Articles written in Pramana – Journal of Physics

    • The δ-function expansion of the modified two-particle Ursell function of a hard-sphere fluid

      N Ansari B Kumar

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      The expansion of the modified two-particle Ursell functionU(r) of a hardsphere quantal fluid is obtained in terms of a series of derivatives of δ-function. This expansion has been used to expand the second virial co-efficientB2 of the fluid. The expansion is correct up to the fourth power in thermal wavelength and the terms of the order of λ8 and λ4 in the first expa nsion are new.

    • Electric field gradients in simple tetragonal lattice at interstitial site

      D P Verma B Kumar H C Verma

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      Electric field gradient (efg) is calculated at the centre of the cell in the simple tetragonal crystal. The method uses Euler-Maclaurin summation formula and makes the planewise summation in the direct crystal space without any special regrouping of charges in point charge model. The results are in fair agreement with previous results of de Wette on the same system using Fourier transform to reciprocal space.

    • Activation energy of hydrogen in Lu

      N Singh B Kumar

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      The impurity induced charge density is calculated in jellium by solving the Schrödinger equation self-consistently following the procedure of Manninen and Nieminen and using Kohn-Sham density functional formalism. The host-ion contribution is included through the spherical solid model potential (SSMP). The calculated activation energy 0.27 eV is found in good agreement with experimental value 0.28±0.02 eV. The estimated residual resistivity 1.02 µΩ cm/at% for Lu-H system using the resulting phase shifts agrees reasonably well with the observed value 1.75±0.10 µΩ cm/at%. The calculated configurational energy shows that hydrogen prefers tetrahedral(T)-sites over octahedral(O)-sites in Lu matrix. This has been confirmed by Bonnet experimentally. A very shallow value ofs-type bound state of energy −0.00316 Ryd predicts that there is no formation of lutetium hydride solution and H+ exists as a free ion in Lu matrix.

    • New modifications in 15 UD pelletron at nuclear science centre

      S Chopra N S Pawar M P Singh Rakesh Kumar J Prasad V P Patel Raj Pal B Kumar S Ojha K Devarani T Nandi M Sota P Barua S Gargari R Joshi D Kanjilal SK Datta

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      The 15 UD pelletron at NSC has been operational and performed well during the last 11 years. There have been major modifications performed for upgradation of pelletron system over this period. Major upgradations which have been implemented are new resistor network system for voltage gradient, doublet to singlet unit conversion for accelerator units, turbopump based gas stripper system etc. In addition accelerator mass spectroscopy program has also been started. A new multi-cathode source, Wien filter etc. have been procured and will be added soon in the system. An overview of the most significant upgradations undertaken and other activities for the system are being reported in the present paper.

    • Successive linearisation approach to analyse thermally radiative stagnation point micropolar nanofluid flow with regression model


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      The present paper is devoted to the investigation of magnetohydrodynamics (MHD) mixed convection stagnation point flow of a micropolar nanofluid with thermal radiation, microrotation, viscous and Joule dissipations, Brownian and thermophoretic diffusions, etc. The present analysis is done because it contains large potential to deal with many industrial processes such as electrical power generation, nuclear energy plant, melt spinning technique for cooling liquids, astrophysical flows, space vehicles, geothermal extractions, solar system, etc. The numerical solutions of the governing equations are obtained by successive linearisation method (SLM). The influence of various developing parameters, such as thermal radiation parameter, mixed convection parameter, thermophoretic parameter, etc., on the flow field is examined through graphs by accumulating sufficient data using SLM. A comparative study is performed between our results and previously obtained results in the limiting sense. Apart from this, the quadratic multiple regression analysis is performed for skin friction coefficient. It indicates that when the free stream is moving with less velocity than stretching velocity then a small variation in microrotation leads to large perturbation in skin friction in comparison to mixed convection parameter but in the opposite case, the buoyancy force becomes more dominant.

    • Features of Jeffrey fluid flow with Hall current: A spectral simulation


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      The Hall current in MHD flow stimulates substantial interest of researchers because of its wide rolein many geophysical, astrophysical and fluid engineering situations (construction of turbines, Hall accelerator and centrifugal machines). Motivated by such wide applications, the present work reports the influence of Hall current and thermal radiation on the three-dimensional Jeffrey fluid flow over a stretching surface. In order to achieve similar solution of the governing equations, transformation technique is adopted. The mathematical model is numerically solved by using a spectral technique, namely successive linearisation method (SLM). To explore the feature of various factors, e.g. Hall current and thermal radiation, the variation of flow dominant parameters on the obtained profiles are carefully elucidated with graphs. It can be sensed from the obtained graphs that primary and secondary velocity increase, but, temperature reduces with the enhancement in Hall current. Radiation parameter has the tendency to increase the temperature of the fluid.

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