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At least 865 records · Page 48

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NASA NTRS1980

A laboratory study on the dissociative recombination of vibrationally excited O2/+/ions

The dissociative recombination of vibrationally excited O2(+) ions is studied in light of the possible importance of this reaction in upper atmospheric chemistry. A plasma spectroscopy experiment was performed in a microwave cavity filled by an argon-oxygen mixture, with O(1S) production monitored by measurements of the 5577-A afterglow, the O2(+) density and the electron concentration. Plasma and optical data reveal the predominant afterglow ions to be Ar2(+) and O2(+), with an effective O(1S) dissociative recombination coefficient of 2.1 x 10 to the -8th cu cm/sec, corresponding to a quantum yield of 10%. Experiments with an argon-krypton-oxygen mixture reveal that vibrationally excited O2(+) ions are the chief source of the O(1S) atoms, with a specific recombination coefficient for the dissociation of O2(+)(2 pi g) into O(1S) and O(1D) of 4.2 x 10 to the -9th cu cm/sec. A comparison of the laboratory results with Atmospheric Explorer data on the 5577-A airglow implies that O2(+) ions in the sunlit ionosphere are vibrationally excited to the same degree as in the laboratory, with the vibrational relaxation of these ions much slower than dissociative recombination. Results also predict a dawn-twilight asymmetry in the effective O(1S) yield due to the normal variation of electron content.

Zipf, E. C.↗

NASA NTRS1980

Observations of Cygnus X-3 with the Einstein /HEAO 2/ X-ray Observatory The period derivative and the asymmetric X-ray light curve

Cygnus X-3 was observed by the Monitor Proportional Counter on the Einstein (HEAO 2) X-ray Observatory for 2.4 days in 1978 December. The analysis of the data from these observations is used in conjunction with a self-consistent re-examination of previous results from the Uhuru, ANS, COS B, and SAS 3 satellites to investigate earlier reports that the 4.8 hour period of Cygnus X-3 is increasing. It is found that there is indeed a period derivative, P = (1.78 plus or minus 0.40) x 10 to the -9th s/s, which confirms the principal conclusion of previous authors. The possibility that the X-ray source is in an elliptical orbit and that some, or all, of the observed period derivative may be due to apsidal motion is discussed. The elliptic orbit hypothesis explains the observed asymmetry in the average X-ray light curve and leads to the conclusion that the most likely companion to the X-ray source is a helium star, possibly with a light hydrogen envelope

Elsner, R. F.↗

NASA NTRS1980

Energetic particles in the pre-dawn magnetotail of Jupiter

A detailed account is given of the energetic electron and proton populations as observed with Voyagers 1 and 2 during their passes through the dawn magnetotail of Jupiter. The region between 20 and 150 R sub J is dominated by a thin plasma sheet, where trapped energetic electron and proton fluxes reach their maximum. Proton spectra can be represented by an exponential in rigidity with a characteristic energy of approximately 50 keV. Proton anisotropies were consistent with corotation even at 100 R sub J. A major proton acceleration event as well as several cases of field aligned proton streaming were observed. The flux of 0.4 MeV protons decreases by three orders of magnitude between 30 and 90 R sub J and then remains relatively constant to the magnetopause. Fine structure in the data indicate longitudinal asymmetries with respect to the dipole orientation. Electron spectra in the magnetosheath and interplanetary space are modulated by the Jovian longitude relative to the subsolar point.

Schardt, A. W.↗

NASA NTRS1980

Studying internal and external magnetic fields in Japan using MAGSAT data

Examination of the total intensity data of CHRONIT on a few paths over Japan and its neighboring sea shows MAGSAT is extremely useful for studying the local magnetic anomaly. In high latitudes, the signatures of field aligned currents are clearly recognized. These include (1) the persistent basic pattern of current flow; (2) the more intense currents in the summer hemisphere than in the winter hemisphere; (3) more fluctuations in current intensities in summer dawn hours; and (4) apparent dawn-dusk asymmetry in the field-aligned current intensity between the north and south polar regions.

