• Volume 53, Issue 5

      November 1999,   pages  795-917

    • Group of contact transformations: Symmetry classification of Fokker-Planck type equations

      P Rudra

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      Fokker-Planck type equations have been classified according to the groups of contact transformations to which they belong. It has been found that there are only five classes as in the case of groups of point transformations. We have also obtained the algebraic structures of the corresponding Lie algebras. However, there are isomorphies in their group properties. The corresponding basis sets of functionally independent invariants formed by the generators of these groups have also been obtained.

    • Adiabatic anholonomy and canonical transformations

      Jagmeet Singh

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      Biswas and Soni [4] have surmised a semiclassical formula for Berry’s phase in terms of a generating function. We derive this formula apart from showing that it is not true in general and investigate its domain of validity. We also derive transformation formulae for Berry’s phase (Hannay’s angle) under general canonical transformations. A simpler proof for total angle invariance than hitherto available, is given.

    • Starobinsky model in Schrödinger description

      S Biswas A Shaw D Biswas

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      In the Starobinsky inflationary model inflation is driven by quantum corrections to the vacuum Einstein equation. We reduce the Wheeler-DeWitt equation corresponding to the Starobinsky model to a Schrödinger form containing time. The Schrödinger equation is solved with a Gaussian ansatz. Using the prescription for the normalization constant of the wave function given in our previous work, we show that the Gaussian ansatz demands Hawking type initial conditions for the wave function of the universe. The wormholes induce randomness in initial states suggesting a basis for time-contained description of the Wheeler-DeWitt equation.

    • Exact scalar field cosmologies in a higher derivative theory

      BC Paul

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      We obtain exact cosmological solutions of a higher derivative theory described by the Lagrangian L=R+2αR2 in the presence of interacting scalar field. The interacting scalar field potential required for a known evolution of the FRW universe in the framework of the theory is obtained using a technique different from the usual approach to solve the Einstein field equations. We follow here a technique to determine potential similar to that used by Ellis and Madsen in Einstein gravity. Some new and interesting potentials are noted in the presence of R2 term in the Einstein action for the known behaviours of the universe. These potentials in general do not obey the slow rollover approximation.

    • 12C induced transfer reactions on 56Fe

      Hari S Patel B Srinivasan B J Roy M G Betigeri

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      Transfer reactions 56Fe(12C, xN) have been investigated. Angular distributions of particles following elastic scattering, one neutron and one proton transfer reaction channels leading to low lying states in respective residual nuclei have been measured. These are analysed using the coupled reaction channel (CRC) formalism. Starting with a double folded real potential, the elastic scattering angular distribution is calculated using the computer code FRESCO. Inclusion of couplings to first excited states in both the target and the projectile already tends to describe the experimental elastic scattering distribution. Additional coupling of one neutron transfer reaction to first five excited states in 55Fe and one proton transfer reaction to first three low lying states in 57Co improves fit to the elastic scattering angular distribution. Further refinement in fit is brought about by addition of a weak imaginary potential to the complex potential calculated by ERESCO to simulate the absorption effects due to those channels whose coupling is not included explicitly. Such a potential describes the experimental angular distributions for elastic, one neutron and one proton transfer channels correctly in shape and magnitude without any arbitrary normalisation.

    • Effect of collimator size and absorber thickness on gamma ray attenuation measurements for bakelite and perspex

      Gurdeep S Sidhu Karamjit Singh Parjit S Singh Gurmel S Mudahar

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      The mass attenuation coefficient (μm) of 662 keV gamma rays have been measured in the extended media of bakelite and perspex under different collimation conditions. The increase in attenuation coefficient is seen with increase in sample thickness as well as with collimator size due to the contribution of multiple scattered photons in the uncollided beam of 662 keV gamma rays.

    • Centrifugal distortion analysis of the microwave spectrum of allyl isothiocyanate (C-gauche conformer)

      A I Jaman

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      The ground state microwave rotational spectrum of the C-gauche conformer of allyl isothiocyanate has been reinvestigated by extending the frequency range up to 37.0 GHz. A detailed centrifugal distortion analysis has been carried out with previously reported and newly assigned microwave rotational transition frequencies. The evaluated rotational and centrifugal distortion constants are presented.

