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The mathematical formulation of electron beam melting and liquid metal transfer model in wire-based additive manufacturing with temperature dependencies of thermophysical properties is described. A description of the model algorithmic implementation based on the use of numerical methods for solving the Navier-Stokes equations system and the Volume of Fluid (VOF) method for tracking the free surface of a liquid on the cubic mesh cells is given. An iterative method for calculating the pressure field that ensures the fulfillment of the incompressibility condition for a viscous fluid is described. The paper also paid attention to the description of methodology for calculating the forces acting on the free surface of the melt, including surface tension forces and metal vapor pressure forces. One of the key elements of the proposed model is method for volumetric distribution of electron losses calculating, considering their scattering during the interaction of an electron beam with a curved melt surface. Electron beam focusing influence on the distribution of energy losses and the dynamics of penetration channel formation has been studied. An algorithm for visualizing the free surface of the melt based on the use of the Gaussian function, is described.

The effect of temperature profile of the water layer surface on the formation and structure of a levitating droplet cluster is studied in the paper. The laboratory experiments indicate that a local temperature maximum of water is a necessary condition for the formation of a cluster. A quantitative criterium of transformation of a monolayer of randomly positioned microdroplets to a self-assembled cluster of relatively large droplets is obtained.

The possibility of improving the mechanization of strengthening the near-contour mass of stope is considered. Variants of improving the supply of injection solution into the mass are proposed, various technological schemes for supplying the injection solution into the near-contour mass are considered, and an optimal injection scheme is proposed. A classification of injection solutions is made in terms of the possibility of their use in rocks of different stability and injection technology.

We consider an X-ray optical system which permits obtaining laser plume images at a wavelength of 13.5 nm with a resolution of up to 70 nm. The X-ray optical system comprises an X-ray Schwarzschild objective made up of two aspherical multilayer mirrors, a scintillator (YAG : Ce ceramics), which converts X-rays to the visible radiation, and a visible-optical system, which images the scintillator surface onto a CCD camera. The spatial resolution of the system is limited by the resolution of the optical system (0.7 μm) and the magnification (10×) of the X-ray objective and is as high as 70 nm. The effect of Schwarzschild objective mirror shapes on the spatial resolution is analysed. The profile of concave mirror aspherisation is considered, which provides the attainment of the diffraction-limited quality of the objective. Data are given for the quantum efficiency of the system at a wavelength of 13.5 nm. We describe the experimental test bench intended for studying the developed X-ray optical system and outline the first experimental data which illustrate its efficiency. Owing to the natural division into the 'X-ray' and 'visible' parts, the optical system under discussion permits an easy change of the magnification and the field of view without realigning the X-ray optical elements. The wavelength may be varied in a range between 3 and 40 nm by changing the multilayer mirrors.

In this work, the behavior of cathodes made from pure tungsten and pure hafnium in the direct current electric arc at 200 A and in atmospheric pressured argon medium was investigated. The research was focused on the processes happening with the cathodes during the arc initiation phase (first 100 ms after the power input). The processes of rapid cathode destruction were registered, and can be characterized as the destruction of the cathode in liquid phase due to electro-magnetic forces. Characteristic times of the whole process were recorded, as well as the changes in temperature fields on the cathodes surfaces and the rate of mass loss for both types of cathodes. It has been shown that the initial destruction of the cathode plays a major role in the cathodes resource life.

With the aim of studying nitrogen plasma flow impacting graphite surfaces, we investigated the evolution of a plasma jet moving from the nozzle of the plasma torch to the target. The motion is accompanied by a decrease in temperature from 10 to 7 kK with a loss of ≈ 60% of the deposited energy and an increase in the density of carbon-containing impurities with partial preservation of the local thermodynamic equilibrium. The main reactions are thermal processes of the formation and decomposition of molecules, dissociative recombination and recharging of nitrogen ions. In the presence of carbon impurities, this set is supplemented with the substitution reaction C + N2 ↔ CN + N, electron-collision processes of stepwise ionization and recombination, and a whole ion-molecular cascades of reloads and substitutions. It has been established that a small admixture of carbon (∼ 0.1%) manifests itself only in ion-molecular kinetics, increasing the electron concentration, determining the ionic composition of the plasma, and thereby violating the equilibrium between its neutral and charged components. This leads, in particular, to the recombination nonequilibrium distribution of carbon atoms over electronic states. Other carbon-containing impurities (CN and C2) are not significant.

