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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 253 records · Page 14
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NASA NTRS1974

Multiplet effects on the L(2,3) fluorescence yield of multiply ionized Ar

The 2p fluorescence yield of argon in the presence of 0 to 6 3p holes was calculated by statistically averaging the fluorescence yields of initial state that consist of individual multiplet configurations. These configurations were formed by coupling the 2p vacancy to the partially filled 3p shell. Results agree reasonably well with experimental fluorescence yields deduced from ion-atom collision measurements.

Chen, M. H.↗
NASA NTRS1974

Limitations to the small scale yielding approximation for crack tip plasticity

Recent finite-element results by S. G. Larsson and A. J. Carlsson suggest a limited range of validity to the 'small scale yielding approximation,' whereby small crack tip plastic zones are correlated in terms of the elastic stress intensity factor. It is shown with the help of a model for plane strain yielding that their results may be explained by considering the non-singular stress, acting parallel to the crack at its tip, which accompanies the inverse square-root elastic singularity. Further implications of the non-singular stress term for crack tip deformations and fracturing are examined. It is suggested that its effect on crack tip parameters, such as the opening displacement and J-integral, is less pronounced than its effect on the yield zone size.

Rice, J. R.↗
NASA NTRS1975

Yield prediction by analysis of multispectral scanner data

A preliminary model describing the growth and grain yield of wheat was developed. The modeled growth characteristics of the wheat crop were used to compute wheat canopy reflectance using a model of vegetation canopy reflectance. The modeled reflectance characteristics were compared with the corresponding growth characteristics and grain yield in order to infer their relationships. It appears that periodic wheat canopy reflectance characteristics potentially derivable from earth satellites will be useful in forecasting wheat grain yield.

Colwell, J. E.↗
NASA NTRS1975

Proceedings of the 1974 Lyndon B. Johnson Space Center Wheat-Yield Conference

The proceedings of the 1974 Lyndon B. Johnson Space Center Wheat-Yield Conference are presented. The state of art of wheat-yield forecasting and the feasibility of incorporating remote sensing into this forecasting were discussed with emphasis on formulating common approach to wheat-yield forecasting, primarily using conventional meteorological measurements, which can later include the various applications of remote sensing. Papers are presented which deal with developments in the field of crop modelling.

Pitts, D. E.↗
NASA NTRS1974

Photodissociation quantum yields of CO2 between 1200 and 1500 A

Measurements of the photodissociation quantum yields of CO2 have been carried out using various atomic line sources between 1200 and 1500 A. The production of CO was monitored by resonance fluorescence, and the results indicate that where the CO2 absorption spectrum is continuous, the CO quantum yield is high, but where there is structure, the yield is low.

Slanger, T. G.↗
NASA NTRS1975

Yield stress of cemented tungsten carbide

Cemented tungsten carbide yields plastically at room temperature in the presence of a large hydrostatic pressure component. By approximate analysis of the state of stress in supported opposed anvils and by measurement of the pressure at which the anvil tips exhibit a permanent deviation from planarity, we have obtained the yield stress of such materials. Our value for the yield stress of a 3% cobalt cemented tungsten carbide is 86 kbar.

Ruoff, A. L.↗
NASA NTRS1976

Measurement of the 13 to 100 eV electron impact excitation cross section for the X 1Sigma /+/-g yields a 1Pi-g transition in N2

An inelastic scattering technique was used to measure the electron impact excitation cross section for the X 1Sigma (+)-g yields a 1Pi-g transition in N2 in the energy range 13 to 100 eV. The relative excitation cross section was calculated by integration of the relative differential scattering cross sections at various energies and the relative values of the excitation cross section were put on an absolute scale by comparing the relative cross sections to those for excitation of the X 1Sigma (+)-g yields C 3Pi-u transition and those of the electron impact optical emission cross section for the C 3Pi-u yields B 3Pi-g transition as a secondary standard. The excitation cross section was found to vary from a maximum value of 3.6 x 10 to the -17 cu cm between 15 and 18 eV to 5.2 x 10 to the -18 cu cm at 100 eV.

Finn, T. G.↗
NASA NTRS1977

Airborne monitoring of crop canopy temperatures for irrigation scheduling and yield prediction

Airborne and ground measurements were made on April 1 and 29, 1976, over a USDA test site consisting mostly of wheat in various stages of water stress, but also including alfalfa and bare soil. These measurements were made to evaluate the feasibility of measuring crop temperatures from aircraft so that a parameter termed stress degree day, SDD, could be computed. Ground studies have shown that SDD is a valuable indicator of a crop's water needs, and that it can be related to irrigation scheduling and yield. The aircraft measurement program required predawn and afternoon flights coincident with minimum and maximum crop temperatures. Airborne measurements were made with an infrared line scanner and with color IR photography. The scanner data were registered, subtracted, and color-coded to yield pseudo-colored temperature-difference images. Pseudo-colored images reading directly in daily SDD increments were also produced. These maps enable a user to assess plant water status and thus determine irrigation needs and crop yield potentials.

Millard, J. P.↗
NASA NTRS1977

Yield spectra and the continuous-slowing-down approximation

The continuous-slowing-down approximation (CSDA) and the modified discrete-energy-bin (MDEB) method are used to calculate a yield spectra U(E, E sub 0) of electrons with energy E resulting from a primary of energy E sub 0. The results of the two calculations are then compared. The MDEB method is found to produce consistently more ions per energy loss while at the same time producing less excitations of some of the low-lying states when compared with the CSDA. These discrepancies can be explained by studying the contributions from the individual generations of electrons to the yield spectra. An integral equation for the solution of the yield spectra is also presented.

