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Ghosh B.,St Pauls Cathedral Mission College | Halder S.,Bose Institute of India | Shannigrahi S.,Institute of Materials Research and Engineering of Singapore | Sinha T.P.,Bose Institute of India
Solid State Sciences | Year: 2017

X-ray photoelectron spectroscopy (XPS) measurements of double perovskite oxides, A2SmTaO6 (A = Ba, Sr, Ca) are performed in the energy window of 0–1300 eV. The electronic structure investigations of AST have been performed using density functional theory. The calculated DOS is compared with the experimental DOS obtained by XPS. It has been observed that the Sm-f and O-2p states are hybridized in the valence band near the Fermi level. The chemical shifts of the constituent elements determined from the core-level XPS spectra deliver information on charge transfer and nature of chemical bonds. These results have been used to explain the conduction mechanism in these materials. © 2017

Mallik A.,Siliguri College | Barik A.K.,St Pauls Cathedral Mission College | Pal B.,St Pauls Cathedral Mission College
RSC Advances | Year: 2017

Transparent oxyfluoride glass-ceramics of heavy metals doped with rare earth metal ions are important materials in optoelectronics. In the present study, we report the preparation of a glass and a glass-ceramic with composition 16.52Al2O3·1.5 AlF3·12.65LaF3·4.33Na2O·64.85 SiO2 (mol%), where both the materials were doped with 1 mol% Pr2O3. All four species were structurally characterized by Transmission Electron Microscopy (TEM). Pr2O3 affected the phase separation in the glass and deferred crystallization compared to the undoped glass. The crystallization mechanism and the location of various components in the glass/glass-ceramics were ascertained through advanced STEM/EDX techniques. The phase separated regions in the mother glass were mostly populated by F and La and also by Pr, Al and Si. The phase separated droplets, after annealing, turned into 10-20 nm LaF3 nanocrystals, which were found to partly include the doping Pr3+ ions in the crystals themselves. The interphase crystal/glassy matrix was thoroughly characterized by EDX. The results suggest that the inner LaF3 crystal core is engulfed by an Al enriched layer that follows a Si enriched surrounding shell as the outer core. This finding also indicates that the crystal surface is too viscous to further enhance the crystal growth, and therefore the overall crystal formation is limited to the nanosize. © The Royal Society of Chemistry.

Mallik A.,Siliguri College | Barik A.K.,St Pauls Cathedral Mission College | Pal B.,St Pauls Cathedral Mission College
Journal of the European Ceramic Society | Year: 2017

Crystallization, microstructure and mechanical behavior of strontium fluorphlogopite glass-ceramics, SrO·4MgO·Al2O3·6SiO2·2MgF2, was studied by varying the fluorine content. A number of glass-ceramics of each glass batch with excess MgF2 [SR0 (0% MgF2), SR5 (5% MgF2) and SR10 (10% MgF2)] were prepared by heating at its respective nucleation temperature followed by at different crystallization temperatures (780–1150 °C). Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Micro Hardness Indenter were used to study the crystallization, microstructure and mechanical behavior of resulting three glass batches. DTA analysis revealed that the peak crystallization (Tp) and glass transition (Tg) temperatures decreased with increasing fluorine content that also lowers down the activation energy (E) as evident from crystallization kinetics. Hardness and fracture toughness values are higher for less fluorine containing glass-ceramics when they are treated isothermally. However, more fluorine based glass-ceramics is found to be more machinable than the less fluorine one. © 2016 Elsevier Ltd

Chakraborty J.,St Pauls Cathedral Mission College | Ianelli S.,Vialedelle Science
Polyhedron | Year: 2013

