V. N. Karazin Kharkiv National University
Recent publications
Here, we introduce and demonstrate nanoprinted all-dielectric nanostructures located on fiber end faces as a novel concept for the efficient coupling of light into optical fibers, especially at multiple incidence angles and across large angular intervals. Taking advantage of the unique properties of the nanoprinting technology, such as flexibly varying the width, height, and gap distance of each individual element, we realize different polymeric axial-symmetric structures, such as double-pitch gratings and aperiodic arrays, placed on the facet of commercial step-index fibers. Of particular note is the aperiodic geometry, enabling an unprecedentedly high average coupling efficiency across the entire angular range up to 80°, outperforming regular gratings and especially bare fibers by orders of magnitude. The excellent agreement between simulation and experiment clearly demonstrates the quality of the fabricated structures and the high accuracy of the nanoprinting process. Our approach enables realizing highly integrated and ready-to-use fiber devices, defining a new class of compact, flexible, and practically relevant all-fiber devices beyond the state-of-art. Applications can be found in a variety of cutting-edge fields that require highly efficient light collection over selected angular intervals, such as endoscopy or quantum technologies. Furthermore, fiber functionalization through nanoprinting represents a promising approach for interfacing highly complex functional photonic structures with optical fibers.
The purpose of the article is to investigate the potential of environmental taxation in the regulation of ecological responsibility and ensuring the pro-environmental behaviour of economic entities. To study the theoretical basis of environmental taxation and environmentally responsible behaviour, a bibliometric analysis of key words in scientific articles published on this topic was conducted. The results of the bibliometric analysis show that aspects of environmentally responsible behaviour are presented in the list of keywords that mediate the study of environmental taxation. Thus, pro-environmental behaviour is defined by the necessity of health risks avoiding, clean energy technology providing, waste generating reducing etc. The impact of environmental taxes on various aspects of environmentally responsible behaviour was modelled on the sample of six European countries (Belgium, France, Austria; Finland and Denmark) for 1994-2019. The results of the calculations show that environmental taxes have limited effectiveness in regulating various aspects of environmental liability. So, the average growth of environmental taxes revenue by 1 USD million provides a decrease in the Eco-Innovation Index by 0.001 point; the slow rise in CO2 emissions (less than 0.000 %) and the growth in tobacco use (about 0.000 %). On the other hand, environmental taxes do not influence the country’s environmental performance, as well as on the total alcohol consumption and renewable electricity consumption and output. Thus, an approach to the establishment of tax benefits for enterprises was proposed, considering the results of changes in the environmentally harmful effects they produce.
Dispersion properties of electromagnetic eigenmodes in a semiconductor nanotube (with quadratic electron dispersion law) filled by a nonmagnetic dielectric and placed in a coaxial dc magnetic field are studied theoretically. A new quantum electrodynamical phenomenon is predicted. Namely, it is shown that increase in the electron density [Formula: see text] in the nanotube results in the appearance of new branches in the eigenmodes spectrum. These branches arise in a bifurcation manner at some critical values of [Formula: see text], when a new electron energy subzone starts to fill in. The number of branches monotonously increases with growth [Formula: see text] and oscillates with increase in the number of magnetic flux quanta through the nanotube (i.e., a peculiar Aharonov–Bohm effect takes place). We also found that the dispersion curves have parts with anomalous dispersion. The analytical expression for electron energy loss due to the excitation of eigenmodes under the Cherenkov resonance condition is derived and numerically analyzed.
The effect of annealing at room temperature on the fluctuation conductivity (FLC) σ′( T) and pseudogap (PG) Δ*(7) in the basal ab plane of ReBa 2 Cu 3 O 7–δ (Re = Ho) single crystals with a lack of oxygen has been studied. It is shown that at all stages of annealing, the FLC near T c can be described by the Aslamazov-Larkin and Maki-Thompson fluctuation theories, demonstrating a 3D-2D crossover with increasing temperature. The crossover temperature T 0 was used to determine the coherence length along the c axis, ξ c (0) = (2.82 ± 0.2) Å. At the intermediate stage of annealing, an anomalous increase in 2D FLC was revealed, which is associated with the influence of uncompensated magnetic moments in HoBa 2 Cu 3 O 7–5 (HoBCO): μ eff , Ho = 9.7μ Β . For the quenched sample S1, the temperature dependence of the PG has a shape typical of single crystals with a large number of defects. However, Δ*( T) has two small additional maxima at high temperature, which is a feature of HoBCO single crystals with pronounced twins and indicates the two-phase nature of the sample. Upon annealing, the shape of Δ*( T) noticeably changes, very likely due to an increase in the magnetic interaction (sample S2). More important is the change in the slope of the data at high temperatures, which has become about 3.5 times steeper. The ordering of the oxygen distribution due to the diffusion process during annealing somewhat compensates for the influence of magnetic interaction. But the slope does not change (sample S3). Interestingly, the slope turns out to be the same as for FeAs-based superconductors, suggesting the possibility of the existence of spin density waves in HoBCO in the PG state. The comparison of the pseudogap parameter [Formula: see text] near T c with the Peters-Bauer theory revealed a slight increase in the density of local pairs < n↑ n↓>, which should explain the observed increase in T c by 9 K during annealing.
