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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Material variability as measured by low temperature electrical resistivity.

Low temperature electrical resistivity was used to determine the material variability (1) between different manufacturers, (2) between different heats from the same manufacturer, and (3) within a given heat for Al 2024, Al-5% Mg alloys, Inconel 718, A286 stainless, and AISI 316. Generally, the coefficient of variation for solution annealed alloys ranged from 1.2 to 14% between manufacturers, 0.8 to 5.1% between heats, and 0.1 to 1.6% within a heat with stainless steels at the low ends and Al 2024 at the high ends. The variability is increased if the material is in a precipitation-hardened condition. A statistical analysis suggests that the variability within a heat is non-normal.

Clark, A. F.↗
NASA NTRS1971

Variable X-ray sources.

The behavior of the quasi-periodic rapid variable Cyg X-1, the periodic variable Cen X-3, and the aperiodic variable Sco X-1 is described. Observations of Cyg X-1 were made by pointing the Uhuru satellite to a position where the object was in the band visible to the X-ray detectors; observations were also obtained by other methods. It appears that the X-ray emitting region is a few light sec in size, and some of the fast variations originate in a region as small as several earth radii in size. It is believed at present that a pulsating white dwarf could explain the X-ray behavior of Cen X-3. X-ray data from Sco X-1 reveal that it behaves in soft X rays much as it is well known to do in visible light.

Kellogg, E. M.↗
NASA NTRS1973

The 3.5 micron light curves of long period variable stars

Infrared observations at an effective wavelength of 3.5 microns of a selected group of long period variable (LPV) stars are presented. Mira type and semiregular stars of M, S, and C spectral classifications were monitored throughout the full cycle of variability. Although the variable infrared radiation does not exactly repeat in intensity or time, the regularity is sufficient to produce mean 3.5 micron light curves. The 3.5 micron maximum radiation lags the visual maximum by about one-seventh of a cycle, while the minimum 3.5 micron intensity occurs nearly one-half cycle after infrared maximum. In some stars, there are inflections or humps on the ascending portion of the 3.5 micron light curve which may also be seen in the visual variations.

Strecker, D. W.↗
NASA NTRS1974

Ultraviolet photometry from the orbiting astronomical observatory. XV - The strongly magnetic variable HD 215441

The Wisconsin Experiment Package on OAO-2 was used to obtain light curves of the strongly magnetic, variable Ap star HD 215441 over the wavelength range 1550 to 4250 A. This star is characterized by a lack of outstanding spectrum variability at wavelengths accessible from the ground, while undergoing UBV photometric variations of large amplitude. The observations of HD 215441 demonstrate that an Ap star need not be a striking spectrum variable at blue-visible wavelengths for its photometric variations to be controlled by opacity variations in the ultraviolet.

Leckrone, D. S.↗
NASA NTRS1974

Recent advances in satellite observations of solar variability and global atmospheric ozone

A description is given of the temporal behavior of the sun as an ultraviolet variable star in relation to daily zonal means of atmospheric ozone from the total amount to that above the 10-mb and 4-mb pressure levels. A significant correlation has been observed between enhancements in the ultraviolet solar irradiances and terrestrial passages of the solar magnetic field sector boundary structure. However, it has not yet been possible to separate solar from the dynamical effects on the variability in the zonal means of ozone. Attention is given to global changes in ozone which have been derived from the satellite observations in terms of season, solar variability, and major stratospheric disturbances such as stratospheric warmings.

Heath, D. F.↗
NASA NTRS1975

Observations of variable X-ray sources in globular clusters

The discovery is reported of a variable X-ray source at midgalactic latitude in the globular cluster NGC 1851, and observations are reported which confirm the existence of variable X-ray sources in NGC 7078 and NGC 6441. The new source, designated MX 0513-40, was found to vary in intensity by a factor of at least 5 over a sixteen-day period and to have a hard spectrum as compared to that of the Crab Nebula in the energy range from 1 to 10 keV. The source in NGC 7078 (3U 2131+11) was found to vary by more than a factor of 2 over a 500-day period. Strong evidence of variability is presented for the source in NGC 6441 (3U 1746-37). It is concluded that both MX 0513-40 and 3U 2131+11 are probably stellar objects and are no more than about 160 kpc distant.

