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Thesis advisor: Ryan Chahrour / The dissertation studies the sources of business cycles taking both an open and a closed economy perspective. A common feature of the two chapters composing the dissertation is the use of simple, but powerful classifications and identifications of sources of business cycles. In particular, the first chapter, titled “What are the Sources of Boom-Bust Cycles?”, concerns the distinction between economic fluctuations due to changes in beliefs, and fluctuations due to changes in fundamentals, showing results that challenge traditional approaches to modeling business cycles. The second chapter, titled “Shocks and Exchange Rates in Small Open Economies”, takes the perspective of small open economies, and concerns the distinc- tion between global and domestic shocks, showing results that are informative for a series of puzzling facts concerning the dynamics of the exchange rate. In “What are the Sources of Boom-Bust Cycles?,” joint with Marco Brianti, we provide a synthesis of two major views on economic fluctuations. One view maintains that expansions and recessions arise from the interchange of positive and negative persistent exogenous shocks to fundamentals. This is the conventional view that gave rise to the profusion of shocks used in modern dynamic stochastic general equilibrium models. In contrast, a second view, which we call the endogenous cycles view, holds that business cycle fluctuations are due to forces that are internal to the economy and that endogenously favor recurrent periods of boom followed by a bust. In this environment, cycles can occur after small perturba- tions of the long run equilibrium. We find empirical evidence pointing at the coexistence of both views. In particular, we find that the cyclical behaviour of economic aggregates is due in part to strong internal mechanisms that generate boom-bust phenomena in response to small changes in expectations, and in part to the interchange of positive and negative persistent fundamental shocks. Motivated by our findings, we build a theory that unifies the dominant paradigm with the endogenous cycles approach. Our theory suggests that recessions and expansions are intimately related phenomena, and that understanding the nature of an expansion, whether it is driven by fundamentals or by beliefs, is a first order issue for policy makers whose mandate is to limit the occurrance of inefficient economic fluctuations. In “Shocks and Exchange Rates in Small Open Economies,” joint with Pierre De Leo, we propose a novel approach to separately identify domestic and external shocks in small open economies. Our results provide guidance about the transmission mechanism of these shocks and revisit recent conclusions drawn on the exchange rate effects of monetary policy in small open economies. The identification method is based on the premise that shocks originating from within a small economy should not influence world variables at any horizon, while external (or global) shocks should affect world variables at least at some horizon. We obtain three empirically related findings. First, external shocks feature large deviations from uncovered interest parity, while domestic shocks do not. Second, external shocks strongly comove with global risk aversion and U.S. macroeconomic variables. Third, recent puzzling estimates of the exchange rate effects of monetary policy stem from an identification of domestic shocks that fails to properly account for international spillovers. We show that a two-country small open economy model with international asset market imperfections is consistent with these facts. In our proposed model, global risk aversion shocks drive exchange rate dynamics, and a country’s net foreign asset position governs their international transmission. We provide empirical evidence that a country’s exposure to external shocks indeed depends on its net foreign asset position. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Economics.

The present study, performed within the framework of evolutionary psychology, is an examination of the influence of hormonal fluctuations, associated with the phases of the menstrual cycle, on judgements of male and female facial attractiveness. It was hypothesized that women in the periovulatory phase would be more discriminating in rating male facial attractiveness than women in the early follicular phase, due to an increased likelihood of conceiving. Alternatively, if peri-ovulatory women are too selective, they may not fmd a mate; therefore, women in the peri-ovulatory phase could be more discriminating than women in the early-follicular phase. Judgements of female facial attractiveness were also examined as it may be associated with same sex competition. Lastly, salivary testosterone was analyzed in order to investigate the relationship between attractiveness ratings and testosterone levels, as testosterone is linked to women's libido and sexuality. To test these hypotheses, 129 undergraduate females who had regular and normally cycling menstrual cycles rated male and female facial attractiveness twice, once during the peri-ovulatory phase and again during the early-follicular phase. Menstrual phase had no significant influence on judgements of facial attractiveness of male and female faces. Female faces were rated as more attractive than male faces independent of phase, and the ratings were more variable for the female faces than the male faces. There was no difference in levels of salivary testosterone during the peri-ovulatory and the early follicular phase, and no significant correlations were obtained to support the hypothesis of a relationship between judgements of attractiveness and testosterone. / Thesis / Master of Science (MSc)

