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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Type III bursts in interplanetary space - Fundamental or harmonic?

ISEE-3 spacecraft observation of 120 relatively simple, isolated bursts in the 30-1980 kHz range are the basis of the present study of Type III bursts in the solar wind. Several characteristics are identified for many of these bursts which imply that the mode of emission changes from predominantly fundamental plasma radiation during the rise phase to predominantly second harmonic during decay. The fundamental emission begins in time coincidence with the start of Langmuir waves, confirming the conventional belief in these waves' causation of Type III bursts. Attention is given to the characteristics of fundamental components, by comparison to harmonics, at km-wavelengths.

Dulk, G. A.↗
NASA NTRS1985

Auroral kilometric radiation - Wave modes, harmonics, and source region electron density structures

A change from extraordinary (X) mode to ordinary (O) mode dominance is observed in the auroral kilometric radiation (AKR) detected on ISIS 1 topside sounder ionograms as the source region plasma to gyrofrequency ratio fN/fH varies from 0.1 to 1.3. The X and O mode AKR, Z (the slow branch of the X mode) and whistler (W) mode are also observed. The Z mode is typically slightly less intense than the O-mode. The W-mode is confined to frequencies less than fH/2, suggesting that it is the result of field aligned ducted signals reaching the satellite from a source at lower altitudes. Harmonic AKR bands are commonly observed and the 2nd harmonic appears to be due to propagating signals. The deduced (fN/fH) at the bottom of the AKR source region is always less than 0.4 and is typically less than 0.2 during the generation of X-mode AKR, but approaches 0.9 for O-mode AKR. No large density enhancements were observed within AKR source region density cavities. It is suggested that the observed intense AKR is cyclotron X-mode radiation rather than plasma frequency O-mode radiation.

Benson, R. F.↗
NASA NTRS1985

Venus gravity - A harmonic analysis and geophysical implications

An improved theoretical model of Venusian global gravity has been obtained by fitting a tenth degree spherical harmonic series to 78 orbital arcs of Doppler tracking data from the Pioneer Venus Orbiter. Maps of the free-air anomaly and its formal error are presented. Isostatic anomaly and 'Geoid' maps are also presented, and their geophysical implications are discussed in details. Comparison with equivalent resolution topographic models reveals a strong correlation between long wavelength gravity and the topography of Venus. Analysis of the second degree harmonics showed two aspects of the orientation of the inertial axes of Venus: (1) a significant (about three degrees) departure of the axis of greatest inertia from the rotational axis; and (2) a near alignment of the axis of least inertia with the location of the subterrestrial point at the time of the next inferior conjunction with earth (December 16, 2101). A series of contour maps of the Venusian free-air anomalies is provided.

Mottinger, N. A.↗
NASA NTRS1985

Adaptation of a modern medium helicopter (Sikorsky S-76) to higher harmonic control

Sikorsky Aircraft has performed analytical studies, design analyses, and risk reduction tests have been performed for Higher Harmonic Control (HHC) on the S-76. The S-76 is an 8 to 10,000 lb helicopter which cruises at 145 kts. Flight test hardware has been assembled, main servo frequency response tested and upgraded, aircraft control system shake tested and verified, open loop controllers designed and fabricated, closed loop controllers defined and evaluated, and rotors turning ground and flight tests planned for the near future. Open loop analysis shows that about 2 deg of higher harmonic feathering at the blade 75% radius will be required to eliminate 4P vibration in the cockpit.

Oleary, J. J.↗
NASA NTRS1985

The zonal harmonic and the yearly and half-yearly waves on the Southern Hemisphere in FGGE compared with the mean

The dominant component in the mean annual cycle of sea level pressure in the latitudes north of approx. 40 deg S is the yearly wave, whereas to the south of this latitude a half-yearly wave dominantes. In FGGE, however, the usually small yearly wave was large in the Antarctic, owing to the extraordinarily low pressure there in the winter of 1979. The half-yearly wave's amplitude was appreciably above normal in the center of each ocean in middle latitudes, and below normal at high latitudes. The yearly wave in the zonal geostrophic wind was larger than normal over the Antarctic Ocean. Similar results are obtained at 500 mb. The three month mean stationary waves (zonal harmonic waves) were larger than the mean in FGGE. The intra-annual variation of both amplitude and phase of the monthly mean harmonic waves in FGGE was large, which is not surprising as they contain an appreciable transient component, unlike the long term monthly mean waves.

