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The results of comparative multifractal studies of the grain structure of different ceramic piezoelectric materials are presented. Hard and soft ferroelectric ceramic materials as well as materials...

A measurement setup based on a transmission microscope with double acousto-optical wavelength selection is proposed for detection of high-quality spectral images with a size of 1920 × 1200 pixels in the visible wavelength range with a spectral resolution of 2.5 nm at a wavelength of 632 nm. The efficiency of the proposed approach and setup is demonstrated in the study of the transition of Misgurnus fossilis embryos from the 32nd to the 33rd stage. Correctness of the conclusions is proven in a comparison with the results of the corresponding ultrasonic study. Analysis of time dependences of the transmission spectra is performed for six spatial regions of the embryo including perivitelline space and head and tail sections. Such substantially different dependences can be used, in particular, for noninvasive monitoring and analysis of changes in the functional state of embryos related to the stage-to-stage transition.

Results of experimental investigation of the evolution and precipitation of a cloud of pneumatically obtained aerosol particles in a closed space under the influence of external physical fields are presented. The precipitation is contributed to by imposing acoustic and electrostatic fields, which leads to an acceleration of the coagulation of fine-aerosol particles. A method of searching for the aerosol′s dispersion characteristics is proposed, which has been implemented in a laser measuring complex. Experimental dependences of the average volume–surface diameter and of the relative concentration of aerosol particles of a model aerosol (talc) on time are presented.

The appropriate magnetic Langevin equation, namely the inertial Landau-Lifshitz-Gilbert equation augmented by thermal noise, is written starting from an analogy with the dynamics of the magnetic dipole moment of a circular current-carrying loop (wire) viewed as a symmetric top. Hence the corresponding Fokker-Planck equation for the evolution of the probability density function in the phase space of angular velocities and orientations and its stationary solution are derived. Moreover, the inertial stochastic magnetization dynamics of ferromagnetic nanoparticles is also seen to be analogous to the stochastic dynamics of the electric dipole moment of a polar molecule visualized as a dipole lying along the axis of symmetry of a symmetric top ignoring friction about that axis--a conclusion reached by replacing electrical parameters with their magnetic analogs in the respective Langevin equations. Therefore, existing results from gyroscopic theory, as applied to dielectric relaxation of polar molecules, may with appropriate modifications be used to study inertial magnetization effects in ferromagnetic nanoparticles.

The room temperature phosphorescence (RTP) of phenanthrene (PH) was studied before and after oxygen removal in a suspension formed by adding tert-butylbenzene (TBB) to an aqueous solution of PH and β-cyclodextrin (CD). The RTP decay curves indicate that PH molecules are located inside solid aggregates within two types of the self-assembled phosphorescent complexes. The structure of one of them, PH@2CD@2TBB (I), was proposed by the method of fluorescence spectroscopy and confirmed by the quantum-chemical (QC) calculation (PM3/PM6-DH+) indicating the presence of the direct contact between PH and TBB inside the CD dimer in aggregate. The structure of the second, PH@3CD@2TBB (II), was calculated by the QC method. The molecular dynamics simulation (MD) was performed to elucidate the stability in an aqueous solution and in solid matrices of both I and II characterized by different degrees of PH packing density inside the aggregate. Due to the higher stability, I turned out to be the preferred structure as the basis of the phosphorescent center in a solid aggregate. To elucidate the mechanism of RTP quenching the O2 molecules was added to the solution and solid systems of both I and II. Oxygen mobility and penetration statistics to PH in these systems were calculated. Both the fluorescence data and computer simulaions show that the longest-lived component of the RTP decay belongs to structure I, in which PH is sandwiched between two TBB molecules in the CD dimer, owing to which RTP is characterized by the minimum values of the quenching and nonradiative relaxation constants. PH molecules located in a less rigid environment like complex II, or as part of other less ordered structures, are characterized by shorter RTP lifetimes. The results demonstrate a high degree of protection of the substrate encapsulated in the CD dimer from oxygen.

X-ray diffraction (XRD) studies of the phases formed on the surface of the Li-doped PbFe0.5Nb0.5O3 (PFN) ceramics sintered under different conditions from the mechanically activated mixture of oxides and Li2CO3 have been carried out. At sintering temperatures exceeding 800°C a partial evaporation of PbO leads to the formation of pyrochlore Pb2Fe4Nb4O21 and lithium ferrites LiFeO2 and LiFe5O8 phases in the surface layer about 100 μm thick. An increase of the Neel temperature by more than 40 K, as compared to single crystal, was achieved in the mechanically activated PFN powder sintered at 600°C.