Strong driving of quantum systems opens opportunities for both controlling and characterizing their states. For theoretical studying of these systems properties we use the rate-equation formalism. The advantage of such approach is its relative simplicity. We used the formalism for description of a two-level system with further expanding it on a case of a multi-level system. Obtained theoretical results have good agreement with experiments. The presented approach can also be considered as one more way to explore properties of quantum systems and underlying physical processes such as, for instance, Landau–Zener–Stückelberg–Majorana transitions and interference.
Aging increases the risk to develop Alzheimer’s disease. Cardiovascular diseases might accelerate this process. Our study aimed at investigating the impact of heart failure on brain connectivity using functional magnetic resonance imaging at resting state. Here we show brain connectivity alterations related to heart failure and cognitive performance. Heart failure decreases brain connectivity in the precuneus. Precuneus dysconnectivity was associated with biomarkers of heart failure—left ventricular ejection fraction and N-terminal prohormone of brain natriuretic peptide—and cognitive performance, predominantly executive function. Meta-analytical data-mining approaches—conducted in the BrainMap and Neurosynth databases—revealed that social and executive cognitive functions are mainly associated with those neural networks. Remarkably, the precuneus, as identified in our study in a mid-life cohort, represents one central functional hub affected by Alzheimer’s disease. A long-term follow-up investigation in our cohort after approximately nine years revealed more severe cognitive impairment in the group with heart failure than controls, where social cognition was the cognitive domain mainly affected, and not memory such as in Alzheimer’s disease. In sum, our results indicate consistently an association between heart failure and decoupling of the precuneus from other brain regions being associated with social and executive functions. Further longitudinal studies are warranted elucidating etiopathological mechanisms.
The dataset represents a comprehensive collection of occurrence records concerning the genus Aconitum (Ranunculaceae) in the Ukrainian Carpathians and adjacent territories. It is based primarily on the results of critical revision of the main herbarium collections of the Carpathian region (i.e. LW, LWS, LWKS, KRA, KRAM, CHER, KW, UU and KWHU). Besides this, the dataset contains the data parsed (and taxonomically revised) from the published materials and other available sources (e.g. Karel Domin's Card Index). In total, 2,280 occurrence records of the genus Aconitum representatives distributed in the Ukrainian Carpathians were published.
Exploiting acid-base indicators as molecular probes is one of the most popular methods for determining the surface electrostatic potential Ψ in hydrophilic colloids like micellar surfactant solutions and related systems. Specifically, the indicator's apparent acidity constant index is measured in the colloid solution of interest and, as a rule, in a nonionic surfactant solution; the difference between the two is proportional to Ψ. Despite the widespread use of this approach, a major problem remains unresolved, namely, the dissimilarity of Ψ values obtained with different indicators for the same system. The common point of view recognizes the effect of several factors (the choice of the nonionic surfactant, the probe's localization, and the degree of hydration of micellar pseudophase) but does not allow to quantitatively assess their impact and decide which indicator reports the most correct Ψ value. Here, based on the ability to predict the reported Ψ values in silico, we examined the role of these factors using molecular dynamics simulations for five probes and two surfactants. The probe's hydration in the Stern layer was found responsible for approximately half of the dissimilarity range. The probe's localization is found important but hard to quantify because of the irregular structure of the Stern layer. The most accurate indicators among the examined set were identified. Supplementing experiments on measuring Ψ with molecular dynamics simulation is proposed as a way of improving the efficacy of the indicator method: the simulations can guide the choice of the most suitable probe and nonionic surfactant for the given nanoparticles.