Molten pool free surface shape calculation and its evaluation in time for analysis of electron beam melting and welding processes is a very important problem. Unfortunately, experimental methods can provide only a part of the necessary information. Electron beam heating creates the conditions for intense metal transfer, and pool surface shape affects the energy absorption efficiency. This paper reports the method which combines the Monte-Carlo simulation for spatial and energy parameters of heating source calculating with the Volume of Fluid algorithm for liquid free-surface numerical evaluation. The velocity and pressure field technique calculation in a molten pool with the action of surface tension forces and vapor recoil pressure is described. It is shown that the proposed simulation method allows to study heat and mass transfer transient processes, including deep penetration channel formation. Model validation was carried out. Simulation results are shown to be consistent with experimental data obtained using a high-speed camera.

The urgency of improving control systems for electron beam metal wire deposition method is proved in terms of creating methods for controlling the geometric parameters of deposited layer. It is shown that to solve this problem in electron beam metal wire deposition method, it is advisable to use reflected electron signal detection when scanning the deposited layer. Using a mathematical model based on the application of continuous loss approximation and Monte-Carlo method, the probe characteristics recorded during cylindrical layer scanning are investigated. Experimental verification of the results obtained was carried out using an electron-beam technological installation. The effect of the distance between the layer and electron collector on the recorded signals is investigated. The possibility of using this method for simultaneous control of deposited layer height and width is shown.

The current epidemiological situation in the world forces the pedagogical community to switch to the use of various forms of education using distance educational technologies. One of the most difficult problems of organizing distance learning is the problem of various forms of monitoring students knowledge. The most promising area for assessing the quality of knowledge is computer testing. Based on many years of experience in the development of computer test tasks, the basic requirements for computer test tasks and for computer tests are formulated, which make it possible to increase the efficiency of their use to control students knowledge. Examples of the correct representation of answer options in tasks with a choice of answer options (in closed test tasks) are given and ways to reduce the probability of guessing the correct answer are considered. With regard to the course "General and Inorganic Chemistry", the features of the use of various forms of test tasks are analyzed using specific examples. For the organization of computer testing of first-year bachelor degree students in the course "General and Inorganic Chemistry" the Moodle system was chosen. This system has various functions for creating tests, as well as for conducting training and control testing. For the convenience of entering test tasks into the Moodle system, these tasks must be converted into GIFT format. After that, GIFT tasks are easily imported into Moodle. Examples of different forms of test items in WORD and GIFT formats are given. The Moodle distance learning system (platform) has introduced a bank of tests for the course "General and Inorganic Chemistry", which is taught to first-year bachelor degree students of the Mendeleev University of Chemical Technology of Russia. The features of using this platform for organizing computer testing when using distance and blended forms of education are shown.

One of the most actual problems during electron beam welding of metal materials is the determination of the laws of primary electrons interaction with a gas (vapor) flow, taking into account existing and generated (by charged particles) electric fields. The paper is devoted to the development of computer simulation method for the process of electron beam passage through a layer of evaporated metal. The analysis of simulation results showed a significant effect of ionization process on electric field in a gas-vapor channel. It was established that at the initial stage of the process, a region with a positive potential is formed in the lower part of gas-vapor channel, and in its upper part, on the contrary, potential decreases.

The paper is devoted to the definition of the minimum electron beam power that is required to obtain stable layer formations during the additive electron beam wire deposition. Correlation between the minimum energy that is needed for stable deposition and the deposition speed has been established. Additionally, the influence of the electron beam oscillation type on geometrical parameters of single layers have been investigated.

The results of a complex study of the destructive effect of a nitrogen plasma jet at atmospheric pressure onto the surface of the MPG-6 graphite are presented. The space-time changes in the rate of decrease in the samples material, the temperature of their surface, the electron temperature of plasma in the oncoming flow and the plasma composition in the region of 'injection' were all experimentally determined. Using spectroscopic methods with high spatial (50 μm) and time (0.5 s) resolutions changes in the concentration of emitting carbon atoms (line CI 247.9 nm) and CN (transition B2Σ+ − X2Σ+) near the surface of isotropic graphite were recorded, which occur in the process of intense and long (100–150 s) exposure of graphite to a nitrogen plasma jet. The change in the vibrational and rotational temperatures of the radical CN and the molecular ion in the near-surface region of the plasma is determined by the method of 2D matrix spectroscopy. An analysis of the relative populations of the excited NI states in the interaction region at the quasistationary stage of sample heating revealed spatial-temporal changes in the electron temperature in the near-surface plasma, indicating an increase in its enthalpy caused by the rapid exothermic CN + N → C + N2 substitution process, which leads to a decrease in the heat flow acting on sample. The analytical solution of the problem of temperature change in a relaxing nitrogen plasma jet in the absence of graphite confirmed the experimentally observed slow cooling of it, caused by a number of exothermic recombination processes taking place in the plasma.

