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 & Standard Model. 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 resonant and nonresonant Higgs boson pair production in the b(b)over-barl nu l nu final state in proton-proton collisions at root s=13 TeV

Abstract: Searches for resonant and nonresonant pair-produced Higgs bosons (HH) decaying respectively into l nu l nu, through either W or Z bosons, and b (b) over bar are presented The analyses are based on a sample of proton-proton collisions at root s = 13 TeV, collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 359 fb(-1) Data and predictions from the standard model are in agreement within uncertainties For the standard model HH hypothesis, the data exclude at 95% confidence level a product of the production cross section and branching fraction larger than 72 fb, corresponding to 79 times the standard model prediction Constraints are placed on different scenarios considering anomalous couplings, which could affect the rate and kinematics of HH production Upper limits at 95% confidence level are set on the production cross section of narrow-width spin-0 and spin-2 particles decaying to Higgs boson pairs, the latter produced with minimal gravity-like coupling

Factors associated with self-rated health status in university students: a cross-sectional study in three European countries

Abstract: Self-rated health status (SRHS) is a reliable and valid measure for assessing the subjective and objective health of individuals. Previous studies have either focused predominantly on the elderly or investigated only a narrow range of factors potentially associated with SRHS. In examining student populations, these past studies were limited to single countries. The objectives of this study were to assess which candidate variables were independently associated with SRHS in university students, to compare these variables by country and by gender, and to investigate which of the variables was most important as a rating frame for SRHS. The data is from the Cross-National Student Health Survey, conducted in 2005 in universities in Germany, Bulgaria, and Poland (n = 2103; mean age = 20.7 years). SRHS was assessed with a single question using a five-point scale ranging from "excellent" to "poor". The study also measured a wide range of variables including: physical and psychological health, studying, social contacts/social support, and socio-demographic status. Psychosomatic complaints (considered an aspect of physical health and, adjusted for psychological health) were the most important indicators in forming a rating frame for students' SRHS. There were few differences in the effects of variables associated with SRHS by gender (well-being: a measure of psychological health) and the variables associated with SRHS by country (well-being and self-efficacy). The remaining variables showed homogenous effects for both genders and for all three countries. The results suggest that SRHS can be reasonably used to compare students' health across countries. SRHS is affected by different physical, psychological and psychosomatic aspects of health; however, its strongest association is with psychosomatic complaints.

Search for new physics with same-sign isolated dilepton events with jets and missing transverse energy

Abstract: A search for new physics is performed in events with two same-sign isolated leptons, hadronic jets, and missing transverse energy in the final state. The analysis is based on a data sample corresponding to an integrated luminosity of 4.98 inverse femtobarns produced in pp collisions at a center-of-mass energy of 7 TeV collected by the CMS experiment at the LHC. This constitutes a factor of 140 increase in integrated luminosity over previously published results. The observed yields agree with the standard model predictions and thus no evidence for new physics is found. The observations are used to set upper limits on possible new physics contributions and to constrain supersymmetric models. To facilitate the interpretation of the data in a broader range of new physics scenarios, information on the event selection, detector response, and efficiencies is provided.

A study of the antimicrobial and tribological properties of TiN/Ag nanocomposite coatings

Abstract: TiN/Ag coatings with varying silver contents have been deposited by pulsed magnetron sputtering. The films were characterised in terms of structure and composition using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The tribological properties of the coatings were assessed by thrust washer wear testing, which showed a marginal reduction in friction coefficient with increasing silver content against a steel counterface. Zones of inhibition were used to determine the extent of silver ion release from the nanocomposite materials, and a NBT (nitro-blue tetrazolium) redox dye was used in an assay to determine the antimicrobial effectiveness of the surfaces following incubation. The microorganisms tested were Pseudomonas aeruginosa and Staphylococcus aureus. Whilst no zones of inhibition were observed on any of the surfaces, for the NBT assays, after incubation, the silver containing coatings revealed a significant reduction in the number of viable cells of both microorganisms, compared to a ‘pure’ TiN surface.

Optical plastic refractive measurements in the visible and the near-infrared regions

Abstract: Some new refractometric results are obtained in the visible and the near-infrared spectral regions. The main optical plastics are analyzed: poly(methyl methacrylate), polystyrene, polycarbonate, and styrene acrylonitrile. New materials, such as methyl methacrylate styrene copolmer, CTE-Richardson, Zeonex, Optorez, and Bayer are examined. The refractive indices are measured for wavelengths from 435.8 to 1052 nm with a new device. Abbe constants and dispersion coefficients are calculated. The measured and computed data is intended for designers and technologists.