共查询到20条相似文献,搜索用时 31 毫秒
1.
A formula at low temperature for the function G() = Iλλ6 has been derived in terms of configuration curve theory and checked on luminescence spectra near 77 K. The vibrational quantum in the excited state has been calculated from the decrease of G(), where λM is the wavelength of the maxima of G at low temperature, as a function of temperature. 相似文献
2.
R.I. Joseph 《Physics letters. A》1976,56(1):1-2
We consider the spin-S Hamiltonian where QS(y) is a polynomial in y of degree 2S whose eigenvalues are ±1 and rigorously show that except for a multiplicative constant, the partition functions for all half-integer values of S are identical. 相似文献
3.
We calculate the effective electron-hole interaction Vre in the presence of an exciton gas, which reads in real space: The parameters Ci and Zi are given explicitly for GaAs. For this material, we show the binding energy of the exciton is weakly modified so long as . (R0, exciton Rydberg, a0 exciyon radius, ?ex exciton density, T temperature). 相似文献
4.
To investigate dynamical (time-dependent) behavior of spins and spin clusters in the two-dimensional ± J Ising spin-glass, we have evaluated the relaxation time τi of individual spins by the Monte Carlo simulation. An interesting finding is that, at least in the temperature range , most of τi are described by with T0?0.5J (Ei being a constant), which suggests that the system undergoes a glass transition obeying Fulcher's law. 相似文献
5.
H. Kleinert 《Physics letters. A》1983,96(6):302-306
We show that defect melting involving dislocations and disclinations is dually equivalent to an extension of an XY model with an energy of the type Σi, j{[cos(?iuj + ?jui) + ? cos ?iωj] }, where is the local rotation field. The. model clarifies the proper choice of defect core energies arising from nonlinear elasticity. These permit the pile-up of dislocations to disclinations which is essential for the first order of the melting transition. 相似文献
6.
7.
Eugene Feenberg 《Annals of Physics》1973,81(1):154-164
A set of normalized linearly independent basis functions φ1, φ2, …, φj, … generates matrix representatives and of the Hamiltonian operator and the identity. An orthonormal basis , , …, , … generated by a Löwdin transformation is characterized by the distance in Hilbert space between and φj. The choice of positive definite minimizes these distances and maximizes the diagonal elements of . Again for positive definite and a finite basis, 1 ? j ? p, the analysis yields a general theorem on Trace (? p for all positive and negative integral values of n except n = ?1 and ? p for n = ?1).Sufficient conditions are determined which permit the application of the binomial theorem to the evaluation of the transform of . Approximate formulas for the energy eigenvalues through third order in nondiagonal matrix elements are presented in a compact form containing characteristic nonorthogonality corrections depending on the exterior or interior location of the matrix element in the perturbation formulas. 相似文献
8.
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
9.
Etude des proprietes thermodynamiques d'un groupement tetranucleaire: Application au compose Na3RuO4
The exact eigenvalues spectrum of the spin hamiltonian have been calculated for a tetranuclear cluster formed by four spins 3/2 at the vertices of a lozenge. Two isotrope exchange interactions J1 and J2 are able to explain the thermodynamic properties (magnetic susceptibility, entropy, specific heat). A ground state transition from singlet to triplet state occurs when the ratio reaches the value . The magnetic susceptibility data of Na3RuO4 fit well with the theoretical values proposed for and J2/k (?22,5 K). 相似文献
10.
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
11.
Masaki Yasuè 《Nuclear Physics B》1984,234(1):252-268
The masses of composite leptons and quarks are discussed in a “dynamical subquark model of pregauge interactions”. In this model, the leptons and quarks are made of a spinor and scalar subquark with equal mass, M, and the gauge bosons and Higgs scalar of the SU(3)c×SU(2)L×U(1)Y model are made of a subquark-antisubquark pair. The SU(2)L×U(1)Y symmetry is spontaneously broken by the composite Higgs scalar and the (scalar) subquark mass parameter is in turn bounded as is the Fermi coupling constant). The spontaneously generated mass of a lepton or quark, mi(n) (i = 1, 2; n = 1 ~ Ng), is calculated to be: are the parameters satisfying that 0 ? ri(n) ? 1 and Σ (ri(n))2 = 1;Ng is the total number of generations of the leptons and quarks; αe.m. is the fine structure constant. The appearance of light composite fermions is related to a specific mechanism of generating global chiral symmetries of the leptons and quarks. Global symmetries of scalar subquarks yield chiral symmetries of the leptons and quarks. Our model turns out to satisfy 't Hooft's anomaly conditions on massless composite fermions. 相似文献
12.
