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.

Measurement of the Polarization of W Bosons with Large Transverse Momenta in W+jets Events at the LHC

Abstract: A first measurement of the polarization of W bosons with large transverse momenta in pp collisions is presented. The measurement is based on 36 pb(-1) of data recorded at root s = 7 TeV by the CMS detector at the LHC. The left-handed, right-handed, and longitudinal polarization fractions (f(L), f(R), and f(0), respectively) of W bosons with transverse momenta larger than 50 GeV are determined by using decays to both electrons and muons. The muon final state yields the most precise measurement: (f(L) - f(R))(-) = 0.240 +/- 0.036(syst) +/- 0.031(syst) and f(0)(-) = 0.183 +/- 0.087(stat) +/- 0.123(syst) for negatively charged W bosons and (f(L) - f(R))(+) = 0.310 +/- 0.036(syst) +/- 0.017(syst) and f(0)(+) = 0.171 +/- 0.085(syst) +/- 0.099(syst) for positively charged W bosons. This establishes, for the first time, that W bosons produced in pp collisions with large transverse momenta are predominantly left-handed, as expected in the standard model.

Measurement of the pseudorapidity and centrality dependence of the transverse energy density in Pb-Pb collisions at √s NN=2.76TeV

Abstract: The transverse energy ET in PbPb collisions at 2.76 TeV nucleon-nucleon center-of-mass energy sqrt(s[NN]) has been measured over a broad range of pseudorapidity eta and collision centrality using the CMS detector at the LHC. The transverse energy density per unit pseudorapidity d(ET)/d(eta) increases faster with collision energy than the charged particle multiplicity. This implies that the mean energy per particle is increasing with collision energy. At all pseudorapidities the transverse energy per participating nucleon increases with the centrality of the collision. The ratio of transverse energy per unit pseudorapidity in peripheral to central collisions varies significantly as the pseudorapidity increases from eta = 0 to abs(eta) = 5.0. For the most central collisions the energy density per unit volume is estimated to be about 15 GeV/fm^3 at a time of 1 fm/c after the collision. This is about 100 times larger than normal nuclear matter density and a factor of 2.8 times higher than the energy density reported at sqrt(s[NN]) = 200 GeV at RHIC.

Comparison of the van der Waals and frumkin adsorption isotherms for sodium dodecyl sulfate at various salt concentrations

Abstract: The adsorption of ionic surfactants at the surface of an aqueous solution leads to a reduction in the surface tension, to an increase of the surface electric charge density, and to the development of an electric double layer.1-10 The addition of nonamphiphilic electrolytes to the solutions of ionic surfactants is accompanied by adsorption (binding) of counterions at the oppositely charged headgroups of the adsorbed surfactant molecules. In other words, the counterions behave as a second surfaceactive component.6-8 Thus the counterion adsorption causes a significant reduction in the magnitude of the net surface electric charge, which could be decreased by more than 50%.8,11-13 The latter effect leads to increasing of the surface density of the adsorbed ionic surfactant but simultaneously suppresses the electric double layer. A recent review was published by Fainerman and LucassenReynders.14 In refs 8 and 15, we demonstrated that the processing of experimental surface-tension isotherms by means of an adequate theoretical model can be rather informative. It can be used for a detailed computer modeling of equilibrium surfactant adsorption layers, of dynamic surface-tension isotherms, and of the properties of thin liquid films formed from the respective solutions. With this end in view, one has to first determine the adsorption constants as adjustable parameters from the best fit of the experimental data. Knowing these parameters and having the respective computer program, one can obtain information about many properties of the system. Indeed, for each combination of surfactant and nonamphiphilic electrolytes one can calculate the surface (interfacial) tension, the adsorption of each specific component (including the bound counterions), the surface electric potential, the surface dilatational (Gibbs) elasticity, and so forth. The two experimental surface-tension isotherms previously fitted by us8 were taken from papers by Tajima et al.16-18 In fact, surface-tension isotherms of sodium dodecyl sulfate (SDS) for 11 different fixed NaCl concentrations can be found in refs 16-18. Our aims in this study are (i) to fit simultaneously all 11 isotherms (SDS at fixed NaCl concentration and temperature of 25 °C) with the same four-parameter model, as in ref 8, and (ii) to compare the fits provided by the Frumkin and van der Waals models.

Carbamylated low-density lipoprotein induces oxidative stress and accelerated senescence in human endothelial progenitor cells

Abstract: Carbamylated low-density lipoprotein (cLDL) plays a role in atherosclerosis. In this study we evaluate the effect of uremia on LDL carbamylation and the effect of cLDL and oxidized LDL (oxLDL; 200 μg/ml) on number, function, and genomic stability of endothelial progenitor cells (EPCs) obtained from healthy volunteers. cLDL was generated after incubation of native LDL (nLDL) with uremic serum from patients with chronic kidney disease (CKD) stages 2-4. Oxidative stress was measured by flow cytometry and fluorescent microscopy, mitochondrial depolarization by flow cytometry, senescence by β-galactosidase activity and telomere length, and DNA damage by phosphorylated histone H2AX (γH2AX). The percentage of cLDL by uremic serum was related to the severity of CKD. Compared with nLDL, cLDL induced an increase in oxidative stress (62±5 vs. 8±3%, P<0.001) and cells with mitochondrial depolarization (73±7 vs. 9±5%, P<0.001), and a decrease in EPC proliferation and angiogenesis. cLDL also induced accelerated senescence (73±16 vs. 12±9%, P<0.001), which was associated with a decrease in the expression of γH2AX (62±9 vs. 5±3%, P<0.001). The degree of injury induced by cLDL was comparable to that observed with oxLDL. This study supports the hypothesis that cLDL triggers genomic damage in EPCs, resulting in premature senescence. We can, therefore, hypothesize that EPCs injury by cLDL contributes to an increase in atherosclerotic disease in CKD.

Nanosize gold catalysts promoted by vanadium oxide supported on titania and zirconia for complete benzene oxidation

Abstract: The complete benzene oxidation reaction was used to test the reactivity of the Au-V 2 O 5 /TiO 2 and Au-V 2 O 5 /ZrO 2 catalytic systems. A strong synergistic effect between gold and vanadia was established when molecular oxygen was used as an oxidizing agent. This effect was more pronounced for titania than for the zirconia support. In the presence of gold, predominantly polyvanadate structures are formed on the surface which are more active in the reaction of complete benzene oxidation in comparison with monovanadate species and bulk V 2 O 5 . The deposition of gold leads to a relative lengthening of the VO bond and to a higher electron delocalization. The B and C parameters calculated from ESR spectra showed no differences for the fresh and spent gold-containing samples, i.e. the catalytic systems seemed to be “stabilized” under the working conditions. The effect of gold on the vanadium oxide reducibility, which could be related to the strength of the VO-support bond, results in a considerable lowering of the temperature of the V 5+ → V 3+ transition. With ozone as the oxidizing agent, an additional lowering of the reaction temperature was achieved and very close values of the catalytic activity on all investigated samples were registered. Upon oxidation by molecular oxygen the oxidant activation takes place on the nanosize gold particles while the vanadium oxide surface species are responsible for the activation of benzene. This is in agreement with synergistic effect between the finely dispersed gold and the surface vanadium structures.