CF6 High Pressure Compressor and Turbine Clearance Evaluations

In the CF6 Jet Engine Diagnostics Program the causes of performance degradation were determined for each component of revenue service engines. It was found that a significant contribution to performance degradation was caused by increased airfoil tip radial clearances in the high pressure compressor and turbine areas. Since the influence of these clearances on engine performance and fuel consumption is significant, it is important to accurately establish these relatonships. It is equally important to understand the causes of clearance deterioration so that they can be reduced or eliminated. The results of factory engine tests run to enhance the understanding of the high pressure compressor and turbine clearance effects on performance are described. The causes of clearance deterioration are indicated and potential improvements in clearance control are discussed

Assay Development for Investigating the Contributions of p75 Neurotrophin Receptor (p75NTR) Signaling to Neurodegeneration Associated with Parkinson’s Disease

The p75 neurotrophin receptor (p75NTR) possesses the ability to promote cell survival or apoptosis upon activation. The specific signaling cascades regulated by p75NTR in neurodegenerative pathologies are poorly understood due to the multifaceted nature of the receptor. Prior studies associate oxidative stress, a cellular condition induced by an overwhelming presence of reactive oxygen species, with promoting proteolysis and subsequent activation of p75NTR in dopaminergic neurons. Dopaminergic neurons express p75NTR and are of interest in neurodegenerative research. The degeneration of these neurons occur during the progression of Parkinson’s Disease. Here, we optimized an in vivo and an in vitro protocol for modeling Parkinson’s Disease. Another aspect of this research was to optimize an automated method to measure the degeneration index (DI) of neurons. Developing an optimized in vivo model of Parkinson’s Disease may provide insight into the role of p75NTR regarding the survival and health of dopaminergic neurons within substantia nigra and striatum regions of the brain. Developing an optimized in vitro model of Parkinson’s Disease may allow for investigation to the effects of p75NTR mediated signaling events associated with oxidative stress on cellular function. The DI is a calculation of neurite degeneration, which allows for the quantification of neurodegenerative diseases. An optimized method of analysis has provided a streamlined approach to calculating the DI and neurite fragmentation in culture. Preliminary data suggests that our optimized protocols serve as a successful model of Parkinson’s Disease and thus allow further analysis into how p75NTR signaling cascades affect cellular outcome in Parkinson’s Disease

Atmospheric drag model calibrations for spacecraft lifetime prediction

Although solar activity prediction uncertainty normally dominates decay prediction error budget for near-Earth spacecraft, the effect of drag force modeling errors for given levels of solar activity needs to be considered. Two atmospheric density models, the modified Harris-Priester model and the Jacchia-Roberts model, to reproduce the decay histories of the Solar Mesosphere Explorer (SME) and Solar Maximum Mission (SMM) spacecraft in the 490- to 540-kilometer altitude range were analyzed. Historical solar activity data were used in the input to the density computations. For each spacecraft and atmospheric model, a drag scaling adjustment factor was determined for a high-solar-activity year, such that the observed annual decay in the mean semimajor axis was reproduced by an averaged variation-of-parameters (VOP) orbit propagation. The SME (SMM) calibration was performed using calendar year 1983 (1982). The resulting calibration factors differ by 20 to 40 percent from the predictions of the prelaunch ballistic coefficients. The orbit propagations for each spacecraft were extended to the middle of 1988 using the calibrated drag models. For the Jaccia-Roberts density model, the observed decay in the mean semimajor axis of SME (SMM) over the 4.5-year (5.5-year) predictive period was reproduced to within 1.5 (4.4) percent. The corresponding figure for the Harris-Priester model was 8.6 (20.6) percent. Detailed results and conclusions regarding the importance of accurate drag force modeling for lifetime predictions are presented

CF6 Jet Engine Diagnostics Program: High pressure compressor clearance investigation

The effects of high pressure compressor clearance changes on engine performance were experimentally determined on a CF6 core engine. The results indicate that a one percent reduction in normalized average clearance, expressed as a fraction of airfoil length, improves compressor efficiency by one percent. Compressor clearances are reduced by the application of rotor bore cooling, insulation of the stator casing, and use of a low coefficient of expansion material in the aft stages. This improvement amounts to a reduction of normalized average clearance of 0.78 percent, relative to CF6-60 compressor, which is equivalent to an improvement in compressor efficiency of 0.78 percent

Anterior segment optical coherence tomography changes with introduction and discontinuation of tamsulosin

published_or_final_versio

Theory of the Hunter-Covey Interface

We established mathematical models and explored the role of a learned response (avoidance behavior) to understand and manage the hunter-covey interface. Furthermore, we examined the dynamic nature of the probability of flush, given encounter, in a population that learned to avoid hunters as time passed. Learning rate was defined as the proportion of a covey that leaves the naive population and enters the experienced population per unit of hunter-covey contact. The conditional probability of flushing and shooting at a covey, given a covey encounter, declined through the season. This is because the probability of flushing was lower for experienced than for naive coveys and the population of experienced coveys grew with exposure. Thus, quality of hunting declined at a faster rate than quail population; i.e., birds became more wary as the hunting season progresses. The birds\u27 ability to avoid hunters provided an explanation of the sudden reappearance of bobwhites contributing to reproduction in areas where hunters were unsuccessful the previous hunting season. Management can use our models to manipulate the interface and obtain a desired population following the hunting season

Produção de plantas medicinais em sistemas agroflorestais: resultados preliminares de pesquisas participativas com agricultores familiares.

bitstream/item/41998/1/CT0070.pd

Minimizing Use of Aquaculture Ponds by Double-Crested Cormorants Phalacrocorax Auritus and Other Fish-Eating Birds

Methods used to minimize abundance of double-crested cormorant (Phalacrocorax auritus), great blue herons (Ardea herodias), and great egrets (Arded alba) at aquaculture facilities have limited success because of the birds\u27 ability to habituate to the applied technique. The primary objectives of this study were to evaluate and quantify the effects of overhead lines on minimizing number of cormorants, egrets and herons. We measured the long-term (01 December 2000 to 14 April 2001) effectiveness of exclusion barriers positioned every 30 m at 8 aquaculture ponds in southeastern Arkansas and the post-removal of the barrier effects from 15 April to 31 May 2001. The exclusion barrier limited the number of cormorants landing on treatment ponds significantly (P \u3c 0.001, by 10-fold), had a greater effect on herons (P \u3c 0.001, by 19-fold), and completely excluded egrets. Over 200 hours of observations with the barriers installed and an additional 90 hours of post-treatment observation resulted in 23,200 cormorant observations at the site. Eight treatment ponds averaged 429 cormorant landings (1.9 birds per hour) compared to 4,240 cormorant s landings (15.6 birds per hour) on 8 control ponds. Although the physical barrier did not exclude all cormorants and other fish-eating birds from a pond, this technique offers a nonlethal, cost-efficient, easy installation and removal, and low maintenance method to minimize depredation at aquaculture ponds