Resistance development and possible non–target effects have been of concern since the first deployment of genetically modified crops with insecticidal properties. It is especially at the third trophic level and with important predators such as lacewings (Chrysoperla spp.) (Neuroptera: Chrysopidae) where negative effects of Cry 1Ab protein could have adverse effects in agro–ecosystems. Monitoring of the effect of genetically modified Bt maize on non–target organisms is required by law in South–Africa. Neuroptera are excellent indicators of environmental and habitat transformation, and also include key species for signifying areas and faunas that require priority protection. Monitoring techniques, especially for insect eggs, are often labour intensive and time consuming. A study was conducted to determine the preferred oviposition site of Chrysoperla spp. on maize plants to facilitate time–effective searching for eggs of these beneficial insects. Furthermore we determined if the presence of aphids on plants influenced Chrysoperla spp. oviposition preference. Another study was conducted to evaluate the effect of indirect exposure of C. pudica to Cry 1Ab protein, through healthy Bt–maize feeding prey, on its biology. Daily flight activity patterns and the height at which chrysopid adults fly above the crop canopy were also determined, as well as the movement of adult Chrysoperla spp. between maize fields and adjacent headlands. A clear spatial oviposition pattern was observed on maize plants and oviposition was not random as reported in earlier studies. This data facilitates rapid monitoring of the presence of eggs in maize cropping systems and is also of use in general pest management. Choicetest data showed that females responded positively to host plants that were infested with aphids. Feeding studies in which C. pudica larvae were indirectly exposed to Bt–toxin at the 3rd trophic level, showed a limited effect of Bt–toxin on only a few of the parameters that were evaluated. The pupal period and percentage adult emergence of larvae exposed to an unusually high amount of Bt–toxin was significantly shorter and lower respectively than that of the control group. The overall result of this study, in which the possible effect of food quality (prey) was excluded, showed that Cry 1Ab protein had an adverse affect only on certain fitness components during the life cycle of C. pudica. However, since this study represented a worst–case scenario where diverse prey was not available to C. pudica, negligible effects is expected under field conditions where prey is more diverse. It was determined that chrysopids was most active between 16:00 – 23:00 and that they fly largely between 0.5 m – 2.5 m above ground level. An attempt was also made to quantify migration between different vegetations types. This part was terminated because of bad weather conditions at several occasions when the experiment was attempted. Chrysopids were never present in grassland vegetation, but an adjacent lucerne field maintained a large population. As the maize crop developed chrysopid population numbers increased inside the field, presumably originating from the lucerne field. / Thesis (M.Sc (Environmental Science))--North-West University, Potchefstroom Campus, 2011.

La tesis consta de dos partes. En la primera parte se analiza la relación entre las fricciones en los flujos de información que llegan a la empresa y la persistencia del patrón de la inflación. En particular, se presenta un nuevo estimador por el modelo de Makiw y Reis (2002) "Sticky Information Phillips Curve", y se aplica usando datos trimestrales de EE.UU. El resultado principal es que el modelo tan solo puede explicar la persistencia de la inflación asumiendo que la variancia de la inflación sea mucho mas grande de la que observamos o, equivalentemente, que el modelo no puede explicar conjuntamente la variancia y la persistencia de la inflación.En la segunda parte se presentan nuevas evidencias sobre la publicidad agregada en EE.UU. y se estudian los efectos de la publicidad en la economía usando un modelo dinámico estocástico de equilibrio general. En particular, el capitulo 2 se enfoca en las relaciones de corto plazo entre las mas comunes variables macroeconómicas - consumo agregado, producto interno bruto, totalidad de horas trabajadas en la economía - y la publicidad agregada, con particular atención a la relación de causalidad entre publicidad y consumo. En cambio, el capitulo 3 se enfoca sobre las relaciones de largo plazo, enseñando como la publicidad agregada afecte el nivel de trabajo de la economía. A través del modelo presentado en el capitulo 2, se demuestra que un mayor nivel de publicidad implica un mayor números de oras trabajadas asociadas con un menor nivel de bienestar por los consumidores. / This thesis is organized in two parts. In the first one, I seek to understand the relationship between frictions in information flows among firms and inflation persistence. To this end, I present a novel estimator for the Sticky Information Phillips Curve (Mankiw and Reis, 2002), and I use it to estimate this model with U.S. postwar data. The main result is that the Sticky Information Phillips Curve can match inflation persistence only at the cost of mispredicting inflation variance. I conclude that the Sticky Information Phillips Curve is a valid model to explain inflation persistence but not an overall valid theory of inflation. The second part presents new evidence about aggregate advertising expenditures in U.S., and analyzes the effect of advertising in the aggregate economy by the mean of a dynamic stochastic general equilibrium model. Chapter 2 focuses on the short run impact of advertising on the aggregate dynamics, and shows that an increase in aggregate advertising significantly increases the aggregate consumption. Chapter 3 focuses on the long run effects of advertising on the labor supply, showing that in economies where aggregate advertising is higher, agents supply more hours of works and are generally worse off in terms of welfare.

