boundary states for (1+1)D conformal field theories on a circle when the reduced density matrix is obtained by tracing over right- or left-moving modes. We derive a general formula for the left-right entanglement entropy in terms of the central charge and the modular S matrix of the theory. When the state is chosen to be an Ishibashi state, this measure of entanglement is shown to precisely reproduce the spatial entanglement entropy of a (2+1)D topological quantum field theory. We explicitly evaluate the left-right entanglement entropies for the Ising model, the tricritical Ising model and the su^(2)k Wess-Zumino-Witten model as examples. © 2015 American Physical Society.

Roychowdhury D.,Indian Institute of Science
Journal of High Energy Physics | Year: 2015

Abstract: In this paper, using the Gauge/gravity duality techniques, we explore the hydrodynamic regime of a very special class of strongly coupled QFTs that come up with an emerging UV length scale in the presence of a negative hyperscaling violating exponent. The dual gravitational counterpart for these QFTs consists of scalar dressed black brane solutions of exactly integrable Einstein-scalar gravity model with Domain Wall (DW) asymptotics. In the first part of our analysis we compute the R-charge diffusion for the boundary theory and find that (unlike the case for the pure AdS4 black branes) it scales quite non trivially with the temperature. In the second part of our analysis, we compute the η/s ratio both in the non extremal as well as in the extremal limit of these special class of gauge theories and it turns out to be equal to 1/4π in both the cases. These results therefore suggest that the quantum critical systems in the presence of (negative) hyperscaling violation at UV, might fall under a separate universality class as compared to those conventional quantum critical systems with the usual AdS4 duals. © 2015, The Author(s).

Roychowdhury D.,Indian Institute of Science
Journal of High Energy Physics | Year: 2015

Abstract: In this paper, based on the holographic techniques, we explore the hydrodynamics of charge diffusion phenomena in non commutative N=4$$\mathcal{N}=4$$ SYM plasma at strong coupling. In our analysis, we compute the R charge diffusion rates both along commutative as well as the non commutative coordinates of the brane. It turns out that unlike the case for the shear viscosity, the DC conductivity along the non commutative direction of the brane differs significantly from that of its cousin corresponding to the commutative direction of the brane. Such a discrepancy however smoothly goes away in the limit of the vanishing non commutativity. © 2015, The Author(s).

Roychowdhury D.,Indian Institute of Science
Nuclear Physics B | Year: 2015

In this paper, based on the AdS2/CFT1 prescription, we explore the low frequency behavior of quantum two point functions for a special class of strongly coupled CFTs in one dimension whose dual gravitational counterpart consists of extremal black hole solutions in higher derivative theories of gravity defined over an asymptotically AdS spacetime. The quantum critical points thus described are supposed to correspond to a very large value of the dynamic exponent (z→∞). In our analysis, we find that quantum fluctuations are enhanced due to the higher derivative corrections in the bulk which in turn increases the possibility of quantum phase transition near the critical point. On the field theory side, such higher derivative effects would stand for the corrections appearing due to the finite coupling in the gauge theory. Finally, we compute the coefficient of thermal diffusion at finite coupling corresponding to Gauss Bonnet corrected charged Lifshitz black holes in the bulk. We observe an important crossover corresponding to z=5 fixed point. © 2015 The Author.

Dutt Konar A.,Indian Institute of Science
Journal of Molecular Structure | Year: 2013

Reverse turns (commonly β-turns and γ-turns), a common motif in proteins and peptides, have attracted attention due to their relevance in a wide variety of biological processes. In an attempt to artificially imitate and stabilize these turns in short acyclic peptides, a series of N-terminally protected pseudopeptides comprising of an α-amino acid and conformationally constrained meta amino benzoic acid (mABA)/meta nitro aniline (mNA) (peptides I-VI) have been synthesized. The molecules were well characterized by various spectroscopic techniques and subjected to a systematic conformational analysis. Our experimental results reveal that only pseudopeptides I and II with methyl as the sidechain, tertiary butyloxy carbonyl as the N-terminal protecting group and (mABA)/(mNA) at the C-terminus adopt γ-turn conformations in solid state as well as in solution. Even slight modification of any of the stated conditions donot support the formation of this γ-turn architecture in the solid state. Interestingly, the peptides III-V which displays extended conformation in solid state forms γ-turn structure in solution. Thus this result reflects the importance of co-operative steric interactions amongst various amino acid residues in stabilizing a particular conformation in peptides in different phases (solid and solution). This report may open a new avenue in introducing γ-turn motifs within the bioactive conformation of selected peptides. © 2012 Elsevier B.V. All rights reserved.

Ananth S.,Indian Institute of Science
International Journal of Modern Physics D | Year: 2010

Three of the four forces of Nature are described by quantum YangMills theories with remarkable precision. The fourth force, gravity, is described classically by the Einstein-Hilbert theory. There appears to be an inherent incompatibility between quantum mechanics and the Einstein-Hilbert theory which prevents us from developing a consistent quantum theory of gravity. The Einstein-Hilbert theory is therefore believed to differ greatly from Yang-Mills theory (which does have a sensible quantum mechanical description). It is therefore very surprising that these two theories actually share close perturbative ties. This essay focuses on these ties between YangMills theory and the EinsteinHilbert theory. We discuss the origin of these ties and their implications for a quantum theory of gravity. © 2010 World Scientific Publishing Company.

Banerjee D.,Indian Institute of Science | Williams J.C.,University of North Texas | Williams J.C.,Ohio State University
Acta Materialia | Year: 2013

The basic framework and - conceptual understanding of the metallurgy of Ti alloys is strong and this has enabled the use of titanium and its alloys in safety-critical structures such as those in aircraft and aircraft engines. Nevertheless, a focus on cost-effectiveness and the compression of product development time by effectively integrating design with manufacturing in these applications, as well as those emerging in bioengineering, has driven research in recent decades towards a greater predictive capability through the use of computational materials engineering tools. Therefore this paper focuses on the complexity and variety of fundamental phenomena in this material system with a focus on phase transformations and mechanical behaviour in order to delineate the challenges that lie ahead in achieving these goals. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Suneeta V.,Indian Institute of Science
Classical and Quantum Gravity | Year: 2015

Fateev's sausage sigma models in two and three dimensions are known to be integrable. We study their stability under renormalization group (RG) flow in the target space by using results from the mathematics of Ricci flow. We show that the three-dimensional sausage is unstable, whereas the two-dimensional sausage appears to be stable at least at leading order as it approaches the sphere. We speculate that the stability results obtained are linked to the classification of ancient solutions to Ricci flow (i.e., sigma models that are nonperturbative in the infrared regime) in two and three dimensions. We also describe a class of perturbations of the three-dimensional sausage (with the same continuous symmetries) which remarkably decouple. This indicates that there could be a new solution to RG flow, which is described at least perturbatively as a deformation of the sausage. © 2015 IOP Publishing Ltd.

Arun S.P.,Indian Institute of Science
Vision Research | Year: 2012

Our everyday visual experience frequently involves searching for objects in clutter. Why are some searches easy and others hard? It is generally believed that the time taken to find a target increases as it becomes similar to its surrounding distractors. Here, I show that while this is qualitatively true, the exact relationship is in fact not linear. In a simple search experiment, when subjects searched for a bar differing in orientation from its distractors, search time was inversely proportional to the angular difference in orientation. Thus, rather than taking search reaction time (RT) to be a measure of target-distractor similarity, we can literally turn search time on its head (i.e. take its reciprocal 1/RT) to obtain a measure of search dissimilarity that varies linearly over a large range of target-distractor differences. I show that this dissimilarity measure has the properties of a distance metric, and report two interesting insights come from this measure: First, for a large number of searches, search asymmetries are relatively rare and when they do occur, differ by a fixed distance. Second, search distances can be used to elucidate object representations that underlie search - for example, these representations are roughly invariant to three-dimensional view. Finally, search distance has a straightforward interpretation in the context of accumulator models of search, where it is proportional to the discriminative signal that is integrated to produce a response. This is consistent with recent studies that have linked this distance to neuronal discriminability in visual cortex. Thus, while search time remains the more direct measure of visual search, its reciprocal also has the potential for interesting and novel insights. © 2012 Elsevier Ltd.

Banerjee J.,Indian Institute of Science | Nilsen-Hamilton M.,Iowa State University
Journal of Molecular Medicine | Year: 2013

Aptamers are single-stranded oligonucleotides that fold into well-defined three-dimensional shapes, allowing them to bind their targets with high affinity and specificity. They can be generated through an in vitro process called "Systemic Evolution of Ligands by Exponential Enrichment" and applied for specific detection, inhibition, and characterization of various targets like small organic and inorganic molecules, proteins, and whole cells. Aptamers have also been called chemical antibodies because of their synthetic origin and their similar modes of action to antibodies. They exhibit significant advantages over antibodies in terms of their small size, synthetic accessibility, and ability to be chemically modified and thus endowed with new properties. The first generation of aptamer drug "Macugen" was available for public use within 25 years of the discovery of aptamers. With others in the pipeline for clinical trials, this emerging field of medical biotechnology is raising significant interest. However, aptamers pose different problems for their development than for antibodies that need to be addressed to achieve practical applications. It is likely that current developments in aptamer engineering will be the basis for the evolution of improved future bioanalytical and biomedical applications. The present review discusses the development of aptamers for therapeutics, drug delivery, target validation and imaging, and reviews some of the challenges to fully realizing the promise of aptamers in biomedical applications. © 2013 Springer-Verlag Berlin Heidelberg.

