• Volume 91, Issue 6

December 2018

• Multiswitching compound–compound synchronisation of six chaotic systems

In this paper, a novel synchronisation scheme involving six chaotic systems is proposed. The proposed scheme is named as ‘compound–compound synchronisation’. Instead of using a scaling system in compound synchronisation, a compound scaling signal is applied to the proposed scheme. The phenomenon of multiswitching synchronisation and the proposed scheme are combined together.Appropriate controllers are designed by employing nonlinear control method and Lyapunov stability theory to achieve asymptotically stable synchronisation states. An example of identical Chen systems is presented to demonstrate the proposed methodology. The proposed scheme is very different and complex in comparison with the previous schemes, as this scheme is first of its kind having five drive systems and one response system. Computational results are presented to justify the theoretical analysis. Numerical results and theoretical studies converge to the same conclusions.

• Lasing without population inversion in a four-level Y-type configuration in double quantum dot system

This work discusses lasing without inversion in Y-scheme in a double quantum dot nanostructure. This new type of lasing, which results from the quantum interference of spontaneous emission components, was not discussed earlier in quantum dot nanostructures. It is found that both pumping and cycling fields control the laser emission. The decrease of the cycling detuning increases the possibility of lasing. Probe detuning controls the width of the absorption bath (electromagnetic-induced transparency window) of this structure. This phenomenon canhave an interesting application for developing sources of coherent radiation in a region of electromagnetic spectrum where the implementation of traditional laser schemes is difficult.

• New stellar models generated using a quadratic equation of state

We obtain new regular exact solutions to the field equations for uncharged relativistic stellar objects with vanishing pressure anisotropy. We assume a quadratic equation of state and a choice of measure of anisotropy and a metric function defining one of the gravitational potentials. In our exact models, we regain anisotropic and isotropic results generated by other researchers as a special case. It is interesting that our results are in agreement withMinkowski space–time and earlier Einstein models. The physical analysis of the plots reveals that the gravitational potentials and matter variables are well behaved in the stellar interior. Using our model, we generate finite relativistic stellar masses which are consistent with the astronomical objects previously found by other researchers.

• Aharonov–Bohm effect in the ghost interference

In the ghost interference experiment, a pair of entangled particles is sent in the opposite directions; one of the particles passes through a Young double-slit while the other continues its way freely. It turns out that the particles passing through the slits do not show any first-order interference while those propagating freely constitute an interference pattern when they are detected in coincidence with those which pass through the slits and detectedat a fixed position. In this work, we consider that the particles are charged and the effect of a confined magnetic field is analysed between the slits in an Aharonov–Bohm configuration.

• Potentials and phase shifts for nucleon–light nuclei systems

Two simple models based on the Coulomb-distorted phase function and supersymmetry-inspired factorisation methods are adapted to deal with the nucleon–light nuclei elastic scattering at low energies. The first one is associated with the derivation of a closed-form expression of the scattering phase shift for motionin Coulomb-distorted separable non-local potentials. The second one deals with the development of an energy dependent phase equivalent local potential to the non-local one for s-wave and its subsequent generation of higher partial wave interactions through the formalism of supersymmetric quantum mechanics. The usefulness of our models is demonstrated through the computation of α–nucleon scattering phase shifts at low energies up to partialwaves $\ell$ = 2. Certain energy-dependent correction factors are also incorporated into energy-dependent higher partial wave potentials to achieve an excellent agreement with the standard data.

• Ionisation of metastable 3P-state hydrogen atom by electron with exchange effects

In the present work, the triple-differential cross-sections (TDCSs) for the ionisation of metastable 3P-state hydrogen atoms at an incident electron energy of 250 eV with exchange effects are computed in the asymmetric coplanar geometry for various kinematic conditions. The final-state wave function of Das and Seal (Phys. Rev. A 47, 2978 (1993)) is used here. The results of the present calculation are compared with the available hydrogenic ground-state experimental data and other existing theoretical results. An analysis of the results reveals qualitative enhancement with other compared results. The implication of the present study offers an extensive scope for experimental verification in such a field of ionisation.

