Caracteritació de models funcionals d'àmfores romanes mitjançant Finite Element Analysis

Projecte de recerca elaborat a partir d’una estada al Laboratory of Archaeometry del National Centre of Scientific Research “Demokritos” d’Atenes, Grècia, entre juny i setembre 2006. Aquest estudi s’emmarca dins d’un context més ampli d’estudi del canvi tecnològic que es documenta en la producció d’àmfores de tipologia romana durant els segles I aC i I dC en els territoris costaners de Catalunya. Una part d’aquest estudi contempla el càlcul de les propietats mecàniques d’aquestes àmfores i la seva avaluació en funció de la tipologia amforal, a partir de l’Anàlisi d’Elements Finits (AEF). L’AEF és una aproximació numèrica que té el seu origen en les ciències d’enginyeria i que ha estat emprada per estimar el comportament mecànic d’un model en termes, per exemple, de deformació i estrès. Així, un objecte, o millor dit el seu model, es dividit en sub-dominis anomenats elements finits, als quals se’ls atribueixen les propietats mecàniques del material en estudi. Aquests elements finits estan connectats formant una xarxa amb constriccions que pot ser definida. En el cas d’aplicar una força determinada a un model, el comportament de l’objecte pot ser estimat mitjançant el conjunt d’equacions lineals que defineixen el rendiment dels elements finits, proporcionant una bona aproximació per a la descripció de la deformació estructural. Així, aquesta simulació per ordinador suposa una important eina per entendre la funcionalitat de ceràmiques arqueològiques. Aquest procediment representa un model quantitatiu per predir el trencament de l’objecte ceràmic quan aquest és sotmès a diferents condicions de pressió. Aquest model ha estat aplicat a diferents tipologies amforals. Els resultats preliminars mostren diferències significatives entre la tipologia pre-romana i les tipologies romanes, així com entre els mateixos dissenys amforals romans, d’importants implicacions arqueològiques.

On locally finite transitive two-ended digraphs

Projecte de recerca elaborat a partir d’una estada al Department de Matemàtica Aplicada de la Montanuniversität Leoben, Àustria, entre agost i desembre del 2006. L’ objectiu ha estat fer recerca sobre digrafs infinits amb dos finals, connexos i localment finits, i, en particular, en digrafs amb dos finals i altament arc-transitius. Malnic, Marusic et al. van introduir un nou tipus de relació d’equivalència en els vèrtexs d’un dígraf, anomenades relacions d’assolibilitat, que generalitzen i tenen el seu origen en un problema posat per Cameron et al., on les classes de la relació d’equivalència eren vèrtexs que pertanyien a un camí alternat del dígraf . Malnic et al. en el mencionat article van establir connexions ben estretes entre aquestes relacions d’assolibilitat i l'estructura de finals i creixement dels digrafs localment finits i transitius. En aquest treball, s’ha caracteritzat per complet aquestes relacions d’assolibitat en el cas de dígrafs localment finits i transitius amb exactament dos finals, en termes de la descomposició en números primers del número de línies que genera el digraf amb dos finals. A més, es nega la Conjectura 1 sostinguda per Seifter que afirmava que un digraf connex localment finit amb més d’un final era necessàriament o be 0-, 1- o altament arc-transitiu. Seifer havia donat una solució parcial a la conjectura pel cas de digrafs regulars amb grau primer que tinguin un conjunt de tall connex. En aquest treball, es descriu una família infinita de dígrafs regulars de grau dos, amb dos finals, exactament 2-arc transitius i no 3-arc transitius. Així, es nega la Conjectura de Seifter en el cas general, fins i tot per grau primer. Tot i així, la solució parcial donada per Seifter en el seu article és en cert sentit la millor possible i l'existència un conjunt de tall connex essencial.

