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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

The Roles of Flares and Shocks in determining SEP Abundances

We examine solar energetic particle (SEP) event-averaged abundances of Fe relative to O and intensity versus time profiles at energies above 25 MeV/nucleon using the SIS instrument on ACE. These data are compared with solar wind conditions during each event and with estimates of the strength of the associated shock based on average travel times to 1 AU. We find that the majority of events with an Fe to 0 abundance ratio greater than two times the average 5-12 MeV/nuc value for large SEP events (0.134) occur in the western hemisphere. Furthermore, in most of these Fe-rich events the profiles peak within 12 hours of the associated flare, suggesting that some of the observed interplanetary particles are accelerated in these flares. The vast majority of events with Fe/O below 0.134 are influenced by interplanetary shock acceleration. We suggest that variations in elemental composition in SEP events mainly arise from the combination of flare particles and shock acceleration of these particles and/or the ambient medium.

Cane, H. V.↗
NASA NTRS2010

A Multi-Spacecraft View of Solar-Energetic-Particle Onsets in the 1977 November 22 Event

We examine the onset timing of solar energetic particles (SEPs) in the large ground-level event (GLE) of 1977 November 22 as observed from six spacecraft at four distinct solar longitudes. In most cases, it was possible to use velocity dispersion of the energetic protons to fix the solar particle release (SPR) time and the path-length traveled by the initial particle burst from each solar longitude. We find that the SPR times do depend upon solar longitude, being earliest for spacecraft that are magnetically well-connected to the source region, and later for longitudes on the flanks of the outward driven shock wave. The earliest SPR time occurs well after peak photon emission from the associated Ha flare. These observations are consistent with conclusions derived from single-longitude observations of different GLE events.

Reames, Donald V.↗
NASA NTRS2001

Effect of Long-Duration Spaceflight on Postural Control During Self-Generated Perturbations

This report is the first systematic evaluation of the effects of prolonged weightlessness on the bipedal postural control processes during self-generated perturbations produced by voluntary upper limb movements. Spaceflight impacts humans in a variety of ways, one of which is compromised postflight postural control. We examined the neuromuscular activation characteristics and center of pressure motion (COP) associated with arm movement of eight subjects who experienced long duration spaceflight (3-6 months) aboard the Mir space station. Surface electromyography (EMG), arm acceleration, and COP motion were collected while astronauts performed rapid unilateral shoulder flexions prior to and after spaceflight. Subjects displayed compromised postural control after flight as evidenced by modified peak-to-peak COP anterior-posterior and medio-lateral motion and COP pathlength relative to preflight values. These changes were associated with disrupted neuromuscular activation characteristics, particularly after the completion of arm acceleration (i.e. when subjects were attempting to maintain their upright posture). These findings suggest that although the subjects were able to assemble coordination modes that enabled them to generate rapid arm movements, the subtle control necessary to maintain bipedal equilibrium evident in their preflight performance is compromised after long duration spaceflight.

Layne, Charles S.↗
NASA NTRS2022

Source and Chemistry of Hydroxymethanesulfonate (HMS) in Fairbanks, Alaska

Fairbanks, Alaska is a subarctic city with fine-particle (PM 2.5 ) concentrations that exceed air quality regulations in winter due to weak dispersion caused by strong atmospheric inversions, local emissions, and the unique chemistry occurring under the cold and dark conditions. Here we report on observations from the winters of 2020 and 2021, motivated by our pilot study which showed exceptionally high concentrations of fine particle hydroxy methane sulfonate (HMS) or related sulfur (IV) species (e.g., sulfite and bisulfite). We deployed an online Particle-Into-Liquid Sampler-Ion Chromatography (PILS-IC) in conjunction with a suite of instruments to determine HMS precursors (HCHO, SO 2 ) and aerosol composition in general, with the goal to characterize the sources and sinks of HMS in wintertime Fairbanks. PM 2.5 HMS comprised a significant fraction of PM 2.5 sulfur (26-41%) and overall PM 2.5 mass concentration (2.8-6.8%) during pollution episodes, substantially higher than what has been observed in other regions, likely due to the exceptionally low temperatures. HMS peaked in January, with lower concentrations in December and February, resulting from changes in precursors as well as meteorological conditions. Strong correlations with inorganic sulfate and organic mass during pollution events suggest HMS is linked to processes responsible for poor air quality episodes. These findings demonstrate unique aspects of air pollution formation in cold and humid atmospheres.

