• Volume 25, Issue 3

      September 1985,   pages  231-340

    • Asymptotic survival probability of random walks on a semi-infinite line

      K P N Murthy

      More Details Abstract Fulltext PDF

      Symmetric and asymmetric random walks on a segment (−∞,T>0) of the real line are considered. There is a non-zero probability for the random walk to get absorbed at a site it visits. We derive for such random walks, expressions for survival probabilities in the asymptotic limit ofT→∞. An application of this asymptotic formulation to the problem of radiation transport through thick shields is presented.

    • Possible evidence for purely power-suppressed correction to scaling

      B P Mahapatra

      More Details Abstract Fulltext PDF

      We show that the scaling violations observed in deep inelastic scattering may be described by purely power-suppressed correction to exact scaling generated by an effective coupling αs(Q2) of possible nonperturbative origin in quantum chromodynamics, given by αs(Q2)=α0m02/(Q2+m02). Excellent simultaneous description of the world data is achieved over the full range ofQ2: 5≲Q2≲200 GeV2 for large values ofx⩾0.35. In contrast, perturbative quantum chromodynamics alone fails to describe these data simultaneously over this entire range ofQ2. The decisive test between the two alternatives is possible athera forQ2>200–300 GeV2.

    • Ground-state occupancies off-p-g shell nuclei

      N Naik S Ramkumar P Shenoy N Tressler

      More Details Abstract Fulltext PDF

      We have calculated the ground-state occupancies of various nuclei in the spectroscopic space of upperf-p shell andg9/2 orbit using spectral distribution methods. The modified fully renormalised Kuo-Brown interaction has been used. The calculated values have been compared with the experimental results.

    • Annealing of heavy ion tracks in cellulose nitrate plastic track detectors

      S M Farid

      More Details Abstract Fulltext PDF

      The effect of heat treatment on the latent tracks in cellulose nitrate plastic track detectors has been studied. The bulk etch rate increases with annealing temperature while the track diameters of different ions in cellulose nitrate decrease with increase in annealing time and temperature. Experimental results show that for heavier ions higher temperatures are needed for their complete erasure. The track length and track etch rate are decreased by the application of heat. Experiments reveal that annealing reduces track density. The vertical tracks are more stable than the oblique tracks and require higher temperature for their complete erasure.

    • Some comments on the Coriolis attenuation problem

      A K Jain Kiran Jain

      More Details Abstract Fulltext PDF

      To explore the Coriolis attenuation problem we have carried out a schematici13/2 rotor plus single quasi-particle band-mixing calculation. The results reveal that the calculations are largely insensitive towards the location of the Fermi energy near the low-K single particle states only, and therefore are incapable of taking into account the transition from ‘full’ decoupling to ‘partial’ decoupling as the Fermi level is increased. We trace the possible reasons for this insensitivity and find that this may be primarily due to thebcs approximation for calculating the quasiparticle energies.

    • L-shell ionization of atoms by relativistic electrons

      S Chakraborty

      More Details Abstract Fulltext PDF

      A theoretical study of theL-shell ionization of atoms by relativistic electrons is made for atomic numbers in the range 47 to 92. A new potential model recently proposed by Das and Chakraborty dealing with atomic screening effect in a better way has been used. The results are in satisfactory agreement when compared with some available experimental results and also with the theoretical results of Scofield.

    • On the direct determination of constrained pure state one-electron density matrices: Part I. A new theoretical model for closed-shell systems

      K K Das Priyotosh Khan S P Bhattacharyya

      More Details Abstract Fulltext PDF

      A new method based on the penalty-function way of satisfying equality constraints is proposed for the determination of constrained pure state one-electron density matrices for closed-shell many-electron systems. The algorithm suggested can handle many constraints simultaneously. Certain interesting features of the proposed algorithm are discussed with numerical examples.

    • Theory of coherent, degenerate two-photon absorption and emission

      Sunil Kumar

      More Details Abstract Fulltext PDF

      The theory of the coherent, two-photon resonant interaction of a monochromatic field with N atoms is given. It is seen that the dynamics of the atom-field system can be completely determined when the field is “strong”. Two specific examples are given: (i) two-photon absorption by atoms in ground state, and (ii) stimulated two-photon emission by fully excited atoms, assuming a coherent field in both cases. In case (ii), the field shows photon-antibunching after the decay of half of the atoms. The merits of our approach are shown by comparing with other treatments. Our results can also be applied to certain degenerate four-wave mixing processes which are described by a similar Hamiltonian.

    • Thermal conduction through porous and dispersed three-phase systems

      Ramvir Singh R S Beniwal R N Pande D R Chaudhary

      More Details Abstract Fulltext PDF

      A loose three-phase system made of metal, non-metal and air is considered resulting from small successive dispersions in effective continuous medium (ecm). The effective thermal conductivity of loose three-phase systems is estimated by extending theecm approach to multi-phase systems. The unsteady state line source (needle) method is employed to determine the effective thermal conductivity of some selected three-phase materials. The calculated and observed values show good agreement suggesting that the continuous medium approach can be applied to estimate effective thermal conductivity of multi-phase systems.

    • A theoretical study of stress-induced effects on Mössbauer impurities forming dislocations in some b.c.c. and f.c.c. metals

      S K Roy N Kundu

      More Details Abstract Fulltext PDF

      The external stress values required to move the dislocations in phase with the Mössbauer impurities, forming edge dislocations in different crystals are evaluated. The vibrating string model of dislocations is considered to calculate the average kinetic energy of dislocation. The kinetic energy of dislocation is found to alter causing an expected energy shift in the γ-ray photon emitted by the atom moving with the dislocation.

      The critical stress values calculated at low temperature are found to change with mass and Debye temperatures of the resonating atoms. The ratio of impurity site moments are also evaluated at low temperatures for a few f.c.c. and b.c.c. metals from Mössbauer data. The results are discussed in the light of bond softening or hardening due to the application of variable stresses in the glide plane. The variation of mean-square displacement, mean-square velocity and impurity moment ratios with stress values are shown for a number of atoms.

    • Secondary electron emission of sputtered alumina films

      N R Rajopadhye S V Bhoraskar

      More Details Abstract Fulltext PDF

      Secondary electron emission yieldδ was measured for thin films of alumina prepared byrf sputtering technique. Single pulse method was used along with 4-gridleed optics system to determineδ. Maximum value of 4·3 was obtained at primary energy of 350 eV. The Dionne’s theory was used to analyse the results and the emission probability escape depth and absorption coefficient of secondaries were also estimated. Fairly good correlation is observed between experimental and theoretical values ofδ for beam energies upto 1 keV.

    • First order quantum correction to the free energy of simple liquids

      S K Datta

      More Details Abstract Fulltext PDF

      Using the perturbation theory of Weekset al the first order quantum correction to the free energy of a simple fluid characterised by a double Yukawa potential function has been expressed in a simple closed analytical form which allows numerical calculation simply on a desk calculator.

  • Pramana – Journal of Physics | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.