Faculty of Applied Sciences

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Cosmic censorship and charged radiation in second order Lovelock gravity
(Elsevier BV, 2022-11) Brassel, Byron P.; Goswami, Rituparno; Maharaj, Sunil D.
The conditions for naked singularity formation are considered for a radiating metric of Boulware–Deser type within an electromagnetic field in second order Lovelock (or Einstein–Gauss–Bonnet) gravity. The spacetime metric remains real only up to certain maximum charge contribution. This differs from general relativity. Beyond a certain maximal charge, there exists no real and physical spacetime since the metric becomes complex. We establish that, under certain parameters and for specific values of the mass function and charge contribution, this branch singularity is indeed a naked singularity. This is in contrast to the neutral case where the spacetime metric is always real for a positive mass function, and further, a weak, initially naked singularity always occurs before it becomes covered by an event horizon for all future time. We highlight that both neutral and charged collapse under gravity in Einstein–Gauss–Bonnet gravity differ significantly to their general relativistic counterparts.
Development of activated carbon by bio waste material for application in supercapacitor electrodes
(Elsevier BV, 2023-03) Devi, Raman; Kumar, Vinay; Kumar, Sunil; Kumar Sisodiya, Avnish; Kumar Mishra, Ajay; Jatrana, Anushree; Kumar, Ashwani; Singh, Paul
Green nanotechnology is now emerging to address society's global sustainability issues by recycling numerous industrial and bio-wastes to produce functional carbonaceous nanomaterials like biochar, 2D graphene, graphene oxide, carbon nanotube (CNT), activated carbon (AC), etc. In this study, we have synthesized AC via the hydrothermal decomposition approach of the walnut shell under high temperature and pressure in a hydrothermal autoclave at temperature ranges from 200 to 250 ℃. The synthesized AC has a high specific surface area of 408.8 m2/g. It has an excellent specific capacitance of 204F/g at 1 A/g of current density with good cyclability up to 10,000 cycles.
Junction conditions for composite matter in higher dimensions
(IOP Publishing, 2021-10-07) Maharaj, Sunil D.; Brassel, Byron P.
We derive the junction conditions for a general higher dimensional spherically symmetric radiating star across a comoving surface with an electromagnetic field. The charged composite interior consists of barotropic matter, a null dust and a null string fluid. The higher dimensional generalised Vaidya geometry describes the exterior radiating atmosphere of the charged composite star. We show at the stellar surface that the pressure is determined by the interior heat flux, anisotropy, null string density, charge distribution and the exterior null string density. The charge distribution affects the stellar pressure in general; the higher dimensional charged Vaidya spacetime is special and does not exhibit this feature. The number of dimensions appears explicitly in the surface pressure showing that the dimensions affect the gravitational dynamics. All previous treatments, for matter which is neutral or charged, emerge as special cases in our treatment.
Stars and junction conditions in Einstein-Gauss-Bonnet gravity
(IOP Publishing, 2023-06-15) Brassel, Byron P.; Maharaj, Sunil D.; Goswami, Rituparno
The junction conditions for a higher dimensional spherically symmetric charged and anisotropic static star are derived in Einstein–Gauss–Bonnet (EGB) gravity with nonvanishing cosmological constant. It is shown that for a timelike boundary hypersurface of zero thickness, the generalised matching conditions across this surface in EGB gravity are satisfied. A sufficient condition is that the Israel-Darmois conditions are valid. Therefore it is possible to generate a complete stellar model in EGB gravity. The interior matches to the exterior higher dimensional charged Boulware–Deser spacetime with cosmological constant. The barotropic radial pressure has to vanish at the boundary of the star which is also the case in general relativity.