Tesis por compendio / [ES] La disponibilidad de recursos hídricos a nivel mundial ha disminuido significativamente. Entre los principales agentes que han provocado esta situación se encuentran el cambio climático, la contaminación ambiental, las actividades humanas y las fallas en las estructuras hidráulicas, entre otros. Cada vez es más complicado acceder a fuentes apropiadas que cumplan con la calidad y cantidad del recurso. A pesar de ello, la pérdida de agua debida a fugas en sistemas de distribución presurizados todavía maneja valores considerables, con pérdidas significativas a nivel mundial. Teniendo en cuenta que la necesidad de agua es cada vez mayor, se deben implementar proyectos sostenibles que permitan optimizar al máximo la disponibilidad y el uso del recurso. El objetivo principal de esta tesis es desarrollar una propuesta metodológica, que permita estimar las curvas características de las bombas que trabajan como turbinas (PATs) a partir del número específico de la máquina y en función de la velocidad de giro, desarrollando las leyes modificadas de semejanza. El cumplimiento de los objetivos de esta tesis es a través de la elaboración de tres artículos publicados, que permitieron: (i) Realizar la contextualización respecto al estado del arte en PATs con énfasis en las metodologías de obtención de la predicción del comportamiento en las mismas tales como la realización de modelos numéricos con CFDs; (ii) Proponer una nueva estrategia para desarrollar un modelo matemático para bombas que funcionan como turbinas (PATs), considerando las leyes de afinidad modificadas; (iii) Ejecutar la modelación numérica a través del paquete de código libre OpenFOAM de una bomba que trabaja como turbina y , (iv)Validar los resultados , tanto de la aplicación de las nuevas expresiones y de la modelación numérica, a través de la comparación con resultados experimentales obtenidos de los ensayos realizados a una PATs. En el Articulo 1, que corresponde a la Fase de Contextualización, se realizó una investigación en la literatura técnica sobre PATs: Características, aplicaciones y diferentes estrategias utilizadas para comprender el comportamiento del flujo. Dentro de estas estrategias, se encuentra la simulación numérica del fenómeno con paquetes CFD (Dinámica Fluido Computacional). Se analizaron 56 casos donde se estudian diferentes tipos de máquinas: axiales, mixtas y radiales bajo operación con velocidad de giro fija y velocidad de giro variable. En función de esta información se calculó el error entre la modelación numérica y los resultados experimentales; y se verificaron las principales características de las modelaciones tales como paquete CFD utilizado, modelos de cierre, tipo de mallado, etc. En el Artículo 2, que corresponde a la primera parte de la Fase del Procedimiento Analítico, se propuso un análisis con diez expresiones generales (polinómicas y exponenciales), considerando las variables más significativas. En función de este análisis se obtuvieron nuevas expresiones para obtener las curvas características de las PATs. Estas expresiones se verificaron y compararon con 15 máquinas diferentes, que se probaron variando su velocidad de rotación y su velocidad específica. En la segunda parte de la Fase del Procedimiento Analítico, se realizó una simulación numérica con el paquete CFD OpenFOAM de una PATs que ha sido ensayada en el instituto CERIS de Portugal. Por medio de los resultados experimentales se logró validar tanto las nuevas expresiones propuestas en el Artículo 2 así como la modelación numérica. En el Artículo 3 se presenta el desarrollo de esta metodología. / [CA] La disponibilitat de recursos hídrics a nivell mundial ha disminuït significativament. Entre els principals agents que han provocat aquesta situació es troben el canvi climàtic, la contaminació ambiental, les activitats humanes i les falles en les estructures hidràuliques, entre altres. Cada vegada és més complicat accedir a fonts apropiades que complisquen amb la qualitat i quantitat del recurs. Malgrat això, la pèrdua d'aigua deguda a fugides en sistemes de distribució pressuritzats encara maneja valors considerables, amb pèrdues significatives a nivell mundial. Tenint en compte que la necessitat d'aigua és cada vegada major, s'han d'implementar projectes sostenibles que permeten optimitzar al màxim la disponibilitat i l'ús del recurs. L'objectiu principal d'aquesta tesi és desenvolupar una proposta metodològica, que permeta estimar les corbes característiques de les bombes que treballen com a turbines (PATs) a partir del número específic de la màquina i en funció de la velocitat de gir, desenvolupant les lleis modificades de semblança. El compliment dels objectius d'aquesta tesi és a través de l'elaboració de tres articles publicats, que van permetre: (i) Realitzar la contextualització respecte a l'estat de l'art en PATs amb èmfasi en les metodologies d'obtenció de la predicció del comportament en les mateixes com ara la realització de models numèrics amb CFDs; (ii) Proposar una nova estratègia per a desenvolupar un model matemàtic per a bombes que funcionen com a turbines (PATs), considerant les lleis d'afinitat