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Davis, J. C.

Publications and source records attributed to Davis, J. C..

9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Optical constants from mirror reflectivities measured at synchrotrons

Improved mirror reflectivity measurement techniques have been introduced to permit more accurate determinations of optical constants delta and beta in the complex index of refraction n = 1 - delta - i(beta) over the energy range 50 to 5000 eV. When the density has been determined by X-ray or other means, one can calculate the real and imaginary parts, f-prime and f-double prime, of the complex atomic scattering factor f = f(o) + f-prime + if-double prime from delta and beta. Preliminary results are given for the Ni LIII edge around 852 eV, and the Au M edge region from 2150 to 3500 eV. Since these are the first experimental evaluations of delta for these element edges, they are compared with appropriate reservations to semiempirical tabulations. There is much potential for this technique applied to synchrotron sources.

Blake, R. L.↗
NASA NTRS1975

Summary and analysis of performance and stability characteristics of the refan JT8D-109 engine

The refan JT8D-109 performance and stability characteristics are reported as determined from sea level testing, altitude testing, and DC-9 flight testing. The test results are summarized as follows: (1) TSFC at SLS achieved design goal of 12.66 percent reduction. (2) TSFC at altitude average cruise power 0.5 percent higher than design goal, (3) TSFC at altitude maximum cruise power 1.7-3.7 percent higher than design goal, (4) ground starting consistent with JT8D-9 base engine, (5) successful flight starts without starter assist, (6) transient surge margin equivalent to JT8D-9, (7) stable engine operation with inlet distortion, and (8) stable engine operation during snap acceleration and deceleration. A flight idle setting is required for acceptable aborted-landing go-around acceleration time due to increase in low-rotor moment of inertia, and a performance improvement program should be conducted as part of any future certification program.

Sanberg, K. G.↗
NASA NTRS1974

Ground pattern analysis in the Great Plains

The author has identified the following significant results. Spatial frequency analysis of ERTS-1 images appears to be useful in discriminating between large scale ground patterns in Kansas. Using parameters derived from the optical data processing of ERTS-1 images, sample areas from large physiographic categories have been accurately identified.

Davis, J. C.↗
NASA NTRS1973

Kansas environmental and resource study: A Great Plains model

The author has identified the following significant results. Improvement in the land use classification accuracy of ERTS-1 MSS multi-images over Kansas can be made using two distances between neighboring grey tone N-tuples instead of one distance. Much more information is contained texturally than spectrally on the Kansas image. Ground truth measurements indicate that reflectance ratios of the 545 and 655 nm wavebands provide an index of plant development and possibly physiological stress. Preliminary analysis of MSS 4 and 5 channels substantiate the ground truth interpretation. Results of the land use mapping experiment indicate that ERTS-1 imagery has major potential in regionalization. The ways in which land is utilized within these regions may then be studied more effectively than if no adequate regionalization is available. A model for estimating wheat yield per acre has been applied to acreage estimates derived from ERTS-1 imagery to project the 1973 wheat yields for a ten county area in southwest Kansas. The results are within 3% of the preharvest estimates for the same area prepared by the USDA. Visual identification of winter wheat is readily achieved by using a temporal sequence of images. Identification can be improve by stratifying the project area into subregions having more or less homogeneous agricultural practices and crop mixes.

Haralick, R. M.↗
NASA NTRS1972

Ground pattern analysis in the Great Plains

The author has identified the following significant results. During preliminary analysis of the ERTS-1 RBV band-2 images it was possible to detect many geologic features and to delineate several geologic formation boundaries. Also, the spatial frequency characteristics of some different geologic formations are distinguishable from each other. At the present time there is not enough data to provide any statistical evaluation of these differences, but it is hoped that more quantitative results will be produced within the next few months. Multispectral analysis will begin when the retrospective order for the other spectral bands of the first images is received. Since many geologic formation boundaries are visible on the single band that has been analyzed so far, even greater visibility is expected with the spectral information available in the additional bands.

Egbert, D. D.↗