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- 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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| 4. |
- Ni, Qiang, et al.
(författare)
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Wireless broadband access : WiMax and beyond - Investigation of bandwidth request mechanisms under point-to-multipoint mode of WiMAX networks
- 2007
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Ingår i: IEEE Communications Magazine. - Piscataway, N.J. : IEEE Press. - 0163-6804 .- 1558-1896. ; 45:5, s. 132-138
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Tidskriftsartikel (refereegranskat)abstract
- The WiMAX standard specifies a metropolitan area broadband wireless access air interface. In order to support QoS for multimedia applications, various bandwidth request and scheduling mechanisms are suggested in WiMAX, in which a subscriber station can send request messages to a base station, and the base station can grant or reject the request according to the available radio resources. This article first compares two fundamental bandwidth request mechanisms specified in the standard, random access vs. polling under the point-to-multipoint mode, a mandatory transmission mode. Our results demonstrate that random access outperforms polling when the request rate is low. However, its performance degrades significantly when the channel is congested. Adaptive switching between random access and polling according to load can improve system performance. We also investigate the impact of channel noise on the random access request mechanism. © 2007 IEEE.
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| 6. |
- Yang, X. C., et al.
(författare)
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The bromination mechanism of 1-aminoanthraquinone-2,4-disulfonic acid in sulfuric acid
- 2006
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Ingår i: Dyes and pigments. - : Elsevier BV. - 0143-7208 .- 1873-3743. ; 71:3, s. 231-235
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Tidskriftsartikel (refereegranskat)abstract
- I-Amino-4-bromoanthraquinotie-2-sulfoiiic acid (bromoamine acid) is an important intermediate for dyes. 1-Aminoanthraquinone2,4-disulfonic acid is the major impurity when 1-aminoanthraquinone is sulfonated in oleum to synthesize bromoamine acid. The mechanism of bromination of 1-aminoanthraquinone-2,4-disulfonic acid in sulfuric acid has been studied. It is proved that I-aminoanthraquinone-2,4-disulfonic acid undergoes de-sulfonation first to form 1-aminoanthraquinoine-2-sulfonic acid, and then bromination to form bromoamine acid. Based on this mechanism, a new optimal process for the synthesis of bromoamine acid is developed. In this way, bromoamine acid is afforded in high yield and good quality.
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