Acoustic emission and thermal expansion of Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> and Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> crystals

The temperature dependence of the elongation per unit length for Pb(Mg_1/3Nb_2/3)O₃ crystals unannealed after growth and mechanical treatment is investigated in the course of thermocycling. It is revealed that this dependence deviates from linear behavior at temperatures below 350°C. The observed deviation is characteristic of relaxors, is very small in the first cycle, increases with increasing number n of thermocycles, and reaches saturation at n≥3. In the first cycle, a narrow maximum of the acoustic emission activity is observed in the vicinity of 350°C. In the course of thermocycling, the intensity of this maximum decreases and becomes zero at n>3. For (1?x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ crystals, the dependence of the temperature of this acoustic emission maximum on x exhibits a minimum. It is assumed that the phenomena observed are associated with the phase strain hardening due to local phase transitions occurring in compositionally ordered and polar nanoregions.     

Determining the stress state of a stretched rod from its measured magnetic characteristics

Stress-strain diagrams and coercive force-strain diagrams for carbon steel samples under uniaxial tension were obtained experimentally during loading and after unloading. These diagrams were used to develop a procedure for determining the stress acting in structural members from the value of the coercive force in the loaded state. A method is proposed to estimate the previous maximum stress from the values of the coercive force measured in the unloaded state. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 5, pp. 205–211, September–October, 2008.     

Screening of the deformation field in a solid by point defects

It is demonstrated that in an isotropic infinite solid body with a high concentration of point defects, the deformation produced by a test defect decreases with the distance from it according to a law similar to that of the decrease in the potential of a point charge with Debye screening.     

Quantum Chemical Modeling the Structure of Complexes of Copolymer of N-Vinylpyrrolidone and Triethylene Glycol Dimethacrylate with Metformin

Russian Journal of Physical Chemistry A - The structure of metformin (dimethylbiguanide) complexes with the copolymer of N-vinylpyrrolidone and triethylene glycol dimethacrylate in aqueous...     

Solvent‐Catalyzed Ring–Chain–Ring Tautomerization in Axially Chiral Compounds

The mechanism of ring–chain–ring tautomerization and the prominent effect of the solvent environment have been computationally investigated in an effort to explain the enantiomeric interconversion observed in 2‐oxazolidinone derivatives, heterocyclic analogues of biphenyl atropisomers, which were isolated as single stable enantiomers and have the potential to be used as axially chiral catalysts. This study has shed light on the identity of the intermediate species involved in the ring–chain–ring tautomerization process as well as the catalytic effect of polar protic solvents. These mechanistic details will prove very useful in predicting and understanding ring–chain tautomeric equilibria in similar heterocyclic systems and will further enable experimentalists to devise appropriate experimental conditions in which axially chiral catalysts remain stable as single enantiomers.     

Optical properties of spherical monodisperse Y2O3-ZnO nanoparticles

Based on the developed technique for synthesizing spherical mesoporous particles of yttrium oxide with a size dispersion of 10?C15% and methods for infiltrating active components into them, spherical nanocrystalline particles of composition Y₂O₃-ZnO have been synthesized. The nanocomposite structure has been studied, and the spectra of diffuse reflection and photoluminescence of heteroparticles, as well as the stimulated emission spectra of zinc oxide excitons, have been analyzed after annealing at various temperatures. The formation of ZnO nanocrystals in Y₂O₃ sphere pores is observed during material synthesis with a single infiltration procedure. The lasing is associated with a change in the effective refractive index and local photon density of states in phosphor nanoparticles, i.e., spherical optical cavities.     

Synthesis of a periodic SiC/C nanostructure

Highly porous periodic structures consisting of a three-dimensional replica of pores in the initial opal lattice have been synthesized by high-temperature thermochemical treatment of opal matrices filled with carbon compounds, followed by dissolution of silicon dioxide. It has been shown that the main phases of the composite are carbon and silicon carbide. Based on the X-ray diffraction, Raman, and IR spectroscopy data, it has been assumed that the composite contains fragments of hexagonal diamond. The photoluminescence and optical reflection spectra of the composites have been measured.     

Investigation of a single barrier discharge in submillimeter air gaps. Nonuniform field

Pulse characteristics of single barrier discharges as well as parameters of charges accumulated on the surface of a dielectric under the atmospheric pressure in the “needle-(0.1–2.0)-mm air gap-polymer barrier-plane” system are investigated. It is found experimentally that for the positive polarity of the needle, the voltage for the discharge initiation is higher than in the case of the negative polarity by ～25–35%. The reversal of the needle polarity from negative to positive increases the amplitude of the discharge current and the accumulated surface charge by ～1.5–3 times. For the positive polarity of the needle, the discharge is governed by a streamer mechanism, while for the negative polarity, the discharge is initiated by the formation of a single Trichel pulse. The single pulse regime is observed for the discharge current up to a certain electrode gap d _CR. For the positive needle and for air gap width d _air > d _CR ≈ 1.5 mm, a multipulse burst corona is formed, while for the negative needle and d _air > d _CR ≈ 0.9 mm, a damped sequence of Trichel pulses evolves in the system.     

A decision support methodology to enhance the competitiveness of the Turkish automotive industry

Three levels of competitiveness affect the success of business enterprises in a globally competitive environment: the competitiveness of the company, the competitiveness of the industry in which the company operates and the competitiveness of the country where the business is located. This study analyses the competitiveness of the automotive industry in association with the national competitiveness perspective using a methodology based on Bayesian Causal Networks. First, we structure the competitiveness problem of the automotive industry through a synthesis of expert knowledge in the light of the World Economic Forum’s competitiveness indicators. Second, we model the relationships among the variables identified in the problem structuring stage and analyse these relationships using a Bayesian Causal Network. Third, we develop policy suggestions under various scenarios to enhance the national competitive advantages of the automotive industry. We present an analysis of the Turkish automotive industry as a case study. It is possible to generalise the policy suggestions developed for the case of Turkish automotive industry to the automotive industries in other developing countries where country and industry competitiveness levels are similar to those of Turkey.