| 1. |
- Ablikim, M., et al.
(author)
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Measurements of (XcJ)-> K+K-K+K- decays
- 2006
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In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 642:3, s. 197-202
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Journal article (peer-reviewed)abstract
- Using 14M psi(2S) events taken with the BESII detector, chi(cJ) -> 2(K+K-) decays are studied. For the four-kaon final state, the branching fractions are B(chi(c0,1,2) ->.2(K+K-)) = (3.48 +/- 0.23 +/- 0.47) x 10(-3), (0.70 +/- 0.13 +/- 0.10) x 10(-3), and (2.17 +/- 0.20 +/- 0.31) x 10(-3). For the phi K+K- final state, the branching fractions, which are measured for the first time, are B(chi(c0,1,2) -> phi K+K-) = (1.03 +/- 0.22 +/- 0.15) x 10(-3), (0.46 +/- 0.16 +/- 0.06) x 10(-3), and (1.67 +/- 0.26 +/- 0.24) x 10(-4). For the phi phi final state, B(chi(c0,2) -> phi phi) = (0.94 +/- 0.21 +/- 0.13) x 10(-3) and (1.70 +/- 0.30 +/- 0.25) x 10(-3).
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| 2. |
- Schael, S, et al.
(author)
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Precision electroweak measurements on the Z resonance
- 2006
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In: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Research review (peer-reviewed)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. |
- Li, Yingming, et al.
(author)
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Levels and vertical distributions of PCBs, PBDEs, and OCPs in the atmospheric boundary layer : observation from the Beijing 325-m meteorological tower
- 2009
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 43:4, s. 1030-1035
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Journal article (peer-reviewed)abstract
- Polyurethane foam disk passive air sampling was carried out to investigate the levels, vertical distributions, and potential sources of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and organochlorine pesticides (OCPs) in the atmospheric boundary layer of an urban site in Asia. Sampling was performed at nine heights (15, 47, 80, 120, 160, 200, 240, 280, 320 m) of the 325-m meteorological tower in Beijing, China over three 2-month periods between December 2006 and August 2007. This is the first study to report vertical variations of PBDEs in the ABL and one of only a few studies to investigate vertical distributions of persistent organic pollutants. The levels of sigma19PCBs and sigma8PBDEs were relatively low, ranging from 22 to 65 and from 2.3 to 18 pg m-3, respectively. Air concentrations of gamma-HCH were high, with values in the range of 39-103 pg m-3 in winter, 100-180 pg m-3 in spring, and 115-242 pg m-3 in summer, respectively. alpha-HCH concentrations ranged from 20 to 86 pg m-3, p,p'-DDT between 7.3 and 78 pg m-3, and HCB between 15 and 160 pg m-3. The seasonal variations of PCBs, PBDEs, and OCPs may reflect different sources for these chemicals, such as those related with regional use (gamma-HCH), volatilization/re-emission (PBDEs, PCBs, alpha-HCH), and pesticide impurities (HCB). Although the performance reference compounds (PRCs) were spiked before deployment, the sampling rates showed strong dependency on wind speeds, resulting in large variations in uptake rates in the ABL, ranging from approximately 7.0 m3 day-1 at ground level to 11 m3 day-1 at 320 m. Levels of PCBs, PBDEs, and OCPs decreased with increasing ABL height indicating the potential of Beijing as the local sources.
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| 8. |
- Li, Dong-gang, et al.
(author)
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Diffusion layer growth at Zn/Cu interface under uniform and gradient high magnetic fields
- 2008
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In: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 495:1-2, s. 244-248
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Journal article (peer-reviewed)abstract
- As a common phenomenon occurring in many material processes, diffusion may induce significant changes in composition and microstructure near the interface. In the present study, liquid/solid (Zn/Cu) interface diffusion experiments in high magnetic fields (up to 12 T) were conducted and the thickness changes of diffusion layer under different magnetic field conditions were examined. It was found that there were no noticeable effects of high magnetic fields on the formation of intermetallic phases at the interface. However, the magnetic flux density exerted a non-linear influence on the diffusion layer thickness. This phenomenon should be attributed to the effect of magnetic fields suppressing natural convection and inducing thermo-electromagnetic convection. In addition, the diffusion of Zn into Cu could be retarded by a magnetic field gradient. These results indicate that both the strength and the gradient of high magnetic fields can be used to control the diffusion behavior.
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| 9. |
- Liu, Ji-Cai, et al.
(author)
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Coherent control of population and pulse propagation beyond the rotating wave approximation
- 2008
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In: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 41:7
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Journal article (peer-reviewed)abstract
- The dynamics of populations of the vibrational states in a NO molecule ( one-photon absorption) and of the electronic states in a 4,4'-bis( dimethylamino) stilbene molecule ( two-photon absorption) is studied versus the frequency, intensity and shape of the laser pulse. We show that specially designed infrared laser pulses can build selective populations of certain vibrational states. A detuning of light frequency from the vibrational resonance qualitatively changes the dynamics of populations. It is found out that the populations of the nonresonant levels follow the pulse shape adiabatically if the detuning significantly exceeds the inverse characteristic time of the change of the pulse. Depopulation of the nonresonant vibrational states leads to a high population of the resonant state at the end of the pulse. Complete breakdown of the standard rotating wave approximation for a two-photon absorption process is observed even for a rather small intensity of the laser pulse. An analytical solution for the interaction of a pulse with a three-level system beyond the rotating wave approximation is obtained, and it is in close agreement with the strict numerical solution of the amplitude equations. Special attention is paid to the population dynamics of randomly oriented molecules. The orientational disorder as well as the vibrations limit the coherent population transfer. Calculations show the strong role of the anisotropy of photoexcitation in the coherent control of populations which can affect the anisotropy of photobleaching.
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| 10. |
- Liu, Ji-Cai, et al.
(author)
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Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse
- 2008
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In: Chinese Physics B. - : IOP Publishing. - 1674-1056. ; 17:11, s. 4211-4217
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Journal article (peer-reviewed)abstract
- This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultras short laser pulse by solving numerically the full-wave Maxwell-Bloch equations. The 4, 40-bis(dimethylamino) stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance.
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