Fukushima, N.↗

NASA NTRS1980

A three-dimensional body-fitted coordinate system for flow field calculations on asymmetric nosetips

A three dimensional body-fitted coordinate system developed for use in the calculation of inviscid flows over ablated, asymmetric reentry vehicle nosetips is described. Because of the potential geometric asymmetries, no standard coordinate system (e.g., spherical, axisymmetric reference surface-normal) is capable of being closely aligned with the nosetip surface. To generate a 3-D, body-fitted coordinate system an analytic mapping procedure is applied that is conformal within each meridional plane of the nosetip; these transformations are then coupled circumferentially to yield a three dimensional coordinate system. The mappings used are defined in terms of hinge points, which are points selected to approximate the body contours in each meridional plane. The selection of appropriate hinge points was automated to facilitate the use of the resulting nosetip flow field code.

Hall, D. W.↗

NASA NTRS1980

Jet-diffuser Ejector - Attached Nozzle Design

Attached primary nozzles were developed to replace the detached nozzles of jet-diffuser ejectors. Slotted primary nozzles located at the inlet lip and injecting fluid normal to the thrust axis, and rotating the fluid into the thrust direction using the Coanda Effect were investigated. Experiments indicated excessive skin friction or momentum cancellation due to impingement of opposing jets resulted in performance degradation. This indicated a desirability for location and orientation of the injection point at positions removed from the immediate vicinity of the inlet surface, and at an acute angle with respect to the thrust axis. Various nozzle designs were tested over a range of positions and orientations. The problems of aircraft integration of the ejector, and internal and external nozzle losses were also considered and a geometry for the attached nozzles was selected. The effect of leaks, protrusions, and asymmetries in the ejector surfaces was examined. The results indicated a relative insensitivity to all surface irregularities, except for large protrusions at the throat of the ejector.

Alperin, M.↗

NASA NTRS1980

Visual evaluation of nystagmus intensity in points to diagnose vestibular dysfunction

The amplitude of nystagmus multiplied by its frequency gives a value commensurate to the velocity of slow phase. If the amplitude and the frequency during the visual observation are expressed in relative units (e.g., in points ranging from 1 to 3) the results of multiplication are used for a relative evaluation of nystagmus intensity. The relative evaluation of nystagmus intensity is used to compare the responses and, in particular, to calculate the coefficients of labyrinth asymmetry and of directional preponderance. A suggestion is made to analyze the formal results of caloric tests using a simple graphic model reflecting the left-right interactions by which the obtained coefficients are conditioned.

Levashov, M. M.↗

NASA NTRS1981

High resolution absolute flux profiles of the MC 2 h and k lines in evolved F8 to M5 stars

The central results of a survey of the Mg II resonance line emission in a sample of over 50 evolved late type stars, including spectral-luminosity type F8 to M5 and La to IV are presented. Observed and surface fluxes are derived and correlations noted. The major findings include: (1) Mg II k emission core asymmetry transition near K1 III, analogous to that known for Ca II K; (2) a small gravity and temperature dependence of the Mg II chromospheric radiative loss rate.

Stencel, R. E.↗

NASA NTRS1981

Japanese Magsat Team. A: Crustal structure near Japan and its Antarctic Station. B: Electric currents and hydromagnetic waves in the ionosphere and the magnetosphere

Efforts continue in compiling tapes which contain vector and scalar data decimated at an interval of 0.5 sec, together with time and position data. A map of the total force field anomaly around Japan was developed which shows a negative magnetic anomaly in the Okhotsk Sea. Examination of vector residuals from the MGST model shows that the total force perturbation is almost ascribable to the perturbation parallel to the main geomagnetic field and that the contribution from the perturbation transverse to the main field to the total force perturbation is negligibly small. The influences of ionospheric current with equatorial electroject and of the magnetospheric field aligned current on the dawn-dusk asymmetry of daily geomagnetic variations are being considered. The total amount of electric current flowing through the plane of the Magsat orbit loop was calculated by direct application of Maxwell's equation. Results show that the total electric current is 1 to 5 ampheres, and the current direction is either sunward or antisunward.

