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At least 1,369 records · Page 76
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NASA NTRS1986

Energy balance in solar active regions - The dip of April, 1985

The presence of a solar active region affects the luminosity of the sun. Sunspots directly produce 'dips' in the total solar irradiance approximately proportionally to their projected area, while faculae produce excess energy. These effects were discovered during the solar maximum period of 1980, and the sunspot effect during solar minimum is examined. The 'dip' due to an active region in April, 1985, as observed in the total solar irradiance by the ACRIM instrument on the Solar Maximum Mission is examined. These data (obtained after the spacecraft repair in May, 1984) have simple variations, relative to those observed in 1980, because of the reduced level of activity approaching solar minimum. It is found that the PSI index of projected sunspot area as defined in 1980 appears to describe this 'dip' satisfactorily.

Hudson, H. S.↗
NASA NTRS1992

Fully energy-dependent HZETRN (a galactic cosmic-ray transport code)

For extended manned space missions, the radiation shielding design requires efficient and accurate cosmic-ray transport codes that can handle the physics processes in detail. The Langley Research Center galactic cosmic-ray transport code (HZETRN) is currently under development for such design use. The cross sections for the production of secondary nucleons in the existing HZETRN code are energy dependent only for nucleon collisions. The approximation of energy-independent, heavy-ion fragmentation cross section is now removed by implementing a mathematically simplified energy-dependent stepping formalism for heavy ions. The cross section at each computational grid is obtained by linear interpolation from a few tabulated data to minimize computing time. Test runs were made for galactic cosmic-ray transport through a liquid hydrogen shield and a water shield at solar minimum. The results show no appreciable change in total fluxes or computing time compared with energy-independent calculations. Differences in high LET (linear energy transfer) spectra are noted, however, because of the large variation in cross sections at the low-energy region. The high LET components are significantly higher in the new code and have important implications on biological risk estimates for heavy-ion exposure.

Shinn, Judy L.↗
NASA NTRS1992

Influence of solar activity upon light curves of comets P/Halley (1986 3) and P/Churyumov-Gerasimenko (1982 8)

It is shown that the comet P/Halley's (1986 3) total magnitudes correlate with changes in the solar activity indices and the solar wind velocity. A statistically reliable correlation between the outbursts of brightness and magnitude variations of the short-period comet Churyumov-Gerasimenko (1982 8) and the level of the solar activity has been discovered.

Churyumov, Klim I.↗
NASA NTRS1992

Comparison of surface fluxes and conductances at two contrasting sites within the FIFE area

Surface flux measurements from two contrasting sites within the FIFE study area are analyzed. The seasonal variation of midday latent heat fluxes and surface conductances at the two sites was found to be very similar even though the ratio of their average total leaf area indices was greater than two to one. Concurrent measurements made at another six flat sites within the FIFE area confirmed the independence of latent heat flux with respect to leaf area index. The surface conductance stress function related to specific humidity deficit was the same for the two sites, whereas the solar radiation stress function showed a difference of 30 percent at a solar radiation input of 300 W/sq m and the soil moisture stress function showed a difference of 16 percent when half the extractable soil moisture had been taken up. However, when the stress functions were combined to determine the surface conductance, these differences virtually canceled out.

