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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Diversity and Distribution of Hydrocarbon-Degrading Genes in the Cold Seeps from the Mediterranean and Caspian Seas

Marine cold seeps are unique ecological niches characterized by the emergence of hydrocarbons, including methane, which fosters diverse microbial communities. This study investigates the diversity and distribution of hydrocarbon-degrading genes and organisms in sediments from the Caspian and Mediterranean Seas, utilizing 16S rRNA and metagenomic sequencing to elucidate microbial community structure and functional potential. Our findings reveal distinct differences in hydrocarbon degrading gene profiles between the two seas, with pathways for aerobic and anaerobic hydrocarbon degradation co-existing in sediments from both basins. Aerobic pathways predominate in the surface sediments of the Mediterranean Sea, while anaerobic pathways are favored in the surface sediments of the anoxic Caspian Sea. Additionally, sediment depths significantly influence microbial diversity, with variations in gene abundance and community composition observed at different depths. Aerobic hydrocarbon-degrading genes decrease in diversity with depth in the Mediterranean Sea, whereas the diversity of aerobic hydrocarbon-degrading genes increases with depth in the Caspian Sea. These results enhance our understanding of microbial ecology in cold seep environments and have implications for bioremediation practices targeting hydrocarbon pollutants in marine ecosystems.

Microbiology↗
NASA NTRS1984

Instantaneous diversity gain in 10-30 GHz satellite systems

As usually defined, diversity gain is a statistical measure which conveys little or no information about the instantaneous behavior of site-diversity reception in a satellite communications system. A new quantity called instantaneous diversity gain is introduced and some measurements of it from an 11.6 GHz low-angle two-site downlink are presented. It is shown how instantaneous diversity gain is related to system reliability and some results are presented which indicate that designs based on statistical diversity gain will achieve their intended reliability levels.

Towner, G. C., III↗
NASA NTRS1991

Software fault tolerance using data diversity

Research on data diversity is discussed. Data diversity relies on a different form of redundancy from existing approaches to software fault tolerance and is substantially less expensive to implement. Data diversity can also be applied to software testing and greatly facilitates the automation of testing. Up to now it has been explored both theoretically and in a pilot study, and has been shown to be a promising technique. The effectiveness of data diversity as an error detection mechanism and the application of data diversity to differential equation solvers are discussed.

Knight, John C.↗
NASA NTRS1992

Diversity imaging techniques in lidar

Diversity imaging techniques have been successfully employed in conventional microwave range-Doppler imaging radars to obtain high resolution images of both natural and man-made targets. These techniques allow microwave radars to achieve image resolution which would otherwise require excessively large antennas. Recent advances in coherent laser radar techniques and signal processing have led to the development of range-Doppler imaging laser radars. While much of the theory and signal processing techniques used in microwave radars can be brought to bear on laser radars, the significant difference in wavelength results in issues peculiar to laser radar systems. Both the fundamental concepts and specific applications of diversity imaging techniques applied to laser radar imaging systems will be discussed. Angle, frequency, and bistatic angle degrees of freedom can be employed in a coherent laser radar imaging system to achieve image resolution which exceeds the traditional Rayleigh criterion associated with the receive aperture. In diversity imaging, angle and frequency degrees of freedom can be used to synthesize an effective aperture providing range and Doppler target information. The ability to vary the bistatic angle provides an additional means of synthesizing an effective aperture. Both simulated and experimentally obtained laser radar images of spinning and/or tumbling objects utilizing both angular and frequency diversity will be presented. In coherent laser radar systems, image quality can be dominated by laser speckle effects. In particular, the signal-to-noise ratio (SNR) of a coherent laser radar image is at most unity in the presence of fully developed speckle. Diversity techniques can be utilized to improve the image SNR; simple incoherent averaging of images utilizing temporal and polarization degrees of freedom can significantly improve image SNR. Both the SNR and image resolution (as defined by the synthetic aperture) contribute to image quality. The relationship between the available degrees of freedom and image quality are discussed.

Schultz, K. I.↗
NASA NTRS1993

Site diversity for satellite earth terminals and measurements at 28 GHz

This paper reviews site diversity concepts and models and presents the results of a site diversity experiment, in which radiometers were used to measure attenuation on earth-space paths, performed at Columbus, Ohio, for a period of one year. Attenuation statistics are presented first in the form of the joint probability density function of attenuation at the two sites. From these are derived the cumulative two-dimensional distribution of attenuation at both sites, the cumulative distribution of attenuation at each site, the effective cumulative distribution of attenuation for a diversity system that always switches to the better of two signals, and the effective cumulative distribution of attenuation for a system with maximal-ratio signal combining. The switched-system diversity gain is compared with Hodge's predictive model, and the diversity improvement is compared with Boithias' model. Fade-duration and interfade-interval statistics are also presented for each site and for systems that employ switching and maximal-ratio combining. Rain-rate and interrainfall interval statistics are also included.

