Synergetic principles of physical mesomechanics

A synergetic methodology of physical mesomechanics is developed. Fundamental principles underlying the approach are discussed and formulated. The methodology is shown to account for and substantiate well-known plastic-deformation and fracture mechanisms in solids under various loading conditions. An analysis of the available experimental evidence suggests that the key meso- and macroscale processes developed in solids under load occur at maximum tangential stresses. Microscale deformation caused by dislocations is self-adaptable. Physical mesomechanics establishes natural relations between the physics of dislocation-induced deformation, continuum mechanics of solids, and fracture mechanics.     

Triisobutylaluminum as cocatalyst for zirconocenes. I. Sterically opened zirconocene/triisobutylaluminum/perfluorophenylborate as highly effective ternary catalytic system for synthesis of low molecular weight polyethylenes

Ethylene polymerizations with catalytic systems Me₂SiCp*N^tBuZrX₂ ( 1 ) [Cp* = C₅(CH₃)₄; X = Cl ( 1Cl ), Me ( 1Me )], triisobutylaluminum (TIBA), perfluorophenylborate CatB(C₆F₅)₄ [Cat = CPh₃ ( 3 ), Me₂NHPh ( 4 )], or Me₂SiCp₂ZrX₂ [X = Cl ( 2Cl ), Me ( 2Me )]/TIBA/ 3 ( 4 ) were performed within a wide range of ethylene pressures of different Al/Zr ratios, and Zr/B = 1. Catalytic systems 1Cl ( 2Cl )/TIBA/ 3 led to the formation of very high linear molecular weight polyethylene (PE) of M_η ∼2,000,000 with low activity. The replacement of both chlorine ligands in the precatalyst for the methyl ones led to the formation of active species producing low molecular weight PE with high activity. Chain transfer to ethylene was shown to be the main reaction controlling PE chain propagation: k_p/k_tr ∼20–30 for 1Me /TIBA/ 3 and k_p/k_tr ∼350–500 for 2Me /TIBA/ 3 . It was suggested that TIBA was present in the active center first in the form of a neutral heterobimetallic Zr–Al bridged complex followed by the formation of a partially polarized Zr–Al(Cl)R₂ (R = ⁱBu) or an unreactive Zr–AlR₃ cationic complex by abstraction of the alkyl ligand under the action of borate. It was concluded that AlR₃ from the latter cationic complex may be easily reversibly replaced under the specific coordination of ethylene or accumulated α-olefin, giving rise to highly labile and sterically accessible cationic species. Experiments on ethylene polymerization with the catalytic systems 1Cl ( 1Me )/TIBA/ 3 /Ph₂NH, 1Cl ( 1Me )/TIBA/ 4, 2Cl ( 2Me )/TIBA/ 3 /Ph₂NH, and 2Cl ( 2Me )/TIBA/ 4 were performed to confirm the suggestion. Catalytic systems derived from dichloride complexes in the presence of a σ-donor substrate also produced low molecular weight PEs with molecular weight characteristics similar to those of products obtained with the dimethylated precatalysts. The specific feature of active species derived from 2Me complexes to isomerize coordinated α-olefin into trans-vinylene polymer chains was also revealed. The catalytic behavior of the ternary catalytic system based on 2Me relative to 2Me or 2Cl precatalysts activated with polymethylaluminoxane at different Al/Zr ratios was compared. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1901–1914, 2001     

Mesoscale deformation and cracking of surface-hardened low carbon steel

Mesoscale deformation patterns of surface-hardened low-carbon steel is investigated by using the television-optical measuring technique (TOMSC-1). Surface hardening was performed by diffusion borating to produce a hardened layer with a heterogeneous structure. Plastic flow at the mesoscale level was observed for primary mesovolume in the form of triangular prism. Self-organization of neighboring primary mesovolume gives rise to formation specimen macrostructure. At certain thickness of borated layer, the tensile elongation is increased by 30% for specimens with brittle-hardened layer when compared with unhardened specimens.     