Stewart, J. B.↗
NASA NTRS1991

Electric propulsion system technology

The work performed on the Ion Propulsion System Technology Task in FY90 is described. The objectives of this work fall under two broad categories. The first of these deals with issues associated with the application of xenon ion thrusters for primary propulsion of planetary spacecraft, and the second with the investigation of technologies which will facilitate the development of larger, higher power ion thrusters to support more advanced mission applications. Most of the effort was devoted to investigation of the critical issues associated with the use of ion thrusters for planetary spacecraft. These issues may be succinctly referred to as life time, system integration, and throttling. Chief among these is the engine life time. If the engines do not have sufficient life to perform the missions of interest, then the other issues become unimportant. Ion engine life time was investigated through two experimental programs: an investigation into the reduction of ion engine internal sputter erosion through the addition of small quantities of nitrogen, and a long duration cathode life test. In addition, a literature review and analysis of accelerator grid erosion were performed. The nitrogen addition tests indicated that the addition of between 0.5 and 1.0 percent of nitrogen by mass to the xenon propellant results in a reduction in the sputter erosion of discharge chamber components by a factor of between 20 and 50, with negligible reduction in thruster performance. The long duration test of a 6.35-mm dia. xenon hollow cathode is still in progress, and has accumulated more than 4,000 hours of operation at an emission current of 25 A at the time of this writing. One of the major system integration issues concerns possible interactions of the ion thruster produced charge exchange plasma with the spacecraft. A computer model originally developed to describe the behavior of mercury ion thruster charge exchange plasmas was resurrected and modified for xenon propellant. This model enables one to calculate the flow direction and local density of the charge exchange plasma, and indicates the degree to which this plasma can flow upstream of the thruster exhaust plane. A continuing effort to investigate the most desirable throttling technique for noble gas ion thrusters concentrated this year on experimentally determining the fixed flow rate throttling range of a 30-cm dia. thruster with a two-grid accelerator system. These experiments demonstrated a throttling capability which covers a 2.8 to 1 variation in input power. This throttling range is 55 percent greater than expected, and is due to better accelerator system performance at low net-to-total voltage ratios than indicated in the literature. To facilitate the development of large, higher power ion thrusters several brief studies were performed. These include the development of a technique which simulates ion thruster operation without beam extraction, the development of an optical technique to measure ion thruster grid distortion due to thermal expansion, tests of a capacitance measurement technique to quantify the accelerator system grid separation, and the development of a segmented thruster geometry which enables near term development of ion thrusters at power levels greater than 100 kW. Finally, a paper detailing the benefits of electric propulsion for the Space Exploration Initiative was written.

Brophy, John R.↗
NASA NTRS1994

Dynamics of the transition zone in coastal zone color scanner-sensed ocean color in the North Pacific during oceanographic spring

A transition zone in phytoplankton concentration running across the North Pacific basin at 30 deg to 40 deg north latitude corresponds to a basin-wide front in surface chlorophyll observed in a composite of coastal zone color scanner (CZCS) images for May, June, and July 1979-1986. This transition zone with low chlorophyll to the south and higher chlorophyll to the north can be simulated by a simple model of the concentration of phytoplankton, zooplankton, and dissolved nutrient (nitrate) in the surface mixed layer of the ocean applied to the North Pacific basin for the climatological conditions during oceanographic springtime (May, June, and July). The model is initialized with a 1 deg x 1 deg gridded estimate of wintertime (February, March, and April) mixed layer nitrate concentrations calculated from an extensive nutrient database and a similarly gridded mixed layer depth data set. Comparison of model predictions with CZCS data provides a means of evaluating the dynamics of the transition zone. We conclude that in the North Pacific, away from major boundary currents and coastal upwelling zones, wintertime vertical mixing determines the total nutrient available to the plankton ecosystem in the spring. The transition zone seen in basin-scale CZCS images is a reflection of the geographic variation in the wintertime mixed layer depth and the nitracline, leading to a latitudinal gradient in phytoplankton chlorophyll.