Three copper(II) tridentate (NNO) Schiff base azido complexes, [Cu(L 1)(N3)] (1), [Cu2(L2) 2(μ2-1,1-N3)2] [Cu(L 2)(N3)] (2) and [Cu(L3)(N3)] (3) have been synthesized and characterized [where HL1 = 1-(N-5-methoxy-ortho-hydroxyacetophenimino)-2,2-dimethyl-aminoethane], HL 2 = 1-(N-ortho-hydroxyacetophenimine)-2,2-diethyl-aminoethane and HL3 = 1-(N-salicylideneimino)-2-(N,N-diethyl)-aminoethane]. The structure of complex (1) has been determined by single crystal X-ray diffraction analysis. In 1, out of four coordination sites of copper(II) ion, three are occupied by the NNO donor atoms of a tridentate Schiff base ligand, HL 1 and the remaining site is occupied by terminal nitrogen of azido moiety. All the complexes exhibit high catalytic activity in epoxidation reactions of a variety of olefins with tert-butyl-hydroperoxide in acetonitrile. The catalytic efficacy of the copper(II) complexes has been studied in different solvent media. The antimicrobial activity of the complexes and their Schiff base ligand has also been studied. © 2013 Elsevier Ltd. All rights reserved.

We present a theoretical investigation of coupling optics involving a laser diode and circular core graded index single mode fiber via a parabolic microlens on the fiber tip to predict the nature of suitable refractive index profile for the first time in connection with optimum coupling. The study is carried out in absence and presence of possible transverse and angular misalignments. By employing Gaussian field distributions for both the source and the fiber and also ABCD matrix for parabolic microlens under paraxial approximation, we formulate analytical expressions for the concerned coupling efficiencies. The investigations are performed for two different light-emitting wavelengths of 1.3 μm and 1.5 μm for such fibers with different refractive index profile exponents. Further, it is observed that out of the studied refractive index profiles, triangular index profile having the dispersion-shifted merit comes out to be the most suitable profile to couple laser diode to such abovementioned fiber for two wavelengths of practical interest. The analysis should find use in ongoing investigations for optimum launch optics for the design of parabolic microlens either directly on the circular core graded index single mode fiber tip or such fiber attached to single mode fiber to achieve long working distance. © 2016 The Optical Society of India

Banerjee R.,Jadavpur University | Banerjee R.,St Pauls Cathedral Mission College | Mandal L.,Jadavpur University | Khan M.,Jadavpur University | Gupta M.R.,Jadavpur University
Physics of Plasmas | Year: 2012

A nonlinear formulation is presented to deal with the combined action of Rayleigh-Taylor and Kelvin-Helmholtz instabilities as well as combined Ricthmyer-Meshkov and Kelvin-Helmholtz instabilities at the two fluid interface under the influence of viscosity and consequent shear flow. Using Layzer's model, the development of the interfacial structures like bubbles is investigated analytically and numerically. It is found that the growth and normal velocity of the structures are dependent on the relative velocity shear and the kinematic coefficient of viscosity of both the fluids. Both the bubble growth and growth rate are reduced significantly for fluids of higher viscosity coefficient with small velocity shear difference. It is also observed that, for viscous fluids, the transverse velocity of the perturbed interface becomes slower under certain conditions. © 2012 American Institute of Physics.

Mahapatra S.,St Pauls Cathedral Mission College
Few-Body Systems | Year: 2012

Calculation of the low-lying resonance state of 15C is performed using a two-body model ( 14C+n) with the application of Supersymmetric Quantum Mechanics (SSQM). The effective two-body potential presents a shallow well followed by a low and wide barrier. Large spatial extension of the halo state causes loss of accuracy due to numerical difficulties in calculating low-lying resonances. Use of SSQM permits one to construct an isospectral potential with a deep well followed by a high barrier which can effectively trap the system and hence facilitates the numerical calculation of resonance states more accurately than the original shallow potential. This method gives quite accurate result for the resonance energy of the 3/4 + state of 15C. Calculated width of this state also agrees fairly well within the experimental error bar. © 2011 Springer-Verlag.

