Electrodynamics of a low-pressure electrode microwave discharge

Results are given of self-consistent two-dimensional simulation of self-sustained steady electrode microwave discharge in a chamber at the end of central conductor of a coaxial line. The discharge parameters are calculated in the diffusion mode in hydrogen at pressures of 0.5, 2, and 8 torr and incident power of 30–200 W. The dependence of matching between the discharge chamber and delivery path on the geometric dimensions of the chamber is investigated in the presence of plasma. It is demonstrated that the length of central electrode is the key factor affecting the structure of plasma formation and its matching with the pumping wave. The maxima and minima of matching alternate when the central electrode is elongated by quarter wave. The maxima and minima of matching for the case of low pressure (< 2 torr) are shifted by λ/4 relative to those for high pressure (> 2 torr). The problem of maximal energy input to the discharge region at the end of antenna-type electrode is analyzed. It is demonstrated that a restriction exists on the maximal energy input to such a discharge (and, accordingly, on the size of plasma formation). These restrictions are associated either with the runaway of discharge toward the generator or with the ignition of discharge in the region of entry of antenna into the chamber.     

Physical characterization of polyurethanes reinforced with the in situ-generated silica-polyphosphate nano-phase

A series (SPUN) of segmented polyurethanes reinforced with the in situ-generated sodium silica-polyphosphate nano-phase (SSP) was characterized by thermogravimetry, differential calorimetry, wide-angle and small-angle X-ray diffraction and stress–strain relationships.

Cross-over from the rubber-like to the solid-like mechanical behavior of the SPUN above the apparent percolation threshold w ≈ 40% was considered as evidence for the onset of the “infinite clusters” of SSP nano-domains spanning the entire volumes of initial (i.e., undeformed) samples. The infinite clusters of SSP nano-domains crossed over from the mass fractal-like to the surface fractal-like behavior at the composition-dependent, characteristic X-ray scattering vectors q*. A continuous nano-phase of the polyurethane coexisting with a continuous nano-phase (infinite cluster) of the SSP is likely to be expanded due to the “negative pressure” effect.     

Multichannel Strain-Gauging System Equipped with Microprocessor for Strength Measurements of Structures

The structure of a 64-channel microprocessor strain-measuring system designed for operation with strain gauges and thermal transducers is discussed. The system measures strain and temperature during strength and thermal-strength tests of structures of machines and buildings. The computer codes have been designed in the Borland C++ Builder medium for operations with isolated transducers (1/4-bridge mode), and in the modes 1/2-bridge, bridge, and thermal transducer. The system has been certified. The paper describes examples of its practical utilization in strength tests of struts of the Tupolev-154B airliner and of the undercarriage foreleg of an aerobatic airplane.     

Heterodyne quasi-elastic light-scattering instrument for biomedical diagnostics

The heterodyne technique has a number of advantages over the homodyne technique when an accurate characterization of particle-size distribution (PSD) of heterogeneous systems is required. However, there are problems related to acoustic vibrations that make it difficult to take advantage of the heterodyne technique. An instrument developed for quasi-elastic light scattering (QELS) that uses the optical heterodyning principle is described. Vibration-related problems are considerably reduced because of the incorporation of all optical elements into one solid optical block. A real-time correlation analysis of the photocurrent fluctuations is performed by a PC-embedded analog-to-digital converter card with a digital signal processor. Investigation of the PSD in biological fluids for medical diagnostics is presented as a typical application. A diagnostic analysis of the PSD requires a simultaneous processing of a huge number of QELS data. An original statistical algorithm to accomplish this analysis has been developed. Technical specifications of instrumentation for heterodyne QELS measurement are discussed.     

