Integrated Science Education and Research Center

Santiniketan, India

Integrated Science Education and Research Center

Santiniketan, India
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Pandit S.K.,Integrated Science Education and Research Center | Chattopadhyay A.,Integrated Science Education and Research Center
Computers and Mathematics with Applications | Year: 2017

A fourth order compact finite difference scheme is proposed for solving general second order steady partial differential equation (PDE) in two-dimension (2D) on geometries having nonuniform curvilinear grids. In this work, the main efforts are focused not only on nonorthogonal curvilinear grids but also on the presence of mixed derivative term and nonhomogeneous derivative source terms in the governing equation. This is in turn suitable for solving fluid flow and heat transfer problems governed by Navier-Stokes(N-S) equations on geometries having nonuniform and nonorthogonal curvilinear grids. The newly proposed scheme has been applied to solve general second order partial differential equation having analytical solution and some pertinent fluid flow problems, namely, viscous flows in a lid driven cavity such as trapezoidal cavity using nonorthogonal grid, square cavity using distorted grid, complicated enclosures using curvilinear grid, and mixed convection flow in a bottom wavy wall cavity. It is seen to efficiently capture steady-state solutions of the N-S equations with Dirichlet as well as Neumann boundary conditions. Detailed comparison data produced by the proposed scheme for all the test cases are provided and compared with existing analytical as well as established numerical results available in the literature. Excellent comparison is obtained in all the cases. © 2017 Elsevier Ltd.


Ghosh M.,Integrated Science Education and Research Center | Nath S.,Bhabha Atomic Research Center | Hajra A.,Siksha Bhavana | Sinha S.,Integrated Science Education and Research Center
Journal of Luminescence | Year: 2013

Self-quenching of the fluorescence emission of tetraphenylporphyrin at high concentrations in toluene at the ambient temperature (300 K) is discussed in detail based on steady state and time-resolved fluorescence measurements. The fluorescence self-quenching is mainly attributed to re-absorption effect and the Förster type resonance energy transfer process (homotransfer). The re-absorption effect is found to deform the fluorescence emission spectra significantly in energy positions as well as relative intensities of different peaks at high concentrations. Nearly ideal fluorescence emission spectra are observed at a concentration ∼10-7 mol/L. Moreover, there is an apparent enhancement of the fluorescence lifetime value of tetraphenylporphyrin in toluene at high concentrations, especially on the blue side of the fluorescence emission spectra. To the best knowledge of the authors, this is the first detail report on the fluorescence self-quenching of porphyrins in liquid medium. This finding carries great importance in view of the widespread research on porphyrins in the fields of solar light harvesting, artificial photosynthesis, photodynamic therapy, etc. © 2013 Elsevier B.V. All rights reserved.


Verma S.,Indian Institute of Petroleum | Nandi M.,Indian Association for The Cultivation of Science | Nandi M.,Integrated Science Education and Research Center | Modak A.,Indian Association for The Cultivation of Science | And 2 more authors.
Advanced Synthesis and Catalysis | Year: 2011

Novel organic-inorganic hybrid mesoporous materials containing diimine moieties inside the pore wall were used for the grafting of an oxo-vanadium Schiff base complex at the mesopore surface. The prepared catalyst was found to be highly active and selective for the oxidation of a variety of primary, secondary and α-hydroxy carbonyl compounds to the corresponding aldehydes, ketones and 1,2-dicarbonyl compounds using tert-butyl hydroperoxide as oxidant under mild reaction conditions. After completion of the reaction, the catalyst could easily be recovered by simple filtration and could be reused several times without significant change in the catalytic efficiency. Importantly, the catalyst did not show any leaching during the reaction, confirming that the prepared catalyst was truly heterogeneous in nature. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Nandi M.,Indian Association for The Cultivation of Science | Nandi M.,Integrated Science Education and Research Center | Mondal J.,Indian Association for The Cultivation of Science | Sarkar K.,Indian Association for The Cultivation of Science | And 2 more authors.
Chemical Communications | Year: 2011

Post-synthesis modification of SBA-15 has been carried out to design highly ordered acid functionalized hybrid mesoporous organosilica, AFS-1. This material has been used as an efficient heterogeneous organocatalyst for the syntheses of xanthenes under mild conditions in the absence of any other metal co-catalyst. © 2011 The Royal Society of Chemistry.


Patra A.K.,Indian Association for The Cultivation of Science | Dutta A.,Indian Association for The Cultivation of Science | Pramanik M.,Indian Association for The Cultivation of Science | Nandi M.,Integrated Science Education and Research Center | And 2 more authors.
ChemCatChem | Year: 2014

An efficient procedure for aerobic oxidation of thiols to disulfides catalyzed by new self-assembled hierarchical mesoporous Mn-MFI in the presence of air under solvent-free conditions as well as in aqueous medium is reported. The mesoporosity and Mn4+ loading, together with a highly crystalline microporous pore wall structure of the MFI framework were achieved through a newly designed hydrothermal process. This hydrothermal approach leads to hierarchical self-assembled mesoporous zeolite structures through isomorphous substitution of Si by Mn and Al. It is shown that Mn-containing mesoporous zeolites are capable to form disulfide bonds from thiols in the presence of air. The zeolitic materials were characterized by XRD, field-emission scanning electron microscopy, high-resolution TEM, X-ray photoelectron spectroscopy, 29Si NMR, 27Al NMR, and EPR spectroscopy, as well as AAS analysis and N2 sorption studies. N2 sorption analysis revealed high surface areas and narrow pore size distributions (1.2-6.0 nm) for different samples. The mesoporous Mn-ZSM-5 acted as an efficient heterogeneous catalyst with maximum catalytic activity in the benzenethiol conversion to diphenyldithiol. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Pandit S.K.,Integrated Science Education and Research Center | Chattopadhyay A.,Integrated Science Education and Research Center
International Journal of Heat and Mass Transfer | Year: 2014

