Localized Excitons and Breaking of Chemical Bonds at III-V (110) Surfaces

Electron-hole excitations in the surface bands of GaAs(110) are analyzed using constrained density-functional theory calculations. The results show that Frenkel-type autolocalized excitons are formed. The excitons induce a local surface unrelaxation which results in a strong exciton-exciton attraction and makes complexes of two or three electron-hole pairs more favorable than separate excitons. In such microscopic exciton "droplets" the electron density is mainly concentrated in the dangling orbital of a surface Ga atom whereas the holes are distributed over the bonds of this atom to its As neighbors thus weakening the bonding to the substrate. This finding suggests the microscopic mechanism of a laser-induced emission of neutral Ga atoms from GaAs and GaP (110) surfaces.Comment: submitted to PRL, 10 pages, 4 figures available upon request from: [email protected]

A Method for Increasing the Efficiency of Assembling Non-detachable Products by Plastic Deformation Using Artificial Intelligence

© Published under licence by IOP Publishing Ltd. The way of achievement of the given parameters of quality of assembling of one-piece products, such as accuracy of geometrical sizes of a product and durability of non-detachable joints at stages of technological preparation and management of technological process with application of an artificial intellect is studied

Methodology development for the sustainability process assessment of sheet metal forming of complex-shaped products

© Published under licence by IOP Publishing Ltd. A methodology was developed for automated assessment of the reliability of the process of sheet metal forming process to reduce the defects in complex components manufacture. The article identifies the range of allowable values of the stamp parameters to obtain defect-free punching of spars trucks

The kinetic cluster-field method and its application to studies of L12-type orderings in alloys

The earlier-described master equation approach to configurational kinetics of nonequilibrium alloys is applied to study L12-type orderings in FCC alloys. We describe the kinetic tetrahedron cluster-field method which generalizes a similar method used for equilibrium systems to the case of non-equilibrium alloys. The method developed is used to simulate A1 → L12 and A1 → A1 + L12 transformations after a quench of an alloy from the disordered A1 phase to the single-phase L12 state or the two-phase A1 + L12 state for a number of alloy models with both short-range and long-range interactions. Simulations of the A1 → L12 transition show a sharp dependence of the microstructural evolution on the type of interaction, and particularly on the interaction range. The simulations also reveal a number of peculiar features in both the transient microstructures and the transformation kinetics, many of them agreeing well with experimental observations. Microstructural evolution under A1 → A1 + L12 transition was found to be less sensitive to the type of the finite-range (‘chemical’) interaction, while in the presence of elastic interaction this evolution shows a number of specific features which were earlier discussed phenomenologically by Khachaturyan and co-workers and are illustrated by our simulations. We also consider the problem of the occurrence of a transient congruent ordering under A1 → A1+ L12 transformation and discuss the microstructural features of this stage

Automated Generation of Rational Sheet Metal Forming Technology Variants at Process Engineering Stage

© 2017 The Authors. Published by Elsevier Ltd. The procedure of automated process reliability evaluation was developed in order to prevent recurrent defects in parts manufactured by die stamping. The procedure is based on the analysis of such factors as part design, material, its mechanical and physical properties; equipment parameters, tool performance, etc. The list of reliability factors may vary according to a type of operation as deformation process is different for each group of operations. The adjustment of stamping process reliability performance prevents any defects emerging during production of critical parts as early as the PPE stage. The automated control system for IE design at the PPE stage provides better part quality and lower production expenses thanks to IP reliability

Design and Manufacture of a Composite Punching Tool

© 2016, Allerton Press, Inc.Proposals are made regarding the design and manufacture of a composite rod-type hole-punching tool by plastic deformation

Imrovement of the cold forming technology of the parts such as longeron

© Published under licence by IOP Publishing Ltd. As a result of modeling in LS-PREPOST preprocessor of the program LS-DYNA a range of radii of curvature edge transition matrix (27,5 °≤ R ≤ 48 °) is obtained, which allows to produce defect-free stamping slots for longeron shock absorbers of tractors KAMAZ-5460