Кафедра фізико-математичних наук

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    The interplay of external and internal semiotics of domain-specific scientific theories
    (University of Tartu, 2022) Gabovich, Alexander; Kuznetsov, Volodymyr
    We suppose that those who are reading this contribution are familiar with the traditional reconstruction of domain-specific scientific theories (DSSTs) as logically ordered and static systems of statements about their domains. The latter split into separate realities with their attributes. However, any DSST (e.g., celestial mechanics, theories of superconductivity, theories of elementary particles) is an ever-improving tool for acquiring new knowledge. It means that a more realistic reconstruction is a varied polysystem. Its interacting and changing subsystems (SS) perform specific functions in the complex process of obtaining and testing the new knowledge. According to the modified structure-nominative reconstruction, there are many SSs in DSSTs [2019; 2021].
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    Improved parametrization of inclusive proton spectra from 3H(α,p)6He reaction using data obtained in a correlation experiment
    (2022) Povoroznyk, Orest; Gorpinich, O.
    The new analysis of inclusive proton spectra from 3H(α, p)6He reaction was performed. The existence of two new excited levels of 6He with energy parameters E2ex.s.*= 2.4 MeV, Γ = 0.4 MeV; E3ex.s.*= 3.0 MeV, Γ = 0.6 MeV was confirmed as a result of new parameterization performed using energy parameters obtained from the correlation kinematic-incomplete experimental study of 3H(α, pα)nn reactions at Eα = 27.2 MeV and Eα = 67.2 MeV in contrast to the initial analysis, in which the resonance observed above the known first excited 6He level E1ex.s. = 1.8 MeV was treated as the second broad excited level E2ex.s. = 2.98 (0.17) MeV, Γ2ex.s. = 2.39 (0.27) MeV.
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    Magneto-optic Kerr effect in Gd20Co80 alloy
    (2022) Kudin, V.; Rozouvan, S.; Stashchuk, Vasyl
    The magneto-optical Kerr effect in Gd20Co80 alloy and cobalt thin films has been studied in a broad spectral range applying spectral ellipsometry experimental technique. The results of the experiments showed the complex nature of the complex Kerr angle dispersion curves. A quantum mechanical formalism for degenerate and non-degenerate Landau levels for quasi-free electrons in ferromagnetic material has been developed in order to analyze the experimental data. The equivalence of relations for off-diagonal dielectric tensor elements for non-degenerate Landau levels to the classical case of the motion of quasi-free electrons along circular trajectories in a magnetic field has been theoretically shown. The degenerate Landau levels in this approach are the result of motion of electrons in small confined volumes near rare-earth alloy atoms. Rotation of light polarization occurs in this case due to transitions between subbands having different magnetic quantum numbers. This theoretical approach allowed us to interpret in detail shapes and sign of the complex Kerr angle dispersion curves, which actually include the contributions of optical transitions between degenerate and non-degenerate energy levels. The complex Kerr angle sign is determined by the magnetization magnetic field direction for non-degenerate Landau levels and the Hund rule for degenerate Landau levels.
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    З'ясування умов збудження поверхневих поляритонiв у керамiцi Mg0,2Zn0,8O методом порушеного повного внутрiшнього вiдбивання
    (2022) Мельничук, О.; Корсунська, Н.; Мельничук, Л.; Хоменкова, Лариса; Венгер, Є.
    Уперше для керамiки Mg0,2Zn0,8O теоретично з’ясовано умови збудження поверхневих поляритонiв та побудовано поверхню порушеного повного внутрiшнього вiдбивання 𝐼(𝜈)/𝐼0(𝜈), яка являє собою тривимiрне подання коефiцiєнта пропускання в IЧ-дiапазонi спектра. Визначено його залежнiсть вiд частоти i кута падiння випромiнювання. Для одержання оптичних i електрофiзичних параметрiв керамiки, необхiдних для розрахункiв, вимiрянi спектри зовнiшнього IЧ-вiдбивання. З них одержано вiдповiднi параметри методом дисперсiйного аналiзу. Продемонстровано можливiсть дослiджень резонансної взаємодiї оптичних фононiв та плазмонiв. Отриманi результати добре узгоджуються з вiдомими в лiтературi даними.
