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At least 649 records · Page 36
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NASA NTRS1986

Solar-Geophysical Data Number 497, January 1986. Part 1: (Prompt reports). Date for December 1985, November 1985 and late data

Solar-Geophysical Data Number 497, January 1986, Part 1 (prompt reports); Data for December 1985, November 1985 and Late Data contains the Data for December 1985-(IUWDS alert periods (advance and worldwide), solar activity indices, Solar flares, Vostok inferred interplanetary magnetic field polarity, Stanford mean solar magnetic field); data for November 1985-(solar active regions, sudden ionospheric disturbances, solar radio spectral observations, cosmic ray measurements by neutron monitor, geomagnetic indices, radio propagation indices); and late data-(geomagnetic indices, calcium plage data).

Coffey, H. E.↗
NASA NTRS1994

Galactic cosmic ray modulation and interplanetary medium perturbations due to a long-living active region during October 1989

During October 1989, three very energetic flares were ejected by the same active region at longitudes 9 deg E, 32 deg W, and 57 deg W, respectively. The shape of the galactic cosmic ray variations suggests the presence of large magnetic cloud structures (Nagashima et al., 1990) following the shock-associated perturbations. In spite of long data gaps the interplanetary observations at Interplanetary Monitoring Platform (IMP) 8 (near the Earth) and International Cometary Explorer (ICE)(approximately 1 AU, approximately 65 deg W) confirm this possibility for the event related to the 9 deg E flare; the principal axes analysis shows that the interplanetary magnetic field variations at both spacecraft locations are mainly confined on a meridian plane. This result suggests that the western longitudinal extension of this cloud is indeed very large (greater than or equal to 5 deg). The nonnegligible depression in the cosmic ray intensity observed inside the possible cloud related to the 57 deg W flare indicates that also the eastern extension could be very wide. The analysis of neutron monitor data shows clearly the cosmic ray trapping effect of magnetic clouds; this mechanism seems to be responsible for the enhanced diurnal effect often observed during the recovery phase of Forbush decreases. We give an interpretation for the anisotropic cosmic ray peak occurring in the third event, and, related to that, we suggest that the Forbush decrease modulated region at the Earth's orbit could be somewhat wider than the magnetic cloud, as already anticipated by Nagashima et al. (1990). By this analysis, based mainly on cosmic ray data, we show that it is possible to do reasonable inferences on the large-scale structure of flare-related interplanetary perturbations when interplanetary medium data are not completely present.

Bavassano, B.↗
NASA NTRS1986

The Comet Giacobini-Zinner magnetotail: Axial stresses and inferred near-nucleus properties

Utilizing the electron and magnetic field data from the ICE tail traversal of comet Giacobini-Zinner along with the MHD equations, a steady state, stress balance model of the cometary magnetotail was developed, and used to infer important but unmeasured ion properties within the magnetotail at ICE and upstream at the average point along each streamline where cometary ions are picked-up. The derived tailward ion flow speed at ICE is quite constant at approx. -20 to -30 km/sec across the entire tail. The flow velocity, ion temperature, density, and ion source rates upstream from the lobes (current sheet) at the average pick-up locations are approx. -75 km/sec (approx. -12), approx. 4 million K (approx. 100,000), approx. 20 cc (approx. 400), and approx. 15 cu cm/sec. Gradients in the plasma properties between the two regions are quite strong. Implications of inferred plasma properties for the near-nucleus region and for cometary magnetotail formation are examined.

Mccomas, D. J.↗
NASA NTRS1973

Velocity structure and evolution of the moon

Seismic data from the Apollo Passive Seismic Network stations are analyzed to determine the velocity structure and to infer the composition and physical properties of the lunar interior. Data from artificial impacts (SIBV booster and LM-ascent stage) cover a distance range of 9 to 1750 km. Travel times and amplitudes, as well as theoretical seismograms, are used to derive a velocity model for the outer 150 km of the moon. The P-wave velocity model confirms an earlier report of a lunar crust in the eastern part of Oceanus Procellarum. The crust is about 60 km thick and may consist of two layers in the mare regions. Possible values for the P-wave velocity in the uppermost mantle are between 7.6 and 9.0 km/sec. The 9 km/sec velocity represents either a localized heterogeneous unit, or a thin layer less than about 40 km in thickness. The elastic properties of the deep interior, as inferred from the seismograms of natural events (meteoroid impacts and moonquakes) occurring at great distances, indicate that there is an increase in attenuation and a possible decrease of velocity at depths below about 1000 km.

