East European Journal of Physics

5-12

Authors: Oryna Ivashtenko

The paper considers a cosmographical approach to analyze cosmological models. Cosmography is a method to describe the kinematics of the cosmological expansion based only on the cosmological principle. We consider a method of treating free parameters of a cosmological model in terms of the directly observable cosmographic values related to the time-derivatives of the Hubble parameter (deceleration, jerk, snap). The method is applied to analyze two cosmological models involving the time-dependence of the cosmological constant in the form Λ(t)→Λ(H) when this approach is especially efficient. Both models interpret the dark energy in the form of the cosmological constant Λ as energy of physical vacuum, which is currently the most supported treatment. The first one means Λ being proportional to the Hubble parameter, and the second one involves a constant and a quadratic term. As a result, the free parameters of both models are expressed in terms of the currently observed values of the Hubble parameter, deceleration, and jerk. The obtained expressions for model parameters are exact, as the method does not involve any additional assumptions. Furthermore, it leads to deal with algebraic equations instead of differential ones. After this procedure, solutions of the evolution equations are obtained in the form of the time-dependence of the Hubble parameter. The obtained model parameters are substituted to the solutions, which are analyzed for a typical range of cosmographic scalars taken from recent observations. Finally, the proposed approach is used to eliminate free parameters from both models and to obtain constraints for the directly observable cosmographic values that can be tested to correspond to present observations data. For the considered cases, such constraints are received respectively for the jerk and the snap parameters with respect to the deceleration. The constraint for the linear model is compared with current observational value ranges for the deceleration and the jerk parameters.

22-29

Authors: U. Tarabara1, O. Ryzhova, K. Vus, A. Kurutos, V. Trusova, G. Gorbenko, N. Gadjev, T. Deligeorgiev

The applicability of the novel cyanine dye AK 3-1 to the detection and characterization of pathogenic protein aggregates, amyloid fibrils, was tested using the absorption spectroscopy technique. In an organic solvent dimethyl sulfoxide (DMSO), absorption spectra of AK3-1 exhibits vibrational structure with the relative intensity of 0-0 sub-band being higher than that for the 0-1 sub-band. In an aqueous phase the dye absorption band undergoes hypsochromic shift relative to DMSO due to H-aggregation of the dye. The interaction of AK3-1 with the native and fibrillar insulin was followed by the decrease of monomer band and the enhancement of H-dimer band. To evaluate the relative contributions of the monomeric and aggregated forms, the absorption spectra of the protein-bound dye were deconvoluted using the asymmetric log-normal (LN) function. The analysis of the set of fitting parameters provides evidence for the protein-induced AK3-1 self-association into the head-to-head dimers, with the magnitude of this effect being much more pronounced for fibrillar protein form. The molecular docking studies showed that the AK3-1 monomer tends to associate with the specific arrangement of side chains in the β-sheet formed by L17 leucine residues (of the insulin B-chain), located on the dry steric zipper interface of the fibril, while the dye dimers form stable complexes with the amyloid groove formed by the residues Q15 and E17 of the A-chain, and located on the wet interface of the fibril. The latter binding site is more easily accessible and is additionally stabilized by the electrostatic interactions between the positively charged dye and the E17 residue. This binding mode seems to be prevailing over that for the AK3-1 monomers. Based on the results obtained, AK3-1 may be recommended as a prospective amyloid marker complementary to the classical amyloid reporters Thioflavin T and Congo Red.

40-47

Authors: K. Lobach, S. Sayenko, V. Shkuropatenko, V. Voyevodin, A. Zykova, E. Bereznyak, Y. Hodyreva, S. Bykanov, A. Bykov, L. Tovazhnyanskyy

The interest in silicon carbide (SiC-based) ceramics and composites as matrix material for nuclear waste immobilization is grown up. Long-term chemical durability and radiation resistance of SiC are important factors for radionuclides immobilization. Advantages of SiC-based ceramics as structural materials in nuclear applications are the high-temperature properties, high density and reduced neutron activation. The use of radiation resistant materials is a strong requirement for safe and environmentally beneficial energy system. The SiC ceramics stability under irradiation for temperatures up to 1273 K is also very important for nuclear power applications. The SiC matrices doped by additives of Cr, Si were fabricated using High Speed Hot Pressing Method. Additives content was in the range from 0.5 to 3 wt %. Microstructural characteristics of silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and infra-red spectroscopy (IR) methods. The results of microcracking under indentation conditions were revealed the lack of cracks in the SiC ceramics with Cr additives before and after irradiation process. In addition, it was demonstrated that samples of SiC with alloying additives Cr and Si possess high mechanical parameters under γ-irradiation process. The strength of ceramics increases with the uniform and fine-grained structure formation. The modification of phase composition and mechanical properties of the SiC ceramics with Cr and Si additives under γ-irradiation were analyzed for further development of radiation resistant and matrix materials for radioactive wastes immobilization.