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    Peculiarities of photoluminescence excitation in ZnO ceramics doped with group-I elements
    (2022) Korsunska, N.; Markevich, I.; Stara, T.; Kozoriz, K.; Melnichuk, L.; Melnichuk, O.; Khomenkova, Larysa
    Extrinsic luminescence, excitation, and absorption spectra of ZnO ceramics doped with acceptors (lithium, copper, or silver), as well as undoped ZnO ceramics sintered in various atmospheres, have been studied. It is shown that the acceptor doping leads to the appearance of luminescence bands in the visible spectral interval, and their intensity significantly exceeds the intensity of the corresponding emission from undoped specimens. A selective maximum at 390–400 nm, which is usually absent in the excitation spectra of self-activated luminescence bands in undoped ZnO specimens, is found to dominate in the excitation spectra of those bands. It is supposed to be caused by the interaction between the emitting centers and defects arising near the impurities, with the Auger process being the most probable mechanism of energy transfer from these defects to the emitting centers. By sintering ZnO ceramics in the presence of carbon, it is shown that the appearance of the selective maximum in the excitation spectra occurs due to the extraction of oxygen from ZnO ceramics. An assumption has been done concerning the nature of the centers responsible for the excitation of extrinsic luminescence.
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    Effects of thermal treatment on the complex structure of luminescence emission of Li-doped ZnO screen-printed films
    (2023) Chukova, O.; Borkovska, L.; Khomenkova, L.; Korsunska, N.; Ponomaryov, S.; Androulidaki, M.; Stratakis, E.
    The ZnO–Li films were synthesized and investigated in an attempt to explore and develop RE-free phosphor materials capable of emitting intense visible light in a wide spectral range. The effects of both heterovalent doping with lithium and high-temperature annealing on the optical properties of ZnO films were studied. The films were deposited on the Al2O3 substrate using the screen-printing method and annealed at 800–1,000°C in air for 0.5–3 h. Both doping and annealing result in the transformation of the shape of reflectance spectra in the range of 300–400 nm and the shift of absorption edge to the long-wavelength region. At the same time, the bandgap value estimated taking into account the exciton peak position and its binding energy is independent of Li-doping. The feature at 300–400 nm and the shift of absorption edge are ascribed to the appearance of the absorption band that excited the yellow photoluminescence band. The photoluminescence spectra of undoped and Li-doped films show the emission bands in the ultraviolet and visible spectral ranges. The ultraviolet emission is due to ZnO exciton recombination. The visible emission band comprises several components peaked at 430, 482, 540, 575, and 640 nm. Their relative intensities depend on Li-doping, annealing temperature, and annealing duration. The 430- and 482-nm luminescence bands were observed in Lidoped films only. Their excitation spectra show the peak located at 330–340 nm, indicating that the energy significantly exceeds the ZnO bandgap energy. Consequently, the 430- and 482-nm luminescence bands are attributed to an additional crystal phase formed under annealing. Other components of visible emission bands are ascribed to the defect-related emission of ZnO. The possible nature of these bands is further discussed. Li-doping and annealing at intermediate temperatures result in blue emission and an enhancement of other visible bands, which makes ZnO–Li films a perspective material in photonic applications.
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    До епістемологічного аналізу наукових теорій
    (2023) Кузнєцов, Володимир
    У статті розглянуто взаємозв’язки науки та філософії науки крізь призму моделювання наукових теорій, які є значно складнішими системами, ніж зазвичай їх описують у фаховій літературі. Багато фахівців, пов’язаних з наукою, її викладанням і адмініструванням, мають спрощені уявлення про компонентний склад теорій, які є основними інструментами наукового мислення. Тому необхідно розробити об’єднуючий, але детальний погляд на теорії. Ґрунтувати його доцільно на аналізі теорій, що використовуються в науковій практиці. Автор пропонує помістити полісистемне бачення теорій у центр філософії науки та інших метанаук про науку (наукознавство, історія науки, соціологія науки, психологія науки, управління наукою тощо). Такий підхід може бути корисним для філософів і науковців, викладачів наукових дисциплін і студентів, а також для тих, хто керує наукою як соціальним інститутом з продукування нового знання, і тих, хто оцінює її результати.
