• Volume 79, Issue 6

December 2012,   pages  1365-1549

• Allowable irreducible representations of the point groups with five-fold rotational axes

Allowable irreducible representations of the point groups with five-fold rotations – that represent the symmetry of the quasicrystals in two and three dimensions – are derived by employing the little group technique in conjunction with the solvability property. The point groups $D_{5h}(\bar{10}m2)$ and $I_{h}(\dfrac{2}{m} \bar{3} \bar{5})$ are taken to illustrate the method.

• A universal projective synchronization of general autonomous chaotic system

This paper investigates the generalized projective synchronization in general autonomous chaotic system. A universal controller is designed and the effectiveness is verified via theoretical analysis and numerical simulations. The controller design is irrelevant to concrete system structure and initial values. It has strong robustness and broad application perspective.

• Open flavour charmed mesons in a quantum chromodynamics potential model

We modify the mesonic wave function by using a short distance scale $r_{0}$ in analogy with hydrogen atom and estimate the values of masses and decay constants of the open flavour charm mesons 𝐷, $D_{s}$ and $B_{c}$ within the framework of a QCD potential model. We also calculate leptonic decay widths of these mesons to study branching ratios and lifetime. The results are in good agreement with experimental and other theoretical values.

• Quantitative assessment of target dependence of pion fluctuation in hadronic interactions – estimation through erraticity

Event-to-event fluctuation pattern of pions produced by proton and pion beams is studied in terms of the newly defined erraticity measures $\chi (p, q)$, $\chi_{q}^{'}$ and $\mu_{q}^{'}$ proposed by Cao and Hwa. The analysis reveals the erratic behaviour of the produced pions signifying the chaotic multiparticle production in high-energy hadron–nucleus interactions ($\pi^{-}$ –AgBr interactions at 350 GeV/c and 𝑝–AgBr interactions at 400 GeV/c). However, the chaoticity does not depend on whether the projectile is proton or pion. The results are compared with the results of the VENUS-generated data for the above interactions which suggests that VENUS event generator is unable to reproduce the event-to-event fluctuations of spatial patterns of final states. A comparative study of 𝑝–AgBr interactions and $p-p$ collisions at 400 GeV/c from NA27, with the help of a quantitative parameter for the assessment of pion fluctuation, indicates conclusively that particle production process is more chaotic for hadron–nucleus interactions than for hadron–hadron interactions.

• Transverse momentum distributions of identified particles produced in $pp$, $p(d)A$, and $AA$ collisions at high energies

Using a unified description on multiplicity distributions of final-state particles, the transverse momentum distributions of identified particles produced in proton–proton $(pp)$, proton– and deuteron–nucleus $[p(d)A]$, and nucleus–nucleus $(AA)$ collisions at high energies are studied in this paper. We assume that the transverse momentum distributions of identified particles measured in final state are contributed by a few energy sources which can be regarded as partons or quarks in the interacting system. The particle is contributed by each source with gluons which have transverse momentum distributions in an exponential form. The modelling results are compared and found to be in agreement with the experimental data at high energies.

• Generation of tunable 16 𝜇m radiation from CO2 by cascade lasing

In this paper we propose a scheme to generate tunable 16 𝜇m radiation from CO2 molecules by cascade lasing. The stimulating 9.5 𝜇m radiation is generated internally by the fast rotating mirror Q-switching technique. The optical scheme proposed by us uses an intracavity prism to separate the 9.5 𝜇m and the 16 𝜇m beams. This facilitates independent tuning of the two beams if required. In the present configuration, only the 16 𝜇m cavity is dispersive. The 9.5 𝜇m beam grows spontaneously in a stable semiconfocal resonator. We have developed a theoretical model to simulate the proposed scheme. The model predicts the energy and power of 16 𝜇m radiation. The calculated values are much higher than the previously obtained experimental values. The results point out the feasibility of developing a laser system based on the theoretical design parameters presented in this paper. Such laser systems can find application in uranium isotope separation studies.

• Influence of pseudorandom bit format on the direct modulation performance of semiconductor lasers

This paper investigates the direct gigabit modulation characteristics of semiconductor lasers using the return to zero (RZ) and non-return to zero (NRZ) formats. The modulation characteristics include the frequency chirp, eye diagram, and turn-on jitter (TOJ). The differences in the relative contributions of the intrinsic noise of the laser and the pseudorandom bit-pattern effect to the modulation characteristics are presented. We introduce an approximate estimation to the transient properties that control the digital modulation performance, namely, the modulation bit rate and the minimum (setting) bit rate required to yield a modulated laser signal free from the bit pattern effect. The results showed that the frequency chirp increases with the increase of the modulation current under both RZ and NRZ formats, and decreases remarkably with the increase of the bias current. The chirp is higher under the RZ modulation format than under the NRZ format. When the modulation bit rate is higher than the setting bit rate of the relaxation oscillation, the laser exhibits enhanced TOJ and the eye diagram is partially closed. TOJ decreases with the increase of the bias and/or modulation current for both formats of modulation.

• Heat transfer in MHD flow of dusty viscoelastic (Walters’ liquid model-B) stratified fluid in porous medium under variable viscosity

The paper investigates the effects of heat transfer in MHD flow of viscoelastic stratified fluid in porous medium on a parallel plate channel inclined at an angle 𝜃. A laminar convection flow for incompressible conducting fluid is considered. It is assumed that the plates are kept at different temperatures which decay with time. The partial differential equations governing the flow are solved by perturbation technique. Expressions for the velocity of fluid and particle phases, temperature field, Nusselt number, skin friction and flow flux are obtained within the channel. The effects of various parameters like stratification factor, magnetic field parameter, Prandtl number on temperature field, heat transfer, skin friction, flow flux, velocity for both the fluid and particle phases are displayed through graphs and discussed numerically.

