Solar radiation force modeling for TDRS orbit determination

The relative orbit determination accuracies resulting from several TDRS models are evaluated. These models include spherical, single-plate, and restricted two-plate models. The plate models can be adjusted in both area and reflectivity through differential correction. The restricted two-plate model has an Earth-pointing plate and a solar plate; the orientation of the solar plate is restricted to rotation about an axis perpendicular to the satellite's orbital plane

A comparative study of the Harris-Priester, Jacchia-Roberts, and MSIS atmospheric density models in the context of satellite orbit determination

The comparisons are summarized. The quantities compared include Bayesian weighted least squares differential correction statistics and orbit solution consistency and accuracy

Comparison of wind velocity in thunderstorms determined from measurements by a ground-based Doppler radar and an F-106B airplane

As a part of the NASA Storm Hazards Program, the wind velocity in several thunderstorms was measured by an F-106B instrumented airplane and a ground-based Doppler radar. The results of five airplane penetrations of two storms in 1980 and six penetrations of one storm in 1981 are given. Comparisons were made between the radial wind velocity components measured by the radar and the airplane. The correlation coefficients for the 1980 data and part of the 1981 data were 0.88 and 0.78, respectively. It is suggested that larger values for these coefficients may be obtained by improving the experimental technique and in particular by slaving the radar to track the airplane during such tests

Government Policy in Support of Domestic Agriculture: Costs and Benefits, The United States

Agricultural and Food Policy,

AN ANALYSIS OF FACTORS THAT AFFECT THE QUALITY OF FEDERAL LAND BANK LOANS

Financial conditions existing in agriculture are placing severe pressure on lenders as well as borrowers. Data from both good and foreclosed Federal Land Bank loans were analyzed to determine the most important characteristics leading to the failure of loans. The analysis was completed by comparing means through t-tests and the development of a discriminant model. The ratio of total debt service to total income, the debt to asset ratio, the ratio of total loan amount to appraised value, and the ratio of acres in security to acres owned were determined to be the most important discriminating variables.Agricultural Finance,

Wave propagation in anisotropic medium due to an oscillatory point source with application to unidirectional composites

The far-field displacements in an infinite transversely isotropic elastic medium subjected to an oscillatory concentrated force are derived. The concepts of velocity surface, slowness surface and wave surface are used to describe the geometry of the wave propagation process. It is shown that the decay of the wave amplitudes depends not only on the distance from the source (as in isotropic media) but also depends on the direction of the point of interest from the source. As an example, the displacement field is computed for a laboratory fabricated unidirectional fiberglass epoxy composite. The solution for the displacements is expressed as an amplitude distribution and is presented in polar diagrams. This analysis has potential usefulness in the acoustic emission (AE) and ultrasonic nondestructive evaluation of composite materials. For example, the transient localized disturbances which are generally associated with AE sources can be modeled via this analysis. In which case, knowledge of the displacement field which arrives at a receiving transducer allows inferences regarding the strength and orientation of the source, and consequently perhaps the degree of damage within the composite

Advanced flight control system study

A fly by wire flight control system architecture designed for high reliability includes spare sensor and computer elements to permit safe dispatch with failed elements, thereby reducing unscheduled maintenance. A methodology capable of demonstrating that the architecture does achieve the predicted performance characteristics consists of a hierarchy of activities ranging from analytical calculations of system reliability and formal methods of software verification to iron bird testing followed by flight evaluation. Interfacing this architecture to the Lockheed S-3A aircraft for flight test is discussed. This testbed vehicle can be expanded to support flight experiments in advanced aerodynamics, electromechanical actuators, secondary power systems, flight management, new displays, and air traffic control concepts

Adaptations of frogs to survive freezing

Five species of frogs from North America survive extensive freezing of their body fluids to temperatures as low as -8C for periods lasting at least 2 weeks. These frogs hibernate in leaf litter where subzero temperatures commonly occur during the winter. The onset of freezing triggers liver glycogenolysis and the production of high concentrations of glucose or glycerol (to 100x normal) that functions as a cryoprotectant against freezing injury. Concomitantly the release of the latent heat of crystallization as body water freezes promotes the continued function of the cardiovascular system for many hours, and serves to distribute glucose throughout the body. The water content of major organs is reduced by 50% or more during the first 24 hours of freezing, with the water being relocated and frozen in other body spaces. Organ dehydration functions to concentrate cryoprotectant and the reduce mechanical damage by ice during freezing. As freezing progresses, breathing, heart beat, and most other vital functions cease, but reanimation occurs within a few hours after thawing. The evolution of freeze tolerance in these animals illustrates the highly flexible capacities of frogs to adapt to stressful environments

Coping with the Cold: An Ecological Context for the Abundance and Distribution of Rock Sandpipers during Winter in Upper Cook Inlet, Alaska