Sahoo R.R.,Indian Central Mechanical Engineering Research Institute | Biswas S.K.,Indian Institute of Science
Tribology Letters | Year: 2014

Lithium stearate soap and layered MoS2 nanoparticles encapsulated in lithium stearate soap are prepared in the laboratory, and their lubricating properties are compared with respect to the particle and particle concentration. The tribotracks after friction test was investigated with Raman Spectroscopy, scanning electron microscopy (SEM) and 3D optical profilometry to understand the action mechanism. The status of the soap particles on a tribotrack changes with time, contact pressure and sliding speed. At low pressure and speed, individual solid undeformed soap particle stand proud of the surface and the topography shows marginal difference with sliding time. In these conditions, no frictional difference between the performance of grease with and without the nanoparticles is observed. Increasing the contact pressure and temperature (low speed and high speed) has a dramatic effect as the soap particles melt and the liquid soap flows over the track releasing the hitherto encapsulated nanoparticles. Consequently, the soap smears the track like a liquid, and the nanoparticles now come directly into the interface and are sheared to generate a low-friction tribofilm. At high particle concentration, the sliding time required for melting of the soap and release of MoS2 is reduced, and the tribofilm is more substantial and uniform consisting of smeared MoS2 and carboxylate soap as observed by SEM and 3D optical profilometry. A change in the Raman Spectra is observed with particle concentration, and this is related to morphology and microstructure of the tribofilm generated. © Springer Science+Business Media New York 2013.

Kapri R.,Indian Institute of Science
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

Using Monte Carlo simulations, we study the hysteresis in the unzipping of double-stranded DNA whose ends are subjected to a time-dependent periodic force with frequency (ω) and amplitude (G). For the static force, i.e., ω→0, the DNA is in equilibrium with no hysteresis. On increasing ω, the area of the hysteresis loop initially increases and becomes maximum at frequency ω∗(G), which depends on the force amplitude G. If the frequency is increased further, we find that for lower amplitudes the loop area decreases monotonically to zero, but for higher amplitudes it has an oscillatory component. The height of subsequent peaks decreases, and finally the loop area becomes zero at very high frequencies. The number of peaks depends on the length of the DNA. We give a simple analysis to estimate the frequencies at which maxima and minima occur in the loop area. We find that the area of the hysteresis loop scales as 1/ω in the high-frequency regime, whereas it scales as Gαωβ with exponents α=1 and β=5/4 at low frequencies. The values of the exponents α and β are different from the exponents reported earlier based on the hysteresis of small hairpins. © 2014 American Physical Society. ©2014 American Physical Society.

Balaram P.,Indian Institute of Science
Biopolymers | Year: 2010

The design of folded structures in peptides containing the higher homologues of α-amino acid residues requires the restriction of the range of local conformational choices. In α-amino acids stereochemically constrained residues like α,α-dialkylated residue, aminoisobutyric acid (Aib), and D-Proline ((D)Pro) have proved extremely useful in the design of helices and hairpins in short peptides. Extending this approach, backbone substitution and cyclization are anticipated to be useful in generating conformationally constrained β- and γ-residues. This brief review provides a survey of work on hybrid peptide sequences concerning the conformationally constrained γ-amino acid residue 1-aminomethyl cyclohexane acetic acid, gabapentin (Gpn). This achiral, β,β-disubstituted, γ-residue strongly favors gauche-gauche conformations about the C(α)-C(β) (θ(2)) and C(β)-C(γ) (θ(1)) bonds, facilitating local folding. The Gpn residue can adopt both C(7) (NH(i)→CO(i)) and C(9) (CO(i-1)←NH(i+1)) hydrogen bonds which are analogous to the C(5) and C(7) (γ-turn) conformations at α-residues. In conjunction with adjacent residues, Gpn may be used in αγ and γα segments to generate C(12) hydrogen bonded conformations which may be considered as expanded analogs of conventional β-turns. The structural characterization of C(12) helices, C(12)/C(10) helices with mixed hydrogen bond directionalities and β-hairpins incorporating Gpn residues at the turn segment is illustrated. 2010 Wiley Periodicals, Inc.

Roy A.K.,Indian Institute of Science
Few-Body Systems | Year: 2014

Bound states of hyperbolic potential is investigated by means of a generalized pseudospectral method. Significantly improved eigenvalues, eigenfunctions are obtained efficiently for arbitrary n, ℓ quantum states by solving the relevant non-relativistic Schrödinger equation allowing a non-uniform, optimal spatial discretization. Eigenvalues accurate up to tenth decimal place are reported for a large range of potential parameters; thus covering a wide range of interaction. Excellent agreement with available literature results is observed in all occasions. Special attention is paid for higher states. Some new states are given. Energy variations with respect to parameters in the potential are studied in considerable detail for the first time. © 2013 Springer-Verlag Wien.

Debnath U.,Indian Institute of Science
Advances in High Energy Physics | Year: 2014

We have assumed FRW model of the universe in Einstein-Aether gravity filled with dark matter and modified Chaplygin gas (MCG) type dark energy. We present the Hubble parameter in terms of some unknown parameters and observational parameters with the redshift z. From observed Hubble data (OHD) set (12 points), we have obtained the bounds of the arbitrary parameters (A,B) of MCG by minimizing the χ2 test. Next due to joint analysis of BAO and CMB observations, we have also obtained the best fit values and the bounds of the parameters (A,B) by fixing some other parameters. We have also taken type Ia supernovae data set (union 2 data set with 557 data points). Next due to joint analysis with SNe, we have obtained the best fit values of parameters. The best fit values and bounds of the parameters are obtained by 66%, 90%, and 99% confidence levels for OHD, OHD + BAO, OHD + BAO + CMB, and OHD + BAO + CMB + SNe joint analysis. The distance modulus z against redshift z for our theoretical MCG model in Einstein-Aether gravity has been tested for the best fit values of the parameters and the observed SNe Ia union2 data sample. © 2014 Ujjal Debnath.

Tibrewala R.,Indian Institute of Science
Classical and Quantum Gravity | Year: 2014

Loop quantum gravity corrections, in the presence of inhomogeneities, can lead to a deformed constraint algebra. Such a deformation implies that the effective theory is no longer generally covariant. As a consequence, the geometrical concepts used in the classical theory lose their meaning. In the present paper we propose a method, based on canonical transformation on the phase space of the spherically symmetric effective theory, to systematically recover the classical constraint algebra in the presence of the inverse triad corrections as well as in the presence of the holonomy corrections. We show, by way of explicit example, that this also leads to the recovery of general covariance of the theory in the presence of inverse triad corrections, implying that one can once again use the geometrical concepts to analyze the solutions in the presence of these quantum gravity corrections. © 2014 IOP Publishing Ltd.

Borges R.M.,Indian Institute of Science
Current Opinion in Insect Science | Year: 2015

The nursery pollination mutualism between figs and pollinating fig wasps is based on adaptations that allow wasps to enter the enclosed inflorescences of figs, to facilitate seed set, and to have offspring that develop within the nursery and that leave to enter other inflorescences for pollination. This closed mutualistic system is not immune to parasitic fig wasps. Although the life histories and basic biology of the mutualists have been investigated, the biology of the fig wasp parasites has been severely neglected. This review brings together current knowledge of the many different ways in which parasites can enter the system, and also points to the serious lacunae in our understanding of the intricate interactions between gallers, kleptoparasites, seed eaters and parasitoids within this mutualism. © 2015 Elsevier Inc. All rights reserved.

Roy A.K.,Indian Institute of Science
Modern Physics Letters A | Year: 2014

Spherical confinement in three-dimensional (3D) harmonic, quartic and other higher oscillators of even order is studied. The generalized pseudospectral (GPS) method is employed for accurate solution of relevant Schrödinger equation in an optimum, non-uniform radial grid. Eigenvalues, eigenfunctions, position expectation values, radial densities in low-and high-lying states are presented in case of small, intermediate and large confinement radius. The degeneracy breaking in confined situation as well as correlation in its energy ordering with respect to the respective unconfined counterpart is discussed. For all instances, current results agree excellently with the best available literature results. Many new states are reported here for the first time. In essence, a simple, efficient method is provided for accurate solution of 3D polynomial potentials enclosed within the spherical impenetrable walls. © 2014 World Scientific Publishing Company.

Nanda K.K.,Indian Institute of Science
Journal of Chemical Physics | Year: 2010

We comment on the paradox that seems to exist about a correlation between the size-dependent melting temperature and the forbidden energy gap of nanoparticles. By analyzing the reported expressions for the melting temperature and the band gap of nanoparticles, we conclude that there exists a relation between these two physical quantities. However, the variations of these two quantities with size for semiconductors are different from that of metals. © 2010 American Institute of Physics.

