Preparation and structural stability of ordered nanocomposites: opal matrix - lead titanates

The conditions for the formation of nanocomposites based on the basis of lattice packings of SiO[2] nanospheres (opal matrices) with included crystallites of lead titanates (PbTiO[3] and PbTi[3]O[7]) in interspherical nanospacing are considered. For the formation of nanocomposites are used sample opal matrices with dimensions of single-domain regions >=0,1 mm.{3} The diameter of SiO[2] nanospheres was ~260 nm. Obtained nanocomposites volume >2 cm{3} in filling >20% of interspherical nanospacing PbTiO[3], PbTi[3]O[7] crystallites were size of 16-36 nm. Using X-ray diffraction and Raman spectroscopy are studied composition and structural stability when heated nanocomposites to 550°C, which allowed the identification of a local phase transition with change of the space group. The dependence of the composition of synthesized materials on the conditions of their preparation is submitted

The use of incorrectly posed inverse problems and catastrophe theory in acoustoplasmic studies

If the discharge current into a plasma contains direct and variable components, the plasma develops wavelike acoustic instabilities and eventually becomes an acoustoplasmа. Such instabilities lead to bistability, multistability, and hysteresis phenomena of the current-voltage characteristics, causing abrupt changes in the state of the plasma medium. These changes can be imagined as phase transitions and described using catastrophe theory. In the present study, the experimental plasma data are approximated by the equations of catastrophes. After reducing the catastrophe equation to canonical form, the points of possible phase transitions are determined. The phase transition coordinates are then converted to coordinates in the experimental system by inverse trans-formations. In this way, we determine the points of possible phase transitions in a real experiment. Finally, the parameter changes in an acoustoplasma discharge are obtained by solving incorrectly posed inverse problems. The inverse problem of the experi-mental data is solved at each current time. Within the neighborhoods of singular points, the incorrectly posed inverse problems are solved by the theory of catastrophes. The proposed methods are applicable to various fields of science and technology.Если ток разряда в плазме содержит прямые и переменные компоненты, плазма развивает волнообразную акустическую нестабильность и в результате становится акустоплазмой. Такие неустойчивости приводят к явлениям бистабильности, мультистабильности и гистерезиса вольт-амперных характеристик, вызывая резкие изменения состояния плазменной среды. Эти изменения могут быть представлены как фазовые переходы. В настоящей работе экспериментальные данные плазмы аппроксимируются уравнениями катастроф. После приведения в соответствие уравнения катастрофы к канонической форме соответствуют точке фазовых переходов. Координаты фазового перехода преобразуются в координаты экспериментальной системы с помощью преобразований.В этом случае мы определяем точки Наконец, изменения параметров в акустической плазме получены с помощью решений. Обратная задача экспериментальных данных решается в каждом текущем моменте времени. В окрестностях особых точек неверно поставлены обратные задачи решаются теорией катастрофы. Предлагаемые методы применимы к различным областям науки и техники

Influence of temperature gradient on diffracted X-ray spectrum in quartz crystal

In this work characteristics of hard X-ray (with energy higher than 30 keV) were investigated. In the experiment we measured spectra of X-ray reflected by a quartz monocrystal in Laue geometry under influence of the temperature gradient. The measurements were made by the spectrometer BDER-KI-11K with 300 eV resolution on the 17.74 keV spectral line of Am241 and the spectrometer XR-100CR with 270 eV resolution on the same spectral line. An existence of temperature gradient leads to increasing of the diffracted beam intensity. The intensity was measured dependently on the temperature of one of the edge of the crystal