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[en] The production of the Higgs boson associated with a pair of top quarks is one of the most important Higgs boson productions still not observed by far. Therefore, its discovery is one of the most challenging searches after the Higgs discovery: not only it will be the first time we observe the existence of this Higgs production mode but moreover it will allow to measure the Yukawa coupling of top to the Higgs. This measurement can probe the basics of the Standard Model (SM) but also can search for any hints of new physics beyond the SM prediction. This makes this production search and measurement one of the most important analyses in post Higgs discovery era. The ATLAS (A Toroidal LHC Apparatus) collaboration is operating since 2009 at the Large Hadron Collider (LHC), at CERN, in Geneva. During the first data taking campaign, so-called Run 1, and with corresponding to an integrated luminosities per experiment of 5 fb-1 at 7 TeV center of mass energy (in 2011) and 20 fb-1 at 8 TeV (in 2012), several Higgs boson decay channels were considered to measure the Higgs Yukawa coupling to the top quark within tt-bar H production through multi-leptons final states. The ATLAS experiment produced individual combinations which were then converted into a combined significances with the CMS collaboration combinations to get a tt-bar H observation significance, statistical of 4.4σ, for a 2.0σ expected from the Standard Model, corresponding to a measured excess of 2.3σ. After a two years shutdown period, the LHC is now running at 13 TeV since 2015 and the cross section of tt-bar H increases by a factor of four compared to the 8 TeV run. The two years upgrade of the ATLAS detector brought substantial improvements to the physics analysis, especially for the SM measurement such as tt-bar H production and new physics searching. After having introduced the theoretical and experimental framework, the work presented in this thesis focuses on the search for the Higgs boson production associated with a pair of top quarks in multi-lepton final states and more particularly those with three leptons. Multi-variable analysis techniques are introduced and employed to have a good discriminate power between signal and background. For one of the main backgrounds, fake leptons, a Matrix Method is used to estimate its contribution. Generally, good modelling of the fake leptons background and better separation are achieved with a Boosted Decision Tree (BDT) distribution. Final results are obtained with a fit on a combined 2D BDT distribution. For a Higgs boson mass of 125 GeV with 36.1 fb-1 at 13 TeV data recorded by ATLAS, an excess of events over the expected background from other Standard Model processes is found with an observed significance of 2.18 standard deviations, compared to an expectation of 1.45 standard deviations. The best fit for the tt-bar H production cross section is 1.54+0.81-0.74 times the SM expectation, and is consistent with the value of the Yukawa coupling to top quarks in the Standard Model. The results are compatible with the latest ATLAS approved results obtained with a further optimized background treatment. Comparing to the Run 1 results, a great improvement has been obtained on the significance and the uncertainty of the signal strength measurement. This results from a higher centre of mass energy hence a higher cross section, but also from the ATLAS performance upgrades as well as a more advanced analysis strategy. Still large uncertainties on the final measurements remains and further optimization of the analysis and higher statistics will be needed to get a more precise results in the future. (author)
[fr]La production du boson de Higgs associee a une paire de quarks top est une des plus importantes productions non encore observee a ce jour. Sa decouverte est donc une des recherches les plus ambitieuses apres la decouverte du Higgs: non seulement cela sera la premiere fois que ce mode sera observe mais surtout il permettra la mesure du couplage de Yukawa du Higgs avec le quark top. Le resultat de cette mesure pourra sonder les bases du Modele Standard (SM) mais aussi rechercher des traces de nouvelle physique au-dela du Modele Standard. Cela fait de cette recherche et de la mesure de cette production une des analyses les plus importantes depuis la decouverte du Higgs. La collaboration ATLAS (A Toroidal LHC Apparatus) opere depuis 2009 le detecteur generaliste ATLAS aupres du grand collisionneur de Hadron (LHC), a Geneve. Durant la premiere campagne de prise