Roychowdhury D.,Indian Institute of Science
Journal of High Energy Physics | Year: 2014

In this paper based on the basic principles of gauge/gravity duality we compute the hall viscosity to entropy ratio in the presence of various higher derivative corrections to the dual gravitational description embedded in an asymptotically AdS4 space time. As the first step of our analysis, considering the back reaction we impose higher derivative corrections to the abelian gauge sector of the theory where we notice that the ratio indeed gets corrected at the leading order in the coupling. Considering the probe limit as a special case we compute this leading order correction over the fixed background of the charged black brane solution. Finally we consider higher derivative (R2) correction to the gravity sector of the theory where we notice that the above ratio might get corrected at the sixth derivative level. © The Authors.

Roychowdhury D.,Indian Institute of Science
Journal of High Energy Physics | Year: 2014

In this paper, based on the AdS4/CFT3 duality, we have explored the precise connection between the abelian Chern-Simons (CS) Higgs model in (2 + 1) dimensions to that with its dual gravitational counterpart living in one higher dimension. It has been observed that theU(1)current computed at the boundary of the AdS4 could be expressed as the local function of the vortex solution that has the remarkable structural similarity to that with the Ginzburg-Landau (GL) type local expression for the current associated with the Maxwell-CS type vortices in (2 + 1) dimensions. In order to explore this duality a bit further we have also computed the coherence length as well as the magnetic penetration depth associated with these vortices. Finally using the knowledge of both the coherence length as well as the magnetic penetration depth we have computed the Ginzburg-Landau coefficient for the Maxwell-CS type vortices in (2 + 1) dimensions. © The Authors.

Venkatapathi M.,Indian Institute of Science
Journal of the Optical Society of America B: Optical Physics | Year: 2014

Optical emission from emitters strongly interacting among themselves and also with other polarizable matter in close proximity has been approximated by emission from independent emitters. This is primarily due to our inability to evaluate the self-energy matrices and radiative properties of the collective eigenstates of emitters in heterogeneous ensembles. A method to evaluate self-energy matrices that is not limited by the geometry and material composition is presented to understand and exploit such collective excitations. Numerical evaluations using this method are used to highlight the significant differences between independent and the collective modes of emission in nanoscale heterostructures. A set of N Lorentz emitters and other polarizable entities is used to represent the coupled system of a generalized geometry in a volume integral approach. Closed form relations between the Green tensors of entity pairs in free space and their correspondents in a heterostructure are derived concisely. This is made possible for general geometries because the global matrices consisting of all free-space Green dyads are subject to conservation laws. The self-energy matrix can then be assembled using the evaluated Green tensors of the heterostructure, but a decomposition of its components into their radiative and nonradiative decay contributions is nontrivial. The relations to compute the observables of the eigenstates (such as quantum efficiency, power/energy of emission, radiative and nonradiative decay rates) are presented. A note on extension of this method to collective excitations, which also includes strong interactions with a surface in the near-field, is added. © 2014 Optical Society of America

Kapri R.,Indian Institute of Science
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

We study by using Monte Carlo simulations the hysteresis in unzipping and rezipping of a double stranded DNA (dsDNA) by pulling its strands in opposite directions in the fixed force ensemble. The force is increased at a constant rate from an initial value g 0 to some maximum value g m that lies above the phase boundary and then decreased back again to g 0. We observed hysteresis during a complete cycle of unzipping and rezipping. We obtained probability distributions of work performed over a cycle of unzipping and rezipping for various pulling rates. The mean of the distribution is found to be close (the difference being within 10%, except for very fast pulling) to the area of the hysteresis loop. We extract the equilibrium force versus separation isotherm by using the work theorem on repeated nonequilibrium force measurements. Our method is capable of reproducing the equilibrium and the nonequilibrium force-separation isotherms for the spontaneous rezipping of dsDNA. © 2012 American Physical Society.

Rana N.K.,Indian Institute of Technology Kanpur | Singh V.K.,Indian Institute of Technology Kanpur | Singh V.K.,Indian Institute of Science
Organic Letters | Year: 2011

Organocatalytic conjugate addition of thiols to R-substituted N-acryloyloxazolidin-2-ones followed by asymmetric protonation has been studied in the presence of cinchona alkaloid derived thioureas. Both of the enantiomers are accessible with the same level of enantioselectivity using pseudoenantiomeric quinine/quinidine derived catalysts. The addition/protonation products have been converted to useful biologically active molecules. ©2011 American Chemical Society.

Barpanda P.,Indian Institute of Science
Chemistry of Materials | Year: 2016

Rechargeable batteries have been the torchbearer electrochemical energy storage devices empowering small-scale electronic gadgets to large-scale grid storage. Complementing the lithium-ion technology, sodium-ion batteries have emerged as viable economic alternatives in applications unrestricted by volume/weight. What is the best performance limit for new-age Na-ion batteries? This mission has unravelled suites of oxides and polyanionic positive insertion (cathode) compounds in the quest to realize high energy density. Economically and ecologically, iron-based cathodes are ideal for mass-scale dissemination of sodium batteries. This Perspective captures the progress of Fe-containing earth-abundant sodium battery cathodes with two best examples: (i) an oxide system delivering the highest capacity (∼200 mA h/g) and (ii) a polyanionic system showing the highest redox potential (3.8 V). Both develop very high energy density with commercial promise for large-scale applications. Here, the structural and electrochemical properties of these two cathodes are compared and contrasted to describe two alternate strategies to achieve the same goal, i.e., improved energy density in Fe-based sodium battery cathodes. © 2016 American Chemical Society.

Mukhopadhyay S.,DNA Diagnostics Center | Balaji K.N.,Indian Institute of Science
Tuberculosis | Year: 2011

India already has earned the dubious distinction of being one of the countries with the highest incidence of tuberculosis (TB). The conventional control measures have had little impact on the relentless march of the TB epidemic. Potential solutions to this problem include the development of new drugs and an effective TB vaccine. In this perspective, identification of the mycobacterial components that have important role(s) in the establishment of the infection assumes crucial importance. Mycobacterium tuberculosis is an intracellular pathogen and it resides inside the macrophage, which is considered to be the most important component of the immune system. M. tuberculosis possesses two highly polymorphic sets of genes called the PE and PPE families. These unique families of proteins account for about 10% of the mycobacterial genome and have drawn considerable interest from different schools of M. tuberculosis researchers across the globe. In this review, we discuss the importance of these proteins in the regulation of dendritic cell and macrophage immune-effector functions, as well as the relevance of these proteins in the clinical manifestation of TB. This information may be helpful to better understand the immunological importance of PE/PPE proteins and their roles in mycobacterial virulence. © 2011 Elsevier Ltd. All rights reserved.

Pradhan D.,Indian Institute of Science
Information Processing Letters | Year: 2012

For a fixed positive integer k, a k-tuple total dominating set of a graph G=(V,E) is a subset TDk of V such that every vertex in V is adjacent to at least k vertices of TDk. In minimum k-tuple total dominating set problem (Min k-Tuple Total Dom Set), it is required to find a k-tuple total dominating set of minimum cardinality and Decide Min k-Tuple Total Dom Set is the decision version of Min k-Tuple Total Dom Set problem. In this paper, we show that Decide Min k-Tuple Total Dom Set is NP-complete for split graphs, doubly chordal graphs and bipartite graphs. For chordal bipartite graphs, we show that Min k-Tuple Total Dom Set can be solved in polynomial time. We also propose some hardness results and approximation algorithms for Min k-Tuple Total Dom Set problem. © 2012 Elsevier B.V.

Narendar S.,Indian Defence Research And Development Laboratory | Gopalakrishnan S.,Indian Institute of Science
Composites Part B: Engineering | Year: 2012

In this paper, the thermal effects on the ultrasonic wave propagation characteristics of a nanoplate are studied based on the nonlocal continuum theory. The nonlocal governing equations are derived for the nanoplate under thermal environment. The axial stress caused by the thermal effects is considered. The wave propagation analysis is carried out using spectral analysis. The influences of the nonlocal small scale coefficient, the room or low temperature, the high temperature and the axial half wave numbers on the wave dispersion properties of nanoplate are also discussed. Numerical results show that the small scale effects and the thermal effects are significant for larger half wavenumbers. The results are qualitatively different from those obtained based on the local plate theory and thus, are important for the development of graphene-based nanodevices such as strain sensor, mass and pressure sensors, atomic dust detectors, and enhancer of surface image resolution. © 2011 Elsevier Ltd. All rights reserved.