[pt] Esta tese incorpora três ensaios acerca de fixação de preços com informação rígida e dispersa (IRD). A estrutura básica mistura o modelo de rigidez de informação proposto em Mankiw and Reis (2002) com o modelo de informação dispersa descrito em Morris and Shin (2002). No capítulo 1, obtémse o equilíbrio do jogo assumindo que as firmas se deparam com complementaridade estratégica em suas decisões de preço. Neste contexto, as firmas tomam suas decisões de preço utilizando a informação disponível para prever os preços das outras firmas e a demanda agregada nominal, o fundamento da nossa economia. Estuda-se a importância de cada parâmetro do modelo em vários contextos. No capítulo 2, estende-se o modelo IRD para analisar como a comunicação do banco central interfere na fixação de preços. Como informação pública ajuda às firmas a prever o estado atual da economia e as ações uma das outras, ela ajuda na sincronia dos preços. Este efeito faz a variância da inflação aumentar com a precisão da informação pública. Além disso, o bem-estar da sociedade é afetado pelo fato de que as firmas tomam suas decisões de preços sem considerar como isto influenciará a decisão das outras firmas. No capítulo 3, utilize-se o modelo com IRD para analisar como a fixação de preços muda quando a taxa de juros, além de ser um instrumento de política capaz de influenciar a dinâmica do fundamento, também é vista como um sinal público que informa a visão da autoridade monetária acerca do estado atual da economia. Sob este arcabouço, firmas utilizam a taxa de juros para embasar suas decisões de preços. Obtêm-se também os parâmetros ótimos do instrumento de política (para três medidas diferentes de bem-estar), considerando-se que o banco central sabe que as firmas extraem informação de suas ações. / [en] This thesis encompasses three essays on price setting under stickydispersed information (SDI). The baseline framework mixes the sticky information model of Mankiw and Reis (2002) with dispersed information models like Morris and Shin (2002) and Angeletos and Pavan (2007). In Chapter 1, we derive the equilibrium of the game assuming that firms face strategic complementarity on their pricing decisions. In this context, firms take their pricing decisions using information to build expectations on the prices set by other firms and on the current state of aggregate nominal demand - the fundamental of the economy. In Chapter 2, we extend the SDI model to analyze how central bank communication affects price setting. As public information help firms to infer the current state of the economy and one another s prices, it improves price synchronization. This effect makes inflation variance increase with the precision of the public information. Social welfare is affected by the fact that firms do not internalize how their prices change other firms pricing decisions. In Chapter 3, we use a SDI model to analyze how price setting changes when the interest rate is a policy instrument that not only partially drives the fundamental dynamics, but also it is understood as a public signal that informs the view of the monetary authority on the current state of the economy. Under this framework, firms use interest rate to support their pricing decisions, influencing inflation dynamics. We also obtain the optimal parameters of the policy instrument (regarding three different efficiency criteria), considering that the central bank knows that firms take information from its actions.

