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  • Articles
  • Other Sources  (96,240)
  • NASA Technical Reports  (96,240)
  • 2000-2004  (41,942)
  • 1980-1984  (54,298)
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  • Articles
  • Other Sources  (96,240)
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  • 1
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    Guidelines for assessment and control of noise (1984)
    In:  CASI
    Details
    Publication Date: 2009-11-17
    Description: There is an obvious need for guidelines and standards with respect to what intensities and durations of noise exposure is considered incompatible with the health and well-being of the people exposed. These guidelines would presumably be useful for the zoning of land areas to avoid overexposure of people to environmental noise and for legislative-judicial adjudication of liabilities for possible damages to individuals and groups from exposure to noise. A number of guidelines for noise exposure were promulgated by various governmental agencies for these purposes. Partly because of the need for an integrated and consistent program of noise control for all elements of the government, the United States Environmental Protection Agency (EPA) was established. In addition to previously issuing some specific documents regarding safe noise exposure limits, the EPA joined several Federal operating and regulatory agencies in issuing guidelines for considering noise in land use planning and control. Government guideline documents, as well as some issued by non-government agencies, are examined. Also, newly proposed guidelines for noise in residential areas, and the scientific basis for these guidelines, are presented.
    Keywords: ACOUSTICS
    Type: Physiol., Psychol., and Social Effects of Noise; p 607-646
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  • 2
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    Phoning Home from Mars in 2025 (2000)
    In:  CASI
    Details
    Publication Date: 2009-11-17
    Description: It's spring at Martian Outpost 3, the year 2025. The Universe Cup's on later today, and next week little Suzie celebrates her fourth birthday. Fortunately, this football fan and parent will be able to participate in both of these activities, albeit at a slight time delay, due completely to the sophisticated, high-speed quasi-real-time multimedia/navigation MarsNet surrounding Mars and tying it to Earth. Capable of moving gigabits a second in either direction, the network supports not only the multiple manned and robotic science needs of teams and devices encircling Mars, but also the very real human need for communication.
    Keywords: Communications and Radar
    Type: Concepts and Approaches for Mars Exploration; Part 1; 1; LPI-Contrib-1062
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  • 3
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    Space flight experience with the Shuttle Orbiter control system (1983)
    In:  CASI
    Details
    Publication Date: 2009-11-17
    Description: Experience gained through the Shuttle Orbital Flight Test program has matured the engineering understanding of the Shuttle on-orbit control system. The geneology of the control systems (called digital autopilots, or DAPs, and used by the Shuttle for on-orbit operations) is reviewed, the flight experience gained during the flight test program is examined within the context of preflight analysis and test results, and issues for the operational phase of the Shuttle, including constraints upon both operations and analysis still required to increase confidence in the Shuttle's ability to handle capabilities not experienced during the flight test program are addressed. Two orbital autopilots have resulted from computer memory and time constraints on a flight control system, with many different, flight phase unique requirements. The transition DAP, used for insertion and deorbit, has more active sensors and redundancy but a less complex data processing scheme excluding state estimation with fewer choices of operational mode.
    Keywords: LAUNCH VEHICLES AND SPACE VEHICLES
    Type: NASA. Langley Research Center Large Space Antenna Systems Technol., Pt. 2; p 949-967
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  • 4
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    Oxidation kinetics and soot formation (1983)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The research objective is to clarify the role of aromaticity in the soot nucleation process by determining the relative importance of phenyl radical/molecular oxygen and benzene/atomic oxygen reactions in the complex combustion of aromatic compounds. Three sets of chemical flow reactor experiments have been designed to determine the relative importance of the phenyl radical/molecular oxygen and benzene/atomic oxygen reactions. The essential elements of these experiments are 1) the use of cresols and anisole formed during the high temperature oxidation of toluene as chemical reaction indicators; 2) the in situ photolysis of molecular oxygen to provide an oxygen atom perturbation in the reacting aromatic system; and 3) the high temperature pyrolysis of phenol, the cresols and possibly anisole.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA. Lewis Research Center, Oxidation Kinetics and Soot Formation: Research Review; p 29-33
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  • 5
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    Shock tube studies of soot formation (1983)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The objective of this research is to record the time histories of the major and minor species which appear in the pyrolysis of toluene, benzene, butadiene, allene, and acetylene; to develop a set of reactions that will model the observed profiles over a wide temperature and concentration range; to identify the critical reactions that influence the pre-particle soot formation process. Toluene and benzene were chosen as two key aromatic compounds which are representative of the pyrolytic process. Butadiene, allene, and acetylene were selected to investigate the formation of aromatic compounds from non-cyclic species. The experimental apparatus used for the study consists of a shock tube coupled to a time-of-flight mass spectrometer Spectra are recorded at 30 microsecond intervals for a total observation time of 0.50 - 1.20 milliseconds. Peak heights of the species of interest in the m/e range 12-300 are measured as a function of reaction time. Calibration curves are constructed which aid the conversion of peak heights to concentrations. The mixtures range from 1 percent-6 percent fuel; the balance is neon diluent.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA. Lewis Research Center, Oxidation Kinetics and Soot Formation: Research Review; p 43-46