Fine-particle↗
NASA NTRS2024

The Plasma Proton Environment within Saturn’s F-G Ring Gap as Observed by the Cassini Plasma Spectrometer Ion Mass Spectrometer during Saturn Orbit Insertion

We report on the detection of protons and the potential detection of H 2 + between Saturn's F and G rings based on Cassini Plasma Spectrometer (CAPS) Ion Mass Spectrometer (IMS) time-of-flight (TOF) composition measurements acquired during Saturn Orbit Insertion (SOI) outbound pass. The range in dipole L shell is 2.3 < L < 2.8. Initial results based on TOF data were presented in E. C. Sittler et al., 2017. Here we present the latest results of our analysis. During the SOI outbound pass between the F and G rings the CAPS IMS was in a mode of reduced post-acceleration voltage at -6 kV instead of the usual -14.6 kV. This reduced voltage still allows the analysis of protons since 6 keV protons are minimally scattered by the instrument’s ultrathin carbon foils when compared to heavier ions O + and O 2 + , scattering. Background noise from penetrating radiation and ghost peaks produced by foil-scattered O + ions within the instrument were considered in our analysis. The analysis allowed determination of the proton density, temperature and flow velocity, accounting for spacecraft potential by assuming a convected Maxwellian for the proton velocity distribution function. We find average proton density n P = 3.2 ± 1.1 #/cm 3 , proton temperature T P = 1.74 ± 0.12 eV, proton rotational flow speed V P = 24 ± 1.5 km/s and spacecraft potential  SC = -0.8 ±1.5 V. These results are compared with previous theoretical estimates of H + and H 2 + ions within Saturn’s inner magnetosphere.

E C Sittler↗
NASA NTRS1992

The mass and dynamics of cD clusters with cooling flows. 1: ROSAT observations of A 496

As a part of a program to determine the mass distribution of cD galaxy clusters with cooling flows, we obtained a ROSAT image of the cluster A 496. The image reveals sharply peaked emission centered on the cD galaxy. Both the peaked cooling flow emission and the more extended emission filling the cluster are centered on the cD galaxy to within 15 sec. The surface brightness profile is consistent with previous Einstein HRI observations. We measure spatially resolved spectra for the x-ray emission, and find a significant decline in temperature in the innermost 2 to 4 min. We also find a gradient in absorption due to cold neutral gas, with excess absorption, however, is far below previously reported values. We caution that this is a progress report, and that our results are preliminary.

Kriss, Gerard A.↗
NASA NTRS1994

The origin of the far-infrared luminosity within the spiral galaxy M101

High resolution 60 and 100 micron images obtained with the Infared Astronomical Satellite (IRAS) are compared with H alpha images in order to investigate the origin of the far-infrared luminosity within the late-type spiral galaxy M101. There is a good correspondence between the far-infrared and H-alpha morphology. The far-infrared and H-alpha luminosities have been measured at 129 independent locations on the star forming disk of M101. After correcting the H-alpha luminosity for extinction and extrapolating the IRAS (40-120 microns) luminosity to 1000 microns we find that the far-infrared luminosity is commensurate with that expected from the O and B stars which are required to ionize the hydrogen gas, at all locations within M101. Additionally, the IRAS HiRes 60 and 100 micron images reveal that the dust temperature peaks coincide identically with the location of H II regions. The far-infrared luminosity of M101 is radiated primarily by dust with temperatures well in excess of that expected for cirrus, but similar to that observed for Galactic and extragalactic H II regions.

Devereux, Nicholas A.↗
NASA NTRS1998

Direction-Finding Measurements of Heliospheric 2-3 kHz Radio Emissions

Using data from the Voyager 1 plasma wave instrument, a series of direction-finding measurements is presented for the intense 1992-93 heliospheric 2- to 3-kHz radio emission event, and several weaker events extending into 1994. Direction-finding measurements can only be obtained during roll maneuvers, which are performed about once every three months. Two parameters can be determined from the roll-induced intensity modulation, the azimuthal direction of arrival (measured around the roll axis), and the modulation index (the peak-to-peak amplitude divided by the peak amplitude). Measurements were made at two frequencies, 1.78 and 3.11 kHz. No roll modulation was observed at 1.78 kHz, which is consistent with an isotropic source at this frequency. In most cases an easily measurable roll modulation was detectable at 3.11 kHz. Although the azimuth angles have considerable scatter, the directions of arrival at 3.11 kHz can be organized into three groups, each of which appears to be associated with a separate upward drifting feature in the radio emission spectrum. The first group, which is associated with the main 1992-93 event, is consistent with a source located near the nose of the heliosphere. The remaining two groups, which occur after the main 1992-93 event, have azimuth angles well away from the nose of the heliosphere. The modulation indexes vary over a large range, from 0.06 to 0.61, with no obvious trend. Although the variations in the directions of arrival and modulation indicies appear to reflect changes in the position and angular size of the source, it is also possible that they could be caused by refraction or scattering due to density structures in the solar wind.

