• Issue front cover thumbnail

      Volume 72, Issue 2

      February 2009,   pages  303-456

    • Slow light with symmetric gap plasmon guides with finite width metal claddings

      S Dutta Gupta

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      We study the dispersion relation and the modes of a symmetric gap plasmon guide, where a dielectric planar slab is coated with finite metallic layers on both top and bottom. The finite conductivity of the metal is taken into account. The modes of the structure exhibit significant differences from those of dielectric waveguides with air or metal as the bounding media. Avoided level crossing phenomenon between the plasmon and the guided modes is shown to exist, leading to leaky modes. The structure sandwiched between two high index media is shown to lead to slow light in transmission. The group delay is shown to be larger for higher order modes.

    • Formulation of statistical mechanics for chaotic systems

      Vishnu M Bannur Ramesh Babu Thayyullathil

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      We formulate the statistical mechanics of chaotic system with few degrees of freedom and investigated the quartic oscillator system using microcanonical and canonical ensembles. Results of statistical mechanics are numerically verified by considering the dynamical evolution of quartic oscillator system with two degrees of freedom.

    • Efficient use of correlation entropy for analysing time series data

      K P Harikrishnan R Misra G Ambika

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      The correlation dimension $D_{2}$ and correlation entropy $K_{2}$ are both important quantifiers in nonlinear time series analysis. However, use of $D_{2}$ has been more common compared to $K_{2}$ as a discriminating measure. One reason for this is that $D_{2}$ is a static measure and can be easily evaluated from a time series. However, in many cases, especially those involving coloured noise, $K_{2}$ is regarded as a more useful measure. Here we present an efficient algorithmic scheme to compute $K_{2}$ directly from a time series data and show that $K_{2}$ can be used as a more effective measure compared to $D_{2}$ for analysing practical time series involving coloured noise.

    • Determination of 68Ga production parameters by different reactions using ALICE and TALYS codes

      Mahdi Sadeghi Tayeb Kakavand Leila Mokhtari Zohreh Gholamzadeh

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      Gallium-68 ($T_{1/2} = 68$ min, $I_{\beta+} = 89%$) is an important positron-emitting radionuclide for positron emission tomography and used in nuclear medicine for diagnosing tumours. This study gives a suitable reaction to produce 68Ga. Gallium-68 excitation function via 68Zn$(p, n)$ 68Ga, 68Zn$(d, 2n)$ 68Ga, 70Zn$(p, 3n)$ 68Ga and 65Cu$(\alpha, n)$ 68Ga reactions were calculated by ALICE-91 and TALYS-1.0 codes. The calculated excitation function of 68Zn$(p, n)$ 68Ga reaction was compared with the reported measurement and evaluations. Requisite thickness of the targets was obtained by SRIM code for each reaction. The 68Ga production yield was evaluated using excitation function and stopping power.

    • Equilibrium and pre-equilibrium emissions in proton-induced reactions on 203,205Tl

      A Kaplan A Aydin E Tel B Şarer

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      In this study, the excitation functions for the reactions 203Tl$(p, n)^{203}$Pb, 203Tl$(p, 3n)^{203}$Pb, 203Tl$(p, 2n)^{202}$Pb, 205Tl$(p, 4n)^{202}$Pb, 203Tl$(p, 3n)^{201}$Pb, 205Tl$(p, 5n)^{201}$Pb, 203Tl$(p, 4n)^{200}$Pb and 205Tl$(p, 6n)^{200}$Pb have been calculated using pre-equilibrium and equilibrium reaction mechanisms. Calculated results based on hybrid model, geometry-dependent hybrid model and cascade-exciton model have been compared with the experimental data.

