共查询到20条相似文献,搜索用时 10 毫秒
1.
Nominal errors on the determination of αs(mZ) from τ decay are so small that it may appear that this is the best method of measuring the strong coupling. While I agree that this way of determining αs(mZ) is a very good one, I think that the theoretical errors involved are larger than often asssumed, even if the QCD sum rule framework is accepted. 相似文献
2.
We compute the complete leading-log terms of the next-to-next-to-next-to-leading-order corrections to potential NRQCD. As a by-product we obtain the leading logs at O(mαs5) in the heavy quarkonium spectrum. These leading logs, when ΛQCDmαs2, give the complete O(mαs5lnαs) corrections to the heavy quarkonium spectrum. 相似文献
3.
We calculate the potential between “quarks” which are in the adjoint representation of SU(2) color in the three-dimensional lattice theory. We work in the scaling region of the theory and at large quark separations R. We also calculate the masses MQg of color-singlet bound states formed by coupling an adjoint quark to adjoint glue (“gluelumps”). Good scaling behavior is found for the masses of both magnetic (angular momentum J = 0) and electric (J = 1) gluelumps, and the magnetic gluelump is found to be the lowest-lying state. It is naively expected that the potential for adjoint quarks should saturate above a separation Rscr where it becomes energetically favorable to produce a pair of gluelumps. We obtain a good estimate of the naive screening distance Rscr. However we find little evidence of saturation in the potential out to separations R of about 1.5Rscr. 相似文献
4.
Courtney H. Lanier Ann N. Chiaramonti Laurence D. Marks Kenneth R. Poeppelmeier 《Surface science》2009,603(16):2574-2579
The so-called Biphase termination on α-Fe2O3 has been widely accepted to be a structure with a 40 Å unit supercell composed of coexisting islands of Fe1−xO and α-Fe2O3. Based on thermodynamic arguments and experimental evidence, including transmission electron diffraction, imaging, magnetic and spectroscopic information, it is found that the previously proposed structure model is inaccurate. The actual Biphase structure is instead a layered structure related to the reduction of α-Fe2O3 to Fe3O4. A model for the Biphase termination is proposed which does not contain islands of Fe1−xO but instead consists of bulk α-Fe2O3 and a Fe3O4-derived overlayer. The proposed model is consistent with all current and previously reported experimental findings. 相似文献
5.
Active-sterile neutrino oscillations provide a mechanism by which large differences in the neutrino and antineutrino number densities can be created in the early universe. The quantum kinetic equations are employed in the study of these neutrino asymmetries, which, when solved analytically in the adiabatic limit, generate physically transparent evolution equations that are very useful for the understanding of the nature of the asymmetry growth. 相似文献
6.
The cavity regularization technique, originally developed for self-energies, is adapted to the calculation of vertex diagrams in the framework of cavity field theory. As a test of this method, the vector and axial-vector coupling constants of the nucleon are computed to order αs Logarithmic divergences of the various Feynman diagrams cancel for massless quarks, yielding gv = 1.0000 and gA = 1.0883 + 0.2425αs, independent of the gauge and renormalisation scheme. 相似文献
7.
Results of a new evaluation of the O(αs2) dressed three-jet cross section for e+e− annihilation are summarized. For vanishing cutoffs, the different results in published three-jet cross section formulae are due to differing definitions of resolvable four-jet events. Subleading terms which were ignored in previous calculations are evaluated and found to be sizeable in the phase space region where three-jet events become more two-jet-like. A simple calculation demonstrates that αs values determined according to the three-jet cross section formulae of Gutbrod, Kramer and Schierholz are systematically too large. 相似文献
8.