modificades; (iii) Executar el modelatge numèric a través del paquet de codi lliure OpenFOAM d'una bomba que treballa com a turbina i , (iv)Validar els resultats , tant de l'aplicació de les noves expressions i del modelatge numèric, a través de la comparació amb resultats experimentals obtinguts dels assajos realitzats a una PATs. En l'Articule 1 , que correspon a la Fase de Contextualització, es va realitzar una investigació en la literatura tècnica sobre PATs: Característiques, aplicacions i diferents estratègies utilitzades per a comprendre el comportament del flux. Dins d'aquestes estratègies, es troba la simulació numèrica del fenomen amb paquets CFD (Dinàmica Fluid Computacional). Es van analitzar 56 casos on s'estudien diferents tipus de màquines: axials, mixtes i radials sota operació amb velocitat de gir fixa i velocitat de gir variable. En funció d'aquesta informació es va calcular l'error entre el modelatge numèric i els resultats experimentals; i es van verificar les principals característiques. dels modelatges com ara paquet CFD utilitzat, models de tancament,tipus d'emmallat, etc. En l'Article 2, que correspon a la primera part de la Fase del Procediment Analític, es va proposar una anàlisi amb deu expressions generals (polinòmiques i exponencials), considerant les variables més significatives. En funció d'aquesta anàlisi es van obtindre noves expressions per a obtindre les corbes característiques de les PATs. Aquestes expressions es van verificar i van comparar amb 15 màquines diferents, que es van provar variant la seua velocitat de rotació i la seua velocitat específica. En la segona part de la Fase del Procediment Analític, es va realitzar una simulació numèrica amb el paquet CFD OpenFOAM d'una PATs que ha sigut assajada en l'institut CERIS de Portugal. Per mitjà dels resultats experimentals es va aconseguir validar tant les noves expressions proposades en l'Article 2 així com el modelatge numèric. En l'Article 3 es presenta el desenvolupament d'aquesta metodologia. / [EN] The availability of water resources worldwide has decreased significantly. Among the main agents that have caused this situation are climate change, environmental pollution, human activities, and failures in hydraulic structures, among others. It is becoming increasingly difficult to access appropriate sources that meet the quality and quantity of the resource. Despite this, water loss due to leaks in pressurized distribution systems still manages considerable values, with significant losses worldwide. Considering that the need for water is increasing, sustainable projects should be implemented to optimize the availability and use of the resource to the maximum. The main objective of this thesis is to develop a methodological proposal that allows estimating the characteristic curves of pumps that work as turbines (PATs) from the specific number of the machine and, depending on the rotation speed, developing the modified laws of similarity. The fulfillment of the objectives of this thesis is through the elaboration of three published articles, which allowed: (i) To carry out the contextualization regarding the state of the art in PATs with emphasis on the methodologies of obtaining the prediction of the behavior in them such as the realization of numerical models with CFDs; (ii) To propose a new strategy to develop a mathematical model for pumps that work as turbines (PATs), considering the modified affinity laws; (iii) To execute the numerical modeling through the OpenFOAM free code package of a pump that works as a turbine and, (iv) Validate the results, both of the application of the new expressions and the numerical modeling, through the comparison with experimental results obtained from the tests carried out to a PATs. In Article 1, corresponding to the Contextualization Phase, an investigation was carried out in the technical literature on PATs: Characteristics, applications, and different strategies used to understand the flow behavior. The numerical simulation of the phenomenon with CFD (Computational Fluid Dynamics) packages is found within these strategies. 56 cases were analyzed where different types of machines were studied: axial, mixed, and radial under operation with fixed rotational speed and variable rotational speed. Based on this information, the error between the numerical modeling and the experimental results was calculated; and the main characteristics of the modeling were verified, such as the CFD package used, closure models, type of meshing, etc. In Article 2, which corresponds to the first part of the Phase of the Analytical Procedure, an analysis was proposed with ten general expressions (polynomial and exponential), considering the most significant variables. Based on this analysis, new expressions were obtained to obtain the characteristic curves of the PATs. These expressions were verified and compared with 15 different machines, which were tested by varying their rotation and specific speeds. In the second part of the Analytical Procedure Phase, a numerical simulation was performed with the OpenFOAM CFD package of a PATs that has been tested at the CERIS Institute in Portugal. The experimental results made it possible to validate both the new expressions proposed in Article 2 and the numerical modeling. The development of this methodology is presented in Article 3. / Plua Aguirre, FA. (2024). Metodología de análisis para la mejora de la predicción de las curvas características de bombas trabajando como turbina operando a velocidad variable [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/203125 / Compendio

