• Volume 63, Issue 3

      September 2004,   pages  481-641

    • Bianchi type-I bulk viscous fluid string dust magnetized cosmological model in general relativity

      Raj Bali Anjali

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      Bianchi Type-I magnetized bulk viscous fluid string dust cosmological model is investigated. To get a determinate model, we have assumed the conditions σ ∝θ andζθ = constant where σ is the shear,θ the expansion in the model andζ the coefficient of bulk viscosity. The behaviour of the model in the presence and absence of magnetic field together with physical and geometrical aspects of the model are also discussed.

    • Flavour-changing neutral currents in models with extraZ′ boson

      S Sahoo L Maharana

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      New neutral gauge bosonsZ′ are the features of many models addressing the physics beyond the standard model. Together with the existence of new neutral gauge bosons, models based on extended gauge groups (rank > 4) often predict new charged fermions also. A mixing of the known fermions with new states, with exotic weak-isospin assignments (left-handed singlets and right-handed doublets) will induce tree-level flavour-changing neutral interactions mediated byZ exchange, while if the mixing is only with new states with ordinary weak-isospin assignments, the flavour-changing neutral currents are mainly due to the exchange of the new neutral gauge bosonZ′. We review flavour-changing neutral currents in models with extraZ′ boson. Then we discuss some flavour-changing processes forbidden in the standard model and new contributions to standard model processes.

    • Three-body analysis of11Li and itsβ-decay to deuteron channel and to halo analog state11Be* (18.3 MeV)

      S Kumar V S Bhasin

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      The ground state wave function of11Li obtained in a three-body model proposed earlier (S Kumar and V S Bhasin,Phys. Rev.C65, 034007 (2002)) has been employed to study the probability distributions, momentum distributions and n−n correlation. Complex scaling method has been used to find the energy positions and widths of the three resonant states of11Li above the breakup threshold. The formalism is extended further to study the β-decay of11Li to two channels. One is the β-transition of11Li into a high lying excited state of11Be at 18.3 MeV, i.e.,11Be* and the second is the decay to deuteron +9Li channel. The11Be* state has been considered as a halo analog state identified as a bound three-body (9Li + n + p) system. The n-9Li interaction incorporates both the virtual state and the p-wave resonance observed experimentally. For p-9Li interaction, a Coulomb corrected separable interaction is constructed using charge indepedendence for strong interaction part. The n-p interaction is operative only in3S1 state corresponding to the isotopic spin Th =0. As a result the11Be* state has the same isotopic spin as that of9Li core, i.e.,T = 3/2. Using these realistic parameters as input and without invoking any other free parameter, the model has been used to predict the strength of the Gamow-Teller β-decay of11Li to11Be*, i.e.,Bgt = 1.5 and the value of the branching ratio to9Li + deuteron channel to be 1.3 × 10-4. These results are found to be in rather good agreement with the recent experimental findings.

    • Photon mass attenuation coefficients, effective atomic numbers and electron densities of some thermoluminescent dosimetric compounds

      Shivalinge Gowda S Krishnaveni T Yashoda T K Umesh Ramakrishna Gowda

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      Photon mass attenuation coefficients of some thermoluminescent dosimetric (TLD) compounds, such as LiF, CaCO3, CaSO4, CaSO4.2H2O, SrSO4, CdSO4, BaSO4, C4H6BaO4 and 3CdSO4.8H2O were determined at 279.2, 320.07, 514.0, 661.6, 1115.5, 1173.2 and 1332.5 keV in a well-collimated narrow beam good geometry set-up using a high resolution, hyper pure germanium detector. The attenuation coefficient data were then used to compute the effective atomic number and the electron density of TLD compounds. The interpolation of total attenuation cross-sections of photons of energyE in elements of atomic numberZ was performed using the logarithmic regression analysis of the data measured by the authors and reported earlier. The best-fit coefficients so obtained in the photon energy range of 279.2 to 320.07 keV, 514.0 to 661.6 keV and 1115.5 to 1332.5 keV by a piece-wise interpolation method were then used to find the effective atomic number and electron density of the compounds. These values are found to be in agreement with other available published values.

    • Muonium/muonic hydrogen formation in atomic hydrogen

      V S Kulhar

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      The muonium/muonic hydrogen atom formation in μ±−H collisions is investigated, using a two-state approximation in a time dependent formalism. It is found that muonium cross-section results are similar to the cross-section results obtained for positronium formation in e+-H collision. Muonic hydrogen atom formation cross-sections in μ--H collision are found to be significant in a narrow range of energy (5 eV–25 eV).

    • Large-eddy simulations of fluid and magnetohydrodynamic turbulence using renormalized parameters

      Mahendra K Verma Shishir Kumar

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      In this paper a procedure for large-eddy simulation (LES) has been devised for fluid and magnetohydrodynamic turbulence in Fourier space using the renormalized parameters. The parameters calculated using field theory have been taken from recent papers by Verma [1,2]. We have carried out LES on 643 grid. These results match quite well with direct numerical simulations of 1283. We show that proper choice of parameter is necessary in LES.

