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Murshidābād, India

Bhattacharya S.,Indian National Metallurgical Laboratory | Roychowdhury A.,UGC-DAE Consortium for Scientific Research | Roychowdhury A.,Krishnath College | Das D.,UGC-DAE Consortium for Scientific Research | Nayar S.,Indian National Metallurgical Laboratory
RSC Advances

Epsilon-iron oxide (ε-Fe2O3) has been synthesized in large yields (≈73.7%) in a colloidal form at ambient conditions. Being embedded in biomimetic graphene, the synthesized thermodynamically unstable monoclinic phase is prevented from transforming to other phases. We have used the same protein-polymer mixture both for exfoliating natural graphite and as templating agents for iron oxide nanoparticles. X-ray diffraction of the composites confirms the formation of the ε-Fe2O3 phase with minor quantities (≈26.3%) of cubic magnetite (Fe3O4). The particle size and distribution was studied using high resolution transmission electron microscopy which clearly shows self-assembled dense nanoparticles on graphene sheets. This exercises strain on graphene; evident from the highly broadened D and G bands of Raman measurements and the blue shifting of the G band. X-ray photoelectron spectra shows signatures of iron oxide, graphene and protein in the sample; deconvoluted C1s, O1s and N1s core level peaks confirm both the attachment of the nanoparticles with the substrate and Fe2p core level peaks reveal the high spin oxidation state of Fe3+ ions. Magnetic measurements confirm the superparamagnetic nature of the composites; the lack of coercivity unexpected of this polymorph may be explained by the low magnetocrystalline anisotropy of the randomly oriented graphene sheets. We suspect that graphene attracts the maximum ferric (Fe3+) ions of the mixed ferrous/ferric ions in the system resulting in ferrous (Fe2+) cation substitution which also results in the reduction of coercivity. Exchange bias was also observed at low temperature in this antiferro-ferrimagnetic hybrid film. © 2015 The Royal Society of Chemistry. Source

Khan B.A.,Krishnath College | Khan B.A.,Visva Bharati University | Sardar S.,Indian Association for The Cultivation of Science | Sarkar P.,Visva Bharati University | Adhikari S.,Indian Association for The Cultivation of Science
Journal of Physical Chemistry A

The major portion of the algorithm of the time-dependent discrete variable representation (TDDVR) method is recently parallelized using the shared-memory parallelization scheme with the aim of performing dynamics on relatively large molecular systems. Because of the astronomical importance of naphthalene and anthracene, we have investigated their radical cations as models for theoretical simulation of complex photoelectron spectra and nonradiative decay process using the newly implemented parallel TDDVR code. The strong vibronic coupling among the six lowest doublet electronic states makes these polynuclear hydrocarbons dynamically important. The aim of the present investigation is to show the efficiency of our current TDDVR algorithm to perform dynamics on large dimensional quantum systems in vibronically coupled electronic manifold. Both the sequential and the parallelized TDDVR algorithms are almost linear scalable for an increase in number of processors. Because a signi ficant speed-up is achieved by cycling in the correct way over arrays, all of the simulations are performed within a reasonable wall clock time. Our theoretical spectra well reproduce the features of the corresponding experimental analog. The dynamical outcomes, for example, population, photoelectron spectra, and diffused interstellar bands, etc., of our quantum-classical approach show good agreement with the findings of the well-established quantum dynamical method, that is, multi configuration time-dependent Hartree (MCTDH) approach. © 2014 American Chemical Society. Source

De A.,Krishnath College | Kundu S.,Indian Central Glass and Ceramic Research Institute
Journal of Materials Engineering and Performance

Cd-Sn oxide nanocomposites were synthesized by sol-gel method from precursor sol containing Cd:Sn = 2:1 and 1:1 mol ratio. Instead of coprecipitation, a simple novel gel calcination route was followed. Cd (NO3)2. 4H2O and SnCl4. 5H2O were used as starting materials. Gel was calcined at 1050 °C for 2 h to obtain nanocomposites. XRD analysis reveals the presence of orthorhombic, cubic Cd2SnO4 along with orthorhombic, hexagonal CdSnO3 phases in both the composites. SEM and TEM studies indicate the development of nanocomposites of different shapes suggesting different degrees of polymerization in precursor sol of different composition. UV-Vis absorption spectra show a blue shift for both the composites compared to bulk values. Decrease of polarization with frequency, dipole contribution to the polarization, and more sensitivity to ethanol vapor were observed for the nanocomposite derived from precursor sol containing Cd:Sn = 2:1 mol ratio. © 2016, ASM International. Source

Sarkar P.,Visva Bharati University | Ahamed B.,Visva Bharati University | Ahamed B.,Krishnath College
International Journal of Quantum Chemistry

The Fourier grid Hamiltonian method for calculating vibrational energy levels of triatomic molecules is presented. We have used direct product basis functions obtained from the Fourier grid Hamiltonian method for one-dimensional Schrödinger equation for radial coordinates and the associated Legendre polynomial for angular coordinate. The resulting matrix is diagonalized by using Lanczos method. The method is tested for the calculation of vibrational energy levels of H2O and MgH2 molecules. Copyright © 2010 Wiley Periodicals, Inc. Source

Bagchi B.,University of Calcutta | Banerjee A.,Krishnath College | Mandal P.,University of Calcutta
International Journal of Modern Physics A

We study a generalized scheme of Swanson Hamiltonian from a second-derivative pseudo-supersymmetric approach. We discuss plausible choices of the underlying quasi-Hamiltonian and consider the viability of applications to systems like the isotonic oscillator and CPRS potential. © 2015 World Scientific Publishing Company. Source

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