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Danilchenko S.N.,Ukrainian Academy of Sciences | Kalinkevich O.V.,Ukrainian Academy of Sciences | Pogorelov M.V.,Sumy State University | Kalinkevich A.N.,Ukrainian Academy of Sciences | And 7 more authors.
Journal of Biomedical Materials Research - Part A | Year: 2011

Chitosan/hydroxyapatite scaffolds could be used for bone regeneration in case the application of auto- or allografts is impossible. The objective of the present work was to characterize and study in vivo biodegradation of simple chitosan/hydroxyapatite scaffolds. For this purpose, a series of chitosan/hydroxyapatite composites has been synthesized in aqueous medium from chitosan solution and soluble precursor salts by a one step coprecipitation method. A study of in vivo behavior of the materials was then performed using model linear rats. Cylindrical-shaped rods made of the chitosan/hydroxyapatite composite material were implanted into tibial bones of the rats. After 5, 10, 15, and 24 days of implantation, histological and histo-morphometric analyses of decalcified specimens were performed to evaluate the stages of biodegradation processes. Calcified specimens were examined by scanning electron microscopy with X-ray microanalysis to compare elemental composition and morphological characteristics of the implant and the bone during integration. Porous chitosan/hydroxyapatite scaffolds have shown osteoconductive properties and have been replaced in the in vivo experiments by newly formed bone tissue. © 2011 Wiley Periodicals, Inc.

Fedchenko O.V.,Sumy State University | Saltykova A.I.,Sumy State Pedagogical University | Protsenko S.I.,Sumy State University
Journal of Nano- and Electronic Physics | Year: 2012

The influence of substrate material on magnetoresistive, magneto-optical properties and diffusion processes in Co(30nm)/Fe(30nm)/S was investigated. The samples were built on amorphous substrate SiO2/Si and MgO(100) crystal and then were annealed up to 300, 500 and 800°S. Crystal structure control and sample's element composition was held by diffraction of low energy electrons (LEED) and energy dispersive X-ray analysis (EDX). After that magneto resistive properties (MR) and magneto-optical Kerr effect (MOKE) were investigated and diffusion profiles were built with help of secondary ion mass spectroscopy (SIMS). It was stated that during oriented film system growth on MgO(100) crystal the significant magnetic anisotropy is observed. It appears in increase of coercive force (BC) in two times and significant variation of magneto resistance at different turn angles. AFM investigations showed that surface roughness of Au(2nm)/Co(30nm)/Fe(30nm)/MgO filem system in four times lower than of sample on amorphous substrate (non-annealed). Besides the diffusion processes in systems that were built on MgO monocrystall proceed less intensive than in case of SiO22/Si. © 2012.

Rusina L.Y.,Moscow Zoo | Ghazali M.A.,Ukrainian Academy of Sciences | Firman L.A.,Sumy State Pedagogical University
Entomological Review | Year: 2016

The paper presents the results of analysis of the relationships of various colony characteristics in the resocial wasp Polistes dominula nesting on plants in the south of Ukraine (Kherson Province, the Black Sea Biosphere Reserve) in 2003–2007. The number of future foundresses and nest size at the end of the life cycle depend on the queen longevity and on the number of workers in the colony. The number of males reared in the colony is positively correlated with the nest size (the number of cells) and negatively correlated with the queen longevity. An increase in the share of the brood infested by the parasitoids Latibulus argiolus (Hymenoptera, Ichneumonidae) and Elasmus schmitti (Hymenoptera, Eulophidae) results in a smaller nest size and a smaller number of males reared. © 2016, Pleiades Publishing, Inc.

Medvedovskaya O.G.,Sumy State Pedagogical University | Lopatkin Y.M.,Sumy State University | Fedorenko T.A.,Sumy State University | Chepurnykh G.K.,Ukrainian Academy of Sciences
Journal of Nano- and Electronic Physics | Year: 2014

For the case when the line of the first order phase transitions does not transform into the line of the second order phase transitions, i.e. not as ends with the tricritical point but not with a critical one: critical lines, limiting the region of metastable states, by using the Landau theory of phase transitions were determined. © 2014 Sumy State University.

Nekislykh E.M.,Sumy State Pedagogical University | Ostrik V.I.,Ukrainian Academy of Sciences
Mechanics of Solids | Year: 2010

We use the Wiener-Hopf method to obtain exact solutions of plane deformation problems for an elastic wedge whose lateral sides are stress free and which has rectilinear cracks on its axis of symmetry. In problem 1, a finite crack issues from the wedge apex edge; in problem 2, a half-infinite crack originates at a certain distance from the wedge apex edge; and in problem 3, the wedge contains an internal finite crack. Earlier, many authors obtained approximate solutions to these problems [1-10] and exact solutions to problem 1 [11-17] and homogeneous problem 2 [18-20] (see also [21]). The method of approximate conformal transformation [1, 2] and that of integral equations [3, 4] were used to study a specific case of problem 1 about equilibrium of an elastic half-plane with a boundary crack perpendicular to the half-plane boundary. The solution to problem 1 was obtained in [11] by reducing the problem to the Riemann problem for analytic functions and in [6, 7], by the Wiener-Hopf method. In [11], the problem coefficient was factorized in terms of Cauchy-type integrals, but no further calculations were presented, and in [6, 7], an approximate factorization was performed by approximating the factorized function. In [8], problems 1 and 2 were reduced to Fredholm integral equations of the second kind, which were solved numerically. In problem 1, values of the integral equation density were calculated, and the normal displacements of the crack edges were expressed in terms of this density in the form of Abel integrals; no calculations were given in problem 2. The exact values of the stress intensity factors in problem 1 were obtained in [12-17] by the Wiener-Hopf method. The paper [12] considered the case of linear normal stresses given on the crack edges in the absence of tangential stresses was considered, the papers [13-16], the case of concentrated forces acting on the crack edges, and the paper [17], the case of concentrated moments applied to the wedge apex. Solutions to the homogeneous problem 2, where the crack edges are stress free and the principal vector and the principal moment of stresses are given at infinity, were constructed by the Wiener-Hopf method in [18-20]. Problem 3 was studied in [6, 7, 9] by different approximate methods: using the asymptotic solution of the integral equation, solving the Fredholm integral equation of the second kind by the method of successive approximations after approximating the Fourier transform of the difference kernel of the original integral equation, and using another approximation of the kernel to reduce the problem to a singular integral equation admitting a solution in closed form. Here, the asymptotic method can be used only in the case of a crack relatively distant from the wedge apex, and the approximation of the kernel transform gives satisfactory results if the angle at the wedge apex exceeds π. The authors present the numerical results for the stress intensity factors and the displacement jump at an internal point of the crack in the case where the wedge is a half-plane. In [6-9], the cases of rigid clamping and hinged support of the faces of an elastic wedge were investigated. Problem 3 was numerically solved by the method of singular integral equations in [10], where the case of fixed sides of the wedge was also considered. In what follows, problems 1 and 2 whose integral equations are given on a half-infinite interval and have distinct kernels are solved by the Wiener-Hopf method [22], and problem 3 is solved by the generalized Wiener-Hopf method, developed in [23-25] for solving integral equations with difference kernel on a finite interval. The coefficient of the functional Wiener-Hopf equation is factorized in terms of infinite products. We also present numerical results for the stress intensity factors, the normal stress distribution on the crack continuation line, and the normal displacements of the crack edges. © 2010 Allerton Press, Inc.

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