[pt] Esta tese consiste em três ensaios teóricos sobre tópicos relativos à fixação de preços sob informação incompleta. Duas características são comuns aos três ensaios: (i) informação heterogênea sobre condições econômicas agregadas e (ii) um grau moderado de complementaridade estratégica nas decisões de preços. No Capítulo 1, estuda-se a transmissão de informação em um modelo com estágios de produção e informação dispersa. Firmas observam sinais sobre os preços dos insumos que endogenizam a precisão da informação que é pública dentro de um estágio, mas não entre os estágios. Em contraste com o caso com sinal público exógeno, as firmas decidem otimamente atribuir menos peso a informação pública ao longo da cadeia. Uma implicação é que a precisão da informação, que ficaria inalterada com sinais públicos exógenos, decresce ao longo da cadeia com sinais semi-públicos endógenos. No Capítulo 2, examinase o processo de repasse cambial (ERPT) para os preços em um modelo de informação dispersa onde a taxa de câmbio nominal fornece informação sobre os fundamentos de forma imperfeita. Quando a informação é completa, ERPT também é completa. Sob informação dispersa, o modelo apresenta três propriedades consistentes com os fatos estilizados de ERPT. Primeiro, ERPT está entre 0 e 1. Segundo, ERPT é normalmente maior para produtos importados do que para produtos ao consumidor. Terceiro, ERPT é maior para economias emergente e diminuiu ao longo do tempo tanto para economias industrializadas quanto emergentes. Finalmente, no Capítulo 3, estuda-se a interação entre rigidez e dispersão de informação através da introdução de sinais com ruído em um modelo padrão de curva de Phillips com rigidez de informação. O modelo de informação rígida e dispersa (SDI) resultante apresenta como casos particulares os modelos de informação completa, dispersa e rígida. Estuda-se a relevância individual dos principais parâmetros do modelo em várias direções. Primeiro, analisa-se o impacto dos valores corrente e passados da inflação com informação completa na inflação corrente. Segundo, consideram-se as respostas da inflação a choques monetários. Finalmente, compara-se a variância da inflação SDI com as variâncias da inflação quando a informação é completa, dispersa ou rígida. / [en] This thesis consists of three theoretical essays on topics in price setting under imperfect information. Unifying the essays are two features: (i) heterogeneous information about aggregate economic conditions and (ii) a moderate degree of complementarity in pricing decisions. In Chapter 1, the transmission of information is studied in a model with a vertical input-output structure and dispersed information. Firms observe input prices with noise that endogenize the precision of information that is public within a stage but not across stages. In contrast to the case with an exogenous and overall public signal, firms find it optimal to rely less on public information along the chain. A direct implication is that, while information precision remains unchanged with exogenous public signals, it decreases along the chain when semi-public signals are endogenous. In Chapter 2, exchange-rate pass-through (ERPT) to prices is examined in a model of dispersed information where the nominal exchange rate imperfectly conveys information about the underlying fundamentals. If the information is complete, ERPT is also complete. Under dispersed information, the model displays three properties that are consistent with the stylized facts of passthrough. First, ERPT lies between 0 and 1. Second, ERPT is usually higher for imported goods prices than for consumer prices. Third, ERPT is higher for emerging market countries and declines over time for both industrial and emerging market economies. Finally, in Chapter 3, the interaction between information stickiness and dispersion is studied by introducing noisy signals in an otherwise standard sticky-information Phillips curve. The model of stickydispersed information (SDI) nests as special cases the complete information, the dispersed information and the sticky information models. The individual relevance of each of the main parameters of the model is studied in several directions. First, the impact of current and past complete-information inflation rates on current inflation is analyzed. Second, the inflation response to monetary shocks is considered. Finally, the variance of SDI inflation is compared with the variances of complete, dispersed, or sticky-information inflations.

