Childhood Food Insecurity in the United States

Childhood food insecurity in the United States is caused by a variety of barriers that lead to negative health outcomes for children. The COVID-19 pandemic has also impacted food insecurity for children. Policies and programs aimed at combating food insecurity have the potential to better serve the community with updates and changes

Towards a population of exoplanetary atmospheres

Today, more that 3500 exoplanets have been detected and, despite the significant progress in the field of atmospheric characterisation in the last decade, we still have a limited understanding for a small number of planets. Similarly to the field of exoplanetary detection, atmospheric population studies are the way forward in constraining which is the current condition of planets, how did they form, and how have they evolved. One of the most successful instruments for observing exoplanetary atmospheres is the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope. In particular, the use of the spatial scanning technique has given the opportunity for even more efficient observations of the brightest targets, achieving the necessary precision of 10 to 100 ppm to the flux of the star. This thesis describes the main characteristics of the WFC3/IR instrument and the process followed to extract the planetary transmission spectrum from time series of spatially scanned infrared spectra. Subsequently, I focus on the development of an automatic pipeline that enabled the analysis of the largest population of exoplanetary atmospheres, with 30 planets. This approach is vital for data processing in the future, as more dedicated instruments will provide a large number of observations. In addition, I describe the use of the above software to extract the transmission spectrum of the hot super-Earth 55 Cancri e, which suggests the existence of a light-weighted atmosphere around this planet. Finally, Wayne, a simulator focused on reproducing the above observations, is presented. The parallel development of both the data analysis and simulation software ensured the validity of the different steps in the data analysis process, especially when coupling between different kinds of instrumental systematics was present

High-precision stellar limb-darkening in exoplanetary transits

Characterization of the atmospheres of transiting exoplanets relies on accurate measurements of the extent of the optically thick area of the planet at multiple wavelengths with a precision $\lesssim$100 parts per million (ppm). Next-generation instruments onboard the James Webb Space Telescope (JWST) are expected to achieve $\sim$10 ppm precision for several tens of targets. A similar precision can be obtained in modelling only if other astrophysical effects, including the stellar limb-darkening, are accounted for properly. In this paper, we explore the limits on precision due to the mathematical formulas currently adopted to approximate the stellar limb-darkening, and to the use of limb-darkening coefficients obtained either from stellar-atmosphere models or empirically. We propose a new limb-darkening law with two coefficients, `power-2', which outperforms other two-coefficient laws adopted in the literature in most cases, and particularly for cool stars. Empirical limb-darkening based on two-coefficient formulas can be significantly biased, even if the light-curve residuals are nearly photon-noise limited. We demonstrate an optimal strategy to fitting for the four-coefficients limb-darkening in the visible, using prior information on the exoplanet orbital parameters to break some of the degeneracies that otherwise would prevent the convergence of the fit. Infrared observations taken with the James Webb Space Telescope (JWST) will provide accurate measurements of the exoplanet orbital parameters with unprecedented precision, which can be used as priors to improve the stellar limb-darkening characterization, and therefore the inferred exoplanet parameters, from observations in the visible, such as those taken with Kepler/K2, JWST, other past and future instruments

Entrepreneurial Capital, Inequality, and Asset Prices

This paper investigates the contribution of entrepreneurship to increasing U.S. wealth inequality. Using data from the Survey of Consumer Finances (SCF), I document that, since 2000, the increase in the wealth shares of the top 0.1% and 1% groups of households is almost exclusively driven by entrepreneurs, identified empirically as private business owner-managers. Additional evidence from the SCF points to an increase in the average returns to entrepreneurial ventures as a likely driver of these patterns. I develop analytical characterizations of summary measures of inequality in the context of a model of wealth accumulation featuring heterogeneity in investment returns and in labor earnings across households in order to examine the restrictions that the wealth distribution imposes on the underlying return heterogeneity. To match the relative position of entrepreneurs across the wealth distribution and the level of top concentration in the SCF data, as well as changing inequality from the 1990s to the 2010s, the model requires high persistence of entrepreneurial status across households and a substantial increase in the average excess return to entrepreneurial investments. The associated slow transition dynamics of the wealth distribution in the model imply that, if not reversed, recent structural shifts may lead to widening inequality for many years to come

Contagion in Futures FOREX Markets for the Post- Global Financial Crisis: A Multivariate FIGARCHcDCC Approach

