Thesis advisor: Robert G. Murphy / Thesis advisor: Fabio Schiantarelli / Thesis advisor: James Anderson / This dissertation consists of four essays. The first two essays investigate macroeconomic fluctuations and their sources. The third and fourth essays examine international capital mobility. / Thesis (PhD) — Boston College, 1994. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Economics.

In the first essay, Distortions in the Neoclassical Growth Model: A Cross Country Analysis, I show that shocks that express themselves as total factor productivity and labor income taxes are comparably more synchronized than shocks that resemble distortions to the ability of allocating resources across time and states of the world. These two shocks are also the most important to model. Lastly, I document the importance of international channels of transmission for the shocks, given that these are spatially correlated and that international trade variables, such as trade openness correlate particularly well with them. The second essay is called Monetary Business Cycle Accounting for Sweden. Given that the analysis is focused in one country, I can extend the prototype economy to include a nominal interest rate setting rule and government bonds. As in the previous essay, distortions to the labor-leisure condition and total factor productivity are the most relevant margins to be modeled, now joined by deviations from the nominal interest rate setting rule. Also, distortions do not share a structural break during the Great Recession, but they do during the 1990’s.  Researchers aiming to model Swedish business cycles must take into account the structural changes the Swedish economy went through in the 1990’s, though not so during the last recession. The third essay, Consumer Confidence and Consumption Spending: Evidence for the United States and the Euro Area, we show that, the consumer confidence index can be in certain circumstances a good predictor of consumption. In particular, out-of-sample evidence shows that the contribution of confidence in explaining consumption expenditures increases when household survey indicators feature large changes, so that confidence indicators can have some increasing predictive power during such episodes. Moreover, there is some evidence of a confidence channel in the international transmission of shocks, as U.S. confidence indices help predicting consumer sentiment in the euro area.

No description available.

D'une part, l'effet Nernst est connu pour ??tre sensible aux fluctuations supraconductrices, c'est-??-dire aux manifestations de l'??tat supraconducteur ?? des temp??ratures sup??rieures ?? la temp??rature critique. D'autre part, les cuprates, en raison de leur caract??re fortement bi-dimensionnel et de leur courte longueur de coh??rence, sont sujets ?? ??tre particuli??rement affect??s par les fluctuations de phase de l'ordre supraconducteur. Ces deux ??l??ments sont ?? l'origine d'une croyance tr??s r??pandue selon laquelle les fluctuations de phase sont la cause de l'amplitude anormalement grande de l'effet Nernst dans les cuprates et sont associ??es ?? la pr??sence du pseudogap du c??t?? sous-dop??. Dans cette th??se, l'effet Nernst d'un cuprate dop?? en ??lectrons a ??t?? mesur?? afin d'??tablir la nature des fluctuations. Les ??chantillons ??tudi??s, des couches minces de PCCO, r??v??lent que la th??orie classique des fluctuations gaussiennes peut ad??quatement d??crire le signal obtenu, ?? condition que la contribution des quasi-particules soit correctement trait??e. L'??volution en fonction du dopage, du r??gime sous-dop?? ?? celui sur-dop??, montre que l'amplitude des fluctuations dans l'effet Nernst suit la d??pendance en d??me de la temp??rature critique, tout comme dans les cuprates dop?? en trous et en opposition avec un sc??nario de fluctuations de phase. Les r??sultats obtenus, en accord quantitatif avec ceux des ??tudes ant??rieures, permettent de conclure que le diagramme de phase des cuprates est domin?? par la comp??tition de phase et la criticalit?? quantique causant une reconstruction de la surface de Fermi.

No description available.

Thesis (Ph.D.)--McMaster University (Canada), 1990. / Source: Dissertation Abstracts International, Volume: 53-01, Section: B, page: 0374. Supervisor: J. P. Carbotte.

