Phase conjugation of CO2-laser radiation by a three-beam interaction

The distortion correction of a CO₂-laser radiation wavefront is studied by using forward resonant parametric scattering in gaseous SF₆ and retrace after retroreflection from a mirror.     

Broadband radio-absorbing materials based on porous composites with carbon nanotubes

The reflection coefficient of an electromagnetic wave has been theoretically studied as a function of the thickness of a material and its dielectric properties. Samples based on spheroplastics with noncovalently modified carbon nanotubes have been obtained. The radio-engineering and electrophysical properties of these composites are discussed as well. The prospects for applying porous nanocomposites with carbon nanotubes in the fabrication of radio-absorbing materials are also shown.     

The formation of nanocrystalline orthoferrites of rare-earth elements XFeO<Subscript>3</Subscript> (X = Y,La, Gd) via heat treatment of coprecipitated hydroxides

Heat treatment of coprecipitated hydroxides in air has afforded isometric nanocrystals of rhombic yttrium, lanthanum, and gadolinium ferrites with average crystallite size 40±4 nm. It has been stated that the formation of XFeO₃ (X = Y, La, Gd) nanocrystals occurs via two mechanisms, from the corresponding coprecipitated hydroxide (main route) and from the products of partial carbonatization of the precursor (side route). It has been shown that the formation of XFeO₃ (X = Y, La, Gd) nanocrystals via the main and the side routes occurs at 500 and 780°С (o-YFeO₃), 646 and 900°С (o-LaFeO₃), and at 769°С (o-GdFeO₃). Basing on the obtained data, we have suggested a scheme of chemical and physical transformations accompanying the formation of nanocrystals of yttrium, lanthanum, and gadolinium ferrites.     

Synthesis and antimicrobial activity of some acridone derivatives bearing 1,3,4-oxadiazole moiety

Novel acridone derivatives bearing 1,3,4-moiety were synthesized by intramolecular cyclization of N´-[2-(9-oxoacridin-10(9H)-yl)acetyl]arylhydrazides. Study of antimicrobial activity of the synthesized compounds reveals that some of them are more active than the comparator drug rivanol.     

Formation mechanism of nanocrystalline yttrium orthoferrite under heat treatment of the coprecipitated hydroxides

Formation of nanocrystalline yttrium orthoferrite of ～30 nm average crystallite size from coprecipitated iron(III) and yttrium hydroxides was studied by thermo-X-ray diffractometry and simultaneous thermal analysis over 25–900°C temperature range. A mechanism of physicochemical transformations leading to the formation of YFeO₃ nanoparticles was suggested.     

Current-conducting properties of paper consisting of multiwall carbon nanotubes

Electrical conductivity σ(T) of the paper consisting of multiwalled carbon nanotubes (MWCNTs) is studied in the temperature range 4.2-295 K, and its magnetoresistivity ρ(B) at various temperatures in magnetic fields up to 9 T is analyzed. The temperature dependence of the paper electrical conductivity σ(T) exhibits two-dimensional quantum corrections to the conductivity below 10 K. The dependences of negative magnetoresistivity ρ(B) measured at various temperatures are used to estimate the wavefunction phase breakdown length L _φ of conduction electrons and to obtain the temperature dependence L _φ = constT ^?p/2, where p ≈ 1/3. Similar dependences of electrical conductivity σ(T), magnetoresistivity ρ(B), and phase breakdown length L _φ(T) are detected for the initial MWCNTs used to prepare the paper.     

Combination of two chromatographic methods in the study of the chemical composition of officinal herbs

Two complementary chromatographic methods, ion exclusion chromatography and gas-liquid chromatography, are suggested for the analysis of the chemical composition and the standardization of raw herbs. The potentialities and limitations of these methods are illustrated by the example of common valerian (Valeriana officinalis) and yarrow (Achillea millefolium). The chromatographic conditions required for the determination of ascorbic acid by the ion exclusion chromatography are determined.     

Synthesis of pyrazole- and thiazole-annulated 3-R-1,5-dinitro-3-azabicyclo[3.3.1]nonanes

The previously unknown 3-R-1,5-dinitro-3-azabicyclo[3.3.1]nonanes fused to the pyrazole or thiazole rings were synthesized by the reductive cyclization of m-dinitroindazoles and benzothiazoles. The method is based on the reduction of carbon-carbon bonds in the benzene ring, which are activated by the meta-nitro groups, with NaBH₄ followed by the Mannich reaction with formaldehyde and primary amines.     

Mechanism of formation of a negative magnetoresistance region in granular high-temperature superconductors

The field dependences of the magnetoresistance of Bi_1.8Pb_0.3Sr_1.9Ca₂Cu₃O _x samples with different densities, which have a foam microstructure and exhibit different diamagnetic responses, were studied at 77.4 K to identify the mechanism responsible for the formation of a negative magnetoresistance region in granular high-temperature superconductors. A region with negative magnetoresistance was found to exist in samples with magnetizations highest in absolute magnitude. This behavior finds a reasonable interpretation as due to the effect exerted by dipole moments of high-temperature superconductor grains on the effective intergranular field. The strength of this effective field has been estimated.     

Quantum Oscillations of the Microwave Sensitivity of a Spin-Torque Diode in a Magnetic Nanobridge

The reduction of the area of the cross section of a spin-valve-like structure to a nanoscale is an important problem of modern spin electronics. However, the transverse quantization of electronic states in the spin valve, which forms a magnetic nanobridge at this scale, additionally affects not only the magnetoresistance but also the spin-transfer torques. In this work, features of the quantization of the magnetoresistance and spin-angular momentum associated with the spin transfer in a Co/Au/Co metallic nanobridge with metallic contacts have been theoretically analyzed. It has been shown that these features are manifested in oscillations of the microwave sensitivity of a spin-torque diode based on the spin-valve structure mentioned above.