Submitted by Filipe dos Santos (fsantos@pucsp.br) on 2018-03-19T12:21:28Z No. of bitstreams: 1 Laysce Rocha de Moura.pdf: 2892378 bytes, checksum: 1cad4916514df7227bcc894f99a272d2 (MD5) / Made available in DSpace on 2018-03-19T12:21:28Z (GMT). No. of bitstreams: 1 Laysce Rocha de Moura.pdf: 2892378 bytes, checksum: 1cad4916514df7227bcc894f99a272d2 (MD5) Previous issue date: 2018-02-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The goal of this thesis was to understand the associative process linking waste pickers to the recyclable material cooperative, seeking to examine the causes and elements that lead to grouping and the types of social interactions ties. The Network Theory, which has the focus of analysis on social relations, helps to understand this dynamic. For this, the homophily and the strength of weak and strong ties theory were the concepts used to answer the guiding question: What are the processes that lead waste pickers to enroll in cooperatives? And the related question: How is characterized the network of waste pickers' in the associative process? The study has a structural approach that used qualitative methods - 'Coding' or grouping data by topic - and quantitative - the software NodeXL Basic - of analysis. In order to choose the precise cases, two criteria of choice were established: origin and the relation with the public initiative. From this, two cooperatives were identified: CooperVida and CooperFlor. The findings indicate that age, education, geographical location, and unemployment were the main elements in CooperVida and CooperFlor that influenced the associative process. These causes of grouping are consequence of the individual characteristics and the context in which the individual is immersed, in that way the associative process is the result of an induced process that can be framed as a structural homophily effect or homophily of status. Nevertheless, the network of relatives and close associates were more used to approach the cooperative, pointing to the strength of strong social ties in the enrolment process. Taking the above, the work done by the waste pickers was recognized as an occupation in the Brazilian labor market. Although it was an achievement for this social segment, the results of this thesis point out that the waste pickers went into the street or to work in the cooperative due to external factors or because of their attributes and not an individual choice (structural homophily effect / status). Moreover, the research findings highlight the importance that strong ties have in associative process and corroborate with the strength of weak and strong ties theory proposed by Granovetter (1983) / O objetivo desta tese foi compreender o processo associativo de vinculação de catadores à cooperativa de materiais recicláveis, buscando examinar as causas que levam ao agrupamento e os tipos de laço das interações. A Teoria de Redes, que tem o foco de análise nas relações sociais, ajuda a compreender essa dinâmica. Para tanto, a homofilia e a força dos laços fracos e fortes foram os conceitos utilizados para responder à questão norteadora: Quais são os processos que levam os catadores se associarem em cooperativas? E a questão associada: Como se caracteriza a rede de relações dos catadores nesse processo associativo? O estudo tem uma abordagem estrutural que utilizou métodos qualitativos - ‘codificação’ ou agrupamento de dados por tema - e quantitativos - o software NodeXL Basic - de análise. Para eleger os casos concretos, estabeleceu-se dois critérios de escolha: origem e a relação com o poder público. A partir disso, duas cooperativas foram identificadas: CooperVida e CooperFlor. Os achados indicam que a idade, a escolaridade, a localização geográfica e o desemprego foram os principais fatores na CooperVida e na CooperFlor que influenciaram o processo associativo. Essas causas de agrupamento são consequência das características do indivíduo e do contexto em que ele está imerso, dessa