Thesis advisor: Jaromir Nosal / This dissertation comprises three self-contained essays that investigate the determination and transmission of exchange rate fluctuations, as well as the impact of import quality on consumers’ gains from globalization. In the first chapter, “Decomposing the (In)Sensitivity of CPI to Exchange Rate", I examine the role of domestic frictions – distribution costs, variable markups and nominal rigidities – in explaining the low sensitivity of domestic prices to exchange rate fluctuations. I begin by modeling what the sensitivity of CPI to exchange rates is expected to be, given the presence of insensitivity in border prices and domestic frictions. Distribution costs, such as transportation and wholesaling costs, introduce a wedge between the retail price, on one side, and the border price of imports and the domestic producers’ costs, on the other. Similarly, domestic firms do not fully adjust their price to changes in their own cost because of changes in the desired markup or because prices are sticky. These frictions introduce wedges between the change in domestic producers’ costs and border prices following an exchange rate shock, and the response of domestic consumption retail prices. Using firm and transaction data from Chile, I document that domestic frictions account for 60% of the overall insensitivity of domestic CPI. Moreover, the presence of domestic frictions also impacts the sensitivity of domestic CPI: contrary to previous literature, most of the sensitivity arises from the direct consumption of imported final goods, rather than through the costs associated to imported inputs in the production of domestic goods. This is because domestic frictions dampen the response of domestically produced goods more significantly. In addition, I quantify a rich heterogeneity in the sensitivity across products, which stems from the interaction of domestic frictions and import exposure. These heterogeneities are relevant for the overall (in)sensitivity, as sectors with higher import exposure face also larger frictions. Overall, my results showcase the importance of domestic frictions and their heterogeneity in studying the response of domestic prices to exchange rate fluctuations, with implications for monetary policy in open economy and redistribution dynamics. In the second chapter, “Strategic Behavior and Exchange Rate Dynamics", joint work with L. Pollio, I examine the impact of heterogeneous investors with different degrees of price impact on exchange rate behavior. The huge trading volume in the currency markets, about $6 trillions per day, is highly concentrated among the market-making desks of few large financial institutions. However, models of exchange rate determination assume that investors take the equilibrium price as given, ignoring the presence of a few large investors who recognize the price impact of their decisions and can exert pressure on market prices. We incorporate heterogeneity in price impact, following of Kyle (1989), into a two-country, dynamic monetary model of exchange rate determination. Our theory of exchange rate determination with heterogeneity in price impact reveals that market structure is a key determinant of exchange rate dynamics. Strategic investors recognize their price impact, which leads them to trade less on any information and reduce the information loading factor of the exchange rate (price informativeness). The presence of strategic investors explains the weak explanatory power of macroeconomics variables in predicting exchange rates (exchange rate disconnect puzzle) and the excess volatility of the exchange rate relative to fundamentals (excess volatility puzzle). We also provide empirical evidence that supports our theoretical predictions by using trading volume concentration data from the NY Fed FXC Reports for 18 currencies from 2005 to 2019. We extend our theoretical framework to include another dimension of heterogeneity among investors, information heterogeneity, that provides similar qualitative predictions in terms of exchange rate dynamics. We demonstrate that both dimensions of heterogeneity are quantitatively relevant in explaining the disconnect of exchange rates and their excess volatility. In the third chapter, “The Quality of US Imports and the Consumption Gains from Globalization", joint work with D. Lashkari, I examine the role of quality improvement in shaping the gains from trade. The existing empirical literature indicates that globalization has offered consumers around the world access to a wider variety of products at cheaper prices. However, since the available data typically lacks detailed information on product characteristics, we may underestimate the value of imports for consumers if the quality of goods within each product rises over time. To overcome this limitation, we propose a novel methodology to estimate demand elasticity and infer unobserved quality using only data on prices and market shares. Our approach builds on the standard framework that models product quality as residual demand. This framework requires estimating price elasticities and the standard approach assumes CES demand and imposes uncorrelated supply and demand shocks. However, the latter assumption is untenable if we associate demand shocks with quality and generates an upward bias in the estimates of price elasticities. Our strategy circumvents this problem by restricting the dynamics of product quality to a Markov process. We apply our new methodology to the US customs data (1989-2006), and find that quality improvements contribute the most to the gains from trade in the US. Quality improvements have lowered the price of US imports relative to the CPI by 17%, with Chinese products contributing the most. In comparison, import prices have fallen by around 11% relative to the CPI and increasing variety has contributed an additional 4%. These findings demonstrate that accounting for quality is essential to better understand and measure the effects of international trade. / Thesis (PhD) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Economics.

