Bulgarian Academy of Sciences

About: Bulgarian Academy of Sciences is a government organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Coupling constant & Catalysis. The organization has 17989 authors who have published 36276 publications receiving 642820 citations. The organization is also known as: Bulgarian Academy of Sciences，簡稱：BAS & Balgarska Akademiya na Naukite.

The P2-Na(2/3)Co(2/3)Mn(1/3)O2 phase: structure, physical properties and electrochemical behavior as positive electrode in sodium battery.

Abstract: Manganese substituted sodium cobaltate, Na(2/3)Co(2/3)Mn(1/3)O(2), with a layered hexagonal structure (P2-type) was obtained by a co-precipitation method followed by a heat treatment at 950 °C. Powder X-ray diffraction analysis revealed that the phase is pure in the absence of long-range ordering of Co and Mn ions in the slab or Na(+) and vacancy in the interslab space. The oxidation states of the transition metal ions were studied by magnetic susceptibility measurements, electron paramagnetic resonance (ESR) and (23)Na magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The charge compensation is achieved by the stabilization of low-spin Co(3+) and Mn(4+) ions. The capability of Na(2/3)Co(2/3)Mn(1/3)O(2) to intercalate and deintercalate Na(+) reversibly was tested in electrochemical sodium cells. It appears that the P2 structure is maintained during cycling, the cell parameter evolution versus the sodium amount is given. From the features of the cycling curve the formation of an ordered phase for the Na(0.5)Co(2/3)Mn(1/3)O(2) composition is expected.

Review of naphthenic acid corrosion in oilrefining

Abstract: Naphthenic acid corrosion is a major concern for the oil refinery business. While much is now known about the phenomenon, it is still not completely understood because of the complex influences on corrosion of the type of acid and other constituents in the crude oil and the effects of both temperature and fluid flow. A review of this form of corrosion has been undertaken with respect to the role of crude oil composition, temperature, fluid velocity, physical state (vapour or liquid), pressure, and materials of construction. Simple measures of corrosivity based on the total acid or neutralisation number are insufficient. The sulphur content of the crude is important but the extent to which the various sulphur containing compounds act as inhibitors or corrodents is not understood. There is little knowledge also of the nature of films formed on the steel surfaces under operating conditions and the role of natural inhibitors that may be present in crudes requires more attention.

Dynamical derivation of vacuum operator-product expansion in Euclidean conformal quantum field theory

Abstract: An expansion of the type ${〈\ensuremath{\phi}({x}_{1})\ensuremath{\cdots}\ensuremath{\phi}({x}_{n})〉}_{0}={〈\ensuremath{\phi}({x}_{1})\ensuremath{\phi}({x}_{2})〉}_{0}{〈\ensuremath{\phi}({x}_{3})\ensuremath{\cdots}\ensuremath{\phi}({x}_{n})〉}_{0}+\ensuremath{\Sigma}\stackrel{}{{\ensuremath{\chi}}_{l}}{C}^{2}({\ensuremath{\chi}}_{l})\ensuremath{\int}(\mathrm{dp}){Q}^{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{l}}({x}_{1},{x}_{2};\ensuremath{-}p){w}_{{\ensuremath{\chi}}_{l}} (p){Q}^{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{l}}(p;{x}_{1},\dots{},{x}_{4})$ is derived, where ${\ensuremath{\chi}}_{l}=[l,{c}_{l}]$ are labels for infinite-dimensional symmetric tensor representations of the Euclidean conformal group ${\mathrm{O}}^{\ensuremath{\uparrow}}(2h+1,1)$,${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{l}=[l,\ensuremath{-}{c}_{l}]$, the constants $C ({\ensuremath{\chi}}_{l})$ are real, and ${Q}^{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}$ and ${w}_{\ensuremath{\chi}}$ have the properties of vacuum expectation values of field products. The starting point is an infinite set of coupled nonlinear integral equations for Euclidean Green's functions in $2h$ space-time dimensions of the type written some 15 years ago by Fradkin and Symanzik. The Green's functions of the corresponding Gell-Mann-Low limit theory are expanded in conformal partial waves. The dynamical equations imply the existence of poles and factorization of residues in the partial waves as functions of the representation parameters. In proving the validity of the expansion we use some differential relations between partially equivalent exceptional representations of ${\mathrm{O}}^{\ensuremath{\uparrow}}(2h+1,1)$, established in an earlier paper. This work completes the group-theoretical derivation of the vacuum operator-product expansion undertaken by Mack in 1973.

An excess of massive stars in the local 30 Doradus starburst.

Abstract: The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large star-formation events in the distant universe. We determined the recent formation history and the initial mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic observations of 247 stars more massive than 15 solar masses (Embedded Image). The main episode of massive star formation began about 8 million years (My) ago, and the star-formation rate seems to have declined in the last 1 My. The IMF is densely sampled up to 200 Embedded Image and contains 32 ± 12% more stars above 30 Embedded Image than predicted by a standard Salpeter IMF. In the mass range of 15 to 200 Embedded Image, the IMF power-law exponent is Embedded Image, shallower than the Salpeter value of 2.35.

Measurements of inclusive W and Z cross sections in pp collisions at \sqrt {s} = 7 TeV

Abstract: Measurements of inclusive W and Z boson production cross sections in pp collisions at sqrt(s)=7 TeV are presented, based on 2.9 inverse picobarns of data recorded by the CMS detector at the LHC. The measurements, performed in the electron and muon decay channels, are combined to give sigma(pp to WX) times B(W to muon or electron + neutrino) = 9.95 \pm 0.07(stat.) \pm 0.28(syst.) \pm 1.09(lumi.) nb and sigma(pp to ZX) times B(Z to oppositely charged muon or electron pairs) = 0.931 \pm 0.026(stat.) \pm 0.023(syst.) \pm 0.102(lumi.) nb. Theoretical predictions, calculated at the next-to-next-to-leading order in QCD using recent parton distribution functions, are in agreement with the measured cross sections. Ratios of cross sections, which incur an experimental systematic uncertainty of less than 4%, are also reported.