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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

National software exchange - An electronic marketplace for software

A potential application is outlined for high-speed and high-performance networks of the future. A discussion is presented of possible contents of the NSE (National Software Exchange) services to be offered by the NSE, mechanisms for controlling software quality, and types of collaboration that might involve the NSE. Services that must be provided by the NREN (National Research and Education Network) to provide adequate support for the NSE are identified.

Johnson, Marjory J.↗
NASA NTRS1992

Air-surface exchange of H2O, CO2, and O3 at a tallgrass prairie in relation to remotely sensed vegetation indices

Parameters derived from eddy correlation measurements of the air-surface exchange rates of H2O, CO2, and O3 over a tallgrass prairie are examined in terms of their relationships with spectral reflectance data remotely sensed from aircraft and satellites during the four 1987 intensive field campaigns of the First ISLSCP Field Experiment (FIFE). The surface conductances were strongly modulated by photosynthetically active radiation received at the surface when the grass was green and well watered; mesophyll resistances were large for CO2 but negligible for H2O and O3.

Gao, W.↗
NASA NTRS1993

Oxygen ionization rates at Mars and Venus - Relative contributions of impact ionization and charge exchange

Oxygen ion production rates above the ionopauses of Venus and Mars are calculated for photoionization, charge exchange, and solar wind electron impact ionization processes. The latter two require the use of the Spreiter and Stahara (1980) gas dynamic model to estimate magnetosheath velocities, densities, and temperatures. The results indicate that impact ionization is the dominant mechanism for the production of O(+) ions at both Venus and Mars. This finding might explain both the high ion escape rates measured by Phobos 2 and the greater mass loading rate inferred for Venus from the bow shock positions.

Zhang, M. H. G.↗
NASA NTRS1985

Application of AVHRR vegetation index to study atmosphere-biosphere exchange of CO2: Results from a 3-D tracer transport model

The 'normalized difference vegetation indices' (NVI) derived from AVHRR radiances are combined with field data of soil respiration and a global map of net primary productivity to prescribe, for the globe, the seasonal exchange of CO2 between the atmosphere and the terrestrial biosphere. The monthly fluxes of CO2 thus obtained are used as inputs to a 3-D tracer transport model which uses winds generated by a 3-D atmospheric general circulation model to advect CO2 as an inert constituent. Analysis of the 3-D model results shows reasonable agreement between the simulated and observed annual cycles of atmospheric CO2 at the locations of the remote monitoring stations. The application is shown of atmospheric CO2 distributions to calibrate the NVI in terms of carbon fluxes. The approach suggests that the NVI may be used to provide quantitative information about long term and global scale variations of photosynthetic activity and of atmospheric CO2 concentrations provided that variations in the atmospheric circulation and in atmospheric composition are known.

Fung, Inez Y.↗
NASA NTRS1992

Factors controlling sulfur gas exchange in Sphagnum-dominated wetlands

Atmosphere-peatland exchange of reduced sulfur gases was determined seasonally in fen in NH, and in an artificially-acidified fen at the Experimental Lakes Area (ELA) in Canada. Dimethyl sulfide (DMS) dominated gas fluxes at rates as high as 400 nmol/m(sup -2)hr(sup -1). DMS fluxes measured using enclosures were much higher than those calculated using a stagnant-film model, suggesting that Sphagnum regulated efflux. Temperature controlled diel and seasonal variability in DMS emissions. Use of differing enclosure techniques indicated that vegetated peatlands consume atmospheric carbonyl sulfide. Sulfate amendments caused DMS and methane thiol concentrations in near-surface pore waters to increase rapidly, but fluxes of these gases to the atmosphere were not affected. However, emission data from sites experiencing large differences in rates of sulfate deposition from the atmosphere suggested that chronic elevated sulfate inputs enhance DMS emissions from northern wetlands.

Demello, William Zamboni↗
NASA NTRS1992

Sulfur gas exchange in Sphagnum-dominated wetlands

Sulfur gases are important components of the global cycle of S. They contribute to the acidity of precipitation and they influence global radiation balance and climate. The role of terrestrial sources of biogenic S and their effect on atmospheric chemistry remain as major unanswered questions in our understanding of the natural S cycle. The role of northern wetlands as sources and sinks of gaseous S was investigated by measuring rates of S gas exchange as a function of season, hydrologic conditions, and gradients in trophic status. The effects of inorganic S input on the production and emission of gaseous S were also investigated. Experiments were conducted in wetlands in New Hampshire, particularly a poor fen, fens within the Experimental Lakes Area (ELA) in Ontario, Canada and in freshwater and marine tundra. Emissions were determined using Teflon enclosures, gas cryotrapping methods, and gas chromatography (GC) with flame photometric detection. Dynamic (sweep flow) and static enclosures were employed. Dissolved gases were determined by gas stripping followed by GC.