forma o processo associativo é resultado de um processo induzido que pode ser enquadrado como um efeito homofilico estrutural ou homofilico de status. Por sua vez, a rede de familiares e de pessoas próximas foram mais utilizadas para o acesso à cooperativa, apontando para a força dos laços fortes no processo associativo. Diante do exposto, o trabalho desenvolvido pelos catadores de material reciclável foi reconhecido como uma ocupação no mercado de trabalho brasileiro. Apesar de ter sido uma conquista para esse segmento social, os resultados desta tese apontam que os catadores entraram para a catação na rua ou para trabalhar na cooperativa em decorrência de fatores externos ou em decorrência de seus atributos e não de uma escolha individual (efeito homofílico estrutural/status). Além disso, os achados da pesquisa evidenciam a importância que os laços fortes têm no processo associativo e corroboram com a teoria dos laços fortes e fracos proposto por Granovetter (1983)

Diversos estudos exploram temas relacionados ao monitoramento do ambiente com o intuito de auxiliar empresas a se protegerem contra ameaças e a aproveitarem oportunidades provenientes do ambiente externo. Outros pesquisadores se dedicaram aos tópicos relacionados à gestão do conhecimento, colocando o conhecimento como elemento central para o desenvolvimento e o sucesso empresarial. Contudo, identificaram-se poucos estudos que explorem as temáticas de monitoramento do ambiente e gestão do conhecimento em conjunto. Com o propósito de contribuir para o preenchimento desta lacuna, o presente estudo investiga o desenvolvimento da capacidade absortiva em processos de exploração de sinais fracos, sob a perspectiva da criação do conhecimento organizacional. Para tal investigação se utilizou método qualitativo e exploratório; tendo como técnicas de coleta de dados entrevistas semiestruturadas e análise de conteúdo para exploração dos mesmos. Constatou-se que o desempenho do processo de Inteligência pode contribuir para o desenvolvimento da capacidade absortiva, além de propiciar a criação, expansão e renovação de conhecimentos individuais e organizacionais. Observou-se, também, que a realização das atividades de Inteligência incentiva a ação e influencia na tomada de decisão de colaboradores e gestores. Os profissionais ao se sentirem melhor informados sobre oportunidades e ameaças provenientes do ambiente externo à organização passam a refletir e se responsabilizar mais por ações e decisões. / Many studies explore topics related to the environmental scanning process in order to assist companies with protecting themselves against threats and seizing opportunities that arise from external environments. Furthermore, a number of researchers have focused broadly and deeply on topics related to knowledge management, placing knowledge as a central resource to a business’s development and success. Nevertheless, there are few studies that combine the themes of environmental scanning and knowledge management. Aiming contribute to fill this gap, this study investigates the absorptive capacity developing in weak signals’ exploration process through the organization knowledge creation’ perspectives. The employed method to this qualitative and explorative research will be interviews by means of techniques for collecting data; and a content analysis for an exploitation of these data. It was found that the Intelligence process performance contributes to the development of absorptive capacity. Futhermore, the practice of Intelligence process facilitates the creation, expansion and renewal of individual and organizational knowledge. It was also observed that the realization of intelligence activities encourages action and influence in employees and managers decision making. Professionals who feel better informed about opportunities and threats from the external environment in regards to the organization start to further reflect and be more accountable for actions and decisions.

