Influence of the deformation type and medium on the mechanodynamic penetration of nitrogen molecules into surface layers of armco iron

The extraction of nitrogen molecules from deformed samples of armco iron with different initial structures (annealed and subjected to equal-channel angular pressing) and different deformation prehistories (deformation in liquid nitrogen at 77 K, rolling in air at room temperature, and their combination) has been studied. It has been shown that the preliminary deformation in liquid nitrogen increases its concentration in the surface layer of the material and shifts the principal peak of its release toward low temperatures during heating. The results are associated with the existence of different types of nitrogen traps in annealed and nanostructured armco iron and with their changes during subsequent deformation.     

Characteristics of a wire preionized nitrogen laser with helium as buffer gas

The operation of a small N₂ laser using wire preionization and He as a buffer gas is discussed. The preionization is found to increase the output power and energy by 50% while the addition of helium can increase fourfold the output power.     

Effect of the gaseous medium in the process of rolling on the microhardness of aluminum and iron

The load dependence of the microhardness of polycrystalline aluminum and iron specimens produced by rolling in a nitrogen, helium, or air medium has been investigated. It has been found that nitrogen and helium have different effects on the microhardness of these metals in the low-load range. This difference is associated with the specific features in the intensity of dynamic penetration of nitrogen and helium into the surface layer of aluminum and iron, which depends on the initial defect crystal structure of the metals, as well as on the type of bonding of helium atoms and nitrogen molecules with metal atoms. It has been shown that the effect of the gaseous medium of the rolling on the microhardness manifests itself only in a very thin surface layer of metal specimens, where the microhardness exhibits a size effect, and an increase in the microhardness indentation depth remains unchanged with an increase in the load and does not depend on the gaseous medium of the prerolling of the specimens.     

Experimental study of the effect of helium/nitrogen concentration and initial droplet diameter on nonane droplet combustion with minimal convection

In this paper, we study the influence of inert concentration and initial droplet diameter on nonane (C₉H₂₀) droplet combustion in an environment that promotes spherical droplet flames. The oxygen concentration is fixed while the inert is varied between nitrogen and helium. A range of initial droplet diameters (D_o) are examined in each ambient gas: 0.4 mm < D_o < 0.8 mm; and an oxidizing ambiance consisting of 30% oxygen (fixed) and 70% inert (fixed), with the inert in turn composed of mixtures of nitrogen and helium in concentrations of 0, 25, 50, 75, and 100% N₂. The experiments are carried out at normal atmospheric pressure in a cold ambiance (room temperature) under low gravity to minimize the influence of convection and promote spherical droplet flames. For burning within a helium inert (0% N₂), the droplet flames are entirely blue and there is no influence of initial droplet diameter on the local burning rate (K). With increasing dilution by nitrogen, droplet flames show significant yellow luminosity indicating the presence of soot and the individual burning histories show K reducing with increasing D_o. The evolution of droplet diameter D(t) is nonlinear for a given D_o in the presence of either helium or nitrogen inerts indicating that soot formation has little to do with nonlinear burning. A correlation is presented of the data in the form where the effective burning rate, K′, and ε are concentration-dependent. Correlations for these parameters are presented in the paper.     

Dynamics of 2D electron wave packets with different initial spin polarization in 2D structures with spin-orbit coupling

The effect of splitting and zitterbewegung of 2D-electrons wave packets in the presence of Rashba spin-orbit coupling has been investigated. It is shown that nonstandard dynamics of wave packets occurs in the systems where the complete system of eigenfunctions is formed by states with different chirality. The time evolution of wave packets depends on the initial electron spin orientation. It is established that the oscillations of packet centers decay with time. Similar effects were studied by us previously for packets with initial spin orientation perpendicular to the 2D electron gas plane.     

Distribution of electric field in GaAs diffused structures doped by iron or chromium

An analysis based on numerical calculations has been done for the distribution of an electric field in GaAs diffused by chromium or iron-doped structures. First, a calculation has been carried out for the non-uniform impurity distribution using experimentally measured Fe and Cr profiles. It is shown that a ν-n-junction is formed in chromium-doped structures, and a π-n-junction is formed in iron-doped ones. A conclusion is made that these junctions are graded. V. D. Kuznetsov Siberian Physical-Technical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 43–48, March 1999.     

