Variations in the Characteristics of a HF Signal over an Oblique Sounding Path during the Solar Eclipse on August 11, 1999

We present the results of measurements of the HF-signal characteristics over the path Praha - Nizhny Novgorod during the solar eclipse on August 11, 1999. A 10-dB increase in the HF-signal amplitude and an increase in the frequency of quasiperiodic fading were observed during daytime in the course of the eclipse with phase about 68-85%. An interpretation of the effects observed is given. On the basis of simulations, we show that the increase in the amplitude is related to a decrease in absorption losses which is caused by the corresponding decrease in the electron density in D- and E-layers by about 30-45%. The increase in the fading frequency results from beating of the modes that have different Doppler shifts due to phase-path variations during the eclipse. An estimate for the rate of electron-density variation during the eclipse was obtained: dN/dt (2-2.5) ·10² cm^-3s^-1.     

Kinetically controlled phase transitions in liquid‐crystalline polymers. III. Influence of the molecular weight and annealing temperature on two‐dimensional K phase formation in a side‐chain polyacrylate

Narrow fractions of a side‐chain acrylate oligomer/polymer with phenyl benzoate side chains are separated in a broad range of the degree of polymerization (7 ≤ P_w ≤ 149). An examination of the phase behavior of the obtained fractions has shown that only the longer macromolecules can form the two‐dimensional K (TDK) mesophase, whereas oligomers of a shorter main chain form the conventional nematic phase only. A critical P_w value has been observed to be necessary for the TDK mesophase formation. The temperatures and enthalpies of liquid‐crystalline phase transitions have been studied as a function of the molar mass, and the phase‐growth kinetics for the TDK phase have been studied with an Avrami treatment. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2352–2360, 2005     

Mass-spectrometric thermal analysis of polymers based on furyl alcohol

Mass-spectrometric thermal analysis of samples of furan polymers obtained by heating furyl alcohol in a closed volume at 200 °C, 250 °C and 300 °C permitted determination of the qualitative composition of the gas products evolved from the polymers upon non-isothermal temperature increase from 20 to 1200 °C. The degree of unsaturation of the samples was evaluated quantitatively. The main features of the formation, degradation, structurization and carbonization of furan polymers were considered.     

Modification of some mono- and bispiperidols exhibiting growth-regulating properties

Procedures for esterification of biologically active mono-and bispiperidols by reactions with benzoyl and terephthaloyl chlorides were developed.     

Influence of thermal conductivity on the heating of a substance by a high-intensity ion beam

Relations describing the process of heat transfer from the energy-dissipation region of a monoenergetic ion beam in an obstructing target within the pulse duration are derived on the basis of an analysis of the fundamental laws governing the interaction of a high-intensity ion beam with condensed media and the solution of the heat-conduction equation. The proposed analytical expressions can be used to assess the feasibility of neglecting thermal conductivity and calculating the temperature fields in the target without solving the heat-conduction boundary-value problem, namely on the basis of the characteristics of a heat-release source approximating the real source.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 16–20, June, 1986.     

Specific features of the melting of poly(ethylene terephthalate) after its thermal and mechanical treatment

Specific features of the melting of PET samples with different molecular masses after their thermal and mechanical treatment (orientational drawing) are studied by the DSC method. Orientational drawing of the samples leads to the development of a supermolecular structure, which depends on the molecular mass and thermal prehistory of the initial samples.     

Unusual electro-optical behaviour of the nematic polyacrylate

ABSTRACT

High sensitivity of liquid crystals to the electric field makes them highly demanded and widely used in different applications. Despite the large number of the electro-optical research on the low-molar-mass liquid crystals electro-optics of the liquid crystalline (LC) polymers is much less studied. Herein, the comparative electro-optical behaviour of two nematic comb-shaped polyacrylates with phenylbenzoate mesogenic side groups was studied in detail. These two polyacrylates have completely the same structure of polymer backbone and spacer length but different in the direction of the ester group in the phenylbenzoate fragments. It was found that this difference predetermines their completely opposite electro-optical properties.

The influence of the electric field of different strength and frequency on the orientation of the mesogenic groups of these polymers is studied. It is shown that application of the electric field at temperatures above the glass transition temperature (~25°C) induces reorientation of the mesogenic groups along or perpendicular to the electric field direction depending in its turn on the ester group direction. For one of the polyacrylates an unusual textural transition is found; during cooling of the polymer sample under applied field at definite temperature a sharp change in the mesogen’s orientation from homeotropic to planar one is found. This electro-optical phenomenon is observed for the first time and probably associated with sharp change in sign of anisotropy of dielectric permittivity from positive (at high temperatures) to negative one (at lower temperatures). Kinetics of the electro-optical switching at different temperatures, influence of the molar masses of the polymer and frequency of the applied AC field on electro-optical behaviour of the polymers are studied. The possibility of the fixation of the electroinduced homeotropic alignment of the mesogenic groups by photopolymerisation of the diacrylate dissolved in the polymer is demonstrated.     

Gas dynamic flow properties in the problem of two incompressible plates propelled by explosion products

The method proposed in [1, 2] is used to construct an analytic solution of the problem of two incompressible plates propelled by the explosion products of a condensed explosive. A solution of the problem by the classical methods of the gas dynamics of a perfect gas with =3 was previously obtained in [3]. However, the analysis carried out in [3] does not reproduce the entire wave configuration which may result from the interaction of expansion waves with moving plates and is limited to the study of the flow configuration realized in the case of single reflection of the waves from the plate contact boundary. This leads to overestimation of the limiting projection velocities when the relative masses of the plates are greater than unity.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 148–152, March–April, 1991.     

New simple method of measuring the surface glass transition temperature of polymers

A lap‐shear joint mechanical testing method has been probed to measure the surface glass transition temperature (T) of the thick bulk films of high‐molecular‐weight polymers. As T, the temperature transition “occurrence of autoadhesion–nonoccurrence of autoadhesion” has been proposed. The influence of chain flexibility, of molecular architecture, of polymer morphology, and of chain ends concentration on the T has been investigated. The correlation between the reduction in T with respect to the glass transition temperature of the bulk (T) and the intensity of the intermolecular interaction in the polymer bulk in amorphous polymers has been found. The effect of surface roughness on T has been discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2012–2021, 2010