General solution of terminal control and observation problems

Mathematical problems of construction of general solutions for terminal control and observation problems are considered. The conditions of existence of a general solution of these problems for linear dynamic systems with a continuous and discrete argument are given. The study was carried out with the support of the Ukrainian Scientific and Technical Center (project No. 545) and the State Fund for Fundamental Research of Ukraine (project No. 1.4/369). Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 80–89, March–April, 2000.     

Dynamic Spirals of Nanoparticles in Light‐Responsive Polygonal Fields

Nanoparticles tend to aggregate once integrated into soft matter and consequently, self‐assembling nanoparticles into large‐scale, regular, well‐defined, and ultimately chiral patterns remains an ongoing challenge toward the design and realization of organized superstructures of nanoparticles. The patterns of nanoparticles that are reported in liquid crystals so far are all static, and this lack of responsiveness extends to assemblies of nanoparticles formed in topological singularities and other localized structures of anisotropic matter. Here, it is shown that gold nanoparticles form spiral superstructures in polygonal fields of cholesteric liquid crystals. Moreover, when the cholesteric liquid crystals incorporate molecular photoswitches in their composition, the pitch of the nanoparticulate spirals follows the light‐induced reorganization of the cholesteric liquid crystals. These experimental findings indicate that chiral liquid crystals can be used as chiral and dynamic templates for soft photonic nanomaterials. Controlling the geometry of these spirals of nanoparticles will ultimately allow modulating the plasmonic signature of hybrid and chiral systems.     

Use of an electromagnetic-acoustic technique in the practice of testing tubes of main gas pipelines

The results of development, design, and industrial testing of an electromagnetic-acoustic (EMA) technique are considered. An ultrasonic EMA pig flaw detector has higher sensitivity to cracks and can work in gas pipelines as well as a magnetic pig flaw detector does. The EMA pig flaw detector reliably detects cracks with a 10-μm opening, which are almost invisible for a magnetic pig flaw detector.     

Mathematical simulation of the formation of heat tornadoes

A numerical simulation of convective swirling jets arising as a result of the rotation of a heated disk in an initially immovable medium has been carried out. It is shown that in the case where a jet is swirled moderately, the flow is relaminarized and the intensity of the heat and mass transfer in the convective jet decreases, which leads to an increase in the buoyancy force and, consequently, an increase in the velocity of the flow. The air mass in the form of a cylindrical column-shaped vortex rises above the disk to a large height and, in doing so, retains its individuality. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 5, pp. 860–867, September–October, 2008.     

Effect of Low-Cycle Fatigue on Fracture Mechanics Parameters According to Speckle Interferometry

Evolution of parameters of fracture mechanics at various stages of low-cycle damage is studied. The developed approach is based on elaboration of optical interference measurements of the deformation response to a small crack length increment. Three sequential symmetrical notches simulate the fatigue crack growth process across the cumulative fatigue damage zone caused by low-cycle fatigue. The values of tangential components of displacement that are measured at several points on cut edges by electronic speckle interferometry are initial experimental information. The coefficients of stress intensity (SIC) and T strains are determined on the basis of the Williams solution. Values of opening and coefficients of stress intensity (SIC) and T strains for cracks of different length with fixed values of preloading cycles N_c equal 0, 100, 1000, 1800, 2500, and 3300 are obtained. The dependences of the parameters of fracture mechanics for cracks of the fixed length on N_c are constructed.     

Laser remote measurements of atmospheric gas components by dial: Modeling and experiments

This paper reports the development of LIDAS (LIdar Differential Absorption Sensing) program-algorithmic system for laser remote sensing of minor gas constituents (MGCs) of the atmosphere by the differential absorption method. The system includes modules for the search of wave-lengths informative for laser gas analysis by the differential absorption method, for numerical simulation of lidar sensing of atmospheric MGCs, and for calculation of errors of methodical, atmospheric, spectral, and instrumental origin. Lidar sensing of gas constituents by the differential absorption method as applied to problems of sensing of atmospheric MGCs is simulated numerically. Results of experiments on remote sensing of gas constituents of the atmosphere with the use of CO laser are presented.     

Synthesis and properties of magnetite nanoparticles with peroxide-containing polymer shell and nanocomposites based on them

Magnetite nanoparticles (Fe₃O₄ NPs) with peroxide-containing polymer shell have been synthesized using the method of coprecipitation from the mixture solutions of Fe (II) and Fe (III) salts in the presence of peroxide-containing copolymer (PCC). Polymer shell presence has been proved by elemental and complex thermal analysis. Synthesized Fe₃O₄ NPs possess superparamagnetic properties. Their specific saturation magnetization decreases gradually from 65 to 54 A·m²·kg⁻¹ with increasing PCC concentration owing to the surface spin pinning effect caused by a polymer shell. The average sizes of Fe₃O₄ NPs estimated from the data of XRD analysis and magnetic measurements are in the range of 9–12 nm. The NP sizes determined by the DLS method lie in the range of 150–270 nm; this result is significantly larger than the sizes estimated by the two aforementioned methods evidencing a tendency for Fe₃O₄ NPs toward self-association. Cross-linked composite films based on polyvinyl alcohol have been obtained via radical curing initiated by the PCC shell of nanoparticles. The resulting composite films are magnetically sensitive films with rather high physico-mechanical properties (tensile strength reaches 48–67 MPa and relative elongation – 4%–21% depending on cross-linking degree), a priori non-toxic and biocompatible, which makes them promising materials for various applications.