The results are presented with regard to experimental studies of dynamic strength characteristics of samples made of 12Cr18Ni10Ti steel powder. They were obtained through selective laser melting with various parameters of a technological process at shock-wave compression up to pressures of ~7 GPa. Critical parameters of a process, in addition to powder characteristics, include laser operating conditions: a laser spot diameter, laser power, a laser beam scanning velocity, as well as a powder layer thickness, protective atmosphere, etc. It has been demonstrated that an increase in the scan laser power and a decrease in a powder layer thickness bring about a decrease in a number of internal defects in initial structures of samples. The results are given, which compare strength characteristics of these steels with properties of steel produced by a traditional technique of hot rolling. Shock-wave experiments were carried out using a light gas gun-type facility, which makes it possible to accelerate flat impactors to speeds of ~700 m/s; internal wave processes in samples were reproduced when recording a rate of movement of the sample's free surface via a PDV laser interferometer; a degree of spall fracture was determined by the help of a metallographic analysis of samples recovered in tests. It has been showed that steel samples made through a selective laser melting technique have high spall strength and a lower degree of damage compared to hot-rolled steel under the same conditions of high-speed shock loading. According to the results of the metallographic studies, the presence of internal defects in initial structures of samples associated with a choice of operating conditions of a manufacturing process does not affect a degree of their spall damage. At the same time, a wave pattern of shock wave propagation differs significantly for samples with and without defects.

Приведены результаты цикла исследований по определению динамических прочностных характеристик образцов, изготовленных по технологии селективного лазерного плавления порошков на основе стали 12Х18Н10Т, и их сравнение со свойствами стали 12Х18Н10Т, полученной по традиционной технологии горячекатаного проката, при ударно-волновом нагружении в диапазоне давлений сжатия 3 ÷ 7 ГПа. Показано, что образцы из стали, изготовленные по технологии селективного лазерного плавления, имеют большую сопротивляемость кратковременному растяжению, возникающему в результате взаимодействия встречных волн разгрузки, по сравнению с горячекатаной сталью 12Х18Н10Т. This paper presents the results of a series of studies to determine the dynamic strength characteristics of samples manufactured using selective laser melting technology of 12Kh18N10T steel powders and compares them with the properties of 12Kh18N10T steel obtained by traditional hot rolling under shock-wave loading in a compression pressure range of 3–7 GPa. It is shown that the steel samples manufactured using selective laser melting technology have greater resistance to short-term tension resulting from the interaction of counter-current unloading waves compared to the hot-rolled 12Kh18N10T steel.

The dynamic structure factor and the eigenmodes of density fluctuations in liquid 3He are studied using a novel non-perturbative approach. This new version of the self-consistent method of moments invokes up to nine sum rules and other exact relations, the two-parameter Shannon information entropy maximization procedure, and the ab initio path integral Monte Carlo simulations which provide necessary reliable input information on the system static properties. Detailed analysis is performed of the collective excitations dispersion relations, the modes' decrements and the static structure factor of 3He at the saturated vapour pressure. The results are compared to available experimental data by Albergamo et al. (Albergamo et al. 2007 Phys. Rev. Lett. 99, 205301. (doi:10.1103/PhysRevLett.99.205301)) and Fåk et al. (Fåk et al. 1994 J. Low Temp. Phys. 97, 445-487. (doi:10.1007/BF00754303)). The theory reveals a clear signature of the roton-like feature in the particle-hole segment of the excitation spectrum with a significant reduction of the roton decrement in the wavenumber range [Formula: see text]. The observed roton mode remains a well-defined collective mode even in the particle-hole band, where it is strongly damped. The existence of the roton-like mode in the bulk liquid 3He is confirmed like in other quantum fluids. The phonon branch of the spectrum is in a reasonable agreement with the same experimental data. This article is part of the theme issue 'Dynamic and transient processes in warm dense matter'.