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La cytokinèse est un processus dont le but est une séparation de deux cellules soeurs en deux entités suite à une mitose. La cytokinèse nécessite la formation d’un anneau contractile (AC) qui va conduire un sillon de clivage vers une ingression à l’équateur de la cellule. L’une des étapes critiques de ce processus est la transition d’un AC dynamique vers une structure stable surnommée l’anneau du midbody (AM), organelle qui va guider la cellule vers l’abscision. La compréhension des mécanismes moléculaires impliqués dans cette transition nous permettrait de mieux comprendre les complexes protéiques impliqués autant au niveau de l’initiation qu’à la terminaison de la cytokinèse. Des défauts ayant lieu lors de cette transition mènent à la formation de cellules binucléées tétraploïdes qui sont observées dans plusieurs pathologies comme le cancer. Afin d’approfondir nos connaissances à ce sujet j’ai utilisé un modèle d’imagerie optique en temps réel dans un modèle cellulaire de Drosophila melanogaster : les cellules S2 de Schneider. Ces études ont mis l’emphase sur un nouveau mécanisme de maturation de la transition AC/AM. Nous avons pu démontrer que la kinase Citron, Sticky, et la septine, Peanut, agissent de manière opposée sur la protéine Anillin pour retenir ou éliminer, respectivement, la membrane plasmique lors de la transition AC/AM. En effet, la diminution d’expression de Sticky par ARNi engendre une perte de contrôle de rétention membranaire de l’AM. À l’inverse, la diminution d’expression de Peanut inhibe la maturation par excrétion membranaire de l’AM. La diminution d’expression simultanée de Sticky et de Peanut conduit l’AC vers des mouvements oscillatoires typiques d’une instabilité de l’AC suite à la perte de fonction de l’Anillin. Sticky est une protéine corticale lors de la cytokinèse dont le rôle et les partenaires d’interaction restent controversés. Pour approfondie nos connaissance de ce sujet, nous avons effectué une étude structurelle et fonctionnelle de Sticky. Cette étude démontre que Sticky possède deux mécanismes de localisation corticale. Le premier dépend de l’Anillin et le deuxième dépend de la petite GTPase Rho1, le régulateur maître de la cytokinèse. Sticky est capable de se localiser à l’AC en présence de l’un ou l’autre de ces deux mécanismes, mais chacun semble être essentiel pour la réussite de la cytokinèse. Le domaine minimal d’interaction entre la Sticky et l’Anillin a été identifié. Une version d’Anillin qui manque le site de liaison à la Sticky est incapable de supporter l’achèvement de la cytokinèse, et les cellules échouent la cytokinèse d’une manière semblable aux cellules dont l’expression de Sticky est diminuée. Similairement, les cellules exprimant une protéine Sticky mutée au site d’interaction avec Rho1-GTP, sont incapables de compléter la cytokinèse lorsque les niveaux endogènes de Sticky sont diminués par ARNi. Ceci suggère que Sticky agit avec Anillin et Rho1 au niveau du cortex pour guider la transition d’un AC dynamique vers un AM stable. Par la mise en évidence et la caractérisation d’un nouveau mécanisme moléculaire essentiel à la cytokinèse, cette thèse constitue des avancements importants au niveau de la cytokinèse. / Cytokinesis is a multistep process that allows two sister cells to undergo complete separation following mitosis. Cytokinesis requires the formation of a contractile ring (CR) that will drive cleavage furrow ingression at the equator of the cell. One of the crucial steps in this process is the transition from a dynamic CR to a more stable structure named the midbody ring (MR), which directs the final separation or abscission. Our knowledge of the molecular mechanisms involved in the CR-to-MR transition would presumably improve our understanding of the molecular complexes involved throughout cytokinesis from initiation to abscission. Defects that occur during this transition can lead to the formation of bi-nucleate tetraploid cells that are often observed in pathological conditions such as cancer. I have used Drosophila melanogaster Schneider’s S2 cells to study the CR-to-MR transition. My findings have highlighted a previously uncharacterized maturation process essential for the transition. More specifically, I demonstrate that the Citron Kinase, Sticky, and the Septin, Peanut, have opposing actions on the scaffold protein Anillin to either retain or extrude, respectively, membrane-positive proteins during the CR-to-MR transition. Indeed, Sticky depletion by RNAi led to uncontrolled loss of membrane-associated Anillin at the MR. Conversely, Peanut depletion led to inhibition of MR maturation by membrane extrusion. Co-depletion of Sticky and Peanut led to oscillatory movements of the CR, typical of Anillin depletion. Sticky is a cortical protein during cytokinesis whose role and interacting partners are controversial. I have performed a structure/function analysis of Sticky to better define its role and regulation during cytokinesis. My work shows that Sticky has two mechanisms of cortical localization. The first is through an Anillin interaction and the second is through the small GTPase Rho1, a master regulator of cytokinesis. Sticky can localize to the cortex in the absence of either one of these mechanisms. However, loss of both inhibits its localization. Following the identification of the minimal interaction sites of Anillin and Sticky, I expressed an Anillin mutant that lacked part of this site and found that cells failed cytokinesis in a similar manner to cells depleted of Sticky. Mutation of the Rho1 binding site on Sticky produced similar cytokinesis failures. Altogether, the results suggest that Sticky interacts with Anillin and Rho1 at the cortex to guide the transition from dynamic CR to stable MR. This thesis advances our understanding of cytokinesis by highlighting a previously uncharacterized process of MR maturation and by defining the importance and regulation of Citron Kinase during this process.