T. Conrad A. Bibik D. Shcherbik E. Lubarsky B.T. Zinn 《Proceedings of the Combustion Institute》2007,31(2):2223-2230
This paper describes an experimental investigation of the feasibility of an “intermittent” active control approach for suppressing combustion instabilities in liquid fueled combustors. The developed controller employs a “smart” fuel injector that can modify the spray properties in response to changes in combustor operating conditions. This action weakens or breaks up the coupling between the combustion process and combustor acoustic modes oscillations, thus preventing the excitation of large amplitude instabilities. This approach differs significantly from previously proposed active control methods, both in concept and implementation, as it requires only “intermittent” modification of the combustion process by a single control action as opposed to the continuous action required by most other active control methods. The “smart” fuel injector used in this study consisted of a double-staged, air-assisted atomizer in which counter swirling, primary (inner stage) and secondary (outer stage) air streams were supplied to the injector through separate sets of tangentially oriented orifices. Control of the ratio of air mass flow rates supplied to these two stages, by use of a diverter valve, resulted in significant changes in the spray shape and its axial, tangential, and radial velocity components. This variation in spray properties of the “smart” injector was characterized for different values of the inner to outer air flow rate ratio in cold flow tests with a PDPA system. These results were then correlated with the characteristics of the “intermittently” controlled combustor. Measured quantities included the instability amplitudes, axial dependence of the mean and oscillatory heat release amplitudes, and the characteristics of the recirculation zones, which were all shown to depend on the fuel spray properties. The results of this study demonstrate the feasibility of using “smart” fuel injectors with capabilities for varying the combustion process characteristics to reduce the amplitudes of detrimental combustion instabilities in real engines to acceptable levels. 相似文献
9.
We present the results of the analytical evaluation of the massless four-loop
(α3s) correction to the correlator of the quark scalar currents and the Higgs decay rate into hadrons. In numerical form we found (in
scheme) that Γ (H →
b ) = (3GF/4
π) MHm2b (MH) [1 + 5.667αs/π + (35.94 − 1.359nf) (αs/π)2 + (164.139 − 25.771nf + 0.259n2f) (αs/π)3] where nf is the number of quark flavour and αs = αs(MH). 相似文献
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10.
We report on the observation of 1 3PJ (χb) production in the reaction ′→γχb→γγ→γγ(e+e− or μ+μ−). The data were recorded with the nonmagnetic CUSB detector at the Cornell Electron Storage Ring, CESR. We observe 124 γγ events with either an electron or muon pair in the final state. In the γγ correlation plot about 40% of the events cluster around (120, 430) MeV. 相似文献
11.
B. Gabioud J. -C. Alder C. Joseph J. -F. Loude N. Morel A. Perrenoud J. -P. Perroud M. T. Tran E. Winkelmann 《Nuclear Physics A》1984,420(3):496-524
A high-statistics measurement of the photon spectrum of the reaction π−d → γnn has been performed. The comparison of this spectrum with theoretical spectra folded with the response curve of the spectrometer (measured by the reaction π−p → γn) has provided precise values of the neutron-neutron scattering length, ann = −18.5 ± 0.4 fm, and of the effective range, rnn = 2.80 ± 0.11 fm. Theoretical uncertainties of 0.20 fm and 0.11 fm, respectively, have been evaluated. 相似文献
12.
Epitaxial thin films of the conductive ferromagnetic oxide SrRuO3 were grown on an (0 0 1) SrTiO3 (STO) substrate by using DC sputtering technique. The magnetic and magnetoresistive properties of the films were measured by applying the magnetic field both perpendicular (out-of-plane) and parallel (in-plane) to the film plane and ever maintaining the direction of the applied field perpendicular to that of the transport current. The films grown on an (0 0 1) STO substrate showed identical magnetization properties in two orthogonal crystallographic directions of the substrate, [1 0 0]S and [0 0 1]S (in-plane and out-of-plane geometry), which suggests the presence of a multi domain structure within the plane of the film. For such samples, no anisotropic field (hard axis) along de [0 0 1]s direction, i.e., perpendicular to the film-plane could be detected. Nevertheless, a distinguishable temperature dependent out-of-plane anisotropic magnetoresistance (MR) along with strong temperature dependent low field hysteretic MR(H) behavior was detected for the studied films. A negative MR ratio MR(T)=[ρ(μ0H=9 T; T)−ρ( μ0H=0 T; T)]/ρ( μ0H=0 T; T) on the order of a few percent, with maximums of 6% and 4% (right at the Curie temperature, TC 160 K) was calculated for an in-plane and out-of plane measuring geometry, respectively. In addition there is an equally strong MR effect at low temperatures, which might be related to the temperature dependence of the magnetocrystalline anisotropy together with a magnetization rotation. Both the MR(T) behavior and the achieved values (except for T<30 K) are similar to those obtained on SrRuO3 films grown on 2° miscut (0 0 1) STO substrates with the current parallel to the field and parallel to the direction, which was identified as the easier axis for magnetization. 相似文献
13.
