Reconfiguring islands

Thinking about islands in a global context offers a perspective that underlines the interconnectedness and flows in new ways that facilitate our understanding of the differences and disparities that are produced and even enforced through long-standing and ongoing global processes. Looking at social, cultural and economic processes in the contemporary clustering of islands that comprise sub-national island jurisdictions underlines the ways in which the intense circulation of commodities, people and ideas, connections and flows are now accentuated in an era of globalization. Gupta and Ferguson (1992: 16) suggest that globalization "differentiates the world as it connects it" and it is from this vantage point that sub-national island jurisdictions may provide an effective lens through which disparities can be viewed. Global economic processes shape and reshape islands in complex and complicated ways, and islanders have long been engaging, accommodating, resisting, embracing and initiating such changes. T he framework and analyses of the diverse experiences of sub-national island jurisdictions highlights the agency of islanders and their political machinery in ways that counter representations of island jurisdictions as dependent, spatially peripheralized and fiscally constrained. It is instructive to examine the experience of a range of islands with the same set of governance issues and structures as PEI.peer-reviewe

Are Quasar Jets Matter or Poynting Flux Dominated?

If quasar jets are accelerated by magnetic fields but terminate as matter dominated, where and how does the transition occur between the Poynting-dominated and matter-dominated regimes? To address this question, we study constraints which are imposed on the jet structure by observations at different spatial scales. We demonstrate that observational data are consistent with a scenario where the acceleration of a jet occurs within 10^{3-4} R_g. In this picture, the non-thermal flares -- important defining attributes of the blazar phenomenon - are produced by strong shocks formed in the region where the jet inertia becomes dominated by matter. Such shocks may be formed due to collisions between the portions of a jet accelerated to different velocities, and the acceleration differentiation is very likely to be related to global MHD instabilities.Comment: to appear in "Astrophysical Sources of High Energy Particles and Radiation", AIP Proceedings Series, eds. T. Bulik, G. Madejski, and B. Rudak (20-24 June 2005, Torun, Poland

Essays on Simulation-Based Estimation

Complex nonlinear dynamic models with an intractable likelihood or moments are increasingly common in economics. A popular approach to estimating these models is to match informative sample moments with simulated moments from a fully parameterized model using SMM or Indirect Inference. This dissertation consists of three chapters exploring different aspects of such simulation-based estimation methods. The following chapters are presented in the order in which they were written during my thesis. Chapter 1, written with Serena Ng, provides an overview of existing frequentist and Bayesian simulation-based estimators. These estimators are seemingly computationally similar in the sense that they all make use of simulations from the model in order to do the estimation. To better understand the relationship between these estimators, this chapters introduces a Reverse Sampler which expresses the Bayesian posterior moments as a weighted average of frequentist estimates. As such, it highlights a deeper connection between the two class of estimators beyond the simulation aspect. This Reverse Sampler also allows us to compare the higher-order bias properties of these estimators. We find that while all estimators have an automatic bias correction property (Gourieroux et al., 1993) the Bayesian estimator introduces two additional biases. The first is due to computing a posterior mean rather than the mode. The second is due to the prior, which penalizes the estimates in a particular direction. Chapter 2, also written with Serena Ng, proves that the Reverse Sampler described above targets the desired Approximate Bayesian Computation (ABC) posterior distribution. The idea relies on a change of variable argument: the frequentist optimization step implies a non-linear transformation. As a result, the unweighted draws follow a distribution that depends on the likelihood that comes from the simulations, and a Jacobian term that arises from the non-linear transformation. Hence, solving the frequentist estimation problem multiple times, with different numerical seeds, leads to an optimization-based importance sampler where the weights depend on the prior and the volume of the Jacobian of the non-linear transformation. In models where optimization is relatively fast, this Reverse Sampler is shown to compare favourably to existing ABC-MCMC or ABC-SMC sampling methods. Chapter 3, relaxes the parametric assumptions on the distribution of the shocks in simulation-based estimation. It extends the existing SMM literature, where even though the choice of moments is flexible and potentially nonparametric, the model itself is assumed to be fully parametric. The large sample theory in this chapter allows for both time-series and short-panels which are the two most common data types found in empirical applications. Using a flexible sieve density reduces the sensitivity of estimates and counterfactuals to an ad hoc choice of distribution such as the Gaussian density. Compared to existing work on sieve estimation, the Sieve-SMM estimator involves dynamically generated data which implies non-standard bias and dependence properties. First, the dynamics imply an accumulation of the bias resulting in a larger nonparametric approximation error than in static models. To ensure that it does not accumulate too much, a set decay conditions on the data generating process are given and the resulting bias is derived. Second, by construction, the dependence properties of the simulated data vary with the parameter values so that standard empirical process results, which rely on a coupling argument, do not apply in this setting. This non-standard dependent empirical process is handled through an inequality built by adapting results from the existing literature. The results hold for bounded empirical processes under a geometric ergodicity condition. This is illustrated in the paper with Monte-Carlo simulations and two empirical applications