On the applicability of mathematics : philosophical and historical perspectives

The present thesis is a contribution to the debate on the applicability of mathematics; it examines the interplay between mathematics and the world, using historical case studies. The first part of the thesis consists of four small case studies. In chapter 1, I criticize "ante rem structuralism", proposed by Stewart Shapiro, by showing that his so-called "finite cardinal structures" are in conflict with mathematical practice. In chapter 2, I discuss Leonhard Euler's solution to the Königsberg bridges problem. I propose interpreting Euler's solution both as an explanation within mathematics and as a scientific explanation. I put the insights from the historical case to work against recent philosophical accounts of the Königsberg case. In chapter 3, I analyze the predator-prey model, proposed by Lotka and Volterra. I extract some interesting philosophical lessons from Volterra's original account of the model, such as: Volterra's remarks on mathematical methodology; the relation between mathematics and idealization in the construction of the model; some relevant details in the derivation of the Third Law, and; notions of intervention that are motivated by one of Volterra's main mathematical tools, phase spaces. In chapter 4, I discuss scientific and mathematical attempts to explain the structure of the bee's honeycomb. In the first part, I discuss a candidate explanation, based on the mathematical Honeycomb Conjecture, presented in Lyon and Colyvan (2008). I argue that this explanation is not scientifically adequate. In the second part, I discuss other mathematical, physical and biological studies that could contribute to an explanation of the bee's honeycomb. The upshot is that most of the relevant mathematics is not yet sufficiently understood, and there is also an ongoing debate as to the biological details of the construction of the bee's honeycomb. The second part of the thesis is a bigger case study from physics: the genesis of GR. Chapter 5 is a short introduction to the history, physics and mathematics that is relevant to the genesis of general relativity (GR). Chapter 6 discusses the historical question as to what Marcel Grossmann contributed to the genesis of GR. I will examine the so-called "Entwurf" paper, an important joint publication by Einstein and Grossmann, containing the first tensorial formulation of GR. By comparing Grossmann's part with the mathematical theories he used, we can gain a better understanding of what is involved in the first steps of assimilating a mathematical theory to a physical question. In chapter 7, I introduce, and discuss, a recent account of the applicability of mathematics to the world, the Inferential Conception (IC), proposed by Bueno and Colyvan (2011). I give a short exposition of the IC, offer some critical remarks on the account, discuss potential philosophical objections, and I propose some extensions of the IC. In chapter 8, I put the Inferential Conception (IC) to work in the historical case study: the genesis of GR. I analyze three historical episodes, using the conceptual apparatus provided by the IC. In episode one, I investigate how the starting point of the application process, the "assumed structure", is chosen. Then I analyze two small application cycles that led to revisions of the initial assumed structure. In episode two, I examine how the application of "new" mathematics - the application of the Absolute Differential Calculus (ADC) to gravitational theory - meshes with the IC. In episode three, I take a closer look at two of Einstein's failed attempts to find a suitable differential operator for the field equations, and apply the conceptual tools provided by the IC so as to better understand why he erroneously rejected both the Ricci tensor and the November tensor in the Zurich Notebook.

Handheld-assisted field data collection for occupational risk assessment.

A computerized handheld procedure is presented in this paper. It is intended as a database complementary tool, to enhance prospective risk analysis in the field of occupational health. The Pendragon forms software (version 3.2) has been used to implement acquisition procedures on Personal Digital Assistants (PDAs) and to transfer data to a computer in an MS-Access format. The data acquisition strategy proposed relies on the risk assessment method practiced at the Institute of Occupational Health Sciences (IST). It involves the use of a systematic hazard list and semi-quantitative risk assessment scales. A set of 7 modular forms has been developed to cover the basic need of field audits. Despite the minor drawbacks observed, the results obtained so far show that handhelds are adequate to support field risk assessment and follow-up activities. Further improvements must still be made in order to increase the tool effectiveness and field adequacy.

AFT3 as a new therapeutic target for skin field cancerization in antagonism with compromised Notch/CSL signaling

