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In order to reach food security in the country, it is necessary to intensify the production of fertilizers in a sustainable manner in order to obtain increases in productivity, generate economic profits, and increase the use of national raw materials to reduce imports. For these reasons it is necessary to determine the optimum conditions for the process of obtaining Single Superphosphate (SFS), from the phosphate rock and sulfuric acid at lab scale, and thus determine the values of the variables which intervene in that process and assure the maximum quality of the product. To carry out the research, the rotational centered factorial design 22 with star points was used in 13 experimental runs and an experiment matrix was elaborated with the independent variables, acid / rock ratio and percentage of sulfuric acid, in the range of 1.61-2.06 and 65% -75% respectively. As a result it was obtained that the optimum parameters in the range studied for the benefited Cuban rock are: H2SO4 concentration of 72% and acid / rock ratio of 2.02. The quality indexes of the Superphosphate Simple cured obtained with the optimum parameters are: assimilable phosphorus content of 12.28%, humidity 8.21% and free acidity 2.05%; acting in accordance with international product specifications. Resumen Con la finalidad de lograr la seguridad alimentaria en el país, es necesario intensificar de manera sostenible la producción de fertilizantes para obtener incrementos de productividad y generar ganancias económicas, potenciando el uso de materias primas nacionales para disminuir las importaciones. Es por ello que, en este trabajo se realizó el estudio de la determinación de las condiciones óptimas del proceso de obtención de Superfosfato Sencillo (SFS) a escala de laboratorio, a partir de la roca fosfórica y el ácido sulfúrico y con ello determinar los valores de las variables que intervienen en el mismo, y que aseguren la máxima calidad del producto. Para la realización de la investigación se utilizó el diseño factorial centrado rotacional 22 con puntos estrellas en 13 corridas experimentales y se elaboró una matriz de experimentos con las variables independientes, relación ácido/roca y porcentaje de ácido sulfúrico, en el intervalo de 1.61-2.06 y 65%-75% respectivamente. Como resultado se obtuvo que los parámetros óptimos en el intervalo estudiado para la roca cubana beneficiada fueron: concentración de H2SO4 de 72% y la relación ácido/roca de 2.02. Los índices de calidad del Superfosfato Sencillo curado obtenido con los parámetros óptimos son: contenido de fósforo asimilable de 12.28%, humedad 8.21% y acidez libre 2.05%; cumpliendo de forma general con especificaciones internacionales del producto.

The paper deals with the traffic control and job optimization in the marine canal system. The moving of vessels can be described as a set of discrete events and states. Some of these states can be undesirable such as conflicts and deadlocks. It is necessary to apply adequate control policy to avoid deadlocks and blocks the vessels’ moving only in the case of dangerous situation. This paper addresses the use of Petri net as modelling and scheduling tool in this context. To find better solutions the authors propose the integration of Petri net with a genetic algorithm. Also, a matrix based formal method is proposed for analyzing discrete event dynamic system (DEDS). The algorithm is developed to deal with multi-project, multi-constrained scheduling problem with shared resources. It is verified by a computer simulation using MATLAB environment.

The writers carried out experimental studies and theoretical conceptions on the plastic deformations of cantilever beams, simple and fixed beams under large impulse, and recognized the approximate calculating methods we proposed were quite in good agreement with the experimental results, so we tried to apply our methods to the more complicated structures, for instance continuous beams and rahmen structured etc. In this paper we treated the plastic deformations of continuos beams under large concentrated impulse. More details are described in the following sections.

This paper presents an application of Poisson distribution method for managing the optimal number of spare modules of the Croatian airspace surveillance system. Out of a large number of modules and electronic parts in operation, a set of 11 critical modules are identified which have experienced failures and replacements with identical modules in three years history data. Using Poisson distribution for the failure forecasting, maintenance planner can make optimal ordering of the critical spare modules for a following period by which is possible to avoid any backordering, spare module shortage and the most important operational shutdowns. The results were the creation of the Poisson model in predicting the failure rate of radar vital modules for sizing the initial stock of spare modules to be ordered along with other electronic equipment.KEYWORDSoptimization, spare parts, Poisson distribution, forecasting, maintenance, reliability, non-repairable parts

Copyright © International Union of Crystallography; After a brief review of the crystallographic Fourier transform problem, this paper compares three methods for its computer implementation with reference to core-storage capacity and computation time: the classic method, the simple Fast Fourier Transform algorithms and a new method. The first method needs, especially for a macromolecular three-dimensional structure, too many operations and therefore too long a computation time and poor accuracy. The remarkable FFT algorithm, on the other hand, leads to large savings in computation time with a better accuracy, but using no crystallographic symmetry wastes too much storage capacity. The third method, using FFT but taking into account Friedel's law by means of a simple in situ process, approximately halves the storage capacity as well as the computation time.