Hydrogel composition based on carboxymethylcellulose and agar-agar

The results are given of a study of the rheological properties of concentrated solutions of CNC and agar-agar and the influence of their quantitative ratio on the anomalous flow behavior of their solutions. A hypothesis is put forward of the formation of intermolecular associates from CMC and agar-agar which leads to the formation of a stronger structural network of solutions of the initial polysaccharides.Institute of the Physics and Chemistry of Polymers, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (371) 1 44 26 61. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 357–361, May–June, 1998.     

Modeling of heat transfer in a melt in growing single crystals by the stockbarger method using the accelerated crucible rotation technique (ACRT)

In model experiments, the layer of melt bounded by the crystallization front and the heater for heating the diaphragm in a growing furnace is shown to determine crystal growth by the Stockbarger method under conditions of induced convection and also to control the crystallization process. The free volume of the melt exerts no effect on its hydrodynamic and thermal structures. Optimum values of the exposure time are estimated for constant maximum and minimum velocities of modulated rotation of the growing ampoule. Institute of Mineralogy and Petrography, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 1, pp. 98–104, January–February, 1998.     

Gas transport through homogeneous and asymmetric polyethersulfone membranes

Both homogeneous and asymmetric polyethersulfone (PES) membranes were prepared by solvent casting. The sorption and permeation behavior of CO₂, O₂, and N₂ using these two kinds of cast PES membranes and commercially available homogeneous PES film was investigated to extract the pressure dependence of gas permeability and the permselectivity for CO₂ relative to N₂, and to confirm the validity of the working assumption that a skin layer in an asymmetric membrane can be essentially replaced by a thick homogeneous dense membrane. The pressure dependence of the mean permeability coefficient to CO₂ in homogeneous membranes obeys the dual-mode mobility model. The ideal separation factor for CO₂ relative to N₂ at an upstream pressure of 0.5 MPa attains ca. 40, while the permeability to CO₂ is about 2.7 Barrer at the same upstream pressure. The same separation factor in asymmetric membranes amounts to 35. The diffusion behavior for the skin layer in an asymmetric membrane with a thin skin layer can be simulated approximately by that in a homogeneous dense membrane. © 1993 John Wiley & Sons, Inc.     

Circulatory flow in the inter-jet zone of a system of free turbulent jets

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 4, pp. 97–99, July–August, 1993.     

Poisson-Lie T-duality and complex geometry in N = 2 superconformal WZNW models

Poisson-Lie T-duality in N = 2 superconformal WZNW models on the real Lie groups is considered. It is shown that Poisson-Lie T-duality is governed by the complexifications of the corresponding real groups endowed with Semenov-Tian-Shansky symplectic forms, i.e. Heisenberg doubles. Complex Heisenberg doubles are used to define on the group manifolds of the N = 2 superconformal WZNW models the natural actions of the isotropic complex subgroups forming the doubles. It is proved that with respect to these actions N = 2 superconformal WZNW models admit Poisson-Lie symmetries. The Poisson-Lie T-duality transformation maps each model onto itself but acts non-trivially on the space of classical solutions.     

Simulation of attenuation of millimeter radio waves in dry snowfalls

Attenuation of millimeter waves in dry snowfalls is numerically simulated with allowance for the actual shape of snowflakes. It is shown that for moderate-intensity snowfalls the values of attenuation cross-sections averaged over the snowflake orientations are well approximated by power-law function depending on the equivalent diameter of the snowflakes. This allows us to obtain an analytical expression for the attenuation coefficient of a plane electromagnetic wave by snowfall for size distributions of particles of the gamma-distribution type and its modifications. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 4, pp. 446–455, April, 1998.     

Chaotic synchronization as an information process

The chaotic synchronization phenomenon is studied from the information point of view. Synchronization of a chaos receiver by a chaos source is considered as copy recovery of the chaotic signal transmitted by the source. The main idea of this paper is to show that the necessary condition of chaotic synchronization is not the level of physical action of one system on another but the transmission of a certain volume of information on the chaotic process and, therefore, the capacity of the “communication channel” between the source and the receiver. This work was presented at the Summer Workshop “Dynamic Days” (Nizhny Novgorod, June 30–July 2, 1998). Institute of Radioengineering and Electronics of the Russian Academy of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 12, pp. 1497–1509, December, 1998.     

Critical thickness and stress relaxation in YBaCuO (123) strained epitaxial layers and YBaCuO based strained superlattices

An energy model has been used to calculate the critical thickness h _c of YBaCuO thin films and YBaCuO based superlattices within an isotropic or anisotropic approximation. The critical thickness of single layers calculated from the anisotropic model (16 nm) is in good agreement with the previously published experimental values which are spread out from 4 to 20 nm. In the case of superlattices, relaxation appears to be governed by the critical thickness of the elementary sub-layers and is then better evaluated through the calculation performed for YBaCuO single layers. XRD measurements on YBa₂Cu₃O₇/PrBa₂Cu_3?xGa_xO₇ superlattices grown on {100{ SrTiO₃ have evidenced a tetragonal stress in the YBaCuO ab plane which remains expanded when the YBaCuO elementary layer thickness is lower than 4.8 nm (4 YBaCuO cells). However the critical temperature of the shortest period superlattices is only slightly affected by this expanded stress in contrast to the effect of an elastic stress externally applied along the ab plane of YBaCuO thin films.     

On the applicability limits of the method of radio-wave refraction scattering

We compare the computational possibilities of the radio-wave refraction-scattering method (RWRSM) and the parabolic-equation method (PEM) in determining the statistical characteristics of radio waves in a medium with large-scale inhomogeneities. It is shown that on the whole the applicability limits of the RWRSM are similar to the corresponding limits of the PEM. However, unlike the PEM, the RWRSM makes it possible, in a number of cases, to use simple means to solve radio-wave-refraction problems in a thick layer with large-scale inhomogeneities.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 11, pp. 1118–1123, November, 1995.