This work explores the physics of micro and nano-scale systems immersed in a fluid. Previous literature has established an understanding of the fluid-solid interaction for systems including cantilevers and doubly clamped beams. Building on these advances, this work extends the theory of doubly clamped beams with an arbitrary amount of tension. Both the driven and stochastic dynamics of a doubly clamped beam are explored. The driven dynamics are investigated for a spatially applied harmonic driving force, and demonstrates quantitative agreement with an experimental beam that is driven electrothermally, in both air and in water. For the stochastic dynamics, the noise spectrum describes the thermal fluctuations at a given frequency. The theoretical model provides an analytical expression for the noise spectrum from an arbitrary number of modes. The noise spectrum of the first eleven modes are computed, and show excellent agreement with the noise spectrum from finite element simulations, which is computed from the deterministic ring down. This agreement is shown across different fluids (air and water), and for multiple measuring points including at the beam midpoint and the quarter point. In addition to exploring the linear dynamics of these systems, the case of large perturbations, resulting in nonlinear dynamics, is explored. This regime is motivated by exploring the theoretical dynamics of a uniformly shrinking doubly clamped beam. The challenges of modeling such a beam using finite element simulations are discussed. As a simpler and more direct alternative to access the nonlinear regime, a virtual beam is defined. The virtual beam controls the nonlinearity of the restoring force by modifying the Young's modulus. This work defines the Young's modulus such that the restoring force is like a Duffing oscillator. Then, the dynamics of this virtual beam are explored in air and water, and it is demonstrated that the Duffing oscillator serves as an appropriate reduced order model for this virtual beam. To understand the stochastic dynamics of the virtual beam, the stochastic Duffing oscillator is solved numerically. The ensemble autocorrelation of the beam dynamics are investigated for nonlinearities varying from linear to strongly nonlinear. The numeric autocorrelation is used to quantify the range of nonlinear strength where a deterministic approach, the ring down, can yield a good approximation. In the strongly nonlinear regime, the stochastic numerical approach is used to determine the autocorrelation. This research was supported by the National Science Foundation, grant number CMMI-2001559, and portions of the computations were conducted using the resources of Virginia Tech's Advanced Research Computing center. / Doctor of Philosophy / This work explores the physics of small systems immersed in a fluid, such as air or water. Previous literature has established an understanding of the force from a fluid acting on solids such as cantilevers and doubly clamped beams. Building on these advances, this work extends theory to doubly clamped beams with any amount of tension. Both the driven and stochastic, or randomly driven, dynamics of a doubly clamped beam are explored. The driven dynamics are developed for a driving force applied over part of the beam, and demonstrates quantitative agreement with an experimental beam, in both air and in water. For the stochastic dynamics, the noise spectrum describes the random thermal fluctuations of the beam at a given frequency. These thermal fluctuations are small, but measureable deviations of the system from equilibrium and are significant for these small scale systems. The noise spectrum can be estimated by computing the statistics from many randomly forced simulations. However, previous literature provides a direct computation of the noise spectrum with a single deterministic ring down. This work provides an analytical expression for the noise spectrum of a doubly clamped beam in tension in fluid for multiple modes. The theoretical noise spectrum shows excellent quantitative agreement with the ring down from finite element simulations. The agreement between theory and simulation is demonstrated in air and water, for a measurement of the noise spectrum at the beam midpoint and at the beam quarter point. In addition to exploring the linear dynamics of these systems, the case of large perturbations, resulting in nonlinear dynamics, is explored. This regime is motivated by exploring the theoretical dynamics of a uniformly shrinking doubly clamped beam. The challenges of modeling such a beam using finite element simulations are discussed. As a simpler and more direct alternative to access the nonlinear regime, a virtual beam is defined. The virtual beam controls the nonlinearity of the restoring force such that the system becomes increasingly stiff as the displacements become larger. This definition results in the restoring force following a Duffing oscillator. Then, the dynamics of this virtual beam are explored in air and water, and it is demonstrated that the Duffing oscillator serves as an appropriate reduced order model for this virtual beam. For varying nonlinear strengths, the stochastic numerical approach is used to quantify the dynamics, and the range of usefulness for the deterministic ring down is investigated. This research was supported by the National Science Foundation, grant number CMMI-2001559, and portions of the computations were conducted using the resources of Virginia Tech's Advanced Research Computing center.

