1,030 research outputs found

    A copula-based quantified airworthiness modelling for civil aircraft engines

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    The aircraft engine serves as the core system of an aircraft and operates under extreme conditions, requiring high reliability and absolute safety. The design, manufacturing, and after-sales services of aircraft engines are complex processes. To ensure safety and performance, maintenance checks are performed periodically and hierarchically throughout the engine’s life-cycle. Among these checks, shop visit (SV) heavy maintenance checks play a crucial role but are also costly, especially when they occur unexpectedly and unplanned. Analysis of the maintenance logbook, recording aviation operations, reveals a significant occurrence of unplanned SVs, which may be attributed to the existing maintenance policy based on a single time-definition. To address this issue, this paper seeks to establish a novel approach to quantifying airworthiness through copula modeling, which combines two time-definitions: the flying hour (FH) and the flying cycle (FC). This approach is unique in the aviation industry. By employing the Gumbel copula with the generalized extreme value (GEV) distribution as the marginal distribution, and utilizing non-parametric association measurement parameter estimation, the quantified airworthiness of civil aircraft engine fleets across multiple product lines can be effectively modeled. This research provides valuable insights into optimizing maintenance policies and enhancing the reliability and safety of aircraft engines

    Pairwise versus mutual independence: visualisation, actuarial applications and central limit theorems

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    Accurately capturing the dependence between risks, if it exists, is an increasingly relevant topic of actuarial research. In recent years, several authors have started to relax the traditional 'independence assumption', in a variety of actuarial settings. While it is known that 'mutual independence' between random variables is not equivalent to their 'pairwise independence', this thesis aims to provide a better understanding of the materiality of this difference. The distinction between mutual and pairwise independence matters because, in practice, dependence is often assessed via pairs only, e.g., through correlation matrices, rank-based measures of association, scatterplot matrices, heat-maps, etc. Using such pairwise methods, it is possible to miss some forms of dependence. In this thesis, we explore how material the difference between pairwise and mutual independence is, and from several angles. We provide relevant background and motivation for this thesis in Chapter 1, then conduct a literature review in Chapter 2. In Chapter 3, we focus on visualising the difference between pairwise and mutual independence. To do so, we propose a series of theoretical examples (some of them new) where random variables are pairwise independent but (mutually) dependent, in short, PIBD. We then develop new visualisation tools and use them to illustrate what PIBD variables can look like. We showcase that the dependence involved is possibly very strong. We also use our visualisation tools to identify subtle forms of dependence, which would otherwise be hard to detect. In Chapter 4, we review common dependence models (such has elliptical distributions and Archimedean copulas) used in actuarial science and show that they do not allow for the possibility of PIBD data. We also investigate concrete consequences of the 'nonequivalence' between pairwise and mutual independence. We establish that many results which hold for mutually independent variables do not hold under sole pairwise independent. Those include results about finite sums of random variables, extreme value theory and bootstrap methods. This part thus illustrates what can potentially 'go wrong' if one assumes mutual independence where only pairwise independence holds. Lastly, in Chapters 5 and 6, we investigate the question of what happens for PIBD variables 'in the limit', i.e., when the sample size goes to infi nity. We want to see if the 'problems' caused by dependence vanish for sufficiently large samples. This is a broad question, and we concentrate on the important classical Central Limit Theorem (CLT), for which we fi nd that the answer is largely negative. In particular, we construct new sequences of PIBD variables (with arbitrary margins) for which a CLT does not hold. We derive explicitly the asymptotic distribution of the standardised mean of our sequences, which allows us to illustrate the extent of the 'failure' of a CLT for PIBD variables. We also propose a general methodology to construct dependent K-tuplewise independent (K an arbitrary integer) sequences of random variables with arbitrary margins. In the case K = 3, we use this methodology to derive explicit examples of triplewise independent sequences for which no CLT hold. Those results illustrate that mutual independence is a crucial assumption within CLTs, and that having larger samples is not always a viable solution to the problem of non-independent data

    Recent Advances in Research on Island Phenomena

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    In natural languages, filler-gap dependencies can straddle across an unbounded distance. Since the 1960s, the term “island” has been used to describe syntactic structures from which extraction is impossible or impeded. While examples from English are ubiquitous, attested counterexamples in the Mainland Scandinavian languages have continuously been dismissed as illusory and alternative accounts for the underlying structure of such cases have been proposed. However, since such extractions are pervasive in spoken Mainland Scandinavian, these languages may not have been given the attention that they deserve in the syntax literature. In addition, recent research suggests that extraction from certain types of island structures in English might not be as unacceptable as previously assumed either. These findings break new empirical ground, question perceived knowledge, and may indeed have substantial ramifications for syntactic theory. This volume provides an overview of state-of-the-art research on island phenomena primarily in English and the Scandinavian languages, focusing on how languages compare to English, with the aim to shed new light on the nature of island constraints from different theoretical perspectives

