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Burkovski Roman G., Andronikova Darya.A., Bronwald Yuri A., Filimonov Alexey V., Vakhrushev Sergey B.

An analysis of the phonon dispersion curves of lead hafnate in the cubic phase using lattice-dynamical models.

Published in category «Condensed matter physics»

We have analyzed the phonon dispersion curves in the paraelectric phase of a lead hafnate crystal (PbHfO3) by means of two different lattice-dynamical models. Both the rigid-ion model and the shell one provided an acceptable description of the available experimental data. The atomic displacement patterns were qualitatively different for the two models. In the rigid-ion model the motion in the characteristic low-energy flattened transverse acoustic branch contained both lead and hafnium displacements, while for the shell model it corresponded mainly to lead displacements with the small contribution of oxygen displacements. The shell model allows simultaneous description of the phonon dispersion curves and the correct value of the dielectric constant.

Views: 564 Comments: 0

Vanina Polina Yu., Naberezhnov Alexander A., Nizhankovskii Victor I., Mamin Rinat F.

Temperature evolution of lanthanum-strontium manganites magnetic properties.

Published in category «Condensed matter physics»

The temperature dependences of the magnetization M(T) for multiferroic single crystal lanthanumstrontium manganites La0.875Sr0.125MnO3 (LSMO-0.125) and La0.93Sr0.07MnO3 (LSMO-0.07) have been obtained. It was shown that the phase transitions (PT) in LSMO-0.07 at TC = 125.8(1,5) K and in LSMO-0.125 at TC1 = 181.2 (1.5) belonged to the second order type. The phase transition in LSMO-0.125 at TC2 = 157.6 (1.5) K is the first order PT. From the M–1(T) curves the values of the magnetic moments were determined. They were equal to μ1 = 2.47(1) μB/Mn and μ2 = 2.82(1) μB/Mn for LSMO-0.125 and LSMO-0.07 respectively.

Views: 435 Comments: 0

Naberezhnov Alexander A., Dolgakov Ivan А., Tovar Michael, Alekseeva Olga A., Vakhrushev Sergey B.

An analysis of the high-temperature phase structure of multiferroic solid solutions of the PFW-PT.

Published in category «Condensed matter physics»

The temperature evolution of multiferroic solid solutions of PFW-PT system, namely (1-x)Pb(Fe2/3W1/3O3)-(x)PbTiO3 crystal structure where x = 0, 0.2, 0.3, has been studied by neutron powder diffraction in the region of the morphotropic phase boundary. The coexistence of cubic and tetragonal phases in the solutions with x = 0.2, 0.3 was found below T = 259 and 285 K, respectively. As a result of the data treatment the atom coordinates, the occupation factors and the temperature dependences of cell parameters were determined in the cubic perovskite phase. The refinement of the crystal structure in terms of ideal perovskite exhibited the anomaly large Debye-Waller factors for the lead cations, indicating the appearance of random static displacements of these cations from the ideal perovskite (000) position. Using the split-ion model we estimated the value of Pb static shifts (~0.1 Å) from their high-symmetry positions along the [110] direction. It was shown that these shifts decrease with increasing the PbTiO3 concentration.

Views: 424 Comments: 0

Kamalov Almaz М., Borisova Margarita E.

The influence of moisture on charge relaxation in modified polyimide films.

Published in category «Condensed matter physics»

The charge relaxation processes in the films based on polyimide and polytetrafluoroethylene (the latter serves as a coating) have been studied. The coating effect on the charge relaxation processes in the films under high humidity conditions was revealed. The obtained experimental data was analyzed in the context of the present-day knowledge of the charge relaxation mechanism. The complex spectra of the thermally stimulated depolarization currents (TSDC) were resolved into individual components described by the first-order kinetics equations using computer simulation. The TSDC activation energies were calculated and interpreted in terms of the mechanism of release of charge carriers.It was shown that the polytetrafluoroethylene coats on film surfaces lead to an essential increase in the electret state stability at elevated temperature and high humidity.

Views: 338 Comments: 0

Musaeva Diana А., Vladimir Ilin К., Geza Vadims, Baake Egbert

Experimental investigation of low-frequency pulsed Lorentz force influence on the motion of galinstan melt.

