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Supercool(ed) Olivine Morphology in Shergottites Revealed Using X-ray Computed Tomography

Shergottites comprise most of the Martian meteorites and have a mafic to ultramafic bulk composition and a diversity of igneous textures [1].Olivine-phyric and poikilitic shergottites are sub-classes of shergottites and characterized by having a crystal cargo of large mafic minerals. Olivine-phyric shergottites have porphyritic textures of large olivinemegacrysts set in a fine-grained groundmass of pyroxene and maskelynite [2]. The poikilitic shergottites have assemblages of olivine chadocrysts poikilitically-enclosed by cm-sized pyroxene oikocrysts set in a coarse-grained groundmass of olivine and maskelynite [3,4]. The large crystal cargos in these samples are some of the first minerals to crystallize from their respective parent melts and have been extensively studied to understand shergottite petrogenesis. For instance, compositions of early-formed olivine and pyroxene in equilibrium with other phases (e.g. spinels) are used to establish depths, temperatures, and redox conditions of crystallization. There is increasing agreement that olivine megacrysts and poikilitic assemblages formed at or near the crust – mantle boundary (~85 km) before entrainment, ascent, and complete crystallization at or near the surface [1,3,4,6,7,8,9]. Additionally, linear olivine megacryst crystal size distribution (CSD)patterns and observations of polyhedral morphologies[8,9,10] are commonly interpreted to reflect steady-state crystallization under equilibrium conditions. However, oscillatory phosphorus zonation patterns in olivine from many samples indicate fluctuations in growth rates[10,12]. Recent studies measuring dendritic phosphorus zonation in terrestrial olivines [13] and experimental studies measuring how undercooling (undercooling is defined as the liquidus temperature minus the temperature being considered) controls changes in olivine morphology [14] have questioned the canonical view that large olivine megacrysts grow slowly and concentrically under equilibrium conditions. Here we present X-ray CT results from olivine-phyric and poikilitic shergottites that challenge the notion that early-formed minerals grew slowly under equilibrium conditions.

S A Eckley↗
NASA NTRS1977

Polarization loss of a satellite - Data collection sensor link

It is noted that the stringent economy of data-collection systems consisting of several widely dispersed satellite-monitored sensor platforms can be partially achieved by using an inexpensive linearly polarized antenna on each platform and that due to Faraday rotation of the ionosphere, the satellite antenna must be circularly polarized to avoid a prohibitive polarization loss. The cumulative probability distribution of polarization loss between a linearly polarized platform antenna and an elliptically polarized satellite antenna is computed for satellite-antenna axial ratios of 3 and 4 dB. The results indicate that a polarization loss of 4.5 dB must be expected for a reliability of 85% and an axial ratio of 3 dB. It is suggested that the conventional assignment of a 3-dB polarization loss to the communication link considered may not insure the required link reliability.

Estep, H.↗
NASA NTRS1989

Statistical study of the correlation of hard X-ray and type 3 radio bursts in solar flares

A large number of hard X-ray events which were recorded by the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM) during the maximum of the 21st solar cycle (circa 1980) are analyzed in order to study their statistical correlation with type 3 bursts. The earlier finding by Kane (1981) are confirmed qualitatively that flares with stronger hard X-ray emission, especially those with harder spectra, are more likely to produce a type 3 burst. The observed distribution of hard X-ray and type 3 events and their correlations are shown to be satisfactorily described by a bivariate distribution consistent with the assumption of statistical linear dependence of X-ray and radio burst intensities. From this analysis it was determined that the distribution of the ratio of X-ray intensity (in counts/s) to type 3 intensity (in solar flux units) which has a wide range and a typical value for this ratio of about 10. The implications of the results for impulsive phase models are discussed.

