Experimental investigation of steel 45 along some smooth curvilinear strain trajectory

В работе представлены экспериментальные результаты деформирования тонкостенного трубчатого образца по гладкой криволинейной траектории деформирования постоянной кривизны, в которой на каждом участке изменяется знак кривизны и смещается ее центр. Экспериментальное исследование выполнено на автоматизированном расчетноэкспериментальном комплексе СН-ЭВМ в девиаторном пространстве деформаций А.А. Ильюшина (жесткое нагружение) при одновременном комбинированном действии на тонкостенный трубчатый образец растяжения-сжатия и кручения. Исследованы скалярные и векторные свойства материала стать 45. Показано, что экспериментальные диаграммы, характеризующие скалярные и векторные свойства материала носят колебательный характер. The paper presents experimental results of deformation of a thin-walled tubular specimen along a smooth curvilinear strain trajectory of constant curvature, in which the sign of curvature changes at each section and its center shifts. Experimental data were obtained on the automated calculation-experimental complex SN-Computer in the deviator space of deformations A.A. Ilyushin (rigid loading) with a simultaneous combined action on the specimen of tensioncompression and torsion. Scalar and vector material properties of steel 45 are investigated. It is shown that experimental diagrams characterizing scalar and vector properties of the material have oscillatory character.

On the Possibilities of Using the Body Mass Index Index to Reveal Trends in Changing the Health Status of Student Youth

The article is devoted to the study of body mass index (BMI) indicators of biology students at Samara University in 20008-2020. For girls, against the background of fluctuations over the years, from 2015-2016 to 2020. there is a consistent decrease in the proportion of people with underweight, an increase in the proportion of people with normal weight. For young men, changes in the BMI structure are of a more pronounced oscillatory character. The negative features of the 2019 and 2020 contingent are the emergence of overweight and obese people. Key words: students, physical health, body weight, Samara region, body mass index.

DETERMINATION OF THE FASTEST TRAJECTORIES OF MATERIAL POINT MOTION IN A HORIZONTAL VECTOR FIELD

The article proposes a solution to the well-known Zermelo navigation problem by classical variational methods. The classical Zermelo problem within the framework of optimal control theory is formulated as follows. The ship must pass through the region of strong currents, the magnitude and direction of the current velocity are set as functions of phase variables. In this case, the relative speed of the ship is set, the module of which remains constant during movement. It is necessary to find such an optimal control that ensures the arrival of the ship at a given point in the minimum time, i.e. control of the ship by fast-action should be determined. In this paper, we consider the brachistochronic motion of a material point in a plane vector field of a mobile fluid, for which the classical variational problem of finding extreme trajectories is formulated. The aim of the study is to obtain equations of extreme trajectories along which a material point moves from a given starting point to a given finish point in the least amount of time. The solution to the problem was carried out using the classical methods of the theory of the calculus of variations. For a given variant of the boundary conditions, algebraic equations of extremals of motion of a material point were established in the form of segments of a power series. A comparative analysis of the fast-action was carried out both along extreme trajectories and along an alternative path — along a straight line that connects two given start and finish points. Analysis of the results showed that the considered variational problem has two solutions, which differ only in sign. However, only one solution provides the minimum time for moving a material point between two given points. It was also found that the extreme trajectory of the brachistochronic motion of a point is not straight, but has an oscillatory character.

A Diagnostic for Seasonality Based Upon Polynomial Roots of ARMA Models

Methodology for seasonality diagnostics is extremely important for statistical agencies, because such tools are necessary for making decisions whether to seasonally adjust a given series, and whether such an adjustment is adequate. This methodology must be statistical, in order to furnish quantification of Type I and II errors, and also to provide understanding about the requisite assumptions. We connect the concept of seasonality to a mathematical definition regarding the oscillatory character of the moving average (MA) representation coefficients, and define a new seasonality diagnostic based on autoregressive (AR) roots. The diagnostic is able to assess different forms of seasonality: dynamic versus stable, of arbitrary seasonal periods, for both raw data and seasonally adjusted data. An extension of the AR diagnostic to an MA diagnostic allows for the detection of over-adjustment. Joint asymptotic results are provided for the diagnostics as they are applied to multiple seasonal frequencies, allowing for a global test of seasonality. We illustrate the method through simulation studies and several empirical examples.

Impact of Malapposed and Overlapping Stents on Hemodynamics: A 2D Parametric Computational Fluid Dynamics Study

Despite significant progress, malapposed or overlapped stents are a complication that affects daily percutaneous coronary intervention (PCI) procedures. These malapposed stents affect blood flow and create a micro re-circulatory environment. These disturbances are often associated with a change in Wall Shear Stress (WSS), Time-averaged WSS (TAWSS), relative residence time (RRT) and oscillatory character of WSS and disrupt the delicate balance of vascular biology, providing a possible source of thrombosis and restenosis. In this study, 2D axisymmetric parametric computational fluid dynamics (CFD) simulations were performed to systematically analyze the hemodynamic effects of malapposition and stent overlap for two types of stents (drug-eluting stent and a bioresorbable stent). The results of the modeling are mainly analyzed using streamlines, TAWSS, oscillatory shear index (OSI) and RRT. The risks of restenosis and thrombus are evaluated according to commonly accepted thresholds for TAWSS and OSI. The small malapposition distances (MD) cause both low TAWSS and high OSI, which are potential adverse outcomes. The region of low OSI decrease with MD. Overlap configurations produce areas with low WSS and high OSI. The affected lengths are relatively insensitive to the overlap distance. The effects of strut size are even more sensitive and adverse for overlap configurations compared to a well-applied stent.

