Thermal contact resistance in vacuum.
Similar or dissimilar materials thermal contact resistance in vacuum with negligible film effect, obtaining constriction resistance
THERMAL CONDUCTOR↗
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Results for “Resistance”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Preliminary Investigation of the Heat Shock Resistant Properties of Molybdenum Disilicide Blades Under Centrifugal Load
An investigation to determine the heat-shock resistant properties of two molybdenum disilicide turbine blades under centrifugal loads imposed by turbine rotation is presented. Molybdenum disilicide turbine blades fabricated by hot-pressing techniques withstood heat-shock conditions under blade centrifugal stresses up to 5350 pounds per square inch. Additional development is required before the heat-shock resistant properties of molybdenum disilicide are satisfactory for turbine-blade application.
MATERIALS, PROPERTIES-THERMAL↗
Resistance Tests of a 1/16 Size Model of the Hughes-kaiser Flying Boat, NACA Model 183
Tank tests were made of a hull model of the Hughes-Kaiser cargo airplane for estimates of take-off performance and maximum gross load for take-off. At hump speeds, with the model free to trim, the trim and resistance were high, which resulted in a load-resistance ratio of approximately 4.0 for a gross load coefficient of 0.75. With a 4000,000-lb load, the full size craft may take off in 69 sec over a distance of 5600 ft.
TANK TESTS (NACA-#1)↗
Skeletal unloading causes resistance of osteoprogenitor cells to parathyroid hormone and to insulin-like growth factor-I
Skeletal unloading decreases bone formation and osteoblast number in vivo and decreases the number and proliferation of bone marrow osteoprogenitor (BMOp) cells in vitro. We tested the ability of parathyroid hormone (PTH) to stimulate BMOp cells in vivo by treating Sprague Dawley rats (n = 32) with intermittent PTH(1-34) (1 h/day at 8 microg/100 g of body weight), or with vehicle via osmotic minipumps during 7 days of normal weight bearing or hind limb unloading. Marrow cells were flushed from the femur and cultured at the same initial density for up to 21 days. PTH treatment of normally loaded rats caused a 2.5-fold increase in the number of BMOp cells, with similar increases in alkaline phosphatase (ALP) activity and mineralization, compared with cultures from vehicle-treated rats. PTH treatment of hind limb unloaded rats failed to stimulate BMOp cell number, ALP activity, or mineralization. Hind limb unloading had no significant effect on PTH receptor mRNA or protein levels in the tibia. Direct in vitro PTH challenge of BMOp cells isolated from normally loaded bone failed to stimulate their proliferation and inhibited their differentiation, suggesting that the in vivo anabolic effect of intermittent PTH on BMOp cells was mediated indirectly by a PTH-induced factor. We hypothesize that this factor is insulin-like growth factor-I (IGF-I), which stimulated the in vitro proliferation and differentiation of BMOp cells isolated from normally loaded bone, but not from unloaded bone. These results suggest that IGF-I mediates the ability of PTH to stimulate BMOp cell proliferation in normally loaded bone, and that BMOp cells in unloaded bone are resistant to the anabolic effect of intermittent PTH therapy due to their resistance to IGF-I.
NASA Discipline Musculoskeletal↗
Insulation Resistance Degradation in Ni-BaTiO3 Multilayer Ceramic Capacitors
Insulation resistance (IR) degradation in Ni-BaTiO3 multilayer ceramic capacitors has been characterized by the measurement of both time to failure and direct-current (DC) leakage current as a function of stress time under highly accelerated life test conditions. The measured leakage current-time dependence data fit well to an exponential form, and a characteristic growth time SD can be determined. A greater value of tau(sub SD) represents a slower IR degradation process. Oxygen vacancy migration and localization at the grain boundary region results in the reduction of the Schottky barrier height and has been found to be the main reason for IR degradation in Ni-BaTiO3 capacitors. The reduction of barrier height as a function of time follows an exponential relation of phi (𝑡)=phi (0)e(exp -2Κt), where the degradation rate constant 𝐾=𝐾o𝑒(𝐸𝑘/𝑘𝑇) is inversely proportional to the mean time to failure (MTTF) and can be determined using an Arrhenius plot. For oxygen vacancy electromigration, a lower barrier height phi(0) will favor a slow IR degradation process, but a lower phi(0) will also promote electronic carrier conduction across the barrier and decrease the insulation resistance. As a result, a moderate barrier height phi(0) (and therefore a moderate IR value) with a longer MTTF (smaller degradation rate constant 𝐾) will result in a minimized IR degradation process and the most improved reliability in Ni-BaTiO3 multilayer ceramic capacitors.