The nonlinear-optical properties of heterogeneous liquid nanophase composites based on high-energy-gap Al2O3 nanoparticles are studied experimentally. The factors determining the nonlinear-optical properties of composites and their strong dependence on the matrix material are analysed and physical mechanisms are proposed to explain the results obtained.

We have carried out cross-correlated high-resolved electrodynamical and spectro-optical measurements of different characterizations in a high-stable regime of the dc positive streamer corona in short gap in atmospheric density laboratory air. Special attention was paid to the measurement of absolute intensities of the second positive (SPS) and first negative (FNS) systems of molecular nitrogen as well as for further improvement in the spatiotemporal resolution along with high synchronization and stability. In the cathode region, the FNS and SPS emission temporal waveforms during primary streamer development have been recorded with the cross-correlated synchronization not worse than 0.1 ns and spatiotemporal resolution around 0.01–0.1 mm along the axis and 0.2–0.4 ns in the multiphoton mode of the PMT-based detector and in the single pulse acquisition mode of the measuring system. The shortest rise-times of the corresponding voltage waveforms were found to be around 0.3–0.4 ns for the SPS (0,0)-band and 0.2–0.3 ns for the FNS (0,0)-band, the full widths at the half-altitude ranging around 1.4–1.5 ns and 0.5–0.6 ns, respectively. Again, the absolute values and the ratio of the synchronized temporal waveforms of the SPS to the FNS (0,0)-bands have been recorded across the entire gap in the accumulation and averaging acquisition mode of the measuring system with somewhat worse temporal resolution but with adequate stability and stochasticity. Various supporting characteristics such as the synchronous anode and cathode electric current waveforms, the streamer velocity and the gas temperature within the streamer channel region have been measured and presented as well. All the data in the aggregate allow reconstruction of the 2D structure of the streamer head generally and of the electric field and the electron number density partially.

In this second of two papers, we have developed a fully self-consistent method of diagnostics of streamer discharge plasmas based on the analysis of absolute intensities of the second positive (SPS) and first negative (FNS) systems of molecular nitrogen. The theory of the method combines a spectroscopic technique for the calculation of temporal waveforms of the nitrogen absolute SPS and FNS (0, 0)-band emission and a self-consistent semi-analytical parametric axially symmetric 1.5D model of the filamentary streamer head. The spectroscopic technique takes into account characterizations of all units of the measuring spectro-optical channel, including spatiotemporal resolution and resolution in wavelength. Also, chromatic aberrations of the focusing lighting lens, errors in the adjustment of the object image onto the input slit as well as the correction of the slit function at the non-uniformly illuminated input slit of the monochromator on width are taken into account. The model of the streamer head is characterized by some trial-consistent allowable parametric on-axis profile of the electric field combined with the electron and total space charge number density profiles fully self-consistent with each other and with the trial electric field. Additionally, the corresponding 2D configuration for the field and the electron number density is constructed via special ellipse-like geodesic lines. The absolute values and the synchronous ratio of the 1L spatially and time-resolved cross-correlated temporal waveforms of the SPS to the FNS (0, 0)-bands, the ratio of their altitudes and the total emission power for both the waveforms measured in paper I have been taken into account to reconstruct the 2D structure of the streamer head. With a procedure fitting the directly computed output voltage waveforms to the experimental ones, the peak values of the electric field and the electron number density within the streamer head at mid-gap distances have been found to be 430?500?Td and (2?3) ? 1014?cm?3, respectively. And the corresponding absolute electric field is thus 70?80?kV?cm?1 at the initial gas temperature within the repetitive streamer region of 450?K.

Fabrication and experimental demonstration of photonic-crystal fibers (PCFs) made of TF10 glass are reported. These fibers integrate a high material nonlinearity with dispersion and field-confinement nanomanagement. A specifically designed array of nanoholes in the fiber core is shown to provide the desired dispersion and nonlinearity properties of PCF modes, allowing efficient frequency upconversion of Cr:forsterite laser pulses through solitonic and four-wave mixing mechanisms.