The effect of high-energy mechanical activation on magnetic phase transition temperature TM of PbFe0.5Nb0.5O3, PbFe0.5Ta0.5O3, and BaFe0.5Nb0.5O3 perovskites has been studied. Mossbauer studies have shown that TM values in all the perovskites studied can be changed substantially by mechanical activation and subsequent annealing. The increase of TM by 40-50 K, as compared to corresponding single crystals and ceramics sintered from the non-activated powders, was achieved in the mechanoactivated powders of both lead-containing and lead-free perovskites studied.

Electromagnetic emission accompanying the serrated deformation of the aluminum‒magnesium alloy Al-6Mg has been revealed and studied experimentally. By means of high-speed video recording and a complex of methods for measuring the strain, load, and electric potential, it has been found that there is a relation between the electromagnetic emission signals and the dynamics of deformation bands. Possible mechanisms of the generation of electromagnetic signals have been discussed.

The x-T phase diagram (T = 25°C) of the PbZr1 − xTixO3 system has been constructed in the entire solubility range of components 0 ≤ x ≤ 1.00. It has been found that the phase composition of solid solutions, the cell volume decreasing rate, the electrical parameters, and density of ceramics periodically vary with increasing x. It has been shown that the nonmonotonic behavior of the electrical parameters is caused by different contributions of the spontaneous strain dominant in the tetragonal phase and domain reorientations different from 180-degree ones in the rhombohedral phase to their formation. Detailed multifractal parametrization of the grain structure of ceramics has been performed. The microstructure evolution features associated with phase changes in the system have been revealed. The data of other studies that tetragonal phase clusters appear in the range 0.11 < x ≤ 0.12 are confirmed; it has been assumed that rhombohedral phase clusters appear in the range 0.675 < x < 0.80.

The concentration range of vacancies that affect the temperature dependence of the heat capacity at constant volume C v has been determined. The times of the establishment of vacancy equilibrium in spherical samples of simple crystals with different radii due to the thermal motion of atoms have been calculated for the process as close as possible to the equilibrium one with a decrease in the temperature from the melting point to the current value T. The free energy of an imperfect crystal has been determined taking into account contributions from interatomic interactions in terms of the Lennard-Jones potential functions and vibrational energies. The properties of an imperfect crystal have been calculated within the Lifshitz approximation linear in the density of vacancies with the frequency distribution function of the perfect crystal with the corresponding corrections, which reflect local vibrations of atoms around vacancies. The free energy of a defect-free perfect crystal has been determined from the calculated frequencies of normal vibrations with the inclusion of up to four nearest neighbors. It has been shown that disregard of acoustic (out-of-phase) parts of the spectrum in the calculation of the heat capacity C v with increasing temperature leads to a decrease (increase) in C v from the values calculated for the total vibrational spectrum. A nonequilibrium state of the imperfect crystal can lead to negative values of the heat capacity at constant volume.

The effect of high-energy mechanical activation on dielectric and magnetic properties of PbFe1/2Ta1/2O3 (PFT) multiferroic was studied. Mossbauer studies have shown that the Neel temperature TN of the antiferromagnetic phase transition in PFT powders can be changed substantially by mechanical activation and subsequent annealing. The increase of TN by more than 70 K, as compared to PFT single crystal, was achieved in the mechanically activated PFT powder annealed at 700°C. Dielectric studies have shown that in contrast to ceramics obtained by usual sintering, PFT ceramics fabricated by sintering of the mechanoactivated powder does not show the relaxor-like behavior.

Optimal sintering temperature of PbFe1/2Nb1/2O3 (PFN) ceramics is 1120–1150°C, but ceramics sintered in this temperature range have low resistivity and high losses. Mechanochemical synthesis allows one to lower the optimal sintering temperature of PFN ceramics down to 1000°C, however dielectric losses remain high and the permittivity exhibits large frequency dispersion. In the present work it has been found that similar to the case of the routine solid state synthesis, Li doping enables one to reduce dramatically the losses of the PFN ceramics obtained by sintering the mechanochemically synthesized powders.

