The results of experimental studies of the influence of a static pressure applied to a flat rough interface between two solids on its nonlinear elastic properties are presented. The studies were ...performed by the spectral method on the basis of an analysis of the efficiency of generation of higher acoustic harmonics, which arise upon the reflection of a longitudinal elastic wave of finite amplitude from the boundary and the passage through it. A nonmonotonic dependence of the amplitudes of acoustic harmonics on the value of the external reversible static pressure applied to the interface was revealed: pronounced amplitude maxima for the amplitudes of the second and third harmonics were observed with a decrease in the external static pressure. It was also found that the amplitudes of the second, third, and fourth acoustic harmonics increase with a decrease in the external static pressure (in comparison with their values at the same pressure values during its increase). The experimentally determined power dependence of the higher acoustic harmonics on the amplitude of the first acoustic harmonic significantly differed from the classical indices for these harmonics. The influence of the external pressure on the values of the nonlinear second- and third-order elastic parameters was analyzed. The experimental results were analyzed on the basis of nonclassical acoustic nonlinearity.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A prototype of a new flaw detector for remote noncontact diagnostics of soft solids is proposed. The operating principle of the flaw detector is based on the features of the nonlinear interaction of ...two ultrasonic waves in the test material with defects. Ultrasonic waves in the test material are excited remotely by ultrasonic beams focused in air. It is demonstrated experimentally that with the help of the proposed flaw detector, subsurface defects with dimensions much smaller than the wavelength of the probing ultrasound can be remotely detected and localized.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The processes of the sublimation and thermal decomposition of the 1-ethyl-3-methylimidazolium hexafluorophosphate ionic liquid (EMImPF6) were studied by a complex approach including Knudsen effusion ...mass spectrometry, IR and NMR spectroscopy, and quantum chemical calculations. It was established that the vapor over the liquid phase primarily consists of decomposition products under equilibrium conditions. Otherwise, the neutral ion pairs are the only vapor components under Langmuir conditions. To identify the nature of the decomposition products, an experiment on the distillation of the ionic liquid was performed and the collected distillate was analyzed. It was revealed by the IR and NMR spectroscopy that EMImPF6 decomposes to substituted imidazole-2-ylidene (C6N2H10PF5) and HF. The measured vapor pressure of C6N2H10PF5 reveals a very low activity of the decomposition products (<10−4) in the liquid phase. The absence of a significant accumulation of decomposition products in the condensed phase makes it possible to determine the enthalpy of sublimation of the ionic liquid assuming its unchanged activity. The thermodynamics of the EMImPF6 sublimation was studied by Knudsen effusion mass spectrometry. The formation enthalpy of EMImPF6 in the ideal gas state was found from a combination of the sublimation enthalpy and formation enthalpy of the ionic liquid in the condensed state. The obtained value is in good agreement with those calculated by quantum chemical methods.
A study is made of Paul Gauguin’s painting “Tahitian Pastorals” painted by him in 1892–1893, during his first stay in Tahiti. The painting was carried out on canvas in the technique of oil painting. ...To study the stratigraphy of the layers and the pigment composition of the paint layers, the method of polarization microscopy and energy-dispersive X-ray microanalysis are used. The results of the study show that chalk from silt deposits was used as the primer. Very thin paint layers, the thickness of which varies from 10 to 30 μm, are applied in one layer on the primer. Pigments such as viridian, ultramarine, cinnabar, arsenic copper, zinc white, lead white, chalk, and barite are revealed in the paint layers. Using the method of pyrolysis-gas chromatography-mass spectrometry, it is shown that beeswax was used as a transparent coating on the surface of the painting, which penetrated into the thickness of the paint layers and the primer of the painting during its life. The conducted research allows the presence of later layers of varnish, restoration records and residues of strengthening glue over the wax coating to be determined. The results of the study of the painting “Tahitian Pastorals” are of practical importance for further study, restoration, storage and transportation in case of the exhibition of paintings in other museums of other works by Gauguin from the collection of the State Hermitage.
Using of sound-absorbing surfaces to weaken and decay of a detonation wave in hydrogen-air mixtures was investigated experimentally. Experiments were carried out in a cylindrical detonation tube open ...at one end. Initiation of the explosive mixture was carried out by a spark discharge, which is located at the closed end of the detonation tube. Acoustical sound absorbing foam element of a specific weight of 0.035 g cm3 with open pores of 0.5 mm was used. The degree of attenuation of the intensity of the detonation wave front was determined.