Hines, Mark E.↗
NASA NTRS1993

Surrogates for numerical simulations; optimization of eddy-promoter heat exchangers

Although the advent of fast and inexpensive parallel computers has rendered numerous previously intractable calculations feasible, many numerical simulations remain too resource-intensive to be directly inserted in engineering optimization efforts. An attractive alternative to direct insertion considers models for computational systems: the expensive simulation is evoked only to construct and validate a simplified, input-output model; this simplified input-output model then serves as a simulation surrogate in subsequent engineering optimization studies. A simple 'Bayesian-validated' statistical framework for the construction, validation, and purposive application of static computer simulation surrogates is presented. As an example, dissipation-transport optimization of laminar-flow eddy-promoter heat exchangers are considered: parallel spectral element Navier-Stokes calculations serve to construct and validate surrogates for the flowrate and Nusselt number; these surrogates then represent the originating Navier-Stokes equations in the ensuing design process.

Patera, Anthony T.↗
NASA NTRS1993

Relativistic proton-nucleus scattering and one-boson-exchange models

Relativistic p-(Ca-40) elastic scattering observables are calculated using four sets of relativistic NN amplitudes obtained from different one-boson-exchange (OBE) models. The first two sets are based upon a relativistic equation in which one particle is on mass shell and the other two sets are obtained from a quasipotential reduction of the Bethe-Salpeter equation. Results at 200, 300, and 500 MeV are presented for these amplitudes. Differences between the predictions of these models provide a study of the uncertainty in constructing Dirac optical potentials from OBE-based NN amplitudes.

Maung, Khin Maung↗
NASA NTRS1993

A browsing tool for the Internet Logical Library of the HPCC Software Exchange

As the quantity of information available on the Internet grows, locating a particular piece of information becomes more difficult. One possible solution is for a database of pointers to all available information to be maintained at a central site. Subject classifications for all the information could also be maintained in order to make searching possible. This paper describes one possible method of searching such an index. In particular a prototype browsing tool has been created using TCL/TK to demonstrate several possible features: rapidly scanning at any rank of the index, narrowing the index to any scope, regular-expression searching, and creation of a list of pointers answering to any set of index terms. The prototype browser is an easy-to-use independent X application designed for use in the Catalog of Repositories of the HPCC (High Performance Computing and Communications) Software Exchange.

Biro, Ross↗
NASA NTRS1993

Energy-loss cross sections for inclusive charge-exchange reactions at intermediate energies

Charge-exchange reactions for scattering to the continuum are considered in a high-energy multiple scattering model. Calculations for (p,n) and (He-3,H-3) reactions are made and compared with experimental results for C-12, O-16, and Al-27 targets. Coherent effects are shown to lead to an important role for inelastic multiple scattering terms when light projectiles are considered.

Cucinotta, Francis A.↗
NASA NTRS1993

Heat exchanger with oscillating flow

Various heat exchange apparatuses are described in which an oscillating flow of primary coolant is used to dissipate an incident heat flux. The oscillating flow may be imparted by a reciprocating piston, a double action twin reciprocating piston, fluidic oscillators or electromagnetic pumps. The oscillating fluid flows through at least one conduit in either an open loop or a closed loop. A secondary flow of coolant may be used to flow over the outer walls of at least one conduit to remove heat transferred from the primary coolant to the walls of the conduit.

Scotti, Stephen J.↗
NASA NTRS1993

High power density proton exchange membrane fuel cells

Proton exchange membrane (PEM) fuel cells use a perfluorosulfonic acid solid polymer film as an electrolyte which simplifies water and electrolyte management. Their thin electrolyte layers give efficient systems of low weight, and their materials of construction show extremely long laboratory lifetimes. Their high reliability and their suitability for use in a microgravity environment makes them particularly attractive as a substitute for batteries in satellites utilizing high-power, high energy-density electrochemical energy storage systems. In this investigation, the Dow experimental PEM (XUS-13204.10) and unsupported high platinum loading electrodes yielded very high power densities, of the order of 2.5 W cm(exp -2). A platinum black loading of 5 mg per cm(exp 2) was found to be optimum. On extending the three-dimensional reaction zone of fuel cell electrodes by impregnating solid polymer electrolyte into the electrode structures, Nafion was found to give better performance than the Dow experimental PEM. The depth of penetration of the solid polymer electrolyte into electrode structures was 50-70 percent of the thickness of the platinum-catalyzed active layer. However, the degree of platinum utilization was only 16.6 percent and the roughness factor of a typical electrode was 274.

