La tecnología en los 70: continuidad, transición y espera

A finales de Julio de mil novecientos sesenta y nueve, las televisiones de todo el mundo repetían una vez y otra las imágenes de Armstrong paseando por la superficie de la Luna. En los diálogos que se oían por los pasillos y las aulas de las universidades americanas se juzgaba que aquello no era sino una forma de distraer la atención de la gente para ocultar el problema que de verdad importaba: las noticias sobre la guerra del Vietnam. En octubre, más de quince millones de personas se manifestaban en Washington pidiendo el fin de la misma. Algunos estudiantes españoles recién llegados miraban a su alrededor tratando de adaptarse al nuevo medio en el que se encontraban. Parecía que en todas partes estaba empezando algo diferente. Les decían que la sociedad tenía que cambiar y que los nuevos tiempos verían nuevas formas de vida. De donde venían también recordaban que habían oído decir cosas similares aunque el sentido fuera otro.

Elastostatics

In this chapter, we are going to describe the main features as well as the basic steps of the Boundary Element Method (BEM) as applied to elastostatic problems and to compare them with other numerical procedures. As we shall show, it is easy to appreciate the adventages of the BEM, but it is also advisable to refrain from a possible unrestrained enthusiasm, as there are also limitations to its usefulness in certain types of problems. The number of these problems, nevertheless, is sufficient to justify the interest and activity that the new procedure has aroused among researchers all over the world. Briefly speaking, the most frequently used version of the BEM as applied to elastostatics works with the fundamental solution, i.e. the singular solution of the governing equations, as an influence function and tries to satisfy the boundary conditions of the problem with the aid of a discretization scheme which consists exclusively of boundary elements. As in other numerical methods, the BEM was developed thanks to the computational possibilities offered by modern computers on totally "classical" basis. That is, the theoretical grounds are based on linear elasticity theory, incorporated long ago into the curricula of most engineering schools. Its delay in gaining popularity is probably due to the enormous momentum with which Finite Element Method (FEM) penetrated the professional and academic media. Nevertheless, the fact that these methods were developed before the BEM has been beneficial because de BEM successfully uses those results and techniques studied in past decades. Some authors even consider the BEM as a particular case of the FEM while others view both methods as special cases of the general weighted residual technique. The first paper usually cited in connection with the BEM as applied to elastostatics is that of Rizzo, even though the works of Jaswon et al., Massonet and Oliveira were published at about the same time, the reason probably being the attractiveness of the "direct" approach over the "indirect" one. The work of Tizzo and the subssequent work of Cruse initiated a fruitful period with applicatons of the direct BEM to problems of elastostacs, elastodynamics, fracture, etc. The next key contribution was that of Lachat and Watson incorporating all the FEM discretization philosophy in what is sometimes called the "second BEM generation". This has no doubt, led directly to the current developments. Among the various researchers who worked on elastostatics by employing the direct BEM, one can additionallly mention Rizzo and Shippy, Cruse et al., Lachat and Watson, Alarcón et al., Brebbia el al, Howell and Doyle, Kuhn and Möhrmann and Patterson and Sheikh, and among those who used the indirect BEM, one can additionally mention Benjumea and Sikarskie, Butterfield, Banerjee et al., Niwa et al., and Altiero and Gavazza. An interesting version of the indirct method, called the Displacement Discontinuity Method (DDM) has been developed by Crounh. A comprehensive study on various special aspects of the elastostatic BEM has been done by Heisse, while review-type articles on the subject have been reported by Watson and Hartmann. At the present time, the method is well established and is being used for the solution of variety of problems in engineering mechanics. Numerous introductory and advanced books have been published as well as research-orientated ones. In this sense, it is worth noting the series of conferences promoted by Brebbia since 1978, wich have provoked a continuous research effort all over the world in relation to the BEM. In the following sections, we shall concentrate on developing the direct BEM as applied to elastostatics.

Current-voltage response of a spherical plasma contactor

A theoretical model for a contactor, collecting electrons from an ambient, unmagnetized plasma and emitting a current Iiis discussed. The relation between Ii and the potential bias of the contactor is found to be crucial for the formation of a quasineutral core around the anode and, consequently, for the current colleted. Approximate analytical laws and charts for the current-voltage response are provided.