In this paper, an extension of the fourth order compact scheme on nonuniform grids (Pandit et al. (2007) [28]) is proposed for solving two dimensional (2D) unsteady natural convection flows in a rectangular cavity (with different aspect ratios) filled with a fluid saturated porous medium. The bottom wall of the cavity is uniformly and non-uniformly heated and the top wall is adiabatic while the vertical walls are cold maintained at constant temperature. We have used streamfunction (ψ)-vorticity (ζ) formulation of Navier-Stokes equations with the consideration of Brinkmann-extended Darcy model to simulate the momentum transfer in the porous medium. The streamfunction-vorticity and the energy equations are all solved as a coupled system of equations for the five field variables consisting of streamfunction, vorticity, two velocities and temperature. In this ψ-ζ formulation, the temperature gradient source term also has been treated as fourth order compact. The higher order compact scheme adopted in the present study yields consistent performance for a wide range of key parameters e.g. Rayleigh number Ra (from 103 to 108), Darcy number Da (from 10-5 to 10-3). Results are presented in the form of streamline and isotherm plots as well as the plots of Nusselt number at the heat source surface under different conditions. The present scheme is not only robust as evidenced from computations at higher Ra, but also accurate as is seen from comparisons with reliable existing results. © 2014 Elsevier Ltd. All rights reserved.


Ghosh M.,Integrated Science Education and Research Center | Roy B.,Integrated Science Education and Research Center | Jha A.,Integrated Science Education and Research Center | Sinha S.,Integrated Science Education and Research Center
Chemical Physics Letters | Year: 2014

Porphyrin derivatives are known to have absorption spectra in the visible region (400-700 nm). In the present Letter, a new (to the best of our knowledge) broad band is reported in the NIR region (700-900 nm) of the absorption spectra of zinc tetraphenylporphyrin, zinc octaethylporphyrin and magnesium octaethylporphyrin in aromatic solvents at high concentrations (∼10 -4 mol/L). The broad absorption band in the NIR region is ascribed to be due to ground state charge transfer complex formation between the presently used metalloporphyrins and aromatic solvents. © 2013 Published by Elsevier B.V. All rights reserved.


Ghosh M.,Integrated Science Education and Research Center | Sinha S.,Integrated Science Education and Research Center
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2015

Solvent effects on the photophysical properties of free base octaethylporphyrin and zinc octaethylporphyrin are investigated at the ambient temperature (300 K). Steady state electronic absorption and emission spectra of the porphyrins are recorded in different organic solvents of varying polarity. By using solvatochromic Stokes shift method, the dipole moments associated with the first excited singlet states of the presently used porphyrin molecules are determined for the first time, to the best of our knowledge, from Lippert-Mataga, Bakhshiev and Reichardt equations. The dipole moments associated with the singlet ground state of the porphyrin molecules are calculated theoretically by using density functional theory (DFT) method by adopting B3LYP/6-31G(d,p) level using Gaussian 03 package. Moreover, some other photophysical properties (fluorescence quantum yield, fluorescence lifetime, decay rates, etc.) of the porphyrins are measured in different solvents of varying polarity. © 2015 Published by Elsevier B.V. All rights reserved.


Mishra S.,Visva Bharati University | Bagdi A.K.,Visva Bharati University | Ghosh M.,Visva Bharati University | Sinha S.,Integrated Science Education and Research Center | Hajra A.,Visva Bharati University
RSC Advances | Year: 2014

ZnI2 was found to be an efficient catalyst for the synthesis of indolizine derivatives by a three-component coupling of pyridine-2- carboxaldehyde/quinoline-2-carboxaldehyde, secondary amines, and terminal alkynes in high yields. This protocol is compatible with a wide range of substrates and is expected to find broad applications due to its operational simplicity, shorter reaction time and low cost. A preliminary photophysical study showed that synthesized morpholinopyrrolo[1,2-a]quinolines represent a new class of fluorophore with high quantum yield. © 2014 The Royal Society of Chemistry.


Basu-Mallick B.,Saha Institute of Nuclear Physics | Bondyopadhaya N.,Integrated Science Education and Research Center | Banerjee P.,Saha Institute of Nuclear Physics
Nuclear Physics B | Year: 2014

We construct polarized spin reversal operator (PSRO) which yields a class of representations for the BC N type of Weyl algebra, and subsequently use this PSRO to find out novel exactly solvable variants of the BC N type of spin Calogero model. The strong coupling limit of such spin Calogero models generates the BC N type of Polychronakos spin chains with PSRO. We derive the exact spectra of the BC N type of spin Calogero models with PSRO and compute the partition functions of the related spin chains by using the freezing trick. We also find out an interesting relation between the partition functions of the BC N type and A N -1 type of Polychronakos spin chains. Finally, we study spectral properties like level density and distribution of spacing between consecutive energy levels for BC N type of Polychronakos spin chains with PSRO. © 2014 The Authors.

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