V. N. Karazin Kharkiv National University
Recent publications
Plasma production experiments in helium at Uragan-2M have been performed to investigate the role of the hydrogen minority in helium. The experiments presented here were carried on with a controlled minority hydrogen concentration. The hydrogen minority allowed one to increase plasma density more than three times as compared with pure helium. The obtained plasma density is highest for whole time of Uragan-2M operation. The developed scenario allowed to decrease the neutral gas pressure at which the plasma production is possible. This is a requirement for achieving regimes of plasma production with full ionization. Although the initial gas mixture 14%H2 + 86%He can be treated as optimum, there is no sensitive dependence on hydrogen minority concentration, which makes the scenario robust. This study, together with initial LHD experiments, confirm the prospects of target plasma production by ICRF waves for stellarator type machines.
The characteristic matrix approach is used to evaluate optical transmission spectra for a 1D multilayered photonic system. The characteristics of transmittance are analyzed for different incident angles, layer thicknesses (from a few to hundred nanometers), and electron densities for the light wave propagating through both periodic and quasi-periodic photonic structures. The shifting trend of photonic band gap in the infrared wavelength regimes is observed for different types of quasi-sequence. Increased electron density, on the other hand, makes the band gap more robust, although collision frequency has a minor effect on the band gap. Moreover, the physical entities play a key role in the appearance of multiple band gaps in the greater wavelength regimes. For example, such nanophotonic devices as optical bandpass filters in the infrared regime can be designed by using the concept of the proposed structure. We further show that the suggested quasi-periodic multilayered structures can function as resilient adjustable photonic lattices with the above-mentioned properties that can be tuned.
Given a pointed metric space M , we study when there exist n -dimensional linear subspaces of $$\mathrm {Lip}_0(M)$$ Lip 0 ( M ) consisting of strongly norm-attaining Lipschitz functionals, for $$n\in {\mathbb {N}}$$ n ∈ N . We show that this is always the case for infinite metric spaces, providing a definitive answer to the question. We also study the possible sizes of such infinite-dimensional closed linear subspaces Y , as well as the inverse question, that is, the possible sizes for a metric space M in order to such a subspace Y exist. We also show that if the metric space M is $$\sigma $$ σ -precompact, then the aforementioned subspaces Y need to be always separable and isomorphically polyhedral, and we show that for spaces containing [0, 1] isometrically, they can be infinite-dimensional.
This publication is a continuation of the authors’ work on the analysis of the current state of roads with non-rigid pavements, including modern computer technologies. The main attention is paid to the use of modern pulsed GPR created in Kharkov and methods of processing the received signals. For data processing, the GeoVizy program was used. As a result of the analysis of the data obtained, it should be concluded that there are significant prospects for the use of pulsed georadar to monitor the current state of roads. The importance of this problem is also related to the large length of the existing road network in developed countries, as well as significant cost savings due to the optimization of maintenance and repair work. Brief description of the results obtained is given, and possible ways for further progress and development of methods for spectral processing of primary data obtained using GPR are proposed.KeywordsNon-rigid paved roadsGPRPulse signal processing methodsNon-destructive testing
In recent years, new steganographic methods have emerged to hide information in various multimedia files, such as images, videos, audio, text, and more. Such cover files, which are also called media or containers, are freely transmitted via the Internet, so they do not arouse any suspicion. An authorized person who has a secret steganographic key can restore the hidden message. This article discusses techniques for hiding data in vector images. Individual elements of vector graphics are represented through special mathematical objects (points, lines, curves, nodes, tangents, control points, etc.). These objects are used to hide information. But there is a problem, which lays in the fact, that affine vector image transformations can destroy a hidden message. In addition, hiding algorithms usually increase the size of vector image files, which is a certain unmasking feature. The main purpose of our study is to examine these problems. To do this, it is programmatically implemented data hiding and conducted a series of experiments. In particular, it is investigated various concealment techniques (bit method and pattern-based method). For different initial conditions, it is evaluated the resistance of hidden data to affine transformations, resizing of vector graphics files, performance, and so on. Based on the results of numerical experiments, it is substantiated the advantages and conditions of using the studied algorithms. To conduct the research, we have developed a cross-platform software implementation (JavaScript programming language), i.e. our scripts can be run on different types of platforms and browsers. Thus, the developed implementation can be used as a framework for individual web client applications, as well as for writing a backend of complex and professional tasks.
