On Approximation of Solutions to One Class of Stochastic Equations

Siberian Mathematical Journal -     

Study of the alternating current electrical properties of ZrO2–7.5 mol% Y2O3 ceramics at room temperature and at 457–595 K

The impedance of a ZrO₂–7.5 mol% Y₂O₃ ceramic specimen was measured using the two-probe technique in the frequency range 20 Hz–1 MHz at room temperature and in the temperature range 457–595 K. The novelty of the research lies in the analysis of the intragrain part of the impedance spectra of the ceramics on the basis of the approach proposed in the literature for impedance of ZrO₂–Y₂O₃ single crystals. The method to determine a value of the intragrain direct current electrical conductivity from an impedance spectrum has been developed. The frequency dependence of the intragrain complex dielectric response was interpreted according to the common model used in the literature. Frequency domains, where a power-law dependence having different exponents n ₁=0.825–0.844 and n ₂=0.571–0.592 is observed, were found. The inner consistency of the model used is verified. Values of the transition frequency and the relaxation frequency were determined for the grain interiors and compared with each other. The values of the activation energies of the direct current conductivity, the transition frequency and the relaxation frequency are found to be the same within experimental uncertainty in the temperature range 457–523 K. Electronic Publication     

From electrochromic phenomena to energy harvesting and storage—an overview of solid state ionics research at the Institute of Solid State Physics,University of Latvia

Journal of Solid State Electrochemistry - Solid state ionics is one of the key research topics of the Institute of Solid State Physics, University of Latvia since its establishment. The research...     

The effect of pretensioned FRP windings on the behavior of concrete columns in axial compression

This paper presents the results of an experimental investigation of concrete columns confined by wound pretensioned epoxy-impregnated carbon filament yarns. The yarn winding equipment, with the ability to set the desired pretension force and thereby to produce confined concrete specimens with different initial lateral pressure, was developed at the Institute of Polymer Mechanics. It is shown that the pressure in creases the axial stress at which intense internal cracking of concrete develops.     

Bionanocomposites poly(ϵ-caprolactone)/organomodified Moroccan beidellite clay prepared by in situ ring opening polymerization: Characterizations and properties

In this study, a series of poly(?-caprolactone) (PCL)/clay bionanocomposites were prepared via in situ ring opening polymerization (ROP) of ?-caprolactone catalyzed by titanium butoxide. The natural Moroccan clay beidellite (BDT), used as nanocharge, was organomodified with cetyltrimethylammonium bromide, CTA, to obtain the organically modified 3CTA-BDT (3 = CTA/BDT equivalent feed ratio). Characteristics of the final nanocomposites are investigated by FTIR, SEC, XRD, SEM, TGA, DSC, optical tensiometry, thermal conductivity and water vapor sorption analysis. The intercalated/exfoliated morphologies, revealed by XRD and SEM analyses, confirm uniform dispersion of the nanoclay within the PCL matrix. Thermal stability of all the nanocomposites is improved by the addition of 3CTA-BDT clay compared to pure PCL polymer. The DSC data show that the addition of 3CTA-BDT particles promotes an increase in the disorder of the crystalline phase, which reduces the crystallinity degree. The hydrophobicity of Polymer/clay compatibility was analyzed by studying surface polarity degree of samples by contact angle measurements. Thermal conductivity and water vapor sorption was also discussed. The permeability (P), the sorption coefficient (S) and the diffusion coefficient (D), showed a significant decrease with increasing 3CTA-BDT loading.     

On implication in MV-algebras

In [1], the authors introduced the notion of a weak implication algebra, which reflects properties of implication in MV-algebras, and demonstrated that the class of weak implication algebras is definitionally equivalent to the class of upper semilattices whose principal filters are compatible MV-algebras. It is easily seen that weak implication algebras are just duals of commutative BCK-algebras. We show here that most results of [1] are, in fact, immediate consequences of two well-known facts: (i) a bounded commutative BCK-algebra possesses a natural upper semilattice structure, (ii) the class of MV-algebras and that of bounded commutative BCK-algebras are definitionally equivalent. Presented by I. Hodkinson. Received November 11, 2005; accepted in final form November 26, 2005.     

Powder X‐Ray Diffraction Investigation of Xylazine Hydrochloride Solid Phase Transformation Kinetics

The kinetics of the solid‐state phase transformation of xylazine hydrochloride form X to A has been investigated using powder X‐ray diffraction and differential thermal analysis. Three different kinetic models have been used to describe transition kinetics: the Avrami–Erofeev equation, the Cardew equation, and the methodology for simulation of solid‐state phase transition kinetics by the combination of nucleation and nuclei growth processes. The latter has been recently developed and has been tested in this paper for the case of a real solid‐state transition. The relative humidity, mechanical pressure, temperature, and sample‐preparation effect on phase‐transition kinetics have been investigated, and rate constant changes have been analyzed.     

A new methodology for the simulation of solid state phase transition kinetics by combination of nucleation and nuclei growth processes

A new methodology for the simulation of solid state phase transition kinetics has been developed by combining the influence of nucleation rate, nuclei growth rate and the power p characterizing the contact area between the growing particles. The equations used in this methodology were well known, and have been used previously for creating some of the most popular solid-state kinetic equations. The developed methodology made possible calculations of separate rate constants for two processes affecting the rate of phase transition—nucleation (described with K ₁) and nuclei growth (described with K ₂). Similar phase transitions were also approximated with the well-known single constant Avrami–Erofeev equation, but we successfully calculated both constants according to the new methodology, which allowed a separate evaluation of these two processes and explained the different induction periods. The effects of empirically adjusted constants on theoretically calculated kinetic curves were thus determined.     

The effective Kerr constant of an electrooptical composite material

A general relationship is derived for the effective Kerr constant of an electrooptical composite material containing nonlinear centrosymmetric dielectric microcrystals; anisotropy of the inclusions and their nonsphericity were taken into account. It is shown that nonsphericity of the particles makes it possible to substantially enhance the Kerr constant of the composite in the case when the glass-matrix permittivity is much smaller than that of the inclusions. The size effects in ferroelectrics, on the one hand, and the required low losses for scattering, on the other, determine the optical range in which the particle shape anisotropy can be efficiently used. This range covers the IR and long-wavelength part of the visible region.     

Limit Theorems in the Boundary Hitting Problem for a Multidimensional Random Walk

Siberian Mathematical Journal -