Lin, Kuan-Ting↗
NASA NTRS1995

Evaluation of phase-diversity techniques for solar-image restoration

Phase-diversity techniques provide a novel observational method for overcomming the effects of turbulence and instrument-induced aberrations in ground-based astronomy. Two implementations of phase-diversity techniques that differ with regard to noise model, estimator, optimization algorithm, method of regularization, and treatment of edge effects are described. Reconstructions of solar granulation derived by applying these two implementations to common data sets are shown to yield nearly identical images. For both implementations, reconstructions from phase-diverse speckle data (involving multiple realizations of turbulence) are shown to be superior to those derived from conventional phase-diversity data (involving a single realization). Phase-diverse speckle reconstructions are shown to achieve near diffraction-limited resolution and are validated by internal and external consistency tests, including a comparison with a reconstruction using a well-accepted speckle-imaging method.

Paxman, Richard G.↗
NASA NTRS1998

Analysis of Land-Use Effects on Landscape Patterns and Biological Diversity in Pacific North Forests: 1972-1991

While there is widespread recognition of the importance of preserving biological diversity there is considerable uncertainty about how to map current patterns of diversity and monitor changes through time. Ground-based approaches are impractical for examining regional patterns of biological diversity, for monitoring change, and they may actually overlook important higher-order phenomena. Thus, there is a critical need for innovative techniques to examine land-use effects on biological diversity at the landscape and regional scales. In this project, we have used satellite-based remote sensing to examine land-use effects on forest ecosystems in the Pacific NorthWest region (PNW) of the U.S.A. Rates and patterns of forest change throughout the region were quantified for the period from 1972 to 1993. This information was then used to map changes in the abundance and distribution of potential habitat for selected vertebrate species. The results of this project will be useful for identifying "keystone" stands that are important in maintaining habitat connectivity at the regional scale and for evaluating the impact of future land-use on vertebrate diversity throughout the region. The approaches developed here will also be useful in other forested regions throughout the world.

Wallin, David O.↗
NASA NTRS2010

Study of the Microbial Diversity of a Newly Discovered East Antarctic Freshwater Lake, L27C, and of a Perennially Ice-Covered Lake Untersee

The microbial communities that reside within freshwater lakes of Schirmacher and Untersee Oases in East Antarctica must cope with extreme conditions that may include cold temperature, annual freeze-thaw cycles, exposure to UV radiation, especially during the austral summer months, low light beneath thick ice-cover, followed by seasonal darkness. The objective of this study was to assess the microbial biodiversity and distribution from samples taken from two freshwater lakes (L27C and Lake Untersee) that were collected during the Tawani 2008 International Antarctic Expedition that conducted research in this region of Antarctica. L27C is a small, previously unreported lake residing 2 km WNW of Maitri Station at Schirmacher Oasis. Biodiversity and distribution of microorganisms within the lake were studied using both culture-independent and culture-dependent methodologies based upon the analysis of eubacterial 16S rRNA gene sequences. Lake Untersee, a perennially ice-covered, ultra-oligotrophic, lake in the Otto-von-Gruber-Gebirge (Gruber Mountains) of central Dronning Maud Land was also sampled and the microbial diversity was analyzed by eubacterial 16S rRNA gene sequences derived from pure cultures. Direct culturing of water samples from each lake on separate R2A growth medium exhibited a variety of microorganisms including: Janthinobacterium, Hymenobacter, Sphingamonas, Subtercola, Deinococcus, Arthrobacter, Flavobacterium, Polaromonas, Rhodoferax and Duganella. The evaluation of samples from L27C through culture-independent methodology identified a rich microbial diversity consisting of six different phyla of bacteria. The culture-independent analysis also displayed the majority of bacteria (56%) belonged to the Class gamma-proteobacteria within the phylum Proteobacteria. Within the Class gamma-proteobacteria, Acinetobacter dominated (48%) the total microbial load. Overall, L27C exhibited 7 different phyla of bacteria and 20 different genera. Statistical analysis (Shannon-Weaver Diversity Index and Simpson Diversity Index) of the biodiversity of L27C displayed a moderately rich and diverse community. Investigations of the biodiversity and distribution of microorganisms in these lakes will help further our understanding of how the physical environment impact the structure and function within these microbially dominated ecosystems.

