• Volume 27, Issue 6

      December 1986,   pages  717-839

    • Effective suppression of period-doubling in two diffusively coupled logistic maps

      S Puri E Atlee Jackson

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      We consider a system of two delay diffusively coupled logistic maps. We find that for moderate values of diffusion coupling, the period-doubling sequence is effectively suppressed. Our study supports the existence of certain generic features for systems consisting of two coupled maps.

    • Velocity-dependent inertial induction—possible explanation for supergravity shift at solar limb

      Amitabha Ghosh

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      A quantitative model of inertial induction has been earlier proposed by the author which not only results in the exact equivalence of inertial and gravitational masses but also gives rise to an exceedingly small drag dependent on the velocity with respect to the mean rest frame of the universe. This leads to a cosmological redshift in close agreement with the observation. When this velocity drag due to local interaction is considered it is seen that a significant proportion of the secular retardation of the earth’s spin and the moon’s orbital motion can be attributed to this drag. This also resolves the problem of the moon’s close approach to the earth in the past as suggested by a purely tidal friction theory. The observed large secular acceleration of the Phobos is also explained. The present article shows that local interaction also yields a redshift. When applied to the solar radiation it is seen that the observed supergravity shift at the limb can be very satisfactorily explained.

    • Relativistic dynamics for spin-zero and spin-half particles

      J Thakur

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      The classical and quantum mechanics of a system of directly interacting relativistic particles is discussed. We first discuss the spin-zero case, where we basically follow Rohrlich in introducing a set of covariant centre of mass (CM) and relative variables. The relation of these to the classic formulation of Bakamjian and Thomas is also discussed. We also discuss the important case of relativistic potentials which may depend on total four-momentum squared. We then consider the quantum mechanical case of spin-half particles. The negative energy difficulty is solved by introducing a number of first class constraints which fix the spinor structure of physical solutions and ensure the existence of proper CM and relative variables. We derive the form of interactions consistent with Lorentz invariance, space inversion, time reversal and charge conjugation and with the above mentioned first class constraints and find that it is analogous to that for the non-relativistic case. Finally the relationship of the present work with some previous work is briefly discussed.

    • Elastic and inelastic scattering of 270 MeV3He particles from58Ni,90Zr,116Sn and208Pb

      P P Singh Q Li P Schwandt W W Jacobs M Saber E J Stephenson A Saxena S Kailas

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      Differential cross-section angular distributions for the elastic scattering of 270 MeV3He particles from58Ni,90Zr,116Sn and208Pb have been measured. Optical model analysis of the cross-sections has yielded the optical model parameters for3He particles at 270 MeV. Angular distributions have also been measured for the inelastic excitation of the low-lying levels in the above mentioned nuclei. A collective model analysis using the distorted wave Born approximation (DWBA) of these cross-sections with the distorted waves generated by the optical model parameters determined from the elastic scattering analysis, has yielded the reduced transition probability (B(EL)) values consistent with those reported in the literature.

    • Quarkonium spectroscopy with vacuum polarization correction

      A K Roy S Mukherjee

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      The quarkonium spectroscopy has been studied by considering a non-relativistic potential which includes the QCD vacuum polarization corrections. The potential consists of a short-range 2-loop QCD potential matched to a Martin-type power law potential for large distances. The Poggio-Schnitzer correction to the leptonic decay width has also been included. The energy levels, leptonic decay widths and E1 transition rates ofψ and γ families have been calculated and have been found to be in good agreement with experimental results. The toponium spectroscopy has also been studied for the range ofM, values suggested by the recent jet events observed by the UA1 collaboration. The contribution of the decay through a virtualZ0 has also been included in the calculation. The potential seems to provide a very good non-relativistic description of the quarkonium systems.

    • Nucleon octet in a relativistic logarithmic potential

      S N Jena D P Rath

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      A simple independent-quark-model based on the Dirac equation with logarithmic potential is used to calculate several properties of octet baryons such as magnetic moment, the axial vector coupling constantgA (n) for neutronβ-decay and the charge radius of the proton. In view of the simplicity of the model, the results obtained are quite good.

    • Magnetic moments of octet baryons in a chiral potential model

      N Barik M Das

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      Incorporating the lowest-order pionic correction, the magnetic moments of the nucleon octet have been calculated in a chiral potential model. The potential, representing phenomenologically the nonperturbative gluon interactions including gluon self-couplings, is chosen with equally mixed scalar and vector parts in a power-law form. The results are in reasonable agreement with experiment.

    • Alpha particle and deuteron impactL-shell ionization of Ar, Cu, Ge, Br, Zr and Ag

      S N Chatterjee B N Roy

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      Alpha particle and deuteron impactL-subshell ionization cross-sections of Ar, Cu, Ge, Br, Zr and Ag have been computed using Vriens’ expressions for ionization cross-section of atoms due to impact of heavy charged particles. The effects of Coulomb deflection of the projectile and increase in binding of the target electron in the presence of projectile have been incorporated. Hartree-Fock velocity distributions for the target electrons have been used in the present calculations. The simple binary encounter approximation model is found to give results which are in satisfactory agreement with those obtained from experiments and from other theories.

    • Design of diamagnetic coil with non-encircling compensation coil system for measuring the plasma diamagnetism in toroidal devices

      S K Mattoo

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      The paper describes a new scheme for suppressing the unwanted and dominant coupling of the diamagnetic coil with the toroidal field coils of a tokamak device.

    • Temperature dependence of luminescence emission from cerium and europium doped MgO under x-ray excitation

      M N Bapat S Sivaraman

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      Temperature dependence of luminescence emission from cerium- and europiumdoped MgO is reported. The emission intensity changes with increase in the phosphor temperature. The phosphor showed peaks in the brightness-temperature curves. The intensities at static temperatures were always lower, indicating that temperature quenching occurs in almost all cases. The same is also evident from spectral distribution curves obtained at different temperatures.

    • XANES and EXAFS study of some metal-metalloid glasses

      K B Garg Kavita S Jerath H S Chauhan Usha Chandra

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      XANES and EXAFS techniques are proving very popular in the study of local environment in disordered systems. Results of such studies in a large number of metal (Fe, Co, Ni, etc)-metalloid (B, Si, C, etc) glasses are reported. Experiments were done with synchrotron radiation as well as an x-ray tube. The values of bond lengths and co-ordination numbers computed from one-electron single scattering Fourier transform method turn out substantially smaller. The values of bondlength determined from the other EXAFS calculation method and the multiple-scattering computation scheme show good agreement. Importance of choice of suitable reference materials for analysis of data is emphasized.

    • High pressure phase transitions in organic solids II: X-ray diffraction study ofp-dichlorobenzene at high pressures

      Hema Sankaran Surinder M Sharma S K Sikka R Chidambaram

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      X-ray diffraction experiments onp-dichlorobenzene at high pressures show a transition at ∼ 0.3 GPa, to a new phase, the diffraction pattern of which cannot be indexed on the anticipated low temperature monoclinic crystal structure. We have instead found an orthorhombic cell, very closely related to the low temperature monoclinic cell, for this new phase. This structure, which also occurs inp-diiodobenzene at ambient conditions, has cell constantsa =14.02,b = 6.06,c = 7.41Å andZ = 4. The space group is Pbca. This new phase has a non-β herring-bone structure, in contrast with the initialα phase which has aβ-structure with ribbon-like arrangement of molecules, with Cl-Cl contacts of ∼ 4A between adjacent molecules. This implies that with pressure the halogen-halogen interaction in this compound plays a less dominant role in crystal engineering.

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