Andreas Junk 《Physik in unserer Zeit》2010,41(5):253-254
Die Geburtsstunde der theoretischen Nanotechnologie wird heute gerne auf den 29. Dezember 1959 zurückdatiert. An diesem Tag äußerte der spätere Nobelpreisträger Richard Feynman in seiner Bankettansprache “There's Plenty of Room at the Bottom” erste Gedanken zu einer extremen Erhöhung von Datenspeicherdichten. Nanotechnologen sehen sich mit ihrer Arbeit in der Tradition seiner Ideen. 相似文献
14.
The theoretical mechanisms for the decays ψ′ → ψπ0 and ψ′ → ψη, which violate SU2 and SU3, respectively discussed. It is argued that symmetry breaking in the decay amplitudes may be as important as π0 −η −η′ mixing. The π0 −η mechanism ψ′ → ψν → ψπ0 leads to Γ(ψ′ → ψπ0) = (3.3±1.0) × 10−3 Γ(ψ′ → ψν), but this number may be enhanced by a factor as large as 12 by π0−η′ mixing and isospin violation in the decay amplitude. The related decays ψ → ηγ and ψ → η′γ are also discussed. 相似文献
15.
We propose to test CP symmetry in the decay J/ψ→γφφ, for which large data sample exists at BESII, and a data sample of 1010 J/ψ's will be collected with BESIII and CLEO-C program. We suggest some CP asymmetries in this decay mode for CP test. Assuming that CP violation is introduced by the electric- and chromo-dipole moment of charm quark, these CP asymmetries can be predicted by using valence quark models. Our work shows a possible way to get information about the electric- and chromo-dipole moment of charm quark, which is little known. Our results show that with the current data sample of J/ψ, electric- and chromo-dipole moment can be probed at order of 10−13 e cm. In the near future with a 1010 data sample, these moments can be probed at order of 10−14 e cm. 相似文献
16.
Alejandro Cabo 《Fortschritte der Physik》1981,29(10):495-503
The extension of the “proper time” method to the statistical field theory is obtained. The procedure is used to calculate the “one loop” contribution to the thermodynamical potential in electrodynamics, when the electron positron gas is located in a combination of an inhomogeneous electrostatic field and an uniform magnetic one. Also, a “proper time” representation of the temperature Green function for this problem is given. 相似文献
17.
We consider the leading twist “T-odd” contributions as the dominant source of the cos2 azimuthal asymmetry in unpolarized di-lepton production in Drell–Yan scattering. This asymmetry contains information on the distribution of quark transverse spin in an unpolarized proton. In a parton-spectator framework we estimate these asymmetries at 50 GeV center of mass energy. This azimuthal asymmetry is interesting in light of proposed experiments at GSI, where an anti-proton beam is ideal for studying the transversity properties of quarks due to the dominance of valence quark effects. 相似文献
18.
The idea of “common path” has been widely applied in optical instrument design for 30 years and even today. But the meaning of “common path” has not yet been explained clearly and sometimes confusion has been created. In this paper an “adaptive principle” is proposed and recommended on optical instrument system. It suggests that the designer not only arranges the measurement system to obtain measurement signal but also sets a channel to give prediction of noise or disturbance in real time or short term. Such a recommendation is based on the recent studies on nonlinear dynamics and atmospheric disturbance by means of experiments as well as theoretical analysis. 相似文献
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20.
Toshiyuki Usagawa Jianguo Wen Tadashi Utagawa Satoshi Koyama Youichi Enomoto 《Physica C: Superconductivity and its Applications》2000,340(4):269-275
We report on I–V characteristics for in situ formed Nb/Au/(1 1 0)YBa2Cu3O7−δ (YBCO) Josephson junction, where the homoepitaxial (1 1 0)YBCO film shows ultra-smooth surface morphology. The field dependence of critical supercurrent Ic shows anisotropic large junction behavior with normal Fraunhofer patterns expected from BCS model of dx2−y2 wave superconductors. This strongly suggests that the Nb/Au/(1 1 0)YBCO junctions cannot be regarded as atomic scaled corner junctions, in contrast with (0 0 1)/(1 1 0)YBCO grain boundary junctions to show “π-junction” with a pronounced dip near zero fields in field modulation of Ic. 相似文献