• Volume 53, Issue 4

      October 1999,   pages  659-794

    • Interesting normal state and superconducting properties of the intermediate valence compound CeRu2

      S B Roy P Chaddah

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      Superconductivity in CeRu2 was discovered 40 years ago, and was extensively studied because alloying with magnetic elements showed the coexistence of superconductivity and magnetic order. The normal state of CeRu2 has been of interest because of its intermediate valuence character. The superconducting state has been studied extensively because of its paramagnetic nature and anomalous pinning properties. This review presents the present status of knowledge, and discusses the puzzling features of CeRu2.

    • Dirac current in expanding spacetime

      NG Sarkar S Biswas A Shaw

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      We study the behaviour of Dirac current in expanding spacetime with Schrödinger and de Sitter form for the evolution of the scale-factor. The study is made to understand the particle-antiparticle rotation and the evolution of quantum vacuum leading to particle production in such spacetime.

    • The longitudinal structure function FL(x, Q2) and the gluon distribution G(x, Q2) at low x

      Abhijeet Das A Saikia

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      We obtain a relation between the longitudinal structure function FL(x, Q2), F2(x, Q2) and G(x, Q2) at small x, using the formalism recently reported by one of the authors [2]. We also obtain a relation between FL(x, Q2), F2(x, Q2) and its slope (dF2(x, Q2))/(dlnQ2). This provides us with the determination of the longitudinal structure function FL(x, Q2) from F2(x, Q2) data and hence extract the gluon distribution G(x, Q2).

    • Relative wavefunctions, vertex functions and coupling constants for the virtual decay of 4He

      VK Sharma BK Chikara

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      The d + d, t + p and h + n relative wavefunctions and their asymptotic normalizations are considered in the framework of the generator coordinate method (GCM) and compared with ATMS (amalgamation of two-body correlation into multiple scattering processes) method which used the realistic Reid soft core interaction. The asymptotic normalization of relative wavefunctions provide various coupling constants, the cluster probability amplitude (the so-called Z1/2-factor) and matter RMS radii. These wavefunctions are also used to obtain 4He − dd, 4He − tp and 4He − hn vertex functions in the virtual decay of 4He. The extrapolation of vertex functions for negative values of q2 upto the corresponding poles provide the vertex constants which are comparable with other estimates. It is noticed that in GCM the coupling constants C2 for 4He − dd vertex is less than 2 as has been obtained in the forward dispersion relation technique.

    • Calculation of magnetic multipole moment integrals using translation formulas for Slater-type orbitals

      I I Guseinov BA Mamedov T Özdoğan M Orbay

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      Using translation formulas for Slater type orbitals (STO’s) the infinite series through the overlap integrals are derived for the magnetic multipole moment integrals. By the use of the derived expressions the magnetic multipole moment integrals, therefore, the magnetic properties of molecules can be evaluated most efficiently and accurately. The convergence of the series is tested by calculating concrete cases. An accuracy of 10−5 for the computer results is obtained in the case 2p-pole magnetic moment integrals for 1 ≤ v ≤ 5, and for the arbitrary values of internuclear distances and screening constants of atomic orbitals.

    • Photoionization of Al IV (neon-type) from its ground 2s22p61Se and excited 2s22p53p3,1P03Se states using the R-matrix method

      Man Mohan M Le Dourneuf A Hibbert PG Burke

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      The R-matrix method is used to calculate the total photoionization cross-sections from the ground 2s22p61Se and the first three excited 2s22p53p3,1Se states of Al IV, for photon energies ranging from the first ionization threshold to just above the second threshold of the residual ion Al V. The two lowest LS terms of Al V − 2s22p52P0, 2s2p62Se, 2s2p62Se, represented by sophisticated configuration interaction wavefunctions, are included in the R-matrix calculation. The resulting cross-sections are affected by Rydberg series of resonances converging to the 2s2p62Se excited threshold.

    • Multiple ionization of argon in coincidence with projectile ions in 60–120 MeV Siq+-Ar collisions

      MJ Singh DO Kataria N Madhavan P Sugathan JJ Das DK Awasthi AK Sinha R Shanker

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      A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer processes in collisions of 60–120 MeV Siq+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time. The total ionization cross-sections for the recoil ions are shown to scale as q1.7/Ep0.5, where Ep is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j2 upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections σqq are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed.

    • Pressure dependence of the superconducting state parameters of metallic glass superconductor Mg70Zn30

      Manish Gupta KS Sharma Lachhman Dass

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      Explicit expressions have been derived for the volume dependence of electron-phonon coupling strength (λ) and the Coulomb pseudopotential (μ*) considering the variation of Fermi momentum (κF) and Debye temperature (θD) with volume. Ashcroft’s model pseudopotential and RPA form of dielectric screening have been used for obtaining pressure dependence of transition temperature (TC) and the logarithmic volume derivative (Φ) of the effective interaction strength (N0V) for metallic glass superconductor Mg70Zn30. It has been observed that TC of the metallic glass Mg70Zn30 decreases rapidly with increase of pressure and the superconducting phase disappears at about 30% decrease of volume, for which the μ* curve shows a minimum and an elbow is formed in the Φ graph.

    • A short range many-body potential for modelling bcc metals

      MM Ali

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      The problem considered is the fitting of a many-body interaction potential to bulk crystal data. A parameterisation of the potential is assumed which is based on physical considerations. The free parameters are determined by using global optimization to perform a least squares fit, to a large number of crystal properties. This has been achieved for body centered cubic (bcc) materials. The approach adopted here fits the bcc crystal structure, as the preferred minimum energy configuration for tungsten, and also fits the dimer energetics and the elastic properties of crystalline tungsten.

    • Pressure-volume calculation in bcc metals using Born stability criteria

      Piyush Kuchhal Narsingh Dass

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      A simple analytical two-body potential φ(r) = −Ar−n + B exp(−prm) is considered for P-V calculations in bcc metals using Born stability criteria. It is shown that the stability of bcc metals can be expressed uniquely as a function of a parameter q (discussed in the text). The P-V calculations are done in ten bcc metals. The calculations are compared with the experimental data of shock-wave measurements and also with other potential available. It is found out that the present potential is better than the other two-body potentials in case of bcc metals. Further, the calculations done for TOEC and the first pressure derivative of SOEC are found in good agreement with the reported results.

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