Fukushima, N.↗

NASA NTRS1981

The radiation-induced rotation of cosmic dust particles: A feasibility study

A crossed beam, horizontal optical trap, used to achieve laser levitation of particles in an effort to determine how solar radiation produces high spin rate in interplanetary dust particles, is described. It is suggested that random variations in albedo and geometry give rise to a nonzero effective torque when the influence of a unidrectional source of radiaton (due to the Sun) over the surface of a interplanetary dust particle is averaged. This resultant nonzero torque is characterized by an asymmetry factor which is the ratio of the effective moment arm to the maximum linear dimension of the body and is estimated to be 5 X 10 to the minus four power. It is hoped that this symmetry factor, which stabilizes the nonstatistical response of the particle, can be measured in a future Spacelab experiment.

Misconi, N. Y.↗

NASA NTRS1980

The hard X-ray pulse profile of GX 1+4

Results are reported from 1976 and 1977 observations of the galactic center X-ray source GX 1+4. On these two occasions, epoch folding at twice the previously reported period of about two minutes has resulted in an asymmetry between the shapes of the two resultant peaks in the light curve, indicating that the true period may be about four minutes. Mean intensity is shown to vary from pulse to pulse.

Strickman, M. S.↗

NASA NTRS1980

A photometric study of the eclipsing binary RX Hercules

A new photoelectric light curve of RX Hercules, a binary system with similar components, has been analyzed using Wood's computer model. RX Her, using Popper's spectroscopic mass ratio of q = 0.8472, turned out to be composed of a dimmer AO component and a larger B9.5 component. This detached system, upon analysis of the residuals in secondary minimum, shows some asymmetry during ingress which then disappears just before secondary minimum. The eccentricity e = 0.022 determined in this study is a little larger than previously published values of e = 0.018. In combination with the spectroscopic analysis of Popper, and ubvy data of Olson and Hill and Hilditch new photometric elements for RX Her were found.

Jeffreys, K. W.↗

NASA NTRS1981

Hinged strakes for enhanced maneuverability at high angles of attack

A controllable-strake concept for alleviating the adverse effects of strake vortex breakdown and asymmetry on the longitudinal and lateral aerodynamics of strake-wing configurations at high angles of attack is presented. The concept aims to control the strake load independently of angle of attack and sideslip by varying the anhedral angle of strakes hinged along the root chord. The strakes may be deflected in a symmetrical or nonsymmetrical mode for a variety of control functions. Results are presented of an exploratory wind-tunnel investigation to evaluate the potential of the hinged-strake concept for enhancing the three-axis controllability in post-stall flight.

Rao, D. M.↗

NASA NTRS1980

Orientations of central peaks in lunar craters - Implications for regional structural trends

Impact craters are dominant features on the lunar surface and all fresh craters with diameters greater than 35 km possess central peaks. Approximately half of these central peaks (54%) have either linear or arcuate geometry and display some preferential orientation. These orientations were measured for 200 lunar craters of Pre-Nectarian to Copernican age. A pervasive regional north-south trend is identified for central peak orientation, with secondary trends at + or - 20-30 deg from this axis. No evidence for regional east-west trends is found. These orientations are shown to persist in craters formed through the last 4 billion years of lunar history. A lack of coincidence between impact direction, as determined from ejecta asymmetries and peak orientation, argues for structural control by the target as a source of the linear peak morphology. This is supported by the regional and temporal persistence of preferred peak orientations. It is proposed that linear central peak orientations in lunar craters reflect a pervasive regional structural system which developed early in lunar history and has persisted through geologic time.

