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Saha A.,Visva Bharati University | Talukdar B.,Visva Bharati University | Das U.,Abhedananda College | Chatterjee S.,Bidhannagar College
Pramana - Journal of Physics | Year: 2017

We examine the effect of dissipation on travelling waves in nonlinear dispersive systems modelled by Benjamin-Bona-Mahony (BBM)-like equations. In the absence of dissipation, the BBM-like equations are found to support soliton and compacton/anticompacton solutions depending on whether the dispersive term is linear or nonlinear. We study the influence of increasing nonlinearity of the medium on the soliton and compacton dynamics. The dissipative effect is found to convert the solitons either to undular bores or to shock-like waves depending on the degree of nonlinearity of the equations. The anticompacton solutions are also transformed to undular bores by the effect of dissipation. But the compactons tend to vanish due to viscous effects. The local oscillatory structures behind the bores and/or shock-like waves in the case of solitons and anticompactons are found to depend sensitively both on the coefficient of viscosity and solution of the unperturbed problem. © Indian Academy of Sciences.

Saha A.,Visva Bharati University | Talukdar B.,Visva Bharati University | Chatterjee S.,Bidhannagar College
Physica A: Statistical Mechanics and its Applications | Year: 2017

We make use of a Hylleraas-type wave function to derive an exact analytical model to quantify correlation in two-electron atomic/ionic systems and subsequently employ it to examine the role of inter-electronic repulsion in affecting (i) the bare (uncorrelated) single-particle position- and momentum-space charge distributions and (ii) corresponding Shannon's information entropies. The results presented for the first five members in the helium iso-electronic sequence, on the one hand, correctly demonstrate the effect of correlation on bare charge distributions and, on the other hand, lead us to some important results for the correlated and uncorrelated values of the entropies. These include the limiting behavior of the correlated entropy sum (sum of position- and momentum-space entropies) and geometrical realization for the variation of information entropies as a function of Z. We suggest that, rather than the entropy sum, individual entropies should be regarded as better candidates for the measure of correlation. © 2017

Sengupta S.,Bidhannagar College | Ganguli S.,AIIST | Singh P.K.,The Biome | Singh P.K.,Bose Institute of India
Genomics Data | Year: 2017

This study reports the root endophytic microbial community profile in rice (Oryza sativa L.), the largest food crop of Asia, using 16S rRNA gene amplicon sequencing. Metagenome of OS01 and OS04 consisted of 11,17,900 sequences with 300 Mbp size and average 55.6% G + C content. Data of this study are available at NCBI Bioproject (PRJNA360379). The taxonomic analysis of 843 OTU's showed that the sequences belonged to four major phyla revealing dominance of Proteobacteria, Firmicutes, Cyanobacteria and Actinobacteria. Results reveal the dominance of Bacillus as major endophytic genera in rice roots, probably playing a key role in Nitrogen fixation. © 2017

Chatterjee S.,Bidhannagar College | Saha A.,Visva Bharati University | Talukdar B.,Visva Bharati University
European Physical Journal D | Year: 2013

The Husimi distribution function is used to study the phase-space localization of Rydberg wave packets produced in a quasi one-dimensional hydrogen atom by the impact of half-cycle pulses (HCPs). The wave packet in a single-kicked atom exhibits transient phase-space localization. A weak second timedelayed HCP is found to extend the time of localization provided it is applied when the wave packet is near the inner turning point of the classical electron trajectory and momentum-transfer vectors of the first and the second kicks have the same sign. Alternatively, application of a similar second HCP increases the atomic ionization probability if the momentum-transfer vectors of the two kicks have opposite directions. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2013.

Chatterjee S.,Bidhannagar College | Saha A.,Visva Bharati University | Talukdar B.,Visva Bharati University
Acta Physica Polonica A | Year: 2011

We study revival and fractional revival phenomena of wave packets in a one-dimensional Rydberg atom irradiated by two time-delayed half-cycle pulses using an autocorrelation function characterized by electronic transition probabilities as weighting factors rather than modeling them by a Gaussian or Lorentzian distribution. If the momentum (q2) delivered to the atom by the second kick is much smaller than that (q1) imparted by the first one, the times of revival and fractional revival coincide with those of the single kicked atom. For q2 ≥ q1/4 appearance of revival and fractional revival depends on both the values of q2 and time delay t1 between the pulses but more sensitively on t1. The number of fractional revivals tends to become numerous as the value of t1 increases.