Gurnett, Donald A.↗
NASA NTRS1999

Classification of ion mobility spectra by functional groups using neural networks

Neural networks were trained using whole ion mobility spectra from a standardized database of 3137 spectra for 204 chemicals at various concentrations. Performance of the network was measured by the success of classification into ten chemical classes. Eleven stages for evaluation of spectra and of spectral pre-processing were employed and minimums established for response thresholds and spectral purity. After optimization of the database, network, and pre-processing routines, the fraction of successful classifications by functional group was 0.91 throughout a range of concentrations. Network classification relied on a combination of features, including drift times, number of peaks, relative intensities, and other factors apparently including peak shape. The network was opportunistic, exploiting different features within different chemical classes. Application of neural networks in a two-tier design where chemicals were first identified by class and then individually eliminated all but one false positive out of 161 test spectra. These findings establish that ion mobility spectra, even with low resolution instrumentation, contain sufficient detail to permit the development of automated identification systems.

Non-NASA Center↗
NASA NTRS2010

Air Traffic Sector Configuration Change Frequency

A Mixed Integer Linear Programming method is used for creating sectors in Fort Worth, Cleveland, and Los Angeles centers based on several days of good-weather traffic data. The performance of these sectors is studied when they are subjected to traffic data from different days. Additionally, the advantage of using different sector designs at different times of day with varying traffic loads is examined. Specifically, traffic data from 10 days are used for design, and 47 other days are played back to test if the traffic-counts stay below the design values used in creating the partitions. The primary findings of this study are as follows. Sectors created with traffic from good-weather days can be used on other good-weather days. Sector configurations created with two hours of traffic can be used for 6 to 12 hours without exceeding the peak-count requirement. Compared to using a single configuration for the entire day, most of the sector-hour reduction is achieved by using two sector configurations -one during daytime hours and one during nighttime hours.

Chatterji, Gano B.↗
NASA NTRS2010

Ring Current Dynamics in Moderate and Strong Storms: Comparative Analysis of TWINS and IMAGE/HENA Data with the Comprehensive Ring Current Model

We present a comparative study of ring current dynamics during strong and moderate storms. The ring current during the strong storm is studied with IMAGE/HENA data near the solar cycle maximum in 2000. The ring current during the moderate storm is studied using energetic neutral atom (ENA) data from the Two Wide-Angle Imaging Neutral- Atom Spectrometers (TWINS) mission during the solar minimum in 2008. For both storms, the local time distributions of ENA emissions show signatures of postmidnight enhancement (PME) during the main phases. To model the ring current and ENA emissions, we use the Comprehensive Ring Current Model (CRCM). CRCM results show that the main-phase ring current pressure peaks in the premidnight-dusk sector, while the most intense CRCM-simulated ENA emissions show PME signatures. We analyze two factors to explain this difference: the dependence of charge-exchange cross section on energy and pitch angle distributions of ring current. We find that the IMF By effect (twisting of the convection pattern due to By) is not needed to form the PME. Additionally, the PME is more pronounced for the strong storm, although relative shielding and hence electric field skewing is well developed for both events.

Buzulukova, N.↗
NASA NTRS2012

The Atacama Cosmology Telescope: Relation Between Galaxy Cluster Optical Richness and Sunyaev-Zel'dovich Effect

