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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 163 records · Page 9

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NASA NTRS1974

Computer program for calculation of real gas turbulent boundary layers with variable edge entropy

A user's manual for a computer program which calculates real gas turbulent boundary layers with variable edge entropy on a blunt cone or flat plate at zero angle of attack is presented. An integral method is used. The method includes the effect of real gas in thermodynamic equilibrium and variable edge entropy. A modified Crocco enthalpy velocity relationship is used for the enthalpy profiles and an empirical correlation of the N-power law profile is used for the velocity profile. The skin-friction-coefficient expressions of Spalding and Chi and Van Driest are used in the solution of the momentum equation and in the heat-transfer predictions that use several modified forms of Reynolds analogy.

Boney, L. R.↗

NASA NTRS1974

Engineering prediction of turbulent skin friction and heat transfer in high-speed flow

A large collection of experimental turbulent-skin-friction and heat-transfer data for flat plates and cones was used to determine the most accurate of six of the most popular engineering-prediction methods; the data represent a Mach number range from 4 to 13 and ratio of wall to total temperature ranging from 0.1 to 0.7. The Spalding and Chi method incorporating virtual-origin concepts was found to be the best prediction method for Mach numbers less than 10; the limited experimental data for Mach numbers greater than 10 were not well predicted by any of the engineering methods except the Coles method.

Cary, A. M., Jr.↗

NASA NTRS1974

A man in the loop trajectory optimization program (MILTOP)

An interactive trajectory optimization program is developed for use in initial fixing of launch configurations. The program is called MILTOP for Man-In-the-Loop-Trajectory Optimization-Program. The program is designed to facilitate quick look studies using man-machine decision combinations to reduce the time required to solve a given problem. MILTOP integrates the equations of motion of a point-mass in 3-Dimensions with drag as the only aerodynamic force present. Any point in time at which an integration step terminates, may be used as a decision-break-point, with complete user control over all variables and routines at this point. Automatic phases are provided for different modes of control: vertical rise, pitch-over, gravity turn, chi-freeze and control turn. Stage parameters are initialized from a separate routine so the user may fly as many stages as his problem demands. The MILTOP system uses both interactively on storage scope consoles, or in batch mode with numerical output on the live printer.

Reinfields, J.↗

NASA NTRS1975

The effects of correlation on goodness of fit

Autocorrelated normal random variates were generated via computer and the effects of various levels of correlation on goodness of fit problems were studied. The results are useful in determining the distribution or estimating the parameters of populations that correlate observations such as wind speeds and temperature. The model used to generate the autocorrelated data is an autoregressive process of order 1. The Kolmogorov-Smirnov and chi-square statistics are used in the analysis. It was observed in the simulation that high positive correlations tend to shift the sample mean away from the population mean and negative correlations tend to shift the sample mean towards the population mean. In many cases, it was observed that positive and negative correlations tend to decrease the standard deviation. However, since this did not occur in all cases, no definite conclusion can be made regarding the standard deviation. Since the autoregressive process is a linear transformation, it is not surprising that normality was preserved. However, a possible extension of this problem could be to generate non-normal data and observe how the distribution is affected by correlation. Another extension might utilize another model such as autoregressive of order k or a moving average process of order k.

Kitchens, L. J.↗

NASA NTRS1974

Explanation of the computer listings of Faraday factors for INTASAT users

Using a simplified form of the Appleton-Hartree formula for the phase refractive index, a relationship was obtained between the Faraday rotation angle along the angular path and the total electron content along the vertical path, intersecting the angular at the height of maximum electron density. Using the second mean value theorem of integration, the function B cosine theta second chi was removed from under the integral sign and replaced by a 'mean' value. The mean value factors were printed on the computer listing for 39 stations receiving signals from the INTASAT satellite during the specified time period. The data is presented by station and date. Graphs are included to demonstrate the variation of the Faraday factor with local time and season, with magnetic latitude, elevation and azimuth angles. Other topics discussed include a description of the bent ionospheric model, the earth's magnetic field model, and the sample computer listing.

Nesterczuk, G.↗

NASA NTRS1975

An improved source flow characteristic technique for the analysis of scramjet exhaust flow fields

The process is discussed of designing a nozzle for a hypersonic airbreathing vehicle which involves a complex study of the inter-relationship among many parameters: internal-external expansion, vehicle lift, drag, pitching moments, and structural and weight limitations. The source flow characteristic approach to the design process was extended and improved, and streamline interpolation procedure was incorporated. All characteristic and boundary calculations were made compatible with frozen, equilibrium and ideal gas thermodynamic options, while slip surface calculations (cowl interaction) were extended to underexpanded flow conditions. Since viscous forces can significantly influence vehicle forces, pitching moments and structural/weight considerations, a local integration via flat plate boundary layer skin friction and heat transfer coefficients was included. These effects are calculated using the Spalding and Chi method, and all force and moment calculations are performed via integration of the local forces acting on the specified vehicle wetted areas.

