Search NASA⌕ Search

SEARCH · Search NASA

Results for “modelling studies”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Model studies of nitric oxide fluorescence in the earth's backscattered spectrum

Fluorescent emissions from nitric oxide appear imposed upon the Rayleigh backscattered spectrum of the earth's atmosphere between 250 and 300 nm in wavelength. Satellite instruments designed to monitor the global ozone distribution can routinely observe these signals although techniques for exploiting the data are not yet available. Application of a radiative transfer equation developed for an atmosphere including absorption by ozone, molecular scattering, and nitric oxide fluorescence shows the three most prominent NO emissions relative to the 250-300 nm backscattered sunlight to be the (1,4), (1,6), and (0,3) gamma bands. Analysis of the contribution function for each emission band indicates that the fluorescent signals can provide useful information on the magnitude and variability of nitric oxide between 40 and 140 km in altitude.

Frederick, J. E.↗
NASA NTRS1982

Water Raman normalization of airborne laser fluorosensor measurements - A computer model study

The technique for normalizing airborne lidar measurements of chlorophyll fluoresence by the water Raman scattering signal is investigated for laser-excitation wavelengths of 480 and 532 nm using a semianalytic Monte Carlo methodology (SALMON). The signal-integration depth for chlorophyll fluorescence Z(90,F), is found to be insensitive to excitation wavelength and ranges from a maximum of 4.5 m in clearest waters to less than 1 m at a chlorophyll concentration of 20 microgram/liter. For excitation at 532 nm, the signal-integration depth for Raman scattering, Z(90,R), is comparable to Z(90,F). For excitation at 480 nm, Z(90,R) is four times as large as Z(90,F) in clearest waters but nearly equivalent at chlorophyll concentrations greater than 2-3 microgram/liter. Absolute signal levels are stronger with excitation at 480 nm than with excitation at 532 nm, but this advantage must be weighed against potential ambiguities resulting from different integration depths for the fluorescence and Raman scattering signals in clearer waters. To the precision of the simulations, Raman normalization produces effectively linear response to chlorophyll concentration for both excitation wavelengths.

Poole, L. R.↗
NASA NTRS1984

A new analysis of charge transfer and polarization for ligand-metal bonding - Model studies of Al4CO and Al4NH3

The nature of the bonding of CO and NH3 ligands to Al is analyzed, and the intra-unit charge polarization and inter-unit donation for the interaction of ligands with metals are studied. The consequences of metal-to-ligand and ligand-to-metal charge transfer are separately considered by performing a constrained space orbital variation (CSOV) with the electrons of the metal member of the complex in the field of frozen ligand. The electrons of the metal atoms are then frozen in the relaxed distribution given by the CSOV SCF wave function and the ligand electrons are allowed to relax. Quantitative measures of the importance of inter-unit charge transfers and intra-unit polarization are obtained using results of SCF studies of Al4CO and Al4NH3 clusters chosen to simulate the adsorption of the ligands at an on-top side of the Al(111) surface. The electrostatic attraction of the effective dipole moments of the metal and ligand units makes an important contribution to the bond.

Bagus, P. S.↗
NASA NTRS1987

Space station architectural elements model study. Space station human factors research review

Presentation visuals and an extended abstract represent a study to explore and analyze the interaction of major utilities distribution, generic workstation, and spatial composition of the SPACEHAB space station module. Issues addressed include packing densities vs. circulation, efficiency of packing vs. standardization, flexibility vs. diversity, and composition of interior volume as space for living vs. residual negative volume. The result of the study is expected to be a series of observations and preliminary evaluation criteria which focus on the productive living environment for a module in orbit.

Taylor, Thomas C.↗
NASA NTRS1987

Space station architectural elements model study

The space station must unite the properties and behavior of individual and place, using proportions from both to make whole the understanding of ourselves at this moment in evolution. Harmonious proportions in any environment are similar to the acceptance and enjoyment of the harmony of many well-tuned musical instruments. A well-tuned or well-ordered environment tends to have invisible proportions. They produce order but do not intrude on the perception and cognitive mapping of the environment. Systems of proportion are not ends in themselves but are a means to select a series of spaces which relate one to another in dimensionally specific terms. These internal relationships create a whole when the forms are harmonious. This harmonic relationship is of intrinsic value for individuals to be physically and psychologically in balance with their universe.

Kalil, Michael↗
NASA NTRS1990

Bioclimatic distribution of vegetation for general circulation model studies

Four global bioclimatic schemes which qualify climates on the basis of the distribution of vegetation, including the Holdridge (1947), Thornthwaite (1948), Koeppen (1936), and Troll and Paffen (1964) schemes, were applied to two global climate data sets to produce maps of global vegetation distribution: the Rand set described by Schutz and Gates (1971, 1973, and 1974) and the Shea (1986) data set. The results show that only 38 to 40 percent of the observed land surface, mapped as 31 vegetation types, could be replicated by applying the four schemes to these data sets. The simulations were significantly improved by further subdividing and regrouping the climates defined by the schemes and by regrouping the observed vegetation types. With these alterations, 77 percent of the predicted vegetative landscape coresponded with the observed distribution of vegetation.

Prentice, Katharine Culbertson↗
NASA NTRS1993

Observational and modeling studies of the influence of snow anomalies on the atmospheric circulation

Current research on the effects of snow covers on the atmosphere over short term, interannual, and decadal timescales is reviewed. Data obtained show that anomalies of snow cover are clearly associated with significant local anomalies of air temperature, at least in the lowest 100-200 mb. The duration of the local anomalies generally ranges from several days to several weeks and is often limited by the weekly and monthly fluctuation of the snow anomalies. The snow-hydrology-soil moisture feedback is capable of producing a meaningful response in the atmosphere during spring and summer.