Les interactions épithélio-mésenchymateuses jouent un rôle important dans le contrôle du développement normal de la peau, son homéostasie et sa tumorigenèse. Les fibroblastes dermiques (DFs) représentent la catégorie cellulaire la plus abondante dans le stroma et leur rôle est de plus en plus considéré. En ce qui concerne particulièrement la tumorigenèse, des facteurs diffusibles produits par les fibroblastes entourant les tumeurs épithéliales, appelés 'fibroblastes associés au cancer (CAF)', interagissent au niveau de l'inflammation impliquée directement ou indirectement dans la signalisation paracrine, entre le stroma et les cellules épiéliales cancéreuses. Le risque de cancer de la peau augmente de façon exponentielle avec l'âge. Comme un lien probable entre les deux, la sénescence des fibroblastes résulte de la production du sécrétome favorisant la sénescence (SMS), un groupe de facteurs diffusibles induisant une stimulation paracrine de la croissance, l'inflammation et le remodelage de la matrice. De façon fort intéressante, l'induction de ces gènes est aussi une caractéristique des CAFs. Cependant, le lien entre les deux événements cellulaires sénescence et activation des CAFs reste en grande partie inexploré. L'ATF3 (Activating Transcription Factor 3) est un facteur de transcription induit en réponse au stress, dont les fonctions sont hautement spécifiques du type cellulaire. Bien qu'il ait été découvert dans notre laboratoire en tant que promoteur de tumeurs dans les kératinocytes, ses fonctions biologique et biochimique dans le derme n'ont pas encore été étudiées. Récemment, nous avons constaté que, chez la souris, l'abrogation de la voie de signalisation de Notch/CSL dans les DFs, induisait la formation de tumeurs kératinocytaires multifocales. Ces dernières proviennent de la cancérisation en domaine, un phénomène associé à une atrophie du stroma, des altérations de la matrice et de l'inflammation. D'autres études ont montré que CSL agissait comme un régulateur négatif de gènes impliqués dans sénescence des DFs et dans l'activation des CAFs. Ici, nous montrons que la suppression ou l'atténuation de l'expression de ATF3 dans les DFs induit la sénescence et l'expression des gènes liés aux CAFs, de façon similaire à celle déclenchée par la perte de CSL, tandis que la surexpression de ATF3 supprime ces changements. Nous émettons l'hypothèse que ATF3 joue un rôle suppresseur dans l'activation des CAFs et dans la progression des tumeurs kératinocytaires, en surmontant les conséquences de l'abrogation de la voie de signalisation Notch/CSL. En concordance avec cette hypothèse, nous avons constaté que la perte de ATF3 dans les DFs favorisait la tumorigénicité des kératinocytes via le contrôle négatif de cytokines, des enzymes de la matrice de remodelage et de protéines associées au cancer, peut-être par liaison directe des effecteurs de la voie Notch/CSL : IL6 et les gènes Hes. Enfin, dans les échantillons cliniques humains, le stroma sous-jacent aux lésions précancéreuses de kératoses actiniques montre une diminution significative de l'expression de ATF3 par rapport au stroma jouxtant la peau normale. La restauration de l'expression de ATF3 pourrait être utilisée comme un outil thérapeutique en recherche translationnelle pour prévenir ou réprimer le processus de cancérisation en domaine. - Epithelial-mesenchymal interactions play an important role in control of normal skin development, homeostasis and tumorigenesis. The role of dermal fibroblasts (DFs) as the most abundant cell type in stroma is increasingly appreciated. Especially during tumorigenesis, fibroblasts surrounding epithelial tumors, called Cancer Associated Fibroblasts (CAFs), produce diffusible factors (growth factors, inflammatory cytokines, chemokines and enzymes, and matrix metalloproteinases) that mediate inflammation either directly or indirectly through paracrine signaling between stroma and epithelial cancer cells. The risk of skin cancer increases exponentially with age. As a likely link between the two, senescence of fibroblasts results in production of the senescence-messaging-secretome (SMS), a panel of diffusible factors inducing paracrine growth stimulation, inflammation, and matrix remodeling. Interestingly, induction of these genes is also a characteristic of Cancer Associated Fibroblasts (CAFs). However, the link between the two cellular events, senescence and CAF activation is largely unexplored. ATF3 is a key stress response transcription factor with highly cell type specific functions, which has been discovered as a tumor promoter in keratinocytes in our lab. However, the biological and biochemical function of ATF3 in the dermal compartment of the skin has not been studied yet. Recently, we found that compromised Notch/CSL signaling in dermal fibroblasts (DFs) in mice is a primary cause of multifocal keratinocyte tumors called field cancerization associated with stromal atrophy, matrix alterations and inflammation. Further studies showed that CSL functions as a negative regulator of genes involved in DFs senescence and CAF activation. Here, we show that deletion or silencing of the ATF3 gene in DFs activates senescence and CAF-related gene expression similar to that triggered by loss of CSL, while increased ATF3 suppresses these changes. We hypothesize that ATF3 plays a suppressing role in CAF activation and keratinocyte tumor progression, overcoming the consequences of compromised Notch/CSL signaling. In support of this hypothesis, we found that loss of ATF3 in DFs promotes tumorigenic behavior of keratinocytes via negative control of cytokines, matrix-remodeling enzymes and cancer-associated proteins, possibly through direct binding to Notch/CSL targets, IL6 and Hes genes. On the other hand, in human clinical samples, stromal fields underlying premalignant actinic keratosis lesions showed significantly decreased ATF3 expression relative to stroma of flanking normal skin. Restoration of ATF3, which is lost in cancer development, may be used as a therapeutic tool for translational research to prevent or suppress the field cancerization process.

Stem cell transplantation in brain tumors: a new field for molecular imaging?

