Faculty Publications
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Item Performance analysis of Free Space Optical links encoded using Luby Transform codes(2012) Prakash, G.; Kulkarni, M.; Sripati, U.; Kalyanpur, M.N.Free Space Optical (FSO) communication is an emerging transmission technique to transmit high data rates without using cables. This technology is expected to revolutionize the present communication system architectures both in the terrestrial and the in -space architecture. Atmospheric effects can significantly degrade the performance of FSO systems. This reduces the SNR and leads to impaired performance. FSO channels can be modeled using Gamma-Gamma, Weibull, Log-Normal, K distribution functions. Error control codes can help to mitigate atmospheric turbulence induced signal fading in free space optical communication links. Luby Transform codes belong to a class of error control codes called Fountain codes and are meant for erasure channels. In this paper, we propose encoding FSO links with Luby Transform (LT) codes for error channels. Decoding is done using belief propagation with Log Likelihood Ratio and results are obtained for different modulation schemes under different channel distributions. © 2012 IEEE.Item Using RBF neural networks and kullback-leibler distance to classify channel models in Free Space Optics(2012) Prakash, G.; Kulkarni, M.; Sripati, U.Free Space Optical (FSO) communication systems offer a license free and cost effective access performance. FSO systems provide virtually unlimited bandwidth. Since the laser beams used in these systems are spatially confined, the links are very secure. However FSO links perform well only in clear weather conditions. Clouds, fog, aerosols, and turbulence drastically affect the performance of FSO systems and lead to fluctuations in both the intensity and phase of the received signal. FSO links can suffer from data packet corruption and erasure. Various statistical models have been proposed to describe the atmospheric turbulence channels. The choice of the appropriate model for varying level of turbulence is dependent on the atmospheric parameters. In this paper we classify the channels using Radial Basis Function Neural Networks to decide the best fit. We also use Kullback-Leibler distance as a measure between the reference distribution and the distribution of observed data. © 2012 IEEE.Item Molecular dynamics investigation of dipeptide - Transition metal salts in aqueous solutions(American Chemical Society service@acs.org, 2010) Santosh, M.S.; Lyubartsev, A.; Mirzoev, A.; Bhat, D.K.Molecular dynamics (MD) simulations of glycylglycine dipeptide with transition metal ions (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) in aqueous solutions have been carried out to get an insight into the solvation structure, intermolecular interactions, and salt effects in these systems. The solvation structure and hydrogen bonding were described in terms of radial distribution function (RDF) and spatial distribution function (SDF). The dynamical properties of the solvation structure were also analyzed in terms of diffusion and residence times. The simulation results show the presence of a well-defined first hydration shell around the dipeptide, with water molecules forming hydrogen bonds to the polar groups of the dipeptide. This shell is, however, affected by the strong electric field of divalent metal ions, which at higher ion concentrations lead to the shift in the dipeptide-water RDFs. Higher salt concentrations lead also to increased residence times and slower diffusion rates. In general, smaller ions (Cu2+, Zn2+) demonstrate stronger binding to dipeptide than the larger ones (Fe2+, Mn 2+). Simulations do not show any stronger association of peptide molecules indicating their dissolution in water. The above results may be of potential interest to future researchers on these molecular interactions. © 2010 American Chemical Society.Item Automated multi-agent search using centroidal Voronoi configuration(2011) Guruprasad, K.R.; Ghose, D.This paper addresses the problem of automated multiagent search in an unknown environment. Autonomous agents equipped with sensors carry out a search operation in a search space, where the uncertainty, or lack of information about the environment, is known a priori as an uncertainty density distribution function. The agents are deployed in the search space to maximize single step search effectiveness. The centroidal Voronoi configuration, which achieves a locally optimal deployment, forms the basis for the proposed sequential deploy and search strategy. It is shown that with the proposed control law the agent trajectories converge in a globally asymptotic manner to the centroidal Voronoi configuration. Simulation