Feedback linearization control for a distributed solar collector field

This article describes the application of a feedback linearization technique for control of a distributed solar collector field using the energy from solar radiation to heat a fluid. The control target is to track an outlet temperature reference by manipulating the fluid flow rate through the solar field, while attenuating the effect of disturbances (mainly radiation and inlet temperature). The proposed control scheme is very easy to implement, as it uses a numerical approximation of the transport delay and a modification of the classical control scheme to improve startup in such a way that results compared with other control structures under similar conditions are improved while preserving short commissioning times. Experiments in the real plant are also described, demonstrating how operation can be started up efficiently.Ministerio de Ciencia y Tecnología DPI2004-07444-C04-04Ministerio de Ciencia y Tecnología DPI2005-0286

The dynamics of correlated novelties

One new thing often leads to another. Such correlated novelties are a familiar part of daily life. They are also thought to be fundamental to the evolution of biological systems, human society, and technology. By opening new possibilities, one novelty can pave the way for others in a process that Kauffman has called "expanding the adjacent possible". The dynamics of correlated novelties, however, have yet to be quantified empirically or modeled mathematically. Here we propose a simple mathematical model that mimics the process of exploring a physical, biological or conceptual space that enlarges whenever a novelty occurs. The model, a generalization of Polya's urn, predicts statistical laws for the rate at which novelties happen (analogous to Heaps' law) and for the probability distribution on the space explored (analogous to Zipf's law), as well as signatures of the hypothesized process by which one novelty sets the stage for another. We test these predictions on four data sets of human activity: the edit events of Wikipedia pages, the emergence of tags in annotation systems, the sequence of words in texts, and listening to new songs in online music catalogues. By quantifying the dynamics of correlated novelties, our results provide a starting point for a deeper understanding of the ever-expanding adjacent possible and its role in biological, linguistic, cultural, and technological evolution

Splashing of liquids: interplay of surface roughness with surrounding gas

We investigate the interplay between substrate roughness and surrounding gas pressure in controlling the dynamics of splashing when a liquid drop hits a dry solid surface. We associate two distinct forms of splashing with each of these control parameters: prompt splashing is due to surface roughness and corona splashing is due to instabilities produced by the surrounding gas. The size distribution of ejected droplets reveals the length scales of the underlying droplet-creation process in both cases.Comment: 6 pages, 6 figure

Isoprenoid emission in trees of Quercus pubescens and Quercus ilex with lifetime exposure to naturally high CO2 environment

The long-term effect of elevated atmospheric CO2 on isoprenoid emissions from adult trees of two Mediterranean oak species (the monoterpene-emitting Quercus ilex L. and the isoprene-emitting Quercus pubescens Willd.) native to a high-CO2 environment was investigated. During two consecutive years, isoprenoid emission was monitored both at branch level, measuring the actual emissions under natural conditions, and at leaf level, measuring the basal emissions under the standard conditions of 30 degreesC and at light intensity of 1000 mumol m(-2) s(-1). Long-term exposure to high atmospheric levels of CO2 did not significantly affect the actual isoprenoid emissions. However, when leaves of plants grown in the control site were exposed for a short period to an elevated CO2 level by rapidly switching the CO2 concentration in the gas-exchange cuvette, both isoprene and monoterpene basal emissions were clearly inhibited. These results generally confirm the inhibitory effect of elevated CO2 on isoprenoid emission. The absence of a CO2 effect on actual emissions might indicate higher leaf temperature at elevated CO2, or an interaction with multiple stresses some of which (e.g. recurrent droughts) may compensate for the CO2 effect in Mediterranean ecosystems. Under elevated CO2, isoprene emission by Q. pubescens was also uncoupled from the previous day\u27s air temperature. In addition, pronounced daily and seasonal variations of basal emission were observed under elevated CO2 underlining that correction factors may be necessary to improve the realistic estimation of isoprene emissions with empirical algorithms in the future. A positive linear correlation of isoprenoid emission with the photosynthetic electron transport and in particular with its calculated fraction used for isoprenoid synthesis was found. The slope of this relationship was different for isoprene and monoterpenes, but did not change when plants were grown in either ambient or elevated CO2. This suggests that physiological algorithms may usefully predict isoprenoid emission also under rising CO2 levels

Defining and identifying communities in networks

The investigation of community structures in networks is an important issue in many domains and disciplines. This problem is relevant for social tasks (objective analysis of relationships on the web), biological inquiries (functional studies in metabolic, cellular or protein networks) or technological problems (optimization of large infrastructures). Several types of algorithm exist for revealing the community structure in networks, but a general and quantitative definition of community is still lacking, leading to an intrinsic difficulty in the interpretation of the results of the algorithms without any additional non-topological information. In this paper we face this problem by introducing two quantitative definitions of community and by showing how they are implemented in practice in the existing algorithms. In this way the algorithms for the identification of the community structure become fully self-contained. Furthermore, we propose a new local algorithm to detect communities which outperforms the existing algorithms with respect to the computational cost, keeping the same level of reliability. The new algorithm is tested on artificial and real-world graphs. In particular we show the application of the new algorithm to a network of scientific collaborations, which, for its size, can not be attacked with the usual methods. This new class of local algorithms could open the way to applications to large-scale technological and biological applications.Comment: Revtex, final form, 14 pages, 6 figure