Dynamical properties of uniform electron fluids are studied within a nonperturbative approach consisting in the combination of the self-consistent version of the method of moments (SCMM) involving up to nine sum rules and other exact relations, the two-parameter Shannon information entropy maximization procedure, and the ab initio path integral Monte Carlo (PIMC) simulations of the imaginary-time intermediate scattering function. The explicit dependence of the dynamic structure factor (DSF) on temperature and density is studied in a broad realm of variation of the dimensionless parameters (2 rs 36 and 1 theta 8). When the coupling is strong (rs 16) we clearly observe a bimodal structure of the excitation spectrum with a lower-energy mode possessing a well pronounced rotonlike feature (theta 2) and an additional high-energy branch within the roton region which evolves into the strongly overdamped high-frequency shoulder when the coupling decreases (rs 10). We are not aware of any reconstruction of the DSF at these conditions with the effects of dynamical correlations included here via the intermediate scattering and the dynamical Nevanlinna parameter functions. The standard static-local -field approach fails to reproduce this effect. The reliability of our method is confirmed by a detailed comparison with the recent ab initio dynamic local field approach by T. Dornheim et al. [Phys. Rev. Lett. 121, 255001 (2018)] available for high/moderate densities (rs 10). Moreover, within the SCMM we are able to construct the modes' dispersion equation in a closed analytical form and find the decrements (lifetimes) of the quasiparticle excitations explicitly. The physical nature of the revealed modes is discussed. Mathematical details of the method are complemented in Appendix. The proposed approach, due to its rigorous mathematical foundation, can find numerous diverse applications in the physics of Fermi and Bose liquids.

On the basis of the generalized Poisson–Boltzmann equation derived from the Bogolyubov chain of equations for the equilibrium distribution functions in the pair correlation approximation, a general expression is proposed for the Helmholtz free energy of a system that contains any number of components and whose particles interact via arbitrary potentials. This opens up an extraordinary opportunity to simultaneously treat a whole range of physical effects including partial ionization, quantum effects of diffraction and electron degeneracy, short- and long-range interactions of charged particles with neutrals, finite size effects, etc. It is shown that all medium constituents are tied together in a single screening matrix, whose determinant and trace determine the excess contribution to the free energy. The approach developed is then applied to the problem of the ionization potential depression (IPD) leading to quite simple analytical expressions, which turn out to be useful for various practical purposes. In particular, for a single ionization from the neutral state the IPD is shown to significantly depend on the ionization degree such that it consists of the difference of charged and neutral contributions for a fully ionized plasma and turns non-zero for an almost neutral medium. On the other hand, for a multiple ionization process finite size effects of atoms and ions are demonstrated to be of great importance and accounted for in order to achieve good agreement with experimental data on the IPD under warm dense matter conditions.

The polarizational stopping power of an electron fluid is studied within the quantum random-phase approximation using the canonical solutions of the Hamburger moment problem for the loss function. The loss function is not an even function here of the frequency as in, for example, non-magnetized one-component plasma. Since the loss function is proportional to the inverse longitudinal dielectric function we can deduce that it is a response function possessing consequtive properties. The moments are calculated using RPA longitudinal dielectric function and the asymptotic expansion of the polarization functions. Polarization function is written in terms of generalized Laguerre polynomial, Landau energy level and Fermi-Dirac distribution. The chemical potential in the Fermi-Dirac distribution obtained from the normalization condition. The final expression for the stopping power contains only one integral of the square of the Bessel function of some integer order and only two summations, one of which is a finite sum.

In the development of special explosion-proof chambers that must meet strict requirements for strength reliability, an important issue is the choice of the material of the load-bearing shell subjected to pulsed (dynamic and shock-wave) loads. As a rule, these structures are made from industrial low-alloy steel pipes of various standard sizes. This always raises the question of choosing the steel grade, especially at the stage of design-basis justification of their explosion resistance, since the dynamic strength characteristics of the pipe material are generally unknown. This paper is the first to present the results of analysis of the static, dynamic, and shock-wave compressive and tensile strengths of 17G1S, 09G2S, 10G2FBYu, and K60 strength class pipe steels. In addition, comparative data are given on the explosion resistance of pipes of 09G2S and 10G2FBYu steels at a strain rate of (2-5)· 10^2 s ^-1 .

We present a theoretical study of two- and three-dimensional massless Dirac one-component plasmas embedded in a constant uniform magnetic field. We determine the wavefunctions and Landau energy levels of a massless Dirac fermion in a constant magnetic field. On this basis we consider magnetism of Fermi fluids of massless charged particles. We show that such a three-dimensional Dirac plasma consisting of fermions with the same helicity has its own magnetic moment. We also consider the limit of strong magnetic fields and investigate the De Haas–van Alphen effect. We derive the Kubo formula for the electrical conductivity tensor of massless Dirac plasmas and consider the Shubnikov–de Haas effect. In addition, we propose a model of the static conductivity tensor and employ the matrix version of the classical method of moments to derive a Drude-like formula for the dynamic conductivity tensor for massless Dirac plasmas. We find that the electrical conductivity tensor for Dirac fermions with the right helicity is not isotropic in the plane perpendicular to the magnetic field.