Crystal structure and properties of the Na1−x Ru2O4 phase

Sodium ruthenium(III,IV) oxide Na_1−x Ru₂O₄ was synthesized by the solid state reaction of Na₂CO₃ and RuO₂ in inert atmosphere and characterized by X-ray powder diffraction, electron diffraction, and high-resolution transmission electron microscopy. The compound crystallizes in the CaFe₂O₄-type structure (space group Pnma, Z = 4, a = 9.2641(7) Å, b = 2.8249(3) Å, c = 11.1496(7) Å). Double rutile-like chains of the RuO₆ octahedra form a three-dimensional framework, whose tunnels contain sodium cations. The structure contains two crystallographically independent sites of ruthenium atoms randomly occupied by the Ru^III and Ru^IV cations. The superstructure with the doubled b parameter found for one of the samples under study using electron diffraction is caused, probably, by ordering of the Ru cations in the rutile-like chains. The Na_{1− x} Ru₂O₄ compound exhibits temperature-independent paramagnetism with χ₀ = 1.9·10⁻⁴ cm³ (mole of Ru⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1655–1660, October, 2006.     

Development of Efficient Zeolite-Containing Catalysts for Petroleum Refining and Petrochemistry

The role of various technologies in oil refining and petrochemistry changes due to amendments to the requirements for fuel quality. The development of these technologies requires the improvement of catalysts. This paper outlines main procedures for the production of dealuminated zeolites, as well as the advantages and drawbacks of these procedures. Catalysts with a high desulfurizing ability for the hydrocracking of vacuum gas-oil to gasoline and diesel fractions and catalysts for the isomerization of fuel hydrocarbons can be prepared using ultrastable Y-type zeolites. The results of testing of zeolite-containing binary catalytic systems in Fischer-Tropsch synthesis are presented.     

Rationality of bundles of conics with degenerate curve of degree five and even theta-characteristic

We consider three-dimensional varieties which can be represented as bundles of conics with degenerate curve C and its two-sheeted unramified covering C. The rationality of such varieties is proved if the curve C is smooth, its degree is equal to five, and the covering C C corresponds to an even point of second order on the Jacobian of C.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 103, pp. 100–105, 1980.     

Method of recurrent construction of Löuwdin spin-adapted wave functions. II. Local representation of creation–annihilation operators

Some compositions of the addition and subtraction operators and recurrence relations for the Sanibel-type coefficients c_{u, v} (n, s, M) generated by these compositions are studied. A local representation of the fermion creation–annihilation operators via the addition and subtraction operators is obtained. Operators of single excitations, coupling, and decoupling operators, in terms of which the unitary group generators can be expressed are defined. The resulting representation of the nonelementary unitary group generators is much more simple than in the Gelfand–Tzetlin basis and in the most general case contains only six logically different terms, each of them possessing quite transparent physical significance.     

Effect of glucocorticoids and their complexes with apolipoprotein A‐I on the secondary structure of eukaryotic DNA

The tetrahydrocortisol–apolipoprotein A‐I complex specifically interacts with eukaryotic DNA isolated from rat liver. This interaction is highly cooperative and of a saturating nature. One DNA molecule binds about 54 molecules of the complex. Small‐angle X‐ray scattering has shown that hydrogen bonds between nitrous bases are destroyed and that single‐stranded structures are formed at the interaction of the tetrahydrocortisol–apolipoprotein A‐I complex with eukaryotic DNA. The most probable site of binding the tetrahydrocortisol–apolipoprotein A‐I complex with DNA is the sequence of the CC(GCC)_n type entering the structure of many genes, among them the structure of the human apolipoprotein A‐I gene. Oligonucleotide of this type has been synthesized. The association constant (K_ass) of its complexation was shown to be 1.66 · 10⁶ M^?1. Substitution of tetrahydrocortisol for cortisol in the complex results in a considerable decrease of K_ass. IR‐spectroscopy study has shown that the interaction of tetrahydrocortisol with oligonucleotide CC(GCC)_3–5 is accompanied by the formation of hydrogen bonds via the CO‐NH, PO₂, and OH groups of desoxycytidinephosphate. The tetrahydrocortisol–apolipoprotein A‐I complex alters the DNA secondary structure formed at the interaction with the hormone, causing the structural transition “order → tangle.” It is assumed that in the GC‐pairs of the given DNA sequence, tetrahydrocortisol initiates the rupture of hydrogen bonds, while the hydrophobic interactions between nitrous bases and apoA‐I intensify this process. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005