Number and Amplitude of Limit Cycles emerging from {\it Topologically Equivalent} Perturbed Centers

We consider three examples of weekly perturbed centers which do not have {\it geometrical equivalence}: a linear center, a degenerate center and a non-hamiltonian center. In each case the number and amplitude of the limit cycles emerging from the period annulus are calculated following the same strategy: we reduce of all of them to locally equivalent perturbed integrable systems of the form: $dH(x,y)+\epsilon(f(x,y)dy-g(x,y)dx)=0$, with $H(x,y)={1/2}(x^2+y^2)$. This reduction allows us to find the Melnikov function, $M(h)=\int_{H=h}fdy-gdx$, associated to each particular problem. We obtain the information on the bifurcation curves of the limit cycles by solving explicitly the equation $M(h)=0$ in each case.Comment: 17 pages, 0 figure

Optimisation of energy supply at off-grid healthcare facilities using Monte Carlo simulation

In this paper, we present a methodology for the optimisation of off-grid hybrid systems (photovoltaic-diesel-battery systems). A stochastic approach is developed by means of Monte Carlo simulation to consider the uncertainties of irradiation and load. The optimisation is economic; that is, we look for a system with a lower net present cost including installation, replacement of the components, operation and maintenance, etc. The most important variable that must be estimated is the batteries lifespan, which depends on the operating conditions (charge/discharge cycles, corrosion, state of charge, etc.). Previous works used classical methods for the estimation of batteries lifespan, which can be too optimistic in many cases, obtaining a net present cost of the system much lower than in reality. In this work, we include an advanced weighted Ah-throughput model for the lead-acid batteries, which is much more realistic. The optimisation methodology presented in this paper is applied in the optimisation of the electrical supply for an off-grid hospital located in Kalonge (Democratic Republic of the Congo). At the moment, the power supply relies on a diesel generator; batteries are used in order to ensure the basic supply of energy when the generator is unavailable (night hours). The optimisation includes the possibility of adding solar photovoltaic (PV) panels to improve the supply of electrical energy. The results show that optimal design could achieve a 28% reduction in the levelised cost of energy and a 54% reduction in the diesel fuel used in the generator, thereby reducing pollution. Furthermore, we discuss possible improvements to the telecommunications of the hospital

Sistema de programación y control automático de un riego por goteo subterráneo en un cultivo de olivar

En esta comunicación se presenta un nuevo sistema de programación y control automático del riego por goteo subterráneo para un cultivo de olivar ecológico de una finca situada en el T.M. de Tabernas en Almería (España) y propiedad de la empresa Rafael Alonso Aguilera S.L. La finca se riega mediante un novedoso sistema de riego subterráneo patentado por esta empresa. El sistema de control propuesto está basado en el establecimiento de un balance hídrico diario en el en el sistema suelo-planta a partir de la estimación de las necesidades de riego del cultivo en tiempo real a partir de los datos climáticos medidos en tiempo real a partir de una estación agroclimática. Se presentan también los resultados de la evaluación del funcionamiento del sistema a lo largo de un periodo de 5 años y se analiza el ahorro de agua proporcionado por la combinación del sistema de control del riego y del método de riego subterráneo

Continental shelf zones influenced by the suspended matter flows coming from Cadiz Bay

Due to the diversity of environments and hydrodynamics in Cadiz Bay, it is of interest to study the dynamics of sedimentary exchange between the coastal zones and continental shelf. The most abundant clay minerals on the floor of the continental shelf and Cadiz Bay, and in the particulate matter in suspension, are: illite, smectite, kaolinite + chlorite, and the interstratified clay minerals illite-smectite. The average concentration of suspended matter is 6.5 mg/l, the lowest (1.37 mg/l) being found on the inner shelf and in the inner zones of the bay less affected by currents and surge. The highest values (14 mg/l) are found in the outer bay, consistent with the distribution of muddy facies on the sea floor. The flow paths have been established from the local variations in the mineralogical associations found at the sampling stations, and by means of the alignments of the lowest values of the factor loadings at those stations most affected by the flows. The mineralogical similarity of the components of the clay fraction is related to the mixing action undergone by the components of the suspended matter reaching the bay from various sources, probably produced by the continuous action of the tidal ebb currents flowing from the inner sectors of the bay towards the continental shelf.El estudio de la dinámica de intercambio sedimentario entre las zonas litorales y la plataforma continental es de gran interés en el caso de la bahía de Cádiz, debido a su diversidad de ambientes y situaciones hidrodinámicas. Los minerales de la arcilla más abundantes en los fondos de la plataforma y la bahía, y en la materia en suspensión, son ilita, esmectita, caolinita + clorita e interestratificados ilita-esmectita. La concentración de materia sólida en suspensión indica un contenido promedio de 6,5 mg/l, apareciendo los mínimos (1,37 mg/l) en la plataforma interna y en zonas internas de la bahía no afectadas por corrientes y oleaje. Los valores más altos se dan en la bahía externa (14 mg/l), de acuerdo con la distribución de facies fangosas en el fondo. Las trayectorias de los flujos salientes se han establecido a partir de las variaciones locales de las asociaciones mineralógicas en las diferentes estaciones de muestreo, alineándose los valores más bajos de los factores en las estaciones más afectadas por la acción de los flujos. La similitud mineralógica de los componentes de la fracción arcilla en todos los ambientes se debe a la mezcla de componentes de la materia en suspensión que, desde diferentes fuentes, llegan a la bahía, y es favorecida por la acción de la corriente de reflujo mareal desde el sector más interno de la bahía a la plataforma continental.Instituto Español de Oceanografí