Cette étude comparative entre le français et l'espagnol s'attarde au positionnement de l'adjectif évaluatif dans le syntagme nominal. Ces deux langues ont la particularité de permettre la prénominalisation et la postnominalisation de ce type d'adjectif. Cependant, la position qu'occupent les adjectifs dans un syntagme affecte le résultat sémantique selon chaque langue. Le mémoire contient une analyse exhaustive du comportement des adjectifs évaluatifs pour chaque langue selon des traits catégoriaux du nom avec lequel ils forment un syntagme soient : +humain, +animé, +événement, +abstrait, +concret, et ce, par rapport avec la position de l'adjectif. L'analyse des données démontrent que le français permet des lectures à la fois intersectives et non intersectives pour les adjectifs prénominaux évaluatifs, ce qui n'est pas possible en espagnol. Les données nous permettent d'expliciter un comportement syntaxique plus souple en français pour ces adjectifs tandis que l'espagnol est plus permissif que le français au niveau sémantique. Nous proposons un mécanisme syntaxique pour rendre compte de la différence de comportement entre les deux langues.

Road safety is a serious societal concern in Riyadh city, Kingdom of Saudi Arabia. Because of the negative impact of traffic crashes which cause losses in the form of deaths, injuries and property damage, in addition to the pain and social tragedy affecting families of the victims, it is important for transport policy makers to reduce their impact and increase safety standards by reducing the severity and frequency of crashes in the city of Riyadh. It is therefore important to fully understand the relationship between traffic crash severity and frequency and their contributing factors so to establish effective safety policies which can be implemented to enhance road safety in Riyadh city. Data used in previous research have only consisted of basic information as there was unavailability of suitable and accurate data in Riyadh and there are very few studies that have undertaken as small area-wide crash analysis in Riyadh using appropriate statistical models. Therefore safety policies are not based on rigorous analyses to identify factors affecting both the severity and the frequency of traffic crashes. This research aims to explore the relationship between traffic crash severity and frequency and their contributing factors by using statistical models and a GIS approach. The analysis is based on the data obtained over a period of five years, namely AH 1425, 1426, 1427, 1428, and 1429 (roughly equivalent to 2004, 2005, 2006, 2007, and 2008). Injury crash severity data were classified into three categories: fatal, serious injury and slight injury. A series of statistical models were employed to investigate the factors that affect both crash severity (i.e. ordered logit and mixed logit models) and area-wide crash frequency (i.e. classical Poisson and negative binomial models). Because of a severe underreporting problem on the slight injury crashes, binary and mixed binary logistic regression models were also estimated for two categories of severity: fatal and serious crashes. The mixed binary logit model and the negative binomial model are found to be the best models for crash severity and crash frequency analyses respectively. The model estimation results suggest that the statistically significant factors in crash severity are the age and nationality of the driver who is at fault, the time period from 16.00 to 19.59, excessive speed, road surface and lighting conditions, number of vehicles involved and number of casualties. Older drivers are associated with a higher probability of having a fatal crash, and, as expected, excessive speeds were consistently associated with fatal crashes in all models. In the area-level crash frequency models, population, percentage of illiterate people, income per capita and income per adult were found to be positively associated with the frequency of both fatal and serious injury crashes whereas all types of land use such as percentages of residential use, transport utilities, and educational use in all models were found to be negatively associated with the frequency of occurrence of crashes. Results suggest that safety strategies aimed at reducing the severity and frequency of traffic crashes in Riyadh city should take into account the structure of the resident population and greater emphasis should be put on native residents and older age groups. Tougher enforcement should be introduced to tackle the issue of excessive speed. This thesis contributes to knowledge in terms of examining and identifying a range of factors affecting traffic crash severity and frequency in Riyadh city.

