Viscoelastic behavior of an amorphous polymer under oscillations of large amplitude

The influence of periodic shear deformation and steady flow on a typical amorphous polymer is discussed. Forced sinusoidal vibrations were applied and the complex viscosity was determined. The action of a vibration of finite amplitude is equivalent to steady flow with a definite finite shear rate. Both processes cause truncation of the long-time part of the relaxation specturm. It may be accepted to a first approximation that the long-time boundary of the remaining part of the relaxation spectrum conforms to the long-time part of the initial spectrum, even if the plateau region of the spectrum is truncated. The concept of limiting truncation of the short-time part of the spectrum is introduced, this corresponding to the minimum absolute value of the complex viscosity versus reduced frequency and the lowest values of the dynamic and apparent viscosities. With an approximate representation of the relaxation spectrum, calculations were made of the maximum values of the viscosity and the coefficient relating the first difference of normal stresses to the square of the shear rate, and also of the apparent viscosity and normal stresses as functions of the shear rate. The calculated values are compared with experimental measurements, and it is shown that the correlation of the apparent viscosity and the absolute value of the complex viscosity is distributed at high frequencies, being superseded by a correlation between the apparent and dynamic viscosities.     

New mechanism of chaos in triangular billiards

A new mechanism of weak chaos in triangular billiards has been proposed owing to the effect of cutting of beams of rays. A similar mechanism is also implemented in other polygonal billiards. Cutting of beams results in the separation of initially close rays at a finite angle by jumps in the process of reflections of beams at the vertices of a billiard. The opposite effect of joining of beams of rays occurs in any triangular billiard along with cutting. It has been shown that the cutting of beams has an absolute character and is independent of the form of a triangular billiard or the parameters of a beam. On the contrary, joining has a relative character and depends on the commensurability of the angles of the triangle with π. Joining always suppresses cutting in triangular billiards whose angles are commensurable with π. For this reason, their dynamics cannot be chaotic. In triangular billiards whose angles are rationally incommensurable with π, cutting always dominates, leading to weak chaos. The revealed properties are confirmed by numerical experiments on the phase portraits of typical triangular billiards.     

Negative viscosity for Rossby wave and drift wave turbulence

The possible occurrence of a “negative viscosity effect” is studied for Rossby wave and drift wave turbulence. It is assumed that (i) the space and time scales of the wave field are much smaller than the scales of the mean field, and (ii) the small-scale field is sufficiently weak, stationary, and maintained by an external source. Such a formulation is fruitful for studying the effects (characterized by the effective viscosity) of smaller-scale motions upon larger-scale ones. The criteria of large-scale instability due to the negative effective viscosity are derived for the coherent wave motions as well as for small-scale isotropic wave turbulence. Zh. éksp. Teor. Fiz. 113, 646–663 (February 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Submillimeter Laser Interferometer-Polarimeter for Plasma Diagnostics

The testing results of a homodyne 0.195-mm laser interferometer-polarimeter based on quasioptical components are presented. The interferometer-polarimeter matched to the multichannel interferometer of a Tokamak-15 machine admits of simultaneous measurements of the plasma electron density and poloidal magnetic field in one of the seven vertical-probing channels without any disturbance in the others. The achieved responce threshold of the electron density is 3.4·10¹¹ cm^–3, the polarization resolution and the phase difference measurement error are no worse than 0,1⁰ and ±4⁰, respectively.     

Fractal description of significant nano-effects in polymer composites with nanosized fillers. Aggregation,phase interaction,and reinforcement

The paper analyzes experimental data obtained on physical and mechanical properties of nanostructured particle-reinforced composites with elastomer matrices and nano- and microsized carbon-containing particles by scanning probe microscopy and nanoindentation with specialized 3D computer processing. The nano-effects observed in the elastomer matrices are described using the fractal approach. A fractal model of nanoparticle aggregation in a polymer matrix is proposed. Phase interactions in the nanostructured polymer materials are described and fractal relations that predict the reinforcing effect of this type of media are presented. It is shown that interphase regions in the nanostructured composites are the same reinforcing elements as a nanofiller for the medium. It is found that reinforcement of elastomer composites by nanosized particles is a true nano-effect.