Four main functions of a Lennard-Jones defect argon crystal with an FCC lattice are considered in the context of the lattice gas model: Helmholtz free energy, entropy, internal energy, and heat capacity at a constant volume (allowing for normal vibrations of a solid). Properties of the defect crystal are calculated from the distribution function of the frequencies of an ideal crystal, and corrections to it that reflect local atomic vibrations around vacancies, in the context of the Lifshits linear approximation according to vacancy density. To find the free energy of a defect-free ideal crystal, frequencies of normal vibrations of the crystal are calculated with allowance for the interactions of the four nearest neighbors. The nonlocality of the chemical potentials of the atoms of a solid is discussed, and the influence of contributions from various segments of the vibrational spectrum to the values of thermodynamic functions is investigated. It is shown that ignoring the acoustic or antiphase segments of the spectrum when calculating the free energy leads to increasing of its deviation from the one calculated using the full vibrational spectrum with an increase in temperature. It is concluded that the nonequilibrium state of the defect crystal can lead to negative values of heat capacity at a constant volume.

The double decoupling version of the thermodynamic integration procedure is applied to perform the molecular dynamical modelling of binding free energies of β-cyclodextrine (CD) with a number of organic ligands. Simulations for water solutions show a satisfactory agreement (within 1–2 kcal/mol) with the experimentally measured equilibrium binding constants. The values are also reported for the gas phase complexation of the same ligands, although no experimental data are available for such systems. These gas phase computations have revealed the large stabilisation effect for the CD complexes of ionic ligands. Only in this special case the attempt of a qualitative rationalising the obtained simulation data proved to be fairly successful. The problems specific for simulations for ionic ligands in water solution are discussed.

A new turbidimetric method for determining the parameters of submicron aerosols was developed and implemented in hardware using a wide range of probe radiation wavelengths and high-speed video recording. The particle size distribution function is found using an original algorithm for solving the inverse problem of the optics of aerosols based on a direct search computational procedure..

To fully understand particle interactions with both substrate and neighboring particles in cold spray, ultrasound wave generation and ultrasonic monitoring of particle impacts were studied. The multi-channel ultrasonic system works in pulse-echo and passive modes. In pauses between pulse-echo data acquisition frames the system is in the passive mode receiving the signals generated by the particle impacts. The particles being deposited generate the ultrasonic signals in a very wideband frequency range at more than 40 dB signal-to-noise ratio. The particle impact signals are considered as a sum of the background wideband noise and the sparse strong pulses observed when the nozzle passes over the location of the transducer. It was shown that these components of the particle impact signal can be separated by threshold processing. The results of the passive monitoring are confirmed by the ultrasonic pulse-echo and direct measurements of a deposited coating geometry.

The molecular model of a polar liquid based on the lattice gas theory was used to study the liquid—gas phase equilibrium. In this theory, the key unknown variables are the probabilities of various mutual pair positions of the molecules. The molecules are considered as non-polarizable point dipoles. The intermolecular interaction potential includes a dipole—dipole component depending on the molecular orientation and the Lennard-Jones contribution stabilizing the system with dipole interactions. The theory provides qualitative agreement with experimental data on the water—vapor equilibrium.

International audience; Spin-transfer torque (STT) effects on the stationary forced response of nanoscale ferromagnets subject to thermal fluctuations and driven by an ac magnetic field of arbitrary strength and direction are investigated via a generic nanopillar model of a spin-torque device comprising two ferromagnetic strata representing the free and fixed layers and a nonmagnetic conducting spacer all sandwiched between two Ohmic contacts. The STT effects are treated via Brown's magnetic Langevin equation generalized to include the Slonczewski STT term thereby extending the statistical moment method [Y. P. Kalmykov et al., Phys. Rev. B 88, 144406 (2013)] to the forced response of the most general version of the nanopillar model. The dynamic susceptibility, nonlinear frequency-dependent dc magnetization, dynamic hysteresis loops, etc. are then evaluated highlighting STT effects on both the low-frequency thermal relaxation processes and the high-frequency ferromagnetic resonance, etc., demonstrating a pronounced dependence of these on the spin polarization current and facilitating interpretation of STT experiments.

Ceramics of (1 − x)NaNbO3− (x)Na0.5Bi0.5TiO3 and (1 − x)NaNbO3 − (x)Sr0.5 NbO3 binary solid solutions exhibit strongly diffused permittivity maxima, when x exceeds a threshold value of about 0.15 and 0.1, respectively, but show weak frequency dispersion of permittivity and small frequency shift of the permittivity maximum temperature. Addition of LiNbO3 to these compositions increases the permittivity maximum temperature and greatly enhances the frequency dependence of both the permittivity maximum temperature and permittivity values.