In this thesis we examine exchange rates and monetary policy of four emerging Asian countries, namely Indonesia, Malaysia, the Philippines and South Korea. We model equilibrium exchange rates using a general behavioural specification consistent with a variety of theoretical approaches; and short-run dynamics using a general non-linear adjustment model. We find in all countries examined, equilibrium nominal and real exchange rates are a function of permanent relative output and one or more variables from domestic and foreign price levels, nominal and real interest rate differentials, the level of and changes in net foreign assets, and a time trend. These results imply that individual countries present significant elements of idiosyncratic behaviour, casting doubt on empirical models using panel-data techniques. We also obtain evidence of non-linear exchange rate dynamics, with the speed of adjustment to equilibrium being in all cases a function of the size, and in two cases, the sign of the misalignment term. With respect to monetary policy, we examined these countries' monetary policy reaction function based on an open economy augmented Taylor rule including the exchange rate and the foreign interest rate. Using a formal testing approach, our tests reject linearity, suggesting that monetary authorities in these four emerging economies are subject to nonlinear inflation effects and that they respond more vigorously to inflation when it is further from the target. Our results also lead us to speculate that policymakers in three countries may have been attempting to keep inflation within the range, while those in the other country may have been pursuing a point inflation target. Finally, we also find monetary policy is asymmetric as policy makers respond differently to upward and downward deviations of inflation away from the target.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Generic use of articles in French This Diploma thesis deals with the generic use of articles in the French language. It is divided into the theoretical and the experimental part. After the broader introduction into the issue of determinants, the most important part of the work treats genericity expressed in French by the definite article in singular and plural as well as by the indefinite article in singular. Firstly, the existing research on the subject of generic articles is studied, including the presentation of various approaches and principal theories, then is formulated proper syntactic and semantic interpretation of genericity which is finally verified in the experimental part of the thesis based on the analysis of model sentences. Keywords determinant, article, genericity, reference, nominal syntagm

The aim of this thesis, thats title is "The monetary policy of the Czech national bank and the prospects of euro adoption. Meeting the Maastricht monetary criteria and possible complications.", is answer the question whether the Czech Republic is ready now to adopt the common european currency (euro) or not. This thesis is divided into three parts. The first part pays attention to the monetary policy of the Czech national bank in connection with the entrance of the Czech Republic into the euro area and other parts deal with the convergence of the Czech Republic to the euro area. The second part discusses the convergence from the perspective of meeting the Maastricht monetary criteria and the third part deals with the real convergence. My conclusion is that the Czech Republic is not ready now to adopt euro and should wait with the adoption of a common european currency till the moment when is prepared better.

