One-step synthesis of [4-(alkylsulfanyl)buta-1,3-diene-1-yl]-triphenylphosphonium iodides from buta-1,3-diene-1,4-diylbis(triphenylphosphonium) iodide

Buta-1,3-diene-1,4-diylbis(triphenylphosphonium) iodide reacted with alkanethiols at room temperature in the presence of triethylamine to give [4-(alkylsulfanyl)buta-1,3-diene-1-yl]triphenylphosphonium iodides and triphenylphosphine in high yields. Two presumable reaction mechanisms involving ethynylvinyl intermediate (formed via the Hofmann decomposition of the starting diiodide and the initially formed 1,4-adduct with a thiol) were discussed.     

Bandwidth limitation of the Fabry-Perot cavity antennas

Frequency-amplitude characteristics of Fabry-Perot cavity antennas are considered on the basis of the circuit theory. It is shown that approaches valid for regenerative amplifiers are applicable to cavity antennas. The expressions for the ultimate frequency band of a cavity antenna with matching circuits are obtained. It is confirmed experimentally that by appropriate choice of partially-reflecting correcting coatings, the frequency band of cavity antennas may considerably be extended.     

Noise in porous silicon structures in air and in conditions of gas adsorption

Low-frequency noise, in the range 1–500 Hz, is measured at room temperature in samples of Au/PS/SCS/Al structure with a layer of porous silicon. Numerical values of the Hooge parameter α_H are estimated and the dependence of α_H on the composition of the gaseous environment, where the sample is placed, is determined. Possible reasons of observed high values of α_H for the samples in air and of the increase in α_H in conditions of gas adsorption are discussed. Introducing of carbon oxide in air changes the shape of spectrum.     

Optical absorption in a semiconductor cylindrical nanolayer

In the effective-mass approximation the single-electron states in a semiconductor cylindrical nanolayer in the regime of strong quantization are considered. The explicit form of the energy spectrum and envelope wave functions of single-electron states is obtained in the case of large and moderate radii of the system. The corresponding absorption bands of dipole and quadrupole optical transitions in the layer are calculated.     

Synthesis and characterization of doped apatite-type lanthanum silicates for SOFC applications

A series of iron- and/or aluminium-doped apatite-type lanthanum silicates (ATLS) La_9.83Si_{6 ‐ x ‐ y}Al_xFe_yO_26 ± δ (x = 0, 0.25, 0.75, and 1.5, y = 0, 0.25, 0.75, and 1.5) were synthesized using the mechanochemical activation (MA), solid state reaction (SSR), Pechini (Pe) and sol-gel (SG) methods. The total conductivity of the prepared materials was measured under air in the temperature range 600-850 °C using 4-probe AC impedance spectroscopy. Its dependence on composition, synthesis method, sintering conditions and powder particle size was investigated. It was found that for electrolytes of the same composition, those prepared via mechanochemical activation exhibited the highest total specific conductivity, which was improved with increasing Al- and decreasing Fe-content. The highest conductivity value at 700 °C, equal to 2.04 × 10^− 2 S cm^− 1, was observed for the La_9.83Si₅Al_0.75Fe_0.25O_26 ± δ electrolyte. La_9.83Si_4.5Fe_1.5O_26 ± δ electrolyte samples synthesized using the Pechini method exhibited higher conductivity when sintered conventionally than when spark-plasma sintering (SPS) was used.     

Explosive chemical transformations of 4-bromo-2,4,6-tri-tert-butylcyclohexa-2,5-diene-1-one in strong uniaxial compression

Conclusions The study of explosive transformations of 4-bromo-2,4,6-tri-tert-butylcyclohexa-2,5-dien-1-one in strong uniaxial compression demonstrated the dependence of the degree of conversion of the starting substance and total yield of products on the value of the explosion pressure. A chemical mechanism of the process which includes heterolysis of the C-Br bond was proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 137–140, January, 1989.     

Relation of initial supermolecular organization in crystalline polymer systems to the organization produced by stretching

An investigation of small-angle scattering produced by polarized light from stretched and annealed polymer systems containing spherulites yields information on the supermolecular transitions that occur during such treatment. A series of semicrystalline polymer systems (films, fibers) show that stretching leads to deformation of spherulites and subsequent transformation to an orientational supermolecular order. The size of the single element C₂ of the supermolecular order in the direction of stretching, determined from the distance between the layer lines of the scattering pattern, is related to the diameter D₀ of the initial spherulites by the relation C₂ = KD₀λ_s, where λ, is the draw ratio of the macrosystem and K is a parameter determining the deformability of the spherulites. For polyethylene at room temperature K is unity and for polychloroprene it is 1.2. Changes of C₂ after annealing and restretching of the systems also obey this ratio.