    • Empirical relation and establishment of shell effects in $(n, 2n)$ reaction cross-sections at 14 MeV

      Sneh Lata Goyal Pratibha Gur

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      The experimental data for $(n, 2n)$ reaction cross-sections around 14 MeV neutron energy have been collected from the literature and analysed for the isotopes having $1 \leq Z \leq 82$. The empirical relations for the reaction cross-sections have been obtained, which show fairly good fits with the experimental values. The shell effects have been established at magic nucleon numbers for $(n, 2n)$ reaction cross-sections around 14 MeV neutron energy. The odd–even effects have also been observed as the cross-sections for odd-mass nuclei are higher than their neighbouring even–even nuclei.

    • Reaction mechanism study of 7Li(7Li, 6He) reaction at above Coulomb barrier energies

      V V Parkar V Jha S Santra B J Roy K Ramachandran A Shrivastava K Mahata A Chatterjee S Kailas

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      The elastic scattering and the 6He angular distributions were measured in 7Li + 7Li reaction at two energies, $E_{lab} = 20$ and 25 MeV. FRDWBA calculations have been performed to explain the measured 6He data. The calculations were very sensitive to the choice of the optical model potentials in entrance and exit channels. The one-step proton transfer was found to be the dominant reaction mechanism in 6He production.

    • Simple parametrization of photon mass energy absorption coefficients of H-, C-, N- and O-based samples of biological interest in the energy range 200–1500 keV

      V Manjunathaguru T K Umesh

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      In this paper, we provide polynomial coefficients and a semi-empirical relation using which one can derive photon mass energy absorption coefficient of any H-, C-, N-, O-based sample of biological interest containing any other elements in the atomic number range 2–40 and energy range 200–1500 keV. More interestingly, it has been observed in the present work that in this energy range, both the mass attenuation coefficients and the mass energy absorption coefficients for such samples vary only with respect to energy. Hence it was possible to represent the photon interaction properties of such samples by a mean value of these coefficients. By an independent study of the variation of the mean mass attenuation coefficient as well as mass energy absorption coefficient with energy, two simple semi-empirical relations for the photon mass energy absorption coefficients and one relation for the mass attenuation coefficient have been obtained in the energy range 200–1500 keV. It is felt that these semi-empirical relations can be very handy and convenient in biomedical and other applications. One possible significant conclusion based on the results of the present work is that in the energy region 200–1500 keV, the photon interaction characteristics of any H-, C-, N-, O-based sample of biological interest which may or may not contain any other elements in the atomic number range 2–40 can be represented by a sample-independent (single) but energy-dependent mass attenuation coefficient and mass energy absorption coefficient.

    • Ultrasonic investigations in intermetallics

      Devraj Singh D K Pandey

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      Ultrasonic attenuation for the longitudinal and shear waves due to phonon–phonon interaction and thermoelastic mechanism have been evaluated in B2 structured in-termetallic compounds AgMg, CuZr, AuMg, AuTi, AuMn, AuZn and AuCd along $\langle 1 0 0 \rangle, \langle 1 1 1 \rangle and \langle 1 1 0 \rangle crystallographic directions at room temperature. For the same evaluations, second- and third-order elastic constants, ultrasonic velocities, Grüneisen parameters, non-linearity parameter, Debye temperature and thermal relaxation time are also computed. Although the molecular weight of these materials increases from AgMg to AuCd, the obtained results are affected with the deviation number. Attenuation of ultrasonic waves due to phonon–phonon interaction is predominant over thermoelastic loss. Results are compared with available theoretical and experimental results. The results with other well-known physical properties are useful for industrial purposes.

    • Magnetoelectronic transport of the two-dimensional electron gas in CdSe single quantum wells

      P K Ghosh A Ghosal D Chattopadhyay

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      Hall mobility and magnetoresistance coefficient for the two-dimensional (2D) electron transport parallel to the heterojunction interfaces in a single quantum well of CdSe are calculated with a numerical iterative technique in the framework of Fermi–Dirac statistics. Lattice scatterings due to polar-mode longitudinal optic (LO) phonons, and acoustic phonons via deformation potential and piezoelectric couplings, are considered together with background and remote ionized impurity interactions. The parallel mode of piezoelectric scattering is found to contribute more than the perpendicular mode. We observe that the Hall mobility decreases with increasing temperature but increases with increasing channel width. The magnetoresistance coefficient is found to decrease with increasing temperature and increase with increasing magnetic field in the classical region.