Ma thèse a pour but l'étude des désignations nominales des événements pour l'extraction automatique. Mes travaux s'inscrivent en traitement automatique des langues, soit dans une démarche pluridisciplinaire qui fait intervenir linguistique et informatique. L'extraction d'information a pour but d'analyser des documents en langage naturel et d'en extraire les informations utiles à une application particulière. Dans ce but général, de nombreuses campagnes d'extraction d'information ont été menées~: pour chaque événement considéré, il s'agit d'extraire certaines informations relatives (participants, dates, nombres, etc.). Dès le départ, ces challenges touchent de près aux entités nommées (éléments « notables » des textes, comme les noms de personnes ou de lieu). Toutes ces informations forment un ensemble autour de l'événement. Pourtant, ces travaux ne s'intéressent que peu aux mots utilisés pour décrire l'événement (particulièrement lorsqu'il s'agit d'un nom). L'événement est vu comme un tout englobant, comme la quantité et la qualité des informations qui le composent. Contrairement aux travaux en extraction d'informations générale, notre intérêt principal est porté uniquement sur la manière dont sont nommés les événements qui se produisent et particulièrement à la désignation nominale utilisée. Pour nous, l'événement est ce qui arrive, ce qui vaut la peine qu'on en parle. Les événements plus importants font l'objet d'articles de presse ou apparaissent dans les manuels d'Histoire. Un événement peut être évoqué par une description verbale ou nominale. Dans cette thèse, nous avons réfléchi à la notion d'événement. Nous avons observé et comparé les différents aspects présentés dans l'état de l'art jusqu'à construire une définition de l'événement et une typologie des événements en général, et qui conviennent dans le cadre de nos travaux et pour les désignations nominales des événements. Nous avons aussi dégagé de nos études sur corpus différents types de formation de ces noms d'événements, dont nous montrons que chacun peut être ambigu à des titres divers. Pour toutes ces études, la composition d'un corpus annoté est une étape indispensable, nous en avons donc profité pour élaborer un guide d'annotation dédié aux désignations nominales d'événements. Nous avons étudié l'importance et la qualité des lexiques existants pour une application dans notre tâche d'extraction automatique. Nous avons aussi, par des règles d'extraction, porté intérêt au cotexte d'apparition des noms pour en déterminer l'événementialité. À la suite de ces études, nous avons extrait un lexique pondéré en événementialité (dont la particularité est d'être dédié à l'extraction des événements nominaux), qui rend compte du fait que certains noms sont plus susceptibles que d'autres de représenter des événements. Utilisée comme indice pour l'extraction des noms d'événements, cette pondération permet d'extraire des noms qui ne sont pas présents dans les lexiques standards existants. Enfin, au moyen de l'apprentissage automatique, nous avons travaillé sur des traits d'apprentissage contextuels en partie fondés sur la syntaxe pour extraire de noms d'événements. / The aim of my PhD thesis is the study of nominal designations of events for automatic extraction. My work is part of natural language processing, or in a multidisciplinary approach that involves Linguistics and Computer Science. The aim of information extraction is to analyze natural language documents and extract information relevant to a particular application. In this general goal, many information extraction campaigns were conducted: for each event considered, the task of the campaign is to extract some information (participants, dates, numbers, etc..). From the outset these challenges relate closely to named entities (elements "significant" texts, such as names of people or places). All these information are set around the event and the work does not care about the words used to describe the event (especially when it comes to a name). The event is seen as an all-encompassing as the quantity and quality of information that compose it. Unlike work in general information retrieval, our main interest is focused only on the way are named events that occur particularly in the nominal designation used. For us, this is the event that happens that is worth talking about. The most important events are the subject of newspaper articles or appear in the history books. An event can be evoked by a verbal or nominal description. In this thesis, we reflected on the notion of event. We observed and compared the different aspects presented in the state of the art to construct a definition of the event and a typology of events generally agree that in the context of our work and designations nominal events. We also released our studies of different types of training corpus of the names of events, we show that each can be ambiguous in various ways. For these studies, the composition of an annotated corpus is an essential step, so we have the opportunity to develop an annotation guide dedicated to nominal designations events. We studied the importance and quality of existing lexicons for application in our extraction task automatically. We also focused on the context of appearance of names to determine the eventness, for this purpose, we used extraction rules. Following these studies, we extracted an eventive relative weighted lexicon (whose peculiarity is to be dedicated to the extraction of nominal events), which reflects the fact that some names are more likely than others to represent events. Used as a tip for the extraction of event names, this weight can extract names that are not present in the lexicons existing standards. Finally, using machine learning, we worked on learning contextual features based in part on the syntax to extract event names.

