A technique of ultrasonic testing of articles with curvilinear surfaces

The results of development of a technique, specimens, and special transducers for ultrasonic testing of valves (taps) for high-pressure pipelines and for the compressed part of pipeline taps (elbows) are discussed. Specific features of adjustment of the scan duration, a depth gauge, and the sensitivity of a flaw detector are considered.     

Identification of parameters of linear interval controllable systems with interval observation

The problem of identification of parameters (and initial conditions) of a linear interval system of differential equations is studied using the interval observation equation of phase trajectory, including the variant with joint restoration of the initial phase state. The main focus is put on constructing universal and subuniversal solutions that ensure minimal and close to minimal residuals in the estimate of the corresponding parameters, respectively.     

Adsorption of sodium and cesium on graphite: Work function calculations

Changes in the charge of adatoms and the substrate work function have been calculated for the adsorption layers of sodium and cesium on graphite using the Anderson-Newns model. The results of calculations are in good agreement with the available experimental data. It is established that there is electron transfer from Na and Cs adatoms to the graphite substrate, which leads to a decrease in the substrate work function.     

Electrochemical behavior and the rate of general corrosion of NiAl intermetallic compound in the unbuffered sodium chloride solutions

Highly reproducible Tafel anodic and cathodic plots were obtained on NiAl intermetallic compound in the neutral and nearly neutral unbuffered NaCl solutions. The corrosion potentials and corrosion current densities were determined by the Tafel extrapolation technique at various pH values and concentrations of NaCl. The corrosion current density and Tafel slopes were determined by fitting the equation for the corrosion current density, which involves both anodic and cathodic reactions, to the experimental anodic and cathodic polarization curves in the pre-Tafel region of polarization curves. The results obtained by two methods are in good agreement.     

Capacitance measurements for diodes in the case of strong dependence of the diode-base series resistance on the applied voltage

Epitaxial-diffused 6H-SiC diodes incorporating a high-resistivity interlayer in the base were studied; the resistance of this interlayer varied when the forward-bias voltage was applied. It is shown that, in spite of the absence of direct indications of the effects of the series resistance (the capacitance is independent of frequency and the value of capacitive cutoff voltage is small), the capacitance measurements for such structures may be incorrect.     

Special features of alpha-particle detection with thin semi-insulating 6H-SiC films

The p ⁺-n-n ⁺ structures based on 6H-SiC films grown by chemical vapor deposition on the n ⁺ substrate were irradiated with 8-MeV protons with a dose of 8×10¹⁵ cm^?2. In order to stabilize the material, it was annealed for 10 min at 450°C. As a result, the resistivity of the film was ρ=5×10⁹ Ω cm. The effect of proton irradiation was studied by alpha spectrometry. The 5.77-MeV alpha particles were detected for both reverse and forward bias voltages applied to the structure. The results of the following two modes of detection were compared: (i) a particle traverses the structure without losing much of its energy, and (ii) a particle is stopped in the structure. It is shown that, in the former case and under a forward bias, a signal is formed by a mechanism involving a “through-conducting channel.” This makes it possible to determine the product of lifetime of electrons by their mobility. The situation in which the particle range R does not exceed the film thickness was analyzed; this situation is typical of spectrometry. It is noted that a decrease in R results in different behavior of the signal for the bias voltages of opposite polarity. Thus, for forward bias, the signal amplitude decreases more rapidly and for larger values of R.     

Magnetic Aharonov-Bohm effect under time-dependent vector potential

A probability distribution for the scintillations caused by electrons hitting a screen after diffraction on a wire is calculated for the case when time-dependent vector potential is applied in the path of electron travel. Negative experimental results are explained and proper conditions for future experiments are proposed using the expression obtained.     

Consideration of spontaneous polarization in the problem of NH-SiC/3C-SiC/NH-SiC heterostructures formed by cubic (3C) and hexagonal (NH) silicon carbide polytypes

The problem of three-layer NH-SiC/3C-SiC/NH-SiC heterostructures was considered within the model previously proposed for describing the heterojunction between NH-SiC/3C-SiC silicon carbide polytypes, taking into account spontaneous polarization of hexagonal regions. The potential in the cubic 3C region was approximated by a model function constructed from physical considerations. Much attention was paid to the study of the effect of spontaneous polarization and the 3C region thickness on energy characteristics of quantum wells formed near heterojunctions. Original Russian Text ? S.Yu. Davydov, A.V. Troshin, 2008, published in Fizika i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 10, pp. 1211–1217.