Kodandapani N.,Indian Institute of Science
Fire Ecology | Year: 2013

Tropical dry forests and savannas constitute more than half of all tropical forests and grasslands, but little is known about forest fire regimes within these two extensive types of ecosystems. Forest fire regimes in a predominantly dry forest in India, the Nilgiri landscape, and a predominantly savanna ecosystem in the Sathyamangalam landscape, were examined. Remote sensing data were applied to delineate burned areas, determine fire size characteristics, and to estimate fire-rotation intervals. Belt transects (0.5 ha) were used to estimate forest structure, diversity, and fuel loads. Mean area burned, mean number of fires, and mean fire size per year were substantially higher in the Nilgiri landscape compared to the Sathyamangalam landscape. Mean fire-rotational interval was 7.1 yr in the Nilgiri landscape and 44.1 yr in the Sathyamangalam landscape. Tree (≥10 cm diameter at breast height) species diversity, tree density, and basal area were significantly higher in the Nilgiri landscape compared to the Sathyamangalam landscape. Total fuel loads were significantly higher in tropical dry and moist deciduous forests in the Nilgiri landscape, but total fuel loads were higher in the tropical dry thorn forests of theSathyamangalam landscape. Thus, the two landscapes revealed contrasting fire regimes and forest characteristics, with more and four-fold larger fires in the Nilgiri landscape. The dry forests and savannas could be maintained by a combination of factors, such as fire, grazing pressures, and herbivore populations. Understanding the factors maintaining these two ecosystems will be critical for their conservation.

Rizopoulos D.,Erasmus Medical Center | Ghosh P.,Indian Institute of Science
Statistics in Medicine | Year: 2011

Motivated by a real data example on renal graft failure, we propose a new semiparametric multivariate joint model that relates multiple longitudinal outcomes to a time-to-event. To allow for greater flexibility, key components of the model are modelled nonparametrically. In particular, for the subject-specific longitudinal evolutions we use a spline-based approach, the baseline risk function is assumed piecewise constant, and the distribution of the latent terms is modelled using a Dirichlet Process prior formulation. Additionally, we discuss the choice of a suitable parameterization, from a practitioner's point of view, to relate the longitudinal process to the survival outcome. Specifically, we present three main families of parameterizations, discuss their features, and present tools to choose between them. © 2011 John Wiley & Sons, Ltd.

Jog C.J.,Indian Institute of Science
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2013

The well-known Jeans criterion describes the onset of instabilities in an infinite, homogeneous, self-gravitating medium supported by pressure.Most realistic astrophysical systems, however, are not isolated - instead they are under the influence of an external field such as the tidal field due to a neighbour. Here, we do a linear perturbation analysis for a system in an external field and obtain a generalized dispersion relation that depends on the wavenumber, the sound speed and also the magnitude of the tidal field. A typical, disruptive tidal field is shown to make the system more stable against perturbations, and results in a higher effective Jeans wavelength. The minimum mass that can become unstable is then higher (super-Jeans) than the usual Jeans mass. Conversely, in a compressive tidal field, perturbations can grow even when the mass is lower (sub-Jeans). This approach involving the inclusion of tidal field opens up a new way of looking at instabilities in gravitating systems. The treatment is general and the simple analytical form of the modified Jeans criterion obtained makes it easily accessible. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Bagchi B.,Indian Institute of Science
Chemical Physics Letters | Year: 2012

Water brings its remarkable thermodynamic and dynamic anomalies in the pure liquid state to biological world where water molecules face a multitude of additional interactions that frustrate its hydrogen bond network. Yet the water molecules participate and control enormous number of biological processes in manners which are yet to be understood at a molecular level. We discuss thermodynamics, structure, dynamics and properties of water around proteins and DNA, along with those in reverse micelles. We discuss the roles of water in enzyme kinetics, in drug-DNA intercalation and in kinetic-proof reading (the theory of lack of errors in biosynthesis). We also discuss how water may play an important role in the natural selection of biomolecules. © 2012 Elsevier B.V. All rights reserved.

Gavara M.,Indian Institute of Science
Numerical Heat Transfer; Part A: Applications | Year: 2012

Three-dimensional numerical study of natural convection in a vertical channel with flush-mounted discrete heaters on opposite conductive substrate walls is carried out in the present work. Detailed flow and heat transfer characteristics are presented for various Grashof numbers. The heat transfer effects on one wall by the presence of heaters on its opposite wall is examined. It is found that heat transfer rates on one wall are increased by the presence of heaters on its opposite wall. The thermal boundary layers on the opposite walls complement each other for enhanced heat transfer. The effects of spacing between the heated walls, spacings between heaters and substrate conductivity on flow and heat transfer are examined. Existence of optimum spacings between the heated walls for maximum heat transfer and mass flow are observed. It is found that the heat transfer and fluid flow do not follow the same optimum spacings. Mass flow rate reaches maximum value at a wall spacing greater than the spacing for maximum heat transfer. This is because the interaction of thermal boundary layers on individual walls ceases at a lower spacing before the velocity boundary layers separate each other. It is found that increased spacings between heaters reduce individual heater temperatures provided the heaters close to exit on both substrates avail sufficient substrate potions on the exit side. Insufficient substrate portions between the exit heaters and the exit cause abnormal local temperature rise in the exit heaters which are the hottest ones among all the heaters. Optimal heater spacings exist for minimum hottest heater temperature rise. Correlations are presented for dimensionless mass flow rate, temperature maximum, and average Nusselt number. © 2012 Copyright Taylor and Francis Group, LLC.

Majumder B.,Indian Institute of Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

Very recently Ali et al. (2009) proposed a new generalized uncertainty principle (with a linear term in Plank length which is consistent with doubly special relativity and string theory. The classical and quantum effects of this generalized uncertainty principle (termed as modified uncertainty principle or MUP) are investigated on the phase space of a dilatonic cosmological model with an exponential dilaton potential in a flat Friedmann-Robertson-Walker background. Interestingly, as a consequence of MUP, we found that it is possible to get a late time acceleration for this model. For the quantum mechanical description in both commutative and MUP framework, we found the analytical solutions of the Wheeler-DeWitt equation for the early universe and compare our results. We have used an approximation method in the case of MUP. © 2011 American Physical Society.

Saha R.,Indian Institute of Science
Astrophysical Journal Letters | Year: 2011

In this Letter, we present a new method to estimate a foreground-cleaned cosmic microwave background (CMB) map at a resolution of 1° by minimizing the non-Gaussian properties of the cleaned map which arise dominantly due to diffuse foreground emission components from the Milky Way. We employ simple kurtosis statistic as the measure of non-Gaussian properties and perform a linear combination of five frequency maps provided by the Wilkinson Microwave Anisotropy Probe (WMAP) in its seven-year data release in such a way that the cleaned map has a minimum kurtosis which leads to a non-Gaussianity-minimized, foreground-cleaned CMB map. We validate the method by performing Monte Carlo simulations. To minimize any residual foreground contamination from the cleaned map we flag out the region near the galactic plane based upon results from simulations. Outside the masked region our new estimate of the CMB map matches well with the WMAP's Internal Linear Combination (ILC) map. A simple pseudo-Cl -based CMB TT power spectrum derived from the non-Gaussianity minimized map reproduces the earlier results of WMAP's power spectrum. An important advantage of the method is that it does not introduce any negative bias in angular power spectrum in the low multipole regime, unlike usual ILC method. Comparing our results with the previously published results we argue that CMB results are robust with respect to specific foreground removal algorithms employed. © 2011. The American Astronomical Society. All rights reserved.

Mandal S.K.,Indian Institute of Science | Roesky H.W.,University of Gottingen
Chemical Communications | Year: 2010

Interstellar space is among the most remarkable chemical laboratories in the universe. The existence of many unstable species with low-valent main group elements in the interstellar medium inspired us to investigate the feasibility of laboratory synthesis of such unstable molecules. Particularly the lighter Group 14 element carbon plays a very important role in space astrochemistry. Low-valent carbon as well as silicon were detected in the interstellar environment. This article describes our recent efforts in developing amazing chemistry of heavier low-valent Group 14 elements. This study unravels that the disproportionation pathway of the low-valent Group 14 elements can be arrested by using a sterically protected ligand, then one can artificially generate the situation observed in the interstellar surrounding where the chance of disproportionation is very low as the molecules are extremely dilute. © 2010 The Royal Society of Chemistry.

Mugesh G.,Indian Institute of Science
Current Chemical Biology | Year: 2013

Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one), a lipid-soluble organoselenium compound, exhibits numerous biological activities both in vitro and in vivo systems. This compound is undergoing clinical trials for a number of disease states such as stroke and hearing loss. It is known that ebselen exhibits glutathione peroxidase activity (GPx) and is a remarkable scavenger of reactive oxygen species (ROS) such as peroxynitrite (PN). The rate of the reaction between ebselen and PN has been shown to be about three orders of magnitude higher than that of naturally occurring small molecules, such as cysteine, methionine and ascorbate. It is also known that ebselen and related compounds effectively protect against lipid peroxidation induced by transition metal ions. However, the mechanism by which ebselen exerts its antioxidant activity and the importance of the cyclic selenazole moiety are still not well-understood. In this article, the complex chemical mechanisms involved in the antioxidant activity of ebselen and related compounds are discussed. © 2013 Bentham Science Publishers.

