Vol 60, No 11 (2018)

Nucleation of Ge islands on a stepped Si(100) surface is studied. It is shown by diffraction of fast electrons that at a temperature of 600°C, constant flux of Si, and deposition rate of 0.652 Å/s, a series of the 1×2 superstructure reflections completely disappears, if the Si (100) substrate deviated by an angle of 0.35° to the (111) face is preliminarily heated to 1000°C. The disappearance of the 1×2 superstructure reflexes is due to the transition from the surface with monoatomic steps to that with diatomic ones. Investigations of the Ge islands’ growth were carried out on the Si(100) surface preliminarily annealed at temperatures of 800 and 1000°C. It is shown that the islands tend to nucleate at the step edges.

The paper represents induced currents in an electrically conductive object as a totality of elementary eddy currents. The proposed scanning method includes measurements of only one component of the secondary magnetic field. Reconstruction of the current distribution is performed by deconvolution with regularization. Numerical modeling supported by the field experiments show that this approach is of direct practical relevance.

Experimental and theoretical studies of the electrophysical characteristics of water with different concentrations of conductive impurity, including the complex dielectric permittivity, complex conductivity, and complex impedance spectra are performed at frequencies in the range from 20 Hz to 40 GHz. It is demonstrated that the complex dielectric permittivity spectrum at frequencies in the range 500 MHz – 40 GHz is well described by the Debye model with a single relaxation time. In the low-frequency range, one more region of dispersion is observed caused by the phenomena occurring on the liquid-electrode interface. The characteristics of this dispersion region depend significantly on the dc electrical conductivity. It is demonstrated that in the examined frequency range, the influence of the interface phenomena on the complex impedance spectra of water with conductive impurity are well described by adding the impedance of an constant phase element. For the examined samples, the electrophysical characteristics and the parameters of the constant phase element are determined. The static dielectric permittivity and the parameters characterizing the double electric layer increase with the electrical conductivity.

Based on an analysis of physics of the phase transition from the quasistatic state field to the running wave field of elementary electric and magnetic dipoles located in absorbing media, it is concluded that the skin layer is formed at the boundary of this phase transition. The possibility is considered of obtaining the diffractive hyperbola of the skin layer and its subsequent application for sensing of objects in strongly absorbing media.

A model of backward reflection is presented which is distinguished by the fact that it takes account of excitation of counterpropagating waves in bounding media. For the case of a homogeneous aqueous medium, it is shown that the proposed model describes distinguishing features of the angular dependence of the backward reflection coefficients for all angles of incidence of the waves on the air–water interface. Characteristic regions of the angular dependence, associated with different mechanisms of formation of the backward reflection, are elucidated.

The paper focuses on anisotropy of the transverse Nernst–Ettingshausen effect in superlattices depending on the degree of mini-band filling and magnetic field direction during scattering on acoustic and polar optical phonons. The authors demonstrate that in the case of scattering on polar optical phonons one observes considerable anisotropy and, depending on the magnetic field direction, the Nernst–Ettingshausen coefficient may change its sign.

The phase structure, structural parameters, and basic magnetic characteristics of BaFe₁₂O₁₉ hexaferrites prepared by the zol-gel combustion method with subsequent annealing at a temperature of 850°С for 6 h are investigated. The influence of the organic fuel type on the properties of synthesized materials is analyzed. Values of the saturation magnetization and the anisotropy field are determined. It is established that they depend on the organic fuel type. It is shown that powders synthesized with citric acid used as a fuel have the largest particle sizes and the highest saturation magnetization.

The remote method of simultaneous determination of the temperature and concentration of hot gases from experimental spectral characteristics is validated on the example of the transmission spectra of water vapor measured with an average error of 5% at temperatures in the range 500–1770 K and concentrations 0.17–1 atm with resolution of 1 cm^–1. When solving the direct optical problem, the parameters of water vapor spectral lines comprised in the HITEMP2010 database are analyzed with allowance for the last measurements of the absorption spectra with high resolution at Т ≈ 1300 K. It is demonstrated that overestimated values of the intensities of some hot water vapor spectral lines can be a reason for the deviation of the theoretical absorption predicted on the basis of the HITEMP2010 database from the experimental one. To increase the accuracy of solving the inverse optical problem, the data from several (up to eight) fragments of the spectral ranges 1000–2500 and 2600–4400 cm^–1 are used. As a result, it is demonstrated that this allows the average error of determining reference values of the water vapor temperature and concentration to be decreased approximately to 0.3%, which corresponds to the average approximation error of theoretical values of its transmission function.

