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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Applications of optical holography to applied mechanics.

This paper provides a brief summary of applications of optical holography and holographic interferometry to applied solid mechanics. Basic equations commonly used in fringe interpretation are described and used to reduce the data contained on holographic interferograms. A comparison of data obtained holographically with analytical prediction is given wherever possible. Applications contained herein include front surface physics, study of bomb breakup, transverse wave propagation, study of mode shapes of panels at elevated temperatures, nondestructive testing, and vibration analysis.

Aprahamian, R.↗
NASA NTRS1972

Coordinated observations of the magnetosphere - The development of a substorm.

Coordinated observations of a substorm are reported by using data from all-sky camera (ASCA) stations near the northern conjugate of the ATS 5 geostationary satellite, plasma and magnetic-field experiments on the ATS 5 satellite, Vela 5B at 18 earth radii in the magnetotail, the Heos 1 interplanetary probe, and ground-based magnetograms. The substorm event occurred after a very quiet day and was preceded by a development period during which the interplanetary field turned southward and the plasma energy density increased near the earth on the nightside. This period was also evidenced by a depression of the midlatitude H component of the geomagnetic field at the earth's surface. The auroral breakup was preceded by the appearance of quiet arcs, the leveling off of the plasma energy density increase at ATS, and the disappearance of the tail plasma at 18 earth radii.

Mende, S. B.↗
NASA NTRS1972

Extreme ultraviolet emissions from an aurora.

Two ultraviolet photometers were flown on a Javelin sounding rocket launched from Fort Churchill, Canada, on February 18, 1970, into a weak auroral breakup. The photometers covered the wavelength bands 300-1000 A and 1050-1500 A and observed the aurora while the rocket was above the emitting regions. The observed radiations were found to originate from the visible and X-ray auroral forms recorded by ground-based all-sky cameras and onboard gas proportional X-ray counters. The intensities in the 1050- to 1500-A band were compatible with previous experimental data and available theoretical intensity calculations.

Paresce, F.↗
NASA NTRS1973

Studies of the inner shelf and coastal sedimentation environment of the Beaufort Sea from ERTS-1

The author has identified the following significant results. Northward flowing rivers of Alaska inundate extensive areas of sea ice during spring breakup. This process has been studied under the ERTS-1 program. Drainage of large volumes of fresh water through the ice at holes and cracks (strudel) causes scour depressions, over 4 m deep, and up to 20 m across in the sea floor below. Strudel scours occur within 30 km of river mouths, generally in areas where ERTS-1 imagery shows less potential for drifting ice to scour the bottom than elsewhere. The shapes and distribution patterns of strudel scours correspond with those of strudel seen in the ice canopy. Densities of scours are highest in the inner areas of overlfow. But strudel scours also occur outside of overflow areas mapped during the last several years. These must be very old. One strudel scour investigated by diving is surrounded by a rim, has vertical walls exposing a tundra horizon, and terminates at a gravel layer 4 m below the lagoon floor. Another terminates at a semi-consolidated layer of silty clay. The gravel and silty clay are pre-Holocene deposits. Mixing of Holocene marine with older sediments by vertical strudel flow causes great variability in sediment types over small areas. These observations complicate interpretation of shallow water deposits of cold climates.

Reimnitz, E.↗
NASA NTRS1973

Evaluate the application of ERTS-A data for detecting and mapping sea ice

The author has identified the following significant results. The results of the analysis of data collected during the spring and summer demonstrate that ERTS-1 imagery has a high potential for monitoring arctic sea ice conditions during the time for maximum ice extent through ice-breakup season. In the eastern Beaufort Sea area, the combination of ERTS-1 orbital overlap and a high incidence of cloud-free conditions during the spring assures a high frequency of repetitive satellite coverage. In the mid-Beaufort Sea, numerous fractures and leads can be identified, even in the early spring data. Ice features that can be identified include: development of fractures leading to the formation of distinct ice floes; growth and deterioration of leads; evidence of shearing movements of ice masses; formation of new grey ice within leads; distinction between grey, grey-white, and older forms of ice; and the deterioration of the ice surface evidenced by the formation of puddles, thaw holes, and drainage patterns. Ice conditions in the Bering Sea near St. Lawrence Island reported by aircraft observers participating in the Bering Sea Expedition are in close agreement with the ice conditions mapped from the corresponding ERTS-1 imagery. Ice features identified were: boundaries between grey ice and first year ice, shear leads, and occurrence of open water.

Barnes, J. C.↗
NASA NTRS1973

Polar mapping with ERTS-1

The applicability of multispectral ERTS-1 imagery to polar ice detection, local current effects, map corrections, relative lake depth measurements, and estimates of ice breakup is discussed.