Glover, David M.↗
NASA NTRS2000

The Dust Content and Opacity of Actively Star-Forming Galaxies

We present far-infrared (FIR) photometry at 150 and 205 micron(s) of eight low-redshift starburst galaxies obtained with the Infrared Space Observatory (ISO) ISOPHOT. Five of the eight galaxies are detected in both wave bands, and these data are used, in conjunction with IRAS archival photometry, to model the dust emission at lambda approximately greater than 40 microns. The FIR spectral energy distributions (SEDs) are best fitted by a combination of two modified Planck functions, with T approx. 40 - 55 K (warm dust) and T approx. 20-23 K (cool dust) and with a dust emissivity index epsilon = 2. The cool dust can be a major contributor to the FIR emission of starburst galaxies, representing up to 60% of the total flux. This component is heated not only by the general interstellar radiation field, but also by the starburst itself. The cool dust mass is up to approx. 150 times larger than the warm dust mass, bringing the gas-to-dust ratios of the starbursts in our sample close to Milky Way values, once resealed for the appropriate metallicity. The ratio between the total dust FIR emission in the range 1-1000 microns and the IRAS FIR emission in the range 40 - 120 microns is approx. 1.75, with small variations from galaxy to galaxy. This ratio is about 40% larger than previously inferred from data at millimeter wavelengths. Although the galaxies in our sample are generally classified as "UV bright," for four of them the UV energy emerging shortward of 0.2 microns is less than 15% of the FIR energy. On average, about 30% of the bolometric flux is coming out in the UV-to-near-IR wavelength range; the rest is emitted in the FIR. Energy balance calculations show that the FIR emission predicted by the dust reddening of the UV-to-near-IR stellar emission is within a factor of approx. 2 of the observed value in individual galaxies and within 20% when averaged over a large sample. If our sample of local starbursts is representative of high-redshift (z approx. greater than 1), UV - bright star-forming galaxies, these galaxies' FIR emission will be generally undetected in submillimeter surveys, unless: (1) their bolometric luminosity is comparable to or larger than that of ultraluminous FIR galaxies and (2) their FIR SED contains a cool dust component.

Calzetti, Daniela↗
NASA NTRS2000

BOREAS RSS-10 TOMS Circumpolar One-Degree PAR Images

The Boreal Ecosystem-Atmosphere Study (BOREAS) Remote Sensing Science (RSS)-10 team investigated the magnitude of daily, seasonal, and yearly variations of Photosynthetically Active Radiation (PAR) from ground and satellite observations. This data set contains satellite estimates of surface-incident PAR (400-700 nm, MJ/sq m) at one-degree spatial resolution. The spatial coverage is circumpolar from latitudes of 41 to 66 degrees north. The temporal coverage is from May through September for years 1979 through 1989. Eleven-year statistics are also provided: (1) mean, (2) standard deviation, and (3) coefficient of variation for 1979-89. The PAR estimates were derived from the global gridded ultraviolet reflectivity data product (average of 360, 380 nm) from the Nimbus-7 Total Ozone Mapping Spectrometer (TOMS). Image mask data are provided for identifying the boreal forest zone, and ocean/land and snow/ice-covered areas. The data are available as binary image format data files. The PAR data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

Dye, Dennis G.↗
NASA NTRS2012

The Size Frequency Distribution of Small Main-Belt Asteroids

The asteroid size distribution informs us about the formation and composition of the Solar System. We build on our previous work in which we harvest serendipitously observed data of the Taurus region and measure the brightness and size distributions of Main-belt asteroids. This is accomplished with the highly sensitive MIPS 24 micron channel. We expect to catalog 104 asteroids, giving us a statistically significant data set. Results from this investigation will allow us to characterize the total population of small, Main-belt asteroids. Here we will present new results on the completeness of our study; on the presence of size distribution variations with inclination and radial distance in the belt; and early result on other archival fields.

Burt, Brian J.↗
NASA NTRS2018

Small-Scale Flux Transfer Events Formed in the Reconnection Exhaust Region Between Two X Lines

We report MMS observations of the ion-scale flux transfer events (FTEs) that may involve two main X lines and tearing instability between the two X lines. The four spacecraft detected multiple isolated regions with enhanced magnetic field strength and bipolar B(sub )n signatures normal to the nominal magnetopause, indicating FTEs. The currents within the FTEs flow mostly parallel to B, and the magnetic tension force is balanced by the total pressure gradient force. During these events, the plasma bulk flow velocity was directed southward. Detailed analysis of the magnetic and electric field and plasma moments variations suggests that the FTEs were initially embedded within the exhaust region north of an X line but were later located southward/downstream of a subsequent X line. The cross sections of the individual FTEs are in the range of ~2.5-6.8 ion inertial lengths. The observations suggest the formation of multiple secondary FTEs. The presence of an X line in the exhaust region southward of a second X line results from the southward drift of an old X line and the reformation of a new X line. The current layer between the two X lines is unstable to the tearing instability, generating multiple ion-scale flux-rope-type secondary islands.

