• A Das

      Articles written in Pramana – Journal of Physics

    • Measurement of diffusion coefficients of thallium ion in H2O and D2O systems at different concentrations

      A Das S N Changdar

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      Sliding cell method, developed in our laboratory, has been used to measure the inter diffusion coefficient of thallium ion in thallous sulphate solution over a wide concentration range using both water and heavy water as solvent at 35°C. The results have been analysed from the point of view of both ion-ion and ion-solvent interactions. The comparison of the diffusivities of the same ion in D2O and H2O electrolyte solutions at the same temperature indicate that the addition of salt affects the two solvents differently.

    • Even harmonics of AC susceptibility in some sintered pellets of high temperature superconductors

      A Das A Bajpai A Banerjee R Srinivasan

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      The real (χ′n) and imaginary (χ″n) parts of even harmonic susceptibility (n⩽6) are measured as a function of external DC field (Hdc) in the field increasing (H↑) and decreasing (H↑) cycle. Hysteresis is observed betweenH↑ andH↓ cycles. In theH↓ cycle, at a field,Hcomp=4·2G, bothχ′ andχ″ of all the even harmonics vanish indicating a true cancellation of fields in the intergrain region (Heff≈0) caused by the balance betweenHdc and the remanent magnetization of the grains. The position of the extrema and the zero of the various harmonics undergo a shift proportional to the remanent magnetization of the grains at that particular field.

    • High-density QCD phase transitions inside neutron stars: Glitches and gravitational waves


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      We discuss physics of exotic high baryon density QCD phases which are believed to exist in the core of a neutron star. This can provide a laboratory for exploring exotic physics such as axion emission, KK graviton production etc.Much of the physics of these high-density phases is model-dependent and not very well understood, especially the densities expected to occur inside neutron stars. We follow a different approach and use primarily universal aspects of the physics of different high-density phases and associated phase transitions. We study effectsof density fluctuations during transitions with and without topological defect production and study the effect on pulsar timings due to changing moment of inertia of the star. We also discuss gravitational wave production due to rapidly changing quadrupole moment of the star due to these fluctuations.

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