Preparation and Characterization of Reduced Graphene-P3HT Composite Thin Films for Use as Transparent Conducting Electrodes

With the aim of producing simple and effective transparent conducting electrodes, the conducting polymer poly(3-hexylthiophene) (P3HT) incorporated with reduced graphene oxide film (rGO) (called rGO-P3HT) was prepared by spin-coating method. Structural, electrical and optical characterization showed that rGO-P3HT films 9.0 wt% P3HT exhibited good stability when exposed to the ambient atmosphere. These composite films of 200 nm thickness possess a sheet resistance and transparency of R□~ 17Ω and T ~ 72%, respectively. Owing to containing conducting polymer, rGO-P3HT-coated glass could be efficiently used in photovoltaic applications, in organic solar cells in particular, with the replacement of the indium tin oxide (ITO) and fluorine tin oxide (FTO) electrodes.

NiO_(x) Nanoparticle Synthesis by Chemical Vapor Deposition from Nickel Acetylacetonate

Ni/NiO nanoparticles were synthesized by metal organics chemical vapor deposition of nickel acetylacetonate in an externally heated tube flow reactor at moderate temperatures, up to 500°C. Particle production and characteristics were studied by evaluating the effects of reactor temperature, precursor concentration, and flow rate through the reactor. In addition, two precursor decomposition methods were examined: thermal decomposition and reduction by hydrogen. Particle production was monitored with a scanning mobility particle sizer, and particle characteristics were studied using transmission electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction, and energy dispersive spectroscopy. The presence of hydrogen in the reaction mixture influenced significantly both particle production and their characteristics.

Regularities of Nanofocusing of the Electromagnetic Field of a Fractal Rough Surface

A consistent physical and mathematical model of the propagation of electromagnetic waves in an inhomogeneous medium with strong discontinuities of the electromagnetic field at the interface of two media, which is a rough surface, was developed. Mathematical modeling of rough surfaces and their profiles was carried out using fractal geometry, which allows us to display the topology of the object as close as possible to reality. For real heterogeneous rough structures, we have developed a through-counting method that takes into account the continuity of the total current at the interfaces of adjacent media, the effect of induced surface charge and surface current. This approach lets one avoid the necessity to set surface impedances depending on the structure of the field being determined and on the material properties.

Electrodynamics of Inhomogeneous (Laminated, Angular) Structures

The consistent physic-mathematical model of propagation of an electromagnetic wave in a heterogeneous medium is constructed using the generalized wave equation and the Dirichlet theorem. Twelve conditions at the interfaces of adjacent media are obtained and justified without using a surface charge and surface current in explicit form. The conditions are fulfilled automatically in each section of counting schemes for calculations. A consistent physicomathematical model of interaction of nonstationary electric and thermal fields in a layered medium with allowance or mass transfer is constructed. The model is based on the methods of thermodynamics and on the equations of an electromagnetic field and is formulated without explicit separation of the charge carriers and the charge of an electric double layer. The influence of a slowly moving medium on the electromagnetic wave propagation is considered. The calculation results show the absence of the influence of the medium’s motion on the phase shift of waves, which is consistent with experimental data.

Non-Monochromatic Electromagnetic Radiation of Inhomogeneous Media

A coordinated physicomathematical model for the propagation of a soliton-like electromagnetic pulse in a heterogeneous medium is developed in the presence of strong discontinuities in the electromagnetic field. The model is based on the reduction of Maxwell’s equations to the well-studied wave equation. When the electromagnetic pulse was specified, its amplitude modulation was taken into account, as was the nonstationary broadening of the spectral line. Conditions for matching the momentum for the first initial boundary-value problem are obtained. The time dispersion of the electrical induction is taken into account in terms of the function of signal conditioning which takes account of the broadening of its spectral line and integration over the continuous spectrum. With this approach, it is not necessary to neglect spatial derivatives, and also to use spatial nonlocal relations to take account of the effect of surface charge, surface current, and spatial dispersion of electrical induction at the interfaces of adjacent media.