• The effect of static external magnetic field on the nonlinear absorption of the S-polarised short laser pulse in collisional underdense plasma

Inverse Bremsstrahlung absorption is a mechanism for generating heat in the inertial confinement fusion (ICF) process. To maximise the heat produced, it is desirable to investigate the possibilities for increasing the absorption rate through the inverse Bremsstrahlung process. It should be noted that some absorption mechanismsfound for nanosecond long laser pulses also appear for ultrashort laser pulses. In this paper, the physics of absorption for S-polarised laser pulse and magnetised underdense plasma interaction in the presence of electrons ohmic heating and ponderomotive nonlinearities is analysed for both collisional isothermal and collisional non-isothermal magnetised plasmas. Here, we show that, in the presence of a static magnetic field, the absorption rate of the S-polarised laser pulse through interaction with underdense plasma can be increased intensively. In other words, by applying an external magnetic field, the laser pulse radiation will penetrate a region of greater plasma density compared to the case of non-magnetised plasma for the S-polarised absorption. It is remarkable that due to the heat of the plasma at the expanse of the wave energy in the case of the non-thermal, magnetised and collisional plasma, the absorption coefficient is increased intensively in comparison with the collisional plasma.

• Time growth rate optimisation of terahertz electromagnetic wave generation by converting occupied plasma region from annular plasma to filled plasma in the core, in an elliptical Cherenkov maser with two energy sources

In this work, a comparison between two different cases of an elliptical Cherenkov maser with two electron beams for the generation and amplification of terahertz electromagnetic waves has been presented. The waveguide is made of a hollow dielectric layer filled with a cold collisionless unmagnetised plasma. In the above mentionedconfiguration, there are two electron beams with opposite velocities. The dispersion relation graph and its characteristics, such as its dependence on geometrical dimensions and characteristics of the electron beam, are presented. The growth rates of the hybrid modes are numerically calculated and their diagrams in some operatingfrequencies are studied. The effective factors on the time growth rate of hybrid electromagnetic waves, such as geometrical dimensions, dielectric constant of the dielectric layer, accelerating voltage, plasma frequency and applied current intensity, are analysed. It is shown that the injection of background plasma into the core region of the waveguide can enhance the output frequency and the wave growth rate of the beam–wave interaction.

• Vernier effect of cascaded dual microring sensor

We demonstrate a Vernier microring sensor consisting of a traditional cascaded dual microring resonator and an additional measurement range unit. The sensor’s performance is simulated for different concentrations of aqueous solutions of ethylene glycol ($\rm{C_{2}H_{6}O_{2}}$). The theoretical sensitivity of our system is as high as 7386 nm/RIU, an order of magnitude much larger than that of the traditional cascaded dual microring sensor (562 nm/RIU), 13.1 times more than the traditional cascaded dual microring sensor. At the same time, the measurement range can reach as high as $2.49 × 10^{−2}$ RIU.

• Coexisting multiscroll hyperchaotic attractors generated from a novel memristive jerk system

In this paper, two kinds of novel non-ideal voltage-controlled multi-piecewise cubic nonlinearity memristors and their mathematical models are presented. By adding the memristor to the circuit of a three dimensional jerk system, a novel memristive multiscroll hyperchaotic jerk system is established without introducing any other ordinary nonlinear functions, from which $2N + 2$-scroll and $2M + 1$-scroll hyperchaotic attractors are achieved. It is exciting to note that this new memristive system can produce the extreme multistability phenomenonof coexisting infinitely multiple attractors. Furthermore, the dynamical behaviours of the proposed system are analysed by phase portraits, equilibrium points, Lyapunov exponents and bifurcation diagrams. The results indicate that the system exhibits hyperchaotic, chaotic and periodic dynamics. Especially, the phenomenon of transient chaoscan also be found in this memristive multiscroll system. Additionally, the MULTISIM circuit simulations and the hardware experimental results are performed to verify numerical simulations.

• Soliton formations for magnetohydrodynamic viscous flow over a nonlinear stretching sheet

In the present paper, the main focus is to study soliton formations of a two-dimensional magnetohydrodynamic flow over a nonlinear stretching sheet with the help of transformed rational function method. The fluid is electrically conductive, normal to the stretching sheet and there is no induced magnetic field. The flowproblem is described by the continuity and momentum equation with suitable boundary conditions. For solving the model, the nonlinearity poses a great challenge. Nonlinear partial differential equation has been converted into a nonlinear ordinary differential equation by using similarity transformations, and then a trial solution is assumed. The results indicate complete consistency and effectiveness of the suggested scheme compared with the existing literature.

