Discretization of implicit ODEs for singular root-finding problems

AbstractThis paper addresses the use of dynamical system theory to tackle singular root-finding problems. The use of continuous-time methods leads to implicit differential systems when applied to singular nonlinear equations. The analysis is based on a taxonomy of singularities and uses previous stability results proved in the context of quasilinear implicit ODEs. The proposed approach provides a framework for the systematic formulation of quadratically convergent iterations to singular roots. The scope of the work includes also the introduction of discrete-time analysis techniques for singular problems which are based on continuous-time stability and numerical stability. Some numerical experiments illustrate the applicability of the proposed techniques

Stability of Singular Equilibria in Quasilinear Implicit Differential Equations

AbstractThis paper addresses stability properties of singular equilibria arising in quasilinear implicit ODEs. Under certain assumptions, local dynamics near a singular point may be described through a continuous or directionally continuous vector field. This fact motivates a classification of geometric singularities into weak and strong ones. Stability in the weak case is analyzed through certain linear matrix equations, a singular version of the Lyapunov equation being especially relevant in the study. Weak stable singularities include singular zeros having a spherical domain of attraction which contains other singular points. Regarding strong equilibria, stability is proved via a Lyapunov–Schmidt approach under additional hypotheses. The results are shown to be relevant in singular root-finding problems

Augmented nodal matrices and normal trees

AbstractAugmented nodal matrices play an important role in the analysis of different features of electrical circuit models. Their study can be addressed in an abstract setting involving two- and three-colour weighted digraphs. By means of a detailed characterization of the structure of proper and normal trees, we provide a unifying framework for the rank analysis of augmented matrices. This covers in particular Maxwell’s tree-based determinantal expansions of (non-augmented) nodal matrices, which can be considered as a one-colour version of our results. Via different colour assignments to circuit devices, we tackle the DC-solvability problem and the index characterization of certain differential–algebraic models which arise in the nodal analysis of electrical circuits, extending several known results of passive circuits to the non-passive context

Monitoring of river contamination derived from acid mine drainage using airborne imaging spectroscopy (HyMap data, South-West Spain)

Imaging spectroscopy is used in this work as an essential mapping tool to monitor changes in contaminated river sediments. Multidate hyperspectral image data (HyMap) are utilized to identify spatial mineral patterns, to detect temporal changes in mineralogy and to link these changes with geochemical processes and short-term climate characteristics. River sediments contaminated by acid mine drainage are covered by crusts with variably hydrated iron sulphate. The mineralogy of the crusts and the grain size of the underlying fluvial sediments overlap. The spectra used to build up maps from HyMap data are diagnosed mineralogically with archive spectral libraries from pyrite oxidation minerals from well-known sequences of minerals. The maps compiled from hyperspectral imagery display generalized oxidation shown by the coatings over river sediments following warm and dry periods with low water level. After the wet periods, the area covered by oxidized mineralogical phases recedes in favour of hydrated sulphate. The iteration of image processing algorithms and the mineralogical and potential contamination in a geological context are described. Change detection of the mineral crusts on the river sediments by mapping using hyperspectral remote sensing data may thus enable a quantitative and qualitative environmental evaluation by the regulators

Ignition and combustion of single particles of coal and biomass under O2/CO2 atmospheres

Biomass energy with carbon dioxide capture and storage (CCS) technologies like oxy-fuel is the only way to achieve net removal of CO2 from the atmosphere in power generation. A single particle apparatus has been developed for rapid heating and combustion of individual fuel particles in air or O2/CO2 atmospheres. This wire mesh apparatus was used as a heating element to heat the particle by radiation while optical access allowed particle combustion characterization by high speed camera recording. Four different biomass and a bituminous coal were used in air and 21, 30 and 40% O2 atmospheres with balance of CO2. High speed video image analysis showed differences in ignition and devolatilization behaviour. The influence of particle size and mass on burnout times was higher in the coal, while biomass particle size can have a greater range of sizes for the same burnout times. The 30%O2 atmosphere was enough to have less burnout time than in air atmosphere for all the samples. During biomass particle combustion, the results showed that the surface tension on the biomass char particle plays a significant role due to partial melting of the char particle. This effect modifies the char particle shape during its combustion, with particles becoming more spherical particle even for those that initially had a fibrous shape

Students’ Active Role on the Assessment of Learning Results in Blended-Learning Environments in Engineering in Spain

[EN]In this paper we present an assessment experience with students, based on the use on Information and Communication Technologies (Hereafter ICTs). This process has been developed in the framework of the Research project I+D+i EDU2009-08758, in which one of the main research areas is that of assessing learning in university context, and, more specifically, in the field of Engineering degrees in Spain. The main objective is that of systematize the assessment process carried out in the subject of Computing Systems, already adapted to the European Space for Higher Education guidelines. For this purpose, we have used EvalCOMIX tool, implementing with it several assessment scales that systematize evaluation processes, make students get involved in the process and provide with necessary feedback when required

