1,721,125 research outputs found
Alien Registration- Caruso, Maria (Rumford, Oxford County)
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Extremes in the hydrological cycle: A metastatistical framework applied to extreme coastal flooding and droughts
No full textThe study of extremes, maxima and minima of random variables, has a long history in applied hydrology for engineering purposes. The magnitude and the frequency of extreme events are described by the right-most part of a probability distribution, usually referred as tail. Therefore, the task for hydrologists is to extract as much information as possible from the data set to assess the tail behavior correctly and reduce the uncertainty in the estimates.
Traditionally, the most widely used probabilistic methods are based on the asymptotic results of the Extreme Value (EV) theory, which is commonly applied using block maxima or via peak-over-threshold analysis. However, despite its theoretical basis, a number of scientific contributions highlights the limits of these traditional approaches. In particular, classical EV methods are considered to waste much of the available observational information, which is reflected into increased estimation uncertainty for quantiles that are large with respect to the observed largest values. This notion is leading to the development of alternative modeling approaches that make a better use of the observations. Among these methods, non-asymptotic models, i.e. statistical models which do not assume the block maximum to arise from a large number of ordinary values, promise to lead to more robust estimates of high quantiles. In particular, this dissertation estimates the probability of extremely large events using a non-asymptotic approach based on the Metastatistical Extreme Value Distribution, MEVD, and its simplified versions, including SMEV, or Simplified Metastatistical Extreme Value distribution. A comparative assessment of the predictive performance of the proposed non-asymptotic model and conventional approaches based on the three-parameter Generalized Extreme Value distribution, GEV, is the focus here. The present work, therefore, investigates the potential of MEVD-based approaches to characterize the probabilistic structure of the tail distribution that governs opposing phenomena such as coastal flooding and drought occurrence. In fact, the proposed general model (i.e., fewer a-priori assumptions on the properties of the event occurrence process and efficient use of the data) yields a reduction of estimation uncertainty in the quantification of extremely rare quantiles. Even though the studied extreme events are different from a process perspective, the results confirm the advantages and flexibility of these novel extreme value distributions.The study of extremes, maxima and minima of random variables, has a long history in applied hydrology for engineering purposes. The magnitude and the frequency of extreme events are described by the right-most part of a probability distribution, usually referred as tail. Therefore, the task for hydrologists is to extract as much information as possible from the data set to assess the tail behavior correctly and reduce the uncertainty in the estimates.
Traditionally, the most widely used probabilistic methods are based on the asymptotic results of the Extreme Value (EV) theory, which is commonly applied using block maxima or via peak-over-threshold analysis. However, despite its theoretical basis, a number of scientific contributions highlights the limits of these traditional approaches. In particular, classical EV methods are considered to waste much of the available observational information, which is reflected into increased estimation uncertainty for quantiles that are large with respect to the observed largest values. This notion is leading to the development of alternative modeling approaches that make a better use of the observations. Among these methods, non-asymptotic models, i.e. statistical models which do not assume the block maximum to arise from a large number of ordinary values, promise to lead to more robust estimates of high quantiles. In particular, this dissertation estimates the probability of extremely large events using a non-asymptotic approach based on the Metastatistical Extreme Value Distribution, MEVD, and its simplified versions, including SMEV, or Simplified Metastatistical Extreme Value distribution. A comparative assessment of the predictive performance of the proposed non-asymptotic model and conventional approaches based on the three-parameter Generalized Extreme Value distribution, GEV, is the focus here. The present work, therefore, investigates the potential of MEVD-based approaches to characterize the probabilistic structure of the tail distribution that governs opposing phenomena such as coastal flooding and drought occurrence. In fact, the proposed general model (i.e., fewer a-priori assumptions on the properties of the event occurrence process and efficient use of the data) yields a reduction of estimation uncertainty in the quantification of extremely rare quantiles. Even though the studied extreme events are different from a process perspective, the results confirm the advantages and flexibility of these novel extreme value distributions
Real time investigation of solvent swelling induced β phase formation in poly(9-9-dioctyl fluorene)
Get PDFThe physical processes leading to solvent swelling induced glassy- to beta-phase transition in poly(9,9-dioctylfluorene) thin films are investigated in real time by photoluminescence and confocal spectroscopy. We
show that the vapor solvent swelling induced beta-phase formation takes place in much shorter times (few
minutes) than the one usually employed in literature (several hours). Moreover, we show that the swelling is
faster if the solvent mainly interacts with the PF8 aromatic rings (toluene) than with the octyl chains (isooctane). On the contrary, no swelling is caused by nonsolvents such as n-butylic alcohol. Finally, we demonstrate
that the beta-phase formation is due to athermal (simultaneous) nucleation followed by diffusion controlled
one dimensional crystallization
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Microscopic Investigation of the Excitons' Intermolecular Energy Migration in the β phase of Poly(9-9-Dioctyl Fluorene) by Confocal Laser Spectroscopy
Get PDFWe investigated, by confocal laser spectroscopy, the role of the microscopic morphology on the fluorescence spectra of poly(9,9-dioctylfluorene) (PF8) thin films self-doped by the PF8 β phase. We demonstrate the existence, on the micron scale, of different regions in the films, characterized by locally different fluorescence spectra. We show that the microscopic morphology irregularities lead to locally nonuniform β-phase density resulting in the switching on or off of the intermolecular energy migration within the β-phase excited-state distribution. This effect causes considerable local variation of the fluorescence spectra consisting of a progressive red shift (up to 26 meV) and a line width narrowing from about 70 (similar to the absorption one) down to 52 meV
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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