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    Conformational flexibility of spermidine3+ interacting with DNA double helix
    (2023) Perepelytsya, Sergiy; Vasiliu, Tudor; Laaksonen, Aatto; Engelbrecht, Leon De Villiers; Brancato, Giuseppe; Mocci, Francesca
    Natural polyamines play a key role in many biological processes, particularly in the stabilization of DNA double helix structure in the cell nucleus. Among others, the conformational flexibility of polyamines, such as spermidine, is an essential property for the formation of complexes with DNA. Yet, the characterization of the conformational space of polyamines has not been fully elucidated. Using atomistic molecular dynamics (MD) simulations, we present a detailed study of the conformational space of spermidine3+ both in solution and in interaction with DNA. We have identified more than 2000 distinct conformations, which can be grouped into seven modes. Notably, the relative population of these modes is highly affected by the interaction of spermidine3+ with DNA, thus representing a fingerprint of complex formation. In particular, three of the seven dihedral angles of spermidine3+ are predominantly in trans conformation (with or without DNA), while the other four dihedral angles are observed to switch between trans, gauche+ and gauche-. The preference between the latter conformational states was analyzed in terms of the distinct energy contributions composing the potential energy. Overall, our results shed light on the conformational equilibrium and dynamics of spermidine3+, which in turn is important for understanding the nature of its interaction with DNA.
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    Optical properties of Zn0.75Mg0.25O:Mn ceramics
    (2023) Markevich, I.; Korsunska, N.; Stara, T.; Polishchuk, Yu.; Vorona, I.; Kozoriz, K.; Ponomaryov, S.; Melnichuk, O.; Melnichuk, L.; Cremades, A.; Khomenkova, Larysa
    Mn-doped ZnO, MgO and Zn0.75Mg0.25O samples ([Mn] = 0.1 at.%) were produced by conventional solid-state technique and investigated by means of XRD, EPR, absorption, photocurrent, photo- and cathodoluminescence methods. It was shown that Zn0.75Mg0.25O solid solution with hexagonal structure has the bandgap of Eg ~3.65 eV. The quenching of host defect-related luminescence in ZnO:Mn and in hexagonal Zn0.75Mg0.25O:Mn was observed, while the Mn-related emission being absent. The energy level of Mn2Z+n center in hexagonal Zn0.75Mg0.25O:Mn was found to be at 2.16 eV below conduction band (c-band) bottom and all excited states of Mn2Z+n ions, including the lowest one, reside in c-band, as it takes place in ZnO:Mn. It is concluded that the necessary condition to obtain Mn-related light emission in Mn-doped alloys is to make deeper the lowest excited level of Mn2Z+n ions. One of the solutions is to produce Zn1-xMgxO:Mn solid solution with the bandgap energy larger than 4.0 eV using nonequilibrium fabrication approaches.
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    Representations of solutions of Lamé system with real coefficients via monogenic functions in the biharmonic algebra
    (2023) Gryshchuk, Serhii
    New representations of solutions of Lamé system with real coefficients via monogenic functions in the biharmonic algebra are found.
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    A mathematical model of transport kinetics of 99mTc radiotracers
    (2021) Shevtsova, Oksana
    The proposed four-compartment mathematical model describes transport kinetics of 99m-technetium radiotracers at intravenous administration process with taking into account radiopharmaceutical accumulation, elimination and radioactive decay. The analytical solution of the model in a form of the well-known sum-of exponential solution was obtained. The dependencies of the tracer concentration versus the time are analyzed. The model can be easily verified by the radioactive tracer concentration data in the circulatory/lymphatic system measured at some time points, and the obtained data can be used to determine the transport coefficients. Time-activity dependencies were obtained and analyzed for each compartment. The model can be used for individual transport parameter calculation at administration of diagnostic/therapeutic dose loads.
