304 research outputs found
O naturalismo de Maddy e a avaliação de candidatos a axioma em teoria dos conjuntos
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas, Programa de Pós-Graduação em Filosofia, Florianópolis, 2012Em um certo sentido, a matemática usual pode ser reduzida à teoria dos conjuntos, isto é, os objetos matemáticos usuais podem ser definidos como conjuntos, e os teoremas que governam esses objetos podem ser provados em ZFC. Todavia, existem enunciados importantes - a hipótese do contínuo é o mais célebre deles - que são independentes de ZFC. A existência de enunciados independentes levanta a questão da necessidade e conveniência de estender ZFC pela adição de novos axiomas. Nesse contexto, é interessante dispor de critérios claros que permitam avaliar candidatos a axioma para uma extensão da teoria dos conjuntos que decidiria enunciados independentes. Maddy tem se dedicado intensamente à filosofia da teoria dos conjuntos, com destaque para a investigação de critérios para seleção de axiomas. Nesta dissertação, nosso objetivo é seguir o percurso de Maddy nessa investigação, atentando especialmente a sua defesa da autonomia da matemática com respeito à filosofia e às ciências naturais e ao correspondente papel preponderante da argumentação extrínseca nas discussões que estabeleceram os axiomas da atual teoria. Como pano de fundo filosófico, o naturalismo em matemática de Maddy é também objeto privilegiado da nossa atenção neste trabalho.Abstract : In a certain sense, ordinary mathematics can be reduced to set theory, i.e., general mathematical objects can be defined as sets and the theorems about them can be proved from ZFC. However, there are important statements - the continuum hypothesis is the most famous among them - which are independent of ZFC. The existence of these statements raises a question about the necessity and convenience of extending ZFC, adding to it new axioms. In this context, it is interesting to have clear criteria for evaluating axiom candidates for an extension of ZFC that would decide independent statements. Maddy has focused intensely on philosophy of set theory, emphasizing the investigation of criteria for selection of set-theoretic axioms. In this dissertation, our goal is to understand and explain Maddy's investigation, with special attention to her defense of the autonomy of mathematics with respect to philosophy and natural sciences and the corresponding leading role of extrinsic arguments in the debates that established the current axioms of set theory. As philosophical background, naturalism in mathematics is also a privileged object of our attention in this work
Imaging Cells Within 3D Cell-Derived Matrix
No full textMuch of what is known about the mechanisms regulating cell adhesion and migration come from in vitro studies of cells plated on 2-dimensional (2D) extracellular matrix (ECM) proteins. The importance of studying these processes in cells within 3-dimensional (3D) environments is becoming increasingly recognised, as a number of studies have now demonstrated that adhesion formation and migration are markedly different in cells within 3D environments (Cukierman et al. Science 1708-1712, 2001). It is also known that the composition and pliability or density of the ECM are important in regulating cell adhesion and migration (Cukierman et al. Science 1708-1712, 2001). Cell-derived matrices (CDM) are naturally deposited fibrillar ECM from fibroblasts that can be used to study the adhesions and migration of cells in a more physiologically relevant environment
Measuring FRET Using Time-Resolved FLIM
No full textCell migration is a process that is controlled by the formation and correct localization of protein complexes and by post-translational modification of individual proteins. Forster or fluorescent resonance energy transfer (FRET) detected using fluorescence lifetime imaging microscopy (FLIM) provides a method by which protein-protein interactions may be detected and spatially localized within a cell. This technique can be used to map protein activation states and the formation and dissolution of protein complexes that control movement of a cell. This chapter describes a protocol for detecting FRET between GFP- and mRFP1-tagged proteins in fixed adherent cells. A background to both FRET and FLIM is provided followed by an overview of the method and a full protocol for sample preparation, data acquisition, and analysis
CAR regulate epithelial cell junction stability through control of E-cadherin trafficking
No full textCAR (Coxsackie and Adenovirus Receptor) is the primary docking receptor for typeB coxsackie viruses and subgroup C adenoviruses. CAR is a member of the JAM family of adhesion receptors and is located to both tight and adherens junctions between epithelial cells where it can assemble adhesive contacts through homodimerisation in trans. However, the role of CAR in controlling epithelial junction dynamics remains poorly understood. Here we demonstrate that levels of CAR in human epithelial cells play a key role in determining epithelial cell adhesion through control of E-cadherin stability at cell-cell junctions. Mechanistically, we show that CAR is phosphorylated within the C-terminus by PKCδ and that this in turn controls Src-dependent endocytosis of E-cadherin at cell junctions. This data demonstrates a novel role for CAR in regulating epithelial homeostasis
'Do it Yourself' Girl Revolution: LadyFest, Performance and Fanzine Culture
No full textRiot grrrl began as an independent music and political movement in the early 1990s emerging initially in the USA and few years later in the UK. From the beginning riot grrrl embraced a 'do-it-yourself' ethos operating outside the mainstream music business organising independent music festivals, workshop events and encouraging self-published fanzines (fan magazines which were distributed primarily through word of mouth, music gigs, artists and zine book fairs or by post). These zines became recognisable forms of personal expression and made visible a specific DIY approach alongside the development of a coherent style of graphic language in the producer's use of the photocopier, handwritten and graffiti texts, cut-n-paste and ransom note lettering style, collage and the co-option of mainstream media imagery. These production techniques made fanzine publishing accessible and played a central role in the development of a non-hierarchical community.