Surface electrostatic potential Ψ is a key characteristic of colloid particles. Since the surface of the particles adsorbs various compounds and facilitates chemical reactions between them, Ψ largely affects the properties of adsorbed reactants and governs the flow of chemical reactions occurring between them. One of the most popular methods for estimating Ψ in hydrophilic colloids, such as micellar surfactant solutions and related systems, is the application of molecular probes, predominantly acid-base indicator dyes. The Ψ value is calculated from the difference of the probe's indices of the apparent acidity constant between the examined colloid solution and, usually, some other colloid solution with noncharged particles. Here, we show how to implement this method in silico using alchemical free energy calculations within the framework of molecular dynamics simulations. The proposed implementation is tested on surfactant micelles and is shown to predict experimental Ψ values with quantitative accuracy depending on the kind of surfactant. The sources of errors in the method are discussed, and recommendations for its application are given.
The main aim of the article is to demonstrate the effectiveness of the use of ground penetrating radars to assess various objects using the example of assessing the current state of highways. The article uses the software developed by the authors and the corresponding mathematical models. The analysis of the results obtained is based on mathematical models that have proven their effectiveness and is time-tested. It should be emphasised that the main problem in assessing roads with non-rigid pavement is associated with a change in the main parameters of the layers – thickness and dielectric constant. Previously, we proposed a scheme for the layer-by-layer determination of the values of the relative permittivity and then - the subsequent determination of the thickness of each layer, starting from the top layer and ending with the base. The paper presents the results of experiments actually carried out by the authors with various GPRs, which not only have different values of the central frequency, but also have significant design differences. In addition, the results of processing real data using the software developed by the authors are presented. As a result, an improved method of signal calibration has been proposed, which makes it possible to increase the reliability of assessing the thickness of road surfaces, as well as other objects.
Planar resonators have a wide usage in modern microwave technologies and perspectives in novel quantum technologies development. As was demonstrated earlier, their utilization allows to achieve high values of microwave photon-magnon coupling strength—an important parameter in technologies of information coherent transfer from electromagnetic GHz range to the optical range. In the present work, the achievement of the high value of the microwave photon-magnon coupling strength by exploiting the increase of the spatial concentration of the magnetic component of the planar resonator electromagnetic field is reported. Starting from the conventional planar split-ring resonator design we increased the coupling strength up to 40% by modifying the resonator shape. The numerical simulation and experimental verification showed a predicted increase in the spatial concentration of the microwave magnetic component and showed the increased value of the microwave photon-magnon coupling strength as a sequence.
The ionization loss of a high-energy electron–positron pair in thin targets is considered. The targets not thinner than about 10 $$\upmu $$ μ m are discussed. The analogue of the Landau distribution function is derived for this loss under the condition when the Chudakov effect of the pair ionization loss suppression is manifested. Expression for the most probable value of the pair ionization loss $$E_{MP}$$ E MP is obtained. It is shown that the magnitude of Chudakov effect for $$E_{MP}$$ E MP can be noticeably different from the magnitude of this effect for the restricted mean value of the pair ionization loss.
Permeabilization of the mitochondrial outer membrane–a point of no return in apoptotic regulation–is tightly controlled by proteins of the Bcl-2 family. Apoptotic inhibitor Bcl-xL is an important member of this family, responsible for blocking the permeabilization, and is also a promising target for anti-cancer drugs. Bcl-xL exists in the following conformations, each believed to play a role in the inhibition of apoptosis: (i) a soluble folded conformation, (ii) a membrane-anchored (by its C-terminal α8 helix) form, which retains the same fold as in solution and (iii) refolded membrane-inserted conformations, for which no structural data are available. In this review, we present the summary of the application of various methods of fluorescence spectroscopy for studying membrane interaction of Bcl-xL, and specifically the formation of the refolded inserted conformation. We discuss the application of environment-sensitive probes, Förster resonance energy transfer, fluorescence correlation spectroscopy, and fluorescent quenching for structural, thermodynamic, and functional characterization of protein-lipid interactions, which can benefit studies of other members of Bcl-2 (e.g., Bax, BAK, Bid). The conformational switching between various conformations of Bcl-xL depends on the presence of divalent cations, pH and lipid composition. This insertion-refolding transition also results in the release of the BH4 regulatory domain from the folded structure of Bcl-xL, which is relevant to the lipid-regulated conversion between canonical and non-canonical modes of apoptotic inhibition.
