1,721,224 research outputs found
Predicciones climáticas estacionales para el sector de la energía eólica : métodos y herramientas para el desarrollo de un servicio climático
Full text linkTesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de la Tierra y Astrofísica, leída el 14-06-2019Seasonal forecasts have shown high potential for their application in different socioeconomic sectors (e.g. energy, agriculture, transport, tourism, health, ...). Nevertheless, the deployment of these forecasts in different decision-making processes requires that the seasonal forecasts are adapted to be easily integrated into different applications. To satisfy this need, the climate services research line has recently emerged to transform climate information into products that can be used by the society and the industry. One of the sectors that could benefit the most from seasonal forecasts is the wind energy sector. Wind energy is one of the most important sources of renewable energy for the mitigation of climate change effects on the society..Las predicciones climáticas estacionales han mostrado un gran potencial para su aplicación en distintos sectores socioeconómicos (energía, agricultura, transporte, turismo, salud, etc). Sin embargo, la integración de estas predicciones en procesos de toma de decisión requiere que éstas sean adaptadas para poder ser utilizadas de una manera automática y sencilla en distintas actividades. Con el fin de satisfacer esta necesidad ha surgido la línea de investigación de los servicios climáticos, que tiene como objetivo la transformación de información climática en productos que puedan beneficiar a la sociedad y la industria. Uno de los sectores que puede obtener un mayor beneficio de las predicciones estacionales es el sector de la energía eólica, que es una de las fuentes de energía renovable más importantes para la mitigación de los efectos del cambio climático...Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEunpu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mediterranean climate change projections from CMIP5 and CMIP6
Full text linkMàster de Meteorologia, Facultat de Física, Universitat de Barcelona, Curs: 2019-2020, Tutors: Francisco J. Doblas-Reyes, Martin Jury, Bernat Codina.The Mediterranean has been identified as a climate change hotspot due to increased warming trends and precipitation decline. To estimate the impacts of the ongoing climate change on the region, projections of various CMIP5 and CMIP6 experiments and scenarios are compared. The changes in temperature and precipitation for the 21st century are studied under scenarios RCP2.6/SSP1-2.6, RCP4.5/SSP2-4.5 and RCP8.5/SSP5-8.5 as well as the high resolution High-ResMIP experiments. Additionally, to give robust estimates of projected changes a model weighting scheme is applied, accounting for historical performance and inter-independence of the multi-member multi-model ensembles. Results indicate a significant and robust warming over the Mediterranean during the 21st century over all the ensembles and experiments. Nevertheless, the amplified Mediterranean warming with respect to the global average is only found for summer. Projected changes vary between CMIP5 and CMIP6, with the latter projecting a stronger warming. In contrast to temperature, precipitation changes show a higher level of uncertainty and spatial heterogeneity.
However, for the high emission scenario, a robust decline in precipitation is projected for large parts
of the region during summer. Results applying the model weighting scheme indicate reductions in CMIP6 and increases in CMIP5 warming trends, making the differences between the two ensembles smalle
NEMO: computational challenges in ocean simulation
Full text linkDepartament responsable de la tesi: Departament d'Arquitectura de Computadors i Sistemes Operatius.Els oceans juguen un paper molt important modulant la temperatura de la Terra absorbint, emmagatzemant i transportant l'energia que ens arriba del sol. Entendre millor la dinàmica dels oceans pot ajudar a millorar les prediccions meteorològiques i a comprendre millor el clima, qüestions d'especial rellevància per la societat. Utilitzant ordinadors ha sigut possible resoldre numèricament les equacions que descriuen la dinàmica dels oceans, i millorant com els models oceànics exploten els recursos computacionals, podem reduir el cost de les simulacions alhora que fem possibles nous desenvolupaments que milloraràn la qualitat científica dels models. Enfrontant els reptes computacionals de la simulació oceànica podem contribuir en camps que tenen un impacte directe en la societat mentre reduïm el cost dels experiments. Per ser un dels principals models oceànics, la tesis s'ha centrat en el model NEMO.Per tal de millorar el rendiment dels models oceànics, un dels objectius inicials va ser entendre millor el seu comportament computacional. Per aconseguir-ho, es va proposar una metodologia d'anàlisis, posant especial atenció en les comunicacions entre processos. Utilitzada amb NEMO, va ajudar a resaltar diverses ineficiències en la implementació que, un cop sol·lucionades, van portar a una millora del 46-49% en la velocitat màxima del model, tot millorant la seva escalabilitat. Aquest resultat ilustra que aquest tipus d'anàlisis poden ajudar als desenvolupadors dels models a adaptar-los tot mostrant l'origen dels problemes que pateixen. Un altre dels problemes detectats va ser que l'impacte d'escollir una descomposició de domini concreta estava molt subestimat, ja que en certes circumstàncies el model triava una descomposició sub-optima. Tenint en compte els factors