Hamilton, Russell J.↗
NASA NTRS1990

The Design of Optical Sensor for the Pinhole/Occulter Facility

Three optical sight sensor systems were designed, built and tested. Two optical lines of sight sensor system are capable of measuring the absolute pointing angle to the sun. The system is for use with the Pinhole/Occulter Facility (P/OF), a solar hard x ray experiment to be flown from Space Shuttle or Space Station. The sensor consists of a pinhole camera with two pairs of perpendicularly mounted linear photodiode arrays to detect the intensity distribution of the solar image produced by the pinhole, track and hold circuitry for data reduction, an analog to digital converter, and a microcomputer. The deflection of the image center is calculated from these data using an approximation for the solar image. A second system consists of a pinhole camera with a pair of perpendicularly mounted linear photodiode arrays, amplification circuitry, threshold detection circuitry, and a microcomputer board. The deflection of the image is calculated by knowing the position of each pixel of the photodiode array and merely counting the pixel numbers until threshold is surpassed. A third optical sensor system is capable of measuring the internal vibration of the P/OF between the mask and base. The system consists of a white light source, a mirror and a pair of perpendicularly mounted linear photodiode arrays to detect the intensity distribution of the solar image produced by the mirror, amplification circuitry, threshold detection circuitry, and a microcomputer board. The deflection of the image and hence the vibration of the structure is calculated by knowing the position of each pixel of the photodiode array and merely counting the pixel numbers until threshold is surpassed.

Greene, Michael E.↗
NASA NTRS1992

Global deformation on the surface of Venus

Large-scale mapping of tectonic structures on Venus shows that there is an organized global distribution to deformation. The structures we emphasize are linear compressive mountain belts, extensional rafted zones, and the small-scale but widely distributed wrinkle ridges. Ninety percent of the area of the planet's compressive mountain belts are concentrated in the northern hemisphere whereas the southern hemisphere is dominated by extension and small-scale compression. We propose that this striking concentration of fold belts in the northern hemisphere, along with the globe-encircling equatorial rift system, represents a global organization to deformation on Venus.

Bilotti, Frank↗
NASA NTRS1983

Conductive flux in the chromosphere derived from line linear polarization observation

It is shown that quantitative information on the mechanisms of energy transport which take place in solar flares can be obtained by measurement of impact line polarization. Linear polarization in two chromospheric lines (H-alpha and SI 1437 A) observed in the gradual phase of solar flares was investigated. The polarized electric vector is shown to be directed towards the center of the disk. The relationship between conductive heat flux and linear line polarization is determined using a function which represents the velocity distribution of electrons carrying heat flux. The relationship between linear polarization and heat flux is applied to the observed degree of polarization, which yields the conductive heat flux in the high chromosphere. It is determined that this conductive flux is of the order of magnitude of the total radiation loss in the chromosphere and below, which is also of the order of magnitude of the conductive flux in the transition zone.

Henoux, J.-C.↗
NASA NTRS1991

Fault-tolerance techniques for high-speed fiber-optic networks

Four fiber optic network topologies (linear bus, ring, central star, and distributed star) are discussed relative to their application to high data throughput, fault tolerant networks. The topologies are also examined in terms of redundancy and the need to provide for single point, failure free (or better) system operation. Linear bus topology, although traditionally the method of choice for wire systems, presents implementation problems when larger fiber optic systems are considered. Ring topology works well for high speed systems when coupled with a token passing protocol, but it requires a significant increase in protocol complexity to manage system reconfiguration due to ring and node failures. Star topologies offer a natural fault tolerance, without added protocol complexity, while still providing high data throughput capability.

Deruiter, John↗
NASA NTRS1988

Calculation of the distributed loads on the blades of individual multiblade propellers in axial flow using linear and nonlinear lifting surface theories

In recent years much attention has been given to the development of methods and programs for the calculation of the aerodynamic characteristics of multiblade, saber-shaped air propellers. Most existing methods are based on the theory of lifting lines. Elsewhere, the theory of a lifting surface is used to calculate screw and lifting propellers. In this work, methods of discrete eddies are described for the calculation of the aerodynamic characteristics of propellers using the linear and nonlinear theories of lifting surfaces.

Pesetskaya, N. N.↗
NASA NTRS1993

Simulating flight boundary conditions for orbiter payload modal survey

An approach to simulate the characteristics of the payload/orbiter interfaces for the payload modal survey was developed. The flexure designed for this approach is required to provide adequate stiffness separation in the free and constrained interface degrees of freedom to closely resemble the flight boundary condition. Payloads will behave linearly and demonstrate similar modal effective mass distribution and load path as the flight if the flexure fixture is used for the payload modal survey. The potential non-linearities caused by the trunnion slippage during the conventional fixed base modal survey may be eliminated. Consequently, the effort to correlate the test and analysis models can be significantly reduced. An example is given to illustrate the selection and the sensitivity of the flexure stiffness. The advantages of using flexure fixtures for the modal survey and for the analytical model verification are also demonstrated.