Dans cette thèse nous examinons différents aspects des fluctuations dans les économies émergentes. Premièrement, afin d’établir les régularités empiriques de ces pays nous examinons le contexte économique des pays du Moyen Orient et d’Afrique du Nord. Ensuite, nous estimons un modèle des cycles réels pour essayer de reproduire les faits stylisés de ces pays, mais aussi pour évaluer la performance de ces modèles néoclassiques augmentés de deux types de chocs de productivité transitoire et permanent. Ceci fait l’objet du chapitre 2 dont le résultat est en faveur de l'hypothèse "Le cycle c'est la tendance" . Le deuxième aspect porte sur l’importance des frictions financières, il est traité dans le troisième chapitre qui introduit des chocs financiers au modèle de croissance stochastique. Nous identifions le rôle des frictions financières dans l’économie tunisienne comme étant un amplificateur de l’effet des chocs de productivité. Le quatrième chapitre porte sur l'analyse de la politique monétaire. Premièrement, nous examinons le régime de ciblage d’inflation où nos résultats empiriques supportent une implémentation de la stricte version du ciblage d’inflation avec une fonction de réaction basée sur des prévisions de l'inflation. Deuxièmement, nous exploitant les règles monétaires optimales en présence de la rigidité d l'information dans le cadre d’un modèle stochastique d’équilibre général (DSGE). Nos résultats, révèlent que les chocs du taux de marge de la force de travail jouent un rôle important dans les fluctuations de l’économie tunisienne, la règle de Taylor produit un taux satisfaisant de bien être, alors que les règles qui ciblent le niveau de prix ne sont pas efficaces. / This thesis investigates different aspects of the fluctuations in emerging economies. First, it examines the MENA countries’ context to establish the empirical regularities. Then, to replicate the MENA countries’ business cycle patterns observed in the annual data, we estimate a standard real business cycle (RBC) model to assess the performance of the neoclassical model with transitory and permanent shocks. This is the purpose of chapter 2 which results support the assumption "The cycle is the trend". The second aspect refers to the importance of financial frictions and is addressed in the third chapter which adds new financial shocks to the stochastic growth model. We determine the role of financial frictions in the Tunisian economy not as the source of business cycle fluctuations but as an amplifier of the effects of total factor of productivity shocks.The fourth chapter analyzes monetary policy in emerging economies. Firstly, we examine the inflation targeting regime under the lens of a New Keynesian forward-looking model. We also, estimate a Taylor rule and some other alternatives in order to determine which rule to adopt within this framework. Empirical results support the implementation of a strict inflation targeting regime, with an inflation forecast based rule as a reaction function. Secondly, we explore the optimal monetary policy rules using a New Keynesian DSGE model. In particular we assume that information stickiness as the only type of rigidity in the model. We find that Whereas, Taylor rule in its original version provides substantial welfare gains, price-level targeting regime was suboptimal.

A large theoretical and empirical literature has studied the response in prices to changes in demands and costs. Three of the essays in this thesis are empirical studies of price-setting. The most important reason for studying the properties of price adjustments is the possible link between pricing and the business cycle. One family of models deals with price rigidities. If prices adjust slowly to changes in costs or demand, it will magnify fluctuations in output. A second family of models examines price changes due to changes in intensity of competition. Many of these models build on the idea that changes in demand affect the possibility of maintaining implicit collusion. Cyclical changes in the intensity of competition may cause a cyclical pricing pattern that magnifies fluctuations in output. Another line of research models the effects of liquidity constraints on the business cycle. One possible effect is that prices in markets where consumers have switching costs may increase, if the firms are hit by increased liquidity constraints. As increased liquidity constraints are common in recessions, prices will get a counter-cyclical tendency, which magnifies fluctuations in output. Another reason for studying price-setting patterns is that they can give an indication of the form of interaction between competing firms, which are of importance for competition policy. The fourth essay models sex discrimination formally. It shows that it is possible that sex discrimination in the labor market might be due to self-fulfilling sex stereotypes on the distribution of time out for child care between men and women. Both an even and an uneven distribution of time out for child care are possible equilibria in the model. The four essays can be read separatelyEssay 1 Price Responses to Seasonal Demand Changes in the Swedish Gasoline MarketA common idea in a number of papers on cyclical pricing is that implicit price collusion may be affected by changes in demand. In these models, tacit collusion