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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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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Collection and analysis of cometary dust during a rendezvous mission

An experimental program has been undertaken to investigate and develop methods for high-efficiency collection of dust particles during a rendezvous mission with a preselected comet. A laboratory apparatus has been designed and tested for acceleration of fine particles (0.1 to 100 microns) to velocities of 0.5 to 50 m/s. Tests of collection efficiency are being conducted under vacuum and with control of substrate temperature. Collection materials include filters, plastic films, metal foils, liquid metals, and sticky organic compounds. Results to date indicate that only certain materials will be adequate to meet collection requirements.

Clark, B. C.↗
NASA NTRS1992

Elevated acetate concentrations in the rhizosphere of Spartina alterniflora and potential influences on sulfate reduction

Acetate is important in anaerobic metabolism of non-vegetated sediments but its role in salt marsh soils was not investigated thoroughly. Acetate concentrations, oxidation (C-14) and SO4(2-) reduction (S-35) were measured in S. alterniflora soils in NH and MA. Pore water from cores contained greater than 0.1 mM acetate and in some instances greater than 1.0 mM. Non-destructive samples contained less than 0.01 mM. Acetate was associated with roots and concentrations were highest during vegetative growth and varied with changes in plant physiology. Acetate turnover was very low whether whole core or slurry incubations were used. Radiotracers injected directly into soils yielded rates of SO4(2-) reduction and acetate oxidation not significantly different from core incubation techniques. Regardless of incubation method, acetate oxidation did not account for a significant percentage of SO4(2-) reduction. These results differ markedly from data for non-vegetated coastal sediments where acetate levels are low, oxidation rate constants are high and acetate oxidation rates greatly exceed rates of SO4(2-) reduction. The discrepancy between rates of acetate oxidation and SO4(2-) reduction in marsh soils may be due either to the utilization of substrates other than acetate by SO4(2-) reducers or artifacts associated with measurements of organic utilization by rhizosphere bacteria.

Hines, Mark E.↗
NASA NTRS2019

High Performance GaN/AlGaN Ultraviolet Avalanche Photodiode Detector Technologies

Detection of ultraviolet (UV) bands provides distinct advantages for NASA, defense, and commercial applications, including increased spatial resolution, small pixel sizes, and large format arrays. AlxGa1-xN semiconductor alloys have attracted great interest for detection in the UV spectral region because of their potential for high optical gain, high sensitivity, and low dark current performance in ultraviolet avalanche photodiodes (UV-APDs). We are developing GaN/AlGaN UV-APDs that demonstrate consistent and reliable UV-APD performance and operation. For these UV detectors we have measured gains of above 5×10(exp 6) and high quantum efficiencies at ~350 nm enabled by a strong avalanche multiplication process. These UV-APDs are fabricated through high quality metal organic chemical vapor deposition (MOCVD) growth on lattice-matched, low dislocation density GaN substrates with optimized GaN/AlGaN UV-APD material growth and doping parameters. The high performance, variable-area GaN/AlGaN UV-APD detectors and arrays can be customized to a wide variety of sizes including large-area formats to enable sensing and high-resolution detection over UV bands of interest.

Sood, Ashok K.↗
NASA NTRS2019

GaN/AlGaN Avalanche Photodiode Detectors for High Performance Ultraviolet Sensing Applications

