St Petersburg Polytechnic University Journal-Physics and Mathematics最新文献

The electrospinning technique has been used to manufacture a composite material based on nanofibers made of aliphatic copolyamide and composite nanofibers made of chitosan and chitin nanofibrils. Experimental in vivo studies of the designed material as wound covering were carried out to treat a vast and multilayered wound on a rat's back. After 28 days and nights of observation, complete epithelialization of the wound surface was established to occur in the experimental rat group. Histological analysis of scar tissue showed the presence of a small minority of capillaries and a low amount of infiltrating cells. The survival of animals was 100%. At the same time, in the control group of animals, lethality was observed in 11% of cases, and suppurative complications were observed in 100% of cases. Thrombocyte gel prepared from the peripheral blood of the patients was used to increase the rate of tissue regeneration, and to reduce the infection probability. The curative effect was proved to increase when wound dressings and autologous blood product separation, i.e., thrombocyte gel and platelet-rich plasma, were applied simultaneously.

Multiparameter analysis of simultaneous optical data for systems of nano- and/or micro-particles (3D disperse systems, dispersions, colloids, ensembles) by presentation of system characteristics as N-dimensional vectors of optical parameters (ND-vectors) can help to elucidate changes in the state of the particles in systems. In this paper, the application of the ND-vector approach is shown on the examples of dispersion mixtures: a mixture of influenza virus particles with albumin proteins (as a model of dispersions at the process of vaccine production); a mixture of coli bacillus and clay dispersions (as natural water model). This approach can serve as an on-line control platform for the management of technological processes with mixtures.

The paper presents the results of an experimental study of impurity-assisted photoluminescence in the far- (terahertz) and near-infrared spectral ranges in n-GaAs/AlGaAs quantum well structures with different well widths under interband photoexcitation of electron–hole pairs. The optical electron transitions between the first electron subband and donor ground state as well as between excited and ground donor states were revealed in the far-infrared photoluminescence spectra. Observation of these optical electron transitions became possible because of the depopulation of the donor ground state in the quantum well due to the non-equilibrium charge carrier radiative transitions from the donor ground state to the first heavy hole subband. The opportunity to tune the terahertz radiation wavelength in structures with doped quantum wells by changing the quantum well width was demonstrated experimentally.

The temperature dependences of the magnetization M(T) for multiferroic single crystal lanthanum-strontium manganites La_0.875Sr_0.125MnO₃ (LSMO-0.125) and La_0.93Sr_0.07MnO₃ (LSMO-0.07) have been obtained. It is shown that the phase transitions (PT) in LSMO-0.07 at T_C = 125.8(1,5) K and in LSMO-0.125 at T_C1 = 181.2 (1.5) belong to the second order type. The phase transition in LSMO-0.125 at T_C2 = 157.6 (1.5) K is the first order PT. From the M^–1(T) curves, the values of the magnetic moments have been determined. They are equal to μ₁ = 2.47(1) μ_B/Mn and μ₂ = 2.82(1) μ_B/Mn, for LSMO-0.125 and LSMO-0.07 respectively.

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.

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.

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

The temperature evolution of multiferroic solid solutions of the PFW–PT system, namely a (1–x)Pb(Fe_2/3W_1/3O₃)–(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 anomalously large Debye–Waller factors for the lead cations, indicating the appearance of random static displacements of these cations from the ideal perovskite (0 0 0) position. Using the split-ion model we estimated the value of Pb static shifts (∼0.1 Å) from their high-symmetry positions along the [1 1 0] direction. It was shown that these shifts decrease with increasing the PbTiO₃ concentration.

In the paper, we suggest widening the scope of cryogenic atomic-force microscopy in order to determine Young's 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. Young's modulus is determined from the obtained data by calculation taking into account the temperature dependence of a cantilever spring constant. As an example we have obtained a temperature dependence of Young's modulus for polylysine in the temperature range stretching from 60 to 300 K (RT) using the proposed technique.

The effect of acoustic shielding of the mental foramina of a bottlenose dolphin (Tursiops truncatus) on its auditory thresholds has been experimentally 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 in the region of the mental foramina over the whole frequency band of the dolphin's hearing. Therefore, the mental foramina of its lower jaw take part in receiving and conducting the sounds into the mandibular fat in the entire frequency range of the 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 the similarity of their morphology.