About the use of generalized forms of derivatives in the study of electromagnetic problems

The use of non-local operators, defining Riemann–Liouville or Caputo derivatives, is a very useful tool to study problems involving non-conventional diffusion problems. The case of electric circuits, ruled by non-integer derivatives or capacitors with fractional dielectric permittivity, is a fairly natural frame of relevant applications. We use techniques, involving generalized exponential operators, to obtain suitable solutions for this type of problems and eventually discuss specific problems in applications

Shaking Scenarios from Multiple Source Models Shed Light on the 8 September 1905 Mw 7 Calabria Earthquake (Southern Italy)

4noThe earthquake (Mw 7) that struck western Calabria (southern Italy) on 8 September 1905 profoundly struck a broad region, causing 557 deaths, injuring more than 2000 people, and leaving about 300,000 people homeless. Historical documents also reported a tsunami, although not devastating, for which effects were observed both along the coast and offshore. For all the damage it caused, this event was much studied but not fully explained. Literature source models for the 1905 earthquake are numerous and diverse, in fault geometry, location, and even associated magnitude. They also differ in nature, because these solutions are either field-based or derived from tsunami modeling and macroseismic data inversion. Above all, few or none of the previously published source models appear to be fully compatible with the damage pattern caused by this earthquake. To contribute to the identification of the seismogenic source of this destructive event, we computed a series of ground-shaking scenarios based on the different fault-source models that various authors associated with this event. The only documented data available that are suitable for our comparative purposes are the macroseismic intensities associated with localities affected by the event. Our results show that shaking scenarios for two out of seven literature source models are compatible with the damage distribution caused by the 1905 earthquake. The different parameters and boundary conditions constraining these two solutions suggest that either seismogenic source should include further complexities. Alternatively, because these two sources are antithetic and partially form a graben, they might have kinematically interacted, if passively, on 8 September 1905. Also, our critical analysis attempts to take site effects into account, at least qualitatively, allowing a more robust evaluation of damage distribution against numerical models.openembargoed_20160430Sandron, Denis; Loreto, Maria Filomena; Fracassi, Umberto; Tiberi, LaraSandron, Denis; Loreto, Maria Filomena; Fracassi, Umberto; Tiberi, Lar

A fast no-rejection algorithm for the Category Game

The Category Game is a multi-agent model that accounts for the emergence of shared categorization patterns in a population of interacting individuals. In the framework of the model, linguistic categories appear as long lived consensus states that are constantly reshaped and re-negotiated by the communicating individuals. It is therefore crucial to investigate the long time behavior to gain a clear understanding of the dynamics. However, it turns out that the evolution of the emerging category system is so slow, already for small populations, that such an analysis has remained so far impossible. Here, we introduce a fast no-rejection algorithm for the Category Game that disentangles the physical simulation time from the CPU time, thus opening the way for thorough analysis of the model. We verify that the new algorithm is equivalent to the old one in terms of the emerging phenomenology and we quantify the CPU performances of the two algorithms, pointing out the neat advantages offered by the no-rejection one. This technical advance has already opened the way to new investigations of the model, thus helping to shed light on the fundamental issue of categorization

Estructura de regulación con generación automática de consignas y control por adelanto para un campo de colectores solares

En este artículo se muestran los resultados de operación de un Campo de Colectores Solares del tipo Cilindro Parabólico de forma automática por una estructura de control por adelanto en paralelo con un controlador tipo I-PD con generación automática de consignas. El objetivo de control para este sistema es mantener la temperatura de salida del fluido que circula por las tuberías del campo a un valor establecido, a pesar de las perturbaciones a las que está sometida la planta. Dichas perturbaciones se producen en la temperatura del fluido que entra al campo, procedente de un tanque de almacenamiento térmico, en la temperatura ambiente o en la radiación solar. Esta última constituye la fuente primaria de energía del sistema. Las dificultades para operar la planta son debidas a las perturbaciones citadas anteriormente y que no son manipulables, a las no linealidades y a su dinámica compleja. Para ello se ha diseñado una estructura de control que mantiene la temperatura de salida de los lazos a un nivel que se determina automáticamente mediante un generador de consignas que tiene en cuenta las condiciones en las que se encuentra la planta (radiación, temperatura a la entrada y temperatura ambiente) y ciertos parámetros necesarios para la operación segura de la planta. La variable manipulada es la velocidad a la que una bomba de alimentación envía al campo solar el aceite procedente del tanque de almacenamiento. La energía térmica almacenada se utiliza para producir agua desalinizada o energía eléctrica.Ministerio de Ciencia y Tecnología DPI2001- 2380-C02Ministerio de Ciencia y Tecnología DPI2002-04375-C0