The shorter wavelengths of the ultraviolet (UV) band enable detectors to operate with increased spatial resolution, variable pixel sizes, and large format arrays, benefitting a variety of NASA, defense, and commercial applications. AlxGa1-xN semiconductor alloys, which have attracted much interest for detection in the UV spectral region, have been shown to enable high optical gains, high sensitivities with the potential for single photon detection, and low dark current performance in ultraviolet avalanche photodiodes (UV-APDs). We are developing GaN/AlGaN UV-APDs with large pixel sizes that demonstrate consistent and uniform device performance and operation. These UV-APDs are fabricated through high quality metal organic chemical vapor deposition (MOCVD) growth on lattice-matched, low dislocation density GaN substrates with optimized material growth and doping parameters. The use of these low defect density substrates is a critical element to realizing highly sensitive UV-APDs and arrays with suppressed dark current under high electric fields.Optical gains greater than 5X10 (exp 6) with enhanced quantum efficiencies over the 350-400 nm spectral range have been demonstrated, enabled by a strong avalanche multiplication process. Furthermore, we are developing 6X6 arrays of devices to test high gain UV-APD array performance at ~355 nm. These variable-area GaN/AlGaN UV-APD detectors and arrays enable advanced sensing performance over UV bands of interest with high resolution detection for NASA Earth Science applications.

Sood, Ashok K.↗
NASA NTRS1981

Fluorescent radiation converter

A fluorescence radiation converter is described which includes a substantially undoped optically transparent substrate and a waveshifter coating deposited on at least one portion of the substrate for absorption of radiation and conversion of fluorescent radiation. The coating is formed to substantially 1000 g/liter of a solvent, 70 to 200 g/liter of an organic polymer, and 0.2 to 25 g/liter of at least one organic fluorescent dye. The incoming incident radiation impinges on the coating. Radiation is absorbed by the fluorescent dye and is re-emitted as a longer wavelength radiation. Radiation is trapped within the substrate and is totally internally reflected by the boundary surface. Emitted radiation leaves the substrate ends to be detected.

Viehmann, W.↗
NASA NTRS1989

Ceramic Honeycomb Panels

Ceramic honeycomb panels serve as lightweight, heat-resistant structural members. Depending on choice of ceramic materials, panels expected to withstand temperatures as high as 1,800 degree C. Honeycomb structure made by vapor-depositing ceramic on fabric substrate woven in honeycomb pattern, then eliminating substrate by oxidizing it. Fabric made of loosely woven polymer such as polyacrylonitrile. Impregnated with organic binder such as phenolic resin for stiffness.

Cagliostro, Domenick E.↗
NASA NTRS1992

Issues/considerations and performance prediction of LEO protective coatings

Organic materials can be used in low earth orbit for long periods only if they are made to be durable to atomic oxygen in addition to the threats of ultraviolet radiation, micrometeoroid and debris impact, thermal cycling, and charged particle radiation. In many materials applications, it is more cost-effective to utilize atomic oxygen protective coatings over materials which are vulnerable to attack by atomic oxygen rather than developing alternative materials which are inherently durable. Many metal and metal oxide coatings have been shown to be potentially suitable for long term protection of organic polymers in low earth orbit. The protection afforded by thin film coatings on polymeric substrates is highly dependent on the completeness of coverage of the coating. Thus, the prime indicator of durability is the size and abundance of pin windows and scratches in the protective coating. Such defects depend on the deposition technique, smoothness of the surface to be protected, and presence of particulate contaminants. Issues and considerations relevant to substrate preparation, deposition of protective coatings, ground laboratory simulation and evaluation of threats in low earth orbit to protective materials, results of in-space tests, and the use of Monte Carlo modeling techniques to predict in-space durability are presented in graphic form.

Banks, Bruce A.↗
NASA NTRS1999

Electric organ discharges and electric images during electrolocation

Weakly electric fish use active electrolocation - the generation and detection of electric currents - to explore their surroundings. Although electrosensory systems include some of the most extensively understood circuits in the vertebrate central nervous system, relatively little is known quantitatively about how fish electrolocate objects. We believe a prerequisite to understanding electrolocation and its underlying neural substrates is to quantify and visualize the peripheral electrosensory information measured by the electroreceptors. We have therefore focused on reconstructing both the electric organ discharges (EODs) and the electric images resulting from nearby objects and the fish's exploratory behaviors. Here, we review results from a combination of techniques, including field measurements, numerical and semi-analytical simulations, and video imaging of behaviors. EOD maps are presented and interpreted for six gymnotiform species. They reveal diverse electric field patterns that have significant implications for both the electrosensory and electromotor systems. Our simulations generated predictions of the electric images from nearby objects as well as sequences of electric images during exploratory behaviors. These methods are leading to the identification of image features and computational algorithms that could reliably encode electrosensory information and may help guide electrophysiological experiments exploring the neural basis of electrolocation.