experiments are provided to validate the strategy. © 2010 IEEE.Item Classification of FSO channel models using radial basis function neural networks and their ber performance with Luby transform codes(2012) Prakash, G.; Kulkarni, M.; Sripati Acharya, U.; Kalyanpur, M.N.Free Space Optical (FSO) communication systems offer a license free and cost effective access performance. FSO links can suffer from data packet corruption and erasure. Error control codes can help to mitigate turbulence induced fading and can improve the error performance of such links. Various statistical models have been proposed to describe the atmospheric turbulence channels. The choice of the appropriate model for varying level of turbulence is dependent on the atmospheric parameters. In this paper we classify the channels using Radial Basis Function Neural Networks to decide the best fit. We then investigate the error performance of FSO channels modeled as Gamma- Gamma and K distribution functions with Luby Transform encoding which are rateless codes. Simulation results are used to compare the performance of different modulation schemes with Luby Transform encoding and also to classify the appropriate distribution function for the channel model. © 2012 by IJAI (CESER Publications).Item Sink attributes analysis for energy efficient operations of wireless sensor networks under randomly varying temporal and spatial aspects of query generation(Elsevier GmbH, 2015) Kumar, P.; Chaturvedi, A.Rapid advances and the development, compactness and economic viability; in IC technology, network hardware components and associated software have completely change the networking paradigm. The wireless sensor networks (WSNs) have also been not isolated from this unexpected changeover. This paper addresses three principal aspects that have been of interest in the WSN researcher community. These are investigating the suitable cluster formation scheme from some prominent scheme, incorporating the Spatio-temporal aspects of random query generation and subsequently model it using appropriate and extensively used probabilistic distribution functions, and exploring the importance of sink node(s) attributes towards much better energy profile of the WSN, as the energy consumption have been a vital component in deciding the overall network service conditions. The integration of these three aspects led to various case studies, which principally involves, uses of SKM, SFCM, DKM and DFCM as clustering schemes, uniform and Poisson probability mass functions uses to mathematically model the Spatio-temporal dependence of query distribution pattern, and the network surveillance by a single stationary sink, a moveable sink and four stationary sinks. The simulation results of various case studies are analyzed and compared. © 2015 Elsevier GmbH.Item Temperature dependent structural properties and bending rigidity of pristine and defective hexagonal boron nitride(Institute of Physics Publishing custserv@iop.org, 2015) Thomas, S.; Ajith, K.M.; Chandra, S.; Valsakumar, M.C.Structural and thermodynamical properties of monolayer pristine and defective boron nitride sheets (h-BN) have been investigated in a wide temperature range by carrying out atomistic simulations using a tuned Tersoff-type inter-atomic empirical potential. The temperature dependence of lattice parameter, radial distribution function, specific heat at constant volume, linear thermal expansion coefficient and the height correlation function of the thermally excited ripples on pristine as well as defective h-BN sheet have been investigated. Specific heat shows considerable increase beyond the Dulong-Petit limit at high temperatures, which is interpreted as a signature of strong anharmonicity present in h-BN. Analysis of the height fluctuations, ?h2?, shows that the bending rigidity and variance of height fluctuations are strongly temperature dependent and this is explained using the continuum theory of membranes. A detailed study of the height-height correlation function shows deviation from the prediction of harmonic theory of membranes as a consequence of the strong anharmonicity in h-BN. It is also seen that the variance of the height fluctuations increases with defect concentration. © 2015 IOP Publishing Ltd.Item Empirical potential influence and effect of temperature on the mechanical properties of pristine and defective hexagonal boron nitride(Institute of Physics Publishing helen.craven@iop.org, 2017) Thomas, S.; Ajith, K.M.; Valsakumar, M.C.The major objective of this work is to present results of a classical molecular dynamics study to investigate the effect of changing the cut-off distance in the empirical potential on the stress-strain relation and also the temperature dependent Young's modulus of pristine and defective