In this paper we try to show how a reasonable equation for crack propagation in brittle materials naturally leads to self-affine or statistically self-similar failure structures. We argue that the fractal behaviours of crack propagation in brittle mate-rials are in essence determined by the scale-invariance of the Fokker-Planck equation. This approach provides a good illustration for understanding the microscopic origin of fractal behaviour in real materials.

With the help of a model calculation, the following features in the multiphoton detachment rate spectrum of negative ions are shown: (1) the global behavior of the rate, as a function of the photon frequency, does follow the so-called ‘step-like' pattern; (2) a Wigner-type cusp occurs at every threshold open for the lower photon number channel; (3) a clear dip appears at a certain frequency point slightly lower than each threshold frequency. All these features are interpreted as the general characteristics of multiphoton detachments on the R-matrix-Floquet analysis. Comparisons are made with the previous results. To the best of our knowledge, the third feature may be for the first time explained in this paper, though it is not first found by us.

In this paper, based on Maxwell's equations and boundary continuity condi-tions of electromagnetic fields, we derive rigorous vector coupled-wave equations of two-dimensional diffractive patterns for an arbitrary polarization in the resonance domain, and describe the solution to these equations. We verify this theory with a practical example, and show the effectiveness of this method for the resonance-domain diffractive optics.

The transmission of rapidly phase modulated signal beams in photorefractive two-wave mixing is studied theoretically. The analytical expressions of output intensities are given both in diffusion regime and in drift regime.

We report the observations of the decay processes of light-induced absorption in one undoped and two Ce-doped BaTiO_{3} crystals. Two decay times were found, they had not a strong dependence on intensity in our experiment. We present a model with two different shallow trap centers to explain the experimental results. The theoretical and experimental resales agree well with each other. The light-induced absorption coefficients and decay times corresponding to the two shallow levels are also given.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Based on Born's criteria we studied phase stability and theoretical strength of fcc crystals of copper and nickel under [100] uniaxial loading. The calculation was carried out using a simple and completely analytical embedded atom method(EAM) potential proposed by the present authors. For Cu, the calculated value of its theoretical strength (0.33×10^{11} dyn·cm^{-2}) agrees well with the experimental value (0.30×10^{11} dyn·cm^{-2}), while the calculated strain (9.76%) is somewhat larger than the experimental one (2.8%). For Ni, its theoretical strength and strain predicted using the EAM potential are found smaller than those predicted using a pair potential. It is worthy to note that unlike previous calculations, in which pair potentials were used and three unstressed fcc, bcc, and fct structures included (for Ni only fcc state is found stable, while for Cu both fcc and bcc states are predicted stable), in present calculations using EAM potential the [100] primary loading path passes through only two zeroes (a stable unstressed fcc structure and an unstable stress-free bcc structure) either for Cu or for Ni.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

By using the well known slave-boson technique and within the framework of mean field approximation, we study the effect of the direct f-f hopping on the low-temperature hybridization gap insulating behavior of the periodic Anderson lattice. The results show that the direct f-f hopping will decrease the hybridization gap or lead it to vanish. In the latter case, the lattice will exhibit no hybridization gap insulating behavior even if the lower renormalized band is fully occupied.

The assembly for EMF measurement with CaF_{2} single crystal or MgO partially stabilized zirconia as solid state electrolyte has been constructed. From the EMF data, the standard Gibbs energies, standard enthalpies of formation and standard entropies of sir complex oxides in the Sm-Ba-Cu-O system were calculated. The decomposition pressures of these complex oxides were derived.

In this paper the quantum size effect in giant magnetoresistance of magnetic superlattices is studied. The electrons are considered to be confined in a set of quantum wells, which are different for the ferromagnetic and antiferromagnetic ordering in magnetic superlattices. The oscillation of giant magnetoresistance with increasing thickness of the nonmagnetic spacer layer is explained. It is shown that the influence of quantum size effects on the giant magnetoresistance of magnetic superlattices is considerable.

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