Chakraborty A.,Indian Institute of Science
Monthly Weather Review | Year: 2010

This study uses the European Centre for Medium-Range Weather Forecasts (ECMWF) model-generated high-resolution 10-day-long predictions for the Year of Tropical Convection (YOTC) 2008. Precipitation forecast skills of the model over the tropics are evaluated against the Tropical Rainfall Measuring Mission (TRMM) estimates. It has been shown that the model was able to capture the monthly to seasonal mean features of tropical convection reasonably. Northward propagation of convective bands over the Bay of Bengal was also forecasted realistically up to 5 days in advance, including the onset phase of the monsoon during the first half of June 2008. However, large errors exist in the daily datasets especially for longer lead times over smaller domains. For shorter lead times (less than 4-5 days), forecast errors are much smaller over the oceans than over land. Moreover, the rate of increase of errors with lead time is rapid over the oceans and is confined to the regions where observed precipitation shows large day-to-day variability. It has been shown that this rapid growth of errors over the oceans is related to the spatial pattern of near-surface air temperature. This is probably due to the one-way air-sea interaction in the atmosphere-only model used for forecasting. While the prescribed surface temperature over the oceans remain realistic at shorter lead times, the pattern and hence the gradient of the surface temperature is not altered with change in atmospheric parameters at longer lead times. It has also been shown that the ECMWF model had considerable difficulties in forecasting very low and very heavy intensity of precipitation over South Asia. The model has too few grids with "zero" precipitation and heavy (.40 mm day-1) precipitation. On the other hand, drizzle-like precipitation is too frequent in the model compared to that in the TRMM datasets. Further analysis shows that a major source of error in the ECMWF precipitation forecasts is the diurnal cycle over the South Asian monsoon region. The peak intensity of precipitation in the model forecasts over land (ocean) appear about 6 (9) h earlier than that in the observations. Moreover, the amplitude of the diurnal cycle is much higher in the model forecasts compared to that in the TRMM estimates. It has been seen that the phase error of the diurnal cycle increases with forecast lead time. The error in monthly mean 3-hourly precipitation forecasts is about 2-4 times of the error in the daily mean datasets. Thus, effort should be given to improve the phase and amplitude forecast of the diurnal cycle of precipitation from the model. © 2010 American Meteorological Society.

Gururaja K.V.,Indian Institute of Science
Zootaxa | Year: 2010

Reproductive modes in anurans are highly diverse despite external fertilization being a constraint. There are 39 reproductive modes documented so far (Wells, 2007). An apparently new reproductive mode is reported in a torrent frog, Micrixalus saxicola, an endemic and ancient anuran frog of the Western Ghats, considering the type of cavity made inside the lotic water body, involvement of the female in digging the cavity and concealing the eggs. Copyright © 2010 Magnolia Press.

Kesavardhana S.,Indian Institute of Science | Varadarajan R.,Jawaharlal Nehru Centre for Advanced Scientific Research
Journal of virology | Year: 2014

UNLABELLED: The HIV-1 envelope glycoprotein (Env) is a trimer of gp120-gp41 heterodimers and is essential for viral entry. The gp41 subunit in native, prefusion trimeric Env exists in a metastable conformation and attains a stable six-helix bundle (6-HB) conformation comprised of a trimer of N-heptad repeat (NHR) and C-heptad repeat (CHR) heterodimers, that drives the fusion of viral and cellular membranes. We attempted to stabilize native Env trimers by incorporation of mutations at the NHR-CHR interface that disrupt the postfusion 6-HB of gp41. The mutations V570D and I573D stabilize native Env of the HIV-1 JRFL strain and occlude nonneutralizing epitopes to a greater extent than the previously identified I559P mutation that is at the interface of the NHR trimers in the 6-HB. The mutations prevent soluble-CD4 (sCD4)-induced gp120 shedding and 6-HB formation. In the context of cell surface-expressed JRFL Env, introduction of a previously reported additional disulfide between residues A501 and T605 perturbs the native conformation, though this effect is partially alleviated by furin coexpression. The data suggest that positions 570 and 573 are surface proximal in native Env and that the NHR homotrimeric coiled coil in native Env terminates before or close to residue 573. Aspartic acid substitutions at these positions stabilize native trimers through destabilization of the postfusion 6-HB conformation. These mutations can be used to stabilize Env in a DNA vaccine format.IMPORTANCE: The major protein on the surface of HIV-1 is the envelope (Env) glycoprotein. Env is a trimer of gp120-gp41 heterodimers. gp120 is involved in receptor/coreceptor binding and gp41 in the fusion of viral and cellular membranes. Like many other viral fusion proteins, the gp41 subunit in native trimeric Env exists in a metastable conformation. gp41 readily forms a stable six-helix bundle (6-HB) conformation comprised of a trimer of N-heptad repeat (NHR) and C-heptad repeat (CHR) heterodimers that drives fusion of viral and cellular membranes. While it is expected that native Env is a good immunogen, its metastability results in exposure of immunodominant nonneutralizing epitopes. In the present study, we stabilize native Env trimers by incorporation of a number of different mutations at the NHR-CHR interface that disrupt the postfusion 6-HB of gp41. The stabilized constructs described here can be incorporated into DNA vaccine candidates. Copyright © 2014, American Society for Microbiology. All Rights Reserved.

Kumaran V.,Indian Institute of Science
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

It is shown that the fluctuation-dissipation theorem is satisfied by the solutions of a general set of nonlinear Langevin equations with a quadratic free-energy functional (constant susceptibility) and field-dependent kinetic coefficients, provided the kinetic coefficients satisfy the Onsager reciprocal relations for the irreversible terms and the antisymmetry relations for the reversible terms. The analysis employs a perturbation expansion of the nonlinear terms, and a functional integral calculation of the correlation and response functions, and it is shown that the fluctuation-dissipation relation is satisfied at each order in the expansion. © 2011 American Physical Society.

Desiraju G.R.,Indian Institute of Science
Crystal Growth and Design | Year: 2011

Comments on aspects of the new definition of the hydrogen bond specific to crystal engineering are given.(Figure Presented) © 2011 American Chemical Society.

Das M.,Indian Institute of Science
Journal of Theoretical and Computational Chemistry | Year: 2012

The nature of electron transfer through intermolecular tunnel junctions has been studied. Intermolecular junctions feature non-hydrogen and hydrogen bonded interactions and are defined by the end groups of pairs of functionalized conjugated alkenes. We compared the distant dependent electron transfer from donor to acceptor group attached to the other sides of those functionalized conjugated alkenes. Study shows electron transfer coupling matrix element for these intermolecular junctions decays exponentially as a function of junction separation and quite substantial in energetically favourable hydrogen bonded intermolecular junctions. © 2012 World Scientific Publishing Company.

Venkatapathi M.,Indian Institute of Science
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2012

The altered spontaneous emission of an emitter near an arbitrary body can be elucidated using an energy balance of the electromagnetic field. From a classical point of view it is trivial to show that the field scattered back from any body should alter the emission of the source. But it is not at all apparent that the total radiative and non-radiative decay in an arbitrary body can add to the vacuum decay rate of the emitter (i.e.) an increase of emission that is just as much as the body absorbs and radiates in all directions. This gives us an opportunity to revisit two other elegant classical ideas of the past, the optical theorem and the Wheeler-Feynman absorber theory of radiation. It also provides us alternative perspectives of Purcell effect and generalizes many of its manifestations, both enhancement and inhibition of emission. When the optical density of states of a body or a material is difficult to resolve (in a complex geometry or a highly inhomogeneous volume) such a generalization offers new directions to solutions. © 2012 Elsevier Ltd.

Kashyap N.,Indian Institute of Science | Zemor G.,Institut Universitaire de France
IEEE Transactions on Information Theory | Year: 2014

In this paper, we revisit the combinatorial error model of Mazumdar et al. that models errors in high-density magnetic recording caused by lack of knowledge of grain boundaries in the recording medium. We present new upper bounds on the cardinality/rate of binary block codes that correct errors within this model. All our bounds, except for one, are obtained using combinatorial arguments based on hypergraph fractional coverings. The exception is a bound derived via an information-theoretic argument. Our bounds significantly improve upon existing bounds from the prior literature. © 2014 IEEE.

Ghosh D.,Indian Institute of Science | Ghanem R.,University of Southern California
International Journal for Numerical Methods in Engineering | Year: 2012

The repeated or closely spaced eigenvalues and corresponding eigenvectors of a matrix are usually very sensitive to a perturbation of the matrix, which makes capturing the behavior of these eigenpairs very difficult. Similar difficulty is encountered in solving the random eigenvalue problem when a matrix with random elements has a set of clustered eigenvalues in its mean. In addition, the methods to solve the random eigenvalue problem often differ in characterizing the problem, which leads to different interpretations of the solution. Thus, the solutions obtained from different methods become mathematically incomparable. These two issues, the difficulty of solving and the non-unique characterization, are addressed here. A different approach is used where instead of tracking a few individual eigenpairs, the corresponding invariant subspace is tracked. The spectral stochastic finite element method is used for analysis, where the polynomial chaos expansion is used to represent the random eigenvalues and eigenvectors. However, the main concept of tracking the invariant subspace remains mostly independent of any such representation. The approach is successfully implemented in response prediction of a system with repeated natural frequencies. It is found that tracking only an invariant subspace could be sufficient to build a modal-based reduced-order model of the system. © 2012 John Wiley & Sons, Ltd.