This paper seeks to investigate the time-varying conditional correlations to the futures FOREX market returns. We employ a dynamic conditional correlation (DCC) Generalized ARCH (GARCH) model to find potential contagion effects among the markets. The under investigation period is 2014-2019. We focus on four major futures FOREX markets namely JPY/USD, KRW/USD, EUR/USD and INR/USD. The empirical results show an increase in conditional correlation or contagion for all the pairsof future FOREX markets. Based on the dynamic conditional correlations, KRW/USD seems to be the safest futures FOREX market. The results are of interest to policymakers who provide regulations for the futures FOREX markets. JEL Classification Codes: C58, C61, G11, G1

A nested circulation model for the North Aegean Sea

International audienceA multi-nested approach has been employed for numerical simulations in the northern part of the Aegean Sea in the framework of the MFSTEP (Mediterranean Forecast System: Toward Environmental Predictions) project. The high resolution (~1.6 km) hydrodynamic model of the North Aegean Sea (NAS) has been nested within a coarser model of the Eastern Mediterranean (resolution ~3.6 km) which is also nested within a basin scale model for the Mediterranean Sea (resolution of ~7 km). The high resolution of the NAS model allows the representation of topographic details that have never been reproduced in modelling studies of the region. Such details can enhance the simulation of coastal features, but can also influence basin-scale processes, such as the pathways of waters of Black Sea origin inflowing at the Dardanelles Straits and bifurcating through island passages. We employ comparisons of the North Aegean and Eastern Mediterranean models in terms of computed flow fields and distribution of hydrodynamic properties, to evaluate the nesting procedure, the initialization requirements and the ability of a nested model to perform reliable short term simulations that employ high resolution atmospheric forcing, when initialized from a coarser OGCM. We show that the topographic details of the high resolution, nested NAS model affect the distribution of the Dardanelles plume and the evolution of coastal currents, while the imposed high frequency, high resolution atmospheric forcing allows for the formation of an overall energetic flow field after a few days of spin-up period. Increased resolution and smaller coastal depth in the NAS simulations influence the flow through island passages and straits. A longer initialization procedure results in the establishment of stronger currents and better-developed buoyant plumes

Forex and equity markets spillover effects among USA, Brazil, Italy, Germany and Canada in the aftermath of the global financial crisis

In this paper, we investigate the spillover effects of FOREX and equity markets for USA, Brazil, Italy, Germany, and Canada on the basis of daily data. We test for contagion co - movements for the period 2010 - 2018 post-global financial crisis, using the trivariate AR - diagonal BEKK model. The estimated dynamic conditional correlations show the strongest contagion effects for the pairs of markets: S&P500 - BOVESPA, S&P500 - FTSEMIB, S&P500 - DAX30, and S&P500 - S&PTSX. For institutions, multinational corporations and active investors, a portfolio consisting of financial assets from the above markets is extremely risky

Asset Pricing of International Equity under Cross-Border Investment Frictions

We develop a tractable asset pricing model of international equity markets to investigate the impact of frictions in cross-border financial investments on equity return dynamics and cross-border equity holdings across countries. We characterize the equilibrium of the model analytically at the limit as one country becomes large relative to all other countries. Our results clarify the distinct impact of cross-border holding costs, cash-flow fundamentals comovement, and preferences on cross-border portfolio holdings, return comovement, and risk premia. The model offers a unified explanation for key empirical regularities in the cross-section of equity markets regarding cross-country return correlations, CAPM pricing errors, and equity portfolio home bias, which we document using aggregate return and portfolio holdings data from the U.S. and a cross-section of 40 other countries. Overall, our results suggest that asset pricing tests for international equity markets should take into account differences across countries in the degree of cross-border frictions

Global Capital and the Cross-Section of International Equity Return Comovement

What makes a country’s stock market more correlated with the U.S. stock market than others? This paper documents and investigates theoretically a strong positive cross-sectional relationship between the share of an equity market held by foreign investors, U.S. investors in particular, and the return correlations of 40 equity markets with the U.S. market. We argue that frictions impeding the cross-border holding of equity are key determinants of cross-border positions and equity market return correlations across countries. We develop an asset pricing model that illustrates how heterogeneity in cross-border asset holding costs can generate the observed cross-sections of cross-border positions, return correlations, and alphas with respect to a global market factor. We provide empirical evidence consistent with the model’s predictions. Overall, our results suggest that the portfolio demand channel emphasized in theoretical models of asset return comovement is indeed the primary driver of the cross-section of international equity return comovement, but only after taking into account the cross-sectional variation in frictions impeding equity investments across borders