Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “lack”

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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The vertical distribution of Mars water vapor

Analysis of observations made from the Viking 1 Orbiter indicates that the water vapor over the Viking 1 landing site is uniformly mixed with the atmosphere and not concentrated near the surface. The analysis incorporates the effects of atmospheric scattering and explains why previous earth-based observations showed a strong diurnal variation in water content. It also explains the lack of an early morning fog and removes the necessity of daily exchange of large amounts of water between the surface and the atmosphere. A water vapor volume mixing ratio of 1.5 x 10 to the -4th is inferred for the Viking 1 site in late summer.

Davies, D. W.↗
NASA NTRS1979

Relationship between proton motive force and potassium ion transport in Halobacterium halobium envelope vesicles

The permeability of Halobacterium halobium vesicle membranes to potassium ions was investigated, and possible mechanisms for the regulation of the gradient of protons by the transmembrane movement of these ions were studied. The lack of a potassium ion diffusion potential in the absence of valinomycin, light-induced electrical potentials in excess of the chemical potential difference for potassium ions, and direct measurements of potassium ion influx during illumination show that the membranes are relatively impermeable to these ions. As a result of sodium ion extrusion during illumination, chlorine ions and water must be lost and the vesicles collapse. The light-induced collapse of vesicles is diminished only if the influx of potassium ions is increased.

Lanyi, J. K.↗
NASA NTRS1979

Double photoionization and doubly charged ions in the thermosphere

It is shown that a plausible cross section for the double photoionization of oxygen at wavelengths less than 254 A accounts for the observed concentration of O(2+) ions in the thermosphere. Due to the lack of laboratory measurements, double ionization cross sections for atomic oxygen were estimated from laboratory measurements of the ionization cross sections of other species. For altitudes between 150 and 400 km, where O(2+) is assumed to be in photochemical equilibrium, calculations reveal a significantly greater contribution to O(2+) production by double ionization of O atoms than by single ionization of O(+) ions. The concentration of O(2+) ions, assuming a double photoionization creation mechanism and a large sink by charge exchange with molecular nitrogen, is calculated to agree with that measured by AE-C down to altitudes of 250 km.

Victor, G. A.↗
NASA NTRS1979

Structure of the magnetopause - Observations and implications for reconnection

The earth's magnetopause is the boundary between a hot tenuous plasma in the magnetosphere and a cooler denser plasma in the magnetosheath. Both of these plasmas contain magnetic fields whose directions are usually different but whose magnitudes are often comparable. Efforts to understand the structure of the magnetosphere have been hampered by the variability and complexity of this boundary. Waves on the magnetopause surface propagate toward the magnetotail and produce the multiple boundary crossings frequently seen by spacecraft. Boundary velocities are poorly known and range anywhere within an order of magnitude of 10 km/s. Typical thicknesses are probably of the order of a few hundred km, which is a few times the gyroradius of a thermal proton. Although conclusive direct evidence for a field component, Bn, across the magnetopause has not been found; this lack of evidence may reflect the difficulty in determining Bn in the presence of magnetopause waves rather than the real absence of this component. Considerable indirect evidence exists for an open magnetosphere, but the importance of the reconnection process thought to produce open field lines has recently been questioned.

Fairfield, D. H.↗
NASA NTRS1979

Clues to the origin of sulfide minerals in CI chondrites

The dominant sulfide in CI carbonaceous chondrites is an Fe-deficient pyrrhotite containing about 1% Ni, Alais, Ivuna, and Orgueil also contain minor cubanite, CuFe2S3, and Alais minor pentlandite, (Fe,Ni)9S8. All pyrrhotites contain 39.4 + or - 0.1% S; Ni contents range from 0.7 to 1.3%. The phase diagrams reveal no temperature at which the observed pentlandite-pyrrhotite assemblage is at equilibrium. Similarly, the pyrrhotite composition alone are inconsistent with equilibrium formation from a gas of solar composition. In Xe from high-purity submilligram Orgueil pyrrhotite separates, the ratios Xe-129/Xe-132 are not significantly larger than those in trapped meteoritic Xe. The lack of positive evidence for extinct I-129 in pyrrhotite does not permit any inferences regarding cooling rates in the early solar nebula. It is concluded that sulfides in CI chondrites cannot be nebular condensates formed under equilibrium conditions. Argon isotopic abundances reveal the presence of significant spallation and trapped gas components in Orgueil pyrrhotite. The Orgueil exposure age is calculated to be at least about 10 m.y.

Kerridge, J. F.↗
NASA NTRS1979

Large eddy simulation - A predictive approach to turbulent flow computation

The filtering approach (Leonard, 1974) to large eddy simulation is described. Large eddy simulation is then surveyed with reference to subgrid scale models, numerical methods, channel flow, and free shear flows. It is concluded that the premise of LES (i.e., that the small eddies are much easier to model than the large ones) seems to be borne out by computational experience to date. The greatest obstacle in LES at present is the lack of computer power which effectively denies the ability to simulate all the significant eddies in flows of interest.