Delguidice, P. D.↗

NASA NTRS1974

Studies of cluster X-ray sources - Size measurements

An examination is conducted of the nine weaker sources in the list of Kellogg et al. (1973) which are well enough observed to be listed in the 3U catalog compiled by Giacconi et al. (1974). The cluster sizes are presented in a table and chi-square plots versus derived core radius and background counting rate are shown in a graph. X-ray luminosities calculated from the 3U catalog counting rates are presented as a function of X-ray size.

Kellogg, E.↗

NASA NTRS1974

Chain pooling to minimize prediction errors in subset regression

The existing theory of subset regression is examined, taking into account optimality criteria, small experiments, nonlinear models, colinearities, and special techniques. Approaches based on chain pooling coupled with principal components regression are discussed, giving attention to a comparison of half-normal plotting with chain pooling, a procedure based on prior ordering, deletion under the F-test, the largest of a set of chi-square variates, and principal components regression and model deletion. The choice of a true (population) model for simulations is considered along with the evaluation of the decision procedure and suitable computer programs.

Holms, A. G.↗

NASA NTRS1975

Tables of critical values for examining compositional non-randomness in proteins and nucleic acids

A binomially distributed statistic is defined to show whether or not the proportion of a particular amino acid in a protein deviates from random expectation. An analogous statistic is derived for nucleotides in nucleic acids. These new statistics are simply related to the classical chi-squared test. They explicitly account for the compositional fluctuations imposed by the finite length of proteins, and they are more accurate than previous tables.

Laird, M.↗

NASA NTRS1975

Interpretation of an urban scene using multi-channel radar imagery

Four channel, SLAR imagery was studied by a group of individuals having no previous experience with either SLAR imagery or the urban area under scrutiny. This tactic was used because it was desired to define the nature of training needed when introducing people to radar imagery of urban scenes. Responses resulting from interpretations based on standard photointerpretation methods were subjected to a Chi-square analysis to determine the level of significance of the interpretations. For the urban scene studied, and for the two wavelengths (X /3.0 cm/ and L /23.0 cm/ Band) and polarizations (HH and HV) used, several types of urban land use were easily and accurately identified. It is shown that little formal training is required for obtaining quite high interpretation accuracies from multi-channel radar images of some urban scenes.

Bryan, M. L.↗

NASA NTRS1975

Inelastic-interaction mean free path of negative pions in tungsten

The inelastic-interaction mean free paths (lambda) of 5-, 10-, and 15-GeV/c pions have been measured by determining the distribution of first-interaction locations in a modular tungsten-scintillator ionization spectrometer. In addition to commonly used interaction signatures of a few (2-5) particles in two or three consecutive modules, a chi-squared distribution is employed to calculate the probability that the first interaction occurred at a specific depth in the spectrometer. This latter technique seems to be more reliable than use of the simpler criteria. No significant dependence of lambda on energy has been observed. In tungsten, lambda for pions is 206 (plus or minus 6) g/sq cm.

Cheshire, D. L.↗

NASA NTRS1976

Isotopic abundances of Hg in mercury stars inferred from the Hg II line at 3984 A

Wavelengths of the Hg II absorption feature at 3984 A in 30 Hg stars are distributed uniformly from the value for the terrestrial mix to a value that corresponds to nearly pure Hg-204. The wavelengths are correlated loosely with effective temperatures inferred from Q(UBV). Relative isotopic abundances derived from partially resolved profiles of the 3984-A line in iota CrB, chi Lup, and HR 4072 suggest that mass-dependent fractionation has occurred in all three stars. It is supposed that such fractionation occurs in all Hg stars, and a scheme whereby isotopic compositions can be inferred from a comparison of stellar wavelengths and equivalent widths with those calculated for a family of fractionated isotopic mixes. Theoretical profiles calculated for the derived isotopic composition agree well with high-resolution interferometric profiles obtained for three of the stars.

White, R. E.↗

NASA NTRS1977

Multivariate-normality goodness-of-fit tests

Computer program applies chi-square Pearson test to multivariate statistics for application in any field in which data of two or more variables (dimensions) are sampled for statistical purposes. Program handles dimensions two through five, with up to thousand data sets.