Chung, Y. T.↗
NASA NTRS1990

Calibration of the 13- by 13-inch adaptive wall test section for the Langley 0.3-meter transonic cryogenic tunnel

A 13 by 13 inch adaptive wall test section was installed in the 0.3 Meter Transonic Cryogenic Tunnel circuit. This new test section is configured for 2-D airfoil testing. It has four solid walls. The top and bottom walls are flexible and movable whereas the sidewalls are rigid and fixed. The wall adaptation strategy employed requires the test section wall shapes associated with uniform test section Mach number distributions. Calibration tests with the test section empty were conducted with the top and bottom walls linearly diverged to approach a uniform Mach number distribution. Pressure distributions were measured in the contraction cone, the test section, and the high speed diffuser at Mach numbers from 0.20 to 0.95 and Reynolds numbers from 10 to 100 x 10 (exp 6)/per foot.

Mineck, Raymond E.↗
NASA NTRS1994

Principal modes of variation of rain-rate probability distributions

Radar or satellite observations of an area generate sequences of rain-rate maps. From a gridded map a histogram of rain rates can be obtained representing the relative areas occupied by rain rates of various strengths. The histograms vary with time as precipitating systems in the area evolve and decay and amounts of convective and stratiform rain in the area change. A method of decomposing the histograms into linear combinations of a few empirical distributions with time-dependent coefficients is developed, using principal component analysis as a starting point. When applied to a tropical Atlantic dataset (GATE), two distributions emerge naturally from the analysis, resembling stratiform and convective rain-rate distributions in that they peak at low and high rain rates, respectively. The two 'modes' have different timescales and only the high-rain-rate mode has a statistically significant diurnal cycle. The ability of just two modes to describe rain variabiltiy over an area can explain why methods of estimating area-averaged rain rate from the area covered by rain rates above a certain threshold are so successful.

Bell, Thomas L.↗
NASA NTRS1993

Birkeland currents in the plasma sheet

A search was conducted for the signatures of Birkeland currents in the Earth's magnetic tail, using observed values of B(sub x) and B(sub y) from large sets of spacecraft data. The data were binned by x and y for -10 greater than x(sub GSM) greater than -35 and absolute value of y(sub GSM) less than or equal to 20 R(sub E) (less than or equal to 30 R(sub E) for x(sub GSM) less than or equal to -25 R(sub E)) and in each bin their distribution in the (B(sub x), B(sub y)) plane was fitted by least squares to a piecewise linear function. That gave average x-y distributions of the flaring angle between B(sub xy) and the x direction, as well as that angle's variation across the thickness of the plasma sheet. Angles obtained in the central plasma sheet differed from those derived near the lobe boundary. That is the expected signature if earthward or tailward Birkeland current sheets are embedded in the plasma sheet, and from this dfiference we derived the dawn-dusk profiles of the tail Birkeland currents for several x(sub GSM) intervals. It was found that (1) the Birkeland currents have the sense of region 1 currents, when mapped to the ionosphere; (2) both the linear current density (kiloamperes/R(sub E)) and the net magnitude of the field-aligned currents decrease rapidly down the tail; (3) the total Birkeland current at x approximately equals -10 R(sub E) equals approximately equals 500-700 kA, which is approx. 30% of the net region 1 current observed at ionospheric altitudes, in agreement with model mapping results; and (4) the B(sub z) and B(sub y) components of the interplanetary magnetic field influence the distribution of Birkeland currents in the tail.