dielectric degradation↗
Temperature Dependence of Electrical Resistance of Woven Melt-Infiltrated SiCf/SiC Ceramic Matrix Composites
Recent studies have successfully shown the use of electrical resistance (ER)measurements to monitor room temperature damage accumulation in SiC fiber reinforced SiC matrix composites (SiCf/SiC) Ceramic Matrix Composites (CMCs). In order to determine the feasibility of resistance monitoring at elevated temperatures, the present work investigates the temperature dependent electrical response of various MI (Melt Infiltrated)-CVI (Chemical Vapor Infiltrated) SiC/SiC composites containing Hi-Nicalon Type S, Tyranno ZMI and SA reinforcing fibers. Test were conducted using a commercially available isothermal testing apparatus as well as a novel, laser-based heating approach developed to more accurately simulate thermomechanical testing of CMCs. Secondly, a post-test inspection technique is demonstrated to show the effect of high-temperature exposure on electrical properties. Analysis was performed to determine the respective contribution of the fiber and matrix to the overall composite conductivity at elevated temperatures. It was concluded that because the silicon-rich matrix material dominates the electrical response at high temperature, ER monitoring would continue to be a feasible method for monitoring stress dependent matrix cracking of melt-infiltrated SiC/SiC composites under high temperature mechanical testing conditions. Finally, the effect of thermal gradients generated during localized heating of tensile coupons on overall electrical response of the composite is determined.
Ceramic Matrix Composites↗
Biophysical Impacts of Earth Greening Largely Controlled by Aerodynamic Resistance
Satellite observations show widespread increasing trends of leaf area index (LAI), known as the Earth greening. However, the biophysical impacts of this greening on land surface temperature (LST) remain unclear. Here, we quantify the biophysical impacts of Earth greening on LST from 2000 to 2014 and disentangle the contributions of different factors using a physically based attribution model. We find that 93% of the global vegetated area shows negative sensitivity of LST to LAI increase at the annual scale, especially for semiarid woody vegetation. Further considering the LAI trends (P ≤ 0.1), 30% of the global vegetated area is cooled by these trends and 5% is warmed. Aerodynamic resistance is the dominant factor in controlling Earth greening’s biophysical impacts: The increase in LAI produces a decrease in aerodynamic resistance, thereby favoring increased turbulent heat transfer between the land and the atmosphere, especially latent heat flux.
Greening↗
Characterizing Antibiotic Resistance in Microgravity Environments
The gram-positive bacterium Staphylococcus aureus and the gram-negative Pseudomonas aeruginosa are two of NASA’s designated “medically important microorganisms” commonly co-isolated from spaceflight environments like the International Space Station (ISS). Prior studies demonstrate evidence of increased virulence and antibiotic resistance of each bacterium when grown as single species in space. “Characterizing Antibiotic Resistance in Microgravity Environments” (CARMEn) is an autonomous 30-day ISS payload experiment probing the phenotypic changes of S. aureus and P. aeruginosa biofilms grown together in microgravity. Phenotypic changes are probed through three parallel experiments measuring Extracellular Matrix (ECM) production, antibiotic tolerance, and RNA expression respectively. The ECM experiment uses time-lapse imaging to collect observational morphological data from biofilms stained with Congo Red and Coomassie Blue, the antibiotic tolerance experiment utilizes E-strip testing once samples return to Earth, and RNA expression is measured through RNAseq of samples treated with RNAProtect® during spaceflight.