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
13.
Richard Brower 《Nuclear Physics B》1981,190(4):699-718
In lattice gauge theory, many computations such as the strong coupling expansions, mean field theory, or the few plaquette models require the evaluation of the one-link integral in the presence of an arbitrary N × N complex matrix source (J). For SU(N) gauge theories, we express our general solution to the external field problem as an integral over the maximal abelian subgroup [U(1)]N?1 where S0 = 2Σkzk cos(φk ? θ), zj are eigenvalues of √JJ+, e2iNθ=detJ/detJ+, and G is an appropriate jacobian determinant. Our explicit solution follows from differential Schwinger-Dyson equations cast in a separable form by using fermionic variables, and the special cases of N = 2, 3 and ∞ agree with earlier derivations. 相似文献
14.
G.P. Srivastava 《Physics letters. A》1973,45(4):321-322
Anharmonicity in lattice potential leads to boundedness of the eigenvalue Spectrum of the phonon collision operator. Considering the deviation, ψq, in the distribution function of the phonons . bar denoting equilibrium value, as an odd function of the phonon wave vector q it has been possible to obtain a lower bound, μ, on the eigenvalue spectrum of the phonon collision operator P. This satisfies the inequelity relation 0?μ?pi?λ, where pi are the eigenvalue of P, and λ is an upper bound on it (as given by Benin). The occurence of μ ensures for the possibility of obtaining a sequence of upper bounds on the lattice thermal transport coefficient. 相似文献
15.
The usual condition for static balance, for two bodies with masses and charges mi and ei (i = 1, 2), is . From a post-Newtonian analysis of the two-body problem, an alternate condition for static balance has been found. We do not know if this condition is exact beyond the post-Newtonian approximation. 相似文献
16.
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
17.
In order to get dipole-moment derivatives, that are free from rotational contributions, we used Crawford's method applied to a new type of reference molecule. The agreement with earlier calculated rotational correction terms is good, the applicability of the new reference molecule is wider. The rotational contributions to the -quantities are presented for a number of C2v- and C3v-type molecules. 相似文献
18.
The temperature dependence of the field emission flicker noise spectral density functions has been investigated for potassium adsorbed on tungsten (112) planes by a probe hole technique. By integration of the spectral density functions the noise power for different frequency intervals Δ? is obtained. From the exponential temperature dependence of noise power “activation energies” qΔ? are determined. Plots of these energies versus coverage show a similar “oscillating” behaviour as recently found for or which indicates phase transitions of the adsorbed potassium submonolayers. The noise activation energies are discussed in terms of existing models and a comparison is made between the experimental q values and surface diffusion energies Ed as determined by conventional methods. 相似文献
19.
M.D. Pollock 《Nuclear Physics B》1982,208(1):182-188
It is known that a scalar field that is non-minimally coupled to the geometry implies a varying gravitational “constant” Geff, and hence a violation of the continuity equations, , where is the uncorrected energy-momentum tensor. This in turn upsets classical thermodynamics. 3he simplest resolution of this difficulty is to multiply all energetic quantities by , where GN is the newtonian gravitational constant. This modified thermodynamics is applied to the scalar-field version of the cosmological model of Zee, for which it is shown to cause restoration of the symmetry above some critical temperature Tc close to the Planck temperature. We also illustrate how the second law of thermodynamics is always obeyed, correcting a recent discussion by Davies. 相似文献
20.
H. Falk 《Physica A》1980,104(3):475-479
The (discrete-time) Glauber model is considered for a one-dimensional system of spins sj = ±1 with nearest-neighbor Ising interaction . The Jj = ±J are treated as random variables with an arbitrary joint probability p(J). The exact time-dependent average 〈sj〉t is determined, and from it the “quenched” average is explicitly found. 相似文献