hexagonal boron nitride. As the temperature increases, the computed Young's modulus shows a significant decrease along both the armchair and zigzag directions. The computed Young's modulus shows a trend in keeping with the structural anisotropy of h-BN. The variation of Young's modulus with system size is elucidated. The observed mechanical strength of h-BN is significantly affected by the vacancy and Stone-Wales type defects. The computed room temperature Young's modulus of pristine h-BN is 755 GPa and 769 GPa respectively along the armchair and zigzag directions. The decrease of Young's modulus with increase in temperature has been analyzed and the results show that the system with zigzag edge shows a higher value of Young's modulus in comparison to that with armchair edge. As the temperature increases, the computed stiffness decreases and the system with zigzag edge possesses a higher value of stiffness as compared to the armchair counterpart and this behaviour is consistent with the variation of Young's modulus. The defect analysis shows that presence of vacancy type defects leads to a higher Young's modulus, in the studied range with different percentage of defect concentration, in comparison with Stone-Wales defect. The variations in the peak position of the computed radial distribution function reveals the changes in the structural features of systems with zigzag and armchair edges in the presence of applied stress. © 2017 IOP Publishing Ltd.Item Hydrophilicity of the hydrophobic group: Effect of cosolvents and ions(Elsevier B.V., 2019) Dilip, H.N.; Chakraborty, D.Classical molecular dynamics simulations were performed to study the effect of cosolvents and ions on the solvation structure of zwitterionic glycine in liquid water. Simulations were carried out for 2 M and 1 M concentration of TMAO, Urea, KCl and LiCl solutions to observe the changes in liquid structure of water near the glycine molecule. Radial distribution functions and spatial distribution functions showed the presence of protective hydration layer near the C ? in presence of TMAO which gets reduced in case of urea, KCl and minimum in case of LiCl. LiCl is found to disrupt severely the solvation structure near the glycine molecule. For LiCl system, a small hydration layer is found near C ? unit at higher distances which is mainly due to the first hydration shell of lithium ion bonded to the carboxylate group. Presence of these hydration layers gives extra stabilization energy to the glycine water system. Stabilizing and destabilizing effect of water near the glycine molecule is calculated in terms of Potential Mean Force. The anomalous behaviour of lithium salts with respect to Group I cation salts in protein stabilization can be explained on the basis of this behaviour. We found maximum hydrogen bond lifetime for water molecules in presence of TMAO followed by LiCl, KCl and least in case of urea. The higher lifetimes in presence of ions are found mainly due to their electrostatic force. The stabilization of the hydrophobic part of the glycine molecule can be correlated with the stabilization of proteins in presence of these cosolvents. © 2019 Elsevier B.V.Item Effect of cosolvents in the preferential binding affinity of water in aqueous solutions of amino acids and amides(Elsevier B.V., 2020) Dilip, H.N.; Chakraborty, D.Effects of two naturally occurring osmolytes, urea and trimethylamine-N-oxide (TMAO) on the solvation structure of hydrophobic moiety of alanine, glycine, N-methylacetamide and acetamide are investigated by classical molecular dynamics simulations. Our results are analysed in terms of site-site radial distribution functions (RDF), spatial distribution functions (SDF), number of hydrogen bonds, orientation profile, KB integrals, preferential binding coefficient and hydrogen bond dynamics. RDF and SDF showed presence of an extra hydration shell near the hydrophobic unit when TMAO is present in the solution. This hydration shell mainly consists of broken hydrogen bonds. In urea-water solution, intramolecular association is favoured compared to intermolecular association: which is in contrast to the TMAO-water solution. Alanine, glycine, NMA and acetamide showed preferred interactions with the water molecules in presence of TMAO compared to urea. Urea and TMAO both are found to be excluded from the alanine, glycine, NMA and acetamide surface but presence of urea was slightly favoured at higher distances in case of NMA and acetamide. The strong hydrogen bond between TMAO-water increases the hydrogen bond lifetime of other hydrogen bonds in the system. The preferential binding affinity of water with the protein molecules and strong hydrogen bonds are found to be the key reasons for stability in presence of TMAO. © 2019 Elsevier B.V.