Procesadores de bajo coste y su aplicación en la docencia de Ingeniería de Computadores

La Informática evoluciona a gran velocidad y es necesario actualizar con frecuencia los recursos de aprendizaje para mantener el interés de los estudiantes. En la actualidad, hay una gran diversidad de plataformas de cómputo de bajo coste que son utilizadas como recursos en los estudios de Informática. Raspberry Pi y algunos modelos de Arduino (como Arduino Due), ambas basadas en procesadores ARM, son ejemplos representativos de este tipo de plataformas. Las arquitecturas ARM son ejemplos de procesadores RISC que actualmente gozan de gran popularidad por su buena relación entre potencia computacional, consumo y coste. De hecho, constituyen el núcleo de muchos de los teléfonos móviles y sistemas empotrados actuales. Al estar tan cerca de los estudiantes, el uso de este tipo de recursos en el aula representa una oportunidad para: (1) motivar a los alumnos de Bachillerato y Educación Secundaria para estudiar el Grado de Informática y (2) potenciar el interés de los alumnos de Grado de Informática por la Ingeniería de Computadores. Existe una serie de eventos consolidados que tienen una gran difusión social. En ellos, se muestran vistosos ejemplos de aplicación y funcionamiento de este tipo de plataformas. En este trabajo se describen el conjunto de sistemas interactivos y basados en plataformas computacionales de bajo coste que se han desarrollado para ser utilizadas en este tipo de eventos. De acuerdo con nuestra experiencia de participación, creemos que están sirviendo para despertar el interés del alumno de secundaria por la Informática en general, y más específicamente por la Ingeniería de Computadores. Por otra parte, un porcentaje de los alumnos que cursan el Grado de Ingeniería Informática no está interesado en el análisis de los componentes hardware y de su organización para construir un computador moderno. Piensan que la asignatura de Arquitectura de Computadores del Grado en Ingeniería Informática está lejos de su futura actividad profesional. En este contexto, nos planteamos seleccionar ARM como arquitectura de referencia para desarrollar los contenidos de la asignatura de Arquitectura de Computadores. Creemos que esta decisión mejora el interés del alumno por dos motivos: (1) el objeto de estudio se usa en multitud de plataformas muy cotidianas para el alumno y (2) es posible diseñar las actividades prácticas de las asignaturas basadas en elementos reales y no únicamente virtuales. Este trabajo muestra las distintas actividades tanto a nivel teórico como práctico que se plantean al alumno en el marco de la asignatura Arquitectura de Computadores.Computer Science is advancing rapidly and it is necessary to keep the educational resources up to date in order to keep the interest of students. Nowadays, there is a wide variety of low-cost computing platforms that are used as educational resources in the Computer Science degree. Raspberry Pi and some models of Arduino (such as Arduino Due), which are both based on ARM processors, are representative examples of this kind of platforms. ARM architectures are instances of RISC processors which nowadays have reached an important popularity due to their good relation between performance, consumption and cost. In fact, they constitute the core of numerous current mobile phones and embedded systems. Considering their proximity to the students, the use of this kind of resources in the classroom is an opportunity to: (1) encourage the high schools pupils to study the Computer Science degree and (2) to increase the interest of the students for the Computer Engineering. There are several consolidated informational events of great social outreach in which different examples of application of this kind of platforms are shown. In this work, the set of interactive systems designed to be used in this kind of events is described. According to our experience, we think that they arouse the interest of high schools pupils for the Computer Science in general, and, more specifically, for the Computer Engineering. Furthermore, a percentage of the students of the Computer Science degree is not interested in the analysis of hardware components and the architecture of modern computers. They think that the subject of Computer Architecture of the Computer Science Degree is far from his/her future career. In this context, we will select ARM as a reference architecture where the contents of the subject Computer Architecture will be developed on. We think this might improve the motivation of the students mainly for two reasons: (1) the object of study is being used in a lot of modern platforms; and (2) it is possible to design the practical activities of the subjects using real platforms and not only virtual ones. This work shows the activities proposed to the students in the context of the subject Computer Architecture, considering both practical and theoretical approaches

