Deformation quantization of framed presymplectic manifolds

Theoretical and Mathematical Physics - We consider the problem of deformation quantization of presymplectic manifolds in the framework of the Fedosov method. A class of special presymplectic...     

Localized spin-wave resonance modes of ferromagnetic microstrips in the field of a magnetic probe

Some results of the micromagnetic modeling of forced magnetization oscillations in planar microstrips of NiFe with easy plane anisotropy and Co/Pt with perpendicular easy axis anisotropy in the field of a magnetic spherical probe are considered. It has been shown that the probe field provokes the appearance of a hedgehog–antivortex coupling state in the NiFe strips, due to its lateral components and a skyrmion magnetization state in the Co/Pt layer. These effects destroy spatial magnetization oscillations in the microstrips and lead to the appearance of additional resonances in the spectrum of oscillations corresponding to the modes localized in the probe field.     

Magnetic and electrical properties of bismuth cobaltite Bi24(CoBi)O40 with charge ordering

The compound Bi₂₄(CoBi)O₄₀ has been synthesized using the solid-phase reaction method. The temperature and field dependences of the magnetic moment in the temperature range 4 K < T < 300 K and the temperature dependences of the EPR line width and g-factor at temperatures 80 K < T < 300 K have been investigated. The electrical resistivity and thermoelectric power have been measured in the temperature range 100 K < T < 1000 K. The activation energy has been determined and the crossover of the thermoelectric power from the phonon mechanism to the electron mechanism with variations in the temperature has been observed. The thermal expansion coefficient of the samples has been measured in the temperature range 300 K < T < 1000 K and the qualitative agreement with the temperature behavior of the electrical resistivity has been achieved. The electrical and structural properties of the compound have been explained in the framework of the model of the electronic-structure transition with inclusion of the exchange and Coulomb interactions between electrons and the electron-phonon interaction.     

Studies of the heat capacity and thermal expansion of the Na0.95K0.05NbO3 solid solution

The heat capacity and thermal expansion of ceramic samples of the Na_0.95K_0.05NbO₃ solid solution have been investigated over a wide temperature range of 100–750 K. The observed anomalies in the heat capacity and thermal expansion at T ₄ = 297 K, T ₃ = 535 K, T ₂ = 665 K, and T ₁ ≈ 710 K correspond to the sequences of phase transitions N → Q → G → S → T1. It has been shown that, as a result of the phase transitions, the unit cell volume at T ₄ and T ₂ decreases, and at T ₃ and T ₁, increases with increasing temperature. The directions of the shift of the phase transition temperatures induced by hydrostatic pressure have been determined. It has been established that all structural transformations are accompanied by relatively small variations in the entropy. Different mechanisms of the structural distortions have been discussed.     

Caloric characteristics of PbTiO3 in the temperature range of the ferroelectric phase transition

The heat capacity and thermal expansion of the PbTiO₃ ceramic sample have been measured in the temperature range 80?C970 K. The electrocaloric and barocaloric efficiencies of lead titanate in the ferroelectric phase transition range have been investigated by analyzing the experimental data in terms of the thermodynamic theory of phase transitions, the electrical equation of state P(T, E), the Pippard equation, and the S(T, p) diagram.     

Disorder and phase transitions in oxyfluoride (NH4)3Ta(O2)2F4

Calorimetric, X-ray, dielectric and DTA under pressure measurements have been performed on oxyfluoride (NH₄)₃Ta(O₂)₂F₄. The succession of nonferroelectric phase transitions was found associated with the order-disorder processes. The comparative analysis tantalate with related niobate has revealed the important role of the central atom in the physical properties behavior, mechanism of structural distortions and barocaloric effect in oxyfluorides with the eight-coordinated anionic polyhedra.     

Justification of the energy variant of the theory of creep and long-term strength of metals

The hypotheses underlying the energy variant of the theory of creep and long-term strength of metals are formulated and justified experimentally.     

Creep of plates made of aluminum alloys under bending

Results of experiments dealing with the creep of a V95pchT2 aluminum alloy are presented. Constitutive equations of steady creep are constructed and used to solve the problem of pure twisting of a square plate. Calculated and experimental values of plate curvature are compared. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 5, pp. 156–159, September–October, 2007.     

Thermal expansion and permittivity of (Ba<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Bi<Subscript>2<Emphasis Type="Italic">x</Emphasis>/3</Subscript>)TiO<Subscript>3</Subscript> solid solutions

The strain, the thermal expansion coefficient, and the permittivity of ceramic samples of (Ba_{1 − x} Bi_2x/3)TiO₃ solid solutions with x = 0, 0.01, 0.03, and 0.05 have been studied in the temperature range 120–700 K. Based on an analysis of the results, the temperature-composition phase diagram has been refined, and the temperature dependence of the polarization has been calculated.     

Heat capacity study of relaxor PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> in a wide temperature range

Heat capacity of the PbMg_1/3Nb_2/3O₃ compound is measured using the methods of adiabatic and differential scanning calorimetry in the temperature range 80–750 K. Two blurred anomalies on the C _p (T) dependence are observed in wide temperature intervals of 200–400 K and 500–700 K. The results of studies are discussed together with data on the structure and phonon spectrum in the framework of spherical random bond-random field model.