Two-dimensional gas of electrons in a strong magnetic field

Translated from Izmeritel'naya Tekhnika, No. 2, pp. 4–7, February, 1990.     

The controllable variband structures in ferroelectric semiconductor

The possibility of formation of the variband structure in a ferroelectric semiconductor is pointed out. The energy scheme of such variband structure depends on temperature, electric bias, light intensity and posseses hysteresis.     

Cycloaddition of cage and polycyclic diazo compounds to C<Subscript>60</Subscript> fullerene catalyzed by Pd(acac)<Subscript>2</Subscript>-2PPh<Subscript>3</Subscript>-4Et<Subscript>3</Subscript>Al

Spirohomofullerenes were synthesized by cycloaddition of cage and polycyclic diazoalkanes generated in situ by oxidation of hydrazones of camphor, 2-adamantanone, and cholestane-3-one to C₆₀ fullerene in the presence of the Pd(acac)₂-2PPh₃-4Et₃Al three-component catalyst. It was found that the spiro-homofullerenes obtained from hydrazones of 2-adamantanone and cholestane-3-one and C₆₀ fullerene do not undergo thermal isomerization to the corresponding spiro-methanofullerenes.     

Selection of the optimum composition of an alumina support of Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for pyrolysis gasoline hydrogenation

To optimize the chemical composition of catalysts for the selective hydrogenation of diene and vinyl aromatic hydrocarbons in pyrolysis gasoline, we study the effect of the acid-base and textural characteristics of a support modified with additives of sodium compounds on the activity and stability of the catalysts in reactions of hydrogenation and oligomerization of unsaturated compounds. It is shown that the rate of formation of oligomeric compounds depends on the number of Lewis (Q _CO > 34 kJ/mol) and Brönsted sites (ν_OH = 3688 cm^?1). An increase in their total amount on the catalyst surface leads to an increase in the rate of formation of oligomeric hydrocarbons. The amount of surface condensation products is determined by the concentration of strong aprotic sites with Q _CO > 35 kJ/mol. Alumina support samples with a high surface concentration of medium-strong Lewis sites, wedge-shaped or conical pores, and the preferential distribution of porometric volume in pores with a diameter of 5–15 nm are characterized by a significant ability to oligomerize unsaturated compounds. Catalysts that contain 0.5 wt % Na exhibit the lowest oligomerization ability and a high stabile activity in reactions of hydrogenation of diene and vinyl aromatic hydrocarbons in pyrolysis gasoline. For the selective hydrogenation of diene and vinyl aromatic hydrocarbons in pyrolysis gasoline, we recommend a catalyst with 0.5 wt % Pd supported from palladium acetylacetonate on δ-Al₂O₃ modified with 0.5 wt % sodium; it is characterized by the absence of wedge-shaped or conical pores, the preferential (60.7%) distribution of porometric volume in a range of d _p > 15 nm, and a low aprotic acidity (L = 3.1 μmol/g), which contributes to the decrease in the amount of resulting condensation products (V = 3.6 μg/(gcat h)) and a high stable activity (DN = 0.68 g J₂/100 g) in reactions of hydrogenation of unsaturated compounds.     

Oxidative dehydrodimerization of methane on Bi-Mn oxides: Catalyst active component and reaction mechanism

A series of Bi-Mn-O catalysts has been studied as a function of bismuth content (from 0 to 100 atom.%). The fresh-prepared samples are found to be a heterophasic mixture of the Bi₂Mn₄O₁₀ compound with the individual manganese or bismuth oxide, the surface of which is enriched in bismuth. At initial period of catalytic work, a part of Bi₂Mn₄O₁₀ decomposes to ga-Bi₂O₃ and -Mn₂O₃ resulting in the formation of rather effective catalyst for methane oxidative coupling. It is postulated that the catalyst active component consists of a Bi₂O₃ phase lying at the surface of a Bi₂Mn₄O₁₀ compound. At a steady state, the oxidative dehydrodimerization reaction occurs via both redox and associative mechanisms whilst the deep oxidation proceeds mainly according to the redox one.     

Identification of the Parameters of a Discrete Gas-Lift Process

Journal of Computer and Systems Sciences International - A time-averaged mathematical model of a discrete gas-lift process is considered. At the first iteration, an analytical expression for the...