We present the measured Sunyaev-Zel'dovich (SZ) flux from 474 optically-selected MaxBCG clusters that fall within the Atacama Cosmology Telescope (ACT) Equatorial survey region. The ACT Equatorial region used in this analysis covers 510 square degrees and overlaps Stripe 82 of the Sloan Digital Sky Survey. We also present the measured SZ flux stacked on 52 X-ray-selected MCXC clusters that fall within the ACT Equatorial region and an ACT Southern survey region covering 455 square degrees. We find that the measured SZ flux from the X-ray-selected clusters is consistent with expectations. However, we find that the measured SZ flux from the optically-selected clusters is both significantly lower than expectations and lower than the recovered SZ flux measured by the Planck satellite. Since we find a lower recovered SZ signal than Planck, we investigate the possibility that there is a significant offset between the optically-selected brightest cluster galaxies (BCGs) and the SZ centers, to which ACT is more sensitive due to its finer resolution. Such offsets can arise due to either an intrinsic physical separation between the BCG and the center of the gas concentration or from misidentification of the cluster BCG. We find that the entire discrepancy for both ACT and Planck can be explained by assuming that the BCGs are offset from the SZ maxima with a uniform random distribution between 0 and 1.5 Mpc. In contrast, the physical separation between BCGs and X-ray peaks for an X-ray-selected subsample of MaxBCG clusters shows a much narrower distribution that peaks within 0.2 Mpc. We conclude that while offsets between BCGs and SZ peaks may be an important component in explaining the discrepancy, it is likely that a combination of factors is responsible for the ACT and Planck measurements. Several effects that can lower the SZ signal equally for both ACT and Planck, but not explain the difference in measured signals, include a larger percentage of false detections in the MaxBCG sample, a lower normalization of the mass-richness relation, radio or infrared galaxy contamination of the SZ flux, and a low intrinsic SZ signal. In the latter two cases, the effects would need to be preferentially more significant in the optically-selected MaxBCG sample than in the MCXC X-ray sample.

Sehgal, Neelima↗
NASA NTRS2014

Type Ia Supernova Rate Measurements to Redshift 2.5 from Candles: Searching for Prompt Explosions in the Early Universe

The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) was a multi-cycle treasury program on the Hubble Space Telescope(HST) that surveyed a total area of approx. 0.25 deg(sup 2) with approx.900 HST orbits spread across five fields over three years. Within these survey images we discovered 65 supernovae (SNe) of all types, out to z approx. 2.5. We classify approx. 24 of these as Type Ia SNe (SNe Ia) based on host galaxy redshifts and SN photometry (supplemented by grism spectroscopy of six SNe). Here we present a measurement of the volumetric SN Ia rate as a function of redshift, reaching for the first time beyond z = 2 and putting new constraints on SN Ia progenitor models. Our highest redshift bin includes detections of SNe that exploded when the universe was only approx. 3 Gyr old and near the peak of the cosmic star formation history. This gives the CANDELS high redshift sample unique leverage for evaluating the fraction of SNe Ia that explode promptly after formation (500 Myr). Combining the CANDELS rates with all available SN Ia rate measurements in the literature we find that this prompt SN Ia fraction isfP0.530.09stat0.100.10sys0.26, consistent with a delay time distribution that follows a simplet1power law for all timest40 Myr. However, mild tension is apparent between ground-based low-z surveys and space-based high-z surveys. In both CANDELS and the sister HST program CLASH (Cluster Lensing And Supernova Survey with Hubble), we find a low rate of SNe Ia at z > 1. This could be a hint that prompt progenitors are in fact relatively rare, accounting for only 20 of all SN Ia explosions though further analysis and larger samples will be needed to examine that suggestion.

Ia↗
NASA NTRS2016

GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence

We report the observation of a gravitational-wave signal produced by the coalescence of two stellar-mass black holes. The signal, GW151226, was observed by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on December 26, 2015 at 03:38:53 UTC. The signal was initially identified within 70 s by an online matched-filter search targeting binary coalescences. Subsequent off-line analyses recovered GW151226 with a network signal-to-noise ratio of 13 and a significance greater than 5(sigma). The signal persisted in the LIGO frequency band for approximately 1 s, increasing in frequency and amplitude over about 55 cycles from 35 to 450 Hz, and reached a peak gravitational strain of 3.4(+0.7/-0.9) x 10(exp -22). The inferred source-frame initial black hole masses are 14.2(+8.3/-3.7 Stellar Mass and 7.5(+2.3/-2.3) Stellar Mass, and the final black hole mass is 20.8(+6.1/-1.7) Stellar Mass. We find that at least one of the component black holes has spin greater than 0.2. This source is located at a luminosity distance of 440(+180/-190) Mpc corresponding to a redshift of 0.090(+.030/-0.04). All uncertainties define a 90% credible interval. This second gravitational-wave observation provides improved constraints on stellar populations and on deviations from general relativity.

Abbott, B. P.↗
NASA NTRS2016

What Would Happen to Superstorm Sandy Under the Influence of a Substantially Warmer Atlantic Ocean?