Dans cette thèse, nous nous intéressons à l’analyse mathématique théorique et numérique des équations deNavier-Stokes compressibles en régime barotrope. La plupart des travaux présentés ici combinent desméthodes d’analyse des équations aux dérivées partielles et des méthodes d’analyse numérique afin de clarifierla notion de solution faible ainsi que les mécanismes de convergence de méthodes numériques approximant cessolutions faibles. En effet les équations de Navier-Stokes compressibles sont fortement non linéaires et leuranalyse mathématique repose nécessairement sur la structure de ces équations. Plus précisément, nousprouvons dans la partie théorique l’existence de solutions faibles pour un modèle d’écoulement compressibled’entropie variable où l’entropie du système est transportée. Nous utilisons les méthodes classiques permettantde prouver l’existence de solutions faibles aux équations de Navier-Stokes compressibles en regime barotrope.Nous étudions aussi dans cette partie la réduction de dimension 3D/2D dans les équations de Navier-Stokescompressibles en utilisant la méthode d’énergie relative. Dans la partie numérique nous nous intéressons auxestimations d’erreur inconditionnelles pour des schémas numériques approximant les solutions faibles deséquations de Navier-Stokes compressibles. Ces estimations d’erreur sont obtenues à l’aide d’une versiondiscrète de l’énergie relative satisfaite par les solutions discrètes de ces schémas. Ces estimations d’erreur sontobtenues pour un schéma numérique académique de type volumes finis/éléments finis ainsi que pour le schémanumérique Marker-and-Cell. Nous prouvons aussi que le schéma Marker-and-Cell est inconditionnellement etuniformément asymptotiquement stable en régime bas Mach. Ces résultats constituent les premiers résultatsd’estimations d’erreur inconditionnelles pour des schémas numériques pour les équations de Navier-Stokescompressibles en régime barorope. / In this thesis, we deal with mathematical and numerical analysis of compressible Navier-Stokes equations inbarotropic regime. Most of these works presented here combine mathematical analysis of partial differentialequations and numerical methods with aim to shred more light on the construction of weak solutions on oneside and on the convergence mechanisms of numerical methods approximating these weak solutions on theother side. Indeed, the compressible Navier-Stokes equations are strongly nonlinear and their mathematicalanalysis necessarily relies on the structure of equations. More precisely, we prove in the theorical part theexistence of weak solutions for a model a flow of compressible viscous fluid with variable entropy where theentropy is transported. We use the classical techniques to prove the existence of weak solutions for thecompressible Navier-Stokes equations in barotropic regime. We also investigate the 3D/2D dimensionreduction in the compressible Navier-Stokes equations using the relative energy method. In the numerical wedeal with unconditionally error estimates for numerical schemes approximating weak solutions of thecompressible Navier-Stokes equations. These error estimates are obtained by using the discrete version of therelative energy method. These error estimates are obtained for a academic finite volume/finite element schemeand for the Marker-and-Cell scheme. We also prove that the Marker-and-cell scheme is unconditionally anduniformly asymptotically stable at the Low Mach number regime. These are the first results onunconditionally error estimates for numerical schemes approximating the compressible Navier-Stokesequations in barotropic regime.

Les relevés à venir comme Euclid, LSST et WFIRST vont nous ouvrir la perspective d’étudier l’univers profond. Pour ces grands relevés, l’astigmatisme cosmique correspond à une sonde indispensable pour étudier la nature de l’énergie noire et la matière noire. Compte tenu de la précision attendue par ces observations, nous devons faire des prédictions basées sur des simulations correspondant à l’état de l’art afin de quantifier avec précision la variance, les biais et les dégénérescences potentielles liés aux baryons. Dans ce contexte, ma thèse se focalise sur la construction d’estimateurs précis basés sur les observables de lentillage. La première partie de ma thèse consiste à caractériser la géométrie des grandes structures par astigmatisme cosmique (Gouin et al. 2017). Une décomposition multipolaire du signal est appliquée afin de quantifier la distribution azimutale de la matière noire, centrée sur les amas. Les propriétés statistiques de ces moments sont estimées à partir d’une simulation cosmologique. Les distorsions harmoniques calculées dans le voisinage des amas tracent la structure filamentaire. Un plus grand nombre de filaments semblent connectés aux amas de forte masse. Dans la dernière partie de ma thèse, je synthétise le signal d’astigmatisme cosmique dans le cône de lumière de la simulation Horizon AGN. Pour ce faire, je propage les rayons de lumière le long du cône dans l’approximation des plans de lentillage multiples. L’effet des baryons est significatif dans la statistique du cisaillement aux échelles angulaires inférieures à l’arc-minute. Le signal de cisaillement galaxie-galaxie est comparée aux observations récentes, et semble être en bon accord. / Upcoming weak lensing surveys such as Euclid, LSST and WFIRST will provide an unprecedented opportunity to investigate the dark Universe. Through these large scale surveys, gravitational lensing is an indispensable cosmological probe to investigate the dark energy and the dark matter. Due to the new level of accuracy in observations, we must perform cosmological predictions in state-of-art simulations, to precisely quantify its variances, biases and potential degeneracies coming from baryonic physics. In this context, my thesis focuses on the construction of accurate weak lensing observables. The first part of my PhD work characterises the geometry of large-scale structure through weak lensing (Gouin et al. 2017). I relied on multipolar decomposition of weak lensing signal to quantify the azimuthal distribution of dark matter centred on galaxy clusters. The statistical properties of these moments are estimated from a large N-body simulation. The harmonic distortions computed in the vicinity of clusters appear to trace the filamentary structure. Larger number of filaments seem to be connected to high-mass clusters.The detection level of this statistical estimator is estimated. In the last part of my thesis, I mock the weak gravitational lensing signal in the light-cone of the Horizon-AGN simulation (Gouin et al. 2019). To do so, I propagate light-rays along the light-cone in the multiple-lens-plane approximation. The impact of baryons is significant in cosmic shear statistics for angular scales below a few arcmins. In addition, the galaxy-galaxy lensing signal is compared to current observational measurements (Leauthaud et al. 2017), and seems in good agreement.