A tribo Oryzomyini abriga 34 dos 86 gêneros sigmodontíneos e apresenta ampla distribuição geográfica, ocorrendo em diversos habitats desde a Terra do Fogo ao sudeste dos Estados Unidos; com representantes cursoriais, arborícolas ou ainda semi-aquáticos, e com diferentes hábitos alimentares, variando de onívoros a insetívoros. Estudos sistemáticos nessa tribo têm sido desenvolvidos com base em dados de morfologia, morfometria, informações citogenéticas e moleculares, o que vêm contribuindo para o reconhecimento de novos táxons. No entanto, a última revisão taxonômica publicada para o gênero Nectomys data da década de 1940, na qual foi reconhecida apenas uma espécie com diversas subespécies, o que aumentou substancialmente a quantidade de nomes associados ao gênero. Diante disso, o cerne desse estudo foi testar a hipótese levantada por Hershkovitz de que Nectomys é representado por apenas uma espécie com ampla distribuição geográfica pela América do Sul. Para testar essa hipótese, reuni informações acerca dos táxons nominais e empreguei análises de variação geográfica com base na metodologia de transectos, tendo como unidades geográficas as bacias hidrográficas da América do Sul. Para isso, apliquei análises univariadas e multivariadas para dados quantitativos, e frequência de caracteres para dados qualitativos. Os resultados apontaram que o gênero Nectomys é composto por oito entidades, assim nomeadas e distribuídas: N. apicalis, encosta oriental da Cordilheira dos Andes do sul do Peru até o norte da Colômbia, no extremo oeste do Estado do Amazonas, no Brasil; N. magdalenae, ao longo do vale do rio Magdalena e ao norte do vale do rio Cauca, no oeste da Colômbia; N. palmipes, Trinidad e Tobago e nordeste da Venezuela; N. rattus, porção norte e central do Brasil, ao norte da bacia do rio Paraná e a oeste do rio São Francisco, Guiana, Suriname, Guiana Francesa, Venezuela (exceto Península de Paria), e rios Ucayali e Huallaga no Peru; N. saturatus, Ibarra, Equador; N. squamipes, Floresta Atlântica, desde Pernambuco até o Rio Grande do Sul, nos Estados de Minas Gerais e na porção leste do Mato Grosso do Sul, Paraguai e na Província de Misiones, na Argentina; Nectomys sp. A, noroeste da Bolívia, encosta oriental da Cordilheira do Andes; e Nectomys sp. B., Amazônia ocidental, nos rios Purus, Juruá e Javari. As análises que conduzi me permitiram estabelecer que a variação morfológica e citogenética não é aleatória: encontrei descontinuidades nítidas entre amostras ao longo da geografia, e com base no conceito de espécie por mim adotado, estabeleço que estas entidades representam oito espécies distintas. / The tribe Oryzomyini holds 34 of 86 sigmodontine genera and presents a wide geographic distribution, occurring in several habitats from Tierra del Fuego to southeast United States ; it includes cursorial, arboreal and semi-acquatic species with distinct food habits, ranging from omnivorous to insectivorous. Systematic studies in Oryzomyini have been based on morphological and morphometric data, as well cytogenetic and molecular information, which is contributing to recognition of new taxa. However, the latest published taxonomic review of the genus Nectomys date from 1940, where was recognized only one species with several subespecies, what increased substantially the amount of names related to the genus. In this way, the main goal of this study was to test the Hershkovitz\'s hypothesis that Nectomys is represented by only one species widely distributed through South America. To test this hypothesis, I gathered information about the nominal taxa and I employed geographical variation analysis based on the transect method, for what I used the South America river basins as a geographic units. To do so, I applied univariated and multivariated analysis for the quantitative data, and character frequency for the qualitative data. The results suggest the genus Nectomys is composed by eight species, which are so named and distributed: N. apicalis, Andean eastern slope, from southern Peru to northern Colombia, and westernmost Amazonas state, in Brazil; N. magdalenae, through Magdalena and Cauca valleys, in Colombia; N. palmipes, Trinidad and Tobago, and northeast Venezuela; N. rattus, central and north region in Brazil, Guyana, Suriname, and French Guyana, Venezuela (except Paria peninsula), and Ucayali and Huallaga rivers in Peru; N. saturatus, Ibarra, Ecuador; N. squamipes, Atlantic Forest, from Pernambuco to Rio Grande do Sul, Minas Gerais and eastern Mato Grosso do Sul in Brazil, Paraguay, and Misiones province, Argentina; Nectomys sp. A, northwestern Bolivia, in the eastern Andean slope; and Nectomys sp. B., western Amazônia, in Purus, Juruá, and Javari rivers. The analysis conducted allowed me to establish that the cytogenetic and morphologic variation is not random: I found marked discontinuities among samples through the geography, and based on the species concept I adopted, I establish that these entities represent eight distinct species.