Based on ensemble numerical simulations, we find that possible responses of Sandy-like superstorms under the influence of a substantially warmer Atlantic Ocean bifurcate into two groups. In the first group, storms are similar to present-day Sandy from genesis to extratropical transition, except they are much stronger, with peak Power Destructive Index (PDI) increased by 50-80%, heavy rain by 30-50%, and maximum storm size (MSS) approximately doubled. In the second group, storms amplify substantially over the interior of the Atlantic warm pool, with peak PDI increased by 100-160%, heavy rain by 70-180%, and MSS more than tripled compared to present-day Superstorm Sandy. These storms when exiting the warm pool, recurve northeastward out to sea, subsequently interact with the developing midlatitude storm by mutual counterclockwise rotation around each other and eventually amplify into a severe Northeastern coastal storm, making landfall over the extreme northeastern regions from Maine to Nova Scotia.

radar reflectivities↗
NASA NTRS2017

Changes in Jupiter's Zonal Wind Profile Preceding and During the Juno Mission

We present five epochs of WFC3 HST Jupiter observations taken between 2009-2016 and extract global zonal wind profiles for each epoch. Jupiter's zonal wind field is globally stable throughout these years, but significant variations in certain latitude regions persist. We find that the largest uncertainties in the wind field are due to vortices or hot-spots, and show residual maps which identify the strongest vortex flows. The strongest year-to-year variation in the zonal wind profiles is the 24 deg N jet peak. Numerous plume outbreaks have been observed in the Northern Temperate Belt and are associated with decreases in the zonal velocity and brightness. We show that the 24 deg N jet peak velocity and brightness decreased in 2012 and again in late 2016, following outbreaks during these years. Our February 2016 zonal wind profile was the last highly spatially resolved measurement prior to Juno s first science observations. The final 2016 data were taken in conjunction with Juno's perijove 3 pass on 11 December 2016, and show the zonal wind profile following the plume outbreak at 24 deg N in October 2016.

Jupiter↗
NASA NTRS1984

Decimetric gyrosynchrotron emission during a solar flare

The implications of high time-resolution observations of a decimetric, microwave, and hard X-ray burst during a solar flare in which the 900-998 MHz, 8.4 GHz, and 10.4 GHz peak fluxes fit the optically thick spectrum of a homogeneous, thermal gyrosynchrotron source are reported and discussed. The hard X-ray spectrum from 30 to 463 keV is well represented by a thermal bremsstrahlung function, and a temperature derived from this spectrum is used to find the source area of about 10 to the 18th sq cm. An electron density of less than about 7 x 10 to the 9th/cu cm and a magnetic field of roughly 120 gauss are deduced from elementary plasma physics considerations and the lack of Razin-Tsytovich absorption of the 900-998 MHz flux. These conditions place the gyrosynchrotron source at high altitude in a coronal loop, in agreement with VLA observations of other flares.

Batchelor, D. A.↗
NASA NTRS1993

Cluster evolution as a probe of primordial density fluctuations

Although COBE's detection of large angle microwave background anisotropies fixes the amplitude of density fluctuations on length scales k exp -1 approximately = (300-6000) h(exp -1)Mpc, what is crucial for the level of large scale clustering is the amplitude of density fluctuations on scales (5-50) h(exp -1)Mpc. The level of dynamical clustering is usually parameterized by the size of the mass fluctuations in 8 h exp -1 Mpc spheres, sigma sub 8. For the cold dark matter model, COBE gives sigma sub 8 approximately = 1, while models with extra large scale power give sigma sub 8 approximately = 1/2. The most massive clusters of galaxies (greater than or approximately = 10 exp 15 solar mass) form from rare 'peak patches' found in the initial mass density distribution. Their abundance as a function of redshift is a sensitive probe of the wave number band k(exp -1) approx. (3-8) h(exp -1)Mpc, hence of sigma sub 8, and so cluster evolution can discriminate among models allowed by the COBE results. We use our Hierarchical Peaks Method, which accurately reproduces the results of P3M N-body simulations, to calculate the evolution of cluster x-ray flux counts, luminosity, and temperature functions as a function of sigma sub 8 for CDM models and those with more large scale power. We find that the EMSS and Edge et al. cluster samples support sigma sub 8 in the range from approx. 0.6-0.9, and that models with more large scale power (and hence flatter fluctuation spectra in the cluster regime) fit the x-ray bright end better.

Bond, J. Richard↗