A decision-making approach to the operation of flexible manufacturing systems

This paper introduces a generic decision-making framework for assigning resources of a manufacturing system to production tasks. Resources are broadly defined production units, such as machines, human operators, or material handling vehicles; and tasks are activities performed by resources. In the specific context of FMS, resources correspond to individual machines; tasks correspond to operations to be performed on parts. The framework assumes a hierarchical structure of the system and calls for the execution of four consecutive steps to make a decision for the assignment of a resource to a task. These steps are 1) establishment of decision-making criteria, 2) formation of alternative assignments, 3) estimation of the consequences of the assignments, and 4) selection of the best alternative assignment. This framework has been applied to an existing FMS as an operational policy that decides what task will be executed on which resource of this FMS. Simulation runs provide some initial results of the application of this policy. It is shown that the policy provides flexibility in terms of system performance and computational effort.     

Should we be surprised at expert system success ?

Abstract. Expert systems proliferate. They are now a usable and used tool in a variety of organizations. However, little research has been undertaken on the quantification of success or failure of expert system projects. By and large the only test carried out for expert system validation is one of comparison of the conclusions of the system with those of an expert or team of experts. While questioning the validity, this paper accepts that this method is being used and analyses whether or not the results obtained from this type of test should be a surprise. That is, what sort of results should be expected and to what extent do the reported ones live up to these expectations? Earlier research from the field of human information processing casts doubts on the success claims made for current expert systems. The implications of this research are then analysed in order to explore the possible redeeming features of expert systems which are not taken into account in such comparisons. The use of linear models as comparators for expert systems may prove beneficial.     

From hospital to municipal cogeneration systems: an Italian case study

A mixed integer linear programming model combined with a more traditional design by scenarios is proposed to optimize facilities size and operation mode of a municipal energy system involving significant civil centres and a hospital. Moving from the need of a new heat and power station for the local hospital due to the construction of new pavilions, the opportunity of involving other centres in the neighbourhood in a distributed cogeneration system is analysed, increasing system complexity step by step. Smaller cogeneration units tailored to hospital needs are rewarding ventures with relatively low risks but, in a country whose traditional power generation systems heavily rely on fossil fuels and where energy policy and market conditions can make it profitable to sell surplus power, district heating systems foster the installation of larger cogenerators and lead thereby to higher profits and to better performance as for primary energy savings and greenhouse gases emission reduction. Copyright © 2006 John Wiley & Sons, Ltd.     

Multivariable controller design in an adaptive control scheme

A multivariable control system design approach in the frequency domain is presented. The issue of control system redesign in an adaptive control scheme is discussed. Expert system techniques have been used for the automated design of controllers for multivariable systems. Design knowledge has been represented using rules, facts and objects. The design process consists of a sequence of operations obtained by heuristics and experience in the the design techniques. An automated design session of a multivariable plant using the expert system demonstrates that the expert system appears to work well in its prototype implementation.     

Pole shifting for matrices over real algebras

Pole shifting of multivariable control system over finite dimensional real algebras is studied. The main results are expressed in terms of the minimal polynomial of A + BF, where F is a feedback.     

Effect of Plate Oscillation on Bubble Residence Time in an Aerated Stagnant Liquid

Gas transfer efficiency during absorption is an important factor in various technological processes involving the interaction between liquid and gaseous systems. It is known that gas bubble motion characteristics strongly affect the efficiency of mass transfer during gas absorption. A device for mechanical vibration of an aerated liquid was designed, based on a cylindrical column filled up with tab water and a plate oscillating in the vertical direction. The goal of the present study is to investigate the effect of vibration parameters such as amplitude, frequency and form of the applied signal on the efficiency of the oxygenation process. Bubble residence time in the liquid and bubble depth of submergence related to the oscillating plate surface were chosen as main parameters for measurements. Furthermore, experiments were conducted to study the effect of the design parameters of the vibrating plate on bubble motion characteristics. The resultant data show that bubble residence time and depth of submergence can be controlled by changing the amplitude, the frequency and the form of the vibration field applied.     

Exergy losses in refrigerating systems. A study for performance comparisons in compressor and condenser

A study is carried out to describe irreversibilities in one stage refrigerating process for vapour compression cycle with refrigerant mixtures R-404A, R-410A, R-410B and R-507 as working fluids. They are calculated as exergy losses by an algorithm developed on the basis of thermodynamics. The proposed relationships have been derived from exergy balances on the system components. Emphasis is placed on parameters influencing the losses and the related results are presented through Grassmann diagrams (diagrams of exergy fluxes). Furthermore, detailed information on the variation of cycle's exergy efficiency with evaporating and condensing temperatures is given. Copyright © 2003 John Wiley & Sons, Ltd.     

An expert decision support system for network routing: a case study

The paper presents a case study of the development of an expert decision support system which uses simple heuristic methods for fast determination of routes for simultaneous signals in a transmission network of limited capacity. It illustrates how heuristic solutions can be embodied in a model-based DSS and how the standard decision support literature, although intuitively appealing, provides little practical assistance in system construction or classification     

CAL delivery selection criteria and authoring systems

Abstract  In the past, authoring systems have been used to generate computer-assisted learning materials that have often followed the rather restrictive programmed learning format. A number of innovative ways of using recently developed systems to develop CAL packages that include a wider range of learning activities (access to data bases, simulations, interactive video, etc.) are described. Analogous to the concept of a media selection model, a computer delivery mode selection model is presented as an aid to decision making for designers. This increase in flexibility should broaden the applicability of computerassisted learning (CAL) to a wider range of educational objectives and raise the level of the cognitive emphasis in learning packages, as well as facilitate the implementation of visually appealing materials. The paper also implies a standard of acceptability for authoring systems.     

Formation of geothermal resources at lithospheric subduction zones

This paper examines in a very broad fashion the formation of geothermal resources at lithospheric subduction zones. Regions of highly silicic calc-alkaline Quaternary volcanoes and/or plutons have been identified as prime candidates for having high-temperature hydrothermal systems. Regions of large tholeiitic Quaternary volcanoes have been identified as prime candidates for having large moderate-temperature hydrothermal systems. In addition, active magmatic, phreatomagnetic, and/or tectonic fracturing must be occurring in order to keep any moderate to high temperature hydrothermal system from chemically sealing. Connate, meteoric and/or oceanic water sources must also be present. Owing to tectonic and magmatic processes, volcanic arcs of subduction zones represent regions of the crust that have anomalously high mechanical and heat energy. Such arc regions are expected to contain significantly more moderate to high temperature hydrothermal systems than what is presently known. Many of these arcs are briefly discussed with respect to their potential for containing such resources.