Structure and properties of core-shell microparticles in paraffin-ultradispersed polytetrafluoroethylene systems

Microsized spherical core-shell particles consisting of hydrocarbon cores encapsulated into fluoropolymer shells are obtained in supercritical carbon dioxide. Paraffins serve as a core material, while the polymer shell is formed from ultradispersed polytetrafluoroethylene. The morphology and molecular structure in the bulk and on the surface of the particles and the influence of conditions of particle formation on the shell thickness and the thermal properties of the materials are studied. The materials are composites comprised of paraffin cores coated with shells of loosened globular fluoropolymer particles with sizes of 0.2–1.7 μm. The shells is built of low- and high-molecular-mass fractions consisting of CF₃(CF₂)nCF₃ molecular chains with different lengths. The shell thickness is governed by preparation conditions, exposure time, and the percentage of the polymer in the initial dispersion.     

A complete set of symmetry operators for the Dirac equation

A complete set of symmetry operators of arbitrary finite order admitted by the Dirac equation is found. The algebraic structure of this set is investigated and subsets of symmetry operators that form bases of Lie algebras and superalgebras are isolated.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 10, pp. 1388–1398, October, 1991.     

HPLC determination of neopterin in biological liquids for clinical purposes

A HPLC method is proposed for determining neopterin in biological liquids. The method was realized using a standard chromatographic instrumentation. Neopterin was isolated from blood serum and urine by solid-phase extraction on cartridges containing 30 mg of supercrosslinked polystyrene. The separation was carried out on an Irica chromatograph (Japan) equipped with means of UV (350 nm) and fluorimetric (es350-em430 nm) detection. The degree of extraction was 96–113%, and the sensitivity of UV and fluorimetric detection was 0.1 and ～0.03 ng, respectively (at signal-to-noise ratio 3). It is shown that the method is suitable for use in routine clinical analysis of neopterin in biological liquids.     

Group classification of systems of non-linear reaction-diffusion equations with general diffusion matrix. II. Generalized Turing systems

Group classification of systems of two coupled non-linear reaction-diffusion equation with a diagonal diffusion matrix is carried out. Symmetries of diffusion systems with singular diffusion matrix and additional first order derivative terms are described.     

MNDO refinement of the Townes-Dailey theory. Calculation of NQR frequencies of chloro-containing compounds

Corrections accounting for the effect of the differences in p-electron energies on the electric field gradient are suggested and justified in the framework of Townes-Dailey theory. MNDO calculations of 31 chloro-containing molecules with full geometry optimization were used to evaluate the³⁵Cl NQR frequencies. The correlational relationships between experimental and calculated NQR frequencies are compared.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 38–42, January, 1995.This work was supported by the Russian Foundation for Basic Research (Project No. 93-03-5201).     

Local Chernoff and Hodges-Lehmann efficiencies of linear rank tests for symmetry

One computes the local asymptotic Chernoff and Hodges—Lehmann efficiencies of linear rank statistics for the testing of symmetry under certain regularity conditions, imposed on the labels and on the distribution of the observations under the alternative. It is revealed that these efficiencies coincide with the previously known Pitman and local Bahadur efficiencies.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova Akademii Nauk SSSR, Vol. 184, pp. 215–226, 1990.     

Frequency mixing in a bistable system in the presence of noise

The dynamics of a bistable system resulting from the action of several periodic perturbations and noise is studied. The response of the system at combination harmonics and the changes in the response caused by high-frequency modulation and a constant field that removes the degeneracy in the bistable system are calculated. The mixing of harmonics is investigated experimentally in an iron garnet thin film. It is shown that the higher harmonics exhibit behavior characteristic of stochastic resonance and that the form and symmetry of the dependence of harmonics on the constant field removing the degeneracy can be used to determine the characteristics of a bistable system with respect to its response to external periodic modulation. Zh. éksp. Teor. Fiz. 112, 628–642 (August 1997)