Greaves, J. R.↗
NASA NTRS1973

Deformation and burst of a liquid droplet freely suspended in a linear shear field

A theoretical method is presented for predicting the deformation and the conditions for breakup of a liquid droplet freely suspended in a general linear shear field. This is achieved by expanding the solution to the creeping-flow equations in powers of the deformation parameter epsilon and using linear stability theory to determine the onset of bursting. When compared with numerical solutions and with the available experimental data, the theoretical results are generally found to be of acceptable accuracy although, in some cases, the agreement is only qualitative.

Barthes-Biesel, D.↗
NASA NTRS1974

Study of a small magnetospheric substorm

Data from a rocket launched into the expansion phase of an auroral substorm have been compared with data from numerous ground stations and several space vehicles. It is shown that this magnetic and auroral substorm has most of the features of larger substorms; thus it is implied that the same plasma processes are involved in all substorms. Some evidence is presented to link the auroral breakup with the field lines conjugate to the inner edge of the plasma sheet. The implications of these two results for substorm morphology and the triggering mechanism of the substorm instability are discussed. It is concluded that spatial gradients in plasma temperature are a likely cause.

Johnstone, A. D.↗
NASA NTRS1973

Chemistry of the moon's surface

The chemical composition of the lunar surface is discussed on the basis of analyses of Apollo samples. Three new minerals, armalcolite, pyroxferroite and tranquillityite, high abundances of Ti, Zr, Sr, Y, Nb, U and Th, and a predominance of radiogenic isotopes of Pb are noted as the prominent features unraveled by sample analysis. Evidence is indicated to support the conclusion that the lunar rocks investigated are products of partial fusion and magmatic crystallization modified in much of the material by mechanical breakup and shock melting, and containing a small amount of meteoritic material. It is inferred from the results that the surface rocks are igneous in origin and that the moon has been a passive object since 3000 million years ago.

Mason, B.↗
NASA NTRS1975

Theory of fluctuations of extended air showers

The Monte Carlo method was used to calculate the probability distribution functions of shower characteristics for primary protons at sea level. The calculation was based on the following model of the elementary event: the interaction paths are 90 g/sq cm for nucleons and 120 g/sq cm for pions. The nonelasticity coefficient for nucleons is uniformly distributed between 0.1 and 0.9, and for pions it is equal to 1. Isobaric pions are taken into account. The spectra of secondary particles were determined using Cocconi's approximation formula. The calculation for the nuclei was carried out on the assumption of a breakup of the nucleus into component nucleons. The mean number of particles and the variances of the distributions for electrons when the number of muons was fixed, and for muons when the number of electrons was fixed, were calculated.

Dedenko, L. G.↗
NASA NTRS1974

Evaluation of ERTS-1 data for certain hydrological uses

The author has identified the following significant results. ERTS-1 MSS data have been used in a variety of hydrologic research including snow-extent mapping; studies of snowmelt, snowmelt runoff, spectral reflectance of snow for assessing snowpack conditions, and snow albedo; lake ice formation, breakup, and migration; lake current measurements; multispectral studies of lake ice; and flood studies. MSS sensing of soil moisture over a well-vegetated test site was unsuccessfully attempted. Although a powerful research tool, ERTS-1 has very limited use as an operational system for hydrologic communities because of its 18-day revisit cycle and its lack of a quick look capability.

Wiesnet, D. R.↗
NASA NTRS1974

Near-earth cosmic dust results from S-149

Three space exposures (34, 46 and 33 days) of thin films and polished metal plates with a total area of 0.12 sq m per exposure were carried out during Skylab via the S-149 experiment. Study of the materials recovered indicates that the S-149 experiment contains important information concerning cosmic dust in the near-earth vicinity. Craters and penetration holes have been found ranging from 135 micron diameter to less than 0.5 micron. A cosmic dust flux curve in the mass range from 10 to the minus 16th to 10 to the minus 7th grams is presented. Evidence is given concerning the directional characteristics of the particles and their breakup in near-earth space is presented.

Hemenway, C. L.↗
NASA NTRS1975

A source for hyperbolic cosmic dust particles

Earlier analyses of the Pioneer 8 and 9 experimental meteoroid data have shown that the detectors on these two spacecraft are intercepting meteoroids with hyperbolic orbital parameters. It is shown in this paper that these results are entirely consistent with and, indeed, to be expected from other observations of the interplanetary meteoroid complex. Collisional breakup of meteoroids and post-collision radiation pressure modification of their orbits is found to be a sufficient cause for the observed results. Details of the calculations as well as of the results are presented.