    • Ultrashort laser pulse suppression of dissociation in a molecule

      Man Mohan Vinod Prasad Rinku Sharma

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      Effect of laser pulse in suppressing the dissociation of a molecule is shown. The time dependent Schrödinger is solved numerically for a molecule in an intense laser pulse whose uppermost state is connected to continuum.

    • Energy spectrum of ejected electrons in ionization of hydrogen atoms by electrons

      J N Das S Dhar

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      Energy spectrum of ejected electrons in ionization of hydrogen atoms has been calculated following a multiple scattering theory of Das and Seal [15]. The results show peaks around two to three Rydbergs of energies of the ejected electrons, for incident electron energy of 250 eV and 500 eV, considered here, and for different combinations of the angular variables of the scattered and the ejected electrons, for scattering in a plane. The peaks are very similar to those observed in relativistic K-shell ionization of Ag atoms by electrons at 500 KeV energy [6]. The physical origin of these peaks may be traced to the second order scatterings, scattering first by the atomic nucleus (or the atomic electron) and then a second time by the atomic electron. These peaks are, however, absent in the first Born results. Experimental verification of the present results and theoretical calculation by some other well-known methods will be interesting.

    • Linear amplifier via the displaced Fock states superposition

      Gamal M Abd Al-Kader

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      The linear amplifier with the superposition of displaced Fock states (DFS’s) as an input field is discussed. The s-parameterized characteristic function (CF) of linear amplifier for the superposition of two DFS’s is considered. Several quantum statistical expectation values for the output of linear amplifier are evaluated once the time dependent CF has been computed. The Glauber secondorder coherence function is calculated. The squeezing properties of the output field are studied. The s-ordered quasiprobability distribution function (QDF) for the output of linear amplifier driven by DFS’s superposition is investigated. The phase properties of the superposition of DFS’s are studied. The s-parameterized phase distribution, obtained by integrating the s-parameterized QDF over radial variable is illustrated.

    • Characteristics of photoconductivity in As-Sb-Se glasses

      G Mathew J Philip

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      Characteristic features of photoconductivity in AsxSb15Se85−x and AsxSb10Se90−x bulk glass systems have been measured and reported. Both a.c and d.c techniques have been employed for the measurements. The temperature dependence of photoconductivity has been analysed in terms of the ABFH model and both systems are found to exhibit type I photoconductivity. Photoconductivity shows a clear change in slope corresponding to the stoichiometric composition in both the systems. The composition dependence of photoconductivity is explained on the basis of chemically ordered covalent network (COCN) model. Photoconductivity response time of the two systems have been determined from frequency-resolved photocurrent (FRPC) measurements. Variation of response time with composition exhibits a clear change in slope at the stoichiometric composition in both the systems.

    • The kinetic limitation of anti-stokes luminescence of Er3+ and Yb3+ doped infrared upconversion materials

      Sachin K Mahajan PK Khare BP Chandra

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      Infrared-to-visible wave-length conversion in the Yb3+−Er3+ doped phosphors system has been described by a simple three level model based on two ions mechanism. The excitation in the range of 900–1000 nm of an IR-photon is first absorbed by Yb3+ ion as a sensitizer attributed to the resonant energy transition in Er3+ ion from 4I3/24S15/2 and 1F9/24I15/2, respectively for green and red emission. The essential energy transfer processes in this system i.e. upconversion from 4I11/2 and 1I13/2, cross-relaxation from 4S3/2 and 1F9/2 are taken into account. The limitations of the rate-equation approach are examined with a focus on the underlying dynamics of this rare-earth system.

    • The breaking of O(6) symmetry in 118Xe and 120Xe

      Bir Singh Rawat P K Chattopadhyay

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      The spectra of the isotopes of xenon are analysed from the point of view of O(6) symmetry breaking. It is pointed out that the excitation energies of the states 03+ can be used in detecting breaking of the symmetry. The nature of symmetry breaking in 118Xe and 120Xe is indicated.

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