## Structural features of indium antimonide quantum dots on the indium arsenide substrate

Published in category «Condensed matter physics»

The properties of InSb/InAs quantum dots (QDs) have been investigated by transmission electron microscopy (TEM). Specific features of diffraction contrast were discovered in plan-view TEM images of big (9–10 nm in height and 38–50 nm in diameter) InSb QDs. To understand the origin of such distortions in the TEM image the model of InSb QD on InAs substrate containing a partial Frank dislocation (FD)was developed and used for calculations of the displacement field and the subsequent diffraction image simulation of InSb QD for the first time. The shape of QD was established to influence insignificantly on the magnitude of radial displacements. The insertion of a misfit defect (a partial Frank dislocation) into QD reduces the strain at the edges of QD almost by 30%. The comparison of experimental and simulated data allowed us to explain the observed features of the moiré pattern in the image of big InSb QD by the presence of a misfit defect (FD) at the QD-substrate interface.

## Predicting the parameters of energy installations with laser ignition: neural network models

Published in category «Simulation of physical processes»

The article considers the possibility of using artificial neural networks for prediction of the parameters of the model energy installation with laser ignition. The main stages of creating a prognostic model based on artificial neural network have been presented. Input data were analyzed by principal component method. The synthesized neural network was built up to predict the parameter value of the model in question. The artificial neural network was trained by back-propagation algorithm. The efficiency of the artificial neural networks and their applicability to prediction of the parameter values of the various elements of rocket engines were demonstrated.

## A modified nodal pressure method for calculation of the flow distribution in hydraulic circuits for the case of unconventional closing relations

Published in category «Simulation of physical processes»

In the paper, we propose a method for numerical solving the problem of the flow distribution in hydraulic circuits with lumped parameters for the case of random closing relations. The conventional and unconventional types of relations for the laws of isothermal steady motion of fluid in the individual hydraulic circuit components are considered. The unconventional relations are represented by those implicitly given by the flow rate and dependent on the pressure of the working fluid. In addition to the unconventional relations, the formal conditions of applicability were introduced. These conditions provide a unique solution to the flow distribution problem. A new modified nodal pressure method is suggested. The method is more universal in terms of the closing relation form as compared to the unmodified one, and has a lower computational cost as compared to the known technique of double iteration cycles. The paper presents an analysis of the new method and its algorithm, gives a calculated example of the gas transportation network, and its results.

## Rough estimates of the Blasius constant

Published in category «Mathematical physics»

Integral properties of homogeneous solutions of the Crocco boundary problem and splitting (flat) decomposition have been used for an approximate estimate of the Blasius constant. The derivative *d*(fi) / *dh* was proved to have a logarithmic singularity at the point *h* = 1, therefore the second one tends to minus zero, and the function in itself tends to plus zero, because h tends to unity minus zero, so the splitting series is not slower to diverge as compared with the harmonic one. The existence of an integral invariant was proved for a uniform solution of the Crocco boundary problem, the solution exhibiting the squared norm of the solution derivative. The condition for distribution minimum was established to be satisfied along the real uniform solutions of the boundary Crocco problem.

## Flatbed scanner as an instrument for physical studies

Published in category «Experimental technique and devices»

A new method for nondestructive testing of the optical properties of various materials (semiconductors, dielectrics and metals) has been presented. It is based on the determination of geometric and optical inhomogeneities of the objects using the measurement data on the objects characteristics of the light scattered by them. It has been proposed to use a flatbed scanner as a physical device for measuring the scattered light. An analysis of the method possibilities showed that it is possible to measure the roughness and surface curvature, identify single defects on the surface, to measure the electrophysical parameters of materials being transparent in the visible region of the spectrum by means of the scanner. The method is simple to implement, it is on par with the accuracy of measurements made with many specialized physical devices, it is superior to the expensive equipment in a body of on-line information, it makes testing material properties under production conditions possible.

## A photointegrator of the molecular condensation nuclei detector

Published in category «Experimental technique and devices»

The problem of calculating the threshold sensitivity of an integrating photoreceiver (photocurrent integrator) is investigated. Photocurrent integrators are used in scientific instruments to achieve high sensitivity of an optical measurement system in case of relatively slow physical processes. Noise model of a photointegrator is used to develop equivalent noise circuits and to calculate the RMS value of the voltage across the output of the photoreceiver. Among all the models of the real photointegrator it is conceivable that the approximation by an ideal photointegrator may be used. The threshold sensitivity of a photointegrator is defined as the power at the input of a photointegrator at which the root mean squared (RMS) voltage across its output is equal to the RMS voltage of total noise i.e. the signal to noise ratio is equal to one. A photomultiplier tube (PMT) can be used to increase the sensitivity. Formulas for calculated the sensitivity of PMT based photointegrator are given. The increase in sensitivity due to the use of PMT can be up to 18-30 times. Experimental study of a photometer of a molecular condensation nuclei (MCN) detector that forms a base of highly sensitive MCN gas analyzers was conducted. Measured sensitivity differed from calculated by 10%, however at femtowatt power levels it is very difficult to get rid of parasitic optical signals that are responsible for a small decrease in sensitivity compared to the theoretical prediction. It is noted that in many practical applications, for example in X-ray absorption method of mineral extraction using position sensitive photodiode X- ray receivers, an approximation of a real photointegrator must be used.

