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  • Experimental qualification for compressive properties of unidirectional carbon-fiber reinforced composite

    Most important information about an environmental resistance (moisture, cyclic change of the temperature, ultraviolet radiation) of high strength composite material can be received at the compressive mechanical testing. The reinforcing fibers that are oriented along the specimens axis (or are oriented on the small angles relative to this axis) carry the main tencile loading. Conversely, at the compression the elastic and strength properties of the material, basically depend on the matrix properties. The specimens for mechanical testing are usually manufactured as relatively thin rectangular plates by winding or laying-up that corresponds to the ready composite parts. In order to eliminate buckling of the specimen at compressive test, its working length must be very shortened. So, this working part is unavalable for the extensometer instalaltion, and compressive strain of the specimen can be determined by the stroke of crosshead only. This stroke is a sum of very small contraction of the specimen and crosshead displacement due to elastic deformation of the testing machine. We determined the dependence of elastic deformation of the testing machine at the preliminary testing to exclude this deformation from the testing data. We present the features of the compressive testings and their numerical processing at the study of high strength GFRPs, and also the character of composite fracture studied by means of the scanning electron microscopy.

    Keywords: Polymeric composite materials, multilayered composites, environmental resistance, experimental technique, compressive testing, scanning electron microscopy

  • Synthesis and electrochemical characteristics of the new composite cathode material of LiMn2O4@LiCoO2 for lithium-ion battery

    The composite cathode material of the core@shell type with the LiMn2O4@LiCoO2 formula of has been successfully synthesized using the solid-state reactions in several stages. Its structure has been studied by means of X-ray diffraction, scanning and transmission electron microscopy and vibrational infrared spectroscopy. Electrochemical investigation in two-electrode cell has been showed improvement of characteristics of the synthesized cathode material than the constituent components. The specific power of LiMn2O4@LiCoO2 is 650 mWh/g, against 450 and 500 mWh/g for LiCoO2 and LiMn2O4, respectively.

    Keywords: lithium-ion batteries, cathode materials, Delafosse, X-ray structural analysis, electron microscopy, electrochemical properties

  • Secure modification of LSB matching steganography method

    The modification of the most common steganography method for various container is presented. This modification allows to increase the resistance of steganography to the statistical analisys. A comparative analysis of the effect of the traditional LSB matching method and the proposed modification to the frequency histogram of sample values ​​in the container is presented.

    Keywords: steganography, steganalysis, information security, embedded data transfer

  • Catalyst-free thermal synthesis of ZNO nanocrystals from zinc vapor by low temperature

    ZnO nanorod arrays have been synthesized on silicon wafers by chemical vapor deposition (CVD) technique with different  temperature modes, without metal catalyst.  With this method   vertically aligned ZnO nanostructures  were grown at the quite low temperatures.  Modification of the method allowed to place silicon substrates in areas with different  ratios of concentrations of the molecules in the vapor phase. Photoluminescence spectroscopy and electron microscopy studies have shown that morphologies and optical properties of nanorods depends on different ratios of concentrations of the molecules in the vapor phase.

    Keywords: ZnO nanorods,chemical vapor deposition (CVD), photoluminescence

  • Raman spectroscopy as a method for structure analysis of individual carbon nanotubes

    In this paper a systematic study of individual single-walled and multi-walled carbon nanotubes was performed by Raman spectroscopy and high-resolution electron microscopy. We have presented the geometrical and electronic structure analysis on the examples of two tubes: individual single-walled and double-walled nanotubes. The role of different environmental effects and their influence on the final structure assignment are discussed. Moreover, we have shown that the Raman spectroscopy gives reliable estimations of the nanotube diameters and the conductivity. Given a non-destructible character of Raman spectroscopy, we may conclude that it is one of the most efficient methods for structure analysis of carbon nanotubes.

    Keywords: Carbon nanotubes, Raman spectroscopy, electron microscopy

  • Оптимизация режима формования полимерных композитных конструкций на основе метода Парето

    Одним из важнейших факторов, исключающих возникновение дефектов типа пор, расслоений, участков с неполной полимеризацией связующего в формуемой высоконагруженной полимерной композитной конструкции, является управляемость процесса во всем объеме композита. Для обеспечения однородности процесса полимеризации связующего предложен метод многокритериальной оптимизации процесса на основе математической модели, связывающей процессы распространения тепла и кинетики полимеризации. Система связанных уравнений процесса, учитывающая экзотермическое тепло, выделяемое при полимеризации термореактивного связующего, изменение теплоемкости и теплопроводности композита при фазовых переходах от жидкого к гелеобразному и, далее, к твердому состоянию, точную геометрию технологической системы, включая прессформу, а также интенсивность тепловыделения независимо управляемых нагревателей, реализована в виде конечноэлементной модели. Предложенный метод синтеза закона оптимального управления нагревателями, использующий метод множеств Парето, проиллюстрирован на примере полимеризации разностенной композитной конструкции, формуемой из стеклопластика.

    Keywords: Композиционные материалы; Процесс полимеризации; Оптимальное управление; Кинетические уравнения; Уравнения в частных производных в задачах управления и оптимизации, Конечно-элементное моделирование, Фронт Парето

  • Modeling the ab initio structure of layered aluminosilicates.

    This work deals with the study of atomic and electronic structure of kaolinite samples (Glukhovtsy deposit) and montmorillonite (Millerovsky deposit) by density functional theory. The applicability of existing exchange-correlation potential in the local density approximation (LDA) and the generalized gradient approximation (GGA) is analised for an adequate description of the physical properties of layered aluminosilicate. An experimental and theoretical study of the IR spectra of minerals, as well as the identification of the most intense absorption bands, performed in the approximation of DFT using the exchange-correlation potential PW91. The analysis of the band structure of these minerals, which showed that these compounds are direct-gap insulators.

    Keywords: DFT, clay, clay minerals, phyllosilicates, atomic and electronic structure, crystalline systems, IR spectrum band strukutra, the electron density

  • Abstracts