Zook, H. A.↗
NASA NTRS1974

VLF emissions and whistlers observed during geomagnetic storms

Whistler-triggered emissions and a narrowband hiss are described which were observed over Japan by ISIS 2 during the main phase of the geomagnetic storm of August 9, 1972. The characteristics of the narrowband hiss and increases in the whistler rate during the storm are discussed, and the ISIS-2 data are compared with data on whistler cutoffs and VLF noise breakups obtained by OGO 4 and Alouette I. Since the whistlers and narrowband hiss are usually observed inside and outside the plasmapause, it is thought that the plasmapause may have been located near the low-latitude end of the narrowband hiss during the main phase of the storm. It is suggested that the increases in the whistler rate may have been caused by the formation of whistler ducts in the disturbed plasmapause.

Ondoh, T.↗
NASA NTRS1976

A study of a sector spectrophotometer and auroral O+(2P-2D) emissions

The metastable O+(2P-2D) auroral emission was investigated. The neighboring OH contaminants and low intensity levels of the emission itself necessitated the evolution of an instrument capable of separating the emission from the contaminants and having a high sensitivity in the wavelength region of interest. A new type of scanning photometer was developed and its properties are discussed. The theoretical aspects of auroral electron interaction with atomic oxygen and the resultant O+(2P-2D) emissions were examined in conjunction with N2(+)1NEG emissions. Ground based measurements of O+(2P-2D) auroral emission intensities were made using the spatial scanning photometer (sector spectrophotometer). Simultaneous measurements of N2(+)1NEG sub 1,0 emission intensity were made in the same field of view using a tilting photometer. Time histories of the ratio of these two emissions made in the magnetic zenith during auroral breakup periods are given. Theories of I sub 7319/I sub 4278 of previous investigators were presented. A rocket measurement of N2(+)1NEG sub 0,0 and O+(2P-2D) emission in aurora was examined in detail and was found to agree with the ground based measurements. Theoretical examination resulted in the deduction of the electron impact efficiency generating O+(2P) and also suggests a large source of O+(2P) at low altitude. A possible source is charge exchange of N+(1S) with OI(3P).

Swenson, G. R.↗
NASA NTRS1976

The application of an optical Fourier spectrum analyzer on detecting defects in mass-produced satellite photographs

Various defects in mass-produced pictures transmitted to earth from a satellite are investigated. It is found that the following defects are readily detectable via Fourier spectrum analysis: (1) bit slip, (2) breakup causing loss of image, and (3) disabled track at the top of the imagery. The scratches made on the film during mass production, which are difficult to detect by visual observation, also show themselves readily in Fourier spectrum analysis. A relation is established between the number of scratches, their width and depth and the intensity of their Fourier spectra. Other defects that are found to be equally suitable for Fourier spectrum analysis or visual (image analysis) detection are synchronous loss without blurring of image, and density variation in gray scale. However, the Fourier spectrum analysis is found to be unsuitable for detection of such defects as pin holes, annotation error, synchronous loss with blurring of images, and missing image in the beginning of the work order. The design of an automated, real time system, which will reject defective films, is treated.

Athale, R.↗
NASA NTRS1976

Theoretical study of reactive and nonreactive turbulent coaxial jets

The hydrodynamic properties and the reaction kinetics of axisymmetric coaxial turbulent jets having steady mean quantities are investigated. From the analysis, limited to free turbulent boundary layer mixing of such jets, it is found that the two-equation model of turbulence is adequate for most nonreactive flows. For the reactive flows, where an allowance must be made for second order correlations of concentration fluctuations in the finite rate chemistry for initially inhomogeneous mixture, an equation similar to the concentration fluctuation equation of a related model is suggested. For diffusion limited reactions, the eddy breakup model based on concentration fluctuations is found satisfactory and simple to use. The theoretical results obtained from these various models are compared with some of the available experimental data.

Gupta, R. N.↗
NASA NTRS1976

Planetary astronomy

Color and spectral data from spectrometer observations and computerized analyses of asteroid spectra are discussed. Potential occultations of bright asteroids by the moon are summarized. Analysis of anisotropic scattering within Saturn's rings indicates that mineral contamination of the 120 particles cannot exceed 5 percent by weight, and that the rings formed from particle breakup rather than from particle condensation. Raman probe applications to Jupiter and Uranus atmospheres indicate the presence of aerosol particles. A review of Mariner 9 Mars cloud topography data establishes that most blue clouds are orographic uplift clouds composed of condensates, and that sporadic red clouds are associated with blue clouds or volcanoes and thus probably do not represent dust storm phenomena.

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