Semi-analytical and numerical methods for computing transient waves in 2D acoustic / poroelastic stratified media

Wave propagation in a stratified fluid / porous medium is studied here using analytical and numerical methods. The semi-analytical method is based on an exact stiffness matrix method coupled with a matrix conditioning procedure, preventing the occurrence of poorly conditioned numerical systems. Special attention is paid to calculating the Fourier integrals. The numerical method is based on a high order finite-difference time-domain scheme. Mesh refinement is applied near the interfaces to discretize the slow compressional diffusive wave predicted by Biot's theory. Lastly, an immersed interface method is used to discretize the boundary conditions. The numerical benchmarks are based on realistic soil parameters and on various degrees of hydraulic contact at the fluid / porous boundary. The time evolution of the acoustic pressure and the porous velocity is plotted in the case of one and four interfaces. The excellent level of agreement found to exist between the two approaches confirms the validity of both methods, which cross-checks them and provides useful tools for future researches.Comment: Wave Motion (2012) XX

Development of Empirical Models to Rate Spruce-Fir Stands in Michigan\u27s Upper Peninsula for Hazard From the Spruce Budworm (Lepidoptera: Tortricidae): A Case History

The procedure used to develop empirical models which estimate potential spruce budworm impact to spruce-fir stands in Michigan\u27s Upper Peninsula is reviewed. Criteria used to select independent variables, to select the best of alternative multiple linear regression models. and to validate final models are discussed. Preliminary, intermediate, and final results demonstrate a cyclic pattern to the development procedure. Validation is emphasized as an important step in the procedure. Implications of using the hazard-rating system as a pest management tool in the stand management process are discussed

Staple Food Consumption Patterns in Urban Kenya: Trends and Policy Implications

This study examines current consumption patterns of the main staple carbohydrate products in Nairobi -- maize, wheat, rice, and cooking bananas -- in an effort to update policy makers’ knowledge of current urban food consumption patterns. The study also identifies the factors driving changes in the amount and form of urban maize meal consumption, in order to better understand how food security policy should be designed to respond to the needs of low-income consumers. The study reveals how consumption and expenditure patterns differ according to household income. The study also examines whether the marketing channels used by the poor to secure their staple carbohydrate products differ from those used by relatively high-income consumers. The data used in this study comes from a cross-sectional random survey of 542 households in Nairobi’s urban areas and environs. The Tegemeo Institute in collaboration with the Central Bureau of Statistics (CBS) using the CBS’s NASSEP IV frame implemented the survey in November/December 2003. An earlier analysis of household survey data conducted in 1995 involving a random survey of 549 in Nairobi was used was a baseline. The results indicate that while generally the volumes of staple carbohydrate consumption have declined, it is the poorest section of the urban population that has been affected the most. Also, on average, there has been a decline in consumption of maize products and rice. The poorest have experienced the greatest decline. Consumption of wheat products has grown significantly among all groups, but particularly among higher income groups. These results also indicate a significant shift in maize meal consumption patterns. Even though posho meal consumption has declined, it continues to be a preserve of the poor because it is relatively inexpensive compared to sifted maize meal. Retail channels used to procure staple carbohydrate products vary substantially by income. The poorest income groups rely mainly on small shops (dukas) while well-off households rely both on dukas and supermarkets. These findings hold some implications for food security policy. Because wheat is emerging as an important expenditure item among the urban households, even the poor, the duty on imported wheat and wheat flour, which currently stands at 35 percent and 60 percent, respectively, may have adverse effects on urban poverty. Because Kenya is a member of COMESA and WTO, there will be external pressures to reduce these duties over time. Measures aimed at enhancing productivity and marketing of domestically produced wheat so as to lower wheat prices for the benefit of the poor should be considered.Food Security, Food Policy, Maize, Wheat, Rice, Kenya, Food Consumption/Nutrition/Food Safety, Q18,