Clark, G. W.↗
NASA NTRS1975

Variable radio source structure on a scale of several minutes of arc

Results are reported for high-frequency (0.75, 1.40, 3.24, 6.63, and 10.63 GHz) flux-density measurements of about 100 radio sources exhibiting low-frequency cutoffs. At least three sources (4C 79.4, 4C 79.15, and PKS 2344+09) showed variable structure on a scale ranging from a fraction of an arcmin to as much as 15 arcmin which appears to change significantly on a time scale of several months. The visual fields of these sources and their companion components are searched for identifiable objects, and complete radio spectra as well as contour maps are presented for some of the sources. It is suggested that the variable structure may result from the existence of several emission centers that are highly variable in flux density but fixed in position.

Ross, H. N.↗
NASA NTRS1976

Atmospheric structure and variability in areas of convective storms determined from 3-h rawinsonde data

The structure and variability of the atmosphere in areas of radar-observed convection were established by using 3-h rawinsonde and surface data from NASA's second Atmospheric Variability Experiment. Convective activity was shown to exist in areas where the low and middle troposphere is moist and the air is potentially and convectively unstable and has upward motion, in combination with positive moisture advection, at either the surface or within the boundary layer. The large variability of the parameters associated with convective storms over time intervals less than 12 h was also demonstrated so as to possibly produce a change in the probability of convective activity by a factor of 8 or more in 3 h. Between 30 and 60 percent of the total changes in parameters associated with convective activity over a 12-h period were shown to take place during a 3-h period. These large changes in parameters are related to subsynoptic-scale systems that often produce convective storms.

Wilson, G. S.↗
NASA NTRS1976

Low-speed wind-tunnel tests of a large scale blended arrow advanced supersonic transport model having variable cycle engines and vectoring exhaust nozzles

A low-speed wind-tunnel investigation was conducted in a full-scale tunnel to determine the performance and static stability and control characteristics of a large-scale model of a blended-arrow advanced supersonic transport configuration incorporating variable-cycle engines and vectoring exhaust nozzles. Configuration variables tested included: (1) engine mode (cruise or low-speed), (2) engine exit nozzle deflection, (3) leading-edge flap geometry, and (4) trailing-edge flap deflection. Test variables included values of C sub micron from 0 to 0.38, values of angle of attack from -10 degrees to 30 degrees, values of angle of sideslip, from -5 degrees to 5 degrees, and values of Reynolds number, from 3.5 million to 6.8 million.

Parlett, L. P.↗
NASA NTRS1974

Relationships between vegetation and terrain variables in southeastern Arizona

The author has identified the following significant results. Relationships were established between eight terrain variables and plant species and 31 vegetation types. Certain plant species are better than others for differentiating or discriminating groups of specified terrain variables. Certain terrain variables are better than others for differentiating or discriminating groups of vegetation types. Stepwise discriminant analysis was shown to be a useful tool in plant ecological studies.

Mouat, D. A.↗
NASA NTRS1976

Aerodynamic Performance of Two Variable-Pitch Fan Stages

The NASA-Lewis Research Center is investigating a variety of fan stages applicable for short haul aircraft. These low-pressure-ratio low-speed fan stages may require variable-pitch rotor blades to provide optimum performance for the varied flight demands and for thrust reversal on landing. A number of the aerodynamic and structural compromises relating to the variable-pitch rotor blades are discussed. The aerodynamic performance of two variable-pitch fan stages operated at several rotor blade setting angles for both forward and reverse flow application are presented. Detailed radial surveys are presented for both forward and reverse flow.