Review, Tutorial↗
NASA NTRS2018

The SPECTRAL Ice Chamber: Application to Titan's Stratospheric Ice Clouds

An ice chamber for obtaining thin-film transmission spectra of Titan-relevant organic ices between 50 and 11,700 cm−1 (200–0.85 μm) is described in detail in this work. The ice chamber, called the SPECtroscopy of Titan-Related ice AnaLogs chamber, is located in the Spectroscopy for Planetary ICes Environments laboratory at NASA Goddard Space Flight Center. Organic vapors are typically deposited between 30 and 150 K via a variable leak valve onto a chemical vapor deposition diamond substrate, where condensation directly into the solid state occurs. Quantitative thin-film infrared transmission spectra of the given ice or ice mixture are then measured, from which optical constants (complex indices of refraction) are computed. These optical constants in turn provide the necessary input for interpreting radiative transfer analyses of Cassini’s Composite InfraRed Spectrometer observations of Titan’s organic stratospheric ice clouds to determine their chemical compositions, abundances, and vertical distributions as functions of Titan latitude and season.

Anderson, C. M.↗
NASA NTRS2018

The SPECTRAL Ice Chamber: Application to Titan's Stratospheric Ice Clouds

An ice chamber for obtaining thin-film transmission spectra of Titan-relevant organic ices between 50 and 11,700 cm(exp −1) (200–0.85 μm) is described in detail in this work. The ice chamber, called the SPECtroscopy of Titan-Related ice AnaLogs chamber, is located in the Spectroscopy for Planetary ICes Environments laboratory at NASA Goddard Space Flight Center. Organic vapors are typically deposited between 30 and 150 K via a variable leak valve onto a chemical vapor deposition diamond substrate, where condensation directly into the solid state occurs. Quantitative thin-film infrared transmission spectra of the given ice or ice mixture are then measured, from which optical constants (complex indices of refraction) are computed. These optical constants in turn provide the necessary input for interpreting radiative transfer analyses of Cassini’s Composite InfraRed Spectrometer observations of Titan’s organic stratospheric ice clouds to determine their chemical compositions, abundances, and vertical distributions as functions of Titan latitude and season.

C. M. Anderson↗
NASA NTRS1990

Additives to reduce susceptibility of thermosets and thermoplastics to erosion from atomic oxygen

Polymeric materials have many attractive features such as light weight, high strength, and broad applicability in the form of films, fibers, and molded objects. In low earth orbit (LEO), these materials, when exposed on the exterior of the spacecraft, have the serious disadvantage of being susceptible to erosion by atomic oxygen (AO). AO is the most common chemical species at LEO altitudes. AO can be an extremely efficient oxidizing agent as was apparent from the extensive erosion of organic films exposed in STS missions. The mechanism for erosion involves the reaction of oxygen atoms at the surface of the substrate to form small molecular species. The susceptibility of polymeric materials varies with their chemical composition. Films with silicon atoms incorporated in the molecular structures have large coefficients of thermal expansion. This limits their utility. In an alternative approach additives were sought that mix physically and form a protective oxide layer when the film is exposed to AO. A large number of organic compounds containing silicon, germanium, or tin atoms were screened. Most were found to have very limited solubility in the polyetherimide (Ultem) films that were being protected from AO. However, one, bis(triphenyl tin) oxide, (BTO), is miscible in Ultem up to about 25 percent. Films of Ultem polyimide containing up to 25 wt percent BTO were prepared by evaporation of solvent from a solution of Ultem and BTO. The effects of AO on these films were simulated in the oxygen atmosphere of a radio frequency glow-discharge chamber. In the second part of this study, atoms were incorporated in epoxy resins. Experiments are in progress to measure the resistance of films of the cured epoxy to AO in the discharge chamber.

