19 research outputs found

    Numerical Simulation of Airflow Structure and Dust Emissions behind Porous Fences Used to Shelter Open Storage Piles

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    Porous fences can reduce dust emissions from storage piles in open storage yards, but their sheltering effect depends on the airflow structure around the pile, and the shear stress distribution on each surface. In this study, static flow fields were numerically simulated using k-epsilon standard The turbulence model; the shear stress characteristics and distribution on the windward side, flat-top surface, and leeward side of a typical prismatic material stack were analyzed. The distribution of the aerodynamic structure of each surface of the storage pile was determined according to the flow field data for fences of the porosities epsilon = 0, 0.2, 0.3, 0.4, 0.5, and 0.6. The results indicated that at low porosities (epsilon = 0, 0.2) a recirculating flow appeared in the region between the fence and the pile. The shear force acted downward the windward slope, and the maximum dust emission occurred at two-thirds the height of the windward side, rather than at the top, as in unfenced conditions. Using the porous fence simulated in this study, shear stress on the windward side and the flat-top surface first decreased, then increased with increasing porosity; the lowest porosity values were 0.2 and 0.3, and the shear stress on the prismatic leeside changed little with increasing porosity. The numerical predictions indicated that a fence with porosity between 0.2 and 0.3 is optimal.</p

    Effects of volatilization on the hydrogen isotope composition of selected n-alkanes

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    The hydrogen isotope composition of n-C15 to n-C32 n-alkanes was measured by GC-IRMS to investigate the behavior of H isotopes during evaporation. The H isotope fractionation of n-C15 to n-C19 ranged from -8.5 to -22.5&permil;, demonstrating the preferential vaporization of the isotopically heavier organic compounds. The H isotope fractionation rates of n-C16 to n-C18 showed no obvious fluctuations with time (average rates were 1.1, 0.5 and 0.3&permil; per day, respectively); this indicated that fractionation followed the Rayleigh model. Although less conclusive, the fractionation of H isotopes in n-C19 also apparently followed the Rayleigh trend. Information on fractionation rates may be useful for identifying the dominant attenuation and degradation processes for organic substances in the environment. The results also highlight potential applications of isotope fractionation factors, which were determined by regression analysis, for investigations into the behavior of organic substances in the environment.</p

    Emissions of polycyclic aromatic hydrocarbons from coking industries in China

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    This study set out to assess the characteristics of polycyclic aromatic hydrocarbon (PAH) emission from coking industries, with field samplings conducted at four typical coke plants. For each selected plant, stack flue gas samples were collected during processes that included charging coal into the ovens (CC), pushing coke (PC) and the combustion of coke-oven gas (CG). Sixteen individual PAHs on the US EPA priority list were analyzed by gas chromatography/mass spectrometry (GC/MS). Results showed that the total PAH concentrations in the flue gas ranged from 45.776 to 414.874 mu g/m(3), with the highest emission level for CC (359.545 mu g/m(3)). The concentration of PAH emitted from the CC process in CP1 (stamp charging) was lower than that from CP3 and CP4 (top charging). Low-molecular-weight PAHs (i.e., two- to three-ring PAHs) were predominant contributors to the total PAH contents, and Nap, AcPy, Flu, PhA, and AnT were found to be the most abundant ones. Total BaPeq concentrations for CC (2.248 mu g/m(3)) were higher than those for PC (1.838 mu g/m(3)) and CG (1.082 mu g/m(3)), and DbA was an important contributor to carcinogenic risk as BaP in emissions from coking processes. Particulate PAH accounted for more than 20% of the total BaPeq concentrations, which were significantly higher than the corresponding contributions to the total PAH mass concentration (5%). Both particulate and gaseous PAH should be taken into consideration when the potential toxicity risk of PAH pollution during coking processes is assessed. The mean total-PAH emission factors were 346.132 and 93.173 mu g/kg for CC and PC, respectively.</p

    Multi-Leptons with High Transverse Momentum at HERA

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    18 pages, 3 figures, revised version with small textual changesEvents with at least two high transverse momentum leptons (electrons or muons) are studied using the H1 and ZEUS detectors at HERA with an integrated luminosity of 0.94 fb^{-1}. The observed numbers of events are in general agreement with the Standard Model predictions. Seven di- and tri-lepton events are observed in e^+p collision data with a scalar sum of the lepton transverse momenta above 100 GeV while 1.94+-0.17 events are expected. Such events are not observed in e^-p collisions for which 1.19+-0.12 are predicted. Total visible and differential di-electron and di-muon photoproduction cross sections are extracted in a restricted phase space dominated by photon-photon collisions

    Search for excited quarks in the gamma plus jet final state in proton-proton collisions at root s=8 TeV

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    A search for excited quarks decaying into the gamma + jet final state is presented. The analysis is based on data corresponding to an integrated luminosity of 19.7 fb(-1) collected by the CMS experiment in proton-proton collisions at root s = 8 TeV at the LHC. Events with photons and jets with high transverse momenta are selected and the gamma + jet invariant mass distribution is studied to search for a resonance peak. The 95% confidence level upper limits on the product of cross section and branching fraction are evaluated as a function of the excited quark mass. Limits on excited quarks are presented as a function of their mass and coupling strength; masses below 3.5 TeV are excluded at 95% confidence level for unit couplings to their standard model partners

    Description and performance of track and primary-vertex reconstruction with the CMS tracker