Dynamical properties of uniform electron fluids (jellium model) are studied within a novel non-perturbative approach consisting in the combination of the self-consistent version of the method of moments (SCMM) involving up to nine sum rules and other exact relations, the two-parameter Shannon information entropy maximization procedure, and the ab initio path integral Monte Carlo (PIMC) simulations of the imaginary-time intermediate scattering function. The explicit dependence of the electronic dynamic structure factor (DSF) on temperature and density is studied in a broad realm of variation of the dimensionless parameters ($2\leq r_s\leq 36$ and $1\leq \theta \leq 8$). When the coupling is strong ($r_s\geq 16$) we clearly observe a bi-modal structure of the excitation spectrum with a lower-energy mode possessing a well pronounced roton-like feature ($\theta \leq 2$) and an additional high-energy branch within the roton region which evolves into the strongly overdamped high-frequency shoulder when the coupling decreases ($r_s\leq 10$). We are not aware of any reconstruction of the DSF at these conditions with the effects of dynamical correlations, included here via the intermediate scattering and the dynamical Nevanlinna parameter functions. The standard static-local-field approach fails to reproduce this effect. The reliability of our method is confirmed by a detailed comparison with the recent ab initio dynamic-local-field approach by Dornheim et al. [Phys.Rev.Lett. 121, 255001 (2018)] available for high/moderate densities ($r_s\leq 10$). Moreover, within the SCMM we are able to construct the modes dispersion equation in a closed analytical form and find the decrements (lifetimes) of the quasiparticle excitations explicitly. The physical nature of the revealed modes is discussed. Mathematical details of the method are complemented in the Supplementary Material.

Experiments on shock-wave loading and spall fracture of tungsten alloys with nickel and iron have been carried out. The alloys have been shown to fracture along the iron–nickel bonding and not to involve tungsten particles. One-dimensional defects, supposedly of twin origin, have been detected in the tungsten alloy (95 wt

Collective processes in a quasi-classical electron gas are investigated within the framework of the interpolational self-consistent method of moments, which makes it possible to express the dispersion and decrement of plasma waves, and the dynamic structural factor of the system exclusively in terms of its static structural factor so that five sum rules are satisfied automatically. Different models are used of the static structure factor; the stability and robustness of the results of the moment approach taking into account the accuracy of these models is confirmed and tested by comparison to the alternative molecular dynamics simulation data.

The paper presents the simulation of the design of an optical amplifier on quantum dots, which includes the application of mathematical modeling for the gain recovery process of an optoelectronic device by changing and finding the optimal values of the characteristics and parameters of the active region of the device.

The self-consistent relaxation theory is employed to describe the collective ion dynamics in strongly coupled Yukawa classical one-component plasmas. The theory is applied to equilibrium states corresponding to intermediate screening regimes with appropriate values of the structure and coupling parameters. The information about the structure (the radial distribution function and the static structure factor) and the thermodynamics of the system are sufficient to describe collective dynamics over a wide range of spatial scales, namely, from the extended hydrodynamic to the microscopic dynamics scale. The main experimentally measurable characteristics of the equilibrium collective dynamics of ions-the spectrum of the dynamic structure factor, the dispersion parameters, the speed of sound, and the sound attenuation-are determined within the framework of the theory without using any adjustable parameters. The results demonstrate agreement with molecular dynamics simulations. Thus a direct realization is presented of the key idea of statistical mechanics: for the theoretical description of the collective particle dynamics in equilibrium fluids it is sufficient to know the interparticle interaction potential and the structural characteristics. Comparison with alternative or complementary theoretical approaches is provided.

We apply a novel 9-moment variational version of the self-consistent non-perturbative method of moments to study how the temperature affects the dynamic response of the electron gas in thermodynamic equilibrium. The theoretical results are obtained with the only input being the static structure factor. Comparison is carried out with the data obtained in the random-phase and the effective static local-field (ESA) (1) approximations. A quite satisfactory agreement is achieved with the system dynamic structure factor evaluated within the ESA interpolation scheme. We analyze the system properties for the temperature values (1 ≤ T / T F ≤ 4) chosen in the range where the electron gas starts to undergo a transition from the degenerate to classical behaviour. The extension of the method to a broader range of temperatures and densities is straightforward and is left for future studies. Nevertheless, we demonstrate a systematic way to investigate the gradual transition from degenerate to classical systems.

