• Volume 45, Issue 3

      September 1995,   pages  221-304

    • Theoretical calculation of acoustic non-linearity parameter B/A of binary mixtures

      J Jugan Roshan Abraham M Abdulkhadar

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      Acoustic non-linearity parameter B/A is calculated for five binary liquid mixtures using Tong and Dong equation along with the Flory’s statistical theory. Similar to other excess thermodynamical quantities an excess non-linearity parameter (B/A)E is defined for binary liquid mixtures. The interactions in the liquid mixtures are explained on the basis of the excess non-linearity parameter.

    • Gyrotropic and piezoelectric coefficients and attenuation of elastic waves in BaTiO3

      B Subramanyam

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      Using Landau theory of phase transition, expressions for gyrotropic coefficients and piezoelectric coefficients are obtained for barium titanate in the tetragonal phase. Both coefficients vanish at the ferroelectric phase transition temperature. The piezoelectric coefficients tallied with the literature values. The attenuation coefficients for elastic waves propagating along the principal directions in tetragonal, orthorhombic and rhombohedral phases are derived based on Landau theory. It is predicted that there will be slight amplification for both longitudinal and transverse modes in the rhombohedral phase at a temperature close to the rhombohedral phase transition temperature.

    • Heat capacity and phonons in poly(L-leucine)

      Seema Srivastava Poonam Tandon V D Gupta Shantanu Rastogi S B Katti L Burman

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      Poly(L-leucine) is one of the polyamino acids having a bulky hydrophobic side-chain. For want of full phonon dispersion curves and density-of-states on this biopolymer Roleset al have interpreted their specific heat data in a limited way. In the present communication we report an analysis of the normal modes and their dispersion for poly(L-leucine) which leads to a very good agreement of the specific heat calculations with experimental measurements. It is observed that the main contribution to specific heat comes from the coupling of the back-bone skeletal and side-chain modes. Several other assignments have been revised. A special feature of some dispersion curves is their tendency to bunch in the neighbourhood of helix angle. It has been attributed to the presence of strong intramolecular interactions. Repulsion between the dispersion curves is also observed.

    • Streaming instability of a dusty plasma in the presence of mass and charge variation

      B P Pandey C B Dwivedi

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      We study the effect of the mass and charge dynamics on the collective behaviour of a dusty plasma. It is shown that the finite non-zero streaming velocity of the dust grains leads to a novel coupling of the dust mass fluctuation with other dynamic variables of the plasma and the grains. The mass fluctuations causes a collisionless dissipation and provides an alternate channel for the beam mode instability to occur. Physically the negative energy wave associated with the beam mode couples to the mass fluctuation induced dissipative medium to produce the instability. We conclude that the higher value of the ion mass density to the dust mass density ratio reduces the threshold value for the onset of the instability. Its application in the astrophysical context is discussed.

    • Geometry effect on the nonlinear magnetic response of YBa2Cu3O7−y

      Parshant Batham S B Roy Shailendra Kumar A K Pradhan A K Grover P Chaddah Ram Prasad N C Soni

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      Results are presented for study of nonlinear magnetization of a sintered YBa2Cu3O7−y pellet of different thickness of a sample subjected to very low magnetic field. On cooling the sample belowTc in zero field a change, in the oscillatory structure of harmonics in increasing dc field is observed in very low ac magnetic field. The effect of finiteness of the sample on the oscillatory structure and on the hysteresis of harmonics is also studied. The results are explained qualitatively.

    • Two photon absorption spectrum ofp-dichlorobenzene

      I B Singh S B Rai D K Rai

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      Two photon absorption spectrum ofp-dichlorobenzene has been studied in the spectral region 497–552 nm (one photon wavelength). Bands involving several frequencies of the excited electronic state not detected in the one photon absorption are seen. The observed two photon spectrum indicates that the electronic transition retains, to a large extent, the salient features of the two photon absorption spectrum of benzene and thus confirms chlorine as weak perturber (in the sense of Goodman and Rava [1]).

    • Picosecond time-resolved laser emission of coumarin 102: Solvent relaxation

      S R Inamdar K Chandrasekhar D C Patil N N Math M I Savadatti

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      The time-resolved laser emission of coumarin 102 was investigated in various aprotic and protic solvents at picosecond resolution by frequency upconversion technique. The spectral shift of the transient emission spectrum is attributed to solvent reorientation and the results are discussed.

    • Development of an experimental facility for studying atomic-field, bremsstrahlung from keV electrons interacting with atoms and molecules

      S K Goel M J Singh R Shanker

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      A dedicated working setup for studying the process of atomic-field bremsstrahlung and its dependence on various parameters for keV electrons incident on a solid or a gaseous target has been indigenously developed. The setup consists of a high vacuum scattering chamber attached with a rotatable X-ray photon detector, a home-built high voltage electron gun with a replaceable tungsten-filament cathode, an isolated floating high voltage system, high vacuum pumping units, various signal processing electronic modules and an IBM PC/XT based 4K-multichannel analyzer. A brief description of the facility is presented. The performance of the facility has been tested by recording the bremsstrahlung spectra from 7.0 keV electrons on thin Ag, Au and 7.5 keV electrons on Hf targets; the corresponding spectra are presented and discussed. The gun can operate in the range of 0–8.0 kV accelerating voltage in the present configuration. Other feasible experiments that can be performed on the setup are also briefly mentioned.

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