Orwoll, Robert A.↗
NASA NTRS1998

Distributed Pore Chemistry in Porous Organic Polymers

A method for making a biocompatible polymer article using a uniform atomic oxygen treatment is disclosed. The sub-strate may be subsequently optionally grated with a compatibilizing compound. Compatibilizing compounds may include proteins, phosphorylcholine groups, platelet adhesion preventing polymers, albumin adhesion promoters, and the like. The compatibilized substrate may also have a living cell layer adhered thereto. The atomic oxygen is preferably produced by a flowing afterglow microwave discharge, wherein the substrate resides in a sidearm out of the plasma. Also, methods for culturing cells for various purposes using the various membranes are disclosed as well. Also disclosed are porous organic polymers having a distributed pore chemistry (DPC) comprising hydrophilic and hydrophobic region, and a method for making the DPC by exposing the polymer to atomic oxygen wherein the rate of hydrophilization is greater than the rate of mass loss.

Koontz, Steven L.↗
NASA NTRS1981

High efficiency thin-film GaAs solar cells

The paper demonstrates the feasibility of producing high-efficiency GaAs solar cells with high power-to-weight ratios by organic metallic chemical vapor deposition (OM-CVD) growth of thin epi-layers on suitable substrates. An AM1 conversion efficiency of 18% (14% AM0), or 17% (13% AM0) with a 5% grid coverage is achieved for a single-crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer. Thin GaAs epi-layers OM-CVD grown can be fabricated with good crystallographic quality using a Si-substrate on which a thin Ge epi-interlayer is first deposited by CVD from GeH4 and processed for improved surface morphology

Zwerdling, S.↗
NASA NTRS1994

Plasma-Spray Metal Coating On Foam

Molds, forms, and other substrates made of foams coated with metals by plasma spraying. Foam might be ceramic, carbon, metallic, organic, or inorganic. After coat applied by plasma spraying, foam left intact or removed by acid leaching, conventional machining, water-jet cutting, or another suitable technique. Cores or vessels made of various foam materials plasma-coated with metals according to method useful as thermally insulating containers for foods, liquids, or gases, or as mandrels for making composite-material (matrix/fiber) parts, or making thermally insulating firewalls in automobiles.

Cranston, J.↗
NASA NTRS1995

Integrated optical components in thin films of polymers

The results will be reported on the study of integrated optical components based on nonlinear optical polymeric films. Polymers poly(methyl methacrylate) (PMMA) and polyimide (PI) doped with organic laser dyes 4-dicyanomethylene-2-methyl-6-p dimethylaminostyryl-4H pyran (DCM) and 1, 3, 5, 7, 8 - pentamethyl-2,6 -diethyl-pyrromethene -BF2-complex (Pyrommethene 567, PM-567) were selected as materials for light guiding films. Additionally, UV polymerized polydiacetylene (PDA) on glass substrate was used as a waveguide material. Optical waveguides were fabricated using spin coating of preoxidized silicon wafers (1.5 micrometer silicon oxide layer) with organic dye/polymer solution followed by soft baking. the modes in slab waveguides were studied using prism coupling techniques. Measured values of mode coupling angles in multimode waveguides were used to calculate film thickness and refractive index for different polarizations. Refractive index anisotropy was found in PDA waveguide. The optimal conditions of spin coating for single mode waveguide fabrication were estimated. Propagation losses were measured by collecting the light scattered from the trace of a propagating mode either by scanning photo detector or by CCD camera. Different types of light coupling techniques were used including end-dire coupling, prism and grating coupling. Mechanical printing technique was developed for coupling grating fabrication resulting in gratings with 4% diffraction efficiency. The gratings demonstrated good stability with diffraction efficiency relaxation rate 2.4 dB/hour at a temperature approximately 15-20 C below glass transition point. Dye doped waveguides were transversally pumped with frequency doubled Nd:YAG Q-switched laser producing intensive light emission with apparent 6 kW/sq cm pump threshold and spectrum narrowing near 617 nm peak in the case of DCM doped waveguide. PM-567 doped waveguide pumped with CW Ar(+) laser (514 nm wavelength) far below threshold (0.1 W/sq.cm pump power) demonstrated emission spectrum narrowing near 616 nm peak with 18% power conversion slope efficiency. In this case emission spectrum modification was caused by the enhanced light absorption along the direction of propagating waveguide modes. Changing length, thickness, and other morphlogical waveguide parameters one can modify emission spectrum in predictable direction. The results show that polymeric waveguides, especially based on high temperature polymers such as Pl, can be used to produce a varietiy of active and passive silicon compatible integrated optical components for aerospace applications.