Mahalingam V.,Indian Institute of Science | Naccache R.,Concordia University at Montreal | Vetrone F.,University of Quebec | Capobianco J.A.,Concordia University at Montreal
Optics Express | Year: 2012

The white light emission of Tm3+/Yb3+/Ho 3+-doped GdVO4 nanocrystals, following excitation with near-infrared light (λexc = 980 nm), via a multiphoton upconversion process is presented. Upconverted blue emission from the Tm 3+ ions as well as green/red emissions from the Ho3+ ions contributes to the observed white light. The calculated Commission internationale de l'éclairage (CIE) color coordinates were calculated to be x = 0.34; y = 0.32 and lie at the center of the white region. Furthermore, the intensity of the upconverted white light was enhanced by the incorporation of monovalent Li+ ions into the GdVO4 matrix. An explanation for this enhancement is proposed based on X-ray diffraction and fluorescence lifetime measurements. © 2011 Optical Society of America.

Rajesh S.R.,Indian Institute of Science
Monthly Notices of the Royal Astronomical Society | Year: 2011

When the cold accretion disc coupling between neutral gas and a magnetic field is so weak that the magnetorotational instability is less effective or even stops working, it is of prime interest to investigate the pure hydrodynamic origin of turbulence and transport phenomena. As the Reynolds number increases, the relative importance of the non-linear term in the hydrodynamic equation increases. In an accretion disc where the molecular viscosity is too small, the Reynolds number is large enough for the non-linear term to have new effects. We investigate the scenario of the 'weakly non-linear' evolution of the amplitude of the linear mode when the flow is bounded by two parallel walls. The unperturbed flow is similar to the plane Couette flow, but with the Coriolis force included in the hydrodynamic equation. Although there is no exponentially growing eigenmode, because of the self-interaction, the least stable eigenmode will grow in an intermediate phase. Later, this will lead to higher-order non-linearity and plausible turbulence. Although the non-linear term in the hydrodynamic equation is energy-conserving, within the weakly non-linear analysis it is possible to define a lower bound of the energy (∝A 2 c, where A c is the threshold amplitude) needed for the flow to transform to the turbulent phase. Such an unstable phase is possible only if the Reynolds number ≥10 3-4. The numerical difficulties in obtaining such a large Reynolds number might be the reason for the negative result of numerical simulations on a pure hydrodynamic Keplerian accretion disc. © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Sharma N.,Indian Institute of Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We present a numerical analysis of helicity independent nucleon generalized parton distributions (GPDs) using the known formalism based on inclusion of higher Fock states in the soft-wall approach of the anti-de Sitter/QCD model. We calculate the momentum space GPDs by matching the electromagnetic form factors in the AdS model to the sum rules in QCD. We investigate their Mellin moments, transverse impact parameter GPDs, transverse mean square radius, and transverse width. We further extend this work to investigate the charge and anomalous magnetization densities for both unpolarized and transversely polarized nucleons. A comparison of results on density functions with phenomenological parametrization is also presented. © 2014 American Physical Society.

Iyer A.M.,Indian Institute of Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Planck scale lepton number violation is an interesting and natural possibility to explain nonzero neutrino masses. We consider such operators in the context of Randall-Sundrum (RS1) scenarios. Implementation of this scenario with a single Higgs localized on the IR brane (standard RS1) is not phenomenologically viable as they lead to inconsistencies in the charged lepton mass fits. In this paper we propose a setup with two Higgs doublets. We present a detailed numerical analysis of the fits to fermion masses and mixing angles. This model solves the issues regarding the fermion mass fits but solutions with consistent electroweak symmetry breaking are highly fine-tuned. A simple resolution is to consider supersymmetry in the bulk and a detailed discussion of which is provided. Constraints from flavor are found to be strong and minimal flavor violation (MFV) is imposed to alleviate them. © 2014 American Physical Society.

Datta S.,Indian Institute of Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We examine relative entropy in the context of the higher spin/CFT duality. We consider 3D bulk configurations in higher spin gravity which are dual to the vacuum and a high temperature state of a CFT with W-algebra symmetries in the presence of a chemical potential for a higher spin current. The relative entropy between these states is then evaluated using the Wilson line functional for holographic entanglement entropy. In the limit of small entangling intervals, the relative entropy should vanish for a generic quantum system. We confirm this behavior by showing that the difference in the expectation values of the modular Hamiltonian between the states matches with the difference in the entanglement entropy in the short-distance regime. Additionally, we compute the relative entropy of states corresponding to smooth solutions in the SL(2,Z) family with respect to the vacuum. © 2014 American Physical Society.

Mondal B.C.,University of California at Los Angeles | Mukherjee T.,University of California at Los Angeles | Mandal L.,University of California at Los Angeles | Mandal L.,Indian Institute of Science | And 4 more authors.
Cell | Year: 2011

Maintenance of a hematopoietic progenitor population requires extensive interaction with cells within a microenvironment or niche. In the Drosophila hematopoietic organ, niche-derived Hedgehog signaling maintains the progenitor population. Here, we show that the hematopoietic progenitors also require a signal mediated by Adenosine deaminase growth factor A (Adgf-A) arising from differentiating cells that regulates extracellular levels of adenosine. The adenosine signal opposes the effects of Hedgehog signaling within the hematopoietic progenitor cells and the magnitude of the adenosine signal is kept in check by the level of Adgf-A secreted from differentiating cells. Our findings reveal signals arising from differentiating cells that are required for maintaining progenitor cell quiescence and that function with the niche-derived signal in maintaining the progenitor state. Similar homeostatic mechanisms are likely to be utilized in other systems that maintain relatively large numbers of progenitors that are not all in direct contact with the cells of the niche. © 2011 Elsevier Inc.

Penmatsa A.,University of Oregon | Penmatsa A.,Indian Institute of Science | Wang K.H.,Amgen | Gouaux E.,Howard Hughes Medical Institute
Nature Structural and Molecular Biology | Year: 2015

Most antidepressants elicit their therapeutic benefits through selective blockade of Na + /Cl â -coupled neurotransmitter transporters. Here we report X-ray structures of the Drosophila melanogaster dopamine transporter in complexes with the polycyclic antidepressants nisoxetine or reboxetine. The inhibitors stabilize the transporter in an outward-open conformation by occupying the substrate-binding site. These structures explain how interactions between the binding pocket and substituents on the aromatic rings of antidepressants modulate drug-transporter selectivity. © 2015 Nature America, Inc. All rights reserved.

Konar A.D.,Indian Institute of Science
CrystEngComm | Year: 2012

Single crystal X-ray diffraction studies reveal that the two terminally protected tripeptides Boc-β-cyano-Ala-Aib-mABA-OMe (I) and Boc-β-hydroxy-Ala-Aib-mABA-OMe (II) with a centrally positioned non-coded amino acid Aib (α-aminoisobutyric acid) and a conformationally constrained mABA (meta-aminobenzoic acid) at the C-terminus, adopt a type II′ β-turn conformation in the solid state, rarely observed in tripeptides. Interestingly, the type II′ β-turn molecules of peptide I self-assemble to form a triple helical assemblage using hydrogen bonding and various non-covalent interactions in the solid state. In contrast, the tripeptide II, exhibiting conformational preference for a type II′ β-turn, does not support the formation of such a triple helical architecture. Instead a double helical assembly is formed, thus emphasizing the importance of the cyanomethyl moiety in triple helix stabilization. To date a significant amount of work has been performed in designing triple helical motifs either using metal co-ordinated complexes or rigid organic templates. However, to the best of our knowledge, this novel example is one of the very few reports of supramolecular triple helix design resulting from the self assembly of a tripeptide solely nucleated by conformational features, namely a type II′ β-turn in the synthesized tripeptides. This journal is © The Royal Society of Chemistry 2012.

Saxena M.,Indian Institute of Science
Cell death & disease | Year: 2011

Development of multidrug resistance (MDR) is a major deterrent in the effective treatment of metastatic cancers by chemotherapy. Even though MDR and cancer invasiveness have been correlated, the molecular basis of this link remains obscure. We show here that treatment with chemotherapeutic drugs increases the expression of several ATP binding cassette transporters (ABC transporters) associated with MDR, as well as epithelial-mesenchymal transition (EMT) markers, selectively in invasive breast cancer cells, but not in immortalized or non-invasive cells. Interestingly, the mere induction of an EMT in immortalized and non-invasive cell lines increased their expression of ABC transporters, migration, invasion, and drug resistance. Conversely, reversal of EMT in invasive cells by downregulating EMT-inducing transcription factors reduced their expression of ABC transporters, invasion, and rendered them more chemosensitive. Mechanistically, we demonstrate that the promoters of ABC transporters carry several binding sites for EMT-inducing transcription factors, and overexpression of Twist, Snail, and FOXC2 increases the promoter activity of ABC transporters. Furthermore, chromatin immunoprecipitation studies revealed that Twist binds directly to the E-box elements of ABC transporters. Thus, our study identifies EMT inducers as novel regulators of ABC transporters, thereby providing molecular insights into the long-standing association between invasiveness and MDR. Targeting EMT transcription factors could hence serve as novel strategies to curb both metastasis and the associated drug resistance.

