Labor demand and information technologies: evidence for Spain, 1980-2005

Utilizando la base de datos EU KLEMS, se contrasta la hipótesis de complementariedad entre habilidad y capital en los distintos sectores productivos en España en el periodo 1980-2005. Se analizan tres tipos de trabajadores clasificados según su nivel de habilidad sea alto, medio o bajo. Los activos de capital se van a clasificar entre activos TIC (tecnologías de la información y la comunicación) y activos no-TIC. La adquisición y el uso de activos TIC son costosos pero ha ido disminuyendo en el periodo en consideración en términos relativos a otros activos y al factor trabajo. El principal resultado que se obtiene es que existe un grado de sustituibilidad entre los trabajadores y los activos TIC a medida que la habilidad del trabajador va aumentando. De hecho, los activos TIC son muy complementarios con los trabajadores de alta habilidad. A lo largo del periodo analizado, la fracción de trabajadores con habilidad media y alta ha crecido un 21% y un 12%, respectivamente, en detrimento de los trabajadores de baja habilidad. Después de descomponer estos cambios, se descubre que existe un ajuste dentro de los sectores más que un ajuste del trabajo entre sectores.capital-skill complementarity, ICT, translog cost function, elasticity of substitution.

Variability in Quasar Broad Absorption Line Outflows I. Trends in the Short-Term versus Long-Term Data

Broad absorption lines (BALs) in quasar spectra identify high velocity outflows that likely exist in all quasars and could play a major role in feedback to galaxy evolution. The variability of BALs can help us understand the structure, evolution, and basic physical properties of the outflows. Here we report on our first results from an ongoing BAL monitoring campaign of a sample of 24 luminous quasars at redshifts 1.2<z<2.9, focusing on C IV 1549 BAL variability in two different time intervals: 4 to 9 months (short-term) and 3.8 to 7.7 years (long-term) in the quasar rest-frame. We find that 39% (7/18) of the quasars varied in the short-term, whereas 65% (15/23) varied in the long-term, with a larger typical change in strength in the long-term data. The variability occurs typically in only portions of the BAL troughs. The components at higher outflow velocities are more likely to vary than those at lower velocities, and weaker BALs are more likely to vary than stronger BALs. The fractional change in BAL strength correlates inversely with the strength of the BAL feature, but does not correlate with the outflow velocity. Both the short-term and long-term data indicate the same trends. The observed behavior is most readily understood as a result of the movement of clouds across the continuum source. If the crossing speeds do not exceed the local Keplerian velocity, then the observed short-term variations imply that the absorbers are <6 pc from the central quasar.Comment: 14 pages, 7 figures, accepted for publication in MNRA

Labor Demand and Information Technologies: Evidence for Spain, 1980-2005

Using the EU KLEMS dataset we test the capital-skill complementarity hypothesis in a cross-section of sectors in Spain between 1980 and 2005. We analyze three groups of workers, who are classed according to skill level: high, medium and low. Capital assets have been broken down into ICT (information and communication technologies) assets and non-ICT assets. Acquisition and usage costs of ICT assets declined throughout the period studied, both in absolute terms and relative to the other capital assets and workers. Our principal finding is that the substitutibility between workers and ICT assets falls as worker skill level rises. In fact, the ICT assets were strongly complement with highly skilled workers and were not substitutive with them. Throughout the period analyzed, the fraction of employed medium- and high-skill workers rose by 21% and 12%, respectively, to the disadvantage of low-skill workers. After decomposing these changes, we found that the latter were dominated by an ajustment within sectors more than by a composition effect or adjustment between sectors. These adjustments may be explained by reference to the estimated elasticities of substitution.capital-skill complementarity, ICT, translog cost function, elasticity of substitution.

Domestic hot water consumption vs. solar thermal energy storage: the optimum size of the storage tank

Many efforts have been made in order to adequate the production of a solar thermal collector field to the consumption of domestic hot water of the inhabitants of a building. In that sense, much has been achieved in different domains: research agencies, government policies and manufacturers. However, most of the design rules of the solar plants are based on steady state models, whereas solar irradiance, consumption and thermal accumulation are inherently transient processes. As a result of this lack of physical accuracy, thermal storage tanks are sometimes left to be as large as the designer decides without any aforementioned precise recommendation. This can be a problem if solar thermal systems are meant to be implemented in nowadays buildings, where there is a shortage of space. In addition to that, an excessive storage volume could not result more efficient in many residential applications, but costly, extreme in space consumption and in some cases too heavy. A proprietary transient simulation program has been developed and validated with a detailed measurement campaign in an experimental facility. In situ environmental data have been obtained through a whole year of operation. They have been gathered at intervals of 10 min for a solar plant of 50 m2 with a storage tank of 3 m3, including the equipment for domestic hot water production of a typical apartment building. This program has been used to obtain the design and dimensioning criteria of DHW solar plants under daily transient conditions throughout a year and more specifically the size of the storage tank for a multi storey apartment building. Comparison of the simulation results with the current Spanish regulation applicable, “Código Técnico de la Edificación” (CTE 2006), offers fruitful details and establishes solar facilities dimensioning criteria