Physico−mathematical model of the voltage−current characteristics of light-emitting diodes with quantum wells based on the Sah−Noyce−Shockley recombination mechanism

Herein,a physical and mathematical model of the voltage−current characteristics of a p−n heterostructure with quantum wells(QWs)is prepared using the Sah−Noyce−Shockley(SNS)recombination mechanism to show the SNS recombination rate of the correction function of the distribution of QWs in the space charge region of diode configuration.A comparison of the model voltage−current characteristics(VCCs)with the experimental ones reveals their adequacy.The technological parameters of the structure of the VCC model are determined experimentally using a nondestructive capacitive approach for determining the impurity distribution profile in the active region of the diode structure with a profile depth resolution of up to 10Å.The correction function in the expression of the recombination rate shows the possibility of determining the derivative of the VCCs of structures with QWs with a nonideality factor of up to 4.

Structure-function integrated magnesium alloys and their composites

Magnesium-based materials not only exhibit desirable characteristics such as low density and high specific strength, but also possess exceptional functional properties, including high damping capacity, high thermal conductivity, high electromagnetic interference shielding capacity, flame retardancy, and dissolvability. However, achieving a balance between strength and functional properties remains a significant challenge in Mg alloys community. Typically, strength depends on the pinning effect of defects, such as solute atoms and second phases,which hinder dislocation motion. On the other hand, optimal functional properties usually necessitate relative perfect crystal structures, as the presence of solute atoms and second phases can have adverse effects on damping capacity and thermal conductivity. Balancing these conflicting requirements is difficult. The trade-off between strength and functional properties of the Mg alloys should be broken to meet the urgent need in aerospace, automotive, 3C(computers, communications, and consumer electronics) and energy industries for high performance structural-functional integrated Mg-based materials. This review summarizes recent progress in understanding the mechanisms and influencing factors for the functional properties of Mg alloys. The mechanisms underlying the trade-off between strength and functional properties of Mg alloys is discussed. The latest developed structural-functional integrated Mg alloys and their composites are summarized, including high strength Mg-based materials with high damping capacity/high thermal conductivity/strong electromagnetic shielding capability/excellent flame-resistance/high dissolution rate. The future works of developing structure-function integrated Mg-based materials are proposed.

Development of Technology and Equipment for Non-destructive Testing of Defects in Sewing Mandrels of a Three-roll Screw Mill 30-80

The conditions of heating and cooling of piercing mandrels made of 4X5MFS steel of a three-roll screw mill 30-80 in the production of a closed cavity of steel vessels of small volume are determined.It is established that multiple cycles of heating up to 600℃ and cooling with water up to 80℃ for about 7 seconds/1 cycle lead to the formation of ridges,shells and cracks on the surface and in the volume of the tool.The loss of structural strength of the material leads to the breakdown of the mandrel during the stitching process.The technique and equipment of magnetic powder control have been developed to establish the dynamics of the growth of internal and external defects of mandrels.An equation is obtained that allows determining the increase in the number of defects in the sewing tool of a screw rolling mill.The technology of non-destructive testing made it possible to develop a rational plan for replacing the sewing mandrels,which allows for predicting the appearance of defects leading to a complex breakdown of the deforming tool at the NPO Pribor machine-building enterprise.