Method of producing buried porous silicon-geramanium layers in monocrystalline silicon lattices

Lattices of alternating layers of monocrystalline silicon and porous silicon-germanium have been produced. These single crystal lattices have been fabricated by epitaxial growth of Si and Si--Ge layers followed by patterning into mesa structures. The mesa structures are stain etched resulting in porosification of the Si--Ge layers with a minor amount of porosification of the monocrystalline Si layers. Thicker Si--Ge layers produced in a similar manner emitted visible light at room temperature

Convective tipping point initiates localization of basaltic fissure eruptions

Basaltic fissure eruptions may evolve rapidly and unpredictably complicating hazard management. Localization of an elongate fissure to one or more focused vents may take days to months, and depends on fluid dynamic processes, such as thermally-driven viscous fingering, in the sub-volcanic plumbing system. However, fluid dynamics in a dyke geometry are poorly understood. We perform scaled analogue experiments to investigate convective magma exchange flow within a dyke-like conduit, and discover flow regimes ranging from chaotic mingling to stable, well-organized exchange, over the parameter space relevant for natural eruptions. Experiments are scaled via the Grashof number Gr, which is a Reynolds number for buoyancy-driven exchange flows. We propose that chaotic exchange at high Gr hinders thermally-driven localization by suppressing viscous fingering, whereas flow organization at low Gr enhances localization. Consequently, progressive decrease in Gr through increasing magma viscosity or decreasing dyke width pushes a fissure eruption towards a tipping point that results in rapid localization. Our findings indicate that current conceptual models for magma flow in a dyke require revision to account for this convective tipping point, and provide a quantitative framework for understanding the evolution of fissure eruptions

Historical perspective on net present value and equivalent annual cost

Net present value and equivalent annual cost are two discounted cash flow criteria for comparing investment proposals. Why have accountants taken to net present value? Why do engineers readily use equivalent annual cost? This paper investigates the historical development of these principles to provide an explanation of why this is so

Buried Porous Silicon-Germanium Layers in Monocrystalline Silicon Lattices

Monocrystalline semiconductor lattices with a buried porous semiconductor layer having different chemical composition is discussed and monocrystalline semiconductor superlattices with a buried porous semiconductor layers having different chemical composition than that of its monocrystalline semiconductor superlattice are discussed. Lattices of alternating layers of monocrystalline silicon and porous silicon-germanium have been produced. These single crystal lattices have been fabricated by epitaxial growth of Si and Si-Ge layers followed by patterning into mesa structures. The mesa structures are strain etched resulting in porosification of the Si-Ge layers with a minor amount of porosification of the monocrystalline Si layers. Thicker Si-Ge layers produced in a similar manner emitted visible light at room temperature

Promoting Fertilizer Use in Africa: Current Issues and Empirical Evidence from Malawi, Zambia, and Kenya

It is generally agreed that increasing agricultural productivity is critical to stimulating the rate of economic growth in Africa. There are many important and often complementary determinants of agricultural productivity. In this brief and the full paper it draws from, the focus is on fertilizer and improved seed, without intending to imply that they are the only or most significant productivity determinants.fertilizer, Africa, Malawi, Zambia, Kenya, Crop Production/Industries, Food Security and Poverty, Q18,

Promoting Fertilizer Use in Africa: Current Issues and Empirical Evidence from Malawi, Zambia, and Kenya

This study was funded jointly by the Regional Strategic Agricultural Knowledge Support System (Re-SAKSS) for Southern Africa, based at International Water Management Institute, Pretoria, South Africa, and by the United States Agency for International Development's Africa Bureau. Much of the data and analysis reported in this study was carried out under the Tegemeo Agricultural Monitoring and Policy Analysis Project, funded by USAID/Kenya; the Food Security Research Project/Markets, Trade and Enabling Environment (MATEP) Program, funded by USAID/Zambia and the Swedish International Development Agency; and by the DFID and USAID offices in Lilongwe, Malawi.fertilizer, Africa, Malawi, Zambia, Kenya, Crop Production/Industries, Q18,

Experimental oak wilt control in Missouri

A joint report by the Central States Forest Experiment Station, Forest Service, U.S. Department of Agriculture and the Missouri Agricultural Experiment Station.Digitized 2007 AES.Includes bibliographical references (page [12])

A Photogrammetric System for Model Attitude Measurement in Hypersonic Wind Tunnels

A series of wind tunnel tests have been conducted to evaluate a multi-camera videogrammetric system designed to measure model attitude in hypersonic facilities. The technique utilizes processed video data and photogrammetric principles for point tracking to compute model position including pitch, roll and yaw. A discussion of the constraints encountered during the design, and a review of the measurement results obtained from the NASA Langley Research Center (LaRC) 31-Inch Mach 10 tunnel are presented