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Results for “correlation and association”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Associations between coronal mass ejections and solar energetic proton events

A comparison between proton events and coronal mass ejections (CMEs) based on nearly three years of observations around the recent maximum of solar activity is presented. Peak proton fluxes are found to correlate with both the speeds and the angular sizes of the associated CMEs. It is shown that CME speeds do not significantly correlate with CME angular sizes, so that peak proton fluxes are correlated with two independent CME parameters. With larger angular sizes, CMEs are more likely to be loops and fans rather than jets and spikes and are more likely to intersect the ecliptic.

Kahler, S. W.↗
NASA NTRS1994

Transition correlations in three-dimensional boundary layers

The stability and transition characteristics of three-dimensional boundary-layer flows are examined. First, the flow over a rotating cone is considered computationally. An increase of stagnation temperature is found to be only slightly stabilizing. Parameter studies on the simple rotating-cone geometry provide a large database of three-dimensional boundary-layer profiles and associated stability characteristics. To determine the possibility of correlating transition location with parameters based purely on basic-state three-dimensional boundary-layer profile characteristics, an empirical transition location of N = 9 is assumed. Transition location does not correlate with the traditional crossflow Reynolds number. A more appropriate definition for crossflow Reynolds number is found and termed R(sub cf(new)). This new parameter appears to correlate for transition location when plotted against maximum crossflow velocity. Then, the flow over a yawed cone is considered experimentally. The correlation results obtained from the rotating-cone work are applied to the actual measured transition locations on two different yawed-cone models under various angle-of-attack conditions in two different experimental facilities and are verified. This correlation is only suggested as a tool for preliminary transition prediction and design in three-dimensional boundary layers; once a preliminary shape is selected, further linear stability theory or parabolized stability equation calculations are strongly urged.

Reed, Helen L.↗
NASA NTRS1974

Green corona and solar sector structure

Analysis of the green-line corona for the interval 1947-1970 suggests the existence of large-scale organization of the emission. The green-line emission at high northern latitudes (approximately 40 to 60 deg) is correlated with the emission at high southern latitudes 6, 15, and 24 days later, while the low-latitude green corona seems to be correlated on both sides of the equator with no time lag. These coronal features are recurrent with a 27-day period at all latitudes between plus or minus 60 deg, and these large-scale structures are believed to be associated with the solar magnetic sector structure. The high correlation between northern and southern high-latitude emission at 15 days time lag is explained as a signature of a two-sector structure, while four sectors are associated with the 6- and 24-day peaks.

Antonucci, E.↗
NASA NTRS1981

Energetic electrons, Type III radio bursts, and impulsive solar flare X-rays

Observations of impulsive hard X-ray and type III radio bursts made during the maximum of the last solar activity cycle are analyzed. Spectral measurements of 10-68 keV X-rays were made with the University of California (Berkeley) experiment aboard the OGO 5 satellite. About 20% of impulsive hard X-ray bursts are correlated with type III radio bursts, whereas only about 3% of the reported type III radio bursts are correlated with impulsive X-ray bursts. The location of the associated H gamma flare on the solar disk has little effect on the X-ray-type III burst correlation. The magnitude of the X-ray-type III burst correlation increases systematically with an increase in the intensity and starting frequency of the radio burst, the peak energy and hardness of the X-ray burst, and the peak nonthermal emission measure and spectral hardness of the electron spectrum not less than 20 keV inside the X-ray source. Observations are consistent with the electron populations responsible for both the X-ray and type III emissions accelerated in a single acceleration process; they also suggest a flare model where the primary instability causing electron acceleration during the impulsive phase occurs in the corona.

Kane, S. R.↗
NASA NTRS1968

Summary report on the Nimbus II satellite.

Nimbus 2 meteorological satellite observations, discussing circulation associated with synoptic scale systems obtained by correlating water vapor and carbon dioxide pictures

Nordberg, W.↗
NASA NTRS1971

The relationship between certain characteristics of industrial research proposals and their subsequent disposition.

