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- 2019
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Tidskriftsartikel (refereegranskat)
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- 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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- Gao, Zhu, et al.
(författare)
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Interfacial Ti-S Bond Modulated S-Scheme MOF/Covalent Triazine Framework Nanosheet Heterojunctions for Photocatalytic C-H Functionalization
- 2023
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Ingår i: Angewandte Chemie International Edition. - 1433-7851 .- 1521-3773. ; 62:27
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Tidskriftsartikel (refereegranskat)abstract
- Constructing photocatalyst systems to functionalize the inert C−H bonds has attracted extensive research interest. However, purposeful modulation of interfacial charge transfer in heterostructures remains a challenge, as it usually suffers from sluggish kinetics. Reported herein is an easy strategy to construct the heteroatom-induced interface for developing the titanium-organic frameworks (MOF-902) @ thiophene-based covalent triazine frameworks (CTF-Th) nanosheets S-scheme heterojunctions with controllable oxygen vacancies (OVs). Specifically, Ti atoms were first anchored onto the heteroatom site of CTF-Th nanosheets, and then grown into MOF-902 via an interfacial Ti−S linkage, generating OVs. Using in situ X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) calculations, the enhanced interfacial charge separation and transfer induced by moderate OVs in the pre-designed S-scheme nanosheets was validated. The heterostructures exhibited an improved efficiency in photocatalytic C3-acylation of indoles under mild conditions with a yield 8.2 times larger than pristine CTF-Th or MOF-902 and enabled an extended scope of substrates (15 examples). This performance is superior to state-of-the-art photocatalyst and can be retained, without significant loss, after 12 consecutive cycles.
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- Li, Liang, et al.
(författare)
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A CORRELATED STUDY OF OPTICAL AND X-RAY AFTERGLOWS OF GRBs
- 2015
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 805:1
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Tidskriftsartikel (refereegranskat)abstract
- We study an extensive sample of 87 gamma-ray bursts (GRBs) for which there are well-sampled and simultaneous optical and X-ray light curves. We extract the cleanest possible signal of the afterglow component. and compare the temporal behaviors of the X-ray light. curve, observed by Swift XRT, and optical data, observed by UVOT and ground-based telescopes for each individual burst. Overall we find that 62% of the GRBs. are consistent with the standard afterglow model. When more advanced modeling is invoked, up to 91% of the bursts in our sample may be consistent with the external-shock model. A large fraction of these bursts are consistent with occurring in a constant interstellar density medium (61%) while only 39% of them occur in a wind-like medium. Only nine cases have afterglow light curves that exactly match the standard fireball model prediction, having a single power-law decay in both energy bands that are observed during their entire duration. In particular, for the bursts with chromatic behavior, additional model assumptions must be made over limited segments of the light curves in order for these bursts to fully agree with the external-shock model. Interestingly, for 54% of the X-ray and 40% of the optical band observations, the end of the shallow decay (t(similar to-0.5)) period coincides with the jet-break (t(similar to-p)) time, causing an abrupt change in decay slope. The fraction of the burst that is consistent with the external-shock model is independent of the observational epochs in the rest frame of GRBs. Moreover, no cases can be explained by the cooling frequency crossing the X-ray or optical band.
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| 7. |
- Yang, Song, et al.
(författare)
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Regulating the Tautomerization in Covalent Organic Frameworks for Efficient Sacrificial Agent-Free Photocatalytic H2O2 Production
- 2024
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Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 57:5, s. 2039-2047
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency of photocatalytic production of H2O2 is constrained by the low selectivity toward oxygen reduction, and the active sites are still under debate. Herein, analogous covalent organic framework photocatalysts were synthesized from triformylphloroglucinol (Tp) and predesigned diamines, in which a molecular engineering strategy was employed to manipulate the energy barrier for the targeted proton transfers. The tautomerization of enol-imine to keto-enamine introduced abundant alkene bonds (C═C), which serve as the primary adsorption sites and have a lower energy barrier for the reduction of the O2 reduction. DHAA-Tp COF displayed a remarkable photocatalytic H2O2 production rate of 219.5 μmol h–1 g–1 without any sacrificial reagent, which stands out among the structure-related materials. A switch from a concerted one-step 2e– to a two-step single e– process in O2 reduction was observed in TCNAQ-Tp COF, which is presumably ascribed to the suppressed tautomerization mediated by the strong electron-withdrawing cyano groups. The results demonstrate a novel concept for the photocatalytic production of H2O2 using an efficient, stable, and recyclable metal-free photocatalytic system.
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