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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Chandra X-Ray Observations of the Spiral Galaxy M81

A Chandra X-Ray Observatory ACIS-S imaging observation is used to study the population of X-ray sources in the nearby Sab galaxy M81 (NGC 3031). A total of 177 sources are detected with 124 located within the D(sub 25) isophote to a limiting X-ray luminosity of approx. 3 x 10(exp 36) ergs/s. Source positions, count rates, luminosities in the 0.3-8.0 keV band, limiting optical magnitudes, and potential counterpart identifications are tabulated. Spectral and timing analysis of the 36 brightest sources are reported including the low luminosity active galactic nucleus, SN 1993J, and the Einstein-discovered ultraluminous X-ray source X6. The nucleus accounts for approx. 86%, or 5 x 10(exp 40) ergs/s, of the total X-ray emission from M81. Its spectrum is well fitted by an absorbed power law with photon index 1.98 +/- 0.08, consistent with previous observations (average index 1.9). SN 1993J has softened and faded since its discovery. At an age of 2594 days, SN 1993J displayed a complex thermal spectrum from a reverse shock rich in Fe L and highly ionized Mg, Si, and S but lacking O. A hard X-ray component, emitted by a forward shock, is also present. X6 is spatially coincident with a stellar object with optical brightness and colors consistent with an O9-B1 main-sequence star. It is also coincident with a weak radio source with a flux density of approx. 95 microJy at lambda = 3.6 cm. The continuum-dominated X-ray spectrum of X6 is most closely reproduced by a blackbody disk model suggesting the X-ray source is an approx. 18 solar mass object accreting at nearly its Eddington limit.

Swartz, Douglas A.↗
NASA NTRS2010

Discovery and Monitoring of a New Black Hole Candidate XTE J1752-223 with RXTE: RMS Spectrum Evolution, BH Mass and the Source Distance

We report on the discovery and monitoring observations of a new galactic black hole candidate XTE J1752-223 by Rossi X-ray Timing Explorer (RXTE). The new source appeared on the X-ray sky on October 21 2009 and was active for almost 8 months. Phenomenologically, the source exhibited the low-hard/highsoft spectral state bi-modality and the variability evolution during the state transition that matches standard behavior expected from a stellar mass black hole binary. We model the energy spectrum throughout the outburst using a generic Comptonization model assuming that part of the input soft radiation in the form of a black body spectrum gets reprocessed in the Comptonizing medium. We follow the evolution of fractional root-mean-square (RMS) variability in the RXTE/PCA energy band with the source spectral state and conclude that broad band variability is strongly correlated with the source hardness (or Comptonized fraction). We follow changes in the energy distribution of rms variability during the low-hard state and the state transition and find further evidence that variable emission is strongly concentrated in the power-law spectral component. We discuss the implication of our results to the Comptonization regimes during different spectral states. Correlations of spectral and variability properties provide measurements of the BH mass and distance to the source. The spectral-timing correlation scaling technique applied to the RXTE observations during the hardto- soft state transition indicates a mass of the BH in XTE J1752-223 between 8 and 11 solar masses and a distance to the source about 3.5 kiloparsec.

Shaposhinikov, Nikolai↗
NASA NTRS1986

Arginine decarboxylase as the source of putrescine for tobacco alkaloids

The putrescine which forms a part of nicotine and other pyrrolidine alkaloids is generally assumed to arise through the action of ornithine decarboxylase (ODC). However, we have previously noted that changes in the activity of arginine decarboxylase (ADC), an alternate source of putrescine, parallel changes in tissue alkaloids, while changes in ODC activity do not. This led us to undertake experiments to permit discrimination between ADC and ODC as enzymatic sources of putrescine destined for alkaloids. Two kinds of evidence presented here support a major role for ADC in the generation of putrescine going into alkaloids: (a) A specific 'suicide inhibitor' of ADC effectively inhibits the biosynthesis of nicotine and nornicotine in tobacco callus, while the analogous inhibitor of ODC is less effective, and (b) the flow of 14C from uniformly labelled arginine into nicotine is much more efficient than that from ornithine.