    On the boundaries between syntax and pragmatics in Ibero-Romance

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    Synopsis: This book offers a comparative perspective on the structural and interpretive properties of root-clause complementizers in Ibero-Romance. The driving question the author seeks to answer is where the boundaries between syntax and pragmatics lie in these languages. Contrary to most previous work on these phenomena, the author argues in favor of a relatively strict distribution of labor between the two components of grammar. The first part of the book is devoted to root complementizers with a reportative interpretation. The second part deals with root complementizers and commitment attribution. Finally, the last part presents the results of empirical studies on the topic

    Temps, espai i intertextualitat a les novel·les de Joan Perucho

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    [cat] Aquest treball analitza, amb voluntat d’exhaustivitat, la presència de textos d’altres autors i de diversos gèneres en les novel·les de Joan Perucho, un dels escriptors més destacats de la literatura catalana de la segona meitat del segle XX. Es tracta, doncs, d’estudiar-ne la intertextualitat en els termes en què ha estat definida per Genette. Dins el corpus examinat, es demostra que gairebé totes les referències i citacions incloses procedeixen d’obres existents, no són pas falses, si bé hi ha nombroses manipulacions. La identificació dels textos i de les seves transformacions al si de cada novel·la permet millorar la interpretació de les obres, eixamplar-ne els significats i descobrir alguns jocs narratius que, fins ara, han passat desapercebuts. Les sis novel·les del corpus són estudiades sota els mateixos paràmetres de manera que la visió de conjunt fa aflorar la gran coherència dels procediments narratius emprats i permet agrupar-les temàticament en dues trilogies. També revela que no totes s’adscriuen de la mateixa manera a la narrativa fantàstica en la qual l’autor ha estat enquadrat. Seguint parcialment Todorov i les noves conceptuacions aplicades sobre la literatura fantàstica del segle XX, s’observa que la novel·lística peruchiana presenta molta més riquesa de la descrita fins ara i abasta realitzacions que van des del fantàstic pur, passant pel neofantàstic fins al realisme màgic. Des de la primera novel·la publicada, la configuració del temps i de l’espai confereix a les obres un caràcter propi, cosa que situa l’autor entre els escriptors més originals de la seva generació. D’una banda, les transgressions del temps narratiu són molt abundants i expressen la gran llibertat amb què és tractada aquesta dimensió. Trobem nombrosos anacronismes –amb violació del temps de la diegesi–, línies narratives desdoblades, duplicació de personatges que simultaniegen la seva presència en èpoques diferents, compressió del temps històric en poques pàgines, protagonistes que es comuniquen malgrat trobar-se en dimensions temporals separades. D’altra banda, com que totes les novel·les s’articulen al voltant d’un viatge, la geografia dels itineraris recorreguts i els espais en general és un element molt rellevant. La continuïtat dels espais geogràfics reals amb els inventats i el recurs a descripcions antigues dels llocs extretes de textos de tots els temps configuren un tractament narratiu molt singular de l’espai –anomenat geografia imaginària–, que esdevé una de les troballes de la creació peruchiana. Finalment, tant l’abundant intertextualitat com l’enfocament fantàstic de la narració manifesta un posicionament crític de l’autor respecte al món del seu temps. Certament, la proposta narrativa de Perucho es presenta com un joc intel·lectual, però va més enllà del seu valor merament lúdic. Els textos del passat plantegen visions de la vida que són rescatades fins al punt que ofereixen un refugi davant d’una realitat poc atractiva. En definitiva, es qüestiona la idea de progrés i es posen objeccions a la modernitat com, per exemple, ha estat dit d’un escriptor amb plantejaments estètics semblants, com ara Italo Calvino. Tot plegat permet resituar l’autor i relativitzar el seu isolament literari. En el treball es proposen alguns punts de contacte amb l’obra d’autors habitualment considerats molt allunyats de l’autor, com ara Josep Pla, Salvador Espriu o Maria Aurèlia Capmany, cosa que obre noves línies de recerca que podrien ser explorades. Joan Perucho es complaïa en la paradoxa del «cant inaudible» de l’avutarda geminis, au barcelonina fantàstica identificada pel protagonista de Les històries naturals; al capdavall, l’objectiu de la recerca és assegurar i incrementar les condicions d’audibilitat, és a dir, de recepció i de lectura de les seves novel·les.[eng] This work analyzes, with the intention of completeness, the presence of texts by other authors and of various genres in the novels of Joan Perucho, one of the most prominent writers of Catalan literature of the second half of the 20th century. It is therefore a question of studying its intertextuality in the terms in which it has been defined by Genette. Within the examined corpus, it is shown that almost all references and citations come from existing works, they are not false, although there are numerous manipulations. This makes it possible to improve interpretation of the works, broaden their meanings and discover some narrative games that, until now, have gone unnoticed. The six novels in the corpus are studied under the same parameters so that the overall view brings out the great coherence of the narrative procedures. Partially following Todorov and the new conceptualizations applied to the fantastic literature of the 20th century, it is observed that Perucho’s novels presents much more richness than described so far and include realizations ranging from the pure fantastic, going through neo-fantasy to magical realism. From the first published novel, transgressions of narrative time are very abundant and express the great freedom with which this dimension is treated. On the other hand, since all the novels revolve around a journey, the geography of the itineraries traveled and the spaces in general is a very relevant element. Both the abundant intertextuality and the fantastic approach to the narration manifest a critical position of the author with respect to the world of his time. Certainly, Perucho's narrative proposal is presented as an intellectual game, but it goes beyond its purely playful value. The texts of the past raise visions of life that are rescued to the point that they offer a refuge from an unattractive reality. Ultimately, the idea of progress is questioned and objections are raised to modernity, as, for example, has been said of a writer with similar aesthetic approaches, such as Italo Calvino. All of this allows us to resituate the author and relativize his literary isolation. The work proposes some points of contact with the work of authors usually considered far from the author, such as Josep Pla, Salvador Espriu or Maria Aurèlia Capmany, which opens up new lines of research that could be explored. Joan Perucho enjoyed the paradox of the "inaudible song" of the avutarda geminis, a fantastic bird from Barcelona identified by the protagonist of Les històries naturals; after all, the aim of the research is to ensure and increase the conditions of audibility, that is, of reception and reading of his novels