58-68

Authors: I.G. Marchenko, I.I. Marchenko, V.I. Tkachenko

Recently, both the experimental data and the data of theoretical research appeared stating that the diffusion coefficient shows nonmonotonic behavior with temperature. The motion of Brownian particles in the space periodic structures is an example of the systems with abnormal temperature dependence of the diffusion. The aim of the work was to study the change in the temperature dependence of the diffusion coefficient with a change in friction, both in underdamp and overdamped systems. This scientific paper studies the diffusion of particles in tilted spatial-periodic potentials in a wide temperature range. It is shown that in both underdempted and overdamped systems, the diffusion coefficient reaches a maximum value for a certain value of an external force, the value of which depends on the value of the friction coefficient. However, in systems with low and high friction, the temperature dependence of the diffusion coefficient differs. It was established that the systems with a low friction level γ’ show temperature abnormal diffusion (TAD) at which the diffusion coefficient D is increased with a decrease in temperature. At the same time, the diffusion is enhanced at high γ values with the rise in temperature. This scientific paper studies the transition procedure from the exponential dependence of TAD to the ordinary power temperature dependence with an increase in γ’. It was shown that the energy hump that separates “running” solutions and “localized” solutions is decreased with an increase in the friction coefficient and it vanishes at . Simultaneously with a decrease in ε, the temperature interval of the TAD also narrows. It was established that the temperature-limited TAD domain appears in the region of intermediate values of the friction coefficient. In a specified force range the diffusion coefficient is first increased with a decrease in temperature and then it begins to decrease again. The diagrams of existence of such domains have been constructed. The results obtained opens up prospects for the creation of new technologies for managing diffusion processes. This is of great importance for the production of nanomaterials with a given structure, the creation of surface nanostructures, etc.

77-86

Authors: А.N. Dovbnya, R.N. Dronov, V.A. Kushnir, V.V. Mitrochenko, S.A. Perezhogin, L.I. Selivanov, V.A. Shevchenko, B.I. Shramenko

The results of the photonuclear production of 11C and 18F isotopes in various target-matrices are summarized. The studies were performed using linear electron accelerators of the R&DE "Accelerator" NSC KIPT NAS of Ukraine in the energy range 10 -40 MeV to determine the possibilities of obtaining the maximum achievable activity levels of 11C isotopes, and 18F with a view to planning further developments on the creation of radiopharmaceutical for these nuclear isotopes. In the framework of the above approach, we measured the activity levels of the 18F which is transferred to the surrounding aquatic environment during irradiation of targets-matrices of fluoroplastic (C2F4) with bremsstrahlung flux. The release of the 18F isotope into the aquatic environment under the most favorable conditions (in terms of energy and average beam current) was 3.6% of the target-matrices activity - 40 MBq/g, which is a very low figure. Despite the encouraging value of the specific activity of 18F isotope in lithium fluoride (LiF) -77 MBq/g target–matrices and hydrofluoric acid (HF) - close to 100 MBq/g, the process of extracting 18F from C2F4, LiF and HF as basis of the radiopharmaceutical is not sufficiently effective and brings into question the feasibility of such a methodology for producing 18F isotope for further use. More efficient was the production of the 11C isotope in the irradiated target-matrix of the standard therapeutic form "glucose monohydrate" (glucose). It was shown that, as a result of irradiation of glucose with a gamma-quanta beam, it is possible to “label” glucose with the 11C isotope, which is formed as a result of the photonuclear reaction 12C(γ, n)11C at the 12C nucleus, which is part of the glucose molecule C6H12O6 H2O. Irradiated sample of glucose dissolved in a given volume of solvent (distilled water) will be ready for use radiopharmaceutical "Glucose, 11C". It has been shown that the “photonuclear method” provides for obtaining the “Glucose, 11C” radiopharmaceutical complex with total activity necessary for performing PET diagnostics. The radiopharmaceutical "Glucose, 11C" by the time of its use has 100% radionuclide purity. “Glucose, 11C” obtained in this way was produced for the first time. The choice of the optimal design of a water-cooled target station, providing a moderate (in terms of heat loads) mode of irradiation of a capsule filled with glucose tablets, is discussed. Using the program “SolidWorks FlowSimulation 2011”, the quantitative characteristics of the flow rates of water flowing around the glucose capsule and the converter are calculated.

