Virtual dielectric waveguide mode description of a high-gain free-electron laser I: Theory

A set of mode-coupled excitation equations for the slowly-growing amplitudes of dielectric waveguide eigenmodes is derived as a description of the electromagnetic signal field of a high-gain free-electron laser, or FEL, including the effects of longitudinal space-charge. This approach of describing the field basis set has notable advantages for FEL analysis in providing an efficient characterization of eigenmodes, and in allowing a clear connection to free-space propagation of the input (seeding) and output radiation. The formulation describes the entire evolution of the radiation wave through the linear gain regime, prior to the onset of saturation, with arbitrary initial conditions. By virtue of the flexibility in the expansion basis, this technique can be used to find the direct coupling and amplification of a particular mode. A simple transformation converts the derived coupled differential excitation equations into a set of coupled algebraic equations and yields a matrix determinant equation for the FEL eigenmodes. A quadratic index medium is used as a model dielectric waveguide to obtain an expression for the predicted spot size of the dominant system eigenmode, in the approximation that it is a single gaussian mode.Comment: 14 page

Egyptian Agriculture in the 21st Century

In order to perform a proper, integrated assessment of potential climate change impacts on Egypt it was necessary to accurately identify important and impending issues and problems which are and will be facing the Egyptian agriculture sector into the next century. To this aim, two experts in the fields of Agronomy and Irrigated Agriculture in the Middle East were asked to travel to Egypt in order to assess the current state of Egyptian agriculture and pose possible questions and scenarios that will face Egypt in light of its current agricultural practices and management strategies. The paper examines two possible future scenarios for Egypt, one from a non-climate change perspective and the other from a climate change outlook. These scenarios are derived from the authors perspective of the current state of Egyptian agriculture. One viewpoint is that of the pessimist, where Egypt continues to practice poor agriculture management; the other is that of the optimist, with Egypt adopting sound management practices - adapting its cropping pattern and water use practices. Also addressed are the potential impacts of climate change on crop yields and recommendations for agronomic research to mitigate its potential impact

Global digital data sets of soil type, soil texture, surface slope and other properties: Documentation of archived data tape

The file structure and coding of four soils data sets derived from the Zobler (1986) world soil file is described. The data were digitized on a one-degree square grid. They are suitable for large-area studies such as climate research with general circulation models, as well as in forestry, agriculture, soils, and hydrology. The first file is a data set of codes for soil unit, land-ice, or water, for all the one-degree square cells on Earth. The second file is a data set of codes for texture, land-ice, or water, for the same soil units. The third file is a data set of codes for slope, land-ice, or water for the same units. The fourth file is the SOILWRLD data set, containing information on soil properties of land cells of both Matthews' and Food and Agriculture Organization (FAO) sources. The fourth file reconciles land-classification differences between the two and has missing data filled in

Microeconomics of Technology Adoption

There is an emerging consensus among macro-economists that differences in technology across countries accounts for the major differences in per-capita GDP and the wages of workers with similar skills across countries. Accounting for differences in technology levels across countries thus can go a long way towards understanding global inequality. One mechanism by which poorer countries can catch up with richer countries is through technological diffusion, the adoption by low-income countries of the advanced technologies produced in high-income countries. In this survey, we examine recent micro studies that focus on understanding the adoption process. If technological diffusion is a major channel by which poor countries can develop, it must be the case that technology adoption is incomplete or the inputs associated with the technologies are under-utilized in poor, or slow-growing economies. Thus, obtaining a better understanding of the constraints on adoption are useful in understanding a major component of growth.technology adoption, review