Search NASA⌕ Search

SEARCH · Search NASA

Results for “UMAS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Angular Resolution of an EAS Array for Gamma Ray Astronomy at Energies Greater Than 5 x 10 (13) Ev

A 24 detector extensive air shower array is being operated at Ootacamund (2300 m altitude, 11.4 deg N latitude) in southern India for a study of arrival directions of showers of energies greater than 5 x 10 to the 13th power eV. Various configurations of the array of detectors have been used to estimate the accuracy in determination of arrival angle of showers with such an array. These studies show that it is possible to achieve an angular resolution of better than 2 deg with the Ooty array for search for point sources of Cosmic gamma rays at energies above 5 x 10 to the 13th power eV.

Apte, A. R.↗
NASA NTRS2002

Photoevaporation of Clumps in Photodissociation Regions

We present the results of an investigation of the effects of Far Ultraviolet (FUV) radiation (6.0eV < hv < 13.6eV) from hot early type OB stars on clumps in star-forming molecular clouds. Clumps in FUV-illuminated regions (or photodissociation regions or PDRs) undergo external heating and photodissociation as they are exposed to the FUV field, resulting in a loss of cold, molecular lump mass as it is converted to warm atomic gas. The heating, if rapid, creates strong photoevaporative mass flows off the clump surfaces, and drives shocks into the clumps, compressing them to high densities. The clumps lose mass on relatively short timescales. The evolution of an individual clump is found to be sensitive to three dimensionless parameters: Nc0, the ratio of the initial column density of the clump to the column N(0) approx. 10(exp 21) cm(exp -2) of a warm FUV-heated surface region; upsilon, the ratio of the sound speed in the heated surface to that in the cold clump material: and t(FUV)t(c), the ratio of the "turn-on time" t(FUV) of the heating flux on a clump to its initial sound crossing-time t(c). The evolution also depends on whether a confining interclump medium exists, or whether the interclump region has negligible pressure, as is the case for turbulence-generated clumps. In this paper, we use spherical 1-D numerical hydrodynamic models as well as approximate analytical models to study the dependence of clump photoevaporation on the physical parameters of the clump, and to derive the dynamical evolution, mass loss rates and photoevaporative timescales of a clump for a variety of astrophysical situations. Turbulent clumps evolve so that their column densities are equal to a critical value determined by the local FUV field, and typically have short photo evaporation timescales, approx. 10(exp 4-5) years for a 1 M(solar mass) clump in a typical star-forming region (Nc0 = 10, upsilon = 10). Clumps with insufficient magnetic pressure support, and in strong FUV fields may be driven to collapse by the compressional effect of converging shock waves. We also estimate the rocket effect on photoevaporating clumps and find that it is significant only for the smallest clumps, with sizes much less than the extent of the PDR itself. Clumps that are confined by all interclump medium may either get completely photoevaporated, or may preserve a shielded core with a warm, dissociated, protective shell that, absorbs the incident FUV flux. We compare our results with observations of some well studied PDRs: the Orion Bar, M17SW NGC 2023 and the Rosette Nebula. The data are consistent with both interpretations of clump origin. turbulence and pressure confinement, with a slight indication for favouring the turbulent model for clumps over pressure-confined

Gorti, Uma↗
NASA NTRS2005

Titania Deposition on PMR-15

The formation, degree of crystallinity and adherence of dense titania (TiO2) thin film coatings on a high-temperature polyimide resin (PMR-15) can be influenced by the chemical composition of the polymer surface. Furthermore, solution deposition conditions can be adjusted to provide additional control over the morphology and crystallinity of the titania films. Recipes for solution-based titania deposition that used a slowly-hydrolyzing titanium fluoride salt in the presence of boric acid as a fluoride scavenger allowed growth of films up to 750 nm thick in 22 h. By adjusting solution pH and temperature, either amorphous titania or oriented crystalline anatase films could be formed. Surface sulfonate groups enhance the adhesion of solution-deposited oxide thin film coatings. While most sulfonation procedures severely damaged the PMR-15 surface, the use of chlorosulfonic acid followed by hydrolysis of the installed chlorosulfonyl groups provided effective surface sulfonation without significant surface damage. In some cases, the oxide deposition solution caused partial hydrolysis of the polymer surface, which itself was sufficient to allow adhesion of the titania film through chelation of titanium ions by exposed benzoic acid groups on the polymer surface.

Meador, Mary B.↗
NASA NTRS2010

Short- and Long-Timescale Thermospheric Variability as Observed from OI 630.0 nm Dayglow Emissions from Low Latitudes

We carried out high-cadence (5 min) and high-spatial resolution (2deg magnetic latitude) observations of daytime OI 630.0 nm airglow emission brightness from a low-latitude station to understand the behavior of neutral dynamics in the daytime. The results indicate that the wave periodicities of 12.20 min, and 2 h exist over a wide spatial range of around 8deg-12deg magnetic latitudes. The 20.80 min periodicities in the dayglow seem to appear more often in the measurements closer to the magnetic equator and not at latitudes farther away. Further, periodicities in that range are found to be frequent in the variations of the equatorial electrojet (EEJ) strength as well. We show that wave periodicities due to the neutral dynamics, at least until around 8deg magnetic latitude, are influenced by those that affect the EEJ strength variation as well. Furthermore, the average daily OI 630.0 nm emission brightness over 3 months varied in consonance with that of the sunspot numbers indicating a strong solar influence on the magnitudes of dayglow emissions.