que fan que una descomposició concreta afecti el rendiment del model, es va proposar un mètode per fer una selecció òptima. Els resultats mostren que parant atenció a la descomposició no només es poden estalviar recursos sinó que la velocitat màxima del model també se'n beneficia, arribant al 41% de millora en alguns casos. Després dels èxits aconseguits en la primera part de la tesis, arribant a doblar la velocitat màxima del model, l'atenció es va posar sobre els algoritmes de precisió mixta. Idealment, un ús adequat de la precisió numèrica ha de permetre millorar el rendiment d'un model sense perjudicar-ne els resultats. Per tal d'aconseguir-ho en models oceànics, es va desenvolupar un mètode que permet determinar quina és la precisió necessària en cada una de las variables d'un codi informàtic. Utilitzat amb NEMO i ROMS va resultar que en ambdós models la major part de les variables pot utilitzar sense problema menys precisió que els 64-bits habituals, mostrant que potencialment els models oceànics es poden beneficiar molt d'una reducció de la precisió numèrica. Finalment, durant el desenvolupament de la tesi es va observar que degut a la no-linealitat dels models oceànics, determinar si un canvi en el codi informàtic perjudica la qualitat dels resultats esdevé molt complicat. Per solucionar-ho, es va presentar un mètode per verificar els resultats de models no-lineals.Encara que les contribucions que donen forma a aquesta tesis han sigut diverses, conjuntament han ajudat a identificar i combatre els reptes computacionals que afecten els models oceànics. Aquestes contribucions no només han resultat en quatre publicacions sinó que també han resultat en la contribució al codi informàtic de NEMO i del consorci EC-Earth. Per tant, els resultat de la recerca realitzada ja estan tenint un impacte positiu en la comunitat, ajudant als usuaris dels models a estalviar recursos i temps. A més a més, aquestes contribucions no només han ajudat a millorar significativament el rendiment computacional de NEMO sinó que han sobrepassat l'objectiu inicial de la tesis i poden ser transferibles a altres models computacionals.The ocean plays a very important role in modulating the temperature of the Earth through absorbing, storing and transporting the energy that arrives from the sun. Better understanding the dynamics of the ocean can help us to better predict the weather and to better comprehend the climate, two topics of special relevance for society. Ocean models had become an extremely useful tools, as they became a framework upon with it was possible to build knowledge. Using computers it became possible to numerically solve the fluid equations of the ocean and by improving how ocean models exploit the computational resources, we can reduce the cost of simulation whilst enabling new developments that will increase its skill. By facing the computational challenges of ocean simulation we can contribute to topics that have a direct impact on society whilst helping to reduce the cost of our experiments. Being the major European ocean model and one of the main state-of-the-art ocean models worldwide, this thesis has focused on the Nucleus NEMO. To find a way to improve the computational performance of ocean models, one of the initial goals was to better understand their computational behaviour. To do so, an analysis methodology was proposed, paying special attention to inter-process communication. Used with NEMO, the methodology helped to highlight several implementation inefficiencies, whose optimization led to a 46-49\% gain in the maximum model throughput, increasing the scalability of the model. This result illustrated that this kind of analysis can significantly help model developers to adapt their code highlighting where the problems really are. Another of the issues detected was that the impact of the domain decomposition was alarmingly underestimated, since in certain circumstances the model's algorithm was selecting a sub-optimal decomposition. Taking into account the factors that make a specific decomposition impact the performance, a method to select an optimal decomposition was proposed. The results showed that that by a wise selection of the domain decomposition it was possible not only to save resources but also to increase the maximum model throughput by a 41\% in some cases. After the successes achieved during the first part of the thesis, that allowed an increase of the maximum throughput of the model by a factor of more than two, the attention focused on mixed-precision algorithms. Ideally, a proper usage of numerical precision would allow to improve the computational performance without sacrificing accuracy. In order to achieve that in ocean models, a method to find out the precision required for each one of the real variables in a code was presented. The method was used with NEMO and with the Regional Ocean Modelling System showing that in both models most of the variables could use less than the standard 64-bit without problems. Last but not least, it was found that being ocean models nonlinear it was not straightforward to determine whether a change made into the code was deteriorating the accuracy of the model or not. In order to solve this problem a method to verify the accuracy of a non-linear model was presented. Although the different contributions that gave form to this thesis have been diverse, they helped to identify and tackle computational challenges that affect computational ocean models. These contributions resulted in four peer-reviewed publications and many outreach activities. Moreover, the research outcomes have reached NEMO and EC-Earth consortium codes, having already helped model users to save resources and time. These contributions not only have significantly improved the computational performance of the NEMO model but have surpassed the original scope of the thesis and would be easily transferable to other computational models
