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At least 271 records · Page 15

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NASA NTRS1979

Effect on head-wind profiles and mean head-wind velocity on landing capacity flying constant-airspeed and constant-groundspeed approaches

A study was conducted to determine the effect of head-wind profiles and mean head-wind velocities on runway landing capacity for airplanes flying constant-airspeed and constant-groundspeed approaches. It was determined that when the wind profiles were encountered with the currently used constant airspeed approach method, the landing capacity was reduced. The severity of these reductions increased as the mean head-wind value of the profile increased. When constant-groundspeed approaches were made in the same wind profiles, there were no losses in landing capacity. In an analysis of mean head winds, it was determined that in a mean head wind of 35 knots, the landing capacity using constant-airspeed approaches was 13% less than for the no wind condition. There were no reductions in landing capacity with constant-groundspeed approaches for mean head winds less than 35 knots. This same result was observed when the separation intervals between airplanes was reduced.

Hastings, E. C., Jr.↗

NASA NTRS1979

Synthesis of national risk profile

The methodology used and results obtained in computing the national risk profile for carbon fibers (CF) released after an aircraft accident (fire or explosion) are presented. The computation was performed by use of twenty-six individual conditional risk profiles, together with the extrapolation of these profiles to other U.S. airports. The risk profile was obtained using 1993 CF utilization forecasts, but numbers of facilities were taken from 1972 and 1975 census data, while losses were expressed in 1977 dollars.

Source record↗

NASA NTRS1978

Remote sensing of the ozone profile in the lower stratosphere using UV and IR measurements from Nimbus-4

A method of combining the information from the infrared interferometer spectrometer (IRIS) and the backscatter ultraviolet spectrometer (BUV) on board the Nimbus-4 satellite to derive the ozone profile from 10 mb to surface is described. The radiance in the IRIS 9-micron band can be related to the ozone profile by the radiative transfer equation. The IR intensity due to ozone is dependent on the pressure broadening of spectral lines, and an estimate of a weighted mean pressure of the ozone layer can be obtained from total ozone supplied by BUV long wave intensity measurements. With the aid of the Chapman function, a model of the ozone concentration profile described by three parameters is obtained. Given the ozone concentration at 10 mb one calculates several possible combinations of the three parameters that can produce the required total ozone, and the final choice of parameter is determined from IR measurements. An ozone profile calculated in this way reproduces well the gross features of balloon ozone sounding results. Meridional cross sections of ozone concentration have also been derived which are in reasonably good agreement with balloon-derived cross-section for the northern latitudes and tropics.

Prabhakara, C.↗

NASA NTRS1979

Hard X-ray time profiles and acceleration processes in large solar flares

The hard X-ray time profiles of the (1972) August 4 and 7 flares are investigated, taking into account a comparison of the time profiles of different energy channels. It is shown that for these flares the temporal features of the intensity profiles of higher energy channels are delayed with respect to those of channel 1. The delay time gradually increases to approximately 5 sec as the channel number increases from 1 to 5, and it jumps to approximately 15 sec for channels 6 and 7. A description is presented of a model in which the delay and other characteristics of the observed time profiles in channels 1-5 are self-consistently explained by the increase of the electron energy loss time with electron energy.

Bai, T.↗

NASA NTRS1980

Statistical wind profile gust model

A statistical wind profile gust model for the Space Transportation Operations and Trade Studies is developed by using 1800 Jimsphere wind profile data collected at Cape Kennedy during 1965 to 1972. Wind profiles from the surface to 20 km in component form, i.e., zonal and meridional are processed through the digital filters of different wave length ranges bases on the Martin-Graham cosine rolloff model. The residuals obtained from the filtering processes for the data base for the statistical analysis. For each wind component the gust and gust length at a specified reference altitude in a residual profile are defined. A two parameter gamma probability marginal distribution seems to fit the component gust amplitude and the gust length when redefined. The problem of finding an appropriate bivariate joint distribution of the gust amplitude and length remains to be solved. The probability distribution of the modulus of the gust amplitudes was derived under the assumption that they are independently distributed as gamma variates.

Doss, D. C.↗

NASA NTRS1980

Illustration of year-to-year variation in wheat spectral profile crop growth curves

Data previously compiled on the year to year variability of spectral profile crop growth parameters for spring and winter wheat in Kansas, Oklahoma, and the Dakotas were used with a profile model to develop graphs illustrating spectral profile crop growth curves for a number of years and a number of spring and winter wheat segments. These curves show the apparent variability in spectral profiles for wheat from one year to another within the same segment and from one segment to another within the same year.