Pallamraju, Duggirala↗
NASA NTRS2010

Effect of an X-Class Solar Flare on the OI 630 nm Dayglow Emissions

We present a striking event that shows a prompt effect of an X-class solar flare (X6.2/3B) in the neutral optical dayglow emissions. This flare occurred on 13 December 2001 at 1424 UT and peaked at 1430 UT. The peak-to pre-flare X-ray intensity ratio as observed by GOES-10 was greater than 300 and the EUV flux observed by SEM/SOHO was greater by around 60%. As a response to this flare, the daytime redline (OI 630 nm) column integrated emission intensity measured from Carmen Alto (23.16degS, 70.66degW), in Chile, showed a prompt increase of around 50%. Our results show that this prompt enhancement in the thermospheric dayglow seems to be caused mainly due to an increase in photoelectrons due to a sudden increase in the solar EUV flux associated with this flare.

Das, Uma↗
NASA NTRS2011

Short- and Long-Timescale Thermospheric Variability as Observed from OI 630.0 nm Dayglow Emissions from Low Latitudes

We carried out high-cadence (5 min) and high-spatial resolution (2deg magnetic latitude) observations of daytime OI 630.0 nm airglow emission brightness from a low-latitude station to understand the behavior of neutral dynamics in the daytime. The results indicate that the wave periodicities of 12.20 min, and 2 h exist over a wide spatial range of around 8deg-12deg magnetic latitudes. The 20.80 min periodicities in the dayglow seem to appear more often in the measurements closer to the magnetic equator and not at latitudes farther away. Further, periodicities in that range are found to be frequent in the variations of the equatorial electrojet (EEJ) strength as well. We show that wave periodicities due to the neutral dynamics, at least until around 8deg magnetic latitude, are influenced by those that affect the EEJ strength variation as well. Furthermore, the average daily OI 630.0 nm emission brightness over 3 months varied in consonance with that of the sunspot numbers indicating a strong solar influence on the magnitudes of dayglow emissions.

Pallamraju, Duggirala↗
NASA NTRS2012

Dynamics of Aboveground Phytomass of the Circumpolar Arctic Tundra During the Past Three Decades

Numerous studies have evaluated the dynamics of Arctic tundra vegetation throughout the past few decades, using remotely sensed proxies of vegetation, such as the normalized difference vegetation index (NDVI). While extremely useful, these coarse-scale satellite-derived measurements give us minimal information with regard to how these changes are being expressed on the ground, in terms of tundra structure and function. In this analysis, we used a strong regression model between NDVI and aboveground tundra phytomass, developed from extensive field-harvested measurements of vegetation biomass, to estimate the biomass dynamics of the circumpolar Arctic tundra over the period of continuous satellite records (1982-2010). We found that the southernmost tundra subzones (C-E) dominate the increases in biomass, ranging from 20 to 26%, although there was a high degree of heterogeneity across regions, floristic provinces, and vegetation types. The estimated increase in carbon of the aboveground live vegetation of 0.40 Pg C over the past three decades is substantial, although quite small relative to anthropogenic C emissions. However, a 19.8% average increase in aboveground biomass has major implications for nearly all aspects of tundra ecosystems including hydrology, active layer depths, permafrost regimes, wildlife and human use of Arctic landscapes. While spatially extensive on-the-ground measurements of tundra biomass were conducted in the development of this analysis, validation is still impossible without more repeated, long-term monitoring of Arctic tundra biomass in the field.

Arctic tundra↗
NASA NTRS2014

Implications of Arctic Sea Ice Decline for the Earth System

Arctic sea ice decline has led to an amplification of surface warming and is projected to continue to decline from anthropogenic forcing, although the exact timing of ice-free summers is uncertain owing to large natural variability. Sea ice reductions affect surface heating patterns and the atmospheric pressure distribution, which may alter midlatitude extreme weather patterns. Increased light penetration and nutrient availability during spring from earlier ice breakup enhances primary production in the Arctic Ocean and its adjacent shelf seas. Ice-obligate marine mammals may be losers, whereas seasonally migrant species may be winners from rapid sea ice decline. Tundra greening is occurring across most of the Arctic, driven primarily by warming temperatures, and is displaying complex spatial patterns that are likely tied to other factors. Sea ice changes are affecting greenhouse gas exchanges as well as halogen chemistry in the Arctic. This review highlights the heterogeneous nature of Arctic change, which is vital for researchers to better understand.