Huang, Jonathan P.↗
NASA NTRS2012

Molecular Technique to Understand Deep Microbial Diversity

Current sequencing-based and DNA microarray techniques to study microbial diversity are based on an initial PCR (polymerase chain reaction) amplification step. However, a number of factors are known to bias PCR amplification and jeopardize the true representation of bacterial diversity. PCR amplification of the minor template appears to be suppressed by the exponential amplification of the more abundant template. It is widely acknowledged among environmental molecular microbiologists that genetic biosignatures identified from an environment only represent the most dominant populations. The technological bottleneck has overlooked the presence of the less abundant minority population, and underestimated their role in the ecosystem maintenance. To generate PCR amplicons for subsequent diversity analysis, bacterial l6S rRNA genes are amplified by PCR using universal primers. Two distinct PCR regimes are employed in parallel: one using normal and the other using biotinlabeled universal primers. PCR products obtained with biotin-labeled primers are mixed with streptavidin-labeled magnetic beads and selectively captured in the presence of a magnetic field. Less-abundant DNA templates that fail to amplify in this first round of PCR amplification are subjected to a second round of PCR using normal universal primers. These PCR products are then subjected to downstream diversity analyses such as conventional cloning and sequencing. A second round of PCR amplified the minority population and completed the deep diversity picture of the environmental sample.

Vaishampayan, Parag A.↗
NASA NTRS2012

Two Years of Site Diversity Measurements in Guam, USA

As NASA communication networks upgrade to higher frequencies, such as Ka-Band, atmospherically induced attenuation can become significant. This attenuation is caused by rain, clouds and atmospheric gases (oxygen and water vapor), with rain having the most noticeable effects. One technique to circumvent the increase in attenuation is to operate two terminals separated by a distance that exceeds the average rain cell size. The fact that rain cells are of finite size can then be exploited by rerouting the signal to the terminal with the strongest link. This technique, known as site diversity, is best suited for climates that have compact (less than 2km) and intense rain cells such as in Guam. In order to study the potential diversity gain at the Tracking and Data Relay Satellite (TDRS) Remote Ground Terminal (GRGT) complex in Guam a site test interferometer (STI) was installed in May of 2010. The STI is composed of two terminals with a 900m baseline that observe the same unmodulated beacon signal broadcast from a geostationary satellite (e.g., UFO 8). The potential site diversity gain is calculated by measuring the difference in signal attenuation seen at each terminal. Over the two years of data collection the cumulative distribution function (CDF) of the site diversity gain shows a better than 3 dB improvement for 90% of the time over standard operation. These results show that the use of site diversity in Guam can be very effective in combating rain fades.

Acosta, Roberto J.↗
NASA NTRS2018

The Diversity of Carbon in Cometary Refractory Dust Particles

When comparing the dark icy surfaces of outer solar system small bodies and the composition of carbonaceous chondrites derived from dark asteroids we find a significant discrepancy in the assessed amounts of elemental carbon: up to 80% amorphous carbon is used to model the dark surfaces of Kuiper Belt Objects and Centaurs whereas at most 5% of elemental carbon is found in carbonaceous chondrites. If we presume that regimes of comet nuclei formation are analogous to disk regimes where other outer solar system ice-rich bodies formed then we can turn to comet dust to gain insights into the diversity in the concentration and forms of carbon available in the outer disk. Comet dust offers important insights into the diversity in the amounts and forms of carbon that were incorporated into aggregate dust particles in the colder parts of the protoplanetary disk out of which comet nuclei accreted. Comet nuclei are amongst the most primitive bodies because they have remained cold and unequilibrated. Comet dust particles reveal the presence of forms of elemental carbon and of soluble and insoluble organic matter, and in a great diversity of concentrations from very little, e.g., Stardust samples of comet 81P/Wild 2, to 80% by volume for Ultra Carbonaceous Antarctic Micro Meteorites (UCAMMs). Cometary outbursts and/or jet activity also demonstrate variations in the concentration of carbon in the grains at different grain sizes within a single comet. We review the diversity of carbon-bearing dust grains in cometary samples, flyby measurements and deduced from remote-sensing to enrich the discussion about the diversity of carbonaceous matter available in the outer ice-rich disk at the time of comet nuclei formation.

