Stereoselective [π4s+π2s]-dipolar cycloaddition of pyridinium ylides to nitriles of the trans-1,3-butadiene series. Crystal and molecular structure of 3-benzoyl-1-(2,2-dicyano-1-cyclopropylvinyl)-2-phenyl-6-cyano-1,2-trans-2,3-trans-1,9-trans-1,2,3,9-tetrahydroindolizine

The interaction of substituted trans-1,1-dicyano-4-phenyl-1,3-butadienes with pyridinium ylides proceeds through the path of [4_s+2_s]-dipolar cycloaddition, highly regioselective and stereoselective, with the formation of substituted 1-(2,2-dicyanovinyl)-2-phenyl-6-cyano-1,2-trans-2,3-trans-1,9-trans-1,2,3,9-tetrahydroindolizines. The stereoselectivity of these reactions is due to endo-addition of molecules of trans-1,3-butadienes to the anti form of the pyridinium ylides; it is confirmed by correlation analysis of the data from double PMR, mathematical calculations of torsion angles, and x-ray structural studies of the substituted tetrahydroindolizines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1354–1360, October, 1991.     

Thermal transformations of lead oxides

Differential scanning calorimetry, differential thermogravimetry, X-ray analysis and electronic microscopic studies of thermal transformations of PbO₂ were carried out. Formation of fine dispersed (less than 100 nm) particles of α-PbO was observed at PbO₂ thermal decomposition at heating to 580°C. Reverse reaction of Pb₃O₄ formation from PbO was found at cooling and annealing at 400°C in air. At heating of α-PbO to 650°C the particle growth to 1 μm with formation of β-PbO took place. Thermal decomposition with formation of β-PbO particles with size from 0.3 to 1 μm at PbO₂ heating to 650°C was observed. Transition from PbO to Pb₃O₄ at cooling of sample heated to 650°C was not detected. Interpretation of observed phenomena from the point of view of particle size influences on the shift of α-PbO↔β-PbO phase transition temperature and on the chemical activity of phases are presented.     

Breaking of Cubic Symmetry in Rare-Earth Dodecaborides with Dynamic Charge Stripes

JETP Letters - The effect of symmetry lowering for the parameters of electron transport in rare-earth dodecaborides RB12 (R = Ho, Er, Tm, Lu) with fcc crystal structure at temperatures T ≤...     

Heat capacity and thermodynamic properties of Mg(Fe<Subscript>0.6</Subscript>Ga<Subscript>0.4</Subscript>)<Subscript>2</Subscript>O<Subscript>4</Subscript> in the 0–800 K temperature range

The heat capacity of Mg(Fe_0.6Ga_0.4)₂O₄ in the temperature range of 4.56–804.9 K is measured by adiabatic and differential scanning calorimetry. The temperature dependence of the heat capacity of Mg(Fe_0.6Ga_0.4)₂O₄ in the 0–800 K range is determined by generalizing the experimental data. The temperature dependences of thermodynamic functions (entropy, enthalpy change, and the reduced Gibbs free energy) are calculated. The abnormal contribution to the heat capacity C _p ^an(T) in the temperature range of 5–52 K is estimated.     

Dynamics of a System of Bodies with Program-Variable Configuration

The dynamics of a system of rigid bodies with program-variable configuration is analyzed. A mathematical model is constructed using methods of analytical mechanics. The behavior of a microsatellite with a deployable gravity-gradient boom is analyzed as a numerical example     

Deployment of Reconfigurable Spacecraft Under Earth Conditions in the Out-Of-Plane Rotation Mode

The cable-suspension method is used to simulate weightlessness on Earth in the general case. By an example of mathematical simulation of a system of rigid bodies connected via hinged joints and suspended from a special facility, it is shown that the method developed provides realistic simulation of orbital processes under earth conditions. The validation criterion for the simulation is the closeness of the values of the forces and moments in joints and the attitude and angular velocities to their theoretical values in orbital motion