• Volume 9, Issue 6

      December 1977,   pages  545-652

    • An ab-initio derivation of the pi-electron hamiltonian by a nonperturbative open-shell formalism

      Debashis Mukherjee Raj Kumar Moitra Atri Mukhopadhyay

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      A method for generating a pi-electron hamiltonian in an ab-initio manner using the non-perturbative open-shell many-body formalism recently developed by us is presented. The π-hamiltonian thus derived is energy-independent, and is also proved to be spin-independent. A recipe is given with the help of which Goldstone—like matrix-elements ofHπ can be extracted up to three body terms. It has been demonstrated that the use of diagrammatics considerably simplifies the algebra and allows one to keep track of the various quantities involved. Up to a given order of approximation, an explicit form ofHπ containing up to the three body terms has been given, and some of the important physical effects embedded in the hamiltonian are discussed. A comparative analysis of the various formalisms currently in use forms the concluding section of the paper.

    • Molecular constants of XeO3F2

      A Natarajan K Chockalingam

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      The force constants of XeO3F2 have been evaluated using the general valence force field. The mean square amplitudes of vibration, the generalised mean square amplitudes and shrinkage constants, Coriolis coupling coefficients and centrifugal distortion constants have also been calculated for the first time using the vibrational frequencies and the structural parameters. The thermodynamic properties have been computed for the ideal gaseous state at 1 atmospheric pressure for 11 temperatures from 100° to 1000°K using a rigid rotor harmonic oscillator approximation.

    • On the calculation of force constants using isotopic frequencies by parametric method: Application to systems of (3×3) order

      K Ramaswamy S Karunanithi

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      A method is proposed for the determination of angle parameters for ONF, ONCl and ONBr, utilising the isotopic frequencies of two isotopically substituted molecules. The force constants, Coriolis coupling constants, inertia defect, mean amplitudes of vibration and rotational distortion constants were also calculated and compared with literature values.

    • Self diffusion in liquid Na-K alloy

      R V Gopala Rao A K Murthy

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      Self diffusion coefficients,Di, in liquid Na-K alloy at 373 K have been computed in the linear trajectory approximation of Helfand, with square well as an attractive tail. From the computedDNa andDK, the mutual diffusion coefficient,DNaK has also been determined.DNa,DK andDNaK all increase with increase of concentration of potassium, while the ratio,DNa/DK remains constant (1.45 ± 0.01) over the entire concentration range.

    • Phonon dispersion in cubic transition metals: A comparison between Fielek and extended Cheveau models

      V B Gohel A R Jani

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      Phonon dispersion in bcc transition metals has been studied by Fielek and extended Cheveau models. A comparative study of the results shows that the wavy nature of [ξ00]-L branch in the dispersion curves of some metals is due to the long range forces which are well accounted for by the extended Cheveau model but not by the Fielek model. The peculiar behaviour of transverse branches are due to the presence ofd-electrons. It is found that the oscillatingd-shell model of Fielek is fairly good for tungsten, α-iron and molybdenum, but does not give satisfactory description ofd-electron effects in the remaining bcc transition metals.

    • A simple microwave kit to convert an X-band ESR spectrometer for K-band operation

      Vinod R Bhagat Balu Venkataraman

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      A kit for the conversion of an X-bandesr spectrometer for K-band operation is described and its performance has been tested withp-benzosemiquinone, vanadyl acetyl acetonate and 2, 5-ditertiary butyl semiquinone. The easy conversion of the X-band spectrometer to K-band operation enables us to distinguish between magnetic field dependent and field independent parameters. A varactor harmonic generator is used as a frequency doubler driving the fundamental power from the existing X-band source to give a power output at K-band without having to modify the electronic circuit; the modification of the microwave circuitry is proposed.

    • Evaluation of nuclear shell correction energies for realistic level schemes by temperature smearing method

      V S Ramamurthy S S Kapoor

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      Calculations of shell correction energies by the temperature smearing method for realistic single particle level schemes of finite depth potentials are described and discussed. It is found that the method provides unique values of the shell correction energies for the various shapes relevant in the fission of actinide nuclei including those shapes where breakdown of the usual Gaussian energy smearing procedure was observed.

    • Multiplicity distribution of prompt gamma rays in spontaneous ternary fission of252Cf

      V S Ramamurthy R K Choudhury J C Mohana Krishna

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      The first and the second moments of the multiplicity distribution of prompt gamma rays in spontaneous ternary fission of252Cf have been measured by the multiple coincidence technique. While both these moments were found to be nearly independent of the energy of the light charged particle accompanying the fission fragments, the width of the multiplicity distribution was larger than that in the case of normal binary fission by about 20%.

    • Violation of the Okubo-Zweig-Iizuka rule in the decay mode B(1235) →φ(1020) +π

      C A Singh

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      The Okubo-Zweig-Iizuka rule forbids the transitionB(1235)→φπ. Unitarity, however, induces a non-vanishing amplitude forBφπ. We estimate the amplitude using dispersion relation. The absorptive part is shown to be small contributing less than 100 keV to the partial width Γ (Bφπ). For the dispersive part we evaluate the contributions of the$$K*\bar K$$ and$$K**\bar K$$ intermediate states and point out that the$$K*\bar K*$$ state does not contribute significantly. The dispersive part contributes about 300 keV to the partial width. Thus unitarity correction to the Okubo-Zweig-Iizuka rule gives the partial width Γ(Bφπ) to be around 300–400 keV compared with the present experimental upper limit of 1·9 MeV.

    • Adjoint representation admixture to weak nonleptonic decays in SU(4) and SU(8)

      Ramesh C Verma M P Khanna

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      In order to remove some of the unsatisfactory features of the GIM model, we consider15-admixture in SU(4). ΔC=±ΔS decays remain unaffected. Lee-Sugawara sum-rule is obtained.15-admixture is extended then to63-admixture in SU(8). The most general Hamiltonian (Hw637201232) in SU(8) is found to give Lee-Sugawara relation and Σ++=0 forS-wave decays of uncharmed baryons. Decay amplitude relations for ΔC=−1, ΔS=0 mode are obtained.

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