Scaling laws for the spatial distributions of the plasma parameters in the positive column of a dc oxygen discharge

Comprehensive self-consistent simulations of the positive column plasma of a dc oxygen discharge are performed with the help of commercial CFDRC software (), which enables one to carry out computations in an arbitrary 3D geometry using fluid equations for heavy components and a kinetic equation for electrons. The main scaling laws for the spatial distributions of charged particles are determined. These scaling laws are found to be quite different in the parameter ranges that are dominated by different physical processes. At low pressures, both the electrons and negative ions in the inner discharge region obey a Boltzmann distribution; as a result, a flat profile of the electron density and a parabolic profile of the ion density are established there. In the ion balance, transport processes prevail, so that ion heating in an electric field dramatically affects the spatial distribution of the charged particles. At elevated pressures, the volume processes prevail in the balance of negative ions and the profiles of the charged particle densities in the inner region turn out to be similar to each other.     

Features of evolution of the substructure in the creep of dispersion-hardened nickel

A study is made of the laws governing high-temperature creep and the evolution of the substructure in dispersion-hardened alloy Ni — 3 vol. % HfO₂ during its free annealing and creep. The polygonized substructure was formed in the alloy prior to annealing. An analysis is made of structural transformations at different structural levels and the mechanism of high-temperature creep in the alloy. Institute of the Physics of Strength and Materials Science, Siberian Branch of the Russian Academy of Sciences. All-Republic Engineering-Technical Center, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 83–89, March, 1998.     

Substantiation of the two-temperature kinetic model by comparing calculations within the kinetic and fluid models of the positive column plasma of a dc oxygen discharge

Results from kinetic and fluid simulations of the positive column plasma of a dc oxygen discharge are compared using commercial CFDRC software (), which enables one to perform numerical simulations in an arbitrary 3D geometry with the use of both the fluid equations for all the components (fluid model) and the kinetic equation for the electron energy distribution function (kinetic model). It is shown that, for both the local and nonlocal regimes of the formation of the electron energy distribution function (EEDF), the non-Maxwellian EEDF can satisfactorily be approximated by two groups of electrons. This allows one to take into account kinetic effects within the conventional fluid model in the simplest way by using the proposed two-temperature approximation of the nonequilibrium and nonlocal EEDF (2T fluid model).     

Finitely convergent deterministic and stochastic iterative methods for solving convex feasibility problems

We propose finitely convergent methods for solving convex feasibility problems defined over a possibly infinite pool of constraints. Following other works in this area, we assume that the interior of the solution set is nonempty and that certain overrelaxation parameters form a divergent series. We combine our methods with a very general class of deterministic control sequences where, roughly speaking, we require that sooner or later we encounter a violated constraint if one exists. This requirement is satisfied, in particular, by the cyclic, repetitive and remotest set controls. Moreover, it is almost surely satisfied for random controls.

     

Stability of zirconium oxides in Nb-Mo-ZrO2 alloy

The paper gives the results of investigations on the rate of coalescence of zirconium oxides in Nb-Mo-ZrO₂ alloy. On the basis of experimental results and theoretical estimates, it is shown that the stability of zirconium oxides in a niobium matrix increases substantially when the oxygen content in the solid solution rises. A high stability of zirconium oxides in niobium, which ensures a considerable (up to T 1800°C) increase in the recrystallization temperature and enhancement of the mechanical properties of the alloys at T 1100°C can be attained at an oxygen content C₀ 0.2–0.5 at.% in the solid solution.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 76–79, May, 1982.     

Structure of inorganic nanoclusters embedded in solid matrixes: an X-ray absorption study

Results of X-ray absorption studies of copper nanoclusters embedded in SiO₂ matrix and selenium chains confined in channels of cancrinite are reported. Initially randomly distributed copper atoms mainly surrounded by silicon species in an as-made film upon annealing form copper nanoclusters with a characteristic size of 80 Å and the structure identical to that of bulk copper. The characteristic size of the clusters does not increase with further annealing. Selenium in cancrinite is shown to form strongly oriented linear dimerised chains with a bond length much larger than that in bulk forms of selenium.     

Role of Supercritical Water and Pyrite in Transformations of Propylene

The effect of supercritical water and pyrite on the transformations of propylene upon the uniform heating (1.5 K/min) of reagents to 718 K is studied. The products are analyzed by IR and ¹H NMR spectroscopy, mass-spectrometry and gas chromatography/mass-spectrometry. It is established based on the temperature dependences of the pressure of reagents that the addition of pyrite in the absence of water gives rise to a decrease in the starting temperature of propylene oligomerization. In the absence of pyrite, the addition of water suppresses propylene oligomerization. A synergetic effect of supercritical water and pyrite on the degree of conversion of propylene is revealed. It is shown that hydrogen sulfide, thiols, and methyl-derivatives of thiophene are formed in the presence of pyrite, as well as the yield of aromatic and polyaromatic hydrocarbons increases. The mechanisms of the observed processes are discussed.     

Heterocyclization of compounds containing diazo and cyano groups. 6. Theoretical and experimental investigations of cyclization of 2-cyano-2-diazoacetamides to 5-hydroxy-1,2,3-triazole-4-carbonitriles

A series of N-alkyl- and N-aryl-2-cyano-2-diazoacetamides was synthesized by the reaction of 2-amino-2-cyanoacetamides with sodium nitrite in hydrochloric acid. The mechanism of their heteroclectrocyclization to 5-hydroxy-1,2,3-triazoles was investigated kinetically and theoretically by the B3LYP/6-31+G^* method. The conclusion was made on the basis of the determined activation energy of the cyclization process. reaction parameters , and kinetic isotope effects, that there is a difference between the mechanisms of cyclization of the N-alkyl and N-aryl derivatives of 2-cyano-2-diazoacetamide; cyclization of the N-alkyl derivatives takes place by a monorotatory mechanism, while cyclization of the N-aryl derivatives takes place by a mechanism where one of the stages is heteroelectrocyclization of 2-diazoacetimidates.For Communication 5, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 26–41, January, 2000.