共查询到20条相似文献,搜索用时 62 毫秒
1.
In the framework of the six-quark model, based on the gauge group SU(2)L × U(1) we have obtained expressions for the amplitudes of transitions at final 4-momenta of external lines Feynman box diagrams. We have estimated the correctness of using the approximation of extremely small 4-,omenta of valence quarks, composing K0-like mesons. The constraints for the parameters of the unitary matrix of weak charged currents have been found at arbitrary value of the t-quark mass. Estimates of numerical values for the mixing parameters and for the parameters of CP violation for neutral systems similar to are given. 相似文献
2.
Aluminum oxide layer dissolution was studied between 700 and 1200 K in the substrate areas of W〈111〉, Mo〈111〉, and on W{110} by means of FEM. Varying the electric field strength, F, between +45 and , two types of dissolution could be observed: dissolution by surface diffusion (low F's) and dissolution by ion desorption (high F's). It is assumed that aluminum suboxides — preferentially AlO — are involved in the dissolution processes. The preexponential factors, AF, of an Arrhenius-Frenkel type equation were measured as a function of F. The field dependence of AF is determined by the dissolution mechanism: (a) dissolution by diffusion: (μ molecular dipole moment, 1T ≡ isokinetic for W〈111〉, log A00 = ? 6.0 and ; for Mo〈111〉, log A00 = ? 3.1 and ; and (b) dissolution by ion desorption: ; for A+0 = ? 22 and ; for W〈111〉, log A+0 = ? 21 and . Using earlier proposed safeguards, isokinetic relationships (compensation effects) could be established for each of the two dissolution processes. The coordinates of the isokinetic points have the following average values: and for diffusion; and for ion desorption. The entropy changes (at , zero field strength, and unit pressure) for the phase changes: solid layer → diffusion layer and solid layer → ion gas, are of the order of · mol and · mol, respectively. The two dissolution mechanisms can be described by the following Arrhenius-Frenkel type equations: for diffusion and for ion desorption. 相似文献
3.
Takashi Tonegawa 《Solid State Communications》1981,40(11):983-986
The transverse spin pair correlation function pxn=<SxmSxm+n>=<SxmSxm+n> is calculated exactly in the thermodynamic limit of the system described by the one-dimensional, isotropic, spin-, XY Hamiltonian . It is found that at absolute zero temperature (T = 0), the correlation function ρxn for n ≥ 0 is given by , , where the plus sign applies when J is positive and the minus sign applies when J is negative. From these the asymptotic behavior as n → ∞ of |?xn| at T = 0 is derived to be with a = 0.147088?. For finite temperatures, ρxn is calculated numerically. By using the results for ?xn, the transverse inverse correlation length and the wavenumber dependent transverse spin pair correlation function are also calculated exactly. 相似文献
4.
Ernest Ma 《Physics letters. [Part B]》1981,100(3):251-253
It is proved that the standard SU(2) × U(1) electroweak gauge model is unique against any extension if the effective low-energy neutral-current interaction is to be precisely of the form naturally. 相似文献
5.
B. Fant T. Weckström T. Lönnroth C.J. Herrlander K. Honkanen A. Källberg 《Nuclear Physics A》1984,429(2):296-312
Levels in 208At were populated in the 209Bi(α, 5n) reaction, and the subsequent radiation was studied using γ-spectroscopic methods including γ-ray excitation function and angular distribution, γγ(t) coincidence and γt measurements, as well as measurements of conversion electrons. The excited spectrum of 208At is found to consist of two almost disconnected parts which are proposed to originate from seniority-three proton and neutron cascades. Two isometric states are observed. A state at 1090 keV is proposed to have the main configuration and Jπ = 10?. A high-spin isomer with is assigned to be the state. Shell-model arguments are used to assign configurations to most of the observed levels. Transition rates are discussed. 相似文献
6.
It is shown explicitly for a soluble model that a random spin system can have an entropy which is non-analytic at (H = 0, T = 0), with and/or non-vanishing in the T → 0 limit, while nevertheless Nernst's law is satisfied. 相似文献
7.
8.
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
9.
