• Volume 23, Issue 6

      December 1984,   pages  675-833

    • Probing proton spin structure through hadronic reactions

      M Rafat R Ramachandran

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      Inclusive and semi-inclusive photon producing polarized proton reactions have been employed to probe the spin structure of the proton. Combinations of cross-sections are suggested which may measure valence quarks polarization and gluon polarization in the proton separately. The general formalism is used to predict numerical results using a model of spin structure based on Altarelli-Parisi equations.

    • On higher order computations in strong coupling

      Carl M Bender Ashok Das Hwa-Aun Lim

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      An algorithm which simplifies manipulation of higher order graphs in strong coupling is presented.

    • Bethe-Salpeter equation with the sine-Gordon interaction

      G P Malik Gautam Johri

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      An attempt is made to study the interaction Hamiltonian,Hint =2(x)U(φ(x)) in the Bethe-Salpeter framework for the confined states of theψ particles interactingvia the exchange of theU field, whereU(φ) = cos (). An approximate solution of the eigenvalue problem is obtained in the instantaneous approximation by projecting the Wick-rotated Bethe-Salpeter equation onto the surface of a four-dimensional sphere and employing Hecke’s theorem in the weak-binding limit. We find that the spectrum of energies for the confined states,E =2m+B (B is the binding energy), is characterized byEn6, wheren is the principal quantum number.

    • Is reggen field theory rendered obsolete byqcd?

      B Sidhanta

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      We affirm the power of the eikonal approximation in reggeon field theory (rft) and point out its merit as contrasted with renormalization group method for calculating reggeon self-energy correction due to pomeron exchanges. Relative merits ofrft andqcd in appropriate momentum regions of hadronic interactions are also examined to suggest a negative answer to the title.

    • Lattice imperfection studies in polycrystalline materials by x-ray diffraction line-profile analysis

      M De S P Sen Gupta

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      This review concerns our recent investigations with a series of binary fcc Ag- and Cu-base alloys (viz Ag-Ga, Ag-Ge, Ag-Al and Cu-Ga, Cu-Ge) from detailed analyses of x-ray diffraction line profiles, the importance of which has been briefly summarized. The theoretical formulations of the Warren-Averbach’s method of Fourier analysis of peak-shapes along with the methods of peak-shift and peak-asymmetry have been outlined. A preview on the significant studies carried out earlier with Ag- and Cu-base (fcc) binary alloys has been made in short. A detailed analyses on the recorded profiles in the present considerations revealed, in general, quantitative estimates of several microstructural parameters characterising the deformed state of the materials namely, propensity of stacking faults (intrinsic, extrinsic and twin faults), rms microstrains, coherent domain sizes, long-range residual stresses, lattice parameter changes, dislocation density and stacking fault energy. The results indicate a general trend of increase in the concentrations of stacking faults, primarily, of intrinsic character, with increase in solute concentrations; which are solely responsible for the observed peak-shifts as well as domain size broadening. Small asymmetry in the profiles is due to the presence of extrinsic stacking faults, relatively less in magnitude compared to the intrinsic ones while the deformation twin faults are almost absent—an observation with significance. The dislocation density, quite appreciable in magnitude, has been evaluated from the anisotropic values of the coherent domain sizes and rms microstrains. The stacking fault energies of pure Ag and Cu, an important parameter have also been estimated and compared with those obtained from electron microscopy. Annealing experiments with a Ag-5·8% Al alloy, aluminium being a precipitating solute, do not reveal any detectable evidence of solute segregation at the stacking faults. The occurrence of stacking faults in the alloy systems has been correlated with a number of physical factors involving solvent-solute types.

    • An explanation of the phenomenon of polytypism

      S Ramasesha

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      Based on the analogy between polytypes and spin-half Ising chains, polytypes can be considered as different phases of a spin-half Ising system with competing nearest neighbour and next nearest neighbour interactions operating in a single direction. It is known that such an Ising system exhibits extremely rich and complicated phase behaviour. This behaviour is shown to be very similar to the phase behaviour exhibited by polytypes.

    • Lattice dynamical study of alkali metals: An unified approach based on CGW model

      V Ramamurthy M Satishkumar

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      The phonon dispersion relations for lithium, sodium, potassium, rubidium and cesium along the principal symmetry directions as well as their lattice specific heats have been deduced using Clark, Gazis and Wallis angular force model. This model which conforms to the translational symmetry of the lattice, reproduces the observed crossover in lithium along [ζ00] direction at ζ = 0·49, without producing any crossovers in other alkali metals. Besides, the theoretical dispersion curves of all alkali metals are in excellent agreement with the corresponding experimental or homologous dispersion relations and theirϑD values compare well with the experimental values over a wide temperature range. It is shown that the strength of electron-ion interactions plays a significant role in the success of any unified lattice dynamical study of alkali metals while the three-body interactions of thecgw model do not. The importance of umklapp processes, failure of the earlier models to produce a crossover and the experimentalϑD-T curve in lithium as well as the apparent variation in the nature and range of atomic interactions of alkali metals are discussed.

    • Light ion fusion in deformation model

      R C Nayak

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      Experiments with heavy ions at moderate energies show the importance of deformation in heavy ion collisions. A deformation model which takes deformation dynamically into account is developed. Having described fusion and deep inelastic collision for a very heavy system (Xe + Bi) and a medium heavy system (Ar + Th) at various energies successfully, we turn to some comparatively lighter heavy ions where fusion is the most dominant feature. Fusion cross-sections for six pairs of lighter systems (35Cl +116Sn,58Ni+62Ni,35Cl+62Ni,32S+24Mg,24Mg+24Mg and12C+27Al) have been obtained using our deformation model which agree well with experiment. The two-slope-behaviour of fusion excitation function which is an important feature of light ion fusion systematics is also obtained, in our model calculations for all the systems studied.

    • Nonlinear distribution function for a plasma obeying Vlasov-Maxwell system of equations

      Saroj K Majumdar

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      The nonlinear distribution function of Allis, generalised to include the transverse electromagnetic waves in a plasma, is used to set up the coupled wave equations for the longitudinal and the transverse modes. These are solved, keeping terms up to the cubic order of nonlinearity, by using the method of multiple scales. The equations of wave modulation are derived, which are solved to discuss the nature of the modulational instability and solitary wave propagation. It is found that the solutions so obtained satisfy conditions which are very similar to the well known Lighthill criterion for stability, appropriately modified due to the coupling of the two modes. The role of the average constant current due to any flow of the resonant and trapped electrons in determining the stability, is also discussed.

    • Quasisymmetry and classification of molecular structures

      M Kondala Rao Ch Suryanarayana

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      Exploring the concept of quasisymmetry, a simple and elegant method, for the classification of molecular structures, has been developed. Examples are given. Results are identified with those of Pople.

    • A neutrino universe with viscosity

      Bijan Modak

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      A solution of the Einstein field equation corresponding to a distribution of fluid with equation of stateρ = 3p but with a nonvanishing shear viscosity is presented. The solution is spherical symmetric and the flow lines are geodetic.

    • An auger electron spectroscopic investigation of the electron states of copper alloys

      P Sen D D Sarma C N R Rao

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      L3VV Auger transitions of copper alloys show a feature due to a band-like states, the shape and intensity of which depend on the composition. The energy separation between this feature and the L3M4·5M4·5 peak increases progressively with Cu concentration.

    • Errata

      S Chakrabarty

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