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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Noise reduction studies of several aircraft to reduce their aural detection distances

A study was conducted to assess the extent to which practicable reductions of the external noise level of various aircraft could be achieved by different methods. The aircraft included in the study are the O-1, O-2, U-10, OV-1, and A-6. The noise signatures obtained from field measurements and the estimated aural detection distance of aircraft operating in low speed cruising flight are presented. The characteristics of each aircraft and the modifications made to reduce the aerodynamic noise are explained. Tables of data are included to show the effectiveness of the noise reduction modifications for each aircraft.

Dingeldein, R. C.↗
NASA NTRS1975

A unique concept for automatically controlling the braking action of wheeled vehicles during minimum distance stops

Test results of a unique automatic brake control system are outlined and a comparison is made of its mode of operation to that of an existing skid control system. The purpose of the test system is to provide automatic control of braking action such that hydraulic brake pressure is maintained at a near constant, optimum value during minimum distance stops.

Barthlome, D. E.↗
NASA NTRS1975

Long-distance recording of the humidity over the sea

A procedure is developed for long distance recording of humidity over the sea that uses humidity detectors of the sorption type, whose electrical properties depend on the relative humidity of the air. The moisture sensitive material of the hygristor is the organic polymer polyacrylonitryl, deposited on silver electrodes and thermally treated. In the measurements of the relative humidity from 60% to 95%, the resistance of the hygristor varies from several hundred kiloohms to a few kiloohms, and is an essentially nonlinear function of the humidity.

Buklanov, V. V.↗
NASA NTRS1975

Some long, rate one-half, binary convolutional codes with an optimum distance profile and the systematic versus nonsystematic code question

A tabulation is given of long systematic and long quick-look-in (QLI) nonsystematic rate R = 1/2 binary convolutional codes with an optimum distance profile (ODP). These codes appear attractive for use with sequential decoders. Simulations for two of the new codes are reported and confirm Massey's conjecture that systematic and non-systematic codes of the same rate yield nearly identical computational and error probability performance with sequential decoding when the number of digits transmitted in the tail of the encoded frame is the same for both codes.

Johannesson, R.↗
NASA NTRS1975

Propagation of aircraft noise over long distances through the lower atmosphere

Propagation of sound through the lower atmosphere is influenced by numerous factors which are difficult to measure and more difficult to predict. In addition to the well known laboratory observable loss mechanisms of heat conduction, gas transport, and molecular absorption, inhomogeneities in a real atmosphere have significant influence on a propagating sound wave. This study presents a qualitative discussion of different categories of atmospheric inhomogeneity and their individual and combined effects on sound propagation. Subsequently, a field test involving the propagation of aircraft noise over distances up to 10 miles is described, and a simplified empirical model for 'excess' atmospheric attenuation due to inhomogeneities in the atmosphere is derived from the data.

Abrahamson, A. L.↗
NASA NTRS1975

The magnetosheath electron population at lunar distance - General features

A study was made of the electron population in the earth's magnetosheath at lunar distance. The data used were collected by the Apollo 14 charged particle lunar environment experiment (CPLEE) during four inbound (dusk) and three outbound (dawn) passages of the moon through the magnetosheath. The magnetotail has a diameter of 52 earth radii, while the bow-shock cross section is about 91 earth radii. The average boundary locations computed from the complete data set are consistent with the prediction of fluid dynamics. The electron characteristics for the two least-disturbed passages are presented in detail. An examination of the energy spectra shows that a high-energy (200-2000 eV) tail is superimposed on the expected low-energy (40-200 eV) magnetosheath distribution. It is argued that the high-energy magnetosheath electron population originates at the bow shock, rather than from the plasma sheet.

