Improvements in meta-heuristic algorithms for minimum cost design of reinforced concrete rectangular sections under compression and biaxial bending

A numerical procedure is proposed in this paper for achieving the minimum cost design of reinforced concrete rectangular sections under compression and biaxial bending by using biologically-inspired meta-heuristic optimization algorithms. The problem formulation includes the costs of concrete, reinforcement and formwork, obtaining the detailed optimum design in which the section dimensions and the reinforcement correspond to values used in practice. The formulation has been simplified in order to reduce the computational cost while ensuring the rigor necessary to achieve safe designs. The numerical procedure includes the possibility of using high-strength concrete and several design constraints, such as mínimum reinforcement and limiting the neutral axis depth. Two numerical examples are presented, drawing comparisons between the results obtained by ACI318 and EC2 standards

An experimental research programme on heterogeneous combustion processes under microgravity conditions. Preliminary results

In the present work preliminary results are given of an experimental programme on flame spreading over the surface of PMMA rods in NgO2 mixtures under microgravity conditions. Results were obtained in the NASA KC-135 aircraft laboratory. Six experiments were carried out in March of this year and 36 more experiments will be conducted in March 1987. These preliminary experiments allowed to determine the flame spreading velocities for three different mixture compositions, showing that they were smaller but of the same order of magnitude than downwards spreading velocities at one g and for the same mixture condition

An Experimental Programme on Flame Spreading at Reduced Gravity Conditions.

An experimental programme on flame spreading over the surface of polymethylmetacrylate (PMMA) samples has been conducted at reduced gravity conditions in the NASA KC-135 air craft laboratory. A total of 36 experiments were performed. From the results of these experiments the flame spreading velocities over PMMA samples have been obtained, as well as their laws of variation with pressure and mixture composition. Both cylindrical and flat samples have been investigated. These results were compared with those obtained for the same conditions of pressure and composition on the ground at 1 g. In this way it was shown how gravity does influence the spreading process and how this influence was affected by pressure and mixture composition

Why do we smile? On the determinants of the implied volatility function.

We report simple regressions and Granger causality tests in order to understand the pattern of implied volatilities across exercise prices. We employ all calls and puts transacted between 16:00 and 16:45 on the Spanish IBEX-35 index from January 1994 to April 1996. Transaction costs, proxied by the bid–ask spread, seem to be a key determinant of the curvature of the volatility smile. Moreover, time to expiration, the uncertainty associated with the market and the relative market momentum are also important variables in explaining the smile.Smiles; Bid–ask spread; Volatility; Causality;

El analista de gestión, la gestión del conocimiento y la personalidad de las organizaciones

El trabajo tiene por objetivo sugerir que el Controller o Analista de la Gestión amplíe la visión de su labor incorporando a la misma el estudio de los comportamientos de los directivos, gerentes y empleados de la empresa en un contexto que se presenta como sumamente incierto y con alto grado de competitividad. Esta nueva competencia trasciende lo meramente económico e incorpora lo “humanístico" en la comprensión del factor humano y su correlación con el sistema de control. A partir de un cuadro muy ilustrativo tomado del autor argentino Ricardo A. Ferraro en su libro “La Marcha de los Locos", los autores de este trabajo se preguntan si las empresas están dando respuestas al macrocontexto existente o si, por el contrario, estarían en camino de emprender aquella marcha. Y agregan que este interrogante debe ser dilucidado, entre otros, por el Controller o Analista de Gestión. Proponen abordar la tarea en un proceso de cuatro fases, a saber: Fase I: Análisis de la situación actual del mundo de las empresas y el trabajo; Fase II: Análisis de las Disciplinas que contribuyen al aprendizaje en las organizaciones (para adaptarse a los cambios situacionales); Fase III: Análisis de perfiles atribuibles líderes, gerentes y empleados como forma de reconocer algunos patrones indicativos del comportamiento y/u orientación de la empresa; Fase IV: Propuesta de formulación de indicadores representativos de la “cultura organizacional". El trabajo incluye la referencia a nuevas disciplinas que han aparecido últimamente como la Economía de la Conducta o la Neuroeconomía, la Sociología y una encuesta de Gallupp sobre 300.000 unidades económicas para finalmente proponer una lista de quince (15) indicadores que entienden como apropiados para comenzar a cumplir la labor previstaFil: Sánchez, Esther. Universidad Nacional de Cuyo. Facultad de Ciencias EconómicasFil: Troncoso, Gregorio Ramón. Universidad Nacional de Cuyo. Facultad de Ciencias Económica

Smiles, Bid-ask Spreads and Option pricing.

Given the evidence provided by Longstaff (1995), and Peña, Rubio and Serna (1999) a serious candidate to explain the pronounced pattern of volatility estimates across exercise prices might be related to liquidity costs. Using all calls and puts transacted between 16:00 and 16:45 on the Spanish IBEX‐35 index futures from January 1994 to October 1998 we extend previous papers to study the influence of liquidity costs, as proxied by the relative bid‐ask spread, on the pricing of options. Surprisingly, alternative parametric option pricing models incorporating the bid‐ask spread seem to perform poorly relative to Black‐Scholes.smiles; bid-ask spread; implied volatility function; option pricing;

El litoral: problemática y gestión

Sin resume

A study of the combustion problems of solid materials at conditions existing in space stations

Combustión of a solid at microgravity conditions at zero or at very small forced flow velocities is in the first place discussed, pointing out that this is the basic process of a fire in a manned spacecraft, in which might exist small air currents originated by the air conditioning equipment or by the motion of the people. Results of an experimental programme carried out in the 23rd ESA Flight campaign 96/12 and utilising a NASA aircraft laboratory, are shown and discussed. Six combustión chambers were utilised provided with video and infrared cameras. Non visible flames in the visual range were originated at two oxygen concentrations, and photographs were taken by means of an infrared camera. Several ignition tests at different oxygen concentrations were performed and flammability limits were obtained. Fíame spread velocities were measured and compared at three different gravity levéis (1 g, ~10"2 g and 10"4 g). A combustión research programme to be carried out in a Texus rocket, already in progress is briefly discussed. Finally, the scope of a complete research programme, which is in the process of being carried out in the NASA combustión module of the International Space Station is briefly resumed

Las enseñanzas técnicas en España

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