is modeled as a game where agents balance gains from deviating from the collusive price, thereby gaining a short-run profit, against the gains from maintaining collusion in future periods. If demand fluctuates, the gains from deviating is high in periods of high demand; collusion may still be sustainable, however, if the collusive price is allowed to vary with demand. A lower price in high demand states reduces the gains from deviating, since it reduces the gain from each unit sold in these demand states. Hence, in order to equalize the profit from deviating and the profit from sticking to the implicit agreement, the price must move in the opposite direction to demand. Changes in demand can, naturally, be correlated with other factors affecting the price, such as cost changes. Thus, prices do not necessarily fall when demand increases in the data. According to the theory the, however, increase in demand should add a tendency to lower prices in order to make implicit collusion sustainable. The basic idea that changes in demand should affect prices if firms are engaged in implicit collusion has been employed in a number of papers, with different models for different assumptions on the pattern of demand changes. The demand for gasoline in Sweden follows a seasonal cycle, with demand being 42 percent higher in July than in January. Haltiwanger and Harrington provide a theory for implicit collusion over deterministic cycles, such as the seasonal cycle. Borenstein and Shepard (1996) tested Haltiwanger and Harrington’s model on the American gasoline retail market and found support for the theory. In this essay the model is tested for Swedish data, but no support for this theory is found. It is also investigated whether the effects on margins of the demand fluctuations induced by tax increases are compatible with theories of implicit collusion, but this is found not to be the case.Essay 2 Price Adjustments by a Gasoline Retail ChainEssay 2 is joint with Marcus Asplund and Richard Friberg. Stickiness of prices is an important building block in many business cycle models. This has spurred an empirical literature on price adjustments. Different types of price rigidities have different policy implications. Price setting can be state dependent, e.g. prices are adjusted when costs have changed by at least some minimal amount since the last price adjustment, or time-dependent e.g. adjusted once a week or once a year. Another issue is whether prices are equally rigid downwards as upwards. The second essay examines price responses in the Swedish gasoline retail market to changes in the Rotterdam spot price of gasoline, exchange rates and taxes. The main results are that cost changes are not fully passed through in the short run, but gradually moves towards the long-run equilibrium. Prices are stickier downwards than upwards. There is a minimum absolute size of price changes. Only very limited evidence of time-dependent price setting is found.Essay 3 Prices, Margins and Liquidity Constraints: Swedish Newspapers 1990-1996Essay 3 is written with Marcus Asplund and Niklas Strand. Chevalier and Scharfstein (1996) provide a model where consumer switching costs in combination with liquidity constraints give rise to a counter-cyclical tendency in prices. Customer stocks can be viewed as an investment, when consumers have switching costs when changing suppliers. Firms can exploit captured customers by setting a high price to raise short-run profits. However, a high price will induce consumers to search for alternatives, and customers once lost are costly to win back. Liquidity constraints, for instance in recessions, may force firms to sacrifice long-run profits for short-run gains. In this case, firms may have to cut back on investments in customer stocks by raising prices. Using firm level data from the Swedish daily newspaper industry, we test the effects of liquidity constraints on prices in markets with consumer switching costs. The newspaper industry is of particular interest, since firms set prices in two markets, the subscription market, where switching costs are high, and the advertising market, where switching costs are low. With accounting data from newspaper firms we can, by solvency, broadly categorize them as being more or less liquidity constrained. When Sweden enters a recession at the beginning of the nineties, we find a relative increase in subscription prices and margins for liquidity constrained firms. This is not the case for advertising prices, however. The results support the theory.Essay 4 Statistical Discrimination and Sex Stereotypes in the Labor MarketTime out for child care is unevenly distributed between the sexes. Parental leave benefits are usually exclusively given to the mother or distributed to both parents according to their choice. In Sweden, one month is reserved for each parent, however. One reason for this is to give the child better contact with both parents, but increased equality between the sexes in the labor market has also been put forward as an argument. This argument implicitly rests on the idea that sex stereotypes create sex discrimination, and that sex discrimination affects the distribution of time out for child care between the sexes. Essay 4 investigates if the uneven distribution of time out for child care can be explained by self-fulfilling sex stereotypes. It provides a model of distribution of time out for child care based on statistical discrimination and human capital investments. The model has three equilibria. In one equilibrium, time out for child care is evenly distributed between the sexes. In the second equilibrium, there is full specialization. The third equilibrium is an intermediate case, where time out for child care is unevenly distributed without full specialization There are no differences in ability or variance of ability between the sexes, the only differences between the equilibria are the self-fulfilling expectations of firms and workers. / Diss. (sammanfattning) Stockholm : Handelshögsk., 2001