## Thermal resistanсe and nonuniform distribution of electroluminescence and temperature in high-power AlGaInN light-emitting diodes

Published in category «Experimental technique and devices»

The paper studies current spreading, light emission, and heat transfer in high-power flip-chip light-emitting diodes (LEDs) and their effect on the chip thermal resistance by experimental and theoretical approaches. The thermal resistance was measured using two methods: by monitoring the transient response of the LED operation voltage to the temperature variation with the Transient Tester T3Ster and by temperature mapping with the use of an infrared thermal-imaging microscope. The near field of the electroluminescence intensity was recorded with an optical microscope and a CCD camera. Three-dimensional numerical simulation of the current spreading and heat transfer in the LED chip was carried out using the SimuLED package in order to interpret the obtained experimental results.

## Nonradiative transitions between the sublevels of the working lower multiplet of the YAG:Nd laser: effects on the generation spectrum

Published in category «Actual problems of education»

The article presents the stationary solution of the Tang–Statz–DeMars system of equations describing the generation spectrum of YAG : Nd laser at a wavelength of 1064.2 nm in terms of seven lines of amplification of the transition 4F3/2 → 4I11/2. The line broadening effect, due to temperature increase, on the generation spectrum of YAG : Nd laser has been calculated. Moreover, the effect of population distribution over the 4I11/2 multiplet sublevels on the laser generation spectrum was also calculated. The generation spectrum shift to the region of 1066 nm with temperature increase was found to result from variations in the population of the 4I11/2 multiplet sublevels.

## Performance evaluation of Sferocell S80 sorbent in the dynamic mode

Published in category «Biophysics and medical physics»

The crucial factor of septic shock and subsequent multiple organ failure is the contamination of circulating blood with a bacterial endotoxin. The most straightforward approach to mitigating this condition is to remove the endotoxin from the bloodstream. The hydrophobic Spherocel S80 sorbent has been used as an experimental one in the present work. It was synthesized on the basis of regenerated cellulose. The dynamic characteristics of endotoxin interactions with the hydrophobic sorbent under flow conditions were studied using chromatographic columns of different sizes. The effects of the rate and perfusion duration on LPS binding by Spherocel S80 were evaluated. The endotoxin quantity in every taken sample of the perfusate was determined through a chromogenic LAL test. The implemented process showed that the sorbent Spherocel S80 proved successful under flow conditions due to its selective, capacitive, and hydrodynamic characteristics. Moreover, the sorbent was as efficient in LPS elimination as the conventional ones, ensuring the required degree of LPS elimination both in biotechnological preparations and biological liquids.

## Phi-meson nuclear modification factors at the lead nuclei collisions in the ALICE experiment at the LHC

Published in category «Nuclear physics»

Hadron spectra measurements in proton-proton and nucleus-nucleus collisions at the LHC provide the means to study the mechanisms of particle production and properties of the medium formed in relativistic heavy ion collisions. Phi-meson is a very rich probe since it is sensitive to several aspects of the collision such as strangeness enhancement, chiral symmetry restoration and parton energy loss. Due to its small inelastic cross-section, phi-meson is not strongly affected by the late hadronic rescattering and is sensitive to the initial evolution of the system. With a mass similar to that of the proton, it is interesting to see how the phi-meson fits within the meson/baryon pattern of observables. Being a pure ss state, it further constrains the energy loss and recombination pictures. This article presents recent results on phi-meson invariant yields and nuclear modification factors measured in a wide range of transverse momentum up to 21 GeV/c2 in (p + p) and (Pb + Pb) collisions at different centralities. The proton-to-(phi-meson) yield (p/phi) ratio as a function of transverse momentum in (Pb + Pb) collisions at an energy of SNN = 2.76 TeV is also presented.

## Determination of phi-meson nuclear modification factors in the proton-lead nucleous interactions in the ALICE experiment at the LHC

Published in category «Nuclear physics»

Hadronic resonances are among the most interesting probes of the hot and dense matter created in Pb + Pb collisions. Due to their short lifetime, they are sensitive to the anticipated chiral symmetry restoration as well as to suppression and regeneration due to hadronic interactions in the final state. At intermediate and high transverse momenta (pT) resonances which cover the range of masses between the light pions and heavier protons contribute in systematic study of the baryon puzzle and parton energy loss in the dense medium. Studies in p + Pb collisions are important for the interpretation of heavy ion results as they allow to decouple and understand the cold nuclear matter effects from final state effects. The systematic study of the phi (1020) meson production at mid-rapidity in p + Pb collisions at LHC energies has been performed. In this article the most recent results of these studies including pT spectra and nuclear modification factor distributions in p + Pb collisions at an energy of √(s_{NN}) = 5.02 TeV are presented.

