Potassium polytitanate gas-sensor study by impedance spectroscopy

Nanocrystalline potassium polytitanates K₂O·nTiO₂·mH₂O represent a new type of semiconducting compounds which are characterized by a high specific surface that makes them promising for use in gas sensors. In this work, we have studied potassium polytitanate mesoporous nanoparticle agglomerates placed over a SiO₂/Si substrate equipped with multiple coplanar electrodes to measure the electrical response to various organic vapors, 1000 ppm of concentration, mixed with air by impedance spectrometry in range of the 10⁻²–10⁶ Hz. The recorded impedance data for each sensor segment are associated with RC components of an equivalent circuit which are applied to selectively recognize the test vapors exploiting a “multisensor array” approach.     

On the Finite‐Time Blowup of a One‐Dimensional Model for the Three‐Dimensional Axisymmetric Euler Equations

In connection with the recent proposal for possible singularity formation at the boundary for solutions of three‐dimensional axisymmetric incompressible Euler's equations (Luo and Hou, Proc. Natl. Acad. Sci. USA (2014)), we study models for the dynamics at the boundary and show that they exhibit a finite‐time blowup from smooth data. © 2017 Wiley Periodicals, Inc.     

Thermal processes in succinic acid–aluminum blends subjected to high-pressure plastic deformation

The thermal characteristics of powdered aluminum–succinic acid blends subjected plastic deformation under pressures of 0.5?2.0 GPa have been studied. When heated, deformed samples exhibit exothermal processes, which occur at temperatures below the T _m of the acid and indicate chemical interactions between succinic acid and aluminum induced by the plastic deformation. The values of the thermal effects depend on the degree of deformation and the pressure of the treatment.     

Electrostatic-interaction-induced phase separation in solutions of flexible-chain polyelectrolytes

A model of a polyelectrolyte solution has been formulated on the basis of the formalism of the thermodynamic perturbation theory. Macromolecules have been described in terms of the model of a flexible chain with an excluded volume and a variable electrical charge. During construction of the thermodynamic perturbation theory, a set of three independent subsystems—polyelectrolyte macromolecules placed in a structureless charge background of counterions, counterions placed in a structureless charge background of macromolecules, and Coulomb gas ions of a low-molecular-mass salt—has been taken as the reference system. In the framework of this model, liquid-liquid phase separation due to strong correlation-induced attraction has been predicted. The behavior of the degree of ionization over a wide monomer concentration range, including the region of phase separation either in a salt-free solution or in the presence of univalent ions of a low-molecular-mass salt in the solution, has been studied. It has been shown that macromolecules in the coexisting phases should have different degrees of ionization. The occurrence of phase separation under normal conditions in the case when dimethylformamide is taken as a solvent and the nonoccurrence of this phase separation in the case of aqueous solutions of flexible-chain polyelectrolytes are predicted.     

Internal Stresses in a Solid with Dislocations

Formulas for calculating internal stresses in a material, generated by continuously distributed dislocations, are found on the basis of the gauge theory of defects. It is shown that internal stresses are selfbalanced and satisfy the equilibrium equations and boundary conditions in the absence of external loads.     

Criterion of formation of a shock wave reflected from a cloud of particles

The problem of the formation of a “collective” shock wave reflected from a cloud of particles, which was previously observed in experiment, is considered. A criterion of formation of a reflected shock wave is obtained based on the numerical and analytical solutions of the problem. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 3, pp. 44–51, May–June, 1998.     

Quenching and Propagation in KPP Reaction-Diffusion Equations with a Heat Loss

We consider a reaction-diffusion system of KPP type in a shear flow and with a non-zero heat-loss parameter. We establish criteria for the flame blow-off and propagation, and identify the propagation speed in terms of the exponential decay of the initial data. We prove the existence of travelling fronts for all speeds c>max(0,c*) in the case Le=1, where c* ∈ ℝ. This seems to be one of the first non-perturbative results on the existence of fronts for the thermo-diffusive system in higher dimensions.     

Effect of Wave Formation during Shock-Wave Compaction of Powders

The problem of shock-wave compaction of a metal powder enclosed in a metal container with a transverse partition is solved. A model of wave formation on the partition and in the compact adjacent to the partition is proposed; the model is based on the loss of strength in the powder due to collapsing of pores and to development of instability of the partition being compressed in the shock wave. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 119–130, January–February, 2006.     

Method of molecular dynamics in mechanics of deformable solids

The basic principles of the method of molecular dynamics are analyzed. Symplectic difference schemes for the numerical solution of molecular dynamics equations are considered. Stability is studied, and the errors in the energy conservation law, which are induced by using these schemes, are estimated. Equations of mechanics of continuous media are derived by means of averaging over the volume of an atomic system. Expressions for the stress tensor are obtained by using the virial principle and the method of averaging over the volume. The principles of construction of EAM and MEAM potentials of atomic interaction in crystals are analyzed. Two problems of fracture of copper-molybdenum composites are solved by the method of molecular dynamics.