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  • 6
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    Role of the hydroxyl radical in soot formation (1983)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The goal of this project is to determine the role of the hydroxyl radical during formation of soot. Correlations will be sought between OH concentration and (1) the critical equivalence ratio for incipient soot formation and (2) soot yield as a function of higher equivalence ratios. The ultimate aim is the development of a quasi-global kinetic model for the pre-particulate chemistry leading to soot nucleation. Hydroxyl radical concentration profiles are measured directly in both laminar premixed and diffusion flames using the newly developed technique, laser saturated fluorescence (LSF). This method is capable of measuring OH in the presence of soot particles. Aliphatic and aromatic fuels will be used to assess the influence of fuel type on soot formation. The influence of flame temperature on the critical equivalence ratio and soot yield will be related to changes in the OH concentration profiles. LSF measurements will be augmented with auxiliary measurements of soot and PAH concentrations to allow the development of a quasi-global model for soot formation.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA. Lewis Research Center, Oxidation Kinetics and Soot Formation: Research Review; p 19-21
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  • 7
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    Shock tube study of the fuel molecular structure effects on the chemical kinetic mechanisms for soot formation (1983)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The objective of this research effort is to investigate the gas-phase mechanisms which lead to soot formation in the combustion of complex hydrocarbon fuels. The fuel decomposition is studied under pyrolytic and oxidative conditions behind incident shock waves, using various optical diagnostics to monitor particle appearance and the behavior of gas phase species. In particular, we are investigating: (1) improved quantification of UV/visible soot yield measurements using infrared attenuation and emission techniques; (2) spectral characteristics of gas-phase emission and absorption in the ultraviolet, visible, and infrared; and (3) a conceptual view of the chemical pathways for fuel decomposition and the gas-phase reactions leading to soot formation.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA. Lewis Research Center, Oxidation Kinetics and Soot Formation: Research Review; p 1-5
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  • 8
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    Single-pulse shock tube pyrolysis of toluene and 1,3-butadiene (1983)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The objective of this research is to investigate the rate limiting chemical mechanisms leading to the formation of soot precursors. A single-pulse shock tube is being used to collect gas samples of stable intermediates and end products of hydrocarbon pyrolysis. These gas samples are analyzed quantitatively using gas chromatography and any mass imbalance is believed to be due to the formation of PAH's and soot. Experimental decomposition rates of the parent hydrocarbon are determined and compared to predictions from the literature. Detailed chemical kinetic mechanisms describing hydrocarbon pyrolysis are being developed and models of soot formation are being compared with the experimental results. Information developed from these pyrolysis studies will provide the fundamental understanding for modeling subsequent oxidation experiments.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA. Lewis Research Center, Oxidation Kinetics and Soot Formation: Research Review; p 11-13
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  • 9
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    Large-Eddy Simulations with Explicit Equations for Subgrid-Scale Quantities (2002)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Various alternative formulations of the LES equations have been explored in which additional evolution equations for variables such as the acceleration, the subgrid-scale stress tensor, or the subgrid-scale force are explicitly carried. Statistics of the velocity field obtained from the equation for the acceleration are shown to depend strongly on the initial conditions. This feature, which is independent of LES modeling issues, seems to prove that the velocity-acceleration formulation of the Navier-Stokes is not useful for numerical simulation. Equations for the subgrid-scale quantities appear to be much more stable. However, models required by this formulation of the LES problem still require additional study.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: Studying Turbulence Using Numerical Simulation Databases - IX: Proceedings of the 2002 Summer Program; 79-86
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  • 10
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    Waves in Turbulent Stably-Stratified Shear Flow (2002)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Two approaches for the identification of internal gravity waves in sheared and unsheared homogeneous stratified turbulence are investigated. First, the phase angle between the vertical velocity and density fluctuations is considered. It is found, however, that a continuous distribution of the phase angle is present in weakly and strongly stratified flow. Second, a projection onto the solution of the linearized inviscid equations of motion of unsheared stratified flow is investigated. It is found that a solution of the fully nonlinear viscous Navier-Stokes equations can be represented by the linearized inviscid solution. The projection yields a decomposition into vertical wave modes and horizontal vortical modes.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: Studying Turbulence Using Numerical Simulation Databases - IX: Proceedings of the 2002 Summer Program; 257-267
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