The main intent of this talk is to explore the idea of 'event as performance' using as a case study the specific activities of riot grrrl and focussing on a series of international events called 'LadyFests' and the graphic language of self-published riot grrrl fanzines. This will be achieved by examining the origins of today's riot grrrl performances (e.g. theatre, spoken word, music events) in 1970s feminist art, as well as locating the activities within the specific context of their counter-cultural predecesors including punk and punk performance
Maddy and Mathematics: Naturalism or Not
No full textPenelope Maddy advances a purportedly naturalistic account of mathematical methodology which might be taken to answer the question \u27What justifies axioms of set theory?\u27 I argue that her account fails both to adequately answer this question and to be naturalistic. Further, the way in which it fails to answer the question deprives it of an analog to one of the chief attractions of naturalism. Naturalism is attractive to naturalists and nonnaturalists alike because it explains the reliability of scientific practice. Maddy\u27s account, on the other hand, appears to be unable to similarly explain the reliability of mathematical practice without violating one of its central tenets. 1 Introduction 2 Mathematical Naturalism 3 Desiderata and the attraction of naturalism 4 Assessment: Naturalism and names 4.1 Taking \u27naturalism\u27 seriously 4.2 Second philosophy (or what\u27s in a name) 5 A way out? 6 Or out of the way? Copyright © The Author 2007. Published by Oxford University Press on behalf of British Society for the Philosophy of Science
Introduction to intuitions
No full textAvtor se v članku na analitičen način loteva pojma intuicije, obravnava intuicijsko stanje, intuicijsko vsebino, intuicijske zmožnosti, intuicijski proces, matematično intuicijo, moralno intuicijo. Formulira tri teze o intuiciji: o perceptualnem izvoru, kognitivni revščini in bogastvu vsebine in pokaže povezanost teh tez s filozofsko tradicijo (Aristotel, Hume, Parsons, Maddy).The author analyses the notion of intuition, discusses the intuitive state, the content of intuition, intuitive abilities, the intuitive process, mathematical intuition and moral intuition. He formulates three theses about intuition: the thesis of perceptual origin, the thesis of cognitive poverty and the thesis of the richness of content. He also points to the links between these theses and the tradition of philosophy (Aristotle, Hume, Parsons, Maddy)
Talin contains a C-terminal calpain2 cleavage site important in focal adhesion dynamics
No full textTalin is a large (~2540 residues) dimeric adaptor protein that associates with the integrin family of cell adhesion molecules in cell-extracellular matrix junctions (focal adhesions; FAs), where it both activates integrins and couples them to the actin cytoskeleton. Calpain2-mediated cleavage of talin between the head and rod domains has previously been shown to be important in FA turnover. Here we identify an additional calpain2-cleavage site that removes the dimerisation domain from the C-terminus of the talin rod, and show that an E2492G mutation inhibits calpain cleavage at this site in vitro, and increases the steady state levels of talin1 in vivo. Expression of a GFP-tagged talin1 E2492G mutant in CHO.K1 cells inhibited FA turnover and the persistence of cell protrusion just as effectively as a L432G mutation that inhibits calpain cleavage between the talin head and rod domains. Moreover, incorporation of both mutations into a single talin molecule had an additive effect clearly demonstrating that calpain cleavage at both the N- and C-terminal regions of talin contribute to the regulation of FA dynamics. However, the N-terminal site was more sensitive to calpain cleavage suggesting that lower levels of calpain are required to liberate the talin head and rod fragments than are needed to clip off the C-terminal dimerisation domain. The talin head and rod liberated by calpain2 cleavage have recently been shown to play roles in an integrin activation cycle important in FA turnover and in FAK-dependent cell cycle progression respectively. The half-life of the talin head is tightly regulated by ubiquitination and we suggest that removal of the C-terminal dimerisation domain from the talin rod may provide a mechanism both for terminating the signalling function of the talin rod and indeed for inactivating full-length talin thereby promoting FA turnover at the rear of the cell