Ultracold quantum gases have nowadays become an invaluable tool in the study of quantum many-body problems. The high level of experimental control available on these systems and well established theoretical tools make ultracold quantum gases ideal platforms for quantum simulations of other systems currently inaccessible in experiments as well as for studies of fundamental properties of matter in the quantum degenerate regime. A key manifestation of quantum degeneracy in samples of ultracold bosonic neutral atoms is the formation of a Bose-Einstein condensate (BEC), a peculiar state of matter in which a macroscopic number of atoms occupy the same single-particle state. Bose-Einstein condensation occurs in extremely rarefied gases of bosonic atoms at temperatures around the nanoKelvin. At such temperatures, the equilibrium state of all known elements (except for helium) in ordinary conditions of density and pressure would be the solid phase. To obtain a BEC it is thus necessary to consider very dilute samples with a density of the order of 1014-1015 atoms/cm3, around eight orders of magnitude smaller then the density of ordinary matter. At such densities, the three-body recombination mechanisms responsible for the formation of molecules, that cluster to form solids, are suppressed. However, despite the extreme diluteness, two-body inter-atomic interactions play a prominent role in determining the physical properties of these systems. In the temperature and density regimes typical of BECs, the theoretical description of the system can be greatly simplified by noticing that the low-energy scattering properties of the real, generally involved, inter-atomic potential, can be perfectly reproduced by a simpler pseudo-potential, usually of the form of an isotropic contact repulsion, and described by a single parameter, the s-wave scattering length. Such parameter can even be tuned, in experiments, via the so-called Feschbach resonances. Despite its simplicity, this zero-range, isotropic interaction is responsible for an enormous variety of physical effects characterizing atomic BECs. This fact stimulated, over the last twenty years, the research of different possible types of interactions, that can eventually lead to the formation of new and exotic phases of matter. In this quest, the dipole-dipole interaction attracted great attention for different reasons. First, there are several experimental techniques to efficiently trap and cool atoms (or molecules) possessing a strong dipole moment. This led, for example, to the experimental realization of BECs of Chromium, Dysprosium and Erbium, which have, in the hyperfine state trapped for condensation, a magnetic dipole moment around ten times larger then the one typical of the particles in a BEC of alkali atoms. Moreover, since the dipole-dipole interaction is anisotropic and long-ranged, its low-energy scattering properties cannot be described by a simple short-range isotropic pseudo-potential. As a consequence, dipolar BECs show unique observable properties. The partially attractive nature of the dipole-dipole interaction can make a dipolar BEC unstable against collapse, similarly to the case of an ordinary (non-dipolar) BEC with negative scattering length. This happens, in particular, if a sample of magnetic atoms, polarized along a certain direction by some magnetic field, is not confined enough along such direction (for example via a harmonic potential). However, differently from ordinary BECs, where the collapse of the system is followed by a rapid loss of atoms and the destruction of the condensed phase, in the dipolar case such instability is followed by the formation of self-bound, (relatively) high density liquid-like droplets. If the geometry of the confinement potential allows it, the droplets spontaneously arrange into a regular, periodic configuration, in a sort of "droplet crystal". Moreover, by fine-tuning the interaction parameters, it is possible to achieve global phase coherence between these droplets. The spatially modulated, phase coherent system that forms is known as supersolid, and is a very peculiar system showing simultaneously the properties of a crystal and a superfluid. Ordinary mean-field theory, so successful in describing the vast phenomenology of ordinary BECs, fails in predicting the existence of the exotic phases of supersolids, quantum droplets and droplet crystals in a dipolar quantum gas. The state of the art description of dipolar BECs in such conditions is instead based on quantum fluctuations, taking into account the local density approximation of the first-order beyond-mean-field correction of the ground state energy of the system. This correction, known as the Lee-Huang-Yang correction, results in a repulsive energy term that balances the mean-field attraction at the relatively high densities that characterize the collapsing state. Using state-of-the-art simulation techniques, in this thesis I study the behavior of a dipolar