Ghorai P.K.,Indian Institute of Science
Journal of Physical Chemistry B | Year: 2010

Molecular dynamics simulations are carried out to investigate the conformational preferences of n-butane inside a confined medium such as zeolite NaY. It is observed that n-butane has a higher gauche population inside the zeolite than in bulk. The dependence of trans and gauche conformations on temperature and concentration has also been studied. The percentage of gauche conformations inside zeolite increases with both temperature and concentration. It is identified that guest-guest interaction is the key factor for the enhancement of the gauche conformation inside a confined medium. Other related properties that depend on n-butane conformations are also computed and compared with iso-butane. © 2010 American Chemical Society.

Chaudhuri S.,Indian Institute of Science
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

Flame particles are mathematical points comoving with a reacting isoscalar surface in a premixed flame. In this Rapid Communication, we investigate mean square pair separation of flame particles as a function of time from their positions tracked in two sets of direct numerical simulation solutions of H2-air turbulent premixed flames with detailed chemistry. We find that, despite flame particles and fluid particles being very different concepts, a modified Batchelor's scaling of the form 〈|ΔF(t)-ΔF(0)|2〉=CF(〈ε〉0FΔ0F)2/3t2 holds for flame particle pair dispersion. The proportionality constant, however, is not universal and depends on the isosurface temperature value on which the flame particles reside. Following this, we attempt to analytically investigate the rationale behind such an observation. © 2015 American Physical Society.

Choudhury P.K.,Indian Institute of Science
Journal of physics. Condensed matter : an Institute of Physics journal | Year: 2011

The strikingly different charge transport behaviours in nanocomposites of multiwall carbon nanotubes (MWNTs) and conducting polymer polyethylenedioxythiophene-polystyrene-sulfonic-acid (PEDOT-PSS) at low temperatures are explained by probing their conformational properties using small-angle x-ray scattering (SAXS). The SAXS studies indicate the assembly of elongated PEDOT-PSS globules on the walls of nanotubes, coating them partially, thereby limiting the interaction between the nanotubes in the polymer matrix. This results in a charge transport governed mainly by small polarons in the conducting polymer despite the presence of metallic MWNTs. At T > 4 K, hopping of the charge carriers following one-dimensional variable range hopping is evident which also gives rise to a positive magnetoresistance (MR) with an enhanced localization length (∼5 nm) due to the presence of MWNTs. However, at T < 4 K, the observation of an unconventional positive temperature coefficient of resistivity is attributed to small polaron tunnelling. The exceptionally large negative MR observed in this temperature regime is conjectured to be due to the presence of quasi-1D MWNTs that can aid in lowering the tunnelling barrier across the nanotube-polymer boundary resulting in large delocalization. © 2011 IOP Publishing Ltd

Mandal S.K.,Indian Institute of Science | Roesky H.W.,University of Gottingen
Accounts of Chemical Research | Year: 2010

(Figure Presented) Assembling a molecule containing two metal centers with entirely different chemical properties remains a synthetic challenge. One of the major motivations for this chemistry is its ability to catalyze various organic transformations. The proximity between two different metals in a heterometallic complex allows more pronounced chemical communication between the metals and often leads to the modification of the fundamental properties of the individual metal atoms through the well-known cooperative interaction. Although various types of heterometallic systems are known, the M-O-M' framework is particularly important because it brings the metals into close proximity with each other. In this Account, we describe several suitable synthetic routes for the assembly of heterometals of entirely different chemical properties through an oxygen atom. The new synthetic strategies for the construction of heterobimetallic complexes take advantage of unprecedented syntheses of a number of hydroxide precursors of the type LMR(OH) [L = CH{N(Ar)(CMe)}2, Ar = 2,6-iPr 2C6H3; M = Al, Ga, or Ge; R = alkyl, aryl, or lone pair of electrons], [LSr(μ-OH)]2 · (THF)3, and Cp*2ZrMe(OH). We used the Brønsted acidic character of the proton in the M(O-H), Sr(O-H), or Zr(O-H) moiety, to build a new class of heterobimetallic complexes based on M-O-M' motif. This synthetic strategy assembles a main group element with another main group element, a transition metal, or a lanthanide metal. This synthetic development provides access to a new class of heterobimetallic complexes through oxygen bridging. In many cases these complexes prove to be excellent candidates for polymerization of monomers including ε-caprolactone, ethylene, and styrene. Some of these catalysts bear a chemically grafted methylalumoxane (MAO) unit in the backbone of an active metal center, which led to efficient ethylene polymerizations at an unusually low MAO concentration. We attribute this reactivity both to the presence of a chemically grafted (Me)Al-O backbone in the active catalysts (a part of externally added cocatalyst, MAO) and to the enhanced Lewis acidity from the bridging oxygen at the active metal center. In addition, we have demonstrated the development of heterometallic systems having two catalytically active centers. Such structures could aid in the development of a catalytic system bearing two active centers with different chemistries. © 2010 American Chemical Society.

Lee H.,Johns Hopkins University | Wang C.,Johns Hopkins University | Deshmukh S.S.,Johns Hopkins University | Deshmukh S.S.,Indian Institute of Science | Knierim J.J.,Johns Hopkins University
Neuron | Year: 2015

Classical theories of associative memory model CA3 as a homogeneous attractor network because of its strong recurrent circuitry. However, anatomical gradients suggest a functional diversity along the CA3 transverse axis. We examined the neural population coherence along this axis, when the local and global spatial reference frames were put in conflict with each other. Proximal CA3 (near the dentate gyrus), where the recurrent collaterals are the weakest, showed degraded representations, similar to the pattern separation shown by the dentate gyrus. Distal CA3 (near CA2), where the recurrent collaterals are the strongest, maintained coherent representations in the conflict situation, resembling the classic attractor network system. CA2 also maintained coherent representations. This dissociation between proximal and distal CA3 provides strong evidence that the recurrent collateral system underlies the associative network functions of CA3, with a separate role of proximal CA3 in pattern separation. © 2015 Elsevier Inc.

Venderbos J.W.F.,Leibniz Institute for Solid State and Materials Research | Daghofer M.,Leibniz Institute for Solid State and Materials Research | Van Den Brink J.,Leibniz Institute for Solid State and Materials Research | Kumar S.,Indian Institute of Science
Physical Review Letters | Year: 2012

We establish that the interplay of itinerant fermions with localized magnetic moments on a checkerboard lattice leads to magnetic flux phases. For weak itineracy the flux phase is coplanar and the electronic dispersion takes the shape of graphenelike Dirac fermions. Stronger itineracy drives the formation of a noncoplanar, chiral flux phase, in which the Dirac fermions acquire a topological mass that is proportional to a ferromagnetic spin polarization. Consequently the system self-organizes into a ferromagnetic quantum anomalous Hall state in which the direction of its dissipationless edge currents can be switched by an applied magnetic field. © 2012 American Physical Society.

Satyabala S.P.,Indian Institute of Science
Remote Sensing of Environment | Year: 2016

The Gangotri glacier is the largest in the Garhwal Himalaya, India and its melt water forms the main source stream of the Ganga River, yet its dynamics are poorly understood. Its long record of terminus retreat measurements (1800-present) shows multi-decadal oscillations and more recently a slowing down of the retreat. Its complex dynamics are also indicated by studies of proglacial melt-water at the terminus. However, there have been no systematic measurements of its surface velocity or how it changes seasonally or over longer-term time scales. Here, I have characterized the spatiotemporal variations of surface velocity of the Gangotri glacier using synthetic aperture radar (SAR) data spanning nearly two decades (1991-2011).The main findings are as follows: (1) The glacier undergoes seasonal fluctuations in surface velocities: there was a clear summer speedup of ~57%-126% compared to winter velocities between 0 and 12.6 km from the terminus, with peak summer speeds of 63.1 ± 5.4 m/yr in 1992, 66.6 ± 6.0 m/yr in 1999, 58.2 ± 4.5 m/yr in 2004 and 42.8 ± 4.2 m/yr in 2007 whereas winter speeds were relatively stable (25-30 m/yr) during the same period. This summer speedup is indicative of increased basal sliding, known to occur when melt-waters penetrate to the glacier bed resulting in reduced friction. (2) These summer velocities exhibited an inter-annual reduction, which was manifest as a reduction in summer speed up from >120% in 2004 to <60% in 2007. This pattern continued into 2011, despite the availability of abundant melt-water during those years. This inter-annual reduction indicates the formation of increasingly efficient melt-water channels year on year resulting in lesser lubrication at the glacier-bed interface.My results show that the Gangotri glacier is dynamic throughout its length with systematic spatiotemporal variations in surface velocity that elucidate its subglacial processes. Based on my results and other evidence in the literature, I propose that the subglacial drainage system of the Gangotri glacier is subject to seasonal and inter-annual hydrodynamic coupling between winters and melt-seasons akin to other glaciers. © 2016.

Roy A.K.,Indian Institute of Science
International Journal of Quantum Chemistry | Year: 2013

The generalized pseudospectral method is used to study the bound-state spectra of some of the exponentially screened Coulomb potentials, namely, the exponential cosine screened Coulomb (ECSC) and general exponential screened Coulomb (GESC) potential, with special emphasis on higher states and stronger interaction. Eigenvalues accurate up to 11 significant figures are obtained through a nonuniform optimal spatial discretization of the radial Schrödinger equation. All the 55 eigenstates of ECSC potential with n ≤ 10 and 36 eigenstates of GESC potential with n ≤ 8 are considered for arbitrary values of the screening parameter, covering a wide range of interaction. Excited states as high as up to n = 18 have been computed with high accuracy for the first time. Excellent agreement with the literature data has been observed in all cases. All the GESC eigenstates are calculated with much greater accuracy than the existing methods available in literature. Many l ≠ 0 states of this potential are reported here. In both cases, a detailed variation of energies with respect to the parameters in potential is monitored. © 2012 Wiley Periodicals, Inc.