Polyteny is an effective mechanism for accelerating growth and enhancing gene expression in eukaryotes. The purpose of investigation was to study the genetic variability of polyteny degree of giant chromosomes in the salivary glands of Drosophila melanogaster Meig. in relation to the differential fitness of different genotypes. 16 strains, lines and hybrids of fruit flies were studied. This study demonstrates the significant influence of hereditary factors on the level of polytenization of giant chromosomes in Drosophila. This is manifested in the differences between strains and lines, the effect of inbreeding, chromosome isogenization, hybridization, adaptively significant selection, sexual differences, and varying degrees of individual variability of a trait in different strains, lines, and hybrids. The genetic component in the variability of the degree of chromosome polyteny in Drosophila salivary glands was 45.3%, the effect of sex was 9.5%. It has been shown that genetic distances during inbreeding, outbreeding or hybridization, which largely determine the selective value of different genotypes, also affect polyteny patterns. Genetic, humoral, and epigenetic aspects of endocycle regulation, which may underlie the variations in the degree of chromosome polyteny, as well as the biological significance of the phenomenon of endopolyploidy, are discussed.
TiO2 nanoparticles (NPs) are widely used in the environmental engineering, medicine, chemical and food industries due to their unique photocatalytic and biocidal properties. NPs may generate reactive oxygen species and, hence, have the toxic effect on the living cells via oxidative stress. An external UV irradiation may magnify the photocatalytic properties of TiO2 NPs. In this regard, we have analyzed the influence of TiO2 NPs on the conformation and thermal stability of native DNA in a buffer suspension without and under UV irradiation exploiting absorption spectroscopy and thermal denaturation in the range of 20–94 °C. The TiO2 NPs size distribution and polydispersity index were examined by dynamic light scattering (DLS) and confirmed by TEM. The DNA:TiO2 NPs assemblies were revealed and characterized by DLS and TEM. Upon heating the DNA suspension with TiO2 NPs from about 25 to 44 °C we have observed decreasing the hyperchromicity coefficient (h) on the DNA melting curves. That is explained by the intensive formation of the DNA:TiO2 NPs assemblies. We have revealed, that partial DNA disordering appears at initial contacts with NPs. DNA binding to TiO2 NPs is manifested in the change of the DNA melting temperature (Tm). We showed that the performed UV treatment of DNA during 3 h leads to partial unwinding of the biopolymer structure. The NPs injection to the biopolymer suspension induced the additional effect on the DNA thermal stability under UV irradiation. The performed analysis of the experimental data suggests that the nature of the impact of NPs on the biopolymer is complex.
We study the operator \(\mathcal {A}\) of multiplication by an independent variable in a matrix Sobolev space \(W^2(M)\). In the cases of finite measures on [a, b] with \((2\times 2)\) and \((3\times 3)\) real continuous matrix weights of full rank it is shown that the operator \(\mathcal {A}\) is symmetrizable. Namely, there exist two symmetric operators \(\mathcal {B}\) and \(\mathcal {C}\) in a larger space such that \(\mathcal {A} f = \mathcal {C} \mathcal {B}^{-1} f\), \(f\in D(\mathcal {A})\). As a corollary, we obtain some new orthogonality conditions for the associated Sobolev orthogonal polynomials. These conditions involve two symmetric operators in an indefinite metric space.