Race, Racisim, and the Representation of Niger-Congo West African Grammar in African American language :Ebonics in Works by Paul Laurence Dunbar, Mark Twain, and Zora Neal Hurston

An analysis of selected works written in African American Language (AAL): Ebonics by Paul Laurence Dunbar, Mark Twain, and Zora Neale Hurston in historical, national American literature are used to document “Race, Racism, and the Representation of Niger-Congo West African Grammar in AAL: Ebonics. This study provides an overview of the Enlightenment period by Dr. Henry Louis Gates, Jr. which proved how world-renowned Euro-American meta-physicists justified slavery and colonization based on unsubstantiated science and religious beliefs. Further, Gates used his research to dispute the outlandish and biased historical documentation provided by some European scholars who claimed that Africans were animals and could not speak languages. During the last 50 years, renown linguist, Dr. Ernie A. Smith has provided research which has proven that slave authors could always speak languages. Evidence has demonstrated that AAs can learn to read and write languages comparable to Caucasians and all other human beings. In this study, Smith has presented a comparative analysis of Niger- Congo grammar with AAL: Ebonics’ grammar which validated that AAL: Ebonics is a continuation of the Niger-Congo grammar structure. Paul Laurence Dunbar, Mark Twain, and Zora Neal Hurston learned to speak fluently in English and “plantation talk”. In fact, when Dunbar and Joel Chandler Harris’s work in Ebonics was looked at diachronically and synchronically, it was proven that both men spoke Ebonics using the same rule-governed language. Mark Twain wrote a novel which proved that language develops through nurture vs. nature. Twain demonstrated how a slave protagonist and the slave owner’s baby learned to speak each other’s home language when the slave protagonist switched her slave son for the plantation owner’s son. In Their Eyes Were Watching God, Hurston built the first all-AA township to demonstrate how AAL: Ebonics was maintained through social isolation for 20 years. In summary, Dunbar, Twain, and Hurston documented AA history through literature. They were able to support the work of great scholars, such as, Gates, Smith and others by writing realistic stories experienced by African Americans by racist groups, such as, Jim Crow and minstrelsy who were the primary culprits of “race and racism.

Poverty and disability: A vicious circle? Evidence from Afghanistan and Zambia

Disability and poverty have a complex and interdependent relationship. It is commonly understood that persons with disabilities are more likely to be poor and that poverty may contribute to sustaining disability. This interdependency is revealed not only through an examination of poverty in terms of income but also on a broader scale through other poverty related dimensions. Just how robust is this link? This paper compares data collected from household surveys in Afghanistan and Zambia, and explores the potential link between multidimensional poverty and disability. We find evidence of lower access to health care, education and labour market for people with disabilities, whatever is the disability status, but poverty measured by an asset index is not statistically different between people with and without disabilities

Corn Productivity: The Role of Management and Biotechnology

The last few decades have seen a rapid increase in corn production, making corn the most important cereal in the world. This evolution is due in large part to rapid productivity growth for corn. Both improved genetics and improved farm management have contributed to large increases in corn yield. The paper reviews how genetics, biotechnology and management have interacted to increase agricultural productivity and reduce farm risk exposure. It documents the stellar performance of corn in terms of productivity growth. It also discusses the recent evolution of corn markets and evaluates the prospects for the future