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.

Search for vectorlike charge 2/3 T quarks in proton-proton collisions at √(s) = 8 TeV

Abstract: A search for fermionic top quark partners T of charge 2/3 is presented. The search is carried out in proton-proton collisions corresponding to an integrated luminosity of 19.7 inverse femtobarns collected at a center-of-mass energy of sqrt(s) = 8 TeV with the CMS detector at the LHC. The T quarks are assumed to be produced strongly in pairs and can decay into tH, tZ, and bW. The search is performed in five exclusive channels: a single-lepton channel, a multilepton channel, two all-hadronic channels optimized either for the bW or the tH decay, and one channel in which the Higgs boson decays into two photons. The results are found to be compatible with the standard model expectations in all the investigated final states. A statistical combination of these results is performed and lower limits on the T quark mass are set. Depending on the branching fractions, lower mass limits between 720 and 920 GeV at 95% confidence level are found. These are among the strongest limits on vector-like T quarks obtained to date.

Plasmon-induced enhancement of quantum interference near metallic nanostructures.

Abstract: We show that the quantum interference between two spontaneous emission channels can be greatly enhanced when a three-level V-type atom is placed near plasmonic nanostructures such as metallic slabs, nanospheres, or periodic arrays of metal-coated spheres. The spontaneous emission rate is calculated by a rigorous first-principles electromagnetic Green's tensor technique. The enhancement of quantum interference is attributed to the strong dependence of the spontaneous emission rate on the orientation of an atomic dipole relative to the surface of the nanostructure at the excitation frequencies of surface plasmons.

Multidimensional performance optimization of conducting polymer-based supercapacitor electrodes

Abstract: Supercapacitors based on conducting polymers promise to bridge the gap between the high power densities of carbon-based double-layer capacitors and the high energy densities of batteries. While much work has focused on improving the specific capacitance of these materials, emerging applications also demand competitive performance with regards to a variety of other criteria, including long-term cycling stability, mechanical robustness, and scalability of fabrication. There is no consolidated summary in the literature, however, of the specific strategies used to target these individual metrics as well as the tradeoffs that exist between them. Herein, we review the most recent progress in engineering high performance conducting polymer-based supercapacitor electrodes, emphasizing the successful techniques for polymer synthesis, nanostructuring, and compositing with carbon or metal oxides which have been used to optimize each of the most important supercapacitor performance metrics.

Dependence of the equilibrium thickness and double layer potential of foam films on the surfactant concentration

Abstract: The effect of the surfactant concentrationc s on the equilibrium thicknessh r , of foam films and the potentialϕ 0 of the diffuse electric layer is studied in a wide concentration range (including cmc). The cell for investigation of thin liquid films is improved and a good reproducibility of the measuredh r is obtained. The possibilities for determination of the capillary pressureP σ in.the cell for investigation of microscopic thin liquid films are discussed. The values ofP σ can be measured with sufficient accuracy by the capillary-rise method, using a tube, identical with the tube of the cell for thin liquid films. The dependenceh r (c s ) is studied for nonionic surfactants (decylmethyl sulphoxide, nonyl-phenol 20-glycol ether and dodecyl 11-ethylene oxide) and the ionic sodium dodecyl sulphate. After reaching a steady value (a plateau in theh r (c s ) curve) at high concentrations (about cmc) a decrease in the equilibrium thickness of nonionic surfactants is found. The possible reasons for this decrease are discussed. It is shown that this effect probably is due to the electrostatic disjoining pressure. The values of theϕ o-potential at the plateau of theh r (c s ) curves are determined by the DLVO-theory using theh r , values. The so determinedϕ 0-values are more correct than the obtained earlier by this method because of the more precise measurement of the equilibrium thickness and the direct experimental determining of the capillary pressure. A qualitative interpreting of theϕ 0(c s ) dependence is made on the basis of the surfactant adsorption at the solution/air interface and it is found that for nonionic surfactants the surface charge saturation is very near to the saturation in the adsorption layer, and for the ionic surfactants the adsorption layer saturation is at higher concentration.

Radial perturbations of the scalarized Einstein-Gauss-Bonnet black holes

Abstract: We study the axial perturbations of spontaneously scalarized black holes in Einstein-Gauss-Bonnet theories. We consider the nodeless solutions of the fundamental branch of the model studied by Doneva and Yazadjiev [Phys. Rev. Lett. 120, 131103 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.131103], which possesses a region of radially stable configurations, as shown by Blazquez-Salcedo et al. [Phys. Rev. D 98, 084011 (2018)PRVDAQ2470-001010.1103/PhysRevD.98.084011]. Here we show that almost all of the radially stable black holes are also stable under axial perturbations. When the axial potential is no longer strictly positive, we make use of the S-deformation method to show stability. As for the radial perturbations, hyperbolicity is lost below a certain critical horizon size for a fixed coupling constant. In the stable region, we determine the spectrum of the quasinormal modes by time evolution and by solving the associated time-independent eigenvalue problem.