Characteristic properties of ZnO random laser pumped by nanosecond pulses

Investigations of UV radiation spectra of powdered zinc oxide and its unordered film were conducted. The samples were pumped by 3-rd harmonics of the two-stage Nd:YAG-laser (λ=355 nm) with pulse duration ∼10 ns. Maximum density of energy of pumping pulses was about 150 mJ/cm². With some of our samples, we achieved lasing. The threshold values of the pumping energy density occurred higher than those under picosecond pumping approximately for one-two orders of magnitude. It was shown that the threshold of lasing and the character of lasing spectra depend on the morphology of particles forming a powder. The long-wavelength shift of the maximum of lasing spectra with a rise of the pumping was observed. It was interpreted as a result of participation of electron–hole plasma recombination in the process of lasing. A chaotic character of lasing spectra was observed and partially analyzed. PACS 42.55.Zz; 78.55.Et; 42.70.Hj     

Radical Nature of Pathways to Alkene and Ester from Thermal Decomposition of Primary Alkyl Diacyl Peroxide

Thermal decomposition of a primary alkyl diacyl peroxide 2 is investigated. Dependence of product yields on temperature, viscosity, and solvent polarity is examined in a variety of media. The excess of the alkene disproportionation product 4 and the presence of ester 3 and acid 5 is argued to demonstrate the existence of a discrete acyloxy-alkyl geminate radical pair. Stereoselective deuterium labeling of 2 and subsequent (1)H-NMR analysis of the resulting isotopomers of 4 confirm the radical nature of detected decomposition products.     

Long-wave instability of a plane multicomponent mixture layer with the Soret effect

Long-wave instability that arises in a plane multicomponent mixture layer with the Soret effect is investigated. The layer is heated from above or below in the gravity field. The solution of the linearized equations of motion is sought in the form of a series in powers of the wave number assumed to be small. For the mixture with an arbitrary number of components the critical parameters of instability are determined. For binary and ternary mixtures the stability maps are plotted. The regions where the long- and short wave perturbations are the most dangerous are distinguished in the space of physical parameters. The analytical results are compared with the numerical solution of the linearized equations over a wide wave number range. As an example, instability in a ternary hydrocarbon mixture is considered.     

Electronic Structure and Chemical Bonding in β-Sialons

Using the discrete variation procedure we investigated the electronic structure, charge distributions, and chemical bonding in solid solutions of variable composition based on -Si₃N₄ with Si substituted by Al and N substituted by O (the general composition ). The electronic processes at the initial stage of SiAlON formation were studied (x = 1, 2) considering different distributions of Al–O pairs in the lattice of -Si₃N₄. The distribution mode of the dopant is found to be a more significant factor affecting the electronic structure of sialons compared to increased Al–O content; in particular, clusterization of dopant pairs leads to increased forbidden gap and splitting of the upper and lower valence bands. The results of calculations are used to interpret the systematic variations in the functional properties of -sialons depending on their chemical composition.     

Theory of concentrational profile at the surface of a decomposing binary alloy

In the self-consistent-field approximation, a statistical theory is constructed for the atomic distribution in the near-surface region of a binary alloy which is able to disintegrate from the atomically smooth free surface of the crystal. The form of the surface-segregation functions of the components is found, in closed form, taking the relaxation of the coordination energies and the atomicinteraction energies at the surface into account. The possibility of the existence of metastable nonmonotonic concentrational profiles at the crystal surface is demonstrated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 51–56, December, 1981.     

Reparametrization of models of non-stationary chemical kinetics as a method of investigation of the inverse problem

A new approach to solve the inverse problem of the non-stationary chemical kinetics by a reparametrization of the initial model is suggested. This approach permits to obtain all solutions of IP in the case of a finite number or some parametric functions in the case of the infinite number of solutions.