Objective : comparative evaluation of output data of a set of trained convolutional neural network (CNN) models and interpretation of pathological changes in lumbar spine by radiologists during ...magnetic resonance imaging. Material and methods . More than 12,000 anonymized archives were collected to generate training and test neural network datasets from patients aged over 18 years. Each archive consisted of a set of programs in two planes containing T2-TSE, T1-TSE and T2 sequences with fat suppression program. Subsequently, the selected studies were tagged in two steps, directly consisting of manual tagging and its validation by experts. CNN training was performed separately for normal analysis, qualitative detection of individual pathological changes, and quantitative analysis. The accuracy of the models was verified by comparing the protocols of five radiologists and the output of CNN models in two steps. The first, intermediate stage evaluated the accuracy of the neural networks in detecting disc bulges, protrusions and extrusions, spinal canal stenosis, lateral stenosis, foraminal stenosis, spondylolisthesis and facet joint arthrosis. In the final stage, in addition to the pathologies considered in the intermediate one, the accuracy of detecting degenerative changes of the occlusive plates, synovitis of intervertebral joints, intervertebral discs degeneration, osteophytes, transitional vertebrae, hypertrophy of yellow ligaments and Schmorl’s hernia was tested. The reference value for all pathological changes considered in this paper was determined by majority vote and, in case of disagreement, by an external radiologist. The radiologists’ interpretations were then compared with those of the trained model. Results . The artificial intelligence (AI) showed comparable sensitivity and specificity values compared to the reference result in a group of experienced radiologists for binary classification (presence/absence) of individual lumbosacral spine degenerative changes. The sensitivity and specificity of AI results were 0.88 and 0.97 for extrusions, 0.81 and 0.94 for protrusions, 0.87 and 0.98 for central stenosis, 0.83 and 0.85 for lateral stenosis, 0.92 and 0.84 for foraminal stenosis, 0.85 and 0.5 for osteoarthritis, 0.73 and 0.96 for occlusive plates degeneration, 0.85 and 0.84 for intervertebral joint synovitis, 0.91 and 0.88 for osteophytes, 0.93 and 0.72 for intervertebral disc degeneration, 1.0 and 1.0 for transitional vertebrae, 0.8 and 1.0 for spondylolisthesis, 0.67 and 0.99 for yellow ligament hypertrophy, and 0.75 and 1.0 for Schmorl’s hernia, respectively. The accuracy of quantitative size characterization of lumbosacral spine protrusions and extrusions showed unsatisfactory results, but improvements in the quality of determination of these parameters are planned in future work. Conclusion . AI models showed comparable performance to expert radiologists in detecting lumbosacral spine degenerative changes. Consistent improvement of CNN models based on comparative evaluation with radiologists improves the sensitivity and specificity of pathologic change detection.
This brief report supplements and refines previous publications Korobov, Phys. Rev. B 76, 085430 (2007); Korobov, Phys. Rev. E 79, 031607 (2009); Korobov, Phys. Rev. E 84, 021602 (2011) to show that ...the scaling properties of the area distribution functions and kinetic curves actually hold for dense plane discrete Poisson-Voronoi tessellations. The previously noted apparent violations are due to the involved structures of boundaries of random domains.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
The results of studying the painting materials of Paul Gauguin’s painting “Scene from Tahitian Life,” painted in 1896, are presented. The choice of the canvas is determined by the degree of ...preservation, which gave it the appearance of a badly damaged exhibit item. The study makes it possible to identify the reasons for the poor state of painting of this canvas and to obtain information about the details of Paul Gauguin’s approach to the creation of paintings of the second Tahitian period (1896–1901). The method of polarization microscopy and energy-dispersive X-ray microanalysis are used to study the stratigraphy, and the pigment composition of the paint layers and primer of the painting. The composition of the cloudy film on the surface of the painting is studied using Fourier-transform infrared spectroscopy. It is established that the painting was painted on thick, coarse-grained linen canvas with plain weave; aluminum silicate (kaolin) with a small content of potassium and iron aluminosilicates with the addition of a small amount of chalk was used as the primer. Pigments such as artificial ultramarine, cobalt blue, cinnabar, chromium yellow, zinc white and barite, lithopone (which is a mixture of the latter two pigments), ocher, red lead, lead white, chalk are revealed in the paint layers. It is determined that oil served as a binder for the primer and paint layers, and a broken-down film of beeswax is present on the surface of the painting. Based on the results obtained, a method for restoring the painting “Scene from Tahitian Life” is developed, which will find practical application in the study and restoration of other works by Gauguin from the collection of the State Hermitage.
We establish the solubility of a group with Sylow 2-subgroup of the least order in the centralizer of an almost regular involution. We also study the structure of a group G with an almost perfect and ...almost regular involution a.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
All independent second- and third-order elastic coefficients were measured in the isotropic polycrystalline aluminum alloy AMg6 (Al–Mg–Mn system) using the Ritec RAM-5000 SNAP SYSTEM ultrasonic ...automated complex operating in the pulsed mode. The third-order elastic coefficients were determined using the Thurston–Bragger method from the experimentally measured velocity of shear and longitudinal elastic waves in AMg6 alloy as a function of uniaxial compression.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
PDF