de donnees appelee Run 1 et correspondant a une luminosite integree de 5 fb-1 a 7 TeV d'energie dans le centre de masse (2011) et de 20 fb-1 a 8 TeV (2012), plusieurs canaux de desintegration du boson de Higgs ont ete consideres pour mesurer le couplage de Yukawa du Higgs avec le quark top dans les productions tt-bar H avec des etats finaux multi-leptoniques. L'experience ATLAS a ainsi produit une mesure combinee qui a ensuite ete associee avec la mesure combinee obtenue par l'experience CMS pour produire une significance globale observee de 4.4σ, pour 2.0σ predite correspondant a un exces mesure de 2.3σ. Apres une periode d'arret de deux ans, le LHC tourne maintenant a 13 TeV depuis 2015 et la section efficace tt-bar H a augmentee d'un facteur quatre par rapport au run a 8 TeV permettant des mesures plus precises voire des decouvertes. Les deux annees de mise a niveau du detecteur ATLAS ont apportees des ameliorations substantielles pour les analyses de physique, et plus particulierement pour les mesures du SM comme la production tt-bar H et la recherche de nouvelle physique. Apres avoir introduit le cadre theorique et experimental, le travail presente dans cette these se concentre ensuite sur la recherche et l'etude de la production du boson de Higgs associee a une paire de quarks top dans des etats finaux semi-leptoniques et plus particulierement ceux a trois leptons. Des techniques d'analyse multi-variables sont introduites et employees pour obtenir une bonne discrimination entre signal et bruit de fond. Pour un des principaux bruits de fond, celui de faux leptons, une methode matricielle est presentee et utilisee pour estimer sa contribution. Une bonne modelisation du bruit de fond de faux leptons et une meilleure separation du signal est obtenue avec une distribution d'arbre de decision stimule (BDT). Les resultats finaux sont obtenus par un ajustement sur les distributions BDT combinees a deux dimensions. Pour un boson de Higgs de 125 GeV de masse, un exces d'evenements par rapport au bruit de fond attendu des autres processus du Modele Standard est obtenu avec une significance observee de 2.18 deviations standard, a comparer a une estimation attendue de 1.45σ. Le meilleur ajustement pour la section efficace de production tt-bar H est de 1.54+0.81-0.74 fois l'estimation du SM et est en accord avec la valeur du couplage de Yukawa du Higgs au quark top dans le Modele Standard. Ces resultats sont compatibles avec les derniers resultats officiels d'ATLAS obtenues avec une optimisation plus poussee du traitement des bruits de fond. En comparant avec les resultats du Run 1, une amelioration importante a ete obtenue sur la significance et l'incertitude sur la mesure de la force du signal. Cela provient non seulement de l'augmentation de l'energie de collision et donc de la section efficace mais aussi de perfor mances ameliorees du detecteur ainsi que d'une strategie d'analyse optimisee. Neanmoins, les incertitudes sur la mesure finale demeurent importantes et une optimisation plus poussee avec une augmentation de la statistique sera necessaire pour obtenir un resultat plus precis dans le futur. (auteur)
[en] Toxicological effects of nanoparticles (NPs) are still poorly documented while there are great demands for industrial applications and daily life. The aim of this study is to evaluate the influence of physicochemical characteristics on TiO2 NP toxicological effects toward protein. In order to better understand the physicochemical basis of the toxic of NP in industrial applications and under conditions of environmental exposure, we performed an array of photophysical measurements to quantify the interaction of TiO2 NP with protein. Fluorescence quenching, circular dichroism, dynamic light scattering and transmission electron microscopy measurements were performed on TiO2 NP having a diameter range from 10 to 35 nm in the performance of protein. We find that the TiO2 NP strongly associates with protein where the binding constant, as well as the degree of cooperativity of particle–protein binding, depends on particle size. We also find tentative evidence that the protein undergoes conformational change upon association with the NP. These results indicate that exposure to TiO2 NP may have an unfavorable effect on human health by inactivating functional proteins. - Highlights: ► The binding constants for fibrinogen onto TiO2 NPs depend on particle size. ► CD results showed that the structural changes of protein are quite small. ► The adsorbed protein to cause the TiO2NP to aggregate was indicated by DLS and TEM.
