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51.
The production and subsequent semi-leptonic decay of charmed particles is investigated in order to determine whether it could account for the prompt lepton data. Most of the central region data is easily accommodated but there are difficulties at large x. Large cross-sections for charmed particle production are implied. Correlations in events are discussed. 相似文献
52.
Sébastien Michelin Stefan G. Llewellyn Smith 《Theoretical and Computational Fluid Dynamics》2009,23(2):127-153
A method is proposed for the study of the two-dimensional coupled motion of a general sharp-edged solid body and a surrounding
inviscid flow. The formation of vorticity at the body’s edges is accounted for by the shedding at each corner of point vortices
whose intensity is adjusted at each time step to satisfy the regularity condition on the flow at the generating corner. The
irreversible nature of vortex shedding is included in the model by requiring the vortices’ intensity to vary monotonically
in time. A conservation of linear momentum argument is provided for the equation of motion of these point vortices (Brown–Michael
equation). The forces and torques applied on the solid body are computed as explicit functions of the solid body velocity
and the vortices’ position and intensity, thereby providing an explicit formulation of the vortex–solid coupled problem as
a set of non-linear ordinary differential equations. The example of a falling card in a fluid initially at rest is then studied
using this method. The stability of broadside-on fall is analysed and the shedding of vorticity from both plate edges is shown
to destabilize this position, consistent with experimental studies and numerical simulations of this problem. The reduced-order
representation of the fluid motion in terms of point vortices is used to understand the physical origin of this destabilization.
相似文献
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55.
High-resolution infrared spectra of SF6 in a xenon matrix give evidence for dynamic exchange among trapping sites on the IR time scale. A 32S-34S kinetic isotope effect has been observed and attributed to differences in the dephasing mode frequencies and the resulting disparity in coupling to the phonon bath. 相似文献
56.
Approval of a project the size of the Large Hadron Collider is an exercise in politics and high finance. 相似文献
57.
Vimont A Travert A Bazin P Lavalley JC Daturi M Serre C Férey G Bourrelly S Llewellyn PL 《Chemical communications (Cambridge, England)》2007,(31):3291-3293
The adsorption mode of CO(2) at low coverage in the nanoporous metal benzenedicarboxylate MIL-53(Cr) or Cr(3+)(OH)(O(2)C-C(6)H(4)-CO(2)) has been identified using IR spectroscopy; the red shift of the nu(3) band and the splitting of the nu(2) mode of CO(2) in addition to the shifts of the nu(OH) and delta(OH) bands of the MIL-53(Cr) hydroxyl groups provide evidence that CO(2) interacts with the oxygen atoms of framework OH groups as an electron-acceptor via its carbon atom; this is the first example of such an interaction between CO(2) and bridged OH groups in a solid. 相似文献
58.
Crowhurst L Lancaster NL Pérez-Arlandis JM Welton T 《Journal of the American Chemical Society》2004,126(37):11549-11555
In this work we report the effect of ionic liquids on a class of charge-neutral nucleophiles. We have studied the reactions of (n)butylamine, di-(n)butylamine, and tri-(n)butylamine with methyl p-nitrobenzenesulfonate in [bmpy][N(Tf)(2)], [bmpy][OTf], and [bmim][OTf] (bmpy = 1-butyl-1-methylpyrrolidinium; bmim = 1-butyl-3-methylimidazolium) and compared their reactivities, k(2), to those for the same reactions in the molecular solvents dichloromethane and acetonitrile. It was shown that all of the amines are more nucleophilic in the ionic liquids than in the molecular solvents studied in this work. Comparison is also made with the effect of ionic liquids on the reactivity of chloride ions, which are deactivated in ionic liquids. The Eyring activation parameters revealed that changes in the activation entropies are largely responsible for the effects seen. This can be explained in part by the differing hydrogen-bonding properties, as shown by the Kamlet-Taft solvent parameters, of each of these solvents and the formation of hydrogen bonds between the solvents and the nucleophiles. 相似文献
59.
We describe in detail the calculation of all first-order electroweak radiative corrections to total and differential neutrino cross sections and to the parity-violating asymmetry in ed scattering. We find that leading log approximations agree well with our exact result for the shape, but not necessarily the magnitude, of the corrections to except for γ → 1. Corrections to total neutrino cross sections have also been calculated by Marciano and Sirlin; our results agree with theirs. The corrections to sin2θw are experiment dependent. If sin2θw is defined in the scheme at a scale Mw, they reduce the average value found from the ratio of charged to neutral current neutrino scattering by 0.012 to 0.215 ± 0.015. They reduce the value obatained from the Paschos Wolfenstein relation by 0.008 to 0.221 ± 0.014. In ed scattering they reduce the value by 0.008 to 0.215 ± 0.015. Using a corrected value of 0.215 ± 0.015 and the first-order corrections to the mass formulae, the SU(2) × U(1) predictions for the vector boson masses are Mw = 83.1?2.8+3.1rmGeV and Mz = 93.8?2.2+2.5 GeV, about five GeV larger than obtained from the lowest order analysis. 相似文献
60.
We calculate cross sections for using the distribution functions for quarks in the photon predicted by QCD. The Drell-Yan contribution to the μ-pair cross section is masked by the Bethe-Heitler process in the region where it is interesting. However, the characteristic cross section for photoproduction of large-pT particles, which is predicted by QCD, is measurable. 相似文献