Strength Improvement in Transformation-Toughened Alumina by Selective Phase Transformation

A1₂O₃-15 vol% ZrO₂ bar-shaped ceramic specimens were fabricated in the green state in such a way that the near surface regions consisted of A1₂O₃ and unstabilized ZrO₂ while the bulk consisted of A1₂O₃ and partially stabilized ZrO₂. After sintering, specimens had macroscopic residual compressive surface stresses and balancing interior tensile stresses due to the tetragonal-to-monoclinic phase transformation in the outer layers which occurs during cooling. The depth of the surface region was controlled during green forming. Residual surface compressive stresses at room temperature varied between 100 and 400 MPa depending on the outer-layer thickness. The increased strengths of the three-layer specimens were obtained in the as-fired unground condition, demonstrating that the stresses introduced are the result of transformation of tetragonal zirconia into monoclinic polymorph which occurred upon cooling from the sintering temperature. Specimens with residual surface compressive stresses were 200 MPa stronger at 750°C than monolithic specimens, demonstrating the viability of this approach for improving elevated-temperature mechanical properties.     

Fraction-free matrix factors: new forms for LU and QR factors

Gaussian elimination and LU factoring have been greatly studied from the algorithmic point of view, but much less from the point view of the best output format. In this paper, we give new output formats for fraction free LU factoring and for QR factoring. The formats and the algorithms used to obtain them are valid for any matrix system in which the entries are taken from an integral domain, not just for integer matrix systems. After discussing the new output format of LU factoring, the complexity analysis for the fraction free algorithm and fraction free output is given. Our new output format contains smaller entries than previously suggested forms, and it avoids the gcd computations required by some other partially fraction free computations. As applications of our fraction free algorithm and format, we demonstrate how to construct a fraction free QR factorization and how to solve linear systems within a given domain.     

Symmetrical overhead in flow networks

Recent work by one of the authors has identified the average mutual information and the conditional entropy as two measures from information theory that are useful in quantifying the system organization and incoherence, respectively. While the scaled average mutual information, or network ascendency, is inherently symmetrical with respect to inputs and outputs, the scaled conditional entropy, or overhead, remains asymmetrical. Employing the joint entropy, instead of the conditional entropy, to characterize the overhead, results in a symmetrical overhead and also permits the decomposition of the system capacity, or complexity, into components useful in following the response of the whole system to perturbations.     

ORGANIZATIONAL BEHAVIOR: A VECTOR OF SINGLE-VALUED TRANSFORMATIONS WITHIN A DETERMINATE MACHINE

The purpose of this paper is to apply W. Ross Ashby's cybernetic closed systems model to educational administration through examples of decision making, feedback form flows, and payroll structures as vectors of single-valued transformations. The application is through the creation of tools for problem solving.     

AN INTELLIGENT DECISIONMAKER FOR OPTIMAL CONTROL

We present an expert system that can handle various complicated decision-making problems of optimal control that are hardly solvable manually or even by computer-aided design techniques. The expert system is the first implementation of solving decision-making problems of optimal control using a computer, which paves the way for us to develop the real-time intelligent optimal control environment. Through a user-friendly interface, the expert system can receive the needed information from the user, perform heuristic search, and provide the results of a decisionmaker quickly both on the screen and from a printer. The important features of this expert system are that it () makes a decision on the problem-solving strategies for optimal control, that is, provides the solution structure and transversality conditions as well as types of some key equations; (2) processes symbolic information; (3) breaks down the whole search into three reasoning levels such that the problem can be solved easily and the search routine can be simplified; (4) utilizes “filter rules” to reduce production rules and enhance the program efficiency; (5) modifies the knowledge base and creates new rules in production rule memory; and (6) applies a “certainty factor” to represent imprecise knowledge. The expert system has been implemented using the AI tool OPS5 on a VAX 11/780 computer running under VMS. An example is also used to illustrate our expert system.     

Non-linear sliding-mode controller and objective function for surge tanks

A non-linear feedback controller is proposed for the ‘averaging’ control of surge tanks subject to step flowrate disturbances. The controller operates by discont-inuously switching between two non-linear feedback rules. A switching function is constructed that results in a sliding-mode that brings the system to a steady state with a finite, bounded, and ultimately monotonic response. The properties of the controller are thoroughly described using a phase plane analysis. The effects of transducer errors are analysed and a controller tuning procedure is described. It is shown that a liquid volume setpoint can be introduced if the relative volume measurement error is less than 26.42 %. A simplified implementation using a piece-wise linear switching function is also proposed for which simulations and phase plane analysis show little performance degradation. Finally, it is shown that (he idealized ‘Ramp Controller’ proposed by McDonald el al. (1986) can be derived from a continuous and differentiable objective function. The objective function is constructed for the maximum rate of change of outlet flowrate by formulating and solving an inverse optimal control problem.     

A User-Friendly Hydrological Data-Management and Reporting System

This article describes the development and implementation of an integrated hydrological management and reporting system on a microcomputer. The system involves the use of peripherals for digitizing, EPROM (Erasable Programmable Read Only Memory) or RAM downloading, storage, reporting, and archiving of hydrological data. Hydrological information is stored on hard disk in compact formats according to the type of data. Self-correcting data routines coupled with simple screen drivers for user interfacing allow semiskilled operators to use the system. An on-line help facility is an integral part of the user interface. Both pattern and color recognition by the operator are used to detect discrepancies in the data.     

Dry kiln scheduling in furniture production

In this paper, a dry kiln scheduling problem from the furniture manufacturing industry is considered. Factory-specified due dates for orders, kiln availability, kiln capacity, and travel time from the kilns to the factories are all incorporated in a model which is formulated as an integer linear program. The objective of the formulation is to minimize the maximum tardiness of orders arriving at the plants by solving a special case of scheduling n independent jobs on m non-identical parallel ciachines. Because of the computational complexity, and the fact that standard integer programming packages appear to perform very poorly on the problem, a heuristic approach is developed. Computational experience is provided which indicates that the heuristic gives very high quality solutions to problems in near real-time.     

FACTORS AFFECTING THE COMPARATIVE ADVANTAGES OF SEQUENTIAL AND BATCHED DECISION MAKING

Whether to batch-process data or to randomly update files in real-time is a common design choice faced by information system analysts. A related (but different) problem is whether or not decisions should be batch processed. Though this latter problem is undoubtedly of greater managerial concern it has received less attention. This paper discusses considerations relevant to the optimal batching and timing of decisions and illustrates these by examples. A simple illustrative mathematical model of the problem is developed and optimized. This topic is of interest to MIS designers since their systems may include automated decision making and always support the decision making process.     

VELOCITY PROFILES OF FLUID/PARTICULATE MIXTURES IN PIPE FLOW USING MRI

Magnetic resonance imaging (MRI) techniques have been utilized to experimentally measure velocity profiles and apparent Theological properties of fluid/paniculate mixtures as functions of flow rate, particle loading, and particle size. The experimental velocity profiles were described by apower law model for these systems. A 3% aqueous sodium alginic acid solution was used to form two particle sizes of 2.5 mm and 5.0mm in diameter. The spheres were suspended in a 0.5% carboxymethyl cellulose solution at loadings ofO, 10, 20, and 30% by weight. The average fluid velocity ranged from 2–35 cm/s. The flow behavior index decreased as flow rate, particle loading or particles size increase. Cumulative residence time curves were evaluated based on this modeling procedure. Results of this research have direct application to aseptic processing of fluid/particulate mixtures.