Specific features of the formation of phase states in a non-Heisenberg magnet with S = 2

Spin states of a non-Heisenberg magnet with a magnetic ion spin of 2 have been determined. It has been shown that the inclusion of the higher-order spin invariants leads to realization of specific phases with the tensor order parameters whose realization is impossible in magnets with S = 1. The free energy of the system in different spin states has been studied. The geometric images of the tensor phases in the spin space have been determined.     

Scattering of sound by an elastic spherical shell immersed in a waveguide with a fluid bottom

The paper is devoted to modeling an acoustic field scattered by an elastic spherical shell. The shell is immersed in a waveguide with a fluid attenuating bottom. Modal analysis is applied to calculations of both the point source field in a free waveguide and the scattering coefficients of the shell. The occurring integrals along a branch cut are expressed via the probability integral. Cases are analyzed when the source frequency differs from the critical frequencies of normal waves and when it coincides with one of them. The method is applied to estimate the effect of the field scattered by a thin elastic shell filled with air with transmission loss of the total acoustic field with distance and its depth distribution.     

Scaling Up of Non-Thermal Gliding Arc Plasma Systems for Industrial Applications

Plasma Chemistry and Plasma Processing - Scaling up of transitional “warm” plasmas to industrial level gives possibility to develop plasma systems that combine advantages of thermal and...     

Ionic mobility and attenuation of ultrasound in doped cerium trifluoride crystals

Dielectric properties of CeF₃ crystals doped by aluminum, erbium, and holmium were studied in the temperature range of 290–450 K and frequency range of 25 Hz-1 MHz. Cole-Cole diagrams are constructed. An equivalent circuit consisting of a resistance, capacitance and CPE element is suggested for interpretation of the obtained results. Ionic movement parameters are determined as dependent on the temperature. An acoustooptic method was used to measure ultrasound attenuation in the frequency range of 200–800 MHz.     

Kinetics of ultrafine coating of SiO2 nanoparticles, suspended in non-thermal CH4/C2H6 plasma

Capacitively coupled RF discharges in methane and ethane (1000–3000 Pa, 5–15 W/cm³) were used for the in-flight coating of SiO₂ nanopowders (NP) with an a-C:H layer [A. Kouprine, F. Gitzhofer, M. Boulos, A. Fridman, Polymer-like C:H thin film coating of nanopowders in capacitively coupled RF discharge, Plasma Chemistry and Plasma Processing 24 (2) (2004) 189–215]. In this present work a model of the chemical kinetics of this plasma processing has been developed, based on the GRI-Mech 3.0 mechanism [G.P. Smith, D.M. Golden, M. Frenklach, Gas Research Institute, Detailed chemical reaction mechanism. Available from: ], and calculations are performed, using the Chemkin-II code. The model includes the formation of two solid phases: an amorphous C:H coating, deposited on the suspended NP, and soot, incepted in the gas phase. Non-equilibrium plasma effects are taken into account by the rates of radical species’ production, using the reference data on the “G-value”. The CH₃ and H species appear to have key roles in surface activation and the nanofilm growth. The results demonstrate the competitive character of the formation of the two solid phases: the C:H coating is dominant under T_gas < 1400–1600 K, depending on the conditions, and soot commencing to dominate at higher temperatures. This division corresponds to the passage from non-thermal plasma conditions, with the dominance of single-valent radicals and solid phase growth on the substrate only, to the plasma thermalisation with the formation of two-valent radicals and v. inception of the solid phase. The results are validated experimentally by the observation of soot formation as a function of the gas temperature, by the mass spectrograph data on the gas composition after plasma reforming, and by the reference data on coating growth rates and induction times for soot formation.     

Theory of gravitational stability of a rotating cylinder

The stability of a rotating dust cylinder against perturbations located in the plane perpendicular to the axis of rotation is investigated. It is shown that a homogeneous rotating cylinder containing a weak inhomogeneity is stable against such perturbations. A weakly inhomogeneous cylinder with opposite streams of equal density is unstable for thel=2 mode in the case of a perturbation of the form_ei(l–t), when the density increases radially. The instability of a system consisting of a homogeneous rotating dust cylinder in a hot homogeneous medium is determined. It is shown that the maximum growth rate corresponds tol = 2 when the density of a cold cylinder is not negligible in comparison with the density of the medium. In the opposite case, the maximum growth rate shifts toward l=3. An attempt is made to associate the existence of the maximum growth rate for l=2 with the presence of two spiral arms in most galaxies. It is shown that, when the longitudinal temperature is high enough, a rotating cylinder which is bounded in the radial direction is stable against arbitrary perturbations.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, Vol.10, No. 3, pp. 3–11, May–June, 1969.     

High-order sliding-mode observation for linear systems with unknown inputs

A high-order sliding-mode observer is designed for linear systems with unknown inputs. The concepts of strong observability and strong detectability are studied and their relation with the relative degree of a plant is established. High-order sliding-mode-based observers for linear time-invariant systems with unknown inputs satisfying the condition of strong observability or strong detectability are developed.     

Principal modes in fiber amplifiers

The dynamics of the state of polarization in multimode fiber amplifiers is presented. The experimental results reveal that although the state of polarizations at the output can vary over a large range when changing the temperatures of the fiber amplifiers, the variations are significantly reduced when resorting to the principal states of polarization in single-mode fiber amplifiers and principal modes in multimode fiber amplifiers.     

Polymer-Like C:H Thin Film Coating of Nanopowders in Capacitively Coupled RF Discharge

Nanopowders of amorphous SiO₂, with typical particle sizes of 30–80 nm, were treated under the non-equilibrium plasma conditions, created by a capacitively coupled (CC) RF discharge formed in pure methane or ethane. The plasma gas flow rate varied between 0.02 and 0.06 slpm, with reactor pressures between 1000 and 5000 Pa, and applied RF power inputs between 700 and 1500 W. The plasma properties were monitored through measurements of the rotational temperature, as derived from the C₂ 5160 Å Swan band and N₂ second positive 3577 Å band, and the atomic hydrogen excitation temperature, from the H_β H_γ and H_δ lines during the powder treatment process. The compositions of the gases that passed through the plasma were analyzed by mass spectrometry. In spite of the evidence for the presence of C_nH_2n+2 and C_nH_2n (n=1–3) species and acetylene in the discharge, the homogeneous formation of soot was not observed. At the same time, the introduced nanoparticles were observed to act as centers for the inception and growth of C:H thin coatings in the form of a polymer-like hydrocarbon layers, of thickness between <5 and 30 nm. The results of TEM, IR spectroscopy, thermo-gravimetric and precision calorimetric analysis performed on the treated powders provide evidence to the formation of an amorphous, high density C:H matrix on the particles' surfaces.