Debnath U.,Indian Institute of Science
Annals of Physics | Year: 2016

We first review the accelerating, rotating and charged Plebanski–Demianski (PD) black hole, which includes the Kerr–Newman rotating black hole and the Taub-NUT spacetime. The main feature of this black hole is that it has 4 horizons like event horizon, Cauchy horizon and two accelerating horizons. In the non-extremal case, the surface area, entropy, surface gravity, temperature, angular velocity, Komar energy and irreducible mass on the event horizon and Cauchy horizon are presented for PD black hole. The entropy product, temperature product, Komar energy product and irreducible mass product have been found for event horizon and Cauchy horizon. Also their sums are found for both horizons. All these relations are dependent on the mass of the PD black hole and other parameters. So all the products are not universal for PD black hole. The entropy and area bounds for two horizons have been investigated. Also we found the Christodoulou–Ruffini mass for extremal PD black hole. Finally, using first law of thermodynamics, we also found the Smarr relation for PD black hole. © 2016 Elsevier Inc.

Tothadi S.,Indian Institute of Science
CrystEngComm | Year: 2014

Polymorphic cocrystals of urea:4,4′-bipyridine and salicylic acid:4,4′-bipyridine were obtained by crystallization from different solvents. The urea tape is a rare phenomenon in cocrystals but it is consistent in urea:4,4′-bipyridine polymorphic cocrystals. The polymorph obtained from MeCN has symmetrical N-H⋯N hydrogen bond distances on either side of the urea tape. However, the other form obtained from MeOH has unsymmetrical N-H⋯N hydrogen bond lengths. In the polymorphic cocrystals of salicylic acid:4,4′-bipyridine, the basic supramolecular synthon acid-pyridine is the same but the 3D packing is different. Both the polymorphic pairs of cocrystals come under the category of packing polymorphs. All polymorphs were characterized by single-crystal X-ray diffraction (SCXRD), PXRD, DSC, FT-IR and HSM. N-H⋯N and the acid-pyridine supramolecular synthons were insulated by FT-IR vibrational spectroscopy. This journal is © the Partner Organisations 2014.

Bagchi K.,St. Josephs College | Roy S.,Indian Institute of Science
Journal of Physical Chemistry B | Year: 2014

In addition to the biologically active monomer of the protein insulin circulating in human blood, the molecule also exists in dimeric and hexameric forms that are used as storage. The insulin monomer contains two distinct surfaces, namely, the dimer forming surface (DFS) and the hexamer forming surface (HFS), that are specifically designed to facilitate the formation of the dimer and the hexamer, respectively. In order to characterize the structural and dynamical behavior of interfacial water molecules near these two surfaces (DFS and HFS), we performed atomistic molecular dynamics simulations of insulin with explicit water. Dynamical characterization reveals that the structural relaxation of the hydrogen bonds formed between the residues of DFS and the interfacial water molecules is faster than those formed between water and that of the HFS. Furthermore, the residence times of water molecules in the protein hydration layer for both the DFS and HFS are found to be significantly higher than those for some of the other proteins studied so far, such as HP-36 and lysozyme. In particular, we find that more structured water molecules, with higher residence times (∼300-500 ps), are present near HFS than those near DFS. A significant slowing down is observed in the decay of associated rotational auto time correlation functions of O-H bond vector of water in the vicinity of HFS. The surface topography and the arrangement of amino acid residues work together to organize the water molecules in the hydration layer in order to provide them with a preferred orientation. HFS having a large polar solvent accessible surface area and a convex extensive nonpolar region, drives the surrounding water molecules to acquire predominantly an outward H-atoms directed, clathrate-like structure. In contrast, near the DFS, the surrounding water molecules acquire an inward H-atoms directed orientation owing to the flat curvature of hydrophobic surface and the interrupted hydrophilic residual alignment. We have followed escape trajectory of several such quasi-bound water molecules from both the surfaces that reveal the significant differences between the two hydration layers. © 2014 American Chemical Society.

Patel K.M.,Indian Institute of Science | Sharma P.,University of Adelaide
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

The ATLAS and CMS experiments at the LHC have found significant excess in the diphoton invariant mass distribution near 750 GeV. We interpret this excess in a predictive nonsupersymmetric SU(5) grand unified framework with a singlet scalar and light adjoint fermions. The 750 GeV resonance is identified as a gauge singlet scalar. Both its production and decays are induced by 24 dimensional adjoint fermions predicted within SU(5). The adjoint fermions are assumed to be odd under Z2 symmetry which forbids their direct coupling to the standard model fermions. We show that the observed diphoton excess can be explained with sub-TeV adjoint fermions and with perturbative Yukawa coupling. A narrow width scenario is more preferred while a simultaneous explanation of observed cross section and large total decay width requires some of the adjoint fermions lighter than 375 GeV. The model also provides a singlet fermion as a candidate of cold dark matter. The gauge coupling unification is achieved in the framework by introducing color sextet scalars while being consistent with the proton decay constraint. © 2016 The Authors.

Bhattacharyya S.,Indian Institute of Science
International Journal of Biochemistry and Cell Biology | Year: 2016

Metabotropic glutamate receptors (mGluRs) are G-protein coupled receptors (GPCRs) that are activated by the neurotransmitter glutamate in the central nervous system. Among the eight subtypes, mGluR1 and mGluR5 belong to the group I family. These receptors play important roles in the brain and are believed to be involved in multiple forms of experience dependent synaptic plasticity including learning and memory. In addition, group I mGluRs also have been implicated in various neuropsychiatric disorders like Fragile X syndrome, autism etc. The normal signaling depends on the precise location of these receptors in specific region of the neuron and the process of receptor trafficking plays a crucial role in controlling this localization. Intracellular trafficking could also regulate the desensitization, resensitization, down-regulation and intracellular signaling of these receptors. In this review I focus on the current understanding of group I mGluR regulation in the central nervous system and also their role in neuropsychiatric disorders. © 2016 Elsevier Ltd.

Prasad V.,Indian Institute of Science
Materials Research Bulletin | Year: 2012

In this paper, the low temperature electrical conductivity and microwave absorption properties of carbon coated iron nanoparticles-polyvinyl chloride composite films are investigated for different filler fractions. The filler particles are prepared by the pyrolysis of ferrocene at 980°C and embedded in polyvinyl chloride matrix. The high resolution transmission electron micrographs of the filler material have shown a 5 nm thin layer graphitic carbon covering over iron particles. The room temperature electrical conductivity of the composite film changes by 10 orders of magnitude with the increase of filler concentration. A percolation threshold of 2.2 and an electromagnetic interference shielding efficiency (EMI SE) of ∼18.6 dB in 26.5-40 GHz range are observed for 50 wt% loading. The charge transport follows three dimensional variable range hopping conduction. © 2012 Elsevier Ltd. All rights reserved.

Mogurampelly S.,Indian Institute of Science
The European physical journal. E, Soft matter | Year: 2013

Negatively charged DNA can be compacted by positively charged dendrimers and the degree of compaction is a delicate balance between the strength of the electrostatic interaction and the elasticity of DNA. We report various elastic properties of short double-stranded DNA (dsDNA) and the effect of dendrimer binding using fully atomistic molecular dynamics and numerical simulations. In equilibrium at room temperature, the contour length distribution P(L) and the end-to-end distance distribution P(R) are nearly Gaussian, the former gives an estimate of the stretch modulus γ1 of dsDNA in quantitative agreement with the literature value. The bend angle distribution P(θ) of the dsDNA also has a Gaussian form and allows to extract a persistence length, L(p) of 43nm. When the dsDNA is compacted by positively charged dendrimer, the stretch modulus stays invariant but the effective bending rigidity estimated from the end-to-end distance distribution decreases dramatically due to backbone charge neutralization of dsDNA by dendrimer. We support our observations with numerical solutions of the worm-like-chain (WLC) model as well as using non-equilibrium dsDNA stretching simulations. These results are helpful in understanding the dsDNA elasticity at short length scales as well as how the elasticity is modulated when dsDNA binds to a charged object such as a dendrimer or protein.

Haldar S.,Indian Institute of Technology Bhubaneswar | Babu G.L.S.,Indian Institute of Science
International Journal of Geomechanics | Year: 2010

This paper presents the response of piles in liquefiable soil under seismic loads. The effects of soil, pile, and earthquake parameters on the two potential pile failure mechanisms, bending and buckling, are examined. The analysis is conducted using a two-dimensional plain strain finite difference program considering a nonlinear constitutive model for soil liquefaction, strength reduction, and pile-soil interaction. The depths of liquefaction, maximum lateral displacement, and maximum pile bending moment are obtained for concrete and steel piles for different soil relative dens