Simplification of the mathematical models of objects in simulator complexes

Mathematical models of control systems are important for problems that are solved in real time in the software for simulator complexes of complicated machinery (pilot simulators, transport simulators, etc.). Simplification of the models by excluding weakly affecting components allows one to reduce loading on the computational medium of simulators. The Schur real decomposition approximates a simplified model to the model of the initial system. A new method to increase the quality of approximation with allowance for transient and established values of object reaction, that is, approximation of transfer functions, is suggested. It is made by decreasing deviations over the matrices of a transfer function between the initial and simplified models. The applicability and effectiveness of this method of simplification are proved using a dynamic model of a pilot system as an example.     

Modeling the operation of field-effect transistors based on GaAs/AlGaAs heterostructures

The parameters of a structure consisting of a doped GaAs channel and an AlGaAs buffer located between the substrate and the channel are optimized using the Synopsys Sentaurus TCAD simulator. It is shown that the use of this buffer increases the breakdown voltage and power of the transistor compared to the basic structure transistor without an AlGaAs buffer. It is also shown that the transistor breakdown voltage is most greatly affected by the buffer composition (the fraction of aluminum in the Al _x Ga_1−x As) solid solution and, that the maximum breakdown voltage is obtained for a buffer containing no less than 18% aluminum.     

Clean boxes with artificial climate for atomic force microscopy: New possibilities for diagnostics of nanodimensional objects

A clean box with an artificial climate is developed and designed to increase the accuracy of measurements by atomic force microscopy in the air and to improve the reproducibility of the results of diagnostics of the surface. The main functions of the box are the provision and maintenance of the temperature and humidity in the working zone with a high degree of accuracy and in various combinations. The main technical characteristics of the box are presented. The main advantages of operation under the conditions of an artificial climate are analyzed. It is shown that the special procedures give the possibility to eliminate the distorting effect of the static electricity on the surface under investigation and, specifically, to remove the already accumulated charge and prevent its appearance in the course of the experiment. The use of the suggested procedures allows one to correctly describe the specific features of the surface topography of dielectrics at the microscopic and nanoscopic levels.     

Topological characterization of the Ge-Sb-Te phase diagram

Topological images of the Ge-Sb-Te phase diagram are constructed on the basis of two versions of the phase relations between the low-temperature forms of Ge_1-δTe in the Ge-Te system. The images have the form of flow diagrams and graphs, with labeled nodes representing the phases existing in the system. The graph edges represent two-phase mixtures and are labeled by the numbers of the phase reactions in which these mixtures appear and disappear. The graphs help to visualize the topology of the phase diagram in a compact form and are convenient for topological characterization and identification of phase reactions at invariant points.     

Formation of the microgeometry of the body surface of cylindrical work rolls during texturing and mat finishing of precision strips

The requirements of the consumers of precision strips imposed on their surface roughness parameters are considered. Various methods of texturing roll bodies are analyzed, and the advantages of electric-discharge texturing are shown. The effect of the roll texturing and stand calibration conditions on the roll roughness parameters is studied, and the formation of a microrelief on a strip surface during mat finishing is investigated. Stand calibration is shown to decrease the roughness height indices and to substantially improve the microrelief uniformity. The optimum conditions of texturing of work rolls and mat finishing of precision strips of various purposes are determined and implemented on a reversing four-high 800 mill.