Toksoz, M. N.↗
NASA NTRS1981

The Viking seismometry

Efforts were made to determine the seismicity of Mars as well as define its internal structure by detecting vibrations generated by marsquakes and meteoroid impacts. The lack of marsquakes recognized in the Viking data made it impossible to make any direct inferences about the interior of Mars and only allowed the setting of upper bounds on the seismic activity of the planet. After obtaining more than 2100 hours worth of data during the quite periods at rates of one sample per second or higher, the Viking 2 seismometer was turned off as a consequence of a landing system failure. During the periods when adequate data were obtained, one event of possible seismic or meteoroid impact origin was recognized; however, there is a significant probability that this event was generated by a wind gust.

Lazarewicz, A. R.↗
NASA NTRS1986

Precise GPS orbit determination results from 1985 field tests

Data from three different receiver types have been used to obtain precise orbits for the satellites of the Global Positioning System (GPS). The data were collected during the 1985 March-April GPS experiment to test and validate GPS techniques for precision orbit determination and geodesy. A new software package developed at the Jet Propulsion Laboratory (JPL), GIPSY (GPS Inferred Positioning SYstem), was used to process the data. To assess orbit accuracy, solutions are compared using integrated doppler data from various different receiver types, different fiducial sites, and independent data arcs, including one spanning six days. From these intercomparisons, orbit accuracy for a well-tracked GPS satellite of three meters in altitude and about five meters in each of down and cross-track components are inferred.

Lichten, S. M.↗
NASA NTRS2000

Sunyaev - Zel'dovich Effect Imaging of Massive Clusters of Galaxies at Redshift > 0.8

We present Sunyaev-Zel'dovich Effect (SZE) imaging observations of three distant (z greater than 0.8) and highly X-ray luminous clusters of galaxies, C1J1226+33, C1J0152-13 and MS1054-03. Two of the clusters, C1J1226+33 and C1J0152-13, were recently discovered in the WARPS X-ray survey. Their high X-ray luminosity suggests they are massive systems and, if confirmed, would provide strong constraints on the cosmological parameters of structure formation models. Our Sunyaev-Zel'dovich Effect data provide confirmation that they are massive clusters similar to the well studied cluster MS1054-03. Assuming the clusters have the same gas mass fraction derived from SZE measurements of eighteen known massive clusters, we are able to infer their mass and electron temperatures from the SZE data. The derived electron temperatures are 10.0, 8.5, and 10.3 KeV, respectively, and we infer total masses of approximately 2 x 10(circumflex) 14 h(circumflex) -l M - sun within a radius of 65" for all three clusters. For C1J0152-13 and MS1054-03 we find good agreement between our SZE derived temperatures and those derived from X-ray spectroscopic measurements. No X-ray derived temperatures are available for C1J1226+33, and thus the SZE data provide the first confirmation that it is indeed a massive system. The demonstrated ability to determine cluster temperatures and masses from SZE observations without access to X-ray data illustrates the power of using deep SZE surveys to probe the distant universe.

Joy, Marshall↗
NASA NTRS1981

Inference of sea surface temperature, near surface wind, and atmospheric water by Fourier analysis of Scanning Multichannel Microwave Radiometer data

The Scanning Multichannel Microwave Radiometer measures thermal microwave emission from the earth in both polarizations at wavelengths of 0.8, 1.4, 1.7, 2.8 and 4.6 cm. Similar instruments were launched on Nimbus 7 and Seasat. Both spatial resolution on the earth and relative sensitivity to different geophysical parameters change with wavelength. Therefore, spatial Fourier components of geophysical parameters are inferred from the corresponding Fourier components of the radiometer measurements, taking into account the different dependence of signal-to-noise ratio on spatial frequency for each radiometer wavelength. The geophysical parameters are sea surface temperature, near-surface wind speed, integrated water vapor mass, integrated liquid water mass, and the product of rainfall rate with height of the rain layer. The capabilities and limitations of the inversion method are illustrated by means of data from the North Atlantic and from tropical storms.

Rosenkranz, P. W.↗
NASA NTRS1974

Apollo laser altimetry and inferences as to lunar structure

Weighted mean laser altimetry data from Apollo 15, 16, and 17 tracks were analyzed, yielding a mean lunar radius of 1737.7 km and an offset of center-of mass from center of figure of 2.55 km toward 24 deg E. Weighted mean elevations with respect to a 1738 km radius sphere for various terrain types are: (1) farside terrae +1.8 km, (2) nearside terrae -1.4 km, (3) ringed maria -4.0 km, and (4) other maria -2.3 km. Comparison of gravity and topography data indicates that there is a variation in density in the outer parts of the moon and that the moon has a crust which is equivalent to at least 60 km of material of 2.95 grams per cu cm density. This result and moment-of-inertia data are consistent with a lunar interior model with a uniform density gradient in the mantle to the bottom of the lithosphere, constant density in the asthenosphere, and no core.

