Volume 48, Issue 4
April 1997, pages 859-958
pp 859-870 April 1997
Surface harmonics for pentagonal point groups
K Rama Mohana Rao P Hemagiri Rao V Satyavathi
Surface harmonics for the seven pentagonal point groups 5(C5), {ie859-1}(S10), {ie859-2}(C5h), {ie859-3}m2(D5h), {ie859-4} 2(D5), 5m(C5v) and 5 2m(D5d) that represent the symmetries of quasicrystals in two and three dimensions are obtained, employing the projection operator method [11] and the simplified (authors) method. The results obtained are tabulated and are briefly discussed.
pp 871-882 April 1997
Characterization of chaos in a serrated plastic flow model
S V M Satyanarayana V Sridhar S Koka
We report new results on a dynamical model of serrated yielding. These essentially pertain to the full spectrum of Lyapunov exponents of the non-linear (chaotic) model and fractal characterization of the associated strange attractor. The power spectrum of scalar time series extracted from the phase space trajectories decays exponentially with increase of frequency and the decay constant is found proportional to the Kolmogorov-Sinai entropy.
pp 883-890 April 1997
Structural phase transition in substituted La2CuO4 and Pr2CuO4−y
Meena Chaudhri Kunal B Modi K M Jadhav G K Bichile
The structural phase transition from orthorhombic (T) phase to tetragonal (T′) phase in substituted La2−xRxCuO4 (R = Pr, Nd, Sm, Eu and Gd) and T′ to T-phase in Pr2−xMxCuO4−y (M = Sr, Ca) has been studied by X-ray diffraction technique. The T-phase of La2CuO4 is transferred to T′ phase abruptly atx=0.8, 0.4, 0.4, 0.3 and 0.4 respectively for substitution of Pr, Nd, Sm, Eu and Gd for La in La2CuO4 without evidence of the T* phase. The T′ structure of Pr2CuO4 (x = 0.0) gets transformed to the T* structure at 30% Ca doping (x=0.6) and then to the T structure at 50% Ca doping (x=1.0), while for Sr-contentx=0.0, 0.4 and 1.0 it shows T′, T* and T structure respectively.
pp 891-922 April 1997
A stochastic model for solidification II. Application to binary metallic melts
Shobha Dass Gautam Johri Lakshman Pandey
A stochastic model to study the solidifcation process developed in part I is applied to various binary alloys having different values of interaction energies. The results obtained for the time evolution of temperature and concentration, rate of growth and shape of the solid-liquid interface are presented.
pp 923-928 April 1997
Manish Gupta K S Sharma L Dass
A linearized form for the screened form factors of electron-phonon interaction in the metallic glass Mg70Zn30 is applied for the first time to predict the superconducting state parameters viz. electron-phonon coupling strength (λ), Coulomb pseudopotential (μ*), transition temperature (Tc), isotope effect exponent (α) and the interaction strength (N0V). Computed results agree with the experimental data available in the literature.
pp 929-935 April 1997
N K Porwal R M Kadam Y Babu M D Sastry M D Aggarwal Putcha Venkateswarlu
Photo-induced charge transfer and its kinetics were investigated in Bi12SiO20 in 10–300 K temperature range, using EPR of Fe3+ centre, underin situ illumination with copper vapour laser (CVL). The decay kinetics was found to follow double exponential behaviour. Relaxation of the photo-induced electron transfer to the preillumination condition occurred even at 10 K. Shallow traps were, therefore, associated with the electron trapping, leading to a better understanding of the fast photorefractive response of BSO.
pp 937-950 April 1997
Resonance de-enhancement in the 21Ag state oftrans-azobenzene
We analyze the origin of de-enhancement for a number of vibrational modes in the 21Ag excited state oftrans-azobenzene. We have used the time-dependent wave packet analysis of the RR intensities by including the multimode damping effects in the calculation. This avoids the use of unrealistically large values for the damping parameter. It is concluded that the de-enhancement is caused by the interference between the two uncoupled electronic states, and that the intensities observed under the so-called symmetry forbidden 21Ag ← 11Ag transition are purely due to resonance excitation. It is also observed that the use of the time-dependent approach to study the de-enhancement effects caused by multiple electronic states on the RR intensities is not necessarily useful if one is interested in the structural dynamics.
pp 951-958 April 1997 Brief Report
Souri Banerjee S Chatterjee B K Chaudhuri
The room temperature reflectance spectra in UV-VIS-NIR region (energy range of 0.6 to 6.2 eV) for glassy, partially crystalline and its fully crystalline superconducting ceramic phases of Bi3.9Pb0.1Sr3Ca3Cu4Ox have been studied by Kramers-Kronig (KK) analysis. A comparative study of the energy loss function [− Im (1/ε)] and the absorption coefficient [α(E)] has been done. Excitions in the superconducting phase hitherto evidenced by the authors are located in the polarizable layers of the superconducting cuprate and their implications for superconductivity have been pointed out. An estimate of the optical band gap energy (Eg) has also been made from the linear fit ofα2 vs.E curve for the superconducting phase. Jezierski’s method ofR-extrapolations in the higher energy has been used to show that both methods yield results that agree quantitatively and can be relied upon.
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