The time dependence of microwave absorption was measured for the J = 2-1 and J = 3-2 transitions of OCS under on- and off-resonant conditions utilizing Stark and source modulation, respectively. The two effective pressure parameters obtained under the two conditions, which correspond to and , respectively, according to the Bloch equation, are different beyond experimental error; the difference is 0.94 ± 0.38 (2.5σ) MHz/Torr for J = 2?1. This difference was also determined to be 1.19 ± 0.30 MHz/Torr from the dependence of the nutation frequency on the microwave power. 相似文献
10.
M. Fähnle 《Journal of magnetism and magnetic materials》1978,8(4):330-332
Within the framework of a perturbation theory and a quasicrystalline approximation we have solved the linearized equation of motion for the circular spin component S+j = Sxj + iSyj in a one-dimensional amorphous ferromagnet with periodic external excitation of the spin S+0 at site j = 0. It is shown that localized spin modes of the simple form with fall-off-length κ-1 are solutions of the ensemble-averaged equation of motion. On the other hand, we have a damping of extended spin waves according to exp(-Γt). A simple relation is derived between the fall-off-length κ-1 of localized spin modes and the damping factor Γ of extended spin waves. Analogous results hold for phonons in amorphous materials. 相似文献
11.
12.
H. Hasegawa 《Solid State Communications》1981,38(5):401-404
We discuss a pair approximation of the spin fluctuation theory, which is an extension of the single-site theory proposed by the present author and can include the effect of the short-range magnetic order (SRMO). Numerical calculations of b.c.c. iron show that SRMO for neighbouring sites j and l, , is about 0.21–0.14 at . This is considerably smaller than the value (Γ~0.8) proposed by Korenman, Murray and Prange for an analysis of sloppy spin waves of iron, while it coincides with the value (Γ≌0.12–0.18) given by Shastry, Edwards and Young with the use of the spherical Heisenberg model with exchange interactions extending to far nearest neighbours. 相似文献
13.
The linearized Fokker-Planck operator reads . The first term is rather simple, but the second one is very complicated. A much simpler - though exact - form of C(f0j, f1k) is proposed, for a special class of f1k occuring in diffusion theory. 相似文献
14.
The influence of self-fields on the equilibrium and stability properties of relativistic beam-plasma systems is studied within the framework of the Vlasov-Maxwell equations. The analysis is carried out in linear geometry, where the relativistic electron beam propagates through a background plasma (assumed nonrelativistic) along a uniform guide field , It is assumed that for the beam electrons (ν is Budker's parameter, and γ0mc2 is the electron energy), but no a priori assumption is made that the beam density is small (or large) in comparison with the plasma density, or that conditions of charge neutrality or current neutrality prevail in equilibrium. It is shown that the equilibrium self-electric and self-magnetic fields, and , can have a large effect on equilibrium and stability behavior. Equilibrium properties are calculated for beam (j = b) and plasma (j = e, i) distribution functions of the form fb0(H, Pθ, Pz) = F(H ? ωrbPθ) × δ(Pz ? P0)(j = b), and (j = e, i), where H is the energy, Pθ is the canonical angular momentum, Pz is the axial canonical momentum, and ωrj (the angular velocity of mean rotation for j = b, e, i), Vj (the mean axial velocity for j = e, i), and P0 are constants. The linearized Vlasov-Maxwell equations are then used to investigate stability properties in circumstances where the equilibrium densities of the various components (j = b, e, i) are approximately constant. The corresponding electrostatic dispersion relation and ordinary-mode electromagnetic dispersion relation are derived (including self-field effects) for body-wave perturbations localized to the beam interior (r <Rb). These dispersion relations are analyzed in the limit of a cold beam and cold plasma background, to illustrate the basic effect that lack of charge neutrality and/or current neutrality can have on the two-stream and filamentation instabilities. It is shown that relative rotation (induced by self-fields) between the various components (j = b, e, i) can (a) result in modified two-stream instability for propagation nearly perpendicular to , and (b) significantly extend the band of unstable kz-values for axial two-stream instability. Moreover, in circumstances where the beam-plasma system is charge-neutralized but not current-neutralized, it is shown that the azimuthal self-magnetic field has a stabilizing influence on the filamentation instability for ordinary-mode propagation perpendicular to . 相似文献
15.
