Synthesis of 5-arylisoxazole- and 4,5-dichloroisothiazole-3-carboxylates derived from natural alcohols,thymol, and its synthetic analogs

Esters derived from 5-phenyl-, 5-(4-methylphenyl)-, and 5-(2,5-dimethylphenyl)-1,2-oxazole-3-carboxylic and 4,5-dichloro-1,2-thiazole-3-carboxylic acids and some natural alcohols (L-menthol, grosshemin), thymol, and synthetic analogs of the latter (4-tert-butylphenol, 4-tert-octylphenol, 2-tert-butyl-4-methylphenol) were synthesized by reactions of the corresponding alcohols with acid chlorides.     

Aggregation of iron-containing fullerenols in aqueous solutions

Endometallofullerenols Fe@C₆₀(OH)₃₀ were synthesized by a new procedure using a special molecular precursor in the course of electric arc evaporation of a composite carbon electrode. Aqueous solutions of fullerenols Fe@C₆₀(OH)₃₀ were studied by small-angle neutron scattering (SANS) and viscometry under the conditions of transition from dilute to concentrated systems in two media: acidic (pH 3.7) and weakly alkaline (pH 7.8). In a weakly alkaline medium, fullerenols form relatively dense clusters (correlation radius R _C ~ 17 nm), and in acidic medium, less dense structures of size R _C ~ 18 nm in the concentration interval с = 0.5–1.4 wt %. The mechanisms of aggregation of fullerenol molecules in aqueous solutions are discussed. The water-soluble derivatives Fe@C₆₀(OH)₃₀ obtained show promise for biomedical applications in magnetic resonance imaging as contrasting agents that are potentially less toxic than presently used contrasts based on gadolinium chelate complexes.     

Corpuscular modeling of the interaction of a laser pulse with plasma

Results from computer modeling according to the particle interaction of ultrastrong and ultrashort laser pulses with a two-layer target are presented. Particle acceleration regimes are demonstrated in a computing experiment.     

Synthesis of aluminum oxides from the products of the rapid thermal decomposition of hydrargillite in a centrifugal flash reactor: II. Physicochemical properties of the products obtained by the centrifugal thermal activation of hydrargillite

A variety of physicochemical methods were used to characterize the product of the rapid thermal decomposition of hydrargillite in a centrifugal flash reactor under the following conditions: the average particle size of the reactant, 80–120 μm; the temperature of the solid heating surface (plate or cylinder), 300–700°C; hot-zone residence time, ～1 s; transfer of the product to the cooled zone of the reactor. The composition of the product and the extent of decomposition of hydrargillite were determined as a function of the processing temperature. The centrifugal thermal activation (CTA) of hydrargillite affords an X-ray-amorphous, highly reactive product with a developed surface and a disordered and inhomogeneous porous structure. This structure is capable of forming different modifications of aluminum hydroxide and oxide. The properties of the CTA product are compared with the properties of the earlier reported hydrargillite rapid decomposition products obtained using a gaseous heat-transfer agent (thermochemical activation product) or a fluidized bed of a granular heat-transfer agent (thermal dispersion product).     

Synthesis of a novel crosslinked superabsorbent copolymer with diazacyclooctadecane crown ether and its sorption capability

A novel crosslinked poly(acrylic acid-copolymer-Kryptofix-22-DM) superabsorbent copolymer, poly(AA-co-Kry22-DM), was synthesised by the reaction of 4,13-dimethylacryloyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (Kyrptofix-22-DM) and acrylic acid (AA). Characterisation of the polymers was achieved by FTIR and ¹H NMR techniques. Sorption capacity of the crosslinked poly(AA-co-Kry22-DM) superabsorbent copolymer was investigated for Pb²⁺, Cu²⁺, Cr³⁺, Cd²⁺, Mn²⁺, Zn²⁺, and Ni²⁺ heavy metal ions at different pH values using Freundlich and Langmuir isotherms. Swelling ratio, q_v, and distribution ratio, log D, values of the crosslinked poly(AA-co-Kry22-DM) superabsorbent copolymer were calculated at various pH values.     

Low-temperature ferromagnetism in a new diluted magnetic semiconductor Bi2−x FexTe3

Single crystals of a new diluted magnetic semiconductor Bi_2?x Fe_xTe₃ (0≤x≤0.08) were grown. For all crystals, the transition into a ferromagnetic state with easy axis parallel to the C ₃ axis was observed at temperature T _c increasing with iron concentration and reaching 12 K at x=0.08. An increase in the Seebeck coefficient, anomalous Hall effect, and resistivity jump at T=T _c were also observed. The frequency of the de Haas-van Alphen oscillations decreases with increasing x, indicating the donor properties of Fe.     

Leggett mode in cuprate superconductors and the electromagnetic properties of Josephson junctions

The effect of multiple Andreev reflections in YBa₂Cu₃O_{7 ? x} and Tl₂Ba₂Ca₂Cu₃O_{10 ? ??} has been studied. Several independent subharmonic gap structures associated with the multigap character of these superconductors have been revealed on the I(V) and dI/dV characteristics of Andreev contacts. An additional fine structure has been observed, which can be attributed to the emission of Leggett plasmons. The electromagnetic properties of Josephson junctions at a microcrack in Tl₂Ba₂Ca₂Cu₃O_{10 ? ??} have been examined. The magnetic-field dependences of the critical current, as well as Fiske geometric resonances, have been studied in the Josephson regime (SIS type). The fundamental frequency of resonances and the Swihart velocity have been determined.     

Structural transformations in nanocrystalline zirconium dioxide

Peculiar features of the phase composition and structure of nanocrystalline powders based on zirconium dioxide, which appear during heating, have been studied. The oscillation of lattice microdistortions has been found, which is caused by variation in the crystallite defect structure. The phase composition of this material is determined according to the level of microdistortions.     

Negative persistent photoconductivity in GaAs (δ-Sn) structures

The effect of illumination with various wavelengths λ (770 nm<λ<1120 nm) on the conductivity of GaAs structures with tin δ-doping of the vicinal faces was investigated in the temperature range 4.2–300 K. Negative persistent photoconductivity was found in strongly doped samples. It was shown on the basis of the results of investigations of the Hall and Shubnikov-de Haas effects that the negative photoconductivity is due to a large decrease in the electron mobility with increasing electron density. The decrease of electron mobility is explained by ionization of DX centers, which destroys the spatial correlation in the distribution of positively charged donors and negatively charged DX centers. Zh. éksp. Teor. Fiz. 116, 2130–2139 (December 1999)     

Quantum Hall effect in the bulk semiconductors bismuth and antimony tellurides: Proof of the existence of a current-carrier reservoir

The quantization of the Hall resistivity ρ_xy in the form of plateaus in the dependence of ρ_xy on the magnetic field B is observed in the semiconductors Bi₂Te₃ and Sb₂Te₃; the minima of the transverse magnetoresistivity ρ_xx correspond to the start of the plateaus. The quantization of ρ_xy is due to the presence of a current-carrier reservoir. An impurity band with a high density of states or a different band with a much higher current-carrier effective mass serves as the reservoir. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 11, 754–758 (10 December 1999)