AISA Eagle II hyperspectral data for carbonate geological mapping in a vegetated high relief area: a geologically orientated atmospheric correction

[EN] Carbonated rocks are crucial targets for oil exploration, outcropping often in large areas with minimum spectral differences among geological units. The typical carbonate spectral absorptions in 2200 nm and 2300 nm, are excluded from the wavelength range of AISA Eagle II. AISA Eagle II hyperspectral data are processed in flight lines of 1024 swath pixels in the visible to near-infrared wavelength range (400 to 970 nm). The flight has a spatial resolution of 1 m and records a total of 128 channels with a spectral resolution of 4,8 nm. The area of study is a carbonate rocky mountain densely vegetated, covered by variably dense trees and bushes. Masking vegetation cover and shade effects is prior to any geological analysis using hyperspectral image processing. Carbonate units occur in mountain slopes, with small areas of ridges of rock outcrops and wide fans of loose material. The background soil of different geological units differ spectrally only by overall reflectance. Instead, limestone rocky outcrops display spectral responses with smooth typical iron oxide absorptions that distinguish them apart from loose boulders of limestone. Trying to enhance spectral differences in the visible wavelength range among carbonate geological units, an atmospheric correction using field spectra from geologically selected targets in a limestone quarry was performed. This way, it was possible to map apart lithologically similar detrital units dominated by carbonate in a river plain. The limy river bottom displays spectra with a straight line in the visible wavelength range due to abundant organic matter and small grain size. The spectra of the upper terraces record spectral absorption features related to iron oxide contents similar to the rock outcrops in ridges of mountains. The use of field spectra from geologically selected targets improves the mapping capability of hyperspectral imagery in areas with geological units with a homogeneous spectral response.[ES] Las calizas son rocas críticas en la exploración de petróleo. Desarrollan series estratigráficas a menudo espesas, que afloran con frecuencia en zonas extensas de la superficie terrestre. Estas formaciones litológicas predominantemente carbonatadas presentan diferencias espectrales mínimas entre sí, que permiten su diagnóstico por su respuesta espectral y su cartografía con imágenes. Las bandas de absorción espectral típicas de los carbonatos en 2200 nm y 2300 nm no forman parte del intervalo de longitudes de onda del espectrómetro AISA Eagle II (400 nm-970 nm), con una resolución espectral de 4,8 nm en 128 canales, y 1 m de resolución espacial en el vuelo de estudio. La zona de estudio se encuentra localizada en el Prepirineo español formando un relieve rocoso carbonatado con vegetación densa. El suelo de las distintas formaciones geológicas carbonatadas cartografiadas se distingue espectralmente sólo por su reflectancia global. Los afloramientos rocosos de calizas in situ presentan respuestas espectrales con absorciones típicas de óxidos de hierro. La expresión espectral de las formaciones calizas en las imágenes iniciales mostraban defectos sistemáticos. Para conseguir espectros geológicamente diagnosticables con espectrotecas de referencia, se ha ensayado una corrección atmosférica con espectros de campo tomados en una cantera de calizas, y en afloramientos rocosos de formaciones calcáreas seleccionados, con un espectrómetro de campo y laboratorio ASD Fieldspec 3. En las imágenes hiperespectrales así corregidas, se cartografían formaciones geológicas litológicamente similares correspondientes a la cuenca fluvial del río Noguera Ribagorzana, a su paso por Alfarrás (Lérida), en la que los sedimentos de la llanura aluvial con limos de materiales comparativamente más finos y materia orgánica, presentan espectros típicos con un trazo rectilíneo en el visible, que no aparecía en las imágenes anteriores a la corrección. El uso de espectros de campo seleccionados con criterios geológicos para la corrección atmosférica de imágenes hiperespectrales, mejora la capacidad de las imágenes para elaborar cartografías de formaciones litológicamente similares usando espectrotecas de referencia.El sensor AISA Eagle II fue cedido en préstamo por SPECIM al Institut Cartogràfic i Geològic de Catalunya (ICGC) para su prueba en vuelo y pre-tratamiento digital. Los estudios de interpretación geológica se han realizado en un convenio entre la Universidad de Barcelona y REPSOL Exploración para formación postdoctoral. Las bases para comenzar este trabajo surgieron durante la tesis doctoral de Buzzi (BES-2008-003648).Buzzi, J.; Costa, E.; Riaza, A.; Fernández, O.; García-Sellés, D.; Corbera, J. (2018). Cartografía