1,086 research outputs found
AuRh/TiO2 nanocatalysts: growth, performance and structural adaptation to hydrogen-rich environments
No full textSSCI-VIDE+ECI2D+LPI:GBE:PAFNational audienceHeterogeneous catalysis is ubiquitous in refining and chemical industries as it enables the formation of desirable products with minimal energy consumption. Since catalysis is a surface process, (metal) nanoparticles (NPs) often constitute the catalyst active phase, which is stabilized by a high-surface-area support and possibly promoted by a second metal.In this work, we have designed AuRh NPs supported on rutile TiO2 nanorods as model catalysts for several reactions involving hydrogen. A simple colloidal co-reduction method using NaBH4 and polyvinyl alcohol (PVA) generates 3 nm-sized bimetallic NPs.[1] However, unlike their Au and Rh counterparts, the AuRh colloids are instable in solution, as monitored in situ by dynamic light scattering and liquid-phase TEM.[2] Thus, once formed the NPs must be readily immobilized on the support in order to avoid their further growth. The AuRh/TiO2 catalysts present synergistic nanoalloying effects in all the investigated processes: stronger oxidation resistance of Rh in air,[1] stronger sulfidation resistance of Rh during tetralin hydrogenation in the presence of H2S,[1] higher selectivity to oxygen-free products in the hydrodeoxygenation of guaiacol,[3] and higher performance in the selective hydrogenation of cinnamaldehyde.[2] The structures of the colloids and their evolutions after immobilization and thermal treatments in a hydrogen atmosphere relevant to the catalytic reactions have been investigated by aberration-corrected STEM, EDX, UV-Vis, CO-FTIR, XPS and XRD. Heating the catalysts to 350 °C eliminates the PVA and leads to the segregation of Au and Rh within the particles: the NPs adopt a Janus configuration with the Rh side in contact with the titania support.[1,4] Further heating to 700 °C leads to NP coalescence and formation of “Au ball-Rh cup” ~10 nm-sized particles.[4] DFT calculations on unsupported and supported clusters show that the observed restructuring is driven by the strong Au-Rh segregation tendency, the lower surface energy of Au with respect to Rh, and the stronger Rh-TiO2 bonding with respect to Au-TiO2.[4–6]References[1]Z. Konuspayeva, P. Afanasiev, T.-S. Nguyen, L. Di Felice, F. Morfin, N.-T. Nguyen, J. Nelayah, C. Ricolleau, Z. Y. Li, J. Yuan, G. Berhault, L. Piccolo, Phys. Chem. Chem. Phys. 2015, 17, 28112–28120.[2]Z. Konuspayeva, G. Berhault, P. Afanasiev, T.-S. Nguyen, S. Giorgio, L. Piccolo, Submitted.[3]T.-S. Nguyen, D. Laurenti, P. Afanasiev, Z. Konuspayeva, L. Piccolo, J. Catal. 2016, 344, 136–140.[4]L. Piccolo, Z. Y. Li, I. Demiroglu, F. Moyon, Z. Konuspayeva, G. Berhault, P. Afanasiev, W. Lefebvre, J. Yuan, R. L. Johnston, Sci. Rep. 2016, 6, 35226.[5]I. Demiroglu, Z. Y. Li, L. Piccolo, R. L. Johnston, Catal. Sci. Technol. 2016, 6, 6916–6931.[6]I. Demiroglu, Z. Y. Li, L. Piccolo, R. L. Johnston, Comput. Theor. Chem. 2017, 1107, 142–151
Azimuthal correlations in Z +jets events in proton–proton collisions at s = 13 Te V
No full textAbstract The production of Z bosons associated with jets is measured in pp collisions at s = 13 Te V with data recorded with the CMS experiment at the LHC corresponding to an integrated luminosity of 36.3 fb - 1 . The multiplicity of jets with transverse momentum p T > 30 Ge V is measured for different regions of the Z boson’s p T ( Z ) , from lower than 10 Ge V to higher than 100 Ge V . The azimuthal correlation Δ ϕ between the Z boson and the leading jet, as well as the correlations between the two leading jets are measured in three regions of p T ( Z ) . The measurements are compared with several predictions at leading and next-to-leading orders, interfaced with parton showers. Predictions based on transverse-momentum dependent parton distributions and corresponding parton showers give a good description of the measurement in the regions where multiple parton interactions and higher jet multiplicities are not important. The effects of multiple parton interactions are shown to be important to correctly describe the measured spectra in the low p T ( Z ) regions
IMF Stabilization Programs and their Effects on the World Economic Crises
No full textAbstractThe aim of this study is that analyzing the relationship between IMF Stabilization Programs and its effect on the experienced world economic crises. The Great Depression and World War I and II faced by the world caused to be deeply shaken of the economies. Eventually, the countries were forced to create barriers against each other to protect the war-damaged economies. The world countries agreed with establishment of IMF to surpass the economic crisis. This article is concentrated on a question is that “Whether the IMF stabilization Programs effected positively or triggered into worse situation and crisis the war-damaged economies?” The examples crises are Mexican Crisis in 1994, South-eastern Asia Crisis in 1997, Russian Crisis in 1998, Argentina Crisis in 2001 and Turkey Crises in 1994, 2000 and 2001
