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At least 973 records · Page 54
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NASA NTRS1985

High-rate convolutional code construction with the minimum required SNR criterion

New short constraint length, high-rate convolutional codes which minimize the required signal to noise ratios (SNR) are found and tabulated for rates 2/3, 3/4, and 4/5, and for constraint length K up to 10. When compared with previously reported codes, most of the new codes reduce the required SNR only slightly. However, there are some pairs of K and code rate for which the new codes require considerably less SNR. The most significant one is the new K = 8, ate 4/5 code which requires 1.2 dB less SNR than the known code with the same parameters, for a desired bit error rate of 0.000001.

Lee, P. J.↗
NASA NTRS1985

Planetary Waves

The mean temperature field at various pressure levels for January and July for both hemispheres are given. In summer (July in the Northern Hemisphere, January in the Southern Hemisphere) the fields are nearly zonally symmetric, but in winter large longitudinal variations are evident. These are mainly of low wave number, i.e., they may be represented by Fourier analysis around the globe using just a few (one or two) waves. This is the basis for representing the climatology of longitudinal variation in terms of wave components, since the fields may be defined with fewer values than by using a grid in longitude that has a sufficiently small interval to adequately represent the smooth variations. The amplitude and phase of temperature and geopotential height for wave numbers one and two, with In(pressure) as the vertical coordinate are given. The fields were calculated and plotted at pressure intervals of 0.2 in In(pressure) and at latitude intervals of 4 deg, but were interpolated to intervals of 0.5 in In(pressure) (approximately 3.5 km) and 10 deg latitude for tabulation. Tables and figures give wave coefficients for the monthly mean temperature fields. Thus they represent the quasi-statinary planetary waves.

Barnett, J. J.↗
NASA NTRS1985

An unbiased X-ray sampling of stars within 25 parsecs of the Sun

A search of all of the Einstein Observatory IPC and HRI fields for untargeted stars in the Woolley, et al., Catalogue of the nearby stars is reported. Optical data and IPC coordinates, flux density F sub x, and luminosity L sub x, or upper limits, are tabulated for 126 single or blended systems, and HRI results for a few of them. IPC luminosity functions are derived for the systems, for 193 individual stars in the systems (with L sub x shared equally among blended components), and for 63 individual M dwarfs. These stars have relatively large X-ray flux densities that are free of interstellar extinction, because they are nearby, but they are otherwise unbiased with respect to the X-ray properties that are found in a defined small space around the Sun.

Johnson, H. M.↗
NASA NTRS1985

Pressure distributions from high Reynolds number tests of a Boeing BAC 1 airfoil in the Langley 0.3-meter transonic cryogenic tunnel

A wind-tunnel investigation designed to test a Boeing advanced-technology airfoil from low to flight-equivalent Reynolds numbers has been completed in the Langley 0.3-Meter Transonic Cryogenic Tunnel. This investigation represents the first in a series of NASA/U.S. industry two-dimensional airfoil studies to be completed in the Advanced Technology Airfoil Test program. Test temperature was varied from ambient to about 100 K at pressures ranging from about 1.2 to 6.0 atm. Mach number was varied from about 0.40 to 0.80. These variables provided a Reynolds number (based on airfoil chord) range from 4.4 X 10 to the 6th power to 50.0 X 10 to the 6th power. All the test objectives were met. The pressure data are presented without analysis in plotted and tabulated formats for use in conjunction with the aerodynamic coefficient data published as NASA TM-81922. At the time of the test, these pressure data were considered proprietary and have only recently been made available by Boeing for general release. Data are included which demonstrate the effects of fixed transition. Also included are remarks on the model design, the model structural integrity, and the overall test experience.

Johnson, W. G., Jr.↗
NASA NTRS1986

PROFILE user's guide

User information for program PROFILE, an aerodynamics design utility for refining, plotting, and tabulating airfoil profiles is provided. The theory and implementation details for two of the more complex options are also presented. These are the REFINE option, for smoothing curvature in selected regions while retaining or seeking some specified thickness ratio, and the OPTIMIZE option, which seeks a specified curvature distribution. REFINE uses linear techniques to manipulate ordinates via the central difference approximation to second derivatives, while OPTIMIZE works directly with curvature using nonlinear least squares techniques. Use of programs QPLOT and BPLOT is also described, since all of the plots provided by PROFILE (airfoil coordinates, curvature distributions) are achieved via the general purpose QPLOT utility. BPLOT illustrates (again, via QPLOT) the shape functions used by two of PROFILE's options. The programs were designed and implemented for the Applied Aerodynamics Branch at NASA Ames Research Center, Moffett Field, California, and written in FORTRAN and run on a VAX-11/780 under VMS.

