• A K Shukla

      Articles written in Pramana – Journal of Physics

    • Internal pressure, ultrasonic velocity and viscosity of multi-component liquid systems

      J D Pandey A K Shukla Neelima Tripathi G P Dubey

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      Ultrasonic velocity, density and viscosity were measured in two ternary liquid systems namely,n-pentane +n-hexane + benzene(I) andn-hexane + cyclohexane + benzene(II) and one quaternary liquid system,n-pentane +n-hexane + benzene + toluene (III). The experimental as well as literature values of thermal expansion coefficient and iso-thermal compressibility of pure liquid components were utilized to deduce the ideal value of internal pressure and excess internal pressure for the above liquid systems at 298·15K using two different approaches. In the conventional approach one needs the experimental values ofα andβT of mixtures for computing internal pressure, which was not possible. The second method which is proposed here utilizes only the density, ultrasonic velocity and viscosity data of the mixture. This method is used in computing internal pressure and its excess value for multicomponent liquid systems. A satisfactory agreement has been observed.

    • Sound velocity in binary liquid mixtures and the statistical mechanical theories

      J D Pandey Shikha A K Shukla Anil K Singh

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      Sound velocity in three binary liquid mixtures benzene+cyclohexane (I), cyclohexane+carbontetrachloride (II) and benzene+carbontetrachloride (III) has been measured. Significant structure and Flory — Patterson theories have been employed to evaluate ultrasonic velocity in the systems. The values are in good agreement with the experimental ones. A comparative study of significant structure theory and Flory-Patterson Theory has been made. Both the theories give satisfactory results for the three liquid mixtures.

    • Metallic/semiconducting ratio of carbon nanotubes in a bundle prepared using CVD technique

      Khurshed Ahmad Shah S S Islam H S Mavi A K Shukla Harsh

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      We present an investigation of the nature of single-walled carbon nanotubes (SWCNTs) in a bundle by resonant Raman spectroscopy. The calculation has been done for the three peak positions in radial breathing mode (RBM) spectra obtained by using a laser excitation wavelength (γ) of 633 nm from He-Ne laser on SWNT bundle sample prepared by chemical vapor deposition (CVD) technique using iron catalyst at 800°C. The detailed analysis in the present study is focused on peak positions 162 cm−1, 186 cm−1, and 216 cm−1. The firs step of the analysis is to construct a list of possible (n, m) pairs from the diameters calculated from the RBM peak positions. The parameters of SWNTs studied gives in-depth understanding of many symmetry, resonance and characteristic properties of SWNT bundles. Our results indicate that the contribution of metallic SWNTs in the bundle is small at RBM peak positions 162 cm−1, 186 cm−1 and in agreement with pervious results at peak position 216 cm−1.

    • The general class of Bianchi cosmological models with dark energy and variable $\Lambda$ and $G$ in viscous cosmology

      R CHAUBEY A K SHUKLA RAKESH RAUSHAN

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      The general class of Bianchi cosmological models with dark energy in the form of modified Chaplygin gas with variable $\Lambda$ and $G$ and bulk viscosity have been considered. We discuss three types of average scalefactor by using a special law for deceleration parameter which is linear in time with negative slope. The exact solutions to the corresponding field equations are obtained. We obtain the solution of bulk viscosity ($\xi$ ), cosmologicalconstant ($\Lambda$), gravitational parameter ($G$) and deceleration parameter ($q$) for different equations of state. The model describes an accelerating Universe for large value of time $t$ , wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.

    • The anisotropic cosmological models in $f (R, T)$ gravity with $\Lambda (T)$

      R CHAUBEY A K SHUKLA

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      The general class of anisotropic Bianchi cosmological models in $f(R, T)$ modified theories of gravity with $\Lambda (T)$ has been considered. This paper deals with $f(R, T)$ modified theories of gravity, where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar $R$ and the trace of the stress-energy tensor $T$ has been investigated for a specific choice of $f (R,T )$ = $f_{1}(R) + f_{2}(T)$. The exact solutions to the corresponding field equations are obtained in quadrature form. We have discussed three types of solutions of the average scale factor for the general class of Bianchi cosmological models by using a special law for deceleration parameter which is linear in time with a negative slope. The solutions to the Einstein field equations are obtained for three differentphysical viable cosmologies. All physical parameters are calculated and discussed in each model.

    • Locally rotationally symmetric Bianchi type-I cosmological model with dynamical $Lambda$ and $G$ in $f (R)$ gravity

      RAKESH RAUSHAN A K SHUKLA R CHAUBEY T SINGH

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      In this paper, we have studied the locally rotationally symmetric (LRS) Bianchi type-I cosmological model filled with a bulk viscous cosmological fluid in $f(R)$ gravity in the presence of time-varying gravitational and cosmological constant. We have used the power-law and intermediate scenario for scale factor to obtain thesolution of the field equations. The evolution of temperature of a viscous Universe is also analysed.

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