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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

A discussion on mobile satellite system and the myths of CDMA and diversity revealed

The paper explores the myths and facts surrounding: link margins and constellation designs; the use of satellite diversity in a mobile satellite channel; trade-offs in multiple access technique. Different satellite constellations are presented, which are comparable with those used by the big LEO proponents, with the associated trade-offs in the system design. Propagation data and results from various narrowband and wideband measurement campaigns are used to illustrate the expected differences in service performance.

Hart, Nicholas↗
NASA NTRS1997

Increasing Mathematics and Science Achievement for Culturally Diverse Students through Teaching Training

The purpose of this proposal was to field test and evaluate a Teacher Training program that would prepare teachers to increase the motivation and achievement of culturally diverse students in the areas of science and mathematics. Designed as a three year program, this report covers the first two years of the training program at the Ronald McNair School in the Ravenswood School district, using the resources of the NASA Ames Research Center and the California Framework for Mathematics and Science.

Mahon, Lee↗
NASA NTRS1999

Workshop on New Views of the Moon 2: Understanding the Moon Through the Integration of Diverse Datasets

This volume contains abstracts that have been accepted for presentation at the Workshop on New Views of the Moon II: Understanding the Moon Through the Integration of Diverse Datasets, September 22-24, 1999, in Flagstaff, Arizona. The workshop conveners are Lisa Gaddis (U.S. Geological Survey, Flagstaff and Charles K. Shearer (University of New Mexico). Color versions of some of the images contained in this volume are available on the meeting Web site (http://cass.jsc.nasa.gov/meetings/moon99/pdf/program.pdf).

Source record↗
NASA NTRS2000

Special Effects: Antenna Wetting, Short Distance Diversity and Depolarization

The Advanced Communication Technology Satellite (ACTS) communications system operates in the Ka frequency band. ACTS uses multiple, hopping, narrow beams and very small aperture terminal (VSAT) technology to establish a system availability of 99.5% for bit-error-rates of 5 x 10(exp -7) Or better over the continental United States. In order maintain this minimum system availability in all US rain zones, ACTS uses an adaptive rain fade compensation protocol to reduce the impact of signal attenuation resulting from propagation effects. The purpose of this paper is to present the results of system and sub-system characterizations considering the statistical effects of system variances due to antenna wetting and depolarization effects. In addition the availability enhancements using short distance diversity in a sub-tropical rain zone are investigated.

Acosta, Roberto J.↗
NASA NTRS1997

GRB Diversity vs. Utility as Cosmological Probes

Recent detections of apparent gamma-ray burst (GRB) counterparts in optical and radio wavebands strongly favor the cosmological distance scale, at least for some GRBs, opening the possibility of GRBs serving as cosmological probes. But GRBs exhibit great diversity: in total duration; in number, width and pulse configuration; and in pulse and overall spectral evolution. However, it is possible that a portion of this behavior reflects a luminosity distribution, and possible that evolution of with cosmic time introduces dispersion into the average GRB characteristics -- issues analogous to those encountered with quasars. The temporal domain offers a rich avenue to investigate this problem. When corrected for assumed spectral redshift, time dilation of event durations, pulse widths, and intervals between pulses must yield the same time-dilation factor as a function of peak flux, or else a luminosity distribution may be the cause of observed time dilation effects. We describe results of burst analysis using an automated, Bayesian-based algorithm to determine burst temporal characteristics for different peak flux groups, and derived constraints on any physical process that would introduce a luminosity distribution.