Antibiotic resistance↗
Evaluation Of Corrosion-Resistant Alloys for Use in Acidic and Marine Launch Environments at NASA Kennedy Space Center: 20-Year Study
After the completion of an initial three-year study to qualify corrosion-resistant stainless steel tubing for use in NASA Kennedy Space Center’s acidic and marine launch environment, test specimens remained exposed at the KSC Beachside Atmospheric Corrosion Test Site for long-term exposure. NASA KSC’s lifetime requirement for most ground support equipment is twenty years. After twenty-one years of marine exposure, NASA KSC took the unique opportunity to reevaluate the tubing after long-term exposure to better understand the corrosion resistance of these alloys as they reached their expected lifetime requirement. Metallurgical and corrosion analysis was performed on the CRES tubing components and the alloys were rated on performance. A summary of CRES alloy tubing corrosion-related performance after 20 years of exposure in a marine launch environment is presented in this work.
NASA KSC↗
Tantalum alloys resist creep deformation at elevated temperatures
Dispersion-strengthened tantalum-base alloys possess high strength and good resistance to creep deformation at elevated temperatures in high vacuum environments. They also have ease of fabrication, good weldability, and corrosion resistance to molten alkali metals.
Buckman, R. W., Jr.↗
Reinforced thermal-shock resistant ceramics
Composite material, made by dispersing short tungsten-rhenium fibers randomly throughout zirconium oxide, is highly resistant to oxidizing environments at temperatures above 2000 degrees F. This reinforced ceramic is also thermal stress resistant.
Crump, D. N.↗
Thermal resistances of solder-boss/potting compound combinations
Formulas, which can be used as a design tool, are derived to calculate the thermal resistance of solder-boss/potting compound combinations, for different depths of a solder boss, in electronic cordwood modules. Since the solder boss is the heat source, its shape and position will affect the thermal resistance of the surrounding potting compound.
Veilleux, E. D.↗
Resistivity measurements of neutron-irradiated pure metals and Al-Zn alloys
Report presents resistivity measurements and their interpretation for neutron-irradiated pure metals and Al-Zn alloys. The influence of temperature, the role of point defects, and the aging behavior on resistivity are considered. The experimental procedures and results are discussed in detail.
Horak, J. A.↗
A theoretical study of the effect of elastic strain on the electrical resistance of thin metal films.
Elastic strain effect on electrical resistance of thin metal films, deriving equations for strain coefficient of resistance
Hudzinski, R. A.↗
Low-temperature radiation-resistant material for ball-bearing retainers
Radiation resistant material, made of polyimide polymers and S-glass cloth, is used in ball bearing retainers for extreme environments. Material displays satisfactory wear resistance, lubricity, and stability. Results of comparative tests with fluorocarbon materials are given.
Desau, P. O.↗
Determination of nonlinear resistance voltage-current relationships by measuring harmonics
Test configuration measures harmonic signal amplitudes generated in nonlinear resistance. Vacuum-type voltmeter measures low frequency sinusoidal input signal amplitude and wave-analyzer measures amplitude of harmonic signals generated in junction. Input signal harmonics amplitude must not exceed that of harmonics generated in nonlinear resistance.
Stafford, J. M.↗
Contact-resistance test probes: A concept
Devices are used in inspection of contact resistance in plated connectors after assembly into cables. System permits rapid inspection of connectors when mating connectors or special apparatus are not available, and enables source of excessive resistance to be precisely determined.
Brooks, C. H.↗
Exploratory study of oxidation-resistant aluminized slurry coatings for IN 100 and WI-52 superalloys
Production of oxidation resistant aluminized iron and nickel slurry coatings for heat resistant alloys
Smialek, J. L.↗