Decay of tripositronium to an electron and two photons

The bound state of a positron and two electrons, called tripositronium, is investigated in this article. The differential probability is calculated for the decay of the ground state of tripositronium to an electron and two photons. It is established that such a decay primarily occurs with the formation of a nonrelativistic electron. It is shown that the integral decay probability is equal to 0.15 · 10⁹ sec^–1. This corresponds to a lifetime for tripositronium of 0.65 · 10^–8 sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedeoii, Fizika, No. 4, pp. 69–73, April, 1978.The author thanks V. S. Vanyashin for formulating the problem and for useful discussions.     

One-dimensional anisotropic magnet in the long-wavelength approximation

The nonlinear equation for the wavefunction of spin excitations in the long-wavelength approximation possessing a soliton-like solution is obtained by means of an exact transition from Pauli operators to Fermi operators.     

Determination of size and concentration of critical clusters of silicon carbide in the vapour phase in homogeneous nucleation process

The concentrations of clusters of various size in the atmosphere during silicon carbide crystal growth have been calculated on the basis of fundamental ideas of homogeneous nucleation theory, taking into account the specific parameters of silicon carbide. It has been shown that the cluster concentration are sufficiently high to conclude that this is the dominant influence during the initial stages of crystal growth. In this way the assumption of the polymer theory of polytypism, namely that the polytype properties of silicon carbide can be determined from the composition of the gas phase, containing sufficiently large clusters with various polytype structures, has been confirmed.     

Bending strength of oriented glass-reinforced plastics

The authors consider the effect of the low shear strength and shear stiffness of oriented glass-reinforced plastics (GRP) on the stress distribution and type of failure in bending. On the basis of relations obtained in [1] it is shown that the effect of shears on the magnitude and law of distribution of the normal and shear stresses is important only for very short beams made of materials with a low shear stiffness. An experimental study of the nature of failure in bending has revealed that the chief cause of extension of the region of shear failure of oriented GRP is the low shear strength of the material, and has made it possible to establish the limits of this region for three typical materials. Anisotropy of the elastic properties has little effect on the type of failure in bending.Mekhanika Polimerov, Vol. 2, No. 4, pp. 535–542, 1966     

Investigation of the spectral and angular distribution of gamma radiation of ultrarelativistic electrons in crystals

A technique and experimental apparatus are described for measuring the properties of radiation from relativistic electrons in crystals as a function of frequency and angle. The results of these measurements are compared with calculations and with the results obtained by other workers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 54–62, June, 1991.     

A study of the propagation of a quasistationary relativistic electron beam in a dense gas. II. Experimental studies

Results obtained from experimental studies of the interaction between a quasistationary electron beam (300 keV, 20 A, 500 sec, 0.3 cm) and a dense gas are presented. These investigations were carried out in air at atmospheric pressure and, for the purpose of modeling the propagation of a magnetostricted REB, at reduced pressure (3–300 torr). The rarefaction dynamics of a channel heated by the beam are studied and its maximum propagation distances in a dense gas are determined. The results obtained are compared with the theoretical model examined earlier.V. I. Lenin All-Union Institute of Electrical Engineering. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 2, pp. 190–197, February, 1991.     

Gravitational field of a family of SU(5) dyons

By solving the coupled SU(5) Einstein-Yang-Mills-Higgs equations, we obtain the exact Reissner-Nordstrom type gravitational field of a family of spherically symmetric SU(5) dyons with magnetic charge 1/2e.     

High energy spin dynamics of La2CuO4 and La1.9Sr0.1CuO4

The magnetic excitations in La₂CuO₄ and La_1.9Sr_0.1CuO₄ were studied by inelastic neutron scattering up to energies of 76 meV. For the pure sample, the results forE15 meV can be well described by conventional spin wave theory with a spin wave velocity c=0.89±0.07 eVÅ. For lower energies, the observed intensities were somewhat higher than expected from spin wave theory and did not follow the Bose-Einstein factor. For the doped sample, the linewidth in constant-E scans at smallE shows a very short correlation length of =7.5 Å only, which is considerably below the value expected from the concentration dependence reported by other authors. An increase of the linewidth for largeE indicates a reduced spin-wave stiffness when compared to the undoped material. However, the use of a spin-wave picture may not be appropriate as the standard expression for damped spin waves in a paramagnetic material is in serious conflict with experiment.