Vanloon, H.↗
NASA NTRS1985

Finite amplitude gravity waves: Harmonics, advective steepening, breaking and saturation

A simple theory is presented which determines details of the breaking and saturation of a gravity wave as it propagates upward in the atmosphere. Breaking and saturation are here due to nonlinear advection analogous to the breaching of a surface wave and to the breaking of a planetary wave. Much simplification is obtained by the assumption that in a wave packet consisting of a primary wave and its harmonics, the primary wave remains dominant. This assumption, referred to a quasi-monochromatic approximation, is suggested by observations. Determined by this approximate theory are: a detailed picture of the waveform as it steepens and breaks; harmonics of the wave; the turbulence generation; and an underlying relationship between superadiabatic lapse rate and saturation by wave-wave interactions.

Weinstock, J.↗
NASA NTRS1985

Fundamental and harmonic electron cyclotron maser emission

The plasma conditions and features of the energetic electron distribution in electron cyclotron maser emission for which growth in a particular mode is favored when the ratio of the plasma frequency omega(p) to the electron cyclotron frequency Omega(e) is greater than about 0.3 are determined. It is shown that growth at the fundamental is suppressed as omega(p)/Omega(e) increases and emission at harmonics of Omega(e) dominates. Growth at harmonics of Omega(e) is not restricted to the O and X modes, but can also occur for the Z mode. Whether or not growth in a particular mode dominates depends both on omega(p)/Omega(e) and on the form of the distribution. If the density of the energetic electrons is sufficiently large, the dispersion relations of the O and X modes are modified so that the group velocities of the growing O and X mode waves can be comparable to that of the growing Z mode waves.

Winglee, R. M.↗
NASA NTRS1986

Analysis of harmonic spline gravity models for Venus and Mars

Methodology utilizing harmonic splines for determining the true gravity field from Line-Of-Sight (LOS) acceleration data from planetary spacecraft missions was tested. As is well known, the LOS data incorporate errors in the zero reference level that appear to be inherent in the processing procedure used to obtain the LOS vectors. The proposed method offers a solution to this problem. The harmonic spline program was converted from the VAX 11/780 to the Ridge 32C computer. The problem with the matrix inversion routine that improved inversion of the data matrices used in the Optimum Estimate program for global Earth studies was solved. The problem of obtaining a successful matrix inversion for a single rev supplemented by data for the two adjacent revs still remains.

Bowin, Carl↗
NASA NTRS1987

Harmonic measurements of the Galileo spacecraft X-band transmitter system

Harmonics of X-band (8.4 GHz) spacecraft transmitter systems can be used to measure the performance characteristics of higher frequency deep space communication links. The Galileo X-band transmitter system was measured at the second, third, and fourth harmonics (16.8, 25.2, and 33.6 GHz, respectively). The effective isotropic radiated power was determined to be approximately 52 dBm at 16.8 GHz, 47 dBm at 25.2 GHz, and 25 dBm at 33.6 GHz. These values can be useful, depending upon the sensitivity of the Earth-based receiving system and the distance of the spacecraft from Earth.

Stanton, P. H.↗
NASA NTRS1986

Harmonically structured ULF pulsations observed by the AMPTE CCE magnetic field experiment

Spectrograms of ULF waves in the 0 to 80 mHz frequency range have been prepared from magnetic field data obtained by the elliptically orbiting AMPTE/CCE satellite (with an apogee of approximately 8.8 earth radii). The most prominent feature of these spectrograms (which cover a full 15.6-h orbit) is the presence of harmonically structured, azimuthally polarized pulsations in the outer magnetosphere during daytime hours. The frequencies of these pulsations decrease with increasing radial distance from the earth, indicating that they represent independent resonances of local magnetic flux tubes. The latitudinal structure of these harmonic pulsations, observed as AMPTE/CCE traveled to + or - 16 deg magnetic latitude, is consistent with accepted field line resonance models.

Engebretson, M. J.↗
NASA NTRS1987

Geomagnetic field-line resonant harmonics measured by the Viking and AMPTE/CCE magnetic field experiments

The first simultaneous observations of multiple harmonic, azimuthally polarized, ULF pulsations at two points along a geomagnetic flux tube in space are reported. In March 1986, the elliptically orbiting equatorial AMPTE/CCE satellite was oriented with the apogee near 0830 h MLT, and the orbital plane of the polar-orbiting Viking satellite was at 1000 MLT. The satellites were situated within approximately the same flux tube but with an effective separation of approximately 10 R(e) near L = 8 on the inbound pass of the AMPTE/CCE orbit. Structured harmonic pulsations were observed by the magnetic field experiments on both spacecraft, and they appeared to turn off and on simultaneously at both locations. Both the observations and the relative amplitudes along the magnetic field lines support recent ideas of multiple field-line resonances of Alfven waves.

