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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 307 records · Page 17

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NASA NTRS1972

Anomalous FIM images of tungsten.

Observation of unusual field-ion images consisting of bright bands of variable width parallel to the 111 (in carets) zones in tungsten at 78 K. Typical conditions for the effect are: pulse width from 1 to 50 microsec and pulse height adjusted so that five to ten pulses are required to remove one (110) plane. The influence of a number of accessible variables was studied and the results lead to a two-mechanism model for field evaporation involving (1) a slow process requiring helium promotion and (2) unpromoted evaporation when the local helium supply is depleted at high rates. The model implies that helium diffusion is rate-limiting in the promotion mechanism and leads to a migration energy of about 0.15 eV during field evaporation. There is a measurable difference in end form in the limits of high- and low-field evaporation rates. High rates are nearly isotropic and yield a more hemispherical end form.

Hren, J. J.↗

NASA NTRS1974

Cyclic-stress analysis of notches for supersonic transport conditions

The feasibility of using the finite element method to account for the effects of cyclic load and temperature on local stresses and strains at a notch was demonstrated. The behavior of a notched titanium panel was studied under variable loads and temperatures representative of flight conditions for the lower wing surface of a Supersonic Transport (SST). The analysis was performed with the use of the BOPACE finite-element computer program which provides capability to determine high temperature and large viscoplastic effects caused by cyclic thermal and mechanical loads. The analysis involves the development of the finite-element model as well as determination of the structural behavior of the notched panel. Results are presented for twelve SST flights comprised of five different load-temperature cycles. The results show the approach is feasible, but material response to cyclic loads, temperatures, and hold times requires improved understanding to allow proper modeling of the material.

Source record↗

NASA NTRS1974

Lateral-directional stability characteristics of a wing-fuselage configuration at angles of attack up to 44 deg

An investigation has been conducted to determine the effects of configuration variables on the lateral-directional stability characteristics of a wing-fuselage configuration. The variables under study included variations in the location of a single center-line vertical tail and twin vertical tails, wing height, fuselage strakes, and horizontal tails. The study was conducted in the Langley high-speed 7-by 10-foot tunnel at a Mach number of 0.30, at angles of attack up to 44 deg and at sideslip angles of 0 deg and plus or minus 5 deg.

Henderson, W. P.↗

NASA NTRS1974

An ellipsometer with variable angle of incidence for studies in ultrahigh vacuum

The windows for the vacuum chamber are incorporated into the optical bench system by means of flexible bellows which allow measurements to be made over a large range of angle of incidence, one of which is chosen so that maximum sensitivity is obtained. The principal angle of incidence was determined, and straightforward corrections for strain birefringence of vacuum chamber windows were made. Atomically clean surfaces of sodium chloride and lithium fluoride were investigated to verify the performance of the system. Submonolayer and monolayer coverage of water on these surfaces could be detected. On cleavage planes of NaCl, a first monolayer of adsorbed water is complete at about one torr only.

Walter, H. U.↗

NASA NTRS1974

Photoelectric spectrophotometry of Wolf-Rayet stars

Photoelectric spectrum scans of five southern Wolf-Rayet stars in the spectral range lambda lambda 4600-4720 were analyzed to study the variability of brightness and of emission line strengths. No variations of any kind in short time scale were found. However, in WC stars night-to-night variations of three to four percent were detected in the emission line strengths.

Bahng, J. D. R.↗

NASA NTRS1975

Photoelectric spectrophotometry of Wolf-Rayet stars

Photoelectric spectrum scans of five southern Wolf-Rayet stars in the spectral range 4600-4720 A were analyzed to study the variability of brightness and of emission line strengths. No variations of any kind in short time scale were found. However, in WC stars night-to-night variations of 3 to 4 per cent were detected in the emission line strengths.

Bahng, J. D. R.↗

NASA NTRS1976

Domestic and world trends affecting the future of aviation (1980 - 2000), appendix C

The results are presented of a study of variables affecting aviation in the United States during the last fifth of the twentieth century. A series of key trends relating to economic, social, political, technological, ecological, and environmental developments are identified and discussed with relation to their possible effects on aviation. From this analysis a series of scenarios is developed representing an array of possibilities ranging from severe economic depression and high international tension on the one hand to a world of detente which enjoys an unprecedented economic growth rate and relaxation of tensions on the other. A scenario is presented which represents the manner in which events will most probably develop and their effect on the aviation industry.

