• Om Prakash

      Articles written in Pramana – Journal of Physics

    • X-ray energy levels: Deviations between experimental and theoretical values

      Amar Nath Nigam Om Prakash Rajput

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      Energy values ofK, LII andLIII levels calculated by the relativistic self consistent field method have been used to compute the energies of1, 2 lines. These values deviate considerably from the experimental values due to Bearden and Burr. The deviations are discussed and given an empirical fit.

    • An apparatus for the measurement of thermal expansion of solids at low temperatures

      Om Prakash Ashok Rao P N Dheer

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      A dilatometer, using the three terminal capacitance technique, suitable for measurement of linear thermal expansion of solids in the temperature range 1.3–300 K is described. The dialtometer is designed such that the mounting system for the specimen does not undergo any significant changes in dimensions when the specimen is heated. The apparatus, therefore, yields in principle absolute values of α, the coefficient of linear thermal expansion. The performance of the apparatus has been checked by measurements on copper in the temperature range of 77–300 K. Some preliminary results on the behaviour of α for Y1Ba2Cu3O6.9 compound in the vicinity of superconducting transition temperature,Tc are also described. The system can detect relative changes in length Δl/l0 of about 10−8. Attempts are being made to improve the sensitivity.

    • Effect of Fe substitution on the thermal expansion of the highTc superconductor Y1Ba2Cu3Oy

      Ashok Rao Om Prakash S N Das P N Dheer

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      Thermal expansion measurements have been carried out on Fe substituted superconducting compounds Y1Ba2(Cu1−xFex)3Oy (0<x<4%) using a high resolution dilatometer employing the three terminal capacitance technique. The experimental set up is sensitive enough to detect changes in α of less than 10−8K−1. Results show that the jump Δα in the coefficient of linear thermal expansion at the superconducting transition temperature,Tc, increases almost linearly with Fe concentration. The normal state thermal expansion coefficient α first decreases, attains a minimum value aroundx=1% and then increases for higher Fe concentrations. The oxygen content per unit formula is almost constant up tox=1% and then increases rapidly withx. It has also been observed that the anomalous behaviour of α around 260 K observed by Meingastet al [22] for Fe concentrationx=5% is due to inadequate annealing of the sample.

    • Free convection effects and radiative heat transfer in MHD Stokes problem for the flow of dusty conducting fluid through porous medium

      Om Prakash Devendra Kumar Y K Dwivedi

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      The present note deals with the effects of radiative heat transfer and free convection in MHD for a flow of an electrically conducting, incompressible, dusty viscous fluid past an impulsively started vertical non-conducting plate, under the influence of transversely applied magnetic field. The heat due to viscous dissipation and induced magnetic field is assumed to be negligible. The governing linear partial differential equations are solved by finite difference technique. The effects of various parameters (like radiation parameter 𝑁, Prandtl number Pr, porosity parameter 𝐾) entering into the MHD Stokes problem for flow of dusty conducting fluid have been examined on the temperature field and velocity profile for both the dusty fluid and dust particles.

    • Heat transfer in MHD flow of dusty viscoelastic (Walters’ liquid model-B) stratified fluid in porous medium under variable viscosity

      Om Prakash Devendra Kumar Y K Dwivedi

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      The paper investigates the effects of heat transfer in MHD flow of viscoelastic stratified fluid in porous medium on a parallel plate channel inclined at an angle 𝜃. A laminar convection flow for incompressible conducting fluid is considered. It is assumed that the plates are kept at different temperatures which decay with time. The partial differential equations governing the flow are solved by perturbation technique. Expressions for the velocity of fluid and particle phases, temperature field, Nusselt number, skin friction and flow flux are obtained within the channel. The effects of various parameters like stratification factor, magnetic field parameter, Prandtl number on temperature field, heat transfer, skin friction, flow flux, velocity for both the fluid and particle phases are displayed through graphs and discussed numerically.

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