Reiff, P. H.↗
NASA NTRS1976

A perceptual channel for information transfer over kilometer distances Historical perspective and recent research

For more than 100 years, scientists have attempted to determine the truth or falsity of claims for the existence of a perceptual channel whereby certain individuals are able to perceive and describe remote data not presented to any known sense. This paper presents an outline of the history of scientific inquiry into such so-called paranormal perception and surveys the current state of the art in parapsychological research in the United States and abroad. The nature of this perceptual channel is examined in a series of experiments carried out in the Electronics and Bioengineering Laboratory of Stanford Research Institute. The perceptual modality most extensively investigated is the ability of both experienced subjects and inexperienced volunteers to view, by innate mental processes, remote geographical or technical targets including buildings, roads, and laboratory apparatus. The accumulated data indicate that the phenomenon is not a sensitive function of distance, and Faraday cage shielding does not in any apparent way degrade the quality and accuracy of perception. On the basis of this research, some areas of physics are suggested from which a description or explanation of the phenomenon could be forthcoming.

Puthoff, H. E.↗
NASA NTRS1976

Solar wind structure at large heliocentric distances - An interpretation of Pioneer 10 observations

Examination of hourly values of the solar wind speed observed by the Pioneer 10 spacecraft beyond a heliocentric distance of 4 AU reveals (1) a prevalent 'sawtoothlike' speed-time profile, most speed fluctuations displaying a rapid rise and a much slower decline, and (2) the nearly universal appearance of abrupt (on the 1-hour time resolution of these data) changes in the speed on the rising portions of the speed fluctuations. These previously unreported characteristics, as well as the rate of decay of stream amplitudes derived earlier by Collard and Wolfe, are in general agreement with the predictions of stream propagation models that neglect any conversion of kinetic energy to thermal energy outside of shock fronts. Thus the Pioneer 10 observations give the first confirmation of the general concept of solar wind stream evolution employed in these models, i.e., that solar wind speed inhomogeneities appear to steepen to form shock waves and that the 'wave amplitudes' decay slowly as the shock waves propagate outward from the sun.

Hundhausen, A. J.↗
NASA NTRS1976

Solar wind stream evolution at large heliocentric distances - Experimental demonstration and the test of a model

A stream propagation model which neglects all dissipation effects except those occurring at shock interfaces, was used to compare Pioneer-10 solar wind speed observations, during the time when Pioneer 10, the earth, and the sun were coaligned, with near-earth Imp-7 observations of the solar wind structure, and with the theoretical predictions of the solar wind structure at Pioneer 10 derived from the Imp-7 measurements, using the model. The comparison provides a graphic illustration of the phenomenon of stream steepening in the solar wind with the attendant formation of forward-reverse shock pairs and the gradual decay of stream amplitudes with increasing heliocentric distance. The comparison also provides a qualitative test of the stream propagation model.

Gosling, J. T.↗
NASA NTRS1976

On the distance to the candidate star coincident with A0620-00

High-dispersion echelle spectra of the candidate star for the transient X-ray source A0620-00 are discussed. No absorption or emission lines attributed to the star were found under visual examination of the spectra, but interstellar sodium D lines were clearly visible. Results are presented for measurements of the profiles and central velocities of the sodium absorption lines, and other observations of interstellar features in the general direction of the star are summarized. While the exact distance to the star cannot be determined due to the patchy distribution of the interstellar gas, it is suggested that the star is located between 1.5 and 2.5 kpc; 2 kpc is adopted as the most reasonable value. It is noted that the possibility cannot be ruled out that the star lies beyond 3 kpc and is seen through a hole in the distant neutral hydrogen gas.

Gull, T. R.↗
NASA NTRS1976

Program documentation: B-average Bhattacharyya distance

The total Bhattacharyya distance is calculated using all N channels. The output of this subroutine is used to construct the B matrix using one or two Householder transformations. FORTRAN calling sequences are given.

Marani, S. K.↗
NASA NTRS1977

Acceleration of nucleons in interplanetary space and modulation of Jovian electrons at distances of 1 to 10 AU by corotating regions of solar origin

Corotating interaction regions (CIRs) are formed in interplanetary space when a fast solar-plasma flow overtakes a slow solar-wind stream. This paper shows that CIRs are closely related to two unusual phenomena observed during the flights of Pioneers 10 and 11. These include corotating periodic nucleon fluxes with energies of several MeV and variations in the intensity of relativistic Jovian electrons. Observational evidence is presented in favor of the idea that the nucleons are accelerated in CIRs located in interplanetary space at heliocentric distances of 1 to at least 10 AU, and a model is analyzed in which the acceleration takes place at the leading edge of a CIR. Pioneer data are cited which demonstrate that modulation by recurrent CIRs can explain the large-scale variations in Jovian electron intensity observed in interplanetary space.

