ON AVERAGED DIFFUSION EQUATIONS

Methods of obtaining averaged diffusion equations are considered in case of non-uniform profile of the velocity in a channel. With the flow of Couette as an example, the comparison of exact and approximate solutions (obtained by means of perturbation method) has been carried out. The peculiarities of function of residence time distribution of liquid in the flows with non-uniform velocity field are noted. It is shown that the distribution function moments values including the zero and first moments values would depend on the degree of the velocity profile irregularity, on efficiency of radial mixing in a system as well as on the averaging method. The averaged diffusion equations which have been found by means of perturbation method are the most general of proposed ones at present in the appropriate literature. The Taylor's model and Goldstein's hyperbolic equations are included in said averaged equations as particular cases. The table of the numerical values of first three moments of RTD-function necessary for determining of the model parameters is given. The problems of application of the obtained averaged equation for calculating real chemical apparatuses, e.g. reactors, are discussed.     

Fault tolerance in FFT arrays: Time redundancy approaches

Fault tolerance in VLSI/WSI FFT arrays acquires relevance when defects and run-time faults become significant, due to large dimensions of processors and arrays. Then, both restructuring to overcome end-of-production defects and reconfiguration to overcome run-time faults are required, to achieve the dual purposes of higher yield and higher reliability.Adopting as basic FFT network the two-dimensions array that directly corresponds to the FFT flow graph, the usual structure redundancy techniques tailored for two-dimensions arrays reconfiguration are not well applicable, since the limited locality of this network leads to relevant area increase due to the augmented interconnection structure.In this paper,time redundancy is suggested as a viable alternative for the two-dimensions FFT array; two different solutions are presented, one based oninter-stage reconfiguration, the other one adoptingintra-state reconfiguration, both allowing for survival to multiple faults with limited increase of network complexity and very small hard-core sections. As usual in many time redundancy methods, both approaches result in a processing speed equal to half the processing speed granted by an ideal, fault-free device.Reliability and survival ratios to multiple faults are evaluated for the two cases, taking into account also the area increments necessary for fault tolerance. The reliability evaluations allow for a direct comparison of the two solutions.     

Microprocessor instruments for measuring nonlinear distortions; algorithms for digital processing of the measurement signal and an estimate of the errors

Rational algorithms for measuring the harmonic coefficient in microprocessor instruments for measuring nonlinear distortions based on digital processing of the codes of the instantaneous values of the signal being investigated are described and the errors of such instruments are obtained.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 56–59, April, 1995.     

Dynamics of the magnetic field transport in a plasma opening switch

It is shown that the process of magnetic field penetration into the plasma bridge in a plasma opening switch is determined by the field diffusion near the magnetic piston, followed by the convective transport of magnetic field in the bridge. This transport is due to the field being “frozen in” to the flow of plasma behind the front of a shock wave, which is formed in the plasma accelerated by the magnetic field pressure.     

Limiting Hardening Stress Levels in Sheet Glass

The limiting level of sheet glass hardening is presented based on three classification strength criteria and is equal to about 500 MPa.     

Propagation of Isothermal Flame in the Low-Pressure Thermal Decomposition of Nitrogen Trichloride

The inhibition and promotion of isothermal NCl₃ flame by NOCl and H₂, respectively, are explained. The crossover from the isothermal mode of flame propagation to the thermal one is analyzed for NCl₃–He mixtures. Calculations based on a kinetic mechanism taking into account energy chain branching are performed, and qualitative agreement between the calculated and observed data is demonstrated. The one-dimensional problem of chain–thermal flame propagation by a chain reaction involving a nonlinear-branching step has two solutions corresponding, one corresponding the isothermal mode of flame propagation and the other corresponding to the chain–thermal one. Nonlinear chain branching shortens the time needed for thermal ignition and increases the flammability of the combustible mixture.     

Application of MHD Effects in Electrolytes for Modeling Vortex Processes in Natural Phenomena and in Solving Engineering-Physical Problems

This paper gives an overview of the experimental results obtained by the method of MHD modeling in thin electrolyte layers and used to solve problems connected with the appearance of monotonic and vibrational instabilities. Primary consideration is given to the generation and interaction of transient vortex processes. As examples, the results of the investigations of flows in systems of two, three, and four vortices and periodic vortex structures, as well as of flows in the presence of obstacles of different permittivity modeling plants or technogenic screening devices intended to protect objects against pollution are presented. We consider the ways of using the results obtained in studying natural phenomena and in solving engineering-technical problems connected with mass and heat transfer and electrotransmission.     

Assessment of Shear Forces on Bridge Abutments: Simplified Method

The conventional application of reduction factors to response spectrum analysis results is inappropriate for the abutment shear forces, which are based on elastic action. On the other hand, adopting the unreduced values from the elastic dynamic analysis does not achieve equilibrium among the abutment shear forces, deck inertia forces, and reduced pier forces. A simplified method is here proposed for the assessment of the shear on the abutments, documented by comparison with response spectrum and time history nonlinear analyses for several bridge configurations. For the analyzed configuration of the bridge with an internal movement joint, the response spectrum analysis underestimates the shear on the abutment for low values of the abutment flexibility and overestimates it when the stiffness of the abutments becomes higher than that of the piers. In all the case studies analyzed, the proposed method approximates the time history results better than the response spectrum.