• Dynamic imaging and hydrodynamics study of high velocity, laser-accelerated thin foil targets using multiframe optical shadowgraphy

The main aim of the study of thin target foil–laser interaction experiments is to understand the physics of hydrodynamics of the foil acceleration, which is highly relevant to inertial confinement fusion (ICF). This paper discusses a simple, inexpensive multiframe optical shadow-graphy diagnostics developed for dynamic imaging of high velocity laser-accelerated target foils of different thicknesses. The diagnostic has a spatial and temporal resolution of 12 𝜇m and 500 ps respectively in the measurements. The target velocity is in the range of $10^{6} - 10^{7}$ cm/s. Hydrodynamic efficiency of such targets was measured by energy balance experiments together with the measurement of kinetic energy of the laser-driven targets. Effect of target foil thickness on the hydrodynamics of aluminum foils was studied for determining the optimum conditions for obtaining a directed kinetic energy transfer of the accelerated foil. The diagnostics has also been successfully used to study ablatively accelerated targets of other novel materials.

• The effect of impurity on transition frequency of bound polaron in quantum rods

The Hamiltonian of a quantum rod with an ellipsoidal boundary is given after a coordinate transformation that changes the ellipsoidal boundary into a spherical one. The properties of the quantum rods constituting the bridge between two-dimensional quantum wells, zero-dimensional quantum dots and one-dimensional quantum wires are explored theoretically using linear combination operator method. The first internal excited state energy, the excitation energy and the transition frequency between the first internal excited and the ground states of the strong-coupled impurity-bound polaron in the rod with Coulomb-bound potential, the transverse effective confinement length, the ellipsoid aspect ratio and the electron–phonon coupling strength are studied. It is found that the first internal excited state energy, the excitation energy and the transition frequency are increasing functions of the Coulomb-bound potential and the electron–phonon coupling strength, whereas they are decreasing functions of the ellipsoid aspect ratio and the transverse effective confinement length. These results can be attributed to the interesting quantum size confining effects.

• Effect of oxygen deficiency on the magnetic field-dependent entropy in YBa2 Cu3 O$_{7−\delta}$

Roulin $\mathit{et}$ $\mathit{al}$ (1988), in one of their experimental papers, have presented a study of field-dependent entropy of high-purity YBa2 Cu3 O$_{7−\delta}$ (YBCO) as a function of oxygen deficiency. In order to explain their experimental results, we have used phenomenological GL-theory of anisotropic HTSCs in the London limit in line with of our earlier paper (Pattanaik $\mathit{et}$ $\mathit{al}$, Physica B405, 3234 (2010)). Moreover, to account for the applicability of the theory at high field, we have incorporated the effect of vortex overlapping in the London theory done by Nanda (1995). Here, we have presented the variation of change in entropy (𝛥S) with magnetic field for different oxygen deficiencies $\delta = 0$, 0.04, and 0.06. On comparison, we found that our results are in good agreement with the experimental data of Roulin $\mathit{et}$ $\mathit{al}$ (1988). The variation of penetration depth (𝜆) and anisotropic ratio of effective masses (𝛾) with concentration is also presented.

• Effect of different donors and a polymer environment on photophysical and energy transfer studies using C540 as the acceptor

The dyes (C450, C480 and C540) and their dye mixtures (C450:C540 and C480:C540) were doped in polymer matrices (solid). Their photophysical studies were recorded. These results were analysed by comparing them with the data of the dyes and the dye mixtures in monomer compositions (liquid). The absorption and fluorescence spectral profiles of the dyes in the polymer matrix were found to be identical to those in the monomer compositions. The effect of different donors on the energy transfer technique using C540 as acceptor, in polymer matrix and monomer compositions, was studied in detail. The results obtained for the energy transfer technique in two binary dye mixtures containing different donors but same acceptor, in solid and liquid media, were intercompared. The gain of the acceptor without donor and with different donors was determined experimentally. The gain coefficient in the polymer matrix (solid) was less than that in the monomer medium (liquid). Also, the gain of the acceptor C540 was found to be more when C450 was used as the donor compared to that when C480 was used as the donor. Using nitrogen laser, the photobleaching effect in the two binary dye-doped polymer rods (with different donors but same acceptor) was studied. It was observed that photobleaching of the acceptor C540 in the presence of C450 as donor is slower than that in the presence of C480 as donor.

• Single-mode fibre coupler as refractometer sensor

We report a simple, non-intrusive fibre-optic refractometer sensor for measuring the refractive index of liquid and optically transparent solid medium. Sensing principle of the proposed sensor is based on monitoring the back-reflected light signal through the second input port of a $2 \times 1$ single-mode fibre coupler when light signal from the output port is focussed at the interface of air and a liquid or solid medium and back-reflected exactly along the same path. Depending on the refractive index of the medium, the amount of back-reflected intensity would vary and in the present work we exploit this principle to measure the refractive index of an optically transparent medium. Variation of refractive index as small as 0.001 RIU can be measured with our proposed sensor.

• Subject Index of Volume 79

• Author Index of Volume 79

• Pramana – Journal of Physics

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• Editorial Note on Continuous Article Publication

Posted on July 25, 2019