• Shikha

      Articles written in Pramana – Journal of Physics

    • 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.

    • Nonlinear dust-ion-acoustic waves in a multi-ion plasma with trapped electrons

      S S Duha B Shikha A A Mamun

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      A dusty multi-ion plasma system consisting of non-isothermal (trapped) electrons, Maxwellian (isothermal) light positive ions, warm heavy negative ions and extremely massive charge fluctuating stationary dust have been considered. The dust-ion-acoustic solitary and shock waves associated with negative ion dynamics, Maxwellian (isothermal) positive ions, trapped electrons and charge fluctuating stationary dust have been investigated by employing the reductive perturbation method. The basic features of such dust-ion-acoustic solitary and shock waves have been identified. The implications of our findings in space and laboratory dusty multi-ion plasmas are discussed.

    • Combination synchronization of time-delay chaotic system via robust adaptive sliding mode control

      AYUB KHAN SHIKHA

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      In this paper, the methodology to achieve combination synchronization of time-delay chaotic system via robust adaptive sliding mode control is introduced. The methodology is implemented by taking identical time-delayLorenz chaotic system. The selection of switching surface and the design of control law is also discussed, which is an important issue. By utilizing rigorous mathematical theory, sufficient condition is drawn for the stability of error dynamics based on Lyapunov stability theory. Theoretical results are supported with the numerical simulations. The complexity of this methodology is useful to strengthen the security of communication. The hidden message can be partitioned into several parts loaded in two master systems to improve the accuracy of communication.

    • Tsallis holographic dark energy in Bianchi-I Universe using hybrid expansion law with $k$-essence

      VIPIN CHANDRA DUBEY SHIKHA SRIVASTAVA UMESH KUMAR SHARMA ANIRUDH PRADHAN

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      In this paper, the proposed dark energy, Tsallis holographic dark energy (THDE), infrared cut-off with the Hubble horizon has been investigated in the Bianchi-I (axially symmetric) anisotropic model with a hybrid expansion law. It has been observed that the THDE is in tune with the accelerating Universe with equation of state (EoS) parameter ($\omega_{T}$ < $−1/3$) in the $k$-essence region. We have used the statefinder diagnostic in our model. In addition, we try to accommodate the perspective of dark energy by the avenue of reconstructing the evolution of scalar field potential. We have considered the $k$-essence for the analysis of this reconstruction, showing the accelerated expansion at present.

    • Importance of self-shielding in mass measurements using $\gamma$-ray spectroscopy

      JESSE D NORRIS SHIKHA PRASAD

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      Due to the exponential attenuation of photons in materials, thick samples will attenuate a large portion of photons. This is a source of error in methods such as neutron activation analysis, which use gamma spectroscopy to characterise a radioactive source. A method is developed to quantify the magnitude of self-shielding with the help of MCNP6. Then the mass of an unknown sample is determined by comparing the known sample mass and the photopeak counts of the unknown and the known samples following activation. The inclusion of self-shielding effects is shown to make this comparative mass analysis measurement technique more accurate. Accounting for the self-shielding effects allows the true source, instead of the shielded source, to be resolved by correcting for the photons that are attenuated as they try to escape the sample and reach the detector. The $\gamma$-ray measurements were made using several samples of varying shapes.

    • Neutron spectrum reconstruction for liquid organic scintillators in low information scenarios via genetic algorithm

      IAN HALVIC SHIKHA PRASAD

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      Construction of neutron energy spectrum is of interest in various scientific fields such as nuclear power, nuclear security, industrial applications of nuclear and fundamental physics. A genetic neutron spectrum unfolding method is proposed to generate neutron energy spectrum giving light output data from a liquid organic scintillation detector. The method presented attempts to unfold given minimum a priori data, specifically it does not require an initial guess spectrum to be supplied. Two response matrices corresponding to an EJ-309 organic liquid scintillator are constructed for testing, with one matrix using the traditional discretisation and the other using an alternate discretisation based on the energy-to-light conversion process. Test cases include MCNPX-PoliMi simulated $^{252}$Cf, AmLi and AmBe spectra with corresponding detector responses. The genetic method can perform a coarse unfolding of the test spectra, potentially enough to perform an initial categorisation of the spectra. Promising results are obtained when genetic method is used in conjunction with the existing MAXED unfolding code, which operates on the maximum entropy principle. In this scenario, accuracy appears to exceed MAXED using its built-indefault a priori spectrum. The $^{252}$Cf test case saw a reduction in the unfolded spectrum error from 5.08×10$^{-3}$ to 9.42×10$^{_5}$. The AmLi and AmBe test cases could not be unfolded by MAXED using its default spectrum; however,when supplied with the genetic method result, MAXED could complete a successful unfold.

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