93-97

Authors: R. Skiba, І. Mysiura, O. Kalantaryan, V. Zhurenko, S. Kononenko

The paper presents the results of an experimental study of Poleskiy amber luminescence excited by narrow band UV radiation (7 nm) at the wavelength range of 310–410 nm with step of 10 nm. The purpose of the study was to determine the relation between an excitation of two luminescence centers, which we found earlier as a result of the mathematical treatment of the spectra obtained during a cycle of experiments on the photo- and X-ray luminescence of amber from the Poleskiy deposit. It was shown that for various samples the spectra of light excited by UV irradiation had a wide band of luminescence with some differences both in shapes and maximum positions. Increasing the exciting UV radiation wavelength, the monotonic displacement of the spectrum maximum position (from 2.62 to 2.5 eV) and the decrease of the full width at half maximum (from 0.92 to 0.62 eV) were observed. To analyze the spectra, we applied the mathematical treatment procedure that we successfully used earlier, namely fitting of experimental curves with Gaussian functions. It was demonstrated that the shape of our spectra could be with high accuracy deconvoluted by two peaks well described by Gaussian functions. The observed differences in shapes of the spectra can be explained by changes in the amplitudes of the two peaks with centers at 2.5 and 2.95 eV. The photoluminescence experiments with excitation by a narrow band UV radiation showed that light generation at wavelengths corresponding to these centers varied significantly by the change of primary UV radiation wavelength. The most intense excitation of the 2.5 eV band (496 nm) corresponds to the UV radiation wavelength of 384 nm (3.23 eV), and for the 2.95 eV band (420 nm) – 287.5 nm (4.32) eV. This led to the conclusion about an independent nature of the excitation of these centers. Spectrum changes can be explained by the different excitation efficiency of both centers.

103-105

Authors: M.A. Grado-Caffaro, M. Grado-Caffaro

It is well-known that II-VI compounds occupy a very relevant place in the whole context of semiconductors. In particular, II-VI semiconductor and isolating or quasi-isolating oxides play an important role. Among these materials, we can mention zinc oxide and cadmium oxide. These oxides, which are transparent (at least in the visible range), are suitable for a number of optoelectronics applications. In this respect, let us consider solar cells; indeed, the above oxides serve as antireflection coatings for these cells. Cadmium oxide, doped or undoped, despite it is hazardous to manipulate, is certainly very interesting for the aforementioned optoelectronics applications. On the other hand, many aspects of this oxide may be regarded from the experimental and theoretical standpoints. In relation to the experimental side, several techniques are currently used to produce cadmium oxide. Among these experimental methods, one can mention metal evaporation, sputtering over a glass substrate, and laser deposition. Perhaps, laser deposition is more advanced and promising than the other techniques. In addition, the fact that laser is involved in this type of deposition gives rise to that the main aspects of the physics and chemistry of cadmium oxide are, say, enhanced. Really, the physics and chemistry of cadmium oxide constitute a significant issue. In order to examine accurately the principal physical mechanisms underlying the formation of cadmium oxide by laser deposition, an in-depth theoretical nonlinear study upon the above formation is presented in this article. As a matter of fact, taking into account that the molecules ( , , ) in the chemical reaction which gives CdO are diatomic, the Morse potential is assumed to act upon the inter-nuclear axis of the molecules which, consequently, behave as quantum anharmonic (nonlinear) oscillators. In fact, associated with the corresponding chemical reaction, inelastic collision between a cadmium molecule and an oxygen one is considered to give rise to two molecules of cadmium oxide. We analyze carefully this collision from the quantum-mechanical point of view (we recall that the molecules in question behave as quantum anharmonic oscillators). From this molecular collision, energy loss is produced due to the laser action. The energy loss is calculated and, from this result, we deduce a mathematical condition to be obeyed for the size of anharmonicity by using a suitable parameter.