1,343 research outputs found
Flame Retardant Effect of Aerogel and Nanosilica on Engineered Polymers
Aerogels are typically manufactured vIa high temperature and pressure-critical-point drying of a colloidal metal oxide gel filled with solvents. Aerogel materials derived from silica materials represent a structural morphology (amorphous, open-celled nanofoams) rather than a particular chemical constituency. Aerogel is not like conventional foams in that it is a porous material with extreme microporosity and composed of individual features only a few nanometers in length with a highly porous dendriticlike structure. This unique substance has unusual properties such as low thermal conductivity, refractive index and sound suppression; in addition to its exceptional ability to capture fast moving dust. The highly porous nature of the aerogel's structure provides large amounts of surface area per unit weight. For instance, a silica aerogel material with a density of 100 kilograms per cubic meters can have surface areas of around 800 to 1500 square meters per gram depending on the precursors and process utilized to produce it. To take advantage of the unique properties of silica aerogels, especially the ultra light weight and low thermal conductivity, their composites with various engineering polymers were prepared and their flammability was investigated by Cone Calorimetry. The flammability of various polystyrene/silica aerogel nanocomposites were measured. The combination of these nanocomposites with a NASA patented flame retardant SINK were also studied. The results were compared with the base polymer to show the differences between composites with different forms of silica
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Fish Bulletin 180. California Coastal Salmonid Population Monitoring: Strategy, Design, and Methods
California’s salmon and steelhead populations have experienced marked declines leading to listing of almost all of California’s anadromous salmonids under the California Endangered Species Act (CESA) and Federal Endan-gered Species Act (ESA). Both CESA and ESA listings require recovery plans that call for monitoring to provide some measure of progress toward recovery. In addition, there are related monitoring needs for other management activi-ties such as hatchery operations and fisheries management
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Clothing Longevity Protocol: final
The Clothing Longevity Protocol offers guidelines for good practice in order to aid moves towards garments that will last longer and thus to help protect brand value, screen out garments which fail prematurely and reduce the environmental impact of the clothing sector
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Bikini Atoll ionizing radiation survey, May 1985-May 1986
Between 1946 and 1958, the United States conducted 23 nuclear tests at the Bikini Atoll in the Marshall Islands, which resulted in extensive radioactive contamination of a number of islands in the atoll and prevented the timely resettlement of the native population. Although the external dose rates from beta and gamma radiation have been previously determined by aerial survey and a variety of ground measurement techniques, technical constraints limited the assessment of external beta dose rates that result from the /sup 137/Cs and /sup 90/Sr//sup 90/Y contamination on the islands. Now, because of the recent development of very thin thermoluminescent dosimeters (TLDs), the external beta dose rates can be measured. 18 refs., 7 figs., 5 tabs
Self-Healing Polymer Materials for Wire Insulation, Polyimides, Flat Surfaces, and Inflatable Structures
Materials based on low melt polyimide, polyurea, or polyurethane chemistry have been developed which exhibit self-healing properties. These high performance polymers can be utilized either by themselves or in combination with microcapsule technology to deliver self-healing properties to electrical wire insulation or in other high performance, thin wall technologies such as inflatable structures
Achilles tendon material properties are greater in the jump leg of jumping athletes
Purpose:
The Achilles tendon (AT) must adapt to meet changes in demands. This study explored AT adaptation by comparing properties within the jump and non-jump legs of jumping athletes. Non-jumping control athletes were included to control limb dominance effects.
Methods:
AT properties were assessed in the preferred (jump) and non-preferred (lead) jumping legs of male collegiate-level long and/or high jump (jumpers; n=10) and cross-country (controls; n=10) athletes. Cross-sectional area (CSA), elongation, and force during isometric contractions were used to estimate the morphological, mechanical and material properties of the ATs bilaterally.
Results:
Jumpers exposed their ATs to more force and stress than controls (all p≤0.03). AT force and stress were also greater in the jump leg of both jumpers and controls than in the lead leg (all p0.05).
Conclusion:
ATs chronically exposed to elevated mechanical loading were found to exhibit greater mechanical (stiffness) and material (Young’s modulus) properties
Paper Session II-A - Polyimide Foam Insulation Materials for Aerospace Vehicles and Spaceport Applications
Advancements in high temperature materials by NASA have led to the development of polyimide foam systems with very attractive properties. The properties generated demonstrate the suitability of these materials for use as insulation for cryogenic fuel tanks on next generation vehicles, commercial and military ships, and potentially commercial aircraft. The significance of structural polyimide foams can be realized with a reduction in the overall weight of a launch vehicle. Due to a polyimide\u27 s high operating temperature ( \u27 \u27 260°C) structural polyimide foams can potentially reduce the amount of Thermal Protection System (TPS) and TPS integration structure that is required on launch vehicles. The lowtemperature elasticity of other polyimide foams is an enabling feature for many new cryogenic applications. These high performance materials also have properties that fulfill the demanding upcoming needs in ground support equipment for a Spaceport Technology Center.
In a research study performed by Kennedy Space Center (KSC) and Langley Research Center (LaRC), polyimide foams were investigated for their physical, mechanical, thermal, and flammability properties. Variations in chemical structure, cell surface area, cell content and density on the resultant physical properties of the foams were studied. Data generated from this research revealed vital information involving foam technology and the interplay of factors such as foam density, open-closed cell content, surface area, and cell structure on the overall performance of the material. By controlling these parameters, new thermal insulation systems based on polyimide foam materials can be designed to meet demanding applications for spaceports and space vehicles
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