Academic literature on the topic 'LD5655.V851 1995.G377'

<p>Infrared sensor satellites are used to monitor the conditions in the earth's upper atmosphere. In these systems, the electronic links connecting the cryogenically cooled infrared detectors to the significantly warmer amplification electronics act as thermal bridges and, consequently, the mission lifetimes of the satellites are limited due to cryogenic evaporation. High-temperature superconductor (HTS) materials have been proposed by researchers at the National Aeronautics and Space Administration Langley's Research Center (NASA-LaRC) as an alternative to the currently used manganin wires for electrical connection. The potential for using HTS films as thermal bridges has provided the motivation for the design and the analysis of a spaceflight experiment to evaluate the performance of this superconductive technology in the space environment The initial efforts were focused on the preliminary design of the experimental system which allows for the quantitative comparison of superconductive leads with manganin leads, and on the thermal conduction modeling of the proposed system (Lee, 1994). Most of the HTS materials were indicated to be potential replacements for the manganin wiresc In the continuation of this multi-year research, the objectives of this study were to evaluate the sources of heat transfer on the thermal bridges that have been neglected in the preliminary conductive model and then to develop a methodology for the estimation of the thermal conductivities of the HTS thennal bridges in space.</p> <p> The Joule heating created by the electrical current through the manganin wires was incorporated as a volumetric heat source into the manganin conductive model. The radiative heat source on the HTS thermal bridges was determined by performing a separate radiant interchange analysis within a high-Tc superconductor housing area. Both heat sources indicated no significant contribution on the cryogenic heat load, which validates the results obtained in the preliminary conduction model.</p> <p> A methodology was presented for the estimation of the thermal conductivities of the individual HTS thermal bridge materials and the effective thermal conductivities of the composite HTS thermal bridges as functions of temperature. This methodology included a sensitivity analysis and the demonstration of the estimation procedure using simulated data with added random errors. The thermal conductivities could not be estimated as functions of temperature; thus the effective thermal conductivities of the HTS thermal bridges were analyzed as constants.</p><br>Master of Science

<p>The effects of grazing by the small oligochaete, Aeolosoma, on periphyton assemblages of different algal composition and on unconditioned detritus were examined. Natural water and periphyton inoculum were collected from a littoral environment and used to construct laboratory microcosms. Changes in algal community composition, microbial respiration, and structural indices (Chlorophyll a, protein, and carbohydrate) were measured in grazed and ungrazed cultures through time in 2 to 12 d experiments.</p> <p> Grazed cultures after 10 to 12 d had dissimilar algal community compositions in both the early and late summer periphytic assemblages as measured by Pinkham and Pearson's Index of Similarity (B). Changes resulted from stimulation (Green coccoids, thin green filaments) and suppression (certain diatoms) of individual algal taxa, and not from the dramatic shifts in comunity composition and structure effected by macroinvertebrate grazing.</p><br>Master of Science

Greenhouse and field studies were conducted to determine the effects of shade on photosynthetic, growth and yield responses of "Redchief" strawberries. Plants were exposed to 0 , 30 , 47 and 63 percent shade in the greenhouse. Net photosynthesis (Pn) as measured under the shade treatments demonstrated a curvilinear decrease. Pn as measured under saturating light levels of 790 μ-tmol· m-2 · s·1 began to decrease in plants grown under 30 percent or higher shade levels. Light saturation curves for leaves expanded in full sun and then transferred to shade treatments for seven days showed a decrease in Pn saturation rate and light saturation point at 63 percent shade. Saturation curves for leaves expanded under the shade treatments exhibited a decreasing trend in saturation rate and point at all shade levels. Heavy shade (63%) reduced leaf thickness and depth of the palisade cell layers. Individual leaf area was not affected by shade treatments. As percent shade increased, total plant dry weight decreased linearly as did specific leaf weight. Shade treatments of 0, 30, 63 or 95 percent were applied over field-grown plants either in the fall during flower bud initiation, or in the fall and spring, during flower bud initiation and spring vegetative growth. Berry number was reduced as percent shade increased. Plants shaded only in the fall had higher berry number than plants shaded both in the fall and spring. Berry weight was also reduced as percent shade increased. Sugar concentration, pH and titratable acidity were not affected by shade levels or time of shade application.<br>Master of Science

<p>The nonmedical use of anabolic-androgenic steroids (AAS) is an emerging public health concern. Despite a recent call for AAS prevention by the National Institute on Drug Abuse (Lin & Erinoff, 1990), little theory-based research has been conducted on the etiology of AAS use. In the present study, the Theory of Reasoned Action (TRA) was used as a model for understanding and explaining the psychosocial factors which motivate weightlifters to use AAS.</p> <p> One-hundred-three male weightlifters (mean age = 23.3 years, range 18-39) completed a survey that assessed past drug use (including past AAS use) and constructs relevant to the TRA: attitudes about personal AAS use, subjective norms regarding personal AAS use, and intentions to use AAS over the next year. In addition, perceived behavioral control was assessed and the TRA was compared to the Theory of Planned Behavior (TPB).</p> <p> Overall, seventeen (16.50/0) of participants reported the past use of AAS and nine (8.7%) reported the intention to use AAS at sometime over the next year. Multiple regression (MR) analyses revealed that respondents' attitudes (Beta = .72, D, < .001) towards personal AAS use significantly predicted AAS intentions and explained 55% of the variability in the intention to use AAS (i.e., R2 = .55). Further, when perceived behavioral control (PBC) was added to the model, both attitudes (Beta=.54, D,<.001) and PBC (Beta =-.37, D,<.001) were significant predictors of AAS intentions. With respect to other drug use behaviors, the past use of AAS was not significantly correlated with the use of alcohol, cigarettes, chewing tobacco, marijuana, or cocaine. Similar results were found for an adolescent sub-sample of 59 male weightlifters (Mean age = 19.9).</p> <p> These results provided strong support for the TRA (TPB) as an accurate model for explaining male weightlifters' motivation (intentions) to use AAS. Implications for the primary prevention of AAS based on these models are discussed in detail.</p><br>Master of Science