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The paper presents the results of experimental and theoretical studies of processes of phase-conjugate ultrasonic wave propagation in a liquid flow containing gas microbubbles. It is shown that a signal from a phase-conjugate wave, which is recorded by a transceiving transducer, contains information on the flow velocity of scatterers and their concentration. In this case, the flow velocity is determined both in the presence and absence of moving scattering objects. A theory developed on the basis of the generalized reciprocity principle for a moving inhomogeneous medium represents the main experimentally observed features of the formation of signals from a phase-conjugate wave scattered by a disperse liquid flow. [ABSTRACT FROM AUTHOR]

During the self-catalyzed GaAs nanowire growth formation of parasitic GaAs crystallites is observed. The reasons for crystallite formation are explained on the base of Monte Carlo simulation results. During simultaneous deposition of gallium and arsenic on the GaAs(111)B substrate coated by a silicon oxide film, liquid gallium droplets nucleate on the oxide surface. After nucleation, droplets enlarge in size with time and etch the oxide layer. Formation of GaAs crystal structures becomes possible only after the Ga droplet contacts underlying crystal substrate. It is shown that excessively high arsenic and gallium deposition rates lead to the crystallite formation at the initial growth stage. The GaAs crystallites collect part of the deposited gallium and arsenic decreasing their surface concentration, thereby, adjusting the growth conditions for the nanowire growth. Therefore, during the self-catalyzed GaAs nanowire growth the self-regulation of growth conditions takes place. [ABSTRACT FROM AUTHOR]

GaSb films are grown by molecular-beam epitaxy using AlSb/As/Si transition layers on vicinal Si(001) substrates miscuted by 6° in (111) plane direction. The effect of GaSb films crystallographic orientation on their structural properties and surface morphology is investigated. It is found that the GaSb(00 )/Si films are characterized by better structural perfection, a lower concentration of point defects, as well as a more planar and isotropic surface morphology as compared with the GaSb(001) films. The possible cause for the observed othernesses between the GaSb films with different orientations is an increased density of antiphase domains in GaSb(001) films. The morphological features of the grown films are caused mainly by the edges of terraces and, to a lesser extent, by anisotropy of the incorporation of Ga adatoms into the edges of the terraces. [ABSTRACT FROM AUTHOR]

The photoluminescence spectra of waveguide AlSb/InAs/GaInSb/InAs/AlSb quantum-well heterostructures designed for the generation of radiation at interband transitions in the mid-infrared region have been studied. The experimentally detected spectral lines are correlated with calculations of the band structure. [ABSTRACT FROM AUTHOR]

GaAs nanowires (NWs) were generated on the surface of GaAs(111)B and GaAs(100) substrates from molecular fluxes by the self-catalytic growth method. A mask for NW growth was fabricated by oxidizing the epitaxial silicon layer that was grown on a substrate surface by the molecular beam epitaxy (MBE) method. Silicon was oxidized in purified air without moving the structures out of the vacuum system of the MBE apparatus. The process of Si/GaAs heterostructure oxidation was investigated using single-wave and spectral ellipsometry. The oxidized silicon surface morphology was studied by the atomic force microscopy methods. The scanning electronic microscopy method was used to examine the samples with NWs. The NW density was about 2.6 × 107 and 3 × 107 cm–2 for (111)B and (100), respectively. [ABSTRACT FROM AUTHOR]

Molecular-beam epitaxy is used to produce GaP/Si hybrid substrates that allow the growth of highly efficient light-emitting heterostructures with GaAs/GaP quantum wells. Despite the relatively high concentration of nonradiative-recombination centers in GaP/Si layers, GaAs/GaP quantum-well heterostructures grown on GaP/Si hybrid substrates are highly competitive in terms of efficiency and temperature stability of luminescence to similar heterostructures grown on lattice-matched GaP substrates. [ABSTRACT FROM AUTHOR]

Problems arising in fabrication of lightweight flexible solar cells based on heteroepitaxial AIIIBV structures with substrate etching are discussed. Possible solutions are proposed. A tandem lightweight flexible solar cell based on a heteroepitaxial InGaP/GaAs structure was fabricated. Its mass and dimensional characteristics were determined, and bending tests were performed. The specific mass of this solar cell was 0.51 kg/m2, and the allowable bend radius was 36 mm. Its current–voltage curves were measured for the AM0 and AM1.5D spectra at 28.6°C and 25°C, respectively. The cell efficiency was found to be 23.1% and 28.3%. [ABSTRACT FROM AUTHOR]

