• Issue front cover thumbnail

      Volume 91, Issue 1

      July 2018

    • General editorial on publication ethics

      More Details Abstract Fulltext PDF
    • Cloaks for suppression or enhancement of scattering of diffuse photon density waves


      More Details Abstract Fulltext PDF

      Enhancement of wave-like characteristics of heavily damped diffuse photon density waves in a random medium by amplification can induce strongly localised resonances. These resonances can be used to either suppress or enhance scattering from an inhomogeneity in the random medium by cloaking the inhomogeneous region by a shell of random medium with the correct levels of absorption or amplification. A spherical core–shell structure consisting of a shell of a random amplifying medium is shown to enhance or suppress specific resonant modes. A shell with an absorbing random medium is also shown to suppress scattering which can also be used for cloaking the core region.

    • Influence of structural and doping parameter variations on Si and $\rm{Si_{1−x} Ge_{x}}$ double gate tunnel FETs: An analysis for RF performance enhancement


      More Details Abstract Fulltext PDF

      This paper deals with the effect of structural and doping parameter variations on RF parameters for Si and $\rm{Si_{1−x}Ge_{x}}$ -based double gate (DG) tunnel FETs (TFETs). For the first time, asymmetric gate oxide is introduced in the gate-drain overlap and compared with that of DG TFETs. The DC parameter subthreshold swing (SS) and RF parameter metrics, unity gain cut-off frequency ($f_{t}$) and maximum oscillation frequency ($f_{max}$) are extracted by varying structural parameters, gate length ($L_{g}$), gate oxide thickness ($t_{ox}$), channel thickness ($t_{ch}$), doping parameters, channel doping ($N_{ch}$), drain doping ($N_{d}$) and source doping ($N_{s}$) in and around their nominal value. For a channel thickness of 15 nm, a very less SS of 8 mV/dec is achieved in $\rm{Si_{1−x}Ge_{x}}$ -based DG TFETs with gate-drain overlap. Variations of gate oxide thickness offer better RF performance enhancement for Si-based asymmetric gate oxide devices. This could be achieved because of the higher tunnelling rate of electrons occurring at the source side of asymmetric gate oxide devices.

    • Tunable microwave generation based on frequency quadrupling


      More Details Abstract Fulltext PDF

      To generate linearly chirped microwave signals with large frequency tunable range, a photonic approach is proposed. A dual-output dual-parallel Mach–Zehnder modulator followed by a polarisation beam combiner and an optical filter are utilised to generate orthogonally polarised $\pm$ second-order optical sidebands. A polarisation modulator is employed to achieve phase modulation of the two wavelengths. The balanced detection is applied to suppress the distortion and background noise. The central frequency of the generated signal is four times that of the local oscillator frequency. Simulation results show that a linear pulse is produced with time-bandwidth as well as a compression ratio for the pulse of 11 and 9.3 respectively. Moreover, a peak-to-sidelobe ratio of 7.4 dB is generated. The system has both good reconfigurability and tunability, and its frequency can be continuously adjusted from about 10 GHz to as much as 50 GHz in principle.

    • Strange non-chaotic attractors in a state controlled-cellular neural network-based quasiperiodically forced MLC circuit


      More Details Abstract Fulltext PDF

      In this paper, we report the dynamical transitions to strange non-chaotic attractors in a quasiperiodically forced state controlled-cellular neural network (SC-CNN) based MLC circuit via two different mechanisms, namely the Heagy–Hammel route and the gradual fractalisation route. These transitions were observed through numerical simulations and hardware experiments and confirmed using statistical tools, such as maximal Lyapunov exponent spectrum and its variance and singular continuous spectral analysis. We find that there is a remarkable agreement of the results from both numerical simulations as well as from hardware experiments.

    • All possible tripartitions of $^{236}\rm{U}$ isotope in collinear configuration


      More Details Abstract Fulltext PDF

      Using the recently proposed unified ternary fission model (UTFM), the tripartition of $^{236}\rm{U}$ isotope was studied for all possible fragmentations, in which the interacting potential barrier is taken as the sum of the Coulomb and proximity potentials with fragments in collinear configuration. The highest yield is obtained for the fragmentation $^{48}\rm{Ca}+^{58}\rm{Ti}+^{130}\rm{Sn}$ and next highest yield is found for $^{58}\rm{Cr}+^{46}\rm{Ar}+^{132}\rm{Sn}$,which stress the importance of doubly magic or near doubly magic nuclei in the tripartition of $^{236}\rm{U}$ isotope. The formation of $^{68}\rm{Ni}$ and $^{70}\rm{Ni}$ as the edge fragments linking the doubly magic nucleus $^{132}\rm{Sn}$ by the isotope of Si is in good agreement with experimental and theoretical studies, in the collinear cluster tripartition of $^{236}\rm{U}$ isotope which reveals the reliability of our model (UTFM) in ternary fission.