Barnes, C. W.↗
NASA NTRS1977

A distance limit for a class of model gamma-ray burst sources

Gamma ray burst sources are presumably not larger than 10 to the 9th power cm as inferred from observed flux variations. If they are homogeneous and isotropically radiating, then from photon density considerations, they would have to be optically thick due to gamma-gamma pair production when assumed to be too far away. Deviations of observed photo spectra from an exponential shape around 1 MeV lead to an upper limit of the possible distance of such sources of only 2 kpc from the sun. Thus the sources must be galactic unless the radiation is highly beamed or emerges from a relativistically moving shell. This conclusion depends only on observed parameters. The possible presence of particles and fields in the sources would require them to be even closer.

Schmidt, W. K. H.↗
NASA NTRS1978

Ground distance covered during airborne horizontal deceleration of an airplane

The distance an airplane floats with respect to the ground during deceleration at constant altitude is analyzed taking into account the effects of a constant wind. By use of suitable nondimensionalizing parameters, data applicable to all airplanes are presented by means of a single family of curves.

Phillips, W. H.↗
NASA NTRS1975

Energy, frequency, and distance of moonquakes at the Apollo 17 site

'Thermal' moonquakes have been detected at the Apollo 17 site. A typical event releases about 1 to 10 million ergs of energy. The annual seismic energy release for the events observed in the Taurus-Littrow Valley is estimated at 100 billion ergs. Such small events would not cause impossibly rapid erosion on either the North Massif or within the craters of the Central Cluster. Seismic events become increasingly frequent after sunrise and reach a maximum at sunset. The largest events, however, occur most commonly near lunar noon. Rise times of the seismic signals, after being calibrated by the well-located Lunar Seismic Profiling Experiment (LSPE) seismic sources, were used to estimate distances to the seismic events. Most seismic events (about 90%) appear to occur within 2.5 km of the seismometer array.

Cooper, M. R.↗
NASA NTRS1979

Efficient feature subset selection with probabilistic distance criteria

Recursive expressions are derived for efficiently computing the commonly used probabilistic distance measures as a change in the criteria both when a feature is added to and when a feature is deleted from the current feature subset. A combinatorial algorithm for generating all possible r feature combinations from a given set of s features in (s/r) steps with a change of a single feature at each step is presented. These expressions can also be used for both forward and backward sequential feature selection.

Chittineni, C. B.↗
NASA NTRS1979

Occurrence of the lobe plasma at lunar distance

Recent analysis has confirmed the existence of the lobe plasma, the extension of the 'boundary layer' and 'plasma mantle' to lunar distances. The observation of the lobe plasma is strongly correlated with the y component of the IMF. Generally, the lobe plasma is observed sporadically for a full day after the moon has entered the tail and a full day before the last magnetopause crossing as it exits the tail. An average extent of approximately 8-10 earth radii inward from the magnetopause is inferred; however, the lobe plasma has been seen all across the tail.

Hardy, D. A.↗
NASA NTRS1979

A cosmological redshift-distance square law

This paper directly examines the claims of Segal (1976) that the (m,z) Hubble diagram is fitted best by a square law z = Kr-squared rather than by the traditional Hubble law z = Hr in the low-redshift range, z no more than about 0.01, corresponding to galaxies brighter than 14th mag. Segal attempts to fit a distance relation to the (m,z) scatter diagram in which each individual galaxy is plotted. The exact relation between the mean redshift for all galaxies in a small magnitude interval and the apparent magnitude is calculated. This relation is independent of luminosity function and peculiar velocity distribution about the general expansion, and is not affected by sample incompleteness as a function of apparent magnitude or the clustering of galaxies in the sample. Segal's method is affected by all of these and requires a highly sophisticated statistical analysis to deal with the non-Gaussian pointwise scatter. The present analysis favors the Hubble law and conclusively rules out the square law for the small redshift region.

Soneira, R. M.↗