This paper presents calculations of electronic states in AlxGa1-x As semiconductor nanostructures and simulates the envelope wave functions of quantum energy levels in a one-dimensional quantum well with infinitely high walls of a given width at various values of x. For the analysis of results the authors choose the function wtmm from the Matlab library that fixes the extremums and which is a characteristic of the fractality of the envelope wave functions of quantum energy levels.

We show how the static dielectric function and other static characteristics of dense warm charged Fermi liquids can be obtained exclusively from the system static structure factor. The non-perturbative self-consistent method of moments is employed to extend onto quantum fluids, a similar reduction stemming from the fluctuation-dissipation theorem and other exact relations for classical one-component plasmas. The results are compared to and complement the numerical data obtained recently by the path-integral Monte Carlo method. Alternative theoretical approaches are discussed and employed as well.

New experimental data on the dynamic strength of the lead-antimony (2.77%) alloy comprised of different structures formed after thermal treatment in various regimes are presented in this work. The optimal alloy thermal treatment regime (quenching from 250°C) providing the best strength characteristics under explosion or high-speed impact is revealed.

The paper presents calculations of electron states in semiconductor nanostructures Al x Ga 1–x As ( x =0) and simulates the energy spectrum of the electron in a one-dimensional quantum well with infinitely high walls of a given width (from 10 to 30 atomic monolayers) using MATLAB application. The data is visualized using a wavelet transform with different wavelet functions.

В настоящее время желание клиентов получить более высокую скорость доступа и снизить стоимость услуг за- ставляет операторов постоянно развивать свои сети. Кроме того, операторы вынуждены увеличивать размеры сетей доступа, чтобы обслужить как можно больше домохозяйств, охватить весь город, район крупного города или его окрестности в радиусе до 60 км. Также остаются актуальными проблемы ограниченного количества сервисов сети, недостаточной зоны покрытия и слишком высокой стоимости услуг для среднего абонента. Довольно много сетей все еще используют наземную беспроводную связь для организации каналов внутри или между городскими кварталами, но есть и операторы, которые используют технологию FTTH (оптоволокно до дома). В статье сравниваются производительность, пропускная способность и максимальный размер действующих сетей доступа и перспективных сетей, использующих адаптивно-модулированное оптическое ортогональное частотное мультиплексирование (AMOOFDM). Также показаны преимущества системы AMOOFDM, в которой в качестве модулятора интенсивности применяется полупроводниковый оптический усилитель. Access networks are under constant development looking for customers satisfaction by enhancing the Internet service speed and the cost of the service. However, a significant percentage of these networks still using the terrestrial radio wave telecommunications to distribute the service inside or between city blocks, while others use the fiber to the home (FTTH). The article compares the performance of the currently operated access networks to the adaptively modulated optical orthogonal frequency multiplexing (AMOOFDM) based access networks, according to the bit-rate, and the distance reach of these networks. The advantages of the AMOOFDM system, in which a semiconductor optical amplifier (SOA) is used as an intensity modulator, are shown.

In this paper, we are going to exhibit the system performance using the single, double and three-electrode quantum-dot semiconductor optical amplifier as an intensity modulator (3E-QD-SOA-IM) of the adaptively modulated optical orthogonal frequency division multiplexing (AMOOFDM) signals in the intensity-modulation direct-detection passive optical network (IMDD-PON) systems. Moreover, to compare the bit-rate versus transmission distance of the proposed fiber link model when using both configurations multi-electrode semiconductor optical amplifier intensity-modulator (ME-SOA-IM) and multi-electrode quantum-dot semiconductor optical amplifier intensity-modulator (ME-QD-SOA-IM), to study the improvement of the transmission capacity, distance reach and power efficiency when applying the proposed configurations for optical access networks for distances ranging from 20 km up to 120 km. The three-electrode configuration solved the nonlinearity of the two-electrode configuration and offered a considerably wider range of optimum operating conditions to achieve up to 35 Gbps. Furthermore, the 3E-QD-SOA-IM showed a better performance over the 3E-SOA-IM over all the 120 km, and a 5 Gbps enhancement in the bitrate with a 20 dB less optical input power at 20 km.