## Mathematical modeling of occasional road disturbances for mobile vehicles dynamic research

Published in category «Mathematics»

This paper focuses on a simulation procedure of occasional road disturbances reasoning from noncanonical occasional functions analysis method in terms of determinate functions depending on only three casual quantities with any distribution law of their probabilities. A developed mathematical method for simulation of random road disturbances gives an accurate representation of the random function perturbations in the framework of the correlation theory using only three random variables. The proposed approach allows obtaining more reliable information about the spectral composition of the microrelief, simplifying studies of the mobile vehicles dynamics and reducing the computation amount as compared to other methods.

## Geometrical aspects of testing the complex statistical hypotheses in mathematical simulation

Published in category «Mathematics»

It is well known that mathematical simulation parameters often are obtained by statistical estimating. Therefore the problem of testing the complex statistical hypotheses such as the one about an adjunct of a vector of model parameters to some domain is of current concern. This article deals with the problem in geometrical aspects. The basic theorem to solve this problem has been stated and proved. The theorem asserts that the solution can be done through testing some simple statistical hypothesis concerning a boundary point of maximum likelihood. The theorem proof is based on the use of generalized Euclidean metric and an affine transformation of parameter space. Typical examples of its use for different mathematical models are also considered. They are the following: (i) Altman’s model of the economic stability and risk estimating; an estimation of specific enterprise is treated in terms of the statistical hypotheses testing; (ii) the method to refine statistical estimations of production function parameters; (iii) the statistical estimation of the space object dynamic stability is considered on the basis of Kepler’s model, as well.

## Fresh approaches to the construction of parameterized neural network solutions of a stiff differential equation

Published in category «Mathematics»

A number of new fundamental problems expanding Vasiliev’s and Tarkhov’s methodology worked out for neural network models constructed on the basis of differential equations and other data has been stated and solved in this paper. The possibility of extending the parameter range in the same neural network model without loss of accuracy was studied. The influence of the new approach to choosing test points and using the heterogeneous complementary data on the solution accuracy was analyzed. The additional conditions in equation form derived from the asymptotic decomposition were used apart from the point data. The classical and non-classical definitions of the problem were compared by entering a parameter into the additional data. A new sampling scheme of test point choice at different stages of minimization (the procedure of test point regeneration) under various initial conditions was investigated. A way of combining two approaches (classical and neural-network) based on the Adams PECE method was considered.

## Simulation of hard X-ray time delays in solar flares

Published in category «Astrophysics»

Hard X-ray radiation (HXR) time-delays have been studied. HXR was recorded during the solar flares using the BATSE spectrometer. The time-delays energy spectra were obtained for 82 flares; thе spectra were classified under three species: decreasing spectra, increasing spectra and U-shaped ones. The spectra were interpreted on the basis of a model of kinetics of accelerated electrons propagating in the flaring loop with the given plasma concentration distribution and magnetic field configuration. The kinetics in question is governed by the processes of Coulomb scattering, reflecting in the converging magnetic field, and with the return current factored in. Solving the time-dependent relativistic Fokker – Planck equation for the given initial conditions allowed to find the time-dependent electron distribution function along the loop. The brightness distribution of the bremsstrahlung of HXR derived from the electron distribution functions was calculated for different photon energies along the flare loop and used to plot the time-delays spectra. The calculated data showed that decreasing time-delays spectra were tractable assuming spaces of electrons acceleration and injection were separated. The distinction between time-delays spectra from the looptop and footpoints was established.

## On the Universe initial state in quantum cosmology

Published in category «Theoretical physics»

The article deals with the problem of an initial state of quantum inflationary Universe. Considering the dynamics of the inflation scalar field at the beginning of the inflation stage in the context of semi-classical approximation, we have identified this field with a cosmic time parameter. The early Universe state was defined as an initial value of the inflation field. Other degrees of the Universe freedom, including the scale factor, are treated within the scope of the quantum theory. Then, the initial state of quantum degrees of freedom at the beginning of the inflation must be defined, as well. A principle of the least excitation of physical degrees of freedom for the Universe has been proposed to determine the initial state of the quantum universe. A uniform anisotropic model of the Universe was considered where its size and the anisotropic parameters were quantum dynamical variables. On the assumption that the Universe size is a radial variable in the configuration space of the theory the definition of the Hamiltonian of the Universe is rendered more precise. A simple exponential form of the Universe initial state is suggested and the Universe initial size being estimated for this form.

## Channeling of ultra-relativistic positrons in bent diamond crystals

Published in category «Theoretical physics»

Results of numerical simulations of channeling of ultra-relativistic positrons are reported for straight and uniformly bent diamond crystals. The projectile trajectories in a crystal are computed using the newly developed module of the MBN Explorer package which simulates classical trajectories in a crystalline medium by integrating the relativistic equations of the motion with account for the interaction between the projectile and crystal atoms. A Monte Carlo approach is employed to sample the incoming positrons and to account for thermal vibrations of the crystal atoms. The channeling parameters and emission spectra of incident positrons with a projectile energy of 855 MeV along C(110) crystallographic planes are calculated for different curvature radii of the crystal. Two features of the emission spectrum associated with positron oscillations in a channel and synchrotron radiation are studied as a function of crystal curvature.