Kaula, W. M.↗
NASA NTRS1977

Detection and interpretation of ocean roughness variations across the Gulf Stream inferred from radar cross section observations

Radar cross section data shows that the Gulf Stream has a higher cross section per unit area (interpreted here as a greater roughness) than the water on the continental shelf. A steep gradient in cross section was often seen at the expected location of the western boundary. There were also longer-scale (10-20 km) gradual fluctuations within the stream of significant magnitude. These roughness variations are correlated with the surface shear stress that the local wind imposes on the sea. Using the available surface-truth information concerning the wind speed and direction, an assumed Gulf Stream velocity profile, and high-resolution ocean-surface temperature data obtained by the VHRR onboard a NOAA-NESS polar-orbiting satellite, the present study demonstrates that the computed surface stress variation bears a striking resemblance to the measured radar cross-section variations.

Weissman, D. E.↗
NASA NTRS2015

Prediction of Tensile Strength of Friction Stir Weld Joints with Adaptive Neuro-Fuzzy Inference System (ANFIS) and Neural Network

Friction-stir-welding (FSW) is a solid-state joining process where joint properties are dependent on welding process parameters. In the current study three critical process parameters including spindle speed (𝑁), plunge force (𝐹𝑧), and welding speed (𝑉) are considered key factors in the determination of ultimate tensile strength (UTS) of welded aluminum alloy joints. A total of 73 weld schedules were welded and tensile properties were subsequently obtained experimentally. It is observed that all three process parameters have direct influence on UTS of the welded joints. Utilizing experimental data, an optimized adaptive neuro-fuzzy inference system (ANFIS) model has been developed to predict UTS of FSW joints. A total of 1200 models were developed by varying the number of membership functions (MFs), type of MFs, and combination of four input variables (𝑁,𝑉,𝐹𝑧,𝐸𝐹𝐼) utilizing a MATLAB platform. Note EFI denotes an empirical force index derived from the three process parameters. For comparison, optimized artificial neural network (ANN) models were also developed to predict UTS from FSW process parameters. By comparing ANFIS and ANN predicted results, it was found that optimized ANFIS models provide better results than ANN. This newly developed best ANFIS model could be utilized for prediction of UTS of FSW joints.

Mohammad W Dewan↗
NASA NTRS1987

Regional sources and sinks of dust on Mars: Viking observations of Cerberus, Solis Planum and Syrtis Major

A study of seasonal variations of albedo features in the Cerberus, Solis Planum, and Syrtis Major regions was based on Viking Orbiter data obtained over more than one complete Martian year. Contour maps of Lambert albedo and single-point thermal inertia were constructed from the Infrared Thermal Mapper (IRTM) experiment data, and Orbiter images were used to determine the pattern and variability of regional winds (inferred from wind streak orientations). Coupled with ground-based radar data, these data allow the regional sediment transport direction, surface properties (texture, morphology, and roughness), and the implications of the observed seasonal and longer term dust redistribution to be investigated. Results are outlined.

Lee, Steven W.↗
NASA NTRS1992

The statistical analysis of circadian phase and amplitude in constant-routine core-temperature data

Accurate estimation of the phases and amplitude of the endogenous circadian pacemaker from constant-routine core-temperature series is crucial for making inferences about the properties of the human biological clock from data collected under this protocol. This paper presents a set of statistical methods based on a harmonic-regression-plus-correlated-noise model for estimating the phases and the amplitude of the endogenous circadian pacemaker from constant-routine core-temperature data. The methods include a Bayesian Monte Carlo procedure for computing the uncertainty in these circadian functions. We illustrate the techniques with a detailed study of a single subject's core-temperature series and describe their relationship to other statistical methods for circadian data analysis. In our laboratory, these methods have been successfully used to analyze more than 300 constant routines and provide a highly reliable means of extracting phase and amplitude information from core-temperature data.

NASA Discipline Regulatory Physiology↗
NASA NTRS2019

An Ensemble of Bayesian Neural Networks for Exoplanetary Atmospheric Retrieval

Machine learning (ML) is now used in many areas of astrophysics, from detecting exoplanets in Kepler transit signals to removing telescope systematics. Recent work demonstrated the potential of using ML algorithms for atmospheric retrieval by implementing a random forest (RF) to perform retrievals in seconds that are consistent with the traditional, computationally expensive nested-sampling retrieval method. We expand upon their approach by presenting a new ML model, plan-net, based on an ensemble of Bayesian neural networks (BNNs) that yields more accurate inferences than the RF for the same data set of synthetic transmission spectra. We demonstrate that an ensemble provides greater accuracy and more robust uncertainties than a single model. In addition to being the first to use BNNs for atmospheric retrieval, we also introduce a new loss function for BNNs that learns correlations between the model outputs. Importantly, we show that designing ML models to explicitly incorporate domain-specific knowledge both improves performance and provides additional insight by inferring the covariance of the retrieved atmospheric parameters. We apply plan-net to the Hubble Space Telescope Wide Field Camera 3 transmission spectrum for WASP-12b and retrieve an isothermal temperature and water abundance consistent with the literature. We highlight that our method is flexible and can be expanded to higher resolution spectra and a larger number of atmospheric parameters.