Published in category «Simulation of physical processes»

The article presents the results of the numerical and physical experiments, aimed to recognize the influence of pulsed force of electromagnetic field on the melt motion and the fluid velocities. The experiment was performed on the eutectic alloy galinstan in the cylindrical volume, where Ultrasonic Doppler Velocimeter was employed for velocity measurements under conditions of pulsed and steady EM field application. A numerical simulation of the melt flow, forced by the steady forcing, involved a 2D axisymmetric model. The k-ε turbulence model was used to obtain the information about the melt velocities. The verification of the numerical model was carried out for the steady case. The effects of pulsed and steadily applied Lorentz force were compared using the physical experiment. An intensity of the velocity pulsations in galinstan for the pulsed frequencies in the range from 0.05 to 1 Hz considerably exceeded the values, measured in the permanently stirred melt. For higher values of pulsed frequencies (from 1 to 10 Hz) the effect decreases and only slightly differs from the influence of the permanently applied Lorentz force.

Views: 410 Comments: 0

Melker Alexander I., Krupina Maria A.

Geometric modeling of midi-fullerenes growth from C24 to C48.

Published in category «Atom physics and physics of clusters and nanostructures»

Axonometric projections together with corresponding graphs for fullerenes are constructed in the range from 24 to 48. The growth of fullerenes is studied on the basis of the mechanism, according to which a carbon dimer embeds in a hexagon of an initial fullerene. This leads to stretching and breaking the covalent bonds which are parallel to arising tensile forces. In this case, instead of the hexagon adjoining two pentagons, one obtains two adjacent pentagons adjoining two hexagons. As a result, there arises a new atomic configuration and there is mass increase of two carbon atoms. We considered direct descendents of fullerene C24; namely, C2n, where n = 13 – 24.

Views: 426 Comments: 0

Melker Alexander I., Vorobeva Tatyana V.

Fusion reactions of cupola half fullerenes.

Published in category «Atom physics and physics of clusters and nanostructures»

Reactions of cupola half fullerenes C10, C12, C16, C20 and C24 with each other are considered on the basis of Arrhenius’s postulate. It means that at first there forms an intermediate compound and only afterwards a usual chemical reaction is going on. We supposed that during the reactions new covalent bonds are formed and some old covalent bonds between the reacting atoms are destroyed. The final structure of a fullerene is obtained through the use of geometric modeling. As applied to fullerenes, geometric modeling supposes that a forming fullerene tends to take the appearance of a perfect spheroid with equal covalent bonds. The graphs describing the process are constructed.

Views: 393 Comments: 0

Krymskaya Ksenia I., Andreeva Nataliya V., Filimonov Alexey V.

A technique for determining the young’s modulus of biological objects using atomic-force microscopy in the widetemperature range below RT

Published in category «Experimental technique and devices»

In the paper, we suggest widening the scope of the cryogenic atomic-force microscopy in order to determine the Young modulus of biological objects over a temperature range stretching from 30 to 300 K. A new technique assumes some modification of the arrangement for the optical system recording the probe position in the cryogenic atomic-force microscope and making measurements of approach and retraction force-distance curves under these conditions. The Young modulus is determined from the obtained data by the calculation taking into account the temperature dependence of a cantilever spring constant. As an example we have obtained a temperature dependence of the Young modulus for polylysine in the temperature range stretching from 60 to 300 K (RT) using the proposed technique.

Views: 419 Comments: 0

Savin Vasily N., Molkov Sergey I.

The effect of electron emission processes on micro- and nanoparticle charges in the dusty plasma: the accounting for engineering

Published in category «Physical electronics»

In this paper, the charge-balance, the energy-balance and the moment equations and Poisson’s equation have been used to describe the charging process for a dust particle in the undisturbed plasma with taking into account an emission variety (secondary electron, electron-ion, thermal-field electron and photoelectron ones) in the intermediate regime of ion motion. Such an approach was associated with the fact that the dust-particle charge specified by the parameters of the above-mentioned plasma depends heavily on the electron emission from the particle surface. Collisions between ions and atoms as well as ionization also essentially affect the formation of the ion flux onto the surface of dust particles. The computational procedure put forward by us allowed solving the chosen set of equations for an arbitrary relationship between the ion mean free path, the particle radius and the Debye length. The electron emission was shown to decrease the absolute value of the dust-particle charge. Moreover, the collisions with atoms lead to the ion flux deceleration onto the particle surface whereas the depth of the disturbance space of plasma increased with decreasing the ionization frequency.

