| 1. |
- Schael, S., et al.
(författare)
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Electroweak measurements in electron positron collisions at W-boson-pair energies at LEP
- 2013
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 532:4, s. 119-244
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Forskningsöversikt (refereegranskat)abstract
- Electroweak measurements performed with data taken at the electron positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb(-1) collected by the four LEP experiments ALEPH, DELPHI, 13 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, m(w) and Gamma(w), the branching fraction of W decays to hadrons, B(W -> had), and the trilinear gauge-boson self-couplings g(1)(Z), K-gamma and lambda(gamma), are determined to be: m(w) = 80.376 +/- 0.033 GeV Gamma(w) = 2.195 +/- 0.083 GeV B(W -> had) = 67.41 +/- 0.27% g(1)(Z) = 0.984(-0.020)(+0.018) K-gamma - 0.982 +/- 0.042 lambda(gamma) = 0.022 +/- 0.019. (C) 2013 Elsevier B.V. All rights reserved.
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| 2. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 3. |
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| 4. |
- Bernal, Ximena E., et al.
(författare)
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Empowering Latina scientists
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 363:6429, s. 825-826
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Requies, J., et al.
(författare)
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Palladium-manganese catalysts supported on monolith systems for methane combustion
- 2008
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 79:2, s. 122-131
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Tidskriftsartikel (refereegranskat)abstract
- Alumina-supported bimetallic and monometallic Mn and Pd monolithic catalysts were prepared and tested in methane combustion. Two different reactor configurations were adopted for catalyst testing, i.e. a fixed-bed laboratory-scale reactor and a pilot-plant reactor which allowed work at different temperatures and pressures. The results of catalyst performance showed that all bimetallic catalysts are considerably more stable for methane combustion than the monometallic palladium catalyst. With the aim to explain the relationship between activity-stability and structure and surface properties, the catalysts were characterized by TPO, XRD, XPS and ICP-AES. The high stability displayed by the bimetallic systems is attributed to the influence of manganese in retarding the decomposition of PdO into metallic palladium. Thus, it appears that manganese oxides inhibit PdO decomposition, as a consequence of the increase in oxygen mobility in the manganese oxide spinel phase.
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| 6. |
- Ojeda, M., et al.
(författare)
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Synthesis of Rh nano-particles by the microemulsion technology - Particle size effect on the CO+H-2 reaction
- 2004
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 274:1-2, s. 33-41
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Tidskriftsartikel (refereegranskat)abstract
- Several alumina-supported rhodium-based catalysts have been prepared using the microemulsion technology. The change of microemulsion properties led to catalysts with different Rh particle size and narrow size distribution while keeping the same metal loading. The metal particle size was determined by XRD and TEM. These catalysts were tested in the CO hydrogenation reaction in order to investigate the influence of the Rh particle size. The catalytic results indicated that turnover frequency (TOF) increased about four times when the Rh particle size increased approximately from
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| 7. |
- Rojas, S., et al.
(författare)
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Preparation of carbon supported Pt and PtRu nanoparticles from microemulsion - Electrocatalysts for fuel cell applications
- 2005
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 285:02-jan, s. 24-35
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Tidskriftsartikel (refereegranskat)abstract
- A series of platinum and platinum ruthenium carbon supported electrocatalyst have been prepared by the microemulsion technique. The influence of parameters such as the preparation route, the metal loading and the PtRu stoichiometry on the morphology of the final nanoparticles has been studied. Irrespective the total metal loading, nanosized particles, displaying a narrow size distribution were obtained. In addition, particle size was found to be independent of the metal loading. Structural characteristics of these systems have been studied by XPS, X-ray diffraction, TEM, and TPR-TPO and their textural parameters by N-2 adsorption. The catalytic performance of the samples was evaluated in the electrochemical oxidation of methanol. The influence of the morphology on the catalytic performance of the catalysts is discussed in terms of their synthesis route. © 2005 Elsevier B.V. All rights reserved.
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| 8. |
- Thevenin, P. O., et al.
(författare)
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Catalytic combustion of methane over cerium-doped palladium catalysts
- 2003
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 215:1, s. 78-86
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Tidskriftsartikel (refereegranskat)abstract
- Various Pd-supported catalysts have been prepared using three different types of alumina as support material: (a) gamma-alumina, (b) Ba-stabilized alumina, and
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| 9. |
- Agrell, J., et al.
(författare)
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Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part I. Catalyst preparation and characterisation
- 2003
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 253:1, s. 201-211
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Tidskriftsartikel (refereegranskat)abstract
- Mixed copper-zinc oxide catalysts (Cu/ZnO) were prepared by two different techniques, i.e. from hydroxycarbonate precursors formed in aqueous solution and from oxalate precursors formed in water-in-oil microemulsion. Their physicochemical properties were characterised by nitrogen adsorption-desorption, N2O chemisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and oxidation (TPO). The BET surface areas ranged from 34 to 87 m(2)/g, depending on the method of preparation. Cu surface areas between 6.6 and 22 m(2)/g were measured. It was a general observation that catalysts prepared by microemulsion technique had lower Cu dispersions than expected (3.4-5.7%), due to a proposed partial embedding of Cu in ZnO. The catalyst prepared by carbonate co-precipitation exhibited a significantly higher Cu dispersion (10.3%). In addition, this catalyst displayed better resistance to successive TPR/TPO than the microemulsion catalysts, which exhibited significant Cu crystallite growth. However, the microemulsion route provided well-mixed materials with a narrow particle size distribution and the possibility to obtain high BET surface areas (up to 87 m(2)/g) by controlling the water/surfactant ratio in the microemulsion. XPS measurements revealed the existence of Cu+ species on the surface of both types of catalysts after exposure to a O-2/CH3OH mixture. The surface composition of the hydroxycarbonate-derived sample was unaffected by reduction in hydrogen and exposure to O-2/CH3OH, while Zn-enrichment on the surface was observed in the microemulsion catalysts after reduction, indicating sintering of the Cu particles. These observations were consistent with the TPR/TPO measurements.
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| 10. |
- Agrell, J., et al.
(författare)
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Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part II. Catalytic activity and reaction pathways
- 2003
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 253:1, s. 213-223
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Tidskriftsartikel (refereegranskat)abstract
- The activity for conversion of methanol into hydrogen was investigated over binary Cu/ZnO catalysts derived from precursors prepared by two different techniques, viz. oxalates formed in microemulsion and hydroxycarbonates formed in aqueous solution. Some distinct differences in the reaction pathways were observed. During partial oxidation of methanol under a sub-stoichiometric oxygen/methanol ratio, the microemulsion materials exhibited considerably higher combustion activity in the low-temperature region than a catalyst prepared in aqueous solution. Over the former, oxygen was quickly converted by methanol combustion, after which steam reforming was initiated, producing hydrogen at the expense of water and gradually decreasing the net heat of reaction. Hence, a reaction sequence for the partial oxidation reaction over microemulsion catalysts is proposed. consisting of consecutive methanol combustion and steam reforming, followed by decomposition when all oxygen has been consumed. Over the hydroxycarbonate catalyst, the reaction ignited at a higher temperature, directly producing hydrogen by partial oxidation of methanol. When the two types of catalysts were evaluated in the steam reforming reaction, all catalysts displayed the typical S-shaped dependence of methanol conversion on temperature. However, there was a downward shift in the temperature at which methanol reached complete conversion, favouring the hydroxycarbonate, material. Hydrogen was produced selectively over all catalysts, but carbon monoxide formation was more pronounced over the microemulsion materials. The differences in catalytic behaviour are discussed in terms of catalyst morphology and the valence state of Cu in the working catalyst.
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