Sarkisov, Sergey↗
NASA NTRS1997

Vinculin promotes cell spreading by mechanically coupling integrins to the cytoskeleton

Mouse F9 embryonic carcinoma 5.51 cells that lack the cytoskeletal protein vinculin spread poorly on extracellular matrix compared with wild-type F9 cells or two vinculin-transfected clones (5.51Vin3 and Vin4; Samuels et al., 1993, J. Cell Biol. 121, 909-921). In the present study, we used this model system to determine how the presence of vinculin promotes cytoskeletal alterations and associated changes in cell shape. Microscopic analysis of cell spreading at early times, revealed that 5.51 cells retained the ability to form filopodia; however, they could not form lamellipodia, assemble stress fibers, or efficiently spread over the culture substrate. Detergent (Triton X-100) studies revealed that these major differences in cell morphology and cytoskeletal organization did not result from differences in levels of total polymerized or cross-linked actin. Biochemical studies showed that 5.51 cells, in addition to lacking vinculin, exhibited slightly reduced levels of alpha-actinin and paxillin in their detergent-insoluble cytoskeleton. The absence of vinculin correlated with a decrease in the mechanical stiffness of the integrin-cytoskeleton linkage, as measured using cell magnetometry. Furthermore, when vinculin was replaced by transfection in 5.51Vin3 and 5.51Vin4 cells, the levels of cytoskeletal-associated alpha-actinin and paxillin, the efficiency of transmembrane mechanical coupling, and the formation of actin stress fibers were all restored to near wild-type levels. These findings suggest that vinculin may promote cell spreading by stabilizing focal adhesions and transferring mechanical stresses that drive cytoskeletal remodeling, rather than by altering the total level of actin polymerization or cross-linking.

NASA Program Space Biology↗
NASA NTRS2001

H2 cycling and microbial bioenergetics in anoxic sediments

The simple biochemistry of H2 is central to a large number of microbial processes, affecting the interaction of organisms with each other and with the environment. In anoxic sediments, the great majority of microbial redox processes involve H2 as a reactant, product, or potential by-product, and the thermodynamics of these processes are thus highly sensitive to fluctuations in environmental H2 concentrations. In turn, H2 concentrations are controlled by the activity of H2-consuming microorganisms, which efficiently utilize this substrate down to levels which correspond to their bioenergetic limitations. Consequently, any environmental change which impacts the thermodynamics of H2-consuming organisms is mirrored by a corresponding change in H2 concentrations. This phenomenon is illustrated in anoxic sediments from Cape Lookout Bight, NC, USA: H2 concentrations are controlled by a suite of environmental parameters (e.g., temperature, sulfate concentrations) in a fashion which can be quantitatively described by a simple thermodynamic model. These findings allow us to calculate the apparent minimum quantity of biologically useful energy in situ. We find that sulfate reducing bacteria are not active at energy yields below -18 kJ per mole sulfate, while methanogenic archaea exhibit a minimum close to -10 kJ per mole methane.

Hoehler, Tori M.↗