• R P Singh

      Articles written in Pramana – Journal of Physics

    • Effect of correlation on the band structure of cerium

      R S Rao C K Majumdar B S Shastry R P Singh

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      The electronic band structure of f.c.c. phase of the rare earth metal cerium (α-cerium) has been calculated using a formulation of the crystal potential where correlation also has been included in addition to exchange. We use the prescription of Cohn and Sham as well as that of Overhauser. The Green’s function method of Korringa-Kohn and Rostoker has been used for obvious advantages in the calculation. The calculations indicate that the s—d bands are hybridized with the f-levels but the f-bands are fairly narrow and lie slightly above the Fermi level. The structure of the bands is qualitatively similar to those of calculations by others except for a general shift of the entire set of bands by about 0·1 Ryd. The density of states has been calculated from the bands obtained. The spin susceptibility ofα-cerium has also been calculated using the Kohn-Sham method. However, the calculated additional contributions to the band structure values cannot still explain the large experimental values reported in the literature.

    • Vibrational spectra of 2, 3 and 2, 6 dichloro anilines

      R P Singh R N Singh

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      The infrared and laser Raman spectra of 2, 3 dichloro aniline and 2, 6 dichloro aniline have been recorded. The vibrational spectra have been analysed assumingCs andC2v point groups for 2, 3 dichloro aniline and 2, 6 dichloro aniline respectively. Assignments for fundamental vibrations, combination and overtone frequencies and internal modes of vibration of amino group have been proposed.

    • Transition strengths and shapes of 2-qp bands in 74Se and 76Kr

      G Mukherjee P Joshi S N Roy S Datta R P Singh S Muralithar R K Bhowmik

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      The lifetimes of the states of −ve parity 2-qp bands of N=40 nuclei 74Se and 76Kr were measured. The transition strengths and quadrupole moments, obtained from the lifetimes, show a large collectivity of such bands in both the nuclei. The alignment frequencies were calculated from Woods-Saxon cranking model. Previously suggested quasi proton nature of band 5 and 6 of 71Se were argued to be based on quasi neutron excitations. The total Routhian surface calculations suggest triaxial shapes with large +ve and −ve values of triaxiality parameter γ after proton and neutron alignments in these bands respectively.

    • Matched filtering-parameter estimation method and analysis of whistlers recorded at Varanasi

      R P Singh R P Patel Ashok K Singh D Hamar J Lichtenberger

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      The matched filtering technique is based on the digital-construction of theoretical whistlers and their comparison with observed whistlers. The parameters estimated from the theoretical and experimental whistler curves are matched to have higher accuracy using digital filters. This yields a resolution ten times better in the time domain. We have tested the applicability of this technique for the analysis of whistlers recorded at Varanasi. It is found that the whistlers have propagated along L>2 and have wave normal angles after exiting from the ionosphere such that they propagate towards equator in the earth-ionosphere wave-guide. High-resolution analysis shows the presence of fine structures present in the dynamic spectrum. An effort is made to interpret the results.

    • Ionospheric plasma by VHF waves

      R P Patel Abhay Kumar Singh R P Singh

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      The amplitude scintillations of very high frequency electromagnetic wave transmitted from geo-stationary satellite at 244.168 MHz have been recorded at Varanasi (geom. lat. 14′ 55′N) during 1991 to 1999. The data are analyzed to determine the statistical features of overhead ionospheric plasma irregularities which are mostly of small duration <30 minutes and are predominant during pre-midnight period. The increase of solar activity generally increases the depth of scintillation. The auto-correlation functions and power spectra of scintillations predict that the scale length of these irregularities varies from 200–500 m having velocity of movement between 75 m/sec to 200 m/sec. These results agree well with the results obtained by other workers.

    • VLF emissions from ionospheric/magnetospheric plasma

      R P Patel R P Singh

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      VLF emissions such as hiss, chorus, oscillating tones, hiss-triggered chorus and whistler triggered emissions have been observed at low latitude Indian stations. In this paper we present dynamic spectra of these emissions and discuss their various observed features. It is argued that most of the emissions are generated during Doppler shifted cyclotron resonance interaction between the whistler mode wave and counter streaming energetic electrons. Resonance energy of the participating electron and interaction length are evaluated to explain the generation mechanism of some of these emissions observed at Indian stations.

    • Hiss emissions during quiet and disturbed periods

      D K Singh R P Singh

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      The characteristic features of VLF hiss emissions during quiet and disturbed conditions observed at ground stations and on-board satellites are summarized. The increased intensity of the hiss emissions during magnetic storm period is explained by considering the enhanced flux of energetic electrons during magnetic storm period. The generation and propagation mechanism of VLF hiss are also briefly discussed.

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