Hwang, K.-J.↗
NASA NTRS2019

PSR J2234+0611: A New Laboratory for Stellar Evolution

We report the timing results for PSR J2234+0611, a 3.6 ms pulsar in a 32 day, eccentric (e = 0.13) orbit with a helium white dwarf. The precise timing and eccentric nature of the orbit allow measurements of an unusual number of parameters: (a) a precise proper motion of 27.10(3) mas yr−1 and a parallax of 1.05(4) mas resulting in a pulsar distance of 0.95(4) kpc; enabling an estimate of the transverse velocity, 123(5) km s−1. Together with previously published spectroscopic measurements of the systemic radial velocity, this allows a 3D determination of the system’s velocity; (b) precise measurements of the rate of advance of periastron yields a total system mass of 1.6518 +0.0033-0.0035 Msun; (c) a Shapiro delay measurement, h3 = 82 ± 14 ns, despite the orbital inclination not being near 90°; combined with the measurement of the total mass yields a pulsar mass of 1.353 +0.014-0.017 Msun and a companion mass of 0.298 +0.015-0.0120 Msun; (d) we measure precisely the secular variation of the projected semimajor axis and detect a significant annual orbital parallax; together these allow a determination of the 3D orbital geometry of the system, including an unambiguous orbital inclination (i = 138.7 +2.5-2.2 deg) and a position angle for the line of nodes ( omega = 44 +5-4 deg). We discuss the component masses to investigate the hypotheses previously advanced to explain the origin of eccentric MSPs. The unprecedented determination of the 3D position, motion, and orbital orientation of the system, plus the precise pulsar and WD masses and the latter’s optical detection make this system a unique test of our understanding of white dwarfs and their atmospheres.

K Stovall↗
NASA NTRS2023

Understanding Volume Estimation Uncertainty of Lakes and Wetlands Using Satellites and Citizen Science

We studied variations in the volume of water stored in small lakes and wetlands using satellite remote sensing and lake water height data contributed by citizen scientists. A total of 94 water bodies across the globe were studied using satellite data in the optical and microwave wavelengths from Landsat 8, Sentinel-1, and Sentinel-2. The uncertainty in volume estimation as a function of geography and geophysical factors, such as cloud cover, precipitation, and water surface temperature, was studied. The key finding that emerged from this global study is that uncertainty is highest in regions with a distinct precipitation season, such as in the monsoon dominated South Asia or the Pacific Northwestern region of the USA. This uncertainty is further compounded when small lakes and wetlands are seasonal with alternating land use as a water body and agricultural land, such as the wetlands of Northeastern Bangladesh. On an average, 45% of studied lakes could be estimated of their volume change with a statistical significant uncertainty that is less than the expected volume in South Asia. In North America, this statistically significant uncertainty in volume estimation was found to be around 50% in lakes eastward of the 108th meridian with lowest uncertainty found in lakes along the East coast of the USA. The article provides a baseline for understanding the current state of the art in estimating volumetric change of lakes and wetlands using citizen science in anticipation of the recently launched Surface Water and Ocean Topography Mission.

Shahzaib Khan↗
DOE OSTI2023

Spatio-temporal and weather characterization of road loads of electrified heavy-duty commercial vehicles across U.S. interstate roads

Adoption of battery electric vehicles (BEV) in heavy duty (HD) commercial freight transportation is difficult due to technological and economic hurdles. Beyond safety and compliance, fleet and operational logistics necessitate both high uptime and parity with diesel system productivity/Total Cost of Ownership to support widespread deployment of electric powertrains. However, relatively high energy storage costs, along with the higher weight of BEV systems, limit the viability of HD commercial freight transport to shorter-range applications where smaller batteries will serve for mission energy requirements (single operational shift). Knowing the energy consumption and operating variations of these commercial vehicle systems is crucial for effectively sizing the energy storage systems. This paper is the first in a series of studies to understand the regional specific operating design domain variations of commercial Class 8 HD trucks and the associated impact to their energy requirements. In particular, the local weather conditions are shown to influence the total vehicle energy usage. Further, the impact of temperature, pressure, and humidity changes are shown to impact the local air density. This is needed to calculate aerodynamic drag on vehicles and has been found to play a significant role in the overall performance of a vehicle. Although the methodology of calculating air density varies only slightly throughout the literature, the application to transportation has still been limited. This study provides a means by which air density can be estimated for the contiguous U.S. using the NOAA MADIS dataset. These air density estimates were then used to determine vehicle performance in varying regions of the country to highlight the importance of consideration of weather variables when monitoring vehicle performance, but also to provide recommendations based on these locales upon fleet conversion to BEVs.