    • Effects of quantum coupling on the performance of metal-oxide-semiconductor field transistors

      Ling-Feng Mao

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      Based on the analysis of the three-dimensional Schrödinger equation, the effects of quantum coupling between the transverse and the longitudinal components of channel electron motion on the performance of ballistic MOSFETs have been theoretically investigated by self-consistently solving the coupled Schrödinger–Poisson equations with the finite-difference method. The results show that the quantum coupling between the transverse and the longitudinal components of the electron motion can largely affect device performance. It suggests that the quantum coupling effect should be considered for the performance of a ballistic MOSFET due to the high injection velocity of the channel electron.

    • Bianchi type-V cosmological models with perfect fluid and heat flow in Saez–Ballester theory

      Shri Ram M Zeyauddin C P Singh

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      In this paper we discuss the variation law for Hubble's parameter with average scale factor in a spatially homogeneous and anisotropic Bianchi type-V space-time model, which yields constant value of the deceleration parameter. We derive two laws of variation of the average scale factor with cosmic time, one is of power-law type and the other is of exponential form. Exact solutions of Einstein field equations with perfect fluid and heat conduction are obtained for Bianchi type-V space-time in these two types of cosmologies. In the cosmology with the power-law, the solutions correspond to a cosmological model which starts expanding from the singular state with positive deceleration parameter. In the case of exponential cosmology, we present an accelerating non-singular model of the Universe. We find that the constant value of deceleration parameter is reasonable for the present day Universe and gives an appropriate description of evolution of Universe. We have also discussed different types of physical and kinematical behaviour of the models in these two types of cosmologies.

    • Locally-rotationally-symmetric Bianchi type-V cosmology in general relativity

      C P Singh

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      A spatially homogeneous locally-rotationally-symmetric (LRS) Bianchi type-V cosmological model is considered with a perfect fluid in general relativity. We present two types of cosmologies (power-law and exponential forms) by using a law of variation for the mean Hubble parameter that yields a constant value for the deceleration parameter. We discuss the physical properties of the non-flat and flat models in each cosmology. Exact solutions that correspond to singular and non-singular models are presented. In a generic situation, models can be interpolated between different phases of the Universe. We find that a constant value for the deceleration parameter is reasonable for a description of different phases of the Universe. We arrive at the conclusion that the Universe decelerates when the value of the deceleration parameter is positive whereas it accelerates when the value is negative. The dynamical behaviours of the solutions and kinematical parameters like expansion, shear and the anisotropy parameter are discussed in detail in each section. Exact expressions for look-back time, luminosity distance and event horizon vs. redshift are derived and their significances are discussed in some detail. It has been observed that the solutions are compatible with the results of recent observations.

    • Effects of three-body atomic interaction and optical lattice on solitons in quasi-one-dimensional Bose–Einstein condensate

      S K Golam Ali B Talukdar Aparna Saha

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      We make use of a coordinate-free approach to implement Vakhitov–Kolokolov criterion for stability analysis in order to study the effects of three-body atomic recombination and lattice potential on the matter–wave bright solitons formed in Bose–Einstein condensates. We analytically demonstrate that (i) the critical number of atoms in a stable BEC soliton is just half the number of atoms in a marginally stable Townes-like soliton and (ii) an additive optical lattice potential further reduces this number by a factor of $\sqrt{1 − b_{g3}$ with $g_{3}$ the coupling constant of the lattice potential and $b = 0.7301$.

    • A relativistic quark–diquark model for the nucleon

      Cristian Leonardo Gutierrez Maurizio De Sanctis

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      We developed a constituent quark–diquark model for the nucleon and its resonances using a harmonic oscillator potential for the interaction. The effects due to relativistic kinetic energy correction are studied. Finally, charge form factor of the model is calculated and compared with experimental data.

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