NASA Discipline Number 40-10↗
NASA NTRS2014

The Atacama Cosmology Telescope: Dusty Star-Forming Galaxies and Active Galactic Nuclei in the Southern Survey

We present a catalogue of 191 extragalactic sources detected by the Atacama Cosmology Telescope (ACT) at 148 and/or 218 GHz in the 2008 Southern survey. Flux densities span 14 -1700 mJy, and we use source spectral indices derived using ACT-only data to divide our sources into two subpopulations: 167 radio galaxies powered by central active galactic nuclei (AGN) and 24 dusty star-forming galaxies (DSFGs). We cross-identify 97 per cent of our sources (166 of the AGN and 19 of the DSFGs) with those in currently available catalogues. When combined with flux densities from the Australia Telescope 20 GHz survey and follow-up observations with the Australia Telescope Compact Array, the synchrotron-dominated population is seen to exhibit a steepening of the slope of the spectral energy distribution from 20 to 148 GHz, with the trend continuing to 218 GHz. The ACT dust-dominated source population has a median spectral index, A(sub 148-218), of 3.7 (+0.62 or −0.86), and includes both local galaxies and sources with redshift around 6. Dusty sources with no counterpart in existing catalogues likely belong to a recently discovered subpopulation of DSFGs lensed by foreground galaxies or galaxy groups.

dusty star-forming galaxies (DSFGs)↗
NASA NTRS2014

The Atacama Cosmology Telescope: Dusty Star-Forming Galaxies and Active Galactic Nuclei in the Southern Survey

We present a catalogue of 191 extragalactic sources detected by the Atacama Cosmology Telescope (ACT) at 148 and/or 218 GHz in the 2008 Southern survey. Flux densities span 14 - 1700 mJy, and we use source spectral indices derived using ACT-only data to divide our sources into two subpopulations: 167 radio galaxies powered by central active galactic nuclei (AGN) and 24 dusty star-forming galaxies (DSFGs). We cross-identify 97 per cent of our sources (166 of the AGN and 19 of the DSFGs) with those in currently available catalogues. When combined with flux densities from the Australia Telescope 20 GHz survey and follow-up observations with the Australia Telescope Compact Array, the synchrotron-dominated population is seen to exhibit a steepening of the slope of the spectral energy distribution from 20 to 148 GHz, with the trend continuing to 218 GHz. The ACT dust-dominated source population has a median spectral index, alpha(sub 148−218), of 3.7 +0.62/-0.86), and includes both local galaxies and sources with redshift around 6. Dusty sources with no counterpart in existing catalogues likely belong to a recently discovered subpopulation of DSFGs lensed by foreground galaxies or galaxy groups.

Telescope↗
NASA NTRS1987

A generalized method for optimization of active noise controllers in three-dimensional spaces

In this investigation, the formulation of an optimal active noise controller for harmonic, enclosed sound fields is derived using an indirect boundary element method. The optimal active noise controller is defined as the volume velocity secondary source strengths which minimize the sound pressure level at a number of discrete interior locations. In addition, the formulation of an optimal active noise controller which minimizes the free field power radiated from a generalized, distributed noise source is presented. Representative results are provided for each formulation. For the enclosure problem, results are given for global control, local control, and passive wall treatments using a rectangular cavity. For the free field radiation problem, the effects of secondary source location and quantity on active noise controller performance are investigated. The relative merits of each formulation are discussed.

Mollo, C. G.↗
NASA NTRS2019

Fractional Polarization of Extragalactic Sources in the 500 deg 2 SPTpol Survey

We study the polarization properties of extragalactic sources at 95 and 150 GHz in the SPTpol 500 deg 2 survey. We estimate the polarized power by stacking maps at known source positions, and correct for noise bias by subtracting the mean polarized power at random positions in the maps. We show that the method is unbiased using a set of simulated maps with similar noise properties to the real SPTpol maps. We find a flux-weighted mean-squared polarization fraction 〈p 2 〉 = [8.9 ± 1.1] × 10 -4 at 95 GHz and [6.9 ± 1.1] × 10 -4 at 150 GHz for the full sample. This is consistent with the values obtained for a subsample of active galactic nuclei. For dusty sources, we find 95 per cent upper limits of 〈p 2 〉95 < 16.9 × 10 -3 and 〈p 2 〉150 < 2.6 × 10 -3 . We find no evidence that the polarization fraction depends on the source flux or observing frequency. The 1σ upper limit on measured mean-squared polarization fraction at 150 GHz implies that extragalactic foregrounds will be subdominant to the CMB E and B mode polarization power spectra out to at least ℓ ≲ 5700 (ℓ ≲ 4700) and ℓ ≲ 5300 (ℓ ≲ 3600), respectively, at 95 (150) GHz.