Zanetti, L. J.↗
NASA NTRS1986

Predicting charmonium and bottomonium spectra with a quark harmonic oscillator

The nonrelativistic quark model is applied to heavy (nonrelativistic) meson (two-body) systems to obtain sufficiently accurate predictions of the spin-averaged mass levels of the charmonium and bottomonium spectra as an example of the three-dimensional harmonic oscillator. The present calculations do not include any spin dependence, but rather, mass values are averaged for different spins. Results for a charmed quark mass value of 1500 MeV/c-squared show that the simple harmonic oscillator model provides good agreement with experimental values for 3P states, and adequate agreement for the 3S1 states.

Norbury, J. W.↗
NASA NTRS1987

Electron cyclotron harmonic waves observed by the AMPTE-IRM plasma wave experiment following a lithium release in the solar wind

An unexpected occurrence following the second lithium release by the AMPTE-IRM spacecraft in the solar wind on September 20, 1984, was the appearance of electron cyclotron harmonic emissions. These emissions began about 50 s after the release and continued for several minutes. Narrow-band emissions polarized perpendicular to the magnetic field with amplitudes of approximately 0.00001 V/m were observed in each of the first five harmonic bands. The diffuse emissions extended from below the lowest measured frequency channel to above the highest narrow-band emission with a maximum below the electron cyclotron frequency. It will be shown that these observations are inconsistent with their generation by several ion beam instabilities.

Roeder, J. L.↗
NASA NTRS1987

Spherical harmonic analysis of steady photospheric flows

A technique is presented in which full disk Doppler velocity measurements are analyzed using spherical harmonic functions to determine the characteristics of the spectrum of spherical harmonic modes and the nature of steady photospheric flows. Synthetic data are constructed in order to test the technique. In spite of the mode mixing due to the lack of information about the motions on the backside of the sun, solar rotation and differential rotation can be accurately measured and monitored for secular changes, and meridional circulations with small amplitudes can be measured. Furthermore, limb shift measurements can be accurately obtained, and supergranules can be fully resolved and separated from giant cells by their spatial characteristics.

Hathaway, David H.↗
NASA NTRS1987

Spherical harmonic expansion of the Levitus Sea surface topography

Prior information for the stationary sea surface topography (SST) may be needed in altimetric solutions that intend to simultaneously improve the gravity field and determine the SST. For this purpose the oceanographically derived SST estimates are represented by a spherical harmonic expansion. The spherical harmonic coefficients are computed from a least squares adjustment of the data covering the majority of the oceanic regions of the world. Several tests are made to determine the optimum maximum degree of solution and the best configuration of the geometry of the data in order to obtain a solution that fits the data and also provides a good spectral representation of the SST.

Engelis, Theodossios↗
NASA NTRS1987

Comparison of the structure of harmonic aqueous glasses and liquid water

Glassy structures of water were generated by rapidly quenching configurations of 64 and 343 molecules of liquid water; and the potential energy was then expanded through quadratic order around local minima generated in this way, and the properties of the resulting harmonic system were calculated. The results obtained were used to test the degree to which the structure of liquid water is similar to that of a harmonic aqueous glass. The radial distribution functions for the glass were found to be remarkably similar to those of the liquid. Translational modes were found to be almost entirely responsible for the broadening of the oxygen-oxygen radial distribution function of the quenched configuration, and also primarily responsible for the broadening of other radial distribution functions.

Pohorille, Andrew↗
NASA NTRS1988

A theory for the radiation at the third to fifth harmonics of the plasma frequency upstream from the earth's bow shock

A theory involving the process L + T' - T is proposed for the observed third to fifth harmonics of the plasma frequency observed upstream from the earth's bow shock. The conditions for which the theory may explain the observed radiation are determined, and the viability of the theory is discussed. The theory is found to require L waves with temperature between about 10 to the 21st and 10 to the 22nd K in the source regions to account for the levels and number of harmonics of the observed radiation. Such L wave temperatures are theoretically possible in the foreshock, but are not consistent with the most intense observed L waves.

Cairns, Iver H.↗
NASA NTRS1989

Making A Circular-Harmonic Filter

Optical image-correlating system made rotationally invariant. Experiment shows circular-harmonic filter generated optically. Hologram made by phase-shifted-double-exposure procedure. Filter used in optical image-recognition system based on correlation between target (image to be recognized) and matched spatial filter. In addition to usual invariance under translation of target, circular harmonic filter invariant under rotation of target; peak intensity of illumination at origin of correlation plane does not vary when target rotated about optical axis.

Cheng, Yeou Yen↗