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NASA NTRS1975

Copernicus observations of a number of galactic X-ray sources

The Copernicus satellite was launched on 21 August 1972. The main experiment on board is the University of Princeton UV telescope. In addition a cosmic X-ray package of somewhat modest aperture was provided by the Mullard Space Science Laboratory (MSSL) of University College London. Following a brief description of the instrument, a list of galactic sources observed during the year is presented. Although the X-ray detection aperture is small, the ability to point the satellite for long periods of time with high accuracy makes Copernicus an ideal vehicle for the study of variable sources.

J. L. Culhane↗

NASA NTRS1980

Pulsation and mass loss in Mira variables

The behavior of pulsation in the outer layers of a typical Mira variable was studied in the adiabatic and isothermal limits. A shock wave propagates outward once per period and the radial velocity obtained from observations of hydrogen emission lines is identified with the velocity of gas in the post shock region. In the adiabatic case, mass loss in the form of a steady stellar wind was produced. In the isothermal case, no continuous mass loss was produced but occasional ejection of shells occur. Pulsation introduced into a star undergoing steady mass loss as a result of radiation pressure acting on grains caused the mass loss rate to increase by a factor of approximately 40, while the terminal velocity of the flow was almost unaltered.

Wood, P. R.↗

NASA NTRS1979

On the dynamic forcing of short-term climate fluctuations by feedback mechanisms

Various internal feedback mechanisms in the ocean atmosphere system were studied. A variability pattern of sea surface temperature with a quasibiennial oscillation (QBO) was detected off the coast of Senegal, in the Gulf of Guinea and even in the Gulf Stream as it leaves the North American continental shelf. Possible physical connections between some of these QBO's were pointed out by a hypothetical feedback model. Interaction of a QBO with the annual cycle may lead to beating frequencies resembling climatic trends of a duration of several years.

Reiter, E. R.↗

NASA NTRS1981

Edge delamination in angle-ply composite laminates, part 5

A theoretical method was developed for describing the edge delamination stress intensity characteristics in angle-ply composite laminates. The method is based on the theory of anisotropic elasticity. The edge delamination problem is formulated using Lekhnitskii's complex-variable stress potentials and an especially developed eigenfunction expansion method. The method predicts exact orders of the three-dimensional stress singularity in a delamination crack tip region. With the aid of boundary collocation, the method predicts the complete stress and displacement fields in a finite-dimensional, delaminated composite. Fracture mechanics parameters such as the mixed-mode stress intensity factors and associated energy release rates for edge delamination can be calculated explicity. Solutions are obtained for edge delaminated (theta/-theta theta/-theta) angle-ply composites under uniform axial extension. Effects of delamination lengths, fiber orientations, lamination and geometric variables are studied.

Wang, S. S.↗

NASA NTRS1982

Optimization of a Non-traditional Unsupervised Classification Approach for Land Cover Analysis

The conditions under which a hybrid of clustering and canonical analysis for image classification produce optimum results were analyzed. The approach involves generation of classes by clustering for input to canonical analysis. The importance of the number of clusters input and the effect of other parameters of the clustering algorithm (ISOCLS) were examined. The approach derives its final result by clustering the canonically transformed data. Therefore the importance of number of clusters requested in this final stage was also examined. The effect of these variables were studied in terms of the average separability (as measured by transformed divergence) of the final clusters, the transformation matrices resulting from different numbers of input classes, and the accuracy of the final classifications. The research was performed with LANDSAT MSS data over the Hazleton/Berwick Pennsylvania area. Final classifications were compared pixel by pixel with an existing geographic information system to provide an indication of their accuracy.