The solution of the equation of the velocity potential of a steady axisymmetric ideal-gas flow in the neighborhood of a given point at the axis of symmetry in the form of a double series in powers of the distance to the axis of symmetry and its logarithm is considered. Recurrent chains of equations with arbitrariness in two analytical functions of the streamwise variable are obtained for coefficients of the series. Convergence of the constructed series is proved by the method of special majorants. The theorem of existence and uniqueness of the solution of the initial-boundary problem for this nonlinear differential equation in partial derivatives with a singularity at the axis of symmetry is obtained as an analog of Kovalevskaya's and Ovsyannikov's theorems.

Thin film titanium/poly-para-xylylene nanocomposites with controlled Ti content are prepared by vacuum coevaporation and cocondensation of Ti and paracyclophane. The structure and chemical composition of as-deposited samples and the changes of electrical resistivity, which they undergo upon heating, are studied by atomic force microscopy, optical absorption spectroscopy, and the temperature coefficient of the electrical resistivity. It is shown that vacuum coevaporation results in the production of nanocomposite thin films with average Ti particle size of 10–50 nm. The inorganic phase is shown to be amorphous Ti for the samples with high metal content, whereas for the low-filled nanocomposites it consists of amorphous titanium oxide. Two types of kinetics of the nanocomposite oxidation process have been found and modeled by (i) inverse logarithmic and (ii) logarithmic functions depending on the metal content within the thin film. After a long preconditioning period in air the electrical conductivity of the thin film nanocomposites was carefully investigated by two-probe DC measurements. A strong correlation between the concentration of Ti in the thin films and the electrical conductivity dependency on temperature is found and modeled by a heterogeneous model of conductivity.

The processes of the formation and evolution of grain structures in binary systems of solid solutions (1−x)NaNbO3-xCa2Nb2O7(Sr2Nb2O7), where 0 ≤ x ≤ 1, are discussed. The multifractal parameterization of the sections of grain boundaries was performed. A correlation between multifractal and electrophysical parameters of niobate ferroelectric ceramics was established. A possibility of the quantitative description of microstructures in the systems under study by means of multifractal ideas is shown. The results obtained were used for optimization of the processes of preparation of new ferroelectric materials.

Simple analytical expressions are derived for the complex longitudinal susceptibility χ∥(ω) of a system of noninteracting superparamagnetic particles with uniaxial and cubic anisotropy within the continuous-diffusion model in the cases of moderate and strong damping.

The interaction of the mixing zone between two gases of different densities with compression waves and shock waves has been investigated. The characteristics of the mixing zone in which the Rayleigh–Taylor instability is developing have been analyzed. The evolution of the mixing zone volume and mass during the accelerated motion has been defined. A qualitative distinction in the evolution of the mixing zone under the influence of a continuous deceleration resulting from the interaction with the reflected compression wave—shockless deceleration—is revealed as compared to deceleration that is accompanied by appearance of a shock wave moving through the mixing zone—shock-induced deceleration.

The Langevin equations of motion of the cage model of polar liquids originally proposed by Hill (1963 Proc. Phys. Soc. 82 723) are solved for the first time for the particular case of rotation about a fixed axis, using a newly developed matrix continued fraction method. It is shown that the cage model predicts both the low-frequency Debye relaxation and a pronounced high-frequency (Poley) absorption peak in the far-infrared (FIR) region. The similarity of the equations of motion of the cage model to the equations which arise in the problem of generalizing the Onsager model of polar fluids to include a time-varying applied field suggests that the FIR (Poley) absorption may have its origins in the combined influence of molecular inertia and the torque due to the reaction field in the frequency-dependent version of the Onsager model. The complex susceptibility yielded by the cage model is shown to be in good agreement with experimental data on CH3Cl that were taken as a typical example. Moreover, a simple approximate formula based on a small-oscillation approximation can describe accurately the dielectric spectra in most cases of interest.

The longitudinal and transverse components of the dielectric susceptibility tensor are calculated for a system of noninteracting symmetrical top molecules subjected to a strong dc electric field. The calculations are carried out using the extended rotational-diffusion model (J-diffusion). The model predicts a strong dependence of the dielectric spectra on the strength of the dc bias field and on the shape of the molecule. Moreover, the dielectric relaxation behavior at low frequencies (ωτγ⩽1, where τγ is the orientation correlation time) is reproduced and the inclusion of inertial effects ensures that optical transparency is regained at very high frequencies (in the far infrared region).