    • Deterministic assisted cloning of an unknown single-particle four-dimensional quantum state


      More Details Abstract Fulltext PDF

      In this paper, we present a scheme which can produce a perfect copy of an unknown single-particle four-dimensional quantum state with assistance from a state preparer. Two stages were included in this scheme. The first stage requires the usual teleportation, after Alice’s (the state sender) generalised Bell state measurement. Bob (the state receiver) can get the original state with unit probability. In the second stage, after having received Victor’s (the state preparer) classical message, and using the rest resource of the teleportation process, the perfect copy of an original unknown state can be produced in Alice’s place. To realise the scheme, several novel sets of measuring basis were introduced. It must be pointed out that, in the present scheme, the total success probability for assisted cloning of a perfect copy of the unknown state can reach 1.

    • The structure of ion-acoustic waves in a low-frequency three-component electron–ion space plasma with two-electron populations


      More Details Abstract Fulltext PDF

      Low-frequency ion-acoustic waves are analysed on the ion time-scale, in a three-component electron–ion space plasma. The solitary waves propagate in the positive $x$ direction relative to an ambient magnetic field $\overrightarrow{B}_{0}$ which forms static background for a configuration consisting of cool fluid ions and both warm and hot Boltzmann distributed electrons with temperatures $T_{ic}$, $T_{ew}$ and $T_{eh}$, respectively. We derive linear dispersion relation for the waves by introducing first-order density, pressure and velocity perturbations into the ion fluid equations. Additionally, the variation in the nonlinear structure of the waves are investigated by carrying out a full parametric analysis utilising our numerical code. Our results reveal that ion-acoustic waves exhibit well-defined nonlinear spikes at speeds of $M \geq 2.25$ and an electric field amplitude of $E_{0} = 0.85$. It is also shown that low wave speeds ($M \leq 2$), higher densities of the hot electrons, antiparallel drifting of the cool fluid ions, and increased ion temperatures all lead to significant dispersive effects. The ion-acoustic plasma waves featured in this paper have forms that are consistent with those classified as the type-A and type-B broadband electrostatic noise (BEN) observed in the data obtained from earlier satellite missions.

    • Geometry of magnetic rotational (MR) band-crossing phenomenon in MR bands


      More Details Abstract Fulltext PDF

      A semiclassical (SC) approach is proposed to calculate the $B(M1)$ transition rates in the band-crossing region of two magnetic rotational (MR) bands. In the present work, a geometry is suggested for the shear blades to govern its behaviour during the band-crossing. In the crossing region, gradual alignment of two nucleons is responsible for the crossing behaviour and it must give a quantised resultant angular momentum. As an example, it is successfully implemented for the MR bands in the mass $A = 110$ and $A = 200$ regions. A good agreement of the present semiclassical calculations with the experimental values is presented and furthermore, it is seen that the present proposal is also helpful to see the core contribution in the MR phenomenon.

    • Exact solutions to (2 + 1)-dimensional Chaffee–Infante equation


      More Details Abstract Fulltext PDF

      In this paper, the canonical-like transformation method and trial equation method are applied to (2+1)- dimensional Chaffee–Infante equation, and some exact solutions are obtained. In particular, a new solution in terms of elliptic functions is given.

    • Applicability of strange nonchaoticWien-bridge oscillators for secure communication


      More Details Abstract Fulltext PDF

      In this paper, experimental realisation of synchronisation of strange nonchaotic attractor inunidirectionally coupled Wien-bridge oscillator is presented. Preliminary work of chaotic and strange nonchaotic dynamics with diode as the nonlinear element is published in J. Nonlinear Dyn. 2015, 1 (2015). In this work, two Wien-bridge oscillators are coupled at the aperiodic dynamics for application in secure communication. The dynamics of the coupled system is explored by experimental and numerical studies. Employing the simple communication masking method with aperiodic dynamics offers some advantages rather than using chaotic attractors, i.e., the range of control parameter value is smaller than the range for which the system exhibits chaotic behaviour. The performance of the system is evaluated and it is found that experimental result agrees with numerical results.

    • Carpet oscillator: A new megastable nonlinear oscillator with infinite islands of self-excited and hidden attractors


      More Details Abstract Fulltext PDF

      In this paper, we design a new two-dimensional nonlinear oscillator with infinite number of coexisting limit cycles distributed in a plane. One-third of these limit cycles are self-excited attractors while two-third of them are hidden attractors. Modifying this new system to its forced version, we obtain a new nonlinear system with infinite number of coexisting torus attractors and limit cycle attractors.