Physically Unclonable Functions (PUFs) are now widely being used to uniquely identify Integrated Circuits (ICs). In this work, we propose a novel Set-Reset (SR) Flip-flop based PUF design. For a NAND gate based SR flip-flop, the input condition S (Set) = 1 and R (Reset) = 1 must be avoided as it is an inconsistent condition. When S=R=1 is applied followed by S=R=0, then the outputs Q and Q' undergo race condition and depending on the delays of the NAND gates in the feedback path, the output Q can settle at either 0 or 1. Because of process variations in an IC, the NAND delays are statistical in nature. Thus, for a given SR FF based $n$-bit register implemented in an IC, when we apply S=R=1 to all flip-flops followed by S=R=0, then we obtain an $n$ bit string that can be interpreted as a signature of the chip. Due to process variations, the signature is highly likely to be unique for an IC. We validated the proposed idea by SPICE-level simulations for 90nm, 45nm, and 32nm designs for both intra- and inter-chip variations to establish the robustness of the proposed PUF. Experimental results for 16-, 32-, 64-, and 128-bit registers based on Monte-Carlo simulations demonstrate that the proposed PUF is robust. The main advantage of the proposed PUF is that there is very little area overhead as we can reuse existing registers in the design.

本研究的主要目的在利用模擬實證研究的方式，探討資訊在我國股市股價形成中所扮演的角色。本研究所定義的資訊均屬最低成本或成本趨近於零的歷史性資訊或隨機亂數資訊，這些資訊包括亂數選擇、加權平均指數之反轉移動，與個股股價反轉移動資訊等。理性預期均衡理論提供了資訊與股價間關係的理論基礎。在理性預期均衡理論中，最基本的觀念是股價與攸關資訊間，若非雜訊，二者應具系統化關係。本研究預期可瞭解我國股市部份資訊效率性的意義，亦可進一步瞭解與歷史性資訊在我國股價形成所扮演的角色。 　　本研究採用模擬式實證研究法，以理性預期理論為基礎，探討隨機亂數資訊與歷史性股價資訊在股價形成過程中所扮演的角色，從而檢定我國股票市場之效率性。為了能評估不同層次之歷史資訊所代表之本質，本研究將採用之資訊分為三層次，分三階段進行。且為了觀察市場多、空頭之差異，又特別分別測試。 　　本研究以266家上市公司為抽樣母體，蒐集自民國83年至民國84年中之股價資料，分多、空頭進行研究，獲致以下結論： 　　一、在不利用任何歷史性資訊（亦即非理性狀態下）以制訂投資決策之情況下，若市場為多頭時期，存在有總累積報酬率擊敗市場且顯著差異之事實，且持有週期愈短，總累積報酬率愈高；而若市場為空頭時期，不論持有週期長短，總累積報酬率皆不能擊敗市場，但以各投資組合而言，仍存在有擊敗市場且顯著差異之事實，以此推論，台灣股票市場屬弱式效率市場之範疇。 　　二、當採用市場發行量加權平均指數之反轉移動為投資買賣點之依據，不論市場是處於多頭或空頭，總累積報酬率皆無法擊敗市場之平均表現。但各個投資組合亦存在有擊敗市場且顯著差異之事實，亦可支持台灣股票市場為弱式效率市場之說法。 　　三、若改以個股股價反轉移動為投資決策參考之指標，在多、空頭時期，且不論就個別投資組合或總累積報酬率來看，皆可輕易獲致超額報酬且顯著差異，暗示我國股市股價形成之過程並不能充分反應此一資訊，據此可推論台灣股票市場為弱式效率市場。 　　四、以市場發行量加權平均指數反轉移動資訊所制訂投資決策之績效不能顯著勝過市場之平均表現看來，台灣股票市場之股票股價形成過程中，深受歷史性加權平均指數移動資訊所影響，以致能大部分反映此部分資訊。而以個股股價反轉移動資訊所制訂投資決策之績效卻能輕易勝過市場且顯著差異看來，我國股市中個別股票股價表現似乎存在重大差異，股價與加權指數間並不皆具有高度正相關，投資人若決策錯誤，可能產生「賺了指數，賠了差價」之情形。 / This study aims to examine the role of information plays in the stock price formation by an application of simulated empirical approach. The results of this study can be used for assessing the appropriateness of Fama's definition of efficient market hypothesis (1970) in the Taiwan stock market. The assessment of information in this study includes random selection, reverse movement of stock index, and reverse movement of an individual stock. The analysis includes 266 samples covering bull/bear markets in the period between 1994 and 1995 on which the findings can be summarized as follows. 　　