• Volume 90, Issue 4

April 2018

• Role of hydrothermal temperature on crystallinity, photoluminescence, photocatalytic and gas sensing properties of $TiO_{2}$ nanoparticles

$TiO_{2}$ nanoparticles were synthesised by hydrothermal method. The degree of crystallinity and phase purity were confirmed from the Raman spectra and X-ray diffraction. By increasing the hydrothermal temperature,crystallinity and AC conductivity of the $TiO_{2}$ nanoparticles increase. Nitrogen adsorption–desorption measurements confirmed that the samples were mesoporous with an average pore diameter of 4.4–7.45 nm. Photocatalytic activity of $TiO_{2}$ nanoparticles was evaluated and the sample hydrothermally treated at 160$^\circ$C has the highest photocatalytic activity. In gas sensing measurements, sensitivity increases as a function of concentration and the response to ethanol vapour was better compared to other gases for the sample synthesised at 160$^\circ$C.

• Bäcklund transformation and soliton solutions in terms of the Wronskian for the Kadomtsev–Petviashvili-based system in fluid dynamics

In this paper, investigation is made on a Kadomtsev–Petviashvili-based system, which can be seen in fluid dynamics, biology and plasma physics. Based on the Hirota method, bilinear form and Bäcklund transformation(BT) are derived. $N$-soliton solutions in terms of the Wronskian are constructed, and it can be verified that the $N$ soliton solutions in terms of the Wronskian satisfy the bilinear form and Bäcklund transformation. Through the $N$-soliton solutions in terms of the Wronskian, we graphically obtain the kink-dark-like solitons and parallel solitons, which keep their shapes and velocities unchanged during the propagation.

• Neutron radiation damage studies in the structural materials of a 500 MWe fast breeder reactor using DPA cross-sections from ENDF/B-VII.1

The radiation damage in the structural materials of a 500 MWe Indian prototype fast breeder reactor (PFBR) is re-assessed by computing the neutron displacement per atom (dpa) cross-sections from the recent nuclear data library evaluated by the USA,ENDF/B-VII.1, wherein revisions were taken place in the new evaluations of basicnuclear data because of using the state-of-the-art neutron cross-section experiments, nuclear model-based predictions and modern data evaluation techniques. An indigenous computer code, computation of radiation damage (CRaD), is developed at our centre to compute primary-knock-on atom (PKA) spectra and displacement cross-sections of materials both in point-wise and any chosen group structure from the evaluated nuclear data libraries. The newradiation damage model, athermal recombination-corrected displacement per atom (arc-dpa), developed based on molecular dynamics simulations is also incorporated in our study. This work is the result of our earlier initiatives to overcome some of the limitations experienced while using codes like RECOIL, SPECTER and NJOY 2016, to estimate radiation damage. Agreement of CRaD results with other codes and ASTM standard for Fe dpa cross-section is found good. The present estimate of total dpa in D-9 steel of PFBR necessitates renormalisation of experimental correlations of dpa and radiation damage to ensure consistency of damage prediction with ENDF/B-VII.1 library.

• Development of a collinear laser spectrometer facility at VECC: First test result

We report here the development of collinear laser spectroscopy (CLS) system at VECC for the study of hyperfine spectrum and isotopic shift of stable and unstable isotopes. The facility is first of its kind in thecountry allowing measurement of hyperfine splitting of atomic levels using atomic beams. The CLS system is installed downstream of the focal plane of the existing isotope separator online (ISOL) facility at VECC and is recently commissioned by successfully resolving the fluorescence spectrum of the hyperfine levels in $^{85,87}\rm{Rb}$. The atomic beams of Rb were produced by charge exchange of 8 keV Rb ion beam which were produced, extracted and transported to the charge exchange cell using the ion sources, extractor and the beam-line magnets of the ISOL facility. The laser propagating opposite to the ion/atom beam direction was allowed to interact with the atom beam and fluorescence spectrum was recorded. The experimental set-up and the experiment conducted are reported in detail. The measures needed to be carried out for improving the sensitivity to a level necessary for studying short-lived exotic nuclei have also been discussed.

• Volterra integral equation-factorisation method and nucleus–nucleus elastic scattering

An approximate solution for the nuclear Hulthén plus atomic Hulthén potentials is constructed by solving the associated Volterra integral equation by series substitution method. Within the framework of supersymmetry-inspired factorisation method, this solution is exploited to construct higher partial wave interactions. The merit of our approach is examined by computing elastic scattering phases of the $\alpha−\alpha$ system by the judicious use of phase function method. Reasonable agreements in phase shifts are obtained with standard data.

• Impact of depth and location of the wells on vibrational resonance in a triple-well system

The effect of depth and location of a triple-well potential on vibrational resonance is investigated in a quintic oscillator driven by a low-frequency force and a high-frequency force. The values of low-frequency $\omega$ and amplitude $g$ of the high-frequency force at which vibrational resonance occurs are derived both numerically and theoretically. It is found that: as $\omega$ varies, at most one resonance takes place and the response amplitude at resonance depends on the depth and the location of the potential wells. When $g$ is altered, the depth and location of wells can control the number of resonances, resulting in two, three and four resonances. The system parameters can be adjusted by controlling the depth and position of the wells to achieve optimum vibrational resonance. Furthermore, the changes induced by these two quantities in the tristable system are found to be richer than those induced in bistable systems.

