GaN Quantum-Dot Formation by a Temperature Increase in an Ammonia Flow

Semiconductors - The transformation of a two-dimensional GaN layer into three-dimensional islands (2D–3D transition) under increasing temperature in a flow of ammonia is investigated...     

Parametric optimization of a synchronous electric drive with improved mass and size parameters

This article describes a possible new synchronous drive with an active concentrated winding and a stator with a number of phases other than three, control laws, and nonsinusoidal phase currents. This drive is characterized by improvements in weight and size achieved by taking into account the interaction of the electric motor and the inverter. Using the criterion of maximum effort to volume ratio of the electric machine, we have carried out parametric geometry optimization of the stator and rotor backs and windings slots. We have listed recommendations on selection of the number of phases and main circuit connections of the electric power converter that feeds the electric machine. We have proven that, by means of intelligent selection of geometrical parameters for an electrical–mechanical converter slot, it becomes possible to improve the mass and size parameters by approximately 30% relative to conventional solutions.     

Effect of the Sapphire-Nitridation Level and Nucleation-Layer Enrichment with Aluminum on the Structural Properties of AlN Layers

The effect of atomic aluminum deposited onto sapphire substrates with different nitridation levels on the quality of AlN layers grown by ammonia molecular-beam epitaxy is investigated. The nitridation of sapphire with the formation of ~1 monolayer of AlN is shown to ensure the growth of layers with a smoother surface and better crystal quality than in the case of the formation of a nitrided AlN layer with a thickness of ~2 monolayers. It is demonstrated that the change in the duration of exposure of nitrided substrates to the atomic aluminum flux does not significantly affect the parameters of subsequent AlN layers.     

Solid-state reorganization,melting and melt-recrystallization of conformationally disordered crystals (α′-phase) of poly (l-lactic acid)

Conformationally disordered α′-crystals of poly (l-lactic acid) were formed by crystallization of the melt at high supercooling at 95 °C. Analysis of their melting temperature as a function of the crystallinity revealed absence of crystal thickening during isothermal crystallization. Annealing of α′-crystals between the crystallization temperature of 95 °C and their zero-entropy production melting temperature of 150 °C leads to their stabilization, mainly by solid-state reorganization. Heating faster than 30 K s⁻¹ suppresses reorganization and permits superheating of the α′-phase. Consequently, isothermal melting followed by melt-recrystallization becomes accessible. Melting is completed within few hundreds of milliseconds, and melt-recrystallization is about two orders of magnitude faster than crystallization of the isotropic melt at identical temperature. The time required for melting decreases with superheating and increases with the lateral dimension of the lamellar crystals. Laterally extended lamellae require long time for melting of the outer crystal layers, which allows stabilization of the central crystal part. These crystal remnants then serve as seed for immediate recrystallization. In case of complete melting of smaller lamellae, melt-recrystallization is retarded but still distinctly faster than cold- and melt-crystallization, due to incomplete isotropization of the melt.     

Linear classifiers and selection of informative features

In this work, to construct classifiers for two linearly inseparable sets, the problem of minimizing the margin of incorrect classification is formulated, approaches to achieving approximate solution, and calculation estimates of the optimal value for this problem, are considered. Results of computational experiments that compare proposed approaches with SVM are presented. The problem of identifying informative features for large-dimensional diagnostic applications is analyzed and algorithms for its solution are developed.     

Improved iron-ore pellets for blast furnaces

A production technology for iron-ore materials with improved metallurgical characteristics is developed and tested. The following materials are considered: fluxed pellets containing residual carbon; fluxed local agglomerates from concentrates with a wide range of silica content; local agglomerates with an elevated iron content; local agglomerates with residual carbon; and local agglomerates with both elevated iron content and residual carbon.     

Wetting and Brazing of Superhard Materials

Powder Metallurgy and Metal Ceramics - The wetting of superhard materials produced from cubic boron nitride and chemical vapor deposition diamond with metallic fillers is studied. The filler...     

Photoelectric characteristics of focal plane arrays based on epitaxial layers of indium antimonide deposited on a heavily doped substrate

Photoelectric characteristics of a 320 × 256-element focal plane array (FPA) with a pitch of 30 μm, whose photosensitive element is formed in the InSb epitaxial layer deposited on a heavily doped substrate, have been investigated. For a relative aperture of 1: 0.94 and an integration time of 1.46 ms, the mean value of the noise-equivalent temperature difference is 10.5 mK, the percentage of defective elements is 0.12%, and the correction time is more than 3 h. The FPA has been compared to similar commercial devices based on bulk InSb.     

Analysis of the microwave loss in AlGaAs/GaAs heterostructure pin-diodes

The dependence of the microwave insertion loss on the parameters of the heterostructure pin-diode is investigated by means of numerical modeling. The mechanisms of the emergence of this loss are determined, and the most influential mechanism is identified.