The Use of Self-Report and Drugs Tests in the Measurement of Illicit Drug Consumpiton

We use data from the New England and Wales Arrestee Drug Abuse Monitoring (NEW-ADAM) programme to assess the validity of self-report measures of illicit drug use and to evaluate the use of alternative drug testing strategies within survey enquiries. Our analysis of the NEW-ADAM data reveals that bio-assay measurements of drug use tend not to be very sensitive to the cut-off levels selected for screening tests, a result that holds for cannabis, cocaine and opiates. We also show that a self-reported history of previous drug use can be used as a way of identifying individuals who are potential under-reporters of current drug use. This suggests a selective drug testing strategy which can reduce dramatically the cost of drug testing without comprising the accuracy of measurements of illicit drug use.Drugs testing; Self-reports; Concordance; Testing Strategies

Nominal and Real Exchange Rate Change by China: Global Impacts on Agricultural Prices

Replaced with revised version of paper 06/15/07.Demand and Price Analysis, International Relations/Trade,

Futures Basis for Cotton: Impact of Globalization and Structural Change

A model of commodity futures contract basis was developed based on Working’s theory of the price of storage. An error-correction model was estimated for the basis for the InterContinental Exchange (ICE) #2 cotton contract maturing in December during 2000-08. The model was also extended to incorporate the impact of changes in market activity that evolved as financial markets and commodity price behavior underwent significant changes after 2005. The model captured the inversion of basis following the collapse of China’s crop in 2003, but the shock realized during 2008 may have been in part driven by one-time events not included in the model. Estimates from the error-correction model suggest an extended period for the return of basis to equilibrium, spanning from about 1 ½ to 2 months.Basis, futures markets, cotton, error-correction model, Agribusiness, Demand and Price Analysis, Marketing,

U.S. Cotton Prices and the World Cotton Market; Forecasting and Structural Change

This report analyzes recent structural changes in the world cotton industry and develops a statistical model that reflects current drivers of U.S. cotton prices. Legislative changes in 2008 authorized USDA to resume publishing cotton price forecasts for the first time in nearly 80 years. Systematic problems have become apparent in the forecasting models used by USDA and elsewhere, highlighting the need for an updated review of price relationships. A structural break in the U.S. cotton industry occurred in 1999, and world cotton supply has become an important determinant of U.S. cotton prices, along with China’s trade and production policy. The model developed here forecasts changes in the U.S. upland cotton farm price based on changes in U.S. cotton supply, the U.S. stocks-to-use ratio (S/U), China’s net imports as a share of world consumption, the foreign supply of cotton, and selected farm policy parameters.forecasting, cotton, price, demand, trade, structural change, farm programs., Agricultural and Food Policy, Agricultural Finance, Crop Production/Industries, Marketing, Production Economics,

U.S. Cotton Prices and the World Cotton Market: Forecasting and Structural Change

The purpose of this study was to analyze structural changes that took place in the cotton industry in recent years and develop a statistical model that reflects the current drivers of U.S. cotton prices. Legislative changes authorized the U.S. Department of Agriculture to resume publishing cotton price forecasts for the first time in 79 years. In addition, systematic problems have become apparent in the forecasting models used by USDA and elsewhere, highlighting the need for an updated review of price relationships. This study concluded that a structural break in the U.S. cotton industry occurred in 1999, and that world cotton supply has become an important determinant of U.S. cotton prices. China’s trade and production policy also continues to be an important factor in price determination. The model developed here forecasts changes in the U.S. upland cotton farm price based on changes in U.S. cotton supply, changes in U.S. stocks-to-use ratio (S/U), changes in China’s net imports as a share of world consumption, selected farm policy parameters, and changes in the foreign supply of cotton.forecasting, cotton, price, demand, trade, structural change, farm programs., Demand and Price Analysis, Q100, Q110, Q130,

Through-life modelling of nano-satellite power system dynamics

This paper presents a multi-fidelity approach to finding optimal, mission-specific power system configurations for CubeSats. The methodology begins with propagation of the orbit elements over the mission lifetime, via a continuous-time model, accounting for orbital perturbations (drag, solar radiation and non-spherical geo-potential). Analytical sizing of the power system is then achieved at discrete long-term intervals, to account for the effects of variations in environmental conditions over the mission life. This sizing is based on worst case power demand and provides inputs to a numerical assessment of the in-flight energy collection for each potential solar array deployment configuration. Finally, two objective functions (minimum deviation about the orbit average power and maximum average power over the entire mission) are satisfied to identify the configurations most suitable for the specific mission requirement. Most Nano-satellites are designed with relatively simple, static-models only and tend to be over-engineered as a result, often leading to a power-limited system. The approach described here aims to reduce the uncertainty in energy collection during flight and provide a robust approach to finding the optimal solution for a given set of mission requirements

Parametric CubeSat flight simulation architecture

This paper presents the architecture of a system of models that provides realistic simulation of the dynamic, in-orbit behaviour of a CubeSat. Time-dependent relationships between sub-systems and between the satellite and external nodes (ground stations and celestial bodies) are captured through numerical analysis of a multi-disciplinary set of state variables including position, attitude, stored energy, stored data and system temperature. Model-Based Systems Engineering and parametric modelling techniques are employed throughout to help visualise the models and ensure flexibility and expandability. Operational mode states are also incorporated within the design, allowing the systems engineer to assess flight behaviour over a range of mission scenarios. Finally, both long and short term dynamics are captured using a coupled-model philosophy; described as Lifetime and Operations models. An example mission is analysed and preliminary results are presented as an illustration of early capabilities