## Energy characteristics of the surfaces of alkali metals with consideration for the friedel oscillations of the electron density

Published in category «Condensed matter physics»

The present work studies possibilities for description of surface characteristics of alkali series in terms of the density functional theory. The metal surface is considered in the model of a metal in which the positive charges are replaced by a uniform charge background of density. The main objective was to build the optimal type of new trial functions for electron number density distribution, which would take into account the Friedel oscillations, and to calculate the variational parameters of those functions. Self-consistent calculation of the surface energy of alkali metals was carried out taking into account the gradient corrections for inhomogeneity of electron gas in the surface region for the kinetic energy. In this paper, we determined surface characteristics, such as the work of exit and the potential barrier height. The effective potentials for selected alkali metals were constructed.

##
Dielectric properties of Pd-NaNO_{2} nanocomposite in porous glass

Published in category «Condensed matter physics»

We have studied composite on the base of nanoporous glass into the pores of which palladium particles (about 10% of the pore volume) are embedded, and the remaining space is filled with ferroelectric – sodium nitrite. The temperature and frequency dependences of the dielectric response for the nanocomposite with metal particles and without it were measured and analyzed. The Pd-NaNO2 nanocomposite (metal – ferroelectric) created was found to have high effective dielectric permittivity (up to 10^9). DC-conductivity of the composite with metal particles was more than an order of magnitude greater than that of pure sodium nitrite in the porous glass, due, apparently, to the appearance of additional electronic conductivity.

## Modeling of structural instability in lead zirconate

Published in category «Condensed matter physics»

Low-energy phonon spectra of lead zirconate being classic antiferroelectric have been simulated using the Vaks model with 5 modes. This model takes into account a flexoelectric coupling between 5 low-energy modes (3 acoustical and 2 optical ones). The Vaks model was shown to allow not only to achieve good agreement of calculated dispersions with experimental data, but to reproduce the temperature behaviour of TA phonon frequencies as well. As our calculations revealed, the system with 5 low-energy modes was close to structural instability stage. Even a weak change in coupling parameters could result in lattice instability which was characterized by qcrit wave vector. The qcriе-vector took any value including irrational one. In latter case the system would be close to go over into an incommensurate phase. As our calculations revealed, the system with 5 low-energy modes was close to structural instability stage. Even a weak change in coupling parameters could result in lattice instability which was characterized by qcrit wave vector. The qcri-vector took any value including irrational one. In latter case the system would be close to go over into an incommensurate phase.

## Type LED dynamically controlled light sources for novel lighting technology

Published in category «Experimental technique and devices»

The article deals with the creation of the LED light sources on the principle of RGB mixing. The design of the high-power (up to ~ 3000 lm) dynamically controlled semiconductor light source based on the matrix of multicolor emitting crystals has been developed. This lighting instrument comprises an emitting module with a control processor, power drivers, and a controlling part with appropriate software and radio-communication channel for information exchange with an emitting module. An analysis in every detail was made, and a network configuration was worked out on the basis of the ZigBee technology for various network coordinators. A circuit for blocking-out the power LED drivers was set up for heavy current (1.5 A). The polychromatic LED matrix including a monolithic white crystal was designed. As a whole the product developed is a finished system of dynamic lighting that maintains the optimal light environment for human life.

## The influence of natural irregularities on surface electron scattering

Published in category «Physical electronics»

Theoretical estimations of the influence of potential natural irregularities near semiconductor surface on the angular and energy dependences of different groups of electrons emitted by crystal have been made. The electrons of low and intermediate energies scattered from a crystal were analyzed. Orientational and resonance dependences were found to be the most sensitive to irregularity of the surface potential. The sensitivity of experimental methods of studying the effects observed can be significantly improved by using spin-polarized electrons. The proposed method can be effectively applied both to the investigation of electron scattering by semiconductor surface and to getting information on the crystal properties. Recommendations how to take account of the influence of surface potential natural irregularities on electron scattering in the experimental data processing are given.