• Synchronisation, electronic circuit implementation, and fractional-order analysis of 5D ordinary differential equations with hidden hyperchaotic attractors

Hidden hyperchaotic attractors can be generated with three positive Lyapunov exponents in the proposed 5D hyperchaotic Burke–Shaw system with only one stable equilibrium. To the best of our knowledge, this feature has rarely been previously reported in any other higher-dimensional systems. Unidirectional linear error feedback coupling scheme is used to achieve hyperchaos synchronisation, which will be estimated by using two indicators: the normalised average root-mean squared synchronisation error and the maximum cross-correlation coefficient. The 5D hyperchaotic system has been simulated using a specially designed electronic circuit and viewed on an oscilloscope, thereby confirming the results of the numerical integration. In addition, fractional-order hidden hyperchaotic system will be considered from the following three aspects: stability, bifurcation analysis and FPGA implementation. Such implementations in real time represent hidden hyperchaotic attractors with important consequences for engineering applications.

• Nucleus-acoustic shock waves in white dwarfs

The nucleus-acoustic shockwaves (NASWs) propagating in a white dwarf plasma system, which contain non-relativistically or ultrarelativistically degenerate electrons, non-relativistically degenerate, viscous fluid of light nuclei, and immobile nuclei of heavy elements, have been theoretically investigated. We have used the reductive perturbation method, which is valid for small but finite-amplitude NASWs to derive the Burgers equation. The NASWs are, in fact, associated with the nucleus-acoustic (NA) waves in which the inertia is provided by the light nuclei, and restoring force is provided by the degenerate pressure of electrons. On the other hand, the stationary heavy nuclei participate only in maintaining the background charge neutrality condition at equilibrium. It is found that the viscous force acting in the fluid of light nuclei is a source of dissipation, and is responsible for the formation of NASWs. It is also observed that the basic features (polarity, amplitude, width, etc.) of the NASWs are significantly modified by the presence of heavy nuclei, and that NASWs are formed with either positive or negative potential depending on the values of the charge density of the heavy nuclei. The basic properties are also found to be significantly modified by the effects of ultrarelativistically degenerate electrons. The implications of our results in white dwarfs are briefly discussed.

• A chaotic jerk system with non-hyperbolic equilibrium: Dynamics, effect of time delay and circuit realisation

The literature on chaos has highlighted several chaotic systems with special features. In this work, a novel chaotic jerk system with non-hyperbolic equilibrium is proposed. The dynamics of this new system is revealed through equilibrium analysis, phase portrait, bifurcation diagram and Lyapunov exponents. In addition, we investigate the time-delay effects on the proposed system. Realisation of such a system is presented to verify its feasibility.

• Novel patterning of CdS/CdTe thin film with back contacts for photovoltaic application

The heterostructure of patterned CdS/CdTe thin films with back contact have been devised with electron beam lithography and fabricated using sputter deposition technique. The metallic contacts for n-CdS and p-CdTe are patterned such that both are placed at the bottom of the cell. This avoids losses due to contact shading and increases absorption in the window layer. Patterning of the device surface helps in increasing the junction area which can modulate the absorption of more number of photons due to total internal reflection. Computing the surface area between a planar and a patterned device has revealed 133% increase in the junction area. The physical and optical properties of the sputter-deposited CdS/CdTe layers are also presented. $J–V$ characteristics of the solar cell showed the fill factor to be 25.9%, open circuit voltage to be 17 mV and short-circuit current density to be 113.68 $\rm{A/m^2}$. The increase in surface area is directly related to the increase in the short circuit current of the photovoltaic cell, which is observed from the results of simulated model in Atlas/Silvaco.

• Control and synchronisation of a novel seven-dimensional hyperchaotic system with active control

In this work, active control method is proposed for controlling and synchronising seven-dimensional (7D) hyperchaotic systems. The seven-dimensional hyperchaotic system is considered for the implementation. Seven-dimensional hyperchaotic system is also investigated via time series, phase portraits and bifurcation diagrams. For understanding the impact of active controllers on global asymptotic stability of synchronisation and control errors, the Lyapunov function is used. Numerical analysis is done to reveal the effectiveness of applied active control method and the results are discussed.

• Some dynamical aspects of interacting quintessence model

In this paper, we consider a particular form of coupling, namely $B = \sigma(\dot{\rho}m − \dot{\rho}\phi)$ in spatially flat $(k = 0)$ Friedmann–Lemaitre–Robertson–Walker (FLRW) space–time. We perform phase-space analysis for this interacting quintessence (dark energy) and dark matter model for different numerical values of parameters. We also show the phase-space analysis for the ‘best-fit Universe’ or concordance model. In our analysis, we observe the existence of late-time scaling attractors.

• # Pramana – Journal of Physics

Current Issue
Volume 93 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019