Submitted by Morgana Andrade (morgana.andrade@ufes.br) on 2016-04-11T20:49:17Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação_Jean.pdf: 1797995 bytes, checksum: b603b8c2f1c6e995111923a3d87928d5 (MD5) / Approved for entry into archive by Patricia Barros (patricia.barros@ufes.br) on 2016-05-16T14:48:42Z (GMT) No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação_Jean.pdf: 1797995 bytes, checksum: b603b8c2f1c6e995111923a3d87928d5 (MD5) / Made available in DSpace on 2016-05-16T14:48:42Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação_Jean.pdf: 1797995 bytes, checksum: b603b8c2f1c6e995111923a3d87928d5 (MD5) / Financiadora de Estudos e Projetos - FINEP, CNPq, CAPES, FAPES / A meleira, causada pelo Papaya meleira virus (PMeV), é uma doença importante no Brasil e no México devido as grandes perdas econômicas que ela causa. Estudos para avaliar a interação patógeno-hospedeiro em nível histológico são fundamentais para compreender os mecanismos responsáveis pela resistência natural das plantas. Neste estudo foram coletadas folhas de mamoeiros saudáveis e sintomáticos para meleira e observou-se a topografia e a dureza da parede celular dessas plantas por microscopia de força atômica (AFM). As imagens em duas dimensões obtidas a partir de diferentes áreas da parede celular mostraram que as paredes celulares das plantas saudáveis são mais uniformes do que as paredes de plantas doentes. As plantas saudáveis também apresentaram características constitutivas da parede celular mais elevadas do que as de plantas doentes e a média da força de adesão máxima observada foi maior em plantas saudáveis do que em plantas doentes. Estes resultados indicam que o PMeV promove alterações nas paredes das células, tornando-as mais frágeis e suscetíveis à ruptura. Estas alterações, associadas ao aumento da captação de água e aumento da pressão interna dos laticíferos, provocam o rompimento celular que leva à exsudação espontânea do látex e facilita a disseminação de PMeV para outros laticíferos. Os resultados deste trabalho fornecem novas percepções sobre a interação mamoeiro-PMeV que podem revelar-se úteis no que se refere a entender e controlar a meleira do mamoeiro. / Papaya sticky disease, caused by Papaya meleira virus (PMeV), is an important papaya disease in Brasil and Mexico due the severe economic losses it causes. Studies to assess the pathogen-host interaction at a histological are fundamental in order to understand the mechanisms that underlie natural resistance. In this study we collected leaves of healthy and symptomatic papaya sticky diseased plants and observed the topography and mechanical properties of plant cell walls by atomic force microscopy (AFM). Two-dimensional images obtained from different areas of the cell wall showed that the cell walls of healthy plants are smoother than the walls of sticky diseased plants. Also healthy plants displayed higher constitutive characteristics of the cell wall than diseased plants and the average maximum adhesion force was higher on healthy plants than on diseased plants. PMeV promotes changes on cell walls, making them more fragile and susceptible to breakage. These changes, associated with increased water uptake and internal pressure of laticifers causes cell disruption that leads to spontaneous exudation of latex and facilitates the spread of PMeV to other laticifers. The results of this work provide new insights on the interaction papaya-PMeV which could prove helpful when trying to understand and control the papaya sticky disease.

Föreliggande kandidatarbete har till syfte att undersöka fenomenet Webskrapning. Webbskrapnings-program (också kända som Web Wanderers, Crawlers, Spiders eller skrapare) är program som söker igenom webben automatiskt för att extrahera information från webbsidor. Ett exempel på web skrapning är när ett företag samlar in data om prissättningar på en vara eller en tjänst och sen använder informationen för att producera billigare erbjudanden. Detta ger företaget en fördel så att de kan fokusera mera på att marknadsföra sin sida/tjänster. Utöver detta så blir de utsatta företagens servrar också hårt belastade med trafik (skrapning) från ”icke kunder”. Efter att ha genomsökt både akademiska och allmänna källor via informationsinsamling, av denna information så dras slutsatsen att man inte fullt ut kan hindra skrapning av hemsidor. Detta på samma sätt som man inte fullt ut kan hindra någon IT-attack, det finns inga 100 % vattentäta system. Av utfallet ifrån informationssökningen var det bara ett akademiskt arbete, av de hundra, som genomsöktes som hade inriktat sig på att förhindra skrapningsbotar.