## The motion of a charged particle in the field of an electromagnetic wave and in the constant magnetic field

Published in category «Physical electronics»

We have done an analysis of the results on the motion of a charged particle in an external field of plane and arbitrarily polarized electromagnetic waves of high intensity in the presence of an external uniform static magnetic field. A point of interest was a solution of the equation of the motion of a charged particle in the field of the electromagnetic wave and a uniform constant magnetic field. We investigated the interaction of high intensity laser pulses with solid targets in relation to the practical development of multi-frequency lasers and the technology development of laser modulation. The problem in question is topical because of the wide practical application of high-temperature plasma forming on the surface of the target, and the search for new modes of laser-plasma interaction. The formulae for the average kinetic energy of a relativistic particle, depending on the initial data, for the amplitude of the electromagnetic wave and for the wave intensity and its polarization parameter were obtained. The dependence of the average kinetic energy on the intensity of the electromagnetic wave in the uniform constant magnetic field was derived.

## An experimental study of industrial air disperse flows

Published in category «Physical optics»

This paper studies the dependence of optical parameters on the aerosol particle average diameter. The air disperse flows were generated using a special duster set-up. This set-up operates in a closed gas circuit with pulse aerosol material injection and makes it possible to sense the air disperse flows by simultaneous laser emission with different wavelengths through both the spectral transparency and integrated light scattering methods. The authors put forward a procedure of the inverse problem solution for the industrial aerosol flows dumped into the atmosphere obviating the application of integral equations by solving the direct problem system by jointly using the two laser sensing methods mentioned above. It was found that the aerosol particles size distribution function could be reconstructed according to the average volume surface diameter being measured in the aerosol flow at the output into the atmosphere. Those measurements could be taken by laser sensing methods based on the Mie scattering theory. The procedure described can serve as a basis for engineering instruments of industrial flows monitoring in real-time processing.

## The structure and properties of one-dimensional composite matrix based on chitosan and chitin nanofibrils and intended for cell technologies

Published in category «Biophysics and medical physics»

The goals of this work are to obtain and to study the structure and properties of chitosan fibers filled with chitin nanofibrils. Biocompatible and bioresorbable composite fibers consisting of chitosan filled with anisotropic chitin nanoparticles (nanofibrils) were prepared by the coagulation method. The structure of the fibers and of the chitin nanofibrils was investigated by the XRD and SEM methods. Chitin powder was obtained by lyophilization of inition chitin suspension, films by drying the aqueous suspension. It was evident that the microparticles have strip type structure with the transverse size approximately 30 μm and with the thickness of 0.1 μm; they consist of nanofibrils of 11-12 nm width and 600-800 nm length. The chitin nanofibrils were used as the filler for obtaining the bioresorbable composite fibers. The results of rheological studies allow to conclude that the dependence of the viscosity (η) on the shear rate (γ) has nonlinear behavior for all investigated solutions. For the chitosan solution not containing the filler, the decrease of viscosity was observed at the shear rate of 10 s^{-1} or more. The threshold value of the shear rate at which the dependence η(γ) becomes nonlinear displaces to the smaller values when the chitin nanofibril content increases. For the mixture containing 20 wt% of chitin filler the dependence η(γ) becomes linear over a wide range of shear rates. It was found that both components (chitin and chitosan) of these composite fibers were oriented. The incorporation of 0.1–0.3 wt.% of chitin nanofibrils (with respect to dry chitosan) into the chitosan matrix led to an increase in strength and Young modulus of composite fibers. Based on these results, a scheme of formation of oriented structure of composite fibers comprising anisodiametric nanoparticles was developed. The adhesion of stem or somatical cells on the material surface is one of the basic criteria of its use as the matrices for the cellular technologies. SEM micrograph of the chitosan fibers taken after the cultivation of stem cells on them indicated that the surface of the fibers contained stem cells, which were well-fixed and split. The fibrillation of the fibers, obtained on high degree of drawing, contributed to the adhesion on fiber surface of the mesenchymal stem cells that changed their form.