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    Two excitation pathways of Pr3+ ion emission in HfO2:Si:Pr films depending on crystalline phase transformations in annealing
    (2023) Garcia Andrade, Maria Alejandra; Torchynska, T.; Casas Espinola, Jose Luis; Vel´azquez Lozada, E.; Polupan, G.; Khomenkova, Larysa; Gourbilleau, F.
    The impact of annealing on the emission and transformation of the crystalline phases in Si rich HfO2:Pr films was investigated by analyzing the morphology, chemical composition, structure, and photoluminescence (PL) characteristics. Films were prepared by RF magnetron sputtering and monitored as-prepared and after annealing at 1000 ◦C for 5–60 min. Emission through host HfO2 defects has only been detected in spectra of as-prepared Si rich HfO2:Pr films. Heat treatment for 30 min stimulates a phase transformation together with the appearance of a tetragonal HfO2 phase and Si quantum dot (QDs). This last process is accompanied by appearance of bright emission of rare earth (RE) ions Pr3+ related to the transitions in the 4f energy levels. Additional annealing for 60 min stimulates the complete oxidation of the Si QDs with the formation of the SiO2 phase along with partial destruction of a tetragonal HfO2 phase. This last process is accompanied by the significant increase of the intensity of Pr3+ ion emission. Two forms of luminescence excitation in 4f energy levels of Pr3+ ions are discussed, related to energy transfer to Pr3+ ions, first from Si QDs and then from host defects in HfO2. These changes in the excitation pathways of Pr3+ ion emissions are stimulated by the transformations of the crystalline phases in the thermal treatment together with the generation of host HfO2 defects. Hafnia-based materials doped with RE elements are interesting for telecommunication technology and applications in waveguides and optoelectronic devices.
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    Огляд сучасної філософії науки : Частина друга: Оцінні графи окремої науки
    (2022) Габович, Олександр; Кузнєцов, Володимир
    Виокремлено різновиди сучасної філософії математичних та природничих наук. Специфічні ознаки цих наук проаналізовано за допомоги графових класифікацій відповідних філософій. Під креслено важливість для всіх різновидів філософії науки використовуваних ними реконструкцій практичних теорій. У першій частині окреслено мету статті та розглянуто предметні та теоретичні, у другій — оцінні, називні, теоретико-реконструктивні та мовно-реконструктивні класифікації філософій науки, а також зроблено висновки щодо доцільності застосування цих класифікацій до філософій суспільних та гуманітарних наук.
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    Огляд сучасної філософії науки : Частина перша: Метапроблема впорядкування та спеціалізація філософій науки
    (2022) Габович, Олександр; Кузнєцов, В.
    Поняття "філософія науки" незаперечно увійшло до сучасного філософського дискурсу. У філософському та науковому середовищах є різні тлумачення філософії науки. Власне науку традиційно вважають суспільною інституцією, створеною з метою здобуття та застосування знань про природні та штучні реалії. Водночас введення поняття "філософія науки" було б тривіальним, якби його обсяг зводився до перетину обсягів понять "наука" і "філософія". Перехід від тлумачення науки загалом до її розуміння як сукупності конкретних наук з особливими предметними галузями викликає виокремлення із загальної філософії науки групоцентрованих філософій наук на кшталт філософії біології, філософії психології, філософії технічних наук, філософії медицини, філософії соціальних наук, філософії інформаційних наук, філософії фізики, філософії математики, філософії філософії тощо. У статті виокремлено різновиди сучасної філософії математичних та природничих наук. Специфічні ознаки цих наук аналізовано за допомоги графових класифікацій відповідних філософій. Підкреслено важливість для всіх різновидів філософії науки використовуваних ними реконструкцій практичних теорій. У першій частині окреслено мету статті й розглянуто предметні та теоретичні класифікації філософій науки, у другій — оцінні, називні, теоретико-реконструктивні та мовно-реконструктивні, а також зроблено висновки щодо доцільності застосування цих класифікацій до філософій суспільних та гуманітарних наук. В підсумку автори висновують , що, незважаючи на популярність у філософсько-науковому середовищі різкого протиставлення класичної та некласичної фізики, для цього немає ґрунтовних об’єктивних підстав.
