Hydrogenation of cyclohexene on different types of catalysts

Hydrogenation of cyclohexene has been studied under pressure in a flow reactor on the following catalysts: Na- and H-forms of Y-type zeolites, erionite, magnesium and lanthanum oxides, palladium on silica and aluminum oxide. This reaction is accompanied by skeletal isomerization to give methylcyclopentane and methylcyclopentenes. The differences in activation energies for isomerization and hydrogenation reactions were estimated as 83–96 kJ/mole for NaY and Na,K-erionite, 33–50 kJ/mole for the H-forms of the zeolites, 33–37 kJ/mole on the Pd catalysts, and 25–33 kJ/mole on magnesium and lanthanum oxides. It is suggested that the cyclohexyl complex, formed as an intermediate during hydrogenation of cyclohexene on Na-forms of the zeolites, is neither a carbocation nor a radical.Deceased.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 791–799, April, 1992.     

Relaxation of a 2D MHD flow across a magnetic field (2D hydrodynamic flow) in a bounded region

The problem on magnetohydrodynamic (MHD) flow of a solitary vortex across a magnetic field in a volume confined by rigid walls is solved numerically for large Reynolds numbers (including magnetic Reynolds numbers) and small Alfven-Mach numbers M _A . In this case, the MHD problem is reduced to that of two-dimensional hydrodynamic turbulence. It is shown that sound is not generated by a turbulent medium for small values of M _A ; consequently, this kinetic energy dissipation channel is closed in this case. Calculations show that, in contrast to 3D turbulence, kinetic energy dissipation for 2D turbulence occurs, as expected, over time periods on the order of L²/v(L is the characteristic size of the system and v is the kinematic viscosity). In our calculations with numerical viscosity v～vΔx (Δx is the unit cell size), this corresponds to time values on the order of ～(L/Δx)(L/v). In the kinetic energy spectra for a turbulent flow in a bounded region in the inertial interval (lying between the energy-carrying and viscosity regions), the values of E(k) decrease with increasing wave numbers k at a higher rate than in proportion to k^?3. The volume distribution of vorticity becomes narrower with time (the characteristic values of curlv decrease) and is blurred; for large time periods, the distribution approximately retains its shape as well as asymmetry with respect to positive and negative values, which is associated with the asymmetry of the initial conditions.     

High temperature spin wave dynamics of the uniaxial antiferromagnets

In the framework of the spin operators diagram technique the dynamical properties of the easy-axis type antiferromagnets at high temperatures are considered. The diagonalization procedure generalizing the Bogoliubov u-v transformation on the spin operators is presented. The spin wave (SW) spectrum allowing for the temperature and the magnetic field dependence of the sublattice magnetizations at T～T_～ is obtained. The SW relaxation frequencies due to the processes of SW scattering on the thermal spin fluctuations are calculated. The latter are in agreement with the data obtained on MnF₂ near the spin-flop transition¹⁰.     

The NSW interaction with nuclear local modes in antiferromagnets

The nuclear spin wave (NSW) relaxation rates due to the interaction with nuclear impurity local modes (NILM) in antiferromagnets are considered in the framework of the Keldysh formalism based on the spin operator diagram technique. It is shown that the NSW relaxation frequency due to the scattering on the fluctuations of impurity nuclear spins is of resonance character. The NSW damping due to the resonance absorption by NILM depends strongly on the NSW amplitude N, which accounts for the “hard” excitation of NSW's in parallel pumping experiments /6/. The NSW relaxation rates due to the processes involving two NSW's and one impurity nuclear excitation are also calculated.     

Calculation of spectral and Rosseland paths in a plasma with multiply charged ions based on a statistical approach

The semiclassical approach to determine the Fourier components of the electron dipole moment disregarding polarization (noninteracting electron model) is used for analyzing ion oscillator strengths and determining the radiation properties of plasmas consisting of multiply charged ions of heavy elements. The oscillator strength distribution df/d?? (proportional to the photoabsorption cross section) is calculated as a function of the degree of ionization and self-similar frequency ?? = ??/Z. It is found that for low degrees of ionization, function df/d?? for an ion is close to function df/d?? for a neutral atom; upon an increase in the degree of ionization, regions are formed in which df/d?? = 0 (transparency windows) and the photoabsorption cross section for high degrees of ionization differs from zero only in small frequency ranges. The resultant distribution of the ion oscillator strengths is used for calculating the polarizability of ions as a function of frequency and the cross section of radiation scattering on ions. For a gold plasma, the absorbance and opacity (both spectral and averaged according to Rosseland and Planck) are calculated. The results of computing the paths and absorption coefficients coincide in order of magnitude with the available data. The effect of scattering on the Rosseland path is estimated.     

Multichannel analyzers of atomic emission spectra: Current state and analytical potentials

The structure and characteristics of a modern tool for recording and processing emission spectra, that is, multichannel analyzer of atomic emission spectra (MAES), based on multicrystal assemblies of photodiode arrays, as well as spectral parameters of the instruments equipped with these analyzers are presented. The analytical potentials of MAES spectrometers are considered.