• Effect of electric field and temperature on the binding energy of bound polaron in an anisotropic quantum dot

The ratio between the confinement lengths in the $xy$-plane and the $z$ direction plays an important role in determining the properties of anisotropic quantum dot. Within a variational approach of Pekar type, we investigated theoretically the effects of electric field and temperature on the ground-state binding energies of hydrogenic impurity polarons in KBr anisotropic quantum dot. The obtained results illustrate that the binding energies increase with the electric field strength and temperature but decrease with the position of the impurity when considering different confinement lengths in the $xy$-plane and the $z$ direction and present the properties of the anisotropic quantum dot.

• Simulation of the wave-absorbing model of a carbonyl iron/silver-coated core–shell structure

The microwave-absorbing performances of carbonyl iron powder/silver core–shell composite particles are studied on the basis of the electromagnetic scattering theory and the energy conservation law. In addition, a calculation method for reflection loss of the carbonyl iron powder/silver core–shell composite particles with microwave is proposed. The calculated reflection loss of the carbonyl iron powder/silver core–shell composite particles is compared with the experimental results. The findings show that the trend of reflection loss of the carbonyl iron powder/silver composite particles can be predicted which can subsequently provide a relevant reference for future experiment and calculation of the absorbing mechanism of electromagnetic wave-microscopic carbonyl ironpowder/silver core–shell composite particles.

• Clusterisation and isospin effects in heavy-ion collisions at intermediate energies

We study the multifragmentation phenomenon in heavy-ion collisions by varying the spatial constraint criterion in minimum spanning tree (MST) clusterisation procedure. Within the framework of isospin-dependent quantum molecular dynamics (IQMD) model, the role of isospin-dependent spatial constraint, i.e. iso-MST version, is investigated on different fragment observables in various isobaric pair of reaction systems varying in the entrance channel isospin (N/Z) content. The fragment observables such as persistence, gain, average yield of free nucleons, light and intermediate mass fragments are slightly sensitive to the isospin-dependent spatial constraint criterion particularly in heavier reaction systems. For a given isobaric pair of reaction systems, the fragment production, however, remains indifferent to isospin content of the colliding nuclei.

• Shape, size and phonon scattering effect on the thermal conductivity of nanostructures

A phenomological model is described here to study the effect of size, shape and phonon scattering on the thermal conductivity of nanostructures. Using the classical model proposed by Guisbiers et al (Phys. Chem. Chem. Phys. 12, 7203 (2010), J. Phys. Chem. C 112, 4097 (2008)) in terms of the melting temperature of nanostructures, the expression for variation of thermal conductivity is obtained in terms of shape and size parameter. An additional term is included in the expression of thermal conductivity to consider the impact of phonon scattering due to the surface roughness with a decrease in size. The expression of thermal conductivity is obtained for spherical nanosolids, nanowires and nanofilms. The thermal conductivity is found to decrease in nanostructures in comparison with the counterpart bulk material. The values of thermal conductivity obtained from the present model are found to be close to the available experimental data for different values of roughness parameter which verifies the suitability of the model.

• Nonlinear propagation of ion plasma waves in dust-ion plasma including quantum-relativistic effect

In this paper we have theoretically investigated the quantum and relativistic effects on ion plasma wave in an unmagnetised dust-ion plasma. By using the method of normal mode analysis, we have obtained a linear dispersion relation. It has been analysed numerically for quantum and relativistic effects on the propagation of ion plasma wave. By using the standard reductive perturbation technique, we have derived a Korteweg–de Vries (KdV) equation which describes the nonlinear propagation of the wave. Numerically, it is shown that only compressive type of soliton can exist in the plasma under consideration. It is found that the solitary wave profile depends significantly on the quantum and relativistic parameters. The dust size, dust charge and the dust number density are also shown to have significant influences on these solitary waves. The results of this present investigation have some relevance to the nonlinear propagation of ion plasma wave in some astrophysical, space and laboratory plasma environments.

• Multistability in coupled different-dimensional dynamical systems

Multistability or coexistence of different chaotic attractors for a given set of parameters depending on the initial condition only is one of the most exciting phenomenon in dynamical systems. The schemes to designmultistability systems via coupling two identical or non-identical but the same-dimensional systems have been proposed earlier. Coupled different-dimensional systems are very useful to describe the real-world physical and biological systems. In this paper, a scheme for designing a multistable system by coupling two different-dimensional dynamical systems has been proposed. Coupled Lorenz and Lorenz–Stenflo systems have been considered to illustrate the scheme. The efficiency of the scheme is shown numerically, by presenting phase diagrams, bifurcation diagrams and variation of maximum Lyapunov exponents.

• # Pramana – Journal of Physics

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