1. If the portfolio is formed upon random selection, the performance of portfolios can significantly beat the market in the bull market. In particular, the shorter turnover is, the higher return can be gained. There exist examples that the random portfolio can beat the market in the bear market no matter which turnover is selected. 　　2. If the portfolio is formed upon the reverse movement of stock index, even though total cumulative returns cannot beat the market average return in all cases, there exist cases beating the market. 　　3. If the portfolio is formed upon the reverse movement of an individual stock, no matter what the bull or bear market is, the portfolio can significantly beat the market for designated cases or total cumulative returns. 　　Thus, the stock price in the Taiwan stock market can be classified as a weak form market or weaker than a weak form market based on the Fama's definition (1970). Future research can consider how the Fama's definition of efficient market hypothesis can be revised in order to be applicable in the Taiwan stock market.

Les systèmes électroniques bidimensionnels sont d'une grande actualité tout particulièrement depuis la découverte de la supraconductivité à haute température. Ici, on se restreint à l'étude d'un modèle de Hubbard étendu, à la limite d'un couplage faible. En général, le gaz électronique subit une instabilité supraconductrice même sans phonons. Cependant, dans le cas spécial d'une bande demi-remplie, la surface de Fermi est emboîtée et se trouve à une singularité de Van Hove. Cette situation conduit à une compétition entre six instabilités différentes. Outre la supraconductivité en onde $s$ et $d$, on trouve des ondes de densités de spin et de charge ainsi que deux phases qui sont caractérisées par des courants circulaires de charge et de spin respectivement. Le formalisme du groupe de renormalisation est présenté en reliant l'idée de la "< sommation parquet "> au concept plus moderne de l'action effective de Wilson. Comme résultat on obtient un diagramme de phases riche en fonction de l'interaction du modèle. Ce diagramme de phase est exact dans la limite d'une interaction infiniment faible, puisque dans ce cas les lignes de transitions sont fixées par des symétries du modèle. Les comportements à basse température de la susceptibilité de spin ainsi que de la compressibilité de charge complètent l'image physique de ces instabilités. Il s'avère que la surface de Fermi à une tendence générale de se déformer spontanément, mais l'emboîtement n'est pas détruit. En résumé, le modèle de Hubbard à couplage faible reproduit deux propriétés essentielles des cuprates: une phase antiferromagnetique à demi remplissage et la supraconductivité en onde $d$ dans le cas dopé. Mais elle n'éxplique pas les propriétés inhabituelles de l'état métallique dans le régime sous-dopé. Une extension systématique de l'approche perturbative pourrait aider à mieux comprendre ces propriétés, mais reste difficile puisque les techniques nécessaires ne sont pas encore complètement développées.