To quantitatively describe the kind of interaction between ion and solvent, it is convenient to use the concept of negative or positive solvation. We have established earlier that diffusion displacement distance (d¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{d}$$\end{document}) of an ion correlates with its solvation type. The ion is solvated positively if the average d¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{d}$$\end{document} value exceeds the crystallographic (structural) radius of an ion ri\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$r_i$$\end{document}; otherwise, ion solvation is negative. In this paper, we have estimated the length, time and velocity of ion diffusion displacement (hop) for singly charged ions Li+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Li}^+$$\end{document}, Na+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Na}^+$$\end{document}, K+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{K}^+$$\end{document}, Rb+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Rb}^+$$\end{document}, Cs+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Cs}^+$$\end{document}, Me4N+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Me}_4\text{N}^+$$\end{document}, Et4N+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Et}_4\text{N}^+$$\end{document}, Bu4N+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Bu}_4\text{N}^+$$\end{document}, F-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{F}^-$$\end{document}, Cl-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Cl}^-$$\end{document}, Br-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Br}^-$$\end{document}, BPh4-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {BPh}_{4}^{-}$$\end{document} over the temperature range from 273.15 K to 473.15 K and for ions Pr4N+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Pr}_4\text{N}^+$$\end{document}, I-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{I}^-$$\end{document}, NO3-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {NO}_{3}^{-}$$\end{document}, ClO4-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {ClO}_{4}^{-}$$\end{document} at 298.15 K in ethylene glycol. The fact of the negative solvation of almost all ions studied (except Li+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Li}^+$$\end{document}, Na+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Na}^+$$\end{document}, F-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{F}^-$$\end{document}) in ethylene glycol has been established for the first time. It has been shown that Me4N+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Me}_4\text{N}^+$$\end{document} ion has turned out solvated solvophilically in EG as well as in water while ions Et4N+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Et}_4\text{N}^+$$\end{document}, Bu4N+,\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Bu}_4\text{N}^+,$$\end{document} and BPh4-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {BPh}_{4}^{-}$$\end{document} appeared to be solvated solvophobically. We have estimated the temperature of transition Ttr\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T_\text {tr}$$\end{document} (from negative to positive ion solvation) for K+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{K}^+$$\end{document} and Rb+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Rb}^+$$\end{document} ions. It physically corresponds to the absence of solvation of the ion (d¯=ri\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{d}=r_i$$\end{document}).
We present a “calculator” for constructing a homogeneous approximation of nonlinear control systems, which is based on the algebraic approach developed by the authors in their previous papers. This approach mainly uses linear algebraic and combinatorial tools, so, it is perfectly adapted to computer realization. We describe the algorithm and discuss its capabilities and limitations. We present its implementation as a web application and show by example how this app works.
The Strategy on reducing greenhouse gas emissions for the period up to 2030 was adopted in October 2021 at COP26. However, it does not take into account the potential of arable soils for carbon sequestration. Meanwhile, on a global scale, carbon sequestration by soils is regarded as one of the most important tools to combat further increases in atmospheric carbon dioxide. According to preliminary estimates, the amount of carbon that can potentially accumulate in the soils of Ukraine is 757,7 million tons, of which 23,3 million tons - in the arable soils of Polisia, 350,3 million tons in the soils of the Forest-steppe and 384,2 million tons soils of the Steppe of Ukraine. At the same time, modern assessments of the sequestration potential, do not usually involve assessment of erosion processes and the spatial heterogeneity of humus accumulation conditions, which significantly change the carbon cycle in slope soils. This article discusses four possible approaches to assessing the potential of soil sequestration as well as the popular, but difficult to implement, method of carbon accumulation modeling. The authors consider three variants of the balance method for assessing the potential capacity of soil sequestration based on the difference between potential and real content of organic carbon. All three approaches give similar results for assessing the sequestration potential of chernozem soils.
This article attempts to provide a comprehensive overview of the academic literature on the subject, examining the different approaches, their similarities and general differences, advantages and disadvantages, and providing a consolidated and critical perspective that will hopefully be useful for future research in the field. The paper presents the results of a systematic review of Western academic studies on the existence of echo chambers in social media, an initial classification of the literature and the identification of research patterns. The authors show how conceptual and methodological choices influence research findings on the topic. Future research should take into account the potential shortcomings of different approaches and the significant potential of linking data.
Traits for prey acquisition form the phenotypic interface of predator–prey interactions. In venomous predators, morphological variation in venom delivery apparatus like fangs and stingers may be optimized for dispatching prey. Here, we determine how a single dimension of venom injection systems evolves in response to variation in the size, climatic conditions and dietary ecology of viperid snakes. We measured fang length in more than 1900 museum specimens representing 199 viper species (55% of recognized species). We find both phylogenetic signal and within-clade variation in relative fang length across vipers suggesting both general taxonomic trends and potential adaptive divergence in fang length. We recover positive evolutionary allometry and little static allometry in fang length. Proportionally longer fangs have evolved in larger species, which may facilitate venom injection in more voluminous prey. Finally, we leverage climatic and diet data to assess the global correlates of fang length. We find that models of fang length evolution are improved through the inclusion of both temperature and diet, particularly the extent to which diets are mammal-heavy diets. These findings demonstrate how adaptive variation can emerge among components of complex prey capture systems.
