Natural laminar flow experiments on modern airplane surfaces

Flight and wind-tunnel natural laminar flow experiments have been conducted on various lifting and nonlifting surfaces of several airplanes at unit Reynolds numbers between 0.63 x 10 to the 6th power/ft and 3.08 x 10 to the 6th power/ft, at Mach numbers from 0.1 to 0.7, and at lifting surface leading-edge sweep angles from 0 deg to 63 deg. The airplanes tested were selected to provide relatively stiff skin conditions, free from significant roughness and waviness, on smooth modern production-type airframes. The observed transition locations typically occurred downstream of the measured or calculated pressure peak locations for the test conditions involved. No discernible effects on transition due to surface waviness were observed on any of the surfaces tested. None of the measured heights of surface waviness exceeded the empirically predicted allowable surface waviness. Experimental results consistent with spanwise contamination criteria were observed. Large changes in flight-measured performance and stability and control resulted from loss of laminar flow by forced transition. Rain effects on the laminar boundary layer caused stick-fixed nose-down pitch-trim changes in two of the airplanes tested. No effect on transition was observed for flight through low-altitude liquid-phase clouds. These observations indicate the importance of fixed-transition tests as a standard flight testing procedure for modern smooth airframes

IMPLICATIONS OF ALTERNATIVE POLICIES ON NITRATE CONTAMINATION OF GROUNDWATER

This study estimates the cost effectiveness of alternative environmental policies for controlling nitrate contamination of groundwater in the Seymour aquifer region of Texas. Results from biophysical simulation model are integrated with a farm-level optimization model. The study also compares the cost of bottled water, used as the lower-bound estimate of benefits of groundwater protection, with the least costly environmental policy. Results indicate that the least-cost policy alternative for the region is about $1 million either to farmers or to the local government and it is approximately three times the cost of bottled water.Environmental Economics and Policy,

Estimating the Market Effect of a Food Scare: The Case of Genetically Modified StarLink Corn

Genetic modification of crops has revolutionized food production, but it remains controversial due to food safety and environmental concerns. A recent food safety scare provides a natural experiment on the corn market's willingness to accept unapproved genetically modified organisms. In 2000, a genetically modified corn variety called StarLink was discovered in the food-corn supply, even though it was not approved for human consumption. To estimate the price impact of this event, we develop the relative price of a substitute method, which applies not only to the StarLink event but also to rare events in other markets. We apply this method to measure the price impact of the StarLink contamination on the U.S. corn market. We find that the contamination led to a 7 percent suppression of corn prices that lasted for at least a year.Food Consumption/Nutrition/Food Safety, Research and Development/Tech Change/Emerging Technologies, Q11, Q18, C22,

The Market Effect of a Food Scare: The Case of Genetically Modified StarLink Corn

Genetic modification of crops has revolutionized food production, but it remains controversial due to food safety concerns. A recent food safety scare provides a natural experiment on the market's willingness to accept an increase in perceived risk from genetically modified (GM) food. We analyze the market impact of contamination of the U.S. food-corn supply by a GM variety called StarLink. We find that the contamination led to a 6.8 percent discount in corn prices and that the suppression of prices lasted for at least a year.Food Consumption/Nutrition/Food Safety, Marketing,

The Effects of Additive Outliers and Measurement Errors when Testing for Structural Breaks in Variance

This paper discusses the asymptotic and finite-sample properties of CUSUM-based tests for detecting structural breaks in volatility in the presence of stochastic contamination, such as additive outliers or measurement errors. This analysis is particularly relevant for financial data, on which these tests are commonly used to detect variance breaks. In particular, we focus on the tests by Inclán and Tiao [IT] (1994) and Kokoszka and Leipus [KL] (1998, 2000), which have been intensively used in the applied literature. Our results are extensible to related procedures. We show that the asymptotic distribution of the IT test can largely be affected by sample contamination, whereas the distribution of the KL test remains invariant. Furthermore, the break-point estimator of the KL test renders consistent estimates. In spite of the good large-sample properties of this test, large additive outliers tend to generate power distortions or wrong break-date estimates in small samples.

Inference on a structural break in trend with fractionally integrated errors

Perron and Zhu (2005) established the consistency, convergence rate and limiting distributions of parameter estimates in time trends with a change in slope with or without a concurrent level change for the cases with I(1) or I(0) errors. We extend their analysis to the general case of fractionally integrated errors with memory parameter d∗. Our results uncover interesting features; e.g., with a level shift allowed, the convergence rate for the break date estimate is the same for all d∗∈(−0.5,0.5). In other cases, it is decreasing as d∗ increases. We also provide results about the so-called spurious break issue

The Impact of Avian Influenza on Vertical Price Transmission in the Egyptian Poultry Sector

In recent years, health risks have received increasing attention among consumers and created interest in analysing the relationship between food scares, food consumption and market prices. One of the most relevant and recent food scares is the avian influenza that has had important effects not only on human and animal health, but also on the economy. We assess effects of avian influenza on price transmission along the Egyptian poultry marketing chain. Although Egypt has been one of the most affected countries by avian influenza, this article is the first attempt to understand this food scare’s impacts on Egyptian poultry markets. In doing so, a multivariate smooth transition vector error correction model (STVECM) is applied to monthly poultry price data. In order to reflect consumer awareness of the crisis, an avian influenza food scare information index is developed and used within the model as a transition variable. Our results suggest that price adjustments to deviations from the market equilibrium parity depend on the magnitude of the avian influenza crisis. Results also suggest that food safety information indices, that have been widely used to assess the economic impacts of food scare crises in developed countries, also contribute to understanding the economic effects of food scare crises in developing countries.Food scare, avian influenza, price transmission, Egypt., Production Economics, C22, Q13,

PHYSICAL AND ECONOMIC MODEL INTEGRATION FOR MEASUREMENT OF THE ENVIRONMENTAL IMPACTS OF AGRICULTURAL CHEMICAL USE

Environmental Economics and Policy,