Thesis advisor: Susanto Basu / The Great Recession is arguably the most important macroeconomic event of the last three decades. Prior to the collapse of national output during 2008 and 2009, the United States experienced a sustained period of good economic outcomes with only two mild and short recessions. In addition to the severity of the recession, several characteristics of this recession signify it as as a unique event in the recent economic history of the United States. Some of these unique features include the following: Large Increase in Uncertainty About the Future: The Great Recession and its subsequent slow recovery have been marked by a large increase in uncertainty about the future. Uncertainty, as measured by the VIX index of implied stock market volatility, peaked at the end of 2008 and has remained volatile over the past few years. Many economists and the financial press believe the large increase in uncertainty may have played a role in the Great Recession and subsequent slow recovery. For example, Kocherlakota (2010) states, ``I've been emphasizing uncertainties in the labor market. More generally, I believe that overall uncertainty is a large drag on the economic recovery.'' In addition, Nobel laureate economist Peter Diamond argues, ``What's critical right now is not the functioning of the labor market, but the limits on the demand for labor coming from the great caution on the side of both consumers and firms because of the great uncertainty of what's going to happen next.'' Zero Bound on Nominal Interest Rates: The Federal Reserve plays a key role in offsetting the negative impact of fluctuations in the economy. During normal times, the central bank typically lowers nominal short-term interest rates in response to declines in inflation and output. Since the end of 2008, however, the Federal Reserve has been unable to lower its nominal policy rate due to the zero lower bound on nominal interest rates. Prior to the Great Recession, the Federal Reserve had not encountered the zero lower bound in the modern post-war period. The zero lower bound represents a significant constraint monetary policy's ability to fully stabilize the economy. Unprecedented Use of Forward Guidance: Even though the Federal Reserve remains constrained by the zero lower bound, the monetary authority can still affect the economy through expectations about future nominal policy rates. By providing agents in the economy with forward guidance on the future path of policy rates, monetary policy can stimulate the economy even when current policy rates remain constrained. Throughout the Great Recession and the subsequent recovery, the Federal Reserve provided the economy with explicit statements about the future path of monetary policy. In particular, the central bank has discussed the timing and macroeconomic conditions necessary to begin raising its nominal policy rate. Using this policy tool, the Federal Reserve continues to respond to the state of the economy at the zero lower bound. Large Fiscal Expansion: During the Great Recession, the United States engaged in a very large program of government spending and tax reductions. The massive fiscal expansion was designed to raise national income and help mitigate the severe economic contraction. A common justification for the fiscal expansion is the reduced capacity of the monetary authority to stimulate the economy at the zero lower bound. Many economists argue that the benefits of increasing government spending are significantly higher when the monetary authority is constrained by the zero lower bound. The goal of this dissertation is to better understand how these various elements contributed to the macroeconomic outcomes during and after the Great Recession. In addition to understanding each of the elements above in isolation, a key component of this analysis focuses on the interaction between the above elements. A key unifying theme between all of the elements is the role in monetary policy. In modern models of the macroeconomy, the monetary authority is crucial in determining how a particular economic mechanism affects the macroeconomy. In the first and second chapters, I show that monetary policy plays a key role in offsetting the negative effects of increased uncertainty about the future. My third chapter highlights how assumptions about monetary policy can change the impact of various shocks and policy interventions. For example, suppose the fiscal authority wants to increase national output by increasing government spending. A key calculation in this situation is the fiscal multiplier, which is dollar increase in national income for each dollar of government spending. I show that fiscal multipliers are dramatically affected by the assumptions about monetary