共查询到20条相似文献,搜索用时 640 毫秒
1.
T.J.M. Symons L.K. Fifield M.J. Hurst A. Pakkanen F. Watt C.H. Zimmerman K.W. Allen 《Physics letters. [Part B]》1976,63(4):409-412
A cryogenically pumped gas target has been used to study resonances in the 15N(α, γ)19F reaction for Eα = 5.1 to 8.6 Mev. Gamma-ray intensity and angular distribution measurements for a resonance at Eα = 8.105 Mev, corresponding to a state at 10.411 MeV in 19F, restrict the spin and parity of the state to or . Comparison with shell model calculations indicate that the state is a strong candidate for the second (2s, 1d)3 level in 19F. 相似文献
2.
Moshe Moshe 《Physics letters. [Part B]》1981,98(4):297-300
Though high twist terms are becoming important as x→1, or equivalently, in large n moments, their detection in this regime in deep inelastic lepton scattering needs special caution. The high order terms in the twist two component are strongly dependent on n; one finds that at the perturbative expansion is invalid whereas higher twist terms are important at . Since grows very fast with n the necessary requirement for any deep inelastic phenomenological analysis, namely , cannot hold for too large moments. The scheme dependence of ak, αk and bk is also discussed. 相似文献
3.
Absolute cross sections are presented for the reactions 37Cl(α, γ)41K for 2.90 MeV ≦ Elabα ≦ 5.23 MeV, for energies near the (α, n0) threshold at , and for 64Ni(α, n)67N from Eαlab = 5.30 MeV up to Eα = 7.45 MeV. Substantial competition cusps were observed in the excitation function for all three (α, γ) reactions. The data were found to be in reasonable agreement with the predictions of the current versions of global Hauser-Feshbach models used in nucleosynthesis calculations. Including width fluctuation corrections and realistic neutron strength functions generally improves the ability of the models to predict the depth of the (α, γ) competition cusps; the depths of the predicted (α,γ) cusps are insensitive to the degree of isospin mixing. Taken together with studies of competition effects in proton-induced reactions, the present data confirm the importance of width fluctuation and strength function effects, and indicate essentially complete isospin mixing between T< and T> states in the compound nucleus. 相似文献
4.
Kentarou Kawaguchi Chikashi Yamada Yoshiaki Hamada Eizi Hirota 《Journal of Molecular Spectroscopy》1981,86(1):136-142
The fundamental bands of the CF radical in the and electronic states were observed by using an infrared tunable diode laser as a source. Zeeman modulation could be used in detecting lines not only in the state, but also in , because the CF radical deviates considerably from Hund's case (a). From the least-squares analysis of the observed spectra, the following molecular constants were obtained: Be = 1.416 704 (37) cm?1, αe = 0.018 419 (50) cm?1, , De = 6.68 (15) × 10?6cm?1, p0 = 0.008 580 (21) cm?1, p1 = 0.008 52 (11) cm?1, and , with three standard errors in parentheses. 相似文献
5.
We have obtained a least upper bound, , on the critical temperature Tc of an isotropic superconductor with paramagnetic impurities described by the scattering matrix t for fixed values of μ1. We have also obtained the corresponding optimal spectrum . The numerical results for the functions are presented for and 0.16 in the form of universal curves representing as functions of the reduced impurity concentration . We have also established an upper limit to the reduced critical concentration for an arbitrary shape of α2F(ω)1. 相似文献
6.
The predictions of perturbative QCD are derived in the deep euclidean region, whereas the physical region for most observables is timelike. The confrontation of these predictions with experiment thus necessitates an analytic continuation. This we find introduces large higher order corrections in terms of αs(|Q2|), the usual choice ofperturbative expansion parameter. These corrections are naturally absorbed by changing to the expansion parameter , where αs(Q2)n is the leading term in the spacelike region. For the intermediate range of Q2 experimentally accessible at present, where is significantly smaller than αs(|Q2|), we find the resulting phenomenology is improved. In particular, we demonstrate how the values of obtained from analyses of quarkonium decays become consistent. 相似文献
7.
The cyclotron resonance of inversion-layer electrons on (100)p-type Si is found to depend sensitively on an externally applied compressive stress. At low temperatures (T ? 10 K) we observe a considerable increase of the cyclotron mass m1c with stress S along the [001] direction. The effect is most strongly observed at low electron densities ns. For and ns~2 × 1011cm-2 we obtain instead of the expected 0.2m0. Along with this change of a strong narrowing of the resonance is noted. Raising the temperature gives an additional ns- dependent increase of . 相似文献
8.
Giorgio Calucci 《Nuclear Physics B》1980,175(1):165-174
Continuing a previous analysis, the divergence of the QED perturbative series for the anomalous magnetic moment is further investigated. Taking into account graphs with three photon lines, with electron-positron vacuum polarization, the leading behaviour, at the (2n+1)th perturbative order is found to be the type . Further possible generalizations are considered. 相似文献
9.
The microwave spectrum of MnO3F has been remeasured and several corrections and new results have been obtained: B0 = 4129.141 MHz, DJ = 1.12 kHz, DJK = 1.87 kHz; , , , |q5| = 16.005, and |q6| = 8.456 MHz. 相似文献
10.
We present approximate analytic calculation of the functional derivative , where Tc is the superconducting critical temperature and is the electron-phonon spectral function, within the “square-well model” for the phonon mediated electron-electron interaction and weak coupling limit is the Debye energy). It is found that where λ is the familiar electron-phonon coupling parameter and is a universal function of the reduced frequency . We compare this formula with accurate numerical results for several weak coupling superconductors. The overall agreement is good 相似文献
11.