Agaricales is the largest order within the class Agaricomycetes (Basidiomycota, Fungi). Most genera have a gilled (lamellate) basidiomata, though gasteroid, secotioid and cyphelloid fruit bodies also occur in several families and genera. Although gilled Agaricales (usually called "agarics") are the most investigated part of the Fungi, the last summary of their diversity in Ukraine was published back in 1996 and needs to be updated. Only several families have undergone an in-depth review over the last 30 years. Most of the data on species occurrences distributed throughout Ukraine are only partially digitised, under-represented on the Web and published primarily in Ukrainian sources. Here, we provide the list of the 1201 scientific names of gilled Agaricales (species and infraspecific taxon ranks) ever reported from the territory of Ukraine, based on the more than 300 sources published from 1900 to 2021, as well as digitised collection specimens from three mycological collections. For each taxon mentioned in the checklist, we provide references to either known collection specimens or published sources, where researchers can find more information about the records – 8797 records in total.
We study the effect of an anomalously strong interaction of electromagnetic radiation with very thin conducting fibers. Metal, semiconductor or graphite fibers, which diameter is several hundred times smaller than the radiation wavelength, strongly absorb and scatter the electromagnetic waves, which electric vector is parallel to the fiber axis. The efficiency factors of attenuation, absorption, scattering and pressure of radiation for fibers with a diameter of several micrometers in the centimeter and millimeter ranges reach several thousand. We determine the nature of this effect. It occurs when the transverse dimension of the fiber is comparable to the thickness of the skin layer. Then the electric field of the incident wave fills the entire volume of the fiber, and the absorbed power is the highest. We also provide a theoretical analysis of such effect, determine conditions for its existence: the ratio between the radiation wavelength and the diameter of the fiber, the value of conductivity. We also provide an experimental study of the effect, when unfocused radiation beam with a wavelength of 8 mm at the output of waveguide with a \(7.2 \times 3.4\) mm cross section transfers more than 10% of the beam power to a 12 μm diameter graphite fiber. We make an analysis of the mathematical model of the process of heating of graphite fiber by a microwave radiation beam. Then we solve a heat conduction equation and find the temperature distribution along the fiber, which is in agreement with the measured one.
The article aimed to substantiate the differentiated impact of critical internal factors of the economic activities on the market value of shares for joint-stock companies accounting for the organizational development cycle. Using the Company’s Financial Statements in the Automotive and Component subsectors listed on the Indonesia Stock Exchange for 2008-2021, the Chow test, path analysis, and t-criterion, we determined the features of the relationship between the share price and the economic performance indicators of joint-stock companies are determined. We used path analysis for modeling to assess the relationship between the price of shares and the number of dividend payments per share, asset turnover, and net profit per share built. A differentiated nature of the relationship between the indicators depending on the accounting company’s life cycle has been established. Knowing the stage of the business, the company can develop the most effective dividend strategy and determine the appropriate management method.
This article analyzes interviews with women who use drugs in Ukraine to understand the care conundrum they face as members of a stigmatized group. In the interviews, the women sought to position themselves as deserving and needing care as members of a vulnerable category—sometimes as women who use drugs or people living with HIV, but also as mothers—yet also themselves capable of providing care for others. We examine how women who use drugs in Ukraine navigate a moral economy of care involving judgments about deservedness and social worth, the obligatory nature of care, and expectations for reciprocity. For programs for women who use drugs to be successful, they must acknowledge and engage with the moral economies of care in which these women operate. We offer recommendations for how health and social service providers can better meet the unique needs of women who use drugs.
Vladimir Putin seeks to build a modern Russian empire on the post-Soviet space, as confirmed by the invasion of Ukraine. In the present article, the author shows why modern Russia represents a geopolitical project called “Putin’s Empire,” and what the ideological justifications for this empire are. The author also proposes to consider what is happening as a clash of different forms of imperial orders—neoliberal democracy and the concept of the “Russian world.” The author concludes that Russia, as an empire, is in a protracted political crisis, but this does not mean the empire will disintegrate.
Since the pioneering works by Landau, Zener, Stückelberg, and Majorana (LZSM), it has been known that driving a quantum two-level system results in tunneling between its states. Even though the interference between these transitions is known to be important, it is only recently that it became both accessible, controllable, and useful for manipulating a growing number of quantum systems. Here, we systematically study various aspects of LZSM physics and review the relevant literature, significantly expanding the review article in Ref. [504].
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2,256 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
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Vil S. Bakirov
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