Artificial Neural Network (ANN) approaches are applied to detect and determine the object class using a special set of the UltraWideBand (UWB) pulse Ground Penetrating Radar (GPR) sounding results. It used the results of GPR sounding with the antenna system, consisting of one radiator and four receiving antennas located around the transmitting antenna. The presence of four receiving antennas and, accordingly, the signals received from four spatially separated positions of the antennas provide a collection of signals received after reflection from an object at different angles and, due to this, to determine the location of the object in a coordinate system, connected to the antenna. We considered the sums and differences of signals received by two of the four antennas in six possible combinations: (1 and 2, 1 and 3, 2 and 3, 1 and 4, etc.). These combinations were then stacked sequentially one by one into one long signal. Synthetic signals constructed in such a way contain many more notable differences and specific information about the class to which the object belongs as well as the location of the searched object compared to the signals obtained by an antenna system with just one radiating and one receiving antenna. It therefore increases the accuracy in determining the object’s coordinates and its classification. The pulse radiation, propagation, and scattering are numerically simulated by the finite difference time domain (FDTD) method. Results from the experiment on mine detection are used to examine ANN too. The set of signals from different objects having different distances from the GPR was used as a training and testing dataset for ANN. The training aims to recognize and classify the detected object as a landmine or other object and to determine its location. The influence of Gaussian noise added to the signals on noise immunity of ANN was investigated. The recognition results obtained by using an ANN ensemble are presented. The ensemble consists of fully connected and recurrent neural networks, gated recurrent units, and a long-short term memory network. The results of the recognition by all ANNs are processed by a meta network to provide a better quality of underground object classification.
The paper considers the instability of intense Langmuir oscillations in nonisothermal (Zakharov's model) and cold (Silin's model) 1D plasma. The main attention is paid to the formation of plasma density caverns in the hydrodynamic and hybrid (electrons are described hydrodynamically, ions are described by model particles) representations. In the hydrodynamic representation, with a small number of spectrum modes, large-scale plasma density caverns are observed, which rapidly deepen. This process is supported by the appearance of small-scale perturbations, and phase synchronization of the Langmuir waves of the instability spectrum is observed. This phase synchronization of the spectrum modes is quite capable of fulfilling the role that was previously proposed to be given exclusively to the effect of extrusion of particles from the cavity by the field. In hybrid models, in the region of consideration, ions are described by model particles, the number of which in the one-dimensional case 104-5*105 (which in the three-dimensional case corresponds to the number of particles 1012-1014). The initial spectrum of perturbations is very wide and rather intense, which leads to an explosive growth of perturbations in the Zakharov model and a rapid development of instability in the Silin model. In this case, in the developed instability regime, the formation of many small-scale plasma density caverns is observed. It is the presence of this small-scale modulation due to the Fermi effect that quickly forms the normal distribution of ions over velocities. In this case, the effect of particle heating due to Landau damping loses its primacy. It is shown that the caverns practically do not change their position; phase changes for the spectral components of the plasma density were not observed. Only individual small-scale caverns demonstrate dynamics similar to the development of caverns in the hydrodynamic representation.
The problem of electromagnetic wave pressure on a thin conductive vibrator located in a rectangular waveguide is solved. Wave H10 falls on the vibrator. The vibrator is located perpendicular to the wide wall of the waveguide. The current in the vibrator arising under the action of the electric field of the wave is calculated. The current distribution along the vibrator is almost uniform. The current in the microwave range depends little on the vibrator conductivity. Two components of the magnetic field - longitudinal and transverse exist in the H10 wave. When these components interact with the current in the vibrator, forces arise, acting on the vibrator across the waveguide and along it. The magnitude of the longitudinal force is greatest when the vibrator is located in the middle of a wide wall. It is almost 2 times greater than the force acting on the vibrator in free space at the same average radiation intensity, When the vibrator length is close to half the radiation wavelength, the force is maximum. The transverse force is determined by the interaction of the current in the vibrator with the longitudinal component of the magnetic field in the waveguide. It is maximum when the vibrator is located at the distance of ¼ of the length of the wide wall from its middle. If the length of the vibrator is less than half the wavelength of the radiation, the force is directed towards the axis of the waveguide, otherwise - in the opposite direction. The possibility of using microwave radiation pressure to create micromachines and to control the position of the vibrator in space has been evaluated. This requires a radiation power of several watts.