    • Coexistence of attractors in autonomous Van der Pol–Duffing jerk oscillator: Analysis, chaos control and synchronisation in its fractional-order form


      More Details Abstract Fulltext PDF

      In this paper, a Van der Pol–Duffing (VdPD) jerk oscillator is designed. The proposed VdPD jerk oscillator is built by converting the autonomous two-dimensional VdPD oscillator to a jerk oscillator. Dynamical behaviours of the proposed VdPD jerk oscillator are investigated analytically, numerically and analogically. The numerical results indicate that the proposed VdPD jerk oscillator displays chaotic oscillations, symmetrical bifurcations and coexisting attractors. The physical existence of the chaotic behaviour found in the proposed VdPD jerk oscillator is verified by using Orcad-PSpice software. A good qualitative agreement is shown between thenumerical simulations and the PSpice results. Moreover, the fractional-order form of the proposed VdPD jerk oscillator is studied using stability theorem of fractional-order systems and numerical simulations. It is found that chaos, periodic oscillations and coexistence of attractors exist in the fractional-order form of the proposed jerk oscillator with order less than three. The effect of fractional-order derivative on controlling chaos is illustrated. It is shown that chaos control is achieved in fractional-order form of the proposed VdPD jerk oscillator only for the values of linear controller used. Finally, the problem of drive–response synchronisation of the fractional-order form of the chaotic proposed VdPD jerk oscillators is considered using active control technique.

    • Numerical simulation of unsteady 3D magneto-Sisko fluid flow with nonlinear thermal radiation and homogeneous–heterogeneous chemical reactions


      More Details Abstract Fulltext PDF

      The chemically reactive unsteady 3D Sisko fluid flow over a bidirectional stretched surface in the presence of nonlinear thermal radiation and magnetic field is considered. The numerical scrutiny of the transformed nonlinear ODEs is performed with the help of a numerical technique known as bvp4c. The mechanism of heat and mass transfer by the applications of chemical reaction and radiation is presented using temperature and concentration graphs. A remarkable enhancing results are estimated in the presence of nonlinear thermal radiation parameter $R_{d}$ and temperature ratio parameter $\theta_{w}$ for the temperature field. Another significant decreasing outcomes are found while plotting the concentration profile with variation of homogeneous and heterogeneous parameters ($k_{1}, k_{2}$). Computational results of the local skin friction and local Nusselt number are tabulated under the influence of physical parameters which governs the flow. Decrease in skin friction with varying values of $\lambda$ is observed. On the other hand, the impact of $R_{d}$ and $\theta_{w}$ on the tabular values of local Nusselt number is found in increasing order. All the graphical results and tabular values are illustrated while testing both cases of power-law fluids including pseudoplastic (0 & lt; n & lt; 1) and dilatant (n & gt; 1) behaviours. A comparison of the bvp4c and shooting technique with RK-45 Fehlberg is presented which shows excellent agreement. Additionally, the present results are compared with the results in the existing literature and both are found to be in very good correlation.

    • Aspects of improved heat conduction relation and chemical processes in 3D Carreau fluid flow


      More Details Abstract Fulltext PDF

      This article communicates the numerical consideration of 3D Carreau liquid flow under the impact of chemical responses over a stretched surface. Moreover, the heat transfer exploration is carried out with a view to improve the heat flux relation. This phenomenon is established upon the theory of Cattaneo–Christov heat flux relation that contributes by the thermal relaxation. On exploitation of an appropriate transformation a system of nonlinear ODEs is attained and then elucidated numerically by means of bvp4c scheme. The descriptions of temperature and concentration fields equivalent to the frequent somatic parameters are graphically scrutinised.Our analysis carries that the concentration of the Carreau liquid displays similar tendency and decline as theheterogeneous–homogeneous reaction parameters ($k_{2}, k_{1}$) augment. Furthermore, it is notable that for shear thinning ($n$ & lt; 1) liquid, the influence of local Weissenberg numbers ($We_{1}, We_{2}$) are absolutely conflicting compared with the instance of shear thickening ($n$ & gt; 1) liquid. Additionally, validation of numerical results is done via benchmarking with previously stated limiting cases with two different schemes namely, homotopy analysis method (HAM) and bvp4c scheme. These comparisons initiate a superb correspondence with these outcomes.

    • Effect of tensile and compressive strain on the magnetic ordering of the $\rm{(LaMnO_{3})_{1}/(SrTiO_{3})_{1}}$ superlattice

      A AEZAMI

      More Details Abstract Fulltext PDF

      We study the effects of tensile and compressive strain on the $\rm{(LaMnO_{3})_{1}/(SrTiO_{3})_{1}}$ superlattice from density functional theory using Quantum-Espresso open source code. In the unstrained superlattice, electron interactions in out-of-plane Mn–O–Ti chains are dominated by superexchange interactions, giving rise to ferromagnetic and half-metallic conducting characters. We found that the most stable magnetic configuration is G-type antiferromagnetic configuration for strong compressive strain and for strong tensile strain it isA-type antiferromagnetic configuration. The results are in accordance with the experimental observations which show that the superlattices can be grown on different substrates, and due to the difference in lattice parameters of the substrate and the main layer, there are also changes in the amount of strain applied to the superlattice.

  • Pramana – Journal of Physics | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.