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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Arctic Research NASA's Cryospheric Sciences Program

Much of NASA's Arctic Research is run through its Cryospheric Sciences Program. Arctic research efforts to date have focused primarily on investigations of the mass balance of the largest Arctic land-ice masses and the mechanisms that control it, interactions among sea ice, polar oceans, and the polar atmosphere, atmospheric processes in the polar regions, energy exchanges in the Arctic. All of these efforts have been focused on characterizing, understanding, and predicting, changes in the Arctic. NASA's unique vantage from space provides an important perspective for the study of these large scale processes, while detailed process information is obtained through targeted in situ field and airborne campaigns and models. An overview of NASA investigations in the Arctic will be presented demonstrating how the synthesis of space-based technology, and these complementary components have advanced our understanding of physical processes in the Arctic.

Waleed, Abdalati↗
NASA NTRS2003

Mechanistic Studies Of Combustion And Structure Formation During Combustion Synthesis Of Advanced Materials: Phase Separation Mechanism For Bio-Alloys

Among all implant materials, Co-Cr-Mo alloys demonstrate perhaps the most useful balance of resistance to corrosion, fatigue and wear, along with strength and biocompatibility [1]. Currently, these widely used alloys are produced by conventional furnace technology. Owing to high melting points of the main alloy elements (e.g. Tm.p.(Co) ~1768 K), high-temperature furnaces and long process times (several hours) are required. Therefore, attempts to develop more efficient and flexible methods for production of such alloys with superior properties are of great interest. The synthesis of materials using combustion phenomena is an advanced approach in powder metallurgy [2]. The process is characterized by unique conditions involving extremely fast heating rates (up to 10(exp 6 K/s), high temperatures (up to 3500 K), and short reaction times (on the order of seconds). As a result, combustion synthesis (CS) offers several attractive advantages over conventional metallurgical processing and alloy development technologies. The foremost is that solely the heat of chemical reaction (instead of an external source) supplies the energy for the synthesis. Also, simple equipment, rather than energy-intensive high-temperature furnaces, is sufficient. This work was devoted to experiments on CS of Co-based alloys by utilizing thermite (metal oxide-reducing metal) reactions, where phase separation subsequently produces materials with tailored compositions and properties. Owing to high reaction exothermicity, the CS process results in a significant increase of temperature (up to 3000 C), which is higher than melting points of all products. Since the products differ in density, phase separation may be a gravitydriven process: the heavy (metallic phase) settles while the light (slag) phase floats. The goal was to determine if buoyancy is indeed the major mechanism that controls phase segregation.

Varma, A.↗
NASA NTRS1997

Smoldering Combustion Experiments in Microgravity

The Microgravity Smoldering Combustion (MSC) experiment is part of a study of the smolder characteristics of porous combustible materials in a microgravity environment. Smoldering is a non-flaming form of combustion that takes place in the interior of porous materials and takes place in a number of processes ranging from smoldering of porous insulation materials to high temperature synthesis of metals. The objective of the study is to provide a better understanding of the controlling mechanisms of smolder, both in microgravity and normal-gravity. As with many forms of combustion, gravity affects the availability of oxidizer and transport of heat, and therefore the rate of combustion. Microgravity smolder experiments, in both a quiescent oxidizing environment, and in a forced oxidizing flow have been conducted aboard the NASA Space Shuttle (STS-69 and STS-77 missions) to determine the effect of the ambient oxygen concentration and oxidizer forced flow velocity on smolder combustion in microgravity. The experimental apparatus is contained within the NASA Get Away Special Canister (GAS-CAN) Payload. These two sets of experiments investigate the propagation of smolder along the polyurethane foam sample under both diffusion driven and forced flow driven smoldering. The results of the microgravity experiments are compared with identical ones carried out in normal gravity, and are used to verify present theories of smolder combustion. The results of this study will provide new insights into the smoldering combustion process. Thermocouple histories show that the microgravity smolder reaction temperatures (Ts) and propagation velocities (Us) lie between those of identical normal-gravity upward and downward tests. These observations indicate the effect of buoyancy on the transport of oxidizer to the reaction front.

Walther, David C.↗
NASA NTRS1992

Collagen in organ development

It is important to know whether microgravity will adversely affect developmental processes. Collagens are macromolecular structural components of the extracellular matrix (ECM) which may be altered by perturbations in gravity. Interstitial collagens have been shown to be necessary for normal growth and morphogenesis in some embryonic organs, and in the mouse salivary gland, the biosynthetic pattern of these molecules changes during development. Determination of the effects of microgravity on epithelial organ development must be preceded by crucial ground-based studies. These will define control of normal synthesis, secretion, and deposition of ECM macromolecules and the relationship of these processes to morphogenesis.