Views: 454 Comments: 0

Ryabov Vyacheslav A.

The study of acoustic signals and the supposed dolphins’ spoken language.

Published in category «Biophysics and medical physics»

This paper continues studies in the problem of animal’s language by registration of acoustic signals from the two quasi-stationary Black Sea bottlenose dolphins (Tursiops truncatus) using two-channel system in the frequency band up to 220 kHz with a dynamic range of 81dB. The packs of mutually noncoherent impulses dolphins (NI) were matched to the animals. The waveforms and the spectra of these impulses changed from one impulse to another one in each pack. In this connection, the suggestion was made that the set of spectral components of each impulse is a «word» of the dolphin’s spoken language and a pack of NI is a sentence. The paper studied the NI pecularities in the context of characteristics of a human spoken language.

Views: 400 Comments: 0

Ryabov Vyacheslav A.

The effect of acoustic shielding the region of a dolphin’s mental foramens on its hearing sensitivity.

Published in category «Biophysics and medical physics»

The effect of acoustic shielding the mental foramens of a bottlenose dolphin (Tursiops truncatus) on its auditory thresholds has experimentally been studied using the method of instrumental conditioned reflexes with food reinforcement. The detection thresholds of short broadband acoustic pulses deteriorated significantly (by 30–50 dB), under conditions of acoustic shielding the region of the mental foramens over the whole frequency band of a dolphin’s hearing. Therefore, the mental foramens of its lower jaw take part in reception and conducting the sounds into the mandibular fat body in the entire frequency range of a dolphin’s hearing. The obtained results give an experimental proof for the assumption that the morphological structures of the lower jaw play a role of the peripheral part of a dolphin’s hearing. Now there are grounds to assume that Odontoceti have the similar peripheral part of their hearing. This assumption is based on similarity of their morphology.

Views: 358 Comments: 0

Sukhoterin Mikhail V., Baryshnikov Sergey O., Lomteva Ksenia O.

On homogeneous solutions of the problem of a rectangular cantilever plate bending.

Published in category «Mechanics»

The paper considers the method, suggested by P.F. Papkovich for rectangular plates and its application for a cantilever plate with a bending under a uniform load. The required function of bendings is chosen in the form of a sum of the corresponding beam function and a biharmonic function, which is a series in terms of unorthogonal eigenfunctions of the problem. The eigenfunctions satisfy the homogeneous boundary conditions on the longitudinal edges (the clamped and the opposite ones). It is suggested to find series coefficients from the condition of the minimum discrepancies work on the corresponding displacements of the transverse edges. It leads to an infinite system of linear algebraic equations for the required coefficients in the complex form. The coefficients of homogeneous solutions were found for the cases in which the approximating series contained sequentially 2, 3,...7 terms. The eigenvalues, the bendings of the edge opposite to the clamped edge, and the bending moments in the clamped section were calculated. Convergence of the reduction method and stability of the computational process were analyzed.

Views: 432 Comments: 0

Yashchurginskaya Olga А., Veis Alexander N.

Professor Mikhail Mikhailovich Bredov (dedicated to the 100th anniversary since his birth)

Published in category «Chronicle»

This ptrsonalia is devoted to the memory of Mikhail Mikhailovich Bredov (1916-1976), who was a prominent scientist in physics, working closely with A.F. Ioffe and B.P. Konstantinov. He worked at Leningrad Physical Technical Institute of the USSR SA from 1938 to 1976 (on and off), at Semiconductor research institute of the USSA SA (1954-1961). He also was a lecturer at the Leningrad Polytechnical Institute (1952-1973). In the scientist's biography, his research work is accented. Bredov's participation in the WW2 is also described. The pedagogical and educational activities of M.M. Bredov are presented.

Views: 377 Comments: 0