153 research outputs found
Modelling of the effect of grain boundary diffusion on the oxidation of Ni-Cr alloys at high temperature
Grain boundaries in oxide scales have a strong effect on oxidation kinetics when they act as diffusion short circuits. This study proposes a quantitative evaluation of the phenomenon by modelling. Various cases of oxide microstructure evolution are treated using both analytical and numerical resolutions. Results showed that the effect of oxide grain growth on the oxidation kinetics can be analysed considering a transitory stage for which the oxidation kinetics is not purely parabolic. Some guidelines for choosing the appropriate post-treatment method for the analysis and extrapolation of experimental oxidation kinetics are given
Growth Kinetics and Characterization of Chromia Scales Formed on Niâ30Cr Alloy in Impure Argon at 700 °C
The oxidation of a Niâ30Cr alloy at 700 °C in impure argon was studied in order to provide new elements of understanding on chromia scale growth in low oxygen partial pressure atmosphere (10â5 atm). Oxidation tests were carried out during 30 min to 50 h in a thermogravimetric analysis system using a symmetrical balance with in situ monitoring of the oxygen partial pressure. The oxidation kinetics were determined as parabolic with an estimated stationary parabolic constant value of 10â15 cm2 sâ1, after a transient stage of about 3 h. The oxide scale was identified as a pure chromia layer by TEM and XPS characterisations. After 50 h at 700 °C, the scale thickness estimated by TEM cross section observation was about 100 nm. A slightly thicker and more porous oxide scale was observed above the alloyâs grain boundaries. The metal/oxide interface also exhibited a deeper recession towards the substrate above the alloyâs grain boundaries. The orientation of chromia grains was determined by TKD (transmission Kikuchi diffraction). A strong preference was noted for the orientation perpendicular to the surface, along the direction of the corundum structure. Finally, the type of semiconduction was determined for the scales formed after 7 h and 50 h of oxidation. For the shorter oxidation time, the chromia scale exhibited an n-type semiconduction, whereas for the longer exposure, both n-type and insulating semiconduction were identified
DMTs and Covid-19 severity in MS: a pooled analysis from Italy and France
We evaluated the effect of DMTs on Covid-19 severity in patients with MS, with a pooled-analysis of two large cohorts from Italy and France. The association of baseline characteristics and DMTs with Covid-19 severity was assessed by multivariate ordinal-logistic models and pooled by a fixed-effect meta-analysis. 1066 patients with MS from Italy and 721 from France were included. In the multivariate model, anti-CD20 therapies were significantly associated (OR = 2.05, 95%CI = 1.39â3.02, p < 0.001) with Covid-19 severity, whereas interferon indicated a decreased risk (OR = 0.42, 95%CI = 0.18â0.99, p = 0.047). This pooled-analysis confirms an increased risk of severe Covid-19 in patients on anti-CD20 therapies and supports the protective role of interferon
Les droits disciplinaires des fonctions publiques : « unification », « harmonisation » ou « distanciation ». A propos de la loi du 26 avril 2016 relative à la déontologie et aux droits et obligations des fonctionnaires
The production of tt⟠, W+bb⟠and W+cc⟠is studied in the forward region of protonâproton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98±0.02 fbâ1 . The W bosons are reconstructed in the decays WââÎœ , where â denotes muon or electron, while the b and c quarks are reconstructed as jets. All measured cross-sections are in agreement with next-to-leading-order Standard Model predictions.The production of , and is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 0.02 \mbox{fb}^{-1}. The bosons are reconstructed in the decays , where denotes muon or electron, while the and quarks are reconstructed as jets. All measured cross-sections are in agreement with next-to-leading-order Standard Model predictions
CMS physics technical design report : Addendum on high density QCD with heavy ions
Peer reviewe
Measurement of the J/Ï pair production cross-section in pp collisions at TeV
The production cross-section of J/Ï pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of TeV, corresponding to an integrated luminosity of 279 ±11 pb. The measurement is performed for J/Ï mesons with a transverse momentum of less than 10 GeV/c in the rapidity range 2.0 < y < 4.5. The production cross-section is measured to be 15.2 ± 1.0 ± 0.9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the J/Ï pair are measured and compared to theoretical predictions.The production cross-section of pairs is measured using a data sample of collisions collected by the LHCb experiment at a centre-of-mass energy of , corresponding to an integrated luminosity of . The measurement is performed for mesons with a transverse momentum of less than in the rapidity range . The production cross-section is measured to be . The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the pair are measured and compared to theoretical predictions