Nikhel Gupta↗
NASA NTRS2012

Computational Ghost Imaging for Remote Sensing

This work relates to the generic problem of remote active imaging; that is, a source illuminates a target of interest and a receiver collects the scattered light off the target to obtain an image. Conventional imaging systems consist of an imaging lens and a high-resolution detector array [e.g., a CCD (charge coupled device) array] to register the image. However, conventional imaging systems for remote sensing require high-quality optics and need to support large detector arrays and associated electronics. This results in suboptimal size, weight, and power consumption. Computational ghost imaging (CGI) is a computational alternative to this traditional imaging concept that has a very simple receiver structure. In CGI, the transmitter illuminates the target with a modulated light source. A single-pixel (bucket) detector collects the scattered light. Then, via computation (i.e., postprocessing), the receiver can reconstruct the image using the knowledge of the modulation that was projected onto the target by the transmitter. This way, one can construct a very simple receiver that, in principle, requires no lens to image a target. Ghost imaging is a transverse imaging modality that has been receiving much attention owing to a rich interconnection of novel physical characteristics and novel signal processing algorithms suitable for active computational imaging. The original ghost imaging experiments consisted of two correlated optical beams traversing distinct paths and impinging on two spatially-separated photodetectors: one beam interacts with the target and then illuminates on a single-pixel (bucket) detector that provides no spatial resolution, whereas the other beam traverses an independent path and impinges on a high-resolution camera without any interaction with the target. The term ghost imaging was coined soon after the initial experiments were reported, to emphasize the fact that by cross-correlating two photocurrents, one generates an image of the target. In CGI, the measurement obtained from the reference arm (with the high-resolution detector) is replaced by a computational derivation of the measurement-plane intensity profile of the reference-arm beam. The algorithms applied to computational ghost imaging have diversified beyond simple correlation measurements, and now include modern reconstruction algorithms based on compressive sensing.

Erkmen, Baris I.↗
NASA NTRS1992

Europa: Prospects for an ocean and exobiological implications

As far as we know, Earth is the only planet in our solar system that supports life. It is natural, therefore, that our understanding of life as a planetary phenomenon is based upon Earth-like planets. There are environments in the solar system where liquid water, commonly believed to be a prerequisite for biological activity, may exist in a distinctly non-Earth-like environment. One such location is Europa, one of the Galilean satellites of Jupiter. The possibility that liquid water exists on Europa presents us with some interesting exobiological implications concerning the potential of the satellite to support life. Topics include the following: an ocean on Europa; thermal evolution of Europa; Europa's three models; exobiological implications; early conditions of Europa; low-temperature abiotic chemistry; possibility of the emergence of life on Europa; prerequisites for the habitability of Europa; energy sources for biosynthesis and metabolic activity; habitability of Europa by anaerobic life; and habitability by aerobic life.

Oro, John↗
NASA NTRS2000

In Situ Activation of Microcapsules

Disclosed are microcapsules comprising a polymer shell enclosing two or more immiscible liquid phases in which a drug, or a prodrug and a drug activator are partitioned into separate phases. or prevented from diffusing out of the microcapsule by a liquid phase in which the drug is poorly soluble. Also disclosed are methods of using the microcapsules for in situ activation of drugs where upon exposure to an appropriate energy source the internal phases mix and the drug is activated in situ.

