Identificación de parámetros con métodos numéricos para el modelado de sistemas eléctricos con dependencia frecuencial;Identification of parameters with numerical methods for the modelling of electrical systems with frequency dependence.

El artículo presenta una descripción detallada de las técnicas más utilizadas para hacer ajuste racional de funciones del dominio de la frecuencia. Las técnicas son: Aproximación Asintótica de Bode, Mínimos Cuadrados Ordinarios, Mínimos Cuadrados Iterativamente Reponderados, Ajuste Vectorial y Levenberg-Marquardt. Estas técnicas se comparan aproximando una función analítica. Después, se aplican al ajuste racional de parámetros dependientes de la frecuencia de una línea de transmisión monofásica. El efecto del ajuste se evalúa considerando los casos de línea abierta, corto circuito y perfectamente acoplada. La transformada numérica de Laplace (NLT) se utiliza como referencia para la evaluación. Se concluye que la adecuada implementación de cada técnica depende de varios factores; del tipo de función a ajustar, del rango de ajuste, y otros. Además, no es posible garantizar que una de las técnicas siempre converja al mejor resultado. El artículo propone algunas guías para seleccionar la técnica más adecuada para una aplicación particular. This paper provides a detailed description of the rational fitting techniques that are most used to approximate frequency domain functions. The techniques are: Bode asymptotic approximations, Ordinary Least-Squares, Iteratively Reweighted Least-Squares, Vector Fitting and Levenberg-Marquardt. These techniques are compared by approximating of an analytic function. Then, the techniques are applied to the rational-fitting of the frequency-dependent parameters corresponding to a single-phase transmission line. The effect of the rational representations is evaluated considering transients on cases of open-ended, short-circuited and perfectly matched lines. The numerical Laplace transform technique (NLT) is used as reference for the evaluations. It follows that the proper implementation of each fitting technique depends on various factors; the type of function being adjusted, the desired frequency range, an others. Moreover, one cannot guarantee that there is one of these techniques that will always yield the best fitting. The paper provides guidelines for selecting the most convenient one for a particular application.</p

Impact of COVID-19 outbreak on ischemic stroke admissions and in-hospital mortality in North-West Spain

Background and purpose Spain has been one of the countries heavily stricken by COVID-19. But this epidemic has not affected all regions equally. We analyzed the impact of the COVID-19 pandemic on hospital stroke admissions and in-hospital mortality in tertiary referral hospitals from North-West Spain.Methods Spanish multicenter retrospective observational study based on data from tertiary hospitals of the NORDICTUS network. We recorded the number of patients admitted for ischemic stroke between 30 December 2019 and 3 May 2020, the number of IVT and EVT procedures, and in-hospital mortality.Results In the study period, 2737 patients were admitted with ischemic stroke. There was a decrease in the weekly mean admitted patients during the pandemic (124 vs. 173, p<0.001). In-hospital mortality of stroke patients increased significantly (9.9% vs. 6.5%, p = 0.003), but there were no differences in the proportion of IVT (17.3% vs. 16.1%, p = 0.405) or EVT (22% vs. 23%, p = 0.504).Conclusion We found a decrease in the number of ischemic stroke admissions and an increase in in-hospital mortality during the COVID-19 epidemic in this large study from North-West Spain. There were regional changes within the network, not fully explained by the severity of the pandemic in different regions.Peer reviewe

Impact of COVID‐19 outbreak in reperfusion therapies of acute ischemic stroke in North‐West Spain

Since the first reported case in early December 2019, severe acute respiratory coronavirus 2 (SARS‐CoV‐2) infection, known as Coronavirus Disease 2019 (COVID‐19), has spread all over the world (1‐3). As of June 4th, more than 6 million cases and 350,000 deaths have been reported worldwide (4). Treating these patients and containing the outbreak has become the main priority in any center, arising the risk of possible collateral damage on patients with other acute diseases due to the collapse of the pre‐ and intra‐hospital emergency care systems.Peer reviewe

Spatial and temporal variability of periglaciation of the Iberian Peninsula

Active periglacial processes are currently marginal in the Iberian Peninsula, spatially limited to the highest mountain ranges. However, a wide variety of periglacial deposits and landforms are distributed in low and mid-altitude environments, which shows evidence of past periods of enhanced periglacial activity. The purpose of this paper is to summarize the present knowledge of past periglacial activity in the Iberian Peninsula. The chronological framework takes four main stages into account: the last glaciation, deglaciation, Holocene and present-day processes. This study focuses on the highest massifs (Pyrenees, Cantabrian Range, NW ranges, Central Range, Iberian Range, Sierra Nevada) as well as other lower elevation environments, namely the central Iberian Meseta. During the last glaciation the periglacial belt extended to much lower altitudes than today, reaching current sea level in the NW corner of the Iberian Peninsula. A wide range of geomorphological landforms and sedimentary records is indicative of very active periglacial processes during that phase, in some cases related to permafrost conditions (i.e., block streams, rock glaciers). Most of the inactive landforms and deposits in low and mid-elevations in Iberia are also related to this phase. The massive deglaciation of the Iberian massifs was caused by a gradual increase in temperatures. The deglaciation phase was only interrupted by a short period with colder conditions (the Younger Dryas) that reactivated periglacial processes in the formerly glaciated cirques of the highest lands, specifically with the widespread development of rock glaciers. During the Holocene, periglacial processes have been only active in the highest ranges, shifting in altitude according to temperature regimes and moisture conditions. The Little Ice Age saw the reactivation of periglacial activity in lower elevations than today. Currently, periglacial processes are only active in elevations exceeding 2500 m in the southern ranges and above 2000e2200 m in the northern massifs, higher in Sierra Nevada, in the south of Iberian Peninsula.info:eu-repo/semantics/publishedVersio