Vol 45, No 8 (2019)

The noise generated by different ferrofluid samples when probed by the fiber-optic method has been investigated. It is shown that switching on a magnetic field significantly increases the noise, which is presumably related to fluctuations accompanying the process of aggregate formation. The dependences of the rms noise on the field strength and probe-light intensity have been experimentally determined. A slow decrease in the rms noise after switching off the magnetic field has been found, which indicates relaxation of the aggregates formed by the field.

The results of an experimental study of the waves on the surface of a vertically falling liquid film in the range of the Reynolds numbers of film flow 80 < Re < 420 have been presented. The experiments have been carried out with the use of the field optical diagnostic methods with high spatial and time resolution. Generation of capillary ripples with a small wavelength has been detected at the crests of large three-dimensional waves. It is in these areas of three-dimensional waves where so-called “turbulence spots,” the occurrence of which is  associated with a transition to a turbulent flow mode, are observed, as noted in the literature. Long-lived rounded depressions with characteristic transverse dimensions of 1–3 mm, which are formed in the region of the interaction of capillary precursors and then propagate as independent structural elements of the flow, have also been recorded.

A multiparameter technique for pulsed eddy current testing is proposed, which allows one to conduct separate quantitative determination of more than seven parameters of multilayer structures containing magnetic components. The use of the proposed technique for quality control of conducting magnetic coatings and laminated composite materials used in the aerospace industry is demonstrated.

In this Letter, we propose a method for quantitative assessment of the explosion and fire hazards of lithium–thionyl chloride elements, describe an experimental setup, and present the results of experiments with lithium–thionyl chloride elements of D and DD sizes.

The results of studying the electric-spark plasma sintering of samarium monosulfide ceramics are presented. The dependence of the microstructure and phase composition of ceramics on the temperature of spark plasma sintering is studied on the basis of the data of scanning electron microscopy, energy dispersion X-ray microanalysis, and powder X-ray diffraction of synthesized samples. It is shown that a dense, nonporous ceramics, the phase composition of which is close to the composition of the initial powder, is formed at a sintering temperature of 1200°C.

The sensitivity at wavelengths in the range 400–1150 nm, dark current, and dynamic characteristics of an silicon avalanche photodiode with an active region 1.5 mm in diameter that we developed have been examined. It has been shown that the avalanche photodiode has the following set of characteristics: sensitivity 80–85 A/W at wavelengths of 900–1010 nm, dark current 1.5 nA, and leading and trailing edges shorter than 2.5 ns at a reverse bias voltage of 350 V.

Oscillations of catastrophic changes of shape (clicking oscillations) of compound supporting and control surfaces interconnected in a statically indefinable manner are treated. The effect of the angle of attack on the nature of oscillations is investigated. The phase patterns of the control surface twist angle at different angles of attack are shown.

Perovskite solar cells with photoactive layer of methylammonium lead iodide and hole transport layer based on a polyaniline complex with poly(2-acrylamido-2-methyl-1-propanesulfonic acid) have been developed for the first time. The power conversion efficiency of obtained cells is comparable with that of known analogs. Results of simulation of the optical parameters of cells in the framework of the Maxwell–Garnet model showed that the experimentally observed weak dependence of the power conversion efficiency on the perovskite layer thickness within 350–500 nm is related to the absence of significant variation of both the energy absorbed by the photoactive layer and the exciton generation rate.

Colloidal InSb-based quantum dots (QDs) without shells and with InP, CdS, InP/CdS, and InP(Cd)/CdS shells were synthesized and studied. The best characteristics of photoluminescence and its stability were obtained for InSb core/shell QDs with InP(Cd)/CdS two-layer shell. The obtained results are explained in the framework of models of the excitonic recombination mechanism and the electron quantum confinement of a QD core by an isomorphous two-layer shell.

A simple, inexpensive, and ecologically safe method has been used to obtain a new hybrid material—biomorphic carbon/nickel nanoparticles (bioC/NiNPs) composite—comprising a highly porous, partly graphitized carbon matrix (bioC) containing uniformly distributed nickel nanoparticles (NiNPs) with 5–70 nm dimensions. Transmission electron microscopy investigation showed that the bioC matrix consists predominantly of onion-like carbon with hollow capsules/pores about 5 nm in size and also contains graphite globules with dimensions up to 200 nm. The obtained bioC/NiNPs composite demonstrates high electrochemical capacitance stable up to about 1000 charge/discharge cycles and can be considered as promising material for monolithic electrodes of supercapacitors.

We consider the task of oscillatory pattern recognition on the fragments of electroencephalogram records obtained during motion and their mental representation for the development of a neurointerface software. Using a multiscale analysis, the number of channels is estimated that will provide reliable separation of motions of various types from background activity.

Mass spectra of residual gas molecules in vacuum system of the cyclotron of the Ioffe Physical Technical Institute (St. Petersburg) were obtained under various experimental conditions using a compact FT-200 time-of-flight mass spectrometer designed and manufactured at the institute. The measurements were performed in the vacuum chamber of cyclotron and in a terminal part of the ion guiding channel near the sample irradiation chamber. It is established that main contributions to residual gas composition in the cyclotron vacuum chamber are related to molecules of the vacuum oil (up to 82 vol %) and water molecules (up to 15–17 vol %), Water molecules also account for the main contribution (up to 63 vol %) to residual gas composition in the terminal part of the ion guiding channel near the sample irradiation chamber with a polymer film. The obtained data provide a basis for upgrade of the cyclotron complex of the Ioffe Physical Technical Institute.

We have studied the role of EL2 centers in formation of the photoelectric response of an array of radial n-type GaAs/Al_xGa_{1 –x}As (x = 0.3) nanowires (NWs) grown by molecular beam epitaxy on a p-type silicon substrate. Results revealed a significant decrease in the time of NW photoresponse recovery as compared to that in a bulk crystal upon the transition of EL2 centers from a metastable nonactive state to the normal ground state.

Crystallographic characteristics of K₂Sr₄Nb₁₀O₃₀ ceramics have been compared to experimental data on the surface piezoresponse studied by method of scanning probe microscopy, which was used to estimate relative values of d₃₃ piezomodulus. Depending on the orientation of a ceramic sample surface relative to the axis of texture, these values turned out to be 62 or 58 times greater than the moduli of isotropic samples. The observed giant piezoresponse of the ceramic surface can be explained by anisotropic deformation of the crystalline lattice under pressure during hot pressing. The role of domain boundaries and polar nanoregions is discussed.

Hybrid solar cells based on InGaP/Ga(In)As/Ge multijunction structures integrated into crystalline Si heat-removal base and provided with sunlight concentrator system based on linear Fresnel lenses and carboplastic mount structure have been developed and investigated. The hybrid solar cells with sunlight concentrators in the photovoltaic module provide a specific electric power of 390 W/m² (AM0, 1367 W/m²) at a photoconverter unit specific weight reduced to 1.0 kg/m². Improved photovoltaic characteristics and high radiation resistance allow using the proposed hybrid solar modules with sunlight concentrators in space solar batteries and autonomous power supply facilities.