INSTITUTIONS AND AGRICULTURAL PRODUCTIVITY IN SUB-SAHARA AFRICA

Agricultural productivity in 41 Sub-Saharan Africa (SSA) countries from 1960 to 1999 is examined by estimating a semi-nonparametric Fourier production frontier. Over the four decades the estimated rate of productivity change was 0.83% per year, although the average rate from 1985-99 was a strong 1.90% per year. Former UK colonies exhibited significantly higher productivity gains than others, while Liberia and countries that had been colonies of Portugal or Belgium exhibited net reductions in productivity. We measure a significant reduction in productivity during political conflicts and wars, and a significant increase in productivity among those countries with a measure of political rights and civil liberties.Institutional and Behavioral Economics, Productivity Analysis,

Progress in Turbulence Detection via GNSS Occultation Data

The increased availability of radio occultation (RO) data offers the ability to detect and study turbulence in the Earth's atmosphere. An analysis of how RO data can be used to determine the strength and location of turbulent regions is presented. This includes the derivation of a model for the power spectrum of the log-amplitude and phase fluctuations of the permittivity (or index of refraction) field. The bulk of the paper is then concerned with the estimation of the model parameters. Parameter estimators are introduced and some of their statistical properties are studied. These estimators are then applied to simulated log-amplitude RO signals. This includes the analysis of global statistics derived from a large number of realizations, as well as case studies that illustrate various specific aspects of the problem. Improvements to the basic estimation methods are discussed, and their beneficial properties are illustrated. The estimation techniques are then applied to real occultation data. Only two cases are presented, but they illustrate some of the salient features inherent in real data

Measuring nanometer, three-dimensional motions with light microscopy

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 173-182).by Charles Quentin Davis.Ph.D

Nonlinear dynamics of a magnetoelastic system

A dynamically buckled elastic beam is a physically realizable system exhibiting both periodic and chaotic behavior. The equations of motion are developed as a finite dimensional Galerkin approximation of an infinite degree of freedom system. Generalized eigenvalues or Lyapunov exponents are introduced as a quantitative characterization of chaos, i.e. unstable but bounded motion. A semi-discrete method for the estimation of the Lyapunov spectrum is used to investigate the influence of the forcing parameters on the system response. The equations of motion are then integrated numerically to correlate the steady state response with the value of the associated largest Lyapunov exponent

Techniques and errors in measuring cross- correlation and cross-spectral density functions

Techniques and errors in measuring cross spectral density and cross correlation functions of stationary dynamic pressure dat

The limiting semigroup of the Bernstein iterates: properties and applications

Imperial Users onl

Solution Approximation for Atmospheric Flight Dynamics Using Volterra Theory

This dissertation introduces a set of novel approaches in order to facilitate and enrich Volterra theory as a nonlinear approximation technique for constructing mathematical solutions from the governing relationships describing aircraft dynamic behavior. These approaches reconnect Volterra theory and flight mechanics research, which has not been addressed in the technical literature for over twenty years. Volterra theory is known to be viable in modeling weak nonlinearities, but is not particularly well suited for directly describing high performance aircraft dynamics. In order to overcome these obstacles and restrictions of Volterra theory, the global Piecewise Volterra Approach has been developed. This new approach decomposes a strong nonlinearity into weaker components in several sub-regions, which individually only require a low order truncated series. A novel Cause-and-Effect Analysis of these low order truncated series has also been developed. This new technique in turn allows system prediction before employing computer simulation, as well as decomposition of existing simulation results. For a computationally complex and large envelope airframe system, a Volterra Parameter-Varying Model Approach has also been developed as a systematically efficient approach to track the aircraft dynamic model and its response across a wide range of operating conditions. The analytical and numerical solutions based on the proposed methodology show the ability of Volterra theory to help predict, understand, and analyze nonlinear aircraft behavior beyond that attainable by linear theory, or more difficult to extract from nonlinear simulation, which in turn leads to a more efficient nonlinear preliminary design tool

Hydrodynamic Wave Contributions to Combustion Instability in Rockets

Experimental measurements suggest that a new source of instability in rocket motors is due to hydrodynamic disturbances. These disturbances, if ignored, could impact our assessment of rocket motor performance. In this work, the corresponding problem of hydrodynamic instability is considered. A mathematical model for these disturbances is carried out by perturbing the continuity and momentum equations. A one dimensional model which represents the wave disturbances in time and space is implemented to quantify the amplification rate, in time or space, and the wave amplitude. The only available measurements of these disturbances arise in cold flow experiments that simulate the gas dynamics in a solid rocket motor and where no real combustion takes place. The reason for cold flow experiments is the difficulty in measuring the hydrodynamic disturbances in real rockets. To gain better understanding of the interaction between hydrodynamic and combustion driven disturbances, a new approach is implemented that accounts for hydrodynamic effects on the combustion instability net system amplitude. In this model the impact of spatial hydrodynamic vortices in solid rocket motors is projected on the net system amplitude calculations. Results show that some factors play a significant role in controlling the hydrodynamic disturbances. These factors include the injection Mach number, chamber aspect ratio, admittance function and the tangential wave number. Here, the influence of each of these factors is examined. Finally, the hydrodynamic energy density is calculated and found to be small in comparison to the vortical-acoustic one

The development of a Geographic information system for environmental monitoring on the Cape Peninsula, and an assessment of the use of spot imagery for vegetation mapping

This thesis concerns the establishment of a Geographic Information System for the Cape Peninsula and the use of SPOT satellite imagery to map land cover classes. The former is seen as a necessary tool to promote judicious conservation management decisions for the fragile "Fynbos" ecosystem, and the latter as a convenient means of acquiring up-to-date information concerning the environment, and to monitor change