An anodeless tether generator

A new simple concept for electron collection by an electrodynamic tether is presented. No anodic contactor Is needed, the tether itself, left bare, drawing a current with neither shielding nor magnetic effects. Application to a generator is discussed.

Application of a Bayesian/Generalised Least-Squares method to generate correlations between independent neutron fission yield data

Fission product yields are fundamental parameters for several nuclear engineering calculations and in particular for burn-up/activation problems. The impact of their uncertainties was widely studied in the past and valuations were released, although still incomplete. Recently, the nuclear community expressed the need for full fission yield covariance matrices to produce inventory calculation results that take into account the complete uncertainty data. In this work, we studied and applied a Bayesian/generalised least-squares method for covariance generation, and compared the generated uncertainties to the original data stored in the JEFF-3.1.2 library. Then, we focused on the effect of fission yield covariance information on fission pulse decay heat results for thermal fission of 235U. Calculations were carried out using different codes (ACAB and ALEPH-2) after introducing the new covariance values. Results were compared with those obtained with the uncertainty data currently provided by the library. The uncertainty quantification was performed with the Monte Carlo sampling technique. Indeed, correlations between fission yields strongly affect the statistics of decay heat. Introduction Nowadays, any engineering calculation performed in the nuclear field should be accompanied by an uncertainty analysis. In such an analysis, different sources of uncertainties are taken into account. Works such as those performed under the UAM project (Ivanov, et al., 2013) treat nuclear data as a source of uncertainty, in particular cross-section data for which uncertainties given in the form of covariance matrices are already provided in the major nuclear data libraries. Meanwhile, fission yield uncertainties were often neglected or treated shallowly, because their effects were considered of second order compared to cross-sections (Garcia-Herranz, et al., 2010). However, the Working Party on International Nuclear Data Evaluation Co-operation (WPEC)

Efficiency of different types of ED-tether thrusters

The efficiencies of electrodynamic-tether (EDT) thrusters made of single bare tethers with different types of cross sections, several parallel bare tethers, or a fully insulated tether with a three-dimensional passive end-collector, are discussed. Current collection, mass, and ohmic resistance considerations are balanced against each other in discussing efficiencies. Use is made of recent results on the validity domain of orbital-motion-limited (OML) collection, the current law beyond that domain, and interference effects between parallel bare tethers; and on current adjustment to variations in electron density encountered in orbit. Comparisons between EDT thrusters and electrical thrusters in terms of the ratio of dedicated mass to the total mission impulse show EDT to be superior for mission times over 50-100 days.

Short tethers for electrodynamic thrust

The operational advantages of electrodynamic tethers of moderate length are becoming evident from studies of collision avoidance. Although long tethers (of order of 10 kilometers) provide high efficiency and good adaptability to varying plasma conditions, boosting tethers of moderate length (- 1 kilometer) and suitable design might still operate at acceptable efficiencies and adequate adaptability to a changing environment. In this paper we carry out a parametric analysis of the performance of 1-km long boosting tethers, to maximize their efficiency. We also discuss the possible use of multiple, parallel such tethers for keeping thrust high when length is decreased. We then estimate the survivability of short tethers to micrometeoroids and orbital debris. Finally, a few considerations are made on the dynamic stability of electrodynamic tether systems versus length.

BETs: Propellant less de orbiting of space debris by bare electrodynamic tethers

As a fundamental contribution to limiting the increase of debris in the Space environment, a three-year project started on 1 November 2010 financed by the European Commission under the FP-7 Space Programme. It aims at developing a universal system to be carried on board future satellites launched into low Earth orbit (LEO), to allow de-orbiting at end of life. The operational system involves a conductive tape-tether left bare of insulation to establish anodic contact with the ambient plasma as a giant Langmuir probe. The project will size the three disparate dimensions of a tape for a selected de-orbit mission and determine scaling laws to allow system design for a general mission. It will implement control laws to restrain tether dynamics in/off the orbital plane; and will carry out plasma chamber measurements and numerical simulations of tether-plasma interaction. The project also involves the design and manufacturing of subsystems: electron-ejecting plasma contactors, an electric control and power module, interface elements, tether and deployment mechanisms, tether tape/end-mass as well as current collection plus free-fall, and hypervelocity impact tests.