Neural stem cells have been proposed as a new and promising treatment modality in various pathologies of the central nervous system, including malignant brain tumors. However, the underlying mechanism by which neural stem cells target tumor areas remains elusive. Monitoring of these cells is currently done by use of various modes of molecular imaging, such as optical imaging, magnetic resonance imaging and positron emission tomography, which is a novel technology for visualizing metabolism and signal transduction to gene expression. In this new context, the microenvironment of (malignant) brain tumors and the blood-brain barrier gains increased interest. The authors of this review give a unique overview of the current molecular-imaging techniques used in different therapeutic experimental brain tumor models in relation to neural stem cells. Such methods for molecular imaging of gene-engineered neural stem/progenitor cells are currently used to trace the location and temporal level of expression of therapeutic and endogenous genes in malignant brain tumors, closing the gap between in vitro and in vivo integrative biology of disease in neural stem cell transplantation.

Simulación de fluidos inmiscibles con el Particle Finite Element Method (PFEM)

Proyecto de investigación realizado a partir de una estancia en el Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC), Argentina, entre febrero y abril del 2007. La simulación numérica de problemas de mezclas mediante el Particle Finite Element Method (PFEM) es el marco de estudio de una futura tesis doctoral. Éste es un método desarrollado conjuntamente por el CIMEC y el Centre Internacional de Mètodos Numèrics en l'Enginyeria (CIMNE-UPC), basado en la resolución de las ecuaciones de Navier-Stokes en formulación Lagrangiana. El mallador ha sido implementado y desarrollado por Dr. Nestor Calvo, investigador del CIMEC. El desarrollo del módulo de cálculo corresponde al trabajo de tesis de la beneficiaria. La correcta interacción entre ambas partes es fundamental para obtener resultados válidos. En esta memoria se explican los principales aspectos del mallador que fueron modificados (criterios de refinamiento geométrico) y los cambios introducidos en el módulo de cálculo (librería PETSc, algoritmo predictor-corrector) durante la estancia en el CIMEC. Por último, se muestran los resultados obtenidos en un problema de dos fluidos inmiscibles con transferencia de calor.

Computation of an integral basis of a quartic number field

"Vegeu el resum a l'inici del document del fitxer adjunt."

Handling the endogeneity of income to health using a field experiment in Taiwan

This paper uses an exogenous increase in income for a specific sub-group in Taiwan to explore the extent to which higher income leads to higher levels of health and wellbeing. In 1995, the Taiwanese government implemented the Senior Farmer Welfare Benefit Interim Regulation (SFWBIR) which was a pure cash injection, approximately US$110 (£70) per month in 1996, to senior farmers. A Difference-in-differences (DiD) approach is used on survey data from the Taiwanese Health and Living Status of Elderly in 1989 and 1996 to evaluate the short term effect of the SFWBIR on self-assessed health, depression, and life satisfaction. Senior manufacturing workers are employed as a comparison group for the senior farmers in the natural experiment because their demographic backgrounds are similar. This paper provides evidence that the increase in income from the SFWBIR significantly improved the mental health of senior farmers by reducing the scale of depression (CES-D) by 1.718, however, it had no significant short term impact on self-assessed health or life satisfaction.

Finite Horizon Learning

Incorporating adaptive learning into macroeconomics requires assumptions about how agents incorporate their forecasts into their decision-making. We develop a theory of bounded rationality that we call finite-horizon learning. This approach generalizes the two existing benchmarks in the literature: Eulerequation learning, which assumes that consumption decisions are made to satisfy the one-step-ahead perceived Euler equation; and infinite-horizon learning, in which consumption today is determined optimally from an infinite-horizon optimization problem with given beliefs. In our approach, agents hold a finite forecasting/planning horizon. We find for the Ramsey model that the unique rational expectations equilibrium is E-stable at all horizons. However, transitional dynamics can differ significantly depending upon the horizon.

Computation of an integral basis of quartic number field

"Vegeu el resum a l'inici del document del fitxer ajunt."

Changing Eating Habits - A Field Experiment in Primary Schools

We conduct a field experiment in 31 primary schools in England to test whether incentives to eat fruit and vegetables help children develop healthier habits. The intervention consists of rewarding children with stickers and little gifts for a period of four weeks for choosing a portion of fruit and vegetables at lunch. We compare the effects of two incentive schemes (competition and piece rate) on choices and consumption over the course of the intervention as well as once the incentives are removed and six months later. We find that the intervention had positive effects, but the effects vary substantially according to age and gender. However, we find little evidence of sustained long term effects, except for the children from poorer socio‐economic backgrounds.