Sofia University

About: Sofia University is a education organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Large Hadron Collider & Laser. The organization has 8533 authors who have published 15730 publications receiving 306320 citations. The organization is also known as: University of Sofia & BFUS.

Microwave plasma based single step method for free standing graphene synthesis at atmospheric conditions

Abstract: Microwave atmospheric pressure plasmas driven by surface waves were used to synthesize graphene sheets from vaporized ethanol molecules carried through argon plasma. In the plasma, ethanol decomposes creating carbon atoms that form nanostructures in the outlet plasma stream, where external cooling/heating was applied. It was found that the outlet gas stream temperature plays an important role in the nucleation processes and the structural quality of the produced nanostructures. The synthesis of few layers (from one to five) graphene has been confirmed by high-resolution transmission electron microscopy. Raman spectral studies were conducted to determine the ratio of the 2D to G peaks (>2). Disorder D-peak to G-peak intensity ratio decreases when outlet gas stream temperature decreases.

Breakdown of i-love-q universality in rapidly rotating relativistic stars

Abstract: It was shown recently that normalized relations between the moment of inertia (I), the quadrupole moment (Q), and the tidal deformability (Love number) exist and for slowly rotating neutron stars they are almost independent of the equation of state (EOS). We extend the computation of the I-Q relation to models rotating up to the mass-shedding limit and show that the universality of the relations is lost. With increasing rotation rate, the normalized I-Q relation departs significantly from its slow-rotation limit, deviating up to 40% for neutron stars and up to 75% for strange stars. The deviation is also EOS dependent and for a broad set of hadronic and strange matter EOSs the spread due to rotation is comparable to the spread due to the EOS, if one considers sequences with fixed rotational frequency. Still, for a restricted sample of modern realistic EOSs one can parameterize the deviations from universality as a function of rotation only. The previously proposed I-Love-Q relations should thus be used with care, because they lose their universality in astrophysical situations involving compact objects rotating faster than a few hundred Hz.

Hydrodynamics of thin liquid films. On the rate of thinning of microscopic films with deformable interfaces

Abstract: The process of thinning of a film formed between a deformable bubble and a solid substratum is considered. The solution is obtained by matching the asymptotic coordinate expansions, valid both in the vicinity of and at a distance from the axis of symmetry. It is demonstrated that when the interfaces are at a short distance from each other, the film can be considered as being practically plane-parallel. An expression is deduced for the rate of thinning of such a film, coincident in form with the well-known law of Reynolds. With the surfaces further apart from each other, equations are obtained for the deformation of the bubble and for the rate of its approach to the solid substratum.

On BPS bounds in D = 4 N = 2 gauged supergravity

Abstract: We determine the BPS bounds in minimal gauged supergravity in four space- time dimensions. We concentrate on asymptotically anti-de Sitter (AdS) spacetimes, and find that there exist two disconnected BPS ground states of the theory, depending on the presence of magnetic charge. Each of these ground states comes with a different superal-gebra and a different BPS bound, which we derive. As a byproduct, we also demonstrate how the supersymmetry algebra has a built-in holographic renormalization method to define finite conserved charges.