Influence of temperature and humidity on the creep of polymeric materials. 4. Prediction on the basis of field test results

Conclusions Comparison was made of the results of prolonged (from 2 to 6 years) control experiments of tubular specimens of PN-3 for creep during tension, torsion, and simultaneous tension and torsion under various temperature-humidity conditions with calculation based on data of short-term (up to 5 h) experiments, in which the creep process was accelerated by increase in temperature and humidity of the material. Calculation of the prolonged creep deformations expected was done from the relationships of viscoelastic properties of a linearly changing solid, generalized for the case of influence of temperature and humidity under the assumption that the volume changes only elastically. On the basis of this generalization, adherence to the temperature-humidity-time analogy is assumed to be experimentally confirmed. Satisfactory agreement of results of prediction and prolonged control experiments is established.For communication 3 see [3].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 982–987, November–December, 1976.     

Low-field peak effect in type II superconductors

The combined effect of a surface (edge) barrier and volume pinning on the dependence of critical current I _c on the magnetic field (I⊥H ₀) in bulk type II superconductors is investigated. In low magnetic fields, there is a portion of the curve I _c(H ₀) where I _c grows with H ₀, causing a nontrivial peak effect in this field range. Such behavior is explained by the combined effect of a surface (edge) barrier and volume pinning, the latter being rather sensitive to the transport current density distribution in a superconductor.     

On the Hall effect in a two-dimensional doped antiferromagnet

The conductivity and the Hall coefficient of a doped 2D antiferromagnet in the normal state are considered using the Kondo lattice model in the multimoment approximation. The anomalous temperature dependence of the kinetic coefficients is explained by the strong anisotropic charge-carrier scattering from the spin subsystem and found to be in qualitative agreement with the experimental data for the normal state of high-T _c superconductors.     

Anomalous tunneling of phonon excitations between two Bose-Einstein condensates

We discuss the tunneling of phonon excitations across a potential barrier separating two condensates. It is shown that a strong barrier proves to be transparent for the excitations at low energy epsilon. Moreover, the transmission is reduced with increasing epsilon in contrast to the standard dependence. This anomalous behavior is due to the existence of a quasiresonance interaction. The origin of this interaction is a result of the formation of a special well determined by the density distribution of the condensate in the vicinity of a high barrier.     

Calculation of the molten pool depth in vacuum arc remelting of alloy Vt3-1

This paper is devoted to a simple heat model of vacuum arc remelting (VAR) including the solution of a nonlinear heat conduction equation with nonlinear boundary conditions typical for VAR. A finite-difference analog of the model’s initial equation is obtained by the finite-volume method. The system obtained is solved by a two-cyclic scheme of component-wise splitting. A simplified model neglecting the magnetohydrodynamic phenomena in the molten pool is tested by comparison of the results of numerical calculations of the pool depth in remelting of the Russian titanium alloy Vt3-1 (Ti-6.5Al-2.5Mo-1.5Cr-0.5Fe-0.3Si) with the results of radiographic experiments. It has been shown that the model fits the experimental data well under various remelting conditions (the ingot diameter and operating current intensity).     

Ab initio calculations of the physical properties of transition metal carbides and nitrides and possible routes to high-<Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> superconductivity

We report ab initio linear-response calculations of the phonon spectra and the electron-phonon interaction for several transition metal carbides and nitrides in a NaCl-type structure. For NbC, the kinetic, optical, and superconducting properties are calculated in detail at various pressures and the normal-pressure results are found to agree well with the experiment. Factors accounting for the relatively low critical temperatures T _c in transition metal compounds with light elements are considered and the possible ways of increasing T _c are discussed. The text was submitted by the author in English.     

Lattice dynamics and ferroelectric instability in ordered and disordered PbSc<Subscript>1/2</Subscript>Ta<Subscript>1/2</Subscript>O<Subscript>3</Subscript> and PbSc<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>O<Subscript>3</Subscript> solid solutions

The dynamic Born charges and the frequency spectra of lattice oscillations in the crystals of ordered and disordered PbSc_1/2Ta_1/2O₃ (PST) and PbSc_1/2Nb_1/2O₃ (PSN) solid solutions have been calculated within the framework of the generalized Gordon-Kim model with allowance for the dipole and quadrupole polarizabilities. The phonon spectra of both compounds contain ferroelectric soft modes. The influence of various interactions on the magnitude of dynamic charges and ferroelectric instability in PSN and PST solid solutions has been studied and it is shown that both these charges and the ferroelectric instability are determined by the competition between long-range dipole-dipole interactions and short-range dipole-charge interactions, the determining role played by the interaction of Nb (Ta) cations and oxygen anions in the Nb-O (Ta-O) bond direction.