Q-BOR–FDTD method for solving Schrodinger equation for rotationally symmetric nanostructures with hydrogenic impurity

An efficient method inspired by the traditional body of revolution finite-difference time-domain (BOR-FDTD) method is developed to solve the Schrodinger equation for rotationally symmetric problems. As test cases, spherical, cylindrical, cone-like quantum dots, harmonic oscillator, and spherical quantum dot with hydrogenic impurity are investigated to check the efficiency of the proposed method which we coin as Quantum BOR-FDTD (Q-BOR-FDTD) method. The obtained results are analysed and compared to the 3-D FDTD method, and the analytical solutions. Q-BOR-FDTD method proves to be very accurate and time and memory efficient by reducing a three-dimensional problem to a two-dimensional one, therefore one can employ very fine meshes to get very precise results. Moreover, it can be exploited to solve problems including hydrogenic impurities which is not an easy task in the traditional FDTD calculation due to singularity problem. To demonstrate its accuracy, we consider spherical and cone-like core-shell QD with hydrogenic impurity. Comparison with analytical solutions confirms that Q-BOR–FDTD method is very efficient and accurate for solving Schrodinger equation for problems with hydrogenic impurity

Analysis on non-stationary gyroscopes and their application in measurement technology

In this work, the main subjects of research are: 1) analysis of the process of rotation of a Chinese top on a flat surface, 2) analysis of the main dependencies and an explanation of the rise of the center of gravity of the top during rotation due to nonlinear friction and the resulting force of the overturning top on the upper axis. Also, an analytical study of the motion of the top along the plane and the laws of rotation was carried out, the rotation of the top was analyzed from the point of view of asymmetry during rotation. The top-top spinning top is an interesting case of raising the center of gravity during rotation. The simplest model of a Chinese top can be a dynamic symmetric inhomogeneous ball, the center of mass of which lies on the axis of dynamic symmetry, but does not coincide with its geometric center. The precession of the Chinese top is based on dry friction. The occurrence of a gyroscopic deflection moment is based on the frictional force. Considering the simplest top-type top, one can distinguish the main forces acting on this body, as well as its characteristics that determine the precession. Based on this fact, it is possible to propose the use of this body of revolution as a working medium for instruments such as tribometers and gravimeters. In the first case, this makes it possible to increase the accuracy of the device, in the second, to create a new scheme for measuring gravitational fields. The relevance of this work is the analysis of the rotation of the Chinese top and the possibility of its use in measuring instruments.

Perspective on the Response of Turbulent Pipe Flows to Strong Perturbations

Pipe flow responds to strong perturbations in ways that are fundamentally different from the response exhibited by boundary layers undergoing a similar perturbation, primarily because of the confinement offered by the pipe wall, and the need to satisfy continuity. We review such differences by examining previous literature, with a particular focus on the response of pipe flow to three different kinds of disturbances: the abrupt change in surface condition from rough to smooth, the obstruction due to presence of a single square bar roughness elements of different sizes, and the flow downstream of a streamlined body-of-revolution placed on the centerline of the pipe. In each case, the initial response is strongly influenced by the pipe geometry, but far downstream all three flows display a common feature, which is the very slow, second-order recovery that can be explained using a model based on the Reynolds stress equations. Some future directions for research are also given.

Investigation of the Influence of Inertia Forces on the Adhesion of the Coating to the Outer Surface of Bodies of Revolution during Thermal Spraying

The article presents the results of a study of the influence of inertial forces on the adhesion of the coating to the external surface of a body of revolution during thermal spraying. A mathematical apparatus is proposed for calculating the inertia forces, acting on a particle of coating, applied to the outer surface of the bodies of revolution. As a result, dependencies have been revealed that allow predicting the adhesion strength of the coating with the steel base during thermal spraying.

Numerical studies on drag reduction of an axisymmetric body of revolution with antiturbulence surface

This article presents numerical studies on the drag evolution of an axisymmetric body of revolution with microgrooves using Reynolds stress model-based computational fluid dynamics simulations. Experimental data of drag evolution along the non-grooved body was used to validate the numerical model predictions. After validation of the model predictions, a series of numerical simulations were performed to study the effect of toroidal grooving of the axisymmetric body on the drag evolution by varying the depth to the surface radius of the grooves at different Reynolds numbers. A maximum drag reduction of more than 43 percent was achieved with such effort. This was possible because of the drastic reduction of turbulent shear stress in the boundary layer, which has a direct relationship with the skin friction drag evolution along the body.

Investigation of performance properties of rubber with metal fillers

The work conducts laboratory tests on the rubber of the first group of GOST 8752-70 with the introduction of the metal components. The filler is introduced into the rubber mixture on laboratory rollers. Fine powders of copper (Cu), tin (Sn) and lead (Pb) are used as fillers. The dependences of the temperature in the contact zone of the sample and the body of revolution on the concentration of the filler and the dependence of wear on the concentration of the filler for the same loads and sliding speeds are obtained, the fillers that give the rubber the greatest wear resistance are revealed, and the rational amount of the filler is determined. The positive results of laboratory tests give grounds to recommend various equipment including aerospace equipment for use in sealing devices of hydraulic systems, rubber products with metal fillers in the indicated concentrations, which will extend their service life and increase their reliability