de calizas con datos hiperespectrales AISA Eagle II en una zona montañosa con vegetación densa: cómo orientar geológicamente la corrección atmosférica. Revista de Teledetección. (51):125-133. https://doi.org/10.4995/raet.2018.8998SWORD12513351ASD. 2006. FieldSpecR 3 User Manual, ASD Document 600540 Rev. F. Analytical Spectral Devices, Inc. Disponible en: http://www.asdi.com [Último acceso: junio de 2018].Buzzi, J. 2012. Imaging spectroscopy to evaluate the contamination from sulphide mine waste in the Iberian Pyrite Belt using hyperspectral sensors (Huelva, Spain), Tesis Doctoral Universidad de León, 212 p.Buzzi, J., Riaza, A., García-Meléndez, Carrère, V., Bachmann, M. 2011. Aplicación de modelos Gaussianos modificados a datos hiperespectrales de una zona contaminada por drenaje ácido. Caso del río Odiel (Huelva, España). XIV Congreso de la Asociación Española de Teledetección, Mieres, 21- 23 Septiembre 2011, 285-288.Clark, R.N., Swayze, G.E., Wise, R., Livo, E., Hoefen, T., Kokaly, R., Sutley, S.J. 2007. USGS Digital Spectral Library splib06a. Digital Data Series 231, USGS: Denver, Co, USA, 2007.EXELIS, 2011. ENVI User's Guide. Exelis Visual Information Solutions: Boulder, Co, USA.Hunt, G.R., Salisbury, J.W. 1971a. Visible and Near-infrared Spectra of Minerals and Rocks: II. Carbonates. Modern Geology, 2, 23-30.Hunt, G.R., Salisbury, J.W., Lenhof, J. 1971b. Visible and Near-infrared Spectra of Minerals and Rocks: III Oxides and Hydroxides. Modern Geology, 2, 191-205.Hunt, G.R., Salisbury, J.W., 1976. Visible and Near-infrared Spectra of Minerals and Rocks: XI. Sedimentary Rocks. Modern Geology, 5, 211-217.López-Mir, B., Antón Muñoz, J., García-Senz, J. 2016, 3D geometric reconstruction of Upper Cretaceous passive diapirs and salt withdrawal basins in the Cotiella Basin (southern Pyrinees), Journal of the Geological Society, 173, 616-627. https://doi.org/10.1144/jgs2016-002Martínez, L., Tardà, A., Palà, V., Arbiol, R. 2006. Atmospheric correction algorithm applied to CASI multi-height hyperspectral imagery. Proceedings Second International Symposium Recent Advances in Quantitative Remote Sensing, 25-29 Septiembre 2006.Riaza, A. Buzzi, J., García-Meléndez, E., del Moral, B., Carrère, V., Richter, R. 2017. Monitoring salt crusts on an AMD contaminated coastal wetland using hyperspectral Hyperion data (Estuary of the River Odiel, SW Spain). International Journal of Remote Sensing, 38(12), 3735-3762. https://doi.org/10.1080/01431161.2017.1302621Riaza, A., García-Meléndez, E., Carrère, V., Mueller, A. 2014. Cartografía de sales marinas y fluviales en estuarios receptores de aguas ácidas con imágenes hiperespectrales Hyperion (Marismas del río Odiel, Huelva). Revista de Teledetección, 41, 1-7. https://doi.org/10.4995/raet.2014.2255Riaza, A., Buzzi, J., García-Meléndez, E., Carrère, V., Müller, A. 2011. Monitoring the extent of contamination from acid mine drainage in the Iberian Pyrite Belt (SW Spain) using hyperspectral imagery. Remote Sensing, 3, 2166-2186. https://doi.org/10.3390/rs3102166Riaza, A., Buzzi, J., García-Meléndez, E., Vázquez, I., Bellido, E., Carrère, V., Müller, A. 2012. Pyrite mine waste and water mapping using Hymap and Hyperion hyperspectral data. Environmental Earth Sciences, 66-7, 1957-1971. https://doi.org/10.1007/s12665-011-1422-

Biomass fuel flexibility in future conventional power generation

Power generation from the combustion of solid fuels has been a conventional technology for electricity production in the UK and most of the world for many decades. While the phasing out of coal as a fuel is an important aspect of the ‘decarbonising’ the electricity sector, the respective power plant technology could still play an important role into the future by use of abundant sources of solid biomass fuels. If such resources are to be effectively utilised, it is then necessary to accommodate the wide variation in the characteristics and behaviour of biomass fuels. Some of the key challenges in this context include: control of burn-out efficiency for different fuels; predictability of ash behaviour including operational problems and emissions arising from high ash and high potassium content fuels; the fate of fuel nitrogen content and the consequent effects on NOx emissions. This article presents an overview of these issues, their significance in the context of power plant design and operation and details of some recent research seeking to address them. Results of laboratory scale experiments showing the variation in properties and behaviour of different types of biomass fuel are also presented. These include studies on the relationship between fuel particle size and burn-out duration, gas-phase potassium release from biomass materials during combustion, variability in biomass ash composition and nitrogen release patterns from fuels in high temperature combustion