Chatterjee S.,Bidhannagar College | Saha A.,Visva Bharati University | Talukdar B.,Visva Bharati University
Pramana - Journal of Physics | Year: 2016

We present a quantum mechanical model to study the ionization of quasionedimensional Rydberg atoms interacting with half-cycle pulses (HCPs) and use it to demonstrate the inadequacy of semiclassical approaches to calculate ionization probabilities of such atoms subject to the impact of more than one HCP. For a single-kicked atom both models correctly reproduce the experimentally observed 's-curve' as can be seen by plotting the ionization probability P as a function of momentum transfer q1. We demonstrate that for a twice-kicked atom, the semiclassical model yields numbers for P which are not physically realizable. For fixed values of momentum transfers q1 and q2, in a twice-kicked atom, the ionization probability as a function of time delay between the kicks exhibits periodic decay and revival. The results of the semiclassical approach appear to agree with the quantum mechanical values at the times of revival of P, else these show considerable deviation. We attempt to provide a physical explanation for the limitation of the semiclassical approach. © 2016 Indian Academy of Sciences.

Saha A.,Visva Bharati University | Talukdar B.,Visva Bharati University | Chatterjee S.,Bidhannagar College
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

The Gardner equation ut+auux+bu2ux+μuxxx=0 is a generic mathematical model for weakly nonlinear and weakly dispersive wave propagation when the effects of higher-order nonlinearity become significant. Using the so-called traveling wave ansatz u(x,t)=φ(ξ), ξ=x-vt (where v is the velocity of the wave) we convert the (1+1)-dimensional partial differential equation to a second-order ordinary differential equation in with an arbitrary constant and treat the latter equation by the methods of the dynamical systems theory. With some special attention on the equilibrium points of the equation, we derive an analytical constraint for admissible values of the parameters a, b, and μ. From the Hamiltonian form of the system we confirm that, in addition to the usual bright soliton solution, the equation can be used to generate three different varieties of internal waves of which one is a dark soliton recently observed in water [A. Chabchoub, Phys. Rev. Lett. 110, 124101 (2013)PRLTAO0031-900710.1103/PhysRevLett.110.124101]. © 2014 American Physical Society.

Mandal P.,Bidhannagar College | Molla A.R.,Taki Government College | Mandal D.K.,Bidhannagar College
Journal of Biochemistry | Year: 2013

Guanidine hydrochloride (GdnHCl)-induced unfolding of bovine spleen galectin-1 (Gal-1) exhibits three-state mechanism involving exclusive, structured tertiary monomer in 0.5M GdnHCl. Gal-1 has one tryptophan residue (Trp 68) per subunit. Phosphorescence spectra of both Gal-1 dimer and intermediate monomer at 77K show single (0,0) band at 405.6 nm, characteristics of free tryptophan environment as of N-acetyl-Ltryptophanamide. Unfolded Gal-1 in 4M GdnHCl gives (0,0) band at longer wavelength (408.6 nm) signifying that Trp 68 is less solvent exposed, being localized in an environment of residual structure. Trifluoroethanol (TFE)- and hexafluoroisopropanol (HFIP)-induced structural changes of Gal-1 dimer and monomer have been investigated by far-UV CD and FTIR. CD results show reversible nature of β-sheet to -helix transition, with 30% helix in 80% TFE or 40% HFIP for Gal-1 dimer. Temperaturedependent studies show that induced helix entails reduced thermal stability. FTIR results reveal partial b-sheet to a-helix conversion but with quantitative yield. At intermediate TFE concentration, both Gal-1 dimer and monomer aggregate as evidenced by FTIR band at ∼1617/cm, however, the onset of aggregation and stability of aggregates for monomer differ from those of dimer. The results may provide important insights into perturbed folding problem of Gal-1. © The Authors 2013. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Chatterjee S.,Bidhannagar College
Physica Scripta | Year: 2012

For a one-dimensional atom, we derive an exact analytical expression for the uncertainty product of a Rydberg wave packet (WP) produced by the impact of two time-delayed half-cycle pulses (HCPs) and use the result to study the problems of its (WP's) phase-space localization. We also investigate how to effectively use the second HCP to increase the atomic ionization probability. The time delay (t 1) between the two HCPs plays a crucial role in both cases. The values of t 1 can be chosen for the second HCP to kick the WP when the latter is near the inner or outer turning point. We found that long-lived localized states are produced by the impact of the second HCP only when the WP is near the inner turning point. In the same situation, if the electron is kicked away from the nucleus, the atomic ionization probability tends to a maximum. © 2012 The Royal Swedish Academy of Sciences.

Talukdar D.,Saha Institute of Nuclear Physics | Chakraborty R.K.,Bidhannagar College | Bose S.,Saha Institute of Nuclear Physics | Bardhan K.K.,Saha Institute of Nuclear Physics
Review of Scientific Instruments | Year: 2011

A low noise constant current source used for measuring the 1f noise in disordered systems in ohmic as well as nonohmic regime is described. The source can supply low noise constant current starting from as low as 1 A to a few tens of milliampere with a high voltage compliance limit of around 20 V. The constant current source has several stages, which can work in a standalone manner or together to supply the desired value of load current. The noise contributed by the current source is very low in the entire current range. The fabrication of a low noise voltage preamplifier modified for bias dependent noise measurements and based on the existing design available in the MAT04 data sheet is also described. © 2011 American Institute of Physics.

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