Audio-frequency heating of particulate magnetic systems

This paper presents theoretical and experimental studies on the magnetodynamics and energy dissipation in suspensions of small ferromagnetic particles with magnetic hysteresis and mechanical mobility in an AC magnetic field. Energy absorption by particles suspended in a solid, liquid or gas environment and subjected to high frequency magnetic fields is of great interest for cancer treatment by hyperthermia, chemical technology, biotechnology and smart materials science. Sub-micron needle-like γ-Fe2O3 particles dispersed in liquid were subjected in this study to a 430 Hz magnetic field with an intensity of up to 10^5 A/m. Dynamic magnetization loops were measured in parallel to the energy dissipated in the samples. Combined magnetomechanical dynamics of particle dispersions was simulated by using a chain-of-spheres model allowing for incoherent magnetic field reversal. In liquid dispersions, within the kilohertz frequency range, the mechanical mobility of particles does not interfere with their hysteretic magnetic reversal that makes heat release comparable to that observed with solids; for instance, in the present study using γ-Fe2O3 particles in liquid subjected to 10^4 Hz field exhibited heat release rates from 250 up to 600W oer 1 cm^3 of the dry oarticle content.

Study of cobalt ferrite nanosuspensions for low-frequency ferromagnetic hyperthermia

High-coercive cobalt ferrite nanoparticles were synthesized and studied for magnetic hyperthermia by direct injection of their suspension into a tumor and application of a strong audio-frequency magnetic field for heating. Physical （dynamic magnetic hysteresis and heat generation in both liquid and solid dispersions）, biological （toxicity and penetration of particles in therapeutic quantities into mouse tumor tissue） as well as other properties of the particles were studied. A model was developed to describe the magnetodynamics in suspensions of magnetic nanoclusters with an account for both Brownian and regular rotations, to provide understanding of observed phenomena. The experimental and theoretical techniques developed have formed a basis for controllable synthesis of the magnetic nanoparticles for low-frequency heat generation in medical and other applications.

Power-law multi-wave model for COVID-19 propagation in countries with nonuniform population density

Background: The purpose of our study is to develop a quite precise mathematical model which describes epidemics spread in a country with non-uniform population density. This model gives explanation of quite long duration of the peak of a respiratory infection such as the coronavirus disease 2019 (COVID-19).Methods: The theory of kinetic equations and fractal analysis are used in our mathematical model. According to our model, COVID-19 spreading takes the form of several spatio-temporal waves developing almost independently and simultaneously in areas with different population density. The intensity of each wave is described by a power-law dependence. The parameters of the dependence are determined by real statistical data at the initial stage of the disease spread.Results: The results of the model simulation were verified using statistical data for the Republic of Belarus. Based on the developed model, a forecast calculation was made at the end of May, 2020. It was shown that the epidemiological situation in the Republic of Belarus is well described by three waves, which spread respectively in large cities with the highest population density (the first wave), in medium-sized cities with a population of 50−200 thousands people (the second wave), in small towns and rural areas (the third wave). It was shown that a new wave inside a subpopulation with a lower density was born 20−25 days after the appearance of the previous wave. Comparison with actual data several months later showed that the accuracy of forecasting the total number of cases for a period of 3 months for total population in the proposed approach was approximately 3%.Conclusions: The high accuracy mathematical model is proposed. It describes the development of a respiratory epidemic in a country non-uniform population density without quarantine. The model is useful for predicting the development of possible epidemics in the future. An accurate forecast allows to correctly allocating available resources to effectively withstand the epidemic.

Dynamic magnetic hysteresis in a liquid suspension of acicular maghemite particles

This paper presents theoretical and experimental studies on the magnetodynamics and energy absorption in a dilute suspension of small ferromagnetic particles with magnetic hysteresis and mechanical mobility in an AC magnetic field. Experiments with 0.1% suspensions of acicular particles of gamma ferric oxide in solid and liquid matrices, subjected to a 430 Hz magnetic field with an intensity of up to 1200 Oe, revealed important role of particle mobility. The main qualitative and quantitative features of the phenomenon are in agreement with a model of joint magneto-mechanical dynamics of particles with a chain-of-spheres mode of incoherent magnetic reversal.