NASA Discipline Cell Biology↗
NASA NTRS1999

New frontiers in design synthesis

The Intelligent Synthesis Environment (ISE), which is one of the major strategic technologies under development at NASA centers and the University of Virginia, is described. One of the major objectives of ISE is to significantly enhance the rapid creation of innovative affordable products and missions. ISE uses a synergistic combination of leading-edge technologies, including high performance computing, high capacity communications and networking, human-centered computing, knowledge-based engineering, computational intelligence, virtual product development, and product information management. The environment will link scientists, design teams, manufacturers, suppliers, and consultants who participate in the mission synthesis as well as in the creation and operation of the aerospace system. It will radically advance the process by which complex science missions are synthesized, and high-tech engineering Systems are designed, manufactured and operated. The five major components critical to ISE are human-centered computing, infrastructure for distributed collaboration, rapid synthesis and simulation tools, life cycle integration and validation, and cultural change in both the engineering and science creative process. The five components and their subelements are described. Related U.S. government programs are outlined and the future impact of ISE on engineering research and education is discussed.

User-Computer Interface↗
NASA NTRS1993

New materials: Fountainhead for new technologies and new science

The role of materials as the benchmark technologies which give epochs of human history their names continues into the present. The discovery of new materials has nearly always been the source of new materials science, and frequently of new technologies. This paper analyzes the actual processes by which new materials are synthesized, i.e. whether driven by serendipitous observations, new knowledge is pulled by the market, or integrated into a technological thrust. This analysis focuses on modern ceramic materials discoveries, since World War 2 and uses 45 years experience in materials synthesis in the author's own laboratory as case studies. A dozen different families of materials or processes are involved: hydrothermal reactions; sol-gel processing; clays and zeolites; electroceramics; zero expansion ceramics; diamond films; and radioactive waste host phases. Nanocomposite concepts introduced by the author a decade ago offer an entire, large, new class of materials which will dominate synthesis for the next period. The future of materials research for the next 25 years cannot be extrapolated from the past 25 years. We are near the asymptote for materials utilization in most metals. Likewise we are approaching saturation in improvement of many useful properties. Justifying much further 'basic' R/D for incremental improvement in civilian-oriented industries will not be easy. In materials synthesis, the near-term future is sure to emphasize not new phases, but tailored micro- and nanocomposites for chemical, electrical, optical, and magnetic uses. Unexpected new discoveries such as the Lanxide process may offer rarer chances for step function advances. The new structure of knowledge management will rely less on local research than on integration of worldwide inputs. Better scientific and technological opportunities will lie in designing knowledge intensive materials to meet the new environmental and conservation goals, and the human needs of the very large numbers at the bottom of the socio-economic structures of the world.

Rustum, Roy↗
NASA NTRS1997

Searching for Biogeochemical Cycles on Mars

The search for life on Mars clearly benefits from a rigorous, yet broad, definition of life that compels us to consider all possible lines of evidence for a martian biosphere. Recent studies in microbial ecology illustrate that the classic definition of life should be expanded beyond the traditional definition of a living cell. The traditional defining characteristics of life are threefold. First, life is capable of metabolism, that is, it performs chemical reactions that utilize energy and also synthesize its cellular constituents. Second, life is capable of self-replication. Third, life can evolve in order to adapt to environmental changes. An expanded, ecological definition of life also recognizes that life is a community of organisms that must interact with their nonliving environment through processes called biogeochemical cycles. This regenerative processing maintains, in an aqueous conditions, a dependable supply of nutrients and energy for growth. In turn, life can significantly affect those processes that control the exchange of materials between the atmosphere, ocean, and upper crust. Because metabolic processes interact directly with the environment, they can alter their surroundings and thus leave behind evidence of life. For example, organic matter is produced from single-carbon-atom precursors for the biosynthesis of cellular constituents. This leads to a reservoir of reduced carbon in sediments that, in turn, can affect the oxidation state of the atmosphere. The harvesting of chemical energy for metabolism often employs oxidation-reduction reactions that can alter the chemistry and oxidation state of the redox-sensitive elements carbon, sulfur, nitrogen, iron, and manganese. Have there ever been biogeochemical cycles on Mars? Certain key planetary processes can offer clues. Active volcanism provides reduced chemical species that biota can use for organic synthesis. Volcanic carbon dioxide and methane can serve as greenhouse gases. Thus the persistence of volcanism on Mars may well have influenced the persistence of a martian biosphere. The geologic processing of the crust can affect the availability of nutrients and also control the deposition of minerals that could have served as a medium for the preservation of fossil information. Finally, the activity of liquid water is crucial to life. Was there ever an Earth-like hydrologic cycle with rainfall? Has aqueous activity instead been restricted principally to hydrothermal activity below the surface? To what extent did the inorganic chemistry driven by sunlight and hydrothermal activity influence organic chemistry (prebiotic chemical evolution)? This paper addresses these and other key questions.

