Yu. G. Yanovskii

Optical properties of the (3 1 1) oriented GaAs/AlAs superlattices and quantum wire-like structures

Abstract Optical vibrational modes in the (3xa01xa01)-oriented GaAs/AlAs superlattices and structures with quantum wires were investigated by the FTIR spectroscopy. A splitting of the fundamental TO vibrational mode localized in the GaAs quantum wire into two ones with a different polarization was observed. The dispersion of the transverse optical GaAs phonons in the (3xa01xa01) direction was obtained.

Description of mechanical properties of particulate-filled nanostructured polymer composites using fractal analysis

A number of the main mechanical characteristics (yield strength, impact toughness, microhardness) of particulate-filled polymer nanocomposites are quantitatively described using fractal analysis. The approach is used to study the main mechanical behavior features of these materials. The influence of the initial particle size of nanofiller and the degree of particle aggregation on the mechanical properties of nanocomposites is shown.

Computer simulation of mechanical properties of carbon nanostructures

The aim of the present paper is the theoretical investigation of the mechanical properties of carbon nanostructures of graphene and single-wall carbon nanotubes by using nanoscopic and macroscopic approaches. The nanoobject structures in free and deformed states were considered and the corresponding energies were computed in the framework of quantum mechanics methods by using the original software package of semi-empirical programsNDDO/sp-spd (developed in the Institute of Applied Mechanics, Russian Academy of Sciences) in parallel computations. The nanostructural deformations were prescribed in the approximation of the mechano-chemical deformation coordinate. The deformation forces were described by the energy gradients in selected coordinates of microscopic deformations. The mechanical characteristics of nanoobjects such as Young’s modulus, rigidity coefficients, works done in deformation, critical stresses, and relative elongations in fracture were calculated in the framework of the macroscopic linear theory of elasticity; the deformation forces determined by quantum mechanical calculations were used in the corresponding relations. It was found that the mechanical characteristics of single-wall carbon nanotubes (CNT) depend on their diameter and chirality, and the deformation properties of a graphene sheet are asymmetric with respect to two normal extension modes directed along the “zigzag” and “armchair” on the sheet edges. The calculated mechanical characteristics are in good agreement with the experimental data known fromthe literature, in both the values and the deformation asymmetrywith respect to different deformation modes.

Estimating the effective rate of fast chemical reactions with turbulent mixing of reactants

On the basis of representation of a turbulent fluid as an aggregation of independent turbulent particles (vortexes), we derive relations for the effective rate of chemical reactions and obtain a closed system of equations describing reactions with turbulent mixing of reactants. A variant of instantaneous reactions is considered that explains the proposed approach simply. In particular, the turbulent mixing events according to this approach are uniquely related to the acts of chemical interaction, which makes it possible to exclude from consideration the mixing of inert impurities–the most difficult point of the theory formulated using classical notions. The obtained system of equations is closed without introducing arbitrarily adopted correlations, by naturally introducing the concept of effective reaction and writing the equations of conservation for both the concentrations of reactants and their volumes.

Optical phonons in quantum-wire structures

The optical vibrational modes in GaAs/AlAs structures grown on a (311)A-oriented GaAs surface are investigated. It is found that the line corresponding to the fundamental TO vibrational mode localized in a GaAs quantum wire is split into two lines with different directions of the polarization vector. The dispersion of the TO phonons of GaAs in the (311) direction is determined from the IR spectra of periodic structures.

Localized optical phonons in GaAs/AlAs superlattices grown on (311)A and (311)B surfaces

A study is reported of optical vibrational modes in [311]-grown GaAs/AlAs superlattices. An analysis of the TO and LO localized modes observed in IR reflectance spectra showed that the difference between the TO and LO mode frequencies in superlattices grown on (311)A and (311)B surfaces is due to the different localization lengths of these modes. The dispersion of transverse optical phonons in GaAs derived from IR reflectance spectra is in a good agreement with Raman scattering data.

Comparison of image recognition efficiency of Bayes, correlation, and modified Hopfield network algorithms

The statistical estimates of the probability of correct recognition of the images, noisy reference by an additive handicap, for Bayes, correlation, and modified Hopfield network algorithms are compared. It is shown that, in the case of complete a priori probability concerning a handicap, the modified Hopfield network algorithm reaches the quality of the Bayes algorithm. At a deviation a priori probability on a handicap, the quality of the Bayes algorithm is worse than that of the modified Hopfield network algorithm. The correlation algorithm is worse than the modified Hopfield network algorithm, in general.

Study of nanostructures on a solar cell surface exposed on the Mir orbital station

It is shown that atomic-force microscopy under normal conditions makes it possible to obtain important information on the topography and features of nanostructures formed on the surface of cover glasses of solar cells exposed on the Mir orbital station for more than ten years. It is found that the nanostructures are multiscale; they are present on all vertical visualization scales from ∼1000 to ∼17 nm and on horizontal scales from ∼1000 to ∼100 nm. The nanoindentation study of mechanical properties of the exposed surface layer shows that the exposed surface at nanodepths is characterized by higher plastic deformation, but lower hardness and effective modulus, in comparison with unexposed surface.

A modified regularization method for calculating viscoelastic material relaxation functions

Conclusions1.The accuracy of solving incorrectly stated problems for the Tikhonov regularization method depends markedly on the accuracy of prescribing additional a priori information with respect to starting data, and in the present case to error parameters.2.If in the case in question error parameters and their statistics are determined with marked errors, then any accurate conformity of the regularization parameter with error parameters given in [16] does not make it possible to obtain a satisfactory regularized solution.3.An estimate of the maximum probability of error parameters for data may also lead to an unsatisfactory regularized solution if it contains gross overshoots.4.In our view the adaptive-robust algorithm for correcting gross experimental anomalies is a more reliable method for improving the accuracy of the regularized solution in the problem of calculating the relaxation spectrum for viscoelastic material from experimentally determined material functions without using a priori information about error parameters.n The work was carried out with the support and sponsorship of the Russian Fund for Basic Research.