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NASA NTRS1986

Polarization in massive X-ray binaries. I - A low-inclination model for Cygnus X-1

The possibility that variable linear polarization in massive X-ray binaries is produced by electron scattering in an asymmetric stellar wind is investigated. The stellar wind is asymmetric because of the gravitational field of the secondary (X-ray source). The degree of asymmetry and the magnitude of the linear polarization are controlled by the degree to which the primary star fills its Roche lobe. For the well-observed X-ray binary Cyg X-1, the present model can produce the correct magnitude for the polarization. Provided that the inclination of the system is less than about 20 deg, the present model should also predict the correct phase dependence of the polarization. Modifications to the model are described which would enable it to apply to systems with higher inclination.

Friend, D. B.↗

NASA NTRS1986

IUE observations of interstellar hydrogen and deuterium toward Alpha Centauri B

A high dispersion profile is presented of the Lyman-alpha emission toward Alpha Cen B as recorded in two images taken with the IUE spacecraft. The spectra were examined with a three-parameter Gaussian or five-parameter solar-type profile to derive the intrinsic background stellar emission. Voight absorption profiles were calculated for the intervening H I and D I gas. A uniform, thermally broadened medium was assumed, with the calculations being based on the free stellar parameters of density, velocity dispersion and the bulk velocity of H I, and the density of D I. The use of a small aperture is shown to have been effective in eliminating geocoronal and interplanetary diffuse Ly-alpha contamination. The H I absorption profile toward Alpha Cen B is found to be equivalent to that toward Alpha Cen A, indicating that the H I profiles derived are essentially independent of stellar emission. Less success, however, was attained in obtaining any definitive D I profile, although an asymmetry in the blue and red wings of the Lyman-alpha emissions did show the presence of absorption by interstellar deuterium and allow setting a lower limit of 0.00001 for the D I/H I ratio.

Landsman, W. B.↗

NASA NTRS1986

Observations of far-infrared line profiles in the Orion-KL region

Measurements of several far-infrared emission line profiles in the Orion-KL region are reported. The emission from the CO, OH, and forbidden O I emission lines toward the BN-KL and H2 peak 1 positions probably comes from dense, hot molecular gas in the Orion-KL shock. The CO and forbidden O I lines have similar profiles, suggesting that the high-velocity forbidden O I emission also arises in magnetohydrodynamic 'cloud' shocks. The velocity centroids of the lines are somewhat blueshifted. The far-infrared data thus support the interpretation that the blue asymmetry of the H2 2 micron lines is not mainly due to differential dust extinction, but rather to the kinematics and geometry of the shocked gas in the Orion-KL outflow. The forbidden O I and CO lines, however, have significantly less extreme blueshifted emission than the H2 lines. Both the forbidden O I 63 micron and forbidden C II 158 micron lines have features strongly supporting a common origin near the surface of the Orion molecular cloud.

Crawford, M. K.↗

NASA NTRS1986

Europa - Characterization and interpretation of global spectral surface units

In the present analysis of the Voyager global multispectral mosaic of the Galilean satellite Europa, which was conducted to map surface units with similar optical properties, color assignments are indicative of the spectral nature of the given unit. The unit maps are noted to exhibit a marked hemispheric asymmetry which is most clearly seen in the UV/violet albedo ratio image. It appears as if the surface has been most darkened at the center of the trailing hemisphere, with a gradual decrease to a minimum at the center of the leading hemisphere as the cosine of the angle from the antapex of motion; this cosine pattern suggests that the darkening is exogenic in origin, and is interpreted as evidence of surface alteration by in bombardment from the Jovian magnetosphere.