Collins, L.↗
NASA NTRS1986

Low-speed stability and control characteristics of a transport model with aft-fuselage-mounted advanced turboprops

A limited experimental investigation was conducted in the Langley 4- by 7-Meter Tunnel to explore the effects of aft-fuselage-mounted advanced turboprop installations on the low-speed stability and control characteristics of a representative transport aircraft in a landing configuration. In general, the experimental results indicate that the longitudinal and lateral-directional stability characteristics for the aft-fuselage-mounted single-rotation tractor and counter-rotation pusher propeller configurations tested during this investigation are acceptable aerodynamically. For the single-rotation tractor configuration, the propeller-induced aerodynamics are significantly influenced by the interaction of the propeller slipstream with the pylon and nacelle. The stability characteristics for the counter-rotation pusher configuration are strongly influenced by propeller normal forces. The longitudinal and directional control effectiveness, engine-out characteristics, and ground effects are also presented. In addition, a tabulated presentation of all aerodynamic data presented in this report is included as an appendix.

Applin, Z. T.↗
NASA NTRS1986

A Monte Carlo study of Weibull reliability analysis for space shuttle main engine components

The incorporation of a number of additional capabilities into an existing Weibull analysis computer program and the results of Monte Carlo computer simulation study to evaluate the usefulness of the Weibull methods using samples with a very small number of failures and extensive censoring are discussed. Since the censoring mechanism inherent in the Space Shuttle Main Engine (SSME) data is hard to analyze, it was decided to use a random censoring model, generating censoring times from a uniform probability distribution. Some of the statistical techniques and computer programs that are used in the SSME Weibull analysis are described. The methods documented in were supplemented by adding computer calculations of approximate (using iteractive methods) confidence intervals for several parameters of interest. These calculations are based on a likelihood ratio statistic which is asymptotically a chisquared statistic with one degree of freedom. The assumptions built into the computer simulations are described. The simulation program and the techniques used in it are described there also. Simulation results are tabulated for various combinations of Weibull shape parameters and the numbers of failures in the samples.

Abernethy, K.↗
NASA NTRS1986

Unsteady transonic flow calculations for wing-fuselage configurations

Unsteady transonic flow calculations are presented for wing-fuselage configurations. Calculations are performed by extending the XTRAN3S unsteady transonic small-disturbance code to allow the treatment of a fuselage. Details of the XTRAN3S fuselage modeling are discussed in the context of the small-disturbance equation. Transonic calculations are presented for three wing-fuselage configurations with leading edge sweep angles ranging from 0 deg to 46.76 deg. Simple bending and torsion modal oscillations of the wing are calculated. Sectional lift and moment coefficients for the wing-alone and wing-fuselage cases are compared and the effects of fuselage aerodynamic interference on the unsteady wing loading are revealed. Tabulated generalized aerodynamic forces used in flutter analyses, indicate small changes in the real in-phase component and as much as a 30% change in the imaginary component when the fuselage is included in the calculation. These changes result in a 2 to 5% increase in total magnitude and a several degree increase in phase.

Batina, J. T.↗
NASA NTRS1982

JPL preferred parts list: Reliable electronic components

The JPL Preferred Parts List was prepared to provide a basis for selection of electronic parts for JPL spacecraft programs. Supporting tests for the listed parts were designed to comply with specific spacecraft environmental requirements. The list tabulates the electronic, magnetic, and electromechanical parts applicable to all JPL electronic equipment wherein reliability is a major concern. The parts listed are revelant to equipment supplied by subcontractors as well as fabricated at the laboratory.