Boyd, R. K.↗

NASA NTRS1983

Ultraviolet studies of nova-like variables with the IUE

KQ Mon is a new UX UMa-type nova-like variable. Optical spectra taken in 1978 reveal very shallow Balmer absorption lines and He I (wavelength 4471) absorption. There was no evidence of orbital variations but the appearance of the optical spectrum and the presence of low amplitude flickering suggested a strong similarity to CD-42 degrees 14462 (=V3885 Sgr) and other members of the UX UMa class. KQ Mon was observed at low dispersion with the IUE satellite. Six spectra taken with the short wavelength prime (SWP) camera are dominated by strong broad absorption lines due to N V, O I, Si III, Si IV, C IV, He II, N IV, and A1 III. There is little evidence of orbital phase modulation over the time baseline of the observations. Unlike UV observations of other UX UMa-type objects, KQ Mon exhibits no emission lines or P Cygni-type profiles and the velocity displacements appear to be smaller, suggesting the absence of a hot, high velocity wind characterizing other UX UMa stars. The relationship of KQ Mon to other UX UMa disk stars is discussed and a model is suggested to explain their observed properties and the lack of major outbursts.

Guinan, E. F.↗

NASA NTRS1985

Towards a study of synoptic-scale variability of the California current system

A West Coast satellite time series advisory group was established to consider the scientific rationale for the development of complete west coast time series of imagery of sea surface temperature (as derived by the Advanced Very High Resolution Radiometer on the NOAA polar orbiter, and near-surface phytoplankton pigment concentrations (as derived by the Coastal Zone Color Scanner on Nimbus 7). The scientific and data processing requirements for such time series are also considered. It is determined that such time series are essential if a number of scientific questions regarding the synoptic-scale dynamics of the California Current System are to be addressed. These questions concern both biological and physical processes.

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NASA NTRS1985

Aerodynamic characteristics of a high-wing transport configuration with a over-the-wing nacelle-pylon arrangement

An investigation has been conducted in the Langley 16-Foot Transonic Tunnel to determine the effects on the aerodynamic characteristics of a high-wing transport configuration of installing an over-the-wing nacelle-pylon arrangement. The tests are conducted at Mach numbers from 0.70 to 0.82 and at angles of attack from -2 deg to 4 deg. The configurational variables under study include symmetrical and contoured nacelles and pylons, pylon size, and wing leading-edge extensions. The symmetrical nacelles and pylons reduce the lift coefficient, increase the drag coefficient, and cause a nose-up pitching-moment coefficient. The contoured nacelles significantly reduce the interference drag, though it is still excessive. Increasing the pylon size reduces the drag, whereas adding wing leading-edge extension does not affect the aerodynamic characteristics significantly.

Henderson, W. P.↗

NASA NTRS1986

RR Lyrae stars - A theoretical study of Bailey type c variables

New theoretical models of stars pulsating in the first overtone have been constructed to simulate RR Lyr variables of Bailey type c. Despite the use of different opacities, these new models agree very well with earlier models built by Christy and Stellingwerf. Quantitative comparisons using empirical light curves and velocity curves of metal-poor type c variables confirm the validity of the models. Masses of 0.55-0.65 solar mass and luminosities of 40-50 solar luminosities derived here for the type c variables, are consistent with previous results obtained for type ab variables. A Christy echo of the kind normally associated with fundamental-mode pulsators was detected in the interior velocity structure of one first-overtone model that happens to have a large velocity amplitude.

Hubickyj, Olenka↗

NASA NTRS1988

Improved Consolidation Of Silicon Carbide

Colloidal techniques used to improve dispersion and suspension of SiC in water. In combination with slurry pressing, resulted in increase in strength of sintered SiC by 87 percent over SiC sintered after dry pressing. Improvement due to reduced porosity and reflected in improved densities of "green" and sintered specimens. Smaller sizes of pores, and reduced sizes of critical flaws contributed to increase in strength. Useful for making parts from particulate-, transformation-, and whisker-toughened ceramics and monolithic ceramics. Provides avenue for study of variables contributing to reliability of current structural ceramics.

Freedman, Marc R.↗

NASA NTRS1990

Cirrus parameterization from the FIRE ER-2 observations

Primary goals for the FIRE field experiments were validation of satellite cloud retrievals and study of cloud radiation parameters. The radiometers and lidar observations which were acquired from the NASA ER-2 high altitude aircraft during the FIRE cirrus field study may be applied to derive quantities which would be applicable for comparison to satellite retrievals and to define the cirrus radiative characteristics. The analysis involves parameterization of the vertical cloud distribution and relative radiance effects. An initial case study from the 28 Oct. 1986 cirrus experiment has been carried out, and results from additional experiment days are to be reported. The observations reported are for 1 day. Analysis of the many other cirrus observation cases from the FIRE study show variability of results.

Spinhirne, James D.↗