On the dynamics of a self-gravitating medium with random and non-random initial conditions

The dynamics of a 1D self-gravitating medium with initial density almost uniform is studied. Numerical experiments are performed with ordered and with Gaussian random initial conditions. The phase space portraits are shown to be qualitatively similar to shock waves, in particular with initial conditions of Brownian type. The PDF of the mass distribution is investigated.     

Atomic and electronic structures of a grain boundary in iron with impurity segregation

We present a short review on our current investigations of the atomic and electronic structures of a grain boundary in iron. Atomic structures of grain boundaries were simulated and the local electronic densities of states were calculated in the simulated structure. When phosphorus impurity atoms segregated at the grain boundaries in iron, trigonal prismatic FeP clusters were formed. Segregated boron atoms tended to stay at the central site of polyhedra constructed by host atoms in the grain boundaries. The non-bonding states of the iron atom at the grain boundary disappear by forming a strong bonding orbital with the orbital of the segregated impurity atom. This bonding orbital is formed in a Fe3d host band in the case of a boron impurity. On the other hand, the bonding orbital is formed at lower energies for the phosphorus impurity and is less-mixed with the Fe3d host band. Non-bonding states are formed around the Fe₉P clusters. These can give a qualitative explanation for the embrittlement of the impurity segregated grain boundary. Finally, we can explain from the viewpoint of the electronic structure why the interstitial impurity is the only cohesive enhancer.     

The analysis of nitrogen rotational and vibrational bands in a helium microhollow gas discharge

Emission spectroscopy is applied to measure the gas temperature T _g and the vibrational distribution of N₂ (C ³Π_u) and N₂ ⁺(B ²Σ_u ⁺) excited states from a helium microhollow gas discharge (MHGD) at atmospheric pressure. The rotational temperature T _rot of N₂ ⁺ is determined from relative intensity of the R‐branch lines of the N₂ ⁺(B ²Σ_u ⁺–X ²Σ_g ⁺) bands at 427.81 and 419.91 nm and the well‐known Boltzmann plot (BP). Using the same diagnostic technique, the rotationally resolved N₂(C ³Π_u–B ³Π_g) band at 380.49 nm is used to measure T _rot. Under our experimental conditions, T _g is equal to T _rot = 550–650 K for nitrogen molecules and shows a slight increase with the discharge current in the current range 3–10 mA. From the intensity ratio of two consecutive vibrational bands of the same sequence, the N₂(C ³Π_u) and N₂ ⁺(B ²Σ_u ⁺) vibrational temperature T _vib = 3,700–4,000 K is determined. It has been found that N₂ ⁺(B ²Σ_u ⁺) ions have non‐Boltzmann distribution in the helium MHGD, while N₂(C ³Π_u) molecules are populated according to the Boltzmann distribution. Following the Franck–Condon principle, the vibrational distribution of the ground state of N₂(X ¹Σ_g ⁺) molecules has been determined from the N₂(C ³Π_u) distribution using the inversion matrix of elements q _XC(ν ,ν ′).     

Phase composition of nanocrystalline iron films deposited in a nitrogen atmosphere

The phase composition of iron films prepared by pulsed-plasma deposition in a controlled nitrogen atmosphere is investigated by Mössbauer spectroscopy. The observed changes in the phase composition are dictated by the nanocrystalline structure of the samples and the dynamics of the substrate temperature during film deposition.     

Plasma-chemical processes with the participation of nitrogen in the active medium of a sealed-off CO laser

The influence of the addition of nitrogen to a He–CO mixture on plasma-chemical processes in a discharge under conditions characteristic of the active medium of a sealed-off CO laser was studied. It was found that the addition of nitrogen noticeably decreased the rate of CO dissociation and the concentrations of C atoms and C₂ and C₃O₂ molecules formed in a discharge in the course of plasma-chemical reactions.     

Investigation of the concentration gradient and extraction of helium atoms from copper deformed in a liquid-helium medium

A complex investigation of the penetration, accumulation, and extraction of helium atoms in porous copper samples deformed in a liquid-helium medium has been performed. The experiments have been carried out using three mass spectrometric techniques: (1) ionization of helium atoms by an electron impact in an MSCh-6 mass spectrometer, (2) secondary ion mass spectroscopy, and (3) an original high-resolution method with a sensitivity threshold of ∼10^{9 4}He atoms. The results obtained have made it possible to determine important characteristics of mechanodynamic diffusion of helium atoms, such as their penetration depth, the true concentration of helium trapped under deformation, and its gradient with an increase in the distance from the surface, as well as to estimate the binding energy of helium in traps.     