The hexachloroiridate(IV) oxidation of α,β-unsaturated compounds such as acrylic acid, acrylamide, and acrylonitrile (CH2=CHX; X = -COOH, -CONH2, and -CN) was carried out in NaOAc-AcOH buffer medium. The reaction follows complex kinetics, being first order in [IrIV] and complex order in [CH2=CHX]. H+ ion has no effect on the reaction rate in the pH range 3.42-4.63. The pseudo-first-order rate constant decreases with a decrease in the dielectric constant and with a decrease of ionic strength of the medium. The oxidation rate follows the sequence: acrylonitrile > acrylamide > acrylic acid. A mechanism is proposed involving the formation of an unstable intermediate complex between the substrate and the oxidant which is transformed to the radical cation in a slow rate-determining step with the concomitant reduction of Ir(IV) to Ir(III). The radical cation subsequently decomposes to the aldehyde that appears as the ultimate product of the carbon-carbon double bond cleavage. The major product of oxidation was identified as HCHO by 1H NMR. Activation parameters for the slow rate-determining step and thermodynamic parameters associated with the equilibrium step of the proposed mechanism have been evaluated. The enthalpy of activation is linearly related to the entropy of activation, and this linear relationship confirms that the oxidation of all the α,β-unsaturated compounds follows a common mechanism. © 2013 Wiley Periodicals, Inc.

We report what to our knowledge is the first theoretical prediction of the coupling efficiency of a laser diode emitting two wavelengths either 1.3 or 1.5 μm, to three elliptic core step index fibers with different aspect ratios via quadric interface microlens of three different focal lengths on the fiber tip. Here, quadric interface microlens contains elliptical (hemispherical included), hyperbolic and parabolic microlenses. Instead of considering special ABCD matrix for individual microlens, a simple, accurate, and popular unified transfer ABCD matrix for refraction of quadric microlens under paraxial approximation is utilized to analyze the theoretical coupling efficiency, based on Gaussian beam approximation. The coupling efficiency can reach as high as 98.63 % with optimizing structure parameters of specific lensed fiber. The analysis can give some guidance for fabricating quadric interface lensed elliptic core fiber which are mainly useful in polarisation-maintaining fiber optic sensors and coherent fiber optic communication systems. © 2015 The Optical Society of India

PubMed | Jadavpur University, St Pauls Cathedral Mission College, University of Bristol and University of North Carolina at Charlotte
Type: Journal Article | Journal: Physical review. E | Year: 2016

From nonlinear models and direct numerical simulations we report on several findings of relevance to the single-mode Rayleigh-Taylor (RT) instability driven by time-varying acceleration histories. The incompressible, direct numerical simulations (DNSs) were performed in two (2D) and three dimensions (3D), and at a range of density ratios of the fluid combinations (characterized by the Atwood number). We investigated several acceleration histories, including acceleration profiles of the general form g(t)t^{n}, with n0 and acceleration histories reminiscent of the linear electric motor experiments. For the 2D flow, results from numerical simulations compare well with a 2D potential flow model and solutions to a drag-buoyancy model reported as part of this work. When the simulations are extended to three dimensions, bubble and spike growth rates are in agreement with the so-called level 2 and level 3 models of Mikaelian [K. O. Mikaelian, Phys. Rev. E 79, 065303(R) (2009)10.1103/PhysRevE.79.065303], and with corresponding 3D drag-buoyancy model solutions derived in this article. Our generalization of the RT problem to study variable g(t) affords us the opportunity to investigate the appropriate scaling for bubble and spike amplitudes under these conditions. We consider two candidates, the displacement Z and width s^{2}, but find the appropriate scaling is dependent on the density ratios between the fluids-at low density ratios, bubble and spike amplitudes are explained by both s^{2} and Z, while at large density differences the displacement collapses the spike data. Finally, for all the acceleration profiles studied here, spikes enter a free-fall regime at lower Atwood numbers than predicted by all the models.

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