Morrison, Dennis R.↗
NASA NTRS1994

Dual-use technologies for the mining, processing, and energy industries

Over the years, NASA has utilized several approaches towards transferring space technologies into the private sectors. Some of these approaches have been successful, others have had mixed results. The conventional approach usually involves identifying advanced NASA technologies and then searching for applications. Some approaches involve joint sponsorship, but mostly focus on technologies for space. The greatest success has occurred when market forces are used to determine technology initiatives. This paper describes an unconventional approach that was structured to drive out customer requirements for advanced technologies where NASA is also a customer on par with others. The approach used herein is best described as entrepreneurial deal-making. This approach is new and is working very well so far, but it is still too early, and the process is too immature, for quantitative evaluation of success. However, it is appropriate to share these experiences at this time in order to obtain feedback and improve our chances for success. In the needs identification stage, NASA is one of many users (customers), and in the subsequent development stage, NASA is one of many suppliers along with industry, academia, and other government organizations. This specific characteristic of the approach was a primary goal that was incorporated from inception. It was the viewpoint of the instigators (the authors) that if the activity was customer focused, it would: (1) have a higher probability for success since it will be driven by those who will reap the benefits; (2) be able to advocate and promote action if necessary, since it would be founded outside the federal government; (3) not be self-perpetuating; that is, if no common need could be found that had a reasonable return on investment, it would self-destruct; and (4) have increased stability from a broader base of support and not be dependent on NASA being the principal funding source. To date, the workshop activities have identified a collection of potential customers in NASA, other federal government, private industry, and academia who have common needs for advanced technologies.

Roberts, Barney B.↗
NASA NTRS1985

Analytical study of acoustic response of a semireverberant enclosure with application to active noise control

The acoustic response of a semireverberant enclosure with two interacting, velocity-prescribed source distributions was analyzed using standard modal analysis techniques with a view toward a better understanding of active noise control. Different source and enclosure dimensions, source separations, and single-wall admittances were studied over representative frequency bandwidths of 10 Hz with source relative phase as a parameter. Results indicate that power radiated into the enclosure agree qualitatively with the spatial average of the mean square pressure, even though the reverberant field is nondiffuse. Decreases in acoustic power can therefore be used to estimate global noise reduction in a nondiffuse semireverberant environment. As might be expected, parametric studies indicate that maximum power reductions of up to 25 dB can be achieved when secondary and primary sources are compact and closely spaced. Although less success is achieved with increasing frequency and source separation or size, significant suppression of up to 8 dB still occurs over the 1 to 2 Hz bandwidth.

Parrott, T. L.↗
NASA NTRS1994

Water maser emission from X-ray-heated circumnuclear gas in active galaxies

We have modeled the physical and chemical conditions present within dense circumnuclear gas that is irradiated by X-rays from an active galactic nucleus. Over a wide range of X-ray fluxes and gas pressures, the effects of X-ray heating give rise to a molecular layer at temperatures of 400-1000 K within which the water abundance is large. The physical conditions within this molecular layer naturally give rise to collisionally pumped maser emission in the 6(sub 16) - 5(sub 23) 22 GHz transition of ortho-water, with predicted maser luminosities of 10(exp 2 +/- 0.5) solar luminosity per sq. pc of illuminated area. Given plausible assumptions about the geometry of the source and about the degree to which the maser emission is anisotropic, such surface luminosities are sufficient to explain the large apparent luminosities observed in water maser sources that are associated with active galactic nuclei.

Neufeld, David A.↗
NASA NTRS1995

On the injection of fine dust from the Jovian magnetosphere

Using a simple aligned dipole model of the Jovian magnetic field, and exploiting integrals of the gravito-electrodynamic equation of motion of charged dust, we obtain an analytic result which characterizes the nature of the orbits of grains of different (fixed) charge-to-mass ratios launched at different velocities from different radial distances from Jupiter. This enables us to consider various possible sources of the dust-streams emanating from Jupiter which have been observed by the Ulysses spacecraft. We conclude that Jupiter's volcanically active satellite Io is the likely source, in agreement with the earlier calculations and simulations of Horanyi et al. using a detailed three-dimensional model of the Jovian magnetosphere. Our estimates of the size range and the velocity range of these dust grains are also in good agreement with those of the above authors and are within the error bars of the observations.