## Porous structure forming of the aliphatic copolyamide films

Published in category «Biophysics and medical physics»

The effects of concentration and viscosity of the copolyamide (CoPA) (copolymer of ε-caprolactam and hexamethylendiaminadipate) solutions in aqueous/alcoholic solvents on their phase state have been studied. To study the CoPA solution phase state the light scattering method was used. The start of the phase separation was estimated by the determination of the turbidity point. The films obtained by the coagulation method were characterized by monodisperse pores distribution with an average pore size of 1.3 µm. Mechanical properties, water permeability of the porous films and the specific surface areas according to BET method were measured. Using scanning electron microscopy it was found that proliferation of mesenchymal ASCs stem cells on such porous films were characterized by good adhesion of cells to CoPA matrix. It was shown that the porous structure, transport and mechanical properties of those CoPA films allowed their application as two-dimensional matrices for cellular technology.

## A structural model for flexible woven and pre-damaged сomposites under conditions of uniaxial tension

Published in category «Mechanics»

In this paper we consider a flexible woven composite materials with plain weave reinforcing fibers and vinyl matrix. The main features of these materials are a geometric nonlinearity and a complexity of their microstructure. Flexible woven composites differ in architecture of plain weave, the percentage of reinforcing fibers and their thickness. The paper puts forward micromechanical structural model describing the complete diagram of deformation of the flexible woven composites under uniaxial tension. The model is laminated with the inelastic deformations. A periodically repeating element was detached, and then it was divided into sub-elements. The strain energy was calculated at each structural element and then it was used to calculate displacements according to the Castellano theorem. The article exemplifies modeling of preliminary damage to the material, and the influence of damage on the stress-strain diagram was analyzed. The damage was introduced by changing in the topology of geometry of reinforcing strands, the change correlating with certain residual deformations. This model is universal for any flexible composite woven plain weave. The simulation results were compared with experimental ones, and the model demonstrated a good fit to the data mentioned and minimum errors.

## Typical and atypical boundary problems for the Crocco equation

Published in category «Mathematical physics»

The traditional formulation of the boundary Crocco problem involves the dependence of a transfer coefficient on the density distribution of the concentration. In this case the boundary problem for the Crocco equation is associated with the condition of the minimum for a positive distribution, and the equation itself is equivalent to the canonical system of two equations. The possibility of immersion of flow of boundary problem in the field of extremals, monotony and convexity of the Crocco potential have been proved. In a number of physical problems, the distribution of the transfer coefficient depends on the flux density of conservative tracer, that is, on density gradient of concentration distribution. In this case, there are simple solutions of the boundary Crocco problem with a compact supporter. In other words, the solutions are grouped on a set of the finite measure.

## Salient features of rarefied gas flow interaction with rough surface in the context of the poly-Gaussian mathematical model

Published in category «Simulation of physical processes»

The properties of randomly rough surface in the rarefied gas flow are investigated on the base of the polyGaussian model. These properties have much to do with surface aerodynamic characteristics. This paper puts forward the representation of probability distribution for z-axis of roughness in the form of the mixture of the Gaussian distributions. Owing to this way we succeeded in deriving analytic expressions for factorial moments of the number of outliers upon a specific level of a trajectory of a gas particle. Those analytic expressions play a key role in finding the scattering function of gas atoms on the surface and the momentum exchange coefficients. The important particular case of the poly-Gaussian processes has been considered, namely – spherically-symmetric random processes, permitting to simplify the conditions. The asymptotic evaluations were found for high level crossings characteristics corresponding to the case of weakly-rough surface. The results obtained allowed to evaluate the influence of surface roughness on the type of gas flow near the surface in comparison to the Gaussian model of roughness.