Temperature resistance coefficient of composite resistive materials in the mixed-structure approximation

A method of calculating the temperature resistance coefficient and its temperature dependence for resistive materials in the approximation of a matrix-statistical structure is outlined.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 3, pp. 477–481, September, 1985.     

On constructivity of involutive divisions

In the paper, the problem of existence of the minimal involutive monomial basis is considered for different involutive divisions. The existence criterion is obtained in the form of a constructivity property. In the paper, new examples of constructive and nonconstructive (> σ)-divisions are presented.     

Flood risk mapping at European scale.

The aim of this article is to illustrate a framework for flood risk mapping at pan-European scale produced by the Weather-Driven Natural Hazards (WDNH) action of the EC-JRC-IES. Early results are presented in the form of flood risk index maps. We assess several flood risk factors that contribute to the occurrence of flood disasters. Among the causal factors of a flood disaster one is triggering a natural event in the form of extreme precipitation and consequently extreme river discharge and extreme flood water levels. The threatening natural event represents the hazard component in our assessment. Furthermore exposure and vulnerability are anthropogenic factors that contribute also to flood risk. In the proposed approach, flood risk is considered on the light of exposure, vulnerability and hazard. We use a methodology with a marked territorial approach for the assessment of the flood risk. Hence, based on mathematical calculations, risk is the product of hazard, exposure and vulnerability. Improvements on datasets availability and spatial scale are foreseen in the next phases of this study. This study is also a contribution to the discussion about the need for communication tools between the natural hazard scientific community and the political and decision making players in this field.     

Optimal scheduling with strict deadlines

The problem of dynamic scheduling of customers (messages) in time-critical environments is discussed. A single station (communication node) is considered, and it is assumed that each customer (message) must begin service (transmission) by an individually varying extinction time or else it is lost. Interest is in minimizing, in the sense of stochastic order, the number of messages lost over any time interval. A variety of results is proved that establishes the optimality of the shortest-time-to-extinction policy under rather general conditions. Similar results are found when messages have constraints on their complete transmission times. A network of M stations in tandem is considered under the hypothesis that a message is never lost and is scheduled irrespective of whether its extinction time (also called due date in this case) has expired or not. Under fairly general assumptions on the arrivals, deadlines, and services, it is shown that the earliest-due-date policy minimizes a form of average tardiness incurred over a finite operating horizon among all non-idling nonpreemptive policies. These problems are formulated in the context of stochastic dominance, and simple interchange arguments are used to establish all results     

An Approximate Model of Multistage Automatic Transfer Lines with Possible Scrapping Of Workpieces

We consider multistage automatic transfer lines with unreliable stages, finite interstage buffer storages, and possible scrapping of workpieces. It is assumed that the first stage never idles and the last stage never becomes blocked. Assuming that uptimes and downtimes of a stage are geometrically distributed, an approximate model is developed to compute different performance measures of the transfer line. The results obtained through the approximate model are compared to the exact results for three-stage transfer lines and to simulation results for longer transfer lines. It is observed that the approximate results are good in almost all cases considered.     

Aggregation of Induction Motor Loads for Transient Stability Studies

This study investigates the dynamic representation of a group of induction motors by one or more equivalent motors. The unknown parameters of the equivalent are estimated through a weighted-least-squares procedure. Verification of simulated results with experimental ones suggests that a fifth order dynamic model of the aggregate with a ninth order parameter model is appropriate. The least squares technique was found to provide good convergence characteristics subject to satisfaction of the following conditions good initial estimate of the parameters, proper selection of acceleration factors and homogenity of the motor group.     

Optical performance of a composite parabolic trough

The effects of receiver misplacement and the trough pointing towards the sun on the concentration characteristics of a composite parabolic trough are discussed. Results from some numerical calculations are presented graphically and discussed.