The ideas produced by three idea generation groups operating within a large industrial R & D laboratory were studied over a period of two years. Data were collected in order to relate idea dispositions by management to subjective evaluations provided by respondents representing the technical staff and to study the roles of urgency, predictability, and expected time horizon in the disposition decision. The findings are (1) a significant positive correlation was found between idea dispositions and associated subjective evaluations despite the fact that management did not know the subjective evaluations at the time the disposition decisions were made; (2) urgency was the dominant consideration in the disposition decisions, but predictability and expected time horizon were dominant in the subjective evaluations; (3) predictability and time horizon are covariants; and (4) management hedges by shelving marginal ideas. Implications for R & D management are drawn.

Baker, N. R.↗
NASA NTRS1972

Application of Rochrome liquid crystal tapes for thermographic testing of bonded structures

The use of ROCHROME liquid crystal tape for thermographic testing of bonded structures for aircraft is described. The techniques for applying the tape, heating the test panels, and photographing the resulting thermal patterns are described and discussed. The results obtained are compared with those reported previously for the same test panels coated directly with liquid crystals applied by spraying. Other panels previously examined by various nondestructive techniques, both by thermography, were also tested. Results for these latter panels are presented and discussed. For both sets of panels good correlation with previous work was obtained. Deficiencies associated with present ROCHROME tape are described. In general, these stem from the lack of optimization for materials testing of the ROCHROME tape, particularly with respect to the adhesive system and supporting film.

Source record↗
NASA NTRS1974

Millimeter radio evidence for containment mechanisms in solar flares

Recent theories of solar flares are reviewed with emphasis on the aspects of pre-flare heating. The heating evident at 3.3-mm wavelength is analyzed in the form of daily maps of the solar disk and synoptic maps compiled from the daily maps. It is found that isotherms defining antenna temperature enhancements of 340 K correspond in shape and location to facular areas reported by Waldmeier. Maximum enhancements occur over sunspots or near neutral lines of the longitudinal magnetic fields which indicates heating associated with chromospheric currents. These enhancements are correlated with flare importance number and are observed to increase during several days preceding flaring. This evidence for a containment mechanism in the chromosphere is collated with current theories of solar flares.

Mayfield, E. B.↗
NASA NTRS1981

Grid-generated isotropic homogeneous turbulence at high Reynolds numbers

Consideration is given to an empirical formula for the longitudinal correlation function for grid-generated incompressible fluid turbulence at Reynolds numbers above 12,800. The formula, which relates the longitudinal correlation function to the inverse cube of a dimensionless geometrical ratio, is shown to minimize the global correlation integrals into which the two-point velocity correlation tensor has been substituted subject to a global constraint on the Sobolev concomitent of the longitudinal correlation function. Furthermore, the energy spectrum function associated with the empirical formula is shown to satisfy a tertiary Helmholtz-type linear condition throughout the initial period of decay.

Rosen, G.↗
NASA NTRS1984

The application of a second generation low-order panel method - program 'Vsaero' - to powerplant installation studies

Results from the application of a second generation low-order panel method to a number of powerplant installations are presented. The method, which retains the advantages of ease of use and low operating cost of earlier panel methods while retaining the aerodynamic modelling rigor of higher-order methods was used to predict the flow in and around typical nacelles and aircraft for a wide range of conditions. The ability of the second generation low-order analysis to calculate internal flows without the leakage problems associated with earlier programs is demonstrated and correlation between calculated and measured surface pressures and flow behavior, including predicting streamlines and locating regions of separated flow, is presented.