Based on the proper connected diagram expansion, we calculated cyclotron resonance widths Γn associated with neighboring Landau states (n, n +1) for free electrons in interaction with more than one kind of impurities. In 3D usual Matthiessen's rule Γn=Γ(1)n+Γ(2)n+…where Γ(i)n represent widths calculated separately for each kind, is obtained. In 2D a new rule: is obtained. 相似文献
12.
The second derivative of current—voltage characteristic, , of a small orifice connecting two pieces of normal metals is shown to be proportional to the function at ω = eV, where F(ω) is the phonon density of states, and α̃2 (ω) the square of the electron—phonon matrix element averaged over the Fermi surface and multiplied by the additional structure factor taking into account the geometry of the orifice. The constriction is shown to work, in a current-carrying state, as a source of non-equilibrium phonons emitted in the immediate vicinity of the orifice. 相似文献
13.
Lifetimes of low-lying states in 19F were measured using the Doppler-shift attenuation method through the 15N(α, γ)19F reaction. Values of τm = 3700 ± 700 fs (1.35 MeV), 140 ± 15 (1.46), 19 ± 7 (4.00) and 63 ± 19 (4.03) were obtained for the lowest , , and members, respectively, of the rotational band and 5 ± 3 fs (1.55 MeV) and 370 ± 25 (2.78) for the and members of the ground-state band. For the Doppler-shift attenuation analysis correction factors of the nuclear and electronic stopping powers were determined by measuring the Doppler-shift attenuation and γ-ray line shape of the 2.78 → 0.20 MeV transition and range values of 100, 200. 300 and 370 keV 19F nuclei in tantalum. All calculations were done with Monte Carlo methods. The transition strengths are discussed in terms of different theoretical predictions. 相似文献
14.
A.H. Mueller 《Nuclear Physics B》1984,241(1):141-154
The order correction to the particle multiplicity ratio in gluon and quark jets is calculated in QCD. We find with r=〈n〉gluon jet/〈n〉quark jet. The method used is systematic and could be used for an order α(Q2) calculation. 相似文献
15.
C. Deutsch 《Physics letters. A》1983,94(1):40-41
The Holtzmark distribution for the thermal electric field at a neutral point in a two-dimensional and uncorrelated electron fluid is given by , with , and E0 = πnZpe in terms of the density n and perturber Zpe. 相似文献
16.
Metastable He2 molecules are produced by a dc discharge in a flowing He stream. Laser excitation downstream of the discharge produces excitation spectra for a number of He2 states. LIF spectra are observed for the series for n = 4–9, excepting 5 and the series for n = 5–15. 相似文献
17.
Evans M. Harrell 《Annals of Physics》1977,105(2):379-406
This is a perturbative analysis of the eigenvalues and eigenfunctions of Schrödinger operators of the form ?Δ + A + λV, defined on the Hilbert space L2(Rn), where , A is a potential function and V is a positive perturbative potential function which diverges at some finite point, conventionally the origin. λ is a small real or complex parameter. The emphasis is on one-dimensional or separable problems, and in particular the typical example is the “spiked harmonic oscillator” Hamiltonian, , where α is a positive constant. When this kind of perturbation is very singular, the first-order Rayleigh-Schrödinger perturbative correction, (u0, Vu0), where u0 is the unperturbed eigenfunction, diverges. This analysis constructs explicitly calculable terms in a modified perturbation series to a finite order, by using linear operator theory in concert with approximation methods for differential equations. Along the way a connection between a W-K-B type approximation and Bessel functions is exploited. 相似文献
18.
Excitation functions and angular distributions of the reactions and have b investigated for the excitation-energy region EX = 21?28 MeV in 8Be ( denotes the first excited state of the α-particle). pronounced resonant structure has been observed in both channels around EX = 24 MeV. It is excited simultaneously by odd and even angular momenta. The experimental results are discussed in the light of two models, the αα1 cluster model and the symplectic model which take into account the configuration interaction (core excitation) in different manners. 相似文献
19.
C.R. Leavens 《Solid State Communications》1976,19(4):395-397
The Eliashberg gap equations relate the transition temperature Tc of an isotropic superconductor to its electron-phonon spectral function α2F(ω) and Coulomb pseudopotential parameter . Recently the Eliashberg theory has been used to derive some supposedly rigorous results bearing on the problem of attaining higher superconducting transition temperatures: Bergmann and Rainer derived an expression for the functional derivative ; Allen and Dynes showed that in the asymptotic limit of very large and Leavens proved that for any isotropic superconductor kBTc ?0.2309A, where A is the area under its electron-phonon spectral function. In this letter we show that the result of Allen and Dynes is not compatible with the other results and is, in fact, incorrect. 相似文献
20.
Tadatsugu Hatori Tetsuo Kamimura Yoshi H. Ichikawa 《Physica D: Nonlinear Phenomena》1985,14(2):193-202
An analytical tool is given to study the statistical properties of the radial twist map, Xn+1 = Xn + α(Yn+1) and Yn+1 = Yn + Af (Xn), with arbitrary rotation number α(Y) and arbitrary periodic force f(X). The case for which f(X) = sin 2 πX and with arbitrary α is treated in the region of large A. The turbulent diffusion coefficient D for the chaotic orbit relaxes as to , except for the case of the standard map, where the eventual value of D is different from . 相似文献