Bose gas confined in a variety of trapping configurations, focusing on ground-state properties, elementary excitations, and the dynamical behavior under several kinds of external perturbations, focusing in particular on the supersolid phase. After reviewing the basic theory of dipolar Bose gases, setting the theoretical background, and describing the numerical techniques used, I first study the behavior of the dipolar Bose gas in an ideal situation, namely when the gas is confined in a harmonic trap along the polarization direction of the dipoles as well as one of the orthogonal directions. Along the unconfined direction, instead, I set periodic boundary conditions, in order to simulate the geometry of a ring. I study in particular the phase diagram of the system, focusing on how the ground state evolves from a superfluid, homogeneous along the ring, to the supersolid regime, and eventually to an array of independent droplets, by tuning a single interaction parameter, namely the s-wave scattering length. The superfluid phase is here characterized by the occurrence of a roton minimum in the energy-momentum dispersion relation. The energy of the roton, called roton gap, decreases when the s-wave scattering length of the system is decreased and the dipole-dipole interaction becomes the dominant interaction mechanism. When the roton minimum touches the zero-energy axis, the superfluid system is not stable anymore against mechanical collapse. The system thus tend to form denser clusters of atoms, regularly arranged in an equally-spaced array of droplets, whose relative distance is fixed by the inverse of the roton momentum. Such droplets are stabilized by quantum fluctuations, which enters in the energy functional of the system via the Lee-Huang-Yang correction. The density profiles of these droplets maintain a finite overlap if the scattering length is not too small. The phase characterized by overlapping, dense droplets of dipolar atoms is called supersolid. The main signatures of supersolid behavior, which in the thesis are shown to occur in this system, are 1. The occurrence of two Goldstone modes, associated with the two symmetries spontaneously broken in the supersolid, namely the symmetry for continuous translations, which is broken in favor of a discrete one, and the U(1) symmetry associated with Bose-Einstein condensation. 2. The manifestation of Non-Classical Rotational Inertia, due to the partially superfluid character of the system. Simply speaking, since the system behaves only partially as a superfluid, any rotational perturbation drags only the non superfluid part of the system. Hence, any measurement of the moment of inertia would give a value which is smaller then the one of a classical system with the same density distribution. Having studied the behavior of the dipolar Bose gas in a ring trap, I move on to explore possible manifestations of supersolid behavior in a fully trapped configuration, namely when the system is confined in an elongated (cigar-shaped) harmonic trap, with the long axis orthogonal to the polarization direction. Part of the results obtained in the three-dimensional harmonic trap have been compared with the first available experiments. The two key signatures of supersolid behavior, namely the occurrence of two Goldstone modes and Non-Classical Rotational Inertia, can be detected, in this case, by studying the low-energy collective oscillations of the system. First, a behavior equivalent to the one of the two Goldstone modes predicted in the ring trap, can be found in the axial compressional oscillations of the harmonically trapped system, which bifurcate at the superfluid-supersolid phase transition. When the system is driven through the supersolid-independent droplet transition, the lower-energy mode, associated with phase coherence, tends to disappear, while the higher energy mode, associated with lattice excitations, tends to assume a constant frequency. This behavior is specular to the one of the two Goldstone modes in the ideal system, and thus signal the presence of supersolidity in the trapped system. Important experimental confirmation of the predictions reported in the thesis have already been found. Instead, as shown in the thesis, a key manifestation non-classical inertia in a trapped dipolar supersolid can be found by studying the rotational oscillation mode known as scissors mode, whose frequency is directly related to the value of the moment of inertia (similar to the frequency of oscillation of a torsional pendulum for a classical system). Studying the behavior of the frequency of the scissors mode across the superfluid-supersolid-independent droplets phase transitions, I demonstrate the actual occurrence of non-classical inertia in a harmonically trapped dipolar supersolid. Another key manifestation of superfluidity in general many-body systems is given by the occurrence of quantized vortices, which I study in the case of the trapped dipolar Bose gas