policy even if the monetary authority is constrained by the zero lower bound. The unique nature of the elements discussed above makes analyzing their contribution difficult using standard macroeconomic tools. The most popular method for analyzing dynamic, stochastic general equilibrium models of the macroeconomy relies on linearizing the model around its deterministic steady state and examining the local dynamics around that approximation. However, the nature of the unique elements above make it impossible to fully capture dynamics using local linearization methods. For example, the zero lower bound on nominal interest rates often occurs far from the deterministic steady state of the model. Therefore, linearization around the steady state cannot capture the dynamics associated with the zero lower bound. The overall goal of this dissertation is to use and develop tools in computational macroeconomics to help better understand the Great Recession. Each of the chapters outlined below examine at least one of the topics listed above and its impact in explaining the macroeconomics of the Great Recession. In particular, the essays highlight the role of the monetary authority in generating the observed macroeconomic outcomes over the past several years. Can increased uncertainty about the future cause a contraction in output and its components? In joint work with Susanto Basu, my first chapter examines the role of uncertainty shocks in a one-sector, representative-agent, dynamic, stochastic general-equilibrium model. When prices are flexible, uncertainty shocks are not capable of producing business-cycle comovements among key macroeconomic variables. With countercyclical markups through sticky prices, however, uncertainty shocks can generate fluctuations that are consistent with business cycles. Monetary policy usually plays a key role in offsetting the negative impact of uncertainty shocks. If the central bank is constrained by the zero lower bound, then monetary policy can no longer perform its usual stabilizing function and higher uncertainty has even more negative effects on the economy. We calibrate the size of uncertainty shocks using fluctuations in the VIX and find that increased uncertainty about the future may indeed have played a significant role in worsening the Great Recession, which is consistent with statements by policymakers, economists, and the financial press. In sole-authored work, the second chapter continues to explore the interactions between the zero lower bound and increased uncertainty about the future. From a positive perspective, the essay further shows why increased uncertainty about the future can reduce a central bank's ability to stabilize the economy. The inability to offset contractionary shocks at the zero lower bound endogenously generates downside risk for the economy. This increase in risk induces precautionary saving by households, which causes larger contractions in output and inflation and prolongs the zero lower bound episode. The essay also examines the normative implications of uncertainty and shows how monetary policy can attenuate the negative effects of higher uncertainty. When the economy faces significant uncertainty, optimal monetary policy implies further lowering real rates by committing to a higher price-level target. Under optimal policy, the monetary authority accepts higher inflation risk in the future to minimize downside risk when the economy hits the zero lower bound. In the face of large shocks, raising the central bank's inflation target can attenuate much of the downside risk posed by the zero lower bound. In my third chapter, I examine how assumptions about monetary policy affect the economy at the zero lower bound. Even when current policy rates are zero, I argue that assumptions regarding the future conduct of monetary policy are crucial in determining the effects of real fluctuations at the zero lower bound. Under standard Taylor (1993)-type policy rules, government spending multipliers are large, improvements in technology cause large contractions in output, and structural reforms that decrease firm market power are bad for the economy. However, these policy rules imply that the central bank stops responding to the economy at the zero lower bound. This assumption is inconsistent with recent statements and actions by monetary policymakers. If monetary policy endogenously responds to current economic conditions using expectations about future policy, then spending multipliers are much smaller and increases in technology and firm competitiveness remain expansionary. Thus, the model-implied benefits of higher government spending are highly sensitive to the specification of monetary policy. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Economics.