Palabras pronunciadas por el Catedrático de la Universidad Politécnica de Madrid Profesor Dr. D. José Antonio Martín Pereda en el acto de investidura de Doctor "Honoris Causa" del Profesor Dr. William A. Gambling

El autor reflexiona sobre la trayectoria investigadora y académica del Dr. William A. Gambling, destacado científico dedicado al campo de las Comunicaciones Ópticas.

Pinceladas de veinte años: algunos recuerdos de un plan

Análisis sobre lo conseguido en veinte años (desde los ochenta hasta principios de este siglo) en el campo de la investigación gracias al Plan Nacional de I+D.

An Assessment of Lithium Resources

Se hace un estudio de los recursos de una sustancia estratégica para la UE, a fin de orientar las investigaciones para un incremento de reservas que garanticen el abastecimiento de esta materia prima de gran demanda

Las estructuras

La afirmación de que las primeras realizaciones arquitectónicas y de ingeniería estructural son tan antiguas como la civilización no es gratuita. En efecto, tan pronto como se desea cubrir un espacio, salvar un vano o transmitir un empuje (vertical u horizontal), es preciso el desarrollo de un conocimiento específico. El dominio de las técnicas para resolver,en particular, tales problemas ha sido transmitido a través de construcciones religiosas o áulicas que han permanecido a través de los siglos como puntos de referencia y muestra de la habilidad, el ingenio y la audacia de las generaciones predecesoras. Obras como el puente de Alcántara (Cáceres), la mezquita de Córdoba y el monasterio de El Escorial (Madrid) -de los siglos I, X y XVI, respectivamente- demuestran la personalidad de sus proyectistas pero también sus conocimientos constructivos, su capacidad organizadora y la ambición y poderío económico de sus promotores. De hecho, aunque la habilidad para combinar mecanismos estructurales se encuentra en todos los artefactos manejados por el hombre, es en el ámbito de la edificación y de las obras públicas donde, hasta épocas relativamente recientes, se encuentran los ejemplos más espectaculares de estructuras resistentes. Éstos sólo aparecen, sin embargo, cuando coincide la calidad de cada uno de los tres factores que intervienen en la obra, es decir, un proyectista con imaginación y conocimientos, una industria de la construcción capaz de ofrecerle los materiales más adecuados y de llevar a cabo los procesos constructivos que aquél imagine, y un promotor con solvencia económica pero también capaz de calibrar las ventajas de las soluciones que se ofrecen y apreciar factores imponderables como la innovación o la estética, que tanto añaden al cumplimiento de los factores utilitarios que se encuentran en la motivación de las construcciones. A lo largo de la historia los proyectistas españoles han dado pruebas de calidad en algunas realizaciones que se comentarán a continuación y siempre han demostrado un buen conocimiento del estado del arte en el exterior.Sin embargo, no puede decirse que ése haya sido el caso de los promotores o de la industria que, por uno u otro motivo, se ha visto muy afectada por avatares políticos o decisiones económicas equivocadas. Las quejas de Pablo Alzola sobre el "espíritu cosmopolita con que abrimos nuestras puertas a quienes nos las cierran herméticamente", el cual, en el siglo XIX, facilitó las franquicias a la importación de materiales relacionados con la industria ferroviaria, condenando esta importación "a muerte el porvenir de la industria española de hierro y acero, base muy principal de prosperidad en todas las naciones juntas", resuenan de nuevo en relación con la integración europea. Ello se explica por la tendencia general hacia el rendimiento inmediato de las capitales con la consiguiente destecnificación propia y penetración de productos extranjeros conseguidos mediante una investigación coordinada entre administración, industria y universidad. La falta de grupos organizados, de lo que es una interesante excepción la industria del hormigón, ha provocado en muchos ámbitos una ausencia de legislación propia que la industria nacional actualmente echa en falta como defensa específica en términos técnicos.

Estudio de Caso Residencia de Carlota Jaramillo

Estudio de caso correspondiente a la rehabilitación de la vivienda en donde nació la reconocida cantante ecuatoriana Carlota Jaramillo, que inmortalizó entre otros la música nacional, ubicada en la población de Calacalí. Construida con técnicas vernáculas de la serrania ecuatoriana, se rehabilitó para convertirla en casa-museo, volviendo a poner en práctica dichas técnicas de construcción, debido al estado ruinoso en que se hallaba, rescatando así un testigo patrimonial de arquitectura popular de inicios del siglo XX.