Maravilla, D.↗
NASA NTRS2022

Newly Identified Climatically and Environmentally Significant High-Latitude Dust Sources

Dust particles from high latitudes have a potentially large local, regional, and global significance to climate and the environment as short-lived climate forcers, air pollutants, and nutrient sources. Identifying the locations of local dust sources and their emission, transport, and deposition processes is important for understanding the multiple impacts of high-latitude dust (HLD) on the Earth’s systems. Here, we identify, describe, and quantify the source intensity (SI) values, which show the potential of soil surfaces for dust emission scaled to values 0 to 1 concerning globally best productive sources, using the Global Sand and Dust Storms Source Base Map (G-SDS-SBM). This includes 64 HLD sources in our collection for the northern (Alaska, Canada, Denmark, Greenland, Iceland, Svalbard, Sweden, and Russia) and southern (Antarctica and Patagonia) high latitudes. Activity from most of these HLD sources shows seasonal character. It is estimated that high-latitude land areas with higher (SI ≥ 0.5), very high (SI ≥ 0.7), and the highest potential (SI ≥ 0.9) for dust emission cover > 1 670 000 km 2 , > 560 000 km 2 , and > 240 000 km 2 , respectively. In the Arctic HLD region (≥ 60◦ N), land area with SI ≥ 0.5 is 5.5 % (1 035 059 km 2 ), area with SI ≥ 0.7 is 2.3 % (440 804 km 2 ), and area with SI ≥ 0.9 is 1.1 % (208 701 km 2 ). Minimum SI values in the northern HLD region are about 3 orders of magnitude smaller, indicating that the dust sources of this region greatly depend on weather conditions. Our spatial dust source distribution analysis modeling results showed evidence supporting a northern HLD belt, defined as the area north of 50◦ N, with a “transitional HLD-source area” extending at latitudes 50–58◦ N in Eurasia and 50–55◦ N in Canada and a “cold HLD-source area” including areas north of 60◦ N in Eurasia and north of 58◦ N in Canada, with currently “no dust source” area between the HLD and low-latitude dust (LLD) dust belt, except for British Columbia. Using the global atmospheric transport model SILAM, we estimated that 1.0 % of the global dust emission originated from the high-latitude regions. About 57 % of the dust deposition in snow- and ice-covered Arctic regions was from HLD sources. In the southern HLD region, soil surface conditions are favorable for dust emission during the whole year. Climate change can cause a decrease in the duration of snow cover, retreat of glaciers, and an increase in drought, heatwave intensity, and frequency, leading to the increasing frequency of topsoil conditions favorable for dust emission, which increases the probability of dust storms. Our study provides a step forward to improve the representation of HLD in models and to monitor, quantify, and assess the environmental and climate significance of HLD.

high latitude dust↗
NASA NTRS1971

Improved neutron activation prediction code system development

Two integrated neutron activation prediction code systems have been developed by modifying and integrating existing computer programs to perform the necessary computations to determine neutron induced activation gamma ray doses and dose rates in complex geometries. Each of the two systems is comprised of three computational modules. The first program module computes the spatial and energy distribution of the neutron flux from an input source and prepares input data for the second program which performs the reaction rate, decay chain and activation gamma source calculations. A third module then accepts input prepared by the second program to compute the cumulative gamma doses and/or dose rates at specified detector locations in complex, three-dimensional geometries.

Saqui, R. M.↗
NASA NTRS1985

Infrared speckle observations of Io - An eruption in the Loki region

Speckle observations of Jupiter's satellite Io at a wavelength of 5 micrometers during July 1984 resolved the disk and showed emission from a hot spot in the Loki region. The hot spot contributed a flux approximately equal to 60 percent of that from the disk. Images reconstructed by means of the Knox-Thompson algorithm showed the spot moving across the disk as the satellite rotated. It was located at 301 deg + or - 6 deg west longitude, 10 deg + or - 6 deg north latitude, and had a radiance of (2.96 + or - 0.54) x 10 to the 22nd ergs/sec cm sr/A where A is the area of the spot. For an assumed temperature of 400 K, the area of the source would be 11,400 square kilometers. An active 'lava lake' similar to that seen by Voyager may be the source of the infrared emission.

Howell, R. R.↗
NASA NTRS1990

Roentgen Satellite (ROSAT)

The Objectives of NASA's participation in the ROSAT mission are to: a) measure the spatial, spectral, and temporal characteristics of discrete cosmic sources including normal stars, collapsed stellar objects, and active galactic nuclei; b) perform spectroscopic mapping of extended X-ray sources including supernova remnants, galaxies, and clusters of galaxies; and c) conduct the above observations of cosmic sources with unprecedented sensitivity and spatial resolution over the 0.1 - 2.0 keV energy band.

Source record↗