Adam D. Cobb↗
NASA NTRS2001

[Limb Scattering Data Analysis]

The primary purpose of this grant was to support analysis of the limb scattering data taken during the 1997 flight of the SOLSE (Shuttle Ozone Limb Sounding Experiment) and LORE (Limb Ozone Retrieval Experiment) instruments. Work was done to assess the performance of the retrieval algorithms for cloudy and clear sky cases in preparation for a poster presentation. The nadir-viewing data were also compared to coincident GOME (Global Ozone Monitoring Experiment) data and to radiative transfer calculations. An algorithm similar to the TOMS (Total Ozone Mapping Spectrometer) ozone retrieval algorithm was developed to infer the ozone column amount from the SOLSE nadir data. Comparison with coincident TOMS ozone column data confirmed that column ozone could be derived successfully from SOLSE nadir radiances, and also revealed significant changes in the SOLSE wavelength resolution and absolute radiometric calibration that were subsequently confirmed by comparing the post-flight instrument characterization to the pre-flight characterization, indicating a potentially useful method for monitoring instrument behavior in-flight.

Loughman, Robert↗
NASA NTRS1976

A comparison of measured and inferred temperatures from AEROS-B

The neutral composition and the temperature data obtained from the AEROS-B Neutral Atmosphere Temperature Experiment (NATE) and the Neutral and Ion Mass Spectrometer (NIMS) are compared, and the general validity of inferring gas temperatures from N2 and Ar density profiles is examined by comparing them with the in situ measured values of the neutral kinetic temperature (NATE). At times serious discrepancies are noted between the inferred and the measured temperature. This is particularly evident during periods of increased magnetic activity when the normally observed latitudinal variations are apparently modulated by waves propagating from the polar region to low latitudes. Under these conditions the N2 and Ar densities and temperature oscillations are usually out of phase, and the temperatures inferred from N2 and Ar at a given point become meaningless.

Chandra, S.↗
NASA NTRS1993

BBXRT and Ginga observations of the Seyfert 1 galaxy Markarian 335

We present new X-ray observations of Mrk 335 in the 0.4-10 keV band using BBXRT and in the 2-20 keV band with Ginga. The BBXRT data show a break to a softer spectrum below about 1 keV. The Ginga data show evidence for variability in absorption, uncorrelated with flux changes of the continuum source. The inconsistency between the opacity observed at the iron K edge and at softer X-ray energies implies that the absorber has an ionization state about FeXV. We suggest that the nuclear emission can be explained by a self-consistent pair cascade model as developed by Zdziarski et al. (1990) and Zdziarski and Coppi (1991), where the compactness parameter inferred from the spectral fits to both data sets is in good agreement with the value calculated from the ratio of observed X-ray luminosity and variability time scale.

Turner, T. J.↗
NASA NTRS2016

Probabilistic Damage Characterization Using the Computationally-Efficient Bayesian Approach

This work presents a computationally-ecient approach for damage determination that quanti es uncertainty in the provided diagnosis. Given strain sensor data that are polluted with measurement errors, Bayesian inference is used to estimate the location, size, and orientation of damage. This approach uses Bayes' Theorem to combine any prior knowledge an analyst may have about the nature of the damage with information provided implicitly by the strain sensor data to form a posterior probability distribution over possible damage states. The unknown damage parameters are then estimated based on samples drawn numerically from this distribution using a Markov Chain Monte Carlo (MCMC) sampling algorithm. Several modi cations are made to the traditional Bayesian inference approach to provide signi cant computational speedup. First, an ecient surrogate model is constructed using sparse grid interpolation to replace a costly nite element model that must otherwise be evaluated for each sample drawn with MCMC. Next, the standard Bayesian posterior distribution is modi ed using a weighted likelihood formulation, which is shown to improve the convergence of the sampling process. Finally, a robust MCMC algorithm, Delayed Rejection Adaptive Metropolis (DRAM), is adopted to sample the probability distribution more eciently. Numerical examples demonstrate that the proposed framework e ectively provides damage estimates with uncertainty quanti cation and can yield orders of magnitude speedup over standard Bayesian approaches.

Warner, James E.↗