• P Chandra Sekhar

      Articles written in Pramana – Journal of Physics

    • Coexistence curve and rectilinear diameter in the critical liquid system carbon disulphide+nitromethane

      E S R Gopal R Ramachandra P Chandra Sekhar

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      The phase boundary of the binary liquid system CS2+CH3NO2 is studied over nearly six decades in reduced temperature 3×10−6<ε=(TCT)/TC<2×10−1 and over the composition range 8-98 mole % of CS2. The critical parameters areTC=335.132K andxC=57.34 mole % of CS2. A single critical exponentβ=0.315±0.004 fits the observations over the entire range with no indication ofβ increasing to the classical value of 1/2 far away fromTC. The diameter of the coexistence curve shows a rectilinear behaviour only far away fromTC. NearTC, the deviation ΔX from the rectilinear law seems to fit a curve of the form ΔX=fε7/8 exp (−h), the derivative of which has a singularity like that of specific heat. An ambiguity in the analysis of the data in terms of mole fractions and volume fractions is pointed out. It is also suggested that the curvature of the diameter may be much weaker in a liquid-gas system and hence might have escaped detection.

    • Critical point phenomena in the electrical resistivity of binary liquid systems: CS2 + CH3CN and CS2 + CH3NO2

      E S R Gopal M V Lele J Ramakrishnan P Chandra Sekhar S V Subramanyam

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      Electrical resistance measurements are reported on the binary liquid mixtures CS2 + CH3CN and CS2 + CH3NO2 with special reference to the critical region. Impurity conduction seems to be the dominant mechanism for charge transport. For the liquid mixture filled at the critical composition, the resistance of the system aboveTc follows the relationR=RcA(TTc)b withb=0·6±0·1. BelowTc the conductivities of the two phases obey a relation σ2−σ1=B(TcT)β with β=0·34±0·02, the exponent of the transport coefficient being the same as the exponent of the order parameter, an equilibrium property.

    • Beam couplings and phase conjugate effects in reflection and transmission in BaTiO3

      Putcha Venkateswarlu M Moghbel P Chandra Sekhar M C George

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      The details of experiments showing the effects of self-pumped phase conjugation on reflection and on transmission in barium titanate crystal are given. The specular reflection and the second-surface reflection of an extraordinary polarized beam, incident on the face of the crystal parallel to itsc-axis, get reduced in intensity as the phase conjugation develops. It has been found that parts of the self-pumped phase conjugate beam emerge out of the crystal as additional transmission beams. They grow in intensity as the phase conjugation develops. Other measurements which combine coherent or incoherent coupling beams are presented and used to explain the observations.

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