Ferziger, J. H.↗
NASA NTRS1979

Geophysical observations pertaining to solid-state convection in the terrestrial planets

Observational evidence for solid-state convection in the interiors of the terrestrial planets is reviewed. For the earth, the motion of the lithospheric plates constitutes clear evidence of large-scale convection in the mantle. Although Mars has been found to lack evidence of plate tectonics, the morphology of the Tharsis uplift and the elevation dichotomy between the northern and southern hemispheres may be evidence of mantle convection at one time. Measurements of lunar heat flow and seismic Q imply a convective mechanism limited to the lower mantle. Evidence for internal convection on Mercury consists of its dipole magnetic field and the 3/2 resonance between its rotational motion and its orbital motion, both of which can also be explained by other processes. The limited radar imagery of Venus has not yet provided conclusive evidence of either the presence or absence of convection features. It is concluded that although interior convection in terrestrial planets is implied by rheological, energy and momentum considerations, only on earth is the lithosphere thin enough to provide conclusive evidence of convection.

Phillips, R. J.↗
NASA NTRS1979

A new concept for the daytime magnetosphere of Venus

A different type of interaction between the solar wind and the ionosphere of a non-magnetized planet suggested by the Pioneer Venus magnetic field measurements is presented. They found that the magnetic field of the shocked solar wind does not penetrate the ionosphere, and it appears that the latter acts approximately as a superconductor, excluding any substantial penetration of interplanetary magnetic field. Just beyond the ionopause is a magnetized region with little plasma whose magnetic pressure is approximately equal to the impact pressure of the solar wind. This suggests an interaction where the current system associated with the enhanced magnetic field region flows along the ionopause and is closed by currents in the shocked solar wind plasma, where the J times B forces slow down the plasma approaching the stagnation region and accelerate the plasma flowing away from it. Thus, the lack of magnetic constraint in the ionosphere would allow ionospheric plasma to flow freely from the day to the night side, and this flow could probably maintain the nighttime ionosphere.

Johnson, F. S.↗
NASA NTRS1979

Volcanic eruption plumes on Io

Preliminary analyses of the eight volcanic eruption plumes detected on Io by Voyager 1 are presented. Plumes were observed on the bright and dark limbs of the satellite corresponding to half of the surface and range from 10,000 to 75 km in width and 280 to 70 km in height. Most plumes were observed to be umbrella-shaped, however one consists of a very diffuse cloud lacking columnar fountain characteristics. Plume sources are characterized by a dark central area, surrounded by a bright ring, which in turn is surrounded by a broad, diffuse region; the presence of similar markings in regions not observed at the limb indicates additional volcanic activity on Io. No changes were detected in the sizes or intensities of the eruptions over the 6.5-day viewing period, however a change in the appearance of a region near one plume suggests a short-lived eruption between observations. Seven of the eight plumes are located within 30 deg of the equator, implying that equatorial surfaces are generally younger than those in the polar regions.

Strom, R. G.↗
NASA NTRS1979

Volcanic resurfacing rates and implications for volatiles on Io

The rates of volcanic resurfacing on Io are estimated on the basis of two separate observations and the implications of these rates for the volatile history of Io and the supply of material to the Jovian torus are discussed. Rates of resurfacing based on the lack of observable impact craters and assuming a Jovian cratering rate similar to those of the moon and Mars are found to be on the order of 0.1 cm/year. Estimated deposition rates of volcanic matter are found to be in general agreement with cratering rate determinations, if large particle deposition, undetected volcanic activity, volcanic flows and gas condensation are taken into account. Escape rates from Io estimated for sulfur, oxygen and sodium, based on their concentrations around Io, indicate that only a fraction of the present volcanic material can escape. Thermal and nonthermal escape mechanisms are suggested to account for the current loss of sulfur and oxygen from Io's upper atmosphere, while sputtering of atoms from the surface by impacting magnetospheric ions is suggested as the mechanism of sodium supply.

Johnson, T. V.↗
NASA NTRS1979

Using population statistics for a first look at the utility of Landsat data for urban areas

The paper reviews the Image Based Information System (IBIS), developed at the Jet Propulsion Laboratory (JPL) which provided the city of Los Angeles with Landsat land use data in a format compatible with the city's land use and population files. Landsat data are compared to other land use files and the comparisons are discussed as an attempt to establish a level of validity. Relationships between population and Landsat data are investigated and reveal the strengths and weaknesses of the use of such data for urban areas. Finally, it is noted that the project verified the flexibility of IBIS for reducing and delivering Landsat data to users lacking the ability to process raw satellite data tapes and points to the system as a model for a potential national census of land use.

