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Kolkata, India

Biswas P.,Scottish Church College
Journal of Theoretical and Computational Chemistry | Year: 2015

A theoretical investigation of the mechanism, kinetics and probable product analysis of the Cl-initiated oxidation reaction of methyl methacrylate (MMA) is presented in this paper. The major degradation pathway of MMA is the Cl-addition to the terminal carbon of the olefinic bond. Beside this, energetic and mechanism of other possible reaction pathways are discussed in detail. In addition, the mechanism for the secondary reactions in presence of O2 and NO has also been presented. Cl-addition to the double bond takes place via formation of the pre-reactive complex as these reaction channel passes through negative activation barrier. Energetics and thermochemical analysis have been studied at the MP2=Full/6-311++g(d,p) level of theory. The rate constant of the Cl-addition reaction has been calculated using conventional transition state theory (CTST) at 1 atm pressure and 250-350 K temperature range. © 2015 World Scientific Publishing Company. Source

Talukdar D.,Saha Institute of Nuclear Physics | Nandi U.N.,Scottish Church College | Poddar A.,Saha Institute of Nuclear Physics | Mandal P.,Saha Institute of Nuclear Physics | Bardhan K.K.,Saha Institute of Nuclear Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

A new scaling formalism is used to analyze nonlinear I-V data in the vicinity of metal-insulator transitions (MIT) in five manganite systems. An exponent, called the nonlinearity exponent, and an onset field for nonlinearity, both characteristic of the system under study, are obtained from the analysis. The onset field is found to have an anomalously low value corroborating the theoretically predicted electronically soft phases. The scaling functions above and below the MIT of a polycrystalline sample are found to be the same but with different exponents which are attributed to the distribution of the MIT temperatures. The applicability of the scaling in manganites underlines the universal response of the disordered systems to electric field. © 2012 American Physical Society. Source

Bhattacharyya S.,Scottish Church College | Das T.K.,University of Calcutta | Chakrabarti B.,Kalyani University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We report the effects of interaction on thermodynamic properties of a repulsive Bose-Einstein condensate confined in a harmonic trap by using the correlated potential harmonics expansion method. This many-body technique permits the use of a realistic interactomic interaction, which gives rise to the effective long-range interaction of the condensate in terms of the s-wave scattering length. We have computed temperature (T) dependence of the chemical potential, specific heat, condensate fraction, entropy, pressure, and the average energy per particle of a system containing a large number (A) of 87Rb atoms in the Joint Institute for Laboratory Astrophysics (JILA) trap. The repulsion among the interacting bosons results in a small but measurable drop of condensate fraction and critical temperature (Tc), compared to those of a noninteracting condensate. These are in agreement with the experiment. Although all thermodynamic quantities have a strong dependence on A and to a smaller extent on the interatomic interaction, our numerical calculation appears to show that a thermodynamic quantity per particle follows a universal behavior as a function of T/Tc. This shows the importance of Tc for all thermodynamic properties of the condensate. As expected, for T>T c, these properties follow those of a trapped noncondensed Bose gas. © 2013 American Physical Society. Source

Bhattacharyya S.,Scottish Church College | Chakrabarti B.,Presidency University of India
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

We present a correlated many-body approach to calculate the distribution function and fluctuations for a Bose-Einstein condensate with N interacting atoms in the harmonic confinement. The present formulation uses the recursion relation for the canonical ensemble partition function (Z). Z is calculated from the energy spectrum of the many-body effective potential, which keeps all possible two-body correlations and uses the realistic interatomic interaction. The condensate statistics are in very good agreement with earlier results of an ideal gas for which exact statistical moments for all temperature are known. We also present the numerical results of condensate statistics for real experimental situations. The calculated moments nicely exhibit the mesoscopic effect for a few hundred atoms, whereas the sharp fall in the variance for the large condensate near the critical temperature shows the possibility of phase transition. We also calculate the critical temperature for the mesoscopic regime. Our present calculation mimics the JILA experiment with Rb87 atoms. © 2016 American Physical Society. Source

Nandi U.,Scottish Church College | Jana D.,University of Calcutta | Talukdar D.,Saha Institute of Nuclear Physics
Progress in Materials Science | Year: 2015

Complex charge transport mechanisms in disordered systems are often difficult to characterize owing to a dearth of suitable probes. Non-Ohmic response to an applied electric field is however a common uniformity which spans across all disordered systems. Static disorder can be of various types so could be the mechanisms causing non-Ohmic response due to the intricate relationship of electric field response to the intrinsic disorder configuration of the material. In this review article, the electrical transport properties of several disordered systems including composites, amorphous/doped semiconductors, conducting polymers and manganites (both in single crystal and poly-crystalline phase) are highlighted from the standpoint of non-Ohmic direct current conduction. This non-Ohmic conduction is characterized by a single voltage scale known as the onset voltage which scales with the Ohmic conductance (i.e.; disorder) with an exponent. The universality of this exponent and the scaling description of similar variation of the conductivity with field in different disordered systems are reviewed in detail. A comparison of experimental data in various disordered systems with the existing theoretical models available in the literature is also included. We hope that the universality of the electrical response of electrical transport across a plethora disordered systems will spur theoretical efforts for developing a microscopic theory to understand the scaling behaviour. © 2015 Elsevier Ltd. Source

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