Periodic arrays of air holes with diameters ranging from about 80 nm up to 400 nm are shown to modify intensity profiles of guided modes in photonic-crystal fibers, suggesting new ways of fiber dispersion engineering and modal birefringence control. Guided modes supported by such fibers provide a high efficiency of anti-Stokes frequency conversion for 100-fs pulses of a Cr: forsterite laser.

Changes in the envelope and the evolution of the spectral phase and chirp of femtosecond pulses propagating through hollow fibres with a photonic-crystal cladding are experimentally studied. Envelope and phase distortions of ultrashort pulses transmitted through such fibres are shown to be controlled by the detuning of the carrier frequency of laser pulses from the central frequency of the passband in the transmission of the fibre. Near the passband edges, which map the edges of photonic band gaps of the fibre cladding, ultrashort pulses transmitted through the fibre display considerable envelope distortions, as well as frequency- and time-dependent phase shifts.

Sequences of picosecond pulses with a total energy in the pulse train of about 1 mJ are transmitted through a hollow-core photonic-crystal fibre with a core diameter of approximately 14 µm. The fluence of laser radiation coupled into the core of the fibre under these conditions exceeds the breakdown threshold of fused silica by nearly an order of magnitude. The laser beam coming out of the fibre is then focused to produce a breakdown on a solid surface. Parameters of laser radiation were chosen in such a way as to avoid effects related to the excitation of higher order waveguide modes and ionization of the gas filling the fibre in order to provide the possibility to focus the output beam into a spot with a minimum diameter, thus ensuring the maximum spatial resolution and the maximum power density in the focal spot.

Glass fibres with a hollow core and a two-dimensionally periodic cladding are studied experimentally and theoretically. The spectrum of modes guided in the hollow core of these fibres displays isolated maxima, indicating that waveguiding is supported due to the high reflectivity of the fibre cladding within photonic band gaps. The main properties of the spectrum of modes guided in a hollow core of a photonic-crystal fibre and radiation intensity distribution in these modes are qualitatively explained in terms of the model of a periodic coaxial waveguide.

A comparative analysis of the results of experimental investigation of mechanical behavior of the rubber sample during biaxial compression testing and numerical simulation results obtained by the finite element method was carried out to determine the correctness of the model applied in the engineering calculations of elastic structural elements made of the rubber. The governing equation represents the five-parameter Mooney-Rivlin model with the constants determined from experimental data. The investigation results showed that these constants reliably describe the mechanical behavior of the material under consideration. The divergence of experimental and numerical results does not exceed 15%.

We report fabrication and characterization of hollow photonic-crystal fibers (PCFs) with a diamond-shaped core and a Kagome-lattice cladding. Air-guides modes strongly confined to the hollow core of the fiber are shown to exist within the ranges of wavelengths from 450 to 560 nm and from 470 to 630 nm for two hollow diamond-shaped-core PCFs with slightly different geometry parameters. Polarization-maintaining air-mode guidance of 100-fs second-harmonic pulses of 625-nm Cr:forsterite laser radiation is demonstrated.

We demonstrate hollow-core photonic-crystal fibers (PCFs) with a core diameter of 45 μm and a period of the photonic-crystal cladding of 7 μm. These fibers are shown to allow a waveguide delivery of 4-mJ 15-ns pulses of 1.06-μm radiation of a Q-switched Nd: YAG laser. Hollow PCFs reported in this work help to bridge the gap between standard, solid-cladding hollow fibers and hollow PCFs in terms of effective guided-mode areas, offering attractive solutions for high-field physics, laser technologies, and ultrafast photonics.

An equilibrium problem for a two-dimensional homogeneous linear elastic body containing a thin elastic inclusion and an interfacial crack is considered. The thin inclusion is modeled within the framework of Euler-Bernoulli beam theory. An explicit formula for the first derivative of the energy functional with respect to the crack perturbation along the interface is presented. It is shown that the formulas for the derivative associated with translation and self-similar expansion of the crack are represented as path-independent integrals along smooth contour surrounding one or both crack tips. These path-independent integrals consist of regular and singular terms and are analogs of the well-known Eshelby-Cherepanov-Rice J-integral and Knowles-Sternberg M-integral.

The semiconductor laser gyro is described, in which the optical frequency dithering implemented by intracavity phase modulation suppresses the frequency lock-in and provides the interference of multimode radiation. The sensitivity of the device amounted to 10–20 deg h{sup -1}. (laser gyroscopes)