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Modeling phase equilibria of semiclathrate hydrates of CH_4,CO_2 and N_2 in aqueous solution of tetra-n-butyl ammonium bromide

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Journal of Natural Gas Chemistry 2012年第4期21卷 459-465页

作者： abhishek joshi Prathyusha Mekala Jitendra S.Sangwai Petroleum Engineering Program Department of Ocean EngineeringIndian Institute of Technology MadrasChennai-600 036India

Semiclathrate hydrates of tetra-n-butyl ammonium bromide （TBAB） offer potential solution for gas storage, transportation, separation of flue gases and CO2 sequestration. Models for phase equilibria for these systems have not yet been developed in open literatures and thus require urgent attention. In this work, the first attempt has been made to model phase equilibria of semiclathrate hydrates of CH4, CO2 and N2 in aqueous solution of TBAB. A thermodynamic model for gas hydrate system as proposed by Chen and Guo has been extended for semiclathrate hydrates of gases in aqueous solution of TBAB. A correlation for the activity of water relating to the system temperature, concentration of TBAB in the system and the nature of guest gas molecule has been proposed. The model results have been validated against available experimental data on phase equilibria of semiclathrate hydrate systems of aqueous TBAB with different gases as guest molecule. The extended Chen and Guo＇s model is found to be suitable to explain the promotion effect of TBAB for the studied gaseous system such as, methane, carbon dioxide and nitrogen as a guest molecule. Additionally, a correlation for the increase in equilibrium formation temperature （hydrate promotion temperature, ATp） of semiclathrate hydrate system with respect to pure gas hydrate system has been developed and applied to semiclathrate hydrate of TBAB with several gases as guest molecules. The developed correlation is found to predict the promotion effect satisfactorily for the system studied.

关键词： gas hydrate phase equilibria semiclathrate hydrate tetra-n-butyl ammonium bromide (TBAB)

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Re-Sheathing the Scimitar Syndrome

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Advances in Computed Tomography 2012年第3期1卷 21-22页

作者： Michael Michail Kaleab N. Asrress abhishek joshi John A. Giles Muhammed Z. Khawaja Eric T. McWilliams Department of Cardiology Conquest Hospital Hastings UK

Scimitar Syndrome is a congenital condition resulting in anomalous pulmonary venous drainage from the lung into the inferior vena cava. It is often associated with cardiac and pulmonary abnormalities, both which are determinants in the severity and timing of presentation. True incidence of this condition is unknown and likely to be significantly underestimated as many patients remain asymptomatic through adult life. The increase in availability and use of medical imaging suggests that more asymptomatic and subacute cases will be detected. The management in those with the delayed presentation of this condition is debated, however the mainstay of therapy remains medical.

关键词： Adult-Onset Scimitar Syndrome Multidetector Computed Tomography

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Modelling effect of magnetic field on material removal in dry electrical discharge machining

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Plasma Science and Technology 2017年第2期19卷 79-88页

作者： abhishek GUPTA Suhas S joshi Department of Mechanical Engineering Indian Institute of Technology BombayPowaiMumbai 400 076India

One of the reasons for increased material removal rate in magnetic field assisted dry electrical discharge machining （EDM） is confinement of plasma due to Lorentz forces. This paper presents a mathematical model to evaluate the effect of external magnetic field on crater depth and diameter in single- and multiple-discharge EDM process. The model incorporates three main effects of the magnetic field, which include plasma confinement, mean free path reduction and pulsating magnetic field effects. Upon the application of an external magnetic field, Lorentz forces that are developed across the plasma column confine the plasma column. Also, the magnetic field reduces the mean free path of electrons due to an increase in the plasma pressure and cycloidal path taken by the electrons between the electrodes. As the mean free path of electrons reduces, more ionization occurs in plasma column and eventually an increase in the current density at the inter-electrode gap occurs. The model results for crater depth and its diameter in single discharge dry EDM process show an error of 9%-10% over the respective experimental values.

关键词： electrical discharge machining dry EDM plasma confinement magnetic field

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MHD Seismology of a loop-like filament tube by observed kink waves

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Research in Astronomy and Astrophysics 2015年第10期15卷 1713-1724页

作者： Vaibhav Pant abhishek K Srivastava Dipankar Banerjee Marcel Goossens Peng-Fei Chen Navin Chandra joshi Yu-Hao Zhou Indian Institute of Astrophysics Department of Physics Indian Institute of Technology(BHU) Center of Excellence in Space Sciences Centre for Mathematical Plasma Astrophysics Department of Mathematics School of Astronomy and Space Science Nanjing University Key Lab of Modern Astronomy and Astrophysics Nanjing University School of Space Research Kyung Hee University

We report and analyze observational evidence of global kink oscillations in a solar filament as observed in Ha by instruments administered by National Solar Observatory （NSO）/Global Oscillation Network Group （GONG）. An M1.1-class flare in active region （AR） 11692 occurred on 2013 March 15 and induced a global kink mode in the filament lying towards the southwest of AR 11692. We find periods of about 61-67 minutes and damping times of 92-117 minutes at positions of three ver- tical slices chosen in and around the filament apex. We find that the waves are damped. From the observed period of the global kink mode and damping timescale using the theory of resonant absorption, we perform prominence seismology. We estimate a lower cut-off value for the inhomogeneity length scale to be around 0.34-0.44 times the radius of the filament cross-section.

关键词： Sun: oscillations -- Sun: magnetic fields -- Sun: filament

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