Moore, Amy↗
NASA NTRS2012

FISM 2.0: Improved Spectral Range, Resolution, and Accuracy

The Flare Irradiance Spectral Model (FISM) was first released in 2005 to provide accurate estimates of the solar VUV (0.1-190 nm) irradiance to the Space Weather community. This model was based on TIMED SEE as well as UARS and SORCE SOLSTICE measurements, and was the first model to include a 60 second temporal variation to estimate the variations due to solar flares. Along with flares, FISM also estimates the tradition solar cycle and solar rotational variations over months and decades back to 1947. This model has been highly successful in providing driving inputs to study the affect of solar irradiance variations on the Earth's ionosphere and thermosphere, lunar dust charging, as well as the Martian ionosphere. The second version of FISM, FISM2, is currently being updated to be based on the more accurate SDO/EVE data, which will provide much more accurate estimations in the 0.1-105 nm range, as well as extending the 'daily' model variation up to 300 nm based on the SOLSTICE measurements. with the spectral resolution of SDO/EVE along with SOLSTICE and the TIMED and SORCE XPS 'model' products, the entire range from 0.1-300 nm will also be available at 0.1 nm, allowing FISM2 to be improved a similar 0.1nm spectral bins. FISM also will have a TSI component that will estimate the total radiated energy during flares based on the few TSI flares observed to date. Presented here will be initial results of the FISM2 modeling efforts, as well as some challenges that will need to be overcome in order for FISM2 to accurately model the solar variations on time scales of seconds to decades.

Chamberlin, Phillip C.↗
NASA NTRS2012

Integration of the Total Lightning Jump Algorithm into Current Operational Warning Environment Conceptual Models

Key points that this analysis will begin to address are: 1)What physically is going on in the cloud when there is a jump in lightning? - Updraft variations, ice fluxes. 2)How do these processes fit in with severe storm conceptual models? 3)What would this information provide an end user (i.e., the forecaster)? - Relate LJA to radar observations, like changes in reflectivity, MESH, VIL, etc. based multi-Doppler derived physical relationships 4) How do we best transistionthis algorithm into the warning decision process. The known relationship between lightning updraft strength/volume and precipitation ice mass production can be extended to the concept of the lightning jump. Examination of the first lightning jump times from 329 storms in Schultz et al. shows an increase in the mean reflectivity profile and mixed phase echo volume during the 10 minutes prior to the lightning jump. Limited dual-Doppler results show that the largest lightning jumps are well correlated in time with increases in updraft strength/volume and precipitation ice mass production; however, the smaller magnitude lightning jumps appear to have more subtle relationships to updraft and ice mass characteristics.

Schultz, Christopher J.↗
NASA NTRS2004

Accuracy and Precision in the Southern Hemisphere Additional Ozonesondes (SHADOZ) Dataset in Light of the JOSIE-2000 Results