Jackman, C. H.↗
NASA NTRS1977

Airborne monitoring of crop canopy temperatures for irrigation scheduling and yield prediction

The aim of the program discussed was to develop techniques for remotely measuring crop irrigation needs and predicting crop yields, with emphasis on wheat. Airborne measurements, using an IR line scanner and color IR photography, were made to evaluate the feasibility of measuring minimum and maximum (dawn and afternoon) crop temperatures to compute a parameter, termed 'stress degree day' (SDD) - a valuable indicator of crop water needs, which can be related to irrigation scheduling and yield. Crop canopy temperature measurements by airborne IR techniques revealed the superiority of thermal IR data over color IR photography. Water stress undetected in the latter technique was clearly detected in thermal imagery. Color IR photography, however, is valuable in discerning vegetation. The pseudo-colored temperature-difference images (and pseudo-colored images, reading directly in daily SDD increments) are shown to be well suited for assessing plant water status and, thus, for determining the irrigation needs and crop yield potentials.

Millard, J. P.↗
NASA NTRS1977

Electron impact on atmospheric gases. II - Yield spectra

A concept yield spectrum is introduced and this two-dimensional function is calculated, using a modified discrete energy bin method for 50-eV to 10-keV incident electrons impacting on the gases Ar, H2, H2O, O2, N2, O, CO, CO2, and He. The yield spectrum is amenable to physical interpretation, accurate analytic representation, and convenient application to the determination of all types of yields needed in aeronomical problems.

Green, A. E. S.↗
NASA NTRS1977

Evaluating soil moisture and yield of winter wheat in the Great Plains using Landsat data

Locating areas where soil moisture is limiting to crop growth is important for estimating winter-wheat yields on a regional basis. In the 1975-76 growing season, we evaluated soil-moisture conditions and winter-wheat yields for a five-state region of the Great Plains using Landsat estimates of leaf area index (LAI) and an evapotranspiration (ET) model described by Kanemasu et al (1977). Because LAI was used as an input, the ET model responded to changes in crop growth. Estimated soil-water depletions were high for the Nebraska Panhandle, southwestern Kansas, southeastern Colorado, and the Texas Panhandle. Estimated yields in five-state region ranged from 1.0 to 2.9 metric ton/ha.

Heilman, J. L.↗
NASA NTRS1978

Char yield and flash-fire propensity of pyrolysis gases from materials

Comparison of the char yield after occurrence of a flash fire in the pyrolysis gases from various materials indicates that increased char yield appears to be associated with reduced flash-fire propensity for certain types of materials. For certain other materials, flash-fire propensity appears to be independent of char yield. The mechanisms of thermal decomposition and char formation may be more important factors in flash-fire propensity than the quantitative degree of char formation.

Hilado, C. J.↗
NASA NTRS1978

Yield strengths of flows on the earth, Mars, and moon

Dimensions of flows on the earth, Mars, and moon and their topographic gradients obtained from remote measurements are used to calculate yield strengths with a view to explore the validity of the Bingham plastic model and determine whether there is a relation between yield strengths and silica contents. Other factors are considered such as the vagaries of natural phenomena that might contribute to erroneous interpretations and measurements. Comparison of yield strengths of Martian and lunar flows with terrestrial flows suggests that the Martian and lunar flows are more akin to terrestrial basalts than they are to terrestrial andesites, trachytes, and rhyolites.

Moore, H. J.↗
NASA NTRS1979

Relativistic L -shell Auger and Coster-Kronig rates and fluorescence yields

Relativistic calculations of radiationless transition rates to L -subshell vacancy states in selected atoms with Z in the 70-96 range have been performed. The Auger and Coster-Kronig transition probabilities are calculated from perturbation theory, assuming frozen orbitals, in the Dirac-Hartree-Slater approach. Transition rates, fluorescence yields, and Coster-Kronig yields are compared with nonrelativistic theoretical results and with experiment. Relativity is found to affect the L -subshell Auger widths by (10-25)% and individual transition rates to certain j-j configurations by as much as 40% at Z = 80. The widths of L sub i vacancy states and the L sub 2 Coster-Kronig yields f33 from these relativistic calculations agree much better with experiment than earlier nonrelativistic theoretical values.

Chen, M. H.↗
NASA NTRS1979

Development of LACIE CCEA-1 weather/wheat yield models

The advantages and disadvantages of the casual (phenological, dynamic, physiological), statistical regression, and analog approaches to modeling for grain yield are examined. Given LACIE's primary goal of estimating wheat production for the large areas of eight major wheat-growing regions, the statistical regression approach of correlating historical yield and climate data offered the Center for Climatic and Environmental Assessment the greatest potential return within the constraints of time and data sources. The basic equation for the first generation wheat-yield model is given. Topics discussed include truncation, trend variable, selection of weather variables, episodic events, strata selection, operational data flow, weighting, and model results.

Strommen, N. D.↗
NASA NTRS1979

A universal model for estimating wheat yields

A universal wheat yield model applicable to both fall- and spring-planted wheat was developed to show separate and joint effects of weather and culture on yields. Data from state experiment stations in a wide range of climates in the U.S. Great Plains were used to build basic relationships among yields, weather, and culture. The application of the model on a macroclimatic scale in the U.S., the U.S.S.R., and India is discussed along with potential improvements.

Feyerherm, A. M.↗
NASA NTRS1979

CCEA second-generation wheat yield model for hard red wheat in North Dakota

The problem of estimating wheat yields for years with unusual planting dates and/or unusual phenological development is investigated. A yield model developed for hard red spring wheat in North Dakota using historical yields for crop reporting districts in conjunction with meteorological predictor variables based on weekly data is assessed.

Leduc, S. K.↗