Falls, L. W.↗

NASA NTRS1976

The C-12/C-13 ratio in stellar atmospheres. VI - Five luminous cool stars

A simple curve-of-growth technique is described for extracting the C-12/C-13 ratio for M stars from high-resolution spectra of CO infrared vibration-rotation lines. The technique is applied to the CO lines at 1.6 and 2.3 microns in spectra of two M supergiants (Alpha Ori and Alpha Sco), two M giants (Alpha Her and Beta Peg), and a Mira-type variable (Chi Cyg). As a check on the CO analysis, the C-12/C-13 ratio is derived from the red CN system at 8000 A for Alpha Sco, Alpha Ori, and Beta Peg. The CO analysis is also applied to the K giant Alpha Boo as a check. The CN and CO results are found to be in general agreement, and the C-12/C-13 ratio in all the examined stars is shown to be considerably lower than the solar-system value. It is suggested that these stars were formed from clouds with a C-12/C-13 ratio of 40 to 89 and that their atmospheres now exhibit an enhancement of C-13 abundance due to internal production and mixing to the surface.

Hinkle, K. H.↗

NASA NTRS1978

Digital controller design: Analysis of the annular suspension pointing system

The analog controllers of the annular suspension pointing system are designed for control of the chi, phi sub 1, and phi sub 2 bandwidth dynamics through decoupling and pole placement. Since it is virtually impossible to find an equivalent bandwidth of the overall system and establish a general eigenvalue requirement for the system, the subsystem dynamics are decoupled through state feedback and the poles are placed simultaneously to realize the desired bandwidths for the three system components. Decoupling and pole placement are also used to design the closed-loop digital system through approximation.

Kuo, B. C.↗

NASA NTRS1978

The high-energy pulsed X-ray spectrum of HER X-1 as observed with OSO-8

Her X-1 was observed from 1977 August 30 to September 10 using the High-Energy X-Ray Scintillation Spectrometer on board the OSO-8 satellite. The observation, during which the source was monitored continually for nearly an entire ON-state, covered the energy range from 16 to 280 keV. Pulsed flux measurements as a function of binary orbit and binary phase are presented for energies between 16 and 98 keV. The pulsed flux between 16 and 33 keV exhibited a sharp decrease following the fourth binary orbit and was consistent with zero pulsed flux thereafter. The pulsed spectrum was fitted with a power law, a thermal spectrum without features, and a thermal spectrum with a superposed gaussian centered at 55 keV. The latter fit has the smallest value of chi - squared per degree of freedom, and the resulting integrated line intensity is 1.5 superscript + 4.1 subscript - 1.4 x .001 photons s superscript-1 cm superscript-2 for a width of 3.1 superscript + 9.1 subscript -2.6 keV. This result, while of low statistical significance, agrees with the value observed by Trumper (1978) during the same On-state.

Maurer, G. S.↗

NASA NTRS1978

Observations of the hard X-ray spectrum of the impulsive phase of solar flares

The impulsive solar hard X-ray spectrum provides a direct diagnostic on the impulsive energy release of the flare. The data from the hard X-ray (14-342 keV) spectrometer on OSO 7 have been examined for events covering a wide energy range to determine the photon spectrum more precisely. This resulted in a sample of 38 events. The data have been fitted with either single- or double-power laws, and with an exponential spectrum, as from thermal bremsstrahlung. The chi-squared statistic between two-parameter fits strongly favors the exponential fit, particularly at peak intensity when the widest energy range is sampled. This result supports a single-temperature thermal source of the impulsive solar hard X-rays with temperatures in the range 4.7-31 keV and emission measures in the range from 8.4 x 10 to the 43rd to 6.0 x 10 to the 46th per cu cm. The temperature reaches a single maximum and then rapidly decays, but the emission measure usually increases throughout, even after temperature maximum, for data with 10-s resolution.

Elcan, M. J.↗

NASA NTRS1978

Does the emission measure decrease during the start of a soft X-ray flare

It is suggested that the apparent emission dip found in soft X-ray flare observations, interpreted as the emission from a single temperature plasma, is an artifact. According to this hypothesis, the flare phenomenon represents a combination of flare plus a stable active region plasma. A small amount of hot flare plasma will dominate the total emission, and the calculated isothermal plasma parameters will trend towards those of the hot flare plasma, so that a decrease in emission measure will be inferred. It is claimed that observed data fit the model of a stable plasma plus a flare plasma better than it does the model of a single plasma, in accordance with a chi square statistic. The model of stable plasma plus flare plasma is also supported by the observation that the plasma parameters in the postflare condition are indistinguishable from those during preflare.

Wolfson, C. J.↗