DesMarais, David J.↗
NASA NTRS2011

Nanoscale Metal Oxide Semiconductors for Gas Sensing

A report describes the fabrication and testing of nanoscale metal oxide semiconductors (MOSs) for gas and chemical sensing. This document examines the relationship between processing approaches and resulting sensor behavior. This is a core question related to a range of applications of nanotechnology and a number of different synthesis methods are discussed: thermal evaporation- condensation (TEC), controlled oxidation, and electrospinning. Advantages and limitations of each technique are listed, providing a processing overview to developers of nanotechnology- based systems. The results of a significant amount of testing and comparison are also described. A comparison is made between SnO2, ZnO, and TiO2 single-crystal nanowires and SnO2 polycrystalline nanofibers for gas sensing. The TECsynthesized single-crystal nanowires offer uniform crystal surfaces, resistance to sintering, and their synthesis may be done apart from the substrate. The TECproduced nanowire response is very low, even at the operating temperature of 200 C. In contrast, the electrospun polycrystalline nanofiber response is high, suggesting that junction potentials are superior to a continuous surface depletion layer as a transduction mechanism for chemisorption. Using a catalyst deposited upon the surface in the form of nanoparticles yields dramatic gains in sensitivity for both nanostructured, one-dimensional forms. For the nanowire materials, the response magnitude and response rate uniformly increase with increasing operating temperature. Such changes are interpreted in terms of accelerated surface diffusional processes, yielding greater access to chemisorbed oxygen species and faster dissociative chemisorption, respectively. Regardless of operating temperature, sensitivity of the nanofibers is a factor of 10 to 100 greater than that of nanowires with the same catalyst for the same test condition. In summary, nanostructure appears critical to governing the reactivity, as measured by electrical resistance of these SnO2 nanomaterials towards reducing gases. With regard to the sensitivity of the different nascent nanostructures, the electrospun nanofibers appear preferable

Hunter, Gary W.↗
NASA NTRS2001

Flame Synthesis of Single- and Multi-Walled Carbon Nanotubes and Nanofibers

Metal-catalyzed carbon nanotubes are highly sought for a diverse range of applications that include nanoelectronics, battery electrode material, catalysis, hydrogen storage media and reinforcing agents in polymer composites. These latter applications will require vast quantities of nanotubes at competitive prices to be economically feasible. Moreover, reinforcing applications may not require ultrahigh purity nanotubes. Indeed, functionalization of nanotubes to facilitate interfacial bonding within composites will naturally introduce defects into the tube walls, lessening their tensile strength. Current methods of aerosol synthesis of carbon nanotubes include laser ablation of composite targets of carbon and catalyst metal within high temperature furnaces and decomposition of a organometallics in hydrocarbons mixtures within a tube furnace. Common to each approach is the generation of particles in the presence of the reactive hydrocarbon species at elevated temperatures. In the laser-ablation approach, the situation is even more dynamic in that particles and nanotubes are borne during the transient cooling phase of the laser-induced plasma for which the temperature far exceeds that of the surrounding hot gases within the furnace process tube. A shared limitation is that more efficient methods of nanoparticle synthesis are not readily incorporated into these approaches. In contrast, combustion can quite naturally create nanomaterials such as carbon black. Flame synthesis is well known for its commercial scalability and energy efficiency. However, flames do present a complex chemical environment with steep gradients in temperature and species concentrations. Moreover, reaction times are limited within buoyant driven flows to tens of milliseconds. Therein microgravity can greatly lessen temperature and spatial gradients while allowing independent control of flame residence times. In preparation for defining the microgravity experiments, the work presented here focuses on the effect of catalyst particle size and reactant gas in 1g.

VanderWal, R. L.↗
NASA NTRS2002

Relative Amino Acid Concentrations as a Signature for Parent Body Processes of Carbonaceous Chondrites

