B. Indrajit Sharma

Effect of Mn 2+ Doping on Structural, Morphological and Optical Properties of ZnS Nanoparticles by Chemical Co-Precipitation Method

Zinc Sulphide (ZnS) nanoparticles doped with different concentrations of Mn 2+ (0%, 2%, 4%, 6%, 8%, 10%) have been synthesized by chemical co-precipitation method using polyvinyl alcohol (PVA) as a capping agent to control the particle growth. The structural characterizations of as synthesized nanoparticles are determined by X-ray diffraction (XRD) which showed cubic zinc blende structures with average crystallite sizes of the range 2.3 nm - 2.1 nm. There is no phase transformation due to Mn 2+ doping and this characteristic has been observed in all the synthesized powder. Scanning electron microscopy (SEM) and energy dispersive X- ray (EDX) analysis show the morphology and elemental analysis of as synthesized nanoparticles.TEM images confirms the spherical shape of the nanoparticles. HRTEM and SAED images show the crystalline nature and confirm the cubic nature of ZnS nanoparticles. Absorption study has been carried out by using UV-Vis spectrophotometer to determine the band gap of ZnS:Mn nanoparticles and they showed a blue shift with respect to the bulk. The effect of Mn 2+ substitution on the photoluminescence properties of doped samples is also studied and doped ZnS:Mn showed enhanced luminescence property compared with that of the undoped ZnS nanoparticles. Radius of the synthesized nanoparticles has been evaluated from the absorption spectrum by using the Effective Mass Approximation (EMA) formula. Fourier Transform Infrared Spectra (FTIR) is recorded in an FTIR spectrometer to verify the presence and effect of capping agent.

Intercellular synchronization of diffusively coupled Ca(2+) oscillators.

We examine the synchrony in the dynamics of localized [Ca2 + ]i oscillations among a group of cells exhibiting such complex Ca2 +  oscillations, connected in the form of long chain, via diffusing coupling where cytosolic Ca2 +  and inositol 1,4,5-triphosphate are coupling molecules. Based on our numerical results, we could able to identify three regimes, namely desynchronized, transition and synchronized regimes in the (T − ke) (time period-coupling constant) and (A − ke) (amplitude-coupling constant) spaces which are supported by phase plots (Δϕ verses time) and recurrence plots, respectively. We further show the increase of synchronization among the cells as the number of coupling molecules increases in the (T − ke) and (A − ke) spaces.

First principles phase transition, elastic properties and electronic structure calculations for cadmium telluride under induced pressure: density functional theory, LDA, GGA and modified Becke–Johnson potential

We report first principles phase transition, elastic properties and electronic structure for cadmium telluride (CdTe) under induced pressure in the light of density functional theory using the local density approximation (LDA), generalised gradient approximation (GGA) and modified Becke–Johnson (mBJ) potential. The structural phase transition of CdTe from a zinc blende (ZB) to a rock salt (RS) structure within the LDA calculation is 2.2 GPa while that within GGA is found to be at 4 GPa pressure with a volume collapse of 20.9%. The elastic constants and parameters (Zener anisotropy factor, Shear modulus, Poissons ratio, Youngs modulus, Kleinmann parameter and Debyes temperature) of CdTe at different pressures of both the phases have been calculated. The band diagram of the CdTe ZB structure shows a direct band gap of 1.46 eV as predicted by mBJ calculation which gives better results in close agreement with experimental results as compared to LDA and GGA. An increase in the band gap of the CdTe ZB phase is predicted under induced pressure while the metallic nature is retained in the CdTe RS phase.

Stochastic synchronization of interacting pathways in testosterone model

We examine the possibilities of various coupling mechanisms among a group of identical stochastic oscillators via Chemical Langevin formalism where each oscillator is modeled by stochastic model of testosterone (T) releasing pathway. Our results show that the rate of synchrony among the coupled oscillators depends on various parameters namely fluctuating factor, coupling constants [symbol; see text], and interestingly on system size. The results show that synchronization is achieved much faster in classical deterministic system rather than stochastic system. Then we do large scale simulation of such coupled pathways using stochastic simulation algorithm and the detection of synchrony is measured by various order parameters such as synchronization manifolds, phase plots etc and found that the proper synchrony of the oscillators is maintained in different coupling mechanisms and support our theoretical claims. We also found that the coupling constant follows power law behavior with the systems size (V) by [symbol; see text] ~ AV(-γ), where γ=1 and A is a constant. We also examine the phase transition like behavior in all coupling mechanisms that we have considered for simulation. The behavior of the system is also investigated at thermodynamic limit; where V → ∞, molecular population, N → ∞ but N/V → finite, to see the role of noise in information processing and found the destructive role in the rate of synchronization.

First principles study on structural, phase transition and electronic structure of Zinc Sulfide (ZnS) within LDA, GGA and mBJ potential

An ab-initio calculation based on full potential linearised augmented plane wave method of density functional theory (DFT) within the localised density approximation (LDA), generalised gradient approximation (GGA) and modified Becke-Johnson (mBJ) for exchange correlation potential is performed to investigate the structural, phase transition and electronic structure of Zinc Sulfide (ZnS). A comparative study is performed for the three approximations and reveal that calculations within the GGA gives better structural stability and phase transition pressure of 17.6 GPa in reasonably close agreement to experimental results. The electronic structure calculation within mBJ predicts higher direct band gap of 3.5eV in comparison to LDA and GGA underestimated value. The trend in the accuracy of energy band gap calculation is found to be LDA<GGA< mBJ-GGA. The electronic band structures are investigated using the total and partial density of states.

Lie Algebraic Study of Infra-Red Active Spectra of Single-Layer Graphene

In this article, using Lie algebraic technique and the expressions of the matrix elements of Majorana and Casimir operators, we obtain an effective Hamiltonian operator, which conveniently describes some stretching infra-red active mode of vibrations of monolayer graphene model of 30 atoms. The model finds the accuracy in results of density functional theory.

Synthesis, Structural and Optical Characterization of PVA Capped Cadmium Sulphide Nanocrystalline Films by Chemical Bath Deposition Method

Nanocrystalline CdS thin films were deposited on glass substrate by chemical bath deposition method using Cadmium Sulphate and Thiourea as Cd+2 and S-2 ion sources for different molarities i.e. 0.1 M, 0.2 M and 0.3 M. The crystallite size and lattice parameters for each sample were determined from X-Ray diffraction data using Scherrers formula. The value of the crystallite size was found to be within the range 14.7 nm-11.4 nm. The optical characterization was done by UV-Visible and photoluminescence spectroscopy. The optical band gap of the films was determined from the transmittance spectra. It was observed that when the molarity increases, the average crystallite size decreases and the band gap energy of the prepared films increases. Photoluminescence studies showed a prominent peak at around 530 nm. The radius of the nanocrystalline films had been evaluated from the absorption spectrum by using effective mass approximation formula.

Measurement of phase synchrony of coupled segmentation clocks

The temporal behavior of segmentation clock oscillations shows phase synchrony via mean field like coupling of delta protein restricting to nearest neighbors only, in a configuration of cells arranged in a regular three dimensional array. We found the increase of amplitudes of oscillating dynamical variables of the cells as the activation rate of delta-notch signaling is increased, however, the frequencies of oscillations are decreased correspondingly. Our results show the phase transition from desynchronized to synchronized behavior by identifying three regimes, namely, desynchronized, transition and synchronized regimes supported by various qualitative and quantitative measurements.