The nonlinear response of superparamagnetic particles with cubic anisotropy to a sudden change in an applied strong static magnetic field is analyzed. The relaxation function spectrum and the relaxation time of the magnetization are calculated for typical values of the anisotropy and dissipation parameters.

The greatest relaxation time for an assembly of three-dimensional rigid rotators in an axially symmetric bistable potential is obtained exactly in terms of continued fractions as a sum of the zero frequency decay functions (averages of the Legendre polynomials) of the system. This is accomplished by studying the entire time evolution of the Green function (transition probability) by expanding the time dependent distribution as a Fourier series and proceeding to the zero frequency limit of the Laplace transform of that distribution. The procedure is entirely analogous to the calculation of the characteristic time of the probability evolution (the integral of the configuration space probability density function with respect to the position co-ordinate) for a particle undergoing translational diffusion in a potential; a concept originally used by Malakhov and Pankratov (Physica A 229 (1996) 109). This procedure allowed them to obtain exact solutions of the Kramers one-dimensional translational escape rate problem for piecewise parabolic potentials. The solution was accomplished by posing the problem in terms of the appropriate Sturm–Liouville equation which could be solved in terms of the parabolic cylinder functions. The method (as applied to rotational problems and posed in terms of recurrence relations for the decay functions, i.e., the Brinkman approach c.f. Blomberg, Physica A 86 (1977) 49, as opposed to the Sturm–Liouville one) demonstrates clearly that the greatest relaxation time unlike the integral relaxation time which is governed by a single decay function (albeit coupled to all the others in non-linear fashion via the underlying recurrence relation) is governed by a sum of decay functions. The method is easily generalized to multidimensional state spaces by matrix continued fraction methods allowing one to treat non-axially symmetric potentials, where the distribution function is governed by two state variables.