Chapter 4.The oceanographic and climatic context

The Alboran Sea is the westernmost basin of the Mediterranean Sea. It is the first one receiving the Atlantic waters flowing through the Strait of Gibraltar and the last one crossed by Mediterranean waters on their way out to the Atlantic Ocean. Therefore, the main factor that determines the Alboran Sea circulation and its water mass distribution is the Atlantic–Mediterranean exchange forced by climatic conditions within the Mediterranean Sea and the Strait of Gibraltar geometry. This general circulation exhibits very strong energetic dynamics with the alternation of cyclonic and anticyclonic circulation cells. The Alboran Sea circulation is highly variable in time at different scales. Some of the shortest ones are semidiurnal and diurnal, associated to the tidal dynamics. The sub-inertial time scale is mainly linked to the wind and atmospheric pressure field variability, and affects the main circulation patterns of the Alboran Sea. Seasonal variability and long-term changes associated with decadal or even longer term changes are caused by alterations in the heat and freshwater fluxes between the Mediterranean Sea, the atmosphere, the nearby Atlantic Ocean and the river basins on land. These changes directly affect the temperature and salinity of the water masses within the Alboran Sea, while it is difficult to predict how they could affect their circulation and dynamics. In this chapter, some of the observed trends in the Alboran Sea water masses are presented. These changes include temperature and salinity increases of the water column, very likely caused by the current climate change process.En prens

Variational approach to a class of nonlinear oscillators with several limit cycles

We study limit cycles of nonlinear oscillators described by the equation $\ddot x + \nu F(\dot x) + x =0$. Depending on the nonlinearity this equation may exhibit different number of limit cycles. We show that limit cycles correspond to relative extrema of a certain functional. Analytical results in the limits $\nu ->0$ and $\nu -> \infty$ are in agreement with previously known criteria. For intermediate $\nu$ numerical determination of the limit cycles can be obtained.Comment: 12 pages, 3 figure

Spatial distribution, inter-annual variability and influence of abiotic factors on molluscan assemblages collected with otter trawl in the northen Alborán Sea