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    Path of modern natural sciences: from discovery of realities to study of their attributes
    (2022) Gabovich, Alexander; Kuznetsov, Volodymyr
    We analyze the development of the natural sciences according to the scheme: "… reality – attributes – reality – attributes". Any material reality is interpreted as a carrier of attributes manifested in a certain range of its experimental study and at a certain theoretical level of data understanding. More sophisticated experiments and refined theories lead to a more detailed and correct vision of realities and their attributes. The latter initiates new experiments and creation of new theories. These cognitive processes lead to the discovery of new material realities with their additional or refined attributes compared to those previously known. The objectivity and relative truth of scientific statements about the realities under study and their attributes are based on a qualitative or quantitative correspondence between theoretically calculated values of attributes and their experimentally measured values. We emphasize that the isolation and adequate historical and philosophical analysis of those cycles requires professional knowledge of the analyzed complex scientific material and cannot be implemented within the framework of oversimplified ideas about science and the role, which theories play in it. Examples of such ideas are the understanding of theories solely in terms of their refutation and confirmation or even the replacement of theories with fuzzy sociological concepts such as a paradigm and sociocultural determination of the scientific results. Those views often become the source of idealistic, irrational, and postmodernist interpretations of science and its history.
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    Elucidation of conditions for excitation of surface polaritons in Mg0.2Zn0.8O ceramics using the disturbed total internal reflection method
    (2022) Melnichuk, Olexandr; Korsunska, Nadiia; Melnichuk, Lyudmyla; Khomenkova, Larysa; Venger, Yevgen
    Conditions for the excitation of surface polaritons in Mg0.2Zn0.8O ceramics have been theoretically analyzed for the first time, and the surface of the disturbed total internal reflection І(ν) / І0(ν) has been plotted, which is a three-dimensional representation of the transmission coefficient in the IR spectral interval. Its dependence on the frequency and incidence angle of radiation is determined. The external reflection IR spectra are measured to calculate the required optical and electrophysical parameters of ceramics using the method of dispersion analysis. The possibility of researching the resonant interaction between optical phonons and plasmons has been demonstrated. The obtained results are in good agreement with the literature data.
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    Comprehensive investigation of Er2O3 thin films grown with different ALD approaches
    (2022) Khomenkova, Larysa; Merabet, H.; Chauvat, M.-P.; Frilay, C.; Portier, Xavier; Labbe, C.; Marie, P.; Cardin, J.; Boudin, S.; Rueff, J.-M.; Gourbilleau, F.
    The effect of Er precursor nature (Er(CpMe)3 or Er(tmhd)3) and annealing treatment at 500–1100 ◦C on the structural and optical properties of Er2O3 films grown on Si substrates by thermal or O2-plasma-assisted atomic layer deposition was studied by means of spectroscopic ellipsometry, Fourier-transform infrared spectroscopy, Xray diffraction, transmission electron microscopy coupled with energy dispersive X-ray spectroscopy as well as photoluminescence method. An annealing at 500–800 ◦C resulted in the film crystallization mainly. Thermal treatment at high temperatures caused the formation of Er silicate phase due to the diffusion of Si atoms from the substrate in the films depth. This phase was found to be Er2SiO5 being crystallized at 1100 ◦C. Light emitting properties of the films are determined by Er2O3 native defects (like oxygen vacancies) and intra-4f shell transition in Er3+ ions. The latter dominated in the films annealed at 1000–1100 ◦C. The most intense Er3+ emission, observed in the films grown with O2-plasma-assisted approach, was explained by a lower contribution of oxygen vacancies as well as by pronounced crystallization of Er silicate phase. In this latter, the effect of concentration quenching of Er3+ luminescence was lower due to a larger distance between Er3+ neighbor ions.