in a harmonic trap which is isotropic in the plan orthogonal to the polarization direction. I study in particular the size of the core of the vortex as function of the interaction parameters, showing that, in the superfluid phase, it increases as the superfluid-supersolid phase transition is approached. Then, in the supersolid phase, I show that quantized vortices settle in the interstices between the density peaks, and their size and even their shape are fixed respectively by the droplet distance and the shape of the lattice cell. I also study the critical frequency for the vortex nucleation under a rotating quadrupolar deformation of the trap, showing that it is related to the frequency of the lower-energy quadrupole mode, associated with the partial superfluid character of the system. In fact, in this configuration, the quadrupole mode splits into three modes, two of which can be associated to lattice excitations, and one to superfluid excitations. I find that the critical rotational frequency for vortex nucleation is related to the lower frequency quadrupole mode only, i.e. the one related to the superfluid character of the system. In ordinary BECs, when many vortices nucleates, they typically tend to arrange in a trinagular lattice. In a supersolid, however, vortices do not form on top of a uniform superfluid background, but rather on the background of the supersolid lattice, which is itself typically triangular. I thus show that the lattice formed by the vortices in the supersolid lattice is not triangular, but rather hexagonal, since the vortices settle in the interstices between the density peaks. Finally, I show that all these features can be observed in an expansion experiment. In the last part of the thesis, I study the behavior of the dipolar Bose gas confined by hard walls. In particular, I investigate the novel density distributions, with special focus on the effects of supersolidity. Differently from the case of harmonic trapping, in this case, the ground state density shows a strong depletion in the bulk region and an accumulation of atoms near the walls, well separated from the bulk, as a consequence of the competition between the attractive and the repulsive nature of the dipolar force. In a quasi two-dimensional geometry characterized by cylindrical box trapping, the consequence is that the superfluid accumulating along the walls forms spontaneously a ring shape, showing eventually also supersolidity. For sufficiently large values of the atom density, also the bulk region can exhibit supersolidity, the resulting geometry reflecting the symmetry of the confining potential even for large systems.

abstract: In very small electronic devices the alternate capture and emission of carriers at an individual defect site located at the interface of Si:SiO2 of a MOSFET generates discrete switching in the device conductance referred to as a random telegraph signal (RTS) or random telegraph noise (RTN). In this research work, the integration of random defects positioned across the channel at the Si:SiO2 interface from source end to the drain end in the presence of different random dopant distributions are used to conduct Ensemble Monte-Carlo ( EMC ) based numerical simulation of key device performance metrics for 45 nm gate length MOSFET device. The two main performance parameters that affect RTS based reliability measurements are percentage change in threshold voltage and percentage change in drain current fluctuation in the saturation region. It has been observed as a result of the simulation that changes in both and values moderately decrease as the defect position is gradually moved from source end to the drain end of the channel. Precise analytical device physics based model needs to be developed to explain and assess the EMC simulation based higher VT fluctuations as experienced for trap positions at the source side. A new analytical model has been developed that simultaneously takes account of dopant number variations in the channel and depletion region underneath and carrier mobility fluctuations resulting from fluctuations in surface potential barriers. Comparisons of this new analytical model along with existing analytical models are shown to correlate with 3D EMC simulation based model for assessment of VT fluctuations percentage induced by a single interface trap. With scaling of devices beyond 32 nm node, halo doping at the source and drain are routinely incorporated to combat the threshold voltage roll-off that takes place with effective channel length reduction. As a final study on this regard, 3D EMC simulation method based computations of threshold voltage fluctuations have been performed for varying source and drain halo pocket length to illustrate the threshold voltage fluctuations related reliability problems that have been aggravated by trap positions near the source at the interface compared to conventional 45 nm MOSFET. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011