A vector error correction forecasting model of the U.S. economy

Any research or policy analysis in economics must be consistent with the time-series properties of observed macroeconomic data. Numerous previous studies of such time series reinforce the need to specify correctly a model's multivariate stochastic structure. This paper discusses in detail the speciation of a vector error correction forecasting model that is anchored by long-run equilibrium relationships suggested by economic theory. The model includes six variables - the CPI, the implicit price deflator for GDP, real money balances (MI), the federal funds rate, the yield on long-term (10-year) government bonds, and real GDP - and four cointegrating vectors. Model forecasts during the 1990's are compared to those made by the Federal Reserve and by private forecasters.Forecasting ; Econometric models

A swimming robot actuated by living muscle tissue

Biomechatronics is the integration of biological components with artificial devices, in which the biological component confers a significant functional capability to the system, and the artificial component provides specific cellular and tissue interfaces that promote the maintenance and functional adaptation of the biological component. Based upon functional performance, muscle is potentially an excellent mechanical actuator, but the larger challenge of developing muscle-actuated, biomechatronic devices poses many scientific and engineering challenges. As a demonstratory proof of concept, we designed, built, and characterized a swimming robot actuated by two explanted frog semitendinosus muscles and controlled by an embedded microcontroller. Using open loop stimulation protocols, the robot performed basic swimming maneuvers such as starting, stopping, turning (turning radius ~400 mm) and straight-line swimming (max speed >1/3 body lengths/second). A broad spectrum antibiotic/antimycotic ringer solution surrounded the muscle actuators for long term maintenance, ex vivo. The robot swam for a total of 4 hours over a 42 hour lifespan (10% duty cycle) before its velocity degraded below 75% of its maximum. The development of functional biomechatronic prototypes with integrated musculoskeletal tissues is the first critical step toward the long term objective of controllable, adaptive and robust biomechatronic robots and prostheses

Air Carrier Technique for Row Crop Spraying Applications

This study focuses on the problem of applying spray material to upper-plant, underside-leaf surfaces of corn and soybean plants. Aircraft and ground pressureatomizer applications of spray solution were quantified. Percent coverage values were generally less than 1 % on the sampling locations. Flat and hollow cone nozzle air carrier units were developed and evaluated for spray application to the upper-plant, bottom leaf surface. The air carrier method tested within a shroud improved spray deposition to the entire plant by 100% for corn and 234% for soybeans. Deposition to the upper-plant, bottom leaf surface was increased by 900% and 400% for corn and soybean plants, respectively. Deposition uniformity was also improved with the air carrier method

Short-term studies underestimate 30-generation changes in a butterfly metapopulation

Most studies of rare and endangered species are based on work carried out within one generation, or over one to a few generations of the study organism. We report the results of a study that spans 30 generations (years) of the entire natural range of a butterfly race that is endemic to 35 km2 of north Wales, UK. Short-term studies (surveys in single years and dynamics over 4 years) of this system led to the prediction that the regional distribution would be quite stable, and that colonization and extinction dynamics would be relatively unimportant. However, a longer-term study revealed unexpectedly high levels of population turnover (local extinction and colonization), affecting 18 out of the 20 patches that were occupied at any time during the period. Modelling the system (using the 'incidence function model' (IFM) for metapopulations) also showed higher levels of colonization and extinction with increasing duration of the study. The longer-term dynamics observed in this system can be compared, at a metapopulation level, with the increased levels of variation observed with increasing time that have been observed in single populations. Long-term changes may arise from local changes in the environment that make individual patches more or less suitable for the butterfly, or from unusual colonization or extinction events that take metapopulations into alternative states. One implication is that metapopulation and population viability analyses based on studies that cover only a few animal or plant generations may underestimate extinction threats

Calculation of steady and unsteady pressures at supersonic speeds with CAP-TSD

A finite difference technique is used to solve the transonic small disturbance flow equation making use of shock capturing to treat wave discontinuities. Thus the nonlinear effects of thickness and angle of attack are considered. Such an approach is made feasible by the development of a new code called CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance), and is based on a fully implicit approximate factorization (AF) finite difference method to solve the time dependent transonic small disturbance equation. The application of the CAP-TSD code to the calculation of low to moderate supersonic steady and unsteady flows is presented. In particular, comparisons with exact linear theory solutions are made for steady and unsteady cases to evaluate shock capturing and other features of the current method. In addition, steady solutions obtained from an Euler code are used to evaluate the small disturbance aspects of the code. Steady and unsteady pressure comparisons are made with measurements for an F-15 wing model and for the RAE tailplane model

Yellow-crowned Night Herons Sighted in North Dakota

Yellow-crowned night herons (Nyctanassa violacea) sighted at four locations in North Dakota during 1976 appear to be the first observations of this species for the State. We sighted a single individual about 8 km south of Medina, North Dakota in western Stutsman County during several visits in June and July 1976. The bird was first seen on 23 June standing in a pasture adjoining an 8.5 ha semi-permanent marsh. On following visits, the heron usually was seen perched in trees at the edge of the wetland. A single yellow-crowned night heron was sighted on the same wetland on three separate occasions in June 1977. It is not known whether this was the same individual that was seen in 1976. The wetland contains dense stands of cattail (Typha spp.), hardstem bulrush (Scirpus acutus), and reed (Phragmites communis), and is bordered by open stands of cottonwood (Populus deltoides) and peach-leaved willow (Salix amygdaloides). Several black-crowned night herons (Nycticorax nycticorax) also were observed at the marsh during 1976 and 1977. Herons may have been attracted to the wetland by the presence of large numbers of leopard frogs (Rana pipiens). No yellow-crowned night heron nests were found during nest searches of the wetland in 1976 and 1977