Measurement of forward production in collisions at TeV
A measurement of the cross-section for production in collisions is presented using data corresponding to an integrated luminosity of fb collected by the LHCb experiment at a centre-of-mass energy of TeV. The electrons are required to have more than GeV of transverse momentum and to lie between 2.00 and 4.25 in pseudorapidity. The inclusive production cross-sections, where the decays to , are measured to be \begin{align*} \begin{split} \sigma_{W^{+} \to e^{+}\nu_{e}}&=1124.4\pm 2.1\pm 21.5\pm 11.2\pm 13.0\,\mathrm{pb},\\ \sigma_{W^{-} \to e^{-}\bar{\nu}_{e}}&=\,\,\,809.0\pm 1.9\pm 18.1\pm\,\,\,7.0\pm \phantom{0}9.4\,\mathrm{pb}, \end{split} \end{align*} where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. Differential cross-sections as a function of the electron pseudorapidity are measured. The cross-section ratio and production charge asymmetry are also reported. Results are compared with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Finally, in a precise test of lepton universality, the ratio of boson branching fractions is determined to be \begin{align*} \begin{split} \mathcal{B}(W \to e\nu)/\mathcal{B}(W \to \mu\nu)=1.020\pm 0.002\pm 0.019, \end{split} \end{align*} where the first uncertainty is statistical and the second is systematic.A measurement of the cross-section for production in collisions is presented using data corresponding to an integrated luminosity of fb collected by the LHCb experiment at a centre-of-mass energy of TeV. The electrons are required to have more than GeV of transverse momentum and to lie between 2.00 and 4.25 in pseudorapidity. The inclusive production cross-sections, where the decays to , are measured to be \begin{equation*} \sigma_{W^{+} \to e^{+}\nu_{e}}=1124.4\pm 2.1\pm 21.5\pm 11.2\pm 13.0\,\mathrm{pb}, \end{equation*} \begin{equation*} \sigma_{W^{-} \to e^{-}\bar{\nu}_{e}}=\,\,\,809.0\pm 1.9\pm 18.1\pm\,\,\,7.0\pm \phantom{0}9.4\,\mathrm{pb}, \end{equation*} where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. Differential cross-sections as a function of the electron pseudorapidity are measured. The cross-section ratio and production charge asymmetry are also reported. Results are compared with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Finally, in a precise test of lepton universality, the ratio of boson branching fractions is determined to be \begin{equation*} \mathcal{B}(W \to e\nu)/\mathcal{B}(W \to \mu\nu)=1.020\pm 0.002\pm 0.019, \end{equation*} where the first uncertainty is statistical and the second is systematic.A measurement of the cross-section for W â eÎœ production in pp collisions is presented using data corresponding to an integrated luminosity of 2 fb collected by the LHCb experiment at a centre-of-mass energy of TeV. The electrons are required to have more than 20 GeV of transverse momentum and to lie between 2.00 and 4.25 in pseudorapidity. The inclusive W production cross-sections, where the W decays to eÎœ, are measured to be where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination
Measurement of the B0sâÎŒ+ÎŒâ Branching Fraction and Effective Lifetime and Search for B0âÎŒ+ÎŒâ Decays
A search for the rare decays Bs0âÎŒ+ÎŒ- and B0âÎŒ+ÎŒ- is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4ââfb-1. An excess of Bs0âÎŒ+ÎŒ- decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B(Bs0âÎŒ+ÎŒ-)=(3.0±0.6-0.2+0.3)Ă10-9, where the first uncertainty is statistical and the second systematic. The first measurement of the Bs0âÎŒ+ÎŒ- effective lifetime, Ï(Bs0âÎŒ+ÎŒ-)=2.04±0.44±0.05ââps, is reported. No significant excess of B0âÎŒ+ÎŒ- decays is found, and a 95% confidence level upper limit, B(B0âÎŒ+ÎŒ-)<3.4Ă10-10, is determined. All results are in agreement with the standard model expectations.A search for the rare decays and is performed at the LHCb experiment using data collected in collisions corresponding to a total integrated luminosity of 4.4 fb. An excess of decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be , where the first uncertainty is statistical and the second systematic. The first measurement of the effective lifetime, ps, is reported. No significant excess of decays is found and a 95 % confidence level upper limit, , is determined. All results are in agreement with the Standard Model expectations
Measurements of prompt charm production cross-sections in pp collisions at TeV