Shorebirds are conspicuous and abundant at high northern latitudes during spring and summer, but as seasonal conditions deteriorate, few remain during winter. To the best of our knowledge, Cook Inlet, Alaska (60.6˚ N, 151.6˚ W), is the world’s coldest site that regularly supports wintering populations of shorebirds, and it is also the most northerly nonbreeding location for shorebirds in the Pacific Basin. During the winters of 1997–2012, we conducted aerial surveys of upper Cook Inlet to document the spatial and temporal distribution and number of Rock Sandpipers (Calidris ptilocnemis) using the inlet. The average survey total was 8191 ± 6143 SD birds, and the average of each winter season’s highest single-day count was 13 603 ± 4948 SD birds. We detected only Rock Sandpipers during our surveys, essentially all of which were individuals of the nominate subspecies (C. p. ptilocnemis). Survey totals in some winters closely matched the population estimate for this subspecies, demonstrating the region’s importance as a nonbreeding resource to the subspecies. Birds were most often found at only a handful of sites in upper Cook Inlet, but shifted their distribution to more southerly locations in the inlet during periods of extreme cold. Two environmental factors allow Rock Sandpipers to inhabit Cook Inlet during winter: 1) an abundant bivalve (Macoma balthica) food source and 2) current and tidal dynamics that keep foraging substrates accessible during all but extreme periods of cold and ice accretion. C. p. ptilocnemis is a subspecies of high conservation concern for which annual winter surveys may serve as a relatively inexpensive population-monitoring tool that will also provide insight into adaptations that allow these birds to exploit high-latitude environments in winter.Le printemps et l’été, les oiseaux de rivage abondent et sont bien en vue dans les latitudes de l’extrême nord, mais au fur et à mesure que les conditions saisonnières se détériorent, peu d’entre eux hivernent dans ces régions. Au meilleur de nos connaissances, l’anse Cook, en Alaska (60,6˚ N, 151,6˚ O), est l’endroit le plus froid du monde où l’on trouve régulièrement des populations d’oiseaux de rivage l’hiver. Il s’agit aussi de l’emplacement le plus nordique du bassin du Pacifique à ne pas être consacré à la reproduction des oiseaux de rivage. Au cours des hivers allant de 1997 à 2012, nous avons réalisé des levés aériens de la partie supérieure de l’anse Cook afin d’être en mesure de répertorier la répartition spatiale, la répartition temporelle et le nombre de bécasseaux des Aléoutiennes (Calidris ptilocnemis) dans l’anse. Le total moyen des levés a permis de repérer8 191 ± 6 143 (DS) oiseaux, tandis que la moyenne du dénombrement le plus élevé au cours d’une seule journée d’hiver était de 13 603 ± 4 948 (DS) oiseaux. Dans le cadre de nos levés, nous n’avons détecté que des bécasseaux des Aléoutiennes, dont tous étaient essentiellement des individus de la sous-espèce désignée (C. p. ptilocnemis). Au cours de certains hivers, les totaux des levés se rapprochaient beaucoup des estimations de population de cette sous-espèce, ce qui laisse entrevoir l’importance de cette région en tant que ressource de non-reproduction pour cette sous-espèce. La plupart du temps, ces oiseaux ne se retrouvaient qu’à quelques endroits de la partie supérieure de l’anse Cook, bien qu’ils se répartissaient plus au sud de l’anse pendant les périodes de froid extrême. Deux facteurs environnementaux permettent aux bécasseaux des Aléoutiennes d’évoluer dans l’anse Cook l’hiver : 1) une source abondante de nourriture acéphale (Macoma balthica) et 2) une dynamique de courants et de marées qui a constamment pour effet d’alimenter les oiseaux en substrat pendant toutes les périodes, sauf celles de froid extrême et d’accrétion de glace. C. p. ptilocnemis est une sous-espèce dont la conservation présente de grandes inquiétudes et pour laquelle les levés hivernaux annuels peuvent constituer un outil de surveillance de population relativement abordable qui permettra également d’en savoir plus sur les adaptations qui permettent à ces oiseaux d’exploiter les milieux de haute latitude l’hiver

Deer Use of Riparian Zones and Adjacent Pine Plantations in Texas

The authors monitored white-tailed deer (Odocoileus virginianus) use of riparian zones (RZ’s) and adjacent pine plantations of 3 age classes (young, 1 to 3 years old; intermediate, 5 to 7 years old; and older, 9 to 13 years old) using radio telemetry for 2 years on a 1,300 ha study area near Alto, TX. Riparian zones comprised 22.0 percent of the area; young, intermediate, and older pine plantations comprised 19.1 percent, 45.7 percent, and 13.2 percent, respectively. Based on data from 4 to 9 deer the first year and 12 to 17 deer the second year, home ranges averaged 103, 71, 95, and 114 ha during spring, summer, fall, and winter, respectively, and were composed primarily of intermediate-age plantations and RZ’s. Deer showed significant preferences for intermediate-age pine plantations during all seasons and for RZ’s during fall and winter. Older plantations produced little forage due to canopy closure, and were generally avoided throughout the year. Young plantations, which provided the most forage but the least cover, received relatively light yearlong use and were a minor component of deer home ranges. For females and young males, this study demonstrates that, where available, RZ’s may comprise an important component of deer home ranges in intensively managed forests