Persistence of Underdevelopment: Does the Type of Natural Resource Endowment Matter?

agricultural and natural resource economies, development, growth, natural resources, underdevelopment, cross-country studies

Interpretation methodology and analysis of in-flight lightning data

A methodology is presented whereby electromagnetic measurements of inflight lightning stroke data can be understood and extended to other aircraft. Recent measurements made on the NASA F106B aircraft indicate that sophisticated numerical techniques and new developments in corona modeling are required to fully understand the data. Thus the problem is nontrivial and successful interpretation can lead to a significant understanding of the lightning/aircraft interaction event. This is of particular importance because of the problem of lightning induced transient upset of new technology low level microcircuitry which is being used in increasing quantities in modern and future avionics. Inflight lightning data is analyzed and lightning environments incident upon the F106B are determined

A geomorphic and hydraulic investigation in the context of floodplain revegetation; based on a soil bioengineering application on the Mattole River, Petrolia, California, USA

As fluvial, riparian and floodplain ecosystem functions are recognised for their role supporting fisheries and ecological values, recovery of streamside vegetation is increasingly important in river 'restoration'. Fluvial geomorphology and hydraulic engineering do not yet account well for the role of vegetation in fluvial processes. This research addresses the need for greater understanding of woody riparian vegetation influences on the hydraulics of overbank flow and floodplains sedimentation. Original hypotheses, research design, and data collection were generated by the student to address this gap in knowledge. A soil bioengineering design was constructed on the Mattole River, California, to revegetate the floodplain for better fish rearing habitat. Field data collection was carried out on this unregulated river for two flood events. The sediment samples resulting from a 1.25-year flow permitted the field testing of an hydraulic flume model of vegetation trapping efficiency. From velocity profiles measured during a I5-year storm event, the bed shear stress reduction caused by the vegetation was computed to be approximately 70-90%. A survey conducted in the UK and internationally evaluated from literature, hydraulic researchers and practitioners of river revegetation, the extent of and gaps in knowledge with regard to river bank stabilisation using live vegetation. A flume flow visualisation study simulated the hydraulic behaviour observed on the Mattole floodplain, which enabled characterisation of flow behaviour through a porous filter medium. Results of this research indicate that flexible woody stems have a profound 'calming' effect on overbank flow. These effects are propagated in the downstream direction at least five and as much as ten times the width of the baffle, much further than previously indicated. This research suggests that flexible vegetation is extremely effective in trapping fine (clay) sediments, contrary to general understanding and of importance for fish habitat. For hydraulic reasons, constructed zones of shrubs, such as the siltation baffle, could be spaced further apart than current design practise indicates

Linear and nonlinear interpretation of the direct strike lightning response of the NASA F106B thunderstorm research aircraft

The objective of the work reported here is to develop a methodology by which electromagnetic measurements of inflight lightning strike data can be understood and extended to other aircraft. A linear and time invariant approach based on a combination of Fourier transform and three dimensional finite difference techniques is demonstrated. This approach can obtain the lightning channel current in the absence of the aircraft for given channel characteristic impedance and resistive loading. The model is applied to several measurements from the NASA F106B lightning research program. A non-linear three dimensional finite difference code has also been developed to study the response of the F106B to a lightning leader attachment. This model includes three species air chemistry and fluid continuity equations and can incorporate an experimentally based streamer formulation. Calculated responses are presented for various attachment locations and leader parameters. The results are compared qualitatively with measured inflight data

Evaluating lightning hazards to building environments using explicit numerical solutions of Maxwell's equations

The objective here is to describe the lightning hazards to buildings and their internal environments using advanced formulations of Maxwell's Equations. The method described is the Three Dimensional Finite Difference Time Domain Solution. It can be used to solve for the lightning interaction with such structures in three dimensions with the inclusion of a considerable amount of detail. Special techniques were developed for including wire, plumbing, and rebar into the model. Some buildings have provisions for lightning protection in the form of air terminals connected to a ground counterpoise system. It is shown that fields and currents within these structures can be significantly high during a lightning strike. Time lapse video presentations were made showing the electric and magnetic field distributions on selected cross sections of the buildings during a simulated lightning strike

The effects of the exhaust plume on the lightning triggering conditions for launch vehicles

Apollo 12 and Atlas Centaur 67 are two launch vehicles that have experienced triggered lightning strikes. Serious consequences resulted from the events; in the case of Atlas Centaur 67, the vehicle and the payload were lost. These events indicate that it is necessary to develop launch rules which would prevent such occurrences. In order to develop valid lightning related rules, it is necessary to understand the effects of the plume. Some have assumed that the plume can be treated as a perfect conductor, and have computed electric field enhancement factors on that basis. The authors have looked at the plume, and believe that these models are not correct, because they ignore the fluid motion of the conducting plates. The authors developed a model which includes this flow character. In this model, the external field is excluded from the plume as it would be for any good conductor, but, in addition, the charge must distribute so that the charge density is zero at some location in the exhaust. When this condition is included in the calculation of triggering enhancement factors, they can be two to three times larger than calculated by other methods which include a conductive plume but don't include the correct boundary conditions. Here, the authors review the relevant features of rocket exhausts for the triggered lightning problem, present an approach for including flowing conductive gases, and present preliminary calculations to demonstrate the effect that the plume has on enhancement factors