Decline↗
NASA NTRS2017

Changing Seasonality of Panarctic Tundra Vegetation in Relationship to Climatic Variables

Potential climate drivers of Arctic tundra vegetation productivity are investigated to understand recent greening and browning trends documented by maximum normalized difference vegetation index (NDVI) (MaxNDVI) and time-integrated NDVI (TI-NDVI) for 19822015. Over this period, summer sea ice has continued to decline while oceanic heat content has increased. The increases in summer warmth index (SWI) and NDVI have not been uniform over the satellite record. SWI increased from 1982 to the mid-1990s and remained relatively flat from 1998 onwards until a recent upturn. While MaxNDVI displays positive trends from 19822015, TI-NDVI increased from 1982 until 2001 and has declined since. The data for the first and second halves of the record were analyzed and compared spatially for changing trends with a focus on the growing season. Negative trends for MaxNDVI and TI-NDVI were more common during 19992015 compared to 19821998.

sea ice↗
NASA NTRS2014

Photoevaporation and the Dispersal of Disks

Disk disperse in a few million years, before which they must form planets. Photoevaporation and viscosity are mainly responsible for disk dispersal. EUV, FUV and X-rays have all been suggested as photoevaporation agents, disk evolutionary scenarios and predicted mass loss rates in each case differ. Stellar mass and radiation field, disk properties, magnitude of viscosity, and dust evolution all play significant roles in determining the evolution of the disk and its lifetime. Observational diagnostics of photoevaperative flows include [Nell] and perhaps [OI]. These are at present inconclusive and better diagnostics are needed.

Stellar accretion↗
NASA NTRS2021

Climate Drivers of Arctic Tundra Variability and Change Using an Indicators Framework

This study applies an indicators framework to investigate climate drivers of tundra vegetation trends and variability over the 1982–2019 period. Previously known indicators relevant for tundra productivity (summer warmth index (SWI), coastal spring sea-ice (SI) area, coastal summer open-water (OW)) and three additional indicators (continentality, summer precipitation, and the Arctic Dipole (AD): second mode of sea level pressure variability) are analyzed with maximum annual Normalized Difference Vegetation Index (MaxNDVI) and the sum of summer bi-weekly (time-integrated) NDVI (TI-NDVI) from the Advanced Very High Resolution Radiometer time-series. Climatological mean, trends, and correlations between variables are presented. Changes in SI continue to drive variations in the other indicators. As spring SI has decreased, summer OW, summer warmth, MaxNDVI, and TI-NDVI have increased. However, the initial very strong upward trends in previous studies for MaxNDVI and TI-NDVI are weakening and becoming spatially and temporally more variable as the ice retreats from the coastal areas. TI-NDVI has declined over the last decade particularly over High Arctic regions and southwest Alaska. The continentality index (CI) (maximum minus minimum monthly temperatures) is decreasing across the tundra, more so over North America than Eurasia. The relationship has weakened between SI and SWI and TI-NDVI, as the maritime influence of OW has increased along with total precipitation. The winter AD is correlated in Eurasia with spring SI, summer OW, MaxNDVI, TI-NDVI, the CI and total summer precipitation. This winter connection to tundra emphasizes the role of SI in driving the summer indicators. The winter (DJF) AD drives SI variations which in turn shape summer OW, the atmospheric SWI and NDVI anomalies. The winter and spring indicators represent potential predictors of tundra vegetation productivity a season or two in advance of the growing season.

Uma S. Bhatt↗
NASA NTRS2023

Oregon Coast Range Ecological Conservation: Mapping Recent Logging Within Drinking Watersheds of Oregon’s Coastal Range to Support Future Resource Management Policies

Logging operations are widespread across the Oregon Coast Range and conventional logging practices pose a risk of contamination to surface water quality. The NASA DEVELOP Oregon Coast Ecological Conservation team partnered with nonprofit Oregon Wild to quantify the extent of clearcutting and commercial thinning in 80 Coast Range drinking watersheds between 2000 and 2022. This project used all available Landsat data from 1997 through June 2023 in Google Earth Engine. Sensors used include Landsat 5 Thematic Mapper, Landsat 7 Enhanced Thematic Mapper Plus, Landsat 8 Operational Land Imager, and Landsat 9 Operational Land Imager-2. The Continuous Change Detection and Classification (CCDC) algorithm was used with Landsat observations to identify clearcutting patches. Percent change in summer median Landsat Normalized Difference Vegetation Index (NDVI) images were used to identify areas of forest disturbance including commercial thinning. The team concluded that logging, including both clearcutting and commercial thinning, impacted 31% of forested area in drinking watersheds and the intensity of logging remained consistent from year to year. Clearcutting occurred primarily on private land while commercial thinning occurred primarily on state and federal lands. This study showed that CCDC effectively identifies clearcutting, and percent change in NDVI successfully identifies disturbances including commercial thinning. Key constraints included the lack of field validation data and the inability to attribute disturbances to logging with certainty. Ultimately, this study identified the drinking watersheds and communities most likely to be impacted by logging activity. These results can inform legislation aimed at balancing the commercial and environmental benefits of forestlands.

Logging↗