[en] A uniform Pd_2Zn_9 layer was formed at the interface between liquid-state Sn–9wt.%Zn and Pd substrate. Detailed observation revealed a unique cruciform pattern formation of the Pd_2Zn_9 phase. The Pd_2Zn_9 layer ruptured at the edges, where no reaction phase was formed. The growth kinetics of Pd_2Zn_9 was systematically investigated at temperatures of 220–260 °C. In particular, a linear reaction-limited growth was found in the initial reaction stage. While growing to approximately 5 μm thick, the growth rate gradually decreased over the subsequent reaction and obeyed a parabolic relationship. The growth kinetics parameters and the corresponding activation energies were determined. Additionally, the microstructure in the Pd_2Zn_9 layer was characterized using focused ion beam microscopy. The Pd_2Zn_9 layer consisted of four distinct sublayers with different grain structures. The growth behavior of Pd_2Zn_9 was further discussed through a series of observations on microstructural evolutions at different reaction durations. - Highlights: • Linear growth of Pd_2Zn_9 was found in the liquid-state Sn–9wt.%Zn/Pd reaction. • After growing to ~5 μm thick, the parabolic growth became dominant. • Unique cruciform pattern formation was observed in the Pd_2Zn_9 phase. • FIB characterization revealed that the Pd_2Zn_9 consisted of four sublayers. • The growth kinetics and mechanism of Pd_2Zn_9 were discussed
[en] In the work, tantalum oxide (TaOx) films were prepared by pulsed DC reactive magnetron sputtering method on Si wafer, corning glass and carrier glass. Ta/tantalum oxide/Ta (metal-insulation-metal, MIM) structures were fabricated to investigate the I-V characteristics of tantalum oxide films. I-V characteristics of MIM capacitors with top-electrode diameters varying from 1 to 4 mm were investigated. Symmetry and zero shifting phenomenons of I-V curves were studied. The effect of substrate roughness on the electrical properties of MIM capacitors was examined. The results show with the increase of top-electrode diameters from 1 to 4 mm the breakdown field strengths decreased from 2.22 to 0.3 MV/cm and the leakage current density at 0.25 MV/cm increased from 1.5E-9 to 7.3E-5 A/cm2. The roughness of the substrate and films, and defects in the films have great effect on the quality and I-V characteristics of MIM capacitors
[en] A Pd layer is frequently deposited on a Ni substrate as a surface finish in electronic packaging. During soldering process, the (Pd,Ni)Sn4 phase is formed at the solder/Ni interface and it is able to reduce electromigration damage. In this study, various interfacial structures, Sn/Pd(1 or 3 μm)/Ni and Sn/Cu(3 μm)/Pd(1 μm)/Ni, were designed to conduct electromigration tests. The results revealed that the electromigration resistance of the (Pd,Ni)Sn4 was closely associated with the Ni content. In the Sn/Pd(1 or 3 μm)/Ni couple, the (Pd,Ni)Sn4 layer with a high Ni solubility of ∼17 at% cannot retard electromigration. The (Pd,Ni)Sn4 phase was massively migrated into the solder matrix and the Ni substrate was considerably consumed. In the Sn/Cu(3 μm)/Pd(1 μm)/Ni couple, the formed (Pd,Ni)Sn4 layer with a low Ni content (<3 at%) can effectively retard electromigration; the interfacial microstructure was similar to that without current stressing. In addition, various Sn–Pd–Ni alloys were prepared to obtain the (Pd,Ni)Sn4 precipitates with different Ni contents. Under current stressing, the (Pd,Ni)Sn4 phase clearly exhibited a better electromigration resistance when the Ni content decreased. Moreover, for the interface with Cu substrate, the (Pd,Ni)Sn4 layer (<5 at%Ni) can act as an effective barrier layer to suppress the electromigration-induced Cu dissolution. - Highlights: • (Pd,Ni)Sn4 layer formed at the Sn/Ni(or Cu) interface was current-stressed. • Electromigration on Sn–Pd–Ni alloys with different (Pd,Ni)Sn4 precipitates were tested. • Electromigration resistance of (Pd,Ni)Sn4 was associated with the Ni content. • (Pd,Ni)Sn4 layer (<5 at%Ni) can effectively suppress the EM-induced Cu dissolution.
[en] MnO2 hollow cubes with nanosheets as the in situ formed building units have been fabricated via a novel template approach. The method is based on hydrothermal deposition of MnO2 nanosheets on silica hollow cubes and the sequential NaOH-dissolution of silica. In virtue of hollow interior voids and higher specific surface area, the MnO2 nanosheet-based hierarchical hollow cubes exhibit improved lithium storage properties compared to MnO2 hierarchical microflowers. - Highlights: • δ-MnO2 hierarchical hollow cubes have been synthesized. • δ-MnO2 hierarchical hollow cubes are built from two-dimensional nanosheets. • Hierarchical hollow MnO2 cubes have uniform shape. • No MnCO3 is used as precursors, and no protective surfactant is used. • Li storage properties of MnO2 hierarchical hollow cubes and hierarchical flowers.