Evolution of geodesic acoustic mode in ohmic H-mode in TUMAN-3M tokamak

The behavior of a geodesic acoustic mode (GAM) in the TUMAN-3M tokamak has been experimentally studied using the heavy-ion beam probing technique. Oscillations of the electric potential under the action of a GAM localized at the plasma periphery have been detected. The GAM was observed in the regime of low confinement (L-mode) with low plasma density (??0.8 × 10¹⁹ m^?3) and disappeared upon the transition to a high confinement regime (H-mode). The possible role of GAM as a precursor of the improved confinement (LH-transition) is discussed.     

Structure and transport properties of nanocarbon films prepared by sublimation on a 6H-SiC surface

The transport properties of nanocarbon layers on a 6H-SiC substrate, grown by vacuum sublimation, are studied. It is found that these layers consist of a graphene layer adjacent to the substrate and a multigraphene layer coated with a polycrystalline carbine-like phase. In this case, the magnetoresistance and Shubnikov-de-Haas oscillation curves exhibit features inherent to single-layer graphene. The resistance at low temperatures is demonstrated to increase with temperature, which also corresponds to the behavior of single-layer graphene (antilocalization). At the same time, the resistance decreased with temperature at higher temperatures, which corresponds to weak localization. We believe that the observed behavior can be explained by the parallel combination of contributions of single-layer graphene and multigraphene to the conductance.     

Comparative study of 3C-SiC layers sublimation-grown on a 6H-SiC substrate

n-3C-SiC/n-6H-SiC heterostructures grown by vacuum sublimation on CREE commercial 6H-SiC substrates are studied. Transmission electron microscopy (TEM) demonstrated that a transitional layer of varying thickness, composed of a mixture of 3C- and 6H-SiC polytypes, is formed on the substrate. A 3C polytype layer was obtained on the interlayer. Cathodoluminescence study of the surface of the film demonstrated that defects in the form of inclusions of another phase (6H-polytype), stacking faults, and twin boundaries (separating domains of cubic modification, grown in various orientations) are found on the surface and in the surface layer with a thickness on the order of 100 μm. Varying the growth conditions changes the concentration of various types of defects.     

Effect of preparation conditions on nanostructural features of the NAFION® type perfluorinated proton conducting membranes

Features of the fine structure of three samples of perfluorinated Nafion® type membranes—Nafion-115, its Russian analogue MF-4SK, and a new similar material PFM-E produced according to our novel water-emulsion technique—have been characterized using the small-angle neutron scattering technique. A difference in the regularity of common elements of fine structure (cylindrical channels) in the membranes has been revealed. Nafion-115 has the most regular structure with a diffraction peak corresponding to the double channel diameter and an additional broad maximum in the scattering curve indicating a long-range order in the arrangement of straight cylindrical channels. For MF-4SK, in addition, twisted and less ordered channels have been observed. In the PFM-E sample channels have a tortuous and branched structure with diameters similar to Nafion-115. Only a short-range order (40–50 Å) in the arrangement of the channels has been detected, and correlation in their mutual orientation at longer distances is weakened. It has been supposed that the observed branched structure of the channels promotes an increase in water content and an improvement in proton conductivity.     

Results from tests of modernized moisture separator-reheater of K-500-65/3000 turbine plants of the power unit No. 4 at the Leningrad Nuclear Power Plants (NPP)

Results from tests of the modernized moisture separator-reheaters MSRs-500-1 with Powervane louvers developed by Balcke-Dürr company are presented. Results fromstudies on the determination of wetness of the heated steam at the outlet from the separating part of the MSR and its temperature between super-heating stages, which demonstrate advantages of modernized MSR are discussed.     

CO2 welding with an additional cold filler wire

The results of investigations carried out to improve the quality of the CO₂ welding process with an additional filler wire (AFW), fed into the tail part of the molten pool in the cold state, are presented. The effect of the AFW on the quality of the produced bead is studied. The results of metallographic studies of the welded joint and also of the impact bend test are presented. When using the AFW, the quality of the welded joint is considerably higher with better external appearance of the welded joint, and the productivity of the process is also increased.