Investigation of the sedimentation of FeNi fine grains entrained in ERF slag

Nickel losses in the slag generated at Larco electric reduction furnaces (ERF) during smelting of Greek laterites account for about 20% of the total nickel of the feed. The recovery of the nickel contained in the slag as well as in its magnetic concentrate was studied under different methods. The experimental results have shown that a nickel recovery in the range of 75-90% is possible by allowing the slag to settle. Washing by low carbon steel can be performed during the final stages of the settling process as it improves the finally attained nickel recovery up to 94.4%. The simultaneous carbon reduction and settling process do not favour the Ni- recovery as the produced carbon monoxide and dioxide cause boiling of the bath which promotes the flotation of the metallic grains. In all cases a reoxidation of nickel was observed after 20min approximately. Settling of the ferronickel grains was described by a mathematical model. The model's results are in good agreement to the experimental ones for the initial 20min of the process. A modified model was elaborated combining the settling of the metallic grains with the nickel reoxidation reaction. This model describes with adequate accuracy the whole Ni- recovery process. The developed model can be proven helpful in the design of a slag cleaning step for metal recovery utilizing a slag settling furnace operating on line to the ERF.     

A New Stochastic Model for Systems Under General Repairs

Numerous stochastic models for repairable systems have been developed by assuming different time trends, and repair effects. In this paper, a new general repair model based on the repair history is presented. Unlike the existing models, the closed-form solutions of the reliability metrics can be derived analytically by solving a set of differential equations. Consequently, the confidence bounds of these metrics can be easily estimated. The proposed model, as well as the estimation approach, overcomes the drawbacks of the existing models. The practical use of the proposed model is demonstrated by a much-discussed set of data. Compared to the existing models, the new model is convenient, and provides accurate estimation results     

Pathological behaviors of fisher confidence bounds for Weibull distribution

The Weibull distribution is widely used in reliability engineering. To estimate its parameters and associated reliability indices, the maximum likelihood (ML) approach is often employed, and the associated Fisher information matrix is used to obtain the confidence bounds on the reliability indices that are of interest. The estimates and the confidence bounds usually behave similarly in terms of monotonic and asymptotic properties. However, the confidence bounds may behave differently under certain circumstances. As a result, the Fisher matrix approach may not always be preferred in obtaining the desired confidence bounds. This paper provides some properties of Fisher confidence bounds for the Weibull distribution. These properties can be used as guidelines when implementing the ML approach and Fisher information matrix to analyze failure time data and plan life tests.     

Décroissance de la perméabilité dans des roches cristallines en fonction de la profondeur d’après des données d’Elassona (Grèce)

In crystalline rocks of Elassona area (Greece) 31 exploration drillings were constructed, for engineering purposes. Water injection tests allowed us to calculate the permeability coefficient K (m/sec) for every 3 meters of depth. The permeability values, which were determined, decrease in relation to the depth. The decrease of the mean values of K, in relation to the depth was expressed by an exponential regression, with a correlation of high significance. However the standard deviation σ of K, (at the same depth) is large and the changes of the variation coefficient V are independant of the depth.     

Modeling decisions in intelligent user interfaces

In this paper, we are concerned with the run-time communication decisions which need to be made by an intelligent user interface. We model communication decisions as a decision-making process, where a selection among a set of alternative constituents is needed, in order to satisfy specific design goals. Based on techniques from the domains of multiple-criteria decision making and decision making under doubt, we propose the use of a model which takes into account the significance of each constituent toward the satisfaction of each design goal, as well as the consideration of the decision maker (interface designer) regarding the significance of each design goal. Following the proposed approach, a design strategy can be represented by a design vector, and thus, we can define properties of, and relationships between, different design strategies, based on their respective vectors. A specific example deploying the proposed model is presented, based on data from the relevant literature. © 1997 John Wiley & Sons, Inc.