Thermodynamic efficiency of thermoacoustic mixture separation

The acoustic power loss in the thermoacoustic mixture-separation process is derived, including the contributions due to a nonzero gradient in concentration. The significance of the gradient-dependent term is discussed. The limiting thermodynamic efficiency of the separation is calculated. Under reasonable circumstances, the efficiency approaches 10(-2) nHnL(delta m/m(avg))2, where nH and nL are the mole fractions of the two components of the mixture, and delta m/m(avg) is the fractional difference between the molar masses of the two components. This efficiency is of the same order of magnitude as that of some other, more conventional separation methods.     

Synthesis of new photosensitive silicon-containing poly(salicylideneazomethynes)

Photosensitive silicon-containing poly(salicylideneazomethynes) have been synthesized. It has been shown that these polymers are characterized by the presence of intramolecular donor-acceptor interactions between valence shells of silicon and nitrogen atoms; as a result, polyconjugation appears according to the nonclassical mechanism. The photo-and electrophysical properties of the polymers have been examined. The introduction of an oxygen spacer into a polymer facilitates an increase in the photosensitivity and quantum yield of free charge carrier photogeneration, and it has almost no effect on the conductive behavior of the polymers.     

Negligible absorption of radiofrequency radiation by colloidal gold nanoparticles

We report quantitative measurement of heat generation in Au-nanoparticle colloidal solutions induced by radiofrequency (RF) electromagnetic waves (13.56 MHz; 25 W). The possible role of Au nanoparticles in RF heating was systematically investigated by separating the metal nanoparticles away from the colloidal solutions by centrifugation. Contrary to the previously made assumption in this field, it is found that Au nanoparticles do not contribute to RF energy absorption. The electrical conductivity measurement of the solutions with and without Au nanoparticles reveals that the Joule heating via ionic conduction in the electrolyte solutions is the dominant mechanism of RF-radiation-to-thermal conversion.     

Photophysical properties of silicon-containing poly[salicylidene azomethine]s

Photophysical properties of new silicon-containing “nonclassical” polyconjugated poly[salicylidene azomethine]s were studied and a free carrier photogeneration mechanism characteristic of them was proposed. It was shown that polymer properties are controlled by the structure of the azomethine fragment and acceptor properties of the silicon atom. Due to multiple specific donor-acceptor interactions of unshared electron pairs of azomethine fragments with vacant d orbitals of silicon atoms, polymers feature photosensitive and photoconductive properties. The estimated photosensitivity S _0.1 ≈ 10⁵ cm²/J and quantum yield of free carrier Photogeneration η ≈ 0.15 correspond to the level of “classical” polyconjugated nitrogen-containing aromatic polymers used in optoelectronics.     

Site occupancy of ferrous ions in iron garnets

Fe²⁺ site occupancy in iron garnets is investigated by means of optical absorption and magnetic circular dichroism. In particular measurements are carried out on bulk single crystals of yttrium iron garnet (YIG) doped with Si⁴⁺, Nb⁵⁺, Sn⁴⁺, Zr⁴⁺, Ti⁴⁺ and Th⁴⁺. The results are discussed in the light of the recent discovery of tetrahedral Fe²⁺ in Nb-doped YIG. We find that, in general, Fe²⁺ occupies both octahedral and tetrahedral sites, the actual distribution being related to site occupancy of the donor centers. This correlation may be relaxed by photoinduced charge transfer between iron sites, at low temperatures. Contrary to recent attributions, no dodecahedral component is found in the infrared spectra above 1 μm wavelength.     

Effect of hot-drawing conditions on the orientation characteristics of carbon-chain fibers determined by the acoustic method

The orientation characteristics of polypropylene, polyacrylonitrile, and chlorinated PVC fibers, determined by the acoustic method, have been investigated in relation to the fiber drawing conditions (draw ratio, speed, and temperature). It is shown that there is a correlation between the mechanical characteristics and the degree of acoustic anisotropy.Tashkent Institute of the Textile and Light Industries. Translated from Mekhanika Polimerov, No. 3, pp. 552–554, May–June, 1971.     

r-tuple colorings of uniquely colorable graphs

An r-tuple coloring of a graph is one in which r colors are assigned to each point of the graph so that the sets of colors assigned to adjacent points are always disjoint. We investigate the question of whether a uniquely n-colorable graph can receive an r-tuple coloring with fewer than nr colors. We show that this cannot happen for n=3 and r=2 and that for a given n and r to establish the conjecture that no uniquely n-colorable graph can receive an r-tuple coloring from fewer than nr colors it suffices to prove it for on a finite set of uniquely n-colorable graphs.