Tsyganenko, Nikolai A.↗
NASA NTRS1995

Inverse sequential procedures for the monitoring of time series

When one or more new values are added to a developing time series, they change its descriptive parameters (mean, variance, trend, coherence). A 'change index (CI)' is developed as a quantitative indicator that the changed parameters remain compatible with the existing 'base' data. CI formulate are derived, in terms of normalized likelihood ratios, for small samples from Poisson, Gaussian, and Chi-Square distributions, and for regression coefficients measuring linear or exponential trends. A substantial parameter change creates a rapid or abrupt CI decrease which persists when the length of the bases is changed. Except for a special Gaussian case, the CI has no simple explicit regions for tests of hypotheses. However, its design ensures that the series sampled need not conform strictly to the distribution form assumed for the parameter estimates. The use of the CI is illustrated with both constructed and observed data samples, processed with a Fortran code 'Sequitor'.

Radok, Uwe↗
NASA NTRS1977

Information distribution in distributed microprocessor based flight control systems

This paper presents an optimal control theory that accounts for variable time intervals in the information distribution to control effectors in a distributed microprocessor based flight control system. The theory is developed using a linear process model for the aircraft dynamics and the information distribution process is modeled as a variable time increment process where, at the time that information is supplied to the control effectors, the control effectors know the time of the next information update only in a stochastic sense. An optimal control problem is formulated and solved that provides the control law that minimizes the expected value of a quadratic cost function. An example is presented where the theory is applied to the control of the longitudinal motions of the F8-DFBW aircraft. Theoretical and simulation results indicate that, for the example problem, the optimal cost obtained using a variable time increment Markov information update process where the control effectors know only the past information update intervals and the Markov transition mechanism is almost identical to that obtained using a known uniform information update interval.

Montgomery, R. C.↗
NASA NTRS1980

Nonlinear state estimation and feedback control of nonlinear and bilinear distributed parameter systems

This paper presents a theory of nonlinear state observers for nonlinear and bilinear distributed parameter systems. Convergence results are proved for these observers. Linear feedback control derived from such state observers is applied to the distributed parameter system and conditions are presented for closed-loop stability. The emphasis is on finite dimensional state observers and controllers (which can be implemented with on-line computers) and conditions for their successful operation with infinite dimensional distributed parameter systems.

Balas, M. J.↗
NASA NTRS1980

Combined linear theory/impact theory method for analysis and design of high speed configurations

Pressure distributions on a wing body at Mach 4.63 are calculated. The combined theory is shown to give improved predictions over either linear theory or impact theory alone. The combined theory is also applied in the inverse design mode to calculate optimum camber slopes at Mach 4.63. Comparisons with optimum camber slopes obtained from unmodified linear theory show large differences. Analysis of the results indicate that the combined theory correctly predicts the effect of thickness on the loading distributions at high Mach numbers, and that finite thickness wings optimized at high Mach numbers using unmodified linear theory will not achieve the minimum drag characteristics for which they are designed.

Brooke, D.↗
NASA NTRS1961

A Method of Determining Aerodynamic-Influence Coefficients from Wind-Tunnel Data for Wings at Supersonic Speeds

A method is described for determining aerodynamic-influence coefficients from wind-tunnel data for calculating the steady-state load distribution on a wing with arbitrary angle-of-attack distribution at supersonic speeds. The method combines linearized theory with empirical adjustments in order to give accurate results over a wide range of angles of attack. The experimented data required are pressure distributions measured on a flat wing of the desired planform at the desired Mach number and over the desired range of angles of attack. The method has been tested by applying it to wind-tunnel data measured at Mach numbers of 1.61 and 2.01 on wings of the same planform but of different surface shapes. Influence coefficients adjusted to fit the flat wing gave good predictions of the spanwise and chord-wise distributions of loadings measured on twisted and cambered wings.

Gainer, Patrick A.↗
NASA NTRS1980

Continuous analysis of stresses from arbitrary surface loads on a half space

A new form of elemental surface load on a half space is introduced, presuming a quasi-pyramidal variation of load which is doubly linear in each of four rectangular parts of a surface rectangle. Approximations of arbitrary load distributions by sums of such elements are continuous, piecewise linear in two directions and well adaptable. The loads may be normal or tangential. The explicit solutions obtained for all stress and displacement components due to each elemental load involve only elementary functions, are free of the discontinuities which arise with stepwise elements, and are suitable for computing. Some illustrative stress distributions are presented for elemental loads and for multiple pyramidal loads involving both normal and tangential loads. The value of the load continuity in the more complicated analyses of surface cracks is also illustrated.

Bell, J. C.↗