Production cross-sections of prompt charm mesons are measured using data from collisions at the LHC at a centre-of-mass energy of TeV. The data sample corresponds to an integrated luminosity of pb collected by the LHCb experiment. The production cross-sections of , , , and mesons are measured in bins of charm meson transverse momentum, , and rapidity, . They cover the rapidity range and transverse momentum ranges for and and for and mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of are determined to be \begin{equation*} \sigma(pp\rightarrow D^0 X) = 1190 \pm 3 \pm 64\,\mu\text{b} \end{equation*} \begin{equation*} \sigma(pp\rightarrow D^+ X) = 456 \pm 3 \pm 34\,\mu\text{b} \end{equation*} \begin{equation*} \sigma(pp\rightarrow D_s^+ X) = 195 \pm 4 \pm 19\,\mu\text{b} \end{equation*} \begin{equation*} \sigma(pp\rightarrow D^{*+} X)= 467 \pm 6 \pm 40\,\mu\text{b} \end{equation*} where the uncertainties are statistical and systematic, respectively.Production cross-sections of prompt charm mesons are measured using data from pp collisions at the LHC at a centre-of-mass energy of 5 TeV. The data sample corresponds to an integrated luminosity of 8.60 ± 0.33 pb collected by the LHCb experiment. The production cross-sections of D, D, D , and D mesons are measured in bins of charm meson transverse momentum, p, and rapidity, y. They cover the rapidity range 2.0 < y < 4.5 and transverse momentum ranges 0 < p < 10 GeV/c for D and D and 1 < p < 10 GeV/c for D and D mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of 1 < p < 8 GeV/c are determined to be where the uncertainties are statistical and systematic, respectively.Production cross-sections of prompt charm mesons are measured using data from collisions at the LHC at a centre-of-mass energy of TeV. The data sample corresponds to an integrated luminosity of pb collected by the LHCb experiment. The production cross-sections of , , , and mesons are measured in bins of charm meson transverse momentum, , and rapidity, . They cover the rapidity range and transverse momentum ranges for and and for and mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of are determined to be \sigma(pp\rightarrow D^0 X) = 1004 \pm 3 \pm 54\,\mu\text{b} \sigma(pp\rightarrow D^+ X) = 402 \pm 2 \pm 30\,\mu\text{b} \sigma(pp\rightarrow D_s^+ X) = 170 \pm 4 \pm 16\,\mu\text{b} \sigma(pp\rightarrow D^{*+} X)= 421 \pm 5 \pm 36\,\mu\text{b} where the uncertainties are statistical and systematic, respectively
Influence de l'aération sur le colmatage des membranes immergées
La thĂšse est consacrĂ©e Ă lâĂ©tude de lâinfluence de lâaĂ©ration sur le colmatage de membranes fibres creuses immergĂ©es en filtration externe/interne. Dans une premiĂšre partie on Ă©tudie la filtration de levures (0.5 g.l-1) dans une cuve de 100 l avec une surface membranaire de 0.032 m2. Deux types dâessais de filtration ont Ă©tĂ© rĂ©alisĂ©s, des essais Ă palier de flux de dĂ©termination des conditions critiques et des essais de filtration en conditions colmatantes. Ces essais ont Ă©tĂ© effectuĂ©s sans aĂ©ration et avec aĂ©ration sous forme de fines bulles et de calottes dâair. La sensibilitĂ© du colmatage Ă la position et au dĂ©bit de lâinjection des fines bulles ainsi quâaux frĂ©quences et volumes de calottes a Ă©tĂ© analysĂ©e. LâĂ©tude de la filtration a inclus la sensibilitĂ© des performances de filtration au mouvement des fibres, des essais ayant Ă©tĂ© rĂ©alisĂ©s soit avec des fibres tendues soit avec des fibres lĂąches. Dans une deuxiĂšme partie, une Ă©tude locale expĂ©rimentale et numĂ©rique de lâhydrodynamique diphasique a Ă©tĂ© entreprise avec des outils dâanalyse dâimage, de P.I.V et avec le code de calcul FLUENT (modĂšle Ă deux fluides pour les fines bulles et modĂšle V.O.F. pour les calottes). La synthĂšse des rĂ©sultats de filtration et dâanalyse de lâhydrodynamique induite par lâaĂ©ration permet de proposer des mĂ©canismes expliquant lâinfluence de lâaĂ©ration sur le colmatage des fibres creuses immergĂ©es. Ce travail contribue Ă clarifier les paramĂštres hydrodynamiques globaux pertinents pour contrĂŽler le colmatage\ud
------------------------------------------------------------------------------------------------------------------------------------------------------------------------- This thesis is about the influence of aeration on submerged hollow fibre membrane fouling in outside/in filtration. In a first part, yeast filtration (0.5 g.l-1) is studied in a 100 l tank with a membrane area of 0.32m2. Two types of filtration experiments were performed: critical condition determination with flux step method and filtration experiment under fouling condition. These experiments were performed without and with aeration with small and spherical cap bubbles. Fouling sensitivity to position and small bubble injection flow rate as well as to frequency and volume of spherical cap was analysed. Filtration experiments involve characterization of filtration efficiency with tight and loose fibres. In a second, part local experimental and numerical studies were performed thanks to the image analysis, P.I.V. measurements and FLUENT numerical simulations (two-fluid model for small bubbles and V.O.F. model for spherical cap bubbles). Filtration and hydrodynamics analysis results lead to the determination of mechanisms explaining aeration effect on submerged hollow fibre fouling. This study contributes to better understand the revelant global hydrodynamic parameters in order to control foulin
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