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Calibration and combination of seasonal climate predictions in tropical and extratropical regionals
Full text linkCurrent technology allows the proliferation of multiple forecast systems developed by different research institutions from all over the world. However, most decision makers need a reliable probabilistic prediction instead of a set of predictions to take an action given the probability of an event to occur. Several studies have shown that the merging of predictions derived from several forecast systems with equal weights yields on average better predictions than the best single forecast system. This approach has been referred to as the simple multimodel (SMM). Nevertheless, none of these studies has shown the existence of a combination method that systematically produces the best predictions. Therefore, this thesis aims at applying different statistical techniques to combine predictions derived from different statistical and dynamical forecast systems to assess whether the performance of the SMM can be improved. These techniques combine the predictions assigning unequal weights to the different forecast systems based on their past performance. A unique feature of this study is the broad nature of the forecast quality assessment, performed using multiple deterministic and probabilistic verification measures and the same verifying observations. This allows comparing the predictions produced by the different combination methods and forecast systems in a coherent way. Besides, most of the forecast systems used in this study are either publicly available or could be easily implemented by the user. This thesis focuses on seasonal prediction of sea surface temperature (SST), near-surface temperature and precipitation in tropical and extratropical regions. It is shown that the predictions of the SMM are often better than the combination methods that assign unequal weights. The difficulty in the robust estimation of the weights due to the small samples available is one of the reasons that limit the potential benefit of the combination methods that assign unequal weights. However, some of the results illustrate under which conditions combination methods that assign unequal weights improve with respect to the SMM predictions. For instance, the combination methods that assign unequal weights improve over the SMM predictions when only a fraction of all single forecast systems have skill as shown for some of the predictions of SST. On the other hand, it is shown that there are cases when combining many forecast systems does not lead to improved forecasts when compared to the best single forecast system. This suggests that a multimodel approach is not necessarily better than a highly skillful forecast system, which highlights the importance of continuously assessing the forecast quality for the specific application of the user.La tecnología existente permite la proliferación de varios sistemas de predicción, desarrollados por diferentes instituciones de investigación de todo el mundo. Sin embargo, la mayoría de los tomadores de decisión generalmente necesitan una única predicción probabilística fiable para tomar una acción dada la probabilidad de ocurrencia de un evento. En este sentido, varios estudios han demostrado que la combinación de predicciones derivadas de varios sistemas de predicción resulta, en promedio, en una mejor predicción cuando se compara con la predicción del mejor sistema de predicción. No obstante, ninguno de estos estudios ha demostrado la existencia de un método de combinación que produzca las mejores predicciones. Por lo tanto, esta tesis tiene el objetivo de aplicar diferentes técnicas estadísticas para combinar predicciones climáticas estacionales derivadas de diferentes sistemas de predicción. Algunas de estas técnicas ponen pesos desiguales a los diferentes sistemas de predicción teniendo en cuenta su calidad en un período pasado y una de ellas combina todos los sistemas de predicción sin poner pesos. Esta última será referenciada como "simple multimodel" (SMM). Un punto importante de este estudio es el amplio carácter de la verificación de la calidad de las predicciones, ya que se usan varias métricas deterministas y probabi I ísti cas y las mismas observaciones. Esta tesis se centra en la predicción estacional de la temperatura de la superficie del mar (TSM), la temperatura atmosférica próxima a la superficie y la precipitación, en regiones tropicales y extratropicales. Pudimos comprobar que las predicciones de la SMM son frecuentemente mejores que las que derivan de métodos de combinación con coeficientes desiguales a los sistemas de predicción. La dificultad a la hora de estimar pesos robustos, debido sobre todo a las pequeñas muestras disponibles, es una de las razones que limita la robustez de las medidas que estiman el beneficio relativo de los métodos de combinación. Sin embargo, hay algunas situaciones en las que los métodos de combinación con coeficientes desiguales son mejores. Se encontró también situaciones específicas en las que la combinación de predicciones de varios sistemas de predicción no mejora la predicción del mejor sistema
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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