Moore, R. D.↗
NASA NTRS1976

Derivatives of a statically reduced stiffness matrix with respect to sizing variables

An expression is obtained for the first derivatives with respect to the sizing variables of a statically reduced stiffness matrix that is a nonlinear function of the sizing variables, where the unreduced stiffness matrix is a linear function of the sizing variables. An accepted procedure to reduce the number of degrees of freedom is to eliminate a number of nodal displacements from the degrees of freedom such that the accuracy of the flutter analysis is not significantly affected. In a typical optimization procedure with flutter constraints, the derivative of the stiffness matrix may be used in a form that contains the characteristic vector of the flutter matrix equation and the transpose of the characteristic vector of the adjoint flutter matrix equation corresponding to a particular solution of the flutter equation.

Oconnell, R. F.↗
NASA NTRS1976

Aerodynamic performance of two variable-pitch fan stages

NASA-Lewis Research Center is investigating a variety of fan stages applicable for short-haul aircraft. These low-pressure-ratio low-speed fan stages may require variable-pitch rotor blades to provide optimum performance for the varied flight demands and for thrust reversal on landing. A number of the aerodynamic and structural compromises relating to variable-pitch rotor blades are discussed. The aerodynamic performance of two variable-pitch fan stages operated at several rotor-blade setting angles is evaluated for both forward- and reverse-flow application. Detailed radial surveys are presented for both forward and reverse flow.

Moore, R. D.↗
NASA NTRS1977

Variable volume maser techniques

The frequency stability of hydrogen masers in variable volume storage bulbs is discussed in terms of wall shift. Variable volume devices discussed include: Brenner flexible bulb, Debely device, and the concertina hydrogen maser. A flexible cone variable volume element outside the cavity is described.

Reinhardt, V. S.↗
NASA NTRS1977

Assessment of Relative Velocity as Independent Variable for Space Shuttle First Stage Guidance Attitude Command Tables

The selection of relative velocity as the independent variable for the space shuttle first stage guidance attitude command tables was assessed to support the first stage guidance point design. The criterion for selecting the independent variable for first stage open loop guidance is to reduce or minimize performance dispersions, primarily those affecting structural loads. The products of angle of attack and angle of sideslip times dynamic pressure are used as load indicators, and minimizing their dispersions will indicate a minimum loads dispersion. Relative velocity is shown to be an acceptable steering independent variable.

Kimbrough, M.↗
NASA NTRS1977

The variety of variables in mathematical expressions

Various distinctions are discussed which can be made regarding evaluation of mathematical expressions: regular evaluation vs. infinite evaluation vs. finite evaluation, regular variables vs. mathematical variables vs. shadow variables vs. labels, simplification vs. evaluation vs. solution of equations. The unsatisfactory state of evaluation strategies in symbolic systems is due to insufficient use of such distinctions in the past.

Moses, J.↗
NASA NTRS1977

Reduced variable technique for predicting grain behavior

The use of reduced variables to account for the time-temperature dependence of the relaxation modulus is a standard and universally adopted technique in the stress analysis of solid propellant grains. Recent work has suggested that the reduced variable technique can also be used to account for the dependence of the relaxation modulus on the crosslink density of an elastomer system. By combining variables, it is now possible to determine the relaxation modulus as a function of both mechanical and chemical parameters over a long period of time. The problems involved, the pitfalls to be avoided, and suggested techniques to be used in acquiring data are discussed.

Lewis, G. W.↗
NASA NTRS1977

Numerical solution of the compressible Navier-Stokes equations using density gradients as additional dependent variables

Numerical solution of two dimensional, time dependent, compressible viscous Navier-Stokes equations about arbitrary bodies was treated using density gradients as additional dependent variables. Thus, six dependent variables were computed with the SOR iteration method. Besides formulation for pressure gradient terms, a formulation for computing the body density was presented. To approximate the governing equations, an implicit finite difference method was employed. In computing the solution for the flow about a circular cylinder, a problem arose near the wall at both stagnation points. Thus, computations with various conditions were tried to examine the problem. Also, computations with and without formulations are compared. The flow variables were computed on 37 by 40 field first, then on an 81 by 40 field.

Kwon, J. H.↗