Norris, J. P.↗
NASA NTRS1998

Modelling the Diversity of Outer Planetary Systems: Formation and Evolution - 1

The process of planetary growth is extremely complicated, involving a myriad of physical and chemical processes, many of which are poorly understood. The ultimate configuration that a planetary system attains depends upon the properties of the disk out of which it grew, of the star at the center of the disk and, at least in some cases, of the interstellar environment. However, this dependence is poorly understood. Thus, in an effort to numerically survey the possible diversity of planetary systems, we have constructed synthetic systems of giant planets and integrated their orbits to determine the dynamical lifetimes and thus the viability of these systems. Our construction algorithm begins with 110 -- 180 planetesimals located between 4 and 40 AU from a one solar mass star; most initial planetesimals have masses several tenths that of Earth. We integrate the orbits of these bodies subject to mutual gravitational perturbations and gas drag for $10^6 - 10^7$ years, merging any pair of planetesimals which passed within one-tenth of a Hill Sphere of one another and adding "gas" to embryos larger than 10 Earth masses. Use of such large planetesimal radii provided sufficient damping to prevent the system from excessive dynamical heating. Subsequently, systems were evolved without gas drag, either with the inflated radii or with more realistic radii. Systems took from a few million years to greater than ten billion years to become stable ($10^9$ years without mergers of ejections). Some of the systems produced with the inflated radii closely resemble our Solar System. Encounters in simulations using realistic radii resulted in ejections, typically leaving only a few planets per system, most of which were in highly eccentric orbits. The structure and dynamics of the resulting "stable" systems is discussed in detail in the abstract by Levison et al.

Lissauer, J. J.↗
NASA NTRS1998

Modelling the Diversity of Outer Planetary Systems

The process of planetary growth is extremely complicated, involving a myriad of physical and chemical processes, many of which are poorly understood. The ultimate configuration that a planetary system attains depends upon the properties of the disk out of which it grew, of the star at the center of the disk and, at least in some cases, of the interstellar environment. In an effort to numerically survey the possible diversity of planetary systems, we have constructed synthetic systems of giant planets and integrated their orbits to determine the dynamical lifetimes and thus the viability of these systems. Our construction algorithm begins with 110 -- 180 planetesimals located between 4 and 40 AU from a one solar mass star; most initial planetesimals have masses several tenths that of Earth. We integrate the orbits of these bodies subject to mutual gravitational perturbations and -as drag for 10(exp 6) - 10(exp 7) years, merging any pair of planetesimals which pass within one-tenth of a Hill Sphere of one another and adding "gas" to embryos larger than 10 Earth masses. Use of such large planetesimal radii provided sufficient damping to prevent the system from excessive dynamical heating. Subsequently, systems were evolved without gas drag, either with the enlarged radii or with more realistic radii. Systems took from a few million years to greater than ten billion years to become stable (10(exp 9) years without mergers of ejections). Some of the systems produced with the enlarged radii closely resemble our outer Solar System. Many systems contained only Uranus-mass objects. Encounters in simulations using realistic radii resulted in ejections, typically leaving only a few planets per system, most of which were on very eccentric orbits. Some of the systems that we constructed were stable for at least a billion years despite undergoing macroscopic orbital changes on much shorter timescales.

Lissauer, Jack J.↗
NASA NTRS2002

The Next Generation of Space Cells for Diverse Environments

Future science, military and commercial space missions are incredibly diverse. Military and commercial missions range from large arrays of hundreds of kilowatt to small arrays of ten watts in various Earth orbits. While science missions also have small to very large power needs there are additional unique requirements to provide power for near-sun missions and planetary exploration including orbiters, landers and rovers both to the inner planets and the outer planets with a major emphasis in the near term on Mars. These mission requirements demand cells for low intensity, low temperature applications, high intensity, high temperature applications, dusty environments and often high radiation environments. This paper discusses mission requirements, the current state of the art of space solar cells, and a variety of both evolving thin-film cells as well as new technologies that may impact the future choice of space solar cells for a specific mission application.

Landis, Geoffrey A.↗
NASA NTRS2002

The Diverse Surface Compositions of the Galilean Satellites

The galilean satellites represent a diverse collection, ranging from the volcanic moon Io, with a surface that is changing yearly, to Callisto, with a dark, ancient surface overlying ice. The composition of these surfaces are also quite different due to a variety of processes and influences, including tidal heating, radiolysis, gardening, a magnetic field (Ganymede), and meteoritic infall. Io's surface contains large quantities of sulfur dioxide (SO2) and colorful sulfur allotropes, both originating in plumes and flows from the tidally driven volcanoes. A broad, 1-micron band is found at high latitudes and may be due to absorption by long-chain sulfur polymers produced by SO2 radiolysis, although iron and iron sulfide compounds are candidates. An unidentified 3.15 micron absorber is equatorially distributed while a 4.62 micron band, perhaps due to a sulfate compound, exhibits a non-uniform distribution. Hot spots are generally dark, and some exhibit negative reflectance slopes (i.e., blue). The composition of these lavas has not been established spectroscopically, but the high temperatures of some volcanoes suggest ultramafic silicates or perhaps more refractory material such as oxides.