Murphy, Oliver J.↗
NASA NTRS1991

Oscillating-flow loss test results in rectangular heat exchanger passages

Test results of oscillating flow losses in rectangular heat exchanger passages of various aspect ratios are given. This work was performed in support of the design of a free-piston Stirling engine (FPSE) for a dynamic space power conversion system. Oscillating flow loss testing was performed using an oscillating flow rig, which was based on a variable stroke and variable frequency linear drive motor. Tests were run over a range of oscillating flow parameters encompassing the flow regimes of the proposed engine design. Test results are presented in both tabular and graphical form and are compared against analytical predictions.

Wood, J. Gary↗
NASA NTRS1994

Ion exchange polymers and method for making

An ion exchange polymer comprised of an alkali metal or alkaline earth metal salt of a poly(carboxylic acid) in a poly(vinyl acetal) matrix is described. The polymer is made by treating a mixture made of poly(vinyl alcohol) and poly(acrylic acid) with a suitable aldehyde and an acid catalyst to cause acetalization with some cross-linking. The material is then subjected to an alkaline aqueous solution of an alkali metal salt or an alkali earth metal salt. All of the film forming and cross-linking steps can be carried out simultaneously, if desired.

Philipp, Warren H.↗
NASA NTRS1995

A probabilistic model of a porous heat exchanger

This paper presents a probabilistic one-dimensional finite element model for heat transfer processes in porous heat exchangers. The Galerkin approach is used to develop the finite element matrices. Some of the submatrices are asymmetric due to the presence of the flow term. The Neumann expansion is used to write the temperature distribution as a series of random variables, and the expectation operator is applied to obtain the mean and deviation statistics. To demonstrate the feasibility of the formulation, a one-dimensional model of heat transfer phenomenon in superfluid flow through a porous media is considered. Results of this formulation agree well with the Monte-Carlo simulations and the analytical solutions. Although the numerical experiments are confined to parametric random variables, a formulation is presented to account for the random spatial variations.

Agrawal, O. P.↗
NASA NTRS1995

A novel unitized regenerative proton exchange membrane fuel cell

A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed in work performed at Lynntech. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel unitized regenerative fuel cell and results obtained on testing it will be presented.

Murphy, O. J.↗
NASA NTRS1995

FTP-Server for exchange, interpretation, and database-search of ion mobility spectra, literature, preprints and software

To assist current discussion in the field of ion mobility spectrometry, at the Institut fur Spectrochemie und angewandte Spektroskopie, Dortmund, start with 4th of December, 1994 work of an FTP-Server, available for all research groups at univerisities, institutes and research worker in industry. We support the exchange, interpretation, and database-search of ion mobility spectra through data format JCAMP-DS (Joint Committee on Atomic and Molecular Physical Data) as well as literature retrieval, pre-print, notice, and discussion board. We describe in general lines the entrance conditions, local addresses, and main code words. For further details, a monthly news report will be prepared for all common users. Internet email address for subscribing is included in document.

Baumbach, J. I.↗
NASA NTRS1994

Stratospheric/tropospheric exchange affecting the northern wetlands regions of Canada during summer 1990

The Arctic Boundary Layer Expedition (ABLE) 3B was conducted over the northern wetlands region of Canada during July and August 1990. Several stratospheric/tropospheric exchange events were noted by zenith-looking airborne lidar and in situ measurements of ozone and other trace gas species. Isentropic trajectories and potential vorticity analyses are utilized to determine the frequency of stratospheric inputs which would have affected the tropospheric column over the Moosonee and Schefferville regions and to describe the favored pathways of transport of stratospheric air arriving at these locations. At the 310 K potential temperature level (middle troposphere), trajectories having 'aged stratospheric' values of potential vorticity at some point in their 5-day history arrived at Moosonee or Schefferville roughly 40% of the time during the ABLE 3B study period, most often via large-scale subsidence enroute from 'stratospheric input regions' over the Arctic Ocean or northern and central Canada. At 325 K (upper troposphere), 'fresh' stratospheric input was evident on about 80% of the trajectories, most often associated with jet streaks within the polar and Arctic jet streams. A case study is presented which illustrates both of these general stratospheric input processes.

Bachmeier, A. Scott↗