An optical layout of a two-cascade frequency converter of the mid-IR laser radiation into the terahertz (THz) radiation is proposed. In the first stage it is assumed to convert the Tm:YLF-laser frequency in a Cr⁺²:ZnSe polycrystal into the radiation with the wavelength ~2–3 μm. The second cascade can be presented as a parametric conversion of the frequencies of two laser sources operating in the ~2–3 μm range into the THz radiation via the difference-frequency mixing in a nonlinear optical ZnGeP₂ crystal. The estimates of the terahertz output signal are reported.

The results of investigations of thermal stability of microstructure and microhardness of alloys of the V–4Ti–4Cr and Mo–47Re systems, subjected to torsional deformation by high quasi-hydrostatic pressure at room temperature, are reported. It is shown that submicrocrystalline and nanocrystalline states, and the respective high values of microhardness, persist up to the upper bound (~0.4 Т_melt) of the temperature interval of their recovery and polygonization in a single-phase state. The main factors ensuring thermal stability of highlydefective states in heterophase alloys are discussed.

The problem of solar radiation transfer by cirrus containing horizontally oriented ice crystals urgent today is considered. The results of a complex radiation experiment are described in which solar radiation fluxes at the Earth’s surface are measured and high-level clouds are vertically sensed by a polarization lidar. The lidar allows the full backscattering phase matrix (BSPM) to be determined. The degree of orientation of ice crystals in cirrus is estimated from the form of the BSPM elements and their interrelations. It is shown experimentally for the first time that the degree of orientation of crystalline particles in cirrus has a significant effect on the direct and scattered solar radiation fluxes arriving at the Earth’s surface.

This paper continues the study of high quality test derivation for verifying digital components which are used in various physical systems; those are sensors, data transfer components, etc. We have used logic circuits b01-b010 of the package of ITC’99 benchmarks (Second Release) for experimental evaluation which as stated before, describe digital components of physical systems designed for various applications. Test sequences are derived for detecting the most known faults of the reference logic circuit using three different approaches to test derivation. Three widely used fault types such as stuck-at-faults, bridges, and faults which slightly modify the behavior of one gate are considered as possible faults of the reference behavior. The most interesting test sequences are short test sequences that can provide appropriate guarantees after testing, and thus, we experimentally study various approaches to the derivation of the so-called complete test suites which detect all fault types. In the first series of experiments, we compare two approaches for deriving complete test suites. In the first approach, a shortest test sequence is derived for testing each fault. In the second approach, a test sequence is pseudo-randomly generated by the use of an appropriate software for logic synthesis and verification (ABC system in our study) and thus, can be longer. However, after deleting sequences detecting the same set of faults, a test suite returned by the second approach is shorter. The latter underlines the fact that in many cases it is useless to spend ‘time and efforts’ for deriving a shortest distinguishing sequence; it is better to use the test minimization afterwards. The performed experiments also show that the use of only randomly generated test sequences is not very efficient since such sequences do not detect all the faults of any type. After reaching the fault coverage around 70%, saturation is observed, and the fault coverage cannot be increased anymore. For deriving high quality short test suites, the approach that is the combination of randomly generated sequences together with sequences which are aimed to detect faults not detected by random tests, allows to reach the good fault coverage using shortest test sequences.

The principles of formation of structure and properties of materials produced by self-propagating hightemperature synthesis (SHS) from the Al–Ti–B/B₄C powder systems are identified. It is shown that the SHSmaterials produced from the Al–Ti–B powder systems consist of a TiAl intermetallic matrix with inclusions of titanium diboride particles. It is found out that an introduction of 1 wt.% of TiB₂ particles into the melt of the AD35 aluminum alloy allows reducing the grain size from 620 to 220 μm and gives rise to an increase in the ultimate tensile strength of as-cast specimens from 100 to 145 MPa and in the plasticity from 7 to 9%.

The possibility of development of a thin-film 1,4-distirylbenzene–based laser lasing in the blue spectral range in solutions and films is investigated. The stimulated emission of 1,4-distirylbenzene in a polymethylmethacrylate film with transverse pumping by a YAG-Nd³⁺ laser is obtained for the threshold power density W = 0.44 MW/cm². It is shown that incorporation of the additional amorphous SiO₂ layer, improving the condition of total internal reflection on the boundary of the active medium, decreases the lasing threshold to 50–70 kW/cm²; in this case, the efficiency of radiation conversion is equal to 20%.

The physical principles of a method for determination of geometrical characteristics of particles and particle recognition based on the concepts of digital holography, followed by processing of the particle images reconstructed from the digital hologram, using the morphological parameter are reported. An example of application of this method for fast plankton particle recognition is given.