On the number of relaxation regions in polyformaldehyde

The mechanical relaxation of a polyformaldehyde homopolymer free from surface grease and the additives normally used as stabilizers has been studied at a frequency of 10^–2 Hz in the temperature region 77–413°K. Six relaxation regions are observed on the curve of tangent of angle of mechanical losses as a function of temperature.T. G. Shevchenko Kiev State University. Translated from Mekhanika Polimerov, No. 5, pp. 925–927, September–October, 1973.     

Effect of supermolecular structure on the relaxation properties of polyformaldehyde in tension and compression

An experimental investigation of the stress relaxation at various strain values in polyformaldehyde blocks has revealed two regions with different stress relaxation mechanisms. The effect of the supermolecular structure on each of these regions is discussed.Scientific Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 787–792, September–October, 1969.     

Some physicomechanical properties of polyformaldehyde (acetal resins)

A method of testing polyformaldehyde (acetyl resin) film has been developed. Comparative tests have been carried out on the homopolymer and trioxane-dioxolan copolymer. Certain physicomechanical characteristics of these polymers have been obtained.Mekhanika Polimerov, Vol. 3, No. 5, pp. 812–820, 1967     

Effect of temperature on the chemical relaxation process in rubbers

The effect of temperature on the chemical relaxation of rubbers has been investigated. With reference to nine industrial rubbers it has been shown that during storage in the stressed state (at =const) chemical relaxation is chiefly determined by two processes proceeding at different rates. Furthermore, the chemical relaxation of rubbers is determined not only by the rate constants of these two processes but also by the pre-exponential constants C_0i, the relationship between which varies with increase in temperature. It is possible to extrapolate the rate constants (k_i) and pre-exponential constants (C_0i) from elevated temperatures (110–50° C) to temperatures in the range 20–25° C. An equation is proposed that makes it possible to calculate the change in the elastic properties of rubbers in the stressed state at storage temperatures (20–25° C) by means of results obtained at elevated temperatures.Mekhanika Polimerov, Vol. 3, No. 3, pp. 448–454, 1967     

Effect of molding conditions on the structure and properties of polyformaldehyde

The effect of molding conditions-melt temperature, dwell time in molten state, and cooling rate-on the structure and mechanical properties of polyformaldehyde is investigated.Mekhanika Polimerov, Vol. 3, No. 5, pp. 782–786, 1967     

Investigation of the supermolecular structure of polyformaldehyde in an injection-molded block

The process of variation of the spherulitic and "superspherulitic" structure in an injection-molded block of polyformaldehyde has been investigated as a function of the molding conditions with allowance for the structural inhomogeneity of the block. The molding conditions corresponding to the formation of "superspherulitic" structures have been determined. The thermal stability of these structures has been investigated.Mekhanika Polimerov, Vol. 4, No. 3, pp. 394–401, 1968     

Influence of diffusion of a liquid on the flexural rigidity of polyformaldehyde specimens

A correlation has been established between the flexural rigidity of polyformaldehyde specimens and the diffusional characteristics of water, acetic acid, and benzine into this material.     

Conditions for existence of relaxation oscillations in singular systems of low dimension

Relaxation oscillations are studied in a singularly perturbed system of ordinary differential equations with m slow and n fast variables for the case of m = 2 and n = 1. Necessary conditions and sufficient conditions for existence of relaxation oscillations are given.     

Effect of structural changes on the sorptivity and mechanical properties of polyformaldehyde fibers

The dependence of the mechanical and sorption properties and structure of polyformaldehyde fibers on the degree of extension has been investigated. By x-ray structural analysis and sorption techniques it is shown that an increase in stretch ratio is accompanied by an increase in structural orientation with a simultaneous increase in porosity. It is established that the change in the mechanical properties associated with drawing depends both on orientation and on the presence of macrodefects in the fiber.Kiev Technological Institute of Light Industry. Translated from Mekhanika Polimerov, No. 6, pp. 1103–1106, November–December, 1971.     