Most meteorites are thought to have originated from objects in the asteroid belt. Carbonaceous chondrites, which contain significant amounts of organic carbon including complex organic compounds, have also been suggested to be derived from comets. The current model for the synthesis of organic compounds found in carbonaceous chondrites includes the survival of interstellar organic compounds and the processing of some of these compounds on the meteoritic parent body. The amino acid composition of five CM carbonaceous chondrites, two CIs, one CR, and one CV3 have been measured using hot water extraction-vapor hydrolysis, OPA/NAC derivatization and high-performance liquid chromatography (HPLC). Total amino acid abundances in the bulk meteorites as well as the amino acid concentrations relative to glycine = 1.0 for beta-alanine, alpha-aminoisobutyric acid and D-alanine were determined. Additional data for three Antarctic CM meteorites were obtained from the literature. All CM meteorites analyzed in this study show a complex distribution of amino acids and a high variability in total concentration ranging from approx. 15,300 to approx. 5800 parts per billion (ppb), while the CIs show a total amino acid abundance of approx. 4300 ppb. The relatively (compared to glycine) high AIB content found in all the CMs is a strong indicator that Strecker-cyanohydrin synthesis is the dominant pathway for the formation of amino acids found in these meteorites. The data from the Antarctic CM carbonaceous chondrites are inconsistent with the results from the other CMs, perhaps due to influences from the Antarctic ice that were effective during their residence time. In contrast to CMs, the data from the CI carbonaceous chondrites indicate that the Strecker synthesis was not active on their parent bodies.

Botta, Oliver↗
NASA NTRS1964

Speech communications

Analysis and synthesis of speech, and use of procedures for studying human speech processes

SPEECH↗
NASA NTRS1979

Feasibility study on the development of tough, moisture-resistant laminating resins

The potential of cyanate resins as replacement for epoxy resins in composites with graphite fiber reinforcement was investigated in an effort to provide improved moisture resistance and toughness in laminating systems at a projected cost, handleability, and processing requirements equivalent to 400 K (260 F) curing epoxies. Monomer synthesis, formulation, blending, resin preparation, catalysis studies, prepreg preparation, laminate fabrication, and testing are discussed. A graphite fiber reinforced laminate was developed with 95 percent retention of the original 363 K (180 F) flexural strength and 70 percent retention of the 363 K (180 F) short beam shear strength after 500 hour exposure to 95 + 7 relative humidity at 324 K (120 F).

Brand, R. A.↗
NASA NTRS1981

Optical processing for landmark identification

A study of optical pattern recognition techniques, available components and airborne optical systems for use in landmark identification was conducted. A data base of imagery exhibiting multisensor, seasonal, snow and fog cover, exposure, and other differences was assembled. These were successfully processed in a scaling optical correlator using weighted matched spatial filter synthesis. Distinctive data classes were defined and a description of the data (with considerable input information and content information) emerged from this study. It has considerable merit with regard to the preprocessing needed and the image difference categories advanced. A optical pattern recognition airborne applications was developed, assembled and demontrated. It employed a laser diode light source and holographic optical elements in a new lensless matched spatial filter architecture with greatly reduced size and weight, as well as component positioning toleranced.

Casasent, D.↗
NASA NTRS1982

A two-dimensional phase separation on the spherical surface of the metallic glass Au55Pb22.5Sb22.5

Recent experiments indicate that a phase separation in a spherical sample of the metallic glass Au55Pb22.5Sb22.5 occurs near the surface of the sphere. This strongly suggests either a contribution of surface-free energy to the decomposition process or a possible influence of near surface impurities absorbed during synthesis of the sphere. The surface phase separation has been studied as a function of cooling rate of the sphere. At high cooling rates (small sphere sizes), the surface separation disappears altogether suggesting that the surface of the parent liquid droplet is initially homogeneous.

Lee, M. C.↗
NASA NTRS1984

Potential utilization of glass experiments in space

Materials processing in space utilizing the microgravity environment is discussed; glass processing in particular is considered. Attention is given to the processing of glass shells, critical cooling rate and novel glasses, gel synthesis of glasses, immiscibility, surface tension, and glass composites. Soviet glass experiments in space are also enumerated.

Kreidl, N. J.↗
NASA NTRS1988

Synthesis, curing and physical behavior of maleimide terminated poly(arylene ethers)

This paper describes the synthesis of maleimide terminated poly(ether ketones) using the solution imidization process described by Summers et al. (1987). Amorphous poly(arylene ether ketones), as well as poly(arylene ether sulfones, of controlled end group functionalities and molecular weights were synthesized by nucleophilic step polymerization of bisphehol-A phenolates with activated halides, such as 4,4'-difluorobenzophenone, and 'monofunctional' end cappers such as m-aminophenol. The thermal properties of the system included glass transition temperature (Tg) values of 160-170 C, with modulus above Tg proportional to cross-link density, which in turn was reciprocally related to oligomer molecular weight. The measurements of the fracture toughness values showed the materials to be very ductile, with the toughness increasing with oligomer molecular weight.

Lyle, G. D.↗
NASA NTRS1994

Synthesis and characterization of advanced materials for Navy applications

The synthesis of ceramics and ceramic coatings through the sol-gel process has extensive application with the United States Navy and a broad range of potential commercial applications as well. This paper surveys seven specific applications for which the Navy is investigating these advanced materials. For each area, the synthetic process is described and the characteristics of the materials are discussed.

Covino, J.↗