Current Issue : October-December Volume : 2023 Issue Number : 4 Articles : 5 Articles
Symbiotic stars are interacting binary systems composed of an evolved star (generally a late-type red giant) and a degenerate or dwarf companion in orbit close enough for mass transfer to occur. Understanding the status of the late-type star is important for developing binary models for the symbiotic systems as it affects the transfer of matter needed to activate the hot component. Infrared observations have been very useful in probing the nature of late-type stars in symbiotic systems. This work presents a set of symbiotic stars observed with SOAR/OSIRIS (R∼3000) in the H-band. We aimed to search for possible molecular circumstellar emission, to characterize the cool companion in these systems, and to confront the new findings with those obtained from the previous K-band classifications. We detected molecular emission from just one object, BI Cru, which displays the second-overtone CO-bands. To fit the observed photospheric CO absorption bands, we used the MARCS atmosphere models. We present our results as a mini atlas of symbiotic stars in the near-infrared region to facilitate the comparison among different observed symbiotic systems....
The water–ethylene glycol (50 : 50) nanofluid has applications in the manufacture of polyester as a raw agent, air conditioning systems, antifreeze formulation, dehydrating agents in the gas industry, a precursor in the plastic industry, and convective heat transfer. These developments in nanotechnology and nanoscience have caught the interest of several researchers. Because it keeps machines and engines cool by reducing friction between their different parts, grease is a vital part of many machinery and engines. Also, due to the extensive use of fractional derivatives, this work seeks to evaluate the combined impacts of free convection flow and heat transfer, magnetic field, and Brinkman-type water–ethylene glycol (50 : 50) dusty nanofluid among microchannel. The flow that the buoyant force provides helps to carry heat naturally via convection. While the left plate moves at a consistent velocity and the right plate stays stationary, the fluid is also evenly dispersed with all dust particles that have a spherical form. Partial differential equations (PDE) are used to present the mathematical modeling. The resultant PDEs are generalized by utilizing the Caputo–Fabrizio fractional derivative. The problem’s closed-form solution is produced by combining a Laplace transformation with a finite sine Fourier transformation. It has also been studied that temperature, Brinkman nanofluid, and dust particle velocity relate to a variety of other factors, such as the magnetic parameter, Grashof number, dusty fluid parameter, and volume friction parameter. The graphical outcomes for the dusty fluid, Brinkman nanofluid, and temperature profiles are plotted using Mathcad- 15. The Brinkman nanofluid and dusty fluid behave similarly for a variety of embedded factors. It is found that compared to the traditional one, the fractional dusty nanofluid model displays more realistic characteristics. The addition of nanoparticles in water–ethylene glycol (50 : 50) dusty nanofluid enhances the rate of heat transfer up to 41.04478% by increasing their volume fractional....
Growing traffic loads, soaring summer temperatures, and moisture damage will render conventional asphalt binder insufficient to maintain the performance standards of asphalt concrete pavement. Thus, it is necessary to modify the virgin asphalt using various polymers or nanomaterials. The primary goal of this research was to examine the rheological effects of combining multiple-walled carbon nanotubes (MWCNTs) and styrene butadiene styrene (SBS) in an asphalt binder. In this study, MWCNTs and SBS were mixed with virgin asphalt at concentrations of 1%, 3%, and 5% by weight. The performance grade (PG) and asphalt binder qualities were determined through Superpave system testing. The addition of 1% MWCNTs had no effect on the (PG) of virgin asphalt, whereas the addition of 3% and 5% MWCNTs resulted in increases of 2° and 4°, respectively. When 1% SBS is added to asphalt, the PG rises by an average of 1°; when 3% and 5% SBS are used, the PG rises by an average of 2° and 3°, respectively. The results also showed that the rutting parameter (G∗/sin) increased by 10%, 73%, and 208% when asphalt was changed with 1%, 3%, and 5% of SBS, and by 18% and 130% when MWCNTs were applied....
Recently, it was argued that the energy density of the supranuclear dense matter inside the cores of massive neutron stars must have reached the uni max , beyond which supranuclear dense matter becomes incompressible entropy- free gluon-quark superfluid. As this matter is also confined and embedded in flat spacetime, it is Lorentz invariant and could be treated as vacuum. The lower bound of matter in the universe may be derived using the following observational constraints: 1) The average energy density of the observable universe is 10 9 OU erg/cc, 2) The observable universe is remarkably flat, and 3) the Hubble constant is a slowly decreasing function of cosmic time. Based thereon, I argue that the energy density in nature should be bounded from below by the average density of our vast and flat parent universe, , which is, in turn, comparable to the vacuum energy density vac , and amounts to 10 9 OU erg/cc. When the total energy density is measured relative to vac , then both GR and Newtonian field equations may consistently model the gravitational potential of the parent universe without invoking cosmological constants. Relying on the recently proposed unicentric model of the observable universe, UNIMOUN, the big bang must have warped the initially flat spacetime into a curved one, though the expansion of the fireball doomed the excited energy state to diffuse out and return back to the ground energy state that governs the flat spacetime of our vast parent universe....
General relativity is one of the pillars of modern physics. For decades, the theory has been mainly tested in the weak-field regime with experiments in the solar system and radio observations of binary pulsars. Until 2015, the strong-field regime was almost completely unexplored. Thanks to new observational facilities, the situation has dramatically changed in the last few years. Today, we have gravitational wave data of the coalesce of stellar-mass compact objects from the LIGO-Virgo-KAGRA collaboration, images at mm wavelengths of the supermassive black holes in M87∗ and Sgr A∗ from the Event Horizon Telescope collaboration, and X-ray data of accreting compact objects from a number of X-ray missions. Gravitational wave tests and black hole imaging tests are certainly more popular and are discussed in other articles of this Special Issue. The aim of the present manuscript is to provide a pedagogical review on X-ray tests of general relativity with black holes and to compare these kinds of tests with those possible with gravitational wave data and black hole imaging....
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