Carlson, R. W.↗
NASA NTRS2002

Toward a Comprehensive Carbon Budget for North America: Potential Applications of Adjoint Methods with Diverse Datasets

A detailed mechanistic understanding of the sources and sinks of CO2 will be required to reliably predict future COS levels and climate. A commonly used technique for deriving information about CO2 exchange with surface reservoirs is to solve an "inverse problem," where CO2 observations are used with an atmospheric transport model to find the optimal distribution of sources and sinks. Synthesis inversion methods are powerful tools for addressing this question, but the results are disturbingly sensitive to the details of the calculation. Studies done using different atmospheric transport models and combinations of surface station data have produced substantially different distributions of surface fluxes. Adjoint methods are now being developed that will more effectively incorporate diverse datasets in estimates of surface fluxes of CO2. In an adjoint framework, it will be possible to combine CO2 concentration data from long-term surface monitoring stations with data from intensive field campaigns and with proposed future satellite observations. A major advantage of the adjoint approach is that meteorological and surface data, as well as data for other atmospheric constituents and pollutants can be efficiently included in addition to observations of CO2 mixing ratios. This presentation will provide an overview of potentially useful datasets for carbon cycle research in general with an emphasis on planning for the North American Carbon Project. Areas of overlap with ongoing and proposed work on air quality/air pollution issues will be highlighted.

Andrews, A.↗
NASA NTRS2004

Variation in sulfide tolerance of photosystem II in phylogenetically diverse cyanobacteria from sulfidic habitats

Physiological and molecular phylogenetic approaches were used to investigate variation among 12 cyanobacterial strains in their tolerance of sulfide, an inhibitor of oxygenic photosynthesis. Cyanobacteria from sulfidic habitats were found to be phylogenetically diverse and exhibited an approximately 50-fold variation in photosystem II performance in the presence of sulfide. Whereas the degree of tolerance was positively correlated with sulfide levels in the environment, a strain's phenotype could not be predicted from the tolerance of its closest relatives. These observations suggest that sulfide tolerance is a dynamic trait primarily shaped by environmental variation. Despite differences in absolute tolerance, similarities among strains in the effects of sulfide on chlorophyll fluorescence induction indicated a common mode of toxicity. Based on similarities with treatments known to disrupt the oxygen-evolving complex, it was concluded that sulfide toxicity resulted from inhibition of the donor side of photosystem II.

Phylogeny↗
NASA NTRS2002

Thin filament diversity and physiological properties of fast and slow fiber types in astronaut leg muscles

Slow type I fibers in soleus and fast white (IIa/IIx, IIx), fast red (IIa), and slow red (I) fibers in gastrocnemius were examined electron microscopically and physiologically from pre- and postflight biopsies of four astronauts from the 17-day, Life and Microgravity Sciences Spacelab Shuttle Transport System-78 mission. At 2.5-microm sarcomere length, thick filament density is approximately 1,012 filaments/microm(2) in all fiber types and unchanged by spaceflight. In preflight aldehyde-fixed biopsies, gastrocnemius fibers possess higher percentages (approximately 23%) of short thin filaments than soleus (9%). In type I fibers, spaceflight increases short, thin filament content from 9 to 24% in soleus and from 26 to 31% in gastrocnemius. Thick and thin filament spacing is wider at short sarcomere lengths. The Z-band lattice is also expanded, except for soleus type I fibers with presumably stiffer Z bands. Thin filament packing density correlates directly with specific tension for gastrocnemius fibers but not soleus. Thin filament density is inversely related to shortening velocity in all fibers. Thin filament structural variation contributes to the functional diversity of normal and spaceflight-unloaded muscles.

