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Author(s):  
О.П. Казарова ◽  
С.С. Нагалюк ◽  
В.А. Солтамов ◽  
М.В. Музафарова ◽  
Е.Н. Мохов

The high-temperature diffusion of an acceptor impurity of beryllium (Be) into bulk single-crystal aluminum nitride (AlN) has been studied. It is shown that the introduction of Be leads to the appearance of green luminescence of AlN, which is stable at room temperature and is observed over the entire thickness of the sample. It was shown by the method of luminescence analysis that the Be diffusion process is most efficiently realized in the temperature range from 1800°C to 2100°C and is characterized by extremely high diffusion coefficients D = 10-7 cm2/s and 10-6 cm2/s, respectively. It is shown that a prolonged diffusion process (t ≥ 1 hour) at a temperature of 2100°C leads to concentration quenching of the luminescence of near-surface AlN layers with a thickness of ≈ 80 μm, which makes it possible to estimate the concentration of beryllium impurities in the near-surface layer on the order of 10E19 cm-3.


Author(s):  
V. M. Somsikov ◽  
I. P. Chunchuzov ◽  
A. Jahanshir ◽  
S. N. Mukasheva

The paper provides a review of studies devoted to the peculiarities of the propagation of radio waves in the ionosphere in the area of the solar terminator, which is the only global and regular source of acoustic-gravitational waves and other disturbances of the ionosphere. It describes the results of theoretical works devoted to the study of perturbations created by the solar terminator in the area of the difference in the intensity of solar radiation in the atmosphere. The paper gives a review of experimental studies of the effects created by the solar terminator in the entire thickness of the atmosphere. These effects, in particular, include the multipath propagation of radio waves, their phase variations, and variations in amplitudes during the propagation of radio waves in the area of the solar terminator. In the interests of science and practice, a number of problems have been proposed for the further study of wave perturbations arising as a result of the movement of the temperature gradient at sunrise and sunset hours.


2021 ◽  
pp. 101-108
Author(s):  
А.В. Санников

В работе рассматривается актуальная задача крепления толстостенных труб в толстых трубных решетках в теплообменных аппаратах. В настоящее время в теплообменных аппаратах с толстыми трубными решетками широко применяются так называемые комбинированные соединения, изготовление которых предусматривает предварительную развальцовку концов труб на конус, сварку концов труб с трубной решеткой и последующую радиальную раздачу труб на всю толщину трубной решетки. В работе проведена оценка технических возможностей пошаговых и ленточно-винтовых вальцовок при развальцовке толстостенных труб в толстых трубных решетках. Дано сравнение качества образцов соединений по критериям герметичности, прочности и состоянию поверхностей на развальцованных участках труб, полученных двумя различными способами развальцовки: пошаговым и непрерывным. Приведена сравнительная количественная оценка затрат времени, требуемого для развальцовки труб тем или иным способом. В процессе развальцовки труб в образцах было установлено, что как пошаговые, так и ленточно-винтовые вальцовки способны развальцовывать толстостенные трубы с соотношением внутреннего и наружного диаметров близким к 0,66 (если это отношение меньше 0,66, то такие трубы принято считать «невальцуемыми»). В результате исследований установлено, что вальцовки ЛВК могут успешно применяться для закрепления особо толстостенных труб малых диаметров в толстых трубных решетках, для которых применение пошаговых вальцовок может быть проблематичным из-за высокой вероятности поломки (скручивания) веретен. The paper considers the actual problem of fixing thick-walled tubes in thick tubesheets in heat exchangers. Currently, so-called combined joints are widely used in heat exchangers with thick tubesheets, the manufacture of which provides for pre-rolling the ends of the tubes into a cone, welding the ends of the tubes with a tubesheet and subsequent radial distribution of tubes to the entire thickness of the tubesheet. The paper evaluates the technical capabilities of step-by-step and band-screw rolling when rolling thick-walled tubes in thick tubesheets. The quality of joint samples is compared according to the criteria of tightness, strength and condition of surfaces on the rolled sections of tubes obtained by two different methods of expanding: step-by-step and continuous. A comparative quantitative assessment of the time required for tube expanding in one way or another is given. In the process of expanding tubes in the samples, it was found that both step-by-step and tape-screw rolling rolls are able to roll thick-walled tubes with a ratio of internal and external diameters close to 0.66 (if this ratio is less than 0.66, then such tubes are considered "non-expanding". As a result of the research, it is proved that LVK rollers can be successfully used for fixing especially thick-walled tubes, for which the use of step-by-step rollers can be problematic due to the high probability of breakage (twisting) of the spindles.