Since 1998 the Southern Hemisphere ADditional OZonesondes (SHADOZ) project has provided over 2000 ozone profiles over eleven southern hemisphere tropical and subtropical stations. Balloon-borne electrochemical concentration cell (ECC) ozonesondes are used to measure ozone. The data are archived at: &ttp://croc.gsfc.nasa.gov/shadoz>. In analysis of ozonesonde imprecision within the SHADOZ dataset, Thompson et al. [JGR, 108,8238,20031 we pointed out that variations in ozonesonde technique (sensor solution strength, instrument manufacturer, data processing) could lead to station-to-station biases within the SHADOZ dataset. Imprecisions and accuracy in the SHADOZ dataset are examined in light of new data. First, SHADOZ total ozone column amounts are compared to version 8 TOMS (2004 release). As for TOMS version 7, satellite total ozone is usually higher than the integrated column amount from the sounding. Discrepancies between the sonde and satellite datasets decline two percentage points on average, compared to version 7 TOMS offsets. Second, the SHADOZ station data are compared to results of chamber simulations (JOSE-2000, Juelich Ozonesonde Intercomparison Experiment) in which the various SHADOZ techniques were evaluated. The range of JOSE column deviations from a standard instrument (-10%) in the chamber resembles that of the SHADOZ station data. It appears that some systematic variations in the SHADOZ ozone record are accounted for by differences in solution strength, data processing and instrument type (manufacturer).

Witte, Jacquelyn C.↗
DOE OSTI2024

Proteogenomic characterization of difficult-to-treat breast cancer with tumor cells enriched through laser microdissection

Abstract Background Breast cancer (BC) is the most commonly diagnosed cancer and the leading cause of cancer death among women globally. Despite advances, there is considerable variation in clinical outcomes for patients with non-luminal A tumors, classified as difficult-to-treat breast cancers (DTBC). This study aims to delineate the proteogenomic landscape of DTBC tumors compared to luminal A (LumA) tumors. Methods We retrospectively collected a total of 117 untreated primary breast tumor specimens, focusing on DTBC subtypes. Breast tumors were processed by laser microdissection (LMD) to enrich tumor cells. DNA, RNA, and protein were simultaneously extracted from each tumor preparation, followed by whole genome sequencing, paired-end RNA sequencing, global proteomics and phosphoproteomics. Differential feature analysis, pathway analysis and survival analysis were performed to better understand DTBC and investigate biomarkers. Results We observed distinct variations in gene mutations, structural variations, and chromosomal alterations between DTBC and LumA breast tumors. DTBC tumors predominantly had more mutations inTP53,PLXNB3, Zinc finger genes, and fewer mutations inSDC2,CDH1,PIK3CA,SVIL, andPTEN. Notably, Cytoband 1q21, which contains numerous cell proliferation-related genes, was significantly amplified in the DTBC tumors. LMD successfully minimized stromal components and increased RNA–protein concordance, as evidenced by stromal score comparisons and proteomic analysis. Distinct DTBC and LumA-enriched clusters were observed by proteomic and phosphoproteomic clustering analysis, some with survival differences. Phosphoproteomics identified two distinct phosphoproteomic profiles for high relapse-risk and low relapse-risk basal-like tumors, involving several genes known to be associated with breast cancer oncogenesis and progression, includingKIAA1522,DCK,FOXO3,MYO9B,ARID1A,EPRS,ZC3HAV1, andRBM14. Lastly, an integrated pathway analysis of multi-omics data highlighted a robust enrichment of proliferation pathways in DTBC tumors. Conclusions This study provides an integrated proteogenomic characterization of DTBC vs LumA with tumor cells enriched through laser microdissection. We identified many common features of DTBC tumors and the phosphopeptides that could serve as potential biomarkers for high/low relapse-risk basal-like BC and possibly guide treatment selections.

Oncology↗
NASA NTRS1974

Rapid variations of balmer line strengths in the spectra of Be stars

Low resolution photoelectric spectrophotometric measurements of the first four members of the Balmer series in the spectra of one Be and five Be (shell) stars were obtained with the 92-cm telescope and image dissecting scanner. Equivalent widths were computed for each observation, and their standard deviations from the mean values were examined. Results indicate that in three of the program stars, at least one of the Balmer lines shows significant fluctuations in equivalent width. These fluctuations amount to a few per cent of total line strength and the time scales appear to be on the order of three to thirty minutes. The fluctuations are not always present in a given star, indicating that the mechanism producing them may not be continuous. The noncontinuous and nonperiodic nature of the variations, along with their short time scale suggest some form of flare-like or shock origin for the phenomenon.

Mcbeath, K. B.↗