Nelson, M. L.↗

NASA NTRS1986

Global dynamics and thermal structure of Jupiter's atmosphere

Voyager flyby observations have yielded the first detailed maps of wind and temperature fields in the Jupiter atmosphere; these data indicate that Jupiter's zonal currents violate the barotropic instability criterion if they extend only a few scale heights below the cloud tops. Microwave observations at mm and cm wavelengths have probed the atmosphere down to a level of about 7 bars, thereby constraining horizontal and vertical thermal structure in a region of the atmosphere about which little was known. Temporal variations in the temperature field suggest that dynamical processes may be important in the establishment of tropopause structure on short time scales. Ground-based and Voyager observations have also indicated a hemispheric asymmetry in temperature in the upper stratosphere.

Flasar, F. M.↗

NASA NTRS1986

Influence of forebody cross-sectional shape on wing vortex burst location

A water tunnel study examining the influence of forebody cross section on the position of the wing vortex burst was carried out in the NASA Ames-Dryden water tunnel for a 55-deg cropped delta-wing model. Two of three cross sections investigated were chine-shaped, where the included angle of the chine was either 7.5-deg, representing a rather small side-edge angle, or 90 deg, representing a more moderate design. The third cross section was circular and served as a baseline for comparison. It is found that the 7.5 deg chine cross section generated the strongest forebody vortices of the three configurations and that these strong forebody vortices interacted with the main wing vortices in such a manner as to dramatically delay wing vortex burst position at zero sideslip. If the configuration is sideslipped, large asymmetries in wing vortex burst location may result.

Hall, R. M.↗

NASA NTRS1985

The effect of microwave backscatter uncertainty on satellite radar altimeter accuracy

The effect of variations in ocean surface roughness characteristics with upwind/downwind direction, reported by other investigators, is used to compute radar cross section (RCS) and to assess the errors which may arise in present and planned altimeter sensors. Based on an analysis of the rough surface impulse response, the uncertainty between attitude angle and RCS asymmetry is found to cause height errors as large as 12 cm, depending on off-nadir angles and sea state. Additionally, the previously reported data in conjunction with computed facet backscatter are found to produce RCS characteristics at large off-nadir angles which are in better agreement with experimental results than those predicted by physical optics Gaussian theory.

Miller, L. S.↗

NASA NTRS1986

Strong electron bidirectional anisotropies in the distant tail - ISEE 3 observations of polar rain

A detailed observational treatment of bidirectional electrons (about 50 to 500 eV) in the distant magnetotail (r not below 100 earth radii) is presented. It is found that electrons in this energy range commonly exhibit strong, field-aligned anisotropies in the tail lobes. Because of large tail motions, the ISEE 3 data provide extensive sampling of both the north and south lobes in rapid succession. These data directly demonstrate the strong asymmetries that exist between the north and south lobes at any one time. The bidirectional fluxes are found to occur predominantly in the lobe directly connected to the sunward interplanetary magnetic field in the open magnetosphere model (north lobe for away sectors and south lobe for toward sectors). Electron anisotropy and magnetic field data are presented which show the transition from unidirectional (sheath) electron populations to bidirectional (lobe) populations. The open nature of the distant magnetopause is demonstrated and it is shown that the source of the higher-energy, bidirectional lobe electrons is the tailward directed electron heat flux population in the distant magnetosheath. Taken together, the present evidence suggests that the bidirectional electrons that were observed in the distant tail are closely related to the polar rain electrons observed previously at lower altitudes. Furthermore, these data provide strong evidence that the distant tail is composed largely of open magnetic field lines in contradistinction to some recently advanced models.

Baker, D. N.↗

NASA NTRS1986

The warped neutral sheet and plasma sheet in the near-earth geomagnetic tail

An analysis of ISEE 2 plasma and magnetic field data indicates that the plasma sheet and neutral sheet in the near-earth magnetotail are warped in such a manner that in summer (winter) the neutral sheet rises above (dips below) the solar magnetospheric equatorial plane near the center of the tail, but dips below (rises above) the equatorial plane along the tail flanks. In the near tail, the neutral sheet crosses the equatorial plane at about 12 earth radii from the aberrated X axis, considerably closer to the center of the tail than has been inferred from data obtained farther downstream. This increase in the warp with decreasing distance from the earth is consistent with theoretical predictions. In the near tail, the warp is sufficiently strong when the dipole tilt angle is large that even in quiet times the upper or lower edge of the plasma sheet can be found close to the solar magnetospheric equatorial plane along the tail flanks. The seasonal dependence of the warp can produce certain dawn-dusk asymmetries in satellite data which are more apparent than real.

