SUB-BARRIER AND ABOVE-BARRIER ELECTRON TRANSPORT THROUGH MULTILAYER SEMICONDUCTORS

In the article the transparency coefficients of the semiconductor structure, consisting of alternating asymmetric potential barriers and wells, where the Bastard condition is taken into account, are calculated. It is shown that in the structure there should be an oscillation of the transmission coefficient of electrons depending on their energy, which is due to the interference of the de Broglie waves reaching the barrier and reflected from the potential barrier. The electronic states of a multilayer semiconductor structure consisting of alternating potential wells and barriers are analyzed. It has been shown that both in the above-barrier and in the barrier passage of electrons, tunneling oscillations arise, which are associated with the interference of the reflected De Broglie waves. The amplitude, in this case, is determined not only by the values of the wave vectors, but from the values of the effective masses of the current carriers. It has also been shown that this oscillation does not disappear even in symmetric structures if they have a difference in the effective masses of current carriers located in two neighbouring regions. It was shown that in an asymmetric (and symmetric, but with different effective masses of electrons in different layers) semiconductor structure, oscillation should be observed depending on the coefficient of transmission through the potential barrier on the electron energy. This oscillation is due to the interference of waves traveling to the barrier and reflected from the potential barrier. Such an interference phenomenon in the structure does not disappear even in a symmetric structure due to the difference in the effective masses of electrons located in different regions of the structure

Analysis of changes in moisture transport parameters in soils under waterlogged conditions

The article considers changes in natural patterns of moisture transport parameters under waterlogging and lowering of groundwater table, in conditions of filtration-anisotropic strata. The nature of anisotropy characteristic of river sediments (alluvial, pluvial, deltaic and their combinations) is the most widespread in the surface zone of the earth’s crust. Impact factors: external and artificial, in the process of waterlogging and drainage, affect both positively and negatively the thickness of the active zone, capacity and water permeability values. The research method is based on the generalization of different approaches, causes and factors of moisture movement and on the results of field experiments to determine the nature to reveal the essence of “gravity moisture discharge”. In more exact statement the problem of stationary filtration is solved by Laplace equation. The state of moisture in the aeration zone has been studied: unsteady, transient and gravitational. By investigating the nature of this process, it is established that the evaporation process takes place not from the surface of groundwater table, but from aeration zone located between air (above ground surface) and water space (lower boundary of aeration zone)

DIMENSIONAL QUANTIZATION IN A SEMICONDUCTOR QUANTUM PIT. DRESSELHOUSE MODEL

The dimensional quantization in a semiconductor quantum well is theoretically researched, where spin-orbit splitting is taken into account by introducing the Dresselhaus term into the effective Hamiltonian of electrons. It is shown that the energy spectrum of electrons in the direction of dimensional quantization consists of a set of non-equidistant discrete levels, depending on the wave vector directed along the interface of the heterostructure

Fluid movement in pipeline with one inflow

In engineering practice, we often encounter issues related to the connection of flows. In which, in the butt places, vortex zones are observed. The article considers the problem of fluid motion in a channel with one inflow. The scientific papers devoted to the connection of flows are studied. The pressure and non-pressure movement of fluid in the channels, as well as the influence of the structural elements of the system on the hydraulic parameters of the flow, are considered. In the article, the functions describing the main parameters of the channel and inflow are constructed using the formulas of the theory of jets, which made it possible to determine the boundary lines of the vortex zone, the angle of expansion, and the inflow with a uniform connection of the flow. The results obtained show that for a uniform connection of the flow along the channel and along the lateral inflow, it is necessary to take απ ≈ 30° – 45° at χπ ≈ 0° – 2°, while the vortex boundary line is very close to the circular arc

Commissioning of the freight wagons with increased axle loads is a guarantee of the further development of railways of the Republic of Uzbekistan

The aim of the study is to select rational axle loads of the rolling stock and establish the conditions for their circulation on the railways of the Republic of Uzbekistan. In this work, research has been carried out to assess the indicators of the stress-strain state of rail track elements from the action of the rolling stock with various axial loads. The dynamic loads from the rolling stock wheel on the rail, tensile stresses at the edges of the rail foot, in wooden sleepers (rubber under-rail pads on reinforced concrete) under the linings, in the ballast under the sleeper, as well as stresses at the main area of the roadbed, were determined. The obtained results of studies on the determination and assessment of the loading of the elements of the permanent way and sub-grade bed under the condition of not exceeding their standard values made it possible to establish the permissible speeds of movement of freight wagons with increased axle loads of 25 and 27 tf on the railways of the Republic of Uzbekistan, depending on the design of the track and the thickness of the ballast layer, which will increase the running and carrying capacity of the most loaded sections of the railway network, reduce operating costs, increase the volume of freight traffic by rail, which will create conditions for the further development of national rail transport in the implementation of export and transit potential