Non-NASA Center↗
NASA NTRS1987

Phylogenetic diversity and position of the genus Campylobacter

RNA sequence analysis has been used to examine the phylogenetic position and structure of the genus Campylobacter. A complete 5S rRNA sequence was determined for two strains of Campylobacter jejuni and extensive partial sequences of the 16S rRNA were obtained for several strains of C. jejuni and Wolinella succinogenes. In addition limited partial sequence data were obtained from the 16S rRNAs of isolates of C. coli, C. laridis, C. fetus, C. fecalis, and C. pyloridis. It was found that W. succinogenes is specifically related to, but not included, in the genus Campylobacter as presently constituted. Within the genus significant diversity was noted. C. jejuni, C. coli and C. laridis are very closely related but the other species are distinctly different from one another. C. pyloridis is without question the most divergent of the Campylobacter isolates examined here and is sufficiently distinct to warrant inclusion in a separate genus. In terms of overall position in bacterial phylogeny, the Campylobacter/Wolinella cluster represents a deep branching most probably located within an expanded version of the Division containing the purple photosynthetic bacteria and their relatives. The Campylobacter/Wolinella cluster is not specifically includable in either the alpha, beta or gamma subdivisions of the purple bacteria.

NASA Discipline Exobiology↗
NASA NTRS1995

Diverse Thermus species inhabit a single hot spring microbial mat

Through an effort to characterize aerobic chemoorganotrophic bacteria in the Octopus Spring cyano-bacterial mat community, we cultivated four Thermus isolates with unique 16S rRNA sequences. Isolates clustered within existing Thermus clades, including those containing Thermus ruber, Thermus aquaticus, and a subgroup closely related to T. aquaticus. One Octopus Spring isolate is nearly identical (99.9% similar) to isolates from Iceland, and two others are closely related to a T. ruber isolated from Russia. Octopus Spring isolates similar to T. aquaticus and T. ruber exhibited optimal growth rates at high (65-70 degrees C) and low (50 degrees C) temperatures, respectively, with the most abundant species best adapted to the temperature of the habitat (50-55 degrees C). Our results display a diversity of Thermus genotypes defined by 16S rRNA within one hot spring microbial community. We suggest that specialization to temperature and perhaps other local environmental features controls the abundance of Thermus populations.

Non-NASA Center↗
NASA NTRS1991

Phylogenetic diversity in the genus Bacillus as seen by 16S rRNA sequencing studies

Comparative sequence analysis of 16S ribosomal (r)RNAs or DNAs of Bacillus alvei, B. laterosporus, B. macerans, B. macquariensis, B. polymyxa and B. stearothermophilus revealed the phylogenetic diversity of the genus Bacillus. Based on the presently available data set of 16S rRNA sequences from bacilli and relatives at least four major "Bacillus clusters" can be defined: a "Bacillus subtilis cluster" including B. stearothermophilus, a "B. brevis cluster" including B. laterosporus, a "B. alvei cluster" including B. macerans, B. maquariensis and B. polymyxa and a "B. cycloheptanicus branch".

NASA Discipline Number 52-30↗
NASA NTRSDate not supplied

Mobile Router Testing with Diverse RF Communications Links

This is a short report on demonstrations using Mobile IP and several diverse physical communications links to connect a mobile network to a fixed IPv4 internet. The first section is a description of the equipment used, followed by descriptions of the tests, the theoretical results, and finally conclusions and the actual data.

David Brooks↗
NASA NTRS1999

The effects of UV radiation A and B on diurnal variation in photosynthesis in three taxonomically and ecologically diverse microbial mats

Photosynthetic primary production, the basis of most global food chains, is inhibited by UV radiation. Evaluating UV inhibition is therefore important for assessing the role of natural levels of UV radiation in regulating ecosystem behavior as well as the potential impact of stratospheric ozone depletion on global ecosystems. As both photosynthesis and UV fluxes are subject to diurnal variations, we examined the diurnal variability of the effect of UV radiation on photosynthesis in three diverse algal mats. In one of the mats (Cyanidium caldarium) a small mean decrease in primary productivity over the whole day occurred when both UVA and UVB were screened out. In two of the mats (Lyngbya aestuarii and Zygogonium sp.) we found a mean increase in the total primary productivity over the day when UVB alone was screened and a further increase when UVA and UVB were both screened out. Variations in the effects of UV radiation were found at different times of the day. This diurnal variability may be because even under the same solar radiation flux, there are different factors that may control photosynthetic rate, including nutritional status and other physiological processes in the cell. The results show the importance of assessing the complete diurnal productivity. For some of the time points the increase in the mean was still within the standard deviations in primary productivity, illustrating the difficulty in dissecting UV effects from other natural variations.

Ultraviolet Rays↗