In this note we prove the following theorem. If in a flat space-time with metric gij(x) treferred to general coordinates xi a vector ξi(x) satisfies (Tijξj);i=0 (semicolon denotes covariant differentiation) for all energy-momentum tensors of the set ; Tij = Tji; Tijuiuj > 0 (where ui is a time-like vector)}, then the vector ξi defines a conformal motion. This theorem, which may be considered as a converse (in flat space-time) to a well-known result of Trautman, is a generalization of a result obtained by J. T. ?opuszański and J. Szczucka-Soko?owska [Reports on Mathematical Physics 11 (1977), 153] in which they assumed the vector ξi was a polynomial in Minkowski coordinates. 相似文献
16.
A.D. Krisch 《Physics letters. [Part B]》1973,44(1):71-75
The model assumes that when two high energy particles collide each behaves as a geometrical object which has a Gaussian density and is spherically symmetric except for the Lorentz-contraction in the incident direction. Folding the two spatial distribution together we obtain the slope (b) of the elastic diffraction peak in terms of the c.m. velocities (βi and βj) and the sizes (Ai and Aj) of the two incident particles. These sizes are assumed to have the experimental s-dependence of σtot ∝ πA2 for each reaction. The combined s-dependence of the σtot's and the β's gives the s-dependence of the elastic slope . This formula agrees with the experimental slope for p-p, -p, K+-p, K?-p and π±-p elastic scattering from 3 to 1500 GeV/c, with only 3 parameters: Aπ2 = 6.1, AK2 = 3.3 and Ap2 = 10.5 (GeV/c)?2. 相似文献
17.
We investigate the structure of phenomenological supergravity models which permit the hierarchy problem to be “solved” in the sense that and mW are determined dynamically to be exp [-O(1)/α] × mP. Such models must have a flat hidden sector potential, which is only possible if the theory has an underlying SU(1, 1) invariance. Flat SU(1, 1) theories necessarily have a zero cosmological constant and the hidden sector is an Einstein space with . The SU(1, 1) invariance is necessarily broken down to U(1) by the gravitino mass. If is the only source of SU(1, 1) breaking then the tree-level gaugino masses are small and , while values of A up to 3 and non-zero gaugino masses are possible if other sources of SU(1, 1) breaking are tolerated. Yukawa couplings may scale as some power of in these models where is generated dynamically, which may explain the hierarchy of Higgs-fermion Yukawa couplings: ? These models also permit the spontaneous violation of CP in the Yukawa coupling matrix. Numerical studies yield 20 GeV < mt < 100 GeV in these phenomenological SU(1, 1) supergravity models. Speculations are presented about their relation to a fundamental theory based on extended supergravity. 相似文献
18.
We suggest that the properties of decoupled bands associated with high -j single-particle orbitals are similar to those of bands associated with orbitals. Special attention is focussed on the so-called antialigned states. As an illustrative example we have studied the bands in 19F and 23Na, where the level energies and electromagnetic transition rates are evaluated in a simple weak-coupling model. 相似文献
19.
A simultaneous analysis of low-energy (W ? 2 GeV) data for the reactions π?p→ KOΛ and K?p → πOΛ has been made using the hypothesis of two-component duality combined with fixed-t dispersion relations. Results are presented for the and couplings. The low-energy amplitudes are used to evaluate FESR integrals and lead to large EXD breaking for the helicity flip amplitudes. 相似文献
20.
L Nemes 《Journal of Molecular Spectroscopy》1978,72(1):102-123
Medium resolution infrared grating spectra of gaseous ketene, H2CCO were recorded between 1000 and 400 cm?1, both at instrument temperature (40°C) and with cooling (?40°C). Interferometric Fourier spectra were also measured at ?70°C with resolution 0.22 cm?1 between 450 and 330 cm?1. The K structure of the fundamentals ν5, ν6, ν8, and ν9 was assigned. These fundamentals are coupled by a-axis Coriolis interactions. These couplings were analysed on the symmetric top basis for setting up the perturbation matrix and by utilizing the K-dependent Coriolis shifts of levels. A preliminary analysis of the Coriolis intensity anomalies was also undertaken.Band center values from combination differences are and . Synthetic spectra indicate the band origins of ν8 and ν9 to be close to 977.8 and 439.0 cm?1, respectively. Estimates of Coriolis coupling constants obtained from synthetic spectra are , , , and . Approximate ratios of unperturbed vibrational transition moments obtained from spectral simulations are . 相似文献