Focus splitting associated with propagation of focused ultrasound through the rib cage

The effect of focus splitting after propagation of focused ultrasound through a rib cage is investigated theoretically. It is shown that the mechanism of this effect is caused by the interference of waves from two or more spatially separated sources, such as intercostal spaces. Analytical estimates of the parameters of splitting are obtained, i.e., the number of foci, their amplitudes, diameter, and the distance between them, depending on the transducer parameters, as well as the dimensions of the rib cage and position of ribs relative to the radiator. Various configurations of the relative positioning of ribs and radiator are considered; it is shown which of them are the most effective for real surgical operations.     

Ion exchange properties of heat-treated NH4Cl-containing cellulose-regenerated

Ion exchange properties of carbon fibers obtained by heat treatment in a temperature range of 200–600°C in an inert atmosphere of cellulose-regenerated impregnated by 0.3–3.0 M ammonium chloride were examined.     

First P,P*-bidentate phosphine-phosphite-type ligand with a P*-stereocenter in the phosphite moiety: synthesis and application in the Pd-catalyzed asymmetric allylic alkylation

A new P,P*-bidentate phosphine-diamidophosphite bearing an asymmetric phosphorus atom in the 1,3,2-diazaphospholidine ring was obtained. A possibility of its application in the palladium-catalyzed enantioselective allylic substitution was demonstrated. A 70% ee was reached in the alkylation of (E)-1,3-diphenylallyl acetate with dimethyl malonate.     

Carbon dioxide adsorption on carbon nanomaterials

The adsorption of CO₂ on a number of activated carbons, thermal carbon black, and oxide materials at 195 K was studied using static and dynamic techniques. The landing surface areas ω(CO₂) ≈ 0.19 nm² on thermal carbon black and the absolute values of sorption for P/P ₀ < 0.4 were determined. The density of adsorbed CO₂ in the micropore volume was estimated at ρ(CO₂) = 0.91 g/cm³. It was demonstrated that the previously found effect of a weakening of the sorption interaction of nitrogen molecules with thin-walled materials (which manifested itself in an analysis of sorption isotherms by a comparative method) was pronounced to a lesser degree for the sorption of CO₂. At the same time, the presence of supermicropores in activated carbon samples resulted in overestimated values of surface areas. A dynamic method was proposed to measure the spectra of CO₂ desorption at 195–260 K using a SORBI-MS system for evaluating the binding energy of sorbate molecules with the surface.     

Synthesis and mesopore-micropore structure characterization of nanodisperse Fe<Superscript>3+</Superscript> hydrogels (xerogels)

A preparation procedure was developed, and samples of nanodisperse Fe³⁺ hydroxide with a narrow particle-size distribution (2.5–3.5 nm) were synthesized. The occurrence of a substructure in the bulk of Fe³⁺ hydroxide nanoparticles was detected for the first time using light-field and dark-field transmission electron microscopy. It was found that structurally ordered regions with sizes of ～1.0 nm, which were disoriented with respect to each other at angles of a few degrees, occurred in the bulk of the nanoparticles. The empirical formula of nanodisperse iron hydroxide was ～Fe₂O₃ · 1.8H₂O; the structure of this hydroxide contained crystal water, OH^?, and O^2?. The coordination number of Fe³⁺ cations with respect to oxygen was 6. It was found that both structural and nonstructural water can be removed almost completely from the bulk of nanoparticles in the course of sample heating to 150–250°C in a vacuum with the retention of their amorphous character and observed sizes. In the course of dehydration, the mutual mobility of nanoparticles within aggregates was retained in Fe³⁺ xerogels; this resulted in a decrease in the total pore volume, whereas the volume of mesopores with diameters of 3.4–3.5 nm progressively increased. The micropore structure of the samples of nanodisperse iron hydroxides was studied by the molecular probe method using the low-temperature (77 K) sorption of nitrogen and molecular hydrogen. It was found that, along with micropores of volume ～0.02 cm³/g, which are accessible to both of the sorbates, the sorption of H₂ exhibited an additional specific absorption of 1.0–1.7 cm³(STP)/g, which can be interpreted as an additional ultramicropore volume accessible to only hydrogen molecules.     

Reaction of methyl 1-bromocyclopentanecarboxylate with zinc and 1-aryl-5-phenylpenta-1,4-dien-3-ones

Methyl 1-bromocyclopentanecarboxylate reacted with zinc and 1-aryl-5-phenylpenta-1,4-dien-3-ones with the formation of isomeric 10-aryl-8-(2-arylethenyl)-7-oxaspiro[4.5]dec-8-en-6-ones.     

On the number of limit cycles which appear by perturbation of two-saddle cycles of planar vector fields

We prove that the number of limit cycles which bifurcate from a two-saddle loop of an analytic planar vector field X ₀ under an arbitrary finite-parameter analytic deformation X _λ , λ ∈ (? ^N , 0), is uniformly bounded with respect to λ.     

Hydrothermal synthesis and characterization of nanorods of various titanates and titanium dioxide

The formation process of titania based nanorods during hydrothermal synthesis starting from an amorphous TiO2.nH2O gel has been investigated. Sodium tri-titanate (Na2Ti3O7) particles with a rodlike morphology were prepared by a simple hydrothermal process in the presence of a concentrated NaOH aqueous solution. The ion exchange reaction of the synthesized Na2Ti3O7 nanorods with HCl under ultrasonic treatment promotes a complete sodium substitution and the formation of H2Ti3O7 nanorods. Low-temperature annealing of the as-produced nanorods of Na2Ti3O7 and H2Ti3O7 leads to a loss of the layered crystal structure and the formation of nanorods of condensed framework phases-sodium hexa-titanate (Na2Ti6O13) and metastable TiO2-B phases, respectively. These transformations proceed without a significant change in particle morphology. The nanostructures were investigated by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), the Brunauer-Emmett-Teller (BET) method, thermogravimetric analysis (TGA), and Raman spectroscopy. The structural defects of the synthesized nanorods were investigated by high-resolution electron microscopy. The presence of planar defects can be attributed to the exfoliation of the zigzag ribbon layers into two-dimensional titanates as well as to the condensation of the layers of TiO6 octahedra into three-dimensional frameworks.     

On the development time of the parametric instability of polariton-polariton scattering in a planar semiconductor microcavity

It has been shown that the development of the threshold instability of polariton-polariton scattering in a planar semiconductor microcavity under the coherent pulsed excitation above the lower polariton branch requires a minimum pulse length on the order of dozens of picoseconds, needed for the population of polariton modes in the regions of the parametric instability to increase from the noise level to a certain value comparable with the population of the driven mode.     

Adsorption of molecular hydrogen on aluminophosphate zeolites at 77 K

The H₂ sorption properties of the aluminophosphate zeolites AlPO-5, AlPO-31, AlPO-11, AlPO-36, and AlPO-8 at 77 K have been investigated. A series of H₂ adsorption isotherms has been obtained for cylindrical micropore channels in the aluminophosphate zeolites. The absolute values of the amount adsorbed α(P) for the mesoporous aluminophosphate materials and the effective density of adsorbed H₂ in the micropore space β*(P, d) have been determined. It has been demonstrated experimentally that the sorbate density depends on the size of the micropore channel of the zeolite d. Hydrogen sorption isotherms have been calculated from experimental isotherms. A procedure allowing β*(P, d) to be estimated for intermediate d values is presented.