O realismo modal de David K. Lewis e suas implicações epistêmicas
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas. Programa de Pós-Graduação em Filosofia.Uma das dificuldades encontradas na lógica modal diz respeito à semântica. Geralmente, não é possível calcular o valor de 9" a partir do valor de ", ou seja, se " é falsa parece claro que 9" também o é, uma vez que 9" significa que " é necessariamente verdadeira. Se pelo contrario, " é verdadeira, como saber se é contingente ou necessária? O mesmo se dá com "". Se " é verdadeira, "" é verdadeira. Mas qual será o valor de "" se " é falsa? Mesmo falsa, " poderia ser possível. Posta esta dificuldade, foi criada por Saul Kripke a semântica dos mundos possíveis. Enquanto na lógica proposicional clássica uma interpretação consiste na atribuição de valores {V,F} às letras sentenciais e, por extensão, uma atribuição de valores a todas as fórmulas, em lógica modal uma interpretação consiste em um conjunto de mundos possíveis com uma atribuição de valores às fórmulas em cada um deles. Chamamos esta interpretação de modelo de mundos possíveis ou modelo de Kripke. A posição realista de David K. Lewis quanto à semântica de Mundos Possíveis para lógicas modais acarreta muitas objeções entre as quais uma epistemológica. Podemos afirmar nosso conhecimento sobre questões modais, uma vez que tal teoria afirma que não há relações espaço-temporais e causais entre os mundos? É possível conhecer algo que não está acessível à inspeção direta? Lewis faz sua defesa utilizando-se de argumentos a favor do realismo matemático. Alguns dos opositores de Lewis fazem objeção a essa estratégia e contra-argumentam de muitas formas. O objetivo geral do trabalho, além de expor da maneira mais clara possível a discussão em torno do tema, é mostrar que, mesmo que uma defesa cabal do realismo modal seja muito complicada, pelo menos no caso das objeções epistemológicas formuladas por Tom Richards, Willian Lycan e Brian Skyrms, Lewis se sai bem na defesa de sua teoria. Por outro lado, o objetivo específico e principal desta dissertação é fazer uma defesa à objeção epistemológica de Charles Chihara, uma vez que a defesa apresentada por Lewis a seus críticos não o satisfez e a resposta à objeção de Chihara deixou de ser dada por Lewis
HGF-Induced DU145 Cell Scatter Assay
No full textEpithelial mesenchymal transition (EMT) is a multi-stage process whereby epithelial cells lose their cell:cell adhesions and acquire the capacity to migrate independently. It is a process that is important in normal development and is thought to be adopted by some invasive cancer cells. EMT requires modifications in cell shape and substratum adhesions and these events are dependent on the reorganisation of the actin cytoskeleton. Hepatocyte growth factor (HGF) is a mitogenic growth factor that is well known to induce such a conversion, termed "cell scattering", in Madin Darby canine kidney (MDCK) cells. Recently, we have developed an alternative model of cell scattering using the human prostate cancer cell line, DU145. Like MDCK cells, DU145 cells normally grow as tight colonies with firm cell:cell junctions, but they can be induced to 'scatter' upon HGF stimulation. Here, we describe the optimised protocol for conducting and analysing an HGF-induced DU145 scatter assay. This model is particularly useful for monitoring changes in actin cytoskeletal organisation and dynamics, cell:cell adhesions, and cell migration in human cells that respond to HGF stimulation
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