Gonzalez, P.↗

NASA NTRS1980

Formation of chromospheric resonance line profiles in supergiants

The formation of chromospheric resonance line profiles is examined for the case of the relatively low-density atmospheres appropriate to late-type supergiants. The effects of partial frequency redistribution control the emergent line profiles, to the extent that even an isothermal atmosphere can give rise to apparent emission features. Schematic model chromospheres are used to demonstrate the effects of different velocity fields and temperature-density structures on the line profiles, as a first step toward a clearer understanding of the chromospheric line profiles and why supergiants have broad emission lines (the Wilson-Bappu effect). Neither the Doppler nor the mass column density explanation alone can explain the Wilson-Bappu effect in supergiants, but both theories may play a role.

Basri, G. S.↗

NASA NTRS1981

Measurements of He D3 profiles in solar plages

Measurements of the profiles of the He D3 lines in solar plages are presented as a probe of the plage atmosphere. Observations were made at selected positions in quiescent plages during the period October 1978-April 1979 by the 25-cm coronagraph/3-m coude spectrograph at the Mees Solar Observatory on Mount Haleakala. Individual D3 plage profiles are fit well with a two-component, differentially moving atmosphere with constant source function and total Doppler width. The principal absorption is attributed to nearly stationary material, with a kinetic temperature less than 17,200 K, and velocity distribution is found to represent a net downflow in the plage atmosphere extending to around 12 km/sec. The present results for individual plage profiles are also noted to be consistent with those of Namba (1963). Time series of D3 profiles at fixed plage positions and the velocity spectra for nearby photospheric lines are observed to show general enhancements at periods of around 5 min, with redshift leading variations in line width by about 49 deg. Interpretations of the width variation as temperature variations are found not to be consistent with the properties of acoustic wave modes in a stratified atmosphere, presumably indicating magnetic field effects.

Landman, D. A.↗

NASA NTRS1982

Tooth profile analysiis of circular-cut, spiral-bevel gears

An analysis of tooth profile changes in the transverse plane of circular-cut, spiral-bevel crown gears is presented. The analysis assumes a straight-line profile in the mid-transverse plane. The profile variation along the centerline is determined by using expressions for the variation of the spiral angle along the tooth centerline, together with the profile description at the mid-transverse plane. It is shown that the tooth surface is a hyperboloid and that significant variations in the pressure angle are possible.

Huston, R. L.↗

NASA NTRS1982

Line profiles of T Tauri stars - Clues to the nature of the mass flow

A set of high resolution observations of the H-alpha Na D, He I 5876 A, and H-gamma lines in several T Tauri stars is presented. Repeated observations of some of these objects yield some indication of the importance of time-dependent effects. The line profiles should be useful for detailed radiative transfer modeling. A cursory survey of the profiles suggests that 'turbulent' velocities in some cases may not be negligible in comparison with the bulk flow speeds and that many emission lines, such as Na D, may be formed in a narrow layer near the stellar photosphere. It is suggested that the effects of geometrical occulation of narrow line-emitting regions in general outflow can account for some of the peculiarities of the line profiles. However, some aspects of the line profiles, such as the large-scale, highly variable redshifted Na D absorption in RW Aur, clearly require more complicated motions.

Hartmann, L.↗

NASA NTRS1982

Evidence of redshifts in the average solar line profiles of C IV and Si IV from OSO-8 observations

Line profiles of C IV and Si V obtained by the Colorado spectrometer on OSO-8 are presented. It is shown that the mean profiles are redshifted with a magnitude varying from 6-20 km/s, and with a mean of 12 km/s. An apparent average downflow of material in the 50,000-100,000 K temperature range is measured. The redshifts are observed in the line center positions of spatially and temporally averaged profiles and are measured either relative to chromospheric Si I lines or from a comparison of sun center and limb profiles. The observations of 6-20 km/s redshifts place constraints on the mechanisms that dominate EUV line emission since it requires a strong weighting of the emission in regions of downward moving material, and since there is little evidence for corresponding upward moving materials in these lines.

Roussel-Dupre, D.↗

NASA NTRS1981

Satellite profile measurements of stratospheric ozone

A description is presented of preliminary results obtained in connection with the Stratospheric Aerosol and Gas Experiment (SAGE). SAGE, which uses a limb scanning solar radiometer, is an experiment aboard the Applications Explorer Mission 2 spacecraft which was launched on February 18, 1979. The instrument utilizes the technique of solar occultation to measure limb-path atmospheric extinction profiles which are inverted to yield vertical profiles of various atmospheric constituents in the latitude range from 79 deg South to 79 deg North. The ozone spectral channel is centered at 0.60 micrometers in the middle of the Chappuis absorption band. The general characteristics of the ozone profile measurements are shown in a graph. Each profile represents a day's average of approximately 15 measurements at the latitude band indicated. The SAGE ozone measurements are generating a highly detailed picture of the stratospheric ozone distribution.

