Methods and Tools for Developing Intelligent Systems for Solving Complex Real-Time Adaptive Resource Management Problems

Automation and Remote Control - We give the statement of the real-time adaptive enterprise resource management problem and provide examples of contemporary adaptive resource management problems in...     

Dynamic compressive behavior of ultrafine-grained pure Ti at elevated temperatures after processing by ECAP

Commercial purity titanium was processed by equal-channel angular pressing (ECAP) for 8 passes and then subjected to dynamic compressive testing using a split-Hopkinson pressure bar (SHPB) facility with an imposed strain rate of ~4000 s^?1 and testing temperatures from 288 to 673 K. The results show that ECAP produces an average grain size of ~0.3 μm in transverse sections, but grains which are elongated in longitudinal sections. During dynamic compressive testing at temperatures ranging from 288 to 473 K, the grain shapes and sizes remain unchanged in the transverse sections, but the elongated shapes in the longitudinal sections evolve into polygons due to cell dislocation evolution. At 673 K, the grains become equiaxed with an average size of ~1.8 μm thereby demonstrating the occurrence of dynamic recrystallization. It is shown that the flow stresses decrease with increasing temperature from 288 to 673 K, and there is also a reduction in the rate of strain hardening.     

Application of the holographic interferometer for modeling of processes in a vapor phase epitaxy reactor

Using holographic interferometry techniques, it is possible to visualize flows in the gas phase and obtain quantitative data about vapor phase density distribution in a given volume. The possibility of using this approach for monitoring processes in a vapor phase epitaxy (VPE) reactor has been studied using an experimental setup comprising a reactor chamber with two transparent windows, a real-time holographic interferometer, a gas supply system, and a system for visual observation of the gas flows. The results show good prospects of this method for optimization of the reactor design and the VPE process parameters.     

Absorption spectra of bulk aluminum nitride crystals doped with Er<Superscript>3+</Superscript> ions

This Letter presents results of analysis of the absorption spectra of AlN:Er³⁺ bulk crystals. In the spectral of 370–700 nm, absorption lines responsible for intraconfiguration electron transition from the ground state ⁴I_15/2 to the excited states of Er³⁺ ions are found. Transitions to the levels of the ⁴F_9/2, ²H_11/2, and ⁴G_11/2 states at 2 K are studied in detail. The number of observed lines for these transitions fully agrees with that theoretically possible for f–f electron transitions in Er³⁺ ions found in a noncubic crystal field. The small width of the observed lines and their number indicate that erbium ions displace mostly one regular crystal position. Most probably, Er³⁺ occupies the position of Al. Energy positions of excited states for the considered transitions are determined.     

Chloride vapor-phase epitaxy of gallium nitride on silicon: Effect of a silicon carbide interlayer

A new approach is described, according to which the use of a thin silicon carbide (SiC) interlayer ensures the suppression of cracking and the simultaneous release of elastic strain in gallium nitride (GaN) epilayers grown by hydride-chloride vapor-phase epitaxy (HVPE) on 1.5-inch Si(111) substrates. Using this method, 20-μm-thick GaN epilayers have been grown by HVPE on Si substrates with AlN (300 nm) and SiC (100 nm) interlayers. A high quality of the obtained GaN epilayers is confirmed by the photoluminescence spectra, where an exciton band with hv_max = 3.45 eV and a half-width (FWHM) of 68 meV is observed at 77 K, as well as by the X-ray rocking curves exhibiting GaN(0002) reflections with a half-width of ω_? = 600 arc sec.     

The dislocation origin and model of excess tunnel current in GaP p-n structures

An excess tunnel current in GaP epitaxial nondegenerate p-n junctions on GaP and Si substrates was studied. An important experimental result is that the slope of exponential current-voltage (I–V) characteristic (in lnI–V coordinates) is independent of the width of the space-charge region, i.e., on n-and p-region doping levels. This fact is unexplained by existing models. A dislocation shunt model based on multihop tunneling through a dislocation line, which may be considered as a chain of parabolic potential barriers, is proposed. The density of dislocations predicted by this model is in agreement with the transmission electron microscopy (TEM) observations.     

Chloride vapor-phase epitaxy of gallium nitride at a reduced source temperature

Gallium nitride (GaN) layers on sapphire substrates have been grown by hydride-chloride vaporphase epitaxy (HVPE) at a Ga-source temperature reduced from 890°C (standard value) to 600°C. All epilayers are transparent and have smooth surfaces. The structural quality of layers was evaluated by measuring the X-ray rocking curve width (FWHM) using a triple-crystal X-ray diffractometer. For the best samples, this quantity amounted to 8 arc min. Analysis of the dependence of the crystal structure quality and photoluminescent properties of GaN layers on the Ga-source temperature showed that a decrease in this parameter to 600°C did not significantly affect the HVPE growth of GaN despite a considerable change in the vapor phase composition (ratio of GaCl and GaCl₃ concentrations).     

Resonator-based superconducting qubit

A resonator-based superconductor realization of the qubit is proposed.