Wooden, D. H.↗
NASA NTRS2017

Inter-Model Warming Projection Spread: Inherited Traits from Control Climate Diversity

Since Chaney’s report, the range of global warming projections in response to a doubling of CO2—from 1.5 °C to 4.5 °C or greater—remains largely unscathed by the onslaught of new scientific insights. Conventional thinking regards inter-model differences in climate feedbacks as the sole cause of the warming projection spread (WPS). Our findings shed new light on this issue indicating that climate feedbacks inherit diversity from the model control climate, besides the models’ intrinsic climate feedback diversity that is independent of the control climate state. Regulated by the control climate ice coverage, models with greater (lesser) ice coverage generally possess a colder (warmer) and drier (moister) climate, exhibit a stronger (weaker) ice-albedo feedback, and experience greater (weaker) warming. The water vapor feedback also inherits diversity from the control climate but in an opposite way: a colder (warmer) climate generally possesses a weaker (stronger) water vapor feedback, yielding a weaker (stronger) warming. These inherited traits influence the warming response in opposing manners, resulting in a weaker correlation between the WPS and control climate diversity. Our study indicates that a better understanding of the diversity amongst climate model mean states may help to narrow down the range of global warming projections.

Climate feedbacks↗
NASA NTRS2020

Diversity Buffers Winegrowing Regions from Climate Change Losses

Agrobiodiversity—the variation within agricultural plants, animals, and practices—is often suggested as a way to mitigate the negative impacts of climate change on crops [S. A. Wood et al., Trends Ecol. Evol. 30, 531–539 (2015)]. Recently, increasing research and attention has focused on exploiting the intraspecific genetic variation within a crop [Hajjar et al., Agric. Ecosyst. Environ. 123, 261–270 (2008)], despite few relevant tests of how this diversity modifies agricultural forecasts. Here, we quantify how intraspecific diversity, via cultivars, changes global projections of growing areas. We focus on a crop that spans diverse climates, has the necessary records, and is clearly impacted by climate change: winegrapes (predominantly Vitis vinifera subspecies vinifera). We draw on long-term French records to extrapolate globally for 11 cultivars (varieties) with high diversity in a key trait for climate change adaptation—phenology. We compared scenarios where growers shift to more climatically suitable cultivars as the climate warms or do not change cultivars. We find that cultivar diversity more than halved projected losses of current winegrowing areas under a 2 °C warming scenario, decreasing areas lost from 56 to 24%. These benefits are more muted at higher warming scenarios, reducing areas lost by a third at 4 °C (85% versus 58%). Our results support the potential of in situ shifting of cultivars to adapt agriculture to climate change—including in major winegrowing regions—as long as efforts to avoid higher warming scenarios are successful.

Morales-Castilla, Ignacio↗
DOE OSTI2025

Exploring diversion-pathway analysis of a generic molten-salt fast reactor using multiphysics informed signatures

Molten salt reactors are being explored by multiple commercial ventures due to their inherent safety features, flexibility in fuel sources, and high fuel utilization and thermal efficiency. The continual flow of fuel salt, large fissile quantities present, and ability to add or divert material due to the liquid nature introduces new challenges for international safeguards. To understand how international safeguards should be applied, it is important to capture the inherent multi-physics nature of a molten salt reactor. This work examines a generic molten salt fast reactor to understand how potential diversion scenarios would affect the concentration of radionuclides in the primary and auxiliary systems. Three types of diversion were examined: a slow drip of fuel salt, gaseous plutonium extraction, and uranium metal plating. The analysis determined that several key isotopes become statistically significant once diversion begins, indicating that detection of such diversion cases would be possible through measuring specific signatures such as gamma spectra.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Preliminary studies on diversion and misuse for TRISO-fueled heat-pipe-cooled microreactors

Microreactors are being developed by multiple reactor designers to mass-produce nuclear facilities for worldwide deployment. Including microreactors in a country’s energy portfolio introduces new concerns for international safeguards regarding the number of reactor locations. Microreactors have smaller quantities of nuclear material compared to current light-water reactors, which makes diverting enough material for clandestine purposes difficult for a single reactor. Diversion or misuse of multiple microreactors to obtain a significant quantity introduces a new acquisition pathway. This work examines diversion and misuse scenarios for a realistic heat-pipe-cooled microreactor to understand how these scenarios would effect reactor operations to determine if monitoring key parameters could reduce the burden of inspection on monitoring agencies. Here, we determined misuse caused too drastic of an effect on core operations to be a valid acquisition pathway for the realistic heat-pipe-cooled microreactor. Diversion was explored across varying levels of severity, where potential diversion scenarios could yield one significant quantity of material from between six and eleven microreactors. Through examining the critical control drum angle, excess reactivity, control drum worth, and power distribution changes from nominal were detected over the operational lifetime, which could indicate a divergence from normal operations.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Global Archaeal Diversity Revealed Through Massive Data Integration: Uncovering Just Tip of Iceberg