Measurement of associated Z + charm production in proton-proton collisions at 8 TeV
No full textA study of the associated production of a Z boson and a charm quark jet (Z + c), and a comparison to production with a b quark jet (Z + b), in pp collisions at a centre-of-mass energy of 8 TeV are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7 fb, collected with the CMS detector at the CERN LHC. The Z boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of c or b flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with 20 GeV, 25 GeV and 2.5. The Z + c production cross section is measured to be 8.8 0.5 (stat) 0.6 (syst) pb. The ratio of the Z + c and Z + b production cross sections is measured to be 2.0 0.2 (stat) 0.2 (syst). The Z + c production cross section and the cross section ratio are also measured as a function of the transverse momentum of the Z boson and of the heavy flavour jet. The measurements are compared with theoretical predictions
Precision measurement of the Z boson invisible width in pp collisions at s=13 TeV
No full textA precise measurement of the invisible width of the Z boson produced in proton-proton collisions at a center-of-mass energy of 13 TeV is presented using data recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 36.3fb−1. The result is obtained from a simultaneous fit to kinematic distributions for two data samples of Z boson plus jets: one dominated by Z boson decays to invisible particles and the other by Z boson decays to muon and electron pairs. The invisible width is measured to be 523±3(stat)±16(syst)MeV. This result is the first precise measurement of the invisible width of the Z boson at a hadron collider, and is the single most precise direct measurement to date, competitive with the combined result of the direct measurements from the LEP experiments
Measurement of the Z / γ∗→ ττ cross section in pp collisions at sqrt(s)=13TeV and validation of τ lepton analysis techniques
No full textA measurement is presented of the Z / γ∗→ ττ cross section in pp collisions at s=13TeV, using data recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 2.3fb-1. The product of the inclusive cross section and branching fraction is measured to be σ(pp→Z/γ∗+X)B(Z/γ∗→ττ)=1848±12(stat)±67(syst \,+\,lumi) pb, in agreement with the standard model expectation, computed at next-to-next-to-leading order accuracy in perturbative quantum chromodynamics. The measurement is used to validate new analysis techniques relevant for future measurements of τ lepton production. The measurement also provides the reconstruction efficiency and energy scale for τ decays to hadrons+ντ final states, determined with respective relative uncertainties of 2.2 and 0.9%
Search for a heavy resonance decaying into a Z boson and a Z or W boson in 2ℓ2q final states at TeV
No full textA search has been performed for heavy resonances decaying to ZZ or ZW in 2ℓ2q final states, with two charged leptons (ℓ = e, μ) produced by the decay of a Z boson, and two quarks produced by the decay of a W or Z boson. The analysis is sensitive to resonances with masses in the range from 400 to 4500 GeV. Two categories are defined based on the merged or resolved reconstruction of the hadronically decaying vector boson, optimized for high- and low-mass resonances, respectively. The search is based on data collected during 2016 by the CMS experiment at the LHC in proton-proton collisions with a center-of-mass energy of TeV, corresponding to an integrated luminosity of 35.9 fb. No excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-1 and spin-2 resonances are derived as a function of the resonance mass, and exclusion limits on the production of W bosons and bulk graviton particles are calculated in the framework of the heavy vector triplet model and warped extra dimensions, respectively.A search has been performed for heavy resonances decaying to ZZ or ZW in 22q final states, with two charged leptons ( e,) produced by the decay of a Z boson, and two quarks produced by the decay of a W or Z boson. The analysis is sensitive to resonances with masses in the range from 400 to 4500 GeV. Two categories are defined based on the merged or resolved reconstruction of the hadronically decaying vector boson, optimized for high- and low-mass resonances, respectively. The search is based on data collected during 2016 by the CMS experiment at the LHC in proton-proton collisions with a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb. No excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-1 and spin-2 resonances are derived as a function of the resonance mass, and exclusion limits on the production of W bosons and bulk graviton particles are calculated in the framework of the heavy vector triplet model and warped extra dimensions, respectively