    • Electron cyclotron resonance heating in a short cylindrical plasma system

      Vipin K Yadav D Bora

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      Electron cyclotron resonance (ECR) plasma is produced and studied in a small cylindrical system. Microwave power is delivered by a CW magnetron at 2.45 GHz in TE10 mode and launched radially to have extraordinary (X) wave in plasma. The axial magnetic field required for ECR in the system is such that the first two ECR surfaces (B = 875.0 G andB = 437.5 G) reside in the system. ECR plasma is produced with hydrogen with typical plasma density ne as 3.2 × 1010 cm-3 and plasma temperature Te between 9 and 15 eV. Various cut-off and resonance positions are identified in the plasma system. ECR heating (ECRH) of the plasma is observed experimentally. This heating is because of the mode conversion of X-wave to electron Bernstein wave (EBW) at the upper hybrid resonance (UHR) layer. The power mode conversion efficiency is estimated to be 0.85 for this system. The experimental results are presented in this paper.

    • Higher order contribution to the propagation characteristics of low frequency transverse waves in a dusty plasma

      A P Misra A Roy Chowdhury S N Paul

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      Characteristic features of low frequency transverse wave propagating in a magnetised dusty plasma have been analysed considering the effect of dust-charge fluctuation. The distinctive behaviours of both the left circularly polarised and right circularly polarised waves have been exhibited through the analysis of linear and non-linear dispersion relations. The phase velocity, group velocity, and group travel time for the waves have been obtained and their propagation characteristics have been shown graphically with the variations of wave frequency, dust density and amplitude of the wave. The change in non-linear wave number shift and Faraday rotation angle have also been exhibited with respect to the plasma parameters. It is observed that the effects of dust particles are significant only when the higher order contributions are considered. This may be referred to as the ‘dust regime’ in plasma.

    • Upconversion of whistler waves by gyrating ion beams in a plasma

      Harsha Jalori Sunil K Singh A K Gwal

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      A gyrating ion beam, with a ring-shaped distribution in velocity, supports negative energy beam modes near the harmonics of beam gyro-frequency. An investigation of the non-linear interaction of high-frequency whistler waves with the negative energy beam cyclotron mode is made. A non-linear dispersion relation is derived for the coupled modes. It is shown that a gyrating ion-beam frequency upconverts the whistler waves separated by harmonics of beam gyro-frequency. The expression for the growth rate of whistler mode waves has been derived. In Case 1, a high-amplitude whistler wave decays into two lower frequency waves, called a low-frequency mode and a side band of frequency lower than that of pump wave. In Case 2 a high-amplitude whistler wave decays into two lower frequency daughter waves, called the low-frequency mode and whistler waves. Generation mechanism of these waves has application in space and laboratory plasmas.

    • Growth of molybdenum disulphide using iodine as transport material

      Rajiv Vaidya Madhavi Dave S S Patel S G Patel A R Jani

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      In the present paper an attempt has been made to describe the chemical vapor transport (CVT) technique used for the growth of molybdenum disulphide (MoS2) single crystals. Iodine (I2) is used as transporting material for this purpose. The energy dispersive analysis by X-ray (EDAX) confirmed the stoichiometry of the as-grown crystals. The lattice parameters of these crystals were determined from the X-ray diffraction analysis. The grown crystals were examined under the optical zoom microscope for their surface microstructure study.

    • Electrical properties of a-GexSe100-x

      Abdolali Zolanvari Navdeep Goyal S K Tripathi

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      In general, the conductivity in chalcogenide glasses at higher temperatures is dominated by band conduction (DC conduction). But, at lower temperatures, hopping conduction dominates over band conduction. A study at lower temperature can, eventually, provide useful information about the conduction mechanism and the defect states in the material. Therefore, the study of electrical properties of GexSe100-x in the lower temperature region (room temperature) is interesting. Temperature and frequency dependence of GexSe100-x (x = 15, 20 and 25) have been studied over different range of temperatures and frequencies. An agreement between experimental and theoretical results suggested that the behaviour of germanium selenium system (GexSe100-x) have been successfully explained by correlated barrier hopping (CBH) model.

    • Search for an interstellar Si2C molecule: A theoretical prediction

      Suresh Chandra

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      We suggest that Si2C molecule may be identified in astronomical objects through its transitions 414 → 505, 515 → 606, 212 → 303, 313 → 404, and 111 → 202 at 15.9, 5.1, 33.6, 24.9, and 42.3 GHz in absorption even against the cosmic 2.7 K background, in a region having low temperature. The absorption phenomenon is found rather large in the first two transitions. Dependence of results on the set of molecular parameters is discussed.

    • Dispersion relation for localized magnetic polaritons propagating at the junction of two ferromagnetic/non-magnetic superlattices

      R T Tagiyeva

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      Localized magnetic polaritons are investigated in the systems consisting of two magnetic superlattices, coupled by a ferromagnetic contact layer. The general dispersion relation for localized magnetic polaritons are derived in the framework of the electromagnetic wave theory in the Voigt geometry by the ‘transfer’ matrix method. The numerical calculations were carried out for different parameters of the superlattices and contact layer and then discussed.

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