Gosling, J. T.↗

NASA NTRS1986

Latitude and depth variation of solar rotation

New measurements of frequencies of various modes of acoustic waves trapped within the sun are reported for degrees up to 98 which allow the convective envelope to be isolated. For degrees between 20 anad 98, no evidence is found that internal rotation differs significantly with depth or latitude from the rotation of surface magnetic field patterns. Modes covering a wide latitude range have systematically lower frequencies than those confined near the equator, indicating the existence of a structural asymmetry within the sun.

Duvall, T. L., Jr.↗

NASA NTRS1985

The LDEF interplanetary dust experiment

Explorer 46 data and the Long Duration Exposure Facility (LDEF) interplanetary dust experiment are examined. Analysis of the Explorer 46 data reveals the existence of particles of 0.1 micron and a mass of 1 x 10 to the -16th gm, the injection of the submicron particles directly by a comet (injection mass of about 5000 tons), and a submicron particle lifetime of about three years. The applications of LDEF data to particles in hyperbolic orbits, particle swarms, morning-to-evening asymmetry, the effects of the earth's orbit eccentricity, and the presence of interstellar dust are discussed. The effects of space debris on data collection are considered.

Singer, S. F.↗

NASA NTRS1986

Transitions to chaos in two-dimensional double-diffusive convection

The partial differential equations governing two-dimensional thermosolutal convection in a Boussinesq fluid with free boundary conditions have been solved numerically in a regime where oscillatory solutions can be found. A systematic study of the transition from nonlinear periodic oscillations to temporal chaos has revealed sequences of period-doubling bifurcations. Overstability occurs if the ratio of the solutal to the thermal diffusivity tau is less than 1 and the solutal Rayleigh number Rs is sufficiently large. Solutions have been obtained for two representative values of tau. For tau = 0.316, R(s) = 10,000, symmetrical oscillations undergo a bifurcation to asymmetry, followed by a cascade of period-doubling bifurcations leading to aperiodicity, as the thermal Rayleigh number R(T) is increased. At higher values of R(T), the bifurcation sequence is repeated in reverse, restoring simple periodic solutions. As R(T) is further increased more period-doubling cascades, followed by chaos, can be identified. Within the chaotic regions there are narrow periodic windows, and multiple branches of oscillatory solutions coexist. Eventually the oscillatory branch ends and only steady solutions can be found. The development of chaos has been investigated for tau = 0.1 by varying R(T) for several different values of R(s). When R(s) is sufficiently small there are periodic solutions whose period becomes infinite at the end of the oscillatory branch. As R(s) is increased, chaos appears in the neighborhood of these heteroclinic orbits. At higher values of R(s), chaos is found for a broader range in R(T). A truncated fifth-order model suggest that the appearance of chaos is associated with heteroclinic bifurcations.

