3 resultados para nonlinear effects
em Digital Commons at Florida International University
Resumo:
This dissertation addresses three issues in the political economy of growth literature. The first study empirically tests the hypothesis that income inequality influences the size of a country's sovereign debt for a sample of developing countries for the period 1970–1990. The argument examined is that governments tend to yield to popular pressures to engage in redistributive policies, partially financed by foreign borrowing. Facing increased risk of default, international creditors limit the credit they extend, with the result that borrowing countries invest less and grow at a slower pace. The findings do not seem to support the negative relationship between inequality and sovereign debt, as there is evidence of increases in multilateral, countercyclical flows until the mid 1980s in Latin America. The hypothesis would hold for the period 1983–1990. Debt flows and levels seem to be positively correlated with growth as expected. ^ The second study empirically investigates the hypothesis that pronounced levels of inequality lead to unconsolidated democracies. We test the existence of a nonmonotonic relationship between inequality and democracy for a sample of Latin American countries for the period 1970–2000, where democracy appears to consolidate at some intermediate level of inequality. We find that the nonmonotonic relationship holds using instrumental variables methods. Bolivia seems to be a case of unconsolidated democracy. The positive relationship between per capita income and democracy disappears once fixed effects are introduced. ^ The third study explores the nonlinear relationship between per capita income and private saving levels in Latin America. Several estimation methods are presented; however, only the estimation of a dynamic specification through a state-of-the-art general method of moments estimator yields consistent estimates with increased efficiency. Results support the hypothesis that income positively affects private saving, while system GMM reveals nonlinear effects at income levels that exceed the ones included in this sample for the period 1960–1994. We also find that growth, government dissaving, and tightening of credit constraints have a highly significant and positive effect on private saving. ^
Resumo:
This dissertation reports experimental studies of nonlinear optical effects manifested by electromagnetically induced transparency (EIT) in cold Rb atoms. The cold Rb atoms are confined in a magneto-optic trap (MOT) obtained with the standard laser cooling and trapping technique. Because of the near zero Doppler shift and a high phase density, the cold Rb sample is well suited for studies of atomic coherence and interference and related applications, and the experiments can be compared quantitatively with theoretical calculations. It is shown that with EIT induced in the multi-level Rb system by laser fields, the linear absorption is suppressed and the nonlinear susceptibility is enhanced, which enables studies of nonlinear optics in the cold atoms with slow photons and at low light intensities. Three independent experiments are described and the experimental results are presented. First, an experimental method that can produce simultaneously co-propagating slow and fast light pulses is discussed and the experimental demonstration is reported. Second, it is shown that in a three-level Rb system coupled by multi-color laser fields, the multi-channel two-photon Raman transitions can be manipulated by the relative phase and frequency of a control laser field. Third, a scheme for all-optical switching near single photon levels is developed. The scheme is based on the phase-dependent multi-photon interference in a coherently coupled four-level system. The phase dependent multi-photon interference is observed and switching of a single light pulse by a control pulse containing ∼20 photons is demonstrated. These experimental studies reveal new phenomena manifested by quantum coherence and interference in cold atoms, contribute to the advancement of fundamental quantum optics and nonlinear optics at ultra-low light intensities, and may lead to the development of new techniques to control quantum states of atoms and photons, which will be useful for applications in quantum measurements and quantum photonic devices.
Resumo:
Groundwater systems of different densities are often mathematically modeled to understand and predict environmental behavior such as seawater intrusion or submarine groundwater discharge. Additional data collection may be justified if it will cost-effectively aid in reducing the uncertainty of a model's prediction. The collection of salinity, as well as, temperature data could aid in reducing predictive uncertainty in a variable-density model. However, before numerical models can be created, rigorous testing of the modeling code needs to be completed. This research documents the benchmark testing of a new modeling code, SEAWAT Version 4. The benchmark problems include various combinations of density-dependent flow resulting from variations in concentration and temperature. The verified code, SEAWAT, was then applied to two different hydrological analyses to explore the capacity of a variable-density model to guide data collection. ^ The first analysis tested a linear method to guide data collection by quantifying the contribution of different data types and locations toward reducing predictive uncertainty in a nonlinear variable-density flow and transport model. The relative contributions of temperature and concentration measurements, at different locations within a simulated carbonate platform, for predicting movement of the saltwater interface were assessed. Results from the method showed that concentration data had greater worth than temperature data in reducing predictive uncertainty in this case. Results also indicated that a linear method could be used to quantify data worth in a nonlinear model. ^ The second hydrological analysis utilized a model to identify the transient response of the salinity, temperature, age, and amount of submarine groundwater discharge to changes in tidal ocean stage, seasonal temperature variations, and different types of geology. The model was compared to multiple kinds of data to (1) calibrate and verify the model, and (2) explore the potential for the model to be used to guide the collection of data using techniques such as electromagnetic resistivity, thermal imagery, and seepage meters. Results indicated that the model can be used to give insight to submarine groundwater discharge and be used to guide data collection. ^