Semiclassic Models of the Dissipative Regime of Instability and Superradiation of a Quantum Radiator System

The paper discusses the similarity between dissipative generation and superradiance regimes for systems of excited quantum emitters placed in an open cavity. In the case of the existence of a resonator field due to reflections from the ends of the system, a dissipative generation regime is usually realized. In this case, the decrement of oscillations in the waveguide in the absence of radiators turns out to be greater than the increment of the arising instability of the system of radiators placed in the resonator. When describing this mode, the influence of the emitters on each other and the sum of their own fields is neglected. The resonator field forces the oscillators to emit or absorb quanta synchronously with it, depending on the local value of the population inversion. Lasing takes on a weakly oscillatory character due to an asynchronous change in the population inversion of the system of emitting dipoles (nutations), which have a ground and excited energy levels. To describe the process, the equations of the semiclassical theory based on the use of the density matrix are quite sufficient. In the case when there is no resonator or waveguide field, taking into account the eigenfields of the oscillators becomes essential. To simulate the superradiance process, large emitting particles are used, to describe which one should use the equations for the density matrix. It is shown that the interaction of quantum emitters in this case is due to electromagnetic fields under conditions when the overlap of their wave functions is insignificant. Equations are obtained that allow considering the process of interaction of emitters. When the emitters interact, an integral field is formed in the resonator, an increase in the intensity of which leads to synchronization of the emitters. It is shown that the characteristic times of the development of the process, as well as the attainable amplitudes of the excited fields for dissipative regimes of generation and regimes of superradiance of emitters filling an open resonator, are comparable.

Влияние толщины слоев гадолиния на магнитные свойства и процессы перемагничивания низкоразмерных Co/Gd/Co-систем

Structural and magnetic characteristics and behavior of thin-film Co/Gd/Co systems obtained by ion plasma sputtering in a magnetic field are reported. X-ray studies showed that cobalt layers in all investigated samples have a nanocrystalline structure. The mean roughness R a of the surface of the samples does not exceed 0.5 nm and is independent of the Gd layer thickness. The shape of hysteresis loops observed for the Co/Gd/Co system depends of the thickness of the Gd layer, t _Gd. The dependence of the saturation field H _S on t _Gd has an oscillatory character. This fact is explained by interaction of the Co layers through the intermediate Gd layer.

CONCERNING THE SPACE EXPERIMENT WITH SCIENTIFIC GEAR MRT ON SPACECRAFT ”FOTON-M” № 4

The short description of scientific equipment of МРТ (multichannel recorder of temperatures) is resulted and experimental results about current temperatures in local zones of containers of the scientific equipment, received in 42 daily flight of a space vehicle ”FOTON-M” № 4 are presented. It is shown, that the most essential factors defining a thermal mode in containers of scientific equipment, their position on the external surface of the spacecraft, focused almost during all flight by panels of solar batteries on the Sun and conditions on coils or, that’s the same, current deviation of a normal to a plane of orbit spacecraft from a direction on the Sun. Thus time numbers of data about values of temperatures have strongly pronounced oscillatory character with the orbital period of movement of spacecraft and with high level of correlation between them, and also dependence values of temperatures from the position of a plane of orbit of a spacecraft concerning the Sun.

Buoyancy Effect on the Flow Pattern and the Thermal Performance of an Array of Circular Cylinders

In this paper, we found, by means of numerical simulations, a transition in the oscillatory character of the flow field for a particular combination of buoyancy and spacing in an array of six circular cylinders at a Reynolds number of 100 and Prandtl number of 0.7. The cylinders are isothermal and they are aligned with the earth acceleration (g). According to the array orientation, an aiding or an opposing buoyancy is considered. The effect of natural convection with respect to the forced convection is modulated with the Richardson number, Ri, ranging between −1 and 1. Two values of center-to-center spacing (s = 3.6d–4d) are considered. The effects of buoyancy and spacing on the flow pattern in the near and far field are described. Several transitions in the flow patterns are found, and a parametric analysis of the dependence of the force coefficients and Nusselt number with respect to the Richardson number is reported. For Ri=−1, the change of spacing ratio from 3.6 to 4 induces a transition in the standard deviation of the force coefficients and heat flux. In fact, the transition occurs due to rearrangement of the near-field flow in a more ordered wake pattern. Therefore, attention is focused on the influence of geometrical and buoyancy parameters on the heat and momentum exchange and their fluctuations. The available heat exchange models for cylinders array provide a not accurate prediction of the Nusselt number in the cases here studied.