Knobloch, E.↗

NASA NTRS1986

Seasonal variations of troposheric ozone at Natal, Brazil

An analysis of ozone measurements from Natal, Brazil (6 deg S, 35 W), with a focus on the seasonal behavior in the troposphere, is presented. The amplitude of seasonal cycle at Natal is much larger than at Panama (9 deg N), the only other tropical site for which similar data are available. Concentrations of ozone in the middle troposphere in the southern spring are unexpectedly high, 60-70 ppb, similar to values found at northern midlatitudes in summer, and larger by 20-30 ppb than values found at Panama and at southern midlatitudes. It is suggested that photochemical production of ozone associated with emissions of CO, hydrocarbons, and NO(x) from biomass burning may contribute significantly to the high values of ozone, but note that stratospheric intrusions could also play a role. The data available at present do not permit a definitive evaluation of the relative importance of these two sources of ozone. The data from Natal, in combination with recent aircraft and surface data, show that tropical ozone exhibits strong spatial and temporal inhomogeneities. The distribution of tropospheric ozone appears to be considerably more complex than the traditional view, which suggested a northern midlatitude maximum and north/-south hemispheric asymmetry. The seasonal cycle in the total column of ozone at Natal appears to mirror the behavior of the tropospheric contribution to the ozone column rather than the stratospheric contribution, and this may account for differences in the annual cycle of the total column at Natal versus other tropical locations.

Logan, J. A.↗

NASA NTRS1986

Model-following control for an oblique-wing aircraft

A variable-skew oblique wing offers a substantial aerodynamic performance advantage for aircraft missions that require both high efficiency in subsonic flight and supersonic dash or cruise. The most obvious characteristic of the oblique-wing concept is the asymmetry associated with wing-skew angle which results in significant aerodynamic and inertial cross-coupling between the aircraft longitudinal and lateral-directional axes. This paper presents a technique for synthesizing a decoupling controller while providing the desired stability augmentation. The proposed synthesis procedure uses the concept of explicit model following. Linear quadratic optimization techniques are used to design the linear feedback system. The effectiveness of the control laws developed in achieving the desired decoupling is illustrated for a given flight condition by application to linearized equations of motion, and also to the nonlinear equations of six degrees of freedom of motion with nonlinear aerodynamic data.

Alag, G. S.↗

NASA NTRS1986

Saturation and beaming in astrophysical masers. III - Asymmetrically pumped masers

There is reason to believe that the physical conditions in many astrophysical masers are far from homogeneous. In particular, if the maser pump involves the absorption of infrared photons, the pump rate may vary rapidly (perhaps exponentially) across the cloud. The consequences of such variation of the pump rate for the maser radiation are calculated, and it is shown that there are substantial asymmetries in the output of the maser. A general result is that the maser radiation is preferentially emitted back toward the source of pump radiation. The implication of this result for the interpretation of the circumstellar 1612 MHz OH masers is briefly discussed.

Alcock, C.↗

NASA NTRS1987

Calculating Sonic-Boom Propagation

Nonlinear effects included, enabling more-realistic modeling. Modified Method of Characteristics Sonic Boom Extrapolation Program (MMOC) is computer program for sonic-boom propagation that includes shock coalescence and incorporates effects of asymmetries due to volume and lift. Numerically integrates nonlinear governing equations using data on initial data line approximately one body length from aircraft and yields sonic-boom pressure at ground as function of time or of position at given time. MMOC written in FORTRAN IV.

Darden, C. M.↗

NASA NTRS1987

Trellis-Coded Modulation for Fading Channels

In proposed communication system, digital signals transmitted efficiently over fading channel by combination of trellis coding and multiple-phase-shift keying with addition of asymmetry to signal set. Coding and modulation schemes not designed separately as in previous systems but integrated to yield bandwidth-efficient modulation and forward-error-correction coding. Helps to satisfy need for reliable high-quality transmission of voice and data between land-mobile units via satellites, where limitations of power and bandwidth imposed simultaneously. Also applicable to ionospheric communications between fixed or mobile units.

Simon, Marvin K.↗

NASA NTRS1987

Binary-Symmetry Detection

Transmission errors for zeros and ones tabulated separately. Binary-symmetry detector employs psuedo-random data pattern used as test message coming through channel. Message then modulo-2 added to locally generated and synchronized version of test data pattern in same manner found in manufactured test sets of today. Binary symmetrical channel shows nearly 50-percent ones to 50-percent zeroes correspondence. Degree of asymmetry represents imbalances due to either modulation, transmission, or demodulation processes of system when perturbed by noise.

Lopez, Hiram↗