Nonlinear response of a uniaxially anisotropic superparamagnetic particle subjected to a dc bias and strong ac field is evaluated. For the third harmonic, a non-monotonic dependence of the response amplitude on the strength of the oscillating field (noise-induced resonance) is found. Introduction Studies on stochastic resonance (SR), the number of which multiplies impressively during last years, have revealed a variety of remarkable properties of noisy dynamic systems. In particular, noise-induced resonance (NIR) [1] has been found for both symmetrical [1] and non-symmetrical [2] potentials. Unlike the ordinary stochastic resonance (see the review [3]), the description of NIR does not involve the signal-to-noise ratio and is given in terms of higher harmonic generation. The phenomenon manifests itself as occurrence of “dips” on the amplitudes of higher harmonics plotted as the functions of the noise power or external field strength. Under imposing of a bias field, complementary odd/even harmonics turn up in the system spectrum. Both these effects are now under intense investigation [4,5] in view of their application to detection/enhancement of weak signals. Assemblies of superparamagnetic particles provide a very clear physical example of an essentially noise-affected system. Conventional SR in them, i.e., the response to a weak magnetic field on the thermofluctuational background, has been studied in Refs. [6–10]. In Refs. [11,12] a step has been made to the case of the finite-amplitude excitation. However, NIR-like phenomena have not been addressed. In the original papers [1,2] the existence of NIR had been established only in a weak-field limit, i.e., in terms of power series expansions. The basic demerit of this method is that when evaluating the amplitude of an l-th harmonic, all the contributions of the order (ξ ) are neglected; here ξ is the ratio of the intensity of the driving field amplitude to the reference thermal (noise) energy. Obviously, the higher the field the greater the expansion results deviate from the true ones. Here we describe a magnetic response of a superparamagnetic particle subjected to a dc (bias) field and an ac harmonic field of an arbitrary strength. The novelty is twofold: (1) we prove the NIR-like effects in superparamagnetic systems and (2) we move far beyond the limits of a small parameter approach. Solution of the micromagnetic Fokker-Planck equation We assume a particle to be single-domain so that its magnetic state is that of a magnetic dipole of the magnitude μ = IV, where I is the magnetization of the particle material, and V its volume. Being well below the Curie temperature, we treat I as a constant. Then all the motions of the dipole are reduced to its rotations, and are described by a unit vector e or the set of spherical coordinates θ and φ, with the polar axis pointing along the particle easy axis. Performing any angular motion, the dipole μ = μe effectively experiences the bulk magnetic anisotropy (a symmetrical two-well potential), a dc bias field co-aligned with the particle easy axis (a one well potential) and a ac field of frequency ω imposed along the same axis. The driving frequency is assumed to be small in comparison with that of the Larmor precession in the effective internal (anisotropy + bias) field. Therefore, in the magnetodynamic equation (taken in the Gilbert form) only the relaxation part must be retained. The system resides in a thermal bath of temperature T, the Boltzmann constant is set to unity. Thermally-affected Gilbert magnetodynamics of a single-domain particle is described by the micromagnetic Fokker-Planck equation derived by Brown [14]. It is written for the orientation distribution function W(e,t) of the particle magnetic moment and reads ( ) ( ) { } 1 1 div 2 W E W W E W t β λ τ − ∂   = ∇ ×∇ + ∇ + ∆   ∂ e , (1) where ∆ is the Laplacian on the surface of a unit sphere, E is the free energy density. The parameter τ = βI(1 + λ)/2γλ (2) is the characteristic relaxation time, where β = V/T, γ is the gyromagnetic ratio for electrons, and η is the damping parameter of the Larmor precession used in the Gilbert equation, so that the combination λ = γηI makes a dimensionless dissipation constant. Interactions between different particles of the system as well as any memory effects are neglected. With Eq. (1), as in any statistical approach, the physically observed quantities are the averages fn(t) = 〈Pn(cos θ)〉(t) = 0 π ∫ Pn(cos θ) W(θ,t) sinθ dθ . (3) In particular, the issue of prime interest is f1(t), that is the dimensionless magnetization of the system. Under superimposed constant uniform magnetic field H0 and an ac field H1 = H1 cosωt (both applied along the polar axis) the energy density takes the form E = –K cos 2 θ – (H0+ H1 cosωt) I cosθ , (4) where K is the uniaxial anisotropy constant. Allowing the magnitudes of both ac and dc fields to be large enough so that the Zeeman energies of the magnetic moment are comparable with or higher than the thermal energy T, one faces an essentially nonlinear problem. To solve it, we use the method developed in Refs. [15,16]. Substituting the energy (4) in Eq. (1) and expanding W(θ,t) in a series of Legendre polynomials Pn(cosθ), one arrives at the set of differential-recurrence equations [12]: τ dt d fn(t) + 2 1 n(n + 1) fn(t) = e(t) [an fn–1(t) + bn fn+1(t)] + σ[cn fn–2(t) + dn fn(t) + gn fn +2(t)], (5) where the following notations for the coefficients are used ( 1) 2(2 1) n n n n a b n + = − = + , ( 1)( 1) (2 1)(2 1) n n n n c n n + − = − + , ( 1) (2 1)(2 3) n n n d n n + = − + , ( 1)( 2) (2 1)(2 3) n n n n g n n + + = − + + , (6) and the dimensionless material parameters are e(t) = ξ0 + ξ cosωt, ξ0 = βIH0, ξ = βIH1 , σ = βK . (7) Here we solely concern ourselves with the steady ac response, which is independent of the initial conditions, so that one needs only the stationary solution of Eq. (3). In view of that, we present the sought for asymptotic (with respect to time) relaxation functions in the form

A method of evaluating the spectral moments Ml 2k of the rotational correlation functions for the first- and second-rank tensors of rigid asymmetric top molecules is developed. It is based on the calculation of the coefficients of a Taylor series expansion of the vector and tensor orientational correlation functions about t = 0 with the help of angular momentum theory, and is applicable to a pair intermolecular interaction potential with arbitrary dependence on the angular variables. Equations for the second (Ml 2), fourth (Ml 4), and sixth (Ml 6) spectral moments are obtained as a demonstration of the ability of the method. The results for (Ml 2) and Ml 4 coincide with previously known values and the equation for Ml 6 is new. As particular cases, the theory contains the results for classical ensembles of symmetric tops, spherical tops, and linear molecules.

An anomalous temperature dependence of carbon fibrils’ electric conductivity in the range of 11–320 K is considered. The fibrils are prepared from polyacrylonitrile by heat-treatment at 1400°C. Our conjecture is that in these carbon fibrils different phases coexist. A heterogeneous model is developed and a good fit to the experimental temperature dependence of the conductivity of our fibrils is obtained.