The paper considers the development of the process of superradiance of radiating oscillators interacting with each other by means of an electromagnetic field. The interaction of oscillators occurs both with the nearest neighbors and with all other oscillators in the system. In this case, the possibility of longitudinal motion of oscillators along the system, due to the action of the Lorentz force, is taken into account. It is shown that, regardless of the motion of the oscillators, for example, due to their different masses, the maximum attainable amplitude of the generation field changes little. However, the radiation efficiency depends on how this field is distributed in the longitudinal direction. In the case of a shift of the field maximum towards the ends of the system, the radiation efficiency can noticeably increase. In addition, the direction of the phase velocity of the external initiating field is important, which accelerates the process of phase synchronization of the oscillators. This can also affect the ejection of particles outside the initial region, and here the total number of ejected particles and their speed turn out to be important. It is discussed how the density of oscillators and the size of the region occupied by oscillators will change.
The paper presents the results of the study of slow surface electromagnetic waves directed along the flat mu-negative metamaterial slab surrounded by ordinary dielectric material. It is considered the case of isotropic and homogeneous metamaterial without losses. This metamaterial possesses the positive permittivity and the negative permeability over a definite frequency band. It is found that two surface modes of TE polarization can propagate along such waveguide structure. The dispersion properties, the spatial distribution of the electromagnetic field, as well as the phase and group velocities of these slow modes are studied. The first mode is a conventional forward wave, and has a lower frequency and lower phase velocity than the second mode. The second mode may have zero group velocity at a certain frequency. Characteristics of these surface modes for different values of the mu-negative slab parameters have been studied. The studied surface electromagnetic waves can be used for practical applications as in laboratory experiments, as in various technologies.
The co-localization of the donor and acceptor fluorophores capable of transferring the energy by the Fӧrster mechanism, on the molecular scaffold of amyloid fibrils offers new opportunities not only for refinement of the amyloid detection and structural analysis, but also for designing photonic nanodevices on their basis. The assembly of these systems involves the non-covalent dye-protein interactions which can hardly be characterized in terms of a precise dye location within the fibril structure that is required for fabricating the FRET-based light harvesting systems or photonic nanowires. In view of this, the dye-fibril binding process deserves a detailed in silico study. In the previous molecular docking studies of the FRET donors and acceptors interacting with the insulin model fibrils we considered only one ligand during the simulation procedure. However, the real situation is much more complicated, when the multiple ligands can compete for the same binding site, a direct complexation between the dyes on the fibril scaffold can take place, the spatial distribution of the bound fluorophores can be unfavorable for the energy transfer, etc. In addition, the mutual orientation of the donor and acceptor molecules essentially contribute to the efficiency of the Förster resonance energy transfer (FRET) in the investigated systems. The present study was undertaken to gain molecular docking insight into the binding of the donor (Thioflavin T) and acceptor (Congo Red or a phosphonium dye TDV) fluorophores to the insulin amyloid fibrils using the multiple docking approach. The employed PatcDock and SwissDock webserves provided evidence for the preferable association of all dyes with the fibril grooves. The protein-ligand interaction profiler (PLIP) was employed for analyzing the (InsF + ThT +CR) and (InsF + ThT + TDV) systems. The revealed binding modes and the types of the dye-fibril interactions may be of importance for a more detailed analysis of the FRET process in amyloid systems and may serve as a background for further in silico studies of the cascade FRET on the amyloid fibril scaffold.
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2,101 members
Alexander Akulov
  • Department of Mycology and Plant Resistance
Konstantin Nosov
  • School of Mathematics and Computer Sciences
Alexander Kyrychenko
  • Research Institute of Chemistry
Andrey O. Doroshenko
  • Department of Organic Chemistry
V. G. Shevchenko
  • Department of Astronomy and Space Informatics
4, Svobody Sqr., 61022, Kharkiv, Ukraine
Head of institution
Vil S. Bakirov