<p>This thesis consists of four papers, all concerning random iteration of isometries. The papers are:</p><p>I. Ambroladze A, Ådahl M, Random iteration of isometries in unbounded metric spaces. Nonlinearity 16 (2003) 1107-1117.</p><p>II. Ådahl M, Random iteration of isometries controlled by a Markov chain. Manuscript.</p><p>III. Ådahl M, Melbourne I, Nicol M, Random iteration of Euclidean isometries. Nonlinearity 16 (2003) 977-987.</p><p>IV. Johansson A, Ådahl M, Recurrence of a perturbed random walk and an iterated function system depending on a parameter. Manuscript.</p><p>In the first paper we consider an iterated function system consisting of isometries on an unbounded metric space. Under suitable conditions it is proved that the random orbit {<i>Z</i>n} ^∞_n=0, of the iterations corresponding to an initial point Z₀, “escapes to infinity" in the sense that <i>P</i>(<i>Z</i>n Є <i>K)</i> → 0, as <i>n</i> → ∞ for every bounded set <i>K</i>. As an application we prove the corresponding result in the Euclidean and hyperbolic spaces under the condition that the isometries do not have a common fixed point.</p><p>In the second paper we let a Markov chain control the random orbit of an iterated function system of isometries on an unbounded metric space. We prove under necessary conditions that the random orbit \escapes to infinity" and we also give a simple geometric description of these conditions in the Euclidean and hyperbolic spaces. The results generalises the results of Paper I.</p><p>In the third paper we consider the statistical behaviour of the reversed random orbit corresponding to an iterated function system consisting of a finite number of Euclidean isometries of <b>R</b>n. We give a new proof of the central limit theorem and weak invariance principles, and we obtain the law of the iterated logarithm. Our results generalise immediately to Markov chains. Our proofs are based on dynamical systems theory rather than a purely probabilistic approach.</p><p>In the fourth paper we obtain a suficient condition for the recurrence of a perturbed (one-sided) random walk on the real line. We apply this result to the study of an iterated function system depending on a parameter and defined on the open unit disk in the complex plane. </p>

Existe-t-il un consensus scientifique sur les conditions de la durabilité ? Est-il possible de construire un indicateur unique de soutenabilité faible ? Quelles sont les composantes objectives et subjectives des indicateurs ? Peut-on envisager des indicateurs objectifs de soutenabilité ? Quelles voies de recherche sont-elles nécessaires pour développer des indicateurs de développement durable ? Telles sont les questions auxquelles cet ouvrage tente de répondre. La comparaison des courants de la soutenabilité faible et de la soutenabilité forte nous sert de fil conducteur pour évaluer la part normative et la part objective du choix des paramètres et de leur méthode d'agrégation. L'agrégation arithmétique implique des hypothèses de substituabilité entre les facteurs, ce qui relève de la soutenabilité faible. La pondération, toujours normative, peut être explicite ou se traduire par le choix d'une unité ou dimension unique. Nous redéfinissons la soutenabilité faible comme étant la réduction de la complexité à une dimension unique. Il y a dès lors autant d'indicateurs de soutenabilité faible que de choix possibles de cette dimension unique. En particulier, l'empreinte écologique par habitant relève d'une forme "écologique" de soutenabilité faible. Le prix de marché est l'unité fondamentale de mesure de sa forme "économique". Nous montrons que les acteurs ne savent pas bien identifier leur intérêt et qu'ils ne sont pas parfaitement égoïstes, ce qui introduit un biais non systématique remarquable dans toute mesure en unité monétaire. La soutenabilité forte se caractérise par la multiplicité de dimensions ou "capitaux critiques" dont le dépassement d'un seul suffit à déterminer la non soutenabilité. Les différentes formes de soutenabilités faibles peuvent représenter des capitaux critiques parmi d'autres. Nous présentons une typologie des acteurs et du partage des responsabilités, également susceptible d'introduire des grandes divergences dans