In the present study we performed an experimental investigation of the Rayleigh–Taylor instability (RTI) in a mixing zone between two gases entrapped into accelerated motion by a nonstationary compression wave. Acceleration g was ∼1.5·107 cm/s2, Atwood numbers ranged from 0.04 to 0.77. A mixing zone was formed by an oxygen-hydrogen mixture and an inert gas (Ne, Ar, Kr, Xe) or SF6. The initial gas pressure was 0.5 atm. A specific feature of our experiment is compressibility of media tested and initially continuous interface between gases of different densities. The present work is a continuation of investigations on nonlinear, transition, and early turbulent stages of the RTI.

Thermal fluctuations of nanomagnets driven by spin-polarized currents are treated via the Landau-Lifshitz-Gilbert equation generalized to include both the random thermal noise field and the Slonczewski spin-transfer torque term. By averaging this stochastic (Langevin) equation over its realizations, the explicit infinite hierarchy of differential-recurrence relations for statistical moments (averaged spherical harmonics) is derived for arbitrary demagnetizing factors and magnetocrystalline anisotropy for the generic nanopillar model of a spin-torque device comprising two ferromagnetic strata representing the free and fixed layers and a nonmagnetic conducting spacer all sandwiched between two ohmic contacts. The influence of thermal fluctuations and spin-transfer torques on relevant switching characteristics, such as the stationary magnetization, the magnetization reversal time, etc., is calculated by solving the hierarchy for wide ranges of temperature, damping, external magnetic field, and spin-polarized current indicating new spin-torque effects in the thermally assisted magnetization reversal comprising several orders of magnitude. In particular, a pronounced dependence of the switching characteristics on the directions of the external magnetic field and the spin polarization exists., an updated version

An earlier proposed quasicluster embedding scheme is applied to the calculations of the ground state potential surfaces, energies, and probabilities of electronic transitions in neutral and charged point defects in KCI, SiO 2 , and diamond crystals. The model is closely related to the periodic supercell approach (providing similar electronic structure characteristics) and the molecular cluster one. Two modified versions of the model are proposed, which improve results of calculations of ground state properties (especially for small quasiclusters) and transition energies. Ground state potential surfaces calculated for defects in ionic and semiionic crystals are better than those obtained using supercell and molecular cluster models.

It is demonstrated that both the area of the dynamic magnetic hysteresis (DMH) loop and the volume power loss of an assembly of uniaxial superparamagnetic nanoparticles with a random distribution of easy axes are very sensitive to damping at low, intermediate, and high frequencies. In particular, a dynamical regime that is resonant in character occurs in the vicinity of the ferromagnetic resonance (FMR) frequency for low to moderate values of the alternating current (ac) field amplitude. The resonant regime is characterized by a diamagnetic-like response of the particles, resulting from a phase lag of the stationary nonlinear magnetization with respect to the applied field greater than \ensuremath{\pi}/2.

The process of indium sulfide film growth on indium phosphide substrates in a quasi-closed volume is investigated by ellipsometric methods. An original ellipsometric technique is suggested for the investigation of optically inhomogeneous structures based on multiangle measurements of Ψ and Δ parameters with an independent determination of the complex reflection factor of the film. The kinetics of In2S3 film growth on InP is shown to be determined by a linear-parabolic law, and the optical inhomogeneity of the film thickness is considered to be associated with the non-uniform distribution of sulfur in the films. [Russian Text Ignored]

This study attempts to test the viability of the examination of the cold spray process using acoustic methods, specifically in situ testing during the actual spray process itself. Multiple composites studied by flat and multi-channel transducers as well as the results of actual online measurements are presented. It is shown that the final thickness as well as the dynamics of buildup can be evaluated (including plotting rates of buildup). Cross sections of the coating thickness are also easy to obtain and show true profiles of the coating. The data can also be used to generate real estimates for nozzle speed and spray diameter. Finally, comparisons of real thickness and acoustically estimated thickness show a close linear relationship. The data clearly show that online acoustic measurement is a viable method for estimating thickness buildup.