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    Enhancement of radiation-induced EPR signal in bioapatites
    (2022) Nosenko, Valentyna; Vorona, Igor; Lemishko, Serhii; Golovina, Iryna; Yukhymchuk, Volodymyr; Okulov, Serhii; Neimash, Volodymyr; Povarchuk, Vasyl; Solopan, Serhii; Belous, Anatolii
    Amplification of a dosimetric EPR signal in mineralized biological materials available in limited quantities has been demonstrated in this paper. Powders of irradiated enamel, dentin, and bone tissue were placed into silica ampoules with the outer diameter close to 1.4 mm. To amplify the signal, the dielectric insert in the form of cylinder with the outer radius 2.85 mm, the inner radius 0.75 mm, and the height 1.85 mm made of a high-κ and low-loss ceramic material BaTi4O9 + 8.5% ZnO has been used. It has been shown that maximum signal amplification (about an order of magnitude) has been achieved when the sample is completely inserted into this dielectric. It has been found that the line shape of the dosimetric signal is not distorted, if using the dielectric insert. Decomposition of the amplified EPR spectra allowed us to determine the relative contribution of two types of CO2– radicals to the dosimetric signal, which coincides with the literature data.
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    Size- and position-controlled Ge nanocrystals separated by high-k dielectrics
    (2022) Lehninger, D.; Honeit, F.; Rafaja, D.; Klemm, V.; Röder, C.; Khomenkova, Larysa; Schneider, F.; Borany, J. von; Heitmann, J.
    Germanium nanocrystals embedded in high-k dielectric matrices are of main interest for infrared sensing application, as a role model for Ge-based nanoelectronics passivation or for nonvolatile memory devices. The capability of the size control of those nanocrystals via rapid thermal processing of superlattice structures is shown for the [Ge–TaZrOx/TaZrOx]n, [Ge–TaZrOx/SiO2/TaZrOx]6, and [ TaZrOx/Ge–SiO2]n superlattice systems. All superlattices were deposited by radiofrequency magnetron sputtering. Transmission electron microscopy (TEM) imaging confirms the formation of spherically shaped nanocrystals. Raman scattering proved the crystallization of Ge above 700°C. The TaZrOx crystallizes above 770°C, associated with a phase separation of Ta2O5 and ZrO2 as confirmed by x-ray diffraction. For the composite layers having 3 nm and 6 nm thickness, the size of the Ge nanocrystals correlates with the deposited layer thickness. Thicker composite layers (above 9 nm) form two fractions of nanocrystals with different sizes. An additional SiO2 layer in the [Ge– TaZrOx/SiO2/TaZrOx]6 superlattice stacks facilitates the formation of larger and better separated Ge nanocrystals. The deposition of Ge-SiO2 composite layers separated by pure TaZrOx illustrates the barrier effect of TaZrOx against Ge diffusion. All three material systems allow the controlled formation of Ge nanocrystals in amorphous matrices at temperatures above 700 and below 770°C.
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    Особливостi процесiв збудження фотолюмiнесценцiї у керамiцi оксиду цинку, легованої елементами I групи
    (2022) Корсунська, Надія; Маркевич, І.; Стара, Т.; Козоріз, К.; Мельничук, Людмила; Мельничук, О.; Хоменкова, Лариса
    Дослiджено спектри домiшкової фотолюмiнесценцiї, спектри її збудження i спектри поглинання керамiки ZnO, легованої лiтiєм, мiддю i срiблом, а також нелегованої керамiки, спеченої в рiзних атмосферах. Показано, що легування керамiки акцепторами приводить до появи смуг люмiнесценцiї у видимому дiапазонi спектра, iнтенсивнiсть яких суттєво перевищує iнтенсивнiсть видимого випромiнювання нелегованих зразкiв. Виявлено, що в спектрах збудження цих смуг домiнує селективний максимум в областi 390–400 нм, зазвичай вiдсутнiй у спектрах збудження самоактивованих смуг люмiнесценцiї в нелегованих зразках. Запропоновано пояснення, що його поява зумовлена взаємодiєю мiж центрами випромiнювання i дефектами, якi виникають в околi домiшок, а оже-процес є найбiльш iмовiрним механiзмом передачi енергiї вiд цих дефектiв до центрiв випромiнювання. За допомогою синтезу керамiки у присутностi вуглецю показано, що поява такого максимуму в спектрах збудження люмiнесценцiї в нелегованих зразках зумовлена видаленням кисню з керамiки. Зроблено висновок щодо природи центрiв збудження домiшкової люмiнесценцiї.