2021 ◽  
Vol 61 (4) ◽  
pp. 526-536
Author(s):  
Muammel M. Hanon ◽  
Ziad A. Taha ◽  
László Zsidai

The ability of COMSOL Multiphysics 5.2 software to carry out the simulation of laser drilling processes in Inconel X-750 and Ti-5Al-2.5Sn sheets was investigated in this study. A JK 701 pulsed Nd:YAG laser was used for drilling through the entire depth of Inconel X-750 and Ti-5Al-2.5Sn plates of 2 mm and 3 mm thicknesses using laser pulses of a millisecond in time. The laser parameters are varied in different combinations for well-controlled drilling through the entire thickness of the plates. Effects of laser peak power and pulse duration have been determined via the studying of the temperature distribution on the cross-section of the images taken in the simulation tests. Characterizing the optimum conditions obtained from the combination of parameters that improve hole quality is an essential aim in this paper. This work's outcomes might be helpful for researchers in terms of the optimum parameters proposed when studying the laser drilling of the mentioned alloys experimentally.


Author(s):  
A. Y. Sokolov ◽  
D. I. Shishkina

The article presents some theoretical and experimental data on promising technologies, namely, the processes of obtaining artificial food materials such as spheres or "caviar". They are derived from molecular processes: solubilization, spherification, etc. Possible applications are the food industry, the food service industry, biotechnology, and others. There are different features of obtaining artificial products based on alginates. The peculiarities of the alginate structuring are that it is possible to form a gel layer-encapsulation and gel formation over the entire thickness of the product due to the special chemical properties of the fixing salt. Based on the theory of the molecular structure of biopolymers, molecular technologies for the synthesis of artificial food products were developed, using the example of molecular "caviar". As a result of our own experiments, we obtained a satisfactory encapsulated product from a biopolymer crosslinked with Ca2+ salts in terms of organoleptic and physico-chemical properties. The colloidal biopolymer solution for forming "eggs" was characterized using the method of rotational viscometry, which showed the features of the sodium alginate solution as a structured thixotropic material, which is characterized by" difficulty " of shear at low speeds of rotation of the viscometer rotor. Further on the rheogram, such material exhibits a predicted relatively stable flow. As a result, it can be used to produce semi-finished products of a given shape and texture as a food semi-finished product or product. If the technology is refined, it is possible to use colloidal systems based on alginates and other biopolymers in biotechnology, including the cultivation of microorganisms of various taxonomic groups.


2021 ◽  
Vol 887 ◽  
pp. 564-574
Author(s):  
Oleksandr H. Kurpe ◽  
Volodymyr V. Kukhar ◽  
Eduard S. Klimov

In the paper the research has been performed to obtain the stress distribution through the thickness of the rolled products along the deformation zone in the conditions of roughing rolling and in the conditions of quasi-stationary temperature distribution during finishing rolling at the Steckel mill. The research has been performed by the simulation based on the Abaqus CAE 6.14-2 software and analytical modeling of the hot rolling process of coils at the Steckel mill with dimensions of 15 mm × 1500 mm, made of steel grade S355JR+AR, according to the requirements of EN 10025-2. The obtained deviations of the rolling force between simulation, analytical modeling and actual data have comparable results and a similar trend of changes through the passes, the average value of which does not exceed 1.54 % and - 1.77 %. The beginning of the continuous layer formation of equivalent stress during roughing rolling has been determined, and, accordingly, the beginning of the deformation penetration through the entire thickness of the semi-rolled product has been also determined that occurs in the pass 6 when reduction equals 14 %.


2021 ◽  
Author(s):  
Wenlong Li ◽  
Sedighe Keynia ◽  
Samuel A. Belteton ◽  
Faezeh Afshar-Hatam ◽  
Daniel B. Szymanski ◽  
...  