Clark, D. R.↗
NASA NTRS1984

Observations of double layer-like and soliton-like structures in the ionosphere

Two types of large electric field signatures, individual pulses and pulse trains, were observed on a sounding rocket launched into the afternoon auroral zone on January 21, 1982. The typical electric fields in the individual pulses were 50 mV/m or larger, aligned mostly parallel to B, and the corresponding potentials were at leat 100 mV (kT approximately 0.3 eV). A lower limit of 15 km/sec can be set on the velocity of these structures, indicating that they were not ion acoustic double layers. The pulse trains, each consisting of on the order of 100 pulses, were observed in close association with intense plasma frequency waves. This correlation is consistent with the interpretation of these trains as Langmuir solitons. The pulse trains correlate better with the intensity of the field-aligned currents than with the energetic electron flux.

Boehm, M. H.↗
NASA NTRS1986

Dynamic loading on parallel shaft gears

A computer-based analysis of the dynamic effects of spur gear systems is presented. The method of analysis with its associated computer code is capable of determining the dynamic response of spur gear systems having involute tooth profiles and standard contact ratios. Various parameters affecting the system dynamic behavior are examined. Numerical results of the analysis are compared with semi-empirical formulae, AGMA (American Gear Manufacturers Association) formulae, and experimental data. A close correlation with the experimental data is obtained.

Lin, H. H. (edward)↗
NASA NTRS1991

Generation of Pc 1 waves by the ion temperature anisotropy associated with fast shocks caused by sudden impulses

The high correlation of Pc 1 events with magnetospheric compressions is known. A mechanism is proposed which leads to the generation of Pc 1 waves. The interaction of a dynamic pressure pulse with the earth's bow shock leads to the formation of a weak fast-mode shock propagating into the magnetoshealth. The shock wave can pass right through a tangential discontinuity (magnetopause) and into the magnetosphere, without disturbing either of the structures. In a quasiperpendicular geometry, the shock wave exhibits anisotropic heating. This anisotropy drives unstable ion-cyclotron waves which can contribute to the generation of the Pc 1 waves which are detected. The viability of the mechanism is demonstrated with simulations. This mechanism could explain the peak in the occurrence of observed Pc 1 waves in the postnoon sector where a field-aligned discontinuity in the solar wind would most often be parallel to the magnetopause surface due to the average Parker-spiral magnetic-field configuration.

Mandt, M. E.↗
NASA NTRS1991

Airframe Noise

Current understanding of airframe noise was reviewed as represented by experiment at model and full scale, by theoretical modeling, and by empirical correlation models. The principal component sources are associated with the trailing edges of wing and tail, deflected trailing edge flaps, flap side edges, leading edge flaps or slats, undercarriage gear elements, gear wheel wells, fuselage and wing boundary layers, and panel vibration, together with many minor protrusions like radio antennas and air conditioning intakes which may contribute significantly to perceived noise. There are also possibilities for interactions between the various mechanisms. With current engine technology, the principal airframe noise mechanisms dominate only at low frequencies, typically less than 1 kHz and often much lower, but further reduction of turbomachinery noise in particular may make airframe noise the principal element of approach noise at frequencies in the sensitive range.

Trailing-Edge↗
NASA NTRS1992

Galileo encounter with 951 Gaspra - First pictures of an asteroid

Galileo images of Gaspra reveal it to be an irregularly shaped object (19 by 12 by 11 kilometers) that appears to have been created by a catastrophic collisional disruption of a precursor parent body. The cratering age of the surface is about 200 million years. Subtle albedo and color variations appear to correlate with morphological features: brighter materials are associated with craters especially along the crests of ridges, have a stronger 1-micrometer absorption, and may represent freshly excavated mafic materials; darker materials exhibiting a significantly weaker 1-micrometer absorption appear concentrated in interridge areas. One explanation of these patterns is that Gaspra is covered with a thin regolith and that some of this material has migrated downslope in some areas.