Molluscs constitute one of the most diverse and best represented invertebrate groups in the marine environment. In the northern sectors of the Alborán Sea and Gulf of Cádiz 1200 spp. of the 1800 spp. occurring in the Mediterranean Sea, have been found so far highlighting the importance of this area for the european molluscan fauna (Gofas et al., 2011). Molluscs are also the second group in abundance and biomass in demersal fisheries and an important component of soft-bottom benthic communities, including ecologically important and/or commercial mollusc species that are also exposed to an increasing trawling impact (Snelgrove, 1998; Kaiser & De Groot, 1999). Previous studies on molluscs of the Alborán Sea has primarily focused on those from infralittoral habitats, with few studies focussing on the composition, structure and dynamics of circalittoral and bathyal molluscan assemblages ( Rueda et al., 2015). The study of soft bottom molluscan assemblages where trawling fishing fleet operates is important for improving the fisheries evaluation and management, as well as the implementation of ecosystemic and biodiversity conservation measures in the context of the new Marine Strategy Framework Directive. In the present study, the distribution and inter-annual variability of molluscan assemblages of circalittoral and bathyal soft bottoms of the Alborán Sea have been analyzed as well as the relationships of fauna with different environmental variables. Samples were collected in 190 otter trawl hauls performed between “Punta Europa” and “Cabo de Gata”, including the Alborán Ridge, at depths from 30 to 800 m during four MEDITS-ES trawl surveys in spring between 2012 and 2015. Several environmental variables from the water column (temperature and salinity) and sediment samples were taken where each haul was performed in order to elucidate their relationships with the molluscan assemblages. Abundances of each species (individuals . h-1) of each haul and trawl survey were pooled in a matrix for performing multivariate methods in order to contrast molluscan assemblages of different sites and years. The Bray-Curtis similarity index was then used to perform non-parametric multidimensional scaling ordinations (nMDS). A fourth root transformation pretreatment was applied on the quantitative data in order to minimize the contribution of the most abundant species to the analyses. Analyses of similarities (ANOSIM) were carried out for statistical comparisons of groups of samples according to different factors (e.g. year, location). Analyses of similitude percentage (SIMPER) were used to identify those species that contributed to the similarity and dissimilarity between groups of samples according to factors. These multivariate analyses were executed using the PRIMER v6 (Plymouth Routines in Multivariate Ecological Research). Average values of abundance of molluscs (N), species richness (S), Shannon-Wiener diversity index (H’: log2), evenness index (J’) and taxonomic distinctness index (Δ*) were calculated for each sample group. Statistical differences between these values were tested with the non-parametric Kruskal-Wallis using SPSS software. The relationships between environmental variables and molluscs abundance in the different hauls were only studied for the 2014 trawl survey using a correspondence canonical analysis (CCA). The statistical significance of the adjusted CCA was assessed using a Monte Carlo permutation test. Prior to this, the environmental variables were screened and those which presented a correlation higher than 0.9 (after a Spearman correlation analysis) were not further considered. These analyses were executed using the R software. Three main molluscan assemblages were detected and belonged to the: I) Continental Shelf (30-200 m); II) Upper Continental Slope (201-350 m), and III) Middle Continental Slope (351-800 m). The multivariate analyses revealed geographical differences within the Alborán Sea, being these differences more acute between the Alborán Island, mainly in the shallower assemblages (30-200 m and 201-350 m) and the remaining locations considered. These differences were due to a lower abundance in the island of species that were dominant in the continental margin, such as Alloteuthis media, Sepietta oweniana and Turritella communis and a higher abundance in the island of species that were less abundant in the continental margin, such as Neopycnodonte cochlear, Arca tetragona, Loligo forbesii and Sepia orbignyana. No significant differences of the abundance, biomass, species richness and diversity index were detected in the assemblages over the four years. Nevertheless, significant abundance declines of A. media, S. oweniana, and increases of N. cochlear were detected in the continental shelf over the years as well as abundance declines of Bathypolipus sponsalis and Galeodea rugosa in the slope assemblages. Regarding the environmental variables, the shallower assemblage (30-200 m) showed a significantly higher temperature, lower salinity and wider variety of sediment types than the others, with a predominance of sandy mud textures followed by muddy sand. As depth increases the sedimentary heterogeneity decreases, with dominant muddy sediments. Depth, temperature and mud percentage were the key variables that better explained the variability of the molluscan assemblage in the CCA. In conclusions: (1) Acute geographical differences occurred between the Alborán Island and the locations of the continental margin, due to its location far from the continental influence and, therefore, with lower fisheries activity and a less muddy and more bioclastic sediment, (2) Inter-annual trends in the abundance, biomass, species richness and diversity of assemblages were not detected, but some species displayed inter-annual changes due to biological aspects or accidental catch of gregarious species and (3) depth and some sedimentological variables displayed the most significant relationships with the molluscan assemblages, as previously observed for other invertebrate assemblages in the Alborán Sea

Cannabinoid receptor CB2 ablation protects against TAU induced neurodegeneration.

Tauopathies are a group of neurodegenerative diseases characterized by the alteration/aggregation of TAU protein, for which there is still no effective treatment. Therefore, new pharmacological targets are being sought, such as elements of the endocannabinoid system (ECS). We analysed the occurrence of changes in the ECS in tauopathies and their implication in the pathogenesis. By integrating gene expression analysis, immunofluorescence, genetic and adeno-associated virus expressing TAU mouse models, we found a TAU-dependent increase in CB2 receptor expression in hippocampal neurons, that occurs as an early event in the pathology and was maintained until late stages. These changes were accompanied by alterations in the endocannabinoid metabolism. Remarkably, CB2 ablation in mice protects from neurodegeneration induced by hTAU P301L overexpression, corroborated at the level of cognitive behaviour, synaptic plasticity, and aggregates of insoluble TAU. At the level of neuroinflammation, the absence of CB2 did not produce significant changes in concordance with a possible neuronal location rather than its classic glial expression in these models. These findings were corroborated in post-mortem samples of patients with Alzheimer’s disease, the most common tauopathy. Our results show that neurons with accumulated TAU induce the expression of the CB2 receptor, which enhances neurodegeneration. These results are important for our understanding of disease mechanisms, providing a novel therapeutic strategy to be investigated in tauopathiespost-print8580 K