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Bhatt H.,M And N Virani Science College | Trivedi R.,H And Hb Kotak Institute Of Science | Sharma S.K.,Physical Research Laboratory | Vats H.O.,Physical Research Laboratory
Solar Physics | Year: 2017

Here we report an in-depth reanalysis of an article by Vats et al. (Astrophys. J.548, L87, 2001) that was based on measurements of differential rotation with altitude as a function of observing frequencies (as lower and higher frequencies indicate higher and lower heights, respectively) in the solar corona. The radial differential rotation of the solar corona is estimated from daily measurements of the disc-integrated solar radio flux at 11 frequencies: 275, 405, 670, 810, 925, 1080, 1215, 1350, 1620, 1755, and 2800 MHz. We use the same data as were used in Vats et al. (2001), but instead of the twelfth maxima of autocorrelograms used there, we use the first secondary maximum to derive the synodic rotation period. We estimate synodic rotation by Gaussian fit of the first secondary maximum. Vats et al. (2001) reported that the sidereal rotation period increases with increasing frequency. The variation found by them was from 23.6 to 24.15 days in this frequency range, with a difference of only 0.55 days. The present study finds that the sidereal rotation period increases with decreasing frequency. The variation range is from 24.4 to 22.5 days, and the difference is about three times larger (1.9 days). However, both studies give a similar rotation period at 925 MHz. In Vats et al. (2001) the Pearson’s factor with trend line was 0.86, whereas present analysis obtained a ∼0.97 Pearson’s factor with the trend line. Our study shows that the solar corona rotates more slowly at higher altitudes, which contradicts the findings reported in Vats et al. (2001). © 2017, Springer Science+Business Media Dordrecht.

Dhruv D.,Gujarat Technological University | Trivedi R.K.,H And Hb Kotak Institute Of Science | Nimavat B.,Saurashtra University | Kansara S.,Saurashtra University | And 6 more authors.
AIP Conference Proceedings | Year: 2013

Substitution of monovalent K+ at La3+ in solid state reaction synthesized La1-xKxMnO3(0.0≤x≤0. 3) manganites results in metallic behavior. Increase in K+ content (x ≤ 0.15) enhances the FM interactions through ZDE mechanism while for higher x > 0.15, structural disorder and AFM interactions between Mn4+ ions become prominent. © 2013 American Institute of Physics.

Lakhani V.K.,H And Hb Kotak Institute Of Science | Modi K.B.,Saurashtra University
Solid State Sciences | Year: 2010

Ultrasonic pulse echo-overlap technique at 300 K (9 MHz) has been employed to study the elastic properties of Al3+-substituted CuFe 2O4 spinel ferrite system. The longitudinal and transverse wave velocities are used to compute elastic moduli and these are corrected to the zero porosity by employing different models. Contrary to expectation, the magnitude of elastic moduli is found to decrease by 75% with only 30% of Al 3+-substitution for Fe3+ in the system. The lowering of elastic stiffness is mainly due to residual stress-induced spontaneous cracking and presence of oxygen vacant sites in the material. The lower value of lattice energy for polycrystalline specimens as compared to their single crystalline counterparts have been explained in the light of an increase degree of disorientation at the grain boundary with Al3+-substitution.

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