Belton, M. J. S.↗
NASA NTRS1994

Einstein-Podolsky-Rosen-Bohm experiment and Bell inequality violation using Type 2 parametric down conversion

We report a new two-photon polarization correlation experiment for realizing the Einstein-Podolsky-Rosen-Bohm (EPRB) state and for testing Bell-type inequalities. We use the pair of orthogonally-polarized light quanta generated in Type 2 parametric down conversion. Using 1 nm interference filters in front of our detectors, we observe from the output of a 0.5mm beta - BaB2O4 (BBO) crystal the EPRB correlations in coincidence counts, and measure an associated Bell inequality violation of 22 standard deviations. The quantum state of the photon pair is a polarization analog of the spin-1/2 singlet state.

Kiess, Thomas E.↗
NASA NTRS2012

Radar Scattering and Block Size Properties of Lunar Crater Ejecta From Mini-RF and LROC NAC Data

A major objective of the Mini-RF experiment is to distinguish lunar surfaces that may contain water/ice deposits [1,2]. Better understanding of the backscattering properties of craters of varying age and size is crucial for interpreting data received from the Mini-RF. The Mini-RF transmits a circularly polarized RF electromagnetic energy and coherently receives orthogonal linear polarization echoes [1]. The Mini- RF maps in two separate bands ( =12.6 and 4.5 cm) at a high resolution mode of 30 m/pixel [1]. Given the variables mentioned, the four stokes parameters are reconstructed. The Circular Polarization Ratio (CPR) is calculated for the purposes of understanding subsurface and surface roughness. The CPR is determined from reflections acquired from the ratio of power of the transmitted radio wave in same sense to the reflected radio wave in the opposite sense [1]. Ice in the permanently shadowed regions (PSRs) would be transparent to radar, but the inclusions of materials and imperfections would cause the radio wave to reflect multiple times [3], enhancing the number of same sense reflections and increasing the CPR. In addition, ice also displays the coherent backscatter opposition effect (CBOE), an interferrometric addition of same sense backscatter that further increases the CPR of ice targets [7]. High CPR values also correlate to multiple reflections and are typically associated with very rough surfaces [3]. The average dry lunar surface has a CPR in the range of 0.2-0.4 at 48deg incidence [3]. The purpose of this study is to begin to quantify degrees of surface wavelength-scale roughness with CPR and to understand how such surface roughness is created and gradually destroyed by erosion on the lunar surface. Another goal is to identify and isolate the possible causes of high CPR within the shadowed areas of anomalous polar craters [3]. All the studied craters are non-polar, so that we can see into their interiors in NAC images. The idea is to understand what controls blockiness in these craters so that we can rule out rocks (and rule in ice) for the anomalous polar dark ones [3].

Spudis, P. D.↗
NASA NTRS2012

A Statistical Approach to Recognizing Source Classes for Unassociated Sources in the First FERMI-LAT Catalog

The Fermi Large Area Telescope (LAT) First Source Catalog (1FGL) provided spatial, spectral, and temporal properties for a large number of gamma -ray sources using a uniform analysis method. After correlating with the mostcomplete catalogs of source types known to emit gamma rays, 630 of these sources are "unassociated" (i.e., have no obvious counterparts at other wavelengths). Here, we employ two statistical analyses of the primary gamma-ray characteristics for these unassociated sources in an effort to correlate their gamma-ray properties with the active galactic nucleus (AGN) and pulsar populations in 1FGL. Based on the correlation results, we classify 221 AGN-like and 134 pulsar-like sources in the 1FGL unassociated sources. The results of these source "classifications" appear to match the expected source distributions, especially at high Galactic latitudes. While useful for planning future multiwavelength follow-up observations, these analyses use limited inputs, and their predictions should not be considered equivalent to "probable source classes" for these sources. We discuss multiwavelength results and catalog cross-correlations to date, and provide new source associations for 229 Fermi-LAT sources that had no association listed in the 1FGL catalog. By validating the source classifications against these new associations, we find that the new association matches the predicted source class in approximately 80% of the sources.

SOURCES↗