AbstractAn integrated, experimental-computational approach is presented to analyze the variation of elastic bending behavior in the primary cell wall of living Arabidopsis thaliana pavement cells and to measure turgor pressure in the cells quantitatively under different osmotic conditions. Mechanical properties, size and geometry of cells and internal turgor pressure greatly influence their morphogenesis. Computational models of plant morphogenesis require values for wall elastic modulus and turgor pressure but very few experiments were designed to validate the results using measurements that deform the entire thickness of the cell wall. Because new wall material is deposited from inside the cell, full-thickness deformations are needed to quantify relevant changes associated with cell development. The approach here uses laser scanning confocal microscopy to measure the three-dimensional geometry of a single pavement cell, and indentation experiments equipped with high magnification objective lens to probe the local mechanical responses across the same cell wall. These experimental results are matched iteratively using a finite element model of the experiment to determine the local mechanical properties, turgor pressure, and cell height. The resulting modulus distribution along the periclinal wall is shown to be nonuniform. These results are consistent with the characteristics of plant cell walls which have a heterogeneous organization. This research and the resulting model will provide a reference for future work associated with the heterogeneity and anisotropy of mechanical properties of plant cell walls in order to understand morphogenesis of the primary cell walls during growth and to predict quantitatively the magnitudes/directions of cell wall forces.One sentence summaryThe distribution of elastic modulus of the periclinal cell walls of livingArabidopsis epidermis is nonuniform as measured by bending the entire thickness of the wall.HighlightsExperimental characterization of the spatial distribution of elastic bending behavior across the periclinal wallQuantification of the turgor pressure of the living plant epidermal cells validated with osmotic treatmentsQuantification of the effect of cell geometry on the measured mechanical responseGraphical abstract


Cells ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 3
Author(s):  
Brandon L. Meyerink ◽  
Neeraj K. Tiwari ◽  
Louis-Jan Pilaz

Radial neuron migration in the developing cerebral cortex is a complex journey, starting in the germinal zones and ending in the cortical plate. In mice, migratory distances can reach several hundreds of microns, or millimeters in humans. Along the migratory path, radially migrating neurons slither through cellularly dense and complex territories before they reach their final destination in the cortical plate. This task is facilitated by radial glia, the neural stem cells of the developing cortex. Indeed, radial glia have a unique bipolar morphology, enabling them to serve as guides for neuronal migration. The key guiding structure of radial glia is the basal process, which traverses the entire thickness of the developing cortex. Neurons recognize the basal process as their guide and maintain physical interactions with this structure until the end of migration. Thus, the radial glia basal process plays a key role during radial migration. In this review, we highlight the pathways enabling neuron-basal process interactions during migration, as well as the known mechanisms regulating the morphology of the radial glia basal process. Throughout, we describe how dysregulation of these interactions and of basal process morphology can have profound effects on cortical development, and therefore lead to neurodevelopmental diseases.


Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5671
Author(s):  
Jacek Szpetulski ◽  
Bohdan Stawiski

During compaction of a concrete mix, when thin slabs are formed in a horizontal position, the components of this mix become segregated. Heavy components fall to the bottom, and light components (air and water) move to the top. This process may suggest that the upper layers of concrete elements formed in a horizontal position may have lower compressive strength than the remaining part of the element. This problem is recognized and documented in many publications, but there was a publication whose test results indicate a lack of variability in the compressive strength of concrete across the thickness of tested elements. The discrepancies appearing in the evaluation of concrete homogeneity was the reason for conducting destructive tests of the compressive strength of concrete across the thickness of horizontally concreted test elements that imitate thin slabs. The obtained results of the destructive compressive strength confirmed previous results regarding the heterogeneity of concrete. They clearly indicate that there is a differentiation of the compressive strength of concrete across the thickness of a thin element, which remained in a liquefied state for a certain time during its formation. The longer the duration of this state across the entire thickness of the formed element, the greater the differentiation of the compressive strength between the top and bottom layers.


Author(s):  
S. Yu. Putrov ◽  
R. V. Litvinenko

The article substantiates the essence of physical therapy of children 7-10 years old with chronic gastritis in the hospital period: problems and prospects. Chronic gastritis is a chronic polyetiological inflammatory-dystrophic disease of the gastric mucosa with impaired cell regeneration and progressive atrophy of the gastric epithelium. The consequences of the disease are damage to the surface layer of the epithelium and glandular apparatus of the gastric mucosa and the development of inflammatory processes in them. Depending on the etiological factor, the inflammatory process may be limited to the superficial epithelium of the mucous membrane or spread to the entire thickness of the glandular apparatus and even the muscular layer. The main symptoms of gastritis are pain and dyspeptic disorders. Patients complain of heartburn, belching sour, feeling of pressure, burning, distension in the epigastric region, constipation, rarely - vomiting. Usually dyspeptic disorders appear during the exacerbation of the disease. Appetite usually does not change, however at the expressed frustration of function of a stomach and a duodenum can amplify or decrease - up to full (short-term) loss. The analysis of modern approaches to physical therapy of patients with chronic gastritis indicates a lack of attention to this issue. The program of physical therapy for children 7-10 years old with chronic gastritis during the hospital period includes: therapeutic physical training, therapeutic massage, physiotherapy and diet therapy.


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