The band structure of three-layer symmetric InAs/GaSb/InAs quantum wells confined between AlSb barriers is analyzed theoretically. It is shown that, depending on the thicknesses of the InAs and GaSb layers, a normal band structure, a gapless state with a Dirac cone at the center of the Brillouin zone, or inverted band structure (two-dimensional topological insulator) can be realized in this system. Measurements of the cyclotron resonance in structures with gapless band spectra carried out for different electron concentrations confirm the existence of massless Dirac fermions in InAs/GaSb/InAs quantum wells. [ABSTRACT FROM AUTHOR]

We investigate hybrid magnetic heterostructures consisting of thin epitaxial films of oxide ferromagnets LaSrMnO and intermetallic superlattices (TeCo/FeCo). The magnetic characteristics of the heterostructures were studied by the ferromagnetic resonance and magneto-optical Kerr effect techniques. The interlayer interaction in a heterostructure is shown to be antiferromagnetic. It was established that the interface with the intermetallic compound broadens the ferromagnetic resonance line of the manganite film. [ABSTRACT FROM AUTHOR]

Optical extinction in a metal-semiconductor metamaterial based on a AlGaAs matrix, which contains random arrays of AsSb plasmon nanoinclusions, is studied. The metamaterial is grown by molecular beam epitaxy at a low temperature. A system of nanoinclusions of various sizes is formed by annealing at temperatures 400, 500, and 600°C. Investigation of the sample's microstructure by transmission electron microscopy shows that the average size of nanoinclusions at the used annealing temperatures is 4-7, 5-8, and 6-9 nm, respectively. It is shown experimentally that AsSb nanoparticle arrays in the AlGaAs matrix cause the resonant absorption of light. It is established that the plasmon-resonance parameters found in the metamaterial are almost independent of the sizes of the AsSb nanoinclusions. The plasmon-resonance energy is (1.47 ± 0.01) eV, while its full width at half maximum is (0.19 ± 0.01) eV. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mesa type InSb photodiodes were fabricated on epitaxial layer grown by MBE. [•] Thermal cleaning of InSb surface was carried out to remove the oxide of the substrate surface. [•] The parameters of photodiodes with small sensitive area are comparable to the parameters of better bulk InSb diodes. [ABSTRACT FROM AUTHOR]

AlGaAsSb and AlGaAs films as thick as 1 μm with Al content as high as 60% were successfully grown by low-temperature (200 °C) MBE. To overcome the well-known problem of growth disruption due to a high aluminum content and a low growth temperature, we applied intermittent growth with the temperature elevation to smooth out the emerging roughness of the growth front. Post-growth annealing of the obtained material allowed us to form a developed system of As or AsSb nanoinclusions, which occupy 0.3-0.6% of the material volume. While the As nanoinclusions are optically inactive, the AsSb nanoinclusions provide a strong optical absorption near the band edge of the semiconductor matrix due to the Fröhlich plasmon resonance. Owing to the wider bandgap of the grown Al 0.6 Ga 0.4 As 0.97 Sb 0.03 compound, we have expanded the spectral range available for studying the Fröhlich plasmon resonance. The grown metamaterial represents an optically active medium of which the formation process is completely compatible with the epitaxial growth technology of semiconductors.

The prevalence of hypercholesterolemia in flying personnel is presented. It is related to duration of service. Correction of lipid metabolism is made by enduracin, long-acting drug of nicotinic acid permitted for use in pilots.

Mitral prolapse (MP) investigations were performed in 76 pilots. MP occurs in pilots rather frequently and in 15% may be responsible for syncope conditions resultant from cardiac arrhythmia, coronaroangiospastic and hypotonic responses to stress. MP diagnosis requires comprehensive examination combining clinical and special instrumental techniques providing more detailed picture in case of ultrasonic scanning, doppler echocardiography. Clinical complications of MP manifesting as cardiac arrhythmia and blockade, angiospasm etc. should be managed on individual basis, require expert evaluation and follow-up care.