• Volume 1, Issue 3

      September 1973,   pages  117-164

    • Photometry of the solar corona of March 7, 1970

      M K V Bappu J C Bhattacharyya K R Sivaraman

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      Isophotes obtained by equidensitometry techniques from four exposures of the March 7, 1970 corona are used for derivation of intensity distributions along the equator, poles, streamers and dark ‘gaps’ in the visible corona. The distributions differ from the van de Hulst curves for a maximum corona. The Kodaikanal measures agree well with the NRL measures of the outer corona made from a rocket coronagraph and together provide data from 1·2R to 8·0R along the solar equator. Radial intensity gradients for different position angles and the Ludendorff parameters obtained, characterize this corona as typical of the solar maximum.

    • The kinetic equation and the equation of momentum transfer for a plasma

      Saroj K Majumdar

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      An attempt is made to derive a simple form of the collision integral of the kinetic equation for a plasma, by using Rostoker’s equation which expresses the pair correlation function in terms of the distribution functions of the particles, and the conditional probability of one particle shielding the other. The conditional probability function is assumed to be given by its equilibrium value. By taking first order velocity-moment of the resulting kinetic equation, the equation of momentum transfer has been obtained.

    • A simple derivation of the three magnon bound state equation

      Chanchal K Majumdar G Mukhopadhyay A K Rajagopal

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      A simple derivation of the equation for determining the bound states of three magnons in the Heisenberg linear chain with longitudinal anisotropy is given. The present method utilizes nothing more than the Schrödinger equation and Faddeev’s three body equations, and avoids the introduction of the ideal spin wave Hilbert space.

    • Plasmon excitation in the x ray absorption process

      Ashok Pimpale Chintamani Mande

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      A simple approach is developed to study the excitation of a plasmon due to valence electronic correlations in the x ray absorption process. Assuming a complete separation between the core and the valence electrons, we introduce the plasmons in the system Hamiltonian externally according to the Bohm-Pines collective formalism and carry out the corresponding canonical transformations to separate the x ray photonplasmon-electron term. According to our calculations, the relative intensity of the plasmon process with respect to the main absorption, which represents single particle excitations is 0·12 times the interelectronic separation measured in Bohr radii. The theoretical estimates of the plasmon intensity agree satisfactorily with the experimental values for the Mn K and the Re LIII absorption discontinuities.

      The shape of the plasmon absorption band resembles the main absorption edge, if the wave vector dependence of the plasmon frequency is neglected. The intensity of the second plasmon harmonic is about 3 per cent of the first plasmon satellite spectrum. The electron plasmon interaction modifies the shape of the plasmon spectrum.

    • Crystallographic and magnetic phase transition in TlMnCl3

      R Vijayaraghavan M D Karkhanavala S D Damle L C Gupta U R K Rao

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      The results of our NMR, EPR and magnetic susceptibility measurements in the paramagnetic state of TlMnCl3 are reported here. The NMR paramagnetic shift of thallium is found to be small but positive. Mn2+ EPR line is exchange narrowed. The susceptibility measurements indicate an antiferromagnetic transition. The heat of crystallographic phase transition ΔH, in TlMnCl3 has been measured using differential scanning calorimetry. The crystallographic phase transition appears to be first order and ΔH is unusually low viz. 10 cal mole−1. In the case of KMnF3 ΔH, which is reported here for the first time, is determined to be 2 cal mole−1.

    • Dynamics of H2O molecules in ferroelectric K4Fe(CN)6 · 3H2O

      P Kumara Acharya P S Narayanan

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      The infrared spectrum of potassium ferrocyanide trihydrate has been recorded both in the para and ferroelectric phases. From a combined study of the IR and Raman spectra, it is concluded that there are two sets of water molecules present in the lattice, one set being involved in stronger hydrogen bonding than the other. The ferroelectric transition appears to be associated with an ordering of the water dipoles.

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