Investigation of the supermolecular structure of polyformaldehyde in an injection-molded block. I

The supermolecular structure of polyformaldehyde has been investigated in an injection-molded block. This structure is a complex one in relation to the distribution of spherulites of various sizes and the ordering of the spherulites within the block.Mekhanika Polimerov, Vol. 4, No. 2, pp. 205–209, 1968     

Localization of plane waves in low temperature regime

Discrete ühling-Uhlenbeck models together with the introduction of an orientation-free parameter are adopted to study the possible localization of plane waves propagating in dilute hard-sphere gases under very-low temperature environment based on the acoustical analog. The curves of the scattering amplitude vs. the disorder and Pauli-blocking measure we obtained here resemble qualitatively those proposed before.     

Localization of plane waves in low temperature regime

Discrete ühling-Uhlenbeck models together with the introduction of an orientation-free parameter are adopted to study the possible localization of plane waves propagating in dilute hard-sphere gases under very-low temperature environment based on the acoustical analog. The curves of the scattering amplitude vs. the disorder and Pauli-blocking measure we obtained here resemble qualitatively those proposed before.     

Minimum quench energies of uncooled low temperature superconductors with temperature dependent thermophysical parameters

An analytical method for calculation of minimum quench energies (MQEs) of uncooled composite low temperature superconductors is presented. The method takes into account transient heat transfer in the conductor as well as temperature dependent ohmic heat generation and temperature dependent thermophysical properties of the conductor. MQE of the conductor is calculated based on the analysis of evolution of peak temperature in the normal zone. The method is validated by comparison of the obtained results with the experimental data as well as with analytical and numerical results taken from literature.     

Instabilities and pattern formation in low temperature plasmas

This paper is concerned with a dynamical systems analysis of an instability occurring in a cylindrical high frequency plasma discharge. Stationary, spatially periodic modulations of the plasma density and temperature have been observed in experiments and reproduced in kinetic simulations. A macroscopic model is proposed in order to determine parameter ranges for which these plasma “striations” may form. The model consists of two nonlinear, coupled partial differential equations which describe ambipolar diffusion of electrons and ions and electron energy transport. We emphasize the importance of a particular thermoelectric transport coefficient, usually neglected in fluid models of plasma discharges, which proves essential in describing the pattern formation mechanism.     

Reflection of magneto-thermoelastic waves with two relaxation times and temperature dependent elastic moduli

The model of the equations of generalized magneto-thermoelasticity with two relaxation times in an isotropic elastic medium under the effect of reference temperature on the modulus of elasticity is established. The modulus of elasticity is taken as a linear function of reference temperature. Reflection of magneto-thermoelastic waves under generalized thermoelasticity theory is employed to study the reflection of plane harmonic waves from a semi-infinite elastic solid in a vacuum. The expressions for the reflection coefficients, which are the relations of the amplitudes of the reflected waves to the amplitude of the incident waves, are obtained. Similarly, the reflection coefficients ratios variations with the angle of incident under different conditions are shown graphically. A comparison is made with the results predicted by the coupled theory and with the case where the modulus of elasticity is independent of temperature.     

Correlation at low temperature: I. Exponential decay

The present paper generalizes the analysis in (Ann. H. Poincaré 1 (2000) 59, Math. J. (AMS) 8 (1997) 123) of the correlations for a lattice system of real-valued spins at low temperature. The Gibbs measure is assumed to be generated by a fairly general Hamiltonian function with pair interaction. The novelty, as compared to [2,20], is that the single-site (self-) energies of the spins are not required to have only a single local minimum and no other extrema. Our derivation of exponential decay of correlations goes through the spectral analysis of a deformed Laplacian closely related to the Witten Laplacian studied in [2,20]. We prove that this Laplacian has a spectral gap above zero and argue that this implies exponential decay of the correlations.