The domain of Archaea has gathered significant interest for its ecological and biotechnological potential and its role in helping us to understand the evolutionary history of Eukaryotes. In comparison to the bacterial domain, the number of adequately described members in Archaea is relatively low, with less than 1000 species described. It is not clear whether this is solely due to the cultivation difficulty of its members or, indeed, the domain is characterized by evolutionary constraints that keep the number of species relatively low. Based on molecular evidence that bypasses the difficulties of formal cultivation and characterization, several novel clades have been proposed, enabling insights into their metabolism and physiology. Given the extent of global sampling and sequencing efforts, it is now possible and meaningful to question the magnitude of global archaeal diversity based on molecular evidence. To do so, we extracted all sequences classified as Archaea from 500 thousand amplicon samples available in public repositories. After processing through our highly conservative pipeline, we named this comprehensive resource the ‘Global Archaea Diversity’ (GAD), which encompassed nearly 3 million molecular species clusters at 97% similarity, and organized it into over 500 thousand genera and nearly 100 thousand families. Saline environments have contributed the most to the novel taxa of this previously unseen diversity. The majority of those 16S rRNA gene sequence fragments were verified by matches in metagenomic datasets from IMG/M. These findings reveal a vast and previously overlooked diversity within the Archaea, offering insights into their ecological roles and evolutionary importance while establishing a foundation for the future study and characterization of this intriguing domain of life.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2016

Comet Dust: The Diversity of Primitive Particles and Implications

Comet dust is primitive and shows significant diversity. Our knowledge of the properties of primitive particles has expanded significantly through microscale investigations of cosmic dust samples (IDPs and AMMs) and of comet dust samples (Stardust and Rosetta's COSIMA), as well as through remote sensing (spectroscopy and imaging) via Spitzer and via spacecraft encounters with 103P/Hartley 2 and 67P/Churyumov-Gerasimenko. Microscale investigations show that comet dust and cosmic dust are particles of unequilibrated materials, including aggregates of materials unequilibrated at submicron scales. We call unequilibrated materials "primitive" and we deduce they were incorporated into ice-­‐rich (H2O-, CO2-, and CO-ice) parent bodies that remained cold, i.e., into comets, because of the lack of aqueous or thermal alteration since particle aggregation; yet some Stardust olivines suggest mild thermal metamorphism. Primitive particles exhibit a diverse range of: structure and typology; size and size distribution of constituents; concentration and form of carbonaceous and organic matter; D-, N-, and O- isotopic enhancements over solar; Mg-, Fe-contentsof thesilicate minerals; the compositions and concentrations of sulfides, and of less abundant mineral species such as chondrules, CAIs and carbonates. The unifomity within a group of samples points to: aerodynamic sorting of particles and/or particle constituents; the inclusion of a limited range of oxygen fugacities; the inclusion or exclusion of chondrules; a selection of organics. The properites of primitive particles imply there were disk processes that resulted in different comets having particular selections of primitive materials. The diversity of primitive particles has implications for the diversity of materials in the protoplanetary disk present at the time and in the region where the comets formed.

Comet dust is primitive and shows significant dive↗
DOE OSTI2024

Plant-specific microbial diversity facilitates functional redundancy at the soil-root interface

Abstract Aims Plant-specific microbial diversity reflecting host-microbe coevolution was frequently shown at the structural level but less on the functional scale. We studied the microbiome of three compartments at the soil root interface (root endosphere, rhizosphere, bulk soil) of medicinal plants cultivated under organic management in Egypt. The study aimed to examine the impact of the rhizosphere on microbial community composition and diversity in desert agricultural soil, as well as to identify specific functions associated with the rhizosphere. Methods The microbiome community structure, diversity, and microbial functioning were evaluated through the utilization of 16S rRNA gene amplicon and shotgun metagenome sequencing. Results We found the typical rhizosphere effect and plant-species-specific enrichment of bacterial diversity. The annual plants Calendula officinalis and Matricaria chamomilla ( Asteraceae ) were more similar than the perennial Solanum distichum ( Solanaceae ). Altogether, plant species explained 50.5% of the variation in bacterial community structures in the rhizosphere. Our results indicate a stronger effect of the plant species in terms of modulating bacterial community structures in the rhizosphere than in root endosphere samples. The plant-driven rhizosphere effect could be linked to redundant plant beneficial functions in the microbiome, while enrichment of specific genes related to amino acid ion transport and metabolism, carbohydrate transport and metabolism, defense mechanisms, and secondary metabolites biosynthesis were more specific. Conclusions The study explores the microbiome continuum at the soil-root interface of medicinal plant species, revealing significant bacterial community structure shifts and plant specificity. The study provides insights into the essential microbiome components contributing to rhizosphere functionality.

Wicaksono, Wisnu Adi (ORCID:0000000215561981)↗