Interplay between morphological and shielding effects in field emission via Schwarz-Christoffel transformation

It is well known that sufficiently strong electrostatic fields are able to change the morphology of Large Area Field Emitters (LAFEs). This phenomenon affects the electrostatic interactions between adjacent sites on a LAFE during field emission and may lead to several consequences, such as: the emitter's degradation, diffusion of absorbed particles on the emitter's surface, deflection due to electrostatic forces and mechanical stress. These consequences are undesirable for technological applications, since they may significantly affect the macroscopic current density on the LAFE. Despite the technological importance, these processes are not completely understood yet. Moreover, the electrostatic effects due to the proximity between emitters on a LAFE may compete with the morphological ones. The balance between these effects may lead to a non trivial behavior in the apex-Field Enhancement Factor (FEF). The present work intends to study the interplay between proximity and morphological effects by studying a model amenable for an analytical treatment. In order to do that, a conducting system under an external electrostatic field, with a profile limited by two mirror-reflected triangular protrusions on an infinite line, is considered. The FEF near the apex of each emitter is obtained as a function of their shape and the distance between them via a Schwarz-Christoffel transformation. Our results suggest that a tradeoff between morphological and proximity effects on a LAFE may provide an explanation for the observed reduction of the local FEF and its variation at small distances between the emitter sites.Comment: 8 pages, 7 figures, published versio

CLIMATE FORECASTING AND EMERGENCY POLICIES EVIDENCE OF OPPORTUNITIES FROM CEARÁ, BRAZIL

We take small steps towards the approximation between economic analysis and the science of climate forecasting in the formulation of policies to alleviate the impact of climatic shocks. We do so by estimating the relationship between climate variables and corn production in Ceará, an important State in the Brazilian semi-arid. Using parametric and non-parametric regression models, we first estimate the relationship between contemporaneous sea surface temperatures (SSTs) for the Pacific and Atlantic oceans and the local rainfed corn market. Next, we investigate the forecasting potential of future corn production conditional on information on current SSTs. We find strong evidence that climate determinants are important in determining current and future corn production, a key indicator of the climatic stress to which a large number of small farmers are subject in the Brazilian semi-arid. Additionally, corn production in the region is negatively correlated with federal government transfers meant to mitigate the impact of local droughts. These resources have been subject to lethargic bureaucracies, corruption and economic inefficiencies in general. The observation and forecasting of corn production can be invaluable in the design of more efficient, expeditious and transparent policies to mitigate the effects of droughts in the region.