[en] Highlights: • MACS and ADE algorithms are hybridized as MACS-ADE method for solving STHGS problem. • An adaptive mutation is integrated into the proposed algorithm to avoid premature convergence. • MACS and ADE are run in parallel in search of better solution. • Several effective heuristic strategies are designed for dealing with various constraints of STHGS problem. - Abstract: Short-term hydro generation scheduling (STHGS) aims at determining optimal hydro generation scheduling to obtain minimum water consumption for one day or week while meeting various system constraints. In this paper, the STHGS problem is decomposed into two sub-problems: (i) unit commitment (UC) sub-problem; (ii) economic load dispatch (ELD) sub-problem. Then, we present a hybrid algorithm based on multi ant colony system (MACS) and differential evolution (DE) for solving the STHGS problem. First, MACS is used for dealing with UC sub-problem. A set of cooperating ant colonies cooperate to choose the unit state over the scheduled time horizon. Then, the adaptive differential evolution (ADE) is used to solve ELD sub-problem. MACS and ADE are run in parallel with adjusting their solutions in search of a better solution. Meanwhile, local and global pheromone updating rules in MACS and adaptive dynamic parameter adjusting strategy in DE are applied for enhancing the search ability of MACS-ADE. Finally, the proposed method is implemented to solve STHGS problem of Three Gorges–Gezhouba cascaded hydropower plants to verify the feasibility and effectiveness. Compared with other established methods, the simulation results reveal that the proposed MACS-ADE approach has the best convergence property, computational efficiency with less water consumption
[en] Highlights: • Air-standard rectangular cycle models are built and investigated. • Finite-time thermodynamics is applied. • Different dissipation models and variable specific heats models are adopted. • Performance characteristics of different cycle models are compared. - Abstract: In this paper, performance comparison of air-standard rectangular cycles with constant specific heat (SH), linear variable SH and non-linear variable SH are conducted by using finite time thermodynamics. The power output and efficiency of each cycle model and the characteristic curves of power output versus compression ratio, efficiency versus compression ratio, as well as power output versus efficiency are obtained by taking heat transfer loss (HTL) and friction loss (FL) into account. The influences of HTL, FL and SH on cycle performance are analyzed by detailed numerical examples.
[en] The manned deep-space exploration is a hot topic of the current space activities. The continuous supply of thermal and electrical energy for the scientific equipment and human beings is a crucial issue for the lunar outposts. Since the night lasts for periods of about 350 h at most locations on the lunar surface, massive energy storage is required for continuous energy supply during the lengthy lunar night and the in-situ resource utilization is demanded. A lunar based solar thermal power system with regolith thermal storage is presented in this paper. The performance analysis is carried out by the finite-time thermodynamics to take into account major irreversible losses. The influences of some key design parameters are analyzed for system optimization. The analytical results shows that the lunar based solar thermal power system with regolith thermal storage can meet the requirement of the continuous energy supply for lunar outposts. - Highlights: • A lunar based solar thermal power system with regolith thermal storage is presented. • The performance analysis is carried out by the finite-time thermodynamics. • The influences of some key design parameters are analyzed.
[en] Highlights: • NPG nanocomposites in porous glass (d = 11.5–300 nm) are prepared. • Solid transition temperature of the nanocomposites can be tuned to ∼11 °C below the bulk. • Latent heat of the pore NPG varies in the range of 65.5–99.6% of the bulk value. • Nanoconfinement provides a way of reusing those ideal heat storage materials. - Abstract: Size-dependent thermal properties of neopentyl glycol (NPG) embedded in controlled porous glasses (CPGs) are investigated using differential scanning calorimetry (DSC), infrared spectroscopy (FT-IR), and powder X-ray diffraction (XRD). In the nanopores of CPGs (diameter d = 11.5–300 nm), NPG shows depressed solid–solid and solid–liquid phase transition temperatures and latent heats, which decrease as the pore size becomes smaller. In thermal cycling around the solid transition, the nano-sized NPG display stable transition temperature and enthalpy change as the bulk. Supercooling in the solid transition increases with the decreasing pore diameter (d > 25 nm). From FT-IR and XRD analysis, NPG in the nanopores maintains the same structure as the bulk. The nanoencapsulated NPG is analogous to a series of new phase change materials (PCMs), through which the ideal heat storage performance of the bulk may be handed down.