The Preparation,Properties, and Application of Nanosilica Based on Hydrothermal Solutions

Experiments on the preparation of sols and nanopowders of SiO₂ based on hydrothermal solutions are performed. In order to achieve a result, processes of polycondensation of orthosilicic acid, ultrafiltration membrane concentration, and cryochemical vacuum sublimation are performed. The physicochemical characteristics of the sols and nanopowders of SiO₂ are determined using a set of methods. In particular, it is shown that the diameters of the nanoparticles of SiO₂ in the sols and nanopowders fall within the range of 5 to 100 nm. The possibility for the application of the obtained nanosilica as a modifying additive for the enhancement of the strength of concrete is justified.     

Pseudotransient Continuation-Based Steady State Solver: Extension to Zero Flow Rates

This paper presents and discusses an extension of the pseudotransient continuation-based steady state solver for hydraulic networks proposed previously to the case of zero flow rates. The original solver, which reduces the solution of the governing nonlinear algebraic equations to the numerical integration of an initial-value problem, has problems in situations in which the head derivative of the flow rate tends to infinity, as is the case with zero flow rates. The extension is on the basis of the use of a model headloss-flow relationship that coincides with the true one at zero and has a finite head derivative at that point. This modified steady state solver is free from some convergence problems that occur in Newton-Raphson method-based solvers when analyzing a pipe network with control devices. The paper includes the results of the numerical analysis of test networks, which demonstrate the convergence of the modified steady state solver for cases in which existing steady state solvers have troubles.     

Effect of backgating on the field distribution in planar thin-film GaAs structures

The distribution of the electric field in planar film–substrate GaAs structures under backgating is considered. It is shown that backgating can make the film exhibit a long-length region of a low-gradient electric field exceeding the threshold of N-type negative differential mobility, the magnitude of negative differential mobility in this region being high enough. At values of the film doping density and film thickness typical of GaAs transferred-electron devices, this region can be as long as several tens of micrometers. The underlying physical mechanism is discussed.     

Interference Switch of a Resonant Microwave Compressor with Distributed Switched Wave Power

Journal of Communications Technology and Electronics - Abstract—An analysis is performed for the characteristics of an interference microwave switch with distributed switched wave power as a...     

High-frequency capacitance-voltage characteristic of GaAs-based, thin-film structures

An analytical calculation of the high-frequency capacitance-voltage characteristic of a GaAs thin-film structure is carried out. It is shown that the peculiarities of this characteristic, namely an abrupt drop followed by a falloff to zero, are due to the merging of the depletion regions of the Schottky barrier and the film-substrate junction and to a lag in the recharging of deep centers in the substrate. Fiz. Tekh. Poluprovodn. 31, 96–99 (January 1997)     

Evolutionary Testing of Hydraulic Simulator Functionality

A method for automatic functional testing of hydraulic simulators is proposed. The method is based on using genetic algorithms to search for network parameter values at which the simulator under test computes solutions that do not satisfy the governing network equations. The search is made by maximizing the residual of the governing equations. The application of the method to the latest version of the EPANET hydraulic simulator demonstrates its efficiency in detecting incorrect results. The results of quantitative assessment of the functional adequacy of the EPANET solver by random testing are presented. The paper provides examples of hydraulic networks and of parameter value combinations for which incorrect results occur. An example of the use of automatic functional testing together with automatic convergence testing in a comprehensive study of the flow control valve model of the EPANET solver is given.