Faculty Publications
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Item Studies on mechanical properties of porous anodic alumina membranes using microindentation test(American Institute of Physics Inc. subs@aip.org, 2015) Reddy, P.R.; Udayashankar, N.K.; Ajith, K.M.Porous anodic alumina (PAA) membranes were prepared using two-step self-organized anodization process carried out in 0.3 M oxalic acid at the temperature of about 5 o C. PAA membranes fabricated underconstant potential of 40 V gave optimum ordering of hexagonal pores. Microhardness of the prepared PAA membranes were studied using Vickers hardness test rig. It was observed that microhardness of prepared PAA membraneswere 2.20 GPa and 0.21 GPa for 100 g and1000 g loads respectively. © 2015 AIP Publishing LLC.Item Uniaxial stress induced band structure changes in h-SiB(American Institute of Physics Inc. subs@aip.org, 2018) Manju, M.S.; Ajith, K.M.; Valsakumar, M.C.Uniaxial stress was applied along zigzag and armchair directions in compressive and tensile regime to see if there is any metal-semiconductor transition in SiB. Metallicity increased with increasing stress both in compression and tension in zigzag and armchair directions instead of a metal-semiconductor transition. SiB maintained energetical stability in the whole range of applied stress. © 2018 Author(s).Item Structural and optical analysis of silver nanoparticles grown on porous anodic alumina membranes by electro-less deposition(Elsevier Ltd, 2019) Ramana Reddy, P.; Ajith, K.M.; Udayashankar, N.K.In this paper, we report our studies on silver nanoparticles which were synthesized inside the pores of porous anodic alumina (PAA) membranes by electro-less deposition method. The morphology of silver (Ag) nanoparticles was studied using FE-SEM. The result of FE-SEM showed that the Ag nanoparticles were spherical in shape and spread in uniform manner throughout the membrane. The elemental composition of Ag nanoparticles was investigated by Energy dispersive X-ray (EDX) spectroscopy. Structural characterization using X-ray diffraction pattern showed that PAA was amorphous and silver nanoparticles on PAA were crystalline in nature. Absorbance and luminescent behaviour of PAA and Ag-PAA were studied using UV-Visible and Photoluminescence (PL) spectra. PL spectra results revealed the presence of a strong peak at 392 nm in blue region, confirming the fact that the silver nanoparticles were embedded in the alumina template. © 2019 Elsevier Ltd.Item Criticality of charged ads black hole with a global monopole(Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2020) Naveena Kumar, A.; Ahmed Rizwan, C.L.A.; Ajith, K.M.We discuss the phase transition of charged AdS black hole surrounded by a global monopole. The cosmological constant is taken as fluid pressure and the corresponding conjugate variable as volume. In this extended phase space, the criticality is investigated from P-V isotherms, Gibbs free energy behavior and coexistence curves. The critical behavior of the Black Hole is analogous to classical van der Waals gas. This is further verified by looking at the critical exponents. The magnetic monopole parameter affects the phase structure of the black hole significantly. © Springer Nature Singapore Pte Ltd 2020.Item The Role of Global Monopole in Joule–Thomson Effect of AdS Black Hole(Springer Science and Business Media Deutschland GmbH, 2021) Naveena Kumara, A.; Ahmed Rizwan, C.L.; Ajith, K.M.We study the throttling process of the AdS black hole with a global monopole in the extended phase space. In the approach followed, the cosmological constant and the black hole mass are identified with the thermodynamic pressure and enthalpy, respectively. We investigate the dependency of the inversion temperature and isenthalpic curves on the global monopole parameter η. Our study shows a close resemblance between the phase transition of the black hole in the extended phase space and Van der Waals fluid. The presence of global monopole plays an important role in the throttling process. © 2021, Springer Nature Singapore Pte Ltd.Item Structure of Protein Interaction Network Associated With Alzheimer’s Disease Using Graphlet Based Techniques(Springer Science and Business Media B.V., 2022) Khasim, A.; Subramanian, V.; Ajith, K.M.; Shajahan, T.K.The crucial step in analyzing a real-world network is to choose an acceptable network model. We try to select an appropriate network model for the protein-protein interaction (PPI) network of Alzheimer’s disease (AD) using Graphlet-based metrics. The Relative Graphlet Frequency (RGF) count in the AD-PPI network is similar to that of the corresponding Scale-Free network. However, based on Graphlet Degree Distribution (GDD), the AD-PPI network has a good match with Geometric random graphs. The graphlet correlation statistics of the AD network show that it has a core-periphery topology. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Vibrational spectra of Ruthenium Carbide structures yielded by the structure search employing evolutionary algorithm(Elsevier Ltd, 2015) Harikrishnan, G.; Ajith, K.M.; Chandra, S.; Valsakumar, M.C.Out of the three dynamically stable structures of Ruthenium Carbides yielded by the exhaustive structure search employing evolutionary algorithm, Born effective charges are computed for the semiconducting RuC in Zinc blende structure using density functional perturbation theory. Using the phonon frequencies and the Born effective charge tensors of Ru and C in this structure, infrared spectrum is generated for this system. Computations of these dynamical quantities and IR spectra from first principles can be helpful in the unambiguous determination of the stoichiometry and structure by comparison of the experimental measurements with the computational predictions. The positive formation energies of the three systems show that high pressure and possibly high temperature may be necessary for their synthesis. Formation energies of these systems at different pressures are computed. One of the structurally stable systems, Ru3C with hexagonal structure (P6¯m2), has negative formation energy at 200 GPa. The system reported from the first synthesis of Ruthenium Carbide also has the same symmetry, though it has a different stoichiometry. © 2015 Elsevier Ltd. All rights reserved.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 Evolutionary algorithm based structure search for hard ruthenium carbides(Institute of Physics, 2015) Harikrishnan, G.; Ajith, K.M.; Chandra, S.; Valsakumar, M.C.An exhaustive structure search employing evolutionary algorithm and density functional theory has been carried out for ruthenium carbides, for the three stoichiometries Ru1C1, Ru2C1 and Ru3C1, yielding five lowest energy structures. These include the structures from the two reported syntheses of ruthenium carbides. Their emergence in the present structure search in stoichiometries, unlike the previously reported ones, is plausible in the light of the high temperature required for their synthesis. The mechanical stability and ductile character of all these systems are established by their elastic constants, and the dynamical stability of three of them by the phonon data. Rhombohedral structure is found to be energetically the most stable one in Ru1C1 stoichiometry and hexagonal structure , the most stable in Ru3C1 stoichiometry. RuC-Zinc blende system is a semiconductor with a band gap of 0.618 eV while the other two stable systems are metallic. Employing a semi-empirical model based on the bond strength, the hardness of RuC-Zinc blende is found to be a significantly large value of ?37 GPa while a fairly large value of ?21GPa is obtained for the RuC-Rhombohedral system. The positive formation energies of these systems show that high temperature and possibly high pressure are necessary for their synthesis. © 2015 IOP Publishing Ltd.Item Contact angle measurement studies on porous anodic alumina membranes prepared using different electrolytes(VBRI Press editorialoffice@vbripress.com, 2016) Ramana Reddy, P.R.; Ajith, K.M.; Udayashankar, N.K.This paper investigates the effect of pore widening duration on the wetting properties of nanostructured porous anodic alumina (PAA) membranes fabricated using sulphuric and oxalic acid as electrolytes by two step anodization process. XRD analysis shows that prepared PAA membranes were amorphous in nature. With increasing of pore widening durations from 0 to 120 min, the contact angle of PAA membranes varied from 21 to 78°. It was noticed that PAA membranes were hydrophilic in nature in the present of water medium. In the presence of acetone medium, PAA membranes prepared with 1hr pore widening time showed super hydrophilic behaviour. © 2016 VBRI Press.