Mccormick, M. P.↗

NASA NTRS1982

A theoretical study of a two-wavelength lidar technique for the measurement of atmospheric temperature profiles

The theory of differential absorption lidar measurements for lines with a Voigt profile is given and applied to a two-wavelength technique for measuring the atmospheric temperature profile using a high J line in the oxygen A band. Explicit expressions for the temperature and pressure dependence of the absorption coefficient are developed for lines with a Voigt profile. An iteration procedure for calculating the temperature for narrow laser bandwidths is described which has an accuracy better than 0.2 K for bandwidths less than 0.01/cm. To reduce the errors in lidar measurements due to uncertainties in pressure, a method for estimating the pressure from the temperature profile is described. A procedure for extending the differential absorption technique to the case of finite laser bandwidth with good accuracy is also described. Simulation results show that a knowledge of the laser frequency is needed to 0.005/cm for accurate temperature measurements. Evaluation of the sensitivity for both ground- and Shuttle-based measurements shows accuracies generally better than 1 K. This technique allows up to an order of magnitude improvement in sensitivity compared to other differential absorption lidar techniques.

Korb, C. L.↗

NASA NTRS1982

Observations and interpretation of the line profiles of excited H2 in Orion

The profiles of the V=1-0 S(1) line of H2 in the Orion molecular cloud show a variation from the center of the emission region where the profiles are broad and have extended blue wings, to the periphery where the profiles are narrow and have a peak at the velocity of the molecular cloud. These observations can be understood by a model of a radially expanding supersonic flow of gas colliding with the surrounding molecular cloud. It is concluded that the high velocity emission originates in the flow and the low velocity emission originates in the molecular cloud. Density variations in the flow and the surrounding cloud are necessary to explain the detailed line profiles and morphology.

Geballe, T. R.↗

NASA NTRS1983

Computer programs for generation and evaluation of near-optimum vertical flight profiles

Two extensive computer programs were developed. The first, called OPTIM, generates a reference near-optimum vertical profile, and it contains control options so that the effects of various flight constraints on cost performance can be examined. The second, called TRAGEN, is used to simulate an aircraft flying along an optimum or any other vertical reference profile. TRAGEN is used to verify OPTIM's output, examine the effects of uncertainty in the values of parameters (such as prevailing wind) which govern the optimum profile, or compare the cost performance of profiles generated by different techniques. A general description of these programs, the efforts to add special features to them, and sample results of their usage are presented.

Sorensen, J. A.↗

NASA NTRS1982

Mass loss in Alpha Cygni - Synthetic H-Alpha profiles

Alpha Cygni (A2 Ia) is the brightest and best-studied A type supergiant. The star's position in the H-R diagram makes the determination of its mass loss rate extremely important. The present investigation is concerned with a semiempirical modeling of the H-alpha profile in Alpha Cyg in connection with the objective of estimating the mass loss rate and further constraining the physical state of the stellar wind. The synthetic H-alpha profiles considered are compared with the observed profiles in Alpha Cyg. It is concluded that a spherically symmetric, steady-state model, with the network of hydrogen transitions treated in detail, can fit the deeper observed profiles but not the shallower ones. The obtained results indicate that, within the context of the turbulent models, the mass loss rate of Alpha Cyg is (1.7 + or - 0.4) x 10 to the -7th solar mass per year.

Kunasz, P. B.↗

NASA NTRS1983

Observations of the line profile of Paschen alpha in 3C 273

Within the uncertainties, the P-alpha line profile is the same as those of H-beta, L-alpha, and C IV. It is therefore contended that if current models of broad-line-emitting clouds in quasars are correct, then the similarity of the P-alpha line profile to the L-alpha profile argues against a velocity field dominated by radial inflow or outflow. It is noted, however, that if the cloud motions are predominantly due to radial inflow or outflow, then the clouds must radiate more isotropically in L-alpha then current models predict. The observed similarity of the line profiles of P-alpha at 1.875 microns and of C IV at 1550 A leads to the conclusion that there is no differential reddening caused by dust between clouds moving at different velocities within the broad line region of 3C 273.

Sellgren, K.↗

NASA NTRS1983

Computations of the current profile influence on tearing instability

Results of computations of tearing instability of a plasma column in a strong longitudinal magnetic field are presented for different current profiles. The power current profiles j=j sub 0(1-(r/a)(P))(nu) are considered and analyzed for various values of the parameters p and v. The tearing instability of the smoothed two-step profiles is studied. Optimal smoothed two-step profiles are constructed which are stable with respect to all helical largescale perturbations.

Blekher, P. M.↗