Comparative investigation of the effect of heat and optical radiation on the structure of island metal films by optical fluctuation microscopy

Variations in the structural parameters of island sodium films on the quartz surface, caused by heating or exposure to optical radiation, are investigated by the optical method proposed earlier. A correct scheme of processing the measured data is developed. It is shown that to determine the structure parameters, the measurements of both the mean values and fluctuations of transmission and reflection coefficients of the film and of their correlator are required. It is also demonstrated that under a number of assumptions, it is possible to determine the character of the process of evaporation of islands and to reveal the evolution of the distribution function by using the data of measurements. It was found experimentally that variations in the structural parameters of a film during its evaporation caused by heating of the substrate or irradiation by light can noticeably differ. This fact is explained by a difference in the mechanisms of action of heating and irradiation on an island.     

Selective binary mobile phase for high-performance liquid chromatography of 12, 13-epoxytrichothec-9-en-8-ones

M. V. Lomonosov Moscow State University. All-Union Scientific-Research Institute of Veterinary Medicine, Moscow. Translated from Khimiya Prirodnykh Soedinenii, Vol. 6, pp. 861–863, November–December, 1989.     

Phase Equilibria in the Fullerene C60-Fullerene C70-Hexane-o-Xylene-Dimethylformamide System

The phase diagram of the hexane-o-xylene-dimethylformamide ternary liquid system was studied at T= 298.15 K. The diagram contained the regions of homogeneous solutions and two-phase liquid systems (systems with stratification), phase I being enriched in dimethylformamide and phase II, in hexane. The distribution of fullerenes C⁶⁰ and C⁷⁰ was considered at various concentrations and simultaneous presence in sections at variable phase compositions. The extraction isotherms of fullerenes C⁶⁰ and C⁷⁰ under various conditions were found to be close to linear, and the C⁷⁰/C⁶⁰ separation factor depended on the composition of the coexisting phases and ranged from 1.25 to 1.8. Fullerene C⁷⁰ was predominantly distributed in phase I.     

Propagation of nonlinear waves along a viscoelastic bar

Various types of nonlinear waves propagating along a viscoelastic bar are considered. The rheological equation of state has strong physical and geometric nonlinearities, and nonisothermal effects are included. Both weak (isentropic) and shock waves of loading and unloading are investigated. It is shown that, for certain rubber-like materials, stable shock waves of extension can exist along with the shock waves of compression at very large strains. We then consider the strike of a viscoelastic bar of finite length against a rigid obstacle. Numerical solutions to this problem illustrate the influence of stress relaxation on nonlinear wave processes. A model for sticking and bouncing off is formulated and the mass-averaged velocity of the bar at the moment when it bounces off the obstacle is calculated.     

Mechanochemistry of hexagonal boron nitride. 2. Reactivity upon interaction with water

Mechanical activation makes boron nitride chemically reactive with respect to water. The fact of the reaction proceeding, which is accompanied by a change in the structure of boron nitride, is confirmed by the data of IR spectroscopy, X-ray diffraction, transmission electron microscopy, differential thermal analysis, adsorption, and gravimetry. It is established that the most defective amorphous part of the material is primarily hydrolyzed. The reaction takes place at room temperature, with the conversion increasing to values of higher than 50% with the dose of mechanical energy supplied during the mechanical activation. In addition to ammonia, hydrolysis gives rise to the formation of ammonium pentaboride, NH₄B₅O₆(OH)₄ · 2H₂O. After the reaction products are removed, residual boron nitride, which is dried at T ≤ 100°C, crystallizes to form nanosized rods.     

Mechanochemistry of hexagonal boron nitride: 1. Destruction and amorphization during mechanical treatment

The regularities of the mechanical activation of hexagonal boron nitride are analyzed using the X-ray diffraction, IR spectroscopy, transmission electron microscopy, dynamic light scattering, and adsorption methods. At the initial state of mechanical activation, the main process is material destruction. At this stage, the specific surface area increases to 400 m²/g and crystallographically oriented nanosized needles are formed. At the same time, boron nitride crystal structure is disordered with an increase in interplanar distance d(002). The disordering is assumed to be due to a shift along planes (001). At a specific dose of supplied mechanical energy above 6–8 kJ/g, the disordering processes dominate and the material is amorphized. At this stage, the specific surface area of samples decreases.     

Transformation of a Rabi oscillation spectrum for a two-level system in a strong resonant field

We have found an analytical expression describing the evolution of a two-level system in a strong resonant quantum field beyond the rotating wave approximation. The solution obtained has allowed us for the first time to identify the qualitative features of the behavior of the system in this case: suppression of the "collapse–revival" effect, and a change in the spectrum and shape of Rabi oscillations for an inverted population. The results are of interest for applied spectroscopy, quantum optics, and nanomechanics.