Volume 25, Issue 3
September 1985, pages 231-340
pp 231-238 September 1985 Mathematical Physics
Asymptotic survival probability of random walks on a semi-infinite line
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.
pp 239-249 September 1985 Particle Physics
Possible evidence for purely power-suppressed correction to scaling
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 α_{s}(Q^{2}) of possible nonperturbative origin in quantum chromodynamics, given by α_{s}(Q^{2})=α_{0}m_{0}^{2}/(Q^{2}+m_{0}^{2}). Excellent simultaneous description of the world data is achieved over the full range ofQ^{2}: 5≲Q^{2}≲200 GeV^{2} for large values ofx⩾0.35. In contrast, perturbative quantum chromodynamics alone fails to describe these data simultaneously over this entire range ofQ^{2}. The decisive test between the two alternatives is possible athera forQ^{2}>200–300 GeV^{2}.
pp 251-258 September 1985 Nuclear Physics
Ground-state occupancies off-p-g shell nuclei
N Naik S Ramkumar P Shenoy N Tressler
We have calculated the ground-state occupancies of various nuclei in the spectroscopic space of upperf-p shell andg_{9/2} 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.
pp 259-265 September 1985 Nuclear Physics
Annealing of heavy ion tracks in cellulose nitrate plastic track detectors
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.
pp 267-273 September 1985 Nuclear Physics
Some comments on the Coriolis attenuation problem
To explore the Coriolis attenuation problem we have carried out a schematici_{13/2} 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.
pp 275-280 September 1985 Atomic Physics
L-shell ionization of atoms by relativistic electrons
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.
pp 281-290 September 1985 Atomic Physics
K K Das Priyotosh Khan S P Bhattacharyya
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.
pp 291-309 September 1985 Atomic Physics
Theory of coherent, degenerate two-photon absorption and emission
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.
pp 311-317 September 1985 Solid State Physics
Thermal conduction through porous and dispersed three-phase systems
Ramvir Singh R S Beniwal R N Pande D R Chaudhary
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.
pp 319-326 September 1985 Solid State Physics
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.
pp 327-334 September 1985 Solid State Physics
Secondary electron emission of sputtered alumina films
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.
pp 335-340 September 1985 Liquid State
First order quantum correction to the free energy of simple liquids
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.
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