Hale, W.↗

NASA NTRS1980

An empirical model of the Venusian outer environment. I - The shape of the dayside solar wind-atmosphere interface. II - The shape and location of the bow shock

Solar wind plasma and magnetic field data and ionospheric data obtained from the Pioneer Venus orbiter are discussed. The variation in the magnetic field pressure within the magnetic barrier is shown to be similar to that expected for the solar wind pressure variations along an obstacle's boundary when a more realistic approximation of the shape of the ionosphere is included. Simultaneous solar wind pressure, ionospheric pressure, and magnetic barrier pressure data reveal that the ionospheric pressure below the ionopause is approximately equal to the solar wind pressure. The magnetic barrier pressure is found to be equal to approximately 2/3 to 3/4 of both the solar wind pressure and the ionospheric pressure. Estimates of the hot plasma pressure contribution to the total pressure in the magnetic barrier vary from 1/4 to 1/3. Just below the ionopause the ionospheric pressure deviations from the mean ionospheric pressure are significant, especially below approximately 400 km; they appear to be indicative of the adjustment of the ionospheric structure to changeing solar wind conditions. A first-order model of the ionopause pressure variations as a function of height and solar-zenith angle is proposed. Venera 9 and Venera 10 bow shock crossings are then analyzed for solar zenith angles in the range from approximately 25 deg to approximately 153 deg. A comparison of Venera 9 and Venera 10 bow shock crossings with those observed by the Pioneer Venus orbiter suggests that both the secular variation and the latitudinal asymmetry may be responsible for the closer shock crossings of the Venera 9 and Venera 10 spacecraft.

Vaisberg, O. L.↗

NASA NTRS1980

Empirical models of the electron temperature and density in the Venus ionosphere

The electron temperature and density of the Venus ionosphere is characterized using data from the Pioneer Venus orbiter electron temperature probe experiment for the full range of solar zenith angles and local times. Values for the electron density are nearly uniform across the day side with a sharp decrease in the vicinity of the terminator. The model shows a substantial night side ionosphere which can be accounted for by a combination of several transport processes, and by local production by precipitating particles. The electron temperature model demonstrates the high temperatures seen on both the day side and night side. It is found that the night side is much more variable than the day side, and that there is no obvious north-south asymmetry in either the temperature or the density.

Theis, R. F.↗

NASA NTRS1980

The character of the thermal emission from Venus

Images of the thermal infrared emission from 10.6 to 12.6 microns from the earth-facing hemisphere of Venus were made from earth on each available opportunity over a 26-day period in 1977 and a 106-day period in 1978-1979, using a 1.5 m telescope. Compact, variable thermal features exist at latitudes higher than about 50 deg, some of which repeat at 5-day intervals. No such repeatability is observed for features near the equator. Day-to-day variations in limb darkening and the contrast of high latitude features appear to differ in the conjunction and post-conjunction images. A strong, solar-fixed component of the emission exists and exhibits wave number 1, 2, and 4 components. The thermal tides provide constraints upon the atmosphere structure. The solar-fixed structure shows significant asymmetries with respect to the equator.

Apt, J.↗

NASA NTRS1980

The effect of radiation pressure on the restricted three-body problem

The classical restricted three-body problem is extended to account for the effects of radiation pressure and the Poynting-Robertson effect on a particle with a surface-to-volume relation such that radiation pressure forces are nonnegligible moving in the gravitational field of two larger, orbiting bodies. The positions of the L4 and L5 Lagrangian points are found as functions of the ratio of radiational to gravitational forces. The inclusion of the Poynting-Robertson effect, however, is found to render the L4 and L5 points unstable on a time scale which is long compared to the rotation period of the two massive bodies. The results imply that space colonies with solar facing adjustable sails may be able to remain stationary at any heliocentric distance between a planet and the sun, and may provide a mechanism for producing asymmetries in the interplanetary dust cloud.

Schuerman, D. W.↗