Search for leptophobic Z' bosons decaying into four-lepton final states in proton-proton collisions at TeV
No full textA search for heavy narrow resonances decaying into four-lepton final states from cascade decays of a Z' boson has been performed using proton-proton collision data at TeV collected by the CMS experiment, corresponding to an integrated luminosity of 19.7 inverse femtobarns. No excess of events over the standard model background expectation is observed. Upper limits for a benchmark model on the product of cross section and branching fraction for the production of these heavy narrow resonances are presented. The limit excludes leptophobic Z' bosons with masses below 2.5 TeV within the benchmark model. This is the first result to constrain a leptophobic Z' resonance in the four-lepton channel
Measurement of the production cross section in pp collisions at 8 TeV and limits on anomalous and trilinear gauge boson couplings
No full textA measurement of the production cross section in pp collisions at 8 TeV is presented, using data corresponding to an integrated luminosity of 19.6 fb collected with the CMS detector at the LHC. This measurement is based on the observation of events with large missing energy and with a single photon with transverse momentum above 145 GeV and absolute pseudorapidity in the range 1.44. The measured production cross section, 52.7 2.1(stat) 6.4 (syst) 1.4 (lum) fb, agrees well with the standard model prediction of 50.0 fb. A study of the photon transverse momentum spectrum yields the most stringent limits to date on the anomalous and trilinear gauge boson couplings.An inclusive measurement of the Zγ→νν‾γ production cross section in pp collisions at s=8TeV is presented, using data corresponding to an integrated luminosity of 19.6 fb −1 collected with the CMS detector at the LHC. This measurement is based on the observation of events with large missing energy and with a single photon with transverse momentum above 145 GeV and absolute pseudorapidity in the range |η|<1.44 . The measured Zγ→νν‾γ production cross section, 52.7±2.1 (stat)±6.4 (syst)±1.4 (lumi) fb , agrees well with the standard model prediction of 50.0−2.2+2.4 fb . A study of the photon transverse momentum spectrum yields the most stringent limits to date on the anomalous ZZγ and Zγγ trilinear gauge boson couplings.A measurement of the Z gamma to nu nu-bar gamma production cross section in pp collisions at sqrt(s) = 8 TeV is presented, using data corresponding to an integrated luminosity of 19.6 inverse femtobarns collected with the CMS detector at the LHC. This measurement is based on the observation of events with large missing energy and with a single photon with transverse momentum above 145 GeV and absolute pseudorapidity in the range |eta| < 1.44. The measured Z gamma to nu nu-bar gamma production cross section, 52.7 +/- 2.1(stat) +/- 6.4 (syst) +/- 1.4 (lumi) fb, agrees well with the standard model prediction of 50.0 +2.4 -2.2 fb. A study of the photon transverse momentum spectrum yields the most stringent limits to date on the anomalous Z-Z-gamma and Z-gamma-gamma trilinear gauge boson couplings
Search for new physics in events with a leptonically decaying Z boson and a large transverse momentum imbalance in proton-proton collisions at = 13 TeV
No full textA search for new physics in events with a Z boson produced in association with large missing transverse momentum at the LHC is presented. The search is based on the 2016 data sample of proton-proton collisions recorded with the CMS experiment at , corresponding to an integrated luminosity of 35.9 . The results of this search are interpreted in terms of a simplified model of dark matter production via spin-0 or spin-1 mediators, a scenario with a standard-model-like Higgs boson produced in association with the Z boson and decaying invisibly, a model of unparticle production, and a model with large extra spatial dimensions. No significant deviations from the background expectations are found, and limits are set on relevant model parameters, significantly extending the results previously achieved in this channel.A search for new physics in events with a Z boson produced in association with large missing transverse momentum at the LHC is presented. The search is based on the 2016 data sample of proton-proton collisions recorded with the CMS experiment at 13 TeV, corresponding to an integrated luminosity of 35.9 fb. The results of this search are interpreted in terms of a simplified model of dark matter production via spin-0 or spin-1 mediators, a scenario with a standard-model-like Higgs boson produced in association with the Z boson and decaying invisibly, a model of unparticle production, and a model with large extra spatial dimensions. No significant deviations from the background expectations are found, and limits are set on relevant model parameters, significantly extending the results previously achieved in this channel
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