Parametric oscillations and stability of systems with large modulation coefficient

We study parametric oscillations of linear systems with one degree of freedom for large values of the modulation coefficient. We use the classical analytic Lyapunov-Poincaré perturbation methods and an original numerically-analytic method of accelerated convergence to construct periodic solutions and the corresponding eigenvalues. We find the boundaries of stability and instability domains. We use specific models to illustrate the main properties of parametric oscillations of systems with singular character of the perturbation dependence on the modulation coefficient. We consider periodic boundary value problems for the modified Mathieu equation and the Kochin equation modeling crankshaft torsional vibrations and show that there are significant differences between weakly and essentially perturbed periodicmotions both for the lowest and arbitrary oscillation modes. We also describe the unusual properties of the boundaries in the domain of the system determining parameters.     

A study of the mechanism and kinetics of interaction between nepheline powder and ammonium hydrofluoride

Behavior of a skeleton silicate, nepheline, in the reaction of fluorination with ammonium hydrofluoride was studied by means of differential-thermal, X-ray phase, and chemical analyses, IR spectroscopy, and scanning electron microscopy.     

Regioorientation in the reaction of side chain activated alkylpyridines with electrophiles

X-ray structural data has shown that condensation of sym-3-nitrocollidine with benzaldehyde occurs at the 6-methyl group. The presence of an acceptor group in the side chain of 2,6-dimethyl-4-cyanomethyl-3-nitropyridine causes condensation to occur at the activated methylene group in the 4-position.M. V. Lomonosov State University, Moscow 119899. A. N. Nesmeyanov Institute of Organoelemental Compounds, Moscow 117813. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11. pp. 1543–1550, November, 1995. Original article submitted June 10, 1995.     

Algebraically Special Gravitational Fields with the Cosmological Constant and Energy-Momentum Tensor of Electromagnetic Radiation

A class of rigorous solutions of the Einstein–Maxwell equations is obtained within the Newman–Penrose formalism for algebraically special gravitational fields with the cosmological constant and energy-momentum tensor of electromagnetic radiation given that the photon flux specifying electromagnetic radiation determines isotropic-geodesic congruence. Designations within the Newman–Penrose formalism and numbers of formulas in references are the same as in [1].     

Polarization experiments with the SPIN setup at the ITEP synchrotron

New experimental data on the spin-rotation parameters A and R measured for elastic π ^± p scattering in the resonance region and on the asymmetry in pC scattering at primary momenta in the range 1.35–2.02 GeV/c, as well as in quasielastic proton scattering on nuclei in the same momentum range, are summarized. All these data were recently obtained by using the proton synchrotron installed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The spectrum and features of seven isospin-3/2 baryon resonances that form a peak in the total cross section at a c.m. energy of 1.9 GeV are analyzed on the basis of new data on the parameters A and R, and the results of this analysis are presented. The experiments surveyed in this article were performed by a collaboration of researchers from ITEP and the Petersburg Nuclear Physics Institute (PNPI, Gatchina), the ITEP-PNPI collaboration.     

On Vortex Dynamics in the Self-Dual Chern–Simons–Higgs System

The dynamics of n vortices in the self-dual Chern–Simons–Higgs system defined on the infinite plane is investigated. In adiabatic approximation, the vortex dynamics is determined by considering a rigid motion of a vortex configuration and a motion around a fixed center of mass. A motion of two vortices is studied in detail.     

Synthesis of Substituted 6-Amino-4-aryl-5-cyano-2H,4H-pyrano[2,3-c]pyrazoles. Crystal and Molecular Structure of 6-Amino-5-cyano-3-methyl-4-(2',4',6'-triethylphenyl)-2H,4H-pyrano[2,3-c]pyrazole

Substituted 6-aminopyrano[2,3-c]pyrazoles were synthesized by the two-component condensation of arylidenemalononitriles and substituted 5-pyrazolones or three-component condensation of aromatic aldehydes, malononitrile, and substituted 5-pyrazolones. It was established by X-ray crystallographic analysis that pyranopyrazoles exist in the 2H and not the 1H tautomeric form.     

Separation of Anions of Organic Acids in Concentrated Solutions by Means of Capillary Isotachophoresis

The separation of a mixture containing anions of nine organic acids is investigated on an instrument for capillary isotachophoresis with an optical detector for the registration of boundaries. The separation is conducted in concentrated solutions of sodium salts. A counterflow is used during the separation.     

Synthesis,alkylation, and molecular and crystal structure ofN-methylmorpholinium 6-amino-3,5-dicyano-1,4-dihydropyridine-4-spirocyclohexane-2-thiolate

The reaction of cyano(cyclohexylidene)thioacetamide with cyanothioacetamide or malononitrile andN-methylmorpholine yieldsN-methylmorpholinium 6-amino-3,5-dicyano-1,4-dihydropyridine-4-spirocyclohexane-2-thiolate. Its structure was established based on the results of alkylation and X-ray structural analysis.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2535–2540, October, 1996.     

Electronic regioselectivity in the reactions of pyridinium ylides with tetracyanoethylene

Highly regioselective reactions of pyridinium ylides with tetracyanoethylene occur via an Ad_N-E mechanism to form Z-isomers of 3-aroyl-3-(1-pyridinio)-1,1,2-tricyano-2-propenides-1, corresponding in structure to 1,4-ylides with maximum charge separation. If the unsaturated nitrite starting material contains a nucleofugal group 1,2-elimination predominates over 1,3-elimination.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1087–1094, August, 1991.