Landini, A. J.↗
NASA NTRS1979

The role of chemical engineering in space manufacturing

A survey of factors involved in space manufacturing is presented. It is shown that it will be more economical to obtain the necessary raw materials from the moon than from earth due to earth's greater gravity and atmosphere. Discussion covers what resources can be mined and recovered from the moon and what ranges of industrial feedstock can be provided from lunar materials, noting that metallurgy will be different in space due to the lack of key elements such as H, C, Na, Cl, etc. Also covered are chemical plant design, space environmental factors such as vacuum and zero gravity, recycling requirments, reagent and equipment mass, and unit operations such as materials handling and phase separation. It is concluded that a pilot plant in space could be an economic boon to mankind.

Waldron, R. D.↗
NASA NTRS1979

Asymmetries of the emission lines of QSOs, Seyfert galaxies, and novae

Calculations of the anisotropy of line emission from photoionized clouds, and the resulting asymmetry in the line profiles are discussed. The permitted emission-line profiles of Seyfert galaxies and QSO's often contain more light in the red than in the violet wing, and this asymmetry can arise from self-absorption of the line radiation in an expanding system of optically thick clouds. It is shown that the Balmer line optical depths are large enough to give strongly asymmetric line profiles for pure expansion, but the observed lack of strong asymmetry in the Balmer lines of most Seyfert galaxies suggests that the broad-line widths may result from random motions, or that clouds radiate isotropically. It is concluded that the frequently observed absorption of the violet wing of Lyman-alpha must occur in a surrounding region undergoing systematic outflow, or that the weakness of the Balmer line asymmetries is explained by the Balmer line emission resulting from collisional excitation from n=2.

Ferland, G. J.↗
NASA NTRS1979

Measurement of chlorophyll a fluorescence with an airborne fluorosensor

Phytoplankton biomass and diversity among various algal species are important for marine productivity assessments. The spatial heterogeneity of phytoplankton in coastal and estuarine environments complicates estimates of total biomass using conventional surface sampling techniques. Since synoptic or near-synoptic data can be quite useful in these studies, this area is a natural focal point for development of remote sensors. However, it is very difficult to sense phytoplankton density and diversity with spacecraft-borne passive sensors primarily because modulation in the signal due to phytoplankton is of the same order as that of atmospheric effects. The same sensors mounted on aircraft may be able to detect and quantify high concentrations of phytoplankton (blooms), but the current lack of knowledge about the spectral reflectance signatures of the major phytoplankton color groups rules out any diversity measurements by this type of sensor. An active fluorosensor mounted on a low-flying aircraft or helicopter is not limited by any of these constraints. A brief survey of the four currently active systems is presented.

Jarrett, O., Jr.↗
NASA NTRS1979

Influence of phase cancellation and pulse shape artifacts on ultrasonic spectrum analysis

Both continuous wave and Fourier transformed pulse ultrasonic spectroscopy are being applied to material and flow characterization. Ideal samples and flaws (flat, parallel, and homogeneous) and ideal ultrasonic apparatus (producing delta function stress waves) provide acoustic spectra which can be partially inverted. However, in the presence of material inhomogeneity, lack of sample flatness or parallelism, or finite risetime pulses, the spectra become quite complex and produce phase cancellations at the transducer as well as pulse shape spectral artifacts. In this paper, we examine the nature of these artifacts for both simple and practical samples. Sample spectra are contrasted for several different transducer/electronic systems. Spectra obtained with a phase insensitive acousto-electric transducer (AET) combined with a frequency tracked tone-burst spectroscopy (TBS) method are presented. Analysis of the test configuration is shown to produce spectra consistent with that obtained with the AET-TBS combination.

Heyman, J. S.↗
NASA NTRS1979

Stability and control of flexible satellites. I - Stability

This investigation has two distinct parts. In this first part the environmental and control torques experienced by a satellite are assumed to be random so as to account for the inherent errors in the control systems and the lack of exact models of the environmental torques. It has been shown that under this assumption the required stability criteria of a satellite is quite different from that obtained by a deterministic approach. It has also been shown that a flexible three-axes stabilized satellite can be made almost certainly asymptotically stable, while the same is not true for a flexible spinning satellite.

Huang, T. C.↗
NASA NTRS1979

Evaluation of verifiability in HAL/S

The ability of HAL/S to write verifiable programs, a characteristic which is highly desirable in aerospace applications, is lacking since many of the features of HAL/S do not lend themselves to existing verification techniques. The methods of language evaluation are described along with the means in which language features are evaluated for verifiability. These methods are applied in this study to various features of HAL/S to identify specific areas in which the language fails with respect to verifiability. Some conclusions are drawn for the design of programming languages for aerospace applications and ongoing work to identify a verifiable subset of HAL/S is described.

Young, W. D.↗
NASA NTRS1980

Real-time film recording from stroke-written CRT's

Real-time simulation studies often require motion-picture recording of events directly from stroke written cathode-ray tubes (CRT's). Difficulty presented is prevention of "flicker," which results from lack of synchronization between display sequence on CRT and shutter motion of camera. Programmable method has been devised for phasing display sequence to shutter motion, ensuring flicker-free recordings.

Hunt, R.↗