Numerical analysis of the spiral Couette flow of a rarefied gas between coaxial cylinders

An implicit quasi-monotone second-order accurate method is proposed for analyzing the spiral Couette flow of a rarefied gas between coaxial cylinders. The basic advantages of the method over the conventional method of stationry iterations are that the former is conservative with respect to the collision integral, has a simple software implementation for any types of boundary conditions, and applies to a wide range of Knudsen numbers.     

Transport of charged particle pulses in interplanetary magnetic fields

The charged particle scattering in the presence of a regular magnetic field is considered starting from the Boltzmann kinetic equation in the case of an arbitrary relation between the mean free path and the distance from a particle source. It is shown that the Green function for the kinetic equation can be represented as the sum of the distribution functions of non-scattered particles which propagate with the injection pitch angle and of the scattered ones. The obtained Green function of the Boltzmann equation and also the particle density describe the space-time-pitch angle cosmic ray distribution that corresponds to an instantaneous particle injection at a particular pitch angle.This work was supported by International Science Foundation (grant N UC 8000) and by Slovak Grant Agency for Science (grant No. 1353/95).     

Cryogenic technologies for preparation of hydrocarbon products and helium from associated petroleum gases

Cryogenic technologies for combined extraction of commercial products, including helium, from associated petroleum gases with minimum energy costs and capital investments were described. The Geliimash Scientific and Production Association, Open Joint-Stock Company, undertakes the manufacture of the whole range of equipment for these technologies.     

Radiation damages under irradiation of the BCS superconductor MgB<Subscript>2</Subscript> by high-energy electrons

This paper reports on the results of investigations of the influence of irradiation of the two-band BCS superconductor MgB₂ by electrons with an average energy $ \bar {\rm E} $ \bar {\rm E} ∼ 10 MeV at high doses (0 ≤ ϕt ≤ ∼2.5 × 10¹⁸ cm⁻²) on the temperature and width of the transition to the superconducting state, the temperature dependence of the electrical resistivity in the normal state, the crystal lattice parameters, and the diffraction line intensity. An increase in the electron irradiation dose ϕt leads to the following effects: a decrease in the critical temperature T _c ; an increase in the width of the superconducting transition ΔT _c ; and a decrease in the “residual electrical resistivity” ρ_{273 K}/ρ_{40 K}, in the parameters a and c of the hexagonal crystal lattice, and in the ratio between the diffraction line intensities I ₁₁₀/I ₁₀₀. From analyzing the results obtained, it has been established that the main type of radiation damages under irradiation of the BCS superconductor MgB₂ by high-energy electrons is the formation of vacancies in the B sublattice, which leads to a narrowing of the large band gap Δ_σ on the Fermi surface.     

Generalization of the Krook kinetic relaxation equation

One of the most significant achievements in rarefied gas theory in the last 20 years is the Krook model for the Boltzmann equation [1]. The Krook model relaxation equation retains all the features of the Boltzmann equation which are associated with free molecular motion and describes approximately, in a mean-statistical fashion, the molecular collisions. The structure of the collisional term in the Krook formula is the simplest of all possible structures which reflect the nature of the phenomenon. Careful and thorough study of the model relaxation equation [2–4], and also solution of several problems for this equation, have aided in providing a deeper understanding of the processes in a rarefied gas. However, the quantitative results obtained from the Krook model equation, with the exception of certain rare cases, differ from the corresponding results based on the exact solution of the Boltzmann equation. At least one of the sources of error is obvious. It is that, in going over to a continuum, the relaxation equation yields a Prandtl number equal to unity, while the exact value for a monatomic gas is 2/3.In a comparatively recent study [5] Holway proposed the use of the maximal probability principle to obtain a model kinetic equation which would yield in going over to a continuum the expressions for the stress tensor and the thermal flux vector with the proper viscosity and thermal conductivity.In the following we propose a technique for constructing a sequence of model equations which provide the correct Prandtl number. The technique is based on an approximation of the Boltzmann equation for pseudo-Maxwellian molecules using the method suggested by the author previously in [6], For arbitrary molecules each approximating equation may be considered a model equation. A comparison is made of our results with those of [5].     

Room Temperature High-Field Spin Dynamics of NV Defects in Sintered Diamonds

Sintered oriented nanodiamond arrays with the extremely high concentrations of the nitrogen-vacancy (NV) centers (up to 10³ ppm) were investigated by the W-band (94 GHz) electron spin echo electron paramagnetic resonance techniques. The NV centers were fabricated by the high-pressure high-temperature sintering of detonation nanodiamonds (DND) without the post or prior irradiation of the samples. The processes of polarization and recovery of the equilibrium population of the spin sublevels by optical and microwave pulses have been examined at room temperature in high magnetic fields corresponding to the fine-structure transitions for the NV defects at 94 GHz (3,250–3,450 mT). A long spin coherence time of 1.6 μs and spin–lattice relaxation time of 1.7 ms were measured. The results were compared with those obtained on the NV centers fabricated by the irradiation and subsequent annealing of the commercially available bulk diamonds. It was shown that the relaxation characteristics of the NV defects were similar in the both types of the samples despite the extremely high concentrations of NV defects and isolated nitrogen donors in the sintered DND.