    Deep Neural Networks and Tabular Data: Inference, Generation, and Explainability

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    Over the last decade, deep neural networks have enabled remarkable technological advancements, potentially transforming a wide range of aspects of our lives in the future. It is becoming increasingly common for deep-learning models to be used in a variety of situations in the modern life, ranging from search and recommendations to financial and healthcare solutions, and the number of applications utilizing deep neural networks is still on the rise. However, a lot of recent research efforts in deep learning have focused primarily on neural networks and domains in which they excel. This includes computer vision, audio processing, and natural language processing. It is a general tendency for data in these areas to be homogeneous, whereas heterogeneous tabular datasets have received relatively scant attention despite the fact that they are extremely prevalent. In fact, more than half of the datasets on the Google dataset platform are structured and can be represented in a tabular form. The first aim of this study is to provide a thoughtful and comprehensive analysis of deep neural networks' application to modeling and generating tabular data. Apart from that, an open-source performance benchmark on tabular data is presented, where we thoroughly compare over twenty machine and deep learning models on heterogeneous tabular datasets. The second contribution relates to synthetic tabular data generation. Inspired by their success in other homogeneous data modalities, deep generative models such as variational autoencoders and generative adversarial networks are also commonly applied for tabular data generation. However, the use of Transformer-based large language models (which are also generative) for tabular data generation have been received scant research attention. Our contribution to this literature consists of the development of a novel method for generating tabular data based on this family of autoregressive generative models that, on multiple challenging benchmarks, outperformed the current state-of-the-art methods for tabular data generation. Another crucial aspect for a deep-learning data system is that it needs to be reliable and trustworthy to gain broader acceptance in practice, especially in life-critical fields. One of the possible ways to bring trust into a data-driven system is to use explainable machine-learning methods. In spite of this, the current explanation methods often fail to provide robust explanations due to their high sensitivity to the hyperparameter selection or even changes of the random seed. Furthermore, most of these methods are based on feature-wise importance, ignoring the crucial relationship between variables in a sample. The third aim of this work is to address both of these issues by offering more robust and stable explanations, as well as taking into account the relationships between variables using a graph structure. In summary, this thesis made a significant contribution that touched many areas related to deep neural networks and heterogeneous tabular data as well as the usage of explainable machine learning methods

    The Typological Diversity of Morphomes: A Cross-Linguistic Study of Unnatural Morphology

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    This is the first typologically-oriented book-length treatment of morphomes, systematic morphological identities, usually within inflectional paradigms, that do not map onto syntactic or semantic natural classes. In the first half of the book, Borja Herce outlines the theoretical and empirical challenges associated with the identification and definition of morphomes, and surveys their links with related notions such as syncretism, homophony, segmentation, and economy, among others. He also presents the different ways in which morphomic structures in a language have been observed to emerge, change, and disappear. The second part of the book contains its core contribution: a database of 120 morphomes across 79 languages from a range of families, which are presented and analysed in detail. A range of findings emerge as a result, including the idiosyncratic nature of morphomes in the Romance languages, the existence of cross-linguistically recurrent unnatural patterns, and the preference for more natural structures even among morphomes. The database also allows further explorations of other issues such as the effect of learnability and communicative efficiency on morphological structures, and the lexical and grammatical informativity of morphs and their distribution

    Assessing Atmospheric Pollution and Its Impacts on the Human Health

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    This reprint contains articles published in the Special Issue entitled "Assessing Atmospheric Pollution and Its Impacts on the Human Health" in the journal Atmosphere. The research focuses on the evaluation of atmospheric pollution by statistical methods on the one hand, and on the other hand, on the evaluation of the relationship between the level of pollution and the extent of its effect on the population's health, especially on pulmonary diseases
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