Volume 16, Issue 6
June 1981, pages 437-518
pp 437-455 June 1981 Statistical Physics
Two-state random walk model of diffusion. 2. Oscillatory diffusion
Continuing our study of interrupted diffusion, we consider the problem of a particle executing a random walk interspersed with localized oscillations during its halts (e.g., at lattice sites). Earlier approaches proceedvia approximation schemes for the solution of the Fokker-Planck equation for diffusion in a periodic potential. In contrast, we visualize a two-state random walk in velocity space with the particle alternating between a state of flight and one of localized oscillation. Using simple, physically plausible inputs for the primary quantities characterising the random walk, we employ the powerful continuous-time random walk formalism to derive convenient and tractable closed-form expressions for all the objects of interest: the velocity autocorrelation, generalized diffusion constant, dynamic mobility, mean square displacement, dynamic structure factor (in the Gaussian approximation), etc. The interplay of the three characteristic times in the problem (the mean residence and flight times, and the period of the ‘local mode’) is elucidated. The emergence of a number of striking features of oscillatory diffusion (e.g., the local mode peak in the dynamic mobility and structure factor, and the transition between the oscillatory and diffusive regimes) is demonstrated.
pp 457-465 June 1981 Atomic And Molecular Physics
Electron impact optical excitation of helium-like ions in Coulomb-Glauber approximation
S N Singh A N Tripathi M K Srivastava
The Coulomb-Glauber approximation is applied to evaluate the electron-impact excitation integrated cross sections for 1^{1}S —n^{1}P (n=2, 3) transitions in helium-like ions, C^{4+}, N^{5+}, O^{6+} and Ne^{8+}. The results are presented in terms of scaled collision strengthn^{3}Z^{2}k_{i}^{2}σ and scaled integrated cross-sectionZ^{4}σ. Our values when compared with other available theoretical results are found to be larger than the Coulomb-Born and distorted wave polarised orbital (DWPO) values.
pp 467-472 June 1981 Atomic And Molecular Physics
Measurement ofL_{III} subshell photoelectric cross-sections in highZ-elements
S K Arora K L Allawadhi B S Sood
L_{III} subshell photoelectric cross-sections in lead, thorium and uranium at 13·596, 16·896 and 17·781 keV respectively have been determined. The results are found to agree well with theory.
pp 473-479 June 1981 Atomic And Molecular Physics
Symmetry coordinates of nonrigid molecules
T S G Krishna Murty L S R K Prasad M Kondala Rao
Motivated by Altmann’s definition of symmetry groups of nonrigid molecules, Wigner’s method of obtaining the symmetry coordinates of a molecule is extended to nonrigid molecules with free internal rotations. The molecule BF_{2} CH_{3} is exemplified.
pp 481-485 June 1981 Atomic And Molecular Physics
Effective potential for ammonia vapour
Pankaj Pathak Om Singh A W Joshi
The modified free-energy averaged potential for water vapour is extended to NH_{3} vapour. The resulting temperature-dependent parameters are used to compute the second virial coefficient of NH_{3} vapour which agrees with experimental results particularly at higher temperatures.
pp 487-492 June 1981 Particle Physics
Masses of charmed andb-quark hadrons in quasinuclear coloured quark model
C P Singh Avinash Sharma M P Khanna
Employing non-relativistic quasinuclear coloured quark model, which provides a unified description of mesons and baryons, masses of charmed andb-quark hadrons are studied. Various mass splittings are estimated, and mass relations among them are obtained.
pp 493-510 June 1981 Particle Physics
First and second order hadron mass formulas in internal SU(6)
We use broken SU(6) internal symmetry to derive the mass formulas amongst hadrons (1/2^{+}, 3/2^{+}, 0^{−}, 1^{−}) including second order mass contributions from symmetric 405 representation. Some hybrid mass relations are also obtained by relating second order parameters.
pp 511-518 June 1981 Solid State Physics
Frequency dependence of the surface states at the N-type Si-SiO_{2} interface
The response of the surface states at then-type Si-SiO_{2} interface to the different a.c. signal frequencies has been studied. The response values have been computed from both the measured capacitance voltage (C-V) and conductance-voltage (G-V) techniques. The results presented show that the frequency response of the effective density of states to different a.c. signal frequencies is proportional to the log of the applied frequencies.
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