The fractional Klein-Kramers ~Fokker-Planck! equation describing the fractal time dynamics of an assembly of fixed axis dipoles rotating in an N-fold cosine potential representing the internal field due to neighboring molecules is solved using matrix continued fractions. The result can be considered as a generalization of the solution for the normal Brownian motion in a cosine periodic potential to fractional dynamics ~giving rise to anomalous diffusion! and also represents a generalization of Frohlich's model of relaxation over a potential barrier. The solution includes both inertial and strong internal field effects, which in combination produce a strong resonance peak ~Poley absorption! at high frequencies due to librations of the dipoles in the potential, an anomalous relaxation band at low frequencies mainly arising from overbarrier relaxation, and a weaker relax- ation band at midfrequencies due to the fast intrawell modes. The high-frequency behavior is controlled by the inertia of the dipole, so that the Gordon sum rule for dipolar absorption is satisfied, ensuring a return to optical transparency at very high frequencies. Application of the model to the broadband ~0-THz! dielectric loss spectrum of a dilute solution of the probe dipolar molecule CH2Cl2 in glassy decalin is demonstrated.

To investigate processes of producing high-quality materials using high pressures of gas VNIIMETMASH has developed 3-400 MN hot isostatic presses (HIPes) with working pressure up to 200 MPa and temperature up to 2000°C. Ar and N2 are used as working gases. Frame and vessel units of such machines are of multi-element structure which eliminates the possibility of its fragmentation failure and instant release of compressed gas energy. HIPes are intended for healing defects in casting and compacting metallic, ceramic and composite materials.

The ion conductivity, crystal structure, and multifractal parameters of the sections of grain boundaries in CuCr1−xVxS2 superionic conductors with 0 ≤ x ≤ 0.3 have been investigated. It is established that an increase in the surface area of grain boundaries and complication of their shape in such compounds facilitate ion transport. The effect of crystal structure peculiarities on the grain structure of these compounds has been revealed.

An anomalous temperature dependence of electric resistivity in carbon fibrils in the range from 11 to 350 K is considered. The fibrils are prepared from the polyacrylonitrile fibrils by heat-treatment. A heterogeneous model of conductivity is developed and a fit to the experimental dependencies of resistivity is obtained. The adequacy of this model to a fibril conductivity problem is explained.

Experimental data related to the impulse photocurrent in emeraldine base (EB) films of various morphology in a wide temperature range are considered. The rate constants for the recombination of the photoinduccd charges are estimated; their dependence on the material morphology is explained. The temperature dependence of photoconductivity is discussed.

A simple kinetic model of photocurrent relaxation in emeraldine base (EB) films is considered. Parameters of a distribution of electrons in traps are evaluated depending on temperature and time after ns-laser excitation. It is shown that carrier traps in EB films are formed by fluctuations of mutual arrangement of polymer fragments.

1. A study was made of the main properties, cold pressing behavior, melting, and isothermal vacuum sintering of Kh18N15 steel powder prepared by the reduction of oxides with calcium hydride. 2. Compared with the fine fractions of this powder, the coarse fractions have a much greater specific surface and smaller apparent density, which is due to the complex shape and high porosity of their particles. Lubricant additions substantially reduce and equalize the apparent density of the powder. 3. The cold compressibility of the powder improves with decrease in particle size. Compacts from the −45μ fraction with lubricant (2 wt.% of paraffin wax) have a density of 85–89% after pressing under a pressure of 8–15 tons/cm2. 4. Kh18N15 steel powder melts in a vacuum in the range 1375–1400°C, and consequently it may be recommended that its vacuum sintering should be performed at 1300°C. 5. In vacuum sintering at 1300°C, final specimen densities in the range 70–97% may be attained by varying the particle size from −150+100 to −45μ, the pressure from 1.6 to 15.2 tons/cm2, and the holding time from 1 to 8 h. 6. In the isothermal sintering of compacts from Kh18N15 steel powder, the effect of pressure on the final density of the material and its grain size is greater than that of the other factors. For the recrystallization of this material, the critical nominal pressure lies between 4 and 6 tons/cm2. 7. Prolonged vacuum sintering close to the solidus point has very little effect on the composition of powder metallurgical Kh18N15 steel, the main change being a slight loss of chromium due to evaporation.

The ordered planes of crystallographic shear inherited from titanium dioxide TiO2 were revealed in complex Ti-containing oxides (Magneli phases) by powder X-ray diffraction. It is assumed that periodic shear in the structure results in the modulation of titanium and oxygen displacements along the direction normal to the shear planes. A method of calculating the amplitude of the displacements of titanium atoms from the centers of oxygen octahedra is suggested. The method provides good agreement of the calculated and experimental data for single crystals. The degree of A-nonstoichiometry in alkaline earth, cadmium, and lead titanates is evaluated as 2–3%.