Antimirror Reflection of a Bounded Planar Optical Waveguide: the String Model

The effect of antimirror reflection from a bounded planar optical waveguide is considered. Earlier, it was used for observing the slow light in a Bragg waveguide. Using the proposed theory of this effect, experimentally observed spectral (Gaussian line shape) and angular (Lorentzian angular distribution) properties of the radiation scattered by the bounded waveguide in the antimirror direction are interpreted.     

A theory of excitation of a planar semiconductor optical waveguide using a diffraction grating: Single-scattering approximation

The problem of excitation of a totally reflecting planar optical waveguide using a coupling diffraction grating in the form of a periodic relief of the waveguide-layer thickness is solved within the single-scattering approximation. The polariton mode in the presence of a quantum well near the waveguide is considered. Based on the developed concepts, the following experimental features of the dependence of the intensity of radiation conducted in the waveguide layer on the angle of incidence of the excitation beam on the coupling diffraction grating are interpreted: the dependence on the mode number, the interference effects in the presence of two coupling diffraction gratings, and the influence of the lower substrate boundary on the thermal behavior of the waveguide structure.     

Multineutron photodisintegration of the 197Au nucleus behind the giant dipole resonance

An experiment in which the gold isotope ¹⁹⁷Au was irradiated with a beam of bremsstrahlung photons having an endpoint energy of E _γ ^m = 67.7 MeV and originating from the RTM-70 racetrack microtron of the Institute of Nuclear Physics at Moscow State University was performed. The gammaray spectra of the residual beta activity of an irradiated sample were measured. Multinucleon photonuclear reactions on ¹⁹⁷Au nuclei were observed in the experiment. Photonuclear reactions on a ¹⁹⁷Au nucleus that involve the emission of up to seven neutrons were recorded for the first time. The experimental results in question suggest the important role of the quasideuteron photodisintegration mechanism in the energy region behind the giant dipole resonance.     

Localized superconductivity and Tamm states

We consider the phenomenon of localized superconductivity (LS), the local raising of temperature of superconductivity transition near a planar imperfection and the surface of a metal. We find a condition for the existence of LS depending on the density of the states on the Fermi surface. We show that the presence of Tamm states is sufficient for LS to occur.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 150, pp. 37–47, 1986.     

Functional representation of the partition function and phase transitions in the Hubbard model

The functional representation of the partition function for the Hubbard model with strong Coulomb repulsion is obtained in the form of an integral with respect to auxiliary Grassmann variables. The approximate study of the phase transitions shows:

1. for a small doping constant δ, the system is an antiferromagnetic dielectric;
2. for δ≥t/V, the system is a ferromagnetic metal if U/t>10 and superconducting metal if U/t? 10. Bibliography:13 titles.

     

Photonuclear reactions on molybdenum isotopes

The results of experimentally and theoretically studying the photodisintegration of molybdenum isotopes are presented. The yields of various photonucleon reactions on stable molybdenum isotopes were determined by the gamma-activation method. Use was made of bremsstrahlung photons from an electron accelerator that were characterized by the endpoint energies of 19.5, 29.1, and 67.7 MeV. Reactions involving the emission of up to three nucleons from the target nucleus were observed. The experimental results in question were compared with theoretical predictions based on the combined photonucleon-reaction model and obtained for 15 molybdenum isotopes. The relations between basic photonucleon reactions on the molybdenum isotopes considered in our present study were explained.