Dynamic stabilization of atomic ionization in a high-frequency laser field with different initial angular momenta

We investigated the ionization of an atom with different orbital angular momenta in a high-frequency laser field by solving the time-dependent Schrödinger equation. The results showed that the ionization stabilization features changed with the relative direction between the angular momentum of the initial state and the vector field of the laser pulse. The ionization mechanism of the atom irradiated by a high frequency was explained by calculating the transition matrix and evolution of the time-dependent wave packet. This study can provide comprehensive understanding to improve atomic nonadiabatic ionization.     

Hyperfine interactions of iron in ternary alloys with B82 type structures

The recoilless absorption spectra of iron in the ternary alloys CoFeGe, CoFeSb and FeMnGe, which possess B8₂ type structure, reveal the existence of different ordering temperatures of moments at 2(a) and 2(d) sites. Using the Einstein model to describe the second order Doppler shift, it has been found thatΘ _E appropriate to the thermal motions of iron atoms at 2(a) and 2(d) sites in CoFeGe are different, which is also suggested by the temperature dependences of the relative areas of the corresponding component spectra. In CoFeSb, on the other hand, relative areas of the component spectra are independent of temperature, and give the relative distribution of iron at the inequivalent sites. A large difference in the isomer shifts of 2(a) and 2(d) site spectra indicates a larger number of d-electrons in the atomi configuration for 2(a) atoms. The isomer shift change is negative for 2(a) site nuclei and positive for 2(d) site nuclei with increase in temperature. The magnetic fields at 2(d) site nuclei in CoFeGe and CoFeSb alloys indicate that the moments of the parent atoms are not much different from the value in iron metal.     

Motion of a helium atom in a quartz crystal with dislocations

The motion of a helium atom through the quartz crystal structure disturbed by dislocations has been considered. Two cases of their action on the motion of the helium atom have been discussed. (1) Dislocations, in particular, screw dislocations, can be represented as contracted or extended helical (six-, four-, three-membered) channels consisting of SiO₄ tetrahedra. In this case, the helium atom moves inside the dislocation as in the crystallographic channel with changed parameters. (2) Dislocations can cross the crystallographic channel. This leads to an excess or a deficit of oxygen atoms of SiO₄ tetrahedra in the immediate environment of the helium atom located in the channel. In both cases, the displacement of the helium atom appears as a Frenkel-Kontorova soliton. However, in the latter case, the dependence of the activation energy of this soliton on the number of defects is discontinuous and exhibits a “mobility gap” of the helium atom.     

Novel considerations of functions of helium and nitrogen in a fast flow CO2 laser

In a research of fast axial flow CO₂ laser sustained by 150 kHz silent discharge, we found the optimized gas mixing ratio was CO₂:N₂:He=1:22:5 or the content of helium was only about 18%. This result upset the situation of common CO₂ lasers in which the most important laser gas is helium. An explanation of our particular results and supporting experimental evidence are given.     

Self-preservation of large-scale structures in a nonlinear viscous medium described by the Burgers equation

We use the asymptotic solution of the one-dimensional Burgers equation to study the self-preservation of large-scale random structures. We show that in the process of their evolution, large-scale structures remain stable against small-scale perturbations for the case of a continuous initial spectrum with a spectral index smaller than unity. We study both analytically and numerically the correlation coefficient of a large-scale structure and of the same structure with a high-frequency perturbation and show that with the passage of time the coefficient tends to unity. Using the asymptotic formulas of the theory of random excursion of stochastic processes, we study the statistical properties of the perturbing field and find that the effect of high-frequency perturbations is equivalent to the introduction of effective viscosity. Zh. éksp. Teor. Fiz. 115, 564–583 (February 1999)     

Generation of runaway electron subnanosecond pulses in nitrogen and helium at a voltage of 25 kV across the gap

The formation of a runaway electron beam in helium and nitrogen at a generator voltage of 25 kV is studied experimentally. At low generator voltages, an ultrashort avalanche electron beam (UAEB) is shown to form at the flat top of the voltage pulse and its delay time relative to the leading edge of the pulse may attain several tens of nanoseconds. The conditions of runaway electron beam generation depend on the pressure in the gas-filled diode. The FWHM of the beam current varies from 200 ps to several nanoseconds. Beam electron energy distributions at different pressures are obtained. It is found that, if the gap is preionized by an additional source, the UAEB generation conditions break.