Proper and precise interpretation of radio occultation soundings of planetary atmospheres requires understanding the signal amplitude and phase variations caused by random perturbations in the complex index of refraction caused by atmospheric turbulence. This research focuses on understanding the turbulence and its impact on these soundings.From aircraft temperature, pressure and humidity measurements we obtained a parametric model for estimating the strength of the atmospheric turbulence in the troposphere. We used high-resolution balloon measurements to understand the spatial spectrum of turbulence in the vertical dimension.We also review and extend electromagnetic scintillation theory to include a complex index of refraction of the propagating medium. In contrast to when the fluctuations in only the real component of the index of refraction are considered, this work quantifies how atmospheric turbulent eddies contribute to the signal amplitude and phase fluctuations and the amplitude frequency correlation function when the index of refraction is complex. The generalized expressions developed for determining the signal's amplitude and phase fluctuations can be solved for planar, spherical or beam electromagnetic wave propagation.We then apply our mathematical model to the case of a plane wave propagating through a homogenous turbulence medium and estimate the amplitude variance for signals at various frequencies near the 22 GHz and 183 GHz water vapor absorption features. The theoretical results predict the impact of random fluctuations in the absorption coefficient along the signal propagation path on the signal's amplitude fluctuations. These results indicate that amplitude fluctuations arising from perturbations of the absorption field can be comparable to those when the medium has a purely real index of refraction. This clearly indicates that the differential optical depth approach devised by Kursinski et al. (2002) to ratio out the effects of turbulence on signals passing through a medium of a purely real index of refraction must be modified to include the effects of turbulent variations in the imaginary part of the refractivity.

The goal of this thesis has been to throw light on a selection of open problems in chemical and biological physics using the general principles of statistical mechanics. These problems are all broadly concerned with the role of fluctuations in the dynamics of macromolecular systems. More specifically, they are concerned with identifying the microscopic roots of a number of interesting and unusual effects, including fractional viscoelasticity, anomalous chain cyclization dynamics in crowded environments, subdifffusion in hair bundles, symmetries in the work distributions of stretched polymers, heterogeneities in the geometries of reptation channels in polymer melts, and non-Gaussianity in the distributions of the end products of gene expression. I have shown here that all these effects are expressions of essentially the same underlying process of stochasticity, which can be described in terms of the dynamics of a point particle or a continuous curve that evolves in simple potentials under the action of white or colored Gaussian noise [8]. I have also shown that this minimal model of time-dependent behavior in condensed phases is amenable to analysis, often exactly, by path integral methods [13-15], which are naturally suited to the treatment of random processes in many-body physics. The results of such analyses are theoretical expressions for various experimentally measured quantities, comparisons with which form the basis for developing physical intuition about the phenomena under study. The general success of this approach to the study of stochasticity in biophysics and molecular biology holds out hopes of its application to other unsolved problems in these fields. These include electrical transport in DNA [143], quantum coherence in photosynthesis [144], power generation in molecular motors [145], cell signaling and chemotaxis [146], space dependent diffusion [147], and self-organization of active matter [148], to name a few. Most of these problems are characterized by non-linearities of one kind or another, so they add a new layer of complexity to the problems considered in this thesis. Although path integral and related field theoretic methods are equipped to handle such complexities, the attendant calculations are expected to be non-trivial, and the challenge to theory will be to devise effective approximation schemes for these methods, or to develop new and more sophisticated methods altogether.

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D'une part, l'effet Nernst est connu pour être sensible aux fluctuations supraconductrices, c'est-à-dire aux manifestations de l'état supraconducteur à des températures supérieures à la température critique. D'autre part, les cuprates, en raison de leur caractère fortement bi-dimensionnel et de leur courte longueur de cohérence, sont sujets à être particulièrement affectés par les fluctuations de phase de l'ordre supraconducteur. Ces deux éléments sont à l'origine d'une croyance très répandue selon laquelle les fluctuations de phase sont la cause de l'amplitude anormalement grande de l'effet Nernst dans les cuprates et sont associées à la présence du pseudogap du côté sous-dopé. Dans cette thèse, l'effet Nernst d'un cuprate dopé en électrons a été mesuré afin d'établir la nature des fluctuations. Les échantillons étudiés, des couches minces de PCCO, révèlent que la théorie classique des fluctuations gaussiennes peut adéquatement décrire le signal obtenu, à condition que la contribution des quasi-particules soit correctement traitée. L'évolution en fonction du dopage, du régime sous-dopé à celui sur-dopé, montre que l'amplitude des fluctuations dans l'effet Nernst suit la dépendance en dôme de la température critique, tout comme dans les cuprates dopé en trous et en opposition avec un scénario de fluctuations de phase. Les résultats obtenus, en accord quantitatif avec ceux des études antérieures, permettent de conclure que le diagramme de phase des cuprates est dominé par la compétition de phase et la criticalité quantique causant une reconstruction de la surface de Fermi.

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