les résultats publiés. Quelques études de cas illustrent ces différents éléments dans des contextes contrastés. L'empreinte écologique de consommation se limite en particulier à une responsabilisation du seul consommateur, alors que les comptes nationaux permettent d'envisager la coresponsabilité de l'ensemble des acteurs. L'indicateur de "dématérialisation de l'économie" appliqué à un village indien montre la pertinence de mesurer l'utilisation absolue de matière sans pondération monétaire. Il est par ailleurs possible de minimiser le coût de dépollution sans toucher à la limite absolue d'émissions globales de centrales thermiques. Les deux dimensions, coûts sociaux et bénéfices environnementaux, peuvent donc être traitées séparément. En conclusion, il est possible d'identifier, dans chaque calcul d'indicateur de développement durable, une composante relativement objective de soutenabilité "forte" et une composante "faible", négociable, de partage des droits et responsabilités. / We study how different world views may influence how to develop sustainable development indicators. The comparison of weak sustainability and strong sustainability serves as a guide to estimate the share of objective versus normative choice of parameters and their method of aggregation. We then present a typology of actors and shared responsibilities, which may also introduce large discrepancies in the results published. Some case studies illustrate these different elements in contrasting contexts. It appears that it is possible to identify in each calculation of sustainable development indicator, a relatively objective component of sustainability and a negotiable component of shared rights and responsibilities.

The extensions of vague predicates like ‘is bald’, ‘is tall’, and ‘is a heap’ apparently lack sharp boundaries, and this makes such predicates susceptible to soritical reasoning, i.e. reasoning that leads to some version of the notorious sorites paradox. This essay is concerned with a certain kind of theory of vagueness, according to which the symptoms and puzzles of vagueness should be accounted for in terms of a particular species of context sensitivity exhibited by vague expressions. The basic idea is that the extensions of vague predicates vary with certain contextual factors, and that this fact can explain why they appear to lack sharp boundaries. This kind of view is referred to as contextualism about vagueness. A detailed characterisation of contextualism about vagueness is given in chapter two and three. In chapter two, a generic version of contextualism about vagueness is developed, and some alternative forms of context sensitivity are introduced. In chapter three, the specific contextual factors appealed to by different contextualists are discussed. In chapter four, different contextualist diagnoses of the sorites paradox are considered, and found to be problematic in various ways. It is argued that contrary to what some of its proponents have claimed, contextualism about vagueness is not superior to other comparable theories of vagueness when it comes to explaining the appeal of soritical reasoning. In chapter five, a certain version of the sorites paradox, known as the forced march sorites, is discussed. It is argued that “data” about how speakers would behave in the forced march cannot lend any firm support to contextualism about vagueness. In chapter six, some problems concerning the instability of the contextual factors are considered. One problem is that contextualist diagnoses of the sorites which locate a fallacy of equivocation in the reasoning seem to render non-soritical reasoning fallacious as well. A model for treating this problem is suggested, but on closer consideration, it turns out to be problematic. Moreover, this model is of no help in solving the more general problem that even if classical logic remains valid for vague language on some contextualist views, the instability of the extensions of vague predicates makes it difficult to know when a certain piece of reasoning instantiates a valid argument form. Other difficulties arise with respect to speech reports and belief contents. Chapter seven concludes with a summary and some methodological remarks.