Walsh, John E.↗
NASA NTRS1994

Observational and modeling studies of heat, moisture, precipitation and global-scale circulation patterns

This research grant was a revised version of an original proposal. The period of the grant was for three years with a six-month no-cost extension; thus, it was from 20 July 1990 to 19 January 1994. The objectives of the grant were to identify periods and locations of active convection centers, primarily over the Southern Hemisphere tropical Indian and Pacific Oceans; determine reasons for any periodic behavior found in the first objective; identify cases where subtropical jets over the South Pacific persisted for several days and examine the influences of tropical versus extra-tropical mechanisms in maintaining them; obtain estimates of precipitation by Q(sub 1) and Q(sub 2) budgets, including the importance of terms in each of the respective budgets, and compare these estimates to those obtained by other methods; and diagnose the distributions of moisture and precipitable water over the North Atlantic Ocean using routine analyses and satellite microwave data. To accomplish these objectives, we used grant funds to purchase several data sets, including the Global Precipitation Climate Project (GPCP) observations of station precipitation, ECMWF WCRP/TOGA archive two analyses for January 1985 - December 1990, ECMWF WMO analyses for January 1980 - December 1987, and OLR data for July 1974 - December 1991. We already had some SSM/I data and GLA analyses from a previous grant. In addition, to improve our computing power, we also used grant funds to purchase an IBM PS/2 with accessories, a NEC laser jet printer, and a microcomputer system for word processing. This report is organized as follows. Our research team is listed first. Section two contains a summary of our significant accomplishments; however, a detailed discussion of research results is not included since this information can be found in the accompanying reprints and preprints. Section three offers some concluding remarks, and a complete bibliographic summary is given in Section four.

Vincent, Dayton G.↗
NASA NTRS1995

Model studies of the beam-filling error for rain-rate retrieval with microwave radiometers

Low-frequency (less than 20 GHz) single-channel microwave retrievals of rain rate encounter the problem of beam-filling error. This error stems from the fact that the relationship between microwave brightness temperature and rain rate is nonlinear, coupled with the fact that the field of view is large or comparable to important scales of variability of the rain field. This means that one may not simply insert the area average of the brightness temperature into the formula for rain rate without incurring both bias and random error. The statistical heterogeneity of the rain-rate field in the footprint of the instrument is key to determining the nature of these errors. This paper makes use of a series of random rain-rate fields to study the size of the bias and random error associated with beam filling. A number of examples are analyzed in detail: the binomially distributed field, the gamma, the Gaussian, the mixed gamma, the lognormal, and the mixed lognormal ('mixed' here means there is a finite probability of no rain rate at a point of space-time). Of particular interest are the applicability of a simple error formula due to Chiu and collaborators and a formula that might hold in the large field of view limit. It is found that the simple formula holds for Gaussian rain-rate fields but begins to fail for highly skewed fields such as the mixed lognormal. While not conclusively demonstrated here, it is suggested that the notionof climatologically adjusting the retrievals to remove the beam-filling bias is a reasonable proposition.

Ha, Eunho↗
NASA NTRS1996

Numerical Model Studies of the Martian Mesoscale Circulations

Studies concerning mesoscale topographical effects on Martian flows examined low-level jets in the near equatorial latitudes and the dynamical intensification of flow by steep terrain. Continuation of work from previous years included evaluating the dissipation of cold air mass outbreaks due to enhanced sensible heat flux, further sensitivity and scaling evaluations for generalization of the characteristics of Martian mesoscale circulation caused by horizontal sensible heat-flux gradients, and evaluations of the significance that non-uniform surface would have on enhancing the polar CO2 ice sublimation during the spring. The sensitivity of maximum and minimum atmospheric temperatures to changes in wind speed, surface albedo, and deep soil temperature was investigated.

Segal, M.↗
NASA NTRS1995

Shock Tube and Modeling Study of the H + O2 = OH + O Reaction over a Wide Range of Composition, Pressure, and Temperature

The rate coefficient of the reaction H + 02 = OH + 0 was determined using OH laser absorption spectroscopy behind reflected shock waves over the temperature range 1050-2500 K and the pressure range 0.7-4.0 atm. Eight mixtures and three stoichiometries were used. Two distinct and independent criteria were employed in the evaluation of k(sub 1). Our recommended expression for k(sub 1) is k(sub 1) = 7.13 x 10(exp 13)exp(-6957 K/T) cm(exp 3)mol(exp -1)s(exp -1) with a statistical uncertainty of 6%. A critical review of recent evaluations of k(sub 1) yields a consensus expression given by k(sub 1) = 7.82 x 10(exp 13)exp(-7105 K/7) cm(exp 3)mol(exp -1)s(exp -1) over the temperature range 960-5300 K. We do not support a non-Arrhenius rate coefficient expression, nor do we find evidence of composition dependence upon the determination of k(sub 1).

Ryu, Si-Ok↗
NASA NTRS1999

Tropospheric Diagnostic Modeling Studies of PEM-Tropics Field Data: Investigation of the HO(x)/NO(x)/O3 Photochemical System and Its Coupling to Sulfur and Halogen Chemistry

Over the time period of this NASA grant the PI has helped plan and execute in the PEM-Tropics A field program. He has also helped organize and co-chair three data workshops which have focused on the detailed analysis of PEM-Tropics A data. His direct participation in these analyses has led to his major involvement in 10 manuscripts, 5 of which are in print, 3 in press, and 2 submitted. A complete list of papers is included in the report.

Davis, Douglas D.↗