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    A description is provided of the software algorithms developed for the CMS tracker both for reconstructing charged-particle trajectories in proton-proton interactions and for using the resulting tracks to estimate the positions of the LHC luminous region and individual primary-interaction vertices. Despite the very hostile environment at the LHC, the performance obtained with these algorithms is found to be excellent. For t (t) over bar events under typical 2011 pileup conditions, the average track-reconstruction efficiency for promptly-produced charged particles with transverse momenta of p(T) > 0.9GeV is 94% for pseudorapidities of vertical bar eta vertical bar < 0.9 and 85% for 0.9 < vertical bar eta vertical bar < 2.5. The inefficiency is caused mainly by hadrons that undergo nuclear interactions in the tracker material. For isolated muons, the corresponding efficiencies are essentially 100%. For isolated muons of p(T) = 100GeV emitted at vertical bar eta vertical bar < 1.4, the resolutions are approximately 2.8% in p(T), and respectively, 10 m m and 30 mu m in the transverse and longitudinal impact parameters. The position resolution achieved for reconstructed primary vertices that correspond to interesting pp collisions is 10-12 mu m in each of the three spatial dimensions. The tracking and vertexing software is fast and flexible, and easily adaptable to other functions, such as fast tracking for the trigger, or dedicated tracking for electrons that takes into account bremsstrahlung

    Measurement of the ratio B(t -> Wb)/B(t -> Wq) in pp collisions at root s=8 TeV

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    The ratio of the top-quark branching fractions R = B(t --> Wb)/B(t --> Wq), where the denominator includes the sum over all down-type quarks (q = b, s, d), is measured in the t (t) over bar dilepton final state with proton-proton collision data at root s = 8 TeV from an integrated luminosity of 19.7 fb(-1), collected with the CMS detector. In order to quantify the purity of the signal sample, the cross section is measured by fitting the observed jet multiplicity, thereby constraining the signal and background contributions. By counting the number of b jets per event, an unconstrained value of R = 1.014 +/- 0.003 (stat.) +/- 0.032 (syst.) is measured, in a good agreement with current precision measurements in electroweak and flavour sectors. A lower limit R > 0.955 at the 95% confidence level is obtained after requiring R 0.975 is set at 95% confidence level. The result is combined with a previous CMS measurement of the t-channel single-top-quark cross section to determine the top-quark total decay width, Gamma(t) = 1.36 +/- 0.02 (stat.)(-0.11)(+0.14) (syst.) GeV

    Koulutusluokitus : Koulutuskoodimuutokset vuonna 1989, Liite 3

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    A measurement of inclusive ZZ production cross section and constraints on anomalous triple gauge couplings in proton-proton collisions at s\sqrt{s} = 8 TeV are presented. A data sample, corresponding to an integrated luminosity of 19.6 inverse-femtobarns was collected with the CMS experiment at the LHC. The measurements are performed in the leptonic decay modes ZZllllZZ \to lll'l', where l=e,μl = e, \mu and l=e,μ,τl' = e, \mu, \tau. The measured total cross section, σ(ppZZ)=7.7±0.5(stat.)0.4+0.5(syst.)±0.4(theo.)±0.2(lum.)pb\sigma (pp \to ZZ) = 7.7 \pm 0.5 (stat.)^{+0.5}_{-0.4} (syst.) \pm 0.4 (theo.) \pm 0.2 (lum.) pb for both Z bosons produced in the mass range mZm_Z within 60 and 120 GeV, is consistent with standard model predictions. Differential cross sections are measured and well described by the theoretical predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZγ\gamma couplings at the 95% confidence level: f4Zf_4^Z in (-0.004,+0.004), f5Zf_5^Z in (-0.005,+0.005), f4γf_4^\gamma in (-0.004,+0.004), and f5γf_5^\gamma in (-0.005,+0.005)

    Measurement of the production cross section for a W boson and two b jets in pp collisions at root s=7 TeV

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    The production cross section for a Wboson and two b jets is measured using proton-proton collisions at v root s = 7 TeV in a data sample collected with the CMS experiment at the LHC corresponding to an integrated luminosity of 5.0 fb(-1). The W + bbevents are selected in the W..decay mode by requiring a muon with transverse momentum pT> 25GeVand pseudorapidity |eta| 25GeVand |eta| < 2.4. The measured W + bbproduction cross section in the fiducial region, calculated at the level of final-state particles, is s(pp. W + bb) xB(W..) = 0.53 +/- 0.05 (stat.) +/- 0.09 (syst.) +/- 0.06 (theo.) 0.01 (lum.) pb, in agreement with the standard model prediction. In addition, kinematic distributions of the W + bbsystem are in agreement with the predictions of a simulation usingMadGraphandpythia

    Search for pair production of third-generation scalar leptoquarks and top squarks in proton-proton collisions at v root s=8 TeV

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    A search for pair production of third-generation scalar leptoquarks and supersymmetric top quark partners, top squarks, in final states involving tau leptons and bottom quarks is presented. The search uses events from a data sample of proton-proton collisions corresponding to an integrated luminosity of 19.7 fb(-1), collected with the CMS detector at the LHC with root s = 8 TeV. The number of observed events is found to be in agreement with the expected standard model background. Third-generation scalar leptoquarks with masses below 740 GeV are excluded at 95% confidence level, assuming a 100% branching fraction for the leptoquark decay to a tau lepton and a bottom quark. In addition, this mass limit applies directly to top squarks decaying via an R-parity violating coupling. lambda(') (333). The search also considers a similar signature from top squarks undergoing a chargino-mediated decay involving the Rparity violating coupling. lambda(')(3jk). Each top squark decays to a tau lepton, a bottom quark, and two light quarks. Top squarks in this model with masses below 580 GeV are excluded at 95% confidence level. The constraint on the leptoquark mass is the most stringent to date, and this is the first search for top squarks decaying via. lambda(')(3jk)
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