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.

Measurement of the differential cross section for isolated prompt photon production in pp collisions at 7 TeV

Abstract: A measurement of the differential cross section for the inclusive production of isolated prompt photons in proton-proton collisions at a centre-of-mass energy of 7 TeV is presented. The data sample corresponds to an integrated luminosity of 36 inverse picobarns recorded by the CMS detector at the LHC. The measurement covers the pseudorapidity range |eta|<2.5 and the transverse energy range 25 < ET < 400 GeV, corresponding to the kinematic region 0.007 < xT < 0.114. Photon candidates are identified with two complementary methods, one based on photon conversions in the silicon tracker and the other on isolated energy deposits in the electromagnetic calorimeter. The measured cross section is presented as a function of ET in four pseudorapidity regions. The next-to-leading-order perturbative QCD calculations are consistent with the measured cross section.

Rapidly rotating neutron stars in R -squared gravity

Abstract: $f(R)$ theories of gravity are one of the most popular alternative explanations for dark energy, and therefore studying the possible astrophysical implications of these theories is an important task. In the present paper we make a substantial advance in this direction by considering rapidly rotating neutron stars in ${R}^{2}$ gravity. The results are obtained numerically, and the method we use is nonperturbative and self-consistent. The neutron star properties, such as mass, radius, and moment of inertia, are studied in detail. The results show that rotation magnifies the deviations from general relativity, and the maximum mass and moment of inertia can reach very high values. This observation is similar to the previous studies of rapidly rotating neutron stars in other alternative theories of gravity, such as scalar-tensor theories, and it can potentially lead to strong astrophysical manifestations.

Some variations of the circle of Willis, important for cerebral protection in aortic surgery — a study in Eastern Europeans

Abstract: Background: During unilateral selective cerebral perfusion (SCP), via canulation of the brachiocephalic trunk, the brain receives blood only through the right common carotid artery and the right vertebral artery. For perfusion of the contralateral (left) hemisphere it is counted on the competence of the circle of Willis (CoW). It is well known that variations of CoWare present in more than 50% of the people. Furthermore, these variations usually affect more than one vessel of the circle. The aim of the present work was to study the variations of CoW, which could have an impact on cerebral blood supply during unilateral SCP. Methods and materials: We study 112 CoWs obtained from cadavers via routine dissection in the Department of Forensic Medicine of Medical University, Sofia. The external diameter of both vertebral arteries and all arteries that form CoW was measured with a caliper-gauge. Results: We identify the variations of CoW such as significant hypoplasy and/or lack of a branch of the circle. Bearing in mind the characteristics of the blood flow during unilateral SCP some of these variations were classified as significant during unilateral SCP. They were subdivided into groups according to most probable stroke site after unilateral SCP. Conclusions: Because of the high percent of the variations, hemodynamically significant during unilateral SCP, a suggestion for routine preoperative CT-angio of CoW could be made. Furthermore, an intraoperative follow-up with NIRO, transcranial Doppler, EEG, and so forth could also be recommended. # 2007 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.