Covey, R. E.↗
NASA NTRS1986

Geometerial description for a proposed aeroassist flight experiment vehicle

One geometry currently under consideration for the Aeroassist Flight Experiment (AFE) vehicle is composed of several segments of simple general conics: an ellipsoidal nose tangent to an elliptical cone and a base skirt with the base plane raked relative to the body axis. An analytic representation for the body coordinates and first and second partial derivatives of this configuration has been developed. Equations are given which define the body radius and partial derivatives for a prescribed axial and circumferential position on the vehicle. The results for a sample case are tabulated and presented graphically.

Cheatwood, F. M.↗
NASA NTRS1985

Improved excitation rate coefficients for the n = 2 and n = 3 levels of Ca XIX and Fe XXV including fine structure

Reently calculated collision strengths, including relativistic and resonance effects, are employed to compute Maxwellian averaged collision strengths for 78 transitions involving states of principal quantum numbers 2-1 and 3-1 in Ca XIX and Fe XXV. These rate parameters are tabulated at temperatures of interest in astrophysical and labortory plasmas with radiation in the hard X-ray wavelength range. For some transitions, significant differences are found with the earlier calculations of Pradhan, Norcross, and Hummer (1981).

Pradhan, A. K.↗
NASA NTRS1985

Extremely metal-deficient red giants. IV - Equivalent widths for 36 halo giants

Further work on a study of 36 metal-poor field red giants is reported. Chemical abundances previously determined were based on model stellar atmosphere analyses of equivalent widths from photographic image-tube echelle spectrograms obtained with with 4-m reflectors at Kitt Peak and Cerro Tololo. A tabulation of the equivalent-width data (a total of 18, 275 equivalent widths) is presented.

Luck, R. E.↗
NASA NTRS1985

Cross sections for H(-) and Cl(-) production from HCl by dissociative electron attachment

A crossed target beam-electron beam collision geometry and a quadrupole mass spectrometer have been used to conduct dissociative electron attachment cross section measurements for the case of H(-) and Cl(-) production from HCl. The relative flow technique is used to determine the absolute values of cross sections. A tabulation is given of the attachment energies corresponding to various cross section maxima. Error sources contributing to total errors are also estimated.

Orient, O. J.↗
NASA NTRS1985

Standard stars for cometary photometry

Interference filters centered at 0.365, 0.387, 0.406, 0.484, and 0.514 microns have been selected to represent UV continuum, CN emission, C3 emission, blue continuum, and C2 emission in cometary spectra, respectively. Adopted magnitudes and colors of this filter system are presented for 50 standard stars, ranging in bue magnitude from 4 to 12, in spectral type from O to K, and distributed primarily around equatorial regins of the sky. The tabulated uncertainties are generally of the order of 0.02 mag or smaller; the zero points of the photometric system are chosen so that blue continuum magnitudes are approximately equivalent to Johnson B, and so that color indices average zero for solar analog stars.

Wisniewski, W.↗
NASA NTRS1985

Pluto-Charon mutual event predictions for 1986

Circumstances are tabulated for 81-Pluto-Charon mutual events occurring during the 1986 opposition. The deepest and longest events will occur in February and reach a depth of about 0.15 mag. Observations of these events will lead to an accurate determination of the satellite's orbit, the diameters of the two bodies, the mean density of the system, and crude albedo maps of one hemisphere on each object.

Tholen, D. J.↗
NASA NTRS1986

Finite size corrections to Madelung number

It is customary in the study of ionic crystals to assume that the ions are point charges at their respective lattice sites; the corresponding electrostatic energy of one such ion is reducible to Madelung's form, where the Madelung number has a value of 1.7467. This paper considers the modifications in the electrostatic energy when the atomic finite size is treated in more detail. The results are tabulated as a direct correction to Madelung's number for alkali halide cubic crystals.

Wilson, J. W.↗
NASA NTRS1986

Finite volume solultion of the compressible boundary layer equations

A box-type finite volume discretization is applied to the integral form of the compressible boundary layer equations. Boundary layer scaling is introduced through the grid construction: streamwise grid lines follow eta = y/h = const., where y is the normal coordinate and h(x) is a scale factor proportional to the boundary layer thickness. With this grid, similarity can be applied explicitly to calculate initial conditions. The finite volume method preserves the physical transparency of the integral equations in the discrete approximation. The resulting scheme is accurate, efficient, and very simple. Computations for similar and non-similar flows show excellent agreement with tabulated results, solutions computed with Keller's Box scheme, and experimental data.

Loyd, B.↗