Vol 44, No 5 (2018)

The results of an experimental study of the rheological properties of clay-particle suspensions with additions of silicon-, aluminum-, and titanium-oxide nanoparticles are given. The concentration of particles in solutions ranges from 0.25 to 2 wt %. The particle sizes are in the range from 5 to 100 nm. The dependences of the effective viscosity and rheological parameters of these solutions on the concentration, size, and chemical nature of nanoparticles are established.

A method for calculating the spectrum of Lyapunov exponents for delay systems is proposed. To validate the method, a delayed-feedback oscillator and the Mackay–Glass equation are considered as model systems. For both systems, bifurcation diagrams and spectra of Lyapunov exponents are constructed as functions of one of the control parameters. The results are shown to be in good agreement with each other, which indicates the efficacy of the proposed method.

A method of local anodic oxidation has been used to obtain graphene-oxide regions on SiC. The change of the surface properties was confirmed by atomic-force microscopy and Raman spectroscopy. Experimental data were obtained on the conductivity, potential, and topography of the oxidized regions. It was shown that the oxidation leads to a rise in the surface potential. A relationship was found between oxidation parameters, such as the scanning velocity and the probe voltage. The method of local anodic oxidation was used to obtain by lithography an ~20-nm-wide nanoribbon and an ~10-nm-wide nanoconstriction.

The total power of oscillations of current flowing through a semiconductor superlattice with different gaps between the first and second minibands is discussed. It is demonstrated that, with a decrease in the band gap, i.e., with an increase in the probability of interminiband tunneling, the total current-oscillation power increases when certain voltages are applied to the superlattice.

Combustion and thermal decomposition of hydrocarbon fuels are used to produce different forms of carbon. Combustion in the detonation mode is of particular interest, as nanocarbon obtained under these conditions differs in properties from products synthesized by other techniques. A pulsed gas-detonation device designed on the basis of a CCDS2000 detonation spraying facility opens up new possibilities for manufacturing of nanocarbon. The device operates in a flow mode of gas supply into the reactor at the atmospheric pressure, which ensures high productivity and industrial safety of this method. Using detonation of acetylene-oxygen mixtures rich in acetylene, nanoscale carbon was obtained with particle morphology depending on the ratio of the components in the gaseous mixture.

A method for determining the number of defects arising under compressive and tensile stress in bended thin transparent conducting coatings on polymer substrates is proposed. This algorithm is based on the use of mathematical methods of artificial neural networks. The network is trained for calculating the average defect density per unit length at the input parameters corresponding to film and substrate sizes, surface resistance of the conducting coating, and bending radius. The application of this method allows one to determine the average defect density with high accuracy.

A bandpass filter of new design comprising dielectric layers with surface metal grids is developed and studied. Dielectric layers act as half-wave resonators, while metal grids act as mirrors with preset reflectivity and ensure optimum coupling between adjacent resonators and between the boundary resonators and free space. A test prototype of the third-order filter with a central bandpass frequency of ~12 GHz and relative bandwidth ~17% showed good agreement of theory and experiment. The proposed design can be used in making panels radio-transparent within a preset bandwidth for covering microwave antennas.

An algorithm of memristor switching with high precision to a state with preset resistance has been developed based on the application of voltage pulses with smoothly increasing amplitude and the duration varying randomly within preset limits. It is shown that the proposed algorithm can be implemented in memristor structures based on (Co₄₀Fe₄₀B₂₀)_x(LiNbO₃)_100–x nanocomposites with x ≈ 10 at. %. Optimum parameters are selected for the algorithm operation with a minimum number of iterations that allows the accuracy of resistance setting to be no worse than 0.5%. The obtained results can be used in the creation of neuromorphic systems.

Raman spectra of films of nearly stoichiometric amorphous silicon nitride (a-Si₃N₄) reveal a contribution due to local oscillations of silicon–silicon (Si–Si) bonds. This observation directly confirms that the almost stoichiometric a-Si₃N₄ contains Si–Si bonds, which, according to theoretical predictions, act as electron and hole traps that are responsible for the memory effect in Si₃N₄.

Experimental data showing a decrease in the work function of carbon nanotube (CNT) bundles and arrays hydrogenated in hydrogen-containing plasma are presented. This plasma treatment leads to hydrogen chemisorption on CNTs, which results in a work-function decrease from 4.8 to 3.3 eV. The experimental data confirm quantum-mechanical calculations for single-walled CNTs of variable chirality. Calculations indicate that a decrease in the CNT work function depends on both the properties of CNT and the degree of its passivation by hydrogen.

The interatomic binary potentials of Mo-Mo, Mo-S and S-S, approved by Molecular Dynamics, were used to calculate elastic phase shifts and cross sections of the atomic pairs in the relative kinetic energy range of 2–200 eV. It is expected the obtained differential and integral cross sections to be of help to describe sputtering of MoS₂ nanometer layers in design of perspective devices of nanoelectronics and photonics.

We propose a method for reconstructing links in a chain of unidirectionally coupled systems by means of three tests for estimating direct and mediated coupling with the aid of Granger conditional causality in terms of prognostic models with polynomial nonlinearity. It is shown that this approach allows the architecture of links in these systems to be correctly identified in more than 80% of cases.

Prospects of using parallel computing technology (PaCT) methods for the stream processing and online analysis of multichannel EEG data are considered. It is shown that the application of PaCT to calculation and evaluation of spectral characteristics of